What is the difference between a POH and an AFM? Some aircraft come with a Pilot Operating Handbook and some come with an Aircraft Flight Manual.  Why the different name, and is there a difference between them?

Both a POH and an AFM meet the "Operating Limitations" requirement in the ARROW acronym.

The difference between the two is mainly in length and content: an AFM is usually a thinner document, satisfying the requirements of FAR 23.1581 and not much else, while a POH contains these required items plus other information like system diagrams (The contents & format of a POH are standardized in GAMA's Specification 1).

Parts of the POH (like the Limitations section) are FAA-Approved, and serve as the AFM, and both documents are typically associated with a specific airframe (by serial number).

A better explanation might be this:
The AFM is a regulatory document (it's contents are prescribed under the section of the regulations the aircraft was certificated under - Part 23, Part 25, etc). The POH is a GAMA-defined document whose contents meet the regulatory requirements of an AFM, and present other information in a standardized way so that a pilot can go from a Cessna to a Piper to a Mooney to a Socata and browse the book to learn about the airplane they're about to fly with all the information presented the same way no matter who the manufacturer is.

The other two types of documents you may encounter are an "Owner's Manual" (which usually goes along with a thinner AFM & provides some of the information found in the newer-style POH) and a Pilot Information Manual (PIM) which is a "generic" version of the POH which many pilots buy so they can study the procedures without removing the regulatory document from the aircraft.

Chapter 9 of the Pilot's Handbook of Aeronautical Knowledge talks a little about the differences between the two documents (and a whole lot of other flight documents).


What is a raw data takeoff and is there a benefit to performing them? I heard a pilot mention a raw data takeoff in offhand conversation. The topic was generally about maintaining hand flying skills. What exactly is a raw data takeoff and is there a benefit to a pilot's flying skills from practicing them?

Raw data means data read on the basic instruments. Not-raw data means enhanced information built from raw data and/or flight management system.

Flight director bars are not raw data, but a computation from basic air data, desired airspeed, roll angle limit, etc. At the next higher level, the autopilot can use the FD data to fly the aircraft. Similarly desired speed can be determined automatically and thrust can be managed by the auto-throttle.

Taking off and climbing with FD, auto-throttle and autopilot

Takeoff with FD and AP, just after liftoff (A320 simulator). Source: Youtube

The green bars of the FD shows what should be the attitude of the aircraft, SRS (speed reference system) guidance law has been used to determine the desired 165 kt speed. The pilot may fly the aircraft manually using these non-raw data.

In the present case the pilot has also activated another layer of assistance: Autopilot and auto-throttle. The AP follows the FD indications, and the thrust is managed by the auto-throttle so that the desired speed is achieved safely as soon as possible.

The indication in the top-left corner means autopilot, flight director and auto-throttle are currently selected / active.

T/O with raw data

Flying with raw data implies not using the FD or the SRS mode, nor the AP other modes or the auto-throttle.

The crew must determine the attitude to be used after the T/O rotation, and during the climb. They also need to manage the thrust required. For example, the roll angle has to be determined manually, depending on all factors discussed above and the desired horizontal track.

Takeoff without FD (A320). Source: Youtube

Benefits

Not using computer assistance helps maintaining and developing pilot skills and prevents dependency on automation that can always fails. The correct attitude, speed and thrust depend on many limits  — some are displayed in the speed indicator band and the attitude indicator when they have video displays — that the pilots must have in mind.

So it's usual that pilots perform manual take-offs and landings and raw-data operations. The frequency of such permanent training may be influenced by the company rules (standard operating procedures, SOP) which can either encourage or discourage crews to use the airplane automatic features at certain phases of the flight.

On modern aircraft there are some mechanisms can't be inactivated as the direct transmission between controls and corresponding actuators have been replaced, partially or totally, by electrical links. The conversion between actual pilot movements and electrical command signals is subject to some level of filtering provided by the fly-by-wire system.

Other raw data operations

Raw data (ILS) approach.
Raw data navigation.

This post consistently uses Airbus-based explanations, as terminology varies between aircraft manufacturers (but principles are mostly the same for this topic).


What is the mathematical relationship between Specific Excess Power and an aircraft's acceleration at a given point on an E-M diagram? If an aircraft is on the x-axis of an E-M diagram plot (zero turn rate) where the Specific Excess Energy (Ps) = 800, we understand this to mean that the aircraft has the potential to either instantaneously gain 800 ft/sec of altitude OR instantaneously accelerate.  If an acceleration rate is desired, this could be determined by converting the 800 ft gained (h) as potential energy to kinetic energy using an equation V = SQRT {2 x g x h}.  Substituting the variables, V = SQRT {2 x 32.2 x 800} yields 227 ft/sec gained each second (or acceleration of 227 ft/sec^2)  However, this is an unusually high amount of acceleration for even a high performance jet accelerating in straight, level flight (7 g's).  There is something clearly wrong with my logic/math but I can't figure it out.  Can someone offer the correct derivation?

You forgot that you accelerate not from standstill, but a considerable speed. So that equivalent potential energy change comes on top of the existing kinetic energy and makes the energy change look much smaller (resulting from the square of speed in kinetic energy). The correct calculation is
$$\frac{\delta E_{pot}}{\delta t} = 800 \;\text{ft/sec}\cdot g=(v_1^2-v_0^2)\cdot \frac{1}{2\cdot \delta t}$$
Your acceleration will decrease as speed increases. If I assume a speed of 800 ft/sec, the resulting acceleration is to a speed of
$$v_1 = \sqrt{v_0^2+2\cdot g\cdot h} = 831.55\;\text{ft/sec}$$
within one second which is 31.55 ft/sec² or just shy of 1 g. The initial acceleration is 1 g and decreases as the aircraft picks up speed. In mathematical terms:
$$\ddot x = SEP\cdot\frac{g}{v} = v_z\cdot\frac{g}{v}$$
When climb speed (or specific excess power) equals flight speed, both cancel, leaving gravitational acceleration equal to horizontal acceleration if all climb potential is used for increasing speed.


Why isn't aircraft structure inspection done by robots? Is there any known active research on the subject? From my research I've found that (correct me if i am wrong):

Structure inspection (in B,C and D Checks) including (visual, thermography, ultrasonic inspections) looking for structure damage of different type of composit materials (like cracks, dis-bonding, delamination, water ingestion, holes, dents ... etc) in commercial airliners specially wide body aircraft takes alot of time, labor and cost.

So why isn't it done by robots which should be more time efficient, accurate and reliable? in a way that robots can do simple but mandatory inspection tasks allowing operators to focus on more skilled tasks (like engine work) reducing the overall plane down time !

Is there any robotic inspection systems exists that I didn't hear about?

How beneficial to airlines would it be to have a robotic system that would assist operators in the inspection process (in terms of time and cost) ?

The robot, or better the software analyzing the sensor output, needs to be programmed for every eventuality. After all, wear and tear does not leave standard traces, and a human is still better in spotting when something does not look quite right. This does not concern the obvious cases, but those where experience and intuition make the difference.

Next, aircraft structures are made with human inspectors in mind. A robotic system would need to be able to access all points at least as well as a human can. This puts some heavy restrictions on the robot's physique.

Eventually, a robotic system will surpass most humans, but only after thousands of man-hours of training. Maybe someone is developing just such a system right now, but I am unaware of this.

One point remains, however: Who will be liable if the robotic system makes a mistake? The manufacturer will need to buy insurance to cover those corner cases where the robot fails, and this will come on top of the hefty expense for developing and training such a system. I expect that the military (e.g. DARPA) will be the first to make the plunge, and only when the robot has a positive track record will civilian operators start to consider using it.

The EasyJet drones are just helping to get a camera on top of the aircraft; the eventual monitoring of the feed will still be performed by humans. They are a high-tech version of a periscope, if you want.


What was this vehicle doing? On a trip a few weeks ago traveling out of Charlotte (CLT), I took this picture of a vehicle at the airport.  Our plane was fueled as we were about to board but due to various factors, boarding didn’t occur until almost five hours later.  As we were finally about to board, this vehicle arrived and connected a tube to a port in the vicinity of the fuel input port.  My question is this:  what was the vehicle doing and what circumstances necessitate the usage of it?

Edit: Although not immediately obvious without zooming in, the yellow pieces visible are the ends of a spool around which the hose is wound.  It is not one single large tank as it appears from a distance.

This looks like an Aircraft Fuel Servicing Cart, which transfers fuel from an underground network to the aircraft. There are two types of vehicles that transfer fuel at larger airports with these fuel networks:

Hydrant trucks:

(image source: Wikimedia)

  Aircraft fuel servicing hydrant vehicles do not have tanks. These vehicles
  connect to a pressurized Airport Fueling System hydrant and transfer the
  fuel to the aircraft through a filter.

(ICAO - International and FAA Fuel Fire Safety)
Towed Carts:

(image source: aeroexpo.online)

  Aircraft fuel servicing carts are equipped with facilities to transfer fuel between a
  Airport Fueling System hydrant and an aircraft and are normally parked at a fixed
  location near a gate.

(ICAO - International and FAA Fuel Fire Safety)

The cart in your picture seems to be the latter of the two (a different model though). You can see the hose that will be connected to the aircraft on the metal staircase. The other hose on the ground connects to the hydrant (hidden behind the aircraft in your image). Your picture shows an Airbus A321, which has the fuel coupling typically located under the right wing (number 11 in the following image):

(image source: Airbus A321 Aircraft Characteristics and Airport and Maintenance Planning Document)

  11 − REFUEL/DEFUEL COUPLINGS (OPTIONAL−LH WING)

Your picture was taken at Charlotte (CLT), which according to this page is equipped with a Jet A Fuel Hydrant Facility. Airports without an underground fuel system will use tank trucks (self-contained fuel trucks) instead:

(image source: shell.com)


How can I use electric motor data with my prop data to obtain a power available versus velocity curve? I'm not entirely sure this is appropriate for this forum but it's worth a shot...

I have propeller data ($C_T$ , $C_P$ , J , and $\eta$) and very very limited electric brushless motor data (motor diameter, shaft diameter, Kv, voltage range, max amperage) I am trying to put together a power available curve (P vs V) but I'm not exactly sure how to use the data I have to do so.  How do I get shaft power from my engine data?  Or what can I use?

A simple mathematical model for electric motors has very clearly been discussed here
All you need is Kv, no-load current and Voltage to calculate the shaft power, efficiencies, etc.


Are there any regulations on fueling aircraft inside hangars? My FBO routinely refuels aircraft with 100LL while they're parked inside hangars. I have complained about this being a dangerous practice. My previous FBO required aircraft to be at least 10ft outside the hangar for refueling. Are there any regulations or advice on this?

Your previous FBO is correct. According to FAA Advisory Circular 150/5230- 4B Aircraft Fuel Storage, Handling, Training and Dispensing on Airports:

Standards The FAA uses the standards contained in the most recent edition of National Fire Prevention Association (NFPA) 407, Standard for aircraft Fuel Servicing. NFPA 407 provides a standard for the storage and delivery of aviation fuel in an airport environment

NFPA 407, on the other hand requires outdoor fueling.

5.10 Aircraft Fuel Servicing Locations.
5.10.1 Aircraft fuel servicing hall be performed outdoors...
5.10.2* Aircraft being fueled shall be positioned so that aircraft fuel system vents or fuel tank openings are not closer than 7.6 m (25 ft) to any terminal building, hangar, service building, or enclosed passenger concourse other than a loading walkway.

A revision of the same standard also looks the same, with some differences in wording. So, the aircraft fueling should be done outdoors. Its doubly important if the hangar/airport where your aircraft is located also follows NFPA 407.


How does a pilot report a person (on the surface) in distress? After a downhill bike ride gone wrong last night.  Around midnight I was climbing up a mountain (to my Jeep) with my bike on my back.

While I was climbing I was thinking about the fact my headlight had an SOS function (I didn't consider using it).  SOS functions of lights are great and all, but then I realized that as a pilot, myself, I am not sure how to report a person in distress on the surface.

As a climber and ROTC cadet, I am well versed in the hand signals, and various ways to flag down airplanes, but as a pilot, if I were to come across someone flashing SOS at night, or flagging me down with a mirror in the day, how would I report their location to get a search and rescue team dispatched?

I would treat an active SOS signal from the ground the same way I would treat an ELT signal on 121.5: Contact ATC (or Flight Service if you're not sure what ATC frequency to use) and inform them of the event.

As with reporting an ELT you should be prepared to tell ATC:

What kind of signal you've observed
(ELT, signal light, signal mirror, "SOS" or "HELP" spelled out with rocks…)
The time you observed the signal
(Ideally you'll report it while overhead & actively monitoring it)
Your location and altitude

Ideally you'll be able to give your location as a GPS fix as SHAF described.
If that's not possible there are other options, in roughly-descending order of accuracy:

A DME fix (radial & DME distance)
A VOR fix (the intersection of two radials from separate stations)
A VOR radial & visual landmark (ideally something on the sectional chart)
While just a radial is not very useful it can be helpful in conjunction with a landmark: "South side of Mt. Greylock, on the 350 radial off Chester VOR" helps narrow down the search area considerably.
A visual landmark based on the sectional chart.

ATC may also ask you to circle the distress signal and ident in order to get a radar fix to supplement any of the above.


What make and model are these two small propeller planes? What are the makes and models of the two planes in the picture? The registration numbers are ZS-JNJ and ZS-LCY, the year was 1981 and the place was Botswana.

They're a couple of Cessna 210s. I can't tell from just looking whether they're Turbo 210s or normally aspirated. You can tell they're not 172s or 182s because they lack wing struts. Cessna 177s also do not have wing struts, but their front windshields are considerably different.


Why would a commercial flight be landing with a tailwind? I just flew into BOS on flight 2539 and we landed either on 22R or 22L even though winds were 19 knots at 010 at the ground and 14 knots at 300 at 3000 feet. There was no change either; the captain had announced northerly winds 30 minutes prior as we approached the destination.

Why would they be landing with a tailwind? Normally flights land at 4L or 4R when winds are like this.

Assuming 'I just' means today 17 Oct UTC time, then American Airlines 2539 arrived at 22:52 local, or 2:52 UTC.
Reported METAR at that time:
KBOS 170254Z 32013KT 10SM SCT060 08/01 A3015 RMK AO2 SLP209 T00780011 51027
The winds being 320/13 and runways 22L/R facing heading 215, that means the tailwind component was 3 knots. Well within the 737-800 limitation of 10 knots tailwind.
As for the why, it's to maintain the preferential runway system or to avoid switching back and forth if the anticipated winds will not shift more toward the other end. The preferred direction can be used in tailwind up to a limit (8 knots component in certain places for example).
For the US, acording to the National Safety and Operational Criteria for Runway Use Programs, it's 7 knots for the clear and dry runways.

Under ideal conditions aircraft takeoffs and landings should be conducted into the wind. However, other considerations such as delay and capacity problems, runway length, available approach aids, noise abatement, and other factors may require aircraft operations to be conducted on runways not directly aligned into the wind.
(...)
Where anemometers are installed near the touchdown zone of the candidate runway for landings, or near the departure end for takeoffs, any tailwind component must not be greater than 7 knots.

If there are no TDZ anemometers, then it's 5 knots.
The forecast agrees the winds will stay roughly the same and will shift more towards 220.
KBOS 162320Z 1700/1806 32010G20KT P6SM SCT150 BKN250
  FM170400 33009KT P6SM FEW250
  FM172000 21006KT P6SM SKC
  FM180400 23007KT P6SM SKC

Reading TAF guide: https://www.aviationweather.gov/static/help/taf-decode.php

According to the flight track, you landed on runway 27. And according to massport.com, below is the normal configuration for the NW winds. I should have checked the track first


How much the true altitude will be lower than indicated altitude by 10°C colder? Aproximately how many perecent the true altitude will be lower than your indicated altitude , if the temperture is 10°C colder than standard ?

It's not a linear deviation so it depends on the altitude and the temperature at that altitude.  The deviation gets worse as you go higher and colder.

Lower and warmer, the error for 10 deg is very small, but higher and colder it can be a couple hundred feet.

Everybody uses a standard table that you can find all over the place with Google.  See here on Page 33 of the General Section of the Canada Air Pilot CAP GEN (IFR approach plates for Canada)  which explains how to apply the corrections, and can also be found in the AIM.  They are only used for IFR use for correcting altitudes for instrument procedures when close to the ground, and are generally not applied unless the temperature at the airport is below freezing.


Would a 50 mph aircraft holding a ground pattern in a 20 mph cross wind risk stalling by abruptly rolling away from a crosswind? This is another play on the "down wind turn myth".

We all know a plane flying in a "uniformly moving airmass" is not affected by wind direction and speed.

But a plane following a ground track must compensate for wind direction and speed.
In this scenario:

Pilot Bob could not wait to fly his ultralight and went out to practice take-offs and landings on runway 270 with a 20 knot westerly wind from 270.  In the pattern, flying heading 180 on the crosswind leg, a heavy crab into the wind had to be applied to hold the ground track.

Instead of adding power, Bob increased AOA to hold altitude (BAD MOVE).
Flying near stall, the pilot abruptly rolled and yawed the aircraft away from the crosswind and began to turn into the 090 "downwind" leg.

Could this maneuver significantly change the AOA of the wing, resulting in a stall?

Your question is flawed because it is creating a link between two different things.  Let's deal with them one at a time:

In the title question you ask whether a plane holding a crosswind correction in a landing pattern risks stalling by rolling abruptly away from a crosswind.  Ignoring for a minute that doing anything "abruptly" imposes some additional level of risk, (depending of course on the severity) the answer is no.  Turning into, or away from the wind in a "uniformly moving airmass" does not alter the airspeed of the aircraft.  You said as much yourself.  When ready for downwind you simply turn to a new heading for that leg as you would normally.  (in this case 090 because you will now have a tailwind.)

The very concept of "wind" only matters when you consider the surface of the earth.  The airplane doesn't recognize or care what the ground is doing, only the airmass matters.

Now to the second part; would flying near stall speed and then abruptly rolling and yawing the aircraft risk a stall?  Yes, absolutely yes!  As well as a spin...  Those are the main two ingredients of a spin, and every pilot is taught to avoid them, especially down low.  Statistically this is probably one of the main GA pilot killers.

So, let's further unlink the two concepts.  You seem to be espousing an unbalanced slip approach to maintaining heading and ground track in the crosswind turn, furthermore, doing it right around stall speed!  (Sorry, that wasn't you, it was pilot Bob...) This is improper and unsafe technique.  You should not attempt to maintain aircraft heading of 180 on the crosswind, you should fly 190, or 195, or whatever heading will allow you to maintain a consistent ground track.  You should do it wings level, in balanced flight, at a safe and appropriate airspeed for your aircraft in the pattern.  The same airspeed you fly when the airmass is not moving relative to the ground.  This wind correction technique is called "crabbing".

Bottom line, it isn't the wind creating any additional risk, it is pilot Bob's improper technique.


How did pilots pee on Rutan Voyager? Rutan Voyager had a very long flight.
Did pilots have a separate toilet room for when they needed to relieve themselves?
How much room did they have to move around anyways?
Is there any visual with the interior of aircraft?

Did pilots have a separate toilet room for when they needed to relieve themselves?

Given the size and weight of the aircraft, this would be near impossible. There wouldn't even have been margins in the weight budget for toilet paper, let alone a toilet room.
I don't know if there is any official documentation about their bodily fluids.
I did find this quote:

Rutan even brought a small plastic bag with an adhesive, circular opening to answer the question he said he is often asked first—how did you go to the bathroom?

So, the answer seems to be that they glued a plastic bag to their bottoms.

How much room did they have to move around anyways?

Practically none. The aircraft had room for exactly one thing: fuel. If there had been room to move around, that means there was room that wasn't being used for fuel, so they would either have designed away the room or filled it with fuel.
The pilot flying was lying in a lightweight pilot seat, the pilot monitoring sat or lay on the floor next to the pilot flying.

Is there any visual with the interior of aircraft?

Yes, there are quite a number of photos, which you can easily find using your favorite search engine, for example:

Dick Rutan and Jeana Yeager in Cockpit of Voyager
Rutan Voyager Cockpit
Jeana Yeager


How do fighter jets stop pitching motion after a elevator deflection? I'm working on a flight simulator , In which the jet has only ailerons , rudder , and two elvators at the back . When I nose up my aircraft via elevator deflection , it just keeps pitching up ( even when I let go of elevators and let them back to neutral)  , after going pitch max , it starts pitching in opposite direction and then back and forth . These oscillations take lot of time to die out and the motion  of my jet is like a sine wave going forward .
I'm using real forces of lift and weight on the aircraft body.
So my queries are ,

How does a fighter jet locks it's nose at a particular pitch angle ( the moment the pilot let go of the deflection) and  does it so smoothly and slowly , that it's possible to aim at whatever direction you like and hold it there , even when flying at 600KM/Hr.
Because when I let go of my elevators , entire plane just goes into oscillations and it becomes tedius task to focus on killing those oscillations .
A cheat that I'm thinking of is , let's say pilot makes +30 degree deflection to elevators and let go , then the computer will immediately put the elevators to -30 degreee deflection . This will exactly cancel out the rotational momentum built up by the initial deflection .  But in real aircraft , it will take time to put the control surface in opposite angle . So how do they do it so quickly .
This person claims to be using a PID controller for pitch damping . How does a PID controller acount for the inherent delay in the actuators of control surface . Let's say controller decides an +10 degree is needed this moment to keep the aircraft stable at the current pitch , but the hydraulics will take their own time to put the control surface at that angle , by that time aircraft will have moved even more from the required stable position .

I know I'm asking too much in a single question . But I've been stuck on this problem for so long that only more and more problems have accumulated in this time .

This depends on what level of realism you want.
If you want high, save yourself a lot of work by using an existing dynamics model like the JSBSim. There are model templates for it that have all the needed functions for reasonably realistic model are predefined and you just tweak the coefficients to get the performance you want.
If you want low, just make the surface deflection correspond to pitch/roll rate rather than acceleration, because that's what actually happens to a level of approximation that is perfectly fine for an arcade gamer.
What really happens is that when you deflect the control surface, the rotation will change the angle at which air hits the surface, and that will negate the effect of the control surface, so the aircraft settles at fixed rate of pitch/roll corresponding to the commanded displacement. And when the pilot centres the surface again, the aerodynamic force still exists that countered the deflection, which will now stop the rotation again.
This is fast enough that pilots normally don't need to stop the rotation with counter-movement of the controls except sometimes for fast rolls in aerobatics.
Regarding PID controller, a “position-integral-derivative” controller, the point is that the derivative term predicts the response delay, while the integral term compensates for any bias. The disadvantage is that if you tune it to have fast response, it always overshoots the target value, because the integral term will overestimate the bias. But it is simple to implement and does not require much modelling, just tweak the numbers until it works. The JSBSim provides PID controller (and some other simpler controllers) for the model definition.


Is there a maximum horizontal acceleration for passengers? Are there any regulations regarding the maximum acceleration forces that passengers should experience during takeoff/flight/landing?

Or what would be considered to be an acceptable horizontal acceleration? 0.5g? 1g?

I am contemplating how to achieve very good STOL characteristics for a small  commuter aircraft while still maintaining a high wing loading.

It depends on several factors:
1) How long is the body subjected to these forces?
2) What's the posture of the body?
3) To what extent are the passengers used to g forces (for example due to training)?
...

However, early experiments showed that untrained humans could withstand g forces as much as 20 g for less than 10 seconds, to 10 g for 1 minute, and 6 g for 10 minutes.


Strange facility out west near California; what is this place? While on a flight to San Francisco from New York, somewhere over California or Nevada, I saw this from my window; what the heck is it?

In case anyone's wondering, it's the Crescent Dunes Solar Energy Project, credit to Trish Ling at Sci-Fi.


What is the difference between fail-safe and fail-soft? I have heard the following terms related to safe system design but I cannot really see a difference between fail-safe and fail-soft (graceful degradation).

To get a common understanding I will just write out the terms that I've heard. Please feel free to correct me, if I don't explain something properly:

Safe life: A system does not show any fault during its lifecycle
Fail-Safe: A system goes into a safe operating mode with reduced functionality after a failure
Fail-Soft: A system goes into a degraded mode after a failure
Fail-Operative: A system still has the full functionality after a failure

From those explanations, it seems to me that Fail-Safe and Fail-Soft are actually the same concepts. I would be glad if someone could explain to me the difference between the concepts by using some examples from aviation.

Fail-safe does not necessarily imply that the system will continue operating after a fail. If the system stops operating but does not create a dangerous situation, it is still fail-safe. A non-essential service on board an aircraft such as the entertainment system can be fail-safe if it just stops operating because a fuse blows. If upon a failure the fuse does not blow and as a result the system catches fire after a short-circuit, it is not fail-safe.

Fail-soft does indeed mean that after a failure, essential services are still functional, although in aviation context this is mostly referred to as graceful degradation. A fly-by-wire system such as on board the A320 is fail soft:

If all flight computers are functioning, the system flies with normal law active, providing protections against getting into unsafe regions of the flight envelope.
Upon certain detected failures, the system switches to alternate law, still with some protections in place.
Upon further failures, the system switches to direct law: no more flight envelope protections, just surface deflection proportional to stick deflection.

So this flight computer system is fail-soft and fail safe. The electronic flight control system as a whole is fail safe: if all flight computers are lost, the system has hydro-mechanical connections from pedals to the rudder and from the trim wheel to the stabiliser.

Hydraulic systems require special attention regarding fail-safety, since a stuck servo valve can command a constant velocity: the actuator runs into one of its stops and has a hard-over failure. An elevator that is stuck in full up deflection is not safe, so the pitch control system needs to make provisions for fail-safety if this fault occurs. For instance by allowing left and right elevators to normally work in unison, but uncoupling them after a detection of a hard-over failure. The working elevator can then be commanded to full opposite position, making the elevator system fail-safe but not fail-soft: pitch command must now be done with the stabiliser trim. One elevator stuck in the mid position would be fail-safe, and control with the other elevator provides graceful degradation.

The flight control system on board an F-16 is fail-operational: upon a system failure, full system function continues, no degradation. It is triple redundant, meaning there are four systems on board that carry out the same function, while only one is required. The four systems function independently, and a monitoring system determines if all four outputs are within a pre-determined range. If three are and one is not, this system is switched off and the other three continue. This can happen once more, but if there are only two systems operational the voting system would not know which of the two has failed.


Are being +30 and having a Ph.D. considered as barriers to become an air traffic controller in NAV CANADA? The requirements to apply to the training phase of NAV CANADA (to become an air traffic controller) are listed here, in which no upper bound corresponding to the age and the education level of a potential applicant is noted.

Does that mean an over-30 Ph.D.-holding person has also chance to be picked for such position (or he may be pruned off the list of successful candidates because of being old and over-qualified)?

PS. Any potential similar piece of knowledge associated with other aviation control bodies is also appreciated.

As a general answer (not pertaining just to Canada): any aspiring air traffic controller is very thoroughly tested before acceptance to a training program. Having any kind of previous education has little effect, say, higher academic merits, in my experience, may only represent someone's ability to function in academia.

Being a doctor of this or that certainly is not bad, but if an applicant holds many different credentials, it usually is, if not a red flag, a signal of the person's tendency to like studying more than doing.

ATC work is very demanding, and it requires a specific type of person: calm, focussed, extremely high tolerance to stress to mention some traits, etc. It is not a profession that I would recommend at first hand to anyone.

Regarding age, well, 50 is +30, so a bit vague definition there. If one is closer to 30, probably not a problem. Closer to 40, things are getting increasingly difficult. Thing with age limitation, or the lack of one is that declaring that age is not a limiting factor might be a politically dictated statement. Legislation probably demands that age cannot be a limiting factor when hiring people.


What resources can direct me to real estate with landing strips? I am looking for a website or places to look at estate / personal residences in PA, DE, MD, VA that have landing strips already in place.

There seem to be many, however, some of those "landing strips already in place" will no doubt be public airports that border the property or shared private community strips that aren't generally inviting the public.

aviationacres.com
aviationhomes.com
hangarnetwork.com
airportairparkhomes.com


What would the ranks most likely be of the crew of a B-1B? I'm currently attempting to write a novel which briefly features a modified B-1B undertaking a risky, highly important mission in support of a Special Access Program. Since a few scenes are set in the cockpit and feature a discussion between the crew, it would be very helpful to know what the ranks of the crew would most likely be.

I've done a little research via a number of sites and e-book previews but so far I've not turned up much other than at least one Lancer pilot who was a Major but I have no idea how the co-pilot, DSO and OSO would compare in rank, or if B-1B pilots of greater rank than Major would be realistic/believable.

In general, the pilot could be a captain, major, or lt col, the copilot probably a 1lt or captain, and the navs any of the above. For a select crew handpicked for a "fate of the world" mission, you might put 2 instructor pilots together along with two senior navs, so all 4 as lt cols wouldn't be impossible. On the other hand, if the crew is essentially detailed off to be "secret squirrels" for a while, it probably wouldn't be stacked quite that high, so maybe a mix of majors & captains. That happens because it quickly becomes disruptive to take senior guys (tactics officers, instructors, the ops officer or commander, etc) away from their regular squadron jobs for a prolonged period. The more important the mission, the more that disruption is accepted.


What prep work can I do before transitioning from SEL to SES? I'm very interested in getting my SES rating.  Is there any personal studying or prep work that I can do to minimize time in the air and with an instructor?

EDIT: I do have my SEL pilot license already.

If you already have a pilot license for single-engine land airplanes you've done a huge amount of prep work already - you know all the airspace, navigation, airwork, etc. that you need to know for your seaplane rating.
Brush up on all of that in the seaplane as you can be tested on it and the aerodynamics will be a bit different with floats hanging out there, but you're already well ahead of the game.
You need to learn how to take off, land, and taxi/sail all over again on water (which is arguably the hard part) but the bulk of your existing knowledge will transfer over.

For studying and prep I imagine the FAA Seaplane Operations Handbook (FAA-H-8083-23) would be the best place to look - it's pretty comprehensive.
Also if you can commandeer a seaplane pilot for some hangar flying (or better a pilot and aircraft for a few real-world touch-and-gos & some practice sailing the plane on water) that would obviously be a great advantage, but coming to your first lesson familiar with the Seaplane Operations Handbook would probably put you well ahead of the curve anyway.


What is the blue range indicating on this manifold pressure gauge? This is baffling me. Does anybody with experience with this type of indicator have any idea what the blue range of this gauge means?

It's mounted in a mock-up panel. I know nothing about where it originally came from, though it seems pretty clear that it's from a turbocharged piston twin.

It's a manifold pressure limit with altitude.  It relates to a limitation on the differential between ambient and total manifold pressure at different altitudes with turbocharged or supercharged engines; a limit on the amount of actual boost with altitude in other words, not the total pressure.

At 30000 ft, standard atmospheric pressure is only just under 9 inches.  20 inches on the gauge is 11 inches of boost above atmospheric.

At 20000 ft, atmospheric pressure is just under 14 inches, and you're limited to 35 inches, which is about 21 inches of boost.

Between 16000 ft and sea level, with atmospheric pressure between roughly 16 and 30 inches, the limitation is the red line of 40, which is anywhere from 10 to 24 inches of boost above atmospheric.

The increasing limitation in maximum boost with altitude is usually related to the reduced cylinder cooling ability of the thinning air with altitude, and the potential for detonation.


What material is the smoothest for air to travel over the wing? Wings are pretty smooth these days and air travels over the wing easier, so what is the smoothest material

Well first let's dispel the rumor that wings are "pretty smooth" - ideally (in the dreams of aircraft designers and the mathematical perfection of fluid dynamics modeling) they would be, and they certainly are from a distance, but when you get up close and personal most aircraft wings are ugly, bumpy things (as you'll see below). Modern composite wings are a notable exception to this general rule, but there are a few other exceptions in the history of aircraft design.

The material is, for the most part, not relevant: We usually paint aircraft, so the smoothness of the underlying material contributes less to the surface than the paint preparation, clear coat, and wax.

What does matter are the construction techniques used. A few examples (in rough order of decreasing smoothness):

A modern composite wing can have an almost completely smooth surface (with no rivets or seams in the airflow) - for example a 787 wing, or this SR-20 wing:

Some aluminum designs use "bonded construction" (glue) with fewer disruptions of the wing surface. One example are the Grumman AA-1 and AA-5 series aircraft, which has a smooth wing except for the fuel caps and contoured seam lines:

Conventional aluminum wings can be assembled with flush rivets, which once primed and painted give a very smooth surface with only slight irregularities around each rivet:

(Please ignore the blue protective film, and open rivet holes. This is from an RV-14 under construction & was the best photo I could find.)
Fabric wings - one of the oldest wing coverings - are actually pretty smooth. They have "rib stitching" to attach them to the substructure, and are stretched taught over the frame (using heat & dope to shrink the fabric), but the overall result is a very smooth surface between the ribs, with some irregularity over them from the stitches:

Typical aluminum aircraft wing is attached with typical rivets - the head of which protrudes into the airflow slightly. You can see some rivet (and screw) shadows in this image:

Note that I've only considered the TOP surface of the wing (where airflow and smoothness is most critical). The underside of a wing usually has many other things sticking out into the airflow (fuel tank vents, access/inspection panels, hinges & tracks for control surfaces, etc.) which are a much greater disturbance to the airflow than whatever fasteners are attaching the skin to the rest of the structure of the aircraft.


What are en-route VHF marker beacons (75 MHz)? ICAO Annex 10, Volume 1 contains a section that gives the specification for en-route VHF marker beacons. What are they?

I suspect they are a relic of the past. Are they still in use anywhere in the world?

En-route marker beacons are close relatives of the outer/middle/inner markers used on ILS approaches. Airway markers use the same audio frequency as inner markers, and some older equipment has indicators for airway/outer/middle. Older versions of the FAA AIM discuss marker beacons, but later versions omit them.
From Wikipedia:

From the 1930s until the 1950s, markers were used extensively along airways to provide an indication of an aircraft's specific position along the route, but from the 1960s they have become increasingly limited to ILS approach installations. They are now very gradually being phased out of service, especially in more developed parts of the world, as GPS and other technologies have made marker beacons increasingly obsolete.
The airway marker was used to indicate reporting points along the centerline of now obsolete "Red" airways
They are only used on a few instrument approaches anymore, to mark positions along the inbound course, when there is only one marker present

The example cited on Wikipedia (KSEE) used to have a marker as part of the LOC-D approach, but it appears that this was replaced with the YAGSU waypoint (and more recently, the DEBEY waypoint). Another example is KSLE where the ARTTY intersection on the LOC BC 13 approach used to have a marker but no longer does. I haven't been able to find any current procedures still using one.


What Transponder code to use flying between Oakland and Hawaii? Where to find the appropriate Transponder code for crossing the Pacific?

Whichever code is assigned to the individual flight by ATC. There isn't a fixed code to use for any one specific route. You might want to see: How does ATC know if you have been assigned a squawk or not?


What material is used to make the interior sidewalls panels, ceiling as well as luggage bins in a commercial aircraft? What material is use to make the interior sidewalls panels, ceiling as well as luggage bins? All these elements seems to be made of similar material.

What is the weight these cabin interior elements represent for a typical single aisle aircraft like the A320?

The materials used in aircraft are similar regardless of airline or type of aircraft, since all passenger-carrying craft must meet  flammability requirements.

The side panels, the ceiling and the luggage bins are made out of a Glass Fiber Reinforced Plastic (GFRP) that must meet fire/smoke/toxicity (FST) requirements.The small window shade panels that slide down to cover airline windows, are typically thermoformed polyetherketoneketone (PEKK) plastic sheet. Some other high performance thermoplastics can be found on an airliner's interior, like the polyetheretherketone (PEEK) and the polyvinyl fluoride (PVF) (mostly as decorative surfaces laminate).

Reference: https://www.compositesworld.com/articles/advanced-materials-for-aircraft-interiors


Has there ever been a US airport with identifier PM2? I have an old entry in my logbook having landed and departed from an airport with identifier PM2. I think I either can't read my handwriting or I made a mistake because I can find no record of such an airport ever existing. Does anyone have a way of finding out?

No. PM2 would not be a valid ID in the FAA system. According to the FAA order defining the system:

  1−2−7. ASSIGNMENT SYSTEM §c. Most one−number, two−letter identifiers have been assigned to aviation weather reporting and observation stations and special−use locations. Some of these identifiers may be assigned to public−use landing facilities within the United States and its jurisdictions, which do not meet the requirements for identifiers in the three−letter series. In this identifier series, the number is always in the first position of the three−character combination.
  (emphasis mine)

So two letters followed by a number is not a valid ID.


Are there any single-pilot aircraft certified in the Part 23 Commuter category? Is it possible to certify an aircraft under FAR 23 Commuter Category with single pilot ops only? Like, there is just one seat in the cockpit and up to 19 passengers.
Does anyone know of such an aircraft flying?

It looks like it's possible but not common. There's an STC for the Twin Otter that authorizes single-pilot operations in the commuter category if various upgrades have been made. At least, that's my reading of it:

  The Twin Otter DHC-6-300HG™ type rating designation is DHC-6HG and may
  be operated with or without a second in command (SIC) with certain
  limitations. The Airplane Flight Manual Supplement (AFMS) lists
  equipment that must be installed and operative to operate the aircraft
  single pilot.

And:

  FAA STC SA02682LA incorporates upgraded engines, upgraded propellers,
  increased maximum takeoff weights (MTOW), structural and aerodynamic
  modifications, and the aircraft category and design characteristics
  were updated to Title 14 of the Code of Federal Regulations (14 CFR)
  part 23 commuter category.


How do fast-flying aircraft avoid overheating? As a follow-up question to What is the typical temperature of an airliner's hull during flight? I wonder how very fast airplanes, such as the SR-71 mentioned, avoid overheating with a total air temperature outside of more than 400 degrees Celsius.

To avoid overheating, the usual trick is to select the right material:

The Concorde used a special aluminium alloy, called Hiduminium, which had higher strength at elevated temperatures and allowed the Concorde to cruise at Mach 2.02. Aluminium melts at 660°C.
The MiG-25 used stainless steel instead of aluminium to make its top speed of Mach 3.1 possible (top speed without engine damage was Mach 2.83). Titanium would had been even better, but was expensive and difficult to work with at that time. Stainless steel melts between 1400°C and 1450°C.
The XB-70 used titanium in addition to stainless steel. Its cruise speed was also Mach 3.0. Titanium melts at 1668°C.
The SR-71 used titanium for 85% of its structure to allow a cruising speed of Mach 3.2.
The X-15 was built from Inconel-X, a nickel-chromium alloy which has excellent strength at high temperature (it starts to melt at 1393°C) and allowed it to go up to Mach 6.5.
The Space Shuttle used a ceramic insulation on top of the load-carrying aluminium structure which kept the heat away from the structure during descent. Note that the Shuttle had to be connected to a heat sink to cool the on-board systems after landing.

The next trick is to fly higher up where air is less dense. Lower density does not reduce the air temperature, but it reduces the heat flow so the airframe will settle at a lower temperature. Remember that the eventual heat is the combination of convection, radiation and heat conductivity. Flying high up allows especially the top surface to radiate heat freely into the black of space above.

The hottest aircraft ever was the North American X-15 A-2. For a speed record attempt, the whole aircraft was covered with pink, ablative paint so the process of sublimation would carry some more heat away. To protect the paint from liquid oxygen, a white topcoat was applied also.

X-15 A-2 shortly after being dropped from the B-52 carrier (picture source). Note the small barrel under the lower fin: This was a ramjet which was test-flown on this occasion.

Damage to the ventral stabilizer. The ramjet separated prematurely due to frictional heating (picture source)

A third trick is to fly fast only for a short time. A heat-seeking air to air missile will easily reach Mach 3, but only for less than a minute. To keep the sensor cooled, a pressurized gas (argon or nitrogen) would be expanded (the AIM-9X even uses a stirling cryo-cooler). By heating the structure or using an internal heat sink, the limited heat load can be tolerated, albeit only for a very limited time.


How to take into account man hours in a Service Bulletin? There are two phrases in any SB included "Total Man hour"and"Elapse time", which quantity should we use in job card for accomplishment an AD or SB?

Elapsed time is the total man hours divided by the number of techs assigned to the task.  So 40 manhours will take one tech 40 hours to complete or 2 techs 20 hours.  If the number of techs to be assigned is up to the supervisor or a scheduler/planner, I would just include the total man hour estimate.  If the job card specifies the number of techs required for the job, then include the elapsed time based on that.

Note that on the first several aircraft modified under an SB, the actual man hours will exceed the SB estimate by a large margin, maybe 50% or more, until the technicians involved get through the learning curve of the task, and even then will probably never get to the SB labour estimate, which assumes perfect conditions and no wasted time.  If the OEM is giving a labour credit that can be charged back to the OEM at some hourly rate, it will be based on the SB estimated labour, which is derived from the proof installation of the SB, not the actual hours used.


What are the reasons behind switching FDs off for a VOR approach? Why do SOPs ask to switch off flight directors and enter Vapp into the FMGC while carrying out a VOR approach on Airbus aircraft? My question pertains to when we disengage the AP. Why do we carry out these actions?

ok two questios there really:

entering vapp as speed constraint at the FAF.
After the FAF you want to be flying a constant 3deg path (or whatever the approach gs is). Changing configurations and deploying flaps while on final will make the aeroplane baloon and deviate from that flightpath. To minimize those (uncorectable) deviations, the SOPs will call for the aircraft to be fully configured (flaps full, gear down and Vapp) at the FAF when starting the final descent.
By entering the vapp in fmgc at the faf you are basically telling the computers I want to slow down early and configure to full flaps before thr FAF. The fmgc will then compute your descent to allow for that deceleration segment. It's not SOP as far as I can tell, just a gimmick people use to tell computer you want early stabilized.

Switching FDs off
Two points here: you are not switching them off at the FAF. You are changing them to a TRK/FPA mode (usually 1nm from FAF) to better control your glidepath angle durring final. Yes, you could use v/s to do that, and use trigonometry to compute the v/s required to maintain 3 deg for a given groundspeed, but why would you.  Changing winds will change your groundspeed, and thermals will mess up your flight path. Setting -3deg in the FCU is much easier.  I can then set -3.2deg if I get, say 20 feet high, and I should be back on profile in about 1nm.
Second point: FDs will be switched off (completely) after disconecting A/P and at least at reaching minimas. Reason is the ap guidance is not certified to guide you after that so it is manual/visual flying using PAPI if available.

Note: this is all about flying a manually-selected non-precision approach (eg in NAV/FPA or TRK/FPA) mode with AP on. Using a fully managed approach is a different story


Wake turbulence: crossing under a final approach path VFR Flying VFR around the Bay Area I’ve had two experiences recently that made me a bit nervous, but I haven’t been able to find recommendations that fit the situation.

The first was flying (C172) north along the east bay hills somewhere between OAK and LVK, around 3500’. We saw a 737 descending towards OAK ahead and above us, crossing right to left. 2 or 3 minutes later, long after I’d forgotten about it, I think we crossed the descending wake: we felt a single very sharp bump, hard enough to feel like we’d hit something.

The second time, I was crossing the bay just east of SQL on a northeast heading. ATC pointed out an A380 on final to SFO ahead of us. They passed in front and above us, and I turned to cross their path at 90 degrees, thinking this would be the right strategy for minimizing the risk of being rolled by the vortices. When I later checked the flightradar data, they were about 1000’ above us where our paths crossed. We never felt a bump, though the controller who watched this asked me how the turbulence was, so he evidently thought we were taking a risk.

Of course I know the mantra about wake turbulence is to just avoid it. But in practice, in a situation like this, I might have to divert for 5 minutes or so to try to fly “around” the wake area (e.g., in this case turn SE paralleling the flight path in reverse before turning back on course) and it seemed to me that crossing a wake at 90 degrees seems like a reasonably safe thing to do, a couple of minutes after the plane had crossed (though I couldn’t really judge the vertical separation).

I can’t find anything in faa docs on this situation. They’re all about takeoff and landing. And the bad stories about planes being damaged/destroyed by wakes seem to always involve a near 0 or 180 relative heading (i.e., flying along the vortex line so the two wings see a large force difference).

I’m curious what others think about this.

Due to the nature of wake turbulence descending over time and weakening as time goes on, I would say that it's possible that you hit the wake of the 737, and just managed to avoid the A380's wake out of luck. It also depends on the wind direction as to the path of the wake, so it's hard to say in your specific case

Skybrary describes crossing wake turbulence as:

  A cross-track encounter en route is likely to lead to only one or two sharp 'jolts' as the vortices are crossed.

Which leads to me to believe you hit their wake, and not just some other form of turbulence.

In terms of wake avoidance the FAA says in 7.3.7(b).9:

  En route VFR (thousand-foot altitude plus 500 feet). Avoid flight below and behind a large aircraft's path. If a larger aircraft is observed above on the same track (meeting or overtaking) adjust your position laterally, preferably upwind.

And skybrary recommends:

  In the case of crossing tracks, it has been found that the time interval necessary to avoid creating a wake vortex hazard is 3 minutes.

In terms of a direction to cross the vortexes at this section of FAA 7.3.3(b).1 implies that you should do as you did and cross perpendicular to the path - as to avoid strong induced rolls:

  During inflight testing, aircraft intentionally flew directly up trailing vortex cores of larger aircraft. These tests demonstrated that the ability of aircraft to counteract the roll imposed by wake vortex depends primarily on the wingspan and counter-control responsiveness of the encountering aircraft. These tests also demonstrated the difficulty of an aircraft to remain within a wake vortex. The natural tendency is for the circulation to eject aircraft from the vortex.

To summarise those points in terms of enroute wake avoidance, and effect limitation:

Fly above their path
Position yourself upwind away from the wake path
Try to be at least 3 minutes behind the aircraft when crossing the path
And cross perpendicular to the wake path, to avoid inducing a roll

Sources: https://www.faa.gov/air_traffic/publications/atpubs/aim_html/chap7_section_3.html
https://www.skybrary.aero/index.php/En-route_Wake_Vortex_Hazard


Do all Bombardier jets have manual reversion? Whatever CRJ 700 or Learjet 35A/45XR.

Do these aircraft have full manual reversion? Can you operate the flying surfaces in a hydraulic failure?

These aircraft are very small – even smaller than a 737 – so I guess they all do.

Can't speak for the Lear, which I believe has manual controls anyway, but the CRJs DO NOT have manual reversion.  The RJs are designed to a technical level similar to the Boeing 767.

The control surfaces are purely hydraulically operated.  For elevator and rudder, which have 3 PCUs each, you'd have to lose all 3 hydraulic systems to lose the surfaces.  For the ailerons, which are 2 PCU and split one of them on each side to Hydraulic System 2 and 3 while the others run on System 1, you have to lose 2 systems to lose one aileron, and all 3 to lose both ailerons.

The probability of this kind of multiple failure event is below the 1:1,000,000,000 risk threshold for catastrophic events, so it's good to go.

It's been discussed before how the hydraulic PCU can kind of be driven manually by hauling on the controls to lever the PCU piston about the bottomed-out servo control valve, but this would only give a bit of movement at the limits of control travel in any case and is not a practical consideration for trying to control the aircraft in flight.


What Blackbird variant is the one at the Kalamazoo Air Zoo? Which one is sitting at the Air Zoo (Kalamazoo Aviation History Museum)? What variant is it?

The Air Zoo refers to it as an SR-71B.  Their image of it shows it in NASA livery as NASA 831. This was originally USAF serial number 61-7956 which was one of two SR-71's built as trainers. 61-7957 was the other and it was destroyed in a crash in 1968.  They were both built as SR-71B's, not A-12's or YF-12's.

Number 956 was transferred to NASA in 1990 when the AF retired the SR-71's the first time. NASA labeled it as #831.

There is only one other dual-control trainer and it is an SR-71C, serial number 61-7981 which replaced the destroyed #956.  It was made from parts of the static test model SR-71 and the aft section of YF-12A #06934.

More info at Habu.org.


Has a small airplane ever been air launched from a heavy-lift helicopter? I would like to know if a small airplane, like a Cessna, has ever been air launched from a heavy-lift helicopter, perhaps as a stunt or as an aviation experiment?

I think it would have been a simple matter of lifting a small airplane with a special detachable hitch on the top of the airplane and then for the helicopter to have taken it up to a height of say 10,000 ft. I imagine the airplane would have then started its engine, detached from the lift cable, gone into an immediate dive, and then would have come out the dive after a thousand feet or so.

I have searched the Internet for a stunt/experiment like this one, but have not found any.

November 2017 the Dream Chaser shuttle craft was dropped from a Chinook helicopter
from over 12,000 feet.  The automated glide test back to a runway near Mojave, California
was a success.


Why are most weapons in AC-130 on the left-hand side? Lockheed AC-130 gunship is a heavily armed ground-attack aircraft variant of the C-130 Hercules transporter. The plane is manufactured by Lockheed and converted by Boeing.

Why are most of the guns in AC-130 installed on the left-hand side (but not right)?

Picture Source

It is not designed to strafe, it is designed to loiter over a target or, to apply suppression fire or support fire for a sustained period of time.

It often circles a target area and a counter clockwise orbit (circling to the left) makes sense since the captain sits on the left and can keep the area in view at all times.

Therefore, the weapons are mounted on the left.


How the Log Periodic Dipole Antenna of Localiser help in varying modulation depth? Here Albert Helfrick speaks about 40% modulation depth for each tone in a localiser radio signal. However latest manuals of ILS manufacturers and google source speaks about 20% modulation depth, not 40%. Albert also says that modulation depth becomes 20% at the centreline of runway.

My question is whether Albert is correct or manufacturers like NORMARC, Thales and SELEX are correct? If Albert is correct then how does 16,20,24
element log periodic dipole array help in achieving this modulation depth variation?

I would appreciate if someone with proper explanation comes up. And this question is not duplicate so please do not confuse it with other modulation varying behaviour of questions asked on this forum.

Mod Depth (more commonly called modulation index in electrical engineering) is the amount a carrier signal is modulated.  Mod depth has nothing to do with antenna configuration and is set by the transmitter (or more precisely the modulator).  The log periodic antenna controls the width of the various beams.  A larger antenna means a smaller beam and smaller beams mean you will have more precision on an ILS approach.  As far as the discrepancy between the 40% and 20% mod depth for ILS systems I will always believe the manufacture.  It seems like the documentation you posted is describing a simple hypothetical setup to help you understand the concept.  I believe most ILS systems use more than two beams. The degree of mod depth shouldn't matter too much as long as your Signal to Noise Ratio is high so I wouldn't get caught with the amount of mod depth in ILS systems.


IFR to VFR Flight Plan Change A pilot has filed an IFR flight plan.  While airborne, he feels like changing to VFR flight. Can he request for it and what are the conditions?

Yes, if in VMC a pilot can cancel IFR, then request VFR flight following for the remainder of the trip.


What is the time derivative of the angle of attack? Suppose a flying missile's velocity vector has components $u, v, w$, as illustrated below.

From my knowledge of flight dynamics, the angle of attack is

$$\alpha = \arctan \left(\frac{w}{u}\right)$$

where $u, w$ are time-varying. Then,

$$\frac{d\alpha}{dt} = \frac{1}{1+\frac{w^2}{u^2}} \left(\frac{w}{u}\right)'= \frac{w'u - wu'}{u^2+w^2}$$

Some books indicate

$$\frac{d\alpha}{dt} = q + \frac{Z}{mu}$$

where $q$ is the second component of angular velocity, $Z$ is the third component of the total force, and $m$ is the mass of missile. How can these two formulas be the same?

Assuming that there isn't an error in the books you've read:

Both formulas are true. It's true that

$$\frac{d\alpha}{dt} = \frac{w'u - wu'}{u^2 + w^2},$$

and it's also true that

$$\frac{d\alpha}{dt}= q + \frac{Z}{mu}.$$

From this, we can conclude that

$$\frac{w'u - wu'}{u^2 + w^2} = q + \frac{Z}{mu}.$$

Both of these two formulas describe the way that the angle of attack changes, but they describe it in different ways.

I'm not sure exactly how the $q + Z/mu$ formula was derived, but it seems to be related to the fact that angle of attack is related to pitch and the flight path. Specifically, for flight with zero bank angle, the angle of attack is the pitch angle minus the climb angle. It looks like the $q$ term comes from the rate of change of pitch, and the $Z/mu$ term comes from the rate of change of climb angle.


How is the Angle of Attack influenced in the slipstream of a propeller? My question is how can the angle of attack be changed when the wing is in the slipstream of a propeller, giving "enough air flow" to the wing. The propeller sends the flow of air in the same direction related to the wing no matter how the aeroplane is oriented in the space. So theoretically the angle of attack should never change.

UPD: The answer should not depend on how the plane is thrusted. Turbo engines are also pushing the plane in the same direction related to the fixed wing. ( I am not talking about engines that can change the vector of thrust).

Not all planes have propellers and not all of the wing is behind the propeller.

In fact only a small part of the wing is behind the propeller. The rest will get clean air depending on the attitude (orientation) of the aircraft. The wing is also not perfectly straight behind the propeller either, usually dropping down a bit so there is a positive angle of attack.

Jet powered planes generally have their engines away from the wings.

In most planes, thrust is surprisingly small compared to the weight, an empty A380 only has a thrust to weight ratio of 0.47 and most of that thrust will be applied horizontally. So as the plane will sink rapidly should there be no lift from the wings. That sink tendency is what provides the angle of attack.

This will max out the sink rate should the wings be level, angle them up a bit and the plane will try to climb.


How did this F/A-18's execute a "low-boom maneuver"? The Engadget article NASA will publicly test quiet supersonic technology in November says:

  The administration plans to conduct a series of public tests around the coastal city of Galveston in November. The F/A-18 Hornet aircraft at the heart of the tests will perform dive maneuvers that produce louder sonic booms out at sea, while quieter sonic "thumps" will take place over Galveston proper. After that, "at least" 500 local volunteers will provide feedback on what they heard, while audio sensors will provide more definitive noise readings.

and links to the NASA YouTube video NASA Social: Low-Boom Maneuver:

  This footage is from a NASA Social event at Armstrong Flight Research Center during which the F/A-18 was flown to produce a regular sonic boom and then a low “boom” by performing the dive maneuver described in this story. The normal sonic double boom occurs at 0:43. The low “boom” occurs at 02:34. The rest of the footage includes a flyby, planes on the ground with NASA Social participants, a visit to the Ikhana UAS and a pilot signing.

Question: What would be a simple way to understand what a "low-boom maneuver" is, and how would an F/A-18 execute it? In this case would it require any modification of the Hornet's configuration?

Is producing the boom during a dive of particular relevance to the reduction in sound level, or is this just a convenient way to do this particular experiment? Since the sound level as well as the reduction of the level for the low-boom maneuver at ground level may have a directional dependence, I'm wondering if the direction of the dive needed to be carefully planned to be representative of how the reduction would work for civilian air travel boom reduction, where dives are (thankfully) less frequent.

I did some reading and this is what I could find out so far:
https://www.nasa.gov/aero/nasa-prepares-to-go-public-with-quiet-supersonic-tech
This article is similar to the Engagdet one but goes into slightly more detail(though not enough for a proper explanation) about the dive maneuver.
However, Lockheed Martin is in the process of designing and building a low sonic boom demonstrator, slated to fly in 2021. The wikipedia page says that to prevent sonic booms from building up, the aircraft will have a long slender body and canards (thought the Concorde had these as well, so I'm not sure what the difference is). They will probably add canards to the F/A-18.
The dive maneuver happens in such a way that while the sonic booms directly underneath the aircraft are strengthened, there is a secondary pair of sonic booms created further ahead that are weaker, giving quiet thumps instead.
Hope this helps.


Are electromechanical actuators used in aircraft other than the Boeing 787? Are there any large (non-experimental) civil or military aircraft that use electromechanical actuators (EMA), other than the Boeing 787?

Electromechanical Actuators are used in many aircraft, and in many applications.
Applications vary from controlling doors,  trims, control surfaces, flaps and air inlets to moving your business class seat to the most comfortable position.

For quite a range of examples see the product website of this manufacturer.

Or this video of an aileron application


How do I calculate the lift force on an aileron? How do I calculate the force of lift acting on an aileron with a deflection of 8° and a flight speed of 40km/h?

Cessna Cardinal planform, I don't know how to put this in a comment


In helicopters, why not have electric motors controlling blade pitch? From my related question comes this idea of electrically controlled blade pitch in helicopters.

Control linkages in helicopter rotors seem to be pretty complex. This surely incurs a lot of friction, especially if you realize that blades have to "flap" back and forth as they rotate around (in order to compensate for retreating blade stall and/or dissymmetry of lift during forward flight). So the swashplate and linkages must surely undergo a lot of friction.

So why not replace all this with electric motors that control blade pitch? They would be small, inside the rod connecting the blade to the hub. No need for any pitch control to be mechanically connected to any other blade(s), so no friction. A computer would control what the pitch should be given the blade's position during its rotation.

This does not mean the main rotor has to be electrically driven. The turboshaft engines can drive the main rotors mechanically as normal. But there would be an electric generator for the blade pitch motors. Note: I'm pretty sure there's already an electric generator on these engines as the computers and radars and stuff have to get their electric power from somewhere.

How would you communicate with (and power) these motors?

The main rotor is spinning constantly - Wires won't work, they would wrap around the shaft and be shredded. A slip ring and brushes (as used in some electically-actuated propellers) would work, but would also wear away quickly and require frequent maintenance as losing control of a helicopter's main rotor blade pitch is a much more serious situation than losing control of a fixed-wing aircraft's propeller pitch (I believe this captures the consequences pretty well).
Because of the rotor speed balance is critical, so any motors, brushes, etc. would need to be balanced around the rotor hub (either by duplicating the equipment, which also provides redundancy, or by adding dummy weight) - get it wrong and the rotor starts vibrating and may come apart.

The motor would also have to be constantly moving: The swashplate adjusts blade pitch through the full 360 degrees of rotation, smoothly changing the pitch of each rotor blade as they rotate. Duplicating this would require the motor(s) to make constant adjustments as the rotor turns, moving and reversing very rapidly). The level of precision required and the forces involved would likely require high-torque stepper motors and a computerized control system of some kind would be needed to drive them and make the necessary blade pitch adjustments at "rotor speed".

So far the motorized solution has added at least one motor, a slip ring & brush system to communicate with it, and a fly-by-wire computer to read the flight control positions and appropriately adjust the blade pitch through 360 degrees of rotation (at whatever speed the rotor is operating).
That is already a lot of complexity and a substantially increased chance of failure versus the (relatively) simple mechanical solution of a swash plate, and I'm not even going out of my way to think of failure modes (actual engineers designing these things are far more paranoid, and could probably imagine all sorts of failure scenarios which eventually result in a helicopter plunging to the ground).


Why is it necessary to fly in visual conditions to certain unmanned airstrips? I have come across certain unmanned airstrips where only VFR flight is allowed not IFR? I wonder what can be the possible reasons for that?

Two reasons:

1) It takes time and money to create an instrument approach procedure, and possibly not enough people have requested that one has been created.

2) A certain amount of obstacle clearance is required, if for some reason the required safety cannot be guaranteed using instruments, the FAA can simply not create a IFR approach


What is a good spin aircraft for someone that is heavy? I've been trying to get a spin endorsement for my CFI, but I've been having a problem trying to find an airplane that I can do it in.

I'm 280 built like a linebacker.  I'm not that "fat" just heavy.  Losing weight for me isn't really a realistic option since I'm on a time crunch.

The closest thing I have found is an Xtreme Decathlon Citabria, but the CFI I go up with needs to weight 110lbs or less, and I'll probably have to stop for fuel in the middle of the flight.

I was told maybe a 172P model might work since it's utility class is 2000lbs, but I've not found one anywhere locally to verify this and see if they would be willing to let me spin the aircraft.

I'm in DFW, but I'd like to keep this question as generic as possible since others may want to know what other aircraft options there are.  But if you know of and airplane in the DFW area (or surrounding areas) please let me know.

A Cherokee 140 should do it. Fill to just below the tabs and get an instructor that weigs 180 lbs.


What PPL routes are available with gliding experience? I'm an early solo glider pilot, with the long term goal of also obtaining a PPL (not a LAPL(A)).  I am planning to do this after I have obtained at least my bronze badge, which I aspire to within the next twelve months.

Originally I thought that the only route open to me was to do the full PPL.  My understanding was that I can get a credit of 10% of P1 hours on a glider deducted from the requirements (max 10 hrs), however the CAA website refers to holders of "a pilot’s licence for another type of aircraft, except balloons".  I'm not sure if that applies to a bronze holder or if I would need to obtain a LAPL(S) or SPL for them to count (for which I would presumably need a bronze XC endorsement to make the required XC flight).

If I obtain a LAPL(S), then according to the CAA I can add a TMG rating (6+ hrs) and then, after hours building (24hrs) do a conversion course (15+ hrs) to the full PPL(A).  It's not clear if this route is available if I obtained an SPL, although for a fee I believe you can swap licences.

Can P1 hours as a glider pilot count towards a PPL(A) without obtaining a LAPL(S)/SPL?

Is the LAPL(S) -> TMG -> PPL route viable? Would I need to go to an "ATO" for TMG training or can my local gliding club do this?

Aside from just doing a PPL from scratch, are there any other viable routes that I've missed (e.g. via a LAPL(A) on a TMG somehow)?

I have a partial answer after more research and some help on pprune.

A Bronze + XC can be used to get a gliding licence, which under the transitional arrangements can be used to obtain a LAPL(S).

In theory the route from there to a LAPL(S)+TMG  and on to a LAPL(A) TMG is feasible, however the BGA is not an ATO yet and there are very few instructors or examiners around.  This route may be problematic at the moment, but should become easier as time goes on.  There's no reason not to claim the LAPL(A) on the way to a PPL(A) if taking this route.

An alternative route is via an NPPL under the transitional arrangements.  After gaining the gliding certificate, a minimum of 10 hours under instruction is needed until reaching the standard for an NPPL SMLG.  After short conversion training, this can then be converted to an NPPL SSEA.  After 6 hours PIC this lot in turn can be traded in for a LAPL(A) SEP+TMG.  Complicated, but overall less hours and my much can be done at a BGA club with a motorglider and instructor.

Regarding the straight PPL(A) route with credit, given the statement

  If you hold a pilot’s licence for another type of aircraft, except
  balloons, you will be credited with 10% of your total flight time as
  PIC up to a maximum of 10 hours

it would seem clear that at that some form of licence is needed, and given the gliding licence qualifies for a LAPL(S) anyway, which one is moot.


What is the true meaning of the word "roger" when used on the radio? What is its origin? When pilots learn to talk on the radio they can generally learn that the word "roger," when used on the radio, is a way to acknowledge that a message was received. What is the textbook definition of the meaning of this word when used on the radio? Also, what is the origin of this word?

In the US, the "textbook" meaning is in the Pilot/Controller Glossary:

  ROGER − I have received all of your last  transmission. It should not be used to answer a  question requiring a yes or a no answer.

The AIM 4-2-3 gives an example of using it to acknowledge instructions:

  Acknowledge  with  your aircraft identification, either at the
  beginning or  at the end of your transmission, and one of the words
  “Wilco,” “Roger,” “Affirmative,” “Negative,” or  other appropriate
  remarks; e.g., “PIPER TWO ONE  FOUR LIMA, ROGER.”

As a counterpoint to that, when I first learned to fly in South Africa I was told never to use Roger in transmissions because it doesn't tell the controller anything useful (obviously the FAA disagrees).

And as for the etymology, that's already been covered in another answer:

  This usage comes from the initial R of received: R was called Roger in
  the radio alphabets or spelling alphabets in use by the military at
  the time of the invention of the radio


What is the risk of a single skydive? I've seen many articles that compares the risk of skydiving with other sports or activities like cycling or driving. However, they are very ambiguous in terms of how the risk was calculated (number of jumps, number of km driven, etc). Here is an example:

Image taken from here.

So, how much is the risk of a single jump?
How does that compares with a common activity like driving a car?

Puzzled by this question I did my own research and found numbers that allows to get a good comparison for year 2016:

According to the United States Parachute Association (USPA), there were 3.2 million jumps in 2016 and 21 fatalities. Therefore, the chances of dying in a single jump were 1 in 152,381.

For a comparison with driving, we can use data from the Insurance Institute for Highway Safety. According to which, in the United States there were on average 1.16 deaths per 100 million vehicle miles traveled.

Crunching those numbers, the chances of dying by driving one km are 1 in 138,103,448. Therefore, to equal those chances to one skydive you have to drive 906 km.

Summarising

In 2016, a single skydiving jump in the US represented the same risk of death as driving 906 km (566 miles).

[UPDATE] Demographics

Many have pointed in that there might be an important component of the risk related with age, experience and how careful a skydiver is.
To approach to an understanding in that regard I've compiled the 147 fatal accidents in the USPA database that happened from 2008 as a result of solo jumps (i.e. not-tandem).
This data do not allow to infer real demographics trends, because I don't know how many total jumps were in each demographic group (I only know how many lead to a fatal accident). However, the visualization of some aspects of the data can be informative.

In the following figure each dot is a fatal accident, and it is plotted based in the numbers of jumps the person involved have performed before the accident (vertical axis) and the age of the person (horizontal axis).

It is clear that the bulk of casualties happen to fairly experienced skydivers (100+ jumps). So, as expected, the more you jump the more chances of dying you have. Note that the vertical axis is logarithmic (so to distinguish between people with relatively small jump counts).

This may lead to think that the first 100 jumps are quite safe, but we can not jump to that conclusion: If you check how many death are there for different jump numbers, you have the following picture

In this plot, the first bar counts deaths during jumps 1 to 50, the second bar for jumps 51 to 100 and so on.
So now it seems that most deaths are in the first 50 jumps. However, that  does not mean that the first 50 jumps are more dangerous, because there were many more jumps corresponding to jump number 1 to 50 than jumps number 900 to 950. So, however informative, this have no real statistical value. And the trend suggesting that jumps become less dangerous as you gain experience might be just an artifact due to the fact that there are more beginner skydivers than experienced ones.


Why does a flight booking mention that the plane has wingtips? Often when booking flights the plane is listed as having wingtips.  For example, it would say 737 (wingtips).  I get what the wingtips are for, but what is the purpose of telling the passengers that the plane has them at time of booking?

This is nothing but a silly marketing exercise. Wingtips (or rather winglets: all airplanes have wingtips:) are seen by the public as a cool and very visible feature, characteristic of newer models. So perhaps they want to say that our airplane is new, and not the 1968 model with the same designation.


Where does the flat plate theory in this paper come from? The aerodynamic model cited in this paper (pdf) as "flat plate theory" was a good first-order approximation of the aerodynamics of a perching glider. I immediately saw the similarity with the Newtonian theory that works well in hypersonics, but it is only a similarity, not the same.

Around the internet I found these other two articles: (1) and (2), which make reference to this flat plate theory in the context of wind turbines.

My questions are:

Where does this flat plate theory come from?
In what textbook or article or other bibliographic reference can I find its derivation?

Edit:

Here is another article that cites this flat plate theory, now in the context of aircraft flight dynamics. This one makes reference to (1).

Here is yet another one in the context of wind turbines.

Ludwig Prandtl's lifting line theory produces a Taylor series as the result of the lift equation, and in almost all books this has been simplified just to the first term of the series, which then was even robbed of its sinus function to simplify it even further by using a small-angle approximation.

What you will find in books today is something like: $$c_L = c_{L\alpha}\cdot\alpha$$

$c_l$ is the lift coefficient, $c_{L\alpha}$ is the lift curve slope and $\alpha$ is the angle of attack in radians.

What the author should at least mention (but I think most are ignorant of this detail) is that a more precise version would be: $$c_L = c_{L\alpha}\cdot\sin\alpha$$

And now the books should tell you that there are more members in the solution to the lift equation; the one above is only the first one which dominates the result for small values of $\alpha$. But they don't. That is OK when the aircraft moves only through the small angle of attack region of attached flow, but for the perching motion you need to look at bigger angles, so the small-angle solution will produce noticeable errors.

The lifting-line theory assumes inviscid flow and does not know about flow separation. Perched flight of birds would be impossible without the high angle of attacks which produce flow separation and makes use of instationary effects which delay separation. All this is not covered by lifting line theory, but nevertheless it produces quite useable results. I guess, however, that the equation in the paper was found empirically.

The lift equation cited in the paper is a consequence of observing forces in a 360° polar, one where the airfoil is rotated through full 360° instead of the narrow range between maybe -8° and +12° where flow is attached and lift forces vary linearly with the angle of attack.

The plot below is from Hoerner's book "Fluid Dynamic Lift" (Scribd) and shows the results of several measurements over 180°. Apart from the spikes around 15° and 175°, the forces correspond well with $c_L = x\cdot\sin\alpha\cdot\cos\alpha$, where $c_L$ is the lift coefficient, $\alpha$ denotes the angle of attack and $x$ is a proportionality factor (the paper postulates $x$ = 2).
$c_L$ over 180° angle of attack from Hörner's book">

A flat plate has no leading edge radius and, consequently, no leading edge suction, which would be responsible for the aforementioned spikes. Therefore, the simple trigonometric approximation will fit the data quite well.

Both the flat plate and Newtonian theories assume the aerodynamic force to be orthogonal to the plane of the wing or plate, and when you take the portion of that force which is orthogonal to the direction of movement, which is how lift is defined, you get above trigonometric equation. This is simple geometry and shows no deeper insight into fluid mechanics.


Do ailerons on opposite wings move together? It seems nicely symmetrical that opposite ailerons would be locked togther, so that when the left wing's ailerons move up, those on the right wing would move down, by the same amount and at the same speed.

Is this in fact generally the case on aeroplanes? Or can they be moved independently, or at different rates or to different positions (and what advantage would that offer)?

Finally, are there any aeroplanes on which they can be moved in the same direction?

On most general aviation airplanes, and other cable-controlled aircraft, they move together and for that matter are cross linked to the same physical cable. You can see this nicely on the control diagram for the B-24

(source)

Some ailerons are designed to counteract adverse yaw and may move such that they are asymmetrical to the flow over the wing.

  1) Differential Ailerons: One aileron is raised a greater distance
  than the other aileron is lowered. The extra upward aileron movement
  produces more drag change than an increase in AOA on the downward
  aileron. This produces an increase in drag on the descending wing,
  which reduces adverse yaw.

  2) Frise Ailerons: The aileron being raised pivots on an offset hinge.
  The leading edge of the aileron is now pushed into the airflow,
  creating drag and reducing adverse yaw. In this case, frise ailerons
  are using form drag to counter induced drag.

But not all aircraft contain such systems. Fly-by-wire systems are theoretically capable of deflecting any control surface as they see fit and may not move symmetrically but generally speaking their direction of movement is opposite. Some fly-by-wire aircraft even have split ailerons which may see parts of a give aileron deflect differently. This answer covers that quite nicely.

If you really want to go back, the 1912 Farman HF.20 had single action ailerons that only deflected downward and were pushed back into position by the airflow. I would say (if these count as ailerons) that they do in fact not move in tandem. There were some other early designs covered here that worked a bit differently than modern ailerons.

As for your second point, aircraft that have elevons, which serve as both the elevator and the aileron (mostly delta wing stuff like the Concorde and other high speed airframes), can move the surfaces in the same direction. Generally other surfaces are employed for the use case of needing to move both ailerons in the same direction (speed brakes).


Is In-Seat Rest used regularly where it is legal, and is it restricted by airline SOPs? This answer says that a pilot who is not flying (PNF) can make use of a procedure called In-Seat Rest to take a nap during flight.

A comment on the same answer says that this is illegal in the US, but allowed in the EU. Is that true? Where else is it allowed and not allowed?

Is this procedure used regularly in the EU (and other places where it is legal)? Do airline SOPs restrict it?

Too complex for me to give a specific answer, and this answer is assuming only airline transport not private flights or business charters.
Duty time limits are different for every country and may involve several pages of tables and definitions, airlines hire people just to track and comply with this.

Time of day relative to the pilots home timezone. If they are working when they are accustomed to sleeping then allowable hours are reduced.
The number of pilots on duty and length of single flight. A flight with 4 pilots is allowed longer shifts than 3 pilots, and a single pilot aircraft will restrict flight time per week more than 2 pilot aircraft.
Total hours worked per week.
Time between rest breaks, length of rest breaks, and location of rest breaks (eg at duty station, break area but expecting quick response(awake), break area without quick response(sleep in bunk)
Shift length, generally the whole period between breaks of 8 or more hours on the ground.(8 hours will vary with jurisdiction, ie some are 7 hours or 10 hours) For example if starting work after holiday: work 8 hours, off for 6 hours, work 7 hours, off for 10 hours. In many jurisdictions this would legally be considered a single shift of 21 hours with a 6 hour meal break.
Days between full 24hour rest days or number of 24hour rest days per month.


Why are some dynamic derivatives not included in DATCOM file? I am trying to understand Flight dynamics, particularly I am using Missile Datcom to get aerodynamic parameters of a missile, then use MATLAB, simulink to simulate its trajectory. It seems there are a lot of dynamic derivatives, have a look at
this, look at some dynamics derivatives.
 So why don't we have Normal-force derivatives due to yaw rate or Normal-force derivatives due to roll rate ? why don't we have Yawing-moment derivatives due to pitch rate ? etc...

A plane is subject to 5 forces: Thrust, Lift, Drag, Weight/gravity (and side force). In addition, there are 3 moments: Rolling, Yawing and Pitching moment. With these 7 vectors you are able to represent how a plane behaves in the air. The problem of simulations is how to compute these 7 vectors for a complex shape like is an aicraft in different flight conditions. To obviate these issues, engineers came up with 'coefficient of ..' which is indicated by C_letter.

To make estimation of these coefficients more accurate, engineers decided to compute the partial derivative of each coefficient due to 'something'. However, some of these derivatives have a small influence on the coefficient such that only for high fidelity simulations they are used (for example in Level-D simulators). Moreover, depending on the type of aircraft, some derivatives may be important or not: if a plane has no slats then there is no lift coefficient due to slat failures.

DATCOM was developed in the seventies and computing power has improved a lot since then, therefore some coefficients are not included (yawing moment due to angle of attack).

A nice reference to understand why coefficients are used if the book Boeing - Jet Transport Performance Methods.


How should control surfaces be modeled in simulations? I am modeling the lift and drag forces of a wing in software of my own creation.

If I have a wing which fits the profile of (for example) NACA 0024, it is a simple operation to look up the proper coefficients for lift and drag based on the current angle of attack for the wing.

But what happens if I slap an aileron on the trailing edge?

Do I need to re classify the wing based on the new geometry?
Should I treat control surfaces as their own aerodynamic bodies and look for lift/drag tables for them?
Since this is just a simulator, would it make sense to just offset the current coefficients by some value based on angle of deflection?

I am admittedly uneducated in aerodynamics and aviation, so please forgive me if I've come at this problem from entirely the wrong direction.
Any help or advice would be greatly appreciated!

Thanks!

Any control surface changes both local camber and local incidence, so it would be best if you change the coefficients accordingly. If you use a panel code, it would be enough to change the local surface inclination (= the flow direction at the local control point) by the deflection angle.

If you need formulas for the coefficients: A control surface with a cord length fraction d (of total chord length) will change the local lift coefficient $c_l$ with
$$\Delta c_l = \sqrt{d}\cdot c_{l\alpha}\cdot sin (\eta),$$
where $\eta$ is the deflection angle in radians and $c_{l\alpha}$ is the lift coefficient gradient over angle of attack of the original airfoil. The additional lift will act at a point between 50% and 25% of wing chord. The higher value is for very short flaps, the lower for all-flying surfaces (technically 100% flap chord), so a control surface deflection will add a torsional load. Drag will not be affected for small deflection angles, but when they get bigger, first drag rises and then the lift increase becomes nonlinear.

If you stay in the linear range (15° with 30% flap chord, 25° with 15% flap chord at moderate angle of attack) you can linearly add the flap effect (offset the coefficients). Going beyond that in both deflection angle and angle of attack will need a reduction in flap effectivity which can (in extreme cases) even become control reversal.

Also note that the aileron especially will twist the wing such that its effectivity is reduced at higher dynamic pressure. The details of this effect depend on the stiffness of the wing.

Your example of a NACA 0024 is already so thick that it will not tolerate big flap deflection angles and show separation on the suction side. Good wing thicknesses for subsonic flight are between 12% and 15%, and the most extreme ones (like the root of highly loaded high aspect ratio wings) will still be below 20%. Supersonic wing thicknesses are generally between 4% and 6%.

If you depend on that control surface for trimming the aircraft, don't let its effectivity decrease (as it would in reality), but give it linear effectivity (without the sine function) into infinity and punish large deflection angles with excessive drag (or whatever runs against your target parameter).


What happens when a propeller is placed in beta while feathered? Could someone explain beta range to me?

What happens when we set the throttle control lever to the beta range (reverse thrust) while the propeller blades are in the feathered position?

Will the blade angle change from feather to reverse pitch or will the engine over torque?

Depends on they type of turboprop engine.  With a straight shaft turboprop engine like a Garrett TPE331, this is not possible as feathering the props are controlled by the conditioning levers and also shut down the engines in the process.  A free turbine turboprop would allow a person to feather the engines and then pull the power levers to the reverse position.  Note that the propeller lever control does not set beta here, rather the power levers do, moving from idle to beta to reverse.


What was the aerial chase scene plane in 'Murder in the Clouds'? I spotted this aircraft (tail number NC-406N) in an aerial chase scene in the movie Murder in the Clouds (1934) on Turner Classic Movies.

It appears to be a Travel Air D-4000. Is this correct?

NC-406N would likely have become N-406N if reregistered or transferred. Since none of the 52 Travel Air 4000's registered nor any of the 6 Travel Air D-4000s still have the NC prefix, I'm guessing this is what has happened.

Tail N406N is listed by the FAA as a D-4000 Registered from 1991 on. If this is what you meant, then yes it is correct. Additionally, the wiki page for the movie does list a "Travel Air Speedwings" [sic] as the aircraft used in the production of the movie. I've not been able to verify if N406N is actually a speedwing vs the other models of Travel Air but a more knowledgeable expert might do so with the serial number: 1337.