Why are engines with carburetors hard to start in cold weather? Why are engines with carburetors hard to start in cold weather?

And why is there a different procedure for hot start scenarios, after you've just shut down the engine and want to power up again?

They are all harder to start in the cold, fuel injected engines included, and need an over-rich mixture for starting.  The rich mixture is required because a lean one is harder for a spark to light off if the fuel/air charge is cold.

Now, it's still cold outside after the engine warms up, so the air charge is still cold, initially, but on a warm engine it gets heated as it extracts heat from the intake passage, valve and cylinder head on its way into the combustion chamber (and on Lycomings, the carburetor, which is bolted directly to the oil sump).

Carbureted aircraft engines use primer systems instead of chokes, as mentioned in AEhere's answer, because it's undesirable to have that sort of obstruction device in the intake passage. The primer injects raw fuel at the intake port using a syringe type hand pump, most of which settles on the intake passage walls and runs down the tubes a bit, and sits there slowly evaporating, and when the engine cranks, the vapours add to the fuel normally drawn at the carburetor.  It does this for a period of time after the engine starts depending on how much prime you used.

Fuel injected aircraft engines are primed the same way, but since there are injectors already there at the intake port they don't require a separate primer system.  You just turn on the fuel pump with the mixture rich for x seconds and it injects raw fuel just like a primer system.

Carbureted aircraft engines also use a slightly richer than necessary setting in the idle circuit to help them run better when cold.  That's why you get a little rpm rise when pulling idle cutoff.

You can have too little primer fuel when starting, or too much, and it varies widely depending on the engine, its temperature, and the air temperature, so you have to learn how much is enough on each engine type.  A typical protocol is:

On a cold engine in warm weather, you might use 4 strokes of prime.
On a cold engine in cold weather, you might use 6 to 8 strokes of prime.
On a warm engine in cold weather, you might use 1 or 2 strokes of prime.
On a warm engine in warm weather, or a hot engine you just shut down, you usually don't need any prime, but may use a little half-shot of prime, or, if the carb has an accelerator pump, a short stroke or two of throttle applied while cranking (to avoid fuel running down into the air box since throttle pumping sprays extra fuel from the accelerator pump right at the carb, and if the engine backfires with fuel in the airbox you can have an intake fire).

Different engine models have different starting quirks, and different primers have varying fuel volumes per stroke.  It's something you learn on that engine type, along with whatever other unique characteristics of a particular aircraft you have to be aware of.


How are evolution and variants of aircraft considered by certification authorities? Recently, both Boeing and Airbus launched "new" aircraft as a modernized version of their respective best sellers (B737MAX and A320neo). To narrow the question down, I will consider the A320 and the FAA, but the same goes for the B737 and almost certainly many more aircraft families, and I hope for other certification authorities as well. I'm not really clear on the difference between type, model and series but I think the difference may be relevant for the certification process. Perhaps highlighting this difference is enough to answer the question.

Wikipedia lists multiple variants of the A318. Do the A318-111 and the A318-121 require different certifications?

Moreover, when adding a variant to the family (here adding the A318 to the family composed of the A319, the A320, and the A321), do the certification authorities consider this aircraft as a totally new one or only as a variant of existing one (many shared components)? Can this consideration lighten the certification process?

Is the new version (A320neo) considered as a new aircraft by the certification authority and does it thus require the same set of tests as a new aircraft?

In short, when a new aircraft is an evolution or a variant of a previous one, how is it considered by certification authorities?

Variants are seen as a modification of an existing airplane design, and only the changed parts need to be certified. The real advantage is that the set of rules the certification has to comply with are frozen at the time of the initial application, so any additional rules that had been added later are not relevant. This is called "grandfather rules".

This definitely lightens the certification process and makes it less complex, but makes the safety enhancements, which were added after the type was certified first, optional for newly built airplanes.

The A318, A319 and A321 are all variants of the original A320, and the subtypes you name differ in their engine. Each engine option has to be certified separately, but all certification work not related to the engine can be shared between the variants. Additionally, the purchaser will select his options for instrumentation and furnishing, chosen from a limited set of previously certified options.

When a new version is introduced, the public will get a very different message from the airplane maker than the certification authorities. For the PR, the new variant is all new, but the FAA and the EASA will hear that almost nothing changed. In the end, it is similar to corporate profits: The shareholders get told the company made oodles of money, while the tax authorities will be presented with a bleak picture of mainly losses.


How come there is no attempt at an "inter-meshing rotorprop" high-speed helicopter? There are some prototypes of high-speed helicopters, such as the Eurocopter X³ (X-Cubed), Sykorsky X2, and older ones such as the AH-56 Cheyenne.

At high speeds, forward and backward traveling rotor blades relative to high speed flight path induce asymmetric lift and drag: Forward helicopter flight speed minus backward rotating rotor blade speed may equal zero relative speed, or even a negative value.

So, how come there's no [known] attempt at making an inter-meshing rotorprop helicopter?

Inter-meshing like K-MAX
Rotorprop (pusher) like Sikorsky S-66

It seems to offer a far more symmetric configuration than the examples mentioned above, and as illustrated below:

Below an illustration of assymetry at some positive AoA (view is normal to relative wind):

If labelled 1 to 3 top to bottom, numbers 2 and 3 in the illustration are identical.

A pair of rotors that are counter-rotating. One set is co-axial, the other set is slightly separated. Aerodynamically (dissymmetry of lift problem), I don't see a difference.

In plan view it looks like this:

(Source)

My guess as to why it was not tried, is because the transmission for concentric shafts is simpler, less bulky, and lighter, compared to that of intermeshing rotors (shown below).

Also, in intermeshing rotors the lift is not completely vertical, which reduces the efficiency (source). High-speed aircraft need to be efficient.

(Source)


What is the difference between a turbofan and a turboprop engine? I'm not an aircraft expert and I just realized that there are two different terms - turbofan and turboprop. I always had them combined in my head as a term for a large jet engine (like you would see on a 747). Apparently this is not the case though. So what is the difference between them? Are there other types of "turbo" engines?

Both engines use a turbine for power. This is where the "turbo" part of the name comes from. In a turbine engine, air is compressed and then fuel is ignited in this compressed air. The energy produced by the ignition turns the turbine. The turbine is then able to drive both the compressor at the front of the engine and also some useful load. In airplanes, it produces thrust.

The first jet engine was a turbojet. This is a simple turbine engine that produces all of its thrust from the exhaust from the turbine section. However, because all of the air is passing through the whole turbine, all of it must burn fuel. This means it is inefficient, and the solution is the turbofan.

In a turbofan, the turbine primarily drives a fan at the front of the engine. Most engines drive the fan directly from the turbine. There are usually at least two separate shafts to allow the fan to spin slower than the inner core of the engine. The fan is surrounded by a cowl which guides the air to and from the fan. Part of the air enters the turbine section of the engine, and the rest is bypassed around the engine. In high-bypass engines, most of the air only goes through the fan and bypasses the rest of the engine and providing most of the thrust.

In a turboprop, the turbine primarily drives a propeller at the front of the engine. There is no cowl around the prop. Some air enters the turbine, the rest does not. The propeller is geared to allow it to spin slower than the turbine. Although this diagram shows only a single shaft, many turboprops have two, with a high pressure shaft driving the compressor and a low pressure shaft driving the propeller. Some engines such as the popular PT6 also reverse the flow direction multiple times.

Turboprops are more efficient at lower speeds since the prop can move much more air with a smaller turbine than the fan on a turbofan engine. The cowl around the turbofan's large fan allows it to perform better than an open propeller at high speeds, but limits the practical size of the fan.

At supersonic speeds, turbojets have more of a performance benefit. They develop all of their thrust from the high velocity turbine exhaust, while turbofans supplement that with the lower velocity air from the fan. Since the air from the fan is also not compressed nearly as much as the core turbine flow, it is also harder to prevent the flow from going supersonic and causing losses.

The Concorde used turbojets because it was designed to cruise for long periods at supersonic speeds. Modern fighter jet engines are turbofans, which provide a compromise between efficiency and speed.

There are other benefits and drawbacks between turbojets, turbofans, and turboprops, but I think they are beyond the scope of this question.

Work has been done on creating a "propfan" engine, in an attempt to get the efficiency of a turboprop and the speed of a turbofan. They have yet to come up with a viable design.

Elsewhere in aviation, turbine engines are used in

helicopters, as a turboshaft engine driving the rotors instead of a propeller, and with a freewheeling clutch to enable autorotations
APUs in jet aircraft and large turboprop aircraft

Turbines also find use outside of aviation in power plants (to generate electricity), and even vehicles (like the Abrams tank).

Turbocharged piston engines use a turbine much differently from the examples above. Instead of being the primary power source, the turbine only assists the piston engine. A turbocharger uses a turbine to compress air sent to the engine intake. The increased compression helps the engine generate more power. The turbine of a turbocharger is driven by engine exhaust gasses, and a supercharger is similar but is directly powered by the engine. See the Wikipedia page for more detail.


How can I properly model paper airplane physics? I am working on a game involving flying and steering a paper airplane for WP7. I want the plane to fly just like how normal paper airplanes (online game) but I can't seem to find an equation for how paper airplanes fly.

Anyone have any experience with this? In my game now, it just follows the usual motion for an object in a vacuum, which makes for some flight, but it doesn't feel perfect, and traveling at a slight downward angle makes you lose speed, which isn't right.

I am asking do paper air planes have a maximum velocity brought on by its paper design even if control and thrust was possible maybe using composite cardboard material?

On Physics.SE: Paper airplane physics

I would model the energy flows between kinetic and potential energy. Start with a full bucket of potential energy plus the appropriate speed and drain kinetic energy away over time depending on flight speed.

To know how much energy is lost to drag, you need to model the drag using two components:

Friction drag, which grows with the square of airspeed, and
Induced drag, which drops with the square of airspeed.

If your drag is the sum of both, its minimum will be at some moderate speed. I plotted the drag components for a glider below, but since the physics are the same for a paper airplane, this plot should do for now.

The nonlinear behavior of the induced drag curve at low speed is due to flow separation, and something very similar will happen for a paper airplane. The important thing is: The drag curve has a minimum.

The energy loss over time is drag $D$ times speed $v$. This energy $E$ has to come from the reduction of height $h$ over time $t$:
$$\frac{\delta E}{\delta t} = \frac{\delta(m\cdot g\cdot h)}{\delta t} = D\cdot v = m\cdot g\cdot v_z$$
with $m$ the mass of the paper airplane, $g$ gravitational acceleration and $h$ its height above ground. Only $h$ changes over time, so derivation is easy and the derivative of $h$ is $v_z$, the vertical speed.

For picking a realistic drag it helps to rephrase the equation above by introducing lift $L = m\cdot g\cdot n_z$. $n_z$ is the load factor and is approximately one in straight flight. The ratio between lift and drag for a paper airplane is somewhere between 4 and 10 - just pick a number which results in a realistic simulation. To calculate the sink speed $v_z$ as a function of flight speed $v$ use this formula:
$$v_z = \frac{c_{D0}\cdot S\cdot v^3\cdot\rho}{m\cdot g\cdot 2} + \frac{m\cdot g\cdot 2}{v\cdot\pi\cdot b^2\cdot\rho}$$
S is the wing area of the paper airplane and $b$ its wing span. $\rho$ is air density, and for the zero-lift drag coefficient $c_{D0}$ you should pick a number which makes the paper airplane look realistic. Start maybe with 0.05.


Cascading Wings: Do they really increase lift by 300%? Cascading Wings for Ultralights: Do they really increase lift by 333%?!?!?

The classic NACA 650-18 airfoil has a Clmax of 1.5 according to airfoiltools.com ( a modified 650-18 is used on the Zenith 701).

Add non-slatted flaps, and the Clmax jumps to about 2.2.

What if one arranges the wing in a cascading fashion as shown below? Javafoil shows the Clmax jumping to 5, that’s an increase of 333% over the plain wing!!!

Not by just adding the same planform, but dividing the original chord by 4, so the a/r ratio is 4 times the original....

So that the quadplane is 400% more efficient than the original monowing, less a quadplane inefficiency of about 50%, so that the quadplane is still 200% more efficient than the monowing(maybe).

This probably only works ( if at all ) for very slow speeds (Re 300-800k) where the form drag and induced drag is very low.

I understand Javafoil uses Xfoil, which I’m told is a robust airfoil performance prediction program and is accurate up to an AOA of +/-20 deg.

Alternately, I’m told the VLM method (XLFR) is good up to only a Clmax of 1.5, +/- 20 deg.

So…. the million dollar question is… is a Clmax of 5 realistic, or is this beyond the scope of Javafoil/xfoil, even though the AOA is only about 8 deg….?

Ultralight Design Data:

See charts and tables below.

Flaps: 20% chord, 50 deg deflection

Wing Loading:51kg/m>2

Aspect Ratio: 7

Atmospheric conditions: Standard

Wing configuration: see chart below

Gap(vertical): 50%

Stagger(horizontal): -10%

Therefore biplane ( not multiplane) lift efficiency as per the table below should be: .26/.34=76% efficiency vs mono wing (Is this correct?) ( ignore the big green arrow, it's from the source I found the table)

Reynolds #: 880k

or......

is there a glitch in the software as per the comment below:

and the Clmax is about: climax 5 / 4 wings = 1.25

given the Clmax for a monowing is 2.2, and a biplane at 50% gap is 22% less efficient, a quadplane with 4 wings can easily be 40-50% less efficient, giving a clmax of about 1.3, which is close to the clmax of 1.25 above.

So what is the likely Clmax, 5 or 1.25?

The software appears to be taking the net plan area or shadow area of the overlapping stack as its area, but is adding the individual lifts of each wing. If you add the individual areas too then the calculation should show a fall in Clmax due to interplane losses.
I'd call it a bug, however I do not know the software so perhaps it is a "feature". It depends on whether you regard your stack as one wing or four.


Why are airplanes riveted and not screwed? Replacing airframe panels and inspecting hard-to-reach parts would be easier with screws, I presume. So why are rivets used?

Rivets need to press the two parts together AND to transmit shear. The pressure results in friction which is responsible for a considerable part of the load transmitted between two riveted panels. In order to hold up to the maximum possible amount of shear, the rivet needs a smooth surface. A thread would make it much more vulnerable due to the notch effect of the thread.
Since skin panels and flanges vary in thickness, a LOT of different screw sizes would need to be kept on stock so that every combination of panel thicknesses is covered with a fitting screw which has just the right amount of smooth shank length. Rivets, on the other hand, will be hammered to the right length during manufacture, so only a few sizes are needed to cover all those panel thicknesses.
Historically, metalworking tools were much less precise than today. For optimum shear transmission, the bolt must sit tightly in its hole. In the past, this could  not be done with screws, but only with rivets which grow thicker when set in place. And since aviation regulation authorities are VERY conservative, the easiest to certify joints are those proven rivet joints.
Repairability is adequate when using rivets, especially if you can reach only one side. The rivets are drilled out with a drill bit which has a diameter slightly smaller than the original hole size. Great care is taken not to oversize their original hole. The rivets are then, in the case of sufficiently thick material, tapped out with a hammer and punch. If the material is too thin or fragile to allow a punch and hammer to be used, the rivet will be drilled out with a drill bit that matches the original size of the rivet hole, with great care taken not to oversize the hole. If the hole is damaged or oversized in the removal process, a larger hole may be drilled and corresponding rivet installed, depending on the conditions present. After inspection or repair the parts are riveted together again.
If you need the lowest mass for a given strength, again rivets win over screws. The difference might be small for the individual rivet, but it adds up for the whole airframe.


Why does the Ka-50 (Hokum) have two main rotors, one on top of another? Why does the Kamov Ka-50 have two main rotors, and is this a better design than a conventional one rotor?

The ka-50, like other coaxial rotor designs, use their contra-spinning rotors to cancel out the torque in the same way a traditional helicopter uses it's tail rotor.

A traditional single rotor:

Source

Contra-rotating rotors:

Source

There are a few benefits of the contra-rotating setup, such as

Reduced vibration
Reduced likelihood of settling with power
Reduced likelihood of anti-torque failure during flight.


Can large airliners be operated without ground support? I'm wondering if large A3x0/B7x7 airliners could be operated without ground support. Short of using the inflatable slides, I guess at least stairs would be required to load/unload passengers. Apart from that, assuming fuel and push-back is not required, would it be possible to land, switch the engines and systems off and then take-off again without electrical, A/C, etc. ground support?

Bonus question:

If possible, are there any circumstances where this is routinely/occasionally done? I know that it's definitely the case for smaller aircraft such as an ATR 72 servicing remote airports - I experienced that at e.g. Luang Prabang airport.

There's a good example which is the A319 LR which flies scientists down to Antartica. They utilize (very) little ground support, except for the stairs (they seem to have inbuilt ones in the front as well, although these are not used on site) and the trucks to offload the cargo. APU provides the power on the ground, and the aircraft has sufficient juice in the tanks to make the round trip without refuelling.

(source: smh.com.au)

You can read up on it here. She does weekly flights from Hobart to Wilkins aerodrome in Summer. 4 hours and 30 minutes of flying right into the uninhabited :)


Can a pilot fly through a restricted area while flying on a Victor Airway? For example if you look at V 23-165-597, from Seal Beach CA to Ocean Side CA, you will notice that it goes through restricted area for Camp Pendleton (R-2503A & D):

I was trying to understand what is the rule as far as ATC Clearance to enter those Airspace or any other Airspace in general when you are on those Victor Airways.

Where can I find the FAA rules about these Victor Airways?

Short answer: yes, with permission. Whether or not you're on an airway isn't really relevant.

The basic regulations on restricted airspace are in 14 CFR 91.133 and they apply to all aircraft on all flights:

  (a) No person may operate an aircraft within a restricted area
  (designated in part 73) contrary to the restrictions imposed, or
  within a prohibited area, unless that person has the permission of the
  using or controlling agency, as appropriate

The AIM 3-4-3 also makes it clear that you can enter restricted airspace (my emphasis):

  Restricted areas contain airspace identified by an area on the surface
  of the earth within which the flight of aircraft, while not wholly
  prohibited, is subject to restrictions.

And it has details of how ATC handles IFR traffic:

  1. If the restricted area is not active and has been released to the controlling agency (FAA), the ATC facility will allow the aircraft to
  operate in the restricted airspace without issuing specific clearance
  for it to do so.

  2. If the restricted area is active and has not been released to the controlling agency (FAA), the ATC facility will issue a clearance
  which will ensure the aircraft avoids the restricted airspace unless
  it is on an approved altitude reservation mission or has obtained its
  own permission to operate in the airspace and so informs the
  controlling facility.

In other words, you can fly through restricted airspace if the controlling agency gives you permission, either directly or via ATC. In the specific case of the Camp Pendleton restricted areas, the Los Angeles sectional says that you should contact LA Center or SoCal TRACON (for R-2503D), and shows that the areas are not active 24 hours per day:

So in theory you can fly through at 3am without asking anyone, but if you're planning a flight that goes through a restricted area you should make sure you get a flight briefing and ask the briefer about that point specifically. And it wouldn't hurt to confirm again in the air before entering, in case the areas 'go hot' suddenly.


Which was the last Boeing crash that didn't send its black boxes back to the US? I couldn't find an answer online, so I am asking the community.

The real question is how frequent it is for a Boeing crash not to send the black boxes back to the USA, and a reply to title's question would be a good basis for the real answer.

My feeling was the black boxes were sent back to the US for analysis (maybe I watched too match Mayday).

Article(s) mention that sending the data recorders to the USA would be to allow a party with a vested interest to be a judge in its own case, but this, I imagine, could be the case in older incidents too - but my feeling that wants the Boeing black boxes to be sent back to US invalidates the article's argument.

Please refer to the following website for more details

https://slate.com/technology/2019/03/ethiopian-airlines-737-max-black-box-sent-to-paris-why.html

The International Civil Aviation Organization, which sets the standards for aircraft accident investigations, says that the country where an incident occurs is in charge of the investigation

If the concerned country has the tool to analyse the black boxes, they are analyzed locally and if necessary with the help of the aircraft manufacturer, therefore

When the concerned country has the knowledge to do the analysis there is no point to send the boxes to the manufacturer country.  What is particular to the Ethiopian case is that even though not having the tools to do the Analysis they preferred the help of a third party, rather than sending the boxes to the US, but this is beyond the scope of the question.

So the Ethiopian government asked Germany to analyze the black boxes, but according to CBS, the Germans also lacked the necessary software, consequently Ethiopia asked the help of France, thus the boxes have been sent to the Bureau of Enquiry and Analysis, the BEA.


Under what conditions can a non-RVSM aircraft or pilot fly in RVSM airspace? After purchasing an aircraft, it takes the FAA a long time to issue RVSM approval for the new owner.

During this time, under what conditions may an aircraft fly in RVSM airspace even though they aren't approved for it?

What is the process to get ATC approval for such flights?

According to the AIM Section 4-6-8, the language to use with ATC is simply, "Negative RVSM."  You have to say it on the request for an RVSM flight level, flight level change, or climb/descent through RVSM airspace.  You must also say "Negative RVSM" on check-in if currently at an RVSM flight level.

NBAA provides a guide for navigating the RVSM approval process.  This guidance is fairly new, and indicates that approval through a prior operator of the airplane is acceptable.  Your FSDO will make the authorization.

See also FAA RVSM Documentation


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

It's very prudent of you to be concerned about the axis frames in which different forces/motions are defined. It's a common mistake to ignore the fact that aerodynamic coefficients are normally defined in wind axes.

The standard approach is to calculate Equations of Motions in the body frame; this is how they are usually defined. For this, you'll indeed need a wind-to-body matrix (DCM). This is a simple matrix because it involves only two angles (beta and alpha), and these angles are normally small to be concerned about gimbal lock (the model is probably not defined where they are not small). Then you

Calculate the forces/moments that are defined in wind axes and rotate them to body.
Likewise, calculate forces and other things that are defined in the ground frame, such as gravity and wind per se, and rotate them to body. (It makes sense to use quaternions for that rather than DCM, but this is another matter).
Finally, you'll have forces that are defined directly in the body frame, such as thrust.

Now you can integrate EoM with all the data available in the body frame.

Regarding p, q, r (and such) used in calculation of the aerodynamic forces, these are usually body angular velocities that you can take directly from your EoM. However, you should double check if the aerodynamic model requires something else; this should be explicitly defined. Note that if you do need to rotate angular velocities, you can't use the same DCM but need to use the matrix that preserves the total angular momentum.


Can I use parachute fabric to cover an aircraft fuselage and wings? ...

Are there disadvantages to using parachute fabric to cover an experimental aircraft? So far I observed the following:

I believe I put this fabric in an open place for a year
I found no cracks after a year, approximately
When I tried to set the fabric on fire after a year it didn't catch on fire. It shrunk, but it didn't burn.
I didn't feel any weaknesses or holes in the fabric
I also checked the tension of fabric
In a weight test it up to 10 kg baggage

Now I'm trusting this imported parachute fabric.

I tested three pieces: one original, a second doped in poly varnish, and a third with a paste of mud/soil/sand mixed with poly varnish. The third is best and resists fire best.

Can I use it cover an aircraft?

Is there an experimental aircraft association in your country? I would advise you to get into contact with them for better advice.

If you want to know whether this fabric is good enough for covering your airplane, you should plan to perform a load test on the finished airplane. For this you need to know which loads the structure will have to endure. That would be about three or four times the weight of the aircraft on the wings and a proportional amount of load on the tail surfaces. Also consider asymmetrical loading conditions - the photo implies you want to cover a fuselage, and there torsional loads will probably produce the highest stresses.

Another consideration are dynamic and aeroelastic loads. Here it is not only the absolute tensile or compressive strength that counts, but also the stiffness of your structure. The material has an influence, but the way you build the airframe is even more important (think fiber direction - fabric has different properties in different directions). Therefore, I cannot give a good answer without more details.

Lastly, how you finish the fabric will have a lot of influence how long the material will endure in real life. Do you intend to use dope? At least plan to add UV protection coating on top.


Is triskaedekiphobia (fear of the number 13) the reason commercial planes normally do not have a row 13? When I first time heard this "legend" I couldn't believe it. I was really surprised, if not shocked, to actually find row 13 missing on my next passenger flight. (I believe it was a Boeing 737.) Is this really due to superstition about the 13th row? Was it so hard to push aircraft producers to renumber all other seat rows?

I know that people can be absurd about their superstitions. But realistically, the odds that a passenger airplane will crash are minimal. And should it really crash, chances that you'll survive due to being seated in row 12 or 14, as opposed to 13, must be below statistical error.

I find it very difficult to believe that people would choose not to fly simply due to superstition about being seated in row 13. Is there a more rational explanation?

EDIT (after Patrick's answer): I don't know, if I expressed myself enough clearly. I don't think, that people are dumb, because the're worried about number 13. I rather think, that thinking, that row 13 is unlucky, specifically on airplanes (where, in case case of crash all seats mostly are equally unlucky) is a bit weird.

Fear of number 13 is known as Triskaidekaphobia.

I randomly entered some flight numbers on SeatGuru and found that this one has row 13 (aircraft is B737):

In this case, there is no 13th row:

However, in this case, several row numbers (12, 13, 14) are skipped to adjust galleys and lavatories. This could be that they were added later or can be removed in future to add more rows.

The bottom line is that regardless of what you name it, there remains a 13th row. If a plane is about to crash (God forbid) I would be worried about being on the plane, rather than just the seat number. There are several studies that safest seats are in the back. So, rows 1-12 may not be as unlucky as row 13.

If you have 12 million dollars and I can give you one million more1, would you not take it?

In several parts of the world 13 is a lucky number.

1Trust me, I will not do it, even if I have that much money.


What causes harsh noise during TX/RX on VHF radio? I am running some trial radio test on PAE VHF main radio and during TX from ATC there is harsh noise at the background even though TX is 5/5. Likewise for the incoming RX from aircrafts. So I swapped the main radio with the standby radio but is giving me same results. I want to know what is causing this noise and how to eliminate it.

If the transmit signal is strong the Signal-to-Noise Ratio is high, which would mean that the noise that you hear is not background white noise filtered through the VHF frequency band. First thing I would look for is an active noise transmitter on the band, which would only be present in a limited set of frequencies.

Hard to say from behind the keyboard what causes the noise that you hear, suggestions for troubleshooting:

Is the noise present at all Xmit frequencies?
Does it diminish if you move away from your present position?
Does your squelch setting help at all?


What is the actual air speed over and under a wing due to Bernoulli's Principle? Bernoulli's Principle states that as a fluid speed increases, its pressure decreases, and vice versa.  Air flowing over the wing of an aircraft flows faster than its neighboring air flowing under the wing.

But how much faster?  Using the cruise conditions listed for a Boeing 747-400 – airspeed Mach 0.85 (567 mph, 493 knots, 912 km/h) flying at 35,000 ft – what are the corresponding maximum and minimum speeds of the airflow over the wing?

For the purposes of the calculation, assume standard atmospheric conditions for an EAS of 273 knots.

In general:

How much does this depend on the shape of the airfoil (or: does this translate to general aviation as well)?
Does changing the angle of attack (without stalling) affect the airspeed/pressure differential?  If so, by how much?
Typically, where on the wing (inboard to outboard) is the most Bernoulli-derived lift generated (i.e. due to airspeed/pressure differential)?  Or does this vary greatly with wing design?
Where on the airfoil (leading edge to trailing edge) is the region of highest and lowest pressures (and thus, the slowest- and fastest-moving air)?

If you know the pressure coefficient of the flow, the rest is easy. The equation for the pressure coefficient $c_p$ is:
$$c_p = \frac{p - p_{\infty}}{q_{\infty}} = 1 - \left(\frac{v}{v_{\infty}}\right)^2$$
$q_{\infty}$ is the dynamic pressure and contains air density $\rho$ and the flight speed $v_{\infty}$:
$$q_{\infty} = \frac{\rho}{2}\cdot v_{\infty}^2$$
The equation for the local speed, relative to flight speed, is:$$\frac{v}{v_{\infty}} = \sqrt{1 - \frac{p - p_{\infty}}{q_{\infty}}} = \sqrt{1 - c_p}$$
Now you need to know the pressure coefficient. At Mach 0.85 the local Mach number of the 747 wing, which has a wing sweep of 37.5°, is 0.674. Since I do not have the airfoil of the 747-400, I used one from the same family (BACJ), found here. If you are interested, many more can be found in Michael Selig's immense airfoil database.

The plot is from a TSFOIL calculation of the 2D flow around BACJ at Mach 0.8, so it needs to be taken with a grain of salt. Note that it shows a stagnation point, and, therefore, Mach = 0 at the leading edge. The leading edge of the 747 wing is swept by 45°, so it will only slow the orthogonal speed component to zero. Consequently, the 747 wing has a stagnation line where the lowest speed will still be Mach 0.6.

On the suction side, the airfoil reaches Mach = 1.2 quickly and even Mach 1.3 near the trailing edge. Modern, so called supercritical airfoils can tolerate mildly supersonic speeds on their suction side, and the Boeing 747-400 makes use of them. However, since the wing sweep reduces Mach effects, the top speed will be Mach 1.2 or slightly lower, and the TSFOIL calculation shown here is not exactly correct for flight at Mach 0.85, but gives a general idea what happens on the wing.

To answer the many questions you posted directly:

The shape of the airfoil is immensely important. Thicker airfoils need to displace more air, and higher flow speeds are created on both sides. Camber will increase the pressure (and speed) difference between both sides.
Changing the angle of attack will add a roughly triangular difference, which is highest at the leading edge, to the difference between both sides. Lower side pressure is increased slightly, and upper side suction goes up by a lot at the nose.
Good wing designs have a triangular lift distribution over wing span, with the highest lift at the root. Since the displacement effect of the fuselage is added to the flow effects, the highest speeds will be encountered at the wing root.
Just look at the pretty pictures ...


Does the Predator drone's design make a tail strike more likely on takeoff and landing? I was reading an article about drones and happened to glance at an included 3-view of the General Atomics Predator series UAV. The inverted-V tail appears to leave, at most, around 6" of clearance to the ground.

On takeoff or landing, how is there enough clearance to allow the operator to rotate? Is the wing designed to have a high angle of incidence on the ground?

The tail arrangement was initially chosen to protect the propeller from touching the ground first. The configuration of what later became the Predator was initially designed to be launched from a submarine, so it needed to fit into a torpedo tube when folded. When this configuration was scaled up, the general arrangement was kept. Now the tail surfaces are much larger relative to the propeller, so the initial reason for their location is not easily discernible.

The high aspect ratio $AR$ of the Predator's unswept wing gives it a much higher lift curve slope than that of the swept wing of an airliner, so less rotation is needed to increase lift for take-off. Also, the highly cambered airfoil has a very low, negative zero-lift angle of attack, so at level attitude the wing already produces substantial lift. This was chosen to fly at optimum endurance speed with a horizontal fuselage attitude. The lift coefficient $c_L$ for optimum endurance is $$c_L = \sqrt{3\cdot\pi\cdot AR\cdot\epsilon\cdot c_{D0}}$$
At that lift coefficient, induced drag $c_{Di} = \frac{c_L^2}{\pi\cdot AR\cdot\epsilon}$ is three times bigger than zero-lift drag $c_{D0}$, which means endurance is longest when the aircraft flies at a high lift coefficient and low speed. Basically, the Predator is a point design, flying almost always at the same attitude and lift coefficient. Ground attitude equals flight attitude, and a rotation beyond a few degrees will make it stall.


How do propeller planes suddenly make noise? I was wondering: how can a propeller plane, single engine or otherwise, be flying along relatively silently and then start making noise, often very loud--and then turn it off just as quickly? Are they descending/ascending? It seems like the engine must be straining.
Thank you.

It is unusual to change prop speed quickly and only briefly, so I would suggest two possible explanations:

On the ground: The pilot tests the propeller pitch control. This he/she does by revving up the engine while the propeller is at a low pitch setting. Then the pitch is increased, which increases the aerodynamic forces on the prop and, consequently, the noise it radiates out. Since this test takes only a few seconds, the result is just what you described (but not while flying overhead).
In the air: Propellers don't radiate noise equally in all directions. This is especially pronounced on the T-6 "Texan", where the noise intensity increases dramatically when you stand directly abeam of the aircraft. The plot below is taken from this report on propeller noise. Probably what you hear is caused by the variation in noise (and dominant frequencies) while the plane flies overhead.

Directivity plot of propeller noise. The details depend a lot on the specific aircraft and propeller type.


Why are flight simulators bad at predicting drag and lift values at high angles of attack? (the nonlinear flow regime) X-Plane is built on something called blade element theory. From my understanding, it says the aircraft performance can be found if the performance of 2D cross sections are calculated and integrated in real time. Laminar Research (the maker of X-Plane) uses that as a selling point for X-Plane, saying it can be used to help aircraft designers try out their designs in flight on the computer before building prototypes. However, as commentators on this forum have written before (Peter Kampf), most flight simulators are bad at predicting the performance of the airframe at high angles of attack without using a table of force coefficients generated through windtunnel data or detailed CFD.

My question is, what in the flow physics drives this? What part of the physics is modeled incorrectly to give garbage data at high angles of attack?

Laminar flow is easy. While there is a complete set of differential equations that describes any fluid flow, there is a wealth of simplifications and assumptions that you can use on laminar flow. This means that X-Plane doesn't need to model all the air around the wing, but can do the calculations based on wing profile and local velocities. Everything is relatively linear, so you can just change some variables and use predetermined parameters. Furthermore, it's completely time-invariant in steady state. You can now easily solve the equations, integrate the calculated pressure profile along the wing, and done!

For turbulent flow, none of that holds. The current way of simulating turbulent flow is to do a Finite Element analysis or similar (e.g., FDM). Basically, you will need to consider all the air in a large volume around the wing, divide it up in a small grid and simulate it. For a good calculation, this takes in the order of seconds to minutes for a single 2D cross-section on my pretty decent laptop. And then we're neglecting the 3D influences. Furthermore, turbulent flow changes w.r.t. time. For example, open your car window on the highway - you will hear the wind roar and pulsate. This means that you will need to get your previous pressure- and velocity field, and use that as a starting point for your next FEM/FDM analysis. Finally, turbulent flow is extremely hard to predict correctly, even with above methods: a slightly rougher surface, a small bolt or a small wind gust can delay flow separation for a few inches, completely invalidating your results. Perhaps this YouTube video (note: this is not simulated in real time!) might shed some light on the vast complexity and time-dependency of turbulent flow - and remember that your horizontal stabilizer will see disturbed air in stall conditions, making it necessary to simulate the entire flow field around the airplane for a correct simulation, not just the wing sections.

Of course, X-plane has a framerate measured in frames per second, not frames per hour. This means that they use a bunch of assumptions to calculate the wing lift. I'm guessing they just have some values for location of flow separation and turbulent pressure for some fixed velocities and angles, and interpolate to the actual values. My guess is that they also have some parameters that aren't actually calculated, but are chosen such that some very basic maneuvers are possible like spin recovery, regardless whether these values correspond to any actual physical phenomena - it's a game, after all.


What are the ejection injury and fatality rates? Most of us have probably heard about how ejecting from a military aircraft is dangerous in and of itself, and that ejection is not a get out of jail free card.

The most common dangers seem to be:

Lacerations during the ejection, by failing to clear the cockpit.
Concussions caused by collisions with the canopy or fuselage.
Insufficient altitude or speed to deploy a parachute before impacting terrain.
Other assorted hazards associated with parachuting down in an unprepared location.

There exist a number of openly-available reports on the topic, from several different countries and time periods that could serve as a starting point.

I have multiple closely-related questions, so I hope it will be self-evident why I chose not to split them up, but feel free to focus only on the first one:

What are the odds of surviving an ejection from a military aircraft? We can presuppose a fit crew member, but make no further assumptions about the particular case.
How likely is the crew member to sustain injuries?
Are there any significant trends in the data, e.g. introduction of 0-0 seats, survival procedures, sub- vs. supersonic ejection?

Survival outcomes in low level ejections from high performance aircraft is a 2013 consolidation of ten separate studies of ejections from 1952-1997, focused on comparing low level to high level ejections. It doesn't state that these were military (though likely) and only considered those where altitude was known. From the abstract:

  There were 562 low-level ejections identified. Out of this number, there were 274 fatalities, giving a low-level ejection survival rate of 51.2%. There were 2607 ejections that occurred above 500 ft (152 m), with a survival rate of 91.4%. There was a significant difference between ejection survival rates below and above 500 ft (152 m). Low-level ejections have a significantly increased risk of a fatal outcome (Odds Ratio 10.07).

So overall the odds of surviving an ejection are 84%.


How are foam cores shaped for tapered and swept back wings? How are foam cores shaped for tapered and swept back wings?
I understand that many constant chord, constant thickness rectangular wings use the same sized airfoil shape from root to tip. Let's assume the wing uses a classic NACA airfoil shape such as 650-18.
How would a foam core wing with a classic NACA airfoil shape, swept back 10 degrees be shaped?  Is the wing, using the same airfoil shape, NACA650-18 just rotated back 10 degrees from the root?  In this case, in cross section longitudinally (along the plane's y axis, in the direction of airflow), the actual airfoil shape would no longer be the same shape as the rectangular non swept wing, even though the geometric perpendicular cross section of both wings is exactly the same. Is this correct thinking?

I'll assume you're already researched the methods for hot wire cutting foam blocks in the Rutan moldless method and are familiar the hot wire tool and airfoil templates you make and the template cutting process.
You can do it two ways; make hotwire templates with the longitudinal axis airfoil contour (the stretched airfoil shape resulting from the sweep) to stick on the end of the foam blocks that you have already truncated with the 10 degree sweep, or make the templates to the airfoil profile perpendicular to the mean chord line, stick them on to the blocks with square ends, and truncate them to the 10 degrees sweep angle after you've cut them out.


How can we calculate the benefit gained from taping glider wing roots? Most (all?) glider pilots will be familiar with the practice of taping wing roots.  As most of the gliders in my glider club (and I would guess, in the world) are stored with the wings detached, the practice of taping wing roots to close the gap between the wing and the fuselage is one which is hard to get through glider training without learning.  Indeed, even the type/brand of tape used can be a subject of hot debate.  This picture shows what a taped wing root looks like:

I've always wondered though how critical this practice is.  The gap in wing roots, once spar pins have been inserted, is typically pretty small.  I've forgotten to tape, but I usually don't forgot, partly because I know someone in the club will point out that I've forgotten and a fresh debate ensues.  I would say I'm currently skeptical (but open minded) about the benefit of doing this.

Question:

How effective is taping wing roots?

Lets take, for example, the Schempp-Hirth Open Cirrus, which has a published maximum glide ratio of 44:1.  Lets assume this glide ratio was calculated with the wing roots taped.  This assumption is bolstered by the fact that the rigging check list (Open Cirrus Flight Manual, Page 20) has taping the wing roots as a step.  What would the glide ratio be reduced to if the wing roots are not taped?  I do understand that the answer would depend on the width of the gap.  Lets assume that is 1/16th inch (1.5 mm) for this example.

Secondary Question:

What would the answer to the same question be applied to the gap tape used between the aileron and the wing, as is shown in this picture:

The two questions actually concern very different issues.

The second question is easier to answer. Let's take your thought on:

  I've always wondered though how critical this practice is.

It is pretty crucial! If you did not tape the gap between the wing and the aileron, you increase chances of a stall. This is especially true at low speed and large angles of attack, i.e. while thermaling or landing. Then an airflow from the lower side of the wing to the upper side might occur, through the gap, destroying the upper side's airflow. This very certainly leads to a performance penalty but also favors stalls. There have been some prototypes experiencing exactly this loss in performance (I could provide more detailed references if desired). I haven't heard of a stall related to this issue, and it actually might be unlikely to happen because under the described circumstances the transition point from laminar to turbulent flow is rather close to the wing's leading edge anyway. Nonetheless, the possibility of increased stall probability should be considered and, imho, is reason enough to never ever fly without aileron tapes.

The first question can only be answered qualitatively, at least with today's methods. It is effective: the airflow, although transitioned to turbulence by the tape, is definitely less turbulent than without the tape. Any kind of turbulence model will consider the "amount" of perturbation, i.e. larger discontinuities of the surface lead to stronger turbulence, thus more drag. You could fly with only one wing taped and see if you can notice a difference. If you notice rolling or yawing, then that's in favor of the corresponding wing. Honestly speaking, I doubt anything can be noticed if the wing consists of one part only, because the asymmetric drag is so close to the center of gravity (only at wing root). But if the wing is made of multiple parts, that might actually lead to some practical result. I am thinking of, e.g., Schleicher's ASW 28 or ASG 29 that have inner and outer wing parts + winglet, meaning 3 tapes distributed over the half wingspan. However, please check the manual of the glider first, if flying without tapes is permitted by the manufacturer.

And then there is also the noise issue.

Given all this information on the one hand and comparing it to the cost of tape and the time it takes to apply it, there is no reason not to use sealing. (Except, of course, around the canopy. You wouldn't expect what kind of ideas people can come up with)


How do airliners facilitate in flight calls for mobile phones? How does an airline facilitate in-flight calls for mobile phones?

I would guess that over open water in flight calls are relayed by an on board link to a communications satellite.  Such a system would likely need to track the location of the aircraft.  The records from this system could provide tracking information that is not available from other sources.

Cribbing liberally from Manfred's answer on a related question, it basically works like this:

The airline contracts with a communication company and installs satellite transceivers and "small cell" cellular equipment on their aircraft. Your phone talks to the on-board cellular equipment just like it would to a cell site on the ground, but the information is relayed to the satellite and sent back to earth to join the regular telephone/data networks.

It's not generally feasible to use these datalinks to track the location of the aircraft -- getting your basic position (latitude/longitude) requires triangulation from at least 3 satellites, while data communication only requires one (satellites are expensive, so providers aren't likely to launch their own constellation of satellites to duplicate the functionality of GPS).

This same type of data uplink could theoretically be used to transmit flight data (including GPS position that the aircraft can get from the existing GPS equipment on board) back to the airline's headquarters, ATC (to fill gaps in RADAR coverage), etc., but I'm not aware of any system or plan to implement that currently.


Can I use audio containing Canadian ATC/broadcast radio transmissions in a YouTube video? I often record my flight training without audio and post some of it to YouTube. I would like to add in audio recording of what I hear and say over the radio as well, but my ground school suggested that it was illegal to make radio transmissions public. On the other hand, I see youtube videos all the time that do include ATC voice traffic.

Can someone clarify for me if it is permissible to record and make public radio transmissions recorded during my own flights?

If it makes any difference, my videos are not/will not be monetized and and my flight training takes place in Canada.

EDIT: finally remembered my source, which is the radio operator restricted certificate study guide, which says:

Radio operators and all persons who become acquainted with radiocommunications are bound to
preserve the privacy of those communications. In accordance with subsection 9(2) of the
Radiocommunication Act, no person shall divulge the contents, or the existence, of communications
transmitted, received or intercepted by a radio station, except as permitted by the addressee of the
message or his/her accredited agent, or to authorized officials of the Government of Canada, officers of
the court or an operator of a telecommunications system as is necessary to forward or deliver the
communication. These restrictions do not apply to a message of distress, urgency, safety or to messages
addressed to “ALL STATIONS” (i.e. weather reports, storm warnings, etc.).
As outlined in section 9.1 of the Act, any person who violates the privacy of communications is liable,
on summary conviction, in the case of an individual, to a fine not exceeding twenty-five thousand dollars
or to imprisonment for a term not exceeding one year, or to both, or, in the case of a person other than an
individual, on summary conviction, to a fine not exceeding seventy-five thousand dollars. https://www.ic.gc.ca/eic/site/smt-gst.nsf/eng/sf01397.html

It sounds like I am able to post radio communications for which I am the addressee (and presumably addressor)

In countries where it is illegal to listen to ATC chatter like the UK, it is also illegal to post it, and you can see this on LiveATC, where you can easily listen to YKZ, YYZ, YVR, YTZ, and YHZ, etc. in Canada, but you can't listen to UK airport feeds or sectors for example LHR, LGW and MAN.

So assuming that liveatc is not an illegal orginization, (we know that for sure because literally the #1 thing that comes up when you search on google atc, liveatc comes up. And if it was illegal, the RCMP would have taken down liveatc at least in canada years ago!) we can say that no, posting atc chatter online is not illegal in Canada.


What restrictions apply to flying RC and UAV planes in India at very low altitudes? We are working on a UAV and will soon get to the testing phase. We intend to fly at a maximum altitude of 300-400 meters. I wanted to know as to what restrictions apply to the airspace in India (specifically Delhi) with respect to flying UAVs as well as the altitudes from which they apply?

We will also be testing autonomous capabilities. Do we need to get any licenses for this?

The Director General of Civil Aviation has published this public notice:

  GOVERNMENT OF INDIA OFFICE OF THE DIRECTOR GENERAL OF CIVIL AVIATION
  OPPOSITE SAFDARJUNG AIRPORT, NEW DELHI – 110 003

  PUBLIC NOTICE   File No. 05-13/2014-AED Dated: 7th October, 2014

  Subject: Use of Unmanned Aerial Vehicle (UAV)/ Unmanned Aircraft
  Systems   (UAS) for Civil Applications

  Of late, lots of interests are being shown for civil use (both
  commercial and recreational) of UAS in the country. International
  Civil Aviation Organization (ICAO) is yet to publish Standards And
  Recommended Practices (SARPs), as far as certification and operation
  of civil use of UAS is concerned.

  UAS has potential for large number of civil applications. However, its
  use besides being a safety issue, also poses security threat. The
  Airspace over cities in India has high density of manned aircraft
  traffic. Due to lack of regulation, operating procedures/ standards
  and uncertainty of the technology, UAS poses threat for air collisions
  and accidents.

  The civil operation of UAS will require approval from the Air
  Navigation Service provider, defence, Ministry of Home Affairs, and
  other concerned security agencies, besides the DGCA. DGCA is in the
  process of formulating the regulations (and globally harmonize those)
  for certification & operation for use of UAS in the Indian Civil
  Airspace. Till such regulations are issued, no non government agency,
  organization, or an individual will launch a UAS in Indian Civil
  Airspace for any purpose whatsoever. The above is for strict
  compliance.

  Director General of Civil Aviation


Flying from right seat of Socata TB9 - confused about Pilot manual limitation (US regulations) I was comfortable flying from the right seat in my Grumman American AA5A and would let non-pilots sit in the left seat to introduce them to flying. I was expecting to do the same in a friend's TB9, but this text gave me pause.

Given the the Socata TB9 (Tampico) is generally considered a primary trainer I was surprised to find the following in section 2 (Limitations) of the Pilot Information Manual

  CREW LIMITATIONS Minimum crew: 1 pilot
  (1 pilot required at L.H.
  station)

I am confused how to interpret this.

How is it legal for a CFI to train a "non pilot"?
Does it mean that as long as there is a body in the left seat anyone can fly it (from the right seat?)
What does "pilot" mean in this case in the Pilot Manual? Is "Student pilot" defined only when there is a CFI in the right seat?

I have seen placards on tandem airplanes that allow "solo flight" from one of the two positions for what I expect are CG limitations - but am baffled by the perceived limitation in this manual as-written.

Most airplanes are designed for the pilot to be in the left hand position, so some have controls on the left side that are inaccessible (or very hard to reach) in the right hand position, like parking brakes, fuel tank selectors, nosewheel tillers (on big jets), sometimes the key is hard to reach. On the TB9 the circuit breaker panel is by the LH pilot's leg, it would be extremely challenging for someone in the RH seat to reach those, and they could be important if one blows in flight or there's a fire.

The important things is that the person in the left seat is capable of and has been briefed on how to operate any controls required during the flight.

Personally I don't see why you need to let people sit in the left seat to give them a taste of flying, the right seat is just as good for that and it is less risky.


Do pilots have the ability to bypass customs when utilizing jump-seat privileges? I wonder if anyone can help with a hypothetical question. Its for a novel I am researching
All passengers with a ticket for a flight will pass through normal passport controls but I am told that Pilots can jump a flight if theres a spare seat. I know it might be outside of procedure but...
Is it feasible that he might join his buddies and get on the plane with them and avoid the official record of him entering and leaving another country say between the USA and Canada?

Just to put down as an answer what has been pretty well covered in the comments...

All pilots, jump-seating or not, will still clear customs.  They may have a separate line, but there will still be the normal record of their entry.

Beyond that, the airline absolutely knows who they let on the jumpseat for each flight -- so "no record" won't really happen in any event.


Why are autonomous vehicles not used at airports for on-ground services? Autonomous vehicles have been around for over an decade, other industries such as the maritime industry have already been using unmanned vehicles at ports. Curious to know why airports are reluctant to implement this despite the clear benefits it has.

Many of the ground vehicles need to have a trained human to make it useful for the plane (for example the fuel truck, mobile stairs, ...) so it makes sense for it to cart the trained human around. If you do that you may as well make said human drive. This means there is a high ratio of human controlled vehicles mixed with the autonomous vehicles. There are also the firetrucks that need priority, giving it to them sometimes needs human intuition in where you stop or move to to make a path.

You don't want the vehicle to path underneath an airplane and cause damage, or potentially end up in the jetblast.

Someone needs to monitor them and coordinate with the ground controller whenever they need to access/cross the taxiways.


Can a non multi-engine rated pilot get a complex endorsement in a multi-engine aircraft? I was wondering if a pilot with only an SEP can get his/her complex endorsement in a multi-engine aircraft? I would guess not but since I didn't find any clear info or FAR that sates you can't, I just wanted to be sure.

If the airplane meets the definition, which almost all multi-engine pistons will, then you can get your complex endorsement. There is even one training center that advertises getting your multi and complex at the same time.

  §61.1   Applicability and definitions.

  Complex airplane means an airplane that has a retractable landing
  gear, flaps, and a controllable pitch propeller, including airplanes
  equipped with an engine control system consisting of a digital
  computer and associated accessories for controlling the engine and
  propeller, such as a full authority digital engine control; or, in the
  case of a seaplane, flaps and a controllable pitch propeller,
  including seaplanes equipped with an engine control system consisting
  of a digital computer and associated accessories for controlling the
  engine and propeller, such as a full authority digital engine control.

  §61.31   Type rating requirements, additional training, and
  authorization requirements.

  (e) Additional training required for operating complex airplanes. (1)
  Except as provided in paragraph (e)(2) of this section, no person may
  act as pilot in command of a complex airplane, unless the person has—

  (i) Received and logged ground and flight training from an authorized
  instructor in a complex airplane, or in a full flight simulator or
  flight training device that is representative of a complex airplane,
  and has been found proficient in the operation and systems of the
  airplane; and

  (ii) Received a one-time endorsement in the pilot's logbook from an
  authorized instructor who certifies the person is proficient to
  operate a complex airplane.

  Complex Airplane Endorsement

  Learn to fly aircraft with retractable landing gear, controllable
  flaps, and a controllable propeller using our Piper Seminole PA-44-180
  airplane. You can earn your complex endorsement, or combine your
  training to earn your complex endorsement and multi-engine rating.*


What would the density profile of this shock wave look like, roughly? The YouTube video titled Shock Wave Formation in Transonic Flight shows a hand-held video of a visible shock wave extending from the top of a jet engine near the front. The shock wave is visible by its refraction of features on the ground (muddy river bed) cause by the large changes in air density over short distances.
I would like to simulate the optics of this strictly for fun and general interest. If one made a simple plot of the density as a function of position crossing the shock wave, roughly what shape would have?
I've plotted six simple examples of shapes, perhaps one is appropriate, but perhaps something else is better.
below: GIF made from this video around 00:31.

below: some example guesses of the density behavior across the part of the shock wave seen to refract ground features in the video.

below: Description from this video.

Published on Oct 18, 2012
Formation of a shock wave around the engine cowl of a Boeing 767 at high speed.
The aircraft itself isn't going supersonic, but it's going fast enough (probably around Mach 0.8) that the local airflow around the engine cowl is supersonic, in a small area. This is called "transonic," and results in the formation of a shock wave at a right angle to the surface of the plane. The air in front of the shock is supersonic, and the air behind it is subsonic.
The shock wave is visible because of the abrupt change in the density of the air. The change in density causes a change in the refractive index of the air, and so the scenery behind it is optically distorted. This is similar to how a spoon in a glass of water looks "bent" at the water's surface, due to the difference between the refractive indices of water and air. It helps that this is seen nearly edge-on... if I had been a couple of rows further forward or back, it might not have been visible.

The shock observed is effectively the same as the one over a wing. Compression waves are normally considered of infinitesimally small thickness, although due to the non-continuous nature of gases made of particles, this normally makes the shock on the same order of magnitude as the mean free path of a gas molecule (See here for the values at different altitudes).

For visualization's sake, here's a CFD from a transonic NACA0012 airfoil with a shock on the suction side, and a plot of the density gradient on its surfaces. The step in density is not a pure discontinuity, as it would be physically, due to the relatively coarse mesh used, but I hope it still delivers the idea.


Are nose wheel tyres designed differently from the main wheel tyres? For the heavy large Jumbos like the Airbus A380 and the Boeing 747-800, considering nosewheel tyres are not subjected to the excessive heating caused by braking from the disks and brake pads, and frictional heat on the outer surfaces caused by contact with the tarmark surfaces and braking, are nose wheel tyres designed and manufactured differently from those of the main gear and do they cost more or less.  Considering they are not fitted with brakes, What is their temperature at landing after and are there instruments to measure this? If not why not?

Wheels on the 747-400 are the same all round.

One operator I worked with had a mixed fleet of -400 and -200s. They used the -200 wheels on the -400 nosewheel (mainwheels had to be -400).


Do adding high thrust in plane prevents it from stalling? I am convinced that fighter jets (every flying object) do stall. So from quora, Why don't fighter jets stall?

But most of the fighters have thrust:Weight ratio > 1 which means that they are not following aerodynamics at that time (during vertical climbs). You can consider them to be like rockets with propulsion system.
It suggests fighter planes don't follow aerodynamics. That means stall can be prevented using the jet power. So  what causes them to stall?

Edit: I realized my question is currently away from singularity. Based on comment, jamesqf, zeus and Robert maybe right. That quora answer might be wrong. It claims that fighter jets don't follow aerodynamics. I mean every flying object do follow it. So my question is if fighter jet has enormous power compared to their weight, will it prevent stall by a bit?
My prediction is stall only depends upon AoA. Regardless of airspeed, if AoA exceeds critical angle, stall can't be prevented (even using high thrust propulsion). Only way to prevent stall is to decrease its AoA. Are my claims correct? What if flying object relies on propulsion engine for lift (lot like missile, rocket), they keep flying and nothing hinders their speed?

Stay Safe...

Every aircraft can be made to stall with a combination of low speed, rear c.g. location and high load factor.

Thrust acts in the airplane's lengthwise direction. Lift acts in a mostly perpendicular direction, so whether the aircraft stalls does not depend on its thrust when lift demand exceeds the available lift capacity.

As you observe, this will not be the case in a climb. We know that lift demand is actually lower in a climb than in steady flight. So we need to look somewhere else.

The obvious case is in turning flight when the aircraft has to counteract not only gravity but also a centrifugal force. Now lift demand can grow to multiples of that in steady flight and any aircraft will readily stall if mass times normal acceleration surpasses the lift capacity of its wings. More installed thrust will only reduce the rate of energy loss in a tight circle.

Only if pitch authority is not sufficient can stall be avoided, but then the control system will not allow to trim the full angle of attack range. This could conceivably happen with a very forward center of gravity location but should place this configuration outside of certifiable limits.

As a side note: Stall depends on more than just the angle of attack.


Where can I find the aerofoil geometry of a commercial aircraft so as to design it in CAD software? As a part of my final year thesis, I need to design a commercial aerofoil for an existing aircraft (such as Boeing/Airbus) to conduct some FEA & CFD analysis. I've been trying to source aerofoil geometry so as to design it on CAD tools, but I haven't had any luck yet.

Note: I've gone through airfoiltools.com and I was looking for more than just the NACA Airfoil. I was hoping I could get the complete airfoil geometry including that of the spars, ribs, skin, slats, ailerons, spoilers & tanks. I've even tried going through the TCDS Database, but I haven't found any relevant information there.

All the current manufacturers develop proprietary airfoils combined with wing planform, washout, etc. using CFD for optimum pressure distribution, low drag, high critical Mach number, high maximum CL, benign stall propagation and benign aeroelastic characteristics. That applies to Boeing, Bombardier, Embraer and Airbus.
This type of info is not normally released by the manufacturers.
TCDS's do not have this kind of data.
You can do your own research starting with a standard NACA airfoils like those found in NACA report 640(Summary of Airfoil Data) and modifying them.


Traversing a tall suspension bridge during low overcast Suppose a pilot is flying VFR with excellent visibility and calm wind but with a ceiling of 1000, along a wide river at 500 feet. At some point she approaches a suspension bridge. Climbing and trying to cross in between pillars would be illegal due to getting too close to the clouds.

Now, would it be illegal and/or be considered excessively hazardous to fly under the bridge assuming that the vertical clearance above the river is around 300 feet?

Sounds pretty hazardous (and almost definitely illegal) to me
Here's the first photo of the first suspension bridge I found when I looked on Wikipedia

Guy Wires
Can you see all the really narrow guy wires below the bridge?  No?  I can't either.  If you can't see them in a photo, how are you going to see them at 100 knots?
"But Steve, maybe there aren't any!"
Yes, or maybe there are.  Are you confident enough to bet your life on it?
I thought you were the one with the plan!

Each pilot in command shall, before beginning a flight, become
familiar with all available information concerning that flight. (FAR 91.103)

Suspension bridges aren't like TFRs, they don't just appear in between the time you took off and the time you get to them.  Why didn't you know there was a bridge there before you took off?  Why didn't you have a plan for what to do when you got there already?
Boats are people too
You need to stay 500 feet from any structure.  Bridges are structures, so you need to be 500 feet away from them.  You also need to be 500 feet away from vessels and people, so if there's anyone on the river, your options just went from "bad" to "none".
But what about my emeeeergency?
All the rules go out the window if you're experiencing an emergency...as long as you're acting in the interests of the safety of the flight.  I spent some time on a foggy morning talking with an FAA inspector about this very topic (flying under bridges in emergencies) a couple years ago, and his words were to the effect of:

"It would have to be a very unique emergency for flying under a
bridge to be the safest course of action."


When do I need a takeoff alternate? Under what conditions do I need to have a takeoff alternate airport listed on a dispatch release?  How far away can my takeoff alternate airport be?  Do I need to worry about this in part 91 operations or is it just a 121/135 thing?

You should refer to the published IAPs for an airport to determine if it has non-standard takeoff minimums (for AeroNav charts, this is the T in the black triangle). There's a section on this in the Instrument Procedures Handbook, Chapter 2 (2-6):

The FAA establishes takeoff minimums for every airport that has published Standard Instrument Approaches. These minimums are used by commercially operated aircraft, namely Part 121 and 135 operators.

14 CFR 135.217 describes the requirements for the alternate airport:

No person may takeoff an aircraft under IFR from an airport where weather conditions are at or above takeoff minimums but are below authorized IFR landing minimums unless there is an alternate airport within 1 hour's flying time (at normal cruising speed, in still air) of the airport of departure.

...and so does 14 CFR 121.617:

(1) Aircraft having two engines. Not more than one hour from the departure airport at normal cruising speed in still air with one engine inoperative.
(2) Aircraft having three or more engines. Not more than two hours from the departure airport at normal cruising speed in still air with one engine inoperative.

Part 91
14 CFR 91 does not require a takeoff alternate. I'm going to quote the IFH again because it's an authoritative FAA source and because I very much agree with it (2-6):

Aircraft operating under Part 91 are not required to comply with established takeoff minimums. Legally, a zero/zero departure may be made, but it is never advisable.


What is the difference between static and dynamic stall? What are the static and dynamic stalls on the aircrafts wing? When would we encounter static and when dynamic one? What is the difference between them?

Static stall is what we typically think of, when we think of stall. Slowly increasing AOA and then loss of lift as the flow separates.

But pitch rate (rate of increase of AOA) has an impact too. At high pitch rates, the wing can go beyond normal stall AOA and still provide significant lift, but for just a short period of time. After that, the bottom falls out. This is dynamic stall.


Where can I find (or how can I calculate) the glide ratio for a PA-28-181? I'm filling out ForeFlight's new glide slope feature, and I'm trying to find the glide ratio for a Piper Archer II (PA-28-181). I know the best glide speed is 76, but can't find the glide ratio. Any help on where to find this?

Edit:

Below is the glide range graph from my PoH, and below that is the information ForeFlight is asking for. I'm not really sure how to read that graph to get a glide slope number.

If you were to take off from an airport at 2,000' ASL on a standard day, and climb to 7,280' ASL you would be exactly 5,280' above the ground which means exactly 1 statute mile above the ground.

If you were to cut the engine, and then use the information available in the chart, you should be able to glide about 10 statute miles which yields about a 10 to 1 glide ratio.


What kind of wing-surface area would Curiosity need to be able to fly in the atmosphere of Mars? The rover - without wings - has around 1000 kg of mass and Mars has 38% of Earths g. The density of the atmosphere is 1% of that of Earth. Assuming the surface area of the wings could be used for photoelectric cells having an efficiency of 40% at 500W/m^2, what wing dimensions, power and speed would this airborne rover need?

Our Flight Environment

First the basics: Mars atmosphere is mainly carbon dioxide and has an average temperature of -47°C and an average pressure of 0.004 to 0.0087 bar. The speed of sound in these conditions is 238.2 m/s, the dynamic viscosity $\nu$ is 1.14$\cdot 10^{-5}$, and for my calculations I use an atmospheric density of 0.0234 kg/m³.

Now I owe all you early upvoters an apology. The earlier answer used an unsuitable methodology; now I have improved the answer with different results.

Operating Point

Next step: The electric power supply makes a propeller the right choice, and for propeller aircraft the minimum power to sustain flight can be achieved when the lift coefficient is
$$c_L = \sqrt{3\cdot c_{D0}\cdot\pi\cdot\Lambda\cdot\epsilon}$$
This makes your zero-lift drag the real sizing parameter: Make the aircraft a little more draggy, and you get punished with a big size increase. Therefore, we strive to keep the zero-lift drag coefficient $c_{D0}$ down to 0.008 in order to keep the aircraft small.

This allows to get an idea which aspect ratio will be best: At minimum power the total drag is four times the zero-lift drag, and the lift coefficient should be as high as possible to keep the aircraft's size small. Realistically, our flight $c_l$ will not grow above 1.6 (which is the best that low-speed airfoils can manage at a reasonable L/D), so the aspect ratio is
$$\Lambda = \frac{c_l^2}{3\cdot c_{D0}\cdot\pi\cdot\epsilon}$$
which yields an aspect ratio of 35.74 when $\epsilon$ is 0.95.

Available Power

Now we can follow the procedure in this answer to calculate power demands for your solar-electric propulsion. Solar radiation on Mars is a lot lower than on Earth, but very reliable as there are no clouds to obstruct the sun. Beware of dust storms, however!

Since you gave the Martian solar constant in your question, I will use it here: The wing will be covered to 80% with solar cells, and each square meter of them will produce your optimistic 200 W (500 W radiation times 40% efficiency). Per square meter of wing we can achieve 160 W, and with an electric efficiency of 96% and a propeller efficiency of 85% this translates into a propulsive power per square meter of 130.5 W.

Matching Thrust to Drag

Now we can equate the drag $D$ and the available thrust $T$ from the power $P$, like this:
$$D = T = \frac{P}{v} => 4\cdot c_{D0}\cdot S\cdot\frac{\rho\cdot v^3}{2} = 130.5\cdot S$$
Luckily, wing area $S$ can be canceled, and we get a result for the airspeed $v$ at which the aircraft's drag can just be supported by the power the wing can generate independent of wing area:
$$v = \sqrt[3]{\frac{130.5}{4\cdot c_{D0}\cdot\rho}} = 55.857 m/s$$

Now for the real size: If we assume that the payload fraction is 25%, the mass of the full aircraft will be 4 tons. To lift this at the dynamic pressure of 36.5 N/m² which corresponds to the found flight speed we need a wing area of 254 m². This can create 40.65 kW of power, 33.17 of which are transformed into thrust. The wing span will be a whopping 95.28 m. How you get this to Mars I leave to your imagination - after all, this is just a tad less than the wingspan of the Hughes H-4.

If you can achieve a higher payload fraction, the wing will become smaller: At 30% the full aircraft mass is only 3.333 tons, and the wing size will become 211.74 m² large. Its wing span will be 87 m. With these dimensions I doubt that a higher payload fraction will be possible. The closest aircraft to this design was the Boeing Condor, which had an empty mass of 3.6 tons (with a propulsion system weighing close to the mass of Curiosity) and a wing span of 61 m.

Last Checks

Mach number: 56 m/s is just Mach 0.2345 on Mars, so we should not run into compressibility effects which would limit the assumed lift coefficient.
Reynolds number. The bigger wing has an average chord of 2.66 m and the smaller one still 2.43 m chord, and per meter the Reynolds number in -47°C cold carbon dioxide at 56 m/s is 4,900,000 - plenty enough to make the selected lift coefficient possible. Size helps here!


What is the theoretical maximum RPM of a typical aircraft piston engine? Given a standard 6 cylinder horizontally opposed engine like the Continental IO-550 or Lycoming IO-540, the maximum RPM for those engines is 2700 RPM. That's due to keeping the propeller tip speed under the supersonic range.

But what is preventing these engines from turning at a higher RPM for another, non-aircraft use?

I'm thinking if they would work up to around 5000 RPM or so. Maybe the fuel mapping must be modified? Will the valvetrain start to float at that RPM? The application would be automotive, so the load would be far, far less from a duty cycle standpoint then an aircraft application: basically, 5000 RPM would only be seen for a second or two at a time under full (or nearly full) load.

Is there anything else I'm missing? I realize this is a weird question, just doing some thought experimenting.

The size and weight of the pistons is going to be a major hurdle. With a 5.25 in bore and a 4.25 inch stroke, the pistons are massive and don't change directions very easily—there's only so many Gs you can put a shape this large through at the top and bottom of each stroke before the metal starts deforming. Bounce an open umbrella up and down really fast, and you'll start to get the picture.

Cooling would also be a major factor for non-aviation use. Aircraft engines (more or less rightly) assume that there's going to be a large fan out front and/or 100+ mph of airflow. Liquid cooling would allow the heads to maintain a more constant temperature, but would also add weight and complexity.

If you want a faster-revving flat six that will put out more than 100hp and is suitable for automotive use, I might suggest pulling an engine out of a Honda Goldwing or Valkyrie. Given the edited description, though, I'm guessing you're thinking of a drag racer.


Why do commercial pilots always engage reverse thrust even if it is not necessary? Most of the time the usage of reverse thrust is not needed. I wonder if it's an authority (e.g. FAA) requirement to land safely.

Obviously, in bad weather conditions or when the runway is contaminated, the brakes might not work as effectively and thus R/T may be required to land safely. However, in most of other situations the aircraft can brake OK. Given that it would probably be more efficient to land without using R/T, why don't airlines routinely do so?

The correct answer is, habit patterns.

If your habit, as a pilot, is to ALWAYS select reverse thrust, you'll do so reliably even when the weather is bad, you're fighting gusty crosswinds, and there is whatever else going on. On the other hand, if you sometimes do & sometimes don't select reverse thrust, that habit pattern isn't there to back you up when you have the proverbial "dark & stormy night" and getting into reverse thrust right away may be the difference between staying on the runway or running off the end.

For example, if I'm landing a fairly light aircraft on a 12,000' dry runway in DEN with a little headwind, it is entirely possible to leave the thrust reversers stowed, roll out with the speed brakes deployed, tap the brakes slightly, and exit on the last high speed taxiway at a normal taxi speed.  And I'd burn less fuel and make less noise doing that.  But at my carrier, I'm not allowed to, because it's considered that the habit pattern of always deploying the T/R is so important that it's worth it to burn that extra gas even when it isn't strictly necessary, so that on the day when it's vital, the habit pattern to grab the T/R's right after touchdown is strong.

I don't think that this is an OpSpec (i.e. FAA) requirement, at least for the aircraft that I fly, but I'm quite certain that it is a requirement in our books, so my supposition is that it's a company requirement.  If that assumption is correct, then other companies might choose to do differently (and I recall one early morning arrival into Frankfort on a Lufthansa A-320 that used NO reverse thrust, but some heavy braking instead -- presumably to reduce noise at that hour of the morning).  The fact that safety is so important, though, probably drives plenty of operators to make the same choice that our carrier does: build the habit of ALWAYS using reverse thrust -- even though that means sometimes using it when it isn't necessary.


Is there any "copyright" for aircraft's design between different manufacturer? Are there any regulations for the copyright of aircraft's model design between competitors in the aircraft industries? Basically is there a regulation for avoid that one company just steals the project of a competitor to produce a version very close to the original?

This is more of a law issue rather than aviation issue. Anyway here it goes: No, there is no copyright to prevent one manufacturer from copying another aircraft because aircraft design is not protected by copyright.

The first rule about copyright is that it "protects an expression of an idea but not the idea itself". It protects technical diagrams, documents, recording etc, but not the idea expressed in them. Therefore if one simply photocopy the schematics, it would be a copyright violation. But if you reproduce what you see, it is legal.

The word you are probably looking for is "patent", which protects an idea. Aircraft manufacturers do have patents when they come up with something revolutionary. A quick search for "Airbus patent" turns up quite a few results. Whether you agree that particular idea was revolutionary enough for a patent though is another story.


How to recognize the horizontal winglet in the Horten design, or the experimental glider in this video? Comments below the NASA Armstrong Flight Research Center video Proving Prandtl- With A Twist! incclude:

This video is entirely a hidden jewel in youtube, it deserves much more attention than what it has had until now. It is both educational and inspirational!

It's a clever, non-obvious idea, using the washout to eliminate adverse yaw...

What, and where is the Horizontal wiglet discussed in the video, or in the Horten design discussed there as well?
When I look at the various images in the video, I just see a flat wing as far as the shape is concerned; what distinguishes the winglet from the rest of the wing?
edit: I see a break in the wing near the end, but as far as I can see, the shape or orientation doesn't change from what the wing would look like anyway. What is it that makes the end of this wing a winglet?

You can't from the planform alone.

First, winglets are no magical device. Calling the wing with bell-shaped lift distribution one with horizontal winglets tries to free-ride on the mystique that NASA marketing has created around the winglet. But the physics behind it are rather mundane and the thrust which is created by the outer wing is a bit of payback for the higher losses at mid-span from a steep lift gradient over span.

Next, all wings create thrust if you define it narrowly enough. This comes from the suction force on the forward upper side of the airfoil and is called leading edge thrust.

Induced drag is the backward tilt of the aerodynamic forces and is caused by lift creation. The least amount of drag for a given amount of lift and wingspan can be achieved with the elliptic distribution over span. The bell-shaped distribution creates more drag for the same lift and wingspan, since it has higher spanwise lift gradients at mid-span.

  What is it that makes the end of this wing a winglet?

This is a matter of definition. The so-called winglet area is where the wingtips carry only little positive or even negative lift. Like in a winglet, this gives the local lift a forward component which works like the opposite of induced drag. Call it induced thrust, if you want: This is what is common to winglets and the negatively loaded wingtip. That in turn is caused by wing twist and local control surface deflection. You cannot see from the top view how lift is distributed over span.

But the bell-shaped lift distribution has some interesting advantages:

Since most lift is created near the wing root, the spar bending moment can be kept low for a given amount of lift. This allows for a lightweight wing structure and is especially important for large aircraft.
With aileron deflection, the lift distribution on the up-going wing becomes nearly elliptical while the one on the down-going wing becomes even worse, increasing induced drag there significantly. This reduces adverse yaw such that no vertical tail is needed.

Sounds great, doesn't it?

Actually no, it doesn't when you take a closer look:

Due to the low maximum lift coefficient of flying wings, the wing surface of a flying wing needs to be much higher than that of a conventional configuration of the same landing speed where a tail surface allows the use of powerful trailing edge flaps, raising wing weight and drag substantially.
The bell-shaped lift distribution is like flying all the time with spoilers half deployed. Aileron deflection retracts the spoiler on the up-going wing and extends it fully on the down-going wing. Kind of like the split ailerons of the B-2. I think it is better to only use spoilers during manoeuvring. Also, the Horten flying wings were all known for marginal directional stability, especially at high speed when sweep did not help much. It was too little to even compensate for unsymmetric thrust. A fin or added artificial stabilization would be highly advisable.


What is the proper procedure after a bird strike in a single engine plane during takeoff? First, let me set this up and then ask a general question.  I'm just trying to give some context as to why I'm asking.

I'm working on my private pilot license and was practicing with my PC simulator (X-plane) this weekend.  I was flying a Mooney m20j out of John Wayne (KSNA, which has two runways, 16R/1L 16L/1R).  I took off from 16R and at about 300AGL I encountered a bird strike and my engine died (though my windshield was intact).

I was just about at the end of the runway so I declared an emergency (yeah, I've been talking to myself...) and said I was going to turn the plane around and land on 1R (so, the parallel runway in the opposite direction.)  I was kind of panicking and had no idea what to do, this was just the first thing that sprang to mind.

I started the turn and quickly realized I was sliding sideways towards the ground, so I leveled out the plane a bit and ended up making a short approach on a taxiway, which I managed to land (though that may be down to the simulator being a bit forgiving and not me, really.)  So the plane survived...

So I've got two questions, the first a little specific (though I'll try to generalize it) and the second nice and general so it applies to a wider audience.

Is the process I described a good approach to a bird strike during take off?
In review, I feel I probably would have been better off just landing straight ahead on a road or open field, but I thought I'd ask.
What is the best way to deal with a bird strike or incident on takeoff that fails the engine?
I'm particularly interested in situations where the plane is about at the end of the runway - if it happens right as you take off you can just put it back down, and if you're much higher up you have a lot of options because you can glide for a while.  But right at the runways end, when you have very little altitude and no more runway...  What's the proper procedure?

You will not find a "single rule fits all" but in general, on PPL training, you are taught < 700 feet, land ahead no matter what.

A skilled pilot, with good currency, in an aircraft they know well, in good conditions they have planned for and with enough altitude, might successfully turn around.  Another pilot in the same aircraft with the same conditions might kill themselves.

The consequences of getting a turnaround wrong are worse then getting a straight ahead landing wrong and, by turning around, you might very well put someone else at risk.  You have much better prospects mushing down straight and level into those trees ahead than stalling out of a turn in an attempt to get back to somewhere you may or may not make.

Forget the flight sim heroics.  Nose down aggressively for best glide (you should already know what that looks like!), then start looking, or even better, go for the area you know is good because you pre-planned for an EFATO.

Bottom line, when you do start training (good luck!), do whatever you are trained to do.


How many type ratings are pilots allowed to hold at once? I think i've read that the B787 has a common type rating with the B767 and B777. But I also think I've read that pilots are only allowed to fly two types of aircraft at a time...

So when they go to fly the 787, do they have to give up one of the their ratings if say they were previously allowed to fly the 767 and 777? Would the same still apply for say a B757 and B767 which have very similar flightdecks?

EASA and FAA perspectives would be appreciated :)

There is no limit to the number of type ratings that a person can hold. The world record for most type ratings held by an individual currently stands at 105!

For safety reasons, most airlines only allow a pilot to be currently assigned to two aircraft types at one time so that they don't start to confuse the different airplanes and mix things up. This isn't a regulation though, at least in the US.

In your example, those airplanes are the same type so would only count as one of the two that they could be assigned to, but this will vary based on individual airline policy and the complexity of the differences between the actual aircraft involved.


Why the number 6 in P6SM in a METAR/TAF? A typical METAR or TAF reads something like this:

VRB04KT P6SM SCT025 BKN040 OVC060

P6SM means "greater than 6 statute miles visibility."  Why in particular is it 6 miles--why not P7SM or P10SM?  Particularly since sometimes METARs and TAFs list actual visibilities greater than 6 statute miles anyway:

28006KT 10SM CLR

Is 6 miles a limitation of commonly used equipment for measuring visibility, or something else?

The METAR format is defined by the World Meteorological Organization's (WMO)  on behalf of ICAO. According to the specification (section 15.6.3), visibility is to be reported in meters. The upper bound for visibility reporting is 9999, which indicates the visibility exceeds 10 kilometers.

In North America, the METARs deviate from the standard format by using non-standard units. Visibility is reported in statue miles. Six statue miles is equivalent to 10 kilometers.

Hence > 6 statue miles is equal to the standard > 10 kilometers.


Fuel jettison in Top Gun, is there any reason to do this other than show-boating? 20 years of watching Top Gun and I only noticed this today, after almost an annual repeat!

At 00:29 in this video, you can see what seems to be condensation swirling in the wake vortices.

Up until today, I thought this was just a cool shot catching some serious condensation under a high-G maneuver. However, if you look closely, you can see that it's actually a fuel jettison! At 00:38, it's very obvious.

I'm guessing that this is nothing more than show-boating and it sure did produce a cool shot.

Fuel jettison/dumping is used to reduce landing weight in emergencies but, is there any tactical/ops reason to do this?

Doesn't look like it was any 'tactical' reason- rather it was used to get a cool shot, which is totally OK with me. From rulit.me:

  While setting up for a filming pass, the camera crew had difficulty spotting the gray F-14 against the mountainous background. Over the radio, Rat asked the pilot to blip the fuel dump switch and make a mini-cloud. The resulting effect of the atomized fuel swirling in the Tomcat’s vortices looked so good that this technique was used several times in the finished film.

I think they're talking about this scene:

Image from youtube screenshot

Looks like they used this technique to frame the aircraft against featureless mountains, sky etc.

Note: The site seems to have taken the quote from Topgun Days: Dogfighting, Cheating Death, and Hollywood Glory as One of America's Best Fighter Jocks by Dave Baranek.