Components on engines, are they removed or blanked out? As a follow up to why doesn't the A380 use outboard thrust reversers, if a component is not used in an engine, is it completely removed (hardware, wiring etc etc) or is it just made inoperative?

In the case of the A380 wouldn't it make it more difficult to maintain and handle 2 engines which are the same, but with different accessories installed?

Wouldn't it be risky as there might be human error factors whilst servicing or installing the thrust reversers?

Short answer

The reverser is not installed on the outer engines. As the linked question mentions: This allows to lighten the engines, this also prevents any unwanted and hazardous opening in flight as well as the costly check time for an unused feature.

The reverser used on the A380 is a cold flow type. It is merely part of the engine by itself. It is actually integrated in the nacelle structure channeling the bypass cold flow.

An engine should be usable in all four nacelles, the nacelles themselves cannot be swapped as they provide the reverser. The answer to this question seems to confirm this possibility.

Principle

Thrust reversal on this aircraft type consists in opening the bypass duct sideways, blocking the bypass flow in the duct and redirecting it through the opening. The opening is created by sliding the aft section of the nacelle case to expose a set of vanes. The blocked flow now escapes sideways and is guided forward by the vanes:

Principle of cold flow thrust reverser (source)

Thrust reverser on the A380 (source)

Engine, reverser, nacelle

The A380 is equipped with Trent 900 from Rolls-Royce or GP7200 from Engine Alliance. The thrust reversers are made by a different provider, Airbus-Aircelle (part of Safran), which also manufactures the nacelles. This is because the thrust reverser is really integrated in the nacelle rather than linked to the engine.

Trent 900

The reverser is in the cold / bypass flow behind the fan section which is the engine section with the largest diameter (in the Trent 900, about 3m!).

Hot flow, cold flow and reversed flow in a Trend XWB (similar to 900).
Based on RR picture

The cold flow duct (fan duct) is similar in both versions of the nacelles.  The duct is fenced by two semi-annular walls behind the fan frame, where the flow is rushed by the fan. This is called a double D-duct (in reference to the shape of the semi-duct).

The two D-ducts of an inner nacelle contain the reverser panes and their associated components. This version is named the thrust reverser unit (TRU). The other version without the reverser is the fixed fan duct (FFD), it doesn't slide.

TRU

The TRU is visible behind the fan section, source

On the image above, the two halves of the TRU are open. Note the outer wall of the duct has some thickness, contrary to the FFD wall (see next). This volume is used to host the mechanism needed to move the panels rerouting the flow.

The inner wall prevents all the flow to reach the core and the components and pipes around it, in order to not create damage or drag and heat. However a limited quantity of air is still directed toward the core for cooling.

More easy to see on this CG view:

Trent 900 duct and reverser. Based on TurboSquid models.
Top: 3D model by BlueGreen. Bottom: Another excellent 3D model by BlueGreen.

FFD

Left D-duct highlighted in blue.

Nacelle duct for cold flow. Based on image by Benny Zheng on Airliners.net


What exactly is a variable incidence tailplane? I've been reading about it regarding trim changes and such, but I don't exactly know what a VIT is? Can someone explain that to me?

Incidence is the angle at which an aerodynamic surface is mounted to the remaining structure of an aircraft. Variable means that this angle can be changed in flight. Normally, a control surface is split between a forward part, called the stabilizer, and the rear part, called the elevator. On aircraft with less powerful wing flaps, the stabilizer incidence is fixed and only the elevator can move, while more complex aircraft can also move the stabilizer.

A third way is to do away with a separate elevator and to move the whole tail surface. This is a variable incidence tailplane.

Benefits of a full-flying tail surface

By avoiding a contour break due to a flap deflection, all-moving control surfaces can avoid the shocks which would otherwise occur at high subsonic speed. This is especially beneficial for supersonic aircraft.
At supersonic speed, the uncambered surface will produce less drag, so for supersonic speed the all-moving control surface is more efficient.
By moving all of the tail surface at high speed, an all-moving control surface will produce the highest rate of moment change over time possible. To produce also the highest sustained moment change, however, it needs to be larger than a comparable stabilizer-elevator combination because it forfeits the benefits of variable camber.
The all-moving control surface has no gaps which could add radar reflections, allowing for a more stealthy design and slightly reducing drag.
Lower mechanical complexity. This is somewhat offset by the need for much beefier hydraulics.

Some gliders have full-flying horizontal tail surfaces for reduced complexity. They have a slight back sweep to shift their aerodynamic center and their center of gravity to the same location. This makes the tail light and simple and avoids the added drag of the elevator hinge gap. However, such tail configurations have caused a number of crashes in the early phase of a winch launch when the pilot did not keep the stick neutral. At low speed a fully deflected tail surface has separated flow on the suction side, rendering the tail less effective. Only when the flow suddenly attaches as speed picks up the tail effectiveness is regained. In combination with the pitch-up moment of the tow line this lead to very steep angles of attack right after take-off which the pilot could not correct with the still ineffective tail, and some gliders stalled, rolled and crashed as a consequence. Therefore, modern gliders avoid this feature.

Schempp-Hirth Cirrus with full-flying tail (picture source)


What other advantage(s) does an adjustable prop give you? From what I understand, the purpose of a variable-pitch propeller (be it manually adjustable, or constant speed) is that it allows the engine to always operate at its most efficient speed, much like the transmission of a car. Is that correct? If so, if an airplane were to accomplish that another way (say, a hybrid gas-electric drive, or an actual transmission with shiftable gears*), would there be any other advantage to having an adjustable propeller?
*No, I don't know why you would want to mount a car transmission on an airplane. It's a hypothetical question. But now I have this picture in my head of a twin-engine plane with two gear shifts in the cockpit and two clutch pedals next to the rudder pedals.

It's not just the operating RPM that is pertinent. It's also the pitch of the blades.
If your propeller blades' pitch is optimized for takeoff/climb performance, it's going to be aerodynamically inefficient at high true airspeeds, like taking little tiny footsteps on a treadmill that's going really fast. (It works, but it wastes energy.)
The opposite is true as well. If you have a "cruise" prop on your airplane, it's going to perform poorly on takeoff when the airspeed is slow, like taking large strides on a treadmill that's just barely moving.
If you want to optimize your body mechanics, you change your gait based on the speed you need to go, so you're not wasting energy. If you want optimize a propeller, you change it's pitch based on the speed of the air that's entering it, so you're not wasting energy.


What is the maximum allowed difference between two altimeters for flying in RVSM airspace? What is the allowable altitude difference reading between two altimeters while flying inside RVSM airspace?

On the ground during the preflight check, the altimeters must be within 75 feet of each other.

In-flight the altimeters must be within 200 feet of each other.

I have been flying the B777 for about 8 years and I have never seen the altimeters disagree by more than about 10 feet, either on the ground or in flight.


Can I add ratings to a NNPL? I have been speaking to a couple of local flying schools. Originally, I was going to train on a Piper Tomahawk to obtain an LAPL. But after explaining to one of them my goals, (just flying for fun, no career aspirations) they suggested an NPPL would be more appropriate.

They explained that it would cost about half the amount (in money and time) to obtain and that their Ikarus C72s are safer, easier and more fun to fly anyway.

I am on board with all of this but I think I would like the freedom to fly in IMC in the future, they said I can add an instrument rating to an NPPL and that I can convert to an LAPL in the future if I want to anyway, is this the case? I have looked on the CAA website, but it's all a bit confusing right now.

Available Ratings:

  You can add class ratings to the NPPL to allow you to fly microlights, self-launching motorgliders (SLMGs) and simple single-engine aeroplanes (SSEAs).

The above are the only available ratings for an an NPPL. An NPPL (and LAPL) is strictly a VFR license, therefore you could not get rated for IMC. However, you can continue your training to receive your PPL, at which point you could recieve a rating for IMC, which would be your IR(R), or Instrument Rating Restricted.

Most flight instructors will provide basic IMC training just in case you find yourself in a bad situation, which can happen to even the most cautious pilots.


Why doesn't flightradar show many flights going over China? I use FlightRadar to track some flights. I am surprised to see that there are very few or no flights at all going to air fields of china.

Is my observation correct? I really doubt that this is correct.

If its true what is the reason behind that?

From the Flighradar How it works page:

  Flightradar24 relies on volunteers around the world for the majority
  of our coverage

Note it implies:

There are people willing to contribute
These people can afford to buy receptors, gather the data and upload it to Flightradar

About point 1. In case of China how much people are willing to contribute? How many are affraid to do it to a foreign organization and how much are affraid of gettign the wrong attention from government?

About point 2. Most people on China cannot afford to buy such equipment (compared to USA).

It's easy to check point 2 by comparing macro economic statistics (So I doubt I need to link it here).

Point 1 is very speculative so each one should try to figure that by him/herself.

In fact I always wondered Fligth radar will got a poor coverage in third world countries (point 1) while getting near 100% coverage in USA.

Note also the size of aviation community (pilots, enthusiasts, aviation industry workers, etc) in USA is so much bigger tha in other corners of the world.

Edit's in response to Jaydeep comments

Flighradar giving away equipment like that is great, I think Wow!
Note also the note on the same page:

  Exceptions to these requirements can be made to applications from
  unique locations.

So that begs the question if they are actually granting such gifts to China. For the sake of the completion I will ask them.

EDIT     and The Answer is:

So I asked Flightradar about it and they sent me the response below:

  Hello Jean,

  Thank you for contacting Flightradar24.com.

  Your Support reference is 219752.

  Yes, that is correct. We provide this free equipment to anyone in the
  world who has a good location with steady internet and power. The
  reason why you don't see many aircraft in the middle and west of China
  is because of the lack of receivers in these area.

  You make an application and we go from there if it's a good location.
  If we already have receivers in the area then we put the application
  on hold but if its a good location then we provide them with a free
  kit.

  https://www.flightradar24.com/apply-for-receiver
  -- Best Regards, Muazzam  Flightradar24

Straight from the horse's mouth the answer is simple "lack of receivers" what causes that is open to speculation but a quick search for "rural china power grid" and "rural china internet coverage" points out "steady internet and power" can be the problem.


How much computing power is needed to keep commercial and military planes flying? I've always wondered, what sort of computing power is needed to keep modern commercial and military planes in the air?

There are many systems of a modern commercial plane (e.g an Airbus A350), that would need to be automated and controlled by computer, one example that springs to mind is autopilot, another is flight instruments.

Similarly I'm assuming that there'd be many systems (e.g fly-by-wire) that need to be controlled by computer in a modern military jet (e.g F-22 Raptor).

What sort of computing power is needed to run commercial planes and military jets, and how do they compare to each other, and how does their computing power compare to the computing power of modern commercial CPU's? (Could my 2nd-gen Intel i7 CPU, with the appropriate hardware to make it into a PC, hypothetically be able to control all the automated systems on a modern commercial plane or military jet?)

For commercial airliners: the computing power is set during development and certification of the type. The A320 was developed in the 1980s and still uses Intel 80186 and Motorola 68020 processors. Your i7 CPU would be able to run rings around anything on board of the average airliner.

But processing capacity is of secondary importance to airliners, safety and redundancy are in the limelight. Any processor capacity that can do the job is good enough, and is only the start of all the aspects that go into certifying an airliner including its systems.

Image source

Military planes are different, in that the requirements are more pressing and the accepted risks are higher. Yes modern fly-by-wire planes use digital systems, however when the F-16 first came out with a fly-by-wire control system, it was a quadruple redundant analog system, with a digital processing requirement of zero. These were upgraded to digital fly-by-wire in the block 40/42 upgrade in the early 90s, so again the fly-by-wire used pretty primitive processors by today's standards.

Generalising, the long development and certification/ready-for-mission time of aircraft systems means that any system on board uses processing power that is behind the latest-to-market specs.


How does a fire suppression system work? On fire events, some aircraft have a complex system, usually called a Fire Suppression System.
Where are they located? Do they work automatically, or it is necessary for the crew to activate them?

The fire suppression system in an aircraft uses both passive and active systems to reduce and eliminate fires. Passive methods include the use of noncombustible materials, separation by routing, compartmentalization (use of firewalls), isolation, proper ventilation and drainage. The active methods include fire detection and extinguishing systems.

The fire extinguishing system in the aircraft consists of a number of components (excluding the fire detection system), which includes,

Portable (handheld) fire extinguishers in cockpit and cabin,
Fire extinguisher bottles for engines and APU
Cargo hold fire extinguisher systems and
Fire extinguishers for toilet waste bins.

All the transport aircraft are required to carry a minimum number of portable fire extinguishers depending on the number of passengers carried. The following table gives the minimum number of portable fire extinguishers to be carried in transport aircraft (the cockpit should have a minimum of one).

Table from FAA document Fire Protection Systems

In case of cabin (or cockpit) fire, the portable fire extinguishers (usually, $CO_{2}$ extinguishers are not used) are used by the crew to extinguish the fire.

The engines and APUs have their own fire extinguishing systems, which have a liquid halogenated extinguishing agent and pressurized gas stored in fixed (typically steel) fire extinguisher containers, which are discharged on pilot command.

The engines have their own fire extinguishing systems, which usually have a pair of fire extinguishing bottles (or a pair for each engine), which supply extinguishing agent (Halon 1301 or Hydrofluorocompounds) to the engine.

Image from Boeing Aero magazine- Fire Protection: Engines and Auxiliary Power Units

The fire detection system from each engine displays the status in the cockpit, which warns of any engine fire. In case the pilot pulls the fire handle, the fuel flow to the engine is shut off and an explosive cartridge is fired in the fire extinguishing bottle, releasing the agent into the engine.

Image from FAA document Fire Protection Systems

The APU fire suppression system is similar to the engine fire suppression system, though only a single fire extinguisher bottle is used. Again, the fire extinguisher operation is commanded by the cockpit crew and results in the shutting down of the APU and the source of air.

Image from Boeing Aero magazine- Fire Protection: Engines and Auxiliary Power Units

In ground, the APU fire extinguishing system can operate automatically.

The cargo hold fire extinguishing system is similar to the above, where the crew can activate the fire extinguishing system if the smoke detectors in the cargo hold activates the warning lights in cabin. The extinguishing system is of two types- a dump system that releases the extinguishing agent directly
when the cargo fire discharge switch is activated or a metered system, where metered bottles discharge slowly which keeps the correct concentration of extinguishing agent in the cargo compartment to keep the fire extinguished for 180 minutes.

Table from FAA document Fire Protection Systems

The toilet waste bin is the only place in the aircraft with an automatic fire extinguishing system (in addition to ashtrays), where the heat sensors (not smoke detectors) trigger fire extinguishers.

Some aircraft have On Board Inert Gas Generating System (OBIGGS), which is used to 'inert' the fuel tank using nitrogen (usually generated by membrane based gas separation).


What data is displayed on civilian ATC radar screens? I am developping an ATC radar for a simulation.

I don't think there is any standard for radars to show aircraft data on radar screens.
But there should be general data to show on radar screens.

For example:

CALL SIGN
ALT ASSIGNED ALT
SPEED HEADING

Can the data shown be changed on the clients?
Is there a difference between ground radar and air radar displayed data?
Is there any standard or can you give me any examples?

There are a few different ATC Systems and Radar Screens being used throughout the world, so there will be no set standard which applies globally, as vendors and setup differ.

The ATC screen can be adjusted to show what information the controller needs, and some items are universal to all positions being served (Callsign, Speed, Altitude, Assigned Altitude), some items are not required on each position to be displayed on the radar tag (Squawk, Routing, Aircraft Type, Wake Turbulence Category).

Some examples:

Source: www.andreas-milde.de

Source: www.euroscope.hu / Air Traffic Simulation Client

Source: fluglotse.wordpress.com


Why is the N-number on the tail of aircraft sometimes shown in both large and small font? Why is the N-number on the tail of aircraft shown again much smaller and above the main N-number? They are both the same group of letters and numbers.

The N-Number marking regulations are outlined in this AC for fixed wing aircraft:

  ... minimum height of 12 inches

  (1) On both surfaces of a single vertical tail or on the outer
  surfaces of a multi-vertical tail, or

  (2) On the fuselage surfaces, on
  both sides of the fuselage between the trailing edge of the wing and
  the leading edge of the horizontal stabilizer. If engine pods or other
  equipment are located in this area and are an integral part of the
  fuselage side surfaces, you may place the marks on those pods or
  equipment.

However for some time 2 inch markings were allowed:

  On an aircraft displaying 2-inch marks before November 1, 1981, and on
  aircraft manufactured between November 2, 1981, and January 1, 1983,
  you may display those marks until the aircraft is repainted or the
  marks are repainted, restored, or changed. Once the aircraft is
  repainted or the marks are repainted, restored, or changed, the
  N-number is required to be 12 inches high.

Its possible the numbers you are seeing are the old ones and the new 12 inch numbers were applied directly beneath it to comply with the new marking regulations while the old ones were simply not removed.


Why do turbine engines take so long to spool up? Piston engines reach full rpm within a second or two, but turbines take much longer. Why is that?

I'm not an engineer (which might be better suited to answer this) so this is from simplified things they feed pilots:

Jet engines take much longer to spool up (i.e. increase RPM) than piston engines, especially at low RPM because of the pressure ratio/increased airflow necessary to keep the compressor from stalling/surging/blowing up every time when changing power settings.

The (simplified) jet engine cycle contains a compressor that pushes air into a combustion chamber, where it burns, and then blows out the rear end rotating a turbine that moves the compressor from back where we started at.

If you "add more power" (i.e. put more fuel in) it takes a while for that extra fuel to produce more thrust, which in turn takes a while to accelerate the turbine, which will make the compressor spin faster, which will finally bring more compressed air into the combustion chamber to utilize all that extra fuel you poured in at step 1.

Adding power all of a sudden will increase the pressure in the combustion chamber, so much that air that is "upstream" (i.e still in the compressor) does not want to advance. The extra pressure in the combustion chamber did not have enough time to spool up the turbine, so now the compressor is underpowered to keep "pushing" compressed air into the combustion chamber. Air starts flowing backwards (i.e. from combustion chamber to compressor), engine surges, all hell breaks loose.

So there is a lag (electronically these days, the pilots can floor the trust levers as fast as they like) when the engines are at low RPM, the FADEC only adds a little bit of extra fuel, waits for the airflow to stabilize, then adds a little more, and so on.

I think the graph below might explain this. Every time you change RPM, you will increase Pressure Ratio (i.e. move up the graph), then you wait a little bit for Air Mass Flow to increase (i.e. move right). If you increase the Pressure Ratio too much, without the accompanying mass flow (which take a while because of inertia) you will enter the surge line.

A similar thing happens on spool down, albeit a gentler one.

Compare this with the piston engine where you put more air/gas mixture into the cylinder, it makes for a bigger bang, accelerates the piston faster, and the very next piston cycle you can theoretically get max power.


Would a piston or turbine engine be best suited for a small UAV flying 8000miles? I am trying to devise a concept that would airdrop medical supplies around remote regions of Africa: vaccines, medicine, blood... etc. I image the payload would be anywhere between 1-2 ton. I think a UAV would make the most sense because then you don't need to worry about flight-time, speed, pressurization, bathrooms and pilot logistics.

Range is an issue because I might need to determine where to set up runways. Africa spans thousands of miles. Ideally, 8000 miles would be great because you can take off from Europe or Egypt or Israel , then fly anywhere in Africa and return without landing to refuel. But landing at a hub to refuel would double the distance -or half the required range.

Payload weight is something I think about a lot and I need to do more research. Like, how light can you make vaccines? There would also be the syringes and other medical supplies. Also, because of the cold-storage cooling and parachutes I think 1-2 ton is a good estimate.

I was looking at electric powered options and these aircraft are typically short range and expensive. Unless you look at the Impulse 2 which has infinite range, but was $128 million to develop.

So in short, long range, light-ish payload, speed doesn't matter and as cheap as possible.

Not to burst your bubble, but doing this "cheap" isn't possible.
First look at range. Light aircraft that have a 2-ton+ payload have limited range, look at the upcoming Cessna 408, it can carry 3 tons but only has a 1,000 mile ferry range. In order to increase the range, you need to carry more fuel, reducing your load. So lets say you dedicated 1 ton to a fuel tank (neglecting the weight of the tank/piping), that gives you an extra ~300 gallons, maybe an extra 500 miles (I don't have info on fuel burn rates at this time, just a generous guess).
Now, you want 8,000 miles, so you need something that can carry a lot of fuel. Now you're in the 767-ish sized territory, so payload won't be a problem, nor will range (when you add , but it will be expensive. A new 767 cost around \$100 million, or you can lease it for between \$600,000 and \$650,000 per month.
If you need an aircraft with air-drop capability, now you need to find something ex-military. A C-130 won't do (range is only about 2000 miles), even the gigantic C-5 Galaxy only has a 4,800 mile range. There just doesn't exist an aircraft to do this.
Add on top of that the cost of developing an autonomous flying system with take-off and landing capability, you are well into the $200 million range at this point.
So now what? You've got a 767 with large payload capability (but no air-drop) that can fly somewhere and back. Time to fly right? Nope! You now (and have been for some time) need to deal with regulatory requirements for multiple jurisdictions since you are crossing a lot of unrelated airspaces in your flight. You need to coordinate demonstration flights and paperwork, along with all the compliance needed for a "one-of-a-kind" aircraft. Many won't want you flying over populated areas, or may deny you completely. Might have to do some lobbying ($$$).
Ok... got it, regulations approved, flight approved, aircraft bought, cargo bought, time to fly? Almost, try getting insurance. It will be expensive, probably hundreds of thousands per month.
A flight crew is the least expensive thing here
If you are serious about this, save yourself \$100m to \$150m and hire a qualified crew. You don't have to go through the development of this automated system, the regulatory approvals, the test flights, the insurance costs, the reluctance to have a 90+ ton aircraft flying without any operator intervention at 500 miles per hour and just hire somebody to fly it.
Pilots aren't the most well-paid, but lets say you have 2 crews making \$100,000/year each ($400,000/year total) with benefits. That's \$33,333/month, for the cost of development (lets say \$100m) of the automation system, you can employ these people for 250 years.


Is it easier to land planes on an aircraft carrier with a high flight deck? The Wikipedia page for the USS Wolverine says that the low flight deck of that carrier is disadvantageous for warplane landing, but it was 70 years ago.

Assuming other things (including displacement, length, width and draft of carriers, flight deck length, width and texture.), is it easier to land the latest planes on an aircraft carrier with a high flight deck?

Then

It used to matter, because aircraft would sometimes approach the carrier at a lower altitude than even the flight deck before pulling up briefly and practically stalling onto the deck, allowing for a lower speed landing. Similarly, the higher flight deck would give an extra couple of metres of acceleration if over-shooting the flight deck and having to go around. As such a high-decked carrier gave a little more margin for error.

Now

It makes virtually no difference - modern aircraft approach at the same angle and airspeed regardless of the height of the deck (within reason). They also perform approaches significantly more accurately. If anything, the higher deck could be considered a (very) slight disadvantage, as it may display a higher rolling moment than a low deck carrier. This is unlikely to cause any issues, however.


How reliable are Lycoming and Continental general aviation piston engines? Statistically speaking, how reliable are Lycoming and Continental general aviation piston engines? What I'd really like to either find or build is a table showing the probability of experiencing engine failure on a properly-maintained piston engine for most of the common models of engine. Is the data out there?

Short (pilot's) Answer

"Reliable enough for you to fly behind one, flaky enough that you should always expect them to fail at the least convenient moment."

Short (Mechanic's) Answer

"More reliable than the pilot!"

Longer Answer

You can't really know the failure rate, but you can know the accident rate attributable to engine failures.

The NTSB looked at this back in 1972 and Embry-Riddle still has the report available. It's very interesting reading, and goes into great detail on the specific causes of engine failure.
Totaling up everything they classified as "engine failure" gave a failure-related-accident rate of just under 18 per 100,000 hours (i.e. "Assuming proper maintenance you could theoretically fly 5,000 hours in piston GA aircraft before you'd have an engine-failure-related accident.")
There may be a more current NTSB study on this, I honestly didn't look too hard as I expect the numbers to be broadly similar today.

The 24th Nall report shows 61 "powerplant" accidents (all engine types, and including the propeller and associated systems) - the number is not broken down per 100,000 hours but doing a little extrapolation from their other figures it works out to about 0.4 accidents per 100,000 flight hours (or "Assuming proper maintenance you could theoretically fly 200,000 hours in piston GA aircraft before you'd have an engine-failure-related accident.")

The mechanic's answer of "More reliable than the pilot!" comes into play when you look at the pilot-related accident numbers: In the 1972 NTSB report I cited engine failures made up 13% of the total accident figure. In the 24th Nall report all mechanical accidents were 14% of non-commercial fixed-wing accidents (17% of commercial accidents) - that includes a number of other systems (e.g. landing gear) which are unrelated to the engine.


Do small airfields provide ATIS? If not, what weather reporting service is available? Would a very small airfield or airstrip be considered to be a 'terminal' and have Automatic Terminal Information Service (ATIS)? Or would it just have minor weather reporting?

As in, would it make sense to provide ATIS (Automatic 'Terminal' Information Service) for a very minor airstrip? How does an airstrip qualify as being a 'terminal' to require those services?

There is no minimum definition of a "terminal" in and of itself. The "destination terminal" of a flight is simply its planned endpoint. That's usually, but not always, a man-made complex designed to facilitate human flight, which we call an airport. However, you can file a VFR flight plan to fly out to a friend's fallow field in BFE, miles from any airfield listed on a sectional:

It's then your responsibility, as it always is in VFR, to ensure you can operate the plane safely at all times, including getting the plane on the ground and then back up in the air without causing personal injury, property damage, infringing private property rights, violating noise ordinances, etc.

Sectional diagrams use the term "airport" to refer to any place that is registered with the FAA to be used for the purpose of aircraft takeoffs and landings. These places may be more specifically called airstrips, airfields, air parks, aerodromes etc to indicate relative size, construction, ownership or facilities.

The only requirements for an airport to be documented by the FAA and appear on a sectional are:

The location must meet minimum guidelines specified in the Airport Certification Manual, including land grading for smoothness and drainage, obstruction/obstacle clearance in three dimensions, and minimum safety markings and wind/traffic pattern indicators that are necessary to support aircraft takeoffs/landings at the location (really the only thing every airport requires along these lines is a windsock; everything else is provided as needed for the specific location or as desired by the field's users). This usually requires a minimum amount of maintenance/upkeep by its owner for the purpose, even if it's just a grass field (it would have to be regularly mown and weeded to remove certain spiky or wood-stemmed plants, for instance).
The location must be registered with the FAA by its owner/manager for this purpose (they can register it as a reserved/private airfield, and then only limited information will be given on the sectional, primarily as an advisory that the location is available for emergency landings).

That's all there is to it. Besides a windsock which is the absolute minimum, no minimum facilities must exist; even the traffic pattern/landing direction indicators are optional if traffic can always use a left-hand pattern and determine the runway approach from the windsock. Rhome Meadows Airport (T76) between Fort Worth and Decatur, TX is a grass strip, with no lights, no tower, no fuel, no hangars, and the displaced threshold on the south end is marked with two white painted tires (no threshold markings to the north). Nearby Heritage Creek Airstrip is only slightly better, with low-intensity runway edge lights. Despite this, both are fairly active for unimproved strips, with about nine flights a day involving each one in some way (TO/L, T&G).

Here's the airport section of the legend for FAA sectionals:

You can see that there's a wide array of symbology available to indicate at a glance what the facility offers; control tower or no, length and configuration of hard surface runways if any, usage type, presence of FBOs for fuel/maintenance, navigational aids, and radio information including ATIS, AWOS, ASOS, control towers, UNICOM etc. Obviously a control tower needs a radio frequency, but there is no requirement that a towered facility have ATIS. ATIS is usually found at towered airports as its purpose is to reduce controller workload, but nontowered airports can have ASOS/AWOS stations which provide practically the same information regarding weather, without the superfluous runway information (at nontowered airports, the pilots usually determine the approach/departure direction). If an airport has no reporting whatsoever, you would usually tune to the nearest listed AWOS/ASOS.


Is spin recovery possible in an airliner? During initial flight training a lot of emphasis is placed on stalls and spins and how to recover from them, but is it possible to recover from a fully developed spin in an airliner? Do these large aircraft have enough rudder authority to pull it off?

Has it ever been done? And is it part of the training for specific type ratings? (in a simulator of course)

There were a lot of other mitigating factors in the Colgan Air 3407 crash. Was that one recoverable? It depends. It never should have got to the point of a stall in the first place. It was more preventable than recoverable.

But in answer to your question, again, it depends. Every aircraft in the air can stall and be recovered, if responded to properly. But the plane may very well bend and break if the stall develops too far. Then it may not be recoverable. And most large airliners (or aircraft bigger than a few thousand pounds with multiple engines) aren't designed for the stresses of spins, so they never teach to a full stall. In those types of aircraft a full stall is much more dangerous, and they can be much more difficult to recover from, especially if you break something. Besides, in aircraft like that, you should receive plenty of direct warning long before you reach the point of a stall.

When I was teaching, stalls and spins were one of my favorite subjects for early pilots. Especially in light trainers like the Cessna 150/152s. Those aircraft were always incredibly good at stalls/spins and incredibly forgiving. You can put a Cessna into a hands-off full stall if you trim it right, and it will stop rotating in a spin if you simply let go of it (and have enough altitude). I always taught my students spin recovery from a full spin, even at the Private Pilot level. And usually shortly after teaching them full stalls. I would stall it, make it rotate at least 3 or 4 times, and have them recover the spin. Then have them do it themselves. I never had to worry about my students not knowing how to recover from an unintentional stall/spin. By the time my students were learning to fly multis, I was teaching them more stall recognition and avoidance than recovery. Recovery is essentially the same in all aircraft. You just have to be sure to not reach that point.

There's only one thing you really need with any aircraft in a stall/spin, and that's altitude. Unfortunately, takeoffs and landings are the most likely places for you to get behind the aircraft and let it unintentionally stall/spin. That's why you learn how to recognize them very early in your pilot training. You can't spin without a stall first, and just about any airplane will give you fair warning before you stall it. The trick is recognizing the situation before it becomes serious.


Are STOL kits that use leading edge slats available for 'typical' GA aircraft? Has anyone tried fitting leading edge slats to any of the 'typical' general aviation aircraft? If so, are the benefits worthwhile? I know they're available for the Piper Super Cub, but I haven't been able to find any for tricycle gear aircraft like a Cessna 182 or Piper Comanche. I know that having a  high wing or low wing will also be a factor.

The Helio Courier, a well known STOL aircraft, has a speed range from 25 knots to 147 knots. I assume that other aircraft may benefit for using leading edge slats or other devices to lower the stall speed to 25 knots or so, leading to slower, safer landings and emergency landings. All the advantages of the Helio, but in a different form that some people may prefer, for example the low wing aircraft configuration.

The only disadvantages I can think of are the limits of the tricycle landing gear in achieving a high enough angle of attack when landing due to the possibility of tail strikes, and the better protection from debris
in soft field takeoffs and landings.

And what would happen if someone fixed a Helio wing on a Piper Commanche, assuming cost no object?

Lowering stall speed is not a benefit in itself, it's only a benefit if it you need it. There are STOL kits for many airplanes, you don't see them much on most airplanes because there's no real benefits in normal flying and they cost a fair chunk of money to install. STOL kits only get you so far, adding a STOL kit onto an airplane with a 50 kt stall speed will not give you a 25kt stall speed, it's a lot less than that. If you have a bush airplane, fly into very short fields or in high density altitudes then a STOL kit can give you extra capabilities. If you don't fly into very short fields then a STOL kit is extra weight and costs for capabilities you won't use.

It's also not as simple as simply sticking some extra bits on the front of the wing, there's many considerations. For one, if you drop an airplane's stall speed substantially then you will run into control authority issues at slow speed. You will have to beef up the ailerons, rudder and elevator to compensate, which is a substantial re-design, adding costs. The most popular STOL kits are for airplanes which already are good STOL aircraft to begin with and have adequate control authority.


Can a helicopter really fly with rotors going this slow? I was watching this youtube video and I noticed that at 3:17 seconds they show a coast guard helicopter rescuing a man from a ship. Whats shocking about this is that the main rotor of the helicopter seem to be going incredibly slowly and the tail rotor has completely stopped.

How was the helicopter able to stay flying with such a low rotational speed? Was this some optical illusion or was the rotor really spinning that slowly?

Also, how was the helicopter not spinning? From what I understand the main purpose of the rear rotor is to counteract the rotational force of the main rotor. Since the rear rotor wasn't moving, shouldn't the helicopter developed a spin counter to the spin of the main rotor (even though it was slow)?

It's an illusion that the blades appear to be going slowly. It's actually a well known effect called the wagon wheel effect.

Essentially the rotor is spinning at close to an even multiple of the camera's framerate divided by the number of rotors.

This means that between frames the blades have moved a full quarter rotation (or a multiple of that). Creating the illusion that the rotor is moving more slowly that it actually is.


What is the lump under the English Electric Lightning's fuselage? What is the lump underneath the English Electric Lightning's fuselage?

Source: www.forwallpaper.com

The lump is a ventral fuel tank, aka conformal fuel tank.

  The F.3A introduced [...] a new, non-jettisonable, 610-imperial-gallon (2,800 L) ventral fuel tank.—Wikipedia


Flight Design CTSW vs Cessna 162 (Light Sport Airplanes) I am going to buy a light sport aircraft in next couple of months and trying to make a decision between Flight Design CTSW and Cessna 162.
I have some budget within 50K and want inexpensive plane.

Flight Design CTSW (not CTLS) pros and cons:
I like its design and I like Rotax 912, but I am afraid of maintenance cost of rotax, parts and mechanics availability.

Cessna 162 pros and cons:
Looks like a little bit cheaper to buy. I like parts availability and mechanics. I don't care about that it burns more fuel and heavier.

Does anyone have some experience with one of these planes or would recommend a different make and model? (LSA only in USA). Thanks.

Don't have any personal experience, but having been around GA since the mid 70s, and looking them over, the CSTW wins hands down.

To have any kind of utility a 2 seater must have more than a 500lb useful load and the CSTW is over 600lbs based on a 701lb empty, although airplanes you find used will always be heavier, probably around 725 to 750lbs empty.  Still that's a pretty impressive useful load. Even if you don't care too much about the useful load because you fly by yourself all the time, at some point you will.

Any Skycatcher you find is going to be 875 lbs empty or more, with more or less the same gross (just about any airplane you buy used is quite a lot heavier than the published factor number as they pick up a pound here and a pound there from this and that over time).

Carbon structure, so no metal.  Made in Europe.  And the 912 family has proven to be a very reliable engine line.

So between the two, the Flight Design.  I wouldn't touch a Skycatcher, which has had structural issues where Cessna had to go out modifying wings, and it kind of has that taint of failure to it due to Cessna just kind of abandoning the program even though they had a fat order book (Almost certainly because they discovered they were losing money on them even with production in China).  Which is why they're cheaper.

Bottom line though is you must go for a ride in each to make an informed decision.


General dimensions for a uav type rc plane? I want to build an rc plane that looks like this one

What are the general dimensions that I should follow? I dont want to copy other designs of real uav's and scale them down. A drawing would be great

I want to build something small, wing span should be about 125 cm

You can start by looking at plans here to get a general idea. When it comes to planes you can't just get some "general" measurements and wing it (pun intended). There are a lot of considerations when it comes to making things fly. With out going into specifics it would be best to use known working plans to build something as apposed to trying to throw something together that looks right.

To Answer your question directly that picture looks like the wing span is the the 3.5 foot range, the center section is about 2.5 feet long and tail poles are about 18 inches.


Why did this aircraft do a ‘spiral’ before landing? There was this WizzAir flight two days ago, from BUD to PMI, and right before landing it did a ‘spiral’ like maneuver. I’ve attached a screenshot.

Why did it do that? It looks strange.

The flight was on the 28th, and before orbiting it was around 12:00 UTC. By using the playback function of FR24, this is the view:

The flight in question was 2383 with call-sign WZZ1161 (FlightAware permalink).

The boxes with numbers and arrows indicate the flight level and either climbing or descending. As you can see, two busy streams were approaching the airport from the north. This orbiting as opposed to a holding track (race track shaped) is common and its phraseology can be:

  for spacing orbit left
  for spacing make a 360 turn left

Fast forward:

And a Ryanair flight did the same before continuing the approach. It was just heavy traffic and it's quite common over Heathrow (live as of writing this):


When do you contact ATC when departing from a non-towered airport into class C controlled airspace? When you're departing from an airport within controlled airspace, when should you contact ATC?  This is when the airport you were departing from is non-towered.

Scenario: I am departing a non-towered airport in class Charlie airspace. I need to request VFR flight following to another airport. When do I contact ATC?

This is spelled out clearly in CFR 91.130:

  (c) Communications. Each person operating an aircraft in Class C airspace must meet the following two-way radio communications requirements:

  (1) Arrival or through flight. Each person must establish two-way radio communications with the ATC facility (including foreign ATC in the case of foreign airspace designated in the United States) providing air traffic services prior to entering that airspace and thereafter maintain those communications while within that airspace.

  (2) Departing flight. Each person—

        (i) From the primary airport or satellite airport with an operating control tower must establish and maintain two-way radio communications with the control tower, and thereafter as instructed by ATC while operating in the Class C airspace area; or

        (ii) From a satellite airport without an operating control tower, must establish and maintain two-way radio communications with the ATC  facility having jurisdiction over the Class C airspace area as soon as practicable after departing.

You can try contacting them while on the ground, but if you can't raise them, you have to do it as soon as you can after take-off.


Mathematical model used in free route airspace As a new researcher in an air traffic institute, I am currently looking into mathematical models - promising or otherwise - that are used in modelling free route airspace.

What is a good place to begin?

Thanks in advance.

En-route simulation by airtopsoft is a good simulation modeling software package that I have utilized in the past to model airspace routing. It also give you some pretty powerful tools to analyze the data afterward.

Another commonly used mathematical tool for modeling airspace and routing is the "Airspace Concept Evaluation System" (ACES). This platform uses four-degrees-of-freedom equations of motion to model aircraft performance and navigation data. Based on the trajectory data, it generates "pseudo-radar" tracks to help predict collision avoidance patterns. I believe this tool is more commonly used to predict routes in the NAS but I believe you could utilize it for free route airspace by playing with the input parameters.

Hope this gives you a good place to start!


At what distance beyond the aiming point is a landing considered a "Deep Landing"? In Flight Data Monitoring (FDM) programmes, the Deep Landing calculation is based on difference between the aim point (or glide slope touchdown point) and the actual touchdown point.

How are the limit values for determining whether a landing qualifies as a Deep Landing specified for long or short runways?

Is there a legal distance after which a landing is qualified as "deep". Does that depend on the runway length?

I believe that needs to be decided by the operator, taking into account their operation and fleets. For a jet on a short, normally wet runway, I would allow for a smaller margin than for a turboprop onto 4000m dry asphalt.

In the absence of any other information, maybe a sensible starting point could also be to look at what assumptions have gone into crew‘s landing performance calculations. On large jets, nowadays often a 7 second (or 1500ft) air distance is assumed between crossing the threshold and touchdown, in line with TALPA ARC recommendations. An air distance longer than that will invalidate the performance calculations (as this value is assumed to contain some margin already, using the full 1500ft will already use up all margin on the air part of the landing) and would thus provide a sensible event threshold. Obviously this would have to be reconciled against runway aiming point markings etc. in the FDM event validation to prevent a non-standard runway marking from generating false positives.


How to locate the coordinates of the Center of Gravity of an airfoil? I am working on the inertial effects on a variable pitch propeller and i need to define the location of the center of gravity on the airfoil to calculate moments of Inertia and angular momentum. What is the best way to do it?

To compute the inertial properties of your blade, you need a couple of things: a way to compute inertial and elastic properties along the blade, a blade layout, and some idea of the expected load you want this to carry.

Starting with elastic properties--this can be either really straightforward or VERY tricky, especially when you start throwing composites around.  That said, this is true primarily because composites can be tailored into having just about whatever material properties you want...but the analysis of composites for essentially what you're doing was the PhD dissertations of two grad students I know.  The one is developing an analysis tool for aeroelastically tailored blades (also mentioned here, in a study by Sandia National Labs: http://energy.sandia.gov/wp-content/gallery/uploads/SAND2001-1303A.pdf), which sounds like what you're trying to do.  In short, these blades take advantage of strategically tailored material properties in order to achieve variations in blade twist purely based on a blade's operating condition.  If you are going to develop your own composites design code (or have one!), I think this is a feasible goal and I'd recommend you to "Analysis and Performance of Fiber Composites" by Agarwal, Broutman, and Chandrashekhara for an intro to composite analysis.  Based on that text, you could develop an analytic design code that might get you into the ballpark, and maybe start developing some finite element models to go beyond that.  It requires a fair amount of setup, and, since I don't think it was the main thrust of your question, I'm not going to write it out.

I think it suffices to say that back-of-the-envelope estimates for composite materials are hard to come by.  That said, it can be a rough approximation to treat composites as "black aluminum", or as an isotropic material with the bulk mechanical properties of the material (though it nullifies the aeroelastic tailoring you're shooting for).  Note that this requires you to have a symmetric layup schedule, as described in this short course from the US Naval Academy (https://www.usna.edu/Users/mecheng/pjoyce/composites/Short_Course_2003/7_PAX_Short_Course_Laminate-Orientation-Code.pdf).  This isn't the main thrust of your question, however, so I'm not going to delve into it further...it's just a head's up since composites can be more trouble then they are worth, especially if you have access to more traditional machining resources that you can use to make blades out of materials that are easier to shape (plastics, etc.).  The FAA has a nice guidebook too, and, depending on how fluent you are with this stuff, it may be of interest: https://www.faa.gov/regulations_policies/handbooks_manuals/aircraft/amt_airframe_handbook/media/ama_Ch07.pdf.

If you're not shooting for aeroelastic tailoring or your analysis, for whatever mission you're planning for doesn't show that you get a terrible performance gain, it may be worth it to just try and make a variable pitch mechanism instead.

Alright -- on to inertial properties.  If you're looking to compute the blade's dynamic stability, you'll need inertial properties around multiple axes of rotation to account for the 3 modes of blade motion: blade flapping (i.e., motion of the blade out of plane with the rotation of the propeller), pitching (or twisting), and lagging (motion of the blade in the plane of rotation that occurs in addition to rotation of the blade itself).  Blade stability is related to the coupling of these three modes.  For an application I had (wing of constant cross section, isotropic material), I assumed the following cross section, including a quarter-chord spar and skin.

To solve for the inertial properties of the section (so that I could do a simplified aeroelastic stability analysis), I moved point by point along the airfoil surface.  For example, take the picture below.  It's a zoom in on the upper surface of the previous image.

To find the signed area of a convex polygon, in this case the quadrilateral defined by P1, P2, P3, and P4, the equation is (where x is in the chordwise direction, z is in the vertical direction, and y is the spanwise direction along the blade):

$A=0.5\sum_{i=0}^{n-1}(x_iz_{i+1}-x_{i+1}z_i)= 0.5\left[((x_{P1}\cdot z_{P2})-(x_{P2}\cdot z_{P1})) + ((x_{P2}\cdot z_{P3})-(x_{P3}\cdot z_{P2})) + ...\right]$

...and so on.  Similarly, the centroid can be determined by

$x_c = \frac{1}{6A}\sum_{i=1}^{n-1}(x_i+x_{i+1})(x_iz_{i+1}-x_{i+1}z_i)$

(formulas are most legibly given at https://en.wikipedia.org/wiki/Polygon#Area_and_centroid).  Just use the parallel axis theorem (essentially just weighted average of the centroids and areas) to get all these individual pieces to yield the sectional area and centroid (which, for an isotropic material at least, is the location of your neutral axis).

Moving on the second moment of area (which you'll need for computing stability), it's a similar formula (found at https://en.wikipedia.org/wiki/Second_moment_of_area#Any_polygon):

$I_{xx}=\frac{1}{12}\sum_{i=1}^n(z_i^2+z_iz_{i+1}+z_{i+1}^2)(x_iz_{i+1}-x_{i+1}z_i)$

($I_{zz}$...is similar -- just swap x and z).  Also:

$I_{xz}=\frac{1}{24}\sum_{i=1}^n(x_iz_{i+1}+2x_iz_i+2x_{i+1}z_{i+1}+x_{i+1}z_i)(x_iz_{i+1}-x_{i+1}z_i)$

Apply the parallel axis theorem to get all these individual moments to combine into a sectional property.

Once you have those implemented, the question is just what area do you want to integrate (i.e., is the blade solid, how large is your LE weight, etc.), and what are the elastic properties of those sections.  Then just apply the above.  The out of plane moment of inertia is the sum of the in-plane moments (i.e., $J = (I_{xx}+I_{zz})$).

Finally, as to actually computing dyanamic/static stability, I have a reference text...but it's a set of course notes and I'm not sure the best way to post it as the method is quite involved.  My apologies, but I'm coming up a little short on a good reference for this and may update this question later if I do find something good, however, in the interim, I'd advise you to look at helicopter dynamics texts, which will be a source of material for performance analysis computations too.  One source I could find online is by Bramlette and seems to have the basics well covered, but doesn't venture into rotor stability analysis: http://airspot.ru/book/file/63/bramwell_helicopter_dynamics.pdf


Can an LLC formed solely to own and operate an aircraft be operated under Part 91? A non-pilot purchases an aircraft and puts it into an LLC. Then non-pilot hires pilots, places insurances, rents a hangar and pays for all other costs and expenses with the sole purpose to fly the his family on personal trips and vacations (no business purpose), can the aircraft still be operated under Part 91? Or, because the non-pilot who owns the LLC is providing funding for the operation of the aircraft, does this constitute operations under Part 135?

The short answer is yes, an aircraft owner can hire a pilot to fly him or her, as well as other friends and family, and operate under Part 91.  This is called private carriage, as opposed to common carriage.
Just to clarify a few points:

The pilot hired would need to have a Commercial Pilot Certificate, even if no money changes hands, because the FAA considers flight time as compensation.
The owner could not charge other passengers because this would constitute common carriage, (operating as a charter) and require a Part 135 Operating Certificate.
It makes no difference whether the owner is a rated pilot or not.  Some owners fly themselves, but want the security of having a more experienced pilot along with them.

P.S.  I realized looking related questions on the right side that this is pretty much a duplicate of this question:  Can an aircraft operator hire a Commercial Pilot to fly their aircraft under part 91?


Are modern aircraft provided with analog consoles in case of a software failure? I am curious about the redundancy they provide in modern era commercial aircraft.
Here are the questions:

If an aircraft suffers partial or complete software malfunction, do the pilots have the choice of flying the craft with help of analog consoles for critical systems(e.g. speed, altitude, heading indicators and basic flight controls). It summarizes to the point whether they provide such analog devices ?
In case of such failure, can the engines keep running so as to provide thrust, fuselage pressurization and breathable air supply to cabin?

All commercial aircraft have some form of redundancy in their instrumentation, but it's not always in the form of "analog" instruments. The backup is often electronic itself. But the overall system is designed with a very high level of redundancy.

A typical modern jet aircraft has an Electronic Flight Instrument System (EFIS), which is the large screen Primary Flight Display (PFD) you see in front of both pilots. There are usually also one or more Multifunction Displays (MFDs) in the middle between the pilots. These displays form the primary instrumentation.

The EFIS itself is designed with a very high level of redundancy between the pilot's and copilot's side displays. Both are on independent electrical circuits and receive information from independent input computers (air-data [ADC], attitude/heading [AHRS], etc.). Both can usually also be switched over to the other set of input computers. Usually, the MFD can also be configured in a "reversionary" mode where it looks and acts like a PFD.

If the entire EFIS system should fail, there is also a backup set of instruments. In modern times this backup is usually one or two Electronic Standby Instrument Systems (ESIS). These are essentially smaller, condensed "PFDs" that display critical information. They usually either contain their own miniature AHRS/ADCs or are connected to isolated computers. They are also powered on a totally independent electrical circuit and often have their own dedicated battery as well, separate from the main aircraft battery.

Modern engines are controlled by completely different computers called Full-Authority Digital Engine Controllers or FADECs. Two or more FADEC channels are provided for each engine, so that if either channel fails, the other can take over. FADECs are also considered flight-critical items, and are designed with fail-passive capability: even if both FADEC channels fail, the engines can still run and be controlled more primitively and less efficiently.

Electronic pressurization controllers don't always have redundant computer modules, but a manual pressurization control mode is always provided. In the worst case, the pilot has the ability to manually open or close the cabin outflow valve to control cabin pressure. And redundant pressurized air sources are available from each engine.


Who has final authority over Air Force One? U.S. FAA FAR 91.3 ("Responsibility and authority of the pilot in command") says that:

  The pilot in command of an aircraft is directly responsible for, and
  is the final authority as to, the operation of that aircraft.

When an aircraft is operating as Air Force One, it would normally be flown by the designated high ranking USAF Officer, as a military flight.

Is the President, as Commander in Chief of the armed forces, able to over-ride the authority of the pilot?

For example, if one of the current Boeing VC-25's engines flames out and the captain announces that he has made the decision to take an option/ turn back - can the President override this decision and force him/her to continue the flight?

The pilot in command has final authority over Air Force One
Air Force Instruction 11-202, Volume 3 says the following in Chapter 1, part 1.1.1 (as in, the very first thing in the document):

1.1.1. Pilot  in  Command  Authority. The Pilot in Command (PIC), regardless  of rank, is responsible for, and is the final authority for the operation of the aircraft.

Just for fun, let's compare it to the civilian version that you referenced, 14 CFR 91.3:

The pilot in command of an aircraft is directly responsible for, and is the final authority as to, the operation of that aircraft.

Wow! Basically identical except that the military version goes out of its way to mention that rank is irrelevant.


Would an 8% reduction in drag outweigh the weight addition from this custom CFD-tested winglet? I'm writing an essay at school about why there is so much variation in winglet design. I am analysing all the primary types of winglets used today in the aviation industry. I'm constructing them in Solidworks (CAD software) and then running them through the in-built CFD. The winglets which gave me the lowest drag were those of the 737MAX. I then went on to design my own winglet and see how it compared - I took on a sort of compund spiroid/MAX winglet mix - according to the numbers fom Solidworks, the drag force with this winglet is 8% lower than that of the MAX winglet.

Now, OBVIOUSLY I am not better than the a team of hundreds of Boeing engineers with this design I stumbled upon, so I was wondering what the reasons would be for Boeing/an aircraft manufacturer not to use this type of winglet. I understand the consequences of weight on the wing root moment/structural reinforcements, etc... but I feel an 8% reduction in drag would outweigh the weight addition from this winglet?

Test parameters:

The wing is the same as that of a 737NG, with the winglet stuck on the end

TAS: 280kts
Air density: 1.2kg/m^3
Airflow: Incident at normal to fuselage direction
AoA: ~1.5 degrees

Images of the CFD and winglet itself are attached

First off, awesome question and great investigation! This kind of let's-see-what-happens inquiry will take you far should you decide to pursue aerodynamics at an advanced level (and, of course, in other pursuits). Not so long ago, I had to write a similar report: lacking the resources and knowledge of the aerospace giants, I, too, wondered why I could seemingly invent designs that on the face of things appeared vastly superior to theirs. I thought that I had winglets down cold.

Then I went to work for Boeing and started talking to the aerodynamicists. I started graduate study of aeronautics. Turns out, unsurprisingly, that there's a lot you can't get out of undergraduate textbooks and publicly available data. While I obviously can't be exhaustive here—and probably won't even answer your question to the letter—I can give you a few things to think about. To be clear, I wouldn't go much further than you have with your modeling and simulation, but if you'd like some discussion points for your paper here are some in no particular order. I've made some assumptions about your level of knowledge, so please forgive me if it's patronizing and ask me if you need clarification.

The fidelity of your baseline model

  The winglets...were those of the 737MAX....The wing is the same as that of a 737NG.

On what data did you base your model? The wing of a 737 is not a simple matter of an airfoil, some taper, and some twist. I notice that you did not include nacelles/pylons or flap-track fairings. The design of a production winglet is heavily tied to the integration of the overall wing design, including all of the extra components hanging off of it.

The reason that the 737 MAX winglets are effective

The 737 MAX uses what's branded as the Advanced Technology (AT) winglet. We know that a well designed wing extension is more aerodynamically efficient than a winglet. But the 737's wingspan must stay within certain limits in order to operate with the same ground infrastructure as previous models, so a winglet is a good solution. But what if we could have a little of both? Well, the AT winglet does exactly that:

  The lower winglet is configured such that upward deflection of the wing under an approximate 1-g flight loading causes the lower winglet to move upwardly and outwardly from the static position to an in-flight position resulting in an effective span increase of the wing.

So to really understand the efficiency of the AT winglet, you'd need to model this deflected geometry.

The other contributing item to the effectiveness of the AT winglet is its natural laminar flow:

  On previous winglets, the drag due to friction from the airflow over the winglet is one of the main detractors from efficient airflow....this is solved by Boeing using detailed design, surface materials and coatings that enable laminar – or smoother – airflow over the winglet.

The flow regime you're modeling

The AT winglets are most effective as their efficiency is aggregated over long, high-speed, high-altitude cruise legs. All you've given is a true airspeed, but for this kind of analysis of transport aircraft the Mach number is much more important. You haven't provided an air temperature, but from the density you've given it looks like this simulation is at sea level, which means your Mach number is not high enough. But this in fact might partially explain your results. Observe the drag curve:

In general, a spiroid winglet like yours reduces the induced drag at the expense of some parasitic drag. As you can see, we can afford some extra parasitic drag at lower speeds because the induced drag dominates.

If I were to make one suggestion, it would be to run your simulation at a realistic Mach number (around 0.8) and see what happens. But beware...

The limitations of your CFD software

We are getting to the point where CFD, when implemented well, is quite good for modeling aircraft performance in cruise flight. Much of the wind-tunnel testing for large aircraft these days is focused on high-lift and maneuvering conditions, where CFD falls much shorter. Of course, we always want to validate our CFD in the wind tunnel for all flight conditions, but for well-understood configurations in cruise the results often match well in terms of calculating overall performance. But the "when implemented well" caveat is key. I personally don't have experience with SOLIDWORKS Flow Simulation, but it looks like it's designed to be a general-purpose CFD software, so I would not trust its results too much for large, complex, high-speed simulations such as the ones required for this analysis.

In particular, there is the issue of turbulence. Not in the sense of unstable air that jostles an airplane around, but in the sense of chaotic flow over the aircraft's surface. So chaotic, in fact, that no computer in the world can accurately model the motion with a sufficiently short computation time. Instead, we use turbulence models that try to approximate what's happening in a way that can be solved quickly enough. SOLIDWORKS uses the k-epsilon model, which is popular for general-purpose software but might not be the best choice here. In particular, notes Wilcox,

  Even the [k-epsilon] model's demonstrable inadequacy for flows with adverse pressure gradient has done little to discourage its widespread use.

As flows over airfoils are quite influenced by adverse pressure gradients, I would exercise caution. I can tell you that Boeing makes good use of the Spalart–Allmaras turbulence model in conjunction with detached eddy simulation (Spalart is an employee). But choosing the correct CFD implementation for a particular problem is a nuanced process requiring a great deal of judgement and care.


What considerations drove the choice of the Solar Impulse engines configuration? Solar Impulse makes me think of a motorglider due to its aspect ratio.

The Upward cranked tips wing configuration along with the engines configuration particularly draw my attention:

The 2 innermost engines are almost close to the thrust line
The 2 outermost ones are right where the wing crank.

Question:

Was the engines configuration mainly adopted out of structural optimization sake or do other relevant considerations (such as ease of flight control in case of asymetric engine failure etc.) come into play?

It reduces moments in the wing spar. Major points of axial drag in this design are the wings and the fuselage. You'll see that two engines are close to the fuselage, and the other two are midway along the wing.
By placing two engines further out, they are also located where the lift is generated, reducing the necessary strength of the wing spar.

Both of the above are especially important since it's such a large wing.

There might also be some possibility of using asymmetrical thrust to ease crosswind landings with this configuration from the yaw from the outboard engines.


When does an UAV need an internal structure? I´ve seen some UAV models without internal structure (stringers, longerons and frame). I guess the drone´s shell is the frame itself. So what is the best approach to calculate the shell thickness to avoid using a more complex internal structure?

Data:

Wingspan: 2.4m
Length: 0.9m
AR: 11
Speed: 16m/s
Estimated weight: 3.2 kg
Fuselage and wings materials: carbon fiber

I very much doubt that you will hit your mass target (kg is a unit of mass, btw) if you build those wings without a proper spar. The shell is for carrying shear loads to provide torsional stiffness, but it cannot give much bending stiffness, especially if there is no internal structure that keeps the upper shell apart from the lower one under bending loads.

So build a light shell and add spar caps, a web and a couple of ribs where loads are locally introduced or where cutouts (say, for ailerons) start.

Regarding the fuselage: If there are many point loads inside from the payload and systems (camera gimbal, engine mounts) it makes sense to have local reinforcements. Otherwise, a shell should be fine given the higher curvature of a typical fuselage. On the other hand, everywhere you have large radii or flat panels, a local stiffener will be advisable.

As for calculating the shell thickness: At that size I expect that handling loads and inertial loads from point masses will determine the minimum size. There is no simple formula and you need to balance ease of operation with performance. Depending on your priorities, the shell will become thicker for a more rugged device or thinner for a lighter but more delicate one.


How do we determine whether the airfoil trailing edge should be cusped or pointed? I'm working on a project and I need to decide whether an airfoil has a cusped or pointed trailing edge given the x and y coordinates of the airfoil.

What is the difference between the two trailing edges?

Both cusped and conventional airfoils have pointed trailing edges. The lower trailing surface is concave on cusped airfoils, so plot it and get your straightedge.


Why have different pattern altitudes for different aircraft? In the FAA AFD for Santa Rosa airport (KSTS), the pattern altitude is given as 1,000’ AGL for small aircraft, and 1,500’ AGL for large aircraft.

Why do these altitudes differ? Doesn’t it compromise having a uniform pattern altitude so aircraft can see each other?

Several possible reasons.

Speed differences between aircraft classes. Larger jets cruise and land at much faster speeds than single-engine props. Keeping their pattern separate from slower traffic minimizes problems posed by a faster plane entering the pattern behind a slower one.
Noise abatement. A jet, even a smaller private one at near-idle in approach, is loud. Keeping them higher increases the distance and number of thermal strata to shield nearby residents from traffic noise.
Prevailing instrument conditions and relative pilot experience levels. A ceiling below 1000 feet, the small craft pattern altitude, would ground VFR flights and thus drastically reduce the number of small craft in the first place. Jets, turboprops and other larger planes are much more likely to be IFR-capable (plane and pilot) and so they're placed higher because they can deal with clouds in the pattern (the airport, if towered, would likely alter pattern height to clear cloud layers but traffic holding above the clouds would still require an IFR approach).


Why is the air inside airliners so dry (low humidity)? The air inside an airliner is very dry which causes all sorts of passenger discomfort such as dry eyes, dry skin and in some cases headaches.

Why is the air so dry and what do or can modern designs do to improve the air humidty on board an airliner?

What happens during a flight cycle is the humidity is high during departure, from ambient air and the moisture from the pax, but over time the air dries out because the bleed being supplied to keep the pressure hull "inflated" is coming from the engine compressors, which at 35000 ft has almost no humidity, and what humidity there is is being extracted by the Air Cycle Machines that condition the bleed (by heat exchanger condensate).

It's important to note the air cycle air conditioning process (787 excluded): Take hot high pressure bleed air, take away some of the heat with heat exchangers while keeping the pressure up, boost the pressure and temperature some more with an air cycle machine - more or less a turbocharger that feeds itself - , cool that off some more with more heat exchangers, then  finally allow the significantly cooled but still very high pressure air to expand and drop down to just above cabin pressure.  This process can take 500F air bleed from the engine compressor and chill it to -40 if you pass all of it through the air cycle machine (only some goes through, and gets mixed with bypassed bleed after, and the air cycle discharge itself is normally kept to not less than > freezing).  Anyway, this process takes whatever humidity there is and removes it, leaving bone dry air.  Moisture control is a big deal with Air Cycle Machines because condensate water that forms during the cooling process will rapidly erode the ACM turbine and ruin the ACM, so you have water separators that extract moisture that condenses from being chilled.

Then at altitude, there's almost no ambient moisture in the first place and you end up with really dry air from ambient being pumped in, how much depending on how leaky the pressure hull is (they can leak quite a lot) offset by humidity coming from all the pax.  At high altitudes after a period of time the dry incoming air wins out and the pax humidity isn't enough and everybody starts to dessicate, again, depending on how leaky the pressure hull is.  An older leaky airplane will get a lot drier inside than a newer relatively tight one.

As Mackk says, one of the big issues is that what moisture does get around the cabin ends up condensing on the inside of the pressure hull.  It slowly gets absorbed into the insulation.  Airliners that operate in humid environments down low will carry hundreds of pounds of water in the cabin insulation because of the condensation cycles from flights, and you will often see insulation set out to dry when airliners are in for heavy check inspections.  What water doesn't soak into the insulation collects at the bottom of the fuselage and promotes corrosion (one solution is to pump dry conditioned air directly into the space between the insulation and skin - so called "zonal dryer" systems).

Anyway, you can see there is a this-or-that problem.  Air moist enough to keep pax happy plays havoc with the interior. Air dry enough for a happy interior generates dry air complaints.  In general, the industry tends to go with the latter.


What is the buzzing noise generated by the engines in this 777 takeoff video? I've flown a few times in my life, both in economy and executive class. Every time I fly in executive, during takeoff, there is a different noise from the engines. In economy class (behind the engines) the wind sound dominates, but in the executive class you hear the noise in the video below until you're high in the skies. Why is that?

That buzzing sound is from the tips of the fan blades breaking the sound barrier.  When you're sitting farther back in the airplane, that sound is overpowered by the sound of the exhaust, which is the roaring part of a jet engine's sound.

So in general, sit forward of the wing, you'll hear the fan sound (the buzz), sit aft of the wing and you'll hear the exhaust sound (roar).  It'll vary from airplane to airplane of course, and when thrust is reduced and the fan speed slows, the buzz will subside.


Can I log PIC time while flying solo in an R22 toward a helicopter addon? I hold a PPL/SEL and I'm training for a helicopter addon. I'm training in a Robison R22 which is subject to SFAR 73. Can I log my solo training hours as PIC time? FOr student pilots, with solo endorsement, I believe the answer is yes.

However, SFAR 73 2.b.1.ii says, "no person may act as PIC of an R22 unless that person ii) Has had at least 10 hours of dual instruction and has received an endorsement from a CFI..."

Is this a different endorsement from the solo endorsement, which I obviously have to fly my solo flights?

The reason I ask - I want to know if my time flying solo counts as PIC time toward my commercial requirements.

Solo time is always PIC time. You're alone in the aircraft, so who else could be PIC?

14 CFR 61.51(e)(ii):

  (e) Logging pilot-in-command flight time. (1) A sport, recreational,
  private, commercial, or airline transport pilot may log pilot in
  command flight time for flights-

  [...]

  (ii) When the pilot is the sole occupant in the aircraft;


Do glow plugs face fouling? Do glow plugs face fouling? I understand that spark plugs foul on occasion, do glow plugs face the same issue?

Fine wire glow plugs, vulnerable to fouling, are not used on manned aircraft.  Glow plugs in most diesel engines have massive elements where the coil is protected from being fouled.


What is the noise level inside the Tu-114's passenger cabin? Was the Tu-114 as noisy inside the passenger cabin as the Tu-95 bomber was said to be?

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.


Where can I find Boeing 777 safety records? I have booked flights for our family to travel Australia - Europe return with EK.  My nine year old son is an aviation geek and since learning some details of the EK B777 crash in DXB (and also the OZ 214 crash)   he has become very concerned about flying B777.  I took that into account when booking flights and booked A380s all the way through (booked with QF due to airpoints but EK flights) but since booking the DXB - PER flight is now showing as a B777-300ER.  He is in tears and refusing to fly on it.  He is prone to some anxiety and is adamant that he won't be getting on the B777.

Is there anyone that can alleviate his fears?  I have read and read articles out to him (which is how I ended up here) but he won't hear any of it.

My only hope is if someone with actual knowledge can provide some safety information that will convince him that it the B777 is a safe aircraft.

Many thanks in advance.

The Boeing 777 has an excellent reputation when it comes to safety.

Just under 1500 have been built which have accumulated more than five million flights and 20 million flight hours.
Only 6 aircraft have been lost in a accident, which is a really low number considering the number of aircraft and flights.

Moreover, of those hull losses, at least one (MH17) was due to a criminal act which cannot be attributed to the safety of this specific aircraft type.

Of the other 5 hull losses:

One cause is unknown (MH370).
One (MS667) was caused by fire while the aircraft was at the gate. No fatalities.
Three crashes were during landing.

Of the three crashes during landing:

One (BA038) is caused by ice in the fuel system which clogged a filter. The filter has been redesigned and can no longer cause a problem. The accident did injure 47 people, there were no fatalities.
One (OZ214) was caused by the pilots committing a number of minor and major errors during the approach to the airport. It can hardly be attributed to the aircraft type. The crash resulted in only 3 fatalities, which is remarkable considering the violence of the crash and amount of damage to the aircraft.
The last accident (EK521) caused no fatalities among the passengers but the cause of the accident is still under investigation. So far, the  Investigation  is  working  to determine  and analyze  the  human  performance  factors  that  influenced  flight  crew  actions  during  the  landing and attempted  go-around. The investigation has revealed no  Aircraft systems  or  engine  abnormalities  up  to  the  time  of the  Accident.

Combined you can see that the aircraft has performed an enormous number of flights with very few severe accidents and very few fatalities.

It is considered as one of the safest aircraft around.


What should be my basis for selecting an airfoil? We're in the process of designing a trainer aircraft and I wanted a high wing aircraft. We calculated this from the profile graphs given on the reports.I know these aren't super accurate since I just projected the values from the graphs.
Don't  mind the highlights

For trainer aircraft, the major design driver in wing profile selection is stalling behaviour. Ample warning, docile & progressive stall, no sudden surprises. Stall behaviour must be demonstrated during certification. From Torenbeek:

  The stall should preferably be characterized by a distinct and initially uncontrollable nose-down pitching motion, and during recovery to level flight it must be possible to prevent angles of roll and yaw of more than approximately 15 degrees (light aircraft)..

The NACA 4- and 5-series have been around for a while and there has been much experience with the application of them. Again from Torenbeek, fig 7-12:

Four-digit

  The NACA four-digit wing sections ... are by no means low-drag profiles, (but)
  the drag increase with lift is fairly gradual. The cambered sections have rel- atively high maximum lift and the stalling is fairly docile.

  In view of the gradual changes in drag and pitching moment with 11ft, the 4-digit sections are frequently used for light trainers, which often fly in different conditions.

Five-digit

  The NACA 5-digit wing sections ... have the highest maximum lift of the standard NACA sections, but the stalling behavior is not particularly favorable and rather sensitive to scale effects.

This can be seen in the $C_l$-$\alpha$ curve B above, which drops off suddenly and dramatically after max $C_l$

NASA report CR-1646 has more information on the stalling behaviour of NACA profiles.


How fast does cabin air pressure leak after a total engine failure? When an airliner loses all engines while at cruising altitude, two things happen:

The plane is a glider. It will descend no matter if you want to or not.
The cabin pressure is no longer maintained. Although the valves are closed automatically, they are not air tight - air will slowly leak out until the air pressure is equal to the atmospheric pressure outside.

My question is, which one happens faster? Are the valves able to maintain cabin pressure until the plane has descended to 10,000 feet, or will the oxygen masks deploy before the pilots can complete their descent at best glide speed?

EDIT: For the purpose of the question, let's assume it's s fuel exhaustion and ignore the APU. I'm specifically interested to know if the crew would encounter a situation where they have to choose between oxygen and best glide.

The valves will not be able to maintain cabin pressure until the plane descends to 10,000 feet at best glide speed. The oxygen masks will deploy before then.

At least that was the case for Air Transat Flight 236, an A332 that ran out of fuel over the Atlantic and glided to a deadstick landing. The occurrence report on page 96 (see the table) estimates that oxygen masks deployed at 06:37:50, when the cabin altitude reached 13,500 ft. This was about 11.5 minutes after fuel exhaustion, and only 7-8 minutes before landing at 06:45. So they would have landed within the 10 minutes of supplemental oxygen. Even a much longer glide would have allowed them to descend below 10,000 ft before the supplemental oxygen stopped. TSC 236 is AFAIK the longest glide in a transport category aircraft to date, so if they did not "encounter a situation where they have to choose between oxygen and best glide" (to use your phrasing), then probably no one else did either.

Note: The report used the 'worst case' leak rate of 700 ft/min for their calculation. The footnotes explain that the leak rate would decrease as the aircraft descended (because the pressure differential between the cabin and the outside would decrease as the aircraft descended). If anyone is interested, there is more info on pages 28-29 of the report about the cabin pressurization.


What happens if the crew do not set a FLT ALT in the cabin pressurization panel and leave it at zero but AUTO is still selected? On the 737NG, will the cabin maintain a lower altitude than the plane or will cabin altitude equal aircraft altitude?
Will there be ANY cabin pressurization or none at all?
When will the HORN sound?
I know this is extremely unlikely to happen but am posing the hypothetical question in order to better understand how the system works.

Consider a similar scenario: the crew selected 28,000 feet, cruised at 28,000 feet, but then step-climbed to 34,000 feet without selecting the higher altitude for pressurization.
The crew operating manual makes no mention of either scenario, unless you read between the lines. The way I tackled those scenarios is by referring to the controller logic in the manufacturer's patent from 1981 (the same digital controller was optional on the 737 Classic):

When the cruise altitude controller senses that the aircraft altitude change is within selected limits [when approx. 1,000 feet below FLT ALT], the system clamps to a scheduled value of cabin altitude [see second note below] (...)
If the aircraft cruise altitude drifts sufficiently to exceed ±500 feet from the altitude at which cruise control was imposed, the cabin altitude simply unclamps and the cabin climbs or descends at a predetermined rate under the control of central processing unit 54. (...)
Central processing unit 54 computes the differences between the pressure altitude and the value of Hcruise-clamp once per minute. If that difference exceeds the predetermined valve Hcruise-clamp is assigned the value of the pressure altitude.

Based on that, after leaving the ground mode (or lower cruising altitude), the controller will still pressurize the cabin – but not in reference to the DP schedule when cruise is reached (see second note below).
During descent (based on both the crew operating manual and patent), the controller will engage the off-schedule descent mode – landing altitude being the same as the departure airport altitude that was automatically sensed and set in ground mode – the crew will be alerted to that.

Notes:

In newer planes the pressurization controller is simply fed this data from the FMS (CDU or MCP entry).
Unlike other jetliners that maintain a cabin altitude with varying differential pressure (DP) for comfort, the 737 maintains a DP based on altitude blocks (consistent structural loads) when the FLT ALT is set. If you don't have the manual, b737.org.uk covers that part and offers a good system description.


What's This Cable Connecting Cockpit to Vertical Stabilizer in Air Tractor AT-401? This is a picture of an AT-401 Sprayer Airplane

I was wondering what's this steel-string stretching from cabin's windshield to the top of the vertical stabilizer
...

The wire shown is a cable deflector which is part of a Wire-Strike Protection System common on most agricultural aircraft.

Wire-strike protection systems
As a last resort, when pilot situational awareness and on-board systems fail to detect a wire in sufficient time to avoid contact, a passive wirestrike protection system (WSPS) may protect the aircraft from the consequences of a wire-strike. These are designed to cut or deflect wires away from an aircraft. The types of WSPS vary depending on whether the aircraft is fixed-wing or rotary-wing. They have proven to be an effective safeguard by extensive testing and over two decades of use by both military and non-military operators' worldwide (Jackson, Boitnott, Fasanella, Jones & Lyle, 2004; RAAF, 1 997). However, to enable the WSPS to operate effectively, the wire must contact the cutter at an appropriate angle and the aircraft must also have adequate forward speed. This combination of circumstances may not always be present during low-level aerial operations.
WSPS for fixed-wing aircraft are designed to cut wires that could pass under the aircraft, in order to prevent the wires from coming into contact with the landing gear, or pass over the aircraft, possibly contacting the tail section. Serrated deflection wires may also be fitted from the cabin to the tail section, with the purpose of cutting the wire or lifting it over the tail section. Fixed-wing aircraft used in aerial agriculture operations have had WSPS fitted as standard equipment for several years.
Fixed-wing aircraft used for other purposes rarely carry WSPS as fitment often requires reinforcing parts of the aircraft and may cost several thousand dollars. In general, they are not fitted unless it is expected that the aircraft will spend many hours in low-level flight.


Does anyone know more about the 1958 Heinkel-211 project? Industria Aeronáutica Argentina worked in the 50s in a Jet airliner, Kurt Tank design, the IA-36, 'Cóndor', with simmilarities to 1958 Heinkel-211 project, turbines intake aspirating fuselage boundary layer as some Messerschmitt wartime fighter projects, eg, Me P-1110.
Impossible finding web info about Heinkel airplane, image is from 'Flaps' an Spanish magazine for young aviation enthousiasts. More info?
Blessings +


Finding Angle of Attack/Angle of Sideslip using East/North/Up Coordinates I've got a set of data that includes:

x rate, y rate, z rate (all ENU) which I'll call xd, yd, zd.
roll, pitch, yaw (which I'll call ϕ, θ, ψ)
roll rates, pitch rates, yaw rates

I'm looking at some math that is meant to convert these values to AoA and AoS, but I'm having trouble understanding exactly what's going on.

As far as I'm aware, this is basically just taking euler angles and making a rotation matrix and using that to find u,v,w. But I'm having trouble verifying the accuracy of this work (it was done by someone who is no longer with the program.)

What you've proposed is a reference frame translation of the aircraft velocity, so instead of the velocity referenced to East, North, and Up (ENU), it's referenced to the direction the aircraft is pointing.  That gives you components of aircraft velocity along the nose, across the wing, and towards the ground. (You can find more details on these conversions by Robert Stengel).  It seems like using velocity across the wing and along the nose you should be able to figure out sideslip, but this approximation only holds in situations where wind is much smaller than true airspeed.

You're assuming here that the motion of the aircraft relative to earth equals its motion through the air.  That means your equations may give an unusual angle of attack when there's simply an unusual vertical wind component, or may report the drift angle as the sideslip where there is no sideslip.  This assumption of zero wind may be valid for rough approximations or in cases of severely limited sensor suites like a low-cost UAV.  This approximation is especially good at high true airspeed, low wind, or if you only care about AOA and AOS derivatives (e.g. for yaw damper control).  However there are some cases where this approximation clearly isn't reliable:

Windshear can result in a dramatically higher angle of attack than expected
Gliders use warm rising air to ascend without the loss of energy that would be anticipated if you're looking at only velocity and pitch
Horizontal surface winds in many places are over 30 kts, and can be much more in the jet stream. (see a wind map for examples).  Many aircraft can land in over 10 knot crosswind component, which your formulas would estimate as a ~10 degree sideslip.

Non-negligible wind is the reason that other methods of estimating AOA are used in practice, such as model-based angle of attack using inertial measurements (sometimes called synthetic air data) is sometimes used instead.  This is the reverse of what you typically do in an aerodynamics course- instead of using known angle of attack and airspeed to find normal and longitudinal acceleration, you're using known accelerations to find angle of attack and airspeed. Ardupilot has an option to do this based on this paper by Joseph E. Zeis, Jr. Another potential alternative implemented by Tor A. Johansen, et al, in addition to inertial measurements, uses airspeed during turns to estimate the constant wind.

Keep in mind there aren't a lot of cheap AOA sensors for a reason besides manufacturing costs: angle of attack is important, but has limits on its practical applications as AOA cannot be considered in a vacuum.  It's usually more important to know your airspeed or acceleration. For example, at high speed if you attempt a high AOA maneuver, the aircraft will rapidly decelerate, and you'd have to lower the nose to prevent the AOA from going into a stall condition. Other limitations are described here.


Has Airbus planned to build a larger version of the A380? The current Airbus A380-800 could carry over 800 people. Has Airbus planned to build a new, larger version that could carry 1000 or more passengers?

Has Airbus planned to build a larger version of the A380?

Yes,

In 2012 they planned to build a larger version of the A380.

"Airbus says 1,000 seat A380 due 2020"

However, manufacturers do change plans from time to time, sometimes in response to market conditions. "Has planned" is not necessarily the same as "is planning". Those plans are not currently (8 Jan 2015) being pursued and consequently, as time goes by without a resumption of those plans, it is increasingly likely that any target dates in those plans may no longer be attained.

If you want to know do Airbus in January 2015 have active plans to build a larger version of the A380 - that would be a new question.