Is the ratio of HP to weight constant for identical air frames of different sizes? (See Scenario) In my head it seems logical that there would be a proportion between engine HP and empty weight. For example, the Wright Flyer weighed around 600 LBS empty and had a 12 HP engine. If I were to make an exact 1/6 size scale replica out of the same materials that weighed 100 pounds and had a 2 HP engine, would that aircraft fly as well? Would the performance be exactly the same? Thanks in advance!!!

(Don't bother accounting for the pilot's weight.)

In an aircraft, engine power is used to overcome drag. Drag is related to weight, but not in an 1:1 ratio.
There are several types of drag:

Parasite drag: related to the surface area of the aircraft, incl. all the aircraft components that don't produce lift.
Lift induced drag: this is related to lift, which is related to weight.
Wave drag: we'll ignore this for low speeds.

(I'm simplifying things here)

Total drag depends on airspeed. like this:

When you scale an aircraft, things get more complicated. The weight scales with the volume of the aircraft. Your 1/6 scale aircraft won't weigh 1/6 of the original, but (1/6)^3.
Drag scales with surface area, so it'll be closer to (1/6)^2. I suspect lift scales with surface area as well.

So as your aircraft gets smaller, its weight drops faster than its lift, so the wing loading gets lower.

This also means the control surfaces become more effective, and the roll/pitch/yaw rates go up.

This means your takeoff and landing speeds become lower.

In practice, model aircraft fly at much lower speeds than their fullsize counterparts. So they're in a different part of the drag vs. speed graph shown above. This complicates the calculation of how much engine power you need for a model.

If you made a video recording of a full-size aircraft and sped it up, you'd get a decent approximation of what the scaled aircraft would look like.


Roller Coaster Airline Could an airliner legally (using a common regional jets or less likely airliners) and safely perform acrobatic maneuvers that would otherwise not be permitted for commercial passenger flights. Why? For thrill seeking passengers. I enjoy turbulence, so maybe others may pay a little more for a short roller coaster flight. Is there a guide book of commercial aircraft acrobatic limitations and thresholds and special instruction on how to fly inverted, barrel rolls, stall recovery, and so forth?

This is the nearest you will get to aerobatics. You can check out their website for more information.

Company History
After 11 years of surmounting meticulous procedures and safety
regulations, co-founders Dr. Peter H. Diamandis, veteran astronaut Dr.
Byron K. Lichtenberg and NASA engineer Ray Cronise acquired FAA
approval for G-FORCE ONE, a specially modified Boeing 727-200, to take
passengers on commercial parabolic flights. In August 2004, ZERO-G
flew its first commercial flight operating under the same safety
standards of all major air carriers and established its place into the
extreme tourism industry as the first and only commercial Zero Gravity
flight for the general public.
Additionally, in April 2006, ZERO-G became the first commercial
company to gain permission from the Kennedy Space Center to use the
shuttle runway and landing facilities to operate its weightlessness
flights.
ZERO-G has provided thousands of individuals the opportunity to
experience weightlessness including clients Stephen Hawking, Martha
Stewart and Buzz Aldrin.
ZERO-G not only caters to private clients but various organizations as
well. For example, National Geographic, Nick News and Discovery
Channel have all flown on G-FORCE ONE.
ZERO-G has also been featured on NBC’s The Today Show, Biggest Loser
and The Apprentice.
Apart from commercial flights, ZERO-G also provides research and
educational flights.


What is typical thrust to braking force ratio for a passenger airliner? Is the ratio fairly constant across aircraft types, sizes and powerplants?

I'd like to ignore the reverse thrust component, since that's not available at the same time as forward thrust.

If we assume that the braking system is designed to leave no unused braking capacity, the maximum braking deceleration is determined by the friction coefficient of the tyres. This NASA report gives a friction coefficient of around 0.5, for dry concrete with a functioning anti-skid system. This results in maximum braking deceleration of 0.5 g, around 5 $m/s^2$

A typical maximum thrust acceleration would occur for a typical airliner, at TO thrust, and medium range TO weight. Let's take typical numbers for an A320:

A320: TO thrust = 2 * 120 = 240 kN, TO weight = 70,000 kg, a = F/m = 240/70 = 3.5 $m/s^2$
B777: TO thrust = 2 * 500 = 1000 kN, weight = 300,000 kg, a = 1000/300 = 3.3 $m/s^2$
Fokker 100: TO thrust = 2 * 67 = 134 kN, weight = 40,000 kg, a = 134/40 = 3.35 $m/s^2$

So across the board, the braking-to-thrust force ratio is around 5/3.3 = 1.5.


Can a US PPL holder log ASES time in Canada while flying with a local FI? I am an FAA PPL, and I'll be visiting Canada. I'd like to log some seaplane time while I'm there. Can I log ASES dual-received time with any Canadian instructor, or do they need to hold an FAA CFI certificate?

In general, you can log time in foreign aircraft. For training time specifically, the foreign instructor must hold an ICAO-compliant license, per 14 CFR 61.41.

So it should be no problem in your situation.


Before the Soviet Union collapsed, what was Russia's official ATC language? In most (all?) countries today, the official language for ATC communications is English.

Before the Soviet Union collapsed, what was the official language for ATC communications in Russia and other Warsaw Pact countries? Was it Russian?

There's surprisingly little information on this to be found via Google, at least in English, but according to this academic paper from Embry-Riddle titled Air Traffic Control in Russia, Soviet controllers operated entirely in Russian, at least within the Soviet Union itself:

  Prior to 1991, Soviet air traffic controllers and pilots flying within
  Soviet airspace were not required to speak English and the majority of
  them spoke only Russian. After the KAL007 incident, translators were
  stationed at each of the three main control centers in order to
  assist with any controllers who encountered English-only pilots, though
  they weren’t used often (Taubman, 1987).

The cited source is a New York Times article which says that "80 percent of the civilian air controllers in the Soviet Far East speak some English" but translators (more correctly, interpreters) would be used "in an emergency", implying that the standard and/or availability of English was very limited.

If you consider the Warsaw Pact in general, then it looks like other languages may have been more common. This history of Hungarian ATC (you have to love the internet!) includes this information about the 1970s:

  The regular international cooperation between Air Traffic Controls
  commenced in the seventies under the aegis of ICAO, since Hungary
  became one of its regular members. It is more than interesting that
  the Hungarian controllers had to be able to speak not less than three
  languages with the flight crews and use not more than three units of
  measurement, namely the Flight Levels and metric systems of ICAO and
  the Soviet metric system. [...] Then at last, in 1975, Hungary applied
  the full ICAO system, but the Russian language as a medium of
  telecommunication remained in constant use until 1991 when the Soviet
  military forces left our country, after the 1989 political changes in
  Hungary.

It also confirms that Russian was a requirement for ATC controllers:

  Boys in their twenties with more than basic English and Russian
  language knowledge were the target as new trainee controllers.

There are also numerous aviation forum threads about Soviet and modern Russian ATC controllers, the overall picture seems to be that there was always some English spoken by ATC but it was often grudging, limited or just hard to understand. However most commenters (e.g. airline pilots) seem to agree that since the end of the Cold War, it's become much more widespread and the general level of ATC professionalism in Eastern Europe and Russia has improved significantly.


Does ducting help to stabilise heavy lift drones? I'm looking to build a UAV that is extremely stable. It doesn't have to be fast, it doesn't have to be agile, but it will have to carry up to 50lbs (agriculture focused UAV that has to operate for at least 8 hours at a time) over private land (where the drone is authorized to be, and with FAA registration) at an altitude of about 15 feet.

Is ducting the way to go here?

I'm looking to do a quadcopter with a very very low center of gravity right now because of it's inherent stability. Is ducting or more rotors the way to go here? And I have very few specifics because I'm still working on the basics of the platform. It will have to carry a lot of weight and potentially deal with being thrown off balance by a rover getting caught on plants.

There is too little information given to make a definite answer here, but things you should take into consideration are:

depending on the construction the bigger crosssection if keeping a similar rotorsize which will likely increase drag at higher windspeeds while on the other hand leading the airflow so with the right construction it might behave better then without ducting.
using at least 6 or better 8 rotors should enable you to increase lifting power and stability
putting the rotors in an angled position should increase stability while it might slightly reduce lifting power

additionally

the ducting will offer protection for the rotors/fans and people/things getting hit by the drone in case of a crash
as you want too operate it for such a long time the increase in weight which might increase the number of refuels/battery changes needed

Also we were talking about drones that produce the whole lift by rotors pushing air downwards. What about using a ballon or some kind of plane? This will make it more sensitive towards wind and sacrifice maneuverability but will allow extended flight time and potentially higher efficiency.


Do Airbus avionics give good deadstick landing outcomes? We have recently had a second good outcome, in Russia, of a no power landing of an Airbus aircraft. The first was the "miracle on the Hudson".

It appears to me that the avionics of this aircraft are very good at handling the stall v. low speed nose up approach problem.

Does anybody have any insight into this programming?

Airbus (A320+) normal flight law will, at slow speed¹, maintain angle of attack according to the side-stick position, where full aft deflection gets you to the onset of stall.

However the ram air turbine (at least on A320-family; not sure about A330) does not provide enough power to keep all units on and then the system degrades to direct law, in which the side-sticks just control the deflection of the control surfaces directly. This is similar to any other aircraft except since there is no force feedback the side-stick does not become stiffer with increasing speed.

In the US-1549 flight case (landing on Hudson), they had enough time to start the APU, so all systems were powered and they had normal law and did take advantage of it to let the airplane settle as slow as possible.

In the recent U6-178 flight case we don't yet have enough information whether they did have normal law available.

¹ Slower than normal approach speed. At normal speeds, the system maintains wing loading at 1G with neutral side-stick, which can be also described as trimming for current speed. Until the trimmed angle of attack exceeds alpha-limit (12.8° IIRC; 17° is onset of stall, on normal approach should be around half of that), when it switches to maintaining angle of attack.


What is required to be an "FAA-qualified helicopter aerobatics pilot"? Chuck Aaron is the only FAA-qualified aerobatic helicopter pilot - How'd he do it?

What requirements does one need to meet in order to perform aerobatics in a helicopter?  Specifically, the training/qualifications and FAA paperwork necessary.
Who certifies said pilot, if there is no one certified themselves to do so?

I think this depends on what "FAA-qualified" means: the FAA defines aerobatic flight in 14 CFR 91.303 but it doesn't issue any pilot certificates or ratings for aerobatics. I did find several references to FAA Form 8710‑7, Statement of Acrobatic Competency (e.g. here), but the form itself isn't even listed on the FAA's form page.

There is an FAA document called Guidelines for Pilots Seeking All-Attitude Training which states that there is no special certification required:

  [...] no separate certificate, rating or endorsement is required to
  specifically qualify an individual as an all-attitude instructor

And:

  Anyone claiming to be an all-attitude instructor must at least hold a
  valid Commercial certificate if working for compensation or hire. The
  instructor must also be a certificated flight instructor (CFI) to
  provide FAA endorsements. Other than that, CFI credentials are not
  necessary for anyone to claim to be an all-attitude instructor.
  Therefore, caveat emptor - buyer beware - applies when seeking
  instruction.

Although their definition of "all-attitude" isn't exactly the same as "aerobatic", the document seems to make it clear that aerobatic training is not directly regulated. And looking through a variety of aerobatic websites including the IAC one, there is no mention of any required FAA certification. Endorsements for tailwheel, high-performance or complex aircraft are often required, but that's because of the aircraft itself, not the aerobatic activity.

But this profile gives some clearer information:

  Once the helicopter was ready, the FAA needed to certify it in order
  for Chuck to perform stunts with it. Once the aircraft was certified,
  the next step was to also get him certified, which ended up being a
  complicated process. The FAA was not sure how they could certify him,
  so they turned to Rich Lee, chief pilot for Boeing, who evaluated him.
  “He wanted to make sure that I did have all my screws in my head and
  that they were not loose”, said Chuck, laughing.

My guess is that the FAA first issued a new airworthiness certificate and/or waiver for the modified helicopter. That's very common and it would be same for a home-built aircraft, for example. Second - and this is a guess - they had the Boeing guy evaluate him for the Statement of Acrobatic Competency that I mentioned above. Although I can't find it on the FAA site, it obviously existed in the past and if you look at this example from the EAA Warbirds site, you can see that the evaluation process was (is?) 'outsourced' by the FAA anyway, presumably because they have no experts available internally:

  I desire to take advantage of an FAA procedure for the evaluation of
  my competency by a Warbird Aerobatic Evaluator (Warbird Evaluator) on
  the list maintained by the EAA Warbirds of America, Incorporated.

I suspect that putting a unique airworthiness certificate together with a unique Statement of Acrobatic Competency resulted in a uniquely "FAA-qualified" acrobatic helicopter pilot.

Finally, according to Aaron's LinkedIn page he is the:

  First FAA Certified Helicopter Pilot to recieve a Helicopter Aerobatic
  Certificate from the FAA.

That again seems to emphasize the helicopter, not the pilot.


Radio communications lost on climb out in IMC: when can I turn on course? Let's assume:

I have been cleared direct from Knoxville Downtown (KDKX) to London-Corbin (KLOZ) at 6000ft. The direct heading is 357°.
I lose comms after take off from runway 26, I squawk 7600 and I'm in IMC
Assume I cannot land where I took off

My plan is to climb to 6000 as filed but I can't turn northbound on course because of obstacles. When can I turn on course? Is the proper procedure to fly the back side of the localizer westbound till I reach 6000 and then turn?

Your assumptions are insufficient.

If your clearance just states "CLIMB 6000 direct", and there are obstacles along the route, you have been given an incorrect clearance.

It should have included the phrase "EXPECT" and an altitude and possibly also a time that would permit you to clear the obstacles.

Also, from your Skyvector link, it looks the Direct course parallels V97 very closely, which has an MEA of 5000, so you should not encounter any obstacles at 6,000.  Once you reach your clearance limit LOZ, you may initiate the approach.

Nevertheless If you lose comms you are expected to climb to the hugest altitude of 1. Your last clearance altitude 2. Minimum IFR altitude. 3. The altitude you were told to expect


Do flight tracking websites also track non-commercial and defense aircraft? Many flight tracking websites have the data about almost all the commercial airplanes in air. Do they have the data about the private jets and/or defense aircraft also and they just don't show that on the websites?

As long as an aircraft transmits (unencrypted) ADS-B information, anyone within radio range can track it. The equipment necessary to receive ADS-B can be as simple as a computer with a TV receiver (USB DVB-T module) and the right software.

Receivers can then send the data stream to, for example, Flightradar24, who will display it on their website.

As Flightradar24 states, not all aircraft are equipped with an ADS-B transponder, and even those that do may not have switched it on. Unless ADS-B is installed and operating, it would not be visible.

@ezra-g mentiones that Steve Jobs' aircraft was blocked, but this is of something one would have to ask for, and the site has to apply the filter so it doesn't display on its website. However, Jobs' plane would still have been visible on the receiving computers. And, of course, the website will only filter your aircraft if they are willing to do so, either on request, through payment, or a government order.

Flightradar.com also has some other data sources, like FAA (Federal Aviation Administration) radar information in the US, which also contains aircraft without a transponder. The FAA may also filter some aircraft.


Can helicopters land in a poor visibility scenario? The Instrument Landing System and some others systems can provide to incoming aircraft guidance to the runway in poor visibility scenarios.

With that in mind, I have these questions:

Can helicopters fly in IMC?
Is there any system that can help the pilot land, just like ILS?

Can helicopters fly IFR?  Yes

Do they use ILS?  Yes.  The only tricky part of it is the need to be slow at the end of the glide slope.

An IFR helicopter can use any of the navigation and landing aids available to any other aircraft.

This PPRuNe discussion is interesting.


How does leading edge flap increase camber? From this post, I've learned that the leading edge flap works by increasing the camber of the airfoil. But how exactly does it work? Since it is a flap, I can guess it works by changing the chord line, just like the trailing edge flap does. But how exactly does the chord line change? Does the leading edge move down to below the original leading edge when the leading edge flap is extended?

Leading edge flaps and droops do increase the camber because when they move, the leading edge actually droops, and with it the leading edge extremity of the chord line, while the mean camber line remains in place for most of the airfoil length:

Droop

The airfoil is dramatically bent down to the point the bottom side is now concave and the top side has a larger convexity.

Effect on the lift coefficient:

For the same angle of attack α, CL is decreased, but it is now possible to reach larger α and with them larger CL. It also means lower speeds are required to generate the same amount of lift.

LE flaps are usually found at the outboard portion of the wing.

More: Aircraft Design, a conceptual approach, Daniel P. Raymer (around page 278 - view it)


What exactly do fighter jets and its pilots do during their peace time sorties? I am located very near to a base with a Sukhoi 30 squadron in India. The Indian Air Force jets keep doing these sorties every day and night. I have always wondered what exactly do these jets do during their sorties. I thought it was always about training. But I found out that the basic training for these pilots happen elsewhere. So what exactly happens on a normal day with these trained pilots and their jets?

As with any job, there will be some initial training to learn the basic skills needed, and that is typically done at a central location. But there will also be ongoing practice to maintain those skills and continue to improve them. Modern fighter jets are complicated machines and take a lot of knowledge and practice to operate. Simulators and classroom learning help but can't completely substitute flying and maintaining real aircraft. In the US, military aviators get about 20 hours per month of flying time. There's a saying in sports that "you play how you practice." When these pilots go into battle, lives are on the line, and they want to be able to recall skills they practiced recently, not years ago in basic training.


What defines a landing gear bogie? (Wikipedia) A Boeing 737 main landing gear arrangement.

What defines a landing gear bogie (truck)?

In its airframe maintenance handbook, the FAA defines it as:

  When more than two wheels are attached to a landing gear strut, the attaching mechanism is known as a bogie.

But, they go on and describe the Boeing 777 main landing gear (MLG) as:

  A triple bogie main landing gear assembly.

That means each lateral pair of wheels is a bogie, which is what the undercarriage arrangements Wikipedia article calls a 2-wheel nose landing gear.

For me, a bogie is when a strut holds a longitudinal arrangement of wheels (like trains). For example, the MLG of a Sukhoi Su-34 (shown below) would be a bogie, but not a Boeing 737 MLG, despite both having two-wheels each.

Are there technical terms to distinguish the two images shown in this post?

(Wikimedia Commons)

The term bogie initially meant (atleast in Britain) an assembly of wheels forming a pivoted support at either end of a railway coach, which provided flexibility on curves.

So, the term bogie refers to the set of wheels, rotating about the (landing gear) axis, while their arrangement- lateral or longitudinal doesn't matter.

An old patent for Bogie undercarriages for aircraft notes:

  ... a bogie having multiple wheel assemblies mounted on transverse rotational axes spaced one behind the other ...

The issue is that the term has been in use for a long time an has come to mean a number of things (even in railways, the entire carriage can be called a bogie)- so while the correct term is to call it a four (or six) wheel bogie rather than double or triple bogie, it is used quite often. Also, as I already noted, whether it is lateral or longitudinal doesn't matter as long as they are attached to the same (nose or main) gear.


What is the minimum radio and navigation equipment for required for VFR and IFR certified aircraft? As per ICAO or FAA, what are the minimum radio and navigation equipment must be fitted in VFR and IFR certified aircraft and helicopters?

In the US, this in in 14 CFR 91.205, Powered civil aircraft with standard category U.S. airworthiness certificates: Instrument and equipment requirements.

There's a lot of detail so you can check the whole thing, but looking only at communication and navigation items, the required equipment is:

VFR (including night VFR)

Magentic direction indicator
Altimeter (for airspace navigation)

IFR

Instruments and equipment as for VFR
Two-way radio communication and navigation equipment suitable for the route to be flown
Rate of turn indicator (for timed turns)
Directional gyro
A clock (this question explains why a clock is needed for IFR navigation)

That list might seem very short, but remember that under VFR there's no requirement to have radios and there are even some vintage aircraft flying around with no electrical system.

Under IFR it's fairly obvious that you need a radio for ATC communication and whatever navigation equipment is needed for your planned flight, e.g. you can't fly a GPS approach unless you have an IFR-certified GPS. But there are multiple approach types and they all have different equipment requirements so the regulations just give a general statement.

Note that commercial flights operating under parts 135 or 121 will have additional requirements; the information above is really the bare minimum that's legally possible for GA flights.


Are there any serious plans for a new supersonic civilian aircraft? Since the retirement of the Concorde and the Tupolev Tu-144, there aren't any civilian airplanes (passengers carrier or business jet) flying supersonic. I heard that Dassault and SAAB had rather advanced studies on this topic but abandoned them due to various problems.

Does anyone have current references indicating that an aircraft manufacturer plans to develop a supersonic transport aircraft?

Aerion is planning a supersonic business jet which has a projected completion year of 2021:

Here's an article Forbes have written about it.


What was the first commercial scheduled flight to Australia from another continent (except Asia)? Australia has been a very isolated country, ships being the only possibility to get there from another continent if someone was not too much in a hurry. Aviation did add a new and radically different possibility.

Source

When and how did occur the first commercial scheduled non-stop flight to mainland Australia (country) from mainland Americas, Europe, Africa or Antarctica? I'm excluding overseas islands and Asia which are easier challenges.

Background
Jumping to Asia then Europe is known as the Kangaroo Route. Excluding that, that leaves us with flights directly to/from the Americas and Africa.
Nonstop to London is still unrealized from Sydney. Although Qantas flew London to Sydney nonstop in 1989, but that was a delivery flight. Flying Perth-London nonstop will begin in 2018 using the Boeing 787. And with the upcoming 777X and A350-900ULR, Sydney-London should be possible. What that media calls a "Kangaroo Route nonstop dream."
(gcmap.com - A330-300 typical range) Range map shows how far Australia is, for context.
Circa August 1957 is when Australia signed an Air Service Agreement with the US to operate across the USA and onto Europe. Thus securing an alternative to the Kangaroo Route. At the time planes were able to reach the West Coast of the US (with many stops) in sea planes such as the Short Solent. Even with the advent of the jet age, the 707 had to make stops in Nadi and Hawaii.
The candidates for the first scheduled non-stops are:
Africa:

On 6 January 1977, the Boeing 747SP made its first scheduled flight between Johannesburg and Sydney. The flight offered in-flight audio entertainment and movies (flysaa.com).

Contiguous US:
Pan Am:

November 4, 1982 – Pan American World Airways inaugurates service from Los Angeles, California, to Sydney, Australia; at 7,487 miles (11,979 km), it is the longest non-stop flight in the world.

Qantas:

[2014] marks thirty years since Qantas began non-stop flights between Sydney, Melbourne and Los Angeles beginning in April 1984. These services were operated by the long-range Boeing 747SP with a flying time of around 16 hours. Today, the flying time is around 13 hours.


Is it legal to smoke in your own plane? I was just curious, in the past, smoking on planes was permitted.

What is the law surrounding smoking in your own private plane?

The short answer to "Can I smoke in my own private aircraft?" is "Yes, usually".

As Promised, I looked up the relevant FAR (23.853 - Passenger & Crew Compartment Interiors).

The actual rule is long and verbose, but pretty common sense. The important regulatory bits for most personal aircraft are just two points though. You must:

Have "an adequate number" of self-contained ash trays
You don't want flicked ash or a snubbed cigarette to start an in-flight fire.
Have "No Smoking" signs you can illuminate, if the passenger/crew compartments are separated
This doesn't apply to most of us since our "personal" airplanes are light singles, but if you've got a fancy twin with a curtain or door between you and the passengers you'll need those signs.

For "commuter category" aircraft there are even more requirements. Those requirements don't apply to most "personal" planes, so even though it's probably a good idea to meet some of those requirements if you're going to allow smoking in your personal aircraft they're not legally required.

All that said, while it's likely legal (unless you've removed your ashtrays or your plane didn't come with them) common sense generally dictates you don't want to smoke in your plane - It's bad for the vacuum-driven instruments' filters, will require even more attention to cleaning the inside of your windows, and a loose cigarette in turbulence or a bunch of ashes blown about by an open air vent can be a pretty substantial distraction.


Why is the FDR and CVR put into water again after a water crash? When a plane crashes in the water and the investigator team looks for the FDR and CVR, why do they put it in a container of water when they find it ?

This is actually a fairly standard thing to do with electronics that have been submerged: They are placed in water (ideally fresh, clean water) to both delay the onset of corrosion and dilute any salts or other chemicals that they came in contact with while submerged.

When you remove electronics from water and let them dry out they begin to form corrosion on all the little exposed bits of metal - chip legs, solder joints, capacitors, etc. - which can badly damage the device when it is powered back on.
Keeping the device submerged in water delays the onset of this corrosion because the dissolved oxygen in the water is lower than the oxygen in the air that would be hitting those parts as they dry out.

The Cockpit Voice Recorder and Flight Data Recorder are water resistant, but they are not necessarily waterproof (particularly after a crash, which may puncture their casings or damage seals), so they get placed in a container of fresh water for their trip to the NTSB's lab.
When the still-immersed equipment arrives at the NTSB laboratory it can be examined and dried in a controlled environment, maximizing the chance to recover data.

  For more gory details check out The NTSB Flight Data Recorder Handbook for Aviation Accident Investigations.

Bonus Factoid: Archaeological recoveries from bodies of water use similar procedures, for similar reasons: If you bring up a clay pot that's been sitting at the bottom of a lake for a thousand years and let it air-dry naturally there's a good chance it will crack and be destroyed.
In archaeological recoveries the usual practice is to keep the item "waterlogged, ideally in waters associated with the original context" (i.e. "in a bucket of water from where you got the thing").


Why don't the US Navy Blue Angels fly Super Hornets? The US Navy demonstration team has been flying the legacy Hornet for a long time and I was wondering why don't they use the Super Hornet? The legacy Hornet is over 30 years old and showing its age. I know there have been numerous incidents during shows where control surfaces have broken off the planes.

Why aren't they using the newer airframes? Is it the cost of upgrading? Performance concerns?

The USN Blue Angel demonstration team is transitioning to Super Hornets. According to this press report:

  “We are supporting the Navy’s plans to transition the Blue Angels to Super Hornet aircraft from classic Hornets by providing engineering for the necessary conversion modifications. ...,” Paul Guse, a spokesman for Boeing, said Thursday in an emailed statement.

The transition will take some time for carrying out the necessary modifications including...

  ..., installing flight auxiliary fuel pumps that can operate in sustained inverted manoeuvres and inserting an oil pump in the tail to emit blue smoke.

...among others. Also, as the aircraft performance is different (the Super Hornet is larger and heavier, for one thing), the aircrew will have to train on the new aircraft before participating in any airshows.

A lot of the weight difference may be handled by removing the combat hardware but the size and handling characteristics will require a lot of training and practice time before the super hornet can be used in the precision flying exercises used in air shows.


Airbus A320 automatic speed mode protection in SRS vertical mode According to the A320 FCOM, capter 22 auto flight, flight guidance, the "automatic speed mode protection" of the auto flight system of the A320 disengages the flight directors upon reaching current VMAX+4kt which will cause A/THR to revert to speed mode. But this protection is only active in climb modes: CLB, OP CLB and EXP CLB.

Does anybody know why the "automatic speed mode protection" is not available in SRS vertical mode where A/THR is also in THR CLB mode?

Also does anybody know if this protection uses the VFE of the selected flap config or of the actual config? E.g. if you are in climb and inadvertently select flaps from UP to CONF ONE then the aircraft won't let you do that but does this (cruise lock) but as far as I know the speed tape on the PFD already shows the maximum airspeed for the selected flap 1 config. So does this already disengage the flight directors? Or do they use the actual flap position or overspeed warning from the flight warning computers?

High speed protection is still available (in normal law) in SRS (check FCOM DSC 27 20-10-20).

What you will not have is the reversion mode of the autothrust to Speed. You will get the protection  (THS freeze, spiral stability to 0deg, max 40 deg bank, nose up order) but thrust will remain in THR CLB.

I suspect the reasoning was that SRS mode implies you are pretty low on altitude, and you do not desire an automatic (and uncommanded) reduction of thrust on, say, a windshear.

Of course, in this particular case the high speed prot will activate at VMO/MMO so if you manage to get that fast while still in SRS you have bigger problems than the thrust

For your second question: mode reversion to Speed will occur at VMAX (which is lower of VMO, VLE or VFE), but for SRS there is no flap overspeed protection so only VMO will trigger it


Are there 5000+ companies with IATA (two-character) codes? From Wikipedia > List of Airlines

  There are around 5000 airlines with IATA codes.

From Wikipedia > List of Airlines Codes

  IATA airline designators [..] are two-character codes [..]

and

  after an airline is delisted, the code becomes available for reuse after six months

The last quotation suggests that no two airline companies can share the same IATA code.

Depending on the characters allowed, a two-character codes can make $26^2=676$ combinations or eventually $36^2=1296$ combinations. It would take at least 71 different characters authorized to register 5000 companies ($71^2=5041$). It is unlikely that 71 or more characters are authorized. It seems paradoxical to me.

What am I misunderstanding?

It's obviously an error in that Wikipedia page. The "5000 airlines with IATA codes" text actually links to:

https://en.wikipedia.org/wiki/List_of_airline_codes

which lists lots of airlines (over 6000), but most of those have ICAO (3 letter) codes, but not IATA (2 letter) codes.


How does the modulation of the transponder work? The transponder works in PCM (pulse code modulation): how does it work in the transponder? I can find explanation of what PCM is, but not if the signal sent from the transponder antenna is digital or analog, and I do not understand which are the advantages of using PCM.

About PCM

  I do not understand which are the advantages of using PCM [in a transponder]

Pulse Code Modulation (PCM) is a method used in codecs, while modulation is a method used in modems. PCM with modulation in the name is a misnomer, PCM doesn't relate to modulation in any way.

PCM is used in audio processing to take an analog signal and encode it into a digital stream by sampling, quantization and companding. It is for instance used for audio storage on a Compact Disc and in a Waveform file (.wav). It can be used for transmission, but CPM is only the portion of the chain which prepares the digital data to be sent.

Some forms of PCM are oriented for audio compression (e.g. DPCM or ADPCM), this aspect might have some interest regarding the larger mode S data blocks, but this compression is lossy, meaning some data would not be transmitted, which is indeed not an option for SSR.

To clear any doubt about PCM (and associated encoding delta modulation, delta-sigma, and differential PCM) not being a modulation technique, from Introduction to Analog and Digital Communications:

  A point that needs to be stressed one last time: In reality, PCM, DM,
  and DPCM are source-encoding strategies, whose purpose is to convert
  analog signals into digital form. For actual transmission of the
  encoded data over a communication channel, the discrete form of
  pulse-amplitude modulation (PAM) is typically used.

Afaik, there are no PCM application in a transponder or in the secondary surveillance radar to which the transponder replies. It would be interesting to see the document where PCM is mentioned in the context of SSR or modulation.

About transponder modulation

  How does the modulation of the transponder work?

Usually a SSR (secondary surveillance radar) ground station or an anti-collision system interrogates aircraft transponders by sending interrogation pulses on 1030 MHz. The transponders answer on 1090 MHz. There are several modes which are used to obtain different information from a compatible transponder. Civil aviation modes are:

Mode A to get the 12-bit identification/squawk code.
Mode C to get the 12-bit identification and the altitude.
Mode S to get 24-bit ICAO identification and various data. In this mode, the transponder also regularly broadcasts data spontaneously for ACAS and/or ADS-B uses.

Modes A/C can be identified by the time elapsed between pulses P1 and P3 (more here) and mode S by the presence of pulse P6 datablock. Transponders answer if they are compatible with the interrogation mode only.

Type of modulation

The basic type of modulation used for everything except the datablock of mode S interrogation (pulse P6) is the On-Off Keying (OOK), a type of Amplitude Shift Keying (ASK) for which amplitude can have two values. Bits of information are transmitted one by one, the carrier is sent or interrupted, according to the bit value:

OOK is a simple class of modulations, used to transmit information at low speed.

Mode S

Mode S (Select) allows the interrogator to specify the ID of the interrogated transponder, to prevent all other transponders to answer. This protocol requires a significantly more information both for the interrogation and the reply. This information is not transmitted as simple pulses using OOK, some form of synchronization must be added, specially when long chain of 0s or 1s are transmitted.

Instead of representing 0 by the absence of carrier and 1 by the presence of carrier (OOK), bits in the P6 datablock are represented by a presence of carrier which some characteristic is changed:

For interrogation, pulse P6 contains information for the Synchronization Phase Reversal (SPR) signal, the interrogation command, the target transponder ID, and 24 bits of the cyclic redundancy check (CRC).

P6 bits are sent using a variant of Differential Phase Shift Keying, the Differential Binary Phase Shift Keying (DBPSK) with phase shift being 0° for 0 and 180° for 1, i.e. consisting in inverting the carrier when bit value is 1:

DBPSK used for in interrogation data

The bit rate is 4 Mbps. In addition, the difference of amplitude of pulse P5 (sent in all directions) and pulse SPR (sent only forwards) is sensed to mute transponders not in front of the interrogator antenna.
Reply data blocks are encoded using Pulse Position Modulation (PPM) which consists in sending a pulse of carrier with a time shift dependent on the value. This ensures a return to zero which is a form of synchronization. For binary values, the pulse is sent either in the first half of the time slot for the bit (for bit 1), or the second half (for bit 0).

PPM with only two values is therefore equivalent to first coding data using Manchester code, then modulating the carrier using OOK already used for mode A/C. This choice was done to simplify airborne electronics when mode S was adopted by FAA.

PPM used for reply data

The bit rate is 1 Mbps. The content of the data block depends on the type of interrogation, or the type of automatic broadcast used. Example for ADS-B squitter sent automatically:

Source

More on ATC interrogation and reply formats here.


What does aerodynamic noise of an airliner sound like in landing configuration? I want to know what aerodynamic noise an airliner makes when flying with both engines shut down. Specifically, it is the sound made by air passing a plane which is in landing configuration, with gear and flaps extended, at a normal approach speed.

I know that it makes a loud noise especially during landing, but normally we cannot distinguish it from the engine sound.

Aerodynamic noise has many sources. It is not white noise, because some frequencies are dominant. Generally it happens when flows of different speed collide, or when a standing wave develops in a cavity. Common noise sources are:

Uncovered openings, like vent holes or control surface gaps. Like when you blow across the top of an open bottle, they produce a howling sound with a dominant frequency that depends on flow speed and opening size.
Tollmien-Schlichting waves in the boundary layer. These frequencies change with speed and their location along the flow path, and generally are responsible for most of the hissing sound of gliders.
Separated flow, which produces alternating separations behind blunt bodies. Here the main frequency is that of the Karman vortex street that forms behind them. It can be calculated if the Strouhal number Sr of the flow is known. This is the equation for the main frequency $f$ of a bracing wire with the diameter $d$: $$f = Sr \cdot \frac{v}{d}$$
Here $v$ is the airspeed, and for bracing wires Sr is normally 0.2. Bracing wires (or a blunt trailing edge, for that purpose) produce a characteristic whistling sound.

As you said, the landing configuration makes most noise. In addition to the factors above, you now have

Extended flaps, mostly with gaps between them which show high local flow speed. This local high-speed flow is very noisy.
Many more blunt objects sticking out of the airframe: Landing gears, gear covers or landing lights. The particular noise of landing gears was once tested with a high-performance glider which had styrofoam gears fitted under the wings. They broke off when it had to land, but yielded valuable data when compared to the noise of the clean glider. Sorry, there is no photo of this experiment on the web!
The gaping hole of the landing gear well. Especially while the gear is moved, this creates a lot of noise, but even after extension a part of the well is uncovered and adds its noise.

Here is a good overview of different noise sources. It is best read with a good working knowledge of German.

To answer your question: The sound is a mixture of hissing and whistling in different frequencies. If you stand close to the Autobahn (best is a section without speed restrictions), the noise of the passing cars is similar, but less intense. At 180 km/h, engine noise starts to vanish in all the aerodynamic and tire noises ...


What is 2D and 3D thrust vectoring? How do we define 2D and 3D thrust vectoring?
What are the differences between the two?
Is there anything called 1 D thrust vectoring?

As previously seen in a comment section, there are two main schools of thought:

The dimensionality indicates the actuation Degree of Freedom (1D has
1 DoF per exhaust vector, 2D has 2).
The dimensionality indicates the aircraft attitudes that can be affected (2 exhaust vectors with 1 DoF each can affect pitch and roll, hence this would be a 2D thrust vectoring, 2 exhausts with 2 DoFs can affect all 3 attitude angles, hence 3D)

Using the definitions of these two approaches, to make a couple of examples, the F22 thrust vectoring is 1D for the first group and 2D for the second, while the Su30 is 2D and 3D respectively.


Can structural damage be detected or predicted using historical data? Can software simulations and structural health monitoring techniques accurately predict damage occurrence in aerospace structures using historical data(stiffness,damping and vibration measurements over a considerable period of time)

or

Are these techniques more suited to real time damage detection rather than damage prediction ?

  For eg. SHM techniques such as parameter estimation using Frequency Response, or Non Destructive Inspection.

Yes it can be done. However, with the advent of technologies, you can also use the real time updates of the monitored system to understand it's health. In some cases where the historical data is not available, it becomes important to assess the structure's condition based on real time updates. I feel the following links could be of interest:

https://journals.sagepub.com/doi/full/10.1177/1475921718760483
https://www.sciencedirect.com/science/article/pii/S0888327017304612


What are the difficulties and dangers faced by low flying aircraft? Aircraft could fly low for various reasons,  Common reasons for low flight are sightseeing, photography, crop dusting, staying below Bravo/Charlie airspaces, flybys, and "just cause I felt like it".  What are the  difficulties and dangers faced by such aircraft?

A lot depends on how low you are and what aircraft you're flying, but any low-level flight has some risks and difficulties. Here are some, I'm sure there are others:

If the aircraft loses power you have much less time and distance available to execute a forced landing, and your choice of landing sites will be more limited
You can't see as far ahead so it's more difficult to look out for obstacles and pilotage may also be more difficult in some circumstances
You may accidentally break the law on minimum safe flying height because the terrain changes too quickly, you don't see an obstacle or town until it's too late etc.
There's a greater risk of collision with terrain or obstacles like radio towers, especially if your aircraft is a fast one and you have less time to react
The likelihood of both thermal and mechanical turbulence is higher when flying low, increasing risks of loss of control and collision with terrain and obstacles
If you're scud-running in VMC there's a high risk of entering IMC accidentally, which is extremely dangerous (incidentally, despite the title of that question, even instrument-rated pilots have a poor safety record when they enter IMC unintentionally)
Radio reception may be poor
ATC radar may not be able to see you
Your engine may not operate very efficiently

That's not to say that low-level flying is always a bad idea, but it I think it does require more preparation, alertness and even local knowledge from the pilot.


What are the minimum requirements for a student to solo a second make and model aircraft? Suppose I've done my Private Pilot training in aircraft Make/Model "A" and the one I have access to breaks two weeks before my checkride.  My instructor also teaches in model "B".  What do I need to do solo in model B, if all of my endorsements are for model "A"?

Is it necessary to complete a Pre-solo exam?
Is it necessary to demonstrate all the maneuvers in 61.87?
Is it necessary to demonstate all the maneuvers in 61.93 for solo cross country privileges?

As long as your training has been done in the same category, class, and type as the aircraft you are switching into, the FARs aren't specific regarding repeat training required.  Instead, this will fall into the realm of flight school policy, and CFI judgement.

For example, if you are transitioning from a high wing to a low wing, or from manual to electric flaps, your instructor will need to ensure that you are safe and comfortable flying the new aircraft before signing you off to solo.  To the first question, it is almost a 100% certainty that you will at a minimum need to complete a presolo exam on the new aircraft to ensure that you know the systems, airspeeds, etc.

If the instrumentation and navigation equipment are similar enough you probably won't need to refly any cross country flights, but again this is at CFI/Owner's discretion.

You will, of course, need a new solo endorsement for the specific make and model.

And don't forget the most important piece, two weeks before your checkride YOU need to be comfortable in the aircraft you will take your practical exam in!  Don't short change yourself, push out the checkride if needed to make sure you are ready.

The best advice is to consult your CFI and/or the flight school chief pilot to put together a re-training/recovery plan to transition.  Good luck!

ADDENDUM:  I see in your profile that you are a CFI with 20 years of flying experience.  What gives?!  (downvote for what I perceive as deception...)


How to make a cockpit LCD display night vision compliant? I am trying to understand what does it means by making an LCD display compatible with Night Vision? The aircraft is an old Mirage of 1950's.
If I use an LCD display in it's cockpit display unit then how would I make the LCD compatible with Night Vision capability?

Do I need to select a specific color (wavelength or frequency on spectrum) to display the data on the screen?
Or do I need to put some filter sheet on top of the LCD screen to make its Night Vision compatible?
Or does it mean something other than these?

Edit:
The only info about the OEM display is follows:
"The display is an ac TFEL flat panel display combined with contrast enhancement bandpass filters to achieve both sunlight-readability and night-vision google compatibility"
I want to replace this TFEL display with an LCD display. But I dont understand how will I do night-vision google compatibility in an LCD?

You can make an LCD screen NVG compatible by adding a filter screen on top of the display that complies with MIL-STD-3009.  You can get a copy of MIL-STD-3009 from several commercial sources or direct from the Defense Logistics Agency website.
There are a few companies that manufacture the filter screens. I would start with a search for NVIS filters.


Why there is no airport IATA code XXX? It seems that there is no XXX IATA code: from Wikipedia, XVL (Vinh Long, Vietnam) is followed by XYA (Yandina, Solomon Islands). There is a source claiming that XXX used to refer to Mena Intermountain Municipal Airport, but from Wikipedia this place seems (rather strangely) to have no IATA code at all (and a source for this claim is given).

What are the reasons for not having the XXX IATA code? Is this a reserved combination? Has it belonged to the Mena Airport in the past, and if so, why has it been deregistered on October 21, 2014, as the source claims?

It looks to me like the source site you quoted is unreliable or at least not current, e.g. it gives results for codes QQQ and ZZZ too, but they haven't been assigned by IATA. The actual IATA code for Mena (ICAO: KMEZ) seems to be MZX.

Anyway, there's no particular reason why XXX, ZZZ or any other specific combination should be assigned; they just haven't been used yet. There's also no reason why IATA should assign a code to every airport: the US alone has over 5,000 public airports but only 500 or so have air carrier service.


Has there ever been a strategic bomber raid completely wiped out? Question in title. All them seem to be heavily damaged but with half surviving at least. Cant find any that were wiped out.

If you mean a "heavy bomber flight" being one that was completely destroyed, then yes... And it happens to be a very famous one...

The Dolittle Raid consisted of 16 bombers that bombed Tokyo on April 18, 1942. All but 1 of the original 16 aircraft crashed in China, with one landing in Russia.

Source: Wikimedia


How does contrail formation differ from turbofan to turbojet? Air forces and intelligence agencies are indeed interested in predicting whether condensation trails (contrails) will be visible or not during aircraft operations.

Photo: C-CYOW at Photobucket

Among existing prediction algorithms, Appleman's method, devised in 1953, is frequently cited, even if more accurate or refined algorithms exist, like JETRAX.

From Predicting Contrails Using an Appleman Chart (Nasa), the principle is based on air saturation characteristics:

  At first, scientists were not sure how contrails formed. We now know
  that they are a type of mixing cloud, similar to the cloud that
  sometimes forms from your breath during a cold winter day.

  Appleman showed that when the air outside of the airplane is cold
  enough and moist enough, the mixture of the jet exhaust and the air
  would form a cloud.

Appleman chart, with a different layout

Since 1953, civil turbofans have replaced turbojets, with various air bypass ratios. What is the effect of this replacement on the occurrence of contrails?

Does turbofan reduce or increase contrail occurrence?
Does bypass ratio play a role?

It appears that the higher bypass engines available today increase the contrail occurrence. From Influence of propulsion efficiency on contrail formation by Ulrich Schumann:

The  thermodynamic  analysis,  which  is  the  result  of first-principle  arguments,  implies  that  aircraft  and  engines, performing with a higher overall propulsion efficiency release a smaller fraction of the combustion heat during cruise  into  the  exhaust  plume, and  hence  cause plume conditions which during mixing reach higher relative  humidity  for  the  same  ambient  temperature  and hence form contrails also at higher ambient temperatures.
Hence aircraft will form contrails more frequently when
using more fuel efficient engines.

TO test the theory, a flight test was conducted between two aircraft with low and high bypass engines:

For a direct test of the theory, a formation flight of two different large  jet aircraft was arranged, wing by wing, during an ascent and a descent f the aircraft. Contrail formation and ambient conditions were observed simultaneously from a research aircraft.
The two contrail forming aircraft were
(i) a Boeing B707 equipped with four jet engines of type JT3D-3B with bypass-ratio of 1.4 and
(ii)  an  Airbus  A340-300 with  four  jet  engines  of  type
CFM56-5C4  with  bypass-ratio  of  6.8.

The results indicated that contrails were formed in more instances in case of the A340 (with higher bypass engines) compared to the B707.

Photo of an A340 with contrail and B707 without one. Image from Influence of propulsion efficiency on contrail formation by Ulrich Schumann

Ambient  conditions were measured and the contrail formation was observed from a research aircraft flying less than 1 km behind the two contrail forming aircraft. As documented in several photos, an altitude range exists in which the A340 causes  contrails while  the  B707  causes  none.

Though the sample size is pretty small, it does appear that the high bypass engines used in modern commercial aircraft are more prone to contrail formation compared to the older turbojets.


Is it possible to export NMEA data from a Garmin GDL-39 to a custom Android App? Hi I was wondering if it's possible to receive NMEA data from a Garmin GDL 39 on an Android device (preferred over Bluetooth) as I can't find any information out there on it.

Well, I think there's a way. Fair warning, it also looks like a fair bit of work, and I haven't tried any of this. Plus, you run the risk that the GDL 39 is going to refuse to connect or do something really weird or otherwise break/invalidate user agreements/warranty.
The user manual for the GDL 39 shows that the GDL 39 has Bluetooth, and this website purports to know the communication protocol and handshake sequence, with code for getting it to work written in Perl. Getting that to work in an Android application shouldn't be impossible, but I haven't looked at it thoroughly and I'm not enough of an Android expert to tell you if it would work off-hand.
You could also go over serial as an option to get NMEA data, which I investigated before I found the website above. I think the Bluetooth option is better, but here's the physical method since I already wrote it up.

You will need a cable like the one here to connect to the GDL over serial. From there, you'll also need a device to take the serial data and get it into the android app over Bluetooth. Here are a few options:

An Arduino or other micro-controller to handle the serial connection to the GDL 39, and then re-broadcast the NMEA data over a Bluetooth connection.

A ioio (pronounced "yo-yo"). Allows you to control a micro-controller with an android application over Bluetooth or via USB. I've used one before, and it's pretty easy to get running, but is a little old. Support still exists for it though.

Your next problem is to actually communicate with the GDL 39 over serial, which will be more complicated.  The GDL 39 appears to have a proprietary handshake protocol over serial, which in theory, should prevent you from using a non-Garmin device to get any data over serial. However, in practice, it may not be hopeless.
This website describes the handshake protocol to negotiate a connection over serial, and data from the GDL 39. I haven't tried to do this, but it looks like it might work. If you can get that to you work, it seems like you'll get a stream of NMEA data, and then you could send it over Bluetooth to an Android application.


How does the position of vortex generators on engine cowlings affect flight? I know what vortex generators (VGs) do. My question is: How come some aircraft have VGs on both sides of the engine, whereas other aircraft have them on the inside only?

For example, in this picture of Boeing 737, a vortex generator is only on the inside of the engine:

On the contrary, the Airbus A319 has them on both sides:

The vortex generator helps only at high angle of attack by energizing the airflow between nacelle and wing. During cruise it will create additional drag without much benefit, especially if the nacelle-wing-combination has been designed well.

However, in the landing configuration it can help to lower minimum airspeed by several knots and make shorter landings possible. Now the aircraft maker has to decide what is worth more: Shorter field length, or slightly less cruise drag.

The Boeing 737 started life with a much more slender engine and had a very short landing gear when more fuel-efficient engines came to market. A lot of brain- and computing-power was needed to develop its pear-shaped engine nacelles, and the vortex generator became an essential element of it. At the inside location it helps to keep the flow path between wing, fuselage and nacelle clear of separated air, whereas on the outside a second generator would make only a minor difference.


Why do fighter pilots use night vision goggles rather than normal light inside the cockpit? I've seen military personnel using night vision goggles (NVGs). With their flight altitude, I don't think the enemy can notice them. I thought it may be due to eye strain, but other units use red lights during long jobs that need looking at a screen. Also, you should consider some fighter pilots have short missions and their eyes won't get tired from light.

I wonder why they don't use normal light. Normal light versus red light versus night vision. I never used night vision, but I don't think it's comfortable to use.

former F-18 pilot here, it's my first post here so be kind :)

NVG's are not for domestic use, they are entirely tactical. Here are some uses;

Night formation (Defensive/Offensive counter air missions), such that formation members can fly lights off or in night mode (which we did all the time). Most fighters have external NVG lighting that can't be seen with the naked eye.
Target acquisition (Offensive Strike/CAS etc) in low/no light environments (permits visual rules of engagement upgrades etc
Laser ID. Laser range finders and target acquisition pod lasers can be seen through NVG's, we can conduct visual 'hand-over' procedures using lasers to talk on a wingman to a target. Lasers are weapons and have their own master arm switch, just like the gun, bombs and missiles.

With NVG's, I can see formation members with low/no light dozens of miles away, which can't even be done during the day. This brings enormous tactical advantage in air-air scenarios.

NVG's are not used to see inside the cockpit.

Hope that answers your question!


Does the 300 hp IO550 conversion require an auxiliary tank on the Cessna 182? Does the 300 hp conversion with a continental IO 550 always require an auxiliary tank when used on a Cessna 182?  I see some of these conversions indicate an auxiliary tank is present under pilot seat but I would like to try to avoid this.

This article gives a slightly dated (2002) overview of the engine upgrade options for a 182. There's no mention of auxiliary tanks being required, but it does note that for at least one option they're typically a good idea:

  The IO-550 engine is a guzzler and if you don't have long-range tanks,
  you'll need them. Indeed, you'll probably want to consider Flint tip
  tanks for your Skylane.

It's possible that you've seen conversions where, for whatever reason, a cabin tank was added instead of - or even in addition to - tip tanks.

If you're looking into an upgrade then if you aren't already a member you should consider joining the Cessna Pilots Association and search through their forums (members only) for whatever you can find. I found one thread on upgrading the C182 to an IO-550 but it didn't mention the fuel tanks at all, although I didn't search thoroughly.


Is it required to have an alternate airport if you don't have a WAAS GPS? I forgotten if an alternate is required if you don't have a WAAS GPS regardless of the 1-2-3 rule which states that 1 hour before and after ETA at your destination airport, the ceilings must be at least 2000' and 3 miles visibility. Must we file an alternate or is it dependent on the 1-2-3 rule? Which regulation talks about this because I can't find it.

FAR 91.167 -
(a) No person may operate a civil aircraft in IFR conditions unless it carries enough fuel (considering weather reports and forecasts and weather conditions) to -
(1) Complete the flight to the first airport of intended landing;
(2) Except as provided in paragraph (b) of this section, fly from that airport to the alternate airport; and
(3) Fly after that for 45 minutes at normal cruising speed or, for helicopters, fly after that for 30 minutes at normal cruising speed.
(b) Paragraph (a)(2) of this section does not apply if:
(1) Part 97 of this chapter prescribes a standard instrument approach procedure to, or a special instrument approach procedure has been issued by the Administrator to the operator for, the first airport of intended landing; and
(2) Appropriate weather reports or weather forecasts, or a combination of them, indicate the following:
(i) For aircraft other than helicopters. For at least 1 hour before and for 1 hour after the estimated time of arrival, the ceiling will be at least 2,000 feet above the airport elevation and the visibility will be at least 3 statute miles.

This regulation (91.167) applies to civil aircraft regardless of the equipment used for navigation (e.g. GPS/WAAS).
However, if your aircraft has a properly installed and operated GPS (see the TSO requirements in the AIM/AC references below) you can flight plan to your destination and alternate as follows:

TSO-C129() and TSO-C196() equipped (GPS aircraft) - Either the
destination or alternate, but not both,  can offer only a GPS
approach (no other type approaches need be available)

TSO -C145/-C146 (WAAS Equipped Aircraft) - Both the destination
and the alternate can be airports with only GPS approaches
available.

References: AIM 1-1-17 b 5 c/d, 1-1-18 c 9 a. AND
AC-105A, paragraph 9.5.1


How come Boeing invested \$32 billion on the 787 program and Airbus only \$15 billion on the A350? How come Boeing invested \$32 billion on the 787 program and Airbus only \$15 billion on the A350? (according to wikipedia)

I don't think the breakdown is public, but there are two main areas that are obvious once you dig into the details.

Part 1 relates to the 787-8 and -9/-10 commonality. Surprisingly, the stretched derivatives only share 50% of the -8 parts. As Wikipedia puts it:

  The 787-8 and 787-9 have 50% commonality: the wing, fuselage and systems of the 787-8 had required radical revision to achieve the payload-range goals of the 787-9.

So you could say Boeing developed 1½ planes, while Airbus developed 1. I tried to find details on the differences before, but it was a futile attempt. All the official statements were as vague as they come. (Boeing will implement at least some of the new -9/-10 developments into the future -8's.)

Part 2, Boeing went with an all-electric design,* introducing many new technologies in one go. The A350 still uses pneumatic engine start and bleed air for pressurization. They were improved on the A350, but still they were existing technologies.

* Lithium-ion batteries are not really part of the differences as they were introduced quietly on the A350.


Does a request for a Pop-Up IFR clearance constitute filing a flight plan? Introduction

Pop-up IFR clearances are an accepted way to transition from VFR to IFR flight by obtaining an IFR clearance. They are well documented from a controller's perspective in this Tarrance Kramer article appearing in AvWeb and from a pilot's perspective in this Rick Durdan article appearing in AvWeb.

These related Aviation.SE questions also address the topic:

How do you request a “pop up” IFR clearance?
How do you open and get a IFR clearance while in the air?
How should I request an IFR approach at the end of a VFR flight?

Clearly, this is an accepted way to obtain an IFR clearance; I have made use of the option myself plenty of times.

Legal Background

Now, pop-up clearances are often requested and granted with no previously filed IFR flight plan which, on the face of it, would seem to be in violation of 14 CFR 91.173 which states (emphasis mine):

  No person may operate an aircraft in controlled airspace under IFR
  unless that person has—
  (a) Filed an IFR flight plan; and
  (b) Received an appropriate ATC clearance.

14 CFR 91.169 gives the information required for filing that required IFR flight plan, which states, in part (emphasis mine):

  Unless otherwise authorized by ATC, each person filing an IFR flight plan must include in it the following information: [...]

(I omit the long list of actual information)

The Question

The first part of my question is:

Does a request for a pop-up IFR clearance constitute filing a flight
plan?

Is there an unwritten (or perhaps written) understanding that the request for the IFR clearance constitutes filing a flight plan to the extent required by 14 CFR 91.173?

The second part of my question is:

Why is the full list of information required
for filing an IFR flight plan not required, in fact, of a pilot
requesting a pop-up IFR clearance?

If ATC issues an IFR clearance without this information, is that a tacit, but legally valid, authorization to exclude the information otherwise required by 14 CFR 91.169?

Is all this actually codified somewhere that I am not aware of?

I think Porcupine911 nailed the first question perfectly with the reference to JO 7110.65W: A "pop-up" IFR clearance counts as filing an IFR flight plan.
ATC considers it an "airfiled" flight plan (VFR-to-IFR), and the controller talking to you will take at least the bare minimum information necessary to enter you into the ATC system and generate a flight plan / strip for your aircraft.

Your second question is a little more complicated, but the short answer is that pop-up IFR clearances aren't "tacit authorization to omit information required by 91.169", but controllers are busy people and don't have time to key all that into the computer when they're supposed to be working traffic.

The longer version is that what you probably should be doing to get an IFR clearance in-flight is calling the local flight service station over the radio and air-filing your IFR flight plan with them, then checking in with ATC (who will have all the information Flight Service took from you and entered into the computer, without having to tie up their frequency interrogating you for it).

The FAA (or at least the ATC organization) is not without a heart though: They understand that if you're calling them for a pop-up IFR clearance it means you're in a bit of a situation (like IMC closing in on you with no good "out" that will allow you to remain VFR) and you need to get into the system before you hit the ground, a building, or another aircraft.
Giving the controller the bare minimum skeleton of a flight plan allows them to get you into the system and under positive ATC control to ensure you're operating at a safe altitude without any traffic conflicts, which satisfies the first of the three ATC operational criteria ("Safe") -- the other two (Orderly & Expedient) are a lower priority and can be dealt with later.


Is it legal to fly in RVSM airspace with an inoperative autopilot? FAR Part 91, Appendix G, Section 2 says:

  (c) Altitude-keeping equipment: All aircraft. To approve an aircraft
  group or a nongroup aircraft, the Administrator must find that the
  aircraft meets the following requirements:

  ...

   (2) The aircraft must be equipped with at least one automatic altitude
  control system that controls the aircraft altitude

Note that it does not say that it must be engaged, or even operative.  Simply "equipped", and also that this is to approve an aircraft for RVSM.  From what I can find, there is no operational requirement for the autopilot to actually be working or engaged.

Assuming that my MEL allows me to defer the autopilot and still fly, can I fly in RVSM airspace?  Some people however say that if you are in RVSM airspace that the autopilot must be working and engaged.  Right or wrong?

About whether or not you can fly with an inoperative autopilot, take a look at §91.180:

  §91.180   Operations within airspace designated as Reduced Vertical Separation Minimum airspace.

  (a) Except as provided in paragraph (b) of this section, no person may
  operate a civil aircraft in airspace designated as Reduced Vertical
  Separation Minimum (RVSM) airspace unless:

  The operator and the operator's aircraft comply with the minimum
  standards of appendix G of this part; and
  The operator is authorized by the Administrator or the country of
  registry to conduct such operations.

  (b) The Administrator may authorize a deviation from the requirements
  of this section.

You also can't say that your aircraft is allowed to operate in RVSM airspace:

  Section 4. RVSM Operations

  (a) Each person requesting a clearance to operate within RVSM airspace
  shall correctly annotate the flight plan filed with air traffic
  control with the status of the operator and aircraft with regard to
  RVSM approval. Each operator shall verify RVSM applicability for the
  flight planned route through the appropriate flight planning
  information sources.

  (b) No person may show, on the flight plan filed with air traffic
  control, an operator or aircraft as approved for RVSM operations, or
  operate on a route or in an area where RVSM approval is required,
  unless:

  The operator is authorized by the Administrator to perform such
  operations; and
  The aircraft has been approved and complies with the requirements
  of Section 2 of this appendix.

If it's not operational, the aircraft no longer qualities for RVSM, and therefore must be provided with 2000 feet vertical separation (each way) between other aircraft. Alternatively, ATC can refuse entry into RVSM airspace.

Regarding having the autopilot engaged, Appendix 4 of AC 91-85, Section "5. In-flight Procedures" states:

  e. An automatic altitude-control system should be operative and engaged during level cruise, except when circumstances such as the need to retrim the aircraft or turbulence require disengagement. In any event, adherence to cruise altitude should be done by reference to one of the two primary altimeters;


What if you approach the VOR station such that your turn OB is not on the holding side? I'm reviewing the Sporty's ground school for VOR approaches, and their example shows the approach to the VOR station then heading OB as tracking on the holding side. What if you approach the VOR station such that your turn OB is not on the holding side? I know conventionally that side is not the protected side of a hold, but does the hold side matter for that timed turn? Are you typically just vectored such that you approach the station and turn OB on the protected side of a holding pattern?

The picture and your description do not really match. The hold represented is a standard, right-turn holding pattern. It is probably meant as a holding pattern of the missed approach. It is not meant as a holding pattern for before you travel outbound for your procedure turn. Based on the standardized format of IAPs, the right-most triangle is the Final Approach Fix. The left-most triangle is the Intermediate Fix. The VOR is an Initial Approach Fix. If, for some reason, you have to hold above the VOR prior to joining the approach, do so at or above the IAF altitude and intercept the outbound radial by continuing your turn after the outbound leg. I would warn against holding over VORs without ATC providing aircraft separation. VORs are busy airspace.

The IAF will have an altitude associated with it at which you can approach the IAF from any direction and be clear of obstacles. If one is not present, approach the IAF at or above the MSA. If that were not the case, the IAP would have a notation designating the IAP Not Applicable/Available coming from certain directions. For instance, flying from left to right on the picture, ATC would clear you to start the IAP at the IF (which can be designated on the chart as an IF/IAF) instead of the IAF (VOR). Aircraft flying from all other directions would fly to the VOR to start the IAP. The IAF, procedure turn, IF (IF/IAF), and FAF would all have their respective altitudes assigned to them in that order. Your profile view would start with the altitude at which you would need to stay above in order to start your procedure turn. If not, start at your MSA and descend down to the PT altitude.

Something else that comes to mind is checking the sectional and charts for the MSA and whether the IAF is a mandatory fly over fix. If it is not, turning onto the indicated radial in a way to intercept it prior to crossing over the VOR would expedite your IAP. Depending on your speed and original heading, you would start your turn a quarter to a full mile out before reaching the VOR or radial.

Also, “the protected side of a hold“ is a misnomer. There is no such thing. There is a holding-side and a nonholding-side. The entire area around the hold is protected airspace based on the dimensions of the hold. See the following question:
what are the dimensions of the protected space provided by a holding pattern


How feasible is it to sell a plane with an expiring annual? I'm preparing to sell my plane, an IFR-equipped, low-time, C150E, but the annual expires at the end of this month.

What's the best course of action?  I know that if I was buying a plane, I would love it if the annual was just expiring - I'd just to a full annual as a pre-buy inspection on the condition that the seller paid for anything non-airworthy.  I also know that a lot of people prefer to sell planes with fresh annuals.

What's the best approach here?  And what happens if the annual expires?  Will that hurt my chances of selling the plane?

I also know that a lot of people prefer to sell planes with fresh annuals.

I think the reality (from what i have seen) is that a a lot of people end up selling planes with a fresh annual. Essentially any smart buyer is going to want a pre-buy inspection and they are often willing to pay for them. In many cases pre-buy inspections are close to if not the same as an annual so the mechanic will often do the remaining work and sign it off as an annual resetting the clock. Any potential buyers are going to want to test fly the plane so its going to need to be air worthy. I would suspect the soon expiring annual has a small impact on price (in and around the cost of the annual which is comparatively low for a 150).

You may find a buyer fast and unload the plane while its still airworthy, taking a bit of a  hit for the soon to expire annual or you may get it done and raise the price close to the cost of the annual.


Are QDM and QDR the same as 'inbound' and 'outbound' courses? I'm about to take my last test to join an airline: the simulator. I've been told they ask to perform some QDR/QDM interceptions, as well as radial ones.

About QDM/QDR:

QDM: Magnetic course from the aircraft towards the station.
QDR: Magnetic course from the station to the aircraft.

I guess we all may agree with that. But:

Could we always take QDM as an inbound course? E.g. the aircraft is at 'radial' 180 and the examiner tells me: "Intercept QDM 320". That would be the same as saying "intercept the inbound course 320", right?
The opposite for QDR. Shall I take it as always an OUTBOUND course?

Probably QDM/QDR is used for NDBs and for practical uses they cannot speak about a radial, but anyways I'd like to know if my points are correct.

QDM is the magnetic bearing to the station.
QDR is the magnetic bearing from the station.

Not to be confused with course, which is the direction in which the aircraft is moving but has nothing to do with the heading of the aircraft. Imagine having a heading of 270 but a course of 090. That means there is so much headwind that you are moving backwards.

Radials are not the same since a radial is always a magnetic bearing from the station. Therefore flying the radial 180 both inbound and outbound will both give you a position south of the station.

This is not the case with QDM and QDR.

Flying a QDM 180 will give you a position north of the station and flying 180 (without taking the wind into account) towards the station.
Flying a QDR 180 will give you a position south of the station and flying 180 (without taking the wind into account) away from the station.

Let's imagine a VOR and an NDB located on top of each other and there is no wind factor:

Flying QDM 180 will put you on radial 000 with a heading of 180.
Flying QDR 180 will put you on radial 180 with a heading of 180.
Flying radial 180 inbound will put you on QDM 000 with a heading of 000.
Flying radial 180 outbound will put you on QDR 180 with a heading of 180.

Long story short, radials are visualised in relation to the beacon. QDM/QDR are magnetic bearings visualised in relation to the plane's nose.


What is this helicopter seen in the Falcon Crest TV series? My next to last "Falcon Crest" related question for the database I'm programming: Does anyone recognize the make and model of this helicopter from episodes # 160 <7.05> (first screen capture) and # 163 <7.08> (second screen grab).
My guess is a Bell Jet Ranger, but I'm not sure.
Any hints are appreciated!  Thanks.

Looks to me like a Bell 206 JetRanger/LongRanger


Can I land my aircraft on the grass next to the runway at a public airport? The pavement is hard on my tires, so I prefer to land in the grass.

It depends on the airfield. Landing on grass is only recommended if the ground is maintained to a reasonable standard and clear of obstructions. Some airfields have grass strips maintained for that purpose, on others the grass has lights, wires and cables, or just lots of holes/ruts which will be far worse than the tarmac.

Some airfields are only grass, tarmac is not a prerequisite for having an airfield.

You want to know before you go, how to find out depends on where you are. There are flight guides and websites in many countries that tell you what is available, but it always makes sense to call ahead and ask the condition of the available grass, and to find out if there are any unofficial grass areas you can use.

There is also ATC, at a towered airfield you must land where you are cleared, you can'd decide to land on the grass nearby because you want to as it's a violation. If there's grass available you need to make sure you ask for it and they will give it to you if they can, most of the time ATC is helpful. If they say no there's probably a good reason. At an untowered airfield it's at your discretion, if there's grass available and it's in decent condition you would state your intention on the frequency and follow normal procedures.


Why would a commercial flight make banked turns five minutes before landing / low altitude? As a passenger on a commercial flight into Essaouira From London Luton a short while ago, I noticed the aircraft made several quite steep banked turns, all to left, very close to landing. When I say close I mean about five minutes before we touched the runway, and I'd estimate 600-1500 feet off the ground at most. It was possible to make out individual bushes in detail in the scrub. What was more concerning was that the terrain became undulating and was rising into rounded hills with a height difference of around 250 feet.

Sky was clear, and I don't remember any turbulence near the airport.

Is it normal to bank that close to the ground? I thought an approach was lined up further out and higher up.

As denizhanedeer said, it was a circling approach. There is only one charted IFR approach to ESU. It comes in from the northwest and would line up for a straight-in approach to runway 16.

Depending on the wind the pilot may have needed runway 34 (same runway from the opposite end) so they would circle around to line up with it.

This flight did just that. (It might even be your actual flight, Easyjet 2039 on 5/17/2016) It did a short hold at the final approach fix to lose altitude then circled to land on runway 34. It landed at 4:09 UTC. It did the first left turn at 4:06 and 1850 ft. The image here shows it during the second turn at 4:07 and 1475 feet.

The altitudes given are MSL. The terrain rises pretty quickly there. I'm guesstimating from some topo maps that at the area of the turns it rises to 175-200 feet. So 1475 ft MSL would be as low as 1275 ft above ground level.


Why are min and max temperatures (TN TX) not published in TAFs in the United States? I know that other countries like Brazil, Argentina, etc. do publish minimum and maximum temperatures in their Terminal Aerodrome Forecasts, abbreviated TN and TX. But why are they not shown in TAFs in the United States? (I guess other countries in Europe also have the temperatures).

BTW, where are the expected min and max temperatures in the US published in an official report? NOAA/NWS? WX-BRIEF?

This isn't much of an explanation, but the National Weather Service says:

  The international TAF also contains forecast temperature, icing, and
  turbulence. These three elements are not included in National Weather
  Service (NWS) prepared TAFs. The U.S. has no requirement to forecast
  temperatures in an aerodrome forecast

That sounds to me like "we don't think it's worth it". There are various temperature forecasts on the NWS aviation site (icing level, surface temperatures, graphical area forecast) but personally speaking, I get low/high temperature information from regular, non-aviation forecasts. You can get those forecasts from the NWS site too, if that's what you mean by "official".


What is the difference in performance between variable pitch prop and two fixed propellers for take-off and cruise speeds? Push-pull configuration aircrafts usually feature identical engines and propellers working only in tandem for multiple reasons like higher speed, better climb rate, reliability, cost, ease of maintenance, etc.

It may sound unpractical for piston engines were saving fuel will not outweigh the downside of one engine being a dead weight but may be a good idea for lighter electric or a combo, where engines may also be optimized for different propellers.

Can it be possibly beneficial to have tractor prop for take-off:

blown lift
no FOD risk
less noise outside

and pusher specifically optimized for cruising:

larger diameter as no ground clearance issue
no parasite drag
more stability
less noise in cabin

Benefits to consider:

efficiency
higher achievable speed
higher altitude
still two motors for redundancy

Problems:

Stowing nose prop.
Foldable prop should be cheaper than VP.

Less take-off power.
Electric motor for tractor could drive 4-bladed prop at peak power.

This doesn't specifically answer the question in the title, but from the body of your question I would say it's possible, if you had an electric push/pull configuration with a motor in the nose and one in the tail, or at the back of a fuselage pod with booms like a Cessna Skymaster.

The aft facing motor could use simple fixed pitch folding propeller that folds aft and trails in the slipstream when not being driven (popular with motor gliders) and it would be used only for take off and climb, with climb-optimized pitch.  In cruise that motor could be shut off and its batteries assigned to the front motor and its blades would fold into a near zero drag trail position.  The front motor could have a fixed pitch prop optimized for cruise.

The key issue would still be worst-case climb performance.  It would have to be able to make enough thrust on the single cruise pitched prop at the front to climb decently if the back motor failed.  Possibly if the front electric motor had some sort of emergency boost feature, where it's torque could be temporarily increased (enough to get its coarse pitched propeller up to red line) for a certain number of minutes without overheating, would be sufficient for single engine safety, with the rear propeller folding back on its own for you.

For single engine performance on the rear motor, you might get away with just a brake for the front propeller to stop it from windmilling if its motor failed.  Not as good as feathering, but far less drag than windmilling.


What is the wording on outline of Wright Flyer on FAA pilot license? I was told once that the outline of the Wright Flyer was taken from a speech given by the Wright Brothers.  In the picture below you can very clearly see the words on the Wright Flyer.  Does anybody know what that speech was?

Picture taken from Wikipedia Commons

Picture taken from Keven's Aviation Adventure

"Without question, flight is represented by countless heroes who have stirred greatness in others. It was a dream that had been waiting to be realized for thousands of years, and chased by countless visionaries, scholars and brave souls. But even as the mass of collected knowledge came to a crucial turning point, it was not until the ingenuity of the Wright Brothers that the puzzle of powered flight was solved. Discovery requires deep understanding, constant interpretation of knowledge and unbridled persistence."

It is part of a speech given by Marion Blakey on December 17, 2002 at the Air and Space Museum for the Centennial of Flight Kick-Off event. Unfortunately I can't find the full text of the speech (for free at least, it is part of a book you can buy for \$5 used, or \$108 new). Marion Blakey was the 15th FAA Administrator from 2002 to 2007.


Do anti-collision lights in aircraft lose intensity over time? Do anti-collision lights installed in aircraft lose their intensity over time and need to be replaced every few hundred hours of operation?

No, however the intensity is a feature of the bulb rather than the purpose.

Historically, incandescent bulbs were used, followed by Xenon flashtubes. Currently, LEDs are used in anti-collision lights and other lights on aircraft.

Please note that there are some requirements needed for bulbs used. They are mentioned in 14 CFR 25.1399:

  Show a white light for at least 2 nautical miles at night under clear
  atmospheric conditions.


What would be the best alternative during a dead-stick approach? (Disclaimer: I am not a pilot so my understanding of things may be really broken)

If a plane has lost engine power, has limited altitude to work with, and is upwind of a landing strip, and the pilot doesn't believe she has enough glide range to pass the appropriate runway and turn around for a landing into the wind on the full length of the runway, would it make more sense to

(a) land directly on the full length of the runway, accepting the tailwind

or

(b) pass part of the runway, turn 180, and land into the wind using only, let's say, half the runway length

Assume that an emergency has been declared, airspace and runway are all cleared, etc. In my particular scenario we're talking about a single-seat, single-engine fighter-type plane with generally poor glide ratio. I'm curious about any contributing factors.

Attempting a tight turn, while low and slow, is an almost certain recipe for disaster.

Your first option of landing with a tailwind is possibly preferable - there is no inherent danger landing with a tailwind - it'll extend your landing, and is not ideal. However, it is much safer than trying to maneuver into a position with a headwind with only part of the runway remaining. And with a short runway to start with (if that was the case) you might not have enough distance to land safely anyway.

There is a third option, with the setup you describe, which is to completly disregard the (seemingly) obvious runway close by and look for a suitable area to land in front - a field, a highway, a beach - any of the usualy places you might make an emergency landing in the case of an engine failure.

(Disclaimer: My experience is with single engine propeller aircraft, but I am fairly sure the mantra of Aviate, Navigate, Communicate applies to all aircraft types. Really, in this situation its only the aviate that is relevant)


Can a helicopter mask itself from radar? I have read somewhere that if a helicopter is traveling under 100 km/h and below 5 meters AGL then most radars will ignore it. From what I understand of this process, the radars can pick up things like cars and vehicles driving on the ground and thus need to ignore certain signals if they are traveling below a certain speed and height.

Is this actually the case, though? Does this also apply to military-grade radars?

Edit: This is not asking if a helicopter can fly under the radars coverage, but whether the helicopter can using techniques to notch its signal from being displayed as a contact on a radar operator's screen.

Note that for advanced radar systems, moving helicopters might always be distinguishable from cars and other objects, due to the fact that helicopters have moving rotors.

While I have no information on military systems, I know the systems by robinradar can separate drones from birds by using doppler shift techniques.

Doing this on an actual, full-size helicopter without rotor guards should be a lot easier than on a drone.

This means avoiding detection by moving slow and staying low might not work, unless you can stay out of the line of sight of the radar system.


Would the solid material inside an airship displace air and be counted towards lift? The hydrogen inside an airship has a mass that is approximately 14 times lower than the mass of air and this difference results in lift.

However the solid material inside an airship including the frame, skin, walkways, gasbag material etc. would also displace air.  Would the air that these materials displace also be counted towards lift?  I'm not sure.
If the extra displacement is counted towards lift is there any reasonable estimate as to how much space the solid material might fill?  1%, 2%, 5%?
A U Class Zeppelin has an outside volume of approximately 59,000 cubic meters.  However if 2% of this volume was solid material that's 1,180 cubic meters of atmosphere displacement or an extra 1,445 Kg of lift.  Although not decisive I'm sure that any little bit helps.

It would, but it is so little it is not noticeable
Duraluminium has a density of 2780 kg/m3, plain air has a density 1.3 kg/m3. So the buoyancy is in the order of 0.05%. The dry weight of the Hindenburg for example was 100 tons, meaning that the buoyancy of the solid material is about 50 kg.
This is so little that other effects on lift — i.e. changes in temperature, internal gas pressure, external atmospheric pressure, dynamic lift from relative wind speed, ballasting, spending fuel, and more — will completely drown out this effect.


In what way are the Concorde's engines considered efficient? The Concorde is powered by a bunch of Rolls-Royce/Snecma Olympus 593 turbojet engines. Much has been said about how efficient they are at speed, and the fact that they allow long-range cruise at Mach 2 because of how fuel-efficient they are.

If I look at the specifications, one thing immediately obvious is the compression ratio of 15.5 - quite high for a no-bypass turbojet. I'm not sure how this translates into efficiency though.

The thrust-specific fuel consumption, on the other hand, looks dismal. Wikipedia states:

  1.195 lb/(lbf·h) (33.8 g/(kN·s)) cruise / 1.39 lb/(lbf·h) (39 g/(kN·s)) sl

Wait, what? The Tumansky R-25, which powered the MiG-21 and was famously fuel-hungry, had a compression ratio of only 9.5, but had a TSFC of

  98 kg/(h·kN) (0.96 lb/(h·lbf)) at maximum military power

The General Electric YJ93, which powered the XB-70 and was also designed for long-range supersonic efficiency, had a TSFC of

  0.700 lb/(lbf·h) or 19.8 g/(kN·s)

This doesn't seem to make sense: in what way are Concorde's engines any good? Is there something I'm missing?

Finally, I've been attempting to model the Olympus 593 in a flight simulator (Advanced Jet Engine in KSP). With the given compression ratio, though, I couldn't get the fuel efficiency to be this bad: it was around 0.9 SL and 0.85 cruise, and I had to do ridiculous things like using extremely inefficient intakes and nozzles.

You compare SFCs at different speeds. That is like comparing payloads for differently sized aircraft. SFC goes up with speed and, therefore, must be compared at the same speed. The work performed by an engine is thrust times distance, and higher speed means that the same thrust will perform more work per unit of time when the engine moves faster. The moving engine needs to slow down the airflow for combustion to take place, and then needs to accelerate the air by more than it has been slowed down to have positive thrust. Hence, SFC goes up in parallel with speed.

To have a meaningful comparison, we need to define efficiency. There are several, and two are of major importance for air-breathing aircraft engines: Thermal efficiency and propulsive efficiency.

Thermal efficiency

This describes how efficiently the chemical energy in the fuel $Q$ is converted into an impulse change of the air flowing through the engine. Formulated using the mass flow per unit of time $\dot{m}$, the impulse is $\dot{m}\cdot\dfrac{\Delta v^2}{2}$. Using $v_{\infty}$ for the incoming air speed and $v_{\infty} + \Delta v$ for the exit flow speed, the thermal efficiency is $$\eta_{therm} = \frac{\dot{m}\cdot \left((v_{\infty} + \Delta v)^2 - v_{\infty}^2\right)}{2\cdot Q}$$
To achieve good efficiency at high speed, a high $\Delta v$ is helpful. This explains why efficiency drops more over speed for high-bypass ratio engines and especially propellers.
Since the thermal energy in fuel is the same for all engines in your question, because all run on kerosene, and we can assume a similar efficiency of combustion, we can neglect $Q$ in the comparison.

Propulsive efficiency

This describes how well the conversion is performed. Using the same variables as above, propulsive efficiency is $$\eta_{prop} = \frac{v_{\infty}}{v_{\infty} + \frac{\Delta v}{2}}$$

This equation explains the better efficiency of high-bypass ratio engines and propellers at the same speed, because propulsive efficiency is proportional to the inverse of $\Delta v$.

Overall efficiency

This is the product of thermal and propulsive efficiency, and the equation is $$\eta_{total} = \frac{T\cdot v_{\infty}}{Q}$$
where $T = \dot{m}\cdot\Delta v$ denotes the thrust. Conveniently, $\Delta v$ is eliminated in the product, allowing turbojet engines like the Olympus 593 to look much better in comparison to other engines.

Intake efficiency

This answer would be incomplete without a look at the intake of the Concorde. At cruise, it would lift the pressure of the air at the compressor face by a factor of more than six over ambient by efficiently decelerating the flow. The compressor added a compression ratio of 12, so the pressure in the combustion chamber was 80 times higher than ambient. This high pressure makes the engine so efficient, but is also needed to maintain combustion. Remember, ambient pressure in 18 km is just 76 mbar, so the absolute pressure in the combustion chamber at cruise was only 6 bar.

The full answer would be like this: The combination of intake and Olympus 593 at Mach 2.02 had a very good total efficiency, and comparisons with other engines at static conditions are misleading.

The comparison of results from a test stand on the ground would yield a very different picture, however.


Where can the FAA versus ICAO official filed differences be found? ICAO has a process where individual countries may file differences from the ICAO standard when the rules of the country do not coincide with the published standards.

Where can the list of differences that the FAA has filed be found?  I have found references saying that it is in the AIP, but I could not find a list in that document.

For instance, there is an ICAO requirement that certain aircraft are covered by a Flight Data Monitoring (FDM) program, but FAA rules say that it is an optional program and not required by 14 CFR.

I found one (expired) document, paragraph 4b which refers to the FAA filing a difference with ICAO and want to see a complete list of all current differences.

The link you provide is for an amendment of the US AIP, not the entire document.

The entire document is available here: (link)

You will have to look at section GEN 1.7 (starts at PDF page 57).