texts: Why does the effective alpha/CL increase at wingtip of swept wing?

texts:
If anybody could explain this in an intuitive way I'd really appreciate it. I haven't been able to find a clear answer on this. I understand that the increase in effective AoA/CL and the spanwise flow & resultant thickened boundary layer at the tip is responsible for the tip stall (if uncorrected for in the wing design), but I can't wrap my head around the reason why the effective AoA and CL increase in the first place. On a rectangular wing they decrease because of the upwash induced from the vorticies, so why doesn't it have the same effect on a swept wing? Most of the explanations I've found on here are geared for aerodynamicists and not the average joe pilot like me, and the explanations given in most pilot resources are overly simple if an explanation at all.

The book "Handling the Big Jets" by D.P Davies says "Too much sweep produces poor oscillatory stability and a tendency for the tip to stall, causing pitch up" and that's it..

ACE the Technical Pilot Interview by Gary V. Bistrow says "A simple swept and/or tapered wing will stall at the tip first [...] This is so because the outer wing section produces a higher wing loading due to the wing taper, which causes a greater angle of incidence to be experienced to a degree where the airflow stalls at the wingtips. The boundary layer layer spanwise airflow, also a result of sweep, further contributes to the airflow stalling at the wing tips."

This ATPL CBT video I watched says the airflow separation starts at the tips because the weak wingtip vortices allow separation earlier than the inboard part of the wing where the stronger vortices from the wider chord reduce the effective angle of attack... what?!

I have an interview coming up where this question could be asked, and I don't feel like I'd be able to deliver an answer with any sort of confidence at this point.


texts: How to design a near vertical take off airplane?

texts:
How to design a near vertical take off airplane, conceptually?

Say I have an airplane, similar to a Zenith 701. Say that it has a stall speed of 50 mph and a wing area of 60 sq ft, and it weighs 500lbs.

Now I want to make it land at 20 mph with full power and my tail volume is sufficient to keep the nose up at 30 deg. I also have slats and flaps to ensure my wing stalls above 30 deg AOA.

Say my max HP is 100.  I understand, as a general rule for GA aircraft, thrust is 4x100hp=400lbs. Vertical thrust would be 400 lbs x sin 30 deg x 65% prop efficiency for a prop in climb, giving me a vertical thrust component of 400 x .6 x 65% = 160lbs vertical thrust.

Now, I only need to produce 500-160=340 lbs of lift from my wings. So I increase my wing size so that I can fly at 20mph with a lift of 340 lbs.

Is this correct, at least conceptually?


texts: Are non-military aircraft allowed to fly with no registration numbers (tail numbers)?

texts:
There have been several news reports about aircraft (light planes and helicopters) flying without visible registration numbers or identifying marks in the USA:

  The NYPD referred to the helicopter only as “23”—a reference to the
  number of police officers killed in the 9/11 terrorist attacks—and
  initially the aircraft had no registration number painted on its tail
  or side. source

and

  Cimbolic was beginning to worry that he had overreacted when he
  noticed, on the same flight-radar Web site, the second plane flying
  higher in the sky, carving bigger loops above West Baltimore. The Web
  site reported that this plane was a Cessna 560 Citation V, a small
  jet. But it showed no tail number, offering no possible trail to
  Federal Aviation Administration records. This only heightened his
  curiosity. source

Eventually these aircraft were identified (and in the case of the former, a registration number found). But the general question I have is:

Are non-military aircraft allowed to fly without visible registration numbers (tail numbers) in the United States?

Fine print: I am aware that military planes usually have visible tail numbers, this question is about non-military craft. So "non-military" in this case includes federal agencies and state and local police.


texts:
From what I know the term bound vortex comes from potential flow theory and is a part of circulation around a wing.

Does it mean the same as circulation or lift?
Is it a cause of generating lift over a wing? If yes or partially yes, what is its role in that?


texts: Can hours logged training to be a Sport Pilot apply toward the Private Pilot Certificate?

texts:
Can my training in a Sport aircraft with a Sport instructor be used to fulfill the requirements to become a Private Pilot?

As an example, assume I've started my training to be a Sport Pilot, but decided I'd rather be a Private Pilot.


texts: Procedure for simulating nonlinear flight dynamics

texts:
I am trying to simulate F/A-18 Hornet on Simulink. So, here is how I have made the model:

Firstly, the initial flight parameters(Alpha, beta, V(magnitude), rho) are being calculated based on the initial values of the states.
Then, these parameters, along with initial values of the states, are used for calculating the aerodynamic forces and moments.
As the Aerodynamic forces and moments are in the Wind Axes, I transformed them from Wind to Body using alpha and beta.
Then, the gravity force, which is transformed from the NED Frame to Body frame, is added to the transformed aerodynamic force.
Similarly, the thrust force is added, assuming that thrust is only in the X-direction( Body Frame), and no moment is generated because of it.
Then, total force and moment are sent into the Body Axes 6-DOF Quaternion Block present in Simulink, which gives me the states for the next iteration and process continues.

Please point any mistakes you find out in the above-mentioned iteration process. Now, for checking if the model is correct or not, I planned to give initial conditions as a trim condition, and if the model is correct, the plane should fly in the stable level flight. The trim point is:

 V = 300.92 ft/s
 [phi, theta, psi] (in rads) = [0, 0.1745, 0] (pitch is 10 degrees)
 [p, q, r] = [0, 0, 0]
 alpha = 0.1745;
 beta = 0;

On giving these initial conditions, the plane flys at a stable level flight. So, is this process of verifying the model enough? If not, then please outline the process which I can use to check my model. Thanks for the help!

PS: Reference for the Aerodynamic Model of FA-18 Hornet:- A. Chakraborty, P. Seiler, and G. J. Balas, “Susceptibility of f/a-18 flight controllers to the falling-leaf mode: Linear analysis,” Journal of guidance, control, and dynamics, vol. 34, no. 1, pp. 57–72, 2011.


texts: Why doesn't a wing in supersonic flow produce a shock that results in flow parallel to the leading edge?

texts:
When we look at a wedge in supersonic flow, a shock emanates from the leading edge such that the flow after the shock is turned and is parallel to the airfoil surface.

The shock angle is based on the flow turning angle (wedge angle) and can be found using the chart below:

I was wondering why a wing in supersonic flow would not have the same behavior (see image below). That is, why wouldn't there be a shock emanating from the apex of the wing (which depends on the sweep angle much like the wedge angle ($ \theta $)? If this were to occur, there would be no component of the flow perpendicular to the wing (as the shock would turn the flow parallel to the surface). I know this doesn't occur physically because there is always a component of flow perpendicular to the wing, but this confused me because the wing seems exactly like a wedge (if we look at a wedge from the top instead of the side).


texts: Why do the outer parts of wings generate less lift?

texts:
In this Wikipedia page it says:

  Constant chord: parallel leading & trailing edges. Simplest to make, and common where low cost is important, e.g. in the Piper J-3 Cub but inefficient as the outer section generates little lift while adding both weight and drag.

Why does the outer section generate less lift?


texts: How to carry out a CFD simulation for determining the stability derivatives of an aeroplane?

texts: I want to create a 3D model of an aircraft to determine the stability derivatives by using a computational fluid dynamics (CFD) simulation. I tried to google for tutorials that explain how it is possible to carry out a CFD simulation for determining the stability derivatives of an aeroplane but was not successful. I would be glad if someone could give some resources that explain the procedure. It would be great if the CFD software would be ANSYS Fluent.


texts: How does landing gear affect thrust on a light twin-engine airplane?

texts:
I'm working on my commercial multiengine rating.  And I got this question from my examiner, and I answered: landing gear produces penalty drag, so it decreases thrust.
 But the examiner says this isn't correct... ?


texts: Aerodrome actual weather - METAR decode - 3 letters for this sky?

texts:
How can I describe this sky, in 3 letters as per the Aerodrome actual weather - METAR  decode?

I found online a comprehensive list of Metar codes


texts:
About a week ago, I was flying from Boston to San Juan in an A320 and noticed that the flight was staying at about 42000 feet for the major part of the trip, according to the flight map screen on the plane's entertainment system. That struck me as an unusually high altitude and I am even more surprised now that I have read a little on the subject. I am wondering if that was even possible, or the altitude readout to the entertainment system was simply wrong. The flight proceeded uneventfully in other ways, and was on time.

What is the ceiling altitude for the Airbus A320?


texts: Has anyone considered putting a hydrofoil on a sea plane?

texts:
One of the main problems with water landings is that you need a bigger engine to counter the various drags caused by the pontoons. The specific case of "run[ing] across our own wake to be able to get up on the step on glassy water" brings some interesting thoughts.

  [B]asically a floatplane has to break the suction of the water - kind of like pulling your boot out of mud - and if the water isn't moving at all then it has to do that all by itself. If there are some waves, or a wake, or any kind of discontinuity in the water, then that gives the aircraft the momentary break it needs to overcome that initial suction. "The step" in this context refers to the step-up shape you see partway down the float (or hull); when you're "on the step" then you're using the part of the float forward of that step to hydroplane.

It is well known that water's significantly higher density makes high speeds difficult. A solution to that problem is the hydrofoil - a small underwater wing that raises some or all of a boat's hull out of water to reduce friction and increase speed.

So here is my dumb question: would placing a hydrofoil under a pontoon save fuel on takeoff? And how likely would the increased drag during flight cancel that advantage on a typical flight?


texts: What can I be allowed to do as a engineering/ maintenance intern at a european airline?

texts:
I am just about to (hopefully) embark on a short internship at the maintenance department of a medium-sized european airline (i.e. under EASA framework).

While the internship has been pushed towards being practical, one thing that bothers me is that I am absolutely clueless what I could be allowed to do (and I'd like to know so I could negotiate to get the most of the time with the carrier).

For instance:

Would I be allowed to handle anything flight-wise with supervision? Could I be allowed to interact with the aircraft or only watch and observe?
Would I be allowed to even loosen a bolt on a wheel, or do you legally need maintenance certification for that?


texts:
As per DO-178 C section 6.2 Overview of Software Verification Activity

  b. When it is not possible to verify specific software requirements by exercising the software on a realistic test environment, other means should be provided and their justification for satisfying the software process objectives defined in the Software Verification Plan or Software Verification Results.

After reading this every/most of verification engineers would understand it as other verification methods like Analysis, Inspection etc...

As per the discussion and Arguments "The real intent of this objective is how do we verify the software when hardware is unavailable" like, using simulator to verify the software needs to be documented under SVP for this objective satisfaction.

The question is, DO (document Order) as evaluated from version A, B to C now and still have ambiguities and different understandings. Why don't FAA/JAA can come up with examples or layman language explanations for each objective?


texts:
Are standardized tail volumes used for swept wing GA aircraft like in straight wing designs?

If so, what are they?

I understand that after roughly 100 years of aircraft design, there are rules of thumb/guiding principles to use regarding tail volume sizing.

As per the MIT open course notes for GA straight winged aircraft:

Horizontal Tail Volume: .3 -.6

Vertical Tail Volume: .02-.05

If applicable, what are the above tail volume values for GA aircraft with swept wings of roughly 20 deg?

Assumptions on stability/geometry of swept wing vs straight wing ( I stand to be corrected):

Pitch stability: the horizontal tail volume would be smaller as the swept wings provide added pitch stability.
Roll Stability: I'm told dihedral is a lot less then on straight wings, so better roll stability.
Yaw Stability: no idea


texts: How are range violations during a launch countdown handled?

texts:
I was watching the ULA Atlas V IBIRS countdown tonight but the launch was scrubbed (after some technical issues) ultimately because of a range violation: an airplane was in the restricted area.

I've seen this happen because of boats before, but I know it also sometimes happens because of wayward planes. Specifically: Is this just a standard airspace violation? Or is it treated differently since this particular launch was military-related? Whose job is it to keep the airspace clear, how do pilots know to stay clear of the area, and what happens to the pilot(s), if anything?

(Here's a more detailed tweet thread that has some interesting discussion.)


texts:
V1 is the speed that an aircraft may abort a takeoff so long as the airspeed is below it, or is committed to flight if it is over that speed.

V1 calculations are based only on the brakes (not sure about spoilers) being available to stop the airplane (regardless of the number of engines), why?


texts: Are there regulatory bodies for investigating UAV accidents?

texts: Is there an international regulatory body for investigating UAV accidents? Does it exist on any national level?


texts: How much thrust does the Lilium aircraft produce?

texts: I have been researching the Lilium aircraft and can’t find information about thrust. An early version of this aircraft was 2 seats with a loaded weight of 1,400 lbs, 36 ducted fans and 320 kW peak power. They are testing a five seater also for vertical takeoff. Either the standard calculations for thrust are wrong in ducted fans or something else is going on. Any guesses?


texts: Does the stream of engine thrust act as a good drag shield against the nacelle?

texts:
Taking a look at the typical large engine of a commercial plane, it looks rather unstreamligned. Nacelle drag is significant IIRC.

However, then I suddenly remembered these engines produce a large jet of thrust (most of the time). Does this air stream of thrust act as a good shield against nacelle drag? Does it effectively form a bell cone, or half of a seers-haak body, around the rear half of the nacelle?

If so, that would appear to cut the nacelle drag in half.


texts: What is that Boeing 757 custom cockpit interface?

texts:
Cropped; flickr.com, 2008

The photo is taken in cruise. The selected display shows takeoff data. There is also a send button (which hints at a datalink capability for communicating values).

I searched for performance calculators and datalink solutions for the 757, but came up empty. Nothing matched that unit.

What are its features? Say compared to Boeing's own ACARS/AOC for datalink (via the standard CDUs).


texts:
How does distributed propulsion work in a pusher configuration?

In a tractor configuration, the wing benefits from a portion of the prop wash flowing over the wing and producing extra lift ( I stand to be corrected).

In a pusher configuration, there is no prop wash flowing over the wing.

So how does distributed propulsion created extra lift and/or thrust in a pusher configuration?


texts: What airspace are ultralight pilots allowed to use?

texts:
So I've been watching videos and thinking about getting into ultra-light aviation. Flying in a personal air-trike or paramotor looks like a lot of fun. Being new to the aviation arena I had a couple questions:

How do the airspace restrictions work?
Do you have to file a flight plan like any typical aircraft/pilot at an airport?

For example, say I wanted to take my paramotor to a large park and take off from there? How would that work with the FAA, talking to ATC and other traffic in the area so they know I'm there? Does it work the same as flying in a Cessna?


texts: What are the advantages and disadvantages of ducted fans in designs such as the Airbus E-Fan?

texts:
I have read that it increases thrust and reduces noise. Is there a downside to this?

(Image source: Wikipedia)


texts: How much testing to commerical aircraft manufacturers typically do on each new plane after it rolls off the production line?

texts:
I just came across an article on Wired about Boeing's new 787-10 where they said the type had been tested for over 5000 hours in a range of conditions.

Obviously, the very first model is tested to extremes but when full scale production starts what kind of testing is typically done on each individual plane ?


texts: How can I find out if the government paid to build a runway?

texts:
I've heard rumors that the government paid to build a runway at a residential fly-in community in the mountains of North Carolina to have it available as an emergency landing strip.  I would appreciate suggestions of how to find out.  I tried calling the FAA but with the automated system, I found it impossible to reach a human being.

Thank you!


texts: What is the purpose of an inboard aileron?

texts: I've noticed that larger Boeing aircrafts (such as the 777, 767, 747, etc) are equipped with inboard ailerons. What is their purpose and why hasn't Airbus incorporated them on the A330 or the A340?


texts: How to secure an aircraft at a transient parking space?

texts:
I've noticed that at many airports, the transient GA parking spaces often don't have tie-down anchors (e.g. bolts drilled into the pavement; heavy steel cables, etc.) or tie-down ropes. They simply have a "T" painted on the ground to indicate the parking alignment. This is true even for many FBO-managed parking spaces.

How should I secure my airplane at these parking spaces? Even if I had my own tie-down ropes, there's nothing to attach the ropes to.

I'm hesitant to just chock the wheels, as this does not prevent a gust of wind from blowing the aircraft around.

Should I ask if there's a patch of grass and use an artificial temporary anchor/Klaw system? Is this even commonly available at your average GA airport?

Note: I only need to park the plane for a few hours, not overnight.


texts: Are altimeters calibrated to ISA geopotential altitude or ISA geometric altitude?

texts:
Altimeters convert a pressure measurement to an indication of altitude. When set to standard pressure setting (1013.25 hPa / 29.92"Hg), they assume the atmosphere is according to the ICAO Standard Atmosphere (ISA) and indicate the altitude accordingly. However, ISA has two altitude definitions; geometric altitude and geopotential altitude.

The ICAO Standard Atmosphere is a model of the atmosphere up to 80 kilometres high, based on the perfect gas law and the hydrostatic equation.  In order to deal with the effects of reduction of gravity with height, it uses the concept of geopotential altitude H:

$$H= \frac{1}{g_0}\int_0^hgdh$$

with:

$h = \textrm{geometric altitude}$
$H = \textrm{geopotential altitude}$
$g_0 = 9.80665\textrm{ m/s, mean gravitational acceleration at mean sea level}$
$g = \textrm{local acceleration of gravity (height dependent)}$

Gravity is given by :

$$g = g_0 \left(\frac{r_e}{r_e + z}\right)^2$$
with:

$r_e = \textrm{the radius of the earth}$

And thus the relation between geopotential altitude and geometric altitude is given by:

$$H = h\frac{r_e}{r_e+h}$$
And
$$h = H\frac{r_e}{r_e-H}$$

In the ISA model, the properties of the atmosphere (pressure, temperature, density) are all calculated with respect to geopotential height.

For a geopotential height of 12 500 meters (41 010.5 ft), which corresponds to a geometric height of 12524.6 meters (41091.3 ft), the ICAO atmosphere gives a pressure of 178.648 hPa.

My question is: what will a perfectly calibrated altimeter indicate when the pressure is 178.648 hPa? Does it indicate 41 010.5 ft (the geopotential altitude) or does it indicate 41091.3 ft (the geometric altitude)?

You might say that the difference is "only" 80 feet, but for RVSM operations that is quite significant.

The ICAO standard atmosphere (as described in ICAO Doc 7488) does not give the answer (at least I couldn't find it). And it includes tables for every 500 meters of both geopotential and geometric altitude, so that does not make it easier.

I'd like to know which altitude is indicated on an altimeter (ISA geopotential or ISA geometric) and where (in which official document) this is specified.


texts: Is Vertical Speed based on True Airspeed or Groundspeed?

texts:
I have edited this for clarity

For the same angle of descent or climb, does vertical speed increase if true airspeed is greater or if ground speed is greater (due to a tailwind)?

Imagine a triangle and assume a three degree angle of descent. The hypotenuse represents the flight path. The opposite end represents the amount of descent. The adjacent side represents the ____. Airspeed or ground speed?

If headwind matched true airspeed, I imagine an aircraft would climb and descend in place (like an elevator) without knowing anything about it's ground speed. However, with large tailwinds, ground speed will obviously be much larger. Going back to the triangle concept--the hypotenuse will be very long--which means the aircraft would descend more quickly.

Furthermore, every Captain I've talked with swears rate of descent increases with a tailwind. However, I believe this may be a result of reduced tailwinds at lower altitudes.

Do you have a source or a formula you can cite?
Thanks.


texts: How does leading edge flap increase camber?

texts: From this post, I've learned that the leading edge flap works by increasing the camber of the airfoil. But how exactly does it work? Since it is a flap, I can guess it works by changing the chord line, just like the trailing edge flap does. But how exactly does the chord line change? Does the leading edge move down to below the original leading edge when the leading edge flap is extended?


texts: If my base month for recurrent 135 checks is June and I fly as PIC in July and subsequently don't complete required testing in July, can I be violated for any July flights?


texts: Does flight training have any impact on my H1B visa?

texts: I'm on an H1B visa, working in the IT industry and I need to know if I take flight training after getting an AFSP clearance from the TSA, does that affect my current visa or IT job?


texts: How should the number of maintenance hours per flight hour for the C-17 be interpreted?

texts:
While reading up on the Boeing C-17 Globemaster III, I came across a reference to its maintenance man-hours which surprised me. As listed in the spec sheet (emphasis mine):

  These requirements include an aircraft mission completion success probability rate of 92 percent, only 20 aircraft maintenance man-hours per flying hour, and full and partial mission availability rates of 74.7 and 82.5 percent, respectively.

Now this strikes me as a rather steep maintenance requirement, especially considering the spec lists "only 20 hours". If I understand that statement correctly, for every hour spent in flight, 20 technicians have to spend that same amount of time maintaining the plane after landing.

Do those 20 hours refer to an average over extended operation of the aircraft? In other words, does this include extended maintenance where the plane might be undergoing days of intensive maintenance, skewing the numbers?
Is this a low number for this class of aircraft?
Do the required maintenance hours scale with: size, complexity, military/commercial use?


texts: Is it possible to have the laminar flow above $Re=10^7$?

texts:
For pipe flow I came across the information that the onset of turbulent flow occurs at approximately $Re=10^3$ to $Re=10^4$, while for boundary layers on the airfoil the onset occurs in between $Re=10^5$ and $Re=5\cdot 10^6$. Therefore, since the onset of turbulent flow ranges greatly, is theoretically still possible in some cases to have the laminar flow above $Re=10^7$ on the airfoil, disregarding the laminar sublayer in every turbulent flow above the surface?

Any reference to books would be highly appreciated.


texts: What material and shape should be used for angle of attack sensors?

texts: Does the material and shape of the vane for an angle of attack sensor have to be identical to the material and shape of the wing? What properties should I consider?


texts: If a pilot takes a MEL checkride and later a SES checkride, is the pilot now also qualified for MES/SEL?

texts:
*Assuming all checkrides are passed.

If a pilot gets a multi-engine land rating on a primary checkride, and later takes a checkride as single-engine sea, is the pilot now qualified for multi-engine sea and single-engine land?

I suppose an unspoken question would be, does a multi-engine rating automatically allow for single-engine PIC privileges, or is the restriction between single and multi-engine a 2-way street?


texts: What modifications are necessary to the airframe and or instrument panel to add an autopilot to a light airplane (like a Cessna 172 or 182)?

texts: If you were going to add an autopilot to a light airplane that never had one, what all needs to be done? I know they need to connect servos somewhere (where exactly), and add instrumentation to the panel, but how invasive is the installation?


texts: How low can a helicopter legally fly over the water with boats below?

texts: My friend was paddling in a big race in Dana Point, California and she said the helicopter was directly over her taking pictures to sell. It looks to be at no more than fifty feet above sea level (if that!); this flight behavior seems insanely dangerous and/or illegal, but maybe I'm wrong. Anyone have hard facts on this type of flying for photos?


texts: Is your average ramp or store employee at an international airport security checked before they are allowed to enter the gate side area or apron?


texts: What is "alternate takeoff" in this PT6A performance table?

texts:
I am flight mechanic, and I would like to know about this performance limitation:

What is the definition of alternate take off?
Why is the alternate take off temperature limit (ITT) lower than max. cont. ITT?


texts: To my knowledge Air France Flight 447 experienced stall. How was the stall detected and why wasn't the crew able to recover?


texts: Can state or local laws regulate where aircraft can take off and land?

texts: Say you have as private strip, but your neighbors get tired of hearing your plane. Can the local authorities pass, and enforce a law saying you can't take off and land there? Or do FAA rules override local authority as to where you can and can't land?


texts: How much is the fuel consumption of a Tecnam P2002?

texts: So I'm gonna have the training for PPL and I wanted to know the fuel consumption of a Tecnam P2002 aircraft. But I couldn't find any aircraft information for this particular plane.


texts: Why is the stagnation point on the upper surface before the start of circulation?

texts:
In many textbooks, such as Anderson (Fundamentals of Aerodynamics), Bertin (Aerodynamics for Engineers), and Houghton (Aerodynamics for Engineering Students), the authors present the idea that there is a starting vortex which is formed. This starting vortex and the bound vortex that form (due to Kelvin's Theorem) co-exist with lift (as Mclean puts it in Understanding Aerodynamics). However, I am unsure on why the starting vortex forms on the upper surface. Why does it not form on the lower surface and have clockwise rotation and lead to counter-clockwise bounded circulation at the airfoil?

While I know that this is not experimentally observed nor does it make intuitive sense, I would like to know why the starting vortex does not form on the bottom.

To shed more light, here are some instances of where authors state that the starting vortex starts on the upper surface, but never explain why it doesn't start on the lower one:
(taken from Bertin):
"At the instant of starting, the flow is a potential flow without circulation, and the streamlines are as shown in Figs. 6.3 a, with a stagnation point occurring on the rear upper surface"

(taken from Understanding Aerodynamics)
"It can be shown, based on starting the flow from rest, that in the absence of viscosity, the nonlifting flow pattern of Figure 7.1.3a is the one that would occur... "

So how can it be shown (mathematically) or using strong rigorous theoretical arguments that the stagnation point cannot be at the lower surface before circulation?


texts: Are there any safety features to prevent reversible-pitch props from reversing in flight?

texts:
Some aircraft have propellers capable of reversing pitch, which is also known as beta angle. The example I saw was an Aviat Husky.

(Youtube demonstration)

I want to know if there are any safety features that prevent this from activating while airborne. For example, what kind of controls activate it? How long does it take to actually reverse the blades, and how much physical effort does the pilot have to exert? Would it be impossible to force the reverse when at high cruising speed?

If it is a mechanically powered reverser, then is it possible for it to be inadvertently triggered?

And if it is activated, can it quickly be set back to original blade angle?

Note, I am interested in any propeller-driven aircraft, not just commercial ones, but smaller ones as well. Piston prop, turboprop, GA, anything.


texts: How would gyroscopic effects affect push-pull configuration vs conventional twin engine in the event of engine failure?

texts:
This answer, and the Wikipedia article on push-pull configuration both claim that aircraft with push-pull configuration are easier to fly in the event of engine failure, because the thrust provided by remaining engine would remain in the centerline.

However, lot of aircraft with push-pull configuration seem to be relatively small ones, so I am wondering how gyroscopic effects would affect the handling of the aircraft in the event of engine failure.

I found this answer comparing WWI era FB19's to F16's. But as I said before, lot of push-pull reconfigured aircraft probably have less mass and much slower than F16, so the calculations in that answer may not apply.

So my question is, is there any noticeable handling difficulties in push-pull configured aircraft, when an engine fails?


texts: Why aren't the passenger seats designed as jump seats (foldable) in commercial airlines?

texts:
We know that the crew seats in an airplane are "jump seats (foldable)", which made me wonder why it isn't the same case with passenger seats.

Some advantages which I see if passenger seats are converted to the "jump seat" design:

Better access and thus easier cleaning of the aircraft
Easy entry exit by passengers
Already available tech (as in the crew jump seats)


texts: What would happen if the Emergency Locator Transmitter was activated wrongly?

texts:
Supposing, after a "bad" landing, performing a high vertical speeed, the crew, unintentionally, activates the ELT, sending the signs to the sattelites, warning the rescue and team about the "accident", that does not happen.
Would the fees for the services be payed?
Is there any penalty for the crew or company?


texts: Why is max power time limited for jet/piston engines?

texts: Usually max power is time limited for jet/piston engines to 10 or 5 minutes. Can anybody explain the reason? What will happen if those limits are exceeded?


texts:
I don't understand exactly how the Wright brothers handled takeoff with the first gliders and powered plane. I know it has something to do with an elevated rail track. Also, if the flying position was head first, body parallel to the ground, how did they land without injury?

Seperate question: for the initial glider flights, did they start at a high elevation and simply glide to the ground, or was there any method of increasing altitude during flight?


texts: How are landing minimums decided for a flight? Does the captain make the decision depending on weather conditions or is it preset for each airport?


texts: Why are Gatwick's runways too close together?

texts:
Gatwick Airport has two runways (08L/26R and 08R/26L), but they are only 200 metres apart - too close (by just ten metres) to allow simultaneous operations on both runways.  As a result, usually only 08R/26L (the older, more southerly, and slightly longer of the two) is used as a runway, with 08L/26R serving only as a taxiway except when 08R/26L is closed for some reason.

Given that Gatwick has plenty of space available that could have been used to put 08L/26R ten metres further north and thus allow simultaneous operations on both runways, and that Gatwick is, and was, bursting at the seams with the amount of traffic it has to fit down 08R/26L, why was the new runway built just slightly too close to the original?


texts: Is a safety pilot required to share costs?

texts:
Where I fly, it is customary for a pilot maintaining instrument currency to pay all the costs associated with the training flight while a safety pilot volunteers their time in exchange for the opportunity to log PIC. I personally don't disagree with this arrangement, since it encourages pilots to help each other out.

The FAA has repeatedly taken the position that building up flight time is considered compensatory in nature when the pilot does not pay the costs to operate the aircraft (see Harrington 1997, Lincoln 1990, and Howell 2013).

So, in this case, is the safety pilot being "compensated" by logging PIC? I vaguely remember seeing something saying that the FAA did NOT consider this compensation, but I can't remember where I saw that...


texts: Why is there such a long displaced threshold on 22R at JFK/KJFK?

texts:
This video seems to raise a whole bunch of questions, but here's one I have:

Why such a long displaced landing threshold on 22R at JFK/KJFK? (Scroll down to the 4L/22R section for details.)

Certainly Rockaway Blvd. is sufficiently distant from the end of the pavement (TODA) to allow closer landings.  And further upstream from that is Idlewild Park.  No residential areas for a good distance away from that runway.

That's a 3425-ft. displaced threshold on a 12079-ft. runway.  Is that some sort of record? ;-)


texts: Are high lift wings bad for faster speeds

texts:
I notice a trend in many aircraft designs. If the aircraft was designed to go slowly but have shorter takeoffs/landings they use airfoils with a high lift.

However for long endurance flights they use a flatter airfoil that produces less lift.

To my understanding the reason for this is because you never get anything for free. When a wing produces lift, it is trading the forward movement of the plane for vertical movement.

I understand that at higher speeds the high lift wing would fight horizontal movement too much and so they chose the flatter airfoil.

However my question is what if you change the angle of attack for the high lift wing? Pointing the front of the wing downward, thus making its lift more of a forward direction.

Would this somehow still be less efficient than a flatter airfoil or do they just chose the flatter foils for design purposes and structural reasons?


texts: How do airliners with engines mounted on places other than wings suppress wing flutter?

texts: Assuming airliners typically have high aspect ratio flexible wings, how are wing flutter suppressed when engines are not available on forward-reaching pylons as weights?


texts: What is the reasoning behind Kamov twin-rudder design?

texts:
Several helicopters, namely the Ka-226, the Ka-25, and the Ka-27, have twin vertical stabilizers that are canted inwards at an angle of about 15 degrees, similar to the feathers on a shuttlecock.

The stated purpose of this design is to increase directional stability during auto-rotation, but I cannot find any information as to why the inwards angle is used in general, and more specifically, why it seems only these models of helicopter need them.

My best guess is that much like the shuttlecock, when in straight flight, both stabilizers will have a positive Angle of attack and will be generating inwards lift, which is a more stable condition for low forward speeds.


texts: How do airliners prevent raising the gear on the ground?

texts: GA aircraft use a squat switch to prevent accidental retraction on the ground. Do airliners use a similar system? I've heard some reference to a manual pin, I'd appreciate clarification on that.


texts: What is this unusual leading edge flap on a B737-200?

texts:
On this video of Air North's gravel runway-equipped B737-200, there's what appears to be a small leading-edge flap (Krueger flap?) inboard of the engine.  Refer to the screen shot below.  What is this?

Addendum

Notice in the video (and screen shot) that this device shows itself while no other flaps are extended.


texts: Are there any scenarios that a controller clear different aircraft at the same altitude?

texts: In the real world, are there any scenarios that the controller clear the same altitude or flight level to different aircraft at the same time?


texts: How is the lift generated by a number of out-of-plane staggered wings calculated?

texts:
I want to calculate the lift generated by a number of out-of-plane staggered wings but I don't think a valid approach is to simply use superposition and add the sum of the lift of all the wing's in isolation.

I have heard of Munk's stagger theorem but am unsure of it's implications.

I think the implication of Munk's theorem is that there is a limit to the amount of downwash and thus lift that can be generated by staggered wings.

Lets do an example:

I can calculate the lift force generated by a single planar wing as:

$$L=\frac{1}{2}\rho V^2SC_L$$

Where $\rho$ is air density, $V$ is free-stream velocity and $C_L$ is the finite wing lift coefficient, which is a function of the wing geometry.

Now, if I have say 5 staggered wings, is this statement:

$$L=5\times\frac{1}{2}\rho V^2SC_L$$

valid?

Now I know that the pressure distributions over the different wings will interact wing each other, but my question assumes that the wings are separated sufficiently far away from each other that this effect is negligible. Or is this interaction of pressure distribution a result of the stagger theorem?

I will appreciate any light being shed on this subject.


texts: PRIM 1 FAULT prior to ETOPS entry, Reroute or Continue?

texts:
As per the Minimum Equipment List (MEL) you cannot dispatch a plane for ETOPS if it has PRIM 1 FAULT (Flight computer fault) However if this fault appears in flight just prior to entering the ETOPS/EDTO segment should you still continue or fly a non ETOPS/EDTO route? Since the MEL is only referred to prior to flight, I cannot refer to this document to justify not flying the ETOPS route. There is a requirement though for twins that all EDTO significant systems should be operational before conducting an
ETOPS/EDTO flight. I haven’t seen an EDTO specific significant systems list only the general list published by ICAO which includes almost all the systems of the plane. The question is, would PRIM 1 fault, which was considered a NO GO on the ground still be considered an EDTO significant system in flight wherein it would only result to a loss of a pair of spoilers and computer redundancy? I hope somebody here would share their EDTO significant systems list.


texts: Why aren't passengers sorted before embarking?

texts:
Boarding a plane takes a bit of time.

Especially if passengers enter the plane in a random order as those stopping to store their baggage might block the lane for others.

Why  airlines don't sort passengers, for example during the dead time in between checking boarding pass and actual boarding?


texts: Is it possible to upgrade a Boeing 747-8 and Airbus A380's engines for greater speed?

texts:
Is it possible to upgrade the Boeing 747-8 and Airbus A380's engines (upgrading to a newer engines) for greater speed, if the engines were more efficient and used less fuel at higher speeds relative to distance?

If so, what are the maximum speeds that the airframes or entire aircraft could handle or are designed to handle?


texts: Is PVC tubing a good material for helicopter airframes?

texts: Been thinking of getting into the hobby of building ultralight helicopters, and would PVC tubing be a good choice to build the overall airframe?


texts: What is the optimal altitude for performance and mileage in normally aspirated GA planes?

texts:
Given atmospheric condition, a typical common engine (say, Lycoming 4-cylinder), and a fixed-pitch normal prop:

What are normally the best altitudes for:

ground-speed and
fuel efficiency (range)?

Is it always highest (reasonable) altitude (say >=10,000')?  the air resistance is low but so is the engine power,  or is it usually some intermediate altitude?

Does it depend on the aircraft?  Is a Cirrus SR-20 different from a Vans RV-9 from a Cessna 182 from a Piper Cherokee?

How does the efficiency of a piston aircraft change with altitude? covers a lot of ground about the primary forces (air resistance and (normally aspirated) piston/prop efficiency) and secondary forces. But it does not answer how these forces typically combine to create "best" altitudes (for mpg and gs).  The question ultimately was about how these forces could create typical optimums at different alternatives, and whether they could be different for an SR-20 or a 182.


texts: Where is the compression on a compression strut in a tube and fabric airplane coming from?

texts:
I understand the functions of every part of a tube and fabric (two spar) ultralight wings and the loads they carry but what keeps puzzling me is the compression strut of a two spar wing as seen above.
My question is where is this compression on a compression strut between the main and rear spar coming from? Is it from the drag and anti wires, the spars itself, where and how do you calculate this conpression force?


texts: I saw this beacon at an old airport; how and in what situations was it used?


texts:
I have data from an aircraft which I am trying to understand. One column contains the baro corrected altitude (in ft, e.g. 256) and another the pressure altitude(also in ft, e.g. -44). The two example data points given were measured at the same time.
I have issues finding a definition of the baro corrected altitude. How is it defined and how does it differ from e.g. pressure altitude or other types of altitudes?


texts: What is this high flying aircraft over Pennsylvania?

texts:
Yesterday afternoon I photographed a Boeing 777-300ER flying over my home, according to radar data it was at approximately 32,000 ft. In the photograph there is another aircraft present, it is much smaller and higher in altitude (40,000-50,000 ft) and it is a small aircraft, possibly a drone or military. It did not appear on any flight tracking sites. I usually see military traffic flying in that particular route and heading. I have numerous "raw" images of this particular aircraft.

I originally though it may be an L-39 although that particular aircraft does not have a T tail design and I think that it would struggle at that altitude. The photographs were taken at 1545 EST over the LVZ VOR.

The aircraft was flying an almost perfect east to west heading usually reserved for military traffic. One interesting note is that it was not leaving a contrail. I routinely photograph B-52's, tankers, and fighter aircraft transitioning over my home at or about that altitude and they almost always leave contrails.


texts: Can a pendulum stabilizer for airplanes really work?

texts:
Can a pendulum really stabilize a plane for both roll and pitch?

I have read about various experiments (the one in the picture being just a simple case) but I still do not find an example of plane that was stabilised beyond any doubt with the help of a pendulum.

As a note:
If the suspension point of a pendulum is at rest or moves at constant speed then after some oscilations the bob will end up by hanging vertically. However this is not the case when the suspension point has an accelerated movement.

Source: Popular Science, December 1939

UPDATE

I have found a description (see the attached image) of a Wright stabilizer that was used successfully!! before February 1914. The roll was controlled by a pendulum (letter A in the picture) that swung along the main wings. At one point the article states that the device gave good results being tested daily for long intervals of time.

Another more recent text says that demonstrations were made before the Aero Club judges on December 31, 1913.

  In the fall of 1913, Orville installed the stabilizer on a special
  Wright Model E airplane that utilized a single pusher propeller. He
  kept the details of the stabilizer secret even from the Wright
  Company. He purposely waited until the last day of the year to fly for
  the prize.

  He invited the Aero Club’s judges to Huffman Prairie to see a
  demonstration of his new device on a cold snowy day, December 31st.

  He turned up his coat collar, put on a pair of goggles and took off.
  He made a total of 17 flights.

  His most spectacular flight consisted of 7 full circles of the field
  with both hands held in the air. The automatic stabilizer kept the
  same angle of bank and almost the same altitude. He wowed the judges
  and was awarded the prize on February 5, 1914.

Source: Wrights Develops Automatic Stabilizer

How is it possible?

Source: The Wright Automatic Stabilizer, L'Aerophile, February 1, 1914


texts: Can I use a LAPL/PPL issued by the UK CAA to fly outside Europe?

texts: Will the Light Aircraft Pilot License (LAPL) or Private Pilot License (PPL) be enough to to be able to fly to other countries outside Europe?


texts: Why is the aircraft boneyard in Tucson, Arizona still active?

texts:
I understand that an aircraft boneyard is an amazing tourist attraction for aviation enthusiasts.

However, the number of planes that the boneyard in Tucson has accumulated today is mind-boggling. I know that, initially, the purpose of the boneyard was to salvage materials from old and obsolete aircraft. However, the pace at which most aircraft are being scrapped is very low. Though it serves as a spectacular sight, why is the boneyard still active?


texts: What is the material of snubber brakes that is used for stopping the spin of the nose landing gear? KC-135, Boeing 747, 727 are the aircraft that I saw with these snubbers.


texts: Why do airliners have to file delays through their handlers?

texts:
Often when listening to ATC (commonly Dublin), when an ATP requests push and start, the controller will reply, "You have missed your pushback window", and/or ask the pilot to call their company or handler to "file a delay" or "update your flight plan with your off-blocks time".

I have two questions about this but I expect the same answer answers both.

Why is it necessary to re-file the plan, rather than simply activating the flight plan with the actual departure time?
Why is it necessary for the pilot to change to the airline's frequency, chat them up, change back, and then wait for the electronic flight plan to be updated, rather than talking to the controller directly?


texts: Why are Russian cockpit panels painted in turquoise?

texts:
Almost all cockpit panels of Russian aircraft types are painted in turquoise, whereas elsewhere the cockpit panels usually exhibit a dark grey color.
As this "rule" seems to be quite prevalent, I am curious as to the reason/origin.

This can be seen in the cockpit of Mikoyan MiG-31:

Image Source


texts: Why does JetBlue have aircraft registered in Germany?

texts:
I recently saw a JetBlue A321 with a German flag on its tail and was wondering why it would be registered in Germany if it was a US-based carrier. I was thinking maybe it had something to do with Airbus but I wasn't 100% sure.
Any thoughts?
Thanks!
Image source: https://www.linkedin.com/feed/update/urn:li:activity:6771365770770309120/


texts: What can I do on the ground in order to help my body acclimate to aerobatics?

texts:
I've just started aerobatics training!  Unfortunately, my middle ear really messes with me, particularly during loops. Strangely, aileron rolls give me no trouble at all.

I know from other experienced aerobatic pilots that you can get used to aerobatic flying, and my tolerance will build up over time.

However, is there anything I can do on the ground in order to help build up my tolerance more quickly?


texts: Do airlines have to get permission from the FAA if they want to change their livery?

texts: Do airlines have to get permission from the FAA to change their livery? It would be great if someone can throw in some examples where this has happened.


texts: Is it standard procedure to unlatch the cockpit door before an emergency landing in a small aircraft?

texts:
I was watching an Air Safety Institute video called "Real Pilot Story: Cemetery Crash – A near-death experience with valuable lessons for all pilots." It discusses a situation where a 1958 Bonanza crash landed in cemetery due to an engine failure.

At the 2:23 minute mark they are discussing the lessons learned and the pilot states that "I should’ve reached across and unlatched the entry door because that could jam in a landing, and in a Bonanza it’s very difficult to get out if you jam that door."

Is that really the proper procedure in the case of a crash landing? It seems a little strange to suggest that, while trying to land safely, the pilot should pop the cockpit door open.


texts: Could a C-130 Hercules be built using WW2 technology?

texts:
I'm looking at this as a "time traveller carrying only designs in his head" scenario.

Obviously turboprop engines are out of the question, but how close in capability would it be possible to get a C-130-style aircraft for use by June 1944 if our hypothetical time traveller arrived at Boeing or Lockheed in September 1939, and was able to prove his bona fides and be put to work with adequate resourcing?


texts: Is there a standard on-board diagnostics protocol for FADEC aviation piston engines?

texts:
Almost any car engine manufactured since 1997 will have on-board diagnostics, either the OBD1 or more recently the OBD2 standard which provides a standard for protocols, standard message codes and a standard connector which is universal across all engines (there are different pinouts used but newer readers can usually read them all), plus the ability for manufacturers to add their own fault codes where applicable. There is also telemetry available from the engine sensors which can be read to diagnose engine health, for example air flow and inlet air temperature, engine coolant temperature, etc.
I am well aware that the vast majority of aviation pistons are completely mechanical, but for the small percentage of electronically controlled engines that are out there is there any such standard? Do they use OBD2, another common standard, or are they all proprietary?


texts: Can planes benefit from Mitsubishi's Air Lubrication System?

texts:
Mitsubishi's Air Lubrication System blows a fine sheet of bubbles below the hull of a ship. The bubbles form a "carpet" on the hull, reducing friction. See Gizmag (yes, sorry) for some more information.

Let's assume that such a similar mechanism - something like the surface of an air-hockey table perhaps - would be feasible to implement on an aircraft.

What aerodynamic effect would it have? Could it, assuming it were feasible, provide any benefit to an aeroplane/helicopter/dirigible?


texts: When departing IFR, when do I switch from Tower to Departure?

texts: When departing IFR from a Class D airport, must you wait until the Tower instructs you to change to Departure?


texts: A320 procedures for one thrust reverser inoperative; why is the old procedure more efficient?

texts:
I recently watched the Mayday series about TAM Airline Flight 3054. Landing on a short runway with only one thrust reverser in use, and the documentary explained something like:

  The old Airbus procedure was to put both engines' controls on IDLE and then put only one of them on REVERSE. The new procedure says that you put both of them on REVERSE, regardless of if one of them doesn't work. The captain seemed to aim at the old procedure, because it is known to be more efficient.

I wonder how it is more efficient? Does the position of the controls for the second motor really influence the behaviour of the first one?


texts: How do aircraft windshields not crack when flying at supersonic speeds through precipitation?

texts:
Randall Munroe (author of XKCD and What If), once wrote a What If about how fast one would have to drive a car in order to have rain water shatter the windshield.

In the post he mentions that water hitting a windshield at supersonic speeds has the potential to shatter the glass.**

The article, unfortunately, is only talking about automobile glass.  And while I'm sure it's true that automobile glass would shatter if rain hit it at super sonic speeds, it's pretty clear to me that the glass on supersonic aircraft is not shattering when it flies through precipitation.

So, what is done to a super sonic aircraft's windshield to keep it from shattering when flying through precipitation?

** Here's a block quote of all the pertinent text in the post from Munroe.  I figured I'd post it for those who are Too Lazy™ to go read the article.  (Though, honestly, you ought to.  It's informative and entertaining.)

  Here's what happens when a raindrop hits a glass surface at high speed:
  When the droplet makes contact with the surface, a shockwave travels back up through the droplet...

  ...Normally, this shockwave would move at the speed of sound within the liquid—about 1300 m/s, four times faster than in air. However, at high impact speeds, this shockwave actually moves substantially faster than the speed of sound in water.

  The water is squeezed between the incoming drop and the glass surface, which makes it squirt sideways in all directions. These jets of water can move even faster than the original (already supersonic) droplet, and even faster than the shockwaves we mentioned...

  ...The sharp pulse from the shockwave can crack glass...

  ...In addition to the direct downward pressure, the water jetting sideways can cause damage, too. If the material has any microscopic holes, cracks, or bumps, those jets can strike them and create new cracks or widen existing ones.

  source: What If #93, Randall Munroe


texts: Have contrails ever occurred at low altitudes, such as at takeoff?

texts: Contrails form from the exhaust of jet engines condensing to water-ice. Has this ever happened at low altitudes, especially during or immediately after takeoff?


texts: What is the reason for this discrepancy regarding the CRJ100/200's stickpusher-activation angle?

texts:
The AC646 accident report contains a discrepancy regarding the angle of attack at which the stickpusher of the accident aircraft (a CRJ100, formally a CL-600-2B19, referred to in the aforelinked AAR as a CL-65) would have activated:

The stick pusher mechanism is designed to prevent the aircraft from entering an aerodynamic stall by applying a control column force to pitch the aircraft nose down as the aircraft reaches its computer-calculated pusher (stall) AOA. The Canadair Regional Jet Airplane Flight Manual (AFM) contains a chart (page 06-01-23) which allows calculation of the aircraft stick pusher (stall) speed for various aircraft weights. For 44 180 pounds, the aircraft’s estimated weight at the time of the accident, with the flaps set at 45 degrees and the landing gear down, the pusher activation speed would have been about 109 knots calibrated (109 knots indicated) at one g. At the moment of the aerodynamic stall, the aircraft was at a g loading of about 1.227, and the pusher activation speed would have been about 120 knots, the natural stall speed would have been about 116 knots, and the pusher activation AOA would have been about 13.5 degrees. [...] At the moment of stall, the flaps had retracted a few degrees from 45 and the g was increasing, both of which would cause a slightly higher pusher activation speed; however, there would be no effect on the pusher activation AOA.
Information from the flight recorders indicates the following events occurred during the attempted go-around: the stick shaker activated when the aircraft was at 129 knots as the pitch was being increased through 4 degrees; and the right roll and stall onset occurred and the warbler tone activated when the aircraft was at 124 knots and with the pitch at 9.7 degrees. At the time the warbler sounded, the left and right AOA vane readings were approximately 8.7 degrees and 9.4 degrees, respectively. The pusher did not activate because, while the right AOA reached its trip point, the left AOA did not.  [TSB Aviation Occurrence Report A97H0011, page 8 (page 18 of the PDF), my emphasis.]

In the first of the paragraphs quoted, the stickpusher-activation angle of attack is stated as approximately 13.5 degrees (a value which, according to the report, would not have been altered by the aircraft's rapidly-increasing AoA); however, the very next paragraph implies that the stickpusher would have activated at an AoA of between 8.7 and 9.4 degrees (the right AoA sensor, reading 9.4 degrees, is stated as having reached the stickpusher point, while the left sensor, reading 8.7 degrees, had not reached the activation threshold by the time the aircraft stalled, thus implying that the threshold AoA for activating the stickpusher was above 8.7 degrees but below 9.4 degrees1), rather than at about 13.5 degrees.
How to reconcile this discrepancy?

1: Due, presumably, to the potentially-catastrophic results of a spurious stickpusher activation at low altitude, the CRJ100/200's2 stickpusher does not activate unless both of the aircraft's angle-of-attack vanes measure an AoA at least as high as the stickpusher-activation threshold; in contrast, all the automatic high-AoA protections that do not alter the aircraft's flightpath (continuous ignition, stickshaker activation, autopilot disengagement [same threshold as for the stickshaker], stall-warbler activation [same threshold as the stickpusher], and stall-warning-flashing-light activation [also same threshold as stickpusher]) activate even if just one of the two vanes measures an angle of attack equal to or greater than the requisite threshold.
2: Although the accident aircraft was a CRJ100, the CRJ200 is identical to the CRJ100 except for using a slightly-different variant of the CF34 engine; the two even share the same CL-600-2B19 classification (making it somewhat difficult, when reading AARs discussing first-generation CRJs, to figure out whether the aircraft being referred to is a CRJ100 or a CRJ200).


texts: What frame of reference should I use for my Simulink simulation of the F/A-18 Hornet?

texts:
I want to simulate the Equations of Motions for F/A-18 Hornet (12 states & 6 DOF) on MATLAB using Simulink.  I have the Aerodynamic model, from which I will get CL, CD, CY, Cl, Cn, Cm that are flight conditions dependent.

Now, the forces and moments calculated from these coefficients will be in Wind Axes because these coefficients are defined in that coordinate system only (correct me if I am wrong). For using these Aerodynamic Forces and Moments in Body Axes, do I need to convert them into body axes by multiplying a Direction Cosine Matrix, that converts vectors from Wind Axes to Body Axes? Or should I use the Wind Axes computation?

Assume, I took the first option and converted the forces and moments into Body Frame. But, there are terms like $p$, $q$, and $r$ in the computation of the coefficients mentioned above. These terms are defined in the body frame. So, should I use these values of $p$, $q$, $r$ that are in body axes and compute coefficients in wind axes? Or should I convert them also into wind axes before using them in the computation?

PS: Reference for the Aerodynamic Model of F/A-18 Hornet:

A. Chakraborty, P. Seiler, and G. J. Balas, Susceptibility of F/A-18 flight controllers to the falling-leaf mode: linear analysis, Journal of Guidance, Control, and Dynamics, Vol. 34, No. 1, pp. 57–72, 2011.


texts:
Are monoplane struts under tension, doubling the stress limit of the spar?

If monoplane struts are under tension, they would be pulling the wing down,
which would put the bottom of the spar under compression, at least between the strut and wing root where the load is the highest.

However, the aerodynamic load when flying is upwards, trying to bend the wing up, so the bottom of spar would have to go from 1/4 max compression ultimate stress, through zero and all the way to 1/4 max tension ultimate stress to reach 1/4 max flying stress limit. Assuming both limits are the same and the safety factor, n is +/-4, hence 1/4 max ultimate stress.

That would roughly double the amount of stress the spar is allowed to  carry.

Sort of like prestressed concrete.

Is this correct?, at least conceptually?


texts: How does one determine the elevation on a sectional?

texts:
(Refer to figure 21) How does one determine the elevation variation of the light tan area between Minot (area 1) and Audubon Lake (area 2)?

A. 2,000 ft to 2,500 ft MSL.
B. 2,000 ft to 2,700 ft MSL.
C. sea level to 2,000 ft MSL.

I want to thank everyone for the help.  I made an 88 on my Drone certification that I took today (10/11/2018)


texts: What happens to the high pressure below an airfoil when the angle of attack increases?

texts:
I recently came across this question in a principles of flight exam:

When the angle of attack of an airfoil increases

the high pressure below the airfoil increases, the induced drag increases
the high pressure below the airfoil decreases
the induced drag decreases
can't remember this option

I chose 1. as the correct answer and it looks like I got it wrong. Although, I cannot tell for sure.

I know the induced drag will increase, but will the high pressure underneath the airfoil increase or decrease with an increase in angle of attack?


texts: Why are there no large turboprop passenger airliners?

texts:
If turboprop engines are more efficient than turbofan/jet engines at lower speeds, and have a lower specific fuel consumption, why are there no large passenger airliners that utilize the turboprop engine?

I expect this would increase flight times, but say for example an airline was to only operate short-medium haul flights within Europe, wouldn't it be in the interest of minimum fuel burn to use the more efficient engine, the turboprop?

Most modern airliners seem to use two turbofan engines. I am curious as to why the largest turboprop aircraft have a passenger capacity of below 100 (ATR 72 and DHC Dash 8) and why there are no 150+ pax turboprop airliners.

With minimum fuel burn as the priority, ignoring costs and flight times, would this be a desirable and achievable design option?


texts:
What WWI biplane is this model?

(own work)


texts: What is the procedure for landing on an aircraft carrier? How is the checklist different from a regular landing?


texts: Is there any class G airspace that extends to 14,500 MSL?

texts:
The U.S. Aeronautical Information Manual, part 3−2−6, lists a variety of airspace areas which may be designated type E.  From reading this section, I get the impression that "typical" class E airspace consists of regions near non-towered airports, plus everything from 14,500' MSL to 18,000' MSL.

The word on the street, however, is that this is not an accurate picture: In reality, class E airspace typically goes all the way from 1,200' AGL to 18,000' MSL, with dips down to 700' AGL around non-towered airports.  I.e. apart from a thin layer of class G airspace near the ground, almost all airspace away from towered airports is class E.  This is hard to notice on sectionals, since the only place it is mentioned is in the legend, where there is a footnote stating "Class E Airspace exists at 1,200' AGL unless otherwise designated as shown above."  I gather this widespread sort of class E airspace falls under the provisions listed in AIM 3-2-6e4 and 3-2-6e5.

So I have two questions regarding this:

Is there anywhere in the Coterminous U.S. where class G airspace extends up to 14,500' MSL?  (Excluding the trivial case of mountainous terrain above 13,000' MSL; c.f. AIM 3-2-6d1b.)
Since the existence of class E airspace from 1,200' MSL upwards is so ubiquitous, why is this not codified like the 14,500' rule is?


texts: What is the effect of opening airplane bay doors on the radar cross section of the airplane?

texts:
How does opening airplane bay doors (especially in the case of bombers), increase the radar cross section of the airplane and make it more visible to the radar?

  These are usually combined with active measures such as carefully planning all mission maneuvers in order to minimize the aircraft's radar cross section, since common actions such as hard turns or opening bomb bay doors can more than double an otherwise stealthy aircraft's radar return

Source


texts: Strange facility out west near California; what is this place?

texts: While on a flight to San Francisco from New York, somewhere over California or Nevada, I saw this from my window; what the heck is it?


texts: Would the Aeroflot Flight 1492 have been able to dump its fuel first before landing?

texts:
In the recent Aeroflot Superjet 100 crash, it seems to me that (at least) the landing gear was spiked upwards, penetrating the fuel tanks, which might be one of the factors that lead to disaster.

In my naive mind, dumping the fuel before landing might have mitigated this factor.

Would it have been possible for this airplane to dump its fuel before landing?


texts: What is the minimum possible number of hours required to carry passengers?

texts:
Not factoring learning curve, personal safety minimums, and pilot proficiency, what is the absolute minimum flight time that must be logged in order to carry a passenger in a piston engine aircraft in the United States?

I'm am looking for an answer for the airplane category. Not gliders or ultralights.


texts: Does windmill restart often work for airliner engines?

texts:
There seems to be a certain class of airline accident where an airliner engine flames out followed by further unfortunate events. Very often, pilots are recorded as having attempted to restart a failed engine by windmilling, which seems to involve attempting to restart an engine from the rotation due to the passage of air due to airspeed. In accident reports this rarely ever succeeds, leaving the impression of a rather worthless exercise.

But, of course, there's a massive bias here because these are the reports of accidents and if the windmill start worked, things wouldn't have deteriorated.

So, in rough terms, how desperate is attempting a windmill start. Is it in the land-on-water level of optimism, or something which usually succeeds which we never hear about?


texts: What prevents someone from hijacking a radio frequency mid-air?

texts:
For someone who wants to stay anonymous and probably terrorize the skies, what protective measures do we have?

Without even thinking too deep, I can imaging the following scenarios for someone who's in a mood to mess around.

Flying in a busy airspace, calling to "Cancel IFR" for someone else.
Abusing recklessly. Maybe stepping-on the frequencies infinitely.
Reporting fake traffic or fake weather conditions, causing re-routes
and delays.

While transponders are required in and around busy airspace, someone who really sets their target on screwing it up can REALLY cause a lot of harm, potentially fatal by flying without one for quite some time as a primary target on ATC's radar.

What are the current preparations to stop this from happening?


texts: Why wasn't a scramjet used for the Concorde?

texts: Why didn't Concorde use a scramjet engine for supersonic flight, but it is used in the Airbus and Skreemr hypersonic flight concepts to achieve supersonic speeds?


texts: What was the first control room--used for flight test--established in aerospace history?

texts:
The control room for space missions in Houston is probably the best, most widely known example of a control room.  It is an operations center used in support and execution of flight and space missions.

Historically, what was the first instance wherein a test team used a control room or operations centers for flight operations support?

This question answers why a control room exists, and this question answers who gets to be in there.


texts: During "partial panel" flying, in what ways is a turn rate indicator more useful than a turn coordinator?

texts:
This question deals with flying by reference to old-fashioned "steam gauges", not a modern "glass cockpit".

I recall hearing some pilots very experienced (ATP) pilots advocate for the older-style "turn rate indicator" (senses rotation about the aircraft's up/down axis) over the newer-style "turn coordinator" (senses rotation around an axis canted about 35 degrees from vertical, to sense roll as well as yaw.)  Specific reasons were given, but I don't recall them. In what ways is a turn rate indicator more useful than a turn coordinator, during "partial panel" flying (no working attitude indicator or heading indicator) in clouds?

The purpose of canting the gyro's axis of rotation to sense roll as well as yaw is to give an earlier warning to the first stages of a developing bank and turn, and in my experience this is indeed helpful, but apparently there are some drawbacks as well.


texts: Acoustic analysis from an aircraft engine?

texts:
I have found it surprisingly easy to find information on jet engines; however, I've been unable to find acoustic information so I can make a noise spectrum model.  I'm looking for oscillations from 100Hz up to 1MHz. I could make some guesses based on the number of blades, diameter and rotation speed, but I believe this information is out there because there exists noise reduction insulation on aircraft, and environmental noise rules.  In my search, I've found that NASA as analysis tools for acoustic liners, but nowhere have I found a study where these frequencies are described (I realize they will be different for different engines)

Ideally, what I'm trying to find is a decibel vs. frequency chart.

My motivation is purely academic as I have found (I think) that certain capacitors inject noise via ultrasonic oscillation into electronics, and I'm trying to find the frequencies involved. (I'm pretty sure that I'm going to have to make a blade/stage/rpm/thrust model for the noise, but I'm really hoping that the acoustic information is out there.)  At this point, it's possibly down to nomenclature and that I am not looking for the correct term as aviation is full of lingo.

Has anyone ever seen acoustic data for a jet engine anywhere?


texts: Can you identify these antenna/items on the belly of a Cessna 172?

texts: Not sure what all these antenna are for. I have my checkride soon and want to make sure I can name everything that might be pointed out. Thank you.


texts: What are the amber triangles on the ECAM bleed page on an A320?

texts:
In FCOM they say that triangle becomes amber when RAM AIR flap is not fully open, and both pack flow control valves are closed.
Here the RAM air flap is emergency ram air or RAM Air flap for the Packs?


texts: If I buy my own aircraft in which to earn my PPL, does my instructor need to be certified to fly the type of aircraft I own/am training in?

texts: It seems the most cost-effective way to earn my PPL is to purchase my own plane (with the intention to keep it for quite some time). I believe I would therefore need to find a CFI that is certified for that aircraft type, correct?


texts: Is there a general approach for designing a Trimmable Horizontal Stabilizer?

texts:
What is the general design flow when designing a Trimmable Horizontal Stabilizer (THS) and the attached elevator?

I assume you would dimension the max. positive/negative deflections of the THS to meet longitudinal trim requirements over all cg ranges, airspeeds, flap configs and then add the elevators on top of that to fulfill the manoeuverability requirements (pitch rate). But I guess there is more to it.

In other words:
How do you derive the maximum deflections of THS and elevator each?
(compared to a non-moving stabilizer design)

I'm not asking for specific formulas, but rather for the general approach. If you can recommend some detailed references about it, I would be really thankful.


texts: At what point does an aircraft need a new type certificate vs a STC?

texts:
First post. Yes, I did search but this specific question has not been asked before. This answer is close, however:

How does a mechanic determine if a repair or alteration requires a Supplemental Type Certificate?

I do not own an aircraft and do not have a PPL. BUT, I love the Piaggio P180.  This question pertains to the difference between getting a new Type Certificate and getting a STC (Supplemental Type Certificate). So, which of these alterations would require a new TC of the aircraft vs a STC?

Lengthening or shortening the fuselage?
Changing the engine(s) from say piston to turbine or turbine to electric fans?
Adding extra components to the airframe, like batteries, controllers, etc. to make a hybrid aircraft?
Changing the wings to newer ones from another certified aircraft (re-winging)?
Changing the landing gear to a newer model with higher load capabilities?
Expanding the fuselage diameter by 10%?

Would implementing one of these changes require STCs or after a certain number of alterations, does the FAA require a new TC?

I'm really trying to understand when STCs are used and when the FAA requires a new Type Certificate.


texts: Where do military aircraft carry flares?

texts:
Many sources on the internet say flares are carried in the fuselage, but do not specify the exact location of the compartment.

Does anybody know exactly where they are stored?


texts:
In a TAF-message downloaded from NOAA I came across "11/2SM" as the reported visibillity. I have previously seen "1 1/2SM" which I've been told to read as 1.5 SM.

is "11/2SM" a typo (should it have been "1 1/2SM") ?
Should it be read as a fraction "11/2" = "5.5" ?
Should it be read as "11+1/2" = 11.5" ?

Edit: Entire TAF (look 4th last line):

CYYZ 090839Z 0909/1012 31015G25KT P6SM FEW020 BKN050
TEMPO 0909/0913 P6SM -SHSN BKN020 BKN050
FM091300 29018G30KT P6SM -SHSN BKN025 OVC080
TEMPO 0913/0920 4SM -SHSN BKN020 OVC080
PROB30 0915/0920 11/2SM -SHSN
FM092000 31020G30KT P6SM -SHSN BKN025 BKN080
FM100100 33020G32KT 6SM -SN BKN020
FM101000 33018G28KT P6SM BKN020 RMK NXT FCST BY 091200Z


texts: Why is the gradient line for climb in a one-engine-inoperative condition during take off under CS-25 described in percentage?

texts: Appeciate an explanation in terms of definition of climb in terms of gradient & an explanation of the reasons behind each percentage condition for the different air craft types: twin engine, three engine, four engine, maybe propeller as well?


texts: How did the BV 141 fly? It looks like it has very uneven weight distribution and the overall design is asymmetric. I'm surprised that it could even take off.


texts: Was there ever a supersonic flight in a non-pressurized plane, and what is/would it be like for the pilot?

texts: If you went supersonic in a plane that has no pressurized cockpit, would you be completely deaf (because of flying faster-than-sound)? Would it be dangerous to the pilot even if he/she was in an enclosed cockpit, and if so, is this the reason why we still don't have supersonic maglev trains? Did anyone ever attempt or conduct a supersonic flight in a non-pressurized plane?


texts: What is this fuselage-side aerial used for?

texts:
(instagram.com)

I have seen this picture, and this feature on the port fuselage called my attention. Does anybody know the purpose of this?


texts: What are the conditions for the percentage power vs fuel consumption figures in the engine operator manual?

texts:
For the Lycoming O-160-A4A, the operator manual says in Economy Cruise, which is 75% Rated power and 2450 RPM, the engine produces 135 HP and burns 9.5 GPH.

How were these figures determined? Were they in standard conditions at sea level, or on the ground at the factory?

It is true that if you assume a power setting to be constant at 65% power and the aircraft is leaned at peak, the aircraft will consume 9.5 GPH, or is this figure not reliable?


texts: What airplanes can I fly with an EASA PPL license?

texts:
Weird as it might seem, I'm not 100% sure what airplanes I can fly
with an EASA PPL(A) license. During the training the instructors would
tell me that I can fly airplanes up to 2000 kg MTOW and 5 passengers
or so, but I think they are wrong and this applies only to the (old)
national rules (Germany in this case).

The license states that I have a SEP (land) class rating. I have
searched through the EASA rules (a cumbersome task on its own) and
nowhere could I find a weight or passenger limit, nor a specific
definition of what exactly qualifies as a SEP.

So the question is, what aircraft am I entitled to fly with my PPL(A)
license? Do aircraft with specificities such as a retractable
gear fall into the same category? Please also point to the source
of the applicable legislation.

By the same token, may I/may I not fly light aircraft such as e.g. a
K-10 Swift?


texts: How can cargo be jettisoned from a C-124 in flight?

texts: I was reading about a C-124 that was carrying three nuclear weapons over the Atlantic, and developed engine trouble. The article said that two of the weapons were jettisoned into the ocean for safety reasons. I was wondering how you can drop something from a C-124 in flight? Unless they were small enough to push out the back side doors. This happened on July 28, 1957.


texts: Why commercial planes fly at high altitudes?

texts:
L= Clq(TAS)^2*S/2
D= Dlq(TAS)^2*S/2

Some say it is due to lower friction drag due to lower density. However if our weight does not change, that means lift does not change as well. So when air density decreases with increasing altitude, TAS increases to maintan required lift force, thus dynamic pressure remains constant. This leads to the fact that drag must not change as well (keeping in mind that Dl and S are constant). What do i miss?


texts:
What are the flying accommodations in Silicon Valley for private pilots? I notice there are two pretty sizable airports: Moffett Airfield and Mineta San Jose. Do both accept GA flights and have landing fees below $50?

What about instruction? Where do pilots generally go for instruction in the San Jose-Palo Alto area?


texts: How could aerodynamicists reduce the intensity of the sonic boom?

texts: My understanding of the sonic boom is that it is caused when shockwaves being emitted from an object travelling at Mach 1 or above compress and superimpose on each other because they cannot move out of the way fast enough causing an explosive release of sound energy. This was an issue throughout the gestation period of Concorde effectively halving its potential route network since no government would allow routine supersonic flight over populated areas. For a future SST are there any ways in which the effects of the boom could be curtailed somewhat?


texts: How are forward and aft CG limits calculated?

texts: I have been tasked to create a POH for my aero engineering coursework and part of this task is to create the CG envelope for the theoretical 65 passenger aircraft. I have figured out weight, moment and cg for all loading scenarios but I am wondering how to create the actual envelope using forward and aft limits, as surely not all these scenarios will be able to fly? TIA


texts: Why don't they build airplanes from 3D printer plastic?

texts:
I'm not an expert in this field.

My assumption is that there are plastics lighter and stronger than the materials used to build planes. So that would make plane lighter and thus would consume less fuel which pollutes less and so on.

Maybe it would be more maneuverable, go faster, be safer as you may be able to safely land it with a number of parachutes in case of engine failure for example.

If these are true, why are planes not built from such a lightweight plastic?


texts: Is a helicopter ride unsafe for young children?

texts:
Recently we were in London and noticed how so many helicopter rides were there. While booking a ride I found out that they do not take a child under 4 years of age, none of the Heli ride companies I found in London allowed any child under 4 to take their rides.

So we were unable to take that ride since our child is  3 years old. I was wondering why is it unsafe for children to fly in a heli when the same or much younger children fly in a commercial airliner all over the world all the time?

Obviously I do not question their judgment and I do appreciate their concern for safety I just would like to know what makes it unsafe so we can prepare accordingly before taking that ride when he is 4.

I have been in helicopters I do not find them particularly challenging for a passenger. Could the primary reason be that these heli tours are not ordinary flight from A to B, they do quite some sprints and sharp turns up there to add to the fun.

Edit

Some references to support the question

  Must be 4 or over, under 16’s must be accompanied by an adult.

HeliAir

  No children under the age of 4 are permitted to fly with us.

RedHill Helicopters

  No children under the age of four are permitted to fly with us.

The London Helicopter

  Minimum age: 4 (under 16s must be accompanied by a paying adult)

Virgin Experience Days


texts: Is turbulence behind an airliner less severe during cruise?

texts:
The turbulence and tip vortices behind an airliner are a familiar hazard for smaller aircraft when near an airport.  But a lightweight glider seems to have not suffered from this, when its tail was actually struck by an Airbus A 320 at altitude.  Page 8 of the accident report mentions only the choc brutal felt by the glider's occupants, and nothing about being blown around like a leaf.
At the time of collision, the airliner was descending through 8600 feet at a true airspeed of 280 knots, if my French can be trusted.  The glider was flying at 53 knots, almost perpendicular to the airliner's path.  So the glider would have encountered the airliner's wake for a good fraction of a second.  Its long wings would be quite sensitive to turbulence.
Compared to the Airbus's high thrust at takeoff, or slow speed and high drag at landing, would its turbulence be less hazardous here, at low thrust and high speed?
https://www.skybrary.aero/index.php/Wake_Vortex_Turbulence#Accidents_and_Incidents mentions some "en-route" turbulence, but only from one aircraft trailing another.  So maybe a cross-track incident is much milder.


texts: Why are there so few aircraft that had inhabited wings?

texts:
According to an answer by John Frazer

  The only successful plane with inhabited wing might have been the
  Ju-38

Is this true?

In the whole history of aviation there was only one aeroplane with inhabited wings (so that people were able to stay in the wings, not just for repair purposes)?

What are the reasons that there were so few of them?


texts: How to find black boxes underwater absent any pinger signals?

texts:
If CVR/FDR cannot be seen visually on the seafloor (because covered by a thick layer of mud/sediments) and no pinger signals are detected, how can they be found? Metal detectors? Any other methods?

case in point: The FDR of crashed Lion Air flight 610 was recovered on 1 Nov 2018, but 2 months later now the CVR still has not been found (while the pinger batteries are rated for 30 days only):

  « The search for the CVR is hampered by thick mud. The signal source is difficult to ascertain its position considering the sea floor is mud with a depth of more than 1 meter. The ping signal from the CVR has not been received for 2 days now (5 Nov). There are other means to find the CVR however. » (source)

Which "other means" are this ?

update 18 Dec 2018: Lion Air contracts MCS to locate and recover the CVR of the 737MAX.

update 21 Dec 2018: an expert answered the question for me. I'll paraphrase his explanation as an answer below.


texts: What is the broadcast rate of an ADS-B message?

texts: From what I know, ADS-B (DF=17) message structure is 112 bits long. In terms of type of messages it transmits, there are aircraft identification, surface position, airborne position with baro altitude or GNSS height, airborne velocities, aircraft status, etc. However, assuming an aircraft is on final approach and it broadcasts the necessary information to ground stations then to ATC, what is its transmission rate in seconds? Is it really 1 second per message or does it differ from the type of messages? What factors affect the transmission rate? Thank you.


texts: Where can I find the exact definition of VFR and IFR?

texts:
Although I have worked as ATC more than 5 years(not US), I don't know the exact definition of VFR and IFR.

Of coure, I know that under VFR, pilot mainly use their eyes to navigate, but I want to know more exact and offical reference.

I tried to search these via google but failed to find offical reference such as ICAO annex or FAA regulations.

Could you guys help me to find the offical reference relating to VFR and IFR?


texts: What would be the safest way to drop thousands of small, hard objects from a typical, high wing, GA airplane?

texts:
The subject pretty much states my question, now I will provide a bit of background.

A family member, who lived on the west coast of Florida Manasota Key, collected tens of thousands of fossilized sharks teeth between the mid-1940s and the late 1970s. I have now become involved in deciding what to do with these sharks teeth. Here is one of the multitude of pictures available showing samples of these types of sharks teeth:

The vast majority of this collection ranges in size between a dime and a quarter and likely has the same level of hardness.

If you've visited one of the beaches in this part of Florida in the last 25+ years, you probably know that finding these treasures is no longer as easy as it used to be.  When I was a kid (late 1970s), I could usually come up with 10+ teeth in about a 2 hours stretch.  However, by the time my kids were of the age where this would be of interest (early 2000s), we were lucky if we found one a day.

What I'd like to do is return these teeth to the area just off shore of this beach thus giving future searchers a better chance of "re-finding" them.

Let's assume for the purposes of this question that the airplane involved would be a Cessna 172S. What would be a good way of doing such a drop without harming the aircraft itself?

I assume just dropping them out the window risks blow back that could damage the aluminum fuselage or tail assembly.

A couple of notes:

This is NOT a question about the legality of dropping items from an airplane in the United States. I am well versed with 14 CFR § 91.15 - Dropping objects, which states:

  No pilot in command of a civil aircraft may allow any object to be dropped from that aircraft in flight that creates a hazard to persons or property. However, this section does not prohibit the dropping of any object if reasonable precautions are taken to avoid injury or damage to persons or property.

I am not interested in a solution harmful to the environment. Thus dropping them in taped boxes or rolled up newspaper would not be warranted, because that would be littering.
I'm certainly aware that renting a boat and dropping them off the side would be an alternative. That said, for the purposes of this question, I am specifically asking how to achieve this using a Cessna 172 (or similar) high wing GA airplane.


texts: Why does cabin air have to be dehumidified?

texts: When air is piped in from outside and into a pressurized cabin, it is also dehumidified in the process.  All airlines provide beverage service on even short-haul flights to combat the dryness of the air.  Why is it necessary to dehumidify cabin air?


texts: Would there be any further restrictions on the Zapata Flyboard Air than current FAA regulations for ultralight aircraft?

texts:
We are seriously considering investing in Zapata Flyboard Air personal hovercraft.  We will use it on the east coast of USA Delaware, Maryland, New Jersey.  The Flyboard Air was designed to fit FAA guidelines for ultralight aircraft.

However this article covers how this vehicle has been banned from flight in France where Zapata is based.  While aviation regulations have always been more stringent in Europe, we don't want to risk our investment.  Would there be any additional regulations for this type of personal hovercraft over and above those already applicable to ultralight aircraft?

Would federal regulations override state and local laws that are bound to come?  How about Homeland security and privacy concerns?


texts: Why aren’t diesel piston engines used on aircraft like the Saab 340 or L-410?

texts:
In contrast to this question (link), I would like to know the opposite - why diesel piston engines aren't used on aircraft with comparable role and configuration to Saab 340, L-410, ATR-42?

There's a very similar question here, but it was mainly focused on small GA aircraft and private owners, while I'm more interested in commuter type piston airplanes.

Here's my thoughts so far after some reading (please note, some of them are just my assumptions and might be wrong).

Pros of diesel engine:

Engine itself is significantly cheaper
Cheaper to maintain
More economical according to this discussion (link)

Cons of diesel engine (vs turbine):

Likely they are heavier and more bulkier than turbine of similar
power output (link to similar discussion)
Diesel engine pylon is less aerodynamic (more drag) due to presence
of necessary air inlets for engine cooling
Possibly altitude (and thus performance) limited. I'm not really sure
about this point though. It's a well-known fact that commuter
turboprops can fly at 20-25k feet. I don't have any data for diesel
piston engines. I can only assume that diesel engine with a
turbo-charger might actually reach similar altitudes and performance.
Require more frequent maintenance

Perhaps this is worth asking as a separate question.

How heavy and big would be diesel piston equivalent of PW120 engine? (some ideas can be found in this discussion)

PW120 EASA data for weight, dimension and thrust (link):

Length 2130 mm
Width 635 mm
Dry weight 417.3 kg
Take off shaft power 1342 kW
Maximum Continuous shaft power 1268 kW


texts: How long does it take to refuel a Cessna Citation X+?

texts: Does anyone have any sources that can tell the the number of fueling nozzles and the fueling rate for a Cessna Citation X+ or a Cessna Citation X?


texts: Replacing or supplementing turbofan with electric fan

texts: Could you replace 2 B747 engines with electric turbofans? Could the 2 standard turbofans produce enough power to allow electric cruise with jets used for take off?


texts: Structural design software for airplanes

texts: What are the main structural design software packages that are used by the most of the aircraft manufacturers. There are a number of software packages but which one is widely accepted and used for the structural design of the aeroplane.


texts: Are there any programs to build a hydrogen powered airplane?

texts:
So called "renewable energy" is a buzzword these days. Auto manufacturers are starting to roll out hydrogen powered cars. Hydrogen may not currently be the most efficient or economic fuel for jet engines, but that doesn't mean there are companies working on this issue or even a new kind of engine.

Are there any such programs in existence today?


texts: How to calculate pressure distribution over an airfoil from its coordinates?

texts:
I need to compute the pressure distribution over an airfoil (I have the coordinates, but any will do) with the streamline curvature method. Unfortunately, I cannot find much on the web.

Can someone point me in the right direction or walk me through it? I understand it qualitatively (the concepts) but have a hard time quantifying it (actually solving the flow field).


texts: Why can't we see the downwash/wake roll-up behind 2D/wall-to-wall airfoil tests?

texts:
Why we can't see the downwash/wake roll-up behind any wall to wall airfoil wind tunnel video?
To make that happen, the air behind the center of the airfoil must go down and the air at the side walls must go up, producing two roll-up vortices. Could you upload video of that if it exists (which I doubt)?
DOWNWASH BEHIND WING VIDEO
here is how downwash and wake roll-up vortex looks at finite wing in wind tunnel:


texts: Could a big plane glide significant distances, same a ordinary glider (1000 km or about)?

texts:
Seems that a usual glider is not limited by its glide descent rate and can fly much more than this. It uses air masses that move upward to gain the altitude.

Are these effects limited by the size of the plane?
Could an airliner gain altitude for free using these "upward blowing winds"?
Could an airliner glide 1,000 km?


texts: What happens to the pressure differential of airflow under and over the wing as the critical angle of attack is reached?

texts:
I've been doing a research project for mathematics which involves calculating the relationship between lift and angle of attack. While this may seem pretty easy, it's not for a 12th-grade student like me.

We all know that the pressure differential is 1/2 ρ〖(v2-v1)〗^2, where v2 is the airflow velocity over the wing and v1 the airflow velocity under the wing.

It is also fairly commonly known that as AoA is increased, so does (v2-v1) leading to a higher lift coefficient.

But, my question is: Whenever the critical AoA (AoA at which the aircraft stalls) is reached, how do we calculate pressure differential? What is the new figure for (v2-v1)? How do these airflow speeds change as the critical AoA is reached?


texts: Is it possible for an airplane to enter another airplane?

texts:
I was making some cool fictional airplane designs and realized that most of my larger airplanes have a bay inside that stores a plane or two. But then I thought, is it even possible to make a plane exit and enter a plane mid-flight? Such a plane to enter another plane would need to have folding wings to take up the least space when stored, and also because the plane it is entering would have to be significantly larger to have a fuselage wide enough to fit a smaller plane's entire wingspan. Note that I am questioning if it is possible to do something NOT in an emergency, but as a tactic or for other reasons. That being said, the question differs from an emergency situation due to the fact that the question is implying that the operation be done over and over, and not in a risky, dangerous, last-resort fashion.
This mainly branches two questions:
Is it possible for a plane to exit a plane mid-flight, and if it is possible for a plane to enter a plane mid-flight. Clearly the plane must enter and exit through the belly of the larger plane, because something like a large hydraulic arm would be necessary to "grab" the small airplane and allow it to fold its wings up before hoisting it into the plane. This came to mind after considering that the plane must folds its wings up before entering the plane, and it also must take at least 5 seconds to fully fold the wings. So, folding the wings mid-flight independently isn't a good idea: The plane will plummet without wings to lift it. And to exit a plane, I'm assuming the arm will have to hold the plane out of the bottom and allow it to fold the wings out before dropping it. But here's what challenges that idea: When the arm is holding the plane and plane's wings are extended, will the little plane's wings effect the flight of the Larger plane? (Since the arm is grabbing it, it is the equivalent of the large plane having two tiny wings below it) and also, what are the effects of dropping a plane mid-flight? Any help on this would be very, very appreciated.
Oh, and a side-question from the above: Would a plane large enough to fit another plane be large enough to reasonably carry the weight of that smaller plane? And if so, how will the larger plane fair considering the fact that such a hydraulic arm necessary for mid-flight entry and exit of the large plane must be considerably heavy?


texts: What happens if drag coefficient increases but the lift coefficient remain the same?


texts: What do these numbers above the terminal jetway mean for pilots?

texts: The sign above the terminal has numbers, I assume, to help the pilot park.  What do they all mean?


texts: What are the "high performance characteristics" of a Boeing 777?

texts:
News of the potential further stretch of the A350-1000 have seen pretty much all journalists discuss the "high performance characteristics" of the competing Boeing 777-9 with Middle Eastern airlines. For example:

  [...] the new Airbus jet would target airlines that need high-capacity, long-range aircraft but not necessarily require the same high-performance characteristics that have made the 777-9 so popular with Middle Eastern airlines. (The Gulf region can be hard on an airliner.)

What exactly are these? Why is the 777-9 suited to them and the A350 not?