How does a turboprop engine work? I don't understand how it works, can someone provide me with details?

The following describes reverse-flow, free-turbine type gas turbine engines such as the Pratt & Whitney Canada PT6 series of turbo-prop engines that I am familiar with. There are also geared turboprop engines such as the Garrett models; I am not very familiar with these.

The Beechcraft systems description for one of the PT6 models provides the following:

  The PT6 engine has a three stage axial, single stage
  centrifugal compressor, driven by a single stage reaction
  turbine. The power turbine, counter-rotating with the compressor turbine, drives the output shaft. Both the compressor turbine and the power
  turbine are located in the approximate center of the engine
  with their shafts extending in opposite directions. Being a
  reverse flow engine, the ram air supply enters the lower
  portion of the nacelle and is drawn in through the aft
  protective screens. The air is then routed into the
  compressor. After it is compressed, it is forced into the
  combustion chamber, and mixed with fuel that is
  sprayed in through nozzles mounted around the gas
  generator case. Two spark igniter plugs are used to start combustion. After
  combustion, the exhaust passes through the compressor
  turbine and two stages of power turbine and is routed through
  two exhaust ports near the front of the engine. A fuel control system schedules fuel flow to maintain the power
  set by the gas generator power lever. Propeller speed within
  the governing range remains constant at any selected
  propeller control lever position through the action of a
  propeller governor, except in the beta range where the
  maximum propeller speed is controlled by the pneumatic
  section of the propeller governor.

  The accessory drive at the aft end of the engine provides
  power to drive the fuel pumps, fuel control, the oil pumps, the starter-generator,
  and the tachometer transmitter.

  The reduction gearbox forward of the power turbine provides
  gearing for the propeller and drives the propeller tachometer
  transmitter, the propeller overspeed governor, and the
  propeller governor.

The following diagram depicts airflow through the compressor stages, the combustion chamber, the power turbines, and the exhaust section. The propeller bolts on the front of the engine at the output shaft (left side in the diagram).

The following diagram depicts the various compressor and turbine stages. Note the physical disconnect between the gas generator and power generator turbines. This is why these types of engines are called "free-turbines": the power turbine (and by extension the propellor) can spin freely from the gas generator section.


How do I track and visualize aircraft from home? I have a R820 USB SDR and I am using ADS-B to track aircraft flying near my home.  I know I could also use ACARS to track nearby aircraft.  Are there any other aircraft signals I can monitor (doesn't necessarily have to give aircraft location, just info)?

Thanks!

Yes, there is other signals broadcasted by aircraft, although not by all. In the General Aviation sector, at least in Europe, an on-board device known as FLARM is being used mostly in Gliders, Helicopters, Single-Engine Piston aircraft and touring motor gliders.

  FLARM is an electronic device to selectively alert pilots to potential collisions between aircraft. It is not formally an implementation of ADS-B, as it is optimised for the specific needs of small aircraft such as gliders, not for long-range communication or ATC interaction.

You can visualize these signals using some tools and you can also feed the data to sites like flightradar.

Related Answers to FLARM: What system is there in the UK to prevent collisions between small aircraft?
How does TCAS work?


Can an issued landing clearance be replaced with "continue approach"? Since the US handles the landing clearance differently, this is limited to Europe (EASA-land).
From Eurocontrol:

Continue Approach
If the runway is obstructed when the aircraft reports ‘final’, but it is expected to be available in good time for the aircraft to make a safe landing, the controller will delay landing clearance by issuing an instruction to ‘continue approach’. The controller may explain why the landing clearance has been delayed. An instruction to ‘continue’ is NOT a clearance to land.

I understand it's also used for sequencing, e.g., continue approach number 2, number 3, etc.

Here's the scenario:
STACK 1 has been cleared to land, and is 8 NM out. STACK 88 was holding short and was requesting sometime to verify something, but now they are ready.

STACK 88: Tower, Stack 88 is now ready for departure.

Tower: Stack 88, traffic 8 mile final, are you ready for immediate departure?

STACK 88: Affirm, Stack 88 is ready.

Tower: Stack 88, cleared for immediate takeoff, no delay.

STACK 88: Cleared for immediate takeoff.

Tower: Stack 1, cancel landing clearance, continue approach number 1, traffic departing, minimum approach speed.

STACK 1: Roger, continue approach, minimum approach speed.

Is the above exchange correct? In terms of both procedures and phraseology, i.e., can a landing clearance be cancelled for reasons other than a go-around instruction?

The example is correct, except that the landing clearance for stack 1 must be cancelled before the takeoff clearance is given to stack 88. The logic is that only one aircraft can ever be cleared to land on or take off from a given runway at any one time. So in your example, you just have to swap the order of instructions 3 and 4.

Stack 1 cancel landing clearance, continue approach
Continue approach, Stack 1
Stack 88 runway 12 cleared for takeoff
Runway 12 cleared for takeoff, Stack 88
...
Stack 1 runway 12 cleared to land


Can an S-duct fit a turbofan exhaust instead of the intake? Can an S-duct fit a turbofan exhaust instead of the intake? The idea here is to merge 2 exhausts into one at the exact center of the tail. This would be for twin-engine aircraft that have both engines at the tail, like the Boeing 717.

There are of course S-ducts for intakes, like on the Tu-154. I have never seen them for exhausts, however, probably because it's much harder due to the heat.

I know it is engineeringly possible somehow, because I've seen vectored thrust devices with variable geometry, like the iris types and swivel types. For a large commercial jet, it would be easier because the geometry would be static--no moving parts.

But I want to know if it is economically feasible. To take the heat, I think it just needs some super-pure graphite, which does not sound so expensive to me. But I am not an expert.

Yes they can, and it has been done in the Garrett AiResearch ATF3. Although the engine was not hugely successful, it is still being used in aircraft today.

From this answer:

  The hot exhaust stream is deflected back into the fan bypass, which cools it down and results in a low IR signature. This engine is used in the Dassault Falcon.

You can see several S-ducts leading the hot exhaust gases internally into the little staircase-like contraptions behind the fan.


What determines the best glide speed? I found the best glide speed of cessna 152 is 60 kts. My question is why it is not more or less than 60 kts? What are the factors upon which the best gliding speed is determined?

Basically, the faster you go, the more lift and drag a wing will produce. These two values are not proportional, though. When speeding up, the amount of drag produced is higher than the extra amount of lift - which is why you need additional power to maintain level at higher speeds.

When you go slower, the amount of drag will reduce more than the amount of lift produced - at least for a while. That's why going slow is better in terms of gliding distance. The amount of "drag per lift" is very low. However, slowing down beyond a certain point, the wing will rapidly start producing less lift, because airflow separates from the wing. This is what's known as a stall. The best glide speed is the speed as which the drag is as low as possible while the wing is still producing a relatively large amount of lift.

This is illustrated on a speed polar, like this one:

The black line indicates the rate of sink for a given airspeed. The optimum glide speed is the speed corresponding to the point where the red line touches the black line (Vbg).

The red line is a straight line going from (0,0) and touching the speed polar at exactly one point.

A change in aircraft mass will shift the curve along the vertical axis, which is why a heavier aircraft has a higher best glide speed than a lighter one. The intersecting point between the black and red line would shift to the right as the black line is shifted down, and vice versa.


Are there regulations on building homes at the end of a runway? I live next to a golf course (Butter Valley Golf Port) in Bally PA that has a paved single engine air strip that runs through a portion of the course.  Off the end of the runway (in one direction) perpendicular to the end of the runway is a single lane public road that runs in both directions.  I live on this road down the street from this same end of the runway. Currently on the opposite side of the road at this end of the runway is 80 acres of farmland.  A developer has submitted plans to build 236 condos on this 80 acres directly across the street from the end of the runway.  Are their regulations about building homes on the landing/take off flight path of a registered runway?  Where could I find these regulations?

The FAA has regulations on the maximum height of obstacles around a runway (page 22):

  The runway Obstacle free zone (OFZ) is a defined volume of airspace centered above the runway airspace above a surface whose elevation at any point is the same as the elevation of the nearest point on the runway centerline. The runway OFZ extends 200 feet (60 m) beyond each end of the runway.

...

  The inner-approach OFZ is a defined volume of airspace centered on the approach area. ... Its width is the same as the runway OFZ and rises at a slope of 50 (horizontal) to 1 (vertical) from its beginning.


What happens to Cessna electric flaps that are moving when power is lost? On final in a C182T you move the flap control arm from 20 to FULL, and when halfway there, the breaker pops (or BUS1 fails, a wire falls off, etc.)

Does the flap stay where it is, slide back to 20°, slide back to UP, or something else? Perhaps the question is “are the stops mechanically significant?”

Would the answer change if instead of blackout it was a brownout? I.e. the motor is still trying to run, but doesn’t have all of its normal oomph.

Stays where it is. The mechanism is a leadscrew and like most leadscrews it's "self-locking", which means that it's held in position by frictional forces whenever the motor isn't turning and it can't be back-driven even by substantial loads. The 20 degree (etc) "stops" are just reference positions for which aircraft performance and load limit data have been determined.


Why is the end of the F-35's jet nozzle 'spiky'? Why is the end of the F-35's jet nozzle 'spiky', is it like that to increase performance or some other factor?

Stealth. The F-35's nozzle is designed in that manner to reduce the IR and radar emissions from the aircraft (sometimes called Low Observable Axisymmetric Nozzle (LOAN)). From the press release which announced the test results:

GE Aircraft Engines' new LO Axi (Low Observable Axisymmetric) Exhaust System was successfully tested recently ... testing being conducted under the Joint Strike Fighter (JSF) Technology Maturation Program ...

According to GE,

... LO Axi Nozzle was installed by the South Dakota Air National Guard in an F-16C and ground-tested to verify installation compatibility with an operational aircraft system. Both infrared (IR) and radio frequency (RF) measurements were made by GE Aircraft Engines (GEAE) with the F110-GE-100 engine operating at power settings ranging from idle to maximum afterburner. The resulting test data verified that the LO Axi Nozzle achieves its installed signature goals during operation.
In addition to geometrical shaping and special materials for signature control, the LO Axi Nozzle also incorporates an ejector that enhances nozzle cooling.

The system was originally tested on a F-16. The following image shows the nozzle while it was under testing

Detailled rear view of a standard P&W F-100-200 still installed in the LOAN aircraft and the LOAN nozzle in the foreground (LMTAS photo); image from f-16.net


Why are the first sounds of an approaching enroute airliner low frequency, booming ones? Often I will hear an intermittent, low frequency, powerful, booming sound that resolves into that of an airliner flying enroute high (FL 300+) overhead. So the first sounds that an airliner flying overhead to be heard are those. Why? I assume it has to do with the atmospheric conditions and how sound waves of different frequencies propagate forward..

The air attenuates high frequencies more than it does low. Thus, lower frequency sounds travel farther, so you hear them first. Also, longer wavelengths will appear to "bend" around obstacles more than ones with shorter wavelengths, so buildings around you will in many cases develop acoustic "shadow" zones for higher frequencies as those buildings' dimensions are significantly larger than their wavelengths.


Can the Kawasaki T-4 carry weapons? The Kawasaki T-4 is a jet trainer aircraft. However, it seems to have two hardpoints.

Armament
Two hardpoints for external fuel tanks

Can these be used to carry weapons? E.g., unguided bombs or unguided missiles?
I suppose guided missiles require avionics for a more sophisticated fire-control system, fire-control radar, and similar — which I suppose the T-4 definitely does not have. However, please correct me if I'm wrong.

The Kawasaki T-4 actually has three hardpoints that can carry weapons
: one underfuselage and two wingpoints (also confirmed here). The possible armament includes gun pods, long-range anti-ship missiles, air-to-air missiles, free-fall or retarded bombs and pods with 70 mm unguided rockets. Hence no way it could be said it cannot be armed.

This aircraft seems more for training but can be used in light attacks.


What is the procedure when being vectored for an approach and ATC allows you to pass through the final approach course? If you are on a heading, being vectored to intercept final on an instrument approach, and it appears that you will fly through the final approach without being cleared to intercept it, what should you do?

Usually when ATC has a need to vector you across the final approach course, they will tell you about it before they do.  Something along the lines of "N1234 fly heading 230, vectors across final for spacing.".  If they don't and you see that you are getting close, you should ask them if they want you to intercept the course.

The AIM addresses this in paragraph 5-4-3 Approach Control:

  (b) After release to approach control, aircraft are vectored to the
  final approach course (ILS, MLS, VOR, ADF, etc.). Radar vectors and
  altitude or flight levels will be issued as required for spacing and
  separating aircraft. Therefore, pilots must not deviate from the
  headings issued by approach control. Aircraft will normally be
  informed when it is necessary to vector across the final approach
  course for spacing or other reasons. If approach course crossing is
  imminent and the pilot has not been informed that the aircraft will be
  vectored across the final approach course, the pilot should query the
  controller.

  (c) The pilot is not expected to turn inbound on the final approach
  course unless an approach clearance has been issued. This clearance
  will normally be issued with the final vector for interception of the
  final approach course, and the vector will be such as to enable the
  pilot to establish the aircraft on the final approach course prior to
  reaching the final approach fix.

The FAA Air Traffic Control Order Section 9 - Radar Arrivals also has the following directive for approach controllers:

  5-9-3. VECTORS ACROSS FINAL APPROACH COURSE

  Inform the aircraft whenever a vector will take it across the final
  approach course and state the reason for such action.

  NOTE-
  In the event you are unable to so inform the aircraft, the pilot is not expected to turn inbound on the final approach course unless
  approach clearance has been issued.

  PHRASEOLOGY-
  EXPECT VECTORS ACROSS FINAL FOR (purpose).

  EXAMPLE-
  “EXPECT VECTORS ACROSS FINAL FOR SPACING.”


Did the XF-84H Thunderscreech really cause "900 sonic booms per minute"? The Republic XF-84H, known as the "Thunderscreech" was an experimental version of the F-84F Thunderstreak. It was intended to be a supersonic turboprop fighter.  Even at idle, the prop tips rotated at supersonic speeds and the plane is often claimed to be the loudest ever built, supposedly audible 25 miles away.

Most sources describe a continuous sonic boom due to the supersonic prop tips. However, a fairly common claim on the internet is that they caused "900 sonic booms per minute."

Is there any truth to the claim that the plane caused 900 sonic booms per minute?

One's first thought should be, "no": because the prop tips are continuously above the speed of sound, they emit a continuous sonic boom (as most sources claim), not 900 separate ones per minute.  However, since the prop tips were supersonic and the roots were not, it follows that a section of the prop's length would be in the transonic range. Any change to the wind or propeller RPM would cause more or less of the propeller to be moving supersonically.  I suppose that, say, an appropriate oscillation in the turbine engine could cause the continuous boom to be modulated by some 15Hz (900-per-minute) component.

I think it is a matter of where you stand (literally).

From the front or the rear the shock waves from the propeller tips would hit your ears continuously, and the result would be constant noise.

When standing laterally, the propeller tips would move towards and away from you and produce a variation of noise intensity of the frequency produced by the product of propeller RPM and blade count.

It seems that the design RPM of the XF-84H propeller was 3000, and since the propeller had three blades, the frequency should have been 9000 per minute, not 900. The airframe could be split ahead of the cockpit to allow the installation of several nose sections with their own gearbox and propeller. Several gearboxes and propellers were prepared with propeller design speeds between 2100 RPM and 3000 RPM, but the test program was ended prematurely, so most of the planned variations were never flown.

I can only judge from the little information available online and count myself lucky not to have witnessed a power-up of the XF-84H (for me personally, the loudest aircraft is still a Sukhoi 22M-4 – you think "man, this afterburner is loud!" and only then the pilot switches the afterburner on), and it seems that the 900 per minute figure must have lost a zero on its way of becoming an internet meme.

Note that I only speak of a variation of noise – as Jon Story writes, a sonic boom is what arrives at your ear, not what is produced by the propeller.


What exactly does it mean, that plane has diverted due to the needs of a passenger? Twitter account for Flightradar24 has reported twice in past 24 hours about two different British Airways flights that has diverted their original route "due to the needs of a passenger" (here and here).

What exactly does it mean? Is it:

a passenger requesting to land on other airport, because he forgot his wallet?
operational decision to put more passengers on-board empty plane?
something else?

The only passenger needs that would result in a non-scheduled landing would be a medical emergency or acts/threats of violence of the level that prompt removal of the passenger is needed (with law enforcement coordination).

A passenger forgetting his wallet would not result in a diversion.  An aircraft deviation to enplane more passengers and proceeding to the scheduled destination would be a highly unusual situation and would not be for passenger needs, it would be for operational needs.


How does headwind influence the results of a pitot tube and therefore the airspeed indicator? What I know so far

I recently read about pitot tubes and their use in aircraft. For the basics I consulted Wikipedia, and also went through the definitions for airspeed, groundspeed, and the various other airspeed definitions (TAS, IAS, EAS, CAS). Furthermore I made myself familiar with aircraft speed indicators.

At first everything seemed logical, I thought I understood the working principle. But then a few days ago I came across the question how wind (headwind, for that matter) is accounted for on the airspeed indicator.

Question

Assume an aircraft that is standing still on the ground, experiencing a 60 kt headwind. Will the airspeed indicator show anything that is related to that headwind? Why/why not?

The pitot-static system (and the airspeed indicator) doesn't care about the speed of the aircraft with respect to the ground. It is concerned only with the speed of air with respect to the aircraft (that is why it is called airspeed and not groundspeed indicator).

So, if your aircraft is on ground and experiences a headwind of 60 kt, the airspeed indicator will show an airspeed of 60 kt, in an ideal case.

This is important because the wing generates lift depending on the airspeed, not the ground speed (forgetting about stuff like ground effect, etc.). This means that if an aircraft is parked on the ground and there is a headwind of sufficient velocity, it will try to lift the aircraft up.


Can small airplanes dump fuel during flight? Can small airplanes, such as a Cessna 172, dump fuel during flight?

My understanding is that large commercial passenger aircraft often have the capability to dump fuel during flight, as can many military aircraft.  However, is that capability available for small 2 or 4 seat planes?  How big does a plane need to be before a fuel dump capability becomes useful?

The short answer is, no, generally only large aircraft have purpose-built fuel dumping systems. Such a system may be helpful in reducing aircraft gross weight to a safe landing weight in the case of a precautionary landing. The approved landing weight of smaller aircraft, such as the C172, is generally the same as the approved takeoff weight.

The longer answer is, yes, it would be possible to "dump" fuel from an aircraft such as a C172, though not by means of a purpose built mechanism. The "dumping" would be more of a slow to moderately fast drain, depending on the means used.

If I wanted to drain the fuel from one of the wing tanks in a C172 while in flight I could use a pen, screw or other such device to drain fuel from the wing tank sump. A faster dumping/draining method—though requiring considerably more work—would be to unscrew and remove the fuel drain valve, thereby releasing all the fuel in the wing. Obviously, this later method would hamper the possibility of draining only a portion of the fuel from the wing tank.

I cannot think of any reason why I would want to drain the fuel in flight apart from reducing the risk of fire in the event of an emergency landing. And in that case, my prefered method of reducing the risk of a post-landing fire would be to concentrate my efforts on the landing, not on eliminating a fuel source.

Generally, I prefer to have more rather than less fuel in the tanks when I fly.


What is the relation between number of crew members (pilots and attendants) and fleet size in airlines? Taking into account relevant elements like the fleet size or the type of flights (short or long haul, passengers or cargo, ...), do airlines use typical ratios between the number of aircraft and the number of pilots and attendants?

Clarification for the type of elements I'm looking for:

Northwings has 120 passenger aircraft and 720 pilots, this is comparable to other US airlines with modern aircraft (6 per passenger aircraft).
There are between 4 and 10 Captains per passenger aircraft. This is dependent on local labor laws and unions.
4 to 6 F/O for cargo aircraft (and no attendants because no passengers).
A380 are atypical at Thing Air with 700 flight attendants for 10 aircraft of that type.
Count 25% less for low cost airlines in the Middle East due to less restrictive labor laws and extended working time.

(Figures are for illustration, I've no idea of what the actual values are.)

My answer may not directly answer your question but from MIT's The Airline Data Project, I extract data for year 2014 and put in table as follow:

Employees Per Aircraft                                  Southwest    United    American Airlines   Delta Airlines    Jetblue Airways
----------------------------------------------------------------------------------------------------------------------------------------
Pilots & Co-Pilots (Crews)                              6.0          8.3       6.8                 7.4               6.5
Flight Attendants (Crews)                               5.9          8.8       7.3                 6.8               5.0
Maintenance (Inhouse)                                   3.5          10.5      17.4                11.4              3.8
Passenger, Cargo and Aircraft Handling (Inhouse)        29.2         63.9      30.7                36.7              27.1
Other (Inhouse)                                         6.9          6.9       10.8                18.1              10.0
----------------------------------------------------------------------------------------------------------------------------------------
Total                                                   70.9         132.2     98.1                107.5             68.2

note that total number of crew does not add up with each type of crew in the table

Hope it gives you some idea about the ratio of pilot and flight attendant


Are there any aircraft that were grounded and later approved for flight? Last year the Boeing 737 Max 8 was grounded after two fatal crashes.

Historically, are there any other commercial aircraft which were grounded (due to safety issues), and later “fixed” by manufacturers and approved by FAA and/or other authorities for flight?

The de Havilland Comet quickly comes to mind, with the airplane grounded after two catastrophic break ups in flight.  The Comet was returned to service once the problem had been identified and corrected in 1958.  Too late, however for the airplane to be a commercial success as the Boeing 707 had captured most of the commercial jet market in the intervening time.

So to was the McDonnell Douglas DC-10, which was grounded due to a faulty cargo door design, leading to two fatal accidents, but after operators implemented the required Airworthiness Directives from the FAA, the airplane was returned to service.

In fact many well known airframes have been temporarily grounded during their service lives then returned to service, including, but not limited to:

McDonnell Douglas DC-8
Aerospatsiale-British Aerospace Concorde
Boeing 767
Boeing 787
BAC One Eleven

Several aircraft were nearly grounded and faced public disfavor for a period of time thereafter.  The Boeing 727 was nearly grounded after 3 727-100s crashed in 1965, killing 131 people.  So, too, was the BAC 146 'WhisperJet', which was nearly grounded by the British government in 2000.

Military aircraft, too, have been temporarily grounded due to defects or service problems.  Lockheed's F-22 was grounded in 2011 after multiple pilots suffered hypoxic symptoms from the plane's malfunctioning OBOGS system.  The F-35 was temporarily grounded last November after a crash of an F-35B near Beaufort, SC.

Despite the best efforts of OEMs to conduct a rigorous and thorough development and flight test program to ensure a safe product, many potential problems simply can’t be identified until an incident or accident occurs in the fleet.  It’s virtually impossible to foresee every potential safety concern with a product that contains 4 million parts, 6 million lines of software code, terabytes of engineering data and tens of thousands of pages of operating protocols.  All of which must be able to function in perfect harmony and unison, without any conflicts.  Unfortunately much of what we know about aviation safety was paid for in the lives of the less fortunate.  Engineering OEMs strive to build better machines with each generation building upon the lessons learned from the past, but it’s not totally foolproof.


What does 'EST' at the end of a NOTAM's valid time mean? In this NOTAM below, the valid time is "2006280446-2007312359EST".
EST does not appear in the FAA NOTAM contractions list.

I assumed this EST meant "Eastern Standard Time", but that conflicts with the information shown below in ForeFlight.
This is what ForeFlight shows for the same NOTAM:

What does this "EST" mean?

If the NOTAM duration is expected to return to service prior to the
End of Validity time, the time is expressed by using a date-time group
followed immediately by EST (estimate).  Any NOTAM that includes an
EST must be canceled or replaced before the NOTAM reaches its  End of
Validity time. If the NOTAM is not canceled or replaced, it will
expire at the end  of validity time regardless of EST.

Reference:
https://www.faa.gov/documentlibrary/media/order/notam.pdf#page=7


What are the rules for driving at a public, uncontrolled airport in the USA? Are there any rules for driving a passenger vehicle on taxiways and/or runways at an uncontrolled airport in the USA?

The FAA has issued an FAA Guide to
Ground Vehicle
Operations -
A Comprehensive Guide
to Safe Driving on the
Airport Surface which covers what they call "non-towered airports"

  NON-TOWERED AIRPORTS
  When the control tower is closed or if there is no tower, the airport
  is referred to as non-towered. At a non-towered airport, you do not
  need controller permission before entering a runway or taxiway.
  Below are some best practices for operating on a non-towered
  airport:

  When you approach the runways and taxiways, STOP, LOOK
  both ways, and LISTEN for aircraft that are landing or taking
  off. Vehicle windows should be open to do this properly.
  Alert others when you are using a taxiway or runway by
  always making an announcement on the radio before you
  enter. Be specific with your location and intentions.
  Always yield the right-of-way to taxiing aircraft and give them
  plenty of room. If an aircraft is headed toward you on the
  same taxiway, move out of the aircraft’s way.
  Always carry a radio tuned to the airport’s Common Traffic
  Advisory Frequency (CTAF) or UNICOM.
  If an aircraft is about to land on a runway that you need to
  cross, stop well clear of the runway. Continue to yield to the
  aircraft until it has landed and taxied off of the runway.
  Be aware that some
  aircraft at non-towered
  airports are not equipped
  with radios.
  Before you cross a runway, ensure that no potentially
  conflicting aircraft are taxiing, landing or taking off. Be
  aware of aircraft at non-towered airports that frequently make
  touch-and-go landings (immediately after landing, full power
  is applied and the aircraft takes off again).
  If your vehicle has a rotating beacon, be sure to turn it on
  anytime you are on the airport surface. Turn on headlights as
  well, being careful not to blind any pilots in the area.


What stops a pilot from flying VFR and going IFR? Even if the pilot is instrument rated, what stops them from doing it anyway? I’d imagine in certain situations where danger is approaching, it may be best to switch to IFR, it can’t be that hard to rely on your instruments to get through a cloud? Would controllers know if you switched from VFR to IFR and this could get you in trouble or something?

You are confusing VFR, VMC, IFR and IMC.  Let’s briefly define the terms before I attempt to answer your question:

VFR – Visual Flight Rules.  The pilot navigates at will, but must comply with cloud clearance and airspace requirements.

VMC – Visual Meteorological Conditions.  The weather is good enough to operate under VFR.

IFR – Instrument Flight Rules.  The pilot must file a flight plan with ATC and be cleared for the altitude and route flown.  This defined and regulated process is required under IMC, but can also be followed when the weather is clear.

IMC – Instrument Meteorological Conditions.  Weather conditions are poor enough that operation under IFR is required.

So to answer your question, if an instrument rated pilot is operating under VFR and finds him or herself unable to maintain VFR cloud clearance requirements, (i.e. the weather is no longer VMC) then they should contact ATC immediately and request an IFR clearance.  By definition it is not possible to fly under IFR without the knowledge and consent of ATC.

And yes, it is possible to fly into IMC without ATC's knowledge or a clearance, but it is neither safe nor legal.  It is unsafe for the non-instrument rated pilot because of the extreme likelihood of spacial disorientation, and for both because of the risk of loss of separation from other traffic.  An instrument rated pilot would of course be able to rely on their skills to penetrate a cloud safely, but it is not something that can be done at pilot's discretion as you suggest.

I am guessing that the origin of your question is what we call “inadvertent IMC”.  In this case, instrument rated or not, the pilot should fly by reference to their instruments and execute a level 180 degree turn to exit the cloud.  This is an emergency situation.


Why is the flow ahead of a shock wave chaotic? Here is the image of a shock wave on a cone in a small supersonic wind tunnel, the white lines are the condensations formed in the test chamber due to flow expansion.

Why are the condensations so chaotic ahead of the shock wave?

I know that the flow shouldn't fall down on the cone but still, why is it so chaotic?

Note: the chamber is 4-5 cm long.

The wind tunnel design is not providing clean smooth airflow. Turbulence at supersonic speed does not travel upstream so the turbulence must be created by the wind tunnel design.


Would failure to put on an oxygen mask during loss of cabin pressure result in death? I was trying to explain to someone why the cabin is pressurized (no one wants hypoxia) and that led to discussion about the emergency oxygen masks available on airliners.

If a person didn't put on their oxygen mask, would they be able to survive the lack of oxygen while making an emergency descent to a safe altitude? Would they sustain severe brain injury?

I did high altitude training about three months ago, up to 30,000 feet simulated altitude.  Here's the timeline:

Within 30 seconds (oximeter 100-95): noticed physical symptoms beginning.  I could tell that something was wrong, but felt functional.

Within 60 seconds (oximeter ~90): mild headache.  Still able to write my name.  Not feeling good, but acceptable.

Within 3 minutes (oximeter ~80):  Able to do simple tasks when specifically directed (thread a nut onto a bolt), but completely unable to multitask at even the simplest things (tried to put my pen down...didn't notice that I missed the desk - it landed on the floor.)

Within ?? minutes (oximeter ~70): I am no longer able to perceive the passage of time.  No longer able to take meaningful notes.  My signature is still legible - instinctive muscle memory apparently doesn't degrade nearly as fast.

Within 6 minutes (oximeter unknown): I have taken another pen from my pocket and am playing the knife game from "Alien" with it.  This is much more interesting than paying attention to the directions from the instructors.  I don't notice anything odd about my behavior.

Immediately after:  An instructor gives me a direct command to put my mask on.  I comply.

Total time in chamber: 7 minutes.  Time of useful consciousness in chamber: about 2 minutes

So, to answer your question: It depends.  I can safely say that seven minutes at 30,000 foot environment won't guarantee death (because I've survived it), and it won't guarantee severe brain injury (they let me keep flying) but on the other hand, I'm young and I exercise.  The best answer I can give is the same one that applies to scud running:
Just because the guy before you was able to do it, doesn't mean you'll be able to do it.


What is the largest aircraft (by max takeoff weight) in which all engines are in the tail? The largest one I'm aware of is the Il-62, with a whopping 4 turbofans at its tail. Max takeoff weight is 165 tons.

I actually don't care how many engines there are, as long as all are at the tail. I don't care what kind either, turbofans, turbojets, anything. Don't care if it's military or civilian.

Edit: Airbreathing engines only. The space shuttle and buran don't go above 109 tons anyway, but the criteria here is max takeoff weight and those rockets "take off" far too differently than airplanes.

I googled this of course, but predictably these kinds of "what's the biggest" questions with specific conditions attached are not well-known. I'm hoping someone will know of an example bigger than 165 tons.

The reason I ask is because I'm curious just how much engine weight can be put at the tail and still have a conventionally-shaped aircraft. I'm a little surprised at the Il-62, actually. Sooner or later, to keep the center of mass ahead of the center of drag, the wings have to move more and more back until suddenly you have a canard config where the wings almost operate like a delta where the ailerons are also elevons and maybe even flaps.

I think you've got it. Surprising to see how much larger it was than the VC.10.

There was a planned development of the VC-10 that used the VC-10 wing and tailplanes with a new double-deck fuselage. This VC-10 Superb (DB.265) had a planned MTOW of 174 tons.


Why aren't airliners spin-tested? According to Wikipedia, only single-engine aircraft with an MTOW no greater than 12500 pounds are required to demonstrate the ability to recover from a spin, and not large or multi-engine aircraft.  This seems backwards to me, as it would seem to be far more critical for an airliner with potentially hundreds of people on board to be able to successfully escape from a spin than it would be for a small GA aircraft where only the pilot's life is at stake, and not anyone else's.

Can someone explain this seeming contradiction?

1. Spins are less frequent on large aircraft

They are less maneuverable
They are flown by more experienced pilots
They have more protection systems (e.g. flight envelope protection, yaw damper) to avoid uncontrolled flight

2. Spins may cause structural damage on large aircraft
The larger the aircraft, the lower its tolerance to stress. While one can quite comfortably spin a Cessna or Cherokee, attempt one on a Boeing 777 and things will break. Gear doors, the bolts holding the vertical stabilizer as well as cabin accessories are not designed to handle stress in that direction, not to mention engine flame-out.
3. Spins may not be recoverable
As discussed in this question.


Which precautions should I take when flying in very cold / hot weather? What are the important precautionary measures to take when a flight (either GA or airliners) is operating in extremely cold (e.g. -10°C or below) or extremely hot (e.g. 40°C or above) weather conditions?

Pre-heat the engine
When the engine is cold, the metals may come in contact to each other, which greatly increases engine wear. The best way to pre-heat is to use a hangar.
Engine oil
Oil viscosity is closely related to temperature. If the temperature is too low, oil becomes too thick. Thick oil cannot flow around the engine compartments freely. Thin oil, on the other hand, may have reduced lubricating effect. Thus, choosing the correct oil type is important. An oil with lower viscosity may be used in cold climate, and likewise oil with high viscosity in a hot climate.
Cabin heat
Cabin heat can be useful for warming the cabin, however a leakage may lead to carbon monoxide poisoning. Carbon monoxide detectors can be useful in providing an early warning.
De-ice
Ice built up can affect aerodynamic surfaces severely. In serious cases, they may cause the wings to lose enough lift and stall. Pitot tubes and engine sensors may also give false readings if their de-ice/anti-ice system is not activated.
Density altitude
The density of cold air is greater than normal. Engine damage may be induced by pushing full throttle, which causes the engine to produce more power than it is rated.
In hot air, the density is reduced. This reduces engine performance, resulting in longer takeoff and landing rolls. Aerodynamic performance is also reduced, resulting in a higher TAS (true airspeed) for the same IAS (indicated airspeed). These effects must be taken into consideration in determining whether runway length is sufficient.
If there is high terrain near an hot airport, it may be necessary to circle the airport to climb as the plane may not have sufficient climb performance.
Surface friction
In cold conditions, the taxiways and runways are often icy and slippery. Heavy braking should be avoided.


In a Cessna 172 flying VFR on long final, when do I extend flaps to 10, 20, and 30 degrees? At the pilot-controlled airfield I use most frequently, we fly a standard rectangular pattern.

The normal-landing C172 flap sequence goes

Downwind: 10 degrees past the “abeam point” and airspeed in flap range
Base: 20 degrees
Final: 30 degrees when assured of making the runway

When making occasional landings at a nearby Class C airport, ATC sometimes puts me on vectors resulting in a long, straight-in final. In relation to such an approach, when do I extend flaps to 10, 20, and 30 degrees?

I visualise the standard lengths of the pattern and pretend I'm simply doing them in a straight line.

I'm sure you could figure out precise lengths or time intervals if you wanted to, but ultimately in a 172 in VFR you don't need to be exact - you just need to be fully configured and established by the usual point on final approach, as if you were completing a circuit.

The trap many people find with a straight-in approach is they leave everything too late - downwind checks, flap, etc. Make sure you allow enough room for about 15-30 seconds between flap extension, otherwise you'll find it difficult to maintain the approach angle.

As with everything, a good straight in approach takes practice!


Why are the wingtips of sailplanes painted red? Modern (plastic) gliders are painted white (I suppose for thermal reasons), except for some shapes on the fuselage (generally blue or red, but it seems the color does not matter). And the aircraft registration is dark, I suppose for maximizing the contrast.

Now, for the wingtips I noticed that there are two possibilities:

white (nothing special)
red marks

My question is: Why red? Is there something special that is preventing the wingtips from being painted in another color?

White is indeed chosen for thermal reasons. Gliders use epoxy resins which cure at room temperature and are then tempered at 60°C. This tempering shifts the glass transition temperature to something close to the tempering temperature, so the structure must not be heated under stress to more than this temperature. To limit heating by solar radiation, black surfaces should be avoided altogether and mostly red, blue or grey is used for markings.

The red wingtips were popular in the 1970s and were meant to improve visual identification when flying in hazy weather and close to clouds. They can be mostly found on gliders of this era. Since structural loads are lowest at the extremities, wing- and fuselage tips can be painted in high-visibility colors.

Schempp-Hirth Cirrus with red wingtips but no markings (picture source). This makes it obvious that this is a British glider.


Is right rudder always needed during go-around/touch and go with a Diamond DA-40? Is application of right pedal always necessary in parallel with advancing power lever in diamond aircraft (DA-40) during go-around/touch and go?

"More right rudder" is like a Flight Instructor's mantra, for most all small single engine planes where the propellor spins clockwise from the pilot's viewpoint, and right rudder is needed when engine power is suddenly increased to counter the engine torque and airflow effects.


Are certain NOPAC routes reserved for military use? Are any Northern Pacific (NOPAC) routes reserved for military use?

A local air force reserves chunks of its airspace as they see fit. But it never applies to publicly published inter-FIR routes. So the answer is no.

From Fundamentals of Air Traffic Control (on Google Books):

The routes stay out of Russian airspace, why that matters? Russia has a history of limiting civilian traffic through areas of their airspace. Like parts of the arctic circle, which only started to relax in the past decade or so.


How is a composite fuselage repaired when structurally damaged? In case of FOD, a fuselage puncture for example, what is the repair process? Considering time, complexity and cost, how is compared if it was an aluminium fuselage?

This is pretty broad and covers a wide range of techniques.  But the airplane Structural Repair Manual (SRM) provides guidance, depending on the extent of the damage.  Typically it involves excising the damaged or delaminated structure and patching the affected area.  As with metal airframes, if the damage it too extensive the airframe may have to be written off as a total loss.


What is the best airfoil for Edge 540 Style Aircraft? I need help picking an airfoil. I'm an artist and have limited knowledge of such things.

It's for a game with an aircraft similar to an Edge 540 / Extra 300.
Unfortunately I have a limited selection of airfoils though and need some suggestions for both wing and tail airfoils. (Don't have the ClCdCm for the real Edge)

I do have access to many (not all) of the airfoils listed on this site though.
https://aerodynamics.lr.tudelft.nl/cgi-bin/afCDb

Any guidance would be appreciated!

For the Extra 300 which has symmetrical airfoils:

Extra 300, image by Ampbomber (source: rcgroups.net)

From the service manual of the Extra 300S:

Wing: from MA 15S (root) to MA 12S (tip). This change in profile allows for good performance both at low and high airspeeds.
Tail, for the 3 surfaces: - Wortmann FX 71-L-150/30

Wing airfoils characteristics seems not available online. On X-Plane.org forum (How X-Plane Uses Reynolds Number), it is suggested to replace the airfoils by NACA 0015 and 0012.

For the pitching moment coefficient Cm:

Cm is null for a symmetrical airfoil (no camber).

Manufacturer manuals:

Maintenance manual, in particular the chapter for the wings
Pilot's Operating Handbook.

Similar project:

On SourceForge: Building an Aerobatics Aircraft for JSBSim: The Su-26.

As an additional information, a study was conducted to evaluate the lift coefficient of the wing (or maybe with the tail) and the lift / drag curve, at a reduced scale:

Experimentally determined drag polar and lift curve for the Extra 300 (Figure 7)

However:

The scale change introduces a different Reynolds number, unknown adjustments must be made to extrapolate to full scale.
The curves are incomplete (alpha max undetermined).
The L/D ratio close to 2 is very low compared to the actual performances.


How can I correct the heading for this navigation problem? I'm a pilot trainee in Hungary and just encountered a navigation question problem which is from the PPL Training Questions book. Would be glad if someone can briefly explain how to do this typical question which I come across a lot.

    An aeroplane has a heading of 090°. The distance which has to be flown
    is 90 NM. After 45 NM the aeroplane is 4.5 NM north of the planned
    flight path. What is the corrected heading to reach the arrival
    aerodrome directly?

  a) 6° to the right,

  b) 9° to the right,

  c) 18° to the right

  d) 12° to the right

The correct answer is 12 degrees.  The problem is as follows:

To determine wind correction use an E6-b or similar.

Set distance off course over distance already flown.  In this case, $\frac{4.5}{45}$. The degrees to eliminate wind drift will be under the rate arrow, in this case: 6.

Then, determine how much additional correction is needed to rejoin.  In this case, $\frac{4.5}{45}$ again.  You must add 6 more degrees to the first 6 to rejoin.

The total (therefore the answer) is 12.


Is this Class G Airspace? So it's been about a decade since I got my private pilot cert and almost as long since I got to fly. My map reading is a little rusty.

I'm trying to fly my drone at a local park and it's warning me that I'm in Class D airspace. I've marked on the map where the park is.

If I'm reading this correctly, then I should be in Class G airspace up to 700ft AGL

Am I missing something or is this probably just a bad GPS signal on start?

I'm not getting repeated warnings so I think it's a bad signal but I figured a prudent pilot would check.

Provided the drone is flying where the red dot is, you are correct and Class G extends from the surface to 700 ft AGL.  If you really wanted to play it safe, call the tower at KBKL to establish two way radio comms before flying there.


What do pilots do to prevent DVT? I was reading an article on deep vein thrombosis in air travel. It seems that the problem is more prevalent than one would think. A great deal of effort goes into preventing planes from crashing but people are many times more likely to die from pulmonary embolism than a plane crash.

I'm wondering what steps have been taken to mitigate the health risks for pilots who spend many more hours sitting in a cramped seat at 8,000 ft of cabin altitude than most passengers. The most common advice for travelers is to do exercises to keep blood flowing and get up and move around occasionally. Is this practical for pilots? It doesn't seem like there is enough leg room to do exercises, not to mention that there are rudder pedals that could cause problems if you push them at the wrong time. If one of the pilots gets up the other pilot is often required to wear his oxygen mask until the first pilot returns. This would tend to make the pilots keep their cockpit excursions to an absolute minimum.

Do most pilots wear pressure stockings? That is another way to help prevent DVT. Is this a priority among the airlines and pilots themselves?

Deep vein thrombosis (DVT) or Traveler’s Thrombosis occurs when blood in a vein (most often in lower extremities) becomes stagnant and then forms clot. If you think about it, the pilots are at less risk compared to passengers in this matter. FAA advices certain steps to prevent DVT, like,

Increasing leg muscle activity during long periods of sitting improves blood flow in the legs. This may include walking around the cabin or exercising your lower legs and ankles while seated.

Drinking adequate fluids, and avoiding alcohol and caffeine, may also help by preventing dehydration.

Some recommend taking short naps, instead of long ones, to avoid prolonged
inactivity.

It would be much easier for the pilots to do these things compared to say, passengers.

Pilots usually have more room in the cockpit compared to passengers in cabin.

In long haul flights, there is usually a standby crew member who is rotated so that the pilot could get some movement and rest.

It is certainly practical for the pilot to get up and stretch his/her legs during flight. It is not as if they are flying the aircraft hands-on every second for the entire flight. In any case, the flying duties could be alternated between the two flight crew without any problem.

It is not unknown for pilots to take short naps in the cockpit

Studies indicate that the DVT is more prevalent among the passengers than the pilots. According to Deep vein thrombosis in commercial pilot:

10 percent of air travel passengers older than 50 years develop symptomless DVT during prolonged flights. DVT among air travellers has been documented, but is rare among pilots flying commercial aircraft.

Also, it seems (some pilots, at least) do wear flight socks.

It seems that the pilots don't take the wearing of oxygen mask seriously.


Why is a plane escorted while in technical difficulties? In a recent incident, where the pilots of an Embraer 190 lost control and started flying erraticly in Portugal, two fighter jets started escorting the troubled plane after the emergency was declared.

Why did they escort it if it wasn't a security/military threat? What could they have done or how did they help?

It's not a common thing, as aircraft have technical problems every day without a jet escort. Generally only extraordinary circumstances would merit it.

In this case, the pilots were struggling with an uncontrollable aircraft as well as difficulty navigating - there was lots of bad weather about, and they repeatedly asked for directions to the ocean to ditch, indicating that they didn't know where west was. The jets were scrambled and were available to help the pilots navigate through the bad weather and towards a safe airfield (I don't know if the navigation systems were malfunctioning or if the crew were just understandably overloaded). Fortunately the pilots were able to get the aircraft under some control, I think before the jets even did anything (but more information might come out soon).

Fighter jets can also help check for damage - being better trained and more maneuverable that a civilian craft allows a closer inspection. An underrated benefit is by just being up there with them, panicked pilots can calm down and focus on the task at hand.

Finally there is the horrible option of shooting the jet down if it has been hijacked. This would absolutely be a last resort though, and it's possible that these fighters weren't even carrying weapons.


How does propellers' pitch change during the use of reverse thrust in turboprop/propfan propelled planes? Which way do proplellers turn during the use of reverse thrust in turboprop/propfan propelled planes:

A) Do the leading and trailing edges of propellers remain the same or...

B) Do the propellers turn in the opposite direction, so that the leading and trailing edges of propellers swap?

I tried to show what I mean in the picture:

source: https://es.123rf.com/photo_69655677_cerca-del-motor-de-turboh%C3%A9lice-del-avi%C3%B3n-con-h%C3%A9lice-partes-del-fuselaje-de-un-avi%C3%B3n-alas-y-cola-sobre-fondo-de.html

They are more like an aerobatic airplane that's flying upside down.  The wing of the propeller blade keeps moving in the same direction but it just rotates so it operates at a negative angle of attack to make lift in the opposite direction from normal.  The blade is in a socket in the hub that allows the blade to rotate on its long axis.  The blade root has a big gear on it and there is a gearset within the hub, driven hydraulically on most props using engine oil, that drives gears simultaneously to rotate the blades.

The only difference between a reversing prop and a non-reversing one is the range of rotation of the blade; the reversing one can rotate far enough that the front face of the blade becomes the "bottom" of the wing so to speak when in reverse.

The magic mostly happens in the control system.  In forward flight there is a flyweight governor (like on a steam engine) that controls blade angle based on an RPM setting from the cockpit. Blade angle is adjusted to keep the RPM set.  Reversible props have what is called BETA mode.  In BETA, the angle of the blades is controlled directly by the throttles (power levers) down through flat pitch (DISCING, that is, the prop is effectively a big disc) and into reverse.

You come into BETA when you come back to flight idle.  This is "flight BETA".  On the ground, after you land, you yank on a latch of some kind and move the power levers back more and the props go into ground BETA into DISC, then reverse pitch.  All this time, in BETA, the rpm is controlled by an engine speed governor that adjusts engine torque to set RPM.

BETA mode is more or less how turbine helicopters work, where you directly control rotor blade angle with collective, and a governor adjusts engine torque to keep the rpm constant for you.


How much revenue do seat-back displays generate? Many airlines are toying with the idea of getting rid of seat-back displays, how much revenue did those seat-back displays bring in the form of in-flight advertisement? I would presume for a long haul flight the revenue might be more than what it is for a mid-range flight.

According to this article from September 2014:

  Thales estimates total revenue from IFE at \$17.6m a year for
  small/mid-sized carriers, up to \$397m a year for large carriers.

But that's for all services, not just advertising. The only specific mention I could find of advertising was this 2012 quote attributed to the CEO of Thompson Aerospace:

  Somewhere in the middle of the second question about advertising on
  the system he said: “… and we are generating somewhere between \$20,000
  and \$30,000 per month per plane with the IFE.”

The revenue is apparently generated in a similar way to internet advertising:

  [...] every 2 weeks the airline and the advertising service bureau receives
  a summary of the requests/viewings and the airline gets a check. At 1
  to 5 cents per click, the tally adds up as daily flights, sometimes
  short as an hour, record revenue and usage every passenger, every
  flight, every day, and every month

However, there's no information in the article about which airlines actually use that specific service, and I have no idea if those numbers are typical or not, or even exaggerated.

If you need more information than that and you can afford USD 4,650 to find out, this looks like a comprehensive report on the IFE industry.


Are any special certs or licenses needed for Snow-ski equipped planes? It has been asked and answered here that the ASEL is for Land operations and ASES for Seaborne. Are there requirements specific to using snow-ski equipped planes?

I am most interested in the US, although discussions of other places is fine.

From the FAA manual:

  Title 14 of the Code of Federal Regulations (14 CFR)
  part 61 does not require specific pilot training and
  authorization to operate skiplanes; however, it is
  important to train with a qualified skiplane flight
  instructor.

  Since most skiplanes operate in a wide variety of conditions,
  such as landing on frozen or snow-covered
  lakes and sloping glaciers, with varying qualities of
  snow, it is important to know how performance is
  affected. Use the performance data provided by the
  manufacturer.

From looking at 14 CFR part 61, section 61.5 lists the different ratings. While it differentiates sea and land, there is no "ski" category.


What are interesting cases of ATC agreements between countries? I'm doing some research about cooperative documents between nations regarding ATC; does anybody can mention interesting cases of agreements across the globe? Relations such as Swiss/Others and Hong Kong/China (during British domain) comes to my mind. Also, is there known, famous cases of events (incidents/accidents) caused by disagreement between ATC of different countries you could mention?

You could look into the situation regarding the airspace above northern Cyprus. This relates to 'disagreements', rather than 'agreements'!

Cyprus was invaded by Turkey in 1974, and since then the country has been split into two sections with a UN 'buffer-zone' between the two. The northern portion of Cyprus is not recognised as a separate country (well, not recognised by many States ...), and whenever 'Cyprus' is mentioned they are talking about the Greek half on the southern side of the island. Turkey still insists that the northern half is a separate country.

There are a few air-corridors that pass north-south (and v-v) over the country. A flight going from the north to south will be handled by Turkish ATC until they are at the FIR boundary mid way across the sea between Turkey and Northern Cyprus, whereupon they are told to contact 'Ercan Control'. Ercan is an illegal ATC station in the occupied part of the island which is not recognized by the International Civil Aviation Organization (ICAO). ICAO only recognises the legal government of Cyprus and has issued instructions to aircraft operators to obey only Nicosia ACC when in the Cyprus FIR.

In practise, flights generally ignore that instruction, and contact Nicosia ATC directly.

Heading in the opposite direction flights are told (by Nicosia ATC) to contact Turkish ATC, completely ignoring Ercan Control.

In practise, there are extremely few flights flying these routes, so the problem rarely arises. The use of Ercan Control is limited to Turkish flights heading from Turkey to northern Cyprus.

See Cyprus ATC


Are there regulations about objects/buildings above (across) taxiways? ICAO doc9157 part2 recommend many standard of taxiway system, including width, separation, slope,etc.

How about height of the object above taxiway, like passenger bridge or rail track? Is there any ICAO doc recommendation or major aviation authorities' rule(like FAA) about the vertical clearance of taxiway?

Bridges over taxiways are not a common airport feature. The FAA does have standards for wingspan clearance on taxiways, but not heights. Airport information will tell pilots if there are wingspan or height limits on certain taxiways, and ATC will know which aircraft are or are not able to take certain routes.

For example, Denver International Airport has a bridge over one taxiway. This provides 42 feet of tail clearance, which leaves 3.5 feet of clearance for the A320 family (except the A318). These are the typical aircraft that use this taxiway. A 737 classic would have 5.5 feet of clearance but the 737 NG and A318 would only have 1 foot of clearance. Since the 42 foot number is only in the center of the taxiway, and accounting for other conditions, 1 foot of clearance does not leave much margin for error. So for regular operations, the A320 and 737 classic are the largest planes that will pass under the bridge.

The bridge at Gatwick Airport provides 22m of clearance, enough for a 747 (19.4m high) but not an A380 (24m high).

This suggests that about 10% margin is enough clearance for taxiway bridges. The FAA requires that taxiways have 20% margin plus 10 feet to objects. While wingtip clearance has many variables that require larger margins, tail height will not change much.


What are the FAI rules for circumnavigating the world? If I want to solo circumnavigate the world by plane as the youngest pilot, what are the FAI requirements regarding the routing?

Most standard routings include the Hawaii to California leg, which is about 2200NM, a bit far for my plane.

However, I found this guy, who had a max leg distance of 975N. Would that max 975NM variant still be officially acceptable to the FAI?

"mins" linked to a set of rules at https://www.fai.org/sites/default/files/documents/sc_section_2_2013.pdf , I will try to interpret these in light of your question. I do not take any position on whether those are the official rules and I do not gaurantee my interpretation is correct. I have not read the entire document, just the parts that seemed relavent after searching.

There does not seem to be an official record for youngest flight around thw world. There are records for the fastest round the world (eastbound and westbound) and a circumnavigator diploma (not a record) for flying around the world.

Neither of them seem to have a restriction on the length of invidiual flight legs. Surprisingly other than the polar circumnavigations there doesn't seem to be any requirement to cross the equator.

The author of the route you posted gives a distance of 21738 NM which translates to 40258 km . The speed around the world (eastbound and westbound) records have a minimum distance of 36,770 km, there does not seem to be a maximum number of control points for this record.

The requirements for the circumnavigator diploma are a bit different, there are a maximum of 20 control points which may reduce the measured distance, but the distance requirement is much lower for the circumnavigator diploma.

So this route seems to pass the critera for both the fastest round the world record and the circumnavigator deploma.


How should private airports or locations not regularly intended for landing be identified if you land at or take off from them? How are runways on sectional charts that are listed as private identified?

Lets say I fly from a public airport to a private strip; I would log the departure airport as BNA, but what would I list the private strip as?

Generally, what is the accepted norm?

In the USA, as far as your logbook is concerned, FAR 61.51(b)(1)(iii) only requires "Location where the aircraft departed and arrived," not the 4-letter ICAO identifier of your airports. When you abbreviate the airport with its identifier, that's all you're doing: abbreviating. You could, for instance, write "Nashville International Airport" instead of "KBNA."

Seaplane and helicopter pilots often land in places that aren't even airports. You might log the destination as "Murphy Lake" or "Walmart Parking Lot." Such is the standard convention.

For purposes of the flight plan, there are a few options if flying to a location that has no identifier. On an ICAO flight plan to a location with no identifier, you would enter ZZZZ as your airport, and in the remarks section include a DEST/ group including the lat/long of your destination. For instance, I think DEST/3607N08641W would work. On an FAA flight plan, you can list the nearest waypoint to your destination, and again, describe your actual destination as a common name or lat/long in the remarks.


What is the origin of the term "military power"? An engine producing 'dry' thrust is said to be at 'military power', a useful distinction from reheat / afterburner.

It's always seemed an odd phrase to me. There's nothing particularly military about it, and why would afterburner not be military? 'Military' has always been used as a word that always relates to soldiering in some form or another - it is a curious choice to define the operation of a jet engine.

It must, of course, be a twentieth-century phrase. Can any light be thrown on its origin?

The etiology of military power is from War Emergency Power (WEP) which in the WWII era was a higher than normal rating power (i.e. >100% rated power) setting on an aircraft engine.  Such power settings were approved for short durations (typically 5 minutes or less) such as takeoff and battle maneuvers.

The term was quickly shortened to military power.

Sometimes military power is assumed to be simply full throttle, but that may not be accurate, particularly in blown engines, where turbochargers or superchargers may be set to permit higher than normal air delivery to the combustion chamber.

Finally, military power was used for more extended periods of times, when conditions dictated, but at a reduction in reliability and service life.  Sometimes in war, service life is not a pilot's greatest concern.


Could a triplane fly using a dihedral wing in the middle? I wonder if a triplane glider whose front view is shown in the figure can be built and flown successfully.  As you can see, the middle wing has a dihedral angle, but the top and bottom wings do not.  The vertical lines represent structural members.  The idea behind this strange design is that a box-shape with diagonal members is structurally very strong, hence my interest.  I realize that the structural members at each end will contribute to the drag, even if they have a streamlined shape.  I also realize that every corner of this shape will not produce much lift, but will produce much interference drag.  Yet, I wonder if this weird triplane will fly properly at low speeds.  Any thoughts?

It would depend on the relationship between span and separation. The dihedral would be too great on a short-span wing, as drawn, leading to all sorts of issues. Since the separation needs to be more than usual, approaching two chord lengths, you would need a very high aspect ratio, maybe 15 or so.

But if you were to leave out the middle wing and cross-brace each side with thin wires, as a biplane it would be just as stiff and perform a heck of a lot better.


How are airliners AoA-Sensors calibrated? Airflow around the fuselage is not free, even near the aircraft nose. I assume some correction is applied to the measured angle to get the corresponding freeflow angle.

How is the reponse curve for this correction obtained (for narrow/wide-body airliners)? There must be some other sensor to compare with. This cannot be GPS, since that would give pitch, not AoA.

During development testing the airplane has a "test boom" which in additional to pitot and static inputs has traditionally used mechanical vanes driving pots or resolvers to measure pitch and yaw in the free stream.  Nowadays they are using "smart booms" that do the same thing by measuring pressure distribution at the tip of the boom and working it out with software, but it's still just a way to measure the free stream out where it's minimally affected by the fuselage body.

From that data and from the AOA vane itself, the variations between AOA vane and true are plotted and calibration tables are loaded into the Stall Protection Computer software so the SPC can correct the AOA data internally before it is used for the various functions that need AOA information.


What are these small propellers in the A330 MRTT's wings? In actual flight there are small propellers rotating at the front of these "pillars". What are they? They are visible in this video.

Those two locations you circled out are the under-wing refuelling pods, mounted on pylons (where, I suspect, the A340 outboard engines would be).

You can find a picture of them on the A330 MRTT Wikipedia entry, under the Design section.

And those propellers on the pods are likely the ram air turbines that power the refuelling pods, according to the manufacturer:

  Wing-mounted aerial refuelling pods feature a drogue refuelling system and an integral fuel boost pump which provides a fuel transfer capability up to 450USGPM (1703 Litres per minute) at 45 to 55 PSI (310 to 379 kPa). Pods operate with aircraft power or are self-powered by a Ram Air Turbine.


If a plane lands vertically in a strong headwind, what will the pilot do to exit the runway? If a plane lands vertically in a strong headwind, what will the pilot do to exit the runway?
If he increases the speed, wouldn't that be dangerous (I mean he will fly again)?

If you're in a situation where you can "land vertically" (I assume that means you are landing into a headwind equal in velocity to your landing airspeed), then it's simply dangerous for an aircraft to be anywhere on the ground without being properly tied down. Even if you were able to turn the aircraft, it would probably be lifted into the air again as the wind caught the fuselage broadside.


What is the dimensionally smallest 2-seat helicopter? Considering only a two place helicopters (2 crew, or 1 crew and 1 passenger).

My vote would be for the RotorWay Scorpion II.  Tiny little things would fit in a living room!


What is the ILS glide slope deviation on a 4 degree VOR check error? On a US IFR flight, it is required to do a VOR check every 30 days and the error tolerance is 4 degree except for airborne check.

Suppose I have 4 degree error on my VOR check. When I fly an ILS and right on the indicated glide slope, what is the maximum degree of deviation from the actual glide slope? (range of my actual glide slope)

The deviation detected on your VOR check is likely to be unrelated to the deviation of the glideslope. Whilst they use the same indicator instrument, the radio systems driving the instrument are typically separate.

The VOR system works on a 108.00-117.95 MHz, frequency & amplitude modulated signal. The glideslope works on a 329.15-335.0 MHz amplitude modulated signal.

Both signals have different paths to the indicator instrument, and they use different needles on the indicator.

Therefor it is unlikely that a systematic error causing a deviation in the VOR omni-bearing indicator will cause a deviation in the glide path indicator.

There may be common error sources in both indications, but that depends really on the internal design of the receiver. For example if there is a voltage bias on some part of the system it may affect both systems. But you can't say anything about the maximum degree of deviation from the actual glide slope based on the observed deviation in the VOR receiver.

The localizer receiver works on the same frequencies as the VOR, but the demodulation is different. In an analogue system with needles, they use the same needle. So for localizer there is a higher system commonality with VOR than in the glide path case, which increase the likelihood of a common source of error.


Is collaring a circuit breaker considered deactivation by the FAA? Let's say you discover that your landing light is inoperable during the preflight. Your aircraft doesn't have a MEL, so you follow 14 CFR §91.213(d). Assuming you do everything else required (placard, etc.), would placing a collar around a circuit breaker be considered deactivation?

If not, is there anything that a private pilot can do that would be considered deactivation?

Based on this Advisory Circular, the answer is yes.

  g. Deactivation means to make a piece of equipment or an instrument unusable to the pilot/crew by preventing its operation

Collaring the circuit breaker prevents it from being pushed in, and therefore prevents its operation.


Is there a generic term for origin and destination seen from an airport point of view? I am trying to create a program that gives you the departures or the arrivals from a given airport.

Thus, in the software code, I would like to refer to both origin anddestination with the same term, in order to print the former if the user requested arrivals, and the latter if the user requested departures.

So basically I want to know if there is a common name for these two terms, when speaking from the airport point of view, i.e. referring to a generic flight, regardless of it being inbound or outbound, what is "the other airport" in the jargon?

Perhaps the “remote” airport — that should work for both arrivals and departures.


Are there any methods to predict the location of a jet aircraft from its sound? At times there are military fighter aircraft flying overhead of my location (MiG-21Bis and Su-30MKI).

The first indication of their presence being the sound, that obviously causes one to look up to try and acquire them visually. The sound can be distinctly made out to be changing, as if for a moving object (not sure pure Doppler shift and/or change of source location).

However, almost all the times the aircraft are actually sighted in a totally different location from where the sound 'seems' to indicate them to be (and sometimes not sighted at all)! This seems obvious due to the relatively slow speed of sound and the fast speed of the aircraft.

However, are there are any suggested method(s) to locate such aircraft visually based on the sound?

From a single spotting location, then yes by training. But for any location, then it's very hard. Our ears get confused when the sound reflects off the surrounding surfaces, e.g., ground, buildings, etc. And when the sound comes from above.

Most mammals are adept at resolving the location of a sound source using interaural time differences and interaural level differences. However, no such time or level differences exist for sounds originating along the circumference of circular conical slices, where the cone's axis lies along the line between the two ears.
Consequently, sound waves originating at any point along a given circumference slant height will have ambiguous perceptual coordinates. That is to say, the listener will be incapable of determining whether the sound originated from the back, front, top, bottom or anywhere else along the circumference at the base of a cone at any given distance from the ear.

Tilting your head might help though.
So much so, airplane spotters in WWII judging only by sound misjudged the direction of Allied bombers and the entire Luftwaffe was sent looking in the wrong direction, only to realize the direction reported was incorrect and they had to land once they started running out of fuel.

Göring freely admitted the laugh was on him, that he had sent the Luftwaffe on a mammoth tour of their own air space.

But with computers it can be done using 3D sound localization. Or good old locators:
(theatlantic.com) Chinese soldiers man a sound detector which directs the firing of 3-inch anti-aircraft guns, around the city of Chongqing, China, on May 2, 1941.
P.S. Same problem arises when trying to figure out where an artillery fire is coming from or going to.


Can one become a CFI with a sport license? Under FAA can a sport pilot get a cfi endorsement for LSA category only? If so do they need a medical?

Same questions for glider pilots.

Yes.

FAR 61.403.

  To be eligible for a flight instructor certificate with a sport pilot rating you must:

    (a) Be at least 18 years old.

    (b) Be able to read, speak, write, and understand English. If you cannot read, speak, write, and understand English because of medical reasons, the FAA may place limits on your certificate as are necessary for the safe operation of light-sport aircraft.

    (c) Hold at least a sport pilot certificate with category and class ratings or privileges, as applicable, that are appropriate to the flight instructor privileges sought.

A CFI never needs a medical certificate.  It is not required for the operation of that certificate.

A medical certificate may be required if the CFI has additional roles.  For example, the CFI also is acting as the legal pilot in command.  A sport pilot acting as the legal pilot in command does not need a medical.

FAR 61.23(b)

  (b) Operations not requiring a medical certificate. A person is not required to hold a medical certificate—

    (1) When exercising the privileges of a student pilot certificate while seeking—

      (i) A sport pilot certificate with glider or balloon privileges; or

      (ii) A pilot certificate with a glider category rating or balloon class rating;

    (2) When exercising the privileges of a sport pilot certificate with privileges in a glider or balloon;

    (3) When exercising the privileges of a pilot certificate with a glider category rating or balloon class rating in a glider or a balloon, as appropriate;

    (4) When exercising the privileges of a flight instructor certificate with—

      (i) A sport pilot rating in a glider or balloon; or

      (ii) A glider category rating;

    (5) When exercising the privileges of a flight instructor certificate if the person is not acting as  pilot in command or serving as a required pilot flight crewmember;

    (6) When exercising the privileges of a ground instructor certificate;

To answer your questions.  A sport pilot or CFI will never need a medical because the operation does not require a medical but a valid driver's license.

A glider pilot or CFI never needs a medical or drivers license, if I am reading the regulation correctly.

A sport CFI does not require a CPL as does a regular CFI. The CPL requirement is found under part 61 subpart H

  Subpart H—Flight Instructors Other than Flight Instructors With a Sport Pilot Rating

    §61.183   Eligibility requirements.
    To be eligible for a flight instructor certificate or rating a person must:

      (c) Hold either a commercial pilot certificate or airline transport pilot certificate with:

But subpart H specifies Other than Flight Instructors With a Sport Pilot Rating. The rules for sport CFI are found in subpart K where no such requirement is found. (see 61.403 above)

It does not relieve the pilot or CFI from adhering to FAR §61.53 Prohibition on operations during medical deficiency though.


Manifold pressure vs power vs rpm From what I know MAP is a way of measuring engine power with variable pitch propeller. Greater throttle setting - greater power - greater MAP on the gauge. It happens because MAP is in fact vacum pressure so opening the throttle gives greater fuel and air flow into the manifold, explained here:
Why does manifold pressure increase with power?

But I also read somwehere that when we reduce rpm without touching the throttle, the MAP will increase, according to this topic:What happens to manifold pressure reading following a reduction in both throttle and RPM?

Reducing throttle decreases manifold pressure. Reducing rpm reduces suction, so the MAP should then increase?

The question is:  why does reducing rpm increase MAP?

Assume cruising at 4,000 ft, throttled to about 20 inches MP and 2,000 rpm. Now reducing the rpm to 1,200 without changing anything else will cause the MP to rise sharply. The ambient pressure hasn’t changed, the throttle plate hasn’t changed. The only thing that has changed is the speed at which the pistons are pumping the air. Since they are moving much more slowly at the lower rpm, they are not sucking nearly as hard – not creating as much of a vacuum – so the MP goes up, towards ambient pressure. The pistons are sucking far less air, the speed of the air going through the intake is less and fuel flow is less. This means there is less power being developed, in spite of a much higher MP.


Why can't I find a tail number in the FAA registery? I'm reviewing my pilot logbook in preparation to move everything over to my EFB logbook. As part of that process, I have been looking up the various aircraft I've flown in the FAA registry to get details about those aircraft to make my log complete (my digital pilot logbook tracks more information on an aircraft than my paper logbook and I'd like to have the details for my own nostalgic purposes).

One particular aircraft I flew in 2005, N7635A, is nowhere to be found. Clearly the plane existed - I flew it! And it's in my logbook 3 times complete with my CFI instructor's signatures in those entries, so he seems to have thought the plane existed as well.

When I look up N7635A, I get a Cessna 180 (circa 1960s). I never flew a 180 (seems like I would have noticed that since the rest of the fleet was made up of 2002 - 2004 Cessna 172SPs and they all had that new plane smell). https://registry.faa.gov/aircraftinquiry/NNum_Results.aspx?NNumbertxt=7635A

My first thought was maybe the FAA drops registration records if a plane leaves the country - but that Cessna 180 is deregistered because it was exported to Canada. Also, another plane I flew, N65460, is also deregistered but still has a record with the FAA: https://registry.faa.gov/aircraftinquiry/NNum_Results.aspx?NNumbertxt=65460

I have tried different combinations:

N7635A - 1960 Cessna 180 (wrong plane)
N763SA - 1979 Cessna 152 (wrong plane)
N7G35A - not valid
N7G3SA - not valid

N60432 is another mystery 172S in my logbook but that's from 2013 and I only have a single entry for that one.

Do I have a correct understanding of the FAA N-Number registry? Am I wrong to think it's a complete record of all FAA N-Number registrations (going back to at least 1960)?

I think wrong to believe N-numbers are not recycled.  The process has changed, but now we (owners) must register every two years (I think two years).  //see comment below, registration update is every 3 years and $5 which is background noise compared to an annual


Do pilots breathe the same air as passengers? Do pilots breathe the same quality of air as passengers ?
(i.e. identical parameters: same O2, CO2 and O3 levels, same temperature, same humidity, etc.)

Do pilots breath the same air as passengers (shared air) ?
(i.e. the air a passenger exhales will be inhaled by the pilot [or vice verca], which also means that smoke in the cabin will inevitably end up in the cockpit)

In General, Yes.

As your image already shows, the same air is distributed throughout the cabin and the flight deck. For example, in the 737 NG FCOMv2 2.30.4 (Air Systems - Air Conditioning Description) it says:

  Since the flight deck requires only a fraction of the air supply provided by the left
  pack, most of the left pack air output is mixed with the right pack supply and
  routed to the passenger cabin.

So on the 737, the left pack supplies air to the flight deck and the cabin, the right pack only to the cabin (in normal operations).

Air from the cabin is also reused in the recirculation system:

  The recirculation fan system reduces the air conditioning system pack load and the
  engine bleed air demand. Air from the passenger cabin and electrical equipment
  bay is drawn to the forward cargo bay where it is filtered and recirculated to the
  mix manifold. The fan is driven by an AC motor. The fan operates with the recirc
  fan switch in AUTO except with both packs on and one or both in HIGH.

This implies, air previously exhaled by a passenger could make its way into the flight deck, but it is filtered first. In case of smoke in the cabin, the recirculation system would be switched off. However, during normal operations, the left pack supplies the flight deck directly:

(source: 737 NG FCOMv2 2.30.4)

All air quality parameters you mentioned should be identical or very similar for the flight deck and the cabin, except for temperature. Most aircraft allow separate temperatures for different zones. E.g. the 737 again:

  There are three zones: flight deck, forward cabin and aft cabin. Desired zone
  temperature is set by adjusting the individual Temperature Selectors. The selector
  range is approximately 65°F (18°C) to 85°F (30°C).
  The packs produce an air temperature that satisfies the zone which requires the

Temperature Selectors in the 737 overhead panel:

(source: 737 NG FCOMv2 2.30.4)

The details will of course depend on the exact aircraft model!


Do horizontal stabilizers on airliners have varying angle of incidence in the span-wise direction (washout or negative twist)? Reading this question and answers, I was wondering if modern airliners with cruciform tail have some noticalbe washout or negative twist along the horizontal stabilizer's span.

During cruise, if wing's downwash angle is larger near the center of the aircraft, shouldn't horizontal stabiliser be slightly twisted according to this particular value, in order to reduce induced drag?

There is little to be gained by twisting the horizontal stabilizer in terms of efficiency.

First, the span of a typical horizontal tail is much smaller than the wing (see A320 illustration below for example). Apart from the small outboard portions, the downwash behind most of the wing is fairly constant. This makes the simplification of a uniform downwash on horizontal tail valid.

Second, the lift and drag contribution of the horizontal tail on the overall aircraft at cruise, during which aerodynamic efficiency is paramount, is fairly small. Even assuming a large static margin of 30% (smaller static margin equates to smaller tail contribution), improving the tail span efficiency from 0.8 (typical) to 1 (elliptical) only reduced the total induced drag by half a drag count using some typical aircraft parameters.

These are the parameters I used if you want to verify yourself:

$C_{L_{trim}} = 0.4$
$\alpha_{wb} = 4.8$
$\frac{\partial\epsilon}{\partial\alpha} = 0.43$
$\epsilon_0 = 2.8$
$C_{m_{ac_{wb}}} = -0.12$
$\overline{V_H} = 0.6$
$a_t = 4$
$\frac{S_t}{S} = 0.25$
$h_{n_{wb}} = 0.22$
$C_{L_{0_{wb}}} = 0.4$
$e_{wb} = 0.85$
$e_t = 0.8$ (typical, compared to fully elliptical of unity)
$A_{wb} = 8$
$A_t = 5$


How to learn the back end of flight simulators? I am an engineering student very passionate about aviation and especially flight simulation. I want to know more about how a flight simulator is coded but unfortunately there's not much available on the internet. I want to learn the software aspect of it and would appreciate some help being a complete beginner.

If someone could assist me answering a few questions or having a discussion regarding what language to learn or what books to read, it would be of great help.

Thanks in advance!

Cheers!

The most advanced open source flight simulator is currently FlightGear. It doesn't fall too far short of its commercial brethren.

The repository is hosted on SourceForge, where you can download the entire codebase.
For documentation and discussion on how it works, see the forum and the mailing lists.

Once you have questions regarding the codebase per se, especially regarding the technical implementation rather than the business end of the simulation, they are best asked on the forums or on the main Stack Overflow site. Aviation.SE mainly deals with the flying aspects and real-life aircraft.


Do Military Turboshaft engines have a distinctly different sound from Civilian ones? I live in India, and near an airbase so there are a moderate amount of helicopters flying overhead. My friend claims that he can distinguish between a civilian helicopter or a military one based on the engine noise. He says that military helicopters have a higher pitched whine in their noise that is absent from civilian ones. I have heard it myself but I have no idea if it's perception after he told me or reality. Is there any truth to this? Keeping in mind that most military choppers are Russian/Soviet designs in India while a lot of civilian choppers are Bells

I think your friend is playing a joke on you. I have worked with helicopters since the late 1970's and there is no way to distinguish military from civilian simply by engine noise. You may be able to distinguish between models of helicopters, and in so doing identify a model used by the military versus a civilian one, but that's about it.


How can the F-15 and Su-27 achieve a high top speed without variable wing geometry? I watched a documentary once that explained, I believe, how the Su-27 and similar aircraft such as the F-15, can achieve a high top speed without variable wing geometry.

How does this work? How do they achieve high performance without swept wings in the F-15, Su-27, and similar aircraft?

They simply have enough thrust to do so with their given wing. There is no rule that high speeds are associated with variable sweep wings or that you need such a wing to go fast. As a matter of fact many of the testbed super sonic aircraft
as well as the really high speed stuff dont have swept wings.

Wing design can effect efficiency (which may or may not be a concern in fighters) and can limit top speeds but that simply means that for a fixed shape wing it must be optimized for a desired speed range.


What are the disadvantages of a tailless ultralight design? What are the disadvantages of a tailless ultralight design with say 20 deg swept back wings with wing tip rudders, 20-60mph, max 25 hp?

I'm not an aerospace engineer, so I stand to be corrected:

The only 2 disadvantages I can think of are:

Increased wing area/more weight/stronger spar

I understand the wing area would need to be larger as the "aerodynamic wing span" would be smaller than the physical wing span. I understand the wing only produces lift with the velocity component perpendicular to the leading edge ( which I understand would be V0*cos(radians(20)))

Possible reduced or no side slip angle.

I understand you're not supposed to side slip a Velocity aircraft as the leeward wingtip vertical tail may stall ( rudders only move outward). I understand only the right rudder deflects outward when turning right ( the left rudder acting only as a vertical stabilizer, in this case) I'm attributing this to too thin of a vertical tail airfoil ( low stall angle ) with too high of an aspect ratio. ( I stand to be corrected on all the above). I understand Velocity reduced this problem by reducing the max angle of rudder deflection.

Are there any other disadvantages in terms of stability, cross wind landing, etc?

See pic below of the Mitchell Flying Wing:

When we designed the SB-13, we also thought that it's not so much different from a regular layout. Boy, were we wrong.

It starts with ground handling: Regular aircraft have some distance between front and main wheels, and even more between main wheels and tail skid in taildraggers. This makes them fairly stable in pitch on uneven surfaces. When both wheels are close together because there is little of a fuselage to space them apart, every bump on a grass field translates into heavy pitching. This is annoying.

It gets worse once you lift off: The little pitch damping (now I am talking of the aerodynamic sort) means that every gust makes the tailless aircraft enter into a noticeable short-period mode. This is normally so much damped that the pilot doesn't even notice. In a tailless plane the damping is just enough to stop the motion once a considerable change in pitch has happened. Of course, the pilot will try to steer against it, but with the unavoidable delay of a human in the control loop. That means the counter action will now make the aircraft pitch against the initial motion just when natural stability does the same, so an overshoot follows. Either the pilot suppresses the learned reflex of actively stopping the pitch motion or a pilot induced oscillation follows. This is even more annoying.

So much for the annoying stuff. The outright dangerous would be:

coupling between fast period mode and wing bending. Flutter at low speed is the consequence.
Nasty stall characteristics once the combination of sweepback and aspect ratio surpasses a certain threshold. For 20° sweep this would be an aspect ratio bigger than 7.

You are right about the larger wing area, but this actually helps to make the spar lighter since there is more height to place it in. Unless you need to stiffen the spar in order to shift its bending eigenfrequency above that of the fast period mode in your allowed speed range (plus 20% safety margin).


Which airport is featured in this Delta commercial? I just saw a Delta commercial with a plane taking off from a runway with a 16R designation (thus, the plane in the commercial was departing from 34L). Does anyone know where this airport is? Climbing out, there appears to be a large body of water ahead, if that helps!

I had always heard that Van Nuys (KVNY) was the only airport with a 16R/16L runway designation, but the airport in the video isn't Van Nuys.

It's Paine Field (KPAE) in Seattle. It has both 16L and 16R and has water (the Puget Sound) directly ahead if you're taking off from the 34s. 34L is also the only runway there large enough for most jet traffic, so that's what a Delta jet would be using if it were there.

It's also worth noting that this commercial is about flight testing and Paine Field just so happens to be the home of an aircraft production facility for some little company named 'Boeing.' You can see their Everett Production Facility on the North side of the airport in the Google Earth view and the aerial photo below. Interesting fact: that facility, originally built in 1967 to produce the Boeing 747, remains the largest building in the world by volume even to today. It's 79% larger than the next largest building and a full 3.63 times the size of NASA's Vehicle Assembly Building, the previous largest building in the world by volume, where NASA performed final integration of the Saturn V and Space Shuttle stacks and where it will do so for the SLS.

Here's the Google Earth view, and it looks like the two islands on the left in the commercial are Hat Island and Camano Island:

Sectional Chart Showing KPAE

Aerial View of Paine Field - Source: Wikipedia

Honestly, the claim of there only being 1 airport with any given runway number seems rather suspicious, since there are only 18 possibilities. Granted, the requirement of having parallel runways makes it a little less unlikely, but still many (if not most) large airports have parallel runways.


What does "28 volts DC" mean, really? The common battery voltage on aircraft is commonly referred to as "28 volts".   What does that really mean in terms of a lead-acid battery?

In many uses, such as cars ("12V"), trucks ("24V") forklifts and golf carts ("36V" or "48V"), locomotives ("64V"), the nameplate number is exactly twice the number of lead-acid "cells".   But in reality, the fully charged/charging/float voltage of the system with alternator running is higher - cars 14V, trucks 28V, locos 75V.

Battery units are generally sized at 3, 6 or sometimes 4 units (6, 12 or 8 volts nominal).

So, when aircraft power is specced at 28 volts -- do they actually  mean a 14-cell lead-acid battery or  two 7-cells (which is almost unheard of)... or do they actually mean a 12-cell battery with a "float" voltage around 28V, (built out of two common-as-dirt "12V to everyone else") batteries?

I hope this isn't overloading this question too much, but when nickel-cadmium packs are used, does that have 20 cells, or 19 or some other number?

It's the second option. In any other context, a small aircraft's electrical system would be called "24V". But the alternator regularly puts out 28V, so that's what's typically expected if you hook up your multimeter while the engine's running. Of course, the on-board equipment can operate over a wide range of voltages, often down to as little as 20V.