What type of visa do pilots who fly from one country to another need? I am little curious about international travel. I would like to know what type of visa allows pilots and cabin crews to fly from one country to another? I mean suppose I am pilot of Japan airline and I have trip a for Netherlands. How could I enter to the Netherlands with Japanese citizenship?

International Airline crews often spend 1 or 2 days laying over at the destination. In most countries, airline crew members who are listed on the Aircraft Customs and Immigration General Declaration are exempt from Visa requirements.
Rules will vary from country to country as to how much travelling freedom you have while staying in the layover country. Most countries require you to always have your passport with you and some countries require some kind of form identifying you as airline crew. Some countries have rules defining how far you can travel while on the layover.
In general practice most airline crews I know leave their passports in their room and just carry a photo copy or digital copy with them, and freely travel just as any tourist would do.


How long does the gear extension/retraction takes on the ATR-42? Which is typical time of landing gear extension in normal conditions ? I would like to know it especially for the ATR-42 but any other typical value is welcome !
Furthermore can you provide any link to data sheet for ATR-42 technical data about landing gear ?

In this youtube video showing landing gear maintenance operations on an ATR42, I'd say about 11 seconds for both extension and retraction.
A more precise timing could be gathered from an uninterrupted cockpit video, measuring from gear lever action action to "three green" on.


What are those buttons pushed after thrust is set to max If you see this video

              at 0:42 you will see both of the pilots pushed a button on the front panel.
can someone tell what that is and what it does?

They're starting the chronometer. This chronometer is displayed on the navigation display.

It lets them keep track of the time limit they are allowed to operate at takeoff thrust. The limit is 5 minutes normally extended to 10 with an engine failure. After this, they must reduce power to the maximum continuous thrust setting (MCT).

There is also a time limit between the setting of thrust and when the engine reaches commanded power. If it is too long, it indicates a malfunction and takeoff should be aborted.


As a passenger, can I use my handheld radio in commercial flights? During flight from one country to another, can I use my hand held radio during flight to listen to ATC?

I don't know if you are "authorized" to... but I can tell you that it likely won't work.

I've tried a handheld aviation radio in a commercial cabin, and was unable to hear the ATC side of transmissions at all.  This was likely due to having a very short antenna inside a large metal cylinder, a long way from the source of the transmission.

It was nearly impossible to follow the communications when I could only hear my flight crew's side of the conversation.


Why do trijets (3 rear engines) usually have a T-tail instead of a normal tail? I'm thinking of trijets like the Tu-154, which has three jet engines in the rear. Not something like L-1011 Tristar which has only one engine at the rear.

Tu-154:
Source: Wikipedia

L-1011 TriStar:
Source: Wikipedia

Why do these kinds of jets have T-tails? Maybe the side jets get in the way of a conventional tail, but it looks to me like you could just raise those engines a little bit and enough room would appear.

My understanding is that T-tails add complexity. The vertical part of the tail has to be strengthened (more weight) since it undergoes more forces. So a conventional tail seems preferable.

A T-tail is not so bad. Its main advantages are:

A smaller vertical tail is required, because the horizontal tail acts like an endplate and enhances the efficiency of the vertical tail.
When the vertical tail is swept, a T-tail will allow to make the horizontal tail smaller as well, because it gains additional lever arm in this configuration.
By designing the junction with the vertical well, the T-tail has less interference drag. It also helps to reduce wave drag, especially when using a well designed Küchemann body (the round, long, spiky thing on the tail junction of a Tu-154) by stretching the structure lengthwise.

As soon as the cruise Mach number demanded tail sweep, the T-tail became the preferred solution. Placing the engines at the rear fuselage put them higher, so FOD became less of a worry, and the wing could be kept clean for maximum lift resulting in shorter runway requirements. In the days before CFD, it was much easier to get the wing right when no pylons with barrels at their ends were sticking from it.

If an engine is mounted near the place where normally the horizontal tail would be, it is much easier to relocate the horizontal to the top of the vertical than trying to join both together. The mass of the engines will require a relatively rearward wing position, so the lever arm of a conventional tail would be rather small. By shifting it up to the top of the swept vertical tail, its lever arm is much larger, making the T-tail especially attractive for configurations with rear-mounted jet engines.

A second reason is better failure tolerance. Note that the T-tail designs are from the early jet age. Their first flight years were: Caravelle 1955, Jet Star 1957 (both not real T-tails, I know, and having little tail sweep), Trident 1962, VC-10 1962, Ilyushin 62 1963, Boeing 727 1963, Tu-134 1963, C-141 1963, Hansa Jet 1964, Tu-154 1968. The designers were afraid an engine failure would also damage the horizontal tail and would turn a survivable accident into a lethal disaster.


What happens when flying on a Victor airway but through a class B or C airspace? I think it´s a very simple doubt but also very important, and i can´t find the answer. If you are flying on a Federal Airway that at some point cross a class B airspace (for example)...do you need authorization or can you keep flying without one?

If you are flying your IFR flight plan which you got clearance for, then you have permission already.
If you are flying VFR you need to ask ATC for clearance.
Class B airspace requires clearance for all traffic and separation is also provided by ATC for all traffic.


In an Airbus A320, when alpha protection is active, is pitch protection no longer available? The A320 FCOM chapter 27 flight controls, normal law, protections, shows a diagram how the sidestick input is used when protections are active. When high angle of attack protection is active the side stick controls angle of attack (alpha protection to alpha max), so far so good.
In several places throughout the FCOM and that diagram I talked about Airbus states that the alpha protection has the highest priority.
Does this mean when alpha protection is active that pitch protection is no longer available? It makes sense that the nose of the aircraft is allowed to drop below the normally protected minimum of 15 degrees but is the maximum pitch of 30 degrees (or 25 depending on config and airspeed I think) still protected?
When alpha prot is active is it possible to pitch up to more than the maximum pitch limit? The diagram would suggest yes.

In normal law « Alpha prot » has the highest priority, if AOA is less than alpha limit, teta (pitch angle) is limited between +25 and -15 at long run. At long run,  since in emergency descent you are allowed for a short time to go beyond - 15° pitch down, to do that you need to pitch down the side stick very quickly after having engaged a steep roll.

If AOA protection is active, I don’t see how you can exceed 25°or 30° pitch up, since the FBW will pitch down the aircraft to follow the AOA protection.


What are the effects of camber location in an airfoil? Am I correct to assume that for a low speed aircraft, the location of the camber in the MAC's airfoil will correspond with the aerodynamic center? Also, does that affect the moment coefficient? And what about a high speed aircraft (M>1)?

[Does] the location of the camber in the MAC's airfoil correspond with the aerodynamic center?

No.

The aerodynamic center is where the additional lift force from a change in angle of attack can be summed up. Since camber only determines the lift portion that is independent of angle of attack, changing the camber will not influence the aerodynamic center.

For a high aspect ratio wing in subsonic flow, the aerodynamic center is at the quarter chord position. With decreasing aspect ratio this point moves slowly forward until it arrives at the forward tip for a slender body.

Also, strictly speaking, there is no "location of camber" — camber is distributed over the whole chord. What you probably mean is the highest point of the camber line, but that point has little aerodynamic significance. The local curvature of that line is much more important.

  Also, does that affect the moment coefficient?

Yes.

Generally, the more an airfoil is cambered towards its rear end, the higher its pitch moment coefficient will be. This is called "rear loading" and is used in order to combine decent thickness with good lift in transsonic airfoils. You can use the lengthwise location of the highest point of the camber line as a guide how high the moment coefficient will be.

  And what about a high speed aircraft (M>1)?

That depends on wing sweep. Normally, aircraft designers try to keep the wing's leading edge subsonic over the full speed range. But I guess you wonder how the camber will influence a wing's performance once it moves at full supersonic speed. Well, the bad news is that camber will drive up wave drag without any influence on lift. Supersonic aircraft, therefore, use thin airfoils with very little camber, and the camber they have is only there because it helps in subsonic flight.


Who pilots an aircraft that is on a delivery flight? Right about now (Jan 28, 2016, 08:12 UTC), a Boeing 737-8AS is cruising over Manitoba/Nunavut on a delivery flight from Seattle Boeing Field (BFI) to Dublin Airport (DUB). The flight is labelled RYR800F, and is clearly a delivery flight for the European low-cost airline Ryanair.

I have always wondered who flies the plane in such situations. I would appreciate if you could give me a few insights into how these events are managed by the manufacturer and the Company. I envision the following cases, but which one of them, or combination of them, is true?

1) The plane is flown by a special pilot unit of the buying Company, which flies to the manufacturer's logistic airport, checks for conformity, signs a few documents, and then flies the plane to the Company's headquarters or hub;

2) The plane is flown by a special pilot unit of the manufacturer. They fly the plane to the Company's headquarters or hub, then meet the buyer to check for conformity and sign the documents. Eventually, the pilot unit flies back to manufacturer's base as regular passengers onboard other flights;

3) The plane is flown by two units: one belongs to the manufacturer and the other to the buyer. They check for conformity, sign the documents, and jointly fly the plane, in order for the manufacturer and the buyer to share immediate feedback on the plane's performance while airborne;

4) The plane is flown by a contracted pilot unit, which performs the duty as a third party payed by the buyer or by both the buyer and the manufacturer. This unit also includes a member of the buyer. They reach the manufacturer's base, the buyer's employee signs the documents, and then the plane is flown to the Company's headquarters or hub.

I assume each Company has its own policy in this regard, but which one of these procedures do you think is the most common? Thanks!

Typically the customer will travel to the manufacturers location for a final inspection and acceptance of the new aircraft. This includes one or several test flights with staff of both the manufacturer and the customer on board, thorough systems checking and final modifications if necessary. The acceptance of the aircraft is then made official by signing off a pack of papers.

Then the customer transfers the final sum of money to the manufacturer and the aircraft is signed over to the customer. The delivery flight is typically operated solely by the customer's staff, however if it is the first aircraft of the specific type for the customer, the manufacturer may send training staff along for final training of the ground staff at the customers location if agreed so.


Can a person with a tibia problem become an air traffic controller? I have a healing tibia. In the worst possible case, if it does not heal fully, will this impede a future attempt to become an air traffic controller?

In the US, an air traffic controller is required to have Class-II medical. However, it is mentioned here that:

  The applicant must have no deformity of spine or limbs of sufficient
  degree to interfere with the requirements of the position of
  employment being sought. Certain limitations of range of motion may be
  acceptable for certain specific options or positions, in which case
  acceptance for employment will be noted specifically for that position
  or option only.

Other than the regulatory standpoint, reaching the top air traffic tower might be hard. There may not be elevators reaching all the way to the top. To save space, many use ladders, not even a staircase.

However, working as air traffic controllers does not always mean in the tower. Many radar rooms are ADA complaint and are wheel chair accessible.


What Oil thickness is used for the geared turbofan jet engine gearbox In light of the huge operating speed of the geared tubofan gearbox gearing down the fan speed, what Oil thickness is used for the geared turbofan jet engine gearbox and does it use use regular gearbox oil used in cars and trucks, also in light of the huge difference in operating speeds of these gearboxes?

The more regular specification for such oils is given for the viscosity in centistokes versus temperature, as an example the Mobil Jet™ Oil 387 lubricant that can be used on Pratt & Whitney PurePower® Geared Turbofan™ PW1900G engines has a viscosity of about 5 cSt at 100°C, and about 25cSt at 40°C

Other parameters are extremely important such as the flash point temperature, the fire point temperature and the autogenous ignition temperature

Also the Total Acid Number is an important parameter for engines oil.

Please refer to the following website for more details about above mentioned oil specifications.

https://www.exxonmobil.com/english-US/Aviation/pds/GLXXMobil-Jet-Oil-387


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

Landing on "The Boat"

Glossary

Approach turn/ 180: The approach turn itself is a 180 degree turn (190 degrees at the boat because of the angled deck) that is usually broken down into 5 segments: the 180 position, the 135, the 90 (halfway through the turn), the 45 and the groove.  Each respective position indicates the number of degrees left in the turn prior to rolling out in the groove.
(The) Ball or Meatball: an orange orb of light emitted from the IFLOLS.  A green horizontal row of lights (known as the datum) indicates proper glide slope.  If the ball is below the datum, the aircraft is low, and if its above the datum, the aircraft is high.  Aircraft should strive to keep the ball on the happy side.
Ball Call: Format: "(Side-number) (aircraft type) ball, (fuel-state), (auto-throttles)" Example: "123 Rhino ball, 9.0"
Carrier Break: A type of left hand overhead performed at 800ft AGL and 350+kts (for hornet guys)
BRC: the basic recovery course.  The course at which the ship is currently traveling, which does not include the offset for the angled deck.
Groove: the final portion of the approach (what civilians might call short-final)
Initial: on BRC, 3-5nm behind the ship, 800ft AGL, 350+kts, the starting point for the day approach
Interval: the specific aircraft in the pattern whose approach will commence just prior to yours, and whose separation you are responsible for not violating.
On speed: the proper AoA that will achieve the correct hook angle to catch the target wire of the carrier.  On speed airspeed can be approximated by the aircraft weight, but the term on speed does not refer to airspeed specifically, but units of AoA.
Side number: The 3 digit number assigned to the aircraft.  This is not the buno number (military aircraft don't have N numbers), it is a squadron specific identifier.  I will hence refer to '123' as the default side number.

Carrier Procedure

For simplicity's sake we'll pick it up at initial.  Glossary items have been italicized for ease of reading.

"123 flight of x, initial", ATC will then give the required instruction.
The flight will then side-step to the right of the carrier island, and begin looking for their interval.
Reaching the carrier, the flight will then perform the carrier break on their interval, ensuring that aircraft will arrive in 60 second intervals.
Landing checklist: 3 down and locked, flaps full, hook down, antiskid off, dispenser off, on speed XXX.
Once turned downwind, the aircraft will descend from 800ft AGL to 600ft AGL (the carrier pattern is flown at 600ft), and the aircraft will ensure it has proper lateral separation (abeam distance) from the carrier so as not to overshoot or undershoot on the approach turn.
Once abeam the LSO shack (or when the white of the round down is visible), the aircraft will increase VSI to approximately 200-300fpm and begin a 27-30 degree AoB turn.  Proper time in the groove is limited to only 15-18 seconds.  Too long or too short in the groove and the LSO can wave you off, so it is paramount that the approach turn be performed at the proper position.
At the 90, altitude should be 450ft AGL, and VSI should increase to 500fpm.
At the 45 the aircraft should be crossing the wake of the carrier, altitude should be 325-375ft AGL, and the ball should appear to rise. Note: Rolling into the groove, the ball should appear either centered or slightly high.
Once in the groove, with a visible ball, the aircraft makes its ball call.  The LSO will respond with "roger ball", which is the aircraft's clearance to land.
Once established in the groove, the aircraft should be roughly 700fpm and flying the ball for glidepath.  The pilot's scan becomes: meatball, lineup, AoA, meatball, lineup, AoA, meatball, lineup, AoA (you get the point).
As the aircraft flies in the groove the runway will constantly slip to the right requiring small, almost imperceptible, lateral stick inputs (and matching power corrections to account for the loss in lift).  The pilot will strive to keep the aircraft on centerline, on speed, with a centered ball.  Note: failure to keep the aircraft on speed can result in either a bolter, or an in-flight engagement.  It is imperative the aircraft maintain the proper AoA.
Just prior to touchdown, as the aircraft passes over the ramp, the pilot's scan will shift to ball, ball, ball, ball, ball, and the touchdown should come as a surprise.  This is referred to as "flying the ball all the way to touchdown".  Pilot's that deck spot (ie, attempt to fly to a specific spot on the deck) often fly down through the glideslope at the last moment and land short.
Once on the deck, the throttles will go to full military power (just shy of AB), and when landing has been assured, then the power will be reduced and the aircraft taxied off the landing area.

Shore Procedure

Naval aviation revolves around flying at the boat.  It is imperative that the procedures used at the boat become second nature, that they become ingrained in muscle memory.  To this effect, all shore based VFR approaches will be flown in exactly the same manner as would be at the carrier, with a few minor exceptions:

Antiskid will be on
The hook (for a non-emergency) will be up
Aircraft aren't required to have 60 seconds of separation, we routinely land with aircraft taxiing down the runway.
The throttles will be retarded unless executing a touch and go.

Otherwise, naval air stations that house carrier based aircraft all have I/FLOLS installed, and the ball is flown during normal VFR approaches to the field.

Further Reading

(Edit)

The following link, provided by the Chief of Naval Air Training Command (CNATRA), is an unclassified, publicly available, training guide used to train potential Naval Aviators to land on the boat for the first time.  The procedures are nearly identical, with a few nuances related to T-45 training operations, to the procedures used daily by fleet aviators.

Legal Notice.

Link to document provided by CNATRA.


How did the F28 have such a good L/D ratio? The second link given on a Google search for "Breguet Equation" is to a PDF document from MIT.  On page 7 of this document is a chart showing L/D ratios for various commercial aircraft (turboprop, regional jet, and "large aircraft") plotted against the year the aircraft entered service.  Below is an image of this chart:

What appears to stand out (at the top of the chart) is the Fokker F28 aircraft.

From an engineering and operational perspective, what enabled that aircraft to have such a high L/D ratio?

Also, I thought that the F50 / F70 / F100 aircraft had the F28's wing (or an evolutionary version).  Why didn't these aircraft have an equally good L/D ratio?

They just got this wrong. I have flown F28-1000 and -4000, the F100 and the B767-300. The most feet per nautical mile lost of these with idle power at any given Indicated Air Speed (say 270-280 below 25000 ft) is the F28-1000 (around 475 fpnm) then the F28-4000 at about 425 fpnm, then the F100 at about 350 fpnm and the best is the B767 at about 300-330.The 425 fpnm figure for the -4000 was measured by me around 2004 to get data for MS Flight Sim. All the rest are educated guesses.


What are some of the differences between piston engines used in aircraft and automobiles? What are some of the differences between piston engines used in aircraft and automobiles?  It seems aircraft engines are much more expensive, I imagine some of that cost must be due to the more extreme environment (temperature, air density, roll angle) that an aircraft engine is expected to run in.

In particular:

Are aircraft engine parts expected to be less likely to fail?
What is done to allow the engine to function at extreme temperatures / altitudes / air densities?
Do changes have to be made to allow a piston engine to function while upside down (in a roll)?
What components are different on an aircraft vs automotive piston engine (magnetos vs. spark plugs, oil system)?

The engine in a typical light airplane (say a Cessna 172 or a Piper Cherokee) has a lot in common with the engine in a classic 1960s VW Beetle (Type 1): Both engines are horizontally opposed four-stroke four-cylinder spark ignition gasoline engines. Their parts even have similar metallurgy, and broadly similar failure rates.
In fact if you remove the gearbox and install a magneto ignition system you basically have one of several "Volkswagen aircraft engines" that are popular in the experimental market, and have proven to be very reliable if well-maintained.

Certificated aircraft engines (the Lycoming and Continentals you would find in our hypothetical Piper or Cessna) have a few other features not found on a Volkswagen engine: They have dual ignition systems (two magnetos, two spark plugs per cylinder) for redundancy in case one fails, and an oil sump designed to hold at least twice the capacity of oil needed for safe operation. They typically also have a manual mixture control to allow the pilot to lean the fuel/air mixture as they climb (the VW Beetle generally didn't get too high above sea level, and when they did the local mechanic could adjust the mixture in the garage because those cars would probably stay at a relatively high altitude for most of their life - aircraft have an annoying habit of climbing and descending a lot, so either a manual mixture control or an altitude-compensating carburetor is necessary).

So what accounts for the price difference? Three things: FAA Certification, Volume, and Liability.

FAA Certificated engines cost quite a bit of money: The manufacturer needs to thoroughly document their design and manufacturing practices, and ensure the engine meets the design requirements and can pass the tests described in FAR 33. Doing (and documenting) all of this to the FAA's satisfaction is not a small burden, and it adds to the cost of the final product.

Volume is the next problem: As a reward for complying with Part 33 and getting your engine certified you now have the opportunity to sell your engine. To a very small market. There are far fewer piston aircraft than cars, and although piston aircraft engines are often "worn out" over the life of an airframe most owners overhaul their engines rather than replacing the whole engine outright. As a result the volume of new engine production is relatively low (and with relatively brisk competition in the overhaul market the manufacturer isn't even guaranteed a substantial amount of that business). As with any other product, when volume is small price goes up to allow a profit.

Liability is the last (and probably largest) factor affecting pricing: Jane Q. Pilot is flying along in his brand new just-off-the-production-line Cessna with her two kids and the family dog when the engine fails. She is unable to make a successful landing, and everyone dies, whereupon her bereaved and distraught husband John immediately sues the mechanic who last worked on the plane, Cessna (who made the airframe), and Lycoming (who made the engine).
Being ready to deal with this kind of high-profile and high-cost event requires a substantial legal team (the cost of which is built into each engine sold), and as the manufacturer is accepting a substantial risk the price gets bumped a bit more to provide a balancing reward (profit).

So to answer your bullet-pointed questions which I largely ignored in the explanation above:

Are aircraft engine parts expected to be less likely to fail?
We may have this expectation given the price tag, but in reality they're probably about as reliable as any other well-maintained air-cooled 1960s engine design.  A modern car engine has a number of design and technological advantages over the typical piston aircraft engine, and if we equipped them with dual independent ignition systems and gave them the kind of maintenance aircraft engines get they may well beat aircraft engines in terms of reliability. (Of course a modern car engine also weighs a lot more than a typical aircraft engine, so some money would have to be spent making it lighter without sacrificing that reliability.)
What is done to allow the engine to function at extreme temperatures / altitudes / air densities?
Surprisingly little: The addition of a mixture control for the carburetor, dual independent ignition systems, and a healthy weight consciousness pretty much covers it.
Do changes have to be made to allow a piston engine to function while upside down (in a roll)?
Yes (the fuel and lubrication systems for need to be designed to handle zero / negative G loads for an extended period of time), but your typical piston aircraft engine isn't designed to function while upside down: Aerobatic aircraft engines are a slightly different beast, and they cost a little more than their non-aerobatic counterparts.
What components are different on an aircraft vs automotive piston engine (magnetos vs. spark plugs, oil system)?
The biggest difference between a 1960s VW engine on a classic Beetle and a 2015 Lycoming O-320 is the dual magneto ignition system. The rest of the parts are largely identical, or at least analogous: Spark plugs look like spark plugs, cylinders look like cylinders, carburetors look like carburetors, etc.
Aircraft engines are also designed for component swaps: Cylinders can be easily unbolted and replaced for example, as can the magnetos, the oil pump, the carburetor, the starter, etc.


Is it legal for an SEP airplane to fly above its service ceiling? Let's take a Cessna 172R for example. According to the POH this airplane has a service ceiling of 13,500 ft.

I know that the service ceiling is the maximum altitude where a 100 foot per minute climb can be maintained.
So that would mean that it can technically continue the climb and fly well above his service ceiling, until full power is required for level flight (Correct me if i'm wrong here).

My question is, besides the physical barrier, is there any regulations that would prevent and aircraft to fly higher than his certified service ceiling?

You didn't say which country you're asking about, but in the US it's legal. Your definition of service ceiling is correct, and there's no regulation that I know of that requires you remain below it.

The only clear case I can think of would be if the POH says that the service ceiling is an actual limitation and you shouldn't operate above it. Exceeding limitations in the POH is a violation of 14 CFR 91.9(a):

  Except as provided in paragraph (d) of this section, no person may
  operate a civil aircraft without complying with the operating
  limitations specified in the approved Airplane or Rotorcraft Flight
  Manual, markings, and placards

The AIM 5-3-3 requires you to report to ATC if you can't maintain a 500ft/min climb rate, so I suppose that not doing that could get you in trouble somehow. But there's no actual regulation, as far as I can see.

There are other, contrived scenarios that you could invent. If exceeding the service ceiling would require specific equipment or training that you don't have, then you could be in violation of various regulations, but that isn't because of the service ceiling itself.

And finally, there's the catch-all 91.13:

  No person may operate an aircraft in a careless or reckless manner so
  as to endanger the life or property of another.

If you do operate above the service ceiling and something goes wrong, then the FAA could bust you on that. Trying to get over mountains at or close to your service ceiling could be an example.


What currency requirements exist specifically for Commercial and ATP pilots that a Private pilot wouldn't know about? Besides a different medical certificate, what other currency requirements do commercial and ATP pilots have to contend with that a private/instrument pilot would not?

Autoland currency

If equipped with autoland, the flight crew will have some requirement to use the system, or else autoland operation in real CAT III weather, where autoland is required, will be prohibited. For many types, this also applies to the aircraft itself.

Currency is satisfied by conducting a successful autoland in any weather, so in periods of good conditions, autolands may be practiced during normal CAT I or CAT II approaches. Crews can also do this in the simulator. All autoland use is reported to the company so they can track currency.

It varies by airline policy and aircraft type, but typical requirements may be one every 30 days, one every 90 days, or 2 or 3 landings between 6 month sim checks.

Some airlines will put a movable placard on the flight deck as a reminder to crews what the status of the aircraft is, e.g. you will see "CAT II" or "NO AUTOLAND" when the system is faulty or not current.


When and how is CPDLC established? On a typical commercial trans-Atlantic flight, say from Frankfurt (EDDF) to New York Kennedy (KJFK), on a typical airliner (B777, A380, B787, etc.), when are Controller–Pilot Data Link Communications CPDLC established?

Is it generally before take-off, or just during the flight?
Is it only used during oceanic crossings, or for continental flights, too?
Will ATC instruct the pilot when to use CPDLC and when to revert back to voice communications?

Using CPDLC makes life easier for pilots so we typically use it whenever it is available and logon shortly after takeoff.

When departing Frankfurt there is no rush as CPDLC is not available until crossing into Maastricht Radar. Continental USA does not have it so you lose CPDLC after Moncton Center.

ATC will often remind you, or ask you to logon if you have forgot as it makes life easier for them too. Where VHF is available we usually use a combination of voice and CPDLC.

Over the ocean, out of VHF range, we have to establish HF radio contact with Shanwick or Gander radio and do a Selcal check to insure we have a backup communication method.


Why is the DC-9-80 ("MD-80") prohibited from taking off with a flap setting between 13 and 15 degrees? A bit of digging into the 7Z9363 accident investigation has brought up some interesting information regarding the DC-9-80 ("MD-80")'s flap system:

Flaps may be positioned in any of the six permanent detents in a 0 to 40-degree range by movement of the Flap/Slat Handle. The authorized flap settings for takeoff in the MD-83 were 4, 6, 11, 15, 17, 20, and 24.73 A “Flap T.O. Sel Wheel” on the center pedestal would allow the pilot to further position the flaps from the position selected by the Flap/Slat Handle position anywhere in the 0- to 13- and 15- to 24-degree range.74 This was used to set the final takeoff flap setting, as determined
by the runway analysis review for the airport/runway.
[...]

[...]
74The Ameristar Air Cargo MD-83 COM, Limitations, page 1-24, stated “Flaps (AFM): Do not use flap settings between 13 and 15 degrees.” [Operations Group Chairman's Factual Report, NTSB docket DCA17FA076, page 32, my emphasis.]

and

4.1.3.1 Flaps
4.1.3.1.1 System Description
The aircraft has an inboard and an outboard flap on each wing. The flaps are mechanically controlled and hydraulically actuated. The crew moves the flap lever to the appropriate detent depending on the flight condition (i.e. take-off, landing). The flap lever has fixed detents at UP, 0, 11, 15, 28, and 40. The lever can also be positioned in one-degree increments for takeoff settings using the Dial-A-Flap from 0 to 24, except for a small do-not-use range at 14. Through a series of cables and pulleys, control valves are exercised and provide hydraulic pressure to the flap actuators to extend or retract the flaps. [Systems Group Chairman's Factual Report, NTSB docket DCA17FA076, page 59, section headings bolded in original, other emphasis mine.]

Reinforcing this prohibition, the DC-9-80's takeoff-flap selector wheel has a yellow "DO NOT USE" label covering the space between the 13-degree and 15-degree markings:

(Image originally by the National Transportation Safety Board [it's on page 32];1 cropped and red-ovalled by me.)
Why does the DC-9-80's flap system come with a prohibition against using flap settings between 13 and 15 degrees for takeoff?

1: The underlying photograph was taken by NTSB personnel, and the red arrow was added by the NTSB to point out the selector wheel in question.

When the FLAP/SLAT handle is in the 0° to 13° range, the slats are in the mid-sealed position. The slats will be in the extended position whenever the FLAP/SLAT is in the 15° to 40° range. The range between 13° and 15° is the DO NOT USE range.[1]

Given the above and the analogue nature of the input (dial-a-flap), between 13 and 15° the slats are very likely not to settle on a position.

(...) with the flaps flap/slat control lever in the cockpit below flaps 14°, the slats extend to their intermediate position (MID); and with flap/slat control lever positions above flaps 14°, the slats are fully extended (EXT).[2]

In other words:
$$0° \le \text{slat}_1 \lt 14°$$
$$14° \lt \text{slat}_2$$
What happens at 14°? Simply "Do Not Use". The slat is both alive and dead.
Chronology of Douglas / McDonnell Douglas flaps/slats for context:

EIS Year
Plane
T.O. Flaps
Slats

1959
DC-8
fixed detents
slots (with an O);[a] doors opened when flaps extended

1965
DC-9-10
fixed detents
no slats

1967
Rest of the Original DC-9 Family
fixed detents
manual slats; separate lever

1971
DC-10
dial-a-flap (patent)
manual slats; separate lever

1980
MD-80
dial-a-flap
automatic flap-based three-position[b] slats (leading to the switch point at 14°)

1990
MD-11
dial-a-flap
automatic slats having only one extension position; slats stow button

1995
MD-90
dial-a-flap
same as MD-80

1999
717 (MD-95)
dial-a-flap
automatic slats having only one extension position

a: the DC-8 slots failed to produce the desired pitch-down on the DC-9 during development; tests revealed it was due to the lack of engine pylons; further experiments led to the invention of mini-pylons – the vortilons[4]
b: counting the retracted position
How can the narrow-body MD-80 be compared to the much larger tri-jet MD-11? The underlying high-lift system is practically unchanged since the 60s:

The DC-10 models utilize the DC-9 high-lift technology, and the MD-11, being a derivative of the DC-10, is very similar to it. (...) All its airplanes today, the MD-80s, MD-90s, and MD-11s are derivatives of the DC-9 and DC-10 airplanes, and they use their almost-30-year-old high-lift system technology with few changes.[3]

1: MD-80 FCOM
2: Report A-032/2008 – Accident involving a McDonnell Douglas DC-9-82 (MD-82) aircraft
3: Peter, K. C. "High-Lift systems on commercial subsonic airliners." NASA Contractor Rept 4746 (1996).
4: Shevell, Richard S. "Aerodynamic anomalies-Can CFD prevent or correct them?." Journal of Aircraft 23.8 (1986): 641-649.


Shock wave on airfoil I was wondering the other day, during the trans sonic regime, when the velocity over the airfoil becomes supersonic,why does the shock wave standing on the airfoil moves downstream when the free stream velocity is further increased?

With a higher flight velocity (still subsonic), the supersonic pocket on the upper side of the wing starts earlier and takes longer until it collapses into the shock. That is quite normal, as the speed over the whole upper wing is increased with increasing flight speed.

Think of what happens at the extreme case of accelerating flight speed towards Mach 1: Now the shock will move towards the trailing edge with increasing Mach number and will stay there once the flight speed is above Mach 1 (NOTE: This is valid only for straight wings; correct the Mach number upwards for sweep effects).

Things become nasty when the shock interacts with lift creation and starts to fluctuate back and forth - this creates a buzzing sound and might even cause flutter. The mechanism is that the stronger shock causes flow separation and lift loss, which in turn shrinks the shock, which allows lift to recover so the shock grows again. With the growth, the shock moves back and jumps forward when it becomes weaker. This back-and-forth jumping of the shock creates not only a fluctuation of lift, but also of pitching moment.


What is the difference between BHP (brake horsepower) and HP (horsepower)? So far as I know, brake horsepower (BHP) and horsepower (HP) are the same.  But some books tell me that the two concepts are totally different.  What is the difference between BHP and HP?

For machinery that involves power transmission via shafts and gears, they are the same- and the actual term is brake (not "break") horsepower, because the apparatus used to measure the horsepower output of a machine is called a brake dynamometer.

For turbomachinery like jet engines where thrust is generated by movement of air, the concept of brake horsepower can't be applied- except in those cases where the turbine drives a propeller on a shaft. In these cases, the turbine's output shaft can be attached to a dynamometer and its horsepower output measured- and the result is quoted as shaft horsepower.


How does maximum speed vary with altitude? Question: How does a commercial jetliner's highest possible groundspeed vary with altitude (assuming wind=0) ?

My understanding is that drag decreases with altitude, therefore maxspeed increases with altitude.

This is also what Cpt. Simon Hardy, a B777 instructor, says:

  « Aircraft [referring to airliners] go faster at altitude than at low
  level. At sea level the aircraft [referring to a B777] can only do 330
  kn. And at altitude, 30.000 ft, it can do Mach 0.86. So it's a sort of
  sliding scale – as you descend, you get slower. » (source)

But today I read exactly the opposite on an aviation blog, which I found curious:

  « When a plane gets so high, you have to fly slower, since the speed of sound (and hence true airspeed for a given Mach number) decreases with altitude. » (paraphrasing, source)

  « Real basic point: You’re flying higher, you’re flying slower. You want to go fast […] you just fly lower. » (source)

... so which is it ?

The perfect answer for me would ...
• include a graph (Y: altitude, X: maxspeed)
• include citable references

EDIT (in response to the comments below):
I specified maxspeed as the highest possible groundspeed (assuming wind=0), although I'd rather prefer not to make that distinction, because from my experience this complicates the issue more than necessary: Of course the altitude will affect the different types of speed more or less, but isn't it nonetheless possible to make an approximate statement like "higher=faster, lower=slower" and explain why that is?

EDIT2
For a concrete example, let's assume:

aircraft = B777
wind = 0 km/h (for argument's sake)
weight = typical weight of a B777 ~45min into a 9 hour long haul flight
aircraft has already reached cruising altitude

If at that point the pilot wanted to "get away" as fast as possible (let's say from waypoint IGARI), what altitude should be chosen?

Is the quoted blog post correct in saying that at an usually high altitude, the plane would fly slower, therefore it would have to go lower to fly faster?

This question isn't clear because "speed" means different things to different people, and this is also engine specific.  Every aircraft will have a different speed vs altitude profile.  In general...

Mach will go up, as you increase in altitude.  This is because the lower density air lowers the speed of sound (in an absolute sense).

True airspeed will go up as you maintain a constant indicated airspeed.  Conversely, maintaining a constant true airspeed will increase your indicated airspeed as you descend.

Normally, a jetliner should not be seeing true air speed at sea level.  For jetliners, even if your engines are good enough to get you there, the aircraft has an indicated airspeed structural limit that keeps you from accelerating.  You can keep the same speed (at structural limit) through higher altitude, which increases your TAS.

There is a chart here which should help show the relationships between altitude and speed:

A simplified chart for determining Mach number and true airspeed from airspeed-indicator readings:


Does bi-wings create essentially double the uplift as single wings? This puzzles me a bit, and I cannot find the answer anywhere.
Does bi-wings create essentially double the uplift as single wings?

In general, no it does not.

If by bi-wings you mean a biplane then the airflow above the lower wing and the airflow below the upper wing interfere with each other and lift is lost. The loss is kept acceptable if the gap is at least 1.25 times the wing chord, but it is still maybe 20% depending on the design. The advantage of the biplane is that it is light and compact, which at slow speeds can more than compensate for the loss of lift.

If by bi-wings you include tandem wings, then the wake of the fore wing creates a disturbed airflow over the aft wing, reducing its efficiency. This can be minimised by mounting the fore wing low and the aft wing high, but that introduces the risk of superstall at high angles of incidence. The advantage of the tandem layout is that it allows a large range of positions for the centre of gravity, giving high operational flexibility.


How does dropping ordnance affect the weight and balance of the aircraft? During a mission, military aircraft often shed a lot of weight from takeoff to landing.

An F-15C (empty weight: 28,000 lbs) carries an internal fuel load of 13,455 lbs (almost a third of take-off weight not including pilot and ordnance).

A cargo plane like the C-17 may perform a combat off-load while airborne.

Meanwhile, the aircraft I worked on in the army were deadlined whenever 1% of total aircraft weight was removed, requiring either the part to be reinstalled or a total reweigh prior to next flight.

Operationally speaking, how are these "fat burning exercises" completed without jeopardizing crew and equipment due to shifting weight and/or CG?

the aircraft I worked on in the army were deadlined whenever 1% of total aircraft weight was removed, requiring either the part to be reinstalled or a total reweigh prior to next flight.

That's for internal equipment, which will affect the empty CG data.

All aircraft lose weight during a trip. Aircraft designed to lose a lot of weight all of a sudden ( C-5 airdrops, B-52 carpet bombing ) have the details and limits calculated during the design. In the case of bombers, the ordinance will be hanging near the wings and will have a specific release order, usually back to front.

A tailgate aircraft dropping something will also have very specific procedures based on the weight of the pallet going out the back door. If it's delivering pizzas the procedure is along the lines of "whenever, dude". If it's a tank, it has to be positioned and locked down until the moment of release.

The above is very noticeable by the flight crew.

If the load stays (or gets stuck) on the back ramp, you're usually done. I used to skydive - 10 people on the back end of a smaller tailgate like a Casa can and do cause the plane to stall. The rules were stay at the front until it's your turn, then position and exit in a prompt manner. If the buzzer goes, let go NOW. Unlike a cargo plane, jump planes have 12,000 feet to recover from the stall.


Does lift equal weight in a climb? This subject keeps coming up in the discussions and questions such as this one, which asks if lift equals weight in level flight. Good answers there, pointing out that upwards force has many sources. But also some that need clarification.

It is also mentioned at several places on this Aviation SE site, in question & comments, that lift always equals weight if the aeroplane is not accelerating upwards or downwards, since only an acceleration requires extra force according to Newton.
With zero wind, lift is always defined as the force perpendicular to the flight path, but gravity does not tilt with the aircraft axes. My question therefore is also about the sum of all vertical forces: in a steady climb, is the total upwards vertical force from all sources (wing, tail, engines, fuselage) larger than, or equal to the weight of the aircraft.

If larger: please quantify.
If equal: please explain why.

Addition
An answer.

It depends on exactly how you define "lift" and "weight". You might say intuitively that lift is all the forces acting on the aircraft in the upward direction, like this:

In this case, lift must equal weight, otherwise the aircraft would be accelerating. That is, it's rate of climb would be changing.

But it's more usual to define lift this way:

Here, lift and weight are equal in magnitude, but in different directions. Of course lift doesn't need to be equal in magnitude: it can be adjusted by the angle of attack. But let's suppose lift is equal to weight and see what happens.

Let's do all our calculations with Earth as the frame of reference1. It's useful to decompose lift into a sum of vertical and horizontal components so we can analyze the horizontal forces and the vertical forces separately:

Comparing the vertical component of lift with weight, we can see they are not equal:

Considering only the vertical forces drawn here, there is a net downward force on the aircraft. So why then is the rate of climb not decreasing?

A similar transformation happens to thrust. In a climb, thrust provides an additional upwards component. And of course we must also consider drag. Point being in a steady climb, lift (by the conventional definition) is not equal to weight, but the sum of all the vertical components of lift, thrust, and drag do equal weight.

Let's add an arbitrary amount of drag, and enough thrust to balance the vertical forces.

Now the vertical forces are balanced, but the horizontal forces must also be balanced if we want stable flight. Adding all the horizontal forces in my drawing, there's a net force to the left. So this aircraft may be maintaining a steady rate of climb at this instant, but it's losing speed and probably headed for a stall.

Remember, we initially set lift equal in magnitude to weight, and this is what happens. Without changing the direction or magnitude of lift, there's no solution that results in stable flight.

Therefore, a climbing aircraft requires less lift. To maintain this direction and velocity, this pilot must reduce lift by reducing the angle of attack, and increase thrust such that the vectors add to zero and there's no net force on the aircraft. Reducing lift will also reduce drag.

1 Any other frame of reference could work. For example we could use the aircraft as the frame of reference, which would mean lift is always up, but weight would change direction.


What is the real impact of biofuels on aviation? I have seen tons of initiatives about using biofuels (like the ASTM D7566), but it is operative at large scale?, there is background info about demonstrative flights, but I don’t see a manufacturer or airline that is making use of the biofuel in regular basis.

It is a viable way of operate or it is a nonviable idea?

The "real" (or at least ideal) impact of biofuels in aviation is a reduction in CO2 emissions. When they burn, they produce exactly the same amount of CO2 as fossil fuels, but, all this CO2 came from CO2 that was already in the atmosphere. So it's only putting back what was already there:

  From the standpoint of human-released carbon dioxide, other greenhouse gas emissions, and contributions to climate change biofuels have one large advantage over gasoline, diesel and other fossil fuels: The feedstocks for biofuels are part of the above-ground carbon cycle. Unlike petroleum or coal, the soybeans, corn, switchgrass and other biological materials that are made into biofuels are not dug up from underground, nor do they release long-stored carbon as carbon dioxide into the atmosphere when burned. Instead, when biofuels are burned, carbon dioxide they recently captured is release back into the atmosphere.

This is sometimes claimed to mean biofuels are carbon neutral. For example, it's claimed here a 95% reduction occurs. But it's a bit more complex than that:

  Producing biofuel with crops like corn often requires converting land from food to fuel production or destroying natural ecosystems that provide valuable services, including carbon sequestration. Crops also require fertilizers, pesticides and large amounts of water, as well as machinery for planting, growing, harvesting, transporting and processing. If forests are cleared for fuel crops and if the entire lifecycle of the fuels is taken into account, biofuels don't always reduce overall greenhouse gas emissions. Palm oil, used for biodiesel, is especially bad, because valuable carbon sinks like peat bogs and rain forests are often destroyed to grow palms.


What does "short parked" mean? Recently, when flying (as a passenger of a regular flight) from Stockholm/Arlanda, there was quite a long bus ride from the gate to the aircraft, because the latter was "short parked", according to the announcements at the gate. What does "short parked" mean? "Faraway parked" would have made more sense from a passenger point of view.

"short parking" seems to be an informal European term for "short-term parking".  So it's referring to the time a vehicle is parked, not the distance.

If I heard it about the location of an airliner, I'd think they meant that the gate areas were full and it had to be put somewhere temporary (and inconvenient) this time.


What damage can occur and what penalties will you face for flying a quad rotor into a restricted airspace? I live near the Cleveland International Airport. I have a Quadrocopter and the fence doesn't seem to be very high. I could probably fly my quadcopter into the airport. Is this legal? Can I crash a plane with it? Is this a new terrorist attack vector? Will the airport security try to jam radio signals or something?

This is just a hypothetical question. I do not intend to wreak havoc and crash planes.

The legal issues are covered in another question. The FAA doesn't currently regulate recreational model aircraft operations, which includes quadcopters.

Were you to actually fly it over the fence, you could be charged with trespassing. If you had any intent to cause harm, other charges might apply (up to attempted murder if you were trying to bring down an airliner).

  Can I crash a plane with it?

Not likely. If you flew the quadcopter into a jet engine intake, you might be able to shut down the engine (similar to ingestion of a bird). This would really annoy the flight crew but would normally not result in a crash. A strike in any other place is probably going to merely dent something on the plane, and utterly destroy your quadcopter. For a small plane, shattering the windshield is a possibility, and this would be a serious hazard that could cause a crash, but is quite unlikely. Without some kind of advanced guidance system, it's going to be very hard to hand-fly the copter into a plane at all, let alone precisely target a vulnerable point.

The bottom line, though, is don't do it.

  Is this a new terrorist attack vector?

Maybe! The use of unmanned aerial systems by terrorists is a subject of concern and research in the defense community. The RAND Institute has published a whole book about it.

Drones are already being used by drug cartels to smuggle drugs across borders. There have also been some high-profile incidents where terrorists were able to tamper with, and in at least one case eavesdrop on, a U.S. military drone by obtaining and decoding its live video feed. I don't know of any publicized instances of someone intentionally causing damage with a UAV or model airplane, but I'm sure the terrorists are thinking about it.


What is the best way to remove stuck screws from Cessna wing tank cover? We need to replace the fuel tanks on a Cessna 150 and the screws holding the wing cover won't come out. They are just frozen in place. I think that the paint also may be working against us: Getting the paint out of the screw heads has been difficult. So far no screw heads have been rounded off.

Have any of you had this problem before?
Also, how is the female part under the skin made? Is it like a j-clip nut that can be replaced, or is the nut part a pressed into the frame?

First the standard disclaimer: If you're in the US and you're not a licensed A&P mechanic, take the plane to your mechanic. (If you're working with your mechanic on this job and helping out by removing the cover plates you've reached the point where it's time to go tap them on the shoulder and ask for help, because the steps to remove frozen screws can do serious damage if you mess up).

Disclaimer over, on with the answer:

Frozen screws on infrequently-opened access panels are pretty common, and there are a few ways to get them free. You'll note I've drawn a line in this answer: Anything above the line you can probably do on your own, if you have to move to the techniques below below the line let your mechanic do the work (at least until you're confident you can do it without messing up).

Step one for removing a frozen screw is to make sure they're not painted in place - you'll need a paint cutter (your mechanic probably has one) and/or an x-acto knife. Cut the paint around the head of the screw using the paint cutter (or the x-acto knife and a very steady hand), and use the x-acto knife to clean out the screw head so your screwdriver can get a good grip.
Sometimes this is all it takes and the screw comes out on the next try. If not, keep going.

Step two for removing a frozen screw is to use a "penetrating lubricant" - Kroil is commonly used, and Corrosion-X can also do a good job (more about that later). Put a little on each screw and let it work its way into the threads for a while (15 minutes is a good starting point), then try to break the screw loose again. It may take more than one application of penetrating oil to do the job.
Two notes about penetrating oils: One, they need to be able to get to the threads in order to work (that's why step 1 involves cutting the paint). Two, don't use one that contains silicones (they will embed in the metal grains and make future paint jobs a major pain).

Hopefully the penetrating oils will work, otherwise you're going to move on to more destructive processes.

Step Three involves getting a little more aggressive with the screw in question. Typically by the time you get here you've at least slightly damaged the head trying everything else, so grab a grinder or dremel and cut a flat line into the screw head. This will give you purchase for using a regular (flat-blade) screwdriver, which will hopefully let you apply more torque to the screw. You also want to keep applying penetrating oil while you do this.
The trick to Step Three is cutting the head deep enough that the blade won't cam out, but not so deep that you compromise the head-to-shank connection in the screw and snap the head off when you try to turn it. This is a bit of an art, so it's best to have your mechanic step in at this point. If you screw up here you're on to step four, and you don't want to get to step four. . .

Step Four is drilling the f#!@ing screw out. When all else fails you take a drill right through the screw, demolishing it. Your mechanic almost certainly has appropriate drill bits for this, and the skill to do it without seriously messing up the screw hole / nut plate / cover panel / surrounding skin.
Even a skilled mechanic may damage rivnuts or nutplates drilling out a screw, and will then have to replace the damaged piece before a new screw can be inserted.

Avoiding the problem in the future

Once you get the screws out (and your mechanic will - eventually - mechanics always win when screws pick a fight) there are some steps you can take so the next person who has to get this panel off doesn't suffer as much as you did.

Don't paint the screws/panel in place.
If you damage the paint getting the screws out touch it up and let the touch-up cure before you put the panel/screws back on so the paint isn't acting as a glue holding it all together.
Also for the love of sanity don't paint the screws - See #2, and if you repaint the plane do it with this panel off.
Replace the standard screws (probably cad-plated steel) with stainless steel screws.
Stainless screws will corrode, but they're much slower at it than the cadmium-plated steel screws (the cadmium plating that keeps them from rusting in place gets rubbed off as you screw them in). Stainless screws also don't need to be painted like the cadmium-plated ones do, so you won't have to pick paint out of the screw head.
Apply a corrosion treatment before reassembly.
Blast the nutplates/rivnuts/etc. with Corrosion-X or similar - also try to hit any other areas you can reach while the panel is open and things are apart.
Apply a corrosion treatment to the airframe regularly.
Less important if the aircraft is kept in a hangar, but for aircraft tied down on a ramp having a corrosion treatment done every few years will help keep screws from freezing in place.


Would supersonic bi/tri/multiplane wings have less lift interference drag than a subsonic version? Biplane wings interfere with each other, reducing the total lift often to about only 20% more than a mono wing of the same chord and span.

But at supersonic speeds - say, Mach 2, where Mach angle is 30 degrees, the wings (now provided with supersonic airfoils, before anyone asks) would have to be 0.5 chord-lengths apart for their shockwaves to interfere.

So, am I correct in saying that for a given chord-length separation, drag due to airfoil interference on vertically stacked multiplane wings interference decreases with Mach number?

Amazingly, at supersonic speeds it can work the other way. In the Busemann biplane the shock waves interfere in such a way as to actually reduce drag and also to reduce the sonic boom. Wide enough separation to avoid interference would actually increase supersonic drag.

See for example:

Wu, Jamieson and Wang
Kusunose, Matsushima and Maruyama


How do diffusers turn velocity into pressure? There are many resources that give explanations for the behavior of nozzles and diffusers. But at the crux point they all say, "Velocity goes down and pressure goes up." As if that doesn't warrant any deeper explanation, or as if it were just a law of nature.

To me, the reason behind this energy transfer isn't obvious.

To maintain a constant mass flow rate, $\dot{m}=const$ , through a small inlet and a large outlet you would need a deceleration of the flow. To decelerate a flow requires a force, $F=ma$. Forces interactions are equal and opposite so the fluid would exert a larger force, relative to the inlet, if forced to slow down. But what is the origin of this decelerating force? Why does this geometry increase the $\frac{F}{A}$ of the molecules that pass through it? I understand the energy conservation, but how is this behavior explained in terms of force interactions?

It's like you asked how an electric motor worked and someone said, "By turning electric energy into rotational motion." and you said, "How?" And they just repeat, "By turning electric energy into rotational motion." Energy balance just isn't descriptive enough.

While we wait for a probably better answer, here's my tentative.

You state that you understand the concept of constant mass flow. Let's for a moment write the mass flow properly:

$$\dot{m} = \rho A v$$

on the left we have the mass flow $\dot{m}$, on the right we have the density $\rho$, the area $A$, and the velocity $v$.

If we want $\dot{m}$ to be constant while changing $A$, we need to change $\rho$ and $v$ accordingly. In these scenarios $\rho$ is taken as roughly constant, leaving only the velocity as free variable. While this might be more true for liquids, it is not too far from the reality also when air is involved (although you might observe minor variations in density).

Where do the forces come from? The walls of the duct and the fluid downstream (when decelerating, the fluid that is already at a slower speed will effectively work as a "wall" for the incoming fluid) or the fluid upstream (when accelerating the incoming fluid will push the rest of the fluid like an extruding piston).

In other terms the required energy comes from the pressure differential (the faster fluid has lower pressure).


Where is the 36 month ATPL theory exam validity before CPL/IR test listed and described? The provider of my EASA Integrated Training Course states that my ATPL theory exams are only valid for 36 months before a CPL or IR skills test.

Where is this regulation listed and described?

Additionally, is this from the date the ATPL theory series is completed, or when the earliest ATPL exam is completed? Finally, do both the CPL and IR skills tests both have to be completed within 36 months, or, just the CPL?

I don't know much about EASA regulations, but this seems to be a reference to Part FCL.025(c)(1):

  (1) The successful completion of the theoretical knowledge
  examinations will be valid:
  [...]
  (ii) for the issue of a commercial
  pilot licence, instrument rating (IR) or en route instrument rating
  (EIR), for a period of 36 months;
  (iii) the periods in (i) and (ii)
  shall be counted from the day when the pilot successfully completes
  the theoretical knowledge examination, in accordance with (b)(2).

Having said that, (c)(2) gives a much longer validity period for the ATPL exams:

  (2) The completion of the airline transport pilot licence (ATPL)
  theoretical knowledge examinations will remain valid for the issue of
  an ATPL for a period of 7 years from the last validity date of:
  (i) an
  IR entered in the licence;
  or (ii) in the case of helicopters, a
  helicopter’s type rating entered in that licence.

My understanding of that is:

Your IR theory exam is valid for 36 months from the date of the exam
Your ATPL exams are valid for 7 years from the date you receive your IR (although the wording is ambiguous, in my opinion)

It's possible that your provider is combining those two points somehow. The easy thing to do here is simply ask them to explain their statement in more detail and include a reference to the regulations.


Can surface roughing effects on an airfoil Reynolds number be quantified? I am building balsa free flight gliders with a chord of 0.10 meters and a velocity of around 3 meters per second.  This works out to a Reynolds number of around 15,000.

The wings are around 1 meter in span, and are made with the wood grain running lengthwise.  They are thin undercambered (no bottom covering) with maximum thickness of 7 mm at 30% of chord from leading edge.

Because of the roughness of the unfinished grain, is my Reynolds more like 50,000, or am I still down in the range where a flat plate might be better?

Roughness has no influence on the Reynolds number. It will, however, help to trigger a laminar-turbulent transition. That is the reason for dimples in golf balls. Also, roughness will increase the friction drag in turbulent boundary layers.

Flat plate friction diagram (picture source). Note the horizontal lines: They show that drag does not drop any more with increasing Reynolds number once the surface roughness exceeds a certain value. Roughness is given here relative to the chord length as $\frac{\epsilon}{l}$, with $\epsilon$ being the mean height of the roughness and $l$ the chord length.

The diagram only starts at Re = 100,000, so it is clearly outside the range of your application. If you sand your wooden surface with fine grit sandpaper, I don't expect that the remaining roughness will increase drag. At those Reynolds numbers it might be advantageous to add a trip wire in order to induce a transition to turbulent flow – see the golf ball example.


What units are used by western airliners? Many different units can be used to designate the same things.

Degrees Celsius va Fahrenheit
Altitude in feets or meters, ...
Sometime different units measure the same thing but have different semantics or measure very similar things:
Speed can be measured in Km/h or Mach number.
Fuel can be measured in Kg or liters.

Some units can be also displayed relative to some other ones (ex we have n min of fuel left)...

What units are typically used in aircraft nowadays.

I'm particularly interested in:

Speeds
Pressure
Altitude
Distance
Weight
Volume
Position

Let's restrict the question to units displayed in the cockpit, and to Airbus or Boeing non military airplanes.

Airspeed, ground speed
Primary unit: km/h. Non-SI unit: knot.
In practise, knot is the main unit. At high levels, the Mach number is used, which is a measurement of speed relative to the local speed of sound.

Pressure
Pascal. Hectopascal is used for altimeter settings. In the USA they use inches of mercury.

Altitude
Primary unit: metres. Non-SI unit: feet.
In practise, feet is the main unit. Whether you say altitude or flight level depends on your reference air pressure.

Distance
Long: nautical mile. Short: metres. Vertical: foot.

Mass
Kilograms.

Volume
Litre or cubic metre.

Position
Latitude and longitude based on WGS84.

The above is according to ICAO Annex 5, which means that it is true for more or less all of the world. A few places prefer to deviate from the standard units, such as the USA, which uses a slightly different system.


Who activates the fasten seat belt warning on commercial flights? Who activates (and de-activates) the "fasten seat belt" warning on commercial flights? I would guess it is either the pilot in command (normally the captain) or the first officer (co-pilot).

If the answer is airline specific, then answer for American Airlines.

It's P1's decision, and P2's hand that moves the switch.
But, there's a really nice position of the switch, "Auto", which switches them on/off automatically based on some rules (which are usually passing through 10,000ft). Using the "Auto" position means that you can't forget them!


How to announce in an ATIS message that two parallel runways are in use? Suppose an airport has two parallel runways and aircraft can use any of them.

How would I announce in the ATIS message that both runways are in use?

By simply stating that both runways are in use.

For example, "arriving and departing runway 16 left and 16 right."


Can I fly through these military airfields' class C airspace? I am a low time private pilot now based in Pensacola. I’m a bit unsure how the Class C of PNS/NAS Whiting Field is handled. As you can see they all overlap. PNS is a civilian field while the others are military. If I was going to fly VFR to the northeast, can I fly through the Class C of Whiting field? I always get flight following when departing.

When entering Class C Airspace:

Since all the airfields are Class C you would need to contact the approach control prior to entering.  Approach control should be able to direct you appropriately from there.  Approach control would handle traffic at all three airports. If the military airfield does not want civilian aircraft to cross the field for any reason approach control will direct you around it.  If there is nothing going on at the military field then approach control could let you cross over the field.

When Departing Pensacola Field:

When departing Pensacola field you can request a Northeast departure through Clearance Delivery.  You could be granted the request to fly Northeast directly from the airport or they could make you fly East for a while then make a turn North to avoid the military airport.  Nevertheless you have to follow ATCs instructions whenever you are in Class C airspace.

Side Note:

It is fairly common that when you have military airfield close to a Class C airport, the class C airspace will be extended over the military fields as well so that one approach control would handle all the traffic and deconflict traffic for all of the fields.  A similar situation exists for the Tucson area where the Class C includes Tucson International and Davis Monthan AFB.


Will a diagnosis of psychosis ban me from getting my recreational pilots license or my private pilots license? I want to get my category 3 or 4 medical so I can either get my private pilots license or my recreational pilots license. I have been diagnosed with psychosis and am currently on Invega Sustenna (anti psychotic) to combat the condition.

My question is: will I ever be able to get my cat 3 or 4 ? I live in Canada.

Well, according to the CAA:

Class 1
(a)  Psychotic disorder
A history of, or the occurrence of, a functional psychotic disorder is disqualifying unless a cause can be unequivocally identified as one which is transient, has ceased and will not recur.
Class 2
Psychotic disorder
A history of, or the occurrence of, a functional psychotic disorder is disqualifying unless in certain rare cases a cause can be unequivocally identified as one which is transient, has ceased and will not recur.

Discussion on another forum suggests that generally speaking they will want the pilot to be off all psychotropic medication for a period of time (1-2 years) without any recurrences but they will generally allow a pilot to be on medication for depression.
I would recommend you work with an appropriate mental health expert in resolving your condition, so that you can be sure future episodes will not recur, you can then hopefully ascertain to yourself and to your medical examiner that your episode was transient, so that you can continue your pursuit of your PPL.
Remember in the worst case scenario (your condition does not pass), even if you cannot get a medical, you can still fly a plane. You just can’t solo. You can fly with a flight instructor or a certificated pilot. And you can fly a single seat ultralight with no certification. So you will still get to fly, don't worry.
Good luck, I'm sure you can do it.


Why there so many pitch control surfaces on the Piaggio P180 Avanti? Picture source.

I have seen that there is kind of sonic aircraft like B-1B Lancer that used elevator and canard or fins at the same time for pitch control. That quite understandable because it is fighter jet that required high precision control. There are another airplane that used canard but not elevator, like Tupelov Tu-144. But this Piaggio P180 Avanti is quite strange for me. It is equipped with elevator, canard, and also another additional device. I am not sure that propeller airplane needs what needed by the above B-1B Lancer.

Then my question are, what is that device (number 2 in the picture), what is that name, and what is that for? Are device number 2 and number 3 controllable?

Surface 1 is a  horizontal stabilizer with elevator, just the same as on any other aircraft with a T tail arrangement.

Surface 2 is called a rear strake or a tail fin. There is one on each side of the fuselage. They provide extra stability during operation at high angles of attack when the fuselage is disturbing the airflow to the vertical tail. They are not movable.

Surface 3 is a canard, providing extra lift. The canards on P.180 have a trailing edge flap. The flap is necessary to counteract the nose down trim of the flaps in the main wing. Without the canard flaps the elevator would not have sufficient authority to maintain adequate pitch control when full flaps are deployed on main wings.

Surfaces 1 and 3 have movable parts, but surface 1 is the only surface connected to pitch axis control of P.180.

Piaggio P.180 article on Flying magazine explaining design features (and a lot more).

Rear strakes- tail fins on Wikipedia


Yet another "Why aren't I soloing yet?" scenario Undoubtedly this question has been asked many times, but perhaps my situation is a little different than others. I'll try to be detailed but succinct:

I've accrued about 18.5 hours, 17.5 under the same CFI. I've checked off the 3 nighttime hour requirement (although my CFI said before my checkride we'll do more to get my nighttime pilotage skills improved), and 2 of the 3 required hours of XC, plus about one hour instrument time. Over the course of all this training time I've accrued 90 landings (my CFI loves touch and goes and we can do 10 landings in little over an hour). Yet still I'm not ready to solo. Now, I know I'm not the most proficient pilot he's seen, and perhaps I'm just average among the overall population, but 90 landings, and not including the hundreds of landings I've done on my simulator and countless hours around the patterns of my local airfield? Rarely do I have a hard(er) landing and some downright kiss that runway on or near centerline. Here's the other compilcation: My CFI is a one-man shop with his own planes, has logged 18,000 hours in his career and is a lifelong instructor, about 29 years experience as a CFI. If my CFI was part of some instructor mill at a flight school, I would certainly consider walking away or having a serious discussion with him at this juncture. However, since I respect his seniority it's creating a lot of cognitive dissonance. Am I missing something? Another little twist: he says I'm on a trajectory to be one of his 45 hour and done students (he has numerous students done in under 50 hours and an extremely low failure rate), so perhaps he's one of those people who solo people later after making sure things are absolutely positively perfect? Has anyone had an instructor who went about the process in this manner?

This question is pretty open ended.  As a CFI myself, I really couldn’t assess whether you are ready to solo or not until I have flown with you and seen how you are handling the airplane on takeoff, landing, and in the traffic pattern.

My general assessment standard for readiness to solo is to see the student exhibit solid knowledge and practical fundamentals for takeoffs and landings and the required airmanship needed to perform them down pat.  They can either correct for errors in the approach and landing or exercise good judgment when a go around should be executed.  Very rarely, if ever, do I need to provide technique guidance, verbally or otherwise.  The student may not yet be acceptable quality for a checkride, but the technique is solid, safe and the student is exercising sound judgment in ADM and risk management for airport operations, including go-around assessment and techniques, pattern spacing, accounting for the effects of wind, solid crosswind skills in light winds.

First off, we want you, the student, to be safe.  The last thing I want as a CFI is to grab a newspaper or turn on my TV and see an airplane crash in the news with my student’s name listed as a casualty.  Secondly the CFI is legally responsible for whatever you do on a solo flight he/she has authorized and their ticket can be on the line if anything happens and the authorities determine they are culpable.  We don’t want you guys going out and breaking the law, unintentionally or otherwise.  Third, we don’t want you to learn and ingrain any bad flying habits and techniques, particularly when sending you out on your own, so it’s best - and particularly during the pre-solo phase - that we route them out early.

Finally, everybody is in a rush to get the magic minimum number of hours to go for a checkride.  Or solo.  Or go on a cross country, etc.  We all have heard stories about people going from no experience to PPL in two weeks (drunks at a bar tell fanciful tales, too, BTW!).  We all expect to do this or better because every pilot thinks he/she is Sierra Hotel and wants to be better than the other guy.  While I can appreciate this, especially from a financial standpoint, keep in mind that that’s just the MINIMUM seasoning the FAA expects in an applicant.  Typically people are getting a PPL these days at around 70 or so total flight hours.  While the regulations provide guidelines for what an knowledge and practical skills an applicant should bring with them for a checkride, solo or any other phase of their flight training, the real answer is are they unconsciously competent at their airmanship to do it.  Like any human endeavor which requires motor control and practice we have good days and bad ones.  When your ‘bad day’ in the airplane is at or above the standards set for that phase of flight training, be it solo, checkride, or otherwise, you’re probably ready to pass.

I hope that helps.


What is the rationale behind very short distance flights? I was impressed to read here that some passenger airline routes are even below 60 km in length.

Even assuming that the passengers are already in the airport past the security check, probably a good bus could depart from the same gate and arrive to the destination gate in a very comparable time, as the plane still needs to taxi before and after the flight.

Why these short haul flights are reasonable?

Because air travel is the best option in those places.

The shortest commercial route in the world is between Westray and Papa Westray in the Orkney Islands, a distance of 1.7 miles.

If you see the list of short routes, almost all of them are between islands. That instantly rules out buses and the like unless a bridge is built, which in most cases is not commercially viable. One can use a boat or ferry, but in most cases, the sea may not be deep enough or calm enough.


Can anyone identify this Autogyro? I've found similar autogyros on the internet, but not this one. Most autogyros appear to have 2 cockpits and this autogyro only has one.  Although I have matched its angle-tipped wings with other autogyros, I cannot match the configuration of the landing gear.  It appears that each wheel has a vertical strut to the wing and then two bars in a triangular configuration that attach to a center bar about 12" below the fuselage. The only autogyro I've found that appears to possibly be the same is in this video, but the craft's make and model not identified.

              The video is from California but I'm assuming my photo was taken in Wisconsin. I sincerely appreciate your assistance.

It looks like a Kellet K-3, I believe...
Photo from 'Cierva Autogiros', by Peter Brooks.


How long is a climb leg in a step-climb cruise flight segment allowed to take, according to regulations (FAA/EASA)? I am working on a trajectory optimisation program for commercial, large aircraft, in which I want to incorporate realistic air traffic control regulations. One of the constraints I want to incorporate is that of ATC requiring step-climb cruise at specific flight levels.
Specifically, the hemispheric rule, though not universal, is a good example of how air traffic is managed by enforcing that westbound flights take even flight levels (FL020, FL040, etc.), whereas eastbound flights take odd flight levels (FL010, FL030, etc.).
So, aircraft should fly at one of these flight levels during cruise, when in level flight, thus resulting in a step-climb cruise, as opposed to a continuous-climb cruise profile. E.g., if an aircraft flying east starts its cruise at FL330, it would want to increase its altitude at some point for increased fuel efficiency. If cleared by ATC, it should climb to FL350 (maybe even FL370, if feasible), and so on.
My question is; are there any restrictions on how long the climb part between each of the level portions can take, at maximum (in terms of distance, time, or some other measure), and if so, what is the specific FAR/JAR or CS25 chapter that mentions it?
One could imagine that if such regulations aren't imposed, the climb segment in between level steps could take up so much time, theoretically, that effectively the cruise would still be continuous-climb. Although this is probably not too much of a problem in real life, it is a problem in my trajectory optimisation program. I.e., without proper bounds on the duration/length of this in-between climb leg, the solution always tends towards a continuous-climb solution by making the level flight portion short and the climb portion large.

The FAA's IFR handbook sheds some light on what they expect (page 2-48)

  If the pilot receives the term “climb at pilot’s discretion” in the
  altitude information of an ATC clearance, it means that the pilot has
  the option to start a climb when they desire and are authorized to
  climb at any rate, and to temporarily level off at any intermediate
  altitude as desired, although once you vacate an altitude, you may not
  return to that altitude. When ATC has not used the term nor imposed
  any climb restrictions, pilots should climb promptly on acknowledgment
  of the clearance. Climb at an optimum rate consistent with the
  operating characteristics of the aircraft to 1,000 feet below the
  assigned altitude, and then attempt to climb at a rate of between 500
  and 1,500 fpm until the assigned altitude is reached.

Its somewhat contradictory, first they say you can climb at any rate you want but then they say in the absence of any specific instructions you should climb at an "optimum" rate to within 1000 feet of your assigned altitude and then climb between 500fpm and 1500fpm.

This is specifically spelled out in the AIM with more or less the same language

  When ATC has not used the term “AT PILOT’S DISCRETION” nor imposed any
  climb or descent restrictions, pilots should initiate climb or
  descent promptly on acknowledgement of the clearance.Descend or climb
  at an optimum rate consistent with the operating characteristics of the
  aircraft to1,000 feet above or below the assigned altitude, and then
  attempt to descend or climb at a rate of between 500 and 1,500 fpm
  until the assigned altitude is reached. If at anytime the pilot is
  unable to climb or descend at a rate of at least 500 feet a minute,
  advise ATC.

Interestingly this adds the note that if you can not climb at 500 f/min then you should alert ATC. I would take this to be a minimum climb rate.

There is at least one permitted case of the drift climb that I know of. The Concorde operated above all other commercial traffic and aside from the SR-71 there really was no one else up where they were. As such once they passed a specific floor they were allowed to drift up freely as they burned fuel. This was, as far as I know unique to their operation and specifically permitted. They had a lot of other specific addendums due to their unique design.


Is there a way to register for updates on certain NTSB investigations? I would like to track the progress of an investigation of a particular accident, NTSB WPR18FA200.

Some areas of the FAA website (advisory circulars, for example) allow users to register to receive updates by email when these items change.  Is there a similar functionality available for users of the NTSB accident database?  If so, where do I find it?

No, the NTSB does not have such a service on their web site. In theory you could track the progress by downloading their database and parsing it to determine if status has changed, or by figuring out how their query system can be invoked, but those options require programming skills.


What is the total pressure of an air stream in motion? This question is from a French aeronautics exam so I translated as best I can but I suck at these terms in English. Anyways, can someone please explain this question to me because I'm just really confused by other explanations.

In an air stream in motion, the total pressure is equal to:

- difference between dynamic pressure and static pressure.
- sum of dynamic and static pressures.
- difference between atmospheric pressure and dynamic pressure.
- sum of static and atmospheric pressures.

The total pressure assumes that the is an isentropic evolution from air in movement up to an static state. The total pressure is the pressure at such state.

The way to compute this "made up" variable you need to compute the static pressure and the dynamic pressure (driven by the air speed).

So the answer is:

the sum of the dynamic and static pressure

But remind that is not "a real property" but more a way to measure the maximum pressure that can be achieved from a fluid in movement without adding extra energy.


Where can I find detailed information about ground lighting systems exist in aviation? While I'm learning jeppesen charts, I find a list of symbols related to lighting ground facilities, there are a lot of weird abbreviation such as:
Standard ALSF - 1/2, MALSR, SSALR, MALS, SALS, RLLS etc.?
I don't want someone explain all of these to me(because there are a lot of them), but give me source, where I can find them all with depiction and explanation.
Which of these are widely used, and why?

I know you said you didn't want to just be told what they meant, however in completeness of answering the question here are some abbreviations:

MALSR: Medium-intensity Approach Lighting System with Runway Alignment Indicator Lights
MALSF: Medium-intensity Approach Lighting System with Sequenced Flashing lights
SALS: Short Approach Lighting System
SSALS: Simplified Short Approach Lighting System
SSALR: Simplified Short Approach Lighting System with Runway Alignment Indicator Lights
SSALF: Simplified Short Approach Lighting System with Sequenced Flashing Lights
ODALS: Omnidirectional Approach Lighting System
ALSF-1: Approach Lighting System with Sequenced Flashing Lights configuration 1
ALSF-2: Approach Lighting System with Sequenced Flashing Lights configuration 2
CALVERT I/ICAO-1 HIALS: ICAO-compliant configuration 1 High Intensity Approach Lighting System
CALVERT II/ICAO-2 HIALS: ICAO-compliant configuration 2 High Intensity Approach Lighting System
LDIN: Lead-in lighting
REIL: Runway End Identification Lights
RAIL: Runway Alignment Indicator Lights

I found them here on wikipedia which has a nice entry on the subject


Why fuel left/right when C172 is secured? The C172 POH checklists say to set the fuel selector to "right" or "left" when securing the plane but "both" while operating the plane.

What is the point of changing the fuel selector when the engine isn't running? IOW, what practical (not legal) problems could it cause to leave it on "both" while secured?

[Edited to remove incorrect understanding of the vent connection between tanks, which is cleverly designed to not cross-feed fuel.]

It's pretty much to limit imbalance when parked on a slope, and if the tanks are full, stop fuel from the high side tank from forcing fuel out of the low side tank's vent or seeping out the fuel cap if it isn't completely fluid tight.

On the '68 Cardinal I used to own, the vents went straight to the wing tip on each tank's side.  If parked on a side slope with fuel on both and full tanks, you might end up with a third of the high side's tank volume on the ground under the left wing tip (later they were cross vented to prevent this).


Are turboprops less safe then jets? On a recent trip to an airport, I noticed a large number of Bombardier Dash 8s. I wanted to know - are turboprops less safe than traditional jets like the 737 or A320? For instance, I would imagine they are less forgiving with bird strikes.

There is no hard answer to this and it should always be looked at carefully as its dangerous to compare these things. The factors vary widely and a clear cut comparison is generally hard. Twin Turbo-Props may have a lower celling than your average regional jet, they often fly shorter routes and see more cycles compared to their total hourly lifetime, some turbo-props are even in reach of private pilots which puts them in a different operational situation all together but will be lumped in on the statistics.

The most comprehensive study I can find on the topic, and one I feel breaks it down nicely, is this one from NASA

  Differences in Characteristics of Aviation Accidents during 1993-2012
  Based on Aircraft Type

Im going to refrain from quoting to much directly as its all relevant and a fairly short 20 page read. The table that seems to sum it up best is the following (refer to study for table explanation):

A bit of a tangent but related, here is a nice article from AOPA comparing the data for Small Jets VS Turbo Props operated under part 91


Do glider pilots have to wear parachute in countries where mandatory even if flying with a foreign glider? Today I saw this video on Vimeo that shows a pilot flying a new solar glider (N- registered aircraft) in Italy without wearing a parachute (I believe in US is not mandatory).

Actually here in Italy it is mandatory to wear parachutes in gliders (at least I- registered). In our club we carry them also on our D- gliders but I don't know if it is also mandatory.

What is the scope of local regulations for foreign aircrafts? Do they have to comply also with this issue or is it up to the user, since it is a factor that only affects him?

Please feel free to edit my question with better words if my text is incomprehensible.

For US (N-reg aircraft), this is defined in 14 CFR 91.703, Operations of civil aircraft of U.S. registry outside of the United States. It says:

  (a) Each person operating a civil aircraft of U.S. registry outside of
  the United States shall—

  (1) When over the high seas, comply with annex 2 (Rules of the Air) to
  the Convention on International Civil Aviation and with §§91.117(c),
  91.127, 91.129, and 91.131;

  (2) When within a foreign country, comply with the regulations
  relating to the flight and maneuver of aircraft there in force;

  (3) Except for §§91.117(a), 91.307(b), 91.309, 91.323, and 91.711,
  comply with this part so far as it is not inconsistent with applicable
  regulations of the foreign country where the aircraft is operated or
  annex 2 of the Convention on International Civil Aviation; [...]

That suggests that in most cases the pilot should follow the foreign (Italian) regulations:

91.703(a)(2) says you have to follow foreign regulations on "flight and maneuver"
703(a)(3) says you should (mostly) follow part 91 unless it's "inconsistent" with the foreign regulations

It all seems a bit vague to me, and what "inconsistent" means is probably the kind of thing that keeps lawyers busy. But also note that there are specific rules applying to operating foreign aircraft in the US. 14 CFR 91.711, Special rules for foreign civil aircraft, begins:

  (a) General. In addition to the other applicable regulations of this
  part, each person operating a foreign civil aircraft within the United
  States shall comply with this section.

So foreign aircraft in the US are expected to follow US regulations as far as possible, which is consistent with 91.703: an N-reg aircraft abroad follows the foreign rules as far as possible, and a foreign aircraft in the US follows US rules as far as possible.

Since both the US and Italy are ICAO members, I would expect Italian law to roughly mirror US law on this, although that may be a dangerous assumption. For an authoritative answer, I would ask both the FAA and the Italian authorities.


How to calculate the flight envelope and maneuvering envelope for the B727-200F? I'm a student and my assignment is to make a flight envelope and maneuvering envelope of the Boeing 727F-223. But I don't find any of the values to calculate the flight envelope and maneuvering envelope. Can someone tell me how to find these values and how to get started with making the envelopes themselves?

Start with the appropriate sections in FAR part 25. The link is to the current version - you will probably collect bonus points if you dig up the version from the Sixties which was current when Boeing applied for the certification of the 727-223. Once the application is started, the rules remain relevant for that particular type - that is why Boeing redesigned the 737 several times over but kept the old name and the certification regulations that came with it. This is called Grandfather policy.

Calculate the minimum speed curve over load factor, then draw the v-n-diagram and the gust lines for 56 ft/s vertical gusts at sea level and repeat with 44 ft/s gusts at 15,000 ft, decreasing to 20.86 ft/s at 60,000 ft for the current version. Older versions used gusts of 50 or 66 ft/s from sea level to 20,000 ft, decreasing to 25 or 38 ft/s between 20,000 and 50,000 ft - the lower level is for the Sixties, the higher one for the Nineties. Note where the  minimum flight speed line will cross the maximum load factor - this is where your $\text{v}_A$ should go. Next, the limit speed in turbulent weather $\text{v}_B$ is determined by the point where the gust line will reach your maximum load factor. Cruise and dive speed are more tricky, but the limit Mach speeds are even listed in Wikipedia or on Airliners.net.

The negative side will involve some speculation unless you have been given a minimum lift coefficient - use 0.7 times the maximum clean value if you have nothing else. Use the intersection of the minimum lift line with the -1g line to continue horizontally and reduce the envelope between $\text{v}_C$ and $\text{v}_D$ from -1g to 0g, and you are done.


Are there any full-size airplanes flying with a Selig S1223 airfoil? Are there any full-size airplanes flying with a Selig S1223 airfoil?

Based on a quick perusal of the "Incomplete Guide to Airfoil Usage", my initial answer is no.  If you look up any of the big name manufacturers that are present on that list (Schempp-Hirth, Schleicher, Grob, Schweizer were my picks offhand), they use a mixture of Wortmann FX, NACA, and Eppler airfoils.  That said, the truer rationale comes a look at a Cl vs Cd curve, or how the lift and drag of an airfoil change with respect to one another.

I have a representative Cl vs Cd curve below (Cl on the vertical axis and Cd on the horizontal axis), where the purple line is a Selig S1223 airfoil, the yellow is a Wortmann FX 61-163 (used on a number of Schleicher sailplanes), and the green is the Eppler 603 (used on a number of Grob sailplanes).  Obviously, the S1223 produces far more lift than any of the other airfoils, and hits its most efficient point (maximum lift for minimum drag) at a very high lift coefficient -- just a shade over 1!

However, this is not necessarily a good thing.  If we work some numbers, it starts to become apparent.  Using a the definition of lift coefficient, we can estimate the typical lift coefficient () of a Grob 103 in trimmed flight something like this, where  is the density of air,  is the aircraft's wing area, and  is it's flight speed.

For a Grob 103, let's assume that it's flying at maximum gross weight (so maximize the necessary lift), so 5978 N, at sea level the density of air is 1.225 kg/m^3, wing area is 17.9 m^2, and its best L/D speed is 52.5 knots (27 m/s). Plugging all those in, we get a wing lift coefficient of 0.75.  Admittedly, this does not translate exactly into an airfoil lift coefficient, but it suits the need for a comparison.

Looking on the Cl vs Cd chart, this value is below the S1223's minimum drag point, and is actually where the S1223's drag is starting to spike.  However, it does hit right in the lower drag region of the Eppler and the FX quite well.  Furthermore, gliders aren't flying straight and level, which is what this calculation implies, but are, actually, descending (when outside a thermal/ridge lift/etc.), so the actual lift coefficient we need is probably somewhat lower, leading to even higher drag production from the S1223 but falling right into the "sweet spot" of the Eppler and FX airfoils' lift/drag characteristics.

In short, while the S1223 does have amazing lift characteristics (at lower Reynolds numbers -- these trends may not hold to a Reynolds number of 3,000,000, which would be closer to an operating sailplane), it is actually not the right airfoil for a regular sailplane.  For model-scale aircraft, however, it does have application, especially when wingspan is limited.