Why do most propeller-powered planes not have an autothrottle? Why does every kind of propeller-powered plane lack an auto-throttle?

No single-props no twin-props, not even turboprops like the Dash-8 Q400. To be honest, I don't know many turboprops, but if the Dash-8 doesn't have one, why shouldn't others? I mean, even a mini Cherokee 180 has an autopilot, whats so hard implementing an auto-throttle? And the Dash-8 is an airliner... without auto-throttle!

Thanks for your answers, I would really appreciate your answers.

Because each jet engine only has one lever; each piston engine has three.
Jet engine's throttle is pretty straight forward - move forward, more power. The computer automatically manages fuel flow to prevent surge, flameout and N1 overshoot.
On a piston engine you have three - a mixture lever, a propeller lever and a throttle lever. Granted, I don't think auto-mixture would be too hard to implement. Now, do I want a high-speed climb or high-power climb? And remember, the prop and throttle must be managed together. You cannot go beyond a certain power range with the props set for low rpm, otherwise you'll damage the engine.
It's like a car's automatic transmission, except it has one more dimension.
Power affects pitch
When you change power you must change the aircraft's pitch altogether. Autopilots on modern airlines have quite a number of vertical modes: ALT, V/S, G/S, VNAV, FLCH, TO/GA, CLB etc. None of those have the concept of gear ratio, which is required for propeller management.
Can you design an autopilot system such that it functions on propeller engines? Absolutely. But it is going to be complicated. Not only the usual operations, but the failure modes, have to be engineered and learnt by the pilots. How do you deal with an auto-mixture failure? RPM mismatch? Such training would add unnecessary cost to an otherwise simple aircraft operation. If your airplane does not have a variable pitch propeller, it is probably too simplistic for this kind of autopilot anyway.
Jets have another property which makes auto throttle a logical choice - the faster you fly, the more powerful the engines. Thus, on a jet, you would have to make continuous throttle adjustment if you change your airspeed. So an auto throttle would be helpful. Pistons do not behave like that.
Turboprops
One of the main reasons for choosing piston aircraft is - it is simple. It just fly. No fancy stuff. No lengthy preflight checks. No computers. I just want to get flying. This thinking also extends to turboprops.
It's worthy to note that the ATR does not have auto throttle as well. The ATR 42 has power management (but not speed management), where activating it will simply move a bug on the torque gauge; the pilots have to manually move the levers to follow it. The ATR 72 has a notch for the pilots to place the throttle levers, but still, no motor to move the levers automatically. I can't think of any reason behind this design philosophy besides simplicity and cost.


Under what circumstances can Part 91 allow compensation for air transportation? Can a commercial pilot fly passengers for hire without an air carrier certificate, considering that the aircraft is owned by a private company that hires the pilot and the plane has room for 5 passengers and 2 crew?

The only way you can carry passengers for hire as a common carrier without an air carrier cert (either 121 or 135) is the sightseeing exemption -- 25 SM, landing at point of takeoff. However you will still need an LOA and to participate in an approved drug enforcement program.

If there is a 'commonality of purpose' e.g. all the passengers are employees of the company that owns the airplane, then it isn't common carriage, and you don't need the air carrier cert. This is how corporate flight depts operate, they're Part 91. (But they can only fly employees etc., they cannot fly the general public.)


Winglets vs Sharklets vs Blended wingtips I tried to look for this answer but I was unable to find a complete one.

What is the differences between Winglets, Sharklets (used for example on A350 XWB), and "Blended wingtips" (used only on 787)?

Especially firt two seems very similar. Anyway, more in general, what are differences/PROs/CONs of these different solutions?

Winglet advantages

With a winglet you see a 3-5% reduction in drag which helps increase efficiency in aircraft by reducing something called a wing tip vortex which forms by the high pressure(under the wing) wraps around the top part of the wing which has the low pressure and results in a wing tip vortex. A winglet works by deflecting the air so less high pressure wraps the wing tip.
Increases lift(the winglet generates lift also like an aircraft wing)

Winglet disadvantages

Adds about 300 lbs of weight to the aircraft depending on the winglet
Reduces maneuverability which is why you don't see a winglet on a fighter jet

Now a sharklet and a winglet are essentially the same thing.

Bts: Its called a raked wing tip

Raked wing tip advantages

Does the same thing as a winglet by deflecting the air. With a raked wing tip you actually see a greater drag reduction than a winglet can give you which leads to great efficiency in aircraft

Raked wing tip advantages

You actually loose a little bit of lift due to the raked wing

Sharklet- The sharklet deflects air just like a winglet and acts in the same way and is a winglet, but Airbus just named it differently.

A350 design- The a350 uses a sharklet and a raked wing. You see great numbers of efficiency in the design because you include a raked wing and a sharklet.

Between the 3 you mentioned there is a big difference and all 3 have different advantages and disadvantages. They all act in the same way by deflecting the air the design is just different for each one. I hope this helped you understand a little bit more about these devices.


Do I use true or magnetic north in headwind component calculations? For the landing performance calculations, I want to calculate the headwind component. I can do this with the runway heading and the reported wind direction and speed. But do I need to make any adjustments for true vs. magnetic north?

Is the reported wind direction towards true or magnetic north? Is the runway heading towards true or magnetic north?

Surface winds, as reported by the tower are magnetic.  Runway headings are magnetic.  However, METARs are reported true, according to Aviation Weather Services and ICAO.  Therefore one has to perform a heading correction in comparing runway headings to METARs.

Wind directions are normally rounded to 10 degrees, as are runway headings.  However, sometimes runway numbering lags isogonic shifts, so care should be used utilizing runway headings.

It is worth noting that the expression, "If it is written it is true, and if it is spoken it is magnetic," may be misleading.  As an example ASOS and AWOS data is recorded as true, and transmitted as true, but is converted to magnetic prior to being broadcast on computer generated voice messages.

Furthermore TWEB are true, as the underlying reports they are generated from are true (winds aloft, TAF, etc.).

To summarize, runways are magnetic, tower wind checks are magnetic, but ASOS, AWOS and METAR are true, unless transcribed to computer generated voice.


How do you communicate with a military drone operator over radio? This article (and other similar ones) states:

  In remarks at the White House on Thursday, US President Donald Trump said the drone had flown to within 1,000 metres of the USS Boxer and had ignored "multiple calls to stand down".

For airplanes, ICAO standardizes 121.5 MHz and 243.0 MHz (military) as common emergency frequencies that aircraft "should" monitor when possible. If approached by an unknown aircraft, this is the frequency I'll try to raise the crew on first.

How does this work for drones? Does the same standard apply? Is it reasonable that in this case the USS Boxer's crew could expect that the drone is monitoring 121.5 (or 243.0) and that its operators will be listening?

Some UAVs carry VHF or UHF airband radios to communicate with air traffic control and other aircraft. The voice channel is relayed to and from the remote pilot operator via satellite or another form of datalink. I've heard UAVs taking with Joshua Approach in the Mojave Desert, and one time Joshua called one out to me as traffic and vice versa. I agreed to maintain visual separation, the remote pilot acknowledged and overall it was very similar to dealing with any other aircraft.

I have no idea whether they monitor 121.5 as well as whatever enroute frequency they're using, but it seems plausible that they could.


How did ATC procedures and airspace structure change after San Diego PSA collision? In 1978, a Pacific Southwest Airlines aircraft collided with a Cessna 172 while approaching the San Diego airport in California. The GA aircraft was piloted by a student, and crossed the approach trajectory of the B727, killing 144 people.

Source

To my understanding, ATC was not aware of the Cessna actual location, The airliner crew didn't see the Cessna, and the Cessna was not wrong being in this airspace near a busy regional airport.

What changed after this accident to make such situation impossible?

The recommendations from the NTSB report are:

  Implement a Terminal Radar Service Area (TRSA) at Lindbergh Airpot, San Diego, CA
  Review procedures at all airports which are used regularly by air carrier and general aviation aircraft to determine which other areas require either a terminal control area or a terminal control radar service area and establish the appropriate one.
  Use visual separation in terminal radar service areas only when a pilot requests it, except for sequencing on the final approach with radar monitoring.
  Re-evaluate its policy with regard to the use of visual separation in other terminal areas.

The most direct change stemming from this accident is the establishment of a TRSA at Lindbergh on May 1, 1979. (It is now a class B area).

Also in 1979 the Lindbergh tower was equipped with some upgrades, including minimum safe altitude warning and conflict alert enhancements.

The other recommendations are fairly vague and I find no indication what, if any action was taken on them.
But as Gerry pointed out in comments, this accident put emphasis on the FAA's effort to create TCAS.  From the TCAS II V7.1 Intro booklet:

  In 1978, the collision between a light aircraft and an airliner over San Diego served to increase FAA's efforts to complete development of an effective collision avoidance system.

The see-and-avoid system is still very much in use. Visual approaches are still used. There really were no immediate systemic changes made in response to the accident. Mostly it was just airspace configuration around KSAN and enhancements to the radar system there. But, like every accident, the NTSB and FAA learned from it and took steps to improve safety. The FAA releases pamphlets appropriately titled, "Lessons Learned," about what can be taken from different types of accidents.


What are the safety concerns and efficiency benefits of two in-line runways? Heathrow Hub is an independent proposal to expand capacity at Heathrow Airport by extending both of the existing runways up to a total length of about 7,000 metres and dividing them into four so that they each provide two pair of full length, in-line runways, allowing simultaneous take-offs and landings.

How to ensure the planes landing and take-off in the same runways safety?
How many flight can be handled by such design, and how efficiency it is compared to two runways using segregated parallel operations (one for landing and another for takeoff)?

How to ensure the planes landing and take-off in the same runways safety?

No one knows.

Note this isn't exactly what is being proposed

  By dividing it in two with a generous central buffer zone, we create two in-line runways, allowing aircraft to simultaneously land on one and take off on the other.

So that isn't simultaneous landing and taking off on the same runway.

Currently only one LHR runway is used for take-offs at any time. The runway is switched to provide respite from noise to local residents in the take-off path.

Also the surrounding airspace isn't set up in a way that would allow separation for concurrent take-off from two runways. A major reorganisation would be needed of airspace in that region of the UK.

I believe that currently, simultaneous take-off require parallel runways a mile or more apart.

  How many flight can be handled by such design

No one knows. Maybe a c 46% increase from 480,000 to 700,000 air transport movements a year. See reference below. Bear in mind that Heathrow is subject to a night-time curfew.

  How efficient is it compared to parallel runways?

No one knows.

According to the airports commission in 2014:

  The concept of an in-line runway is unconventional, has never been used elsewhare and is not envisaged in international, EU or national regulatory instruments, standards or recommendations for safe design or operation.


Why hang glider dont over pitch when inrease AoA? Glider change AoA with changing c.g.
To do that,you must push control bar forward,your c.g. move back,so we have torque in clockwise direction which wants rotate glider..
Situation can be even worse,because increased AoA shift center of pressure(lift) more forward.
Why glider dont over pitch(and stall),what stop this dangerous torque when you must fly with higer AoA?What gives glider restoring torque if he dont has tail?

The short answer is that the wing itself is designed to have sufficient excess pitch stability such that the glider-pilot system is still stable in pitch when the pilot's weight is shifted somewhat aft.  If the pilot's weight is shifted sufficiently far aft, however, a stall may occur. The glider might not recover into stable flight if the control bar is kept pushed that far forward, i.e. if the pilot's weight is kept shifted that far aft.
It is normal to trim a hang glider to fly in wings-level flight at an airspeed near the minimum sink rate, not too far above stall speed, when the pilot is exerting no pressure on the control bar.  It would be normal for the glider to stall if the pilot extends his arms as far forward as he can reach, in wings-level flight.  A hang glider pilot would not necessarily expect to see benign flight characteristics if he keeps the bar pushed forward as far as his arms can reach, in wings-level flight.


Why/when is the blunt nose better? Most large aircraft and some fighters have blunt, rounded nose cone. OTOH many fighters (that don't use the nose for air intake) and notably the two supersonic airliners (Concorde, TU-144) have the sharp tip for a nose cone.

What is the aerodynamic justification for that? What advantages and disadvantages does the "blunt" nose cone provide - or why don't all airplanes have the sharp spike nose cone (which "feels" like the obviously optimal aerodynamic choice - obviously that "feel" is somehow flawed?)

In subsonic flow the air can react to the approaching vehicle since the pressure field around it extends forward, too. This means that a suction area on one side of the fuselage or wing will already start to pull molecules in before they reach the vehicle itself which causes this suction. A round nose allows the flow to come from a range of angles without creating too much drag. Aerodynamically speaking, the stagnation point can be moved without problems.

In supersonic flow, the air has no indication of the approaching vehicle. The first contact will cause a sudden change in direction, called a shock. For drag reduction it is important to make the shock as weak as possible, which means that the change in direction should be as small as possible. This can best be achieved by a slender, pointy tip.

Note the downward position of the intake cone of the SR-71 engine nacelle in the picture below: It is angled so that at Mach 3.2 the cone is symmetrical to the oncoming flow (which gives you a pretty good indication of the angle of attack of the whole plane).

SR-71 during take-off (picture source). Not only is the cone angled downward, but also canted in because the flow is pressed sideways by the aircraft's forebody in supersonic flight.

In hypersonic flow (Mach > 5) a blunt nose might again be preferable if the nose's materials put an upper limit on aerodynamic heating. A pointed tip will produce an attached shock which will heat the tip to something close to the stagnation temperature of the flow. A blunt nose, however, will cause a separated shock. This creates more drag and a higher amount of heat overall, but allows to spread this heat over a larger area and dump most of it into the air, producing lower peak loads. The Space Shuttle had such a blunt nose, since drag minimization is not a priority for a re-entry vehicle.


Does anyone know if RHP (assumed to be rotor horse power) is equivalent to SHP (shaft HP)? I was recently reading a NAVAER aircraft characteristics summary of the proposed XHCH-1 helicopter of 1951. In the engine section it gives the engine power in "Rhp" and later in a 1956 summary gives the value in Brake HP (Bhp). See https://www.alternatewars.com/SAC/XHCH-1_CS_-_1_November_1951.pdf
Does anyone know if there is a difference between RHP and BHP. I'm "assuming" (and I stress assuming) that RHP is 'rotor horse power' and equivalent to shaft horse power. I'm again "assuming" that the technical description simply changed over the last 70 or so years.
Any thoughts or suggestions from any learned person out there? Thank you, much appreciated.

This answer is somewhat speculative, but I have strong grounds for the speculations, pls read through:
I've only ever seen bhp used as hp measured directly at engine output shaft, although by definition bhp can be measured at any location of the driveline:
Wikipedia: brake horsepower
In the particular case in question, I strongly believe the reason for the use of the obscure "Rhp" is the unusual way the powertransfer is arranged in this contraption: there is/seems to be no mechanical connection between the actual engine and the rotor. The rotor is actuated pneumatically by jets at the tips of the rotor blades.
There would be no point in measuring the brake horsepower or shaft horsepower of the actual engine due to "weird" power delivery.
It is therefore most likely the hp is measured at rotor hub, but since the rotor in this case sort of "is the engine itself", to avoid confusion, Rhp is used to declare power. The declared Rhp probably is shaft horsepower. Kinda confusing though :)
Note: several sources list rhp (with some variation in caps) to mean "rated horsepower, which according to Merriam Webster means "the maximum power an airplane engine can develop without failure when operated continuously or for a specified long period under specified conditions". Even with this definition, I think in this case it refers to hp measured at rotor shaft, produced by the tip jets.


How do turbochargers aid engine performance as density altitude increases? How do turbochargers improve engine performance at high altitudes / density altitudes?
Could you also address how this benefit could become a liability at low density altitudes, for example when the density altitude is negative?

An oversimplification for sure: Turbochargers essentially compress the air going into the engine (cylinders) to maintain (near) sea level pressure internally, so the external density altitude doesn't affect the performance of the engine.

The "liability" at low density altutudes is that it is possible to over-boost the engine, potentially damaging it. See the related question for more in-depth explanation and the liability of having a turbocharger at low density altitude.


Could the Busemann's biplane concept be used in a turbofan engine? Would incorporating the Busemann's biplane concept in the turbofan engine fan blades and engine casing make it more efficient, if fan tip speeds were allowed to move above the speed of sound by cancelling out the sonic boom and sonic shock waves?

No.

The Busemann biplane is a clever concept to have all shocks cancel each other, but unfortunately, the same canceling happens to all the lift. Therefore, a Busemann fan would not create any thrust.

The key of the idea is that shocks occur only between the two wings, the outer surfaces being aligned with the external flow so no shocks are created there. This means the concept would only be workable if every other gap functions as a Busemann biplane, the rest having straight and parallel walls.

In addition, the concept only works at one specific supersonic speed which depends on the geometry of the gap between the wings. On a fan you get a continuous increase in Mach number when moving from the spoke to the fairing. At Mach = 1 the chord of the wing would have to be zero for the concept to work over the whole span.


When must delegated airspace be listed in the AIP? Two states can agree, through a bilateral letter of agreement, to delegate the responsibility for providing air traffic services (ATS) within a certain airspace from one state to the other. There can be numerous reasons for this. For example, a part of Scottish airspace is delegated to the Danish air navigation service provider (ANSP), because Denmark has better radar coverage within the specific area. In this area, which is within Scottish airspace, ATS is provided by the Danish ANSP.

My question is regarding the need to publish details about such airspace delegations in the national aeronautical information publications (AIP).

The previously mentioned delegated airspace is described in AIP Denmark section ENR 2.2 (Other regulated airspace). However, a part of German airspace within Hannover upper flight information region (UIR) is also delegated to Denmark, but this airspace is not shown anywhere in the AIP. To me, this seems very inconsistent, which brings me to my question: under which circumstances are states required to publish information about delegation of ATS? I am interested in references to ICAO SARPs or PANS, or, alternatively, EU regulations.

The below chart (AIP Denmark ENR 6.2 – 1) clearly indicates some delegated areas in Scottish airspace and around the border to Sweden (which I have marked with blue), but, the delegated area in Germany (which I have marked with red) is not shown.

The area is, however, shown on this "Sector Boundary Structure Chart" chart published by Eurocontrol:

I have looked in ICAO Annex 4 and Annex 15 without any luck.
Appendix 1 of Annex 15 states that:

ENR 2.1 shall contain, among other things:

  Detailed description of flight information regions (FIR), upper flight information regions (UIR), and terminal control areas (TMA), including:
  (…)
  2) identification of unit providing the service;
  (…)

I usually see delegated airspaces listed in ENR 2.2, though, so they do not seem to need to be covered in ENR 2.1.

ENR 2.2 shall contain:

  Where established, a detailed description of other types of regulated airspace and airspace classification.

It is not specified exactly what this includes.

Principles under ICAO agreements

Delegation of ATC services is contracted between ICAO members using bilateral or multilateral letters of agreement. Cases of such delegation exist typically to cover remote large airspace (e.g. Arctic agreement between multiple countries), or small areas (e.g. islands).

ICAO members are committed to fulfill the decisions of their constituent act, the Chicago Convention signed in 1944. Among the annexes to the Convention, annex 15 is related to the provision of aeronautical information services (AIS):

  Annex 15 defines how an aeronautical information service shall receive
  and/or originate, collate or assemble, edit, format, publish/store and
  distribute specified aeronautical information/data. The goal is to
  satisfy the need for uniformity and consistency in the provision of
  aeronautical information/data that is required for the operational use
  by international civil aviation.

Impact on AIP

Annex 15 includes these generic articles:

  3.1.1.2 Each Contracting State shall take all necessary measures to
  ensure that the aeronautical information/data it provides relating to
  its own territory, as well as areas in which the State is responsible
  for air traffic services outside its territory, is adequate, of
  required quality and timely. This shall include arrangements for the
  timely provision of required information/data to the aeronautical
  information service by each of the State services associated with
  aircraft operations.

and

  3.1.7 An aeronautical information service shall receive and/or
  originate, collate or assemble, edit, format, publish/store and
  distribute aeronautical information/data concerning the entire
  territory of the State as well as areas in which the State is
  responsible for air traffic services outside its territory.
  Aeronautical information shall be published as an Integrated
  Aeronautical Information Package.

I was not able to find the decision to use AIP ENR 2.2 (other regulated airspace), but it's a matter of fact the information is found here, e.g. in the Norway AIP:

  5: Delegation of Responsibility for Provision of ATS

  5.1: General Denmark, Norway, Sweden and the United Kingdom have
  arranged through the exchange of bilateral Letters of Agreement to
  transfer the responsibility for provision of ATS within parts of their
  own area of responsibility, to their neighbouring State.

  Procedures and communication within the said areas will be as if the
  airspace was an integral part of the FIR for which the nation
  mentioned is responsible.

Bidirectional scope

An effect of these articles is both the delegating and the providing states shall publish information about related areas. For example in the Spanish AIP, two cases are described.

Spain delegating to Portugal:

  By agreement between Sevilla ACC and Lisboa ACC, the air traffic
  service is provided by Lisboa ACC within the airspace defined by [...]

Spain receiving delegation from Portugal:

  By agreement between Lisboa ACC and Madrid ACC, the air traffic
  service is provided by Madrid ACC within the airspace defined by [...]


May a VFR-only pilot without high-performance or complex endorsements be the safety pilot for an IFR currency flight? For an IFR currency flight in a high-performance and/or complex airplane where the pilot flying has all the appropriate ratings and endorsements to be PIC, does another pilot with strictly a private ASEL certificate meet the legal requirements to be the safety pilot?

If so, I would assume the entire flight must be conducted in VMC. What other constraints or restrictions apply in such a scenario?

If permissible, how may the safety pilot log the flight so as to count toward future ratings and so on?

First, can a pilot without an HP endorsement act as safety pilot in an HP aircraft? Since 14 CFR 91.109 only requires a safety pilot to have category and class ratings, there's no need to have any additional endorsements.

That's confirmed in this FAA legal interpretation:

  there is no regulatory requirement that a safety pilot have a
  high performance endorsement to act as safety pilot

The same document says that safety pilots are "encouraged to be thoroughly familiar and current in the aircraft that is used" - which is great advice - but that's it.

As for the flight conditions (IMC/VMC) and rules (IFR/VFR), I'm not sure what you're asking. Is either pilot IFR current? If not, then the flight can only be VFR. This question might be relevant.


How do I set up G1000 GFC700 autopilot for takeoff? I want to be able to engage autopilot right away at a safe altitude, while taking advantage of flight level control at Vy for the climb.
Heading is set for the runway. I’d switch to NAV mode when I was ready to make the turn out.
Altitude is set for cruise altitude.
Does this look like I’m all set to just hit “AP” at a safe altitude, or am I missing anything? Thanks!

This looks like a proper setup for an autopilot controlled climb up to 5000 feet. One way to know for sure is to see what the Flight Director tells you. Does it seem reasonable and correct?
Also, prior to taking the runway, you should test the autopilot disconnects. Some of the more common ones are:

Can you overpower the autopilot manually.
The Control Wheel Steering button
The Autopilot immediate disconnect button on the yoke.
The electric trim buttons on the yoke.
The Take Off Go Around button on the panel.
The AP button itself
The Autopilot circuit breaker (this can only be tested during preflight inspection since completely restarting the G1000 will be necessary).


Have we seen the last significant experiments in the configuration of jet airliners? By the 1940s, passenger airliners had pretty much settled down on the shape that has dominated the industry since then: a monoplane, with wing-mounted engines, a roughly cylindrical single fuselage and a tailplane.

The 707 set the template for jet airliners: low wings, and pylon-mounted engines.

Source: Wikipedia

Apart from the few, smaller, models that place their engines on the rear of the fuselage, there are almost no models currently in production that adopt a different template (in fact, the only one I am aware of is the Antonov An-148).

There are no more tri-jets. There are no more radical experiments like Concorde on the horizon, never mind in production. There are no serious proposals for significantly different shapes or configurations.

The only significant configuration choice for medium-to-large size airliners seems to be two engines or four.

Since the 707 slung its engines under the wing on pylons in the 1950s, the only significant development that I can think of is the adoption of winglets in the 1980s.

You might consider the 747's hump and the A380's twin decks to be significant variations, but they are still only variations on the theme, not fundamentally different configurations.

Assuming that jet engines remain viable in 40 years' time, will the airliners of 2058 still look fundamentally like 707s?

If you're concerned that question seems too open to mere speculation, let me ask it another way: is there a fundamental design reason why the low-wing/pylon-mounted engine/cylindrical fuselage/tailplane configuration established by the 707 shows no sign of being displaced by alternatives?

Or, why have the enormous advances in (for example) materials and aerodynamics made so little difference to the fundamental shape of airliners?

With current fuel prices: Yes, we have arrived at a mature design which will not change much. Recent trends like the increase in aspect ratio and engine bypass ratio will continue, but the general arrangement will remain unchanged.

Just look what happened in the first 50 years of airline operations, and how much changed after that in regards of aircraft configurations:

If fuel prices rise to 200 USD per barrel and more, expect slower airliners with less sweep, much higher aspect ratio and probably even braced wings. To enable bracing the wings will be mounted on top of the fuselage, like on the Hurel-Dubois HD.31.

Boeing SUGAR Freeze concept. Note the third engine in the back which ingests the fuselage boundary layer, thereby reducing separation and pressure drag.

While you might read about two more new design directions, a supersonic airliner and the blended wing-body (BWB), I am rather skeptical that any of those will be adopted in the future.


Descent of Light attack aircraft to loiter altitude How do Light Attack Aircraft (LAA) such as the Embraer Super Tucano descend from their cruise altitude to their loiter altitude to be on-station above ground troops? I want to know the way these airplanes descend and what are typical rate of descent and descent gradient. Do they descend steeply and accelerate?
I know that commercial airplanes descend at a 3 degree angle. Do the LAA also descend at this angle?

I cannot answer for the Supertocano, or even light attack aircraft, but I can tell you that in a tactical environment nobody cares about your rate of descent or descent angle, only that you are in your assigned block altitude at the appropriate time.
Descents aren't planned or adhered to in same way that airline descents are, and fighter type aircraft aren’t controlled in the same manner.  There is no need to be smooth for paying passengers either - As long as airspeed and G restrictions for your type aircraft are followed, and you don’t violate any theater safety rules, (like blowing through another airplane’s block altitude while they are on station) the area commander just needs you to be on-station, on-target, on-time.
One day you might make an easy cruise descent, the next you might do a split-S.  The threat environment plays a part as well.  You may have the luxury of making a long easy fuel efficient descent, or you may need to stay high to avoid ground threats, then expedite your descent overhead your station.
I used to like to make a slow descending barrel roll because it was a good way to lose a lot of altitude quickly while visually clearing the airspace 360 degrees around me.


Why are flying-boom tankers restricted to a single boom? Tanker aircraft can use one or both of two refuelling systems:

Flying boom: A rigid boom is lowered from the tanker and inserted into a receptacle on the roof of the recipient aircraft.
Probe\drogue: A flexible hose with a (usually) canvas cone on the end is unreeled from the tanker, and the recipient aircraft flies a forward-pointing probe into the center of the cone.

Aircraft can have multiple drogue units...

...but are limited to a single boom.

What prevents a tanker aircraft from having two or more booms?

There are several reasons why it is hard to support multiple booms on a single tanker:

1) Booms need an operator who is located in the fuselage. Video systems provide for remote control on newer tankers, but older ones still use direct view or looking straight down the boom at the refueling point in the receiving aircraft.

2) The boom is physically large. Its weight, large diameter and telescoping tube length would be difficult to install on a wing.

3) A wing bounces around a lot more than the fuselage does. Since the boom is rigid, this complicates keeping a good connection.

4) The high flow rate of a boom is only useful for larger aircraft like bombers, which are too big for simultaneous refueling. This somewhat reduces the advantage of having multiple refueling points.

Probe and drogue has a lower flow rate through a lighter, narrower hose. It is passive from the tankers point of view, and it is flexible.


Why aren't there more passenger helicopters? I've observed helicopters being used often

in the military
for medical flights
for other special use purposes, such as sightseeing and news reporting

Why aren't there any commercial passenger transport helicopter flights? Or are there any examples of this? Are airplanes simply that much more efficient?

Airplanes are much more efficient, much faster and scale better.

Helicopters are limited to around 150 knots because when flying forward the tip of the advancing blade must not exceed the speed of sound while the retreating blade must still move aft fast enough to produce lift.

Helicopters are also difficult to make large, because for efficiency the rotor disk needs to be large, but the diameter is again limited by the tip speed having to remain subsonic. And the material requirements to make the blades strong enough without making them too large to keep drag low.


Will a non-certified GPS source work the same in ADS-B mandated airspace? What happens if you use a non-WAAS GPS position source in ADS-B mandated airspace? Doesn't it work the same, except for the positional accuracy?

It may work. It may not work. Nobody knows. If you use a non-certify equipment when you are required to use the certified one you are breaking the law. Nobody can be sure your equipment will work as required but everybody are sure you are breaking the law.

Don't do it. You are endangering your life and others.


How can I know if North Atlantic Tracks have been amended? Information about the North Atlantic Tracks is issued through Track Messages. The NAT Doc 007 document states that every track message is identified by the TMI (Track Message Identifier) number:

The originating OAC identifies each NAT Track Message, within the
Remarks section appended to the end of the NAT Track message, by means
of a 3-digit Track Message Identification (TMI) number equivalent to
the Julian calendar date on which that OTS is effective. For example,
the OTS effective on February 1st will be identified by TMI 032. (The
Julian calendar date is a simple progression of numbered days without
reference to months, with numbering starting from the first day of the
year.).

In case the North Atlantic Tracks are modified, a letter is appended to the TMI number:

If any subsequent NAT Track amendments affecting the entry/exit
points, route of flight (co-ordinates) or flight level allocation are
made, the whole NAT Track Message will be re-issued. The reason for
this amendment will be shown in the Notes and a successive alphabetic
character, i.e. ‘A’, then ‘B’, etc., will be added to the end of the
TMI number (e.g. TMI 032A).

I would like to know how such change is notified to the interested parties; is some ATCs issuing a NOTAM to declare that some changes have been done to the TM? If yes, where can I visualize such NOTAM?
One possible way to overcome my problem would consist in constantly checking if the TMI number has changed but this is not a very efficient way to proceed. I would rather expect some NOTAM which notifies the TMI number change.
Can you tell me if what I ask is plausible? If yes how can I proced?

For starters I am not completely knowledgeable with the North Atlantic Tracks but work with some of the other Flex track systems in the world. And they are all very similar.
The Track Messages are a type of NOTAM. They are released everyday and revised NOTAM (Track Message) is released if there are changes. They increment the alphabet character on the end of the TMI so that when a clearance is   issued by Air Traffic Control(ATC) they know which track they are flying including the version and ATC can correct it if the pilot has old information.
Extract from one of the Track Message:

REMARKS.

TMI IS 013 AND OPERATORS ARE REMINDED TO INCLUDE THE TMI NUMBER AS
PART OF THE OCEANIC CLEARANCE READ BACK.

When there is any changes they reissue the entire NOTAM (Track Message). So requesting accessing the message again will tell you straight away what is current. Usually aviation doesn't care about what it was, only what it is and what it will be. The computer systems that the airlines use get the most up to date data when they create the Flight Plans.
The question is what you want to do with the data to how the best way to get the data. But the link you supplied will always have the most recent ones.
Visualization of the these tracks, plus others, can be done on SkyVector. Go to layers to change any settings. The link automatically loads up on an ERC High with North American and Pacific Tracks Selected.


What does the letter G mean in a runway identifier? Boulder Municipal Airport (KBDU) has runways 8 / 26 and also runways 8G / 26G. What is the significance of the letter G following the runway numbers?

For runways with other than hard surfaces it is common to list the runways with a letter G for grass or in the case of a seaplane base, with W for water.

An example of this is runway 8G at Boulder (KBDU) and runway 35W at David Wayne Hooks (KDWH).

You can see this information in the Chart Supplement pages and diagrams for each airport.


Do runways need some special kind of tar or protective layer? Do runways of the airports have some special kind of tar or protective layer to avoid the wear and tear in comparison to that of the Highways as they need to handle the much high pressure and the weights than normal highways?

Airport designers may use any type of material, based on construction research status and local meteorological conditions. Pavements may be flexible or rigid. There is no single technique to protect against wear and tear, and none specific to airports, this is similar to regular road construction.

Information on pavement types at Texas Dept of Transportation.
E.g. a rigid pavement:

FAA provides advisories to help designers. ICAO requires airports to report their pavement characteristics.

(source: Detroit Free Press)

FAA documentation related to pavement design:

Pavement Design & Construction
Airport Pavement Design and Evaluation

ICAO requires member states to report aerodrome-related aeronautical data, including pavement strength. The standardized method is known as the Pavement Classification Number (ACN-PCN) method.

As a critical characteristic of a pavement is the friction, this matter is refined in Measurement, Construction, and Maintenance of Skid-Resistant Airport Pavement Surfaces. This document includes data on rubber removal frequency, e.g.

Busy runway end:

(source: Bridgepoint Road Markings Ltd)

A technique for rubber removal:

(source: Waterblasting Technologies)

This thesis describes how to optimize runway pavements in order to increase friction and how to remove rubber deposit:

Optimizing Airport Runway Performance by Managing Pavement Infrastructure by Samantha Theresa Pinto. Note that:

  Rubber accumulation on a dry runway is generally not a problem since
  the rubber interaction between the aircraft tire and the rubber on the
  runway creates traction that may actually improve friction. However,
  in wet conditions, rubber accumulation leads to loss of friction on
  the runway by clogging the pavement texture and creating an especially
  slick surface with minimal drainage capability when the runway surface
  is wet. Additionally, rubber accumulation causing decreased friction
  values means pilots have less directional control of the aircraft than
  expected on a bare and dry runway.


How are the TRACON location IDs determined? Most of the TRACONs in the US are colocated with a control tower. The location IDs of these match their airport IDs, which makes sense.

There are also several TRACONs that are not located at a control tower. Most of these are designated with a letter and two numbers, such as A11 for Anchorage. The first letter usually matches the TRACON name, but not always. Where did these IDs come from? Does the number signify anything?

Also, there are a few of these non-tower TRACONs that use three letters and no number - what makes them special?

An "up/down" facility is where the tower and TRACON are in the same building and most of the traffic is to/from that airport (typically one class C or TRSA), so they share the identifier. They do provide services for satellite (class D or untowered) airports, but their traffic levels are usually negligible.

A "standalone" facility is where the TRACON is separate building, often on the grounds of a large airport but not the same building, and serves multiple airports (typically one or more class Bs plus any underlying class Cs, plus any satellites) so it gets a distinct identifier with numbers, which can't be confused with an up/down. I've never found a source for where the specific numbers come from; they don't seem random, but there isn't any obvious pattern either.

Recently, the FAA has created "consolidated" TRACONs that merge several neighboring standalone facilities. I'm not sure why the FAA has assigned them all-letter identifiers (e.g. PCT for Potomac Consolidated TRACON), but perhaps it's because there are so few of them (so far) and they cover such large areas that they're relatively well known and there isn't much risk of confusion.


Are German, Japanese, and Chinese companies not able to build aircraft jet engines on their own? As far as I know, only 4 countries can build aircraft jet engines on their own:

USA {GE, P&W}
Russia {Klimov, NPO Saturn}
France {Safran}
UK {Rolls-Royce}

All other countries use jet engines bought from companies of these 4 countries.

Is that true?
Are German, Japanese, and Chinese companies not able to build aircraft jet engines on their own?
Why is building jet engines so tough for companies from other countries?

Well Rolls Royce designs and builds jet engines in Germany with their RR Deutschland division.  Rolls Royce Deutschland is a subsidiary of Rolls Royce and is a collaboration between RR and BMW.

The Shenyang Aerospace Corporation and Aero Engine Corporation of China are homegrown Chinese jet engine manufacturers, making their names largely for the manufacture of copies of Russian military jet engines for PLAAF need, but are now manufacturing their own designs for military and civilian applications.

Japan’s Aero Engine Corp is a partnership between Rolls Royce and several Japanese industrial powerhouses, most notably Mitsubishi Heavy Industries, who has begun to develop a line of small to medium thrust high bypass turbofan engines for regional airliners use.

While the basics of a jet engine are fairly well understood - it is, after all just a Brayton Cycle gas turbine - the details of designing and manufacturing modern high efficiency jet engines requires quite a bit of technical talent and capital to accomplish.  A new engine program often takes longer, and is more expensive than, the aircraft program it is being designed to power.  Most likely many entrepreneurs and prospective OEMs are deterred by this as any improvement they are likely to offer can be either bought out by an existing engine OEM eg Pratt and Whitney, etc. or simply crushed by the economies of scale.


Should I connect the AR6203 COM radio to the GMA324 audio panel using symmetric or asymmetric wiring? I have this little project to change the Audiopanel and COM to GMA342, GNS430 and Becker AR6203. Airplane is a Piper 28-181.

I would like to know if I have to connect the AR6203 to GMA342 in symmetrical or asymmetrical wiring?
As far as I have researched it, I would say it is symmetric.

Is it a good idea to ground the audio shields at aircraft gnd/power gnd?

Since you're talking about a DC power system, chassis ground and power ground should be the same. So the power ground is commonly used for grounding shields. The question is: should you ground one end of the shields or both?

The purpose of the shields on the audio connections is to prevent induced audio frequency noise. To do that, the shields must have at least one ground point. RF engineers I've worked with will explain that the best solution is to have the shields grounded at both ends if the units at both ends are properly grounded and bonded. That's a big if, especially in general aviation avionics where slide-in mounting trays are used.

While the connections may be good when you install them, over time the connections can degrade and resistances increase. When that happens the "grounds" at the connected units are no longer at equal potential which can induce current flow through the shields. This 'ground loop' can induce a lot of noise into the lines.

Most installers I've worked with recommend terminating the shields only at one end thus eliminating any possibility of a ground loop. The key to this method is making sure any 'gap' necessary in the shield at the open end connector is as small as possible while still ensuring it doesn't make a connection. The small gaps aren't a big concern here as you're dealing with audio frequencies.


How are NATs connected to European Airways? The North Atlantic Tracks connect Northern Europe to North America. To enter/exit NATs over North America, the North American Routes (NARs) are used.

Questions:
What about the European side? What are the rules to enter/exit NATs? What airways must be flown? Can I find the official information written anywhere?

Note: Ideally I would like to find a list of routes (directs?) that suggests the pair of waypoints linking the generic NAT and the european airways system. In the past North Atlantic European Routing Scheme (NERS) was used but nowadays it appears they have been dismissed.

There is no equivalent in Europe to the North Atlantic Routes, you simply file direct from point to point.
This is the routing for a flight on Wednesday 18th of January, 2017 (DAL4).

KJFK
MERIT HFD PUT WITCH ALLEX N263A JOOPY NATS RESNO NATS NETKI NIBOG REMSI UL603 SOGPO UT149 OTSOP T149 LIPMI T150 ROLIS
EDDF

You see that the route terminates NAT S at NETKI NIBOG REMSI which are directs, until the flight joins the upper airway UL603 at REMSI.

Here is the routing in SkyVector.

And here is the screenshot from the FlightAware flight.

(Image Source: FlightAware)


What is the effect of a taildragger on P-factor? By looking an image of P-40 Warhawk with taildragger (and other vintage warplanes), one can conspicuously find the propeller disc of this aircraft isn't perpendicular to the relative airflow which induces P-factor.

Doesn't this design forces the aircraft to further left which causes difficulty for pilot to direct rudder to right?

Is this the reason why all the modern airliner's (including single engine aircraft like Cirrus SR22, Kestrel K-350) fuselage isn't made inclined?

By inclined, do you mean that the conventional (taildragger) landing gear configuration angles the propeller? If that is in fact your question, know that the propeller is not “inclined” in flight any more than a tricycle landing gear aircraft. Straight and level is basically (very roughly) the same between the P-40 and the SR-22. And, P-factor is only induced when the aircraft has sufficient forward motion. At very low airspeeds, there is hardly any P-factor.

In a conventional (tail-dragger) landing gear aircraft, once you are above the customary taxiing speed (the sufficient airspeed mentioned earlier), you pitch the nose forward. This raises the tail. In effect, you eliminate the “incline” in question. You are, at that point, almost flying the aircraft as if it had tricycle landing gear.

The conventional landing gear was the norm in those days. And, they were more conducive to landings on unimproved runway surfaces. Although, the conventional gear is more advantageous on non-hardened surfaces. Its biggest disadvantage is its difficulty in steering at low speeds. The lack of a steerable nose wheel means you must rely on differential braking only at low speeds and the rudder at medium to high taxi speeds.

This leaves you prone to what is called ground loops. A ground-loop is caused by the center of gravity being positioned behind the point of lateral rotation (the main landing gear in this case). Any over use of differential braking or miscalculation of the leverage applied by the long leverage arm of the rudder can cause the aircraft to violently and uncontrollably spin around. Think of trying to steer your car while driving at high speeds in reverse.

The old adage is that you have to fly a taildragger from the moment you leave the hangar till the time you park it to put it away. Tail-draggers require you to be a lot more adept on the rudder.

It also leaves you vulnerable to prop strikes due to nothing stopping the nose from over-pitching. Something very easy to do by applying the brakes too hard during roll out from landing.


What model of aircraft is this? So, what type of airplane is it?

It's an Antonov An-2.

[It] is a Soviet mass-produced single-engine biplane utility/agricultural aircraft designed (...) in 1946. Its remarkable durability, high lifting power, and ability to take off and land from poor runways have given it a long service life. The An-2 is still produced and remains in service with military and civilian operators around the world.

Original image here (no description though).
(commons.wikimedia.org)
(commons.wikimedia.org)


How can an Airbus Beluga fly only with two engines and use short runways? She could land and take off fully loaded on 2000 meters of runway at Hawarden Airport as seen here in this video. At my local airport the runway is 2500 meters long and an Airbus A300 is not allowed to land there. Maximum Airbus A321.

This airplane is based on the Airbus A300-600. The maximum take-off weight of the aircraft is 155 tonne as published in the wikipedia. In addition, the the manufacturer has published the Aircraft Characteristics for the base aircraft.

If we assume that the aircraft low-aerodynamic aerodynamic characteristics has not been changed for the take-off phase (which the runway length depends highly on the aircraft lift and the engine power, and considering that the wing which contributes to the lift has not been changed and engines remained the same), then we can estimate the runway length for take-off and landing from that "Aircraft Characteristics" documents.

For the aicraft at its max take-off weight, in Sea/level, the required take-off runway length is predicted as 1800 m:

For the landing, the maximum landing weight is 140 tonne. Based on the document, the landing field length is 1554 m.

It should be mentioned that these aircraft are used for transportation of another aircraft sub-assemglies, which are large and light structures, such as wing, fuselage plugs, and tails. For this reason, the take-off and landing weight will be far lower from the above mentioned values, which permits them to operate on shorter runways.


How do I contact Flight Service while in flight? How do I contact a Flight Service Station (FSS) in the United States in order to receive weather information or open a flight plan after I've already departed.

For filing and opening VFR flight plans, pushing back your ETA because of a delay, and a few more obscure things which you can find in section 4-1-21 of the AIM you would contact Flight Service (addressed as "region Radio" - e.g. "New York Radio" or "Bridgeport Radio")

The universal flight service frequency is 122.2, and above 5000 feet you should be able to get someone on that frequency, but it's not guaranteed.

If yo can't raise someone on 122.2, or you're below 5000 feet, there are local Flight Service frequencies are listed on VORs as shown below. As a general rule if you can receive the VOR you can talk to Flight Service with the frequencies listed, and using these local frequencies helps avoid congestion on the universal frequency.

(skyvector.com)

Initial calls to Flight Service should take the form:
<Facility Name> Radio, Cessna 12345, 5 northeast of Hampton VOR
(as above for Flight Watch, Who you're talking to ("New York Radio" in the example above), Who you are, and Where you are.)

There's a little catch with Flight Service frequencies: If there is an R after the frequency (as shown for 122.1 here) it is a receive-only frequency. You will talk to flight service on that frequency, but you will listen to the VOR's audio channel to hear Flight Service's responses.
When you call Flight Service using one of these frequencies make sure your nav radio is tuned to the VOR and the voice channel volume is up, and let them know which VOR you're listening to as opposed to your location.
In this example if you were contacting Flight Service on 1221 the call would be New York Radio, Cessna 12345, receiving on Hampton VOR.

For weather (giving PIREPs or asking for a weather report) you will also talk to Flight Service: There used to be a separate service (Flight Watch) and frequency for this, but weather-related tasks were consolidated into the general Flight Service frequency in late 2015.

Radio coverage and contact procedures are identical to what was mentioned above for dealing with flight plan stuff, but you should make it clear you're looking for weather updates (add "requesting enroute weather") or that you want to give a PIREP (add "With a pilot report") so the Flight Service Specialist on the other end of the radio knows what you're looking for.

As weather is generally a localized phenomenon (and weather updates or PIREPs can take some time to relay) it is probably be a good idea to use the local flight service frequencies for weather-relatedrather than the universal 122.2 frequency to avoid congestion there, though I don't believe the FAA or Flight Service has issued any official guidance on this since Flight Watch was consolidated with the rest of Flight Service.


Which aircraft maintenance repairs require a test flight? 14 CFR 91.407 requires an "Operational Check Flight" of an aircraft before passengers may be carried in certain situations:

  §91.407   Operation after maintenance, preventive maintenance,
  rebuilding, or alteration.

  ...

  (b) No person may carry any person (other than crewmembers) in an
  aircraft that has been maintained, rebuilt, or altered in a manner
  that may have appreciably changed its flight characteristics or
  substantially affected its operation in flight until an appropriately
  rated pilot with at least a private pilot certificate flies the
  aircraft, makes an operational check of the maintenance performed or
  alteration made, and logs the flight in the aircraft records.

  ...

Does the FAA have any guidance that includes examples which better explain the bolded section from the regulation? It seems like that could be open to interpretation which could lead to different people having different ideas about when an operational check is required.

For example, is one required for routine maintenance like an engine change or prop change?  What about a flight control change or a flap change?  A new paint job (including the flight controls)?

I've been in aircraft maintenance for over 15 years, and have worked about 10 different types of narrow and wide body aircraft, and have never once seen a maintenance manual direct me to test fly an aircraft.

There is a reason for this, though. Repairs done during routine maintenance are designed by the manufacturer such that the repair itself makes the aircraft airworthy. That is usually part of the manufacturing and STC process, if I'm not mistaken.

That being said, it's not entirely uncommon to have maintenance control or even maintenance management request a test flight. Usually this is done for troubleshooting or for repair verification. This is largely due to the fact that there are some problems that maintenance cannot duplicate on the ground. For example, I recently worked an airplane whose window heat failed at the top of descent about once every ten or eleven flights. I can simulate a lot of things on the ground, but what I can't simulate is the actual descent of the aircraft at about 37,000 feet! The problem had been ongoing for four or five months, but was sporadic enough not to trigger any alarms in the analysts office. It was only when you paid careful attention to the history of the problem that you realized it had major issues.

Due to regulatory requirements, and the way our GMM is written, if the aircraft had another occurrence on the next flight, it'd be "dead" at the next station it landed with no MEL relief. We made a repair, but it was really only a guess because there were no actual signs of wear/fatigue/damage and everything tested normally. Management requested a test flight, and asked the test crew to run it through the wringer, to see if it would fail.

On the other hand, there are certain systems that may require flight crew verification during flight prior to recertification. An auto land system that has had chronic failures may require the flight crew to perform an automatic landing before it can be recertified back to full CAT III landing status. But, this can often be done on a revenue flight, and is often not a dedicated flight meant to specifically test the system.

There is also the rare case in which major structural repairs may require a test flight. I once saw a wide body aircraft that had a tail strike on landing. The damage was so severe, it literally twisted part of the empennage. In order to be repaired, our company required major involvement from the aircraft manufacturer. The manufacturer did provide a repair, but for obvious reasons, the engineers actually mandated several test flights afterward.

However, as far as I know, there is no regulatory requirement which says that a certain repair requires a test flight. From what I've seen, and perhaps this may sound awful, you kind of "know" when an airplane needs a test flight.


How far would an all electric A380 fly? I have edited this to one question and thank you for all the feedback .

I am trying to understand if there are any theoretical improvements in range when applying electric propulsion to large commercial craft such as the A380, or if the theory favours smaller commercial turbine powered craft.

A good answer for a Cessna seems to be the specific capacity of the battery = range in nautical miles. However the weight of the fuel in a Cessna is under 10% of its MTOW, whereas an A380 tops 40%.
The second good answer asserts that you would design a new aircraft, you don't convert an existing one that has been optimised for chemical combustion at the point of propulsion. The proof here is provided by the Sun Flyer.
The third theory is that doesn't matter how big or small the craft is, it's a ratio of battery weight to MTOW.

Whether we decide to convert an aircraft or design a new one, suppose we had to make an all electric commercial aircraft with the greatest possible range, would you start big, such as with an A380 or start with the smallest aircraft and why?

Some A380 facts to use are here: https://web.archive.org/web/20161012152549/http://www.airbus.com/fileadmin/media_gallery/files/tech_data/jetFamily/media_object_file_A380_specifications.pdf
Maximum landing weight= 386 tonnes
Empty weight=282 tonnes
Typical payload=66 tonnes

Thanks for the careful thought on the replies already.

Let's suppose we had to convert a commercial aircraft to an all electric craft tomorrow and use all the available parts, batteries, thrust devices and airframes becoming available, as well as take off and land on conventional runways, with a typical payload etc, would this thing fly?

This amount of specificity makes what would normally be pretty silly into something that can, if only just, work for a question.

The best aviation-specific electric engines are only somewhat heavier per unit weight (but much less powerful in absolute terms) than the best turbine engines, and will make up for it in using bus bars and distribution boards instead of extensive fuel piping, heating and pumps.

You could not simply stack a lot of small electric engines under the wings, as that would ruin the aerodynamics - the wing couldn't produce any lift due to fast jet air flowing under it. It would either have to be an all-custom design, or the engines would have to replace the turbines directly. Such engines are not currently available, but, with superconducting rotors and stators, are potentially achievable within the next decade.

Per calculations done here based on the Breguet equation, a perfect electric airliner will fly up to 10 nmi for each 1% of its weight that is dedicated to the battery. More precisely it's 9.9 nmi at a 0-100% discharge cycle with 100% efficient fans. A more realistic but still optimistic number is 7 nmi, with less than perfect fans and allowing for a 20%-95% cycle that accounts for degradation and emergency reserves.

At takeoff, the A380 can carry up to 254 metric tons of fuel, but that would only leave 44 tons for the payload, supporting up to 400 passengers, and its maximum landing weight would require less than 100 tons of fuel aboard.

Assuming the hypothetical electric 380 is reinforced for a MLW equal to MTOW (575 tons), and counting on savings from general modernization and removing the fuel system to absorb that reinforcement weight, a more realistic battery weight is 230 tons, allowing for a 68-ton payload, supporting the usual 600-passenger capacity. This makes for a 40% battery weight, and thus approximately 280 nmi or 520 km operational range.

So the short answer is: if electric engines with similar power and size to the Trent 900's cores can be produced, the airplane will fly, but its operational range would be just ~500 km, less than 4% of what the current A380 is capable of.

Practically, you would not use an A380 to fly short distances, due to its complexity in ground handling of the two flight decks. There was the Boeing 747SR, built just for the Japanese domestic market, to save on airport slots. The largest plane you'd use has to be something versatile and quick to load and unload, such as the A350 XWB.

But there are short routes for small aircraft 1that are simply begging to be electrified, and if the legacy factor and lack of infrastructure don't interfere, they likely will.


What are (wing area)/(weight) ratio in birds and airplanes? I like to know the usual ratio of wing area over weight in birds and airplanes?

I mean if total weight of an airplane is 100 Lbs(Kg), how much should be the least total area of it's wings?

And also like to know this ratio in birds, if there are information about?

I need this ratio to estimate the wings size, if I want to create an aircraft to lift different weights(it's weight + load weight).

For example, if a person with 150 Lbs wants to fly, how much should be the least area of his wings?

From 'The Simple Science of Flight', by Henk Tennekes, MIT Press

https://mitpress-request.mit.edu/sites/default/files/titles/content/9780262513135_sch_0001.pdf


Are crossing restrictions on an ILS/LOC approach mandatory when flying on the glideslope? Some "ILS or LOC" approaches have crossing restrictions that are shown before and/or after the final approach fix/glideslope intercept.

Are these restrictions for the LOC only approach, or do they also apply when tracking the glideslope?

As an example, KSFO ILS 28L and KSFO ILS 19L (see below) both have crossing restrictions before and after glideslope intercept.

For the fixes after intercept though, notice that NEPIC does not have a '*' next to the crossing restriction (which means "LOC only") while ROGGE does:

Closest regulatory thing I could find :

ICAO Doc 8168 Section 4 Arrival and approach procedures

  1.7.5 Any constant descent angle shall clear all stepdown fix minimum crossing altitudes within any segment.

  5.2.5.1 A stepdown fix may be incorporated in some non-precision approach procedures

  5.5.5.2    The  protection  area  assumes  that  the  pilot  does  not  normally  deviate  from  the  centre  line  more  than  half-scale
  deflection  [...]   more  than  half  course  fly-up [...]  could
  place  the  aircraft  in  [...] airspace where loss of protection from
  obstacles can occur.

The writing leads me to believe that a precision approach should not contain stepdown fixes, and that the descent should be a continuous descent from FAP to MAP.

Then again, I could find nothing specific to prevent anyone from inserting an altitude restriction in a precision approach.

I cannot imagine what would be the point of coming down on a constant GS only to level off at 1000' then try to re-capture the GS just two miles from thouchdown. Talk about a stable approach...


Must a CFII be instrument current to provide instrument training? Can a CFII conduct training for an instrument student in VFR conditions if the CFII isn’t instrument current?

The requirements for providing instrument instruction are in 14 CFR 61.195(c) and they don't mention currency at all. There are also various FAA legal interpretations on whether or not CFIs (not CFIIs) require an instrument rating to provide instrument training (see this question), and what instrument training requires a CFII in the first place (see this question) and none of them mention currency either.

So no, there is no requirement for a CFII to be instrument current when providing instrument training.

Having said that, 61.65(d)(2)(ii) requires instrument students to do a cross-country under IFR with an instructor. An instructor who isn't instrument current couldn't provide that specific training flight, although obviously the student could use a different instructor. And many CFIIs like to take their instrument students into IMC to let them experience how different it is from being under the hood.

All in all, it's in a CFII's best interests to remain instrument current but it isn't required.


What are the "spur" devices on this U2 pilot's boots? From this video on YouTube:

What are those devices and what is their purpose?

These are part of the foot restraint system fitted to the seats used in the SR-71, later U-2 and some Space Shuttles. (They're all derived from the same basic design).

The spurs engage in two ball nipples that protrude from the lower part of the seat. The nipples are connected via cables to reels beneath the rear of the seat which pull the pilots feet in during the ejection sequence.

The seat separation sequence severs these cables (amongst other things) allowing the seat to drop away.

You can see the nipples on the lower part of this Space Shuttle seat:

Source:The Ejection Site


How can I calculate the fuel required for a specific route and aircraft? Okay, I'm writing a online game. I've got two airports and the equipment. For example: Heathrow - LAX on a 744.

What I want to work out is the fuel required, as this will apply a cost to the airline. I know there are many many things such as wind, temperature, regulatory requirements like alternate airport etc but I want something simple.

How can I work out simply the fuel required? Are there charts I can use for working out takeoff, each hour in cruise and descent?

If you just want something simple, just look up the average fuel consumption for the aircraft type (in gallons per hour), and multiply that by the duration of the flight. Although airlines have more sophisticated tools to plan refuelling, this is how GA pilots estimate how much fuel there should be in the tank.

Official fuel consumption figures can be hard to get hold of because the Pilots' Operating Handbook and other documentation for the aircraft might not be publicly available, but it's easy to find out rough figures from web forums populated by pilots of that type.

If you are interested in something more complex (and accurate), see How can I calculate the fuel consumption of an Airbus 320-200 at various loads?


How do long-haul pilots cope with boredom? Imagine you're in a large jet on a long route on a major airway -- say, for example, you're in a 747 going LHR-JFK at night. It's dark, you're over the Atlantic, and ATC has cleared you to just keep on heading along at FL330 (or equivalent) for another ~1500 nautical miles.

As it has throughout much of the flight, the autopilot is effectively flying the plane. There's nothing on the weather radar, no adverse meteorological effects expected, and ATC ensures that aircraft are well separated. In short, other than occasionally changing radio frequencies, there is very little for you to do.

Just a week ago, you were in the simulator, practicing spin recovery, instrumentation inop procedures, engine failures epsilon before V1, and all sorts of other fun things that required your attention. In your spare time, you're a private pilot and enjoy flying VFR at lower altitudes with the occasional bit of aerobatics mixed in, and practicing what to do in all sorts of rare eventualities at odd attitudes. In other words, you like flying planes. Now, your job is to check that the sophisticated flight computers are still flying this plane, and that ATC have done their job properly. They are, and they have. For the next few hours, you're going to be doing nothing but sitting in a chair watching blackness roll past. You can't even talk to the guy next to you about the weather -- there isn't any!

How do long-haul pilots cope with boredom on long, uneventful segments? Is my above scenario completely not plausible (aside from the lack of weather) -- is there always something meaningful to do during a 7+ hour long flight? I would expect that pilot boredom or distraction would be a safety-critical situation, yet I cannot imagine a situation that involves two humans sitting in chairs in a small room for a long period of time where they will not be bored or distracted at some point.

Do airline transport pilots ever "hope" for "something interesting" to happen?

From what I know, airline transport pilots do not get large chunks of free time on a typical long-haul flight which you described. They may get small intervals of free time (e.g. 10-20 minutes), but for sure, not hours. They do need to constantly monitor if the airplane is flying on the correct course, on the assigned altitude, remaining fuel amounts and several other tasks, even when auto-pilot is engaged.

So what do pilots do when they are not flying at all?

Primarily, it depends on company policies. Delta does not allow pilots to do anything not related to flying the airplane:

  "You can't read a novel, but you could read a manual about procedures
  or about the airplane," ... "You can't read a newspaper. You can't use
  a laptop. That's strictly prohibited."

But generally speaking, pilots engage in causal chats between themselves and flight attendants (when they visit the cockpit)1.

When there are more than two pilots, one is generally allowed to get some rest. They can also browse through magazines or read some books or flight-related material, but mostly stay alert and available. Some will study for an upcoming proficiency or rating. One of the two pilots can go to the bathroom too. Getting locked out depends on pure luck.

So in a nutshell, there are several different activities/tasks pilots will engage into, each different for a particular flight.

This is a funny little anecdote I recently read, which fits this discussion very well:

  Murphy's law grants you a heap of emergencies once you start feeling
  bored in the cockpit.

1: As a ordinary passenger, I don't visit the cockpit, but I have noticed a few times what the flight attendants do. When they have free time, they have many things to talk about between themselves. Sometimes, they engage in small talk with passengers. They check their schedule and flights for the remainder of the day. Although the duties of flight attendants and pilots are entirely different, there are a bunch of activities which require their attention, and they can pass the time without getting too bored.


Where can I find a list of past flights at LHR? I am doing a project based on some data recorded from London Heathrow during October 2012, to quality control the data I need to know when aircraft flew past the detectors.

Are there any online databases of when flights took off and landed at Heathrow during this period?

If the data contains which runway the aircraft landed on that would also be desirable,

Thanks for the help

If you're lucky, you might just get it for free (see halfway down this page):

  We have provided a data drop of historical flight information for
  specific airports or airlines, on a one-off basis.

As for the runway data, it's harder, since I don't know of any website which records it. You can have a look on Flightradar24 for which runway is in use at the moment depending on the aircraft positions, but apart from that it's probably not going to be easy. You might want to email the airport directly and ask if they could provide a figure for that month for each runway, but I'll doubt that a single source has the details for each and every flight.

If you get to it, have fun sorting out 40,000 flights ;)


What is this pipe on the tail of this helicopter? In this picture of a CH-53 you can see a pipe or rail on the tail section of the aircraft. What is that?

This device is the antenna for the HF transceiver.

Source

The antenna is the rigid wire running along the top of the fuselage and ending near the window, supported by insulators at regular intervals to move it away from the metallic fuselage for better efficiency.

HF antennas used on helicopters are often loop ("towel bar") and inverted-L antenna (the one you have found).

Length: RF signals travel in a wire and bounce at its extremities. This is also valid when this wire is used as an antenna. In that case the wire takes the name of radiator. The antenna radiates a stronger electromagnetic field when the direct signal and the bounced signal combine in an additive way in the radiator (resonance). This efficiency gain is also valid when working in reception.

RF signals travel in a wire at about 66 to 95% of the speed of light (velocity factor). To make the resonance happen the length of the radiator must be a multiple of the wavelength, or a carefully selected fraction of it, e.g. $\small 1/4$, $\small 1/2$, $\small 5/8$, ... (more) corrected by the velocity factor. The radiator size is therefore proportional to the wavelength used, and the radiator used in HF is longer than the radiator used in VHF.

Diameter: HF band also usually requires higher power (and higher voltage) for the long distance communications it is aimed to.

The result of both requirements is an HF antenna radiator should be longer and should have a larger diameter than for a higher frequency. This leads to designs similar to CH-53 antenna.

In practical the antenna won't resonate for all aviation HF frequencies which are spread over a large range (100 m to 10 m), shorter wavelengths will be privileged.

Some examples:

Source. Notice the smaller VOR/LOC antenna

Source

Source

See also: Why did some Caravelles have a very long dorsal fin?


What is the altitude required to bypass Russia's airspace restrictions for airlines? Given that Russia charges a lot for flights over Siberia from Europe to Asia, would flying above the
Kármán line (100km)
effectively bypass this restriction (from legal perspective) ?
If not, what is that altitude ?

The Kármán line is considered to be the upper limit of airspace and the lower limit of outer space. According to the Outer Space Treaty of 1967 outer space cannot be appropriated by nations (nations cannot claim ownership of parts of outer space).

In that sense, one would be able to fully legally avoid navigation (and other) fees and bureaucracy imposed by any country one was to fly over if it was done above the Kármán line, but since the stunt would require a spacecraft, it hardly would pay off...


Are there modern airplanes with two propellers driven by one single engine? Except 1903 Wright flyer, are there any other airplane using one single engine driving two coplanar propellers?

Coplanar means push-pull and coaxial designs are not in the question's frame.
Tilt rotor aircraft that able to fly with one engine driving two rotors in case of an engine failure are also outside the question's frame.

NASA has proposed to use single gas generator cores to mechanically drive multiple fans in various advanced vehicle concepts, but those are a long way from actually being built.

Airbus and others are also proposing hybrid-electric airlines where a few gas generator cores drive many small fans, although in that case the power is electrically distributed rather than mechanically linked. There are some hybrid-electric vehicles in development that might qualify (Airbus E-Fan-X, UTC 804).  With all the current development in electric aircraft, it is likely some vehicle that meets your description will fly in the near future, with the caveat that the linkage between the engine and multiple propellers is likely to be electrical and not mechanical.

Images from NASA


Does a standalone EASA Multi-Engine Instrument Rating exist? I'm starting an A320 type rating in a couple of months, but my MEP/IR is expiring before that. The pre-entry requirements were only a ME IR. Got me wondering: can I just revalidate my ME IR and let my MEP expire? In other words: is there such a thing as a standalone ME IR (meaning no class or type rating that goes with it)? Thanks and happy landings!

This was just published in CAP1855 from the CAA a few days ago, which may answer your question:

Instrument Rating validity, revalidation and renewal for aeroplanes and helicopters
To revalidate, you must hold a valid relevant class or type rating, unless the IR revalidation is combined with the renewal of the relevant class or type rating; no “empty” IR to be endorsed
The UK CAA has deferred this requirement until 10 January 2020 as stated in ORS4 N.1329.
References: Subpart G, FCL.625, FCL.625(A), FCL.625(H))


Are pilots required to notify the tower when they are flying "under the hood" for IFR training? I was reading a question about flying under the hood for Instrument Flight Rules (IFR) training when this question popped to mind.  Are pilots flying under the hood required to notify the tower?  Does it change the towers approach to that plane at all (especially in VMC conditions)?

No, because the responsibilities aren't any different. And, with a safety pilot on board, the capabilities really shouldn't be either.


How does an aircraft descend without its nose pointing down? I have seen many cockpit videos of airplanes landing, and nearly none of them have their nose down for losing altitude. How does this happen? and how does an airplane, such as A320, descend without its nose pointing down?
And how does this happen in a controlled manner?

A plane descends when it does not have enough thrust to maintain its altitude. A plane can descend with its nose pointed up or down so long as there is not enough thrust to maintain altitude. Altering the pitch of an aircraft is used to control airspeed: pitching up slows an aircraft down (and may cause a climb if done from a level attitude) and pitching down generally speeds up an aircraft (and causes a descent if done from a level attitude). So if you want to descend at a slow speed you reduce power and pitch the nose up.

Since you want to land at a slow speed you will need to pitch up and slow the aircraft down while reducing power to descend nicely. This article covers it nicely in terms of flying an approach. It's also covered in this question.


Can spar stresses be calculated using zero (wing) fuel? For a homebuilt prototype aircraft meant for the primary or Canadian JAR-VLA category, is it OK to assume that spar stresses (other than landing loads) can be calculated using zero-wing-fuel numbers? Or perhaps the landing loads usually negate that zero-fuel stress relief?

So, when specifying plus and minus stresses, both the wing and its fuel content can be discounted except for full-fuel aileron loads?

In general, combining an empty wing with a full fuselage will give the highest stresses in the wing spar at positive and negative load factors. If the wing tanks held fuel, the weight of the fuel mass would reduce the wing spar bending moment inboard of the tanks at the same load factor.

However, details depend on the particular configuration. Make also sure you look at the most forward c.g. location and at the added load from aileron deflections.

Also, don't assume that the critical load case of one design will also be the critical of another. Please look at cases in all corners of the envelope to make sure you do catch the critical one.


How are Max Brake Energy Speed & Weight affected by other factors? I'm a student pilot and I'm trying to understand how different factors affect VMBE and Maximum Brake Energy Limited Take-off Mass. I made some researches but I couldn't find anywhere a clear answer.

What is the effect of Density, Flaps, Mass, Runway Slope, Runway Contamination ?

I know that to solve these kind of problems we use the kinetic energy formula: $\small Eb = \frac 1 2 MV^2$ but I don't know how to use it to explain the effect of every factor mentioned above.

(I need your help because I don't want to just learn things by heart and not be able to explain that in an interview or whatever).

The factors you mention will affect how much energy the aircraft has that's going to be transferred into the brakes, and how much will be lost otherwise.  The more energy you have, the slower you can go before the brakes are overwhelmed -- thus, reducing your VMBE.

With more flaps, energy will be dissipated in aerodynamic drag, although probably not all that much (though going from the least possible to the greatest possible flaps may make some difference -- or it may be sufficiently slight that the charts are published with a worst-case scenario & if you have greater flaps then your situation will be slightly better than what's charted).  With runway gradient, you'll dissipate some energy rolling uphill, while you'll have more energy (potential energy becomes kinetic energy) rolling downhill.

The really significant factor is aircraft weight, as your formula makes clear... an aircraft stopping at 100,000# will have 2/3 of the energy of an aircraft stopping at 150,000#, all else being equal.  So, in those two cases VMBE would be much higher for the 100k case... if Limit = 0.5 * wt * V-squared, you can have a higher V-squared to reach the same limit with a lower weight.

Contamination probably wouldn't matter much: while you would be transferring energy more slowly into the brakes stopping on a slick runway than on a dry one, the total energy absorbed into the brakes would be the same.  So unless the rate that the energy is absorbed changes the maximum energy that the brakes can absorb (seems like it would be unlikely, although in some cases... who knows), contamination wouldn't affect VMBE.  (Unless the charts take stopping credit for the deceleration due to "plowing through" contamination -- which would actually help out to some extent.

The most likely effect would be to make the stopping distance more limiting in the contaminated case than it would be otherwise -- so you might be limited by the ability to stop before the end of the runway in a contaminated case, where you'd be limited by brake energy in a dry runway case.

The effect of weight, flaps, and slope on the actual VMBE would be that things which give the aircraft more energy (more weight, less flaps, downhill slope) would reduce the VMBE.  Think of it in an extreme case... if you had the brakes of a bicycle, a one-pound vehicle could go insanely fast before you could put enough energy into the brakes to cause a problem, but if your vehicle were, say, the Space Shuttle, even at slight speed, the brakes would be overwhelmed by the KE of that much mass.  Consider likewise, a 45 degree downslope vs a 45 degree upslope, or the drag caused by a huge drag chute vs the drag of a pencil flying through the air.


Are winds that are not from the prevailing wind direction more often gusty, and why? It seems to me that, looking at the ground weather forecasts (as opposed to, say, low level forecasts), it's far more common for the wind to be predicted to be significantly gusty when it is blowing across the runway direction of my local airport, than along with it.

Now, obviously, the wind doesn't particularly care about the direction of the slab of asphalt on the ground, but the slab of asphalt is normally aligned with the prevailing wind in the area.

Is a wind that blows at a significant angle to the prevailing wind direction more likely to be gusty, than a wind blowing in the prevailing wind direction in the area? If so, what's the mechanism behind that? Or is this just a case of me being more frustrated about gusty crosswind conditions, thereby noticing it more?

My area is relatively flat.

To clarify, since there seems to be some confusion about this; I'm referring to area ground-level weather forecasts intended for the general public (as those offer a longer-term outlook, typically with reduced resolution and accuracy up to ten days ahead), not METARs or TAFs (however presented) which are about weather conditions specifically at the airport now and in the next several hours.

A little more info about where your airfield is would be helpful.

The generic answer would be that a significant weather event would be required to over come the prevailing winds.  Also, as winds changed from prevailing to cross, gusts and shears would be more likely.  Local low level factors such as terrain, buildings, and trees may also taken into account. The airspace along the runway is generally more clear of these effects as compared with across it for a single runway.  Larger airports with multiple runways provide more options.


Why does A320 Main Wheel need to be tightened 3 times during installation? I have another question related to maintenance practices. During replacing MLG wheel of A320, it is said that we need to tighten the wheel nut 3 times with different torque values.
The first one has the highest value. Then, we need to loosen and tighten the wheel nut again, however, with lower torque values.
In my opinion, I think that the highest torque value is to put the wheel all the way on the axle, however, I was unable to find the answer for why we need to torque the nut again for 2 different values.
And are there any other reasons for tightening the wheel nut with different value?
Thanks for your answer.

FreeMan - Commercial jet aircraft wheels are installed with a single nut on the axle, like a wheel hub on a car.
The commercial jet aircraft axle is a few inches in diameter and is hollow. The wheel bearings are tapered, and while the axle nut is being tightened the wheel is spun ih the normal direction of rotation. A higher initial torque is applied to the nut, and the pressure on the bearings helps to get the races properly seated while the bearings are rolling over them.
The nut is loosened, then the process is repeated using the torque specs specified in the manual.
One of the airlines I worked for had a policy that required that the final time the nut was tightened, it would be turned by hand. After a while, they went back to following the manufacturer's recommendations.
To recap, really tight to seat the bearings, looser for in service operation.
I hope that helps.


Did Airbus do anything about Qantas Flight 72? I recently read about Qantas Flight 72
I'm wondering if Airbus did anything else besides release an Operators Information Telex? And I'm also wondering if this threat is still possible today? One last question, does the new Airbus A330-900neo and new Airbus A340 BLADE have the same ADIRU system as the other Airbus A330 and Airbus A340 or was something changed or fixed?

The ADIRUs presently used are totally different:

for exemple the hardware is of different generation bringing their physical dimension about twice smaller.

Todays AIRBUS used ADIRUs manage the GPS received data too. Internally the technical implementation of parameters is different, just due to technology evolution.

Most of these changes are not directly related to Qantas flight 72, but to new technology, for instance data interchange (such as sending the data of a label such as 224 as being the data of another label such as  204) due to a « bit » failure is not likely to happen nowadays as was the case in previous equipments because internally a « bit » failure is nowadays more precisely detected. Thus sending the altitude as being the AOA won’t happen today.


How much lag does an Attitude Indicator experience? How much lag does an Attitude Indicator exhibit when it is working as designed? Other than well-known problems like tumbling beyond certain limits in pitch and roll, and precession errors from the erecting system, does a gyroscopic AI experience lag that makes it unusable for turbulent or gusty conditions?

Similarly, are there any conditions that would cause an AHRS-based AI to exhibit lag or otherwise show an incorrect indication of the horizon relative to the aircraft?

(Inspired by comments on this answer)

There is no virtually no lag on attitude indicators. The traditional ones are based on a mechanical gyroscope. Due to the gyroscope being gimbaled, it remains in a fixed attitude.

When the aircraft changes attitude, the gyroscope in the attitude indicator remains at its original orientation. When you look at the attitude indicator you are looking basically directly at the gyroscope, packed in a nice horizon displaying wrapping.

The modern attitude indicator in a glass cockpit gets the attitude information from the Attitude and heading reference system (AHRS). There is of course some lag associated with digital data transfer and display refresh rate, but these effects are too tiny to be noticeable by humans.

The first generation of these systems used mechanical gyroscopes as well. Nowadays most AHRSs uses Ring Laser Gyros or Fibre Optic Gyros. These gyroscopes use relativistic effects of light travelling clockwise and counter-clockwise through a circular path. The accuracy of these systems is very high and there is no delay.

Another technology that is used is are Micro-electromechanical Systems (MEMS) gyroscopes. The are based on a vibrating structure. The direction of a vibration tends to remain in the original direction, even though the supporting structure rotates. MEMS are relatively cheap compared to RLG and FOG but they are less accurate. Due to developments in the automotive and mobile telephony industry where attitude sensors are used for various applications the accuracy of MEMS gyroscopes has improved while their costs have decreased. This makes them now interesting for application in avionics.


How is a light plane's nose wheel straightened during retract? Assuming a light aircraft has direct cable linkage to the rudders, during taking off in a very strong crosswind with the pilot correcting with hard rudder, what keeps the nose wheel from remaining off center and jamming as it retracts?

Left: Cessna 172RG nose gear strut (source). Right: nose gear centering cam (FAA).

With the weight off the nose gear after rotation, the strut extends to the unloaded position, and the two internal cams shown on the right mate and center the nose gear.

  Centering cams built into the shock strut structure accomplish this. An upper cam is free to mate into a lower cam recess when the gear is fully extended. This aligns the gear for retraction. When weight returns to the wheels after landing, the shock strut is compressed, and the centering cams separate allowing the lower shock strut (piston) to rotate in the upper strut cylinder (FAA).

On a Cessna 172RG this is achieved by the centering block (circled on the left) during retraction. The rudder is still allowed to move through a bungee link.

  Kinematics of the system automatically straighten the nose wheel as the landing gear is retracted. During retraction, the centering block on the upper torque link aligns and locks the nose wheel in the neutral position. Continued free movement of the rudder pedals is assured by the steering bungee (Cessna 172RG service manual).


How could the Helios 522 passengers have survived so long without oxygen? I've noticed some strange inconsistencies regarding the documentation of Helios Airways Flight 522.

So first:

  Autopsies on the crash victims showed that all were alive at the time of impact

But then:

  The emergency oxygen supply in the passenger cabin of this model of Boeing 737 is provided by chemical generators that provide enough oxygen, through breathing masks, to sustain consciousness for about 12 minutes

So, the oxygen masks in the passenger cabin automatically deployed at 18,000 feet, probably around 09:20. The aircraft did not impact until 12:04. 2 hours, 44 minutes later. Obviously the oxygen masks didn't keep them alive for that long, so:

How could they have survived so long?

To add to Daniele's answer, from the final report:

  The  forensic  report  concluded  that  the  aircraft  occupants  had  heart  function  during  the  impact.    The  report  noted  that  this
    did  not  necessarily  imply  that  they  were alert.    The  report  further  estimated  that  they  were  in  deep  non-reversible  coma  due  to
  their prolonged exposure (over 2.5 h) to the high hypoxic environment.

So, again, saying that they were alive does not mean that they were well.


Trying to find the vertical acceleration by subtracting weight from lift I'm trying to determine the vertical acceleration component of a plane with the following specifications:

Density of air: 1.29kg/m3
Speed: 33 m/s
Wing area: 13.97 m2
Lift Coefficient: 1.5
Mass:560 kg

Lift formula : 1/2*1.29*33^2*13.97*1.5 = 14718 N.

(Lift-Weight)/Mass = (14718-(560*9.8))/560 = 16.48

From this I deduce that the plane has a vertical acceleration of 16.48 m/s2 which I find way too much.(I was expecting to get somewhere from 3 to 5 m/s2)

Your math looks right to me. If an airplane has the statistics that you listed there, then it will accelerate upwards at $16.48\ \mathrm{m}/\mathrm{s}^2$, as you calculated. The occupants will experience about 3 g's of proper acceleration (1 g from gravity, and about 2 g's from the acceleration).

But here's what would actually happen, in context.

To start, assume that the plane is in straight and level flight at 33 m/s. (Here's why I'm making this assumption: You're subtracting weight from lift, which only makes sense if the lift vector is pointing straight up. And if the lift vector is pointing straight up, then the plane is probably in straight and level flight.)

While the plane is in straight and level flight, the lift must equal the weight, so the coefficient of lift must be much less than the 1.5 you have here.

Then, the pilot suddenly pulls back on the yoke, causing the plane to pitch up. This causes the angle of attack to quickly increase, which causes the coefficient of lift to increase to 1.5. The plane starts accelerating upwards at $16.48\ \mathrm{m}/\mathrm{s}^2$.

At this point, let's assume that the pilot maintains a constant pitch after this initial pull-up.

As the plane's vertical speed increases, its climb angle also increases, which causes the angle of attack to decrease. This, in turn, causes the coefficient of lift to decrease again, until the lift and weight approximately balance out again. At this point, the plane is in a steady climb. The vertical acceleration is now $0\ \mathrm{m}/\mathrm{s}^2$, and the occupants are feeling just 1 g again.

(I'm making a couple of small simplifying assumptions in the above: I'm assuming that there is no updraft or downdraft, and that plane's engine is not producing a significant amount of upward force.)