Why does the A380 not have front windows on the top floor?

(flightglobal.com)

You'll need to zoom above 100% to read the legend, but up there it's not empty. There's the crew rest area (5), where the pilots rest for example, and it is easily accessible from the cockpit (see below for how it interacts with the upper deck).

There is also an electronics bay (29), and toilets (12).

Note that the cockpit is not on the main deck, it's between the main and upper decks, the mezzanine if you will.

Design-wise, the forehead is very sloped for aerodynamics, so to offer a forward-facing window view (if the area was empty), there will be an enormous unused legroom (for head clearance). The view also wouldn't allow seeing a big distance ahead and below, so it will be more like a skylight window, especially that airliners typically cruise with the nose pointing above the horizon. And with the area clear of walls and supporting structures, the plane will gain weight to strengthen the shell in that area.

For the secondary question see, 'Has any passenger airliner ever offered forward-facing windows?'

(source)


Where can I find US ARTCC sector boundary coordinates?

For any ARTCC you can contact their Airspace and Procedures office. Be polite, and specific. They will have that information. It should be publicly available. The cities for the lower 48 where ARTCCs are (associated city name and actual location)
Albuquerque (NE side of town) 505-856-4500
Atlanta (Hampton GA you should hear it when the speedway fires up) 770-210-7600
Boston (Nashua NH) 603-879-6633
Chicago (Aurora IL) 630-906-8200
Cleveland (Oberlin OH) 440-774-0300
Denver (Longmont, my facility, tell 'em CD from training sent ya) 303-651-4100
Fort Worth (north side of DFW airport) 866-835-5322
Houston (just south of airport) 281-230-5600
Indianapolis (at the airport) 317-247-2234
Jacksonville (Hillyard FL) 904-845-1500
Kansas City (Olathe) 913-254-8400
Los Angeles (Palmdale) 510-745-3000
Memphis (NE of airport) 901-368-8101
Miami (North Miami in a warehouse district...) 305-716-1500
Minneapolis (Farmington MN) 651-463-5514
New York (Ronkonkoma) 631-468-1001
Oakland (Fremont) 510-745-3000
Salt Lake City (airport) 801-575-2400
Seattle (Everett WA) 866-835-5322
Washington DC (Leesburg VA)703-377-3401
These numbers are for their respective switchboards, select "Airspace and Procedures" from the menu.


Generally it enters the ramp drainage system and flows out with the rest of the runoff. Sometimes its recycled and sometimes its just filtered out of the runoff water and disposed. The EPA has a lengthy report on it you can find here various airports have different methods for recycling it or filtering it out as well as water drainage systems that vary in complexity and scope. The report sheds some light on the various systems involved at different airports.

Longer blurbs are available in the report (see section 7-1) for deeper descriptions.

Ultimately the components of De-Ice fluid break down fairly rapidly when released.

  When released into the environment, both ethylene glycol and propylene
  glycol are expected to partition to surface or groundwater. They are
  expected to rapidly biodegrade and not to persist in the environment.
  Biodegradation rates depend on temperature and oxygen conditions and
  glycols biodegrade more slowly under anaerobic conditions. The
  half-life of ethylene glycol and propylene glycol in water under
  aerobic and anaerobic conditions, and in soil are shown below. Note
  that these data were not conducted under the same laboratory
  conditions and may not be directly comparable (5).

Smaller fields or those that can not afford complex systems may allow it to flow into installed drainage systems right off the ramp. The small field I fly out of has no formal system to dispose of it.


How do airports generate "indirect" income?

One way to approach this question is to look at the annual budget for an airport. I'm going to assume that you mean a large passenger airport as opposed to one focused on serving general aviation, cargo, etc...

Let's use SFO (San Francisco International) as our example. It's a city-owned airport, so the budget is a public document. Here's the budget for FY2014/15 and FY2015/16.

Page 5 (page 7 in the PDF) breaks down major sources of revenue. We have some that fall into the category of "direct" revenue in your question: landing fees, terminal rentals, etc... under the "aviation" category. Some of the terminal rental fees include space for purposes you might not consider aviation uses, like back offices for airline staff We also have $60-80M in "PFC Revenue." PFC stands for "Passenger Facility Charge"; it's a charge that is added to the ticket price of everyone flying out of that airport.

Finally, there are the non-aviation revenues. The bulk of those come in two categories: parking and concessions. Parking is self-explanatory. Concessions describes all the independent businesses that operate at the airport. Many businesses lease terminal space for retail shops (including duty-free), restaurants and take-out food, lounges, currency exchange, etc... They all pay rent and/or a share of revenue to the airport based on the terms of their lease. SFO also books about $23M/year in revenue off the sale of electricity, as the airport sells electricity to its tenants (airlines, concessions, etc...). I suspect, but am not positive, that these electricity sales are a nice moneymaker for the airport, as it can purchase hydropower from the City at extremely low cost and resell it at market (utility company) rates to its tenants. This is a quirk particular to San Francisco however.

If you scroll through the detailed budget in the PDF, you'll find entries for other revenue categories. Examples include advertising fees (Clear Channel pays the airport to put up ads in the terminals and other areas), revenue for things like ATMs and baggage carts, leases to rental car companies, fees paid by taxicabs and airport buses for the right to access airport property, and even permit fees paid by filmmakers and photographers using the airport. Heck, the airport even charges the regional transit agency $3.2M/year in rent and custodial fees for the airport train station. Browsing through the budget should give you a pretty good idea where a large US airport can make money from non-aviation services.


What is the difference between a Mechanic and a Repairman?

The basic difference is that a mechanic can perform maintenance on any aircraft; a repairman can perform maintenance only on aircraft for their employer, or that they own.

The full details are in 14 CFR 65 Subpart D (mechanics) and Subpart E (repairmen). Here are the basic privileges for each one (emphasis mine):

  A certificated mechanic may perform or supervise the maintenance,
  preventive maintenance or alteration of an aircraft or appliance, or a
  part thereof, for which he is rated (but excluding major repairs to,
  and major alterations of, propellers, and any repair to, or alteration
  of, instruments), and may perform additional duties in accordance with
  §§65.85, 65.87, and 65.95.

And:

  A certificated repairman may perform or supervise the maintenance,
  preventive maintenance, or alteration of aircraft or aircraft
  components appropriate to the job for which the repairman was employed
  and certificated, but only in connection with duties for the
  certificate holder by whom the repairman was employed and recommended.

"Repairman" also applies to experimental and light sport aircraft owners. If you build your own aircraft you have repairman privileges to maintain it, but you can't use those privileges to work on other aircraft, per 65.104(b) (emphasis mine):

  The holder of a repairman certificate (experimental aircraft builder)
  may perform condition inspections on the aircraft constructed by the
  holder in accordance with the operating limitations of that aircraft.


What short-term alternatives do airlines have to replace their grounded Boeing MAX 8s?

Airlines really don't have a lot of options to carry through with the flights they planned with the grounded airplanes.

Older models of the 737 aren't much of an option. Most of the MAXes weren't intended to replace retiring aircraft, and even if they were, various costs of bringing the older aircraft into service for just a few months would be too expensive to make sense in the long run. The A320 would be the most direct replacement, but even then the situation is similar. New aircraft are ordered years in advance, so they can't just go buy an A320neo and get it right now.

It's possible to use a larger aircraft like the 757, but they would have to be pulled off another route and would burn more fuel.

The summer is peak travel season, so there just isn't any spare capacity out there that's economical to bring on board on short notice for just a few months. Even if they did, once the hundreds of MAXes return to service, the excess capacity is a liability.

Aircraft are a very expensive asset. Fleet needs are planned well in advance to have only as many as they absolutely need. Even an unexpected increase in maintenance time causes cancellations. The downside to this is that they're in trouble if a large disruption hits. The cheapest option is to just cancel a lot of the flights.


Do some helicopters require classes, type ratings, or special endorsements, the way some airplanes do?

I can't see a connection between "classes" of helicopters and ratings.

You also don't specify which jurisdiction so I will answer for the UK CAA which I know.

To fly any helicopter under VFR needs nothing more than your license, gained on any type, and a type rating for the specific aircraft.

For example, I gained my license on the R22.  I am therefore also type rated on it.  The second aircraft I learned to fly was the B206 which is jet powered.  I didn't need anything extra than the appropriate type rating.

I can fly any helicopter for which I am rated under VFR.  If I had an IFR certification, I could fly any helicopter I am rated for under VFR, and any IFR certified helicopter for which I am rated under IFR.

"Difference training" is simply part of the the type rating.  For example, if I ever learned to fly a craft with a retractable undercarriage, I would be rated to fly that type, but not another type with retractable gear.

What does differ is the type of license, e.g. CPL or ATP.  I would need that license in order to carry passengers for hire and to conduct other commercial operations, but I still need a type rating on whatever helicopter I use to carry those passengers.

Put it this way, the day after I gained my license, I could climb into any helicopter and act as pilot under training.

Hope that's all clear!


Is an ultralight aircraft allowed to fly near Class B airspace?

Yes, an ultralight aircraft operated under 14 CFR 103 can be operated within the "Mode C Veil" within the limitations of §103.

As you note, 14 CFR 91—including §91.215, ATC transponder and altitude reporting equipment and use—does not apply to ultralights governed by §103.

The limitations of §103 do generally prohibit: operations over congested areas; operations in certain types of airspace; operations in certain types of airspace.

  §103.15   Operations over congested areas.

  No person may operate an ultralight vehicle over any congested area of a city, town, or settlement, or over any open air assembly of persons.

  §103.17   Operations in certain airspace.
  No person may operate an ultralight vehicle within Class A, Class B, Class C, or Class D airspace or within the lateral boundaries of the surface area of Class E airspace designated for an airport unless that person has prior authorization from the ATC facility having jurisdiction over that airspace.

  §103.19   Operations in prohibited or restricted areas.
  No person may operate an ultralight vehicle in prohibited or restricted areas unless that person has permission from the using or controlling agency, as appropriate.

Let's look at an example, the MSP Class B area:

Point A, near A R S Sports Strip (7Y7), would be an area where operations under §103 would be allowable. It is not a congested area, and is not a type of airspace for which operations under §103 are prohibited.

Points B, C, and D, however, would be areas where operations under §103 are generally prohibited. Point B is arguably over congested areas, and by that determination would therefore be prohibited under §103.15. Points C and D are in Class D and B airspace, respectively, and are therefore prohibited under §103.17. The exception would be where the operation has received prior authorization as specified in §103.17 above.

For what it is worth, I have personally witnessed ultralight type aircraft flying in the area of Point A.


What type is this aircraft with "inverted" wings?

If I am not horribly mistaken, it seems to be an Antonov 72 or 74, that were produced together, hence the similarity.

Another image (not included for copyright reasons) can be found here.

The wikipedia article classifies it as a "transport aircraft". It mentions a VIP transport variant and a maritime patrol one for the An72, several more variants are listed for the An74 version.

EDIT:

Flightradar24 lists only one An72 in the possession of CAVOK Air (thanks to bjelleklang for identifying the livery), registration UR-CKC.

The historical data indicates that this aircraft landed in Tampa on the 24th of May after a stop in St. John's on its way from Reykjavik.

  It has an odd combination of a negative dihedral and pylonless overwing engines, all traits I've seen individually but not together.

Concerning the anhedral (the name of "negative dihedral") angle, you can find more info here, but we can summarize here that it has more to do with the high wing mount rather than the engine one.

The overwing mount of the engine contributes to reducing the risk of foreign object ingestion on unpaved runways.

Update:

The aircraft has been damaged beyond repair in a runway overrun accident occurred on Jul 29th 2017.


Why does "airplane mode" turn off Bluetooth and WLAN if I can just turn them on again?

"Airplane mode" is a convenience feature provided by the phone manufacturer. You can choose to turn it off anytime in violation of the rules, so there is no difference there.

What it does may not match the regulation in any particular geography as rules vary. Regardless of any particular device the airline sets rules to ensure that no device:

1) Interferes with navigation signals required by the aircraft, particularly at landing

2) Confuses cellphone towers on the ground which expect radio signals in roughly a planar orientation near the ground

The airline gets its rules from the FAA/EASA... and indirectly from the FCC... What was considered "airplane mode" by the FAA changed in 2013. Testing determined that wifi and bluetooth did not cause sufficient interference with ground based nav signals, so that prohibition was relaxed. An old phone's "airplane mode" may be too restrictive.

There was no change to the rule on cellphone voice communication, which remained prohibited. Once the aircraft is sufficiently high no ground based cell tower can receive any signal, so this prohibition mid-flight is effectively meaningless.


Why didn't we see many VTOL aircraft in the history of aircraft development?

VTOL (and STOVL) are concepts which were conceived as a result of not having large aircraft carriers or the space for a long runway. The primary feature of these aircraft is to enable them to take off and land using a minimum of runway distance, but in order to achieve this compromises have been made with the designs. This affects several aspects of the aircraft; complexity goes up as it requires at minimum additional controls for low-speed maneuvers where traditional control surfaces are inefficient and some way to distribute the thrust or add thrust to balance when flying vertically.

This tends to add weight and occupy internal volume which could otherwise be used for other things, such as fuel. It drives complexity when flying the aircraft and also in terms of maintenance, and thus cost.

Take the F-35 as an example. There are three models of a single design, where the A-model is designed to operate from regular air bases on land, the B-model for VTOL operations on amphibious attack ships or forward air bases, and the C-model for regular aircraft carriers. Compared to the other two models, the B-model has less internal fuel and a lower max takeoff weight. Because of this it will be required to refuel more often and/or carry less payload, which in turn will drive the complexity of operating the aircraft due to the logistics.

Another issue with VTOL airplanes, is that they (as far as I can tell) haven't been designed to takeoff vertically with a full fuel load and carrying a full payload. I could not find any numbers for the F-35, but for the AV-8B+ Harrier the max vertical take-off weight is around 9,5 tons, while a rolling take-off increases this to 14 tons. ([Wikipedia])1 This is quite a difference, and it shows how much you sacrifice to be able to do a vertical takeoff.

While having the option of VTOL is nice, cost is generally what drives decisions (even in the military). An AV-8 cost around \$19.000 USD to operate per hour, according to DefenceIssues. While older than eg. a JAS-39 Gripen (age tends to drive costs upwards), the Gripen which is of a similar size and empty weight has a longer range and only cost $4.700 USD per hour to operate. And according to the source that number is high, as labor costs more in Europe than in the US.

Use on aircraft carriers

While some VTOL aircraft have been developed, the reason for why they aren't used more is related to everything above. Many of the non-VTOL carrier aircraft used today have a basis in aircraft originally designed to operate from land-bases using regular runways. If you decide to use VTOL aircraft on an aircraft carrier, the carrier can generally be smaller than a carrier operating STOL or catapult-launched aircraft, but this will also affect how you can use the carrier.


How to remove clogging in aircraft fuel nozzles?

Hoppes No. 9 is often used for cleaning aircraft fuel injection nozzles in general. This solvent is widely available for cleaning firearms. The cleaning procedure typically involves submerging the detached nozzles in the solvent for as long as necessary, typically 10-60 minutes depending on the level of fouling.

Disclaimer: I don't have any specific maintenance data on your nozzles, so you may want be wary of the applicability of the information I offer.


Does the FAA require a rating for night VFR?

There's no separate night rating or endorsement in the US, it's included in the private pilot flight proficiency requirements (14 CFR 61.107) and the specific required experience is in 14 CFR 61.109:

  (2) Except as provided in §61.110 of this part, 3 hours of night
  flight training in a single-engine airplane that includes—

  (i) One cross-country flight of over 100 nautical miles total
  distance; and

  (ii) 10 takeoffs and 10 landings to a full stop (with each landing
  involving a flight in the traffic pattern) at an airport.

Some very minimal instrument training is also required, which can be helpful at night:

  (3) 3 hours of flight training in a single-engine airplane on the
  control and maneuvering of an airplane solely by reference to
  instruments, including straight and level flight, constant airspeed
  climbs and descents, turns to a heading, recovery from unusual flight
  attitudes, radio communications, and the use of navigation
  systems/facilities and radar services appropriate to instrument
  flight;

That all applies to private pilots; sport pilots may not fly at night. And as David pointed out, there is an exception to the night requirements under 61.110 for pilots in Alaska: they can skip the night training but if they do, they can't fly at night.


What is the security policy for getting into a Control Tower in the US?

It is still possible (and in my experience not that difficult) to get FAA tower tours (and sometimes even TRACON or Center tours), though you should be reasonable in your expectations here -- You are probably NOT going to get a tour of the tower at JFK or LAX.

The FAA used to actively encourage pilots with an instrument rating (or pursuing instrument training) to sign up for ATC facility tours under a program called "Operation Raincheck" -- This program is still running, though it's been substantially scaled back (Poke around on the FAA Safety Team's SPANS system, or sign up for notices in your area and keep a sharp eye out. Tours usually have a very limited number of slots available, and they fill up fast!).
(As an example of how quickly the slots fill up, when N90 (New York TRACON) last had a Raincheck event it was full within a few hours of being announced. No, I didn't get a slot.)

At towered GA airports - particularly ones with a lot of flight training - you can also contact the tower directly. The printed AOPA Airport Directory has facility numbers in it but that's a little out of date. You can also get the phone number from Flight Service, the local FSDO, or ask the tower/ground controller for the number if they're not too busy.

When you call the facility explain that you're a pilot/student pilot and would like to arrange to tour the facility (and if possible shadow a controller). They will usually ask for your name, address, airman certificate number, and a few other things to run a check and get approval to let you in to the facility. You will also be expected to have government issued photo ID with you when you show up.

My experience arranging a tour of our local tower was extremely pleasant - they are happy to do the tours and let you shadow a controller, and I even got to pick their brains about some peculiarities in local procedures.
It's a great educational experience, and I would recommend it for any pilot/student pilot.


Why was the Junkers Ju 87 not upgraded with a jet engine?

First, the Ju-87 was not easily shot down. It had manoeuvrability superior  to all fighters due to its lower wing loading and Junkers flaps, and it could take a lot of damage. With the rear-facing observer the Ju-87 pilot was in a much better position to evade all maneuvers of a pursuer. Only when faced with large numbers of enemy fighters could a Ju-87 not escape.

Battle damage on a Ju-87 (picture source)

But to put a jet engine into an airplane with a fixed landing gear will not make it faster than the much sleeker piston-powered designs to its days. Instead, the idea was to develop a new design with a retractable gear and a prone pilot position. This was the Henschel Hs-132, pictured below (source)


Is triskaedekiphobia (fear of the number 13) the reason commercial planes normally do not have a row 13?

Fear of number 13 is known as Triskaidekaphobia.

I randomly entered some flight numbers on SeatGuru and found that this one has row 13 (aircraft is B737):

In this case, there is no 13th row:

However, in this case, several row numbers (12, 13, 14) are skipped to adjust galleys and lavatories. This could be that they were added later or can be removed in future to add more rows.

The bottom line is that regardless of what you name it, there remains a 13th row. If a plane is about to crash (God forbid) I would be worried about being on the plane, rather than just the seat number. There are several studies that safest seats are in the back. So, rows 1-12 may not be as unlucky as row 13.

If you have 12 million dollars and I can give you one million more1, would you not take it?

In several parts of the world 13 is a lucky number.

1Trust me, I will not do it, even if I have that much money.


(Airbus) A320 landing gear approach paths.
It's important to approach the landing gear from the right angle, because an explosion could throw deadly debris at the firefighters.
Cooling
According to Airbus, water-mist is to be used to cool the brakes.
Water, CO2, or foam, are not to be used. All those cause sudden cooling that can lead to wheel cracks or rim burst.
Fire
If there is fire, then large amounts of water or water-mist is to be used. Foam is to be used if fuel tanks are at risk.
(YouTube) Fire crew attending to 1400°C brakes.

Not an emergency, but interesting:
(airliners.net)

Upon deplaning back in Pyongyang, we noticed the brakes of the main gear were being cooled down with water. Naturally, this led to a mass gathering downstairs, as everyone wanted to take a photo of this event. We learned that this is actually standard procedure, which seemed legit as I remembered seeing water on the apron after our [Ilyushin Il-62] flight as well.

Related: When the brakes are checked, what do the firemen actually do?


Why does Martin-Baker use a Gloster Meteor as a testbed for ejection seats?

Aviation week did a bit on the plane last year

  "In spite of its considerable vintage, the sturdy British attack
  aircraft has all the attributes required for a stable, high-speed test
  platform" says Andy Gent, Martin-Baker’s head of flying and chief
  pilot. “From a test perspective the Meteor is ideal. The tail boom is
  fairly long and the fin is not very high. The engines are also spaced
  out a fair way out along the wing, so the efflux from the ejection
  test and exhaust from the gun and rocket motor isn’t potentially going
  down the engine intakes,” he says.

  Based at Martin-Baker’s Chalgrove, England, test facility, the fleet
  is made up of two Meteors, WA638 and WL419, both of which have been
  with the company since the 1960s. “They are doing the job so why would
  you ever go through the heartache of getting another aircraft?” says
  Gent.

In short, it does not fly all too much, it gets the job done and its well built. Similar reason most older aircraft are still flying these days.

The article goes on to say that they have little intention of changing this any time soon:

  Marketing Director Andrew Martin notes the company is one of only a
  handful that performs airborne ejection tests, and that the Meteor
  will continue to be used for the foreseeable future. “It is a tough
  thing to evaluate, and right now while we have these phenomenal assets
  we are not going to really think about a replacement in great detail,”
  he says. With the final retirement of the last Royal Air Force
  (RAF)-operated aircraft in the target towing role in the early 1980s,
  Martin-Baker acquired a large stock of spares and Rolls-Royce Derwent
  8 turbojets. Because of that and the ample remaining airframe life,
  the company is no rush to find a successor.

Also a bit of a side note, this is not their only testbed. MB also uses a high speed sled for testing at their Langford Lodge, Ireland facility. This allows ground testing of the seats at flight speeds. They also test static scenarios in what appears to be cockpit mock ups as generally speaking seats are certified for Zero-Zero use. Varying governing bodies may require different testing and live demonstrations as per their certification process leading to different testing procedures.


What is the noise level inside the Tu-114's passenger cabin?

Perhaps not "as noisy as" due to at least some insulation that must have been installed, but by all accounts (including those of my acquaintances who flew it), Tu-114 was by far the noisiest airliner.

Wikipedia quotes the noise level in the cabin of around 110 dB. This is the level when one needs to yell to other's ear to be heard - which is about how it was.


Can a fixed-wing plane jump up by blowing air over its wings?

As a partial answer to your question, air moving over a stationary (relative to the ground) wing will generate lift. There have been several weather related incidences where aircraft were picked up off the ground by significantly strong winds. Videos of these incidents showed that it was lift and not force from form drag that lifted the aircraft off the ground. In the case that the planes were tied down, they would come back down to earth in place. Unfortunately, the force of the decent, in some cases, was still enough to damage the planes.

I am uncertain about what you mean by “This would require that the lift generated would exceed ground friction reacting the propellor thrust...“. Lift would be acting roughly perpendicular to the wings chord line, and the plane’s longitudinal, and lateral axes. On the other hand, any friction created by the relative wind would be acting roughly parallel to the relative wind and the plane’s longitudinal axes. The only ground friction would be that caused by the wheels touching the ground.

Thrust is a function of Newton’s Laws of Motion. The propellers turn chemical energy (in this case electrical energy) into thermal and mechanical energy. The mechanical energy is used to accelerate a mass of air. The mass of the air is accelerated by the propellers creating force. This force acts on the mass of the airplane to accelerate the airplane. The relative wind created by the propellers would act upon the airplane in the form of thrust and upon the wings to create lift regardless of how close to the ground the airplane was.

P.S.
Edited to include a new link pertinent to the discussion. Here is a new VTOL aircraft soon to be on the market.

Blackfly


Why are some pitot tubes more prone to icing than others?

Actually the answer is quite complex, but essentially depends on the local aerodynamics, shape of the probe and the anti-icing power (heating).

Imagine an airplane flying around a cloud, it essentially approaches air with small drops of water floating around, those drops of water impact the pitot tube and some of them keep over the pitot tube surface.

Now, the key question is if that water will or will not become ice. That essentially depends how long the water keeps over the surface and the local temperature.

Keeping on the surface depends on the shape of probe and the local pressure. The water temperature will depend on a balance between the external temperature (also dependent on the local pressure) and the balance of power applied to the probe to avoid freezing.

So, the phenomena is quite complex and depends on all of these factors, and the potential case of pitot tubes prone to icing will likely being a condition unexpected and outside margins as all these factors are taken usually into account.


What are the crewing requirements for a B787 flying LAX to SIN?

I can't provide a specific answer but rest times are contract matter and airline specific. Also, most curiously, you won't find rest crews on private jets.

Depending on the airline you will have anything between 3 and 5 pilots on longer flights (anything above 8h). Three being the most common. Start and landing are handled by captain and co pilot, in between the aircraft is flown by a "cruise pilot" of a lower rank.

Rest crew regulations can cause problems, if there is a delay. Even a small delay may cause to require a standby crew, which will incur a further delay.

As a rule of thumb, airlines have around 10 flight crews per aircraft to allow for relief crews, training, holidays, ...


How much fuel did this Boeing 787-9 have on board for this flying display?

Looks like he is zooming after taking off: gain as much horizontal speed as he can, then pull up very steeply to convert some of the kinetic energy into potential energy. He only spends about 4-5 seconds at the crazy steep angle.

For zooming at these speeds, the mass is not very relevant: it appears in both kinetic and potential energy terms and cancels out.

$$\frac{1}{2}\cdot m \cdot \Delta V^2 = m \cdot g \cdot \Delta h \Rightarrow \Delta h = \frac{\Delta V^2}{2 \cdot g} $$

He just needs to take a longer take-off run at higher take-off weight to reach the same speed.


Why are most helipads in São Paulo blue coated and identified by a "P"?

According to the Rules for Heliports in Sao Paulo, the P means that it is private heliport. H for public Heliports,  M is for military. Hospitals use the letter H on a red cross, also when they are private or military hospitals. Examples are given in the pictures below.
It seems that the color blue is not required by the regulations; there are various other colors used in Sao Paulo (see a few examples below I found on Google maps).
I think blue is used mostly because it provide good visual contrast with the white or yellow markings. White paint on concrete can be difficult to see under bright sunlight conditions. The blue color also stands out from the urban environment, making the helipads easy to spot from the air. Try it on Google maps; the blue helipads are relatively easy to find on the satellite view.
This video explains the markings (in Portuguese)

Hospital helipad with H marking and red cross

Military helipad with M marking

Green helipad with circular border and 05 Marking

Concrete helipad with circular border and 05 Marking

Red private helipad

Green private helipad
All images are screenshots from Google maps


What punishment will I get from CASA if I fly in a cloud while a student pilot?

I have had a fair bit of experience with CASA, including a close friend who worked for them for a number of years. They have a bad reputation these days but I'm not sure it's entirely deserved. I obviously cannot predict exactly what they would do but I hope to give you some advice.

First things first, I would believe your version of events much more than someone on the ground - slant visibility and all that.

The regulations (CAR 172) effectively states that if you fly into cloud the penalty is 50 penalty points - I think each penalty point is currently 110 dollars so the answer to your question is you could be fined $5500. However, CASA uses discretion as to when to enforce this fine - and the Department of Public Prosecutions gets the final say. If it is not a good use of their time, or if it doesn't really serve the public interest, they won't bother with it. A student pilot who accidentally flew into cloud? I would be very very surprised if they followed it up - particularly because as a student you are under the care of an instructor, who shouldn't let you fly solo if there was cloud in the immediate vicinity.

I don't think this would apply to your situation, but a more common course of action for CASA is the "fit and proper person" catch-all. Basically it means CASA must be comfortable that you will be responsible with the powers your licence gives you. CASA uses this power to remove the licences of people who frankly, shouldn't have one. It tends to be reserved for people who break the law either intentionally or through gross negligence. Also for example if you are charged with a non aviation offence, like fraud, CASA might take your licence claiming you are not a fit and proper person to hold one.

Other items in CASA's arsenal include temporary licence suspension, forced re-training or re-sitting of an exam or flight test. There is also a 'demerit points' system if you are a repeat offender.

Some general advice now (remembering that I'm not a lawyer) - don't lie. According to my friend (who should know), CASA is more concerned about your attitude than anything. They want to see people taking responsibility for their mistakes and accepting the consequences. This certainly doesn't assure you immunity but you might find that this reduces a licence suspension from 24 months to 6 months. If you are particularly worried, remember that you don't need to tell CASA anything if you are the person under investigation - like in other legal matters, you have the right to remain silent. Before any action is taken against you you will receive a "show cause" notice, which tells you what they are planning to do and invites you to tell them why they should not do that. If you don't like what they propose I'd advise upon getting a lawyer to respond on your behalf.

But all pilots make mistakes and only 'temporary pilots' pretend otherwise. If you really did fly into that cloud, thoroughly debrief with your instructor and turn it into a learning opportunity. If CASA does come knocking then you can talk about what you have learned and that you are a better pilot for it.

But, in the circumstances you've described, especially as a student pilot, if CASA comes down on you I would be questioning where my taxes are going. What you are going through must be intimidating but don't be fearful - if your goal is to get into the airlines you will quite likely experience this sort of situation again. As long as your intent was never to break the rules or put anyone in danger, you honestly should be fine.


How is thrust of engines on the two sides of an airplane kept exactly equal to prevent yawing?

It isn't. The rudder is used.

Yes, if there is asymmetry in thrust, the plane will yaw. And there is asymmetry in thrust. The engine thrust decreases slightly with wear and the engines are often worn out differently. There are effects like P-factor that shift the thrust axis depending on speed and attitude. And of course an engine may fail.

So thrust asymmetry happens and needs to be compensated. And it is compensated by generating some sideways force with the rudder. Either by pilot pushing the pedal, or by applying trim.

As @mins mentions, there are also effects that can cause asymmetry of drag, e.g. icing, and there are situations where the aircraft intentionally needs to fly somewhat sideways, e.g. cross-wind take-off and landing, so rudder is needed for many other things too. And when it's there, it can compensate thrust asymmetry (often, though, the engine failure dictates the minimum size of the vertical stabilizer and rudder).

Note, that P-factor occurs in single-engine propeller aircraft too, so they also have some thrust asymmetry.


Is there a list of aircraft which squawked 7700?

An ATC facility probably has a method of recording any aircraft they dealt with each day which declared an emergency, via the transponder code or otherwise.  One is probably safe in assuming that this information is passed along up the food chain for some sort of collection at a national level, although such an aggregated list may not be immediately available to the general public.  My first guess is that a FOIA request might be able to get what you're looking for, although if the requested scope is "every emergency aircraft at every facility in the US over the last two decades," you may be out of luck.  (That would be a huge volume of data anyway.)

Understand a couple of things about declaring an emergency:

Most aren't accompanied by actually squawking 7700.  Of the (relatively few) emergencies that I've declared in a couple decades of military + civilian flying, I can't think of any that required us to change the transponder code -- we declared the emergency with ATC on the radio, kept our assigned squawk, and did what we needed to do.
Many aren't related to the aircraft at all.  I had occasion about a year ago to ask our airline safety department what the most common cause was for declared emergencies in our operation, and was told that far & away, sick passengers (medical emergencies) were #1 by a huge margin, and everything else (which includes all the aircraft-related events) was far down in the weeds in comparison. Given that, seeing that aircraft 123XY declared an emergency 5 times last year doesn't necessarily mean that it has had more mechanical issues than its fleetmate 234XY that only did so once; it may just mean that 123 got more than its share of sick passengers.

In fact, in airline operations at least, mechanical issues are almost always caught on the ground, so an aircraft with "gremlins" will usually manifest them in terms of maintenance delays and cancellations, rather than in-flight emergencies.


How difficult is it to design a high bypass turbofan given a military derived core?

As of 2015, the #1 selling jet engine, the CFM56, is exactly that.

The core is from the General Electric F101, which powers the Rockwell B-1 Lancer no less.

The development was shrouded in secrecy, and politics were involved, and at least at one point only the Americans had access to the core details, while the French built around it (the new LP spool – which does include the turbines).

  Engines assembled in France were subject to the initially strict export agreement, which meant that GE's core was built in the U.S., then shipped to the Snecma plant in France where it was placed in a locked room into which even the President of Snecma was not allowed.

The linked Wikipedia featured article is a must read, and trying to summarize it here wouldn't do it any justice. But yes, it's not only possible, it's been done. Judging by the specifications, the civilian CFM56 has higher OPR (a jump from 26.8 to upwards of 27.5–38.3 depending on the variant).

According to the image above and this webpage, technology from the CFM56 fed back into the F110, which went on to power the F-14, F-15, and F-16.


It does rotate. In fact, in aerodynamics, this rotation force has a name: pitching moment. Pitching moment changes depending on the angle of attack.

Airfoils can be designed with almost any pitching moment and still generate lift, from positive (trailing edge rotates upwards as you describe), to zero (no rotation) to negative (trailing edge rotates downwards). In general, high lift airfoils have positive pitching moment (because, as you noticed, downwash caused by the Coanda effect increases lift). But zero and negative pitching moment airfoils are useful for tailless and flying wing aircraft. Helicopter blades are long, narrow and flexible so must use zero pitching moment airfoils to prevent them twisting.

If you use an airfoil with a positive pitching moment you need something to counter the rotation. For most aircraft the solution is the horizontal stabilizer (the tail). An alternative solution is the canard.

For chevron shaped (V-shaped) flying wings and tailless planes the solution is to twist the wing (in regular planes it's called washout but flying wing designers call it "twist"). The twist causes the wing tips to have less angle of attack (sometimes negative) so that the overall rotation force for the entire aircraft is zero.


What are the Radarless approach control services in the United States?

Twin Falls, ID
Helena, MT

The Chart Supplement shows if a facility has radar or not. The entries for KTWF and KHLN show that there's no radar at the local TRACONs.


What license is needed to fly the electric "Volocopter" helicopter?

The German transportation ministry has decided to create a new aircraft category for this machine.

From Aviation Week:

  Karlsruhe-based E-volo says the Ministry has commissioned a two- to three-year trial program to create a new category of ultralight aviation to cover the two-seat VC200 rotorcraft now in development. [...] Under the trial program, the German Ultralight Aircraft Association, Sport Aircraft Association and Federal Aviation Office will work with E-volo to create a manufacturing specification, legal regulations and training requirements for the new "Volocopter" ultralight rotorcraft category.

So according to this, the exact licence, and training requirements will be deteremined by the currently running trial program. It seems the manufacturer tries to position the craft as some sort of rotational-wing ultralight.


Is it more efficient to have many or a few rotors?

Rotors need something to power them and the current generation of aircraft (once you get bigger than model size) burn hydrocarbons to get that power. If you want twelve rotors, then you either need twelve engines or you need a smaller number of engines plus a bunch of heavy driveshafts and gearboxes.

I assume from the fact that most contemporary aircraft designs use a small number of engines (usually one or two; sometimes three or four) that having a few larger engines is generally more efficient than having more smaller engines. This seems to apply equally to jet engines, turboprops and piston engines.

It's possible that the tradeoffs will change if you move to electric motors. However, at the moment, batteries are so heavy that electric motors don't seem to be a practical option.


Is there a website which highlights airport locations on a map?

SkyVector is a great resource for aviation maps and data of all kinds. It offers worldwide sectional- and low-ifr-type charts, and a fully-featured Airports section.

I'm not sure if you also want airport diagrams, but you may also get some decent results with OpenStreetMap. The open source maps have some hit-or-miss levels of detail for airports, some including full taxiway and runway data. Others are just property outlines.


Why is it not a good idea to climb higher than a level at which you would have a cruise weight-climb speed less than 500 ft/min?

Because ATC expects you to climb with at least 500 fpm when crossing to the next level. Otherwise you will block intermediate levels for an extended period of time.

If you are climbing 2000ft to the next available level for your direction of travel, that will take at most 4 minutes at 500fpm or more. This means the flight level you are crossing will need to be free of traffic from the opposite direction for four minutes to ensure legal separation is maintained. If you climb slower, ATC can't properly accomodate your climb.


Paint stripper. Lots of paint stripper.
(originally I said thinner, but I have been corrected, it's more accurately called stripper)

Seriously though, it's actually not too different to other things that you paint. You need to spray on paint stripper. But, just like when painting the aircraft, it's imperative that you cover up all the delicate systems on the aircraft fuselage.

See here:

Also, I think it would be rare to paint a new livery over and existing one without first removing the old paint (maybe only if you were just changing small details), because covering an aircraft in paint weighs A LOT. For a 747 or 777 sized aircraft the paint job can weigh over 1000lbs

Carrying that around costs fuel and fuel costs a lot!


What geographical area does a METAR cover?

Geographically METARS are for a single specific location (the station identified in the report).

An automated METAR with no human supervision covers the conditions within approximately 6 inches of the weather station reporting it (for example, a badly positioned AWOS/ASOS station may be shielded from wind in some directions which affects what it reports).

A manual (or manually augmented) METAR covers the conditions the weather observer can physically see (clouds, precipitation, visibility, etc.) in addition to the ones they can measure (temperature, dew point, barometric pressure), which are valid for the point of measurement.

Practically speaking if the weather station is positioned well a METAR (like a TAF) is probably fairly representative of conditions within 5 miles, assuming there are no geographic features such as mountains which may mess with the weather. The data is still still "useful" within about 20 miles (e.g. KMTP uses the weather reported by KHTO, about 17 miles away), though you should obviously cross-check it - in that example the winds at Montauk (right on the water) can be noticeably different from the winds at East Hampton (further inland).

Some information is broadly useful over a wider area. FAR 91.121 requires you to set your altimeter to the value reported by a station "within 100 nautical miles" of your position when you're operating below 18,000 feet because things like barometric pressure tend to affect relatively large areas.


How do balloon pilots avoid birdstrikes?

The airspeed of a hot air balloon is always... zero.  So it's completely up to the bird to do the avoiding.  Which shouldn't be too difficult for the bird, on account of this humongous giant brightly coloured monster thing floating in its way.  Ya gotta be a pretty dumb or drunk bird to run into one.


Is there a pressure rise and velocity change across a turbofan fan and stator?

The answer is kind of yes and no.

Actually the thrust is always the force with balances the pressure forces on all the parts of an aero-engine.

This means (clarification in the next paragraph) that both propeller and jet-engine "create" thrust with the pressure and suction side pressure distribution of the blades. The following picture from Rolls-Royce's The Jet Engine illustrates that nicely.

Actually nozzle and turbine create drag, because the pressure forces in them do not point into the direction of flight. (Thought-Experiment: Just imagine the bolts of the nozzle would fail: If the nozzle would create thrust it would stay attached to the engine. But as one can imagine the nozzle would fly away from the aircraft).

The nozzle is needed to control the pressure level of the whole engine in order to allow for the engine-process-cycle to work properly. And because of this link one can use momentum conservation to calculate the thrust based on the inlet and exit momentum (velocity) of the airflow.

Looking at a turbo-fan engine the answer stays the same.
From the turbo machinery point of view: The fan does the same two things every compressor stage does. Two things: adding static pressure and whirl. The whirl is converted into pressure in the guide vanes, downstream of the fan.

From the thrust point of view: The fan-blades create the thrust, the stator-vanes (OGVs) down-stream of the fan-blades create drag. But as with the compressor and the nozzle above, without the OGVs the pressure-ratio of the fan would be lower and so would the fan-thrust.

One additional part is needed: The nozzle of the bypass. The above picture by JAXA nicely illustrates that (at least for modern engine installations) the bypass airflow is guided through a convergent-divergent nozzle.

So to sum up. Yes there is a pressure rise (at least locally) across the rotor and a velocity change as well. But the thrust (and drag) is produced by the pressure forces on blades and vanes (and all other engine parts).
And yes the fan operates very similar to a rotor stator setup of a compressor.
But the vanes in a compressor work like a diffuser, reducing the flow velocity. In order to keep the flow velocity mostly constant the annulus is shaped like a nozzle to balance the increased density.


Is a holding pattern always counter-clockwise?

No. The holding pattern can have any inbound course, and any direction. The holding pattern course/direction, depends on departing/arriving traffic, and many other factors. London Heathrow has a clockwise and counterclockwise hold on the fix LYDD.
Thanks to Pondlife for pointing LYDD out!


Can a US PPL holder log ASES time in Canada while flying with a local FI?

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.


What, if any, would be the most correct term for the aerodynamic flight control surfaces of SpaceX's Starship?

As far as I know, the only other example of this flight profile in aviation is post-stall maneuvering, especially for flat spin recovery. For planes, control in these flight regimes is mainly accomplished by thrust vectoring and canard/stabilator actuation. The Starship flaps don’t match these.
Another close sibling of this flight profile is the Shuttle reentry. The Shuttle used a body flap as well as conventional Delta-wing control surfaces in combination with RCS to maintain a specific, high AoA during hypersonic reentry, then transitioned to gliding for approach and landing. The Shuttle body flap (under the engines) has the closest resemblance to the Starship flaps out of any space vehicle I know. It has a much smaller actuation range, though.
Of course, the control surface naming depends on how you define the vehicle frame; with thrust direction-forward, the flaps are variable-dihedral. With velocity direction-forward, the flaps are variable-AoA with a wide actuation range.
The noun I would go with would be variable-drag flaps. Spoilers aren’t correct; there isn’t another airfoil to spoil. Airbrakes usually don’t contribute to attitude control.


Why does the Apache create much more rotor noise than the A-129?

Because they are very different helicopters, as egid already pointed out.

The Apache is twice as heavy as the Mangusta (5165 kg vs 2530 kg empty)
The rotor diameter is also bigger accordingly (14.6 m vs 11.9 m)

A Chinook transport will make more noise than an Apache. An Apache will make more noise than a Mangusta. Different helicopters and different weights that have to be kept airborne.


Your question is rather broad and somewhat unclear, but what you have is a picture of a baggage tug and cart.

The carts are loaded with passenger baggage or cargo, then strings of them are pulled to the aircraft by the tug before being loaded on to the plane.

Based on the additional pictures, I think what you're after would be called palletized cargo. It's stuff, put in boxes, placed on pallets, wrapped with stretch wrap, with a net thrown over the top and hooked down to keep it from sliding off the pallet.

It is most likely not passenger baggage. That's either loaded one piece at a time by hand, or in a ULD.

If you're asking what's in those particular boxes, you'd have to zoom in quite close to find a label on a box to even have a chance of figuring it out. Just about anything can be and is shipped in a brown cardboard box, from anywhere to anywhere in the world. This question is far too broad and off topic for Aviation.SE, and probably any SE.


Is there any benefit of using a swept wings at low-subsonic speeds?

Birds adjust wing area by pulling in their humerus and ulna so the wing sweeps first forward, and to compensate for that, have to sweep their outer wing backwards which is accomplished by folding the digits backwards. Instead of adjusting lift coefficient, they adjust wing area to not expose more surface to air friction than necessary.
The picture below shows how the wing is opened for maximum lift at low speed. As Zeiss Ikon correctly observes, folding the digits back and fore is the bird's way of pitch control, so the sweep is a consequence of pitch control, not aerodynamics.

Red-tailed Hawk, captive bird, Bacara, Santa Barbara, California. By Steve Jurvetson / CC BY (https://creativecommons.org/licenses/by/2.0)


What makes a visual approach quicker than an ILS approach?

Visual approaches can be conducted from any point around the airport where the runway is in sight, e.g. if you are approaching from the north of the airport, you can be vectored to a position which is closer to the airport and be cleared for a visual approach from a position where you can turn visually and reach the runway threshold.
ILS approaches begin at the approach gate before the final approach fix (FAF) for the localizer and glidepath indications to be correctly used and the aircraft configured for the approach. The FAF is at many airport around 10 NM from the runway threshold at 3.000ft AGL, thus placing the approach gate at around 12-14 NM.
A pilot on a forum has summed it up like this:

Visual approaches are usually shorter than instrument approaches. By that, I mean that the turn to final is accomplished closer to the runway when on a visual approach.
When traffic is heavier, or weather is around, or it's hazy, smoggy, etc, ATC will usually route everyone out for an ILS.
Many times, a pilot will call runway in sight, yet be sequenced behind someone who is on the ILS. So, he'll get routed out for an ILS approach, even though he'll go visual within the cockpit.
Airport size doesn't have a whole lot to do with it. Also, even though an aircraft may be on a visual approach, that does not absolve ATC of separation resposibility.

(Source: www.airliners.net - Author: Tom in NO)
Effectively, this means that visual approaches tend to be shorter and quicker than ILS approaches with vectors to the FAF/approach gate.


Is it permitted to deviate from yellow lines, during taxi?

There's no rule that you have to follow the lines, they're there purely as a guide, a reference for pilots to know where the center of the taxi lane is. Following it is at a pilot's discretion, to be deviated from at any point. Generally you follow the line because it's easy and it should keep you out of trouble, common reasons for deviating are:

Obstructions: vehicles, people, debris
Clearance: airplanes with large wingspans may need to hug one side of a taxiway to get around parked airplanes or buildings. In a small airfield you'll often have to get around a parked airplane or two


Can an A&P who is also a private pilot receive compensation for conducting maintenance test flights?

Yes, the mechanic can fly the aircraft, according to this FAA legal interpretation (Williams, 2014):

  The scenario you present is a mechanic who, as part of his duties,
  conducts flight tests after performing maintenance on the aircraft,
  and does not carry passengers or property for compensation or hire.
  The mechanic holds a private pilot certificate with a valid third
  class medical certificate. This situation is covered under §
  61.113(b), which states that, "[a] private pilot may, for compensation or hire, act as pilot in command of an aircraft in connection with any
  business or employment if (1) the flight is only incidental to that
  business or employment and (2) the aircraft does not carry passengers
  or property for compensation or hire." As these flight tests are
  incidental to his employment as a mechanic, the mechanic is not in
  violation of § 61.113 when conducting these flight tests


How much thrust is gained from placing a propeller in a duct?

Relative to MAV, as opposed to large scale rotors:

Compared to the baseline open rotor, the shrouded rotors showed increases in thrust by up to 94%, at the same power consumption, or reductions in power by up to 62% at the same thrust.
At rotor collectives above 10°, all shrouded-rotor models showed improvements in performance over the isolated (‘open’) rotor — that is, higher thrusts and lower power requirements. At the same power consumption, increases in thrust over the open rotor by up to 94% were observed, or, conversely, up to 49% reductions in power at the same thrust, for the condition where the open and shrouded rotors are required to have the same tip speed. If, instead, the rotor disk areas are required to be the same, then up to 90% increases in thrust at the same power.
The effects of changing any one of the four parameters (tip, rlip, d, Ld) on the shrouded-rotors’ performance became more pronounced as the other three
parameters were changed to degrade the performance. It is therefore not possible to categorically state that any one particular parameter has a greater
effect on performance than any other, since the amount of influence of any
parameter depends on the values of the other parameters. The exception to
this seems to be the lip radius, changes in which had almost same effect no
258 matter what the values of the other parameters are.
Thus, in general, it would seem that changing the value of any shroud parameter so as to improve performance results in less sensitivity of the performance to changes in any of the other parameters; similarly, improving the efficiency of the rotor itself would seem to result in less of a performance benefit from the presence of a shroud.

Extracted from:
HOVER AND WIND-TUNNEL TESTING
OF SHROUDED ROTORS FOR IMPROVED
MICRO AIR VEHICLE DESIGN
Jason L. Pereira
Doctor of Philosophy, 2008
Dissertation directed by: Professor Inderjit Chopra
Department of Aerospace Engineering University of Maryland College Park
Rotor parameters including tip gaps, tilt and relative wind, collective, and motor characteristics will influence rotor RPM, and are indirectly addressed in Pereira's dissertation.  Again, there are very broad assumptions in the OP question, but Pereira substantiates generalized efficiency improvements for specific configurations.


What does the snowflake with temperature symbol on an approach plate mean?

From FAA INFO 15002:

  A [snowflake] -XX°C icon will be incrementally added to airport approach plates, beginning Mar 5, 2015. The
  icon indicates a cold temperature altitude correction will be required on an approach when the reported
  temperature is, “at or below” the temperature specified for that airport.

This looks to be a work-in-progress, as they started adding the icons in March, and compliance with applying the cold temperature altitude corrections becomes mandatory in September, 2015.

More info from the NBAA:

  Background: In response to aviation industry concerns over cold weather altimetry errors, the FAA
  conducted a risk analysis to determine if current 14 CFR Part 97 instrument approach procedures, in the
  United States National Airspace System, place aircraft at risk during cold temperature operations. This study
  applied the coldest recorded temperature at the given airports in the last five years and specifically determined
  if there was a probability that during these non-standard day operations, anticipated altitude errors in a
  barometric altimetry system could exceed the Required Obstacle Clearance (ROC) used on procedure
  segment altitudes. If a probability, of the ROC being exceeded, went above one percent on a segment of the
  approach, a temperature restriction was applied to that segment. In addition to the low probability that these
  procedures will be required, the probability of the ROC being exceeded precisely at an obstacle position is
  extremely low, providing an even greater safety margin.

  Action:
  Pilots must make an altitude correction to the published, “at”, “at or above” and “at or below” altitudes on
  designated segment(s) (see list below), on all published procedures and runways, when the reported airport
  temperature is at or below the published airport cold temperature restriction.

  Pilots without temperature compensating aircraft are responsible to calculate and make a manual cold
  temperature altitude correction to the designated segment(s) of the approach using the AIM 7-2-3, ICAO Cold
  Temperature Error Table.

  Pilots with temperature compensating aircraft must ensure the system is on and operating for each segment
  requiring an altitude correction. Pilots must ensure they are flying at corrected altitude. If the system is not
  operating, the pilot is responsible to calculate and apply a manual cold weather altitude correction using the
  AIM 7-2-3 ICAO Cold Temperature Error Table. PILOTS SHOULD NOT MAKE AN ALTIMETER
  CHANGE to accomplish an altitude correction.

  Pilots must use the corrected MDA or DA/DH as the minimum for an approach. Pilots must meet the
  requirements in 14 CFR Part 91.175 in order to operate below the corrected MDA or DA/DH. Pilots must
  see and avoid obstacles when descending below the MDA.

  The temperature restriction at a “Cold Temperature Restricted Airport” is mutually exclusive from the charted
  temperature restriction published for “uncompensated baro-VNAV systems” on 14 CFR Part 97 RNAV
  (GPS) and RNAV (RNP) approach plates. The charted temperature restriction for uncompensated
  baro-VNAV systems is applicable to the final segment LNAV/VNAV minima. The charted temperature
  restriction must be followed regardless of the cold temperature restricted airport temperature.

There's more info in the NBAA document (I only included the exciting parts), including a list of affected airports, listed by state.  Lots in Alaska, none in Florida, unsurprisingly.  Applying this in flight looks like an absolute can of worms, as far as I can tell from the examples presented.

We'll probably see more come out about this as cold weather approaches, so stay tuned!


Can I fly for commercial jobs with just my temporary certificate?

A temporary certificate is valid for everything that a permanent one is valid for; it's just, well, temporary.

14 CFR 61.3:

  No person may serve as a required pilot flight crewmember of a civil
  aircraft of the United States, unless that person:

  (1) Has in the person's physical possession or readily accessible in
  the aircraft when exercising the privileges of that pilot certificate
  or authorization—

  [...]

  (iii) A temporary certificate issued under §61.17;

61.17:

  A temporary pilot, flight instructor, or ground instructor certificate
  or rating is issued for up to 120 days, at which time a permanent
  certificate will be issued to a person whom the Administrator finds
  qualified under this part.

(See this question for what happens when the 120 days are up.)

As far as the FAA is concerned, your temporary certificate is no different from a permanent one. I suppose it's possible that an employer might decline to hire you until you get a permanent certificate but I think that's highly unlikely within the US (employers abroad might be a different story). I've seen people pass a CFI checkride and start instructing within a few days, for example.


What happens when more than one agency investigates a plane crash?

Two reports are published and everybody is free to believe whichever they choose.

According to ICAO rules the (investigation board1 of) country of occurrence (or country of operator if it happens over international waters) leads the investigation and (investigation boards of) country of operator, country of aircraft registration and country of aircraft manufacture are asked to take part in the investigation2. So it is expected that the investigators from country where the accident happened will publish the official report.

But some investigators may choose to publish their own report if agreement about the probable cause is not reached. Since even the official report does not have any legal effect (the investigation boards don't have any legal power), so it does not really matter much.

An accident report identifies factors that contributed to the accident and suggests improvements to safety practices to reduce risk of the accident reoccurring. But whether the recommendations are implemented depends on aviation authorities3, which are separate governmental bodies with legislative power. And they decide which recommendations they will incorporate into the legal rules.

Of course each such authority only has power over that country. So while the accident is investigated just once (even when multiple reports are published, the investigation is joint effort, just the investigators don't agree on the conclusion), the rules may be implemented differently in different countries. ICAO tries to coordinate, but it does not have any legal powers itself either. So it is up to the aviation authorities to choose which report they believe more.

Assigning blame is explicitly not purpose of the investigation according to ICAO rules. A criminal trial or civil litigation may be started about the accident by complaint from police, state attorney or damaged person, in which case the investigation report will likely appear as expertise in the court, but if there is not agreement between the investigators, it is again up to the court to decide which explanation it believes most.

Finally, the investigators not agreeing is rare in practice. Usually the investigation continues until they get something they can agree on; for several years if needed. Suspected intentional crashes by pilot (which is both cases you mention) seem to be the main exception as there may be political reasons why the leading investigators (from the same country the pilots were) don't want to accept that resolution.

1Investigation board in USA is NTSB, in Canada TSB (the most rigorous investigation board in the world (or at least they very carefully collect and report even the smallest incidents, see here)), in UK AAIB, in France BEA etc.

2It is not strictly necessary, but it is the usual setup. The country of occurrence handles most investigation on site, country of registration takes care of interviewing operator and maintenance personnel and country of manufacture cooperates with manufacturer on identifying mechanical damage and usually reads the FDR and CVR data as there are only a few labs in the world that do that. Plus some of the large investigation boards may be asked for additional help. And in politically sensitive cases like MH17 additional countries may be involved to reduce risk of manipulation with the results.

3Aviation authority in USA is FAA. In Europe there is EASA, which coordinates the regulations, and separate authorities in each country that carry out the actual oversight.


Is the user interface design of ATC equipment generic across countries?

Most ATC software systems are developed by a few large companies. Companies that produce such software include Lockheed Martin, Thales, Raytheon, Indra, Comsoft, Adacel (and maybe a few others). It's not a big market since there are only a limited number of customers (countries) and safety critical software is very expensive to develop.

One interesting offering is the Albatross open source ATC software. This isn't a complete system (yet?) but some parts are available now. I'm not sure whether this software is actually used in operations anywhere at this point.

Most ATC providers (which are usually run or owned by their government, though not always) do not do their own software development. They buy a system from one of the established vendors, who may do some amount of customisation work ranging from none to extensive, perhaps with a support contract for future fixes or enhancements. There are a few exceptions though, for example Airways New Zealand uses software originally developed by a large vendor but also has an in-house software development group who maintains, enhances, and extends the existing software.

Each system has the same general operating concept - an ASD (Air Situation Display) which shows the locations of aircraft, plus auxiliary windows that may contain all kinds of other things used for communication and coordination. Like any sophisticated computer software, the general idea of two different systems might appear the same, but be completely different to actually operate (think of Photoshop vs. Gimp, or Microsoft Word vs. Apple Pages).

A qualified controller from the US would not be expected to be able to operate in Australia straight away. Not only will the software be different (different mouse clicks, or different key commands), but also the rules of air traffic control can be different between countries. Furthermore, a controller must become familiar with the local airspace and operating procedures.

Having said that, the general skills of air traffic controllers are portable between countries. On moving from one country to another, a controller would be expected to go through a certain amount of training in their new country, which could range from brief familiarisation to more rigorous retraining.


Can we show through simple geometry rather than formulae or graphs that the best glide ratio occurs at the maximum ratio of Lift to Drag?

Let's start with a Lift/Drag/Weight diagram, and draw the velocity vector as well:

Since no thrust is involved, Lift+Weight+Drag must sum to zero. Let's shift the origin of these vectors around a bit:

Now, let's finish the velocity triangle, drawing a (horizontal distance), and b (vertical distance). The ratio between a and b is by definition the glide ratio.

The key idea here is to notice that the triangles L-W-D and V-a-b are similar, that is, they are the same triangle up to a scale.
The similitude goes: W <-> v, D <-> b, L <-> a.
This means that the ratio between a and b is the same as the ratio between L and D. The latter is of course the Lift-To-Drag ratio.
So, in any condition, the glide ratio is the same as the Lift-To-Drag ratio.
It then follows that the best glide ratio is achieved for the best Lift-To-Drag ratio.


How changes in Air masses, Air flow direction and intensity affect lift?

For sake of simplicity, lets state that lift is produced by airflow over and under the wings (the rest of the airframe also contributes, but in the scope of this question we can neglect that).

Lift for any given airfoil is basically dependent on airspeed and angle of attack. Up to a certain limit any increase in airspeed or angle of attack will amount to increasing lift and vice versa. So, the question:

Case 1. and 2. The situation is the same. Sudden tailwind of 40kts will lead to a sudden 40kt drop of airspeed and sudden decrease of lift. The groundspeed will start to increase (slowly, because of inertia of the plane). If immediate corrective action is not taken, some altitude will be lost. Near the ground this would be catastrophic.

Case 3. I'm a assuming a level turn here: During or after the turn the wind will not have any effect on the airspeed or lift of the aircraft.

The aircraft is flying embedded in an airmass. If we are considering aerodynamics (lift and stuff), all changes made in the flightpath of the plane are made in relation to the airmass. Not the wind, not the ground. The wind is simply the movement of the airmass in relation to the ground.

If the wind does not change, nothing changes for the plane (overly simplified, of course, there's temp, pressure etc, but that's not on subject here). In cases 1 and 2, the wind changes, as the velocity is momentarily different (gust). In case 3 there is no change in the wind.

Your example of the event you've witnessed, with increasing groundspeed and decreasing airspeed is a simple case of flying into a region of tailwind. Tailwind would simultaneously reduce your airspeed and push you to go faster in relation to the ground, increasing your groundspeed. This event might happen as a result of flying somewhat perpendicularily through top or bottom part of a jetstream.

Since this subject has proven to be somewhat difficult to comprehend (here and in this question too), let us end this answer in a humouresque article on Flying Magazine website, that might help understand the misconception of turning in wind: The Last Word on Downwind Turns, Really.

As a sidenote, in case 3 you have described a rather steep turn without increase in engine power, the aircraft will bleed energy during the turn resulting in loss of airspeed, if airspeed is not maintained with power or glide. I'm also pretty sure that a constant 25°/second rate of turn is just too much to sustain for most fighters, even with full afterburners, and it is definitely too much for any pilot to handle for long. F-16 has a max rate of turn of about 27°/sec at about 380kts and 9g's.


The first aircraft jet engine was ground tested by Frank Whittle in April 1937. In September of the same year, Hans von Ohain (ground) tested his jet engine.

The first jet aircraft, He 178 flew in August 1939.


What is the purpose of these winglets on the Chinese version of the An-2?

As you said, the Y-5 and Y-5B are Chinese variants of the Antonov AN-2. The Wikipedia page gives this info on the Y-5B:

  Shijiazhuang Y-5B-100 – Y-5B aircraft fitted with triple tipsails on the upper wing tips, which reputedly gave 20% higher climb rate and improved L/D ratio by 15%.

Here is a research paper on tipsails which may help a little bit.

There doesn't seem to be a lot of empirical evidence of the performance gains that China claims with the Y-5B. I can't find examples of the triple tipsail design used on any other aircraft.

Just look at the aircraft though, all the struts, wires, hinges, etc hanging out in the wind, and these 3 little tip sails improve L/D by 15% and climb rate by 20%? That's a hard pill to swallow. If it were that simple, it would be a feature of nearly every aircraft.


Are there any NACA airfoils that resemble the X-29's wing?

From Mason’s Perspective on the X-29:

  The other issue with this airfoil is that every Grumman aerodynamicist felt the need to “improve” it, so that there were many variations. I think the airfoil that was used on the X-29 was known as K-Mod 2. I’m not sure anybody can say with certainty what the actual airfoil coordinates are. Grumman was not good with
  documentation

The airfoil appears on page 9 of that memo:

The reference given for it is Boppe, which I assume to mean the article "Computational Aerodynamic Design: X-29, the Gulfstream Series and a Tactical Fighter" by Charles W. Boppe in SAE Transactions, Vol. 94, Section 6 (1985), pp. 424-468.

Supposedly you can access that article in exchange for signing up with the host service, but I'm not willing to try from my current machine.


Why does the DC 4 airplane not tip backwards?

Although the landing gear are pretty far forward on the DC-4 the weight of the engines places the center of gravity in front of the main landing gear. It's unlikely that a passenger would be heavy enough to tip it, but freight certainly can. When loading freight tipping is prevented with the use of a tail stand, as can be seen in the photos below.

Image source

Image source


Do pilots ever use the aircraft's ICAO 24-bit address when communicating with ATC?

Typically pilots do not know the 24-bit aircraft address of their aircraft.

The 24 bit address is intended for data protocol level of communications and is not used in voice communication. Therefor there is no need for pilots to be aware of their ICAO 24-bit aircraft address. They use the aircraft's registration if they need to identify the aircraft they are using for the flight.

The 24-bit address is used by transponders for communication with Mode-S radars, ADS-B transmissions, by TCAS for tracking traffic and coordinating Resolution Advisories and by Data-Link communications.


For posterity, I found what I needed here: https://www.icao.int/safety/istars/pages/api-data-service.aspx

They currently have 58 datasets. The one satisfying my needs is "Flight Information Regions - Names".

When registering for an API key, I am allowed to do 100 requests for free each month. Downloading the entire list counts as 1 request. So the way I read it, I am complying with their EULA. If I'm wrong, please comment.


What is the effect of aileron deflection on the centre of pressure?

The CP of local sections where the ailerons are deflected should shift aft. In an asymmetric deflection case, very little pitch moment would be generated. For symmetric deflection (e.g. maneuver load alleviation, flaperon), there will be a net pitch moment, but should be small due to the outboard location of the panels, unless the wing is highly swept.

To estimate the effect, you can view ailerons as part-span plain flaps. You can use any of the semi-analytical methods from ESDU, DATCOM or Roskam. You can also use any vortex lattice method to get the answer. The estimates should agree fairly well for small deflections and low Mach.


What is the average aerodynamic load on a control surface of a commuter-sized airplane?

I think you don't actually want to know the load but rather the hinge moment of control surfaces. The actuator load is the hinge moment divided by the length of the control horn. Below is a rather poor sketch for a typical aileron linkage, but the principle is correct (source):

It already shows one popular way of reducing control forces: The tab, a little auxiliary control surface which moves against the "real" control surface. This reduces effectivity a bit, but forces by a lot. Here, the amount of deflection of the tab is controlled by a spring in its linkage, which is a clever way to adjust its deflection such that the actuation forces become more constant over speed.

Another way of reducing control forces is a horn: An extension of the surface forward of its hinge line, so the aerodynamic loads here balance those on the surface behind the hinge line. The picture below shows the left aileron of the ATR-72 which is moved by mechanical linkage (source)

This way, the lift loads on the control surface are mostly carried by the hinge and only the actuation loads need to be carried by the control rod or actuator. If you think you don't need all those nifty tricks, your actuator and hydraulic system will become much heavier than needed.

Why are two different methods used? The tab reduces the loads from deflection changes while the horn reduces those from angle of attack changes, too. When sized properly, both together will drive the hinge moment close to zero.

Why do I explain all this? It shows that your question does not have a simple answer. Rather, you need to specify exactly how your control surface looks and is moved, and only then can you start to calculate the actuator loads. I also want to show that a subsonic airplane for 10 - 20 passengers will be perfectly flyable with manual controls. The ATR-72 needs hydraulics only for the flaps, the spoilers, the brakes and the landing gear. Avoiding hydraulics for primary flight controls also lets it get away with single redundancy in its hydraulics system.


What is the ALT INTV on the 737's autopilot?

From the FCOMv2 4.10.10 (emphasis mine):

  Altitude Intervention (ALT INTV) Switch

  [Option - With speed and altitude intervention]

  Allows manual deletion of next FMC altitude constraint via altitude SEL and ALT
  INTV switch.

  Push – (during VNAV climb)

  lowest FMC altitude constraint below selected MCP altitude is deleted
  if airplane is currently at an FMC altitude constraint, deletion allows airplane to resume climb. MCP altitude must be set above current altitude
  for each press of switch, one deletion occurs
  if MCP altitude is set above current FMC altitude, FMC cruise altitude
  resets to MCP altitude. FMC cruise altitude cannot be decreased using
  ALT INTV switch.

  Push – (during VNAV cruise)

  if MCP altitude is set above current FMC cruise altitude, FMC resets
  cruise altitude to MCP altitude and initiates a cruise climb
  if MCP altitude is set below current FMC cruise altitude, an early descent
  is initiated. Lower FMC cruise altitude cannot be entered using ALT
  INTV switch.

  Push – (during VNAV descent)

  the highest FMC altitude constraint above MCP altitude is deleted
  if airplane is currently at an FMC altitude constraint, deletion allows
  airplane to continue descent. MCP altitude must be set below current
  altitude

  [Option - FMC U10.6 and above]

  if all FMC altitude constraints are deleted during VNAV path descent, an
  automatic transition to a VNAV speed descent is made.


Why is the most common hydraulic fluid so poisonous?

Fume events are from two sources in the vast majority of cases:  Deicing fluid, and engine oil.
The Aviation Herald event linked was poisoning from (really severe) engine oil contamination (mainly the toxic TCP additive; it's the same stuff used as a lead scavenging agent for running 100LL fuel on low octane engines, and it's also the oil additive that Lycoming specifies for the H2AD piston engines for the cam spalling problem). Phosphate Ester hydraulic fluid had nothing to do with it.
The oil contamination comes from 3 sources:

A failed compressor section seal on the main engine at some forward bearing that is able to feed oil into the compressor upstream of the bleed port used for air conditioning.
A blown seal on an air cycle machine (the turbocharger-like cooling unit in an air conditioning pack) allowing ACM lube oil into the conditioned bleed flow.
An APU compressor seal failure (more or less the same as an engine oil seal failure) getting into the APU bleed and into the A/C packs.

Probably the majority of fume events are from oil traces, only enough to make smells, but which is really hard to remove, and deicing fluid (when airplanes get deiced and too much was sprayed into the engine and the engine didn't get enough of a purge run to clean the compressor out before turning on the bleeds).  Deicing fluid fume events happen a lot and are probably the most common cause of fume turn-backs.
Skydrol/Hyjet is mostly a hazard to the techs that work on the planes.  Anyone here who turns wrenches on transport airplanes will tell you that Phosphate Ester fluid is nasty, nasty stuff to get on your skin and probably the single most unpleasant aspect of the job.


ASTERIX category 240 fields placement in a UDP packet

The Asterix structure is explained in detail on this document on the Eurocontrol site.

Wireshark.org has a page explaining the protocol as well.


What is this plane with its thick cockpit?

Potentially a Piaggio Avanti, based on OPs description of an unusual nose.


Why do passenger jets accept input that will cause the aircraft to perform dangerous maneuvers it was not designed for?

Generally speaking, pilots don't like it when a computer interprets or limits their actions. They want final control. They don't always get their way on this but that's their preference.

If I recall correctly, Boeing tends to stick with the philosophy that "the pilot is the final arbiter." Airbus is more likely to preempt pilot inputs and modify them.

Although the majority of crashes and incidents wind up being pilot error, there is a serious flaw to modifying pilot inputs. That flaw is in the case of systems failure.

By definition, failure modes involve things going wrong.  When things go wrong it's effectively impossible to plan, in automation, for all contingencies. People are much better at responding to the unknown than automation systems are.

Take for instance the rule that "bank angles > 45 degrees are dangerous, and are therefore prohibited". How does the plane know that the bank angle is > 45 degrees? Well it's a sensor of course, but what if the sensor has failed? A failed sensor will either signal to take action when none is needed or fail to signal when action is called for. What if the control surfaces have failed and the plane cannot correct the bank angle?

The usual answer to that is redundant systems, high reliability parts and design, etc.  All those are great of course and certainly help a lot. However we still have incidents and accidents.

In the end the question is: Who do you trust more? A pilot or a machine? And statistics and science only help you part-way here. A person's experience, biases and feelings will have a lot to say about how they answer. And by "person", understand that I'm including the customers, the paying public.


How can one calculate the maximum instantaneous bank angle a plane can do in a certain time?

This question has been asked and answered in over 20 various forms, a few are....

How much g-force is experienced in a 45° turn?

What is the relation between airspeed and rate of turn?

Best procedure to Turn around in Canyon, Turn radius as a function of velocity

How to calculate angular velocity and radius of a turn?


Is it possible to tilt a propeller for attitude control, similarly to jet thrust vectoring?

Yes, on airships.

The Zeppelin NT can rotate its two forward and one rear propellers to create lift instead of thrust, a capability of particular value when the airship descends in an atmosphere with a strong temperature gradient. From this page about the Zeppelin NT:

  The two forward propellors swivel to 120° and the aft one to 90°, and
  a fixed aft lateral propeller give a high level of manoeuverability,
  and enable smooth, quiet flight and impressive fuel economy. Some of
  the unique flight characteristics come from the swivelling propellers,
  like vertical take offs, precise landings, hovering over exact
  locations, turns on its axis and flying backwards.

Tail propellers of the Zeppelin NT Airship. While the sideways mounted propeller is fixed, the rear propeller can swivel through 90° (picture source)

Front view of the Zeppelin NT with the forward propellers tilted up (picture source)

Another example would be the V-22 Osprey, obviously, but you might prefer to call those whirly things rotors, not propellers.


What is the answer to this question about aircraft position based on an NDB?

Yes, "D" is correct. A picture is worth a thousand words......


What's the difference between a two-blade prop and three-blade?

At the absolute simplest, compared to a two-bladed propeller, a slightly smaller three-bladed propeller can produce more thrust at a given RPM, improving climb performance. Because of the smaller diameter, the propeller tips actually travel slower than the equivalent two-bladed design, reducing noise inside and outside the airplane.

Hartzell Propeller has a great set of technical answers about propellers. Their explanation of why more blades produces less noise is pretty good:

  A 2-blade propeller produces two pressure pulses per revolution, where a 3-blade propeller will produce three smaller pulses per revolution (for the same amount of total thrust) which is inherently smoother and therefore quieter. The 3-blade propeller will generally have a smaller diameter than the 2-blade propeller that it replaces, which also reduces the tip speed and noise.


Do wingtip vortices cause a decrease in the lift component of aerodynamic force, and do planes need to pull more AoA to compensate?

What you know about wingtip vortices is what can be found all over the Internet, but it is not really true. It is like saying that wet streets cause rain.

Your way of explaining things confuses cause and effect. The vortex is the effect but not the cause of drag-creating flow. And lift-creating flow, by the way. But nobody claims that the tip vortex is the source of lift, which is equally false and uses the exact same logic.

Wingtip vortices are just the tip of a full vortex sheet which leaves the wing. This vortex sheet is the consequence of the wing accelerating air downwards. Now instead of repeating myself all over again, please allow me to point you to the many other answers which explain what is going on:

This answer explains in detail how lift is created and how the downward acceleration of air is accomplished.
This answer goes into the formation of the wake and the wingtip vortices.
This answer shows why more wingspan reduces induced drag. It matters little whether the wingtips are turned up, down or continue straight: A larger wingspan reduces induced drag.

You will find that your picture of a tilted-back lift vector is correct, and indeed will a narrower wing experience larger tilting. Also, to achieve the same lift, a narrower wing needs more angle of attack and will create more induced drag. You are right again here, but instead of an ever increasing snowball effect, drag is just growing with the square of lift when the angle of attack is increased.

Ideally, all aircraft would have infinite wing span. But that would drive wing weight up a lot, so the designers settle for some compromise where the wing creates the least drag for a given net lift (total lift minus the lift needed to carry the wing).

Now to the questions in the comments:

  so the point of a higher AR ratio wing isn't to reduce vortices... It's simply to reduce the required AoA that is needed?

The point of a higher AR (more precise: More span per lift) is to involve more air in the creation of lift. This reduces the strength of the bound vortex, so indirectly it is about vortex reduction. The AoA reduction is not an issue here - in inviscid 2D flow an airfoil produces no drag, regardless of AoA. What does produce drag is the vortex flow field when span is limited.

  the reduction in vortices is simply how we see that it is working, per se?

Yes, reduced bound vortex strength results in reduced wake vortex strength.

  why do [designers] also care about the chord?

For that, allow me to refer you to this answer, and maybe this, too.

  Is it correct to say that we can measure the energy an aircraft loses due to induced drag by measuring the energy in the vortices?

Yes. But measuring the vortex strength is harder than measuring the downwash angle over span, which gives the same result. For viscous losses this is indeed a practical way of measuring drag by use of a wake rake (see the answers to this question for more).


What kind of assistance can another aircraft provide to an incapacitated pilot?

This is speculative and I haven't looked at the links you gave, but I can think of a few things:

Having another aircraft there gives ATC a way to gather information that they otherwise couldn't. For example, if the second pilot had observed that the 'incapacitated' pilot was actually awake and alert and there was a second person in the cockpit brandishing a gun, I think it's safe to assume that the response from ATC, law enforcement and the military would have been different.
The worst case is that the incapacitated pilot never recovered and simply crashed. In that case the second pilot could give ATC a precise location for rescuers, which could be important in a more remote area. Especially if ATC had no radar coverage.
The incapacitated pilot could have recovered but still been disorientated and unable to communicate properly. It's possible that the second pilot could have led them to a nearby airfield. That would still require some understanding and communication between them, and the second pilot might not have been comfortable with doing it, but it's an option.
It's possible that the incapacitated pilot recovered but couldn't talk directly with ATC. That could be because they drifted down to an altitude below ATC's radio coverage, or couldn't change frequencies, or whatever. The second pilot could relay calls from ATC in that case, assuming that they could work out which frequency the incapacitated pilot was on. Relaying calls from ATC to another aircraft is fairly common.

I'm sure we could all come up with other ideas, but I think the first point is the most important: when something strange is happening then it's best to gather as much information as possible.


Why is it said that the Tupolev Tu-144 had superior aerodynamics to the Concorde?

Unfortunately, there is no hard data available (at least in open literature) to back up these claims.

One for the claim may be due to the fact that the Tu-144 was designed to fly higher than Concorde as its primary flight path was over land rather than water. Because of this, the L/D ratio of the Tu-144 was higher than that of Concorde (7 vs 8 in Tu-144D). Also, the Tu-144 was bigger and was meant to carry more passengers.

Photo Courtesy: globalsecurity.org

The Tupolev site offers an interesting explanation for this claim. Basically, they say that despite the engines and other subsystems being inefficient, the Tu-144 performed similar to the Concorde due to superior aerodynamics of the aircraft. The performance of the Tu-144's RD-36 engines was later brought up to that of Concorde's Olympus 593, at least in fuel consumption.

To quote,

  It should be added that the engines were less perfect (by specific parameters the engines of TU-144 a/c were brought close to “Olympus” only in their last modification). All these negative initial data were compensated in the course of development of the project by high aerodynamic cleanness of TU-144 which was achieved by making the design more complicated and by lowering maintainability of the aircraft.

But without any hard data, it is not possible to compare the two aircraft directly.


The slot helps to prevent early separation, so the flap stays effective for larger deflection angles. What that means in reality can be read in this old NACA report which compares two NACA23012 sections, one with a plain flap and the other with a slotted flap. I have copied the pressure distributions below from that PDF:

Now I need to explain a little how to read the pressure distribution plots. The solid line shows the local pressure on the upper surface while the dashed line shows the pressure on the lower surface of the airfoil. The X-axis runs along the chord. The Y-axis represents pressure (suction is up) and y=0 represents ambient pressure. The area between the dashed and the solid lines is proportional to the lift coefficient, which is helpfully shown below each plot.

Now to the curvature: As long as the lines show a gradient, flow is attached. Separated flow can be recognized by a horizontal line slightly above the X-axis. As you can see, we have already fully separated flow on the upper plain flap surface at 30° flap angle and 8° angle of attack. At the same angles the slotted flap still shows fully attached flow on both surfaces. Attached flow creates a suction peak at the nose of the flap, which in turn allows a higher suction value at the end of the fixed part of the airfoil. This in turn allows a much higher suction peak at the nose of the airfoil, so that the suction force over the whole chord of the airfoil with the slotted flap is much higher than on the airfoil with the plain flap.

Only at 50° flap deflection will the slotted flap also show flow separation over the rear part of the flap, but there is still a suction peak which helps to stabilize the flow over the fixed part and increases lift. Unfortunately, the plain flap was not measured at the same angle, but from the small change between the 30° and 45° flap angles you can see already that moving the flap to 50° will change little.

The reason for this difference is simple: While the plain flap has only the old, thick and tired boundary layer coming from the fixed part of the airfoil to work with, the slot allows the slotted flap to create a new, thin and vigorous boundary layer which can tolerate much higher pressure gradients. Another benefit is the unchanging direction of the local flow behind the fixed airfoil: This allows to use a thin, highly cambered flap airfoil which maximizes lift production. The old NACA airfoil did not take advantage of this, but modern airliner flaps certainly do.