Can a private pilot get an RVSM LOA? Can a private pilot get a Reduced Vertical Separation Minimums Letter of Authorization from the FAA?

I am looking at this checklist on the FAA site and it asks for a business address. Can private pilots get this as well?

An RVSM LOA is given to an operator not a pilot.

RVSM airspace can be used under part 91, so it is not limited to commercial operations. It can be a private owner or a non-aviation business. FAA Advisory Circular 91-85A says this:

  3.4.1 Who is the Correct Person to Apply for and Have Issued the RVSM Authorization?
  The person exercising operational control of the aircraft during the operation requiring an RVSM authorization is the proper person to be the applicant for that authorization. It is important to note it is the RVSM applicant’s responsibility to submit a request for RVSM authorization in the name of the person having operational control of the aircraft, not the responsibility of the FSDO or a specific ASI to make such a determination. The following general information may be useful in assisting the RVSM applicant in determining if the appropriate party has been properly designated as the legal Operator with respect to the RVSM authorization request:

  For non-commercial operations conducted under part 91 and part 125
  (A125 LODA holders), the authorization applicant and legal Operator should normally be one of the following persons, in which event the authorization will be issued in the form of an appropriate letter of authorization (LOA):

  A registered owner of the aircraft operating the aircraft incidental to its own non-air transportation business or personal activity.
  A person assuming operational control of the aircraft through a lease or use agreement for that person’s operation of the aircraft incidental to that person’s own non-air transportation business or personal activity.

  *emphasis mine

So if it is a company plane then the company will be the holder of the RVSM authorization, and there must be a responsible party within the company that is knowledgeable about the operation of the aircraft (i.e. responsible to ensure maintenance requirements are met, the pilots are “RVSM-knowledgeable,” that proper procedures are followed, etc. - not necessarily a pilot).

The authorization will be specific to the aircraft (or a group of similar aircraft) and it must meet the equipment requirements laid out in Part 91 apppendix G.

So, what makes the pilot “RVSM-knowledgeable?”

The same advisory circular says:

  3.3.1.1 For an applicant operating only under part 91 or part 125 (including
  A125 Letter of Deviation Authority (LODA) holders), demonstrating it has RVSM-Knowledgeable Pilots will consist of providing sufficient evidence each pilot has an adequate knowledge of RVSM requirements, policies, and procedures as required in part 91 appendix G, section 3(c)(2).

  The following are acceptable means for the Operator to show the FAA its pilots have adequate knowledge of the RVSM operating practices and procedures: 14 CFR part 142 training center certificates without further evaluation; certificates documenting completion of a course of instruction on RVSM policy and procedures; and/or an Operator’s in-house training program.

  Note: The FAA, at its discretion, may evaluate a training course prior to accepting a training certificate.

  *emphasis mine

Most likely, in a non-aviation company there won’t be an acceptable in-house training program, so any pilots will need certificates documenting completion of a course of instruction on RVSM policy and procedures. There are several flight schools with approved courses that can provide such certificates.

What it boils down to is the company that owns or leases the plane must get an LOA for their aircraft. The aircraft must meet RVSM requirements and to use RVSM airspace the pilot also must be certified.

If you own your own aircraft then you are, by default, the operator. So you can apply for an LOA as the operator. You would be your own responsible party and anyone who flies the aircraft in RVSM airspace, be that yourself or someone else, must be an “RVSM-knowledgeable” pilot.

If you rented your personal plane out to someone, say to a flight school, then they would become the operator while it is in their possession, so they would need to have their own LOA to operate in RVSM airspace.


Can an aircraft be stalled at low altitude and safely land on water? P.S Its just a random question...please consider the fact I have zero knowledge of aerodynamics of a plane.

That is the normal procedure for water landings with land airplanes. You fly parallel to the water as low as possible until the flight speed is too low to carry the full weight of the airplane. If it can be done safely, however, depends on a lot more than only the landing technique. Some aircraft will not swim and the drag of the landing gear might cause the aircraft to topple over.


What is the highest muzzle velocity of a gun on any fighter aircraft? I'm looking for the greatest muzzle velocity of a gun on any fighter aircraft.

I looked up the GAU-8 Avenger from the A10 Warthog first. Its muzzle velocity is 1,070 m/s, which is pretty darn high (almost 3 times the speed of sound). Are there any faster bullets out there from an aircraft gun?

Note: Don't really care about the firing rate (rounds per minute), or bullet caliber. All I'm looking for is highest muzzle velocity.

The muzzle velocity of guns is based on multiple factors and generally sees a wide range. Most importantly how the bullet is loaded (gun powder wise) and what mass the bullet is. For example the P-51 mustang carried 6 50 caliber BMG's (M-2). Which (although not available at the time) is capable of accepting the Caliber .50, Saboted Light Armor Penetrator, M903 round which has a quoted muzzle velocity of 4,000 ft/s (1,219 m/s). It should also be noted that the base muzzle velocity of an M2 is 2,910 ft/s (890 m/s) for M33 ball round. So it really depends what round you are loading in.

The F-35 Joint Strike Fighter has the GAU-22 Gatling Gun which with the TP HEI ammunition has a quoted muzzle velocity of 3,560 feet (1,085m) per second (15 m/s faster than the GAU-8 on the warthog).

(Not sure about you guys but I often test my gatling guns with my multi-meter...)
image source


What are the regulations for lighting fixtures around an airport? I work for a company that is right next to an Air Force base and we were wondering what and if there are regulations for the lighting fixtures that we can install on our lot since we have a couple of lights that are out of service and we were looking into upgrading them to LEDs

what is the temperature limit etc etc

I don't know much about aircraft regulation so i get lost in all the documents.

thank you!

To start you off there's these two:

14 CFR Part 139 - Certification of Airports and

14 CFR Part 157 - Notice of Construction, Alteration, Activation and Deactivation of Airports.

Part 139.311 covers all the lighting related requirements.

Part 157 is there just so you can inform the FAA about the changes you're going to make in the airport.

for specifics about LED lights, I would suggest looking for Advisory Circulars with LED lighting for airports in particular.


What happens when a turbo-prop is over-torqued? What does one need to do when a turboprop engine gets over-torqued?

I haven't over-torqued an engine before, but it seems it could happen inadvertently, say while doing a go-around.

My questions are:

Why is important not to over-torque an engine?
What happens if you do over-torque an engine?

This short answer is that you could break something if you over torque the engine.  And that's really about all that we can tell you in general terms.  The manufacturer or an engine repair shop could tell you what is most likely to fail for a particular model, but the failure modes won't be consistent from engine to engine.

As far as what to do if you were to over torque one, refer the the aircraft flight manual.  They will have a limitations section, and most airplanes will have "transient" limits in addition to the "normal" limits.  For instance, the limitation could be 100%, with a transient limit of 103% for 10 seconds and 105% for 5 seconds.  If the transient limits are exceeded, then you (or more likely a mechanic on your behalf) would need to refer to the maintenance manual for instructions.  Depending on the severity of the exceedance, it can be anything from simply logging it in the engine logbooks to a complete tear down and overhaul of the engine.

I'll also add that some pilots lean towards pretending that the exceedance never happened, and hope that nobody noticed.  This is not a good idea for several reason, the main one being that something could have been damaged that is not immediately obvious.  Even though things are running correctly now doesn't mean that all is well, and if an inspection is required, it's for a reason.  Another issue is that a lot of modern engines are computer controlled and monitored.  The next time that the computer information is downloaded, maintenance will see the exceedance anyway and if you have flown it since then you could be in even more trouble.

In short, follow the AFM procedures for your airplane.  They are there to help keep you safe!


Can we replace an attitude indicator with a ball half full of liquid? Attitude indicators (artificial horizons) use a gyro to display pitch and bank.

I was wondering if it would work to use a ball half full of liquid to replace the artificial horizon (using the water level as reference)?

Nope.  In a perfectly flown turn, the ball of liquid would appear to indicate level flight.

You might argue that it could replace the "ball" of a turn & bank indicator, but that's about it.

It would also be tough to read in turbulence.

See also this YouTube video showing Bob Hoover pouring iced tea while flying the plane through a roll, even while inverted.  Your liquid would behave similarly.


Are there design differences between propellers powered by air (wind-power) and propellers for aviation? What is the difference of design between a propeller designed to be powered by the wind (i.e. those huge wind power turbine blades) and those designed to be used to propel a plane that are powered by an engine (i.e. a Cessna 172's props)?

(To be clear, I'm talking about one that is powered by the air vs one that powers through the air.)

Blades of wind turbines, airplanes and helicopters are essentially the same. They are all wings, roughly to do the same job. However, each one is designed or enhanced to do their special job. The differences can be:

Number of revolutions
Wing span
Rate of flow
Tip speed
Density of medium
Material
Load

Turbine blades are designed to move in large volumes of rather slow moving air (usually 10-30 mph, 16-50 km/h) and not create turbulence that fouls the next blade. Aircraft propellers are designed to move high velocity air and avoid the turbulence by moving out of the way.

Wind turbines use blade pitch to adjust the rotation speed and the generated power. Wind turbine's control system adjusts the blade pitch to keep the rotor speed within operating limits as the wind speed changes. In aircraft, blade pitch is usually described as "coarse" for a coarser angle, and "fine" for a finer.


Why should passengers not delay donning emergency oxygen masks after they deploy from the overhead compartments? Assumptions:

The typical oxygen generator, on a plane, lasts twelve to twenty minutes.
(Source: Gizmodo.com)
Even in the event of cabin decompression, the oxygen in the cabin does not disappear or extinguish instantaneously.
If 1 is correct, then after how long would the oxygen usually need to vanish?
Waiting 2-5 minutes after the mask drops does not harm or injure; but obviously one must not wait too long, and should apply the mask sooner than later.

The question is motivated by wishing to maximise the use of the oxygen mask, whose oxygen supply is limited.

The point is not that the oxygen is used up. Even after a depressurization, the air around you still contains so much oxygen that it would take your body (at rest) hours to burn it all. But this oxygen is spread out so thinly that a standard set of lungs will not be up to getting enough of it from the cabin air into your blood at the rate your brain needs. This goes into effect immediately when the pressure drops.

As soon as the oxygen masks fall down, the flight crew will know, and they will make it an immediate priority to get the aircraft down to an altitude where the masks are not needed anymore because the outside pressure is high enough to breathe by. This takes less than the time the oxygen generators last for.

(Usually descending will take much less time than the masks are good for -- the critical design factor for the oxygen mask duration is that if you happen to be over tall mountains when the pressure drops you may need to fly for a bit of time to reach terrain low enough to dispense with the masks. There are a few places, such as over the Tibetan plateau, where airline flights simply don't go because it's too far from sufficiently low terrain for the masks to last).

There is no realistic chance of the oxygen generators running dry while you still need them. If you delay putting your mask on, all you buy is a danger of fainting or otherwise being unable to don it (from low pressure, not depletion of oxygen in the air) before you decide to put it on -- and then you may end up in a low-oxygen state for long enough to risk permanent harm.

There's a reason why the safety briefing always instructs you to put your own mask on before helping others -- because the time it takes to help someone else may well be enough to incapacitate yourself.


Hub-and-spoke networks: fixed and variable costs In the economic literature, many authors sustain that hub-and-spoke networks:

Increase the fixed costs sustained by the airlines (due to minimising the risk of congestions at the hubs). In particular, the fixed costs of a hub is expected to increase with the number of spokes.

Reduce the marginal costs (by allowing for a more  efficient use of aircraft and other inputs).

Could you explain this with an example?

The fixed cost problem with the hub and spoke model is mainly due to the need for banked flights to minimize average connection times.
Ideally, every plane starts the morning at a spoke and arrives at the hub at roughly the same time. Then passengers have an hour or two to change planes, and all the planes fly back to their spokes. This cycle is repeated again in the afternoon, and then the planes spend the night at their spoke to start the cycle again the next morning.
The problem is that this requires duplicate gate space at the hub and spokes, even though planes will only use one or the other at any given time (or neither, while flying). It also requires sufficient planes to serve every spoke in every bank even if there’s not enough demand to fill them. And it requires much larger airports and terminals at the hubs to serve massive numbers of passengers and flights during the banks, which goes unused the rest of the day.
Of course, nobody operates quite this stupidly in practice, but every flight that deviates from the model means longer connection times for its passengers because if it arrives at the hub between banks, passengers have to sit in the terminal and wait for the next bank to connect, which makes your flights less desirable than a competitor’s.
The upside is that you can (in theory) size the aircraft serving each spoke to its average demand, and likely use fewer, larger aircraft since one plane can serve every passenger connecting to every destination, which reduces variable costs.


Why is the King Air avionics switching system wired normally closed? In the King Air 200 and B200 (perhaps other King Air models as well), the avionics electrical bus relays are normally closed. With the Avionics Master switch in the "OFF" position—which is electrically closed—when the Battery master switch is turned on, DC power is supplied through the closed Avionics Master switch to the avionics bus relay solenoids causing these relays to open and disconnect the avionics buses from DC electrical power. Subsequently selecting the Avionics Master switch to the "ON" position opens the switch which disconnects the DC power to the avionics bus relay solenoids, allowing the relays to default to the closed position thereby supplying DC power to the avionics buses. The checklist action item for the Avionics Master switch power failure is to pull the 5 amp Avionics Master circuit breaker, which electrically opens the avionics master switch circuit thereby restoring DC power to the avionics buses.

See the following circuit diagram:

(Source: own work)

This system works, and works well, by all appearances. However, the design does seem to be somewhat counter-intuitive.

My question is, what is the purpose of designing the avionics master switching system normally closed?

Despite being counter-intuitive, I can understand that the electrical loads required by the avionics demand the use of relays, and that the design allows for the relay solenoids to be powered for a minimal time. I think this is the most reasonable explanation for the design, but I am looking for documented confirmation. Is there some other design consideration that I have overlooked? Does anyone know of a documented reason for this design?

NOTE: While you are welcome to speculate with me on this issue in the comments or chat room, I am not looking speculative answers. I am looking for an answer coming from persons familiar with the King Air electrical system and preferably backed up with documentation, such as the maintenance manual, or other sources that I have overlooked.

Design elements like this generally have to do with failure modes and how you want the system to fail when (not if) it fails. In this case, if there was a momentary or worse, permanent, loss of DC power to the relay or it failed for another reason you would want them to stay closed (and continue in the "ON") position so you would not lose your avionics (provided the power supply was some how still operational to them). Unlike most other electric components (semiconductors) relays are actually electro-mechanical components and they do have moving parts with in them that can fail. In my experience (non avionics mostly) relays have a much lower cycle lifetime than their semiconductor friends.

If we dive even a bit deeper into them, a relay is effectively an electromagnet coil that actuates a small metal rod that generally moves a copper (or similar) strip to close a switch connect. Applying a steady state voltage to a coil to generate a magnetic field (and keep the relay in a desired position) also drives current through the coil. The coils, being very thin gauge heat, act like resistors and can generate a substantial amount of heat. Due to the very thin gauge of the wire this can lead to melting and shorting of the coil. The wire also tends to be resin coated which can heat and melt as well causing a short. In turn you are correct that they don't want to he help on for a long period of time.

This is the electrical equivalent of many mechanically similar ideas in aircraft design. For example some landing gear in planes is held up using positive pressure so should the pumps fail the landing gear may simply deploy or be able to be shaken down by releasing a lock, the idea being its better it can come down in the case of a system failure than be stuck up.


How did this Vampire's takeoff damage the runway so much? This appears to be real, but, what's the cause?

Aircraft is a DeHavilland Vampire on takeoff from a small airfield, but the runway's surface disintegrates from jet blast

Full file at https://i.imgur.com/NaK5yAr.mp4

Is the Vampire's jet blast that strong?  Or is it weak/old tarmac which is being pushed over the limit of adhesion?

I suspect the field would be closed for repairs becuase of this damage, and the the runway's now lack of smoothness,  but could that plane land again right away?   If the loose bits were picked up?  Would it have to land on the grass verge instead?

Would this have happened with other aircraft on the same runway?  Or is the vampire special?

Other info

Plane's registration number is WZ507

https://www.facebook.com/Vampire-WZ507-351376189100/

This airframe is also the poster photo on https://upload.wikimedia.org/wikipedia/commons/thumb/d/d5/Vampire_3_%28cropped%29_copy.jpg/450px-Vampire_3_%28cropped%29_copy.jpg

Partly it's that the Vamp's tail pipe is only a foot above the surface, angled toward it, so with most jets that wouldn't happen quite as easily.  Plus it looks to me like the airport operator cut corners with a really cheap driveway quality paving job with an asphalt layer only an inch or two thick.


What aircraft did this canopy come from? This canopy was found near Wetumka, Oklahoma in a small creek running through my best friend's property. The canopy is about 12 feet long. Can anyone tell me what aircraft it came from, or who I could contact to ask?

A loving cup from 1906 dedicated to a Miss Grace Walling Spore from the USS Alliance Navy Ship was also found in same creek recently. I contacted the family myself and they knew nothing about the loving cup or any crashed plane that may have been carrying it.

Here is another picture... I do not know if was in a crash.

It could have washed down creek I suppose, but why would a jet canopy have been in a creek? I am searching for what kind of craft it belongs to.

Location: A creek in Wetumka, Oklahoma
Rumored date/pilot: 1944 / Loyde Christian
Object length: ~12 ft

This canopy probably came off a Boeing B-47.

I do know of at least two mishaps involving B-47s in Oklahoma but both occurred in places other than Wetumka.  I'll do a little more investigating on this.

Another possibility is that the previous landowners acquired this part as scrap at some point and left it there on their property for whatever reason.


Where can I find a free/cheap small airplane wing? I am looking for a small airplane wing (e.g. Cessna 172, but not necessarily) to run some experiments prior to seeking an STC for a modification I am working on. Do you know where I can find a free abandoned wing, or a very cheap one? It doesn't have to be airworthy or functional at all, as I will just use it for standalone tests on the ground.

Thanks!

Wings may be tough to come by as they generally last the life of the plane and can be re-skinned/fixed if need be so they are not scrapped all that frequently. You can try a used parts dealer like this one or this one but they generally deal in air worthy parts which will not be cheap. Here is a guy parting out a 152 in FL he "has wings", you may want to give him a call and check other part out barnstormers adds.

Your best bet may be to wonder on down to your local GA field and ask some questions at the FBO or maintenance facility if there is one. Its more than likely someone has a wing or wing section that is no longer air worthy from some accident or the like. You may even just see a junked wing sitting in a field behind a hangar...

STC's are specific to part or aircraft/engine so testing on a generic wing may not be a good basis (depending on what  you are doing) you may want to get the wing from the aircraft you intend to STC.


Is it possible to obtain a PPL after having a brain surgery? I am a 24 year old who has always aspired to become a pilot. I've decided to eventually get a private pilot's license so I can fly just for fun. However, a few months ago I was diagnosed with brain tumor which I had removed. There were no complications, I have never had any seizures, I'm not epileptic, etc. As far as I am concerned (and my doctors as well), I am now in perfect health.

With this in mind, is it still possible for me to obtain a PPL?

According to AOPA's medical guru on their discussion board (members only, or I would link to an example) it is possible to get a medical certificate following a tumor removal but only after a 5-year wait and a battery of tests.

But having said that, medical issues are very individual and the FAA's AME guidance suggests that one year is enough in some cases. In the end the only way to get a definite answer is to find a good AME who can review your case in detail and advise you. Note that standard advice is to schedule a consultation first, rather than go straight for the actual flight medical.

Disclaimer: I'm not a doctor or AME and I have no idea how brains work :-)


What are the FAA requirements for when to use an airline call sign & flight number versus the aircraft registration number? Is there any FAA guidance which specifies when a call sign & flight number or registration number must be used for Part 91 & 135 operations?

I am familiar with the guidance on how to obtain an ICAO call sign (and in fact work for a company who has one), but am unable to find anything which specifies when one must be used versus the other.

So basically, can commercial flights file under the registration number and can private flights (re-positioning flights, etc.) file under the company call sign?  I understand that this is backwards from "typical" use, but is it legal?

I found something relevant buried in the depths of JO 7340.2 on contractions (i.e. abbreviations) for airlines, aircraft types etc. Section 1-4-2 says:

  The company designator, together with a flight number, serves as the
  aircraft identification in the ATC system. Company designators are
  valid only for company business in accordance with the provisions of
  its operating certificate or servicing organization. Pilots will use
  standard identification procedures for personal flying

Compare that to the quote from your safety organization:

  commercial flights are always conducted under a flight number, and
  private operations (e.g. repositioning flights) are always conducted
  under the aircraft registration number.

If you remove the words "e.g. repositioning flights" then it's saying almost exactly the same thing. What's really odd is that the checklist uses repositioning as an example of a "private operation" (the JO uses the words "personal flying", which has different connotations). I think most people would say repositioning is definitely company business. Perhaps it's just sloppy wording or a poorly chosen example.

As for the safety organization's claim that there are specific requirements in 8900.1, I couldn't find anything. The only vaguely similar thing I found is the 'use it or lose it' clause in 2-275:

  B.    Failure to Use Three-Letter Company Designator and Telephony
  Designator. ATO AJV-2 will place on a watch list any company that does
  not use an assigned three-letter company designator and telephony
  designator for 2 years on an instrument flight rules (IFR) flight plan
  in U.S.-controlled airspace. ATO AJV-2 will revoke and release any
  three-letter company designator and telephony designator that are not
  used for 3 years on an IFR flight plan in U.S.-controlled airspace.

Whoever wrote your checklist might be saying that you need to make sure that you're using your company call sign regularly to make sure you don't have it revoked, but that seems like a real stretch to me. And even if that is the case, it wouldn't explain why repositioning flights should be different. Since 8900.1 is a very large reference library, I'd ask the safety guys to point you to the exact document and wording.

Looking in the other usual sources (FARs, AIM, P/CG, ATC orders etc.) that you and Ron mentioned, I couldn't find any specific legal or regulatory requirements either. Almost every reference in FAA sources says "registration or call sign" or something similar (e.g. the AIM's instructions on filing flight plans), and the FCC regulations allow either in radio use (47 CFR 87.107).


Does using wings with different wing loadings work the same as a swing wing, without swinging the wing? Does using wings with different wing loadings work the same as a swing wing, without swinging the wing?

Was just wondering: we need the maximum co-efficient of lift at slower speeds at takeoff, but a much smaller co-efficient of lift at cruising speed.

For a triplane, wouldn't you want the top wing for flying and the other wings just for takeoff?

In other words:

you could make the top wing, a classic unsymmetrical wing like a NACA2415, set at around 5 deg angle of incidence, where I believe these airfoils are most efficient.

The other wings could be a wing with a high wing loading, like a high speed laminar foil, like the canard of a velocity, set at a incidence of 0 deg during straight and level flight.

In that way, the lower wings provide no lift, but also no induced drag ( drag due to lift) during straight and level flight, just like a classic tail airfoil.

During takeoff, you would have to rotate early prior to takeoff, ( like the Concorde) to get an angle of attack for all wings.

Say all 3 wings are the same size and you size your wings to get an overall wing loading of 7psf, which means you can land slow and short, but during cruise you would only be using 1 wing, so your effective wing loading is a very efficient 21psf. If it's gusty out, you could always land long and fast , using all 3 wings.  So this would be like a swing wing, without the complexity of actually swinging the wing.

Is this correct, at least conceptually?

For a triplane, wouldn't you want the top wing for flying and the other wings just for takeoff?

No.

Form drag is proportional to dynamic pressure and frontal area. By varying the lift coefficient between the planes you are not doing much to the frontal area, so the form drag is roughly the same.
Induced drag is proportional to square of lift and inversely proportional to square of span and dynamic pressure. By generating three times more lift with one of the wings, you are making it produce more than tree times the induced drag.

It is not all the nine times the basic equation suggests, because the efficiency is still significantly reduced by interference when all the wings are producing lift, but it is still worse, and it is worse whenever the lift is not distributed uniformly (maybe the interference makes a slight increase in the middle wing desired, I am not sure here, but it won't be big difference).

So the configuration is not better than evenly distributed lift in any flight regime.


How hard is it to certify a kit aircraft if it is based on a production design like a Cessna 180? I was looking at older planes, specifically the Cessna 180. It is discontinued, but people love them, so they fetch premiums. I saw St. Just Aviation has a kit Cessna 180. There are only 25ish planes in existence.

I'm curious if it would still take a large amount of testing to certify their replicated design - since the Cessna 180 already went through all that years ago?

The FAA requires all aircraft above a certain weight (>ultralight) to be certified. You can certify the design and production process so that everything that comes out of the factory has a guaranteed level of safety, or you can certify the result. The former gets a standard certificate, the latter gets a special airworthiness certificate. Other jurisdictions make similar distinctions, with minor variations.

Kit planes, such as your 180 replica, get a special airworthiness - amateur built certificate. FAA AC 20-27G outlines the process for satisfying this requirement. It is sixty pages of instructions, limitations and forms. The two most commonly mentioned requirements are for majority construction by the amateur and for flight testing.

  It is important to document the entire fabrication and assembly process from the beginning to the end, in a continuous and sequential manner. This is because, at the time of certification, the FAA is required to ascertain whether the amateur builder(s) fabricated and assembled the major portion of the aircraft. Making this finding requires adequate, sufficient, and credible documentation.

For flight testing

It does not matter to the FAA whether or not it was based on some production certified aircraft.

  We do not certify amateur-built aircraft designs or require that you modify the design before airworthiness certification. However, we may deny airworthiness certification when we inspect your aircraft if we find it does not meet the requirements for the certification you request or is not in a condition for safe operation.

This is far less stringent that the requirements for a standard certificate. You will have to decide whether you consider this "a large amount of testing".


How can one change the wingtip geometry to enhance the wingtip vortices? I'm doing some research on enhancing wingtip vortices as part of my Honours project. After spending a fair bit of time in the literature and on this forum I have some models which should kick-start my simulations. Because this is such a under-researched field (understandably) I wanted to mine the wisdom of those here: What design elements for a wingtip geometry would be conducive to creating a strong wingtip vortex?
The context is that I am studying how to enhance the efficiency of autonomous formation flight, using one drone as the 'tug-boat' for the other trailing drone. The leading drone would be outfitted with vortex-enhancing wingtips in order to increase the upwash experienced by the trailing drone. The overall purpose is to increase the range of the secondary drone at the expense of the first, in situations like scientific aircraft stationed in Hobart anf flying round-trip to Antarctica.
So far I have identified the Aspect Ratio, Lift Coefficient and Oswald Factor as parameters I'll need to change, based simply off the induced drag equation $C_{d_i} = \frac{C_L^2}{\pi*AR*e}$. This has given rise to potential solutions like using vortex generators on the wing surface to enhance lift while removing the winglet to allow the flow to curl around the tip, pitching the winglet up to increase its local angle of attack (effectively the same principle), and using a wingtip fence that runs from the leading edge to half the chord length and stops there, creating a high-pressure difference and then allowing the vortex to develop rapidly.
I'm aware I may have fundamental issues with this theory but also that I don't know what I don't know. If this won't work physically, then an explanation as to what I should be focusing on to create greater upwash outboard of the trailing edge of the leading wing would be much appreciated.

You are not interested in wingtip vortices. For now you are barking up the wrong tree. For that tug idea to work, you need to focus on the trailing vortex which is a result of the whole wing, not the wingtip.
How to maximize trailing vortex intensity? Fly slow, use a small aspect ratio and create lots of lift. This means a heavy airplane with a high span loading, flying close to stall. Niceties like the spanwise lift distribution are much less important; all low aspect ratio wings will show an elliptical or nearly elliptical lift distribution anyways.
Next, position the following airplane right. Between the two vortex cores of the leading airplane you will find severe downwash. What goes up must go down. This is not only true for aircraft, but also for the air surrounding them. So any part of the following airplane needs to stay outside of the immediate wake. In order to maximize the recovery of the energy wasted in the leading airplane you need two following airplanes, one to the left and one to the right, and ideally both need to be specific to their side since both will fly in an asymmetric flow field. If you don't account for that by optimising wing twist and weight distribution, your rudder and ailerons on the following airplanes will do that, albeit less efficiently, just in order to stay inside the upwash part of the wake.
To answer what you asked: For maximum wingtip vortex intensity you need a steep gradient of lift at the tip. This means a spanwise lift distribution which peaks near the tip. Of course this is what a good airplane design will avoid at all cost, because it not only makes it less efficient, it also results in dangerous stall behavior.


Is it possible to embed CL, CD, dCLda, etc, into a tensor? Is it possible to form a tensor (i.e. matrix) such that this tensor applied to the apparent wind vector produces a vector representing the resulting aerodynamic force?

Yes, actually the vector of the nondimensional aerodynamic coefficients is related to the nondimensional forces using a coordinate transformation tensor. Then, this tensor depends on your coordinate system (stability axes, wind axes) which in turn depends on which coordinate system is more convenient for your job. For example
\begin{gather}
\begin{Bmatrix} C_{D_i} \\ C_Y \\ C_L \end{Bmatrix} = \Bigg[ \bar{\bar T^s} \Bigg] \begin{Bmatrix} \overline{F}_x \\ \overline{F}_y \\ \overline{F}_z \end{Bmatrix}
\end{gather}
where $\bar{\bar{T^s}}$ is your stability axes coordinate transformation tensor which incorporates the sines and cosines of the rotation angles and the right hand side vector is the nondimensional force components. For detailed derivations regarding this coordinate systems and their use you may want to check Chapter 6 of the book of Mark Drela, $\textit{Flight Vehicle Aerodynamics}$ from MIT Press.


IAP / "Instrument Approach Procedure (IAP) Charts" What does "Procedure NA" Mean? The image below is of an FAA "Instrument Approach Procedure"

The entire thing is the "Procedure"

It contains a "Procedure Turn", which when not required typically states: "NoPT"

Now, in some places it states "Procedure NA" (red arrow near top) which seems to implicates the entire Procedure NOT the Procedure Turn.  However, the red arrow indication at top also seems to implicates the Procedure Turn because we're basically straight in from that location, so it wouldn't be needed, But again, NoPT would make more sense.  And why would the entire procedure be NA?

If we look at the two "Procedure NA" notes on the plan, then the entire "Procedure" would be NA from most approach directions.

So, Which is it?
Does "Procedure NA" mean The entire Instrument Approach Procedure?  or just the Procedure Turn?  If just the Procedure Turn, why does it use different vocabulary? Why not just say NoPT ?
Is there some other significance?

I looked in the chart user guide and can't find "Procedure NA" in it

Thanks

Although the wording on the chart is very confusing, it appears to indicate that you can not make a course reversal at the VORs themselves. Probably due to the congestion of the airspace and associated airways. This is only the case when using the VORs for navigation to the IAFs since neither of the VORs is an IAF. However, the IAP is an RNAV IAP. So, you can disregard the VORs and use GPS only to navigate to the IAFs as long as you stay above he 4200 foot Minimum Sector Altitude and cross the IAFs at or above 4400 feet. Beware of the higher terrain with MAximum Elevation Figures of 5600 and 6600 feet NNE of the IAP.

In other words, it means that the entire procedure is invalid if you are using VORs to navigate to the area in some circumstances. If you are coming from the North and West, you are required to use LEB. If you are coming from the South and East, you are required to use CON. If you are using GPS only, you are required to navigate to the IAFs directly (not necessarily Direct-to) using GPS and not VORs.


Is drift and sideslip angle the same in the accompanied figure? Consider the following figure:

Initially aircraft is moving along dotted line. But due to wind, aircraft ground track is changed to solid line but body still pointing parallel to dotted line. I've the following questions:
(1) What is sideslip angle in this case?
(2) What is direction of relative wind?

The answer to the title question is no, sideslip angle and drift angle are not the same thing.  (in this figure, or any other...)
What the diagram shows is drift angle, and drift angle only.  If you are moving through a uniform airmass that is itself moving relative to the ground, your path across the ground (ground track, or course) will be affected by the movement of the air.  The difference between your heading (simply the direction the aircraft is pointing) and your actual ground track is the drift angle.  That is the teaching point, and purpose of this figure.
Regarding the numbered questions:

There is not enough information in the diagram to determine this.  Sideslip angle is the lateral angle between the relative wind and the longitudinal axis of the aircraft.  If the aircraft is in balanced flight, with the balance ball centered in the slip indicator, the sideslip angle will be zero.  It doesn’t matter what your heading is, it doesn’t matter which direction the wind is moving, or whether the aircraft may be drifting from its intended course.

The direction of the relative wind is always opposite to the direction the aircraft is traveling through the airmass.  In this example, presuming balanced flight, the relative wind is coming directly from the East.  If the aircraft was unbalanced, (balance ball out to one side or the other) there would be a sideslip, and relative wind would be striking against the side of the fuselage instead of head-on.  That angle is the sideslip angle.

There are different and better illustrations that show sideslip angle if you need more help understanding what it is.


Are there benefits in training instrument students how to fly a DME arc? With more instrument approach procedures being designed for RNAV/GPS equipped aircraft, and considering the high level of radar coverage currently available, is there a need to spend much valuable training time teaching students the skills and techniques for flying an approach using a DME arc?

Apart from the fact that it is required to learn, the obvious "benefit" is that you know what to do when flying to an airport that uses a DME Arc approach. RNAV/GPS approaches are becoming more common, but have far from taken over from conventional approaches. Even if an airport has radar, it does not necessarily mean that radar vectoring for final approach course is available - consider, for example, uncontrolled airports. Here is an example of a DME Arc approach still in use today, at an uncontrolled airport in Denmark that does have radar, but no radar vectors are provided (since it is uncontrolled):

And an example from Norway:

(images from AIP Denmark and AIP Norway respectively)


Does a trent 900 engine have the ability to spin extra or more fans? Given that the most modern geared turbo fans gear down spinning the fan, which essentially translates to requiring less torque or horse power to spin the fans.  If the gearing down is in the magnitute of (10:1)(correct me if I'm wrong) and comparable engines were able to spin the fans at a higher speeds without gears, how many more fans can the engine spin if there was a modifaction of an additional propshaft to spin the other fans, because there is a gearbox.  How much of an impact on fuel consumption would the be for an extra 1,2,3, and 4 fans if at all it was possible?

A geared turbofan can spin a different fan at a different speed than an otherwise equivalent non geared engine. But a geared turbofan does not have the ability to spin additional fans at the same rpm, or spin the same fan faster, than a non geared turbofan (if that's what you are asking?). What is required to compress air (by spinning the fan) is shaft power. The level of power provided by the turbine is not increased by adding a gearbox. Indeed, a gearbox adds friction and hence mechanical inefficiency, so the level of power that is available to the fan will actually decrease in a geared turbofan.

HP = Torque (in ft-lbs) x RPM ÷ 5252

A gearbox which reduces rpm, increases torque, but with a slight loss of power due to invetitable inefficiencies.

Your question is quiet confusingly written, but it appears to imply the Trent 900 is a geared turbofan, which it isn't. The Trent is a 3 spool engine, and is the first of the Trent family with a counter rotating HP spool.

The only large geared turbofan in current use is P&W's PW1000G family. (See comment below regard two smaller geared turbine engines). This uses a star design  gearbox to transmit 30,000 hp at a 3:1 ratio. The PW1100G, the largest engine in the family, is a 12.5:1 bypass ratio, and a max thrust of 35,000 lb. In comparison, Rolls Royce is developing their "UltraFan", and is expected to use a planetary design gearbox to transmit 70,000 hp at about a 4:1 ratio. They hope to eventually get to bypass ratio of 15:1, and an overall pressure ratio of 70:1. The thrust for the UltraFan is said to be in the range from 25,000 to 110,000 lbs, so it looks like being a signifficantly bigger engine the P&W's geared turbofan.

Power loss in the gearbox is mostly due to friction, which generates heat. In miniature gearboxes, heat is not much of a problem because the power losses and the absolute amounts of power involved are relatively small. However, it's much more of an issue in large gearboxes which usually require oil coolers to remove the heat caused by the inefficiencies.

Thus, gearbox efficiency depends on friction. This in turn depends on the quality of the gearing, the number of tooth engagements (how many times one wheel drives another) and the load torque (how much "moment" the gearbox has to deliver).

This article says that a spur gear, the type used in geared turbofans, have an mechanical transmission efficiency of about 98 to 99%. If you look at the picture above, you will notice 8 points where the gears mesh, and efficiency will be lost at ech contact point, so needs to be kept to a minimum.

For a comprehensive overview of geared turbofans, see this "flying engineer" article.


When do the Boeing 737 Next Generation aircraft reach End-of-life? When can we expect the Boeing 737 Next Generation aircraft to reach End-of-life / stop flying?

The Next Generation is the name given to the −600/-700/-800/-900 series of the Boeing 737 airliner.

Airliners aren't given "end-of-life" dates, unlike, say, Windows 95. They also don't eventually become "unsupported", like an iPhone.

A plane will be kept flying while it's safe and economical to do so.

In the case of a particular aircraft, that will depend on many things that have nothing to do with the aircraft itself (oil prices, perhaps) that make it uneconomical to operate.

Older planes are less fuel-efficient, and at a certain point a passenger airliner may be transferred to cargo duties (where fuel is a smaller proportion of the total cost of owning and operating it) and eventually, if no-one wants to keep flying it, it will be retired.

The point at which a plane becomes uneconomical to operate also has to do with how the aircraft is used - an aeroplane that has been through more pressurisation cycles will enter a more expensive regime of checks or maintenance sooner than one that has not (if an aeroplane will need to undergo more extensive checks for fatigue after say 50 thousand cycles, that might be the point at which an operator decides to replace it).

Almost any aircraft can in fact be kept safe to fly (if it were safe to fly in the first place) if you're willing to spend enough money doing so. This is why the comparison with iPhones and operating systems is instructive; probably nobody on earth has enough money to persuade Apple to keep providing iOS updates and manufacturing spare parts for the iPhone 4, but the economics of operating and obtaining spares and doing maintenance on 737s is quite a different matter.

The 737 −600/-700/-800/-900 models are still being produced, and past experience suggests that such aircraft have something like a 30-year working life span.

You never know however if unexpected events (like an oil crisis, or the discovery that airliners cause serious health issues in law-makers' children) will dramatically change the economic environment in which they operate - that's in the hands of fate.


How do fuel trim and air bubbles prevention work in inverted flight? I was reading Why do many GA aircraft not have a "Both" fuel selector? and voretaq7's excellent answer got me to thinking.

He cites the regulations noting that the plane must only draw fuel from one tank or have a method for preventing air from entering the fuel lines. However all his examples assume gravity in a somewhat constant direction.

What do you do when this is not the case? For example in a barrel roll do you set the fuel selector for the wing going up first? Does it depend on the plane? Do planes in air shows have special fuel systems?

How does this regulation apply to aerobatic aircraft, and how is the regulation satisfied for such aircraft?

A typical GA airplane will draw fuel from at or near the bottom of the tank.

An aerobatic airplane will have a hose from the engine to the middle of the tank, then on the inside of the tank there will be another flexible hose with a weight on the end.  This inside hose is called a "flop tube".

When the plane is in upright flight, the "clunk weight" on the bottom of the "flop tube" (these are the real terms for them, I'm not making this up!) will rest on the bottom of the tank and draw fuel from there.

When the plane is inverted, the weight will move (along with the fuel) to what was formerly the top of the tank.

This ensures that as long as the tank has a reasonable amount of fuel in it, the clunk weight will be submerged most of the time.  There are occasions (usually rolls while going straight up or down) where the weight (and end of the flop tube) is momentarily exposed to air in the tank.  The engine will "hiccup", but there's usually enough inertia in the propeller and engine parts to restart the engine by itself when fuel flow is restored a fraction of a second later.

There's an additional component - a special header tank - that helps by confining the flop tube to a very small tank that's 100% full of fuel 99% of the time.


Can anyone explain the reflex wings used in powered paragliding? There are some paramotoring wings presumably designed for higher speeds. The method is to allow a portion of the wing near trailing edge to flutter in high speed, rendering it unaccountable for development of lift, but still accountable for drag (in my opinion). I believe is called reflex because the trailing edge will flex up in high speed.

The speed gain is minimal though. These wings fly at around 40km/h with stall at 24km/h and the reflex promises 60km/h, while the same wing trimmed non-reflex achieves 55km/h.

If there is anyone with piloting experience on those wings, please explain the reflex from your perspective.

I'm haven't flown them but am very familiar with them and the reflex wing controversy because I was interested in getting into the sport (I normally fly power and gliders).

A reflex wing when in "reflex mode" offloads the aft part of the wing and shifts the pressure distribution forward.  Effectively, the rear part of the wing is being allowed to "trail", or partly trail, up and not do any (or much less) work.  It's a bit similar to gliders with flaps that have a reflex setting, where the flap is angled trailing edge up a few degrees for high speed penetration flying, which off loads the trailing edge and moves the wing's pressure distribution forward and makes it behave as if it had a narrower chord.

It's not related to reflexing flying wing aircraft trailing edges for pitch stability, where the trailing edge provides downforce in place of the absent tail; that simply can't work and isn't necessary in a paraglider.

The effect of reflex is to somewhat reduce the effective wing area, increase the effective aspect ratio, and reduce induced drag in the process.  A 26 sqm wing becomes effectively a 20 sqm wing (I'm just picking numbers here) with a narrower chord and what amounts to some loose fabric (the unloaded trailing edge) trailing behind it.  Because the TE is unloaded, you can't use the normal trailing edge drag brake steering and have to use "tip steering" controls.

The different pressure distribution increases the inflation pressure at the front of the wing and makes it more collapse resistant, and this is one of the reflex wing's selling features besides slightly higher cruising speed.  The downside is that when they do collapse, they do so violently with way more altitude loss and if you are close to the ground your wing will pretty much fling you into the dirt like a rag doll if you get a collapse.  I don't believe there are any current wings that can meet EN cert requirements while in reflex mode.  This means if you value your life you don't use reflex below a recoverable altitude, say 500 ft.

Having researched it a lot myself and noted the same thing you did, only a 5 kmph benefit, I'm not keen on reflex myself, especially after watching videos of how they behave when they collapse.


Can a software "hard freeze" or serious hardware problem completely disable the whole cockpit? I think that the glass cockpit of a modern plane has some sort of a central power supply or at least some central controlling software.

What happens if this central power suddenly disappears, or the central software freezes? Yes, of course, this would be a severe failure and would put everybody's life on the plane in serious danger.

Is such a failure possible?

If the power suddenly disappears to any aircraft (ie, a total electrical failure including the batteries), then all the aircraft systems will be failed regardless of whether or not they were glass.  This is highly unlikely because there are several power generation backups that would have to fail, including the batteries themselves, before this ever became a reality.  Unfortunately though, if the aircraft only has electrically controlled, hydraulically actuated control surfaces (fly-by-wire), vice actual mechanical linkages (or backup controls), then a total electrical failure would be 100% fatal if power cannot be restored.  The control surfaces would not be movable.

However, more to the question regarding software bugs, all primary flight instruments are backed up to prevent such disasters from happening.  I have personally lost all the digital displays in my cockpit and flown a no-gyro, surveillance approach in bad weather using nothing but a peanut gyro.  Its possible, but definitely not a good time.

Anything is possible.  However, even though the odds of a total electrical failure, or complete loss of instrumentation (including backups) is nominally greater than 0%, the statistical probably can still probably be rounded to 0.


I live directly south in the line of a north-south landing strip of a low-traffic airport. What should I know? There is an airport in my city that is relatively low traffic. It has a landing strip that runs north-south, and it looks like if you were to go ten miles straight south from that landing strip, you'd pass over my property.

The noise is infrequent and quiet enough that it isn't very bothersome, but I'm more or less in the flight path. But I'm ten miles away in its airpath. What should I be concerned about?

Should I be concerned about jet fuel exhaust or anything as far as my personal health and safety are concerned?
Is there any precaution I should take in the event that aircraft were to fall into my property?

What else should I know?

1: At large international airports there has been at least some research to suggest that there may be affects on your health (http://www.latimes.com/local/la-me-0529-lax-pollution-20140529-story.html) but I'm assuming this is quite a small general aviation airport. With the low traffic, small planes, and far distance away frorm the airport, you are probably not experiencing much as a direct result of exhaust.

2: There is an almost no chance that an aircraft would land on your property. If one did happen to land on your property the NTSB does provide some guidance for public saftey personel: https://www.ntsb.gov/tda/TDADocuments/SPC0402.pdf.

This PDF is aimed at public safety personnel. If you want to be an active participant in this emergency, feel free to follow it and the rest of this post. If you don't want to get involved, please just stay at a safe distance away from the accident and report it to emergency services.

If you are going to try to help you probably want to receive training on first aid before anything happens. Once an accident occurs you can do several things. For the most part, you initially respond just as you would to any other emergency, first by securing the scene and making sure you are not in immediate danger and then calling emergency services. Be careful when approaching the plane, especially if anything is still moving (propeller spinning etc). There are also many dangerous substances that could be present at the site of a plane crash (listed in the NSTB PDF). No one on the ground needs to be injured unnecessarily after a plane crash.

Once everyone is out of the plane, get far away from it and wait for emergency services to arrive.

Administer first aid (if trained) to anyone who was injured
Call the NTSB at 1-844-373-9922 to report the accident (It is the pilots responsibility to report the accident)
Take photos and video of the crash and surrounding area so investigators have plenty of documentation to look through to determine the cause of the crash. This will also be useful for insurance purposes.
If you see anyone else around who may have witnessed the accident, try to get their name and contact information to emergency services or the NTSB so they can be contacted if needed in any investigation


What do "LC/P" and "PTD" stand for in reference to airport communications? When I pull up the Colorado Springs (KCOS) Airport Comm frequencies in Skyvector or in FAA database there are some frequency listed as "LC/P" and "PTD". Would someone explain what those acronyms stand for?

  LC/P: 119.9 360.6
  PTD:    122.85 372.2

LC/P: Local control, primary frequency, from LC, local control, which is a usual control position in the tower.

"The Local Controller is primarily responsible for separating and providing safety alerts to aircraft in the airspace surrounding the airport and aircraft on the active runways" (source)

Source

PTD: As @Riccati commented, it means Pilot to Dispatcher, according to the Airport / Facility Directory Legend.

Airlines are required by regulation to provide direct communication means for aircrew.

Aircraft dispatcher training (source)

See also: Can airline pilots communicate with dispatchers?


Is this takeoff of a 767 in bad weather conditions a normal procedure? In this video, a 767 takes off in bad weather conditions. The comments of the video aren't very professional, so I ask here:

Is this a legitimate takeoff?
Some comments say that this was a close takeoff. Some comments do point out that on rotate, you can see the end of the strip of the lefter runway. Was it airborne before?

Take-off within the crosswind limits is a normal procedure. From the video it's hard to tell what the crosswind was in this particular situation, so it is impossible to tell about the legitimacy of this take-off.

Rotation seems to be on the 1000ft marker, i.e. 1000 ft from the runway threshold. But in case of a displaced threshold the take-off distance available may be more than 1000ft from that point. It was airborne before the end of the runway.


How do aircraft stall warning systems work? If an aircraft stalls, there are stall warning systems called as Stall computers. Anyone has idea how they predict that its a stall and how they raise the alarm/warning?

Audible Warning
On light aircraft there is a reed (much like used on a musical wind instrument) mounted on one wing root, which is angled such that at the Angle of Attack which would cause a stall, the reed "plays" which can be heard in the cockpit.
Here is a view of where this system is mounted on a Cessna:

(source: weekendcfii.com)
On some aircraft, it is a similar principle; however instead of a reed, it uses a fin which at critical AoA pushes a micro-switch which activates a buzzer/horn inside the cockpit.
Here is the assembly on a Beech 18:

(source: eaa1000.av.org)

So, if you ever see anyone doing this:

They are not kissing their aircraft for good luck, merely testing the stall warn as part of pre-flight checks!
Tactile Warning
In addition to an audible reed/buzz/horn, most aircraft also provide tactile feedback to the pilot of an impending stall. In purely mechanical aircraft the aerodynamic forces on the control surfaces are transmitted through the mechanisms and are felt directly by the pilot when approaching a stall. In hydraulic or fly-by-wire aircraft, this is provided by a mechanical "stick shaker" linked to the same system as sounding the audible alarm.


Why are so many tail-strike incidents not verified until later inspection? One often reads of a "suspected tail-strike" at take-off (for example suspected because a controller has seen something from the tower, or because a cabin crew member sitting at the back of the plane has felt a jolt or heard a noise).

What puzzles me is why this must remain merely "suspected" until an inspection.

As an example, a 737 suffered a tail strike that appears to have at least been considered a possibility by the crew. Apparently doubting that it actually had occurred, the flight crew continued to their destination; had there been a clear indication, they presumably would not have.

Aircraft are festooned with external sensors and measuring devices; I would expect aeroplanes susceptible to tail strikes to have sensors measuring movement of, deformation of or contact with a plane's skid plate, to provide a cockpit alert, so that there need not be any doubt.

Since this often doesn't appear to be the case, there must be good reasons why such systems are not usefully employed - what are they?

On one hand tail strikes are mitigated long before the need for a sensor. Aircraft makers generally address it from a design standpoint before the aircraft ever flys. If that is not enough control augmentation or tighter procedures are developed to prevent it from an operational level.

Ultimately such sensors do exist and do warn the crew of a tail strike they may just not yet be certified or installed on every airframe. For example it came in handy in this incident:

  After the passengers had disembarked, the captain conducted an
  inspection of the tail skid of VZR and noticed some paint damage and
  scrape marks, however the cartridge containing the sensor for a
  tailstrike was still intact. This indicated that the tailskid had only
  just contacted the runway during the take-off.


How accurate are these Stall Diagrams depictions of relative wind? Why in diagrams of a stall, the relative "wind" comes in horizontally no matter how the airplane is orientated? Doesn't the engine, which produces the thrust for the "wind", stay parallel to the wing making the diagrams of wind at higher AoAs much more inaccurate because of the direction of thrust?

Image source

The diagrams are accurate.¹

The thrust, produced by the engine, is one of the forces acting on the airframe. The others are lift, drag and weight (a.k.a. gravity).

(from How It Flies, chapter 4)

When these forces are in equilibrium, i.e. their (vector) sum is zero, the aircraft flies straight, in whatever direction it does (that is what Newton's first law says: an object remains at rest or continues to move at constant velocity unless acted upon by external force).

When the forces are not in equilibrium, the aircraft accelerates in the direction of their sum (that is what Newton's second law says: the sum of external forces on an object is equal its mass times its acceleration). But direction of acceleration and direction of velocity are independent. If the aircraft is turning, acceleration is to the side while velocity is (approximately) forward. If it is slowing down, acceleration is aft and velocity is still forward.

So thrust and direction of flight don't have to be parallel.

For a more practical argument, imagine an airplane doing the tailslide aerobatic manoeuvre. The nose points up and the engine is running and producing thrust up. But because the thrust is less then the gravity, the aircraft slows down until it stops midair and starts to fall back to the ground, tail first. So for a moment, the relative wind will come from aft while the engine is still producing forward thrust. Only then will the aircraft pitch over to restore normal airflow over the wings and return to fully controlled flight.

Now of course since the lift and drag forces depend on the relative wind. The lift, which is the aerodynamic force perpendicular to the relative wind, increases with angle of attack, which is the angle between the relative wind and the wing planform, until stall angle of attack is reached.

So when the plane is flying level slowly, the nose is pointed up to create sufficient angle of attack. The thrust is thus pointing slightly up, so small part of it balances a bit of weight, reducing the lift requirement. That is why aircraft actually stall at slightly slower speed when the engine is developing full power than when it is stopped.

Read the How It Flies chapter 4 for more details on the forces. And the rest of How It Flies; it explains the physics pretty well.

¹ That is accurate regarding the direction of oncoming relative wind. They are not accurate regarding the flow around and behind the wings.


When does a flight require a copilot? I was wondering if there are regulations for when a flight requires both a pilot and copilot.
I always assumed a copilot is required once civilian passengers are aboard, but when I recently was a passenger in South-African and South-American sight seeing flights, the pilot was always flying alone. Flights in europe however always had a pilot and copilot.

Is this regulated by laws or can the pilot / airline company decide it on their own?

A flight requires pilot & copilot when the aircraft being flown requires it.

A multi-crew aeroplane is one that requires a flight crew of at least two pilots. One of them is the pilot-in-command (the captain) and the other is the co-pilot (or first officer). All jet air transport aeroplanes and the vast majority of turbine powered air transport aircraft and business jet are multi-crew aeroplanes.

The definition in Annex 1 — Personnel Licensing states that it is: "an aircraft required to be operated with a co-pilot as specified in the flight manual or by the air operator certificate."

So the secondary answer is no, it cannot be decided by a pilot or an operator, it is a statutory requirement.


How does a subsonic jet engine intake design ensure correct air intake? I think I understand that inlets are there to slow down the airflow and increase the pressure to stop the compressors stalling?. If this is the case, I don't understand how the nacelle or intake achieves this?

Has it got something to do with the relationship between pressure, velocity and area?

I am only looking for an explanation on jet engines which operate below the supersonic range.

Subsonic speed makes the inlet self-regulating. Add blunt edges, and the inlet works for a wide variety of engine and flight speeds, as it should.

An inlet is always a compromise. Therefore, it is quite a bit larger than what is needed in cruise in order to keep losses at low speed low. At low flight speed and full throttle the engine needs much more air than what is flowing into the inlet without the engine actively sucking air in. The flow lines converge from a much larger capture area when closing in on the inlet face and the stagnation point lies on the outer edge of the inlet lip.

Watch what happens when an airliner engine spools up on a rainy day, with puddles on the ground. When the engine reaches full speed, it starts to suck up even the water in the puddles below the intake! Some streamlines even come from behind, wrap around the inlet lip and get sucked in. With water droplets in them, they are very visible indeed.

At high speed, the capture area is much smaller than the inlet face. Only the central streamline stays straight, all others diverge away from that central streamline and now the stagnation point is on the inner edge of the inlet lip. Streamlines bordering the capture area flow around the lip and along the outside of the nacelle. This divergence of the streamlines is caused by the pressure increase ahead of the inlet, when the air is slowed down and exchanges kinetic for static energy. This even happens without friction losses, so the most efficient compression of an inlet happens ahead of it (in subsonic flow - supersonic speed removes that luxury).

The air speed at the compressor face is fairly constant at the same throttle setting, regardless of flight speed. Therefore, the pressure at the compressor face is lower than ambient at low flight speed (because air had to be accelerated) and higher at high flight speed.


Would it be feasible for a typical passenger jet to carry along its own Oxidizer? We know that many Space Shuttles / Rockets etc. carry their own oxidizer with them. This is partly because at the heights they operate the atmosphere is too rarefied to have enough oxygen to sustain the combustion rates they need.

But also, the liquid oxidizer means small pumps can be used instead of massive compressor stages. Which motivates the following question:

Would it be feasible for a typical passenger jet to carry along its own Oxidizer? I am looking for a back of the envelope feasibility calculation. It intuitively sounds impractical but I'm just curious to see some back of the envelope estimates of how much ( weight / volume) of Liq. O2 tanks would be needed if we hypothetically had something like a B-747  with its own cryogenic Oxygen tanks in addition to already extant massive fuel tanks.

Partially motivated by this related SE Aviation Question and a comment by User @Freeman:

How do rocket engines produce more thrust than aircraft jet engines?

Short answer: Yes for a short-range airliner, but it would cost a couple of seat rows. No for long-range travel.

Longer answer: To burn 1 kg of Kerosene you need 15.6 kg of air or 3.59 kg of O$_2$. Its density as a liquid is 1.14 kg/l, so it will use 2.65 times the volume of fuel. A cryogenic tank with sufficient insulation is required, though. This means it should have as little surface area per volume as possible. You could not put the LOX into the wing tanks, but need something with a spherical shape somewhere in the fuselage.

If a large commercial airliner needs 100 tons of fuel, it would need to add 359 tons of oxygen. This would be already close to its own takeoff mass, so adding the oxygen will make the airplane too heavy. If, however, you are content with a short-range version of the same airliner that consumes just 20 tons of kerosene for its trip, the needed 72 tons of LOX would require a volume of 63 m³ which is equal to a sphere of 5 m diameter. This would fit nicely into the cabin of a wide body airliner and allow for some insulation. For cg reasons the tank would be right after the wing spar carrythrough, so the airliner would have two short cabins, one ahead and one aft of the tank.

Sorry, the 747 hump cannot be used for LOX storage - the cg shift would be too big.

For running regular jet engines you would still need lots of process gas. To carry that along as well is impossible, even for a short hop. Process gas is all the nitrogen and extra oxygen which is compressed, heated and then ducted through the turbines and accelerated on the way out, but does not actively take part in the combustion. Without that mass of gas thrust would be much lower, or the exhaust speed would need to be much higher for the same thrust, turning the engine into a rocket.


How often is the fuel sampled in turbine aircraft? In planes using avgas, sampling fuel from the tanks is generally done before every flight, or at least before the first flight of the day and then after any refueling. This is done because water contamination is fairly high risk. Gasoline does not mix with water, so it collects at the bottom of the tank, and because it does not burn, when it gets to the engine, the engine will quit.
Water does mix with kerosene though so this isn't as big risk and it can't be checked this way anyway because it won't collect in the sump. It could detect other contamination though. For example in this incident hugely excessive addition of biocide caused damage to the engines, and in this case the report says the biocide did form a separate layer below the fuel.
So how often is fuel in turbine (turboprop and jet) aircraft usually sampled? And is it subjected to any additional tests beyond visual inspection?

Water and microbiological contamination are a threat to turbine aircraft even if water mixes with kerosene based fuels:

Industry-wide, the major threat to FQIS [Fuel Quantity Indication System]
availability is microbiological contamination of
the fuel (see FAST 38) and water in the fuel tanks.
Settled water in the fuel tanks may affect FQIS
indications, typically driving FQIS probe readings
out of limits and leading to aircraft delays for tank
draining. Therefore, a regular water drain task
is essential for smooth aircraft operations.

(Airbus FAST 42)
The reason is that both water and microbiological contamination in the fuel lead to a higher dielectric capacitance, which is used for fuel quantity sensing:

The FQIS system is calibrated for
use with jet fuel and the probes
measure from 'unusable' to full
tank capacity. However, the
dielectric of water is approximately eight times higher than the
jet fuel dielectric. Therefore, when
there is water in the proximity of
the probes, the fuel measured capacitance changes. Typically, the
probes will read a higher capacitance level than the actual fuel
level.

(Airbus FAST 42)
If only a small amount of water is suspended in the jet fuel, it can be safely fed to the engines without causing a flameout. However, water collecting at the bottom of the tanks must be drained:

All modern civil
aircraft incorporate water drainage
and/or scavenge systems to help
achieve this. The Airbus wing
design ensures water is maintained
in suspension and fed to the
engines; any remaining water is
then drained at regular intervals
via the water drain valves.

(Airbus FAST 38)
For an Airbus A320, this fuel tank draining must be performed at least once every 36 hours:

The amount of water drained is about 200 ml per week and per tank on an A340 after improvements done in 2007 (Airbus FAST 42).
Airbus recommends to visually inspect the drained water and to perform a fuel analysis at least once a year to detect contamination:

A second key element of prevention is monitoring. Often overlooked is the need to visually
inspect any water resulting from
the MPD water drain task. Drained
water and fuel will separate within
the container with the water
settling to the bottom. Both should
be clear with no particulates
evident to the naked eye. Any
'cloudiness' in either fluid indicates
possible contamination and action
is required.
Currently, Airbus recommends an
annual analysis of fuel from each
aircraft to test for fuel/water contamination, which should be considered a minimum for all operators.

(Airbus FAST 38)
Should the visual inspection show any contamination, or should the pilots notice discrepancies in their fuel analysis (see e.g. here for example calculations), or should the FQIS show fluctuations or degrading (fuel quantity indicates XXX), a detailed analysis should be performed according to this flow chart:

(Airbus FAST 38)


Do MD-11 pilots ever use flaps 50? I'm curious if there is ever a purpose to use full flaps like that? Was it a bit of an overkill?

The MD-11 has one of the highest approach speeds, which is comparable to the 747-400 (Boeing), while having higher wing loading: 806 vs. 756 kg/m$^2$. In other words, the MD-11's wing is small, so flaps 50 is not an overkill.

The standard MD-11 landing flaps are either 35 or 50 depending on the weight, altitude, available stopping distance, etc.

Aircraft manufacturers don't usually go for overkill items. The bigger the flaps deflection the more loads and stresses there will be, and the stronger and heavier the flaps and wing support need to be made.

Further, the MD-11's flaps arrangement is covered in a NASA study, from which:

  Because of high wing sweep, the slant angle on the inboard closure rib of the outboard flap is about 30°. When the flaps deploy, the slanted inboard rib exposes a forward-facing surface. The same out-of-streamline angle applies to the aft portion of the hinge fairings when the flap is deployed. (See fig. 1.24.) Both of these features degrade flap lift performance and cause drag. [emphasis added]

If McDonnell Douglas had went for an all-new wing for the MD-11, and not just adapt the DC-10's, it would have doubled the development cost, see: How much does it cost to design a jetliner's wing?


What is the difference between a "compass swing" and "check swing" procedure? What is the difference between a "compass swing" and a "check swing" procedure?

Based upon the terminology I have heard over the years, a compass swing is the alignment of the compass, normally using a compass rose painted on a surface. The compass is adjusted and a deviation card is created for cardinal points on the compass.

A check swing, as I have heard it referred to, is the checking of the compass, and done with the aircraft running, and electrical loads on, similar to a compass swing, but without the adjustment.  The deviation card is verified, but there is no intent of adjusting anything.  This was typically done before we ferried aircraft over the ocean, where there would be extended dead-reckoning (before GPS and LORAN), and where flights were close to the polar regions, and compass operation needed to be verified prior to the flight.

Not that a compass is worth much near the poles (grin).

My guess is that check swing is merely a slang term, whereas compass swing is well understood and extensively documented.


How energy efficient is an aircraft take off? How much work is generally done by an aircraft (e.g. B737NG) in order to reach V_rotate, and how does this compare to the energy content of the fuel that is used?

You can make a decent approximation with very basic numbers. Take for example the CFM56-7B (which is incidentally also used on the 737NG).

Maximum thrust specific fuel consumption $TSFC$ at takeoff: ~10.9 g/s/kN
Maximum thrust $F$ at takeoff: 121 kN
Jet fuel specific energy $e$:  43 MJ

Combining these figures gives a fuel burn of 1.4 kg/s at takeoff, or 57 MJ of chemical energy released every second ($P=57MW$).

To get an airplane of mass $m$ to a certain speed $v$, it needs $$E=\frac{1}{2}mv^2$$ of kinetic energy. It does so in $$t=\frac{v}{a} = \frac{vm}{F}$$ seconds (remember, $F=ma$). The efficiency $\eta$ is useful work done $E$ divided by input energy ($Pt$),
$$\eta =\frac{mv^2}{2Pt} = \frac{vF}{2P} = \frac{v}{2\cdot TSFC \cdot e}$$

Immediately, we see why TSFC is an important figure. Plugging in some numbers, let's say $V_R =145\mathrm{kts} \approx 75\mathrm{m/s}$, we get a total efficiency of $\eta \approx 8\%$ until rotation.

Note that this calculation assumes constant TSFC while in reality it is very much a function of $v$ (indeed, with this calculation you could have $\eta>1$ if $v\to\infty$ which is clearly impossible).


In Polikarpov I-153, Were the gulled wings very important? Lets look to the I153

It looks like it was made in order to make space for pilot to see its front just like here
But What about in the aerodynamics study ?
Are Gulled wing design very important in order to make wings farther away from each other ?
Also what would happen if it was straight just like  ?

The I-153 was a development of the I-15, of which 671 were built. However:

  The upper wing of the I-15 was unpopular with some pilots, as it was felt to restrict visibility, so Polikarpov's design bureau produced a revised version, again powered by the M-25, with a longer span un-gulled upper wing.2 This version, the I-15bis, commenced production in 1937,[7] a total of 2,408 I-15bis' being delivered by the time production finished in 1940.2

So the straight upper wing version was built to improve visibility, and many more units were produced than of the I15.

Structurally and aerodynamically, straight or gulled in this way makes little difference. Structurally, any bend is a weak spot, but the upper wing of biplanes usually had pylons in that position anyway to fix the upper wing to the fuselage. Aerodynamically: the bit missing in between the gull pylons reduces drag a tiny bit - the cross wires have phenominal drag though, and that fat little body also drags a lot of air with it.


Why are the Boeing 737 nacelles odd shaped? Why is a Boeing  737 NG engine not completely round in shape? It seems to be flat at the bottom and round at the top and sides. Earlier Boeing 737 versions (100 and 200) seem to have a more rounded shape.

(Source)

The engine in question is a CFM56 turbofan engine which is larger than the JT8D the plane was originally designed for and thus has less ground clearance. This meant that they needed to flatten the bottom by moving the accessory gearbox to the side from the bottom and shrinking the fan.

To quote Wikipedia:

  In the early 1980s Boeing selected the CFM56-3 to exclusively power
  the latest Boeing 737 variant, the 737-300. The 737 wings were closer
  to the ground than previous applications for the CFM56, necessitating
  several modifications to the engine. The fan diameter was reduced,
  which reduced the bypass ratio, and the engine accessory gearbox was
  moved from the bottom of the engine (the 6 o'clock position) to the 9
  o'clock position, giving the engine nacelle its distinctive
  flat-bottomed shape. The overall thrust was also reduced, from 24,000
  to 20,000 lbf (107 to 89 kN), mostly due to the reduction in bypass
  ratio.

They also mounted the engine in front of the wing rather than below to get every bit of clearance they could.


Are there any safety or technical reason airlines do not display flight information to passengers in real-time? A newer addition to commercial airliners is seatback screens, that allow the passengers to watch movies, TV, and so forth. On most airlines, there is also a map, that shows you the aircraft's flight path, position, airspeed, and altitude.

I have noticed that the information displayed on the map screen only updates in roughly 15-second intervals. Is there any reason for this? I can't imagine that there would be any bandwidth limitation issue for such a small amount of text data (for example, I can drive a ton of data to my ForeFlight app with my relatively mid-range GA IFD), so I imagine there must be a safety or technical reason for it.

If data is continually updated, nervous flyers will fixate on every minor change.

The altitude changed by 30 ft in one second?That is a descent rate of 1,800 FPM!  Surely we're going to crash!
The speed changed from 480kts to 470kts in one second?At this rate, we will stall in less than a minute!
The plane was at 260kts at 9,800ft?
This crazy pilot is breaking FAA regulations and must be reported!

By updating less frequently, there is a natural filtering and smoothing of the data to obscure tiny measurement changes due to instrument limitations or conditions like turbulence.


What kind of test is going on in this image? Some times we see images of jet engines on the net that have strange colors. For example take a look at the bellow image. What the operator is doing? Why the color of blades are white with red on its borders? why are they numbered? why is the color of spinner yellow?

Source of image

This is most likely some kind of a test where high speed photography (as in 5,000 - 10,000 frames/second) will be used to capture the detailed motion of the fan blades.
Types of tests that might require this type of video include fan blade out testing, bird strike testing, and icing / hail testing.  There may be others but those are the most common.

Why the color of blades are white

In order to get 10,000 frames per second you need a lot of light. There will be many high powered lights shining on the engine.  You don't want harsh reflections from the lights, so you need a matte finish, the flatter the better.  The normal blade finish is way too shiny. So they are painted.

with red on its borders?

just for contrast, so you can very clearly tell in video where the blade stops and the fan case starts.  The exact color is arbitrary, and different OEMs have different traditions.  You are just looking for a set of colors are very different from one another.

why are they numbered?

So in the high speed video, you can see what happens to what blade.  For example, in a hail test, you might observe that a giant chunk of hail hit blade #15.  You could then go inspect blade #15 afterwards and see if there is any damage.

why is the color of spinner yellow?

Same as the red border. Just for contrast, so you can see where the blades stop and the spinner starts.

What the operator is doing?

I don't know exactly. Obviously some kind of assembly or disassembly procedure.  You can tell in that photo that the inlet is not attached, he's right up against the plane of the fan blades.  So it's not a fully assembled engine on the airplane or on a test stand.  It's clearly in the factory somewhere.  But what exactly he's doing I don't know.  Honestly could just have been "hey we need some publicity photos for Aviation Week, pretend to do something interesting with the engine".


How do engine manufacturers derive varying amounts of thrust from a single engine model? What changes do manufacturers make to an engine to vary the amount of thrust it produces for different applications? Take the GE CF34 for example where there is a 10780lb difference between the thrust produced by the smallest CF34-3 and CF34-10E.

The CF34-3and CF34-10E are quite different engines. The -10 produces more thrust for a number of reasons:

It has a higher mass flow. The CF34-3 has a 44 inch fan, while the -10E has a 54 inch fan. So, the mass flow will be higher in the -10E, and thrust is related to mass flow.

The bypass ratio is different, the -3 is 6.2 while the -10E is 5.4.  This is also due to the different fan diameters, and will cause a difference in thrust (even if the mass flow was the same.)

They are significantly different engines. The -3 weighs 700kg, while the -10E weighs 1700 kg. So, it's a lot more than just a tweak of the blades, or a change in fuel scheduling, neither of which will change the weight. With such a weight difference, you would actually expect the -10E to be about twice as powerful, so a question would actually exist if it wasn't considerably higher than the -3.

The turbine temperatures are also different, due to the large difference in technology levels of each engine. The -3 was certified in 1995, in comparison to the -10E in 2013.The EASA type certificate EASA for the -10E shows the max allowed EGT at takeoff is 983 Celsius. The -3 max EGT for takeoff is only 871 Celsius, in comparison.

With regards to overhaul intervals, this info is generally proprietary, as it's commercially sensitive. So, you won't find much info. Suffice to say, airlines don't make money if the engines need to be overhauled often, so later versions with better high temperature material capability are likely to have longer overhaul intervals, than earlier generation engines made in a time when shorter periods was the norm, and acceptable then, but not now.


Where does the gate drop-off bagage go? Sometimes I am asked to give-off my cabin luggage case at the gate and it will be returned to me upon arrival. I often don't mind, as long as I do get it back at the gate upon arrival and don't have to go to the baggage pick-up belts. Is this luggage stored in some particular place (so I can be more assured the gate drop-off won't delay me)?

It's typically stored in the cargo bin with the checked luggage.  If it is to be returned to the jetway, it will be tagged with a distinctive tag so that it's clear that it has been screened already (i.e. it came in through security, so it can go back out into the terminal with you at your destination).  In many cases, though, once an item has been gate-checked, it will be delivered to baggage claim to be picked up there.

The exception to that is baby strollers -- they should be returned to the jetway since parents tend to need those to get the young ones around the airport.

Individual airline policies, of course, will vary.  With small jets (not a 737, but a regional jet or turboprop, perhaps), the carry-on space is so limited that all sorts of things that would be accepted as a carry-on for a larger aircraft can't go into the cabin, so those may go into a dedicated cargo hold & all returned as the passengers deplane.


What are reasonable values for the position of an airplane's center of gravity compared to that of its center of lift? I understand that if the center of gravity is in front of neutral point, it is stable. If the center of gravity is behind the neutral point, it is unstable. Based on the diagram, is it implied that h (center of gravity) cannot be greater than 1? When h = 1, there will only be c (mean aerodynamic chord). What does it mean if h>1? Is it off the wing basically?

hnwb = 0.25 (typically)

When I solved a problem, my h value was greater than 1. Isn't that incorrect because it is off the wing?

If I understand your question correctly, h is a fraction of mean aerodynamic chord c. That fraction can be >1. It could be that the aircraft is stable with a huge download on the tail.

The mean aerodynamic chord is an aid, to simplify calculations. It is not a hard limit for the equilibrium points. Whether the value is reasonable or not is hard to say without having seen the full problem to be solved.


Why are fuel pump switches separate? Since engines are run only when the fuel pumps are on and vice versa , why are there separate switches for this? Why can't it be automated ?

Since engines are run only when the fuel pumps are on and vice versa<<

Not true. Engines can be run without fuel pumps, to allow for fuel pump failure.

The need for fuel pumps depends on the location of the fuel tanks relative to the engines, and the relative thirstiness of the engines - there are some airplanes where the fuel pumps are only used at some times (i.e. near the ground).

So it all depends.


Why does an increase of airspeed result in a decrease of angle of attack? In Chapter 02:  Aerodynamics of Flight of Helicopter Flying Handbook, on page 10, it says:

  Induced flow velocity is increased, resulting
  in a decrease in AOA.

I don't understand how airspeed can change AOA. Looking at other posts on the topic, it seems that everybody assumes that to be true without an explanation. Can anyone tell me why?

PS: the statement above explains why there is a positive stall region in a helicopter's retreating blades when the rotor speed is too fast.

On page 2-10 under the heading "Induced Flow (Downwash)", the book is making the point that if you have a wing moving forward horizontally at some fixed speed relative to the ground and some fixed positive pitch attitude relative to the horizon, and you surround the wing with a descending airmass, the wing's angle-of-attack will be less than if the airmass were not descending.  A rotor blade of a helicopter can be viewed as such a wing, at least at a given instant in time.

The book is using the term "induced flow velocity" specifically to refer to the downward velocity of the airmass caused (induced) by the rotor blades.  I.e., downwash.

The exact sentence you quoted was under the subheading "Out of Ground Effect (OGE)".  Since the ground is no longer acting like a "floor" to impede the downflow of air through the rotor system, you have more downflow than you would in ground effect.

If you were hovering in ground effect and the ground suddenly disappeared, the downflow velocity would increase and the angle-of-attack of rotor blades would decrease.


What were the advantages of the L-1011 AoA sensor design? The Lockheed L-1011 had an unusual type of AoA sensor. Instead of the usual vanes it used a tube with two rows of holes in it about 90° apart. A diaphragm sensed the pressure differential between the two sets of holes and a motor adjusted the sensor until the differential went away. The AoA was them determined from the angle the sensor was to the fuselage.

 Source: NTSB accident report TWA 843

This seems particularly complex, requiring a motor and possibly introducing lag into the reading. Why did Lockheed decide on such an unusual sensor design? Does it have some a advantages to a conventional vane? Was it used on any other aircraft besides the L-1011?

I found several patents that resemble the L-1011's, dating back to at least the 50s. One such patent remarks that there are two main types, the vane, and the rotating pneumatic tube (also comes in conical shape).

The advantages of the latter when compared to the vane-type are:

  [B]etter balancing characteristics, lower air friction, greater sensitivity, and less tendency to flutter or otherwise yield erroneous readings under adverse flying conditions. Also, it requires less power to prevent ice accumulations on a probe than a vane.

A disadvantage is keeping the moisture/dirt out:$^1$

  There is one difficulty in making this a rugged instrument. The movable cylinder must be mounted to move as freely as possible so as to have good sensitivity. This requirement makes it difficult to make a good seal around the moving cylinder to keep out dust and moisture.

A motor would solve this seal issue. But the advantages of the form should hold whether motorized or not. A more recent patent uses the tube design to combine the AoA and static/dynamic pressure sensors into one probe.

Was it used on any other aircraft besides the L-1011?

The F-14, for example, uses the pneumatic (conical) type:$^2$

(primeportal.net) The left (port) side of the F-14's nose.

$^1$ https://apps.dtic.mil/dtic/tr/fulltext/u2/102442.pdf page 50.
$^2$ The location is confirmed by the F-14D manual (only 1 probe), and it's referred to as probe (not vane).


What's the reason for pilots wearing uniforms? Just came across an interesting answer to a question on uniforms for PPL Human Performance and Limitations:

Pilots wear uniforms:
a) so they can be easily recognised
b) so that they can be perceived to be important
c) so that they can feel important

Apparently the correct answer is b (I said a). Is this so that their authority is respected, is this a valid reason?

The Smithsonian's National Air and Space Museum says:

By the early 1930s, airlines were introducing distinctive uniforms for their employees, and women were entering the ranks of flight attendants.
Pilots were given military-style uniforms to reflect their status. Pan American emulated luxurious ocean liner service by calling its flying boats "Clippers" and its pilots "Captains," and attiring its crews in naval-style uniforms with white hats and navy-blue, double-breasted jackets and rank insignia on the sleeve cuffs. Other airlines followed suit. Many of these customs continue today.

This is why choice b is the correct one. A military-derived uniform projects importance / reflects [high] status. While a flight jacket—or a cap that reads 'pilot' for that matter—might adequately serve the purpose of identification (choice a).
Look no further than Wilhelm Voigt, an imposter in an officer's uniform can command real soldiers, place people under arrest, and make away with a treasure.
(Navy Officer, Pilot) Side-by-side comparison.


How does turning a small plane by opening the doors work? I've just watched a video of a small Cessna turning not with ailerons or rudder but by opening its doors. They said that the door acts like a rudder, but in the video one of the guys opens the left door and the airplane rolls right. That doesn't  make too much sense to me...

I've been searching on the internet and I found a different explanation which  stated that the airflow stacks up below the wing because of the door and then an over-pressure is exerted making the airplane roll into the opposite direction, in this case to the right (which is what can be seen on the video). Can anyone confirm this second explanation?

And if I wanted to roll a Piper or any other low-wing aircraft by using the doors, what would the airflow's behaviour be?

The second explanation is right. The blocking effect of the door below the wing will force more air above it, so suction and lift above get higher. Of course, the blocking effect will also increase pressure locally on the lower side of the wing.

If you do the same on a low wing aircraft, it will roll to the opposite direction. Now the door acts like a spoiler and reduces lift.

Generally, such a one-sided creation of a disturbance will upset the aircraft and will make it roll and yaw in an uncoordinated manner. And the "rudder" explanation is wrong - a rudder creates a sideforce at a distance to the center of gravity, while the door is pretty much where the pilots and the center of gravity are. The better explanation would say that the door acts like a spoiler, and those are used routinely for roll control:

in airliners
in unmanned vehicles


A320 procedures for one thrust reverser inoperative; why is the old procedure more efficient? I recently watched the Mayday series about TAM Airline Flight 3054. Landing on a short runway with only one thrust reverser in use, and the documentary explained something like:

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

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

Does the position of the controls for the second motor really influence the behaviour of the first one?

No, it influences the activation of various other systems like the autothrust, the airbrakes, as well as the thrust reversers.

  how it is more efficient?

Because in the new procedure the engine with non-functioning reverser starts to spool up before the system realizes the reverser did not deploy and cuts it again, so for a moment it produces forward thrust. The old procedure avoids this.