In what ways do air traffic controllers communicate with pilots in class A airspace? I know they use two-way radio, but is that the only communication pilots receive from air traffic controllers? Also, in general in class A airspace, how often do pilots hear from air traffic controllers?

Methods

VHF radio is one method. HF is used in oceanic areas, but it is in decline.

Data comms are also used, it's called CPDLC (Controller–pilot data link communications). The ATC sends a digital message to the pilot, and they respond the same way.

Too Much Static Noise (HF)

On long flights, the controller can grab the crew's attention by poking them using SELCAL. Too much static noise for a long time is tiring to listen to.

Chatter

Most of the chatter is handing off the plane from one controller to another.

If there's bad weather en-route, the pilot will ask to deviate. That's another type of chatter.

Also climb, step-climb, and descent instructions.

Changes to route are also relayed.

When flying over areas not covered by radar, position reports are also provided by the crew and confirmed by the controllers.

PIREP's—or pilot reports—often include information like "watch out there's icing, tell the folks behind me."

Traffic separation instructions and traffic advisory information are also quite common.


Why are only some aircraft in this formation creating contrails? The Republic Day celebrations at New Delhi, India had a series of flypasts by the Indian Air Force.

What struck me the most was that in a formation with a C-17 in middle and two Su-30MKI flanking it, there were contrails visible from the Su-30MKI but not from the C-17:

Both the C-17 and Su-30MKI have turbofan engines. For C-17, Pratt & Whitney F117-PW-100 and for Su-30MKI Lyulka AL-31.

As per 'How does contrail formation differ from turbofan to turbojet?', contrails depend on the bypass ratio of the turbofan engine:

  (...) higher bypass engines available today increase the contrail occurrence.

As per available sources, the F117 has a bypass ratio of 5.9:1 and the AL-31 has a bypass ratio of 0.59:1. So, the F117 has higher bypass compared to the AL-31 (or maybe I'm wrong).

What would be the reason that in the first two photographs, the C-17 engines do not form contrail whereas the Su-30MKI seem to?

One possibility is that, this difference is due to possible different power settings on the two aircraft engines for the same speed (considering the different intended role).

Another thing was that such contrails were not visible on any other fighter aircraft (e.g., Tejas/LCA). Or even another pair of Su-30MKI along with a AEW&CS aircraft:

Notes:

Sorry for the poor quality of photos due to the poor visibility in Delhi (winter fog/smog).
Some photos are here:

thequint.com
blogs.wsj.com
indiatimes.com

This 'party trick' is covered nicely on metabunk.org.

  [It's the Su-30's] ability to inject unburnt fuel into the exhaust plume via the afterburner system. The super hot air of the exhaust instantly evaporates the volatile fuel, and then when it mixes with the cold air behind the plane the fuel reforms as a fine mist, essentially a fuel smoke cloud.

(YouTube)


Is it acceptable to use VNAV data in lieu of localizer recommended altitudes? My airline's vertical navigation data isn't certified for use and is considered 'advisory' only.  But, 90% of the time it provides highly accurate data.

Some instructors at my company contend that 'localizer recommended altitudes' are required to be used as the primary / only reference for a CANPA style continuous descent to our DDA (derived decision altitude) on localizer approaches.

I contend that any method chosen for a descent to DDA is purely technique and as long as our advisory VNAV data is backed up with other data & looks accurate, there's nothing wrong with using it.

Are localizer recommended altitudes regulatory in any way?  Is it legal to use an 'advisory' Vnav data to fine-tune your descent from the FAF to DDA? Any links, references, or regulations you can point me to on the subject would also be greatly appreciated.

If your company uses CANPA (continuous descent) approaches, the whole point is using artificial VNAV on non-precision approaches where no vertical navigation is part of the approach. This involves determining a DDA, or derived decision altitude, based on the published minimums and some other criteria. Arrival at the DDA requires a go-around just like if you were arriving at a DA on a precision approach.

In defense of your point, if you aren't using any form of vertical navigation, one might argue that it's no longer a CANPA approach at all. How can be maintain a constant angle without vertical nav?

Then again, if you are flying the CRJ a localizer approach would involve having the Proline 4 in "green needles." Advisory VNAV only works in "white needles," so if they're saying you shouldn't use advisory VNAV on a localizer only approach that might be the reason. You can't.

In reference to the main question in the title, you can't use advisory VNAV "in lieu" of the published minimums or minimums derived from your company regulations, but if you want to use advisory VNAV to plan your descent to the appropriate minimums, that's okay unless specific language in the company manuals forbids it.


How to decide which aerodromes should have Electronic Terrain and Obstacle Data? What is the meaning of "aerodrome that is regularly used in international civil aviation"?

Is there any explanation or reference material in support of Aeronautical Information System (AIS)?

I found several things in Eurocontrol document but there is no exact explanation and solution to decide which aerodromes should have Electronic Terrain and Obstacle database.

An aerodrome or airdrome is a location from which aircraft flight operations take place, regardless of whether they involve cargo, passengers, or military. Aerodromes include small general aviation airfields, large commercial airports, and military airbases.

  An airport is an aerodrome with extended facilities, mostly for commercial air transport. Airports often have facilities to store and maintain aircraft, and a control tower. An airport consists of a landing area, which comprises an aerially accessible open space including at least one operationally active surface such as a runway for a plane to take off or a helipad, and often includes adjacent utility buildings such as control towers, hangars and terminals. Larger airports may have fixed-base operator services, airport aprons, taxiway bridges, air traffic control centers, passenger facilities such as restaurants and lounges, and emergency services.

With this definitions of aerodrome and airport from Wikipedia, we understand that all airports are aerodrome but not all aerodromes are airport i.e. airport is a subset of an aerodrome.

The Civil Aviation Safety Authority under CASR part 139 classifies the Aerodrome into below categories:

Certified Aerodromes
Registered Aerodromes
Other Aerodromes - more than 9 but not more than 30 passengers
Other Aerodromes - operations under proposed CASR part 135


Can i get A&P course materials in .pdf format? I would be very grateful if you provide me any material about A&P basic course for mechanics.

Go here for the PDF material.

Aircraft Handbooks & Manuals


What is the meaning of sub-paragraph 3-9-6 j. in FAA JO 7110.65X? In JO 7110.65X, section 3-9-6(j) says in reference to the 3 minute rule:

  j. Separate an aircraft behind another aircraft that has departed or
  made a low/missed approach when utilizing opposite direction takeoffs
  or landings on the same or parallel runways separated by less than
  2,500 feet by the following minima:

  Heavy, large, or small behind super − 4 minutes.
  Heavy, large, or small behind heavy − 3 minutes

Do you think this applies to an aircraft in the pattern making approaches to the runway in use after a heavy departs opposite direction?

If you search for the words "opposite direction" in the order it seems clear that they simply mean what they say, e.g. 3-9-7(a)(1):

  Separate a small aircraft weighing 12,500 lbs. or less taking off from
  an intersection on the same runway (same or opposite direction
  takeoff) [...]

This is confirmed in JO7210.3AA, Facility Operation and Administration:

  2−1−31. OPPOSITE DIRECTION OPERATIONS

  Opposite Direction Operations consists of IFR/VFR Operations conducted
  to the same or parallel runway where an aircraft is operating in a
  reciprocal direction of another aircraft arriving, departing, or
  conducting an approach.


Does the flight crew in big airliners hear the cabin crew PAs? In big airliners, does the flight crew hear the PAs the cabin crew is doing to the passengers, e.g. on their headsets? If not, how do they make sure they’re not talking simultaneously to the passengers?

Yes, when the pilot makes the selection to speak on the PA, he will hear if anyone else is using the PA. They would just wait until the other party is finished, or they can take priority and speak over them.


Why are military drones shaped so strangely? Military drones, such as the Predator drone or the Global Hawk, tend to have a weird shape with a whale-like head, and engines concentrated at the back. The wings tend to be of very high aspect ratio, and v-shaped tails seem to be popular:

Why aren't there, say, Cessna-shaped drones? If Cessna 172s work fine for human pilots, why not for computer pilots? The Cessna 172's low speed and stability also seems like a good asset for military recon drones.

The whale-shaped forward fuselage covers a parabolic antenna for a high-bandwidth datalink. The operators want to receive the reconnaissance data in real time, and by giving the antenna the best place in the aircraft, it will be able to connect to communications satellites even when they are just above the horizon.

Global Hawk cut-away drawing (picture source)

The V-tail of the Predator is an inheritance from its origins as a Navy drone which could be folded to fit into a torpedo tube. Read all about it in this answer. If you want more info on the benefits of an inverted V-tail, make sure you read KeithS's answer, too.

In the Global Hawk the V-tail was chosen to mount the engine above the fuselage for better IR shielding from below. The two tail surfaces also shield the exhaust from the side without affecting aerodynamics negatively.

The Aerosonde's configuration was chosen after Tad McGeer had experienced in 1990 from the 1/5th scale RC model of the Perseus UAV of Aurora that a tail-mounted propeller would stabilize the aircraft to the point that it became practically uncontrollable. A pusher propeller is more efficient than a tractor propeller, which also explains the propeller location on the Predator.

If it strikes you how many of the UAVs have V-tails: This allows to use fewer components (surfaces, connectors, actuators), and since all are moved by computer control, the issue of a mechanical mixer does not exist. The lower damping of V-tails can also be easily tolerated, since the FCS can react much more quickly and commensurately to disturbances than any human pilot. The lower maneuverability possible with V-tails is also not an issue - reconnaissance UAVs fly mostly straight and level.

The high aspect ratio wings are helping in extending the range and especially the flying time of observation drones. Similar to glider wings, the long and slender wing will offer the lowest drag for a given lift at subsonic speed.

In the end, each detail has been chosen deliberately and can be well explained. There is no conspiracy to make UAVs look different from Cessnas.


How do I properly report sighting a drone or hobby UAV to ATC? How would one go about reporting a drone (hobby UAV) sighted in the airspace of an airport on frequency, specifically to Tower?

For example: I am doing patterns around the airport when to the northeast of my nose I see an object flying through the airport field, looking as though it is a drone entering the airport. What is my responsibility in this situation?

Great question, and I'm not sure there is an entirely established procedure for this yet, as drones are still a relatively new development.

First, your responsibility as a VFR pilot is "See and Avoid".
So if you think its headed towards you, maneuver to avoid it (provided you're not making dangerous, drastic moves!)

Secondly, I'd report it to the tower as:
"Bay View Tower: N227TW:  I see a drone in the airspace, my 2 o'clock, slightly below, less than one mile, headed towards the airport"

At best, the tower may be able to say they're already talking to the drone operator.  Otherwise, tower may simply say, "Roger: keep me updated, deviate from the pattern at your discretion"


Does Rolls Royce produce any engine that matches the capabilities of the GE9x? Does Rolls Royce produce any engine that matches the capabilities of the GE9x?

If not, does Rolls Royce have any public plans for such an engine in the future?

First let's talk about thrust.  Jet engines are designed for very specific thrusts for every specific applications.  For example, look at the GEnx-1B versus the GEnx-2B.  The Boeing 787-8 has GEnx-1B engines rated for ~70k lbf takeoff thrust.  At about the same time as Boeing was developing 787-8, it was also developing the 747-8.  That plane needed slightly less thrust per engine, about 5% less. Boeing could have just put the GEnx-1B on that plane.  But they didn't. Instead they had GE develop the GEnx-2B, rated for 66.5k lbf thrust.  They did that because an engine that had five percent too much thrust was a completely unfeasible option.  The GEnx-2B is smaller and several hundred pounds lighter.  So my point here is that RR is never going to develop an engine the size of the GE9X unless they have a very specific contract for a plane that needs exactly that much thrust.  Every engine RR makes is going to be sized exactly as big as it needs to be and no bigger.

RR certainly could make an engine that big if they had a contract to do so.  If you know how to make an engine that produces 70klbf of thrust, you know how to make an engine that produces 100 klbf of thrust.  Just make everything a little bit bigger. Turbomachinery is not perfectly scaleable, so just because you know how to make an engine with 100 lbf of thrust does not mean you know how to make an engine with 100,000 lbf of thrust.  But from 70k to 100k is not a big leap. Definitely within their capability.

As for everything else, I'd say just look at the market share. There's some interesting statistics here.  http://www.alafco-kw.com/upload/Media_Library__March_2016____Aircraft_Market_Report__March_2016__921.pdf

For example: RR has 59% of the A330 market, a plane on which there are 3 different engine options available (GE, RR, P&W).  RR is certainly behind GE on the 787, but not by a lot.  And RR has an exclusive contract on the A350.  Overall RR is competitive in the market versus the other manufacturers. If RR was "losing out in the technological advancement", you would see this reflected in their market share, but this is not what is happening.


what are the advantages and disadvantages of tilt rotor vs ducted jet engine for a VTOL aircraft? Please could someone summarize the main advantages and disadvantages of a tilt-rotor (the V22 Osprey) vs jet (F35) system for VTOL. I have been trying to look into this but found details very sparse and not in comparison to each other.

Among other advantages and disadvantages I am very interested in

speed
energy efficiency
ease of maintenance and why.

Well, engines and rotors obey the same laws regarding induced drag (induced power in this case) as wings: larger fan/propeller/rotor is more efficient, but limited to lower speeds. And from that, the advantages should be obvious:

Tiltrotors (V-22, AW609) are only a little less efficient in hover than normal helicopters, but they can only go around 300 knots (both aircraft have max speed quoted at 275 knots); above that, the tips would become supersonic and generate too much drag.
These can be built with engines similar to what a comparable fixed-wing turboprop aircraft would need and can cary comparable payloads with only slightly higher fuel burn. The AW609 is a product for civilian market aiming at charter operators supplying oil platforms and similar remote stations where it should be more efficient than helicopter.
The main disadvantage is that they are more complex and therefore more expensive to build and maintain.

Tiltjets/vectored thrust jets (VJ-101, Harrier, Yak-38, F-35B) are horribly inefficient in hover, but they can go fast.
Jet engine for thrust/weight ratio 1 (needed for hover) takes up most of the aircraft, leaving very little room for payload. Such design and thrust/weight ratio is common in fighters, but out of question for anything else.
This configuration also consumes a lot of fuel for take-off and landing. Absolutely no way would anything like that be competitive for commercial operation. However, the military is willing to pay it if they can have a fighter jet that can be deployed from an assault ship. And even they prefer conventional aircraft when possible.
This is really niche design, but one that offers enough tactical advantage that the Marines and the Royal Navy want it (US Navy will use the conventional F-35C with CATOBAR, Royal Navy decided it will be cheaper to use the STOVL F-35B version than upgrading the carrier they are building to CATOBAR).

I can't really compare maintenance. Obviously both are more complex than conventional aircraft and even than helicopters. But also, anything military is usually much more maintenance intensive than civilian designs, because military usually wants to squeeze out every bit of performance at the cost of simplicity.


Should reliance on Auto-Flight Systems continue to increase in favor of manual flying skills? In recent years there has been ongoing debate as to whether or not increased reliance on auto-flight systems (autopilot, auto-thrust, etc.) in favor of manual flying proficiency has had a negative impact on safety.

Are there any data or objective examples supporting either position?

The FAA certainly believes that manual flying skills are eroded in an airline environment, although to what degree is unclear. SAFO 13002, Manual Flight Operations, says:

  Autoflight systems are useful tools for pilots and have improved
  safety and workload management, and thus enabled more precise
  operations. However, continuous use of autoflight systems could lead
  to degradation of the pilot’s ability to quickly recover the aircraft
  from an undesired state.

The SAFO is very brief, but there's a little more information in this document from the Air Carrier Training Aviation Rulemaking Committee (ACT ARC):

  The Flight Deck Automation Working Group (FltDAWG) identified that the
  lack of practice with automation has contributed to the degradation of
  manual flying skills. European Aviation Safety Agency (EASA) safety
  information bulletin 2013-05 comments that continuous use of automated
  systems does not contribute to maintaining pilot manual flying skills.

That document references a 2014 NASA study called The Retention of Manual Flying Skills in the Automated Cockpit. Its conclusion was:

  We found that while pilots' instrument scanning and aircraft control
  skills are reasonably well retained when automation is used, the
  retention of cognitive skills needed for manual flying may depend on
  the degree to which pilots remain actively engaged in supervising the
  automation.

The detailed analysis showed that motor skills are generally not degraded much (e.g. hand flying approaches) but cognitive (mental) skills like navigation and visualization are much more significantly affected:

  Pilots sometimes struggled to maintain an awareness of where the
  airplane was with respect to the planned route, to reference their
  charts to keep track of what came next, to configure the airplane anew
  as they passed each important waypoint along the planned route, and to
  recognize and deal with instrument systems failures when they arose.

At least based on that information, it appears that the physical activity of manual flying isn't badly affected by automation, even flying on instruments. The risks that NASA found seem to be broader and related to mental awareness and alertness, including the ability to troubleshoot.


What is the most cost effective way of combining an instrument and multi engine check ride? I have a single engine land commercial without an instrument rating. I am currently completing the instrument rating. Now if I need a single engine and multi engine commercial with instrument ratings, what would be the most cost effective way of going about this?

The cheapest way (I'm talking Canada here) is to do the basic instrument training in the single, then do the multi rating and check ride separately, then the do some practice approaches and emergencies in the twin and multi simulator to prepare for the multi-IFR checkride , and do that.  There's no point in doing an SE check ride.  When I did it some years ago I bit the bullet and did almost of the air time in a Seminole because I was uncomfortable with going into a multi-IFR checkride with maybe only 15 hours in the twin, and the kind of sims available today didn't exist.

Go to a school that has one of those Red Bird motion simulators or equivalent and take maximum advantage of the portion of the training that can be in a sim.  That'll save a ton of money.

Also use MS Flight Sim or Xplane to practice practice practice at home.  It is a very powerful tool if used properly.  By "properly" I man make sure the stuff you practice on your own is being correctly done, and are not reinforcing incorrect stuff.


What is the typical fatigue life of a helicopter airframe? For military helicopters such as the Sikorsky UH-60 Black Hawk, what is the typical fatigue life of a helicopter airframe (in cycles and hours) ?

Typical helicopters do not have cycles or hours limits on the non-dynamic components.

Since they are not pressurised, there is no concept of "cycles" and the fuselage is neither stressed, nor subject to the same kinds of forces that airliners are.

They are inspected on fixed hours cycles and specific types might have areas which are subject to non-destructive testing in accordance with operator, manufacturer or regulatory instructions.  Some, most notably Robinsons, are rebuilt by the manufacturer on hours based cycles and return as new.  However, the fuselage and it's major components are not replaced.  They are inspected and refurbished.

The dynamic components are of course lifed but I see that you have a separate question for that.


Am I required to report entering the hold in lieu, persuant to the IFR mandatory reporting points? You are cleared for the RNAV (GPS)-A approach at 0S9.

You are cleared direct JIGEB then at or above 3200 to YAYUB then cleared RNAV GPS A.  You are not asked to report anything.  Upon arriving at YAYUB you perform a parallel entry to the hold reverse course and the proceed inbound.

If this was a procedure turn I am not required to report the procedure turn unless ATC requests it.  However, this is a hold in lieu of a procedure turn.  Am I required to report entering the hold persuant to the IFR mandatory reporting points?

If you're in radar contact with ATC, the answer is no, you will not need to report it unless requested to.  If you are not in radar contact (which would be unusual as that is in Class E airspace) you would not have to report your position entering the hold at YAYUB unless you were instructed to hold at this point with an EFC time.  From the AIM 5-4-9

  When a holding pattern replaces a procedure turn, the holding pattern must be followed, except when radar vectoring is provided or when NoPT is shown on the approach course. The recommended entry procedures will ensure the aircraft remains within the holding pattern’s protected airspace. As in the procedure turn, the descent from the minimum holding pattern altitude to the final approach fix altitude (when lower) may not commence until the aircraft is established on the inbound course. Where a holding pattern is established in-lieu-of a procedure turn, the maximum holding pattern airspeeds apply.

But 5-4-9 also states that

  If cleared for the approach prior to returning to the holding fix, and the aircraft is at the prescribed altitude, additional circuits of the holding pattern are not necessary nor expected by ATC. If pilots elect to make additional circuits to lose excessive altitude or to become better established on course, it is their responsibility to so advise ATC upon receipt of their approach clearance.

You would have to report leaving YAYUB inbound and to report crossing WIKUV FAF inbound as well.


How are Virgin Galactic's SpaceShipTwo's windows so large? From Virgin Galactic on SpaceShipTwo:

  Windows in the passenger compartment will be 13 inches (33 centimeters) wide by 17 inches (43 centimeters) tall.

IMO that's enormous for an airplane, especially for a spaceplane! But, wouldn't such large windows cause problems? The Concorde had particularly small windows (passengers say that it's almost passport book sized) to maintain the integrity of the airframe and cabin pressure if a window happened to crack at 60,000 feet AMSL.

But wouldn't such a large window cracking at 110 km AMSL on SpaceShipTwo definitely cause cabin pressure to equalize to atmospheric pressure in seconds? What redundancy does SS2 have to prevent catastrophe in such an event?

Here are a few ideas:

First and foremost, we're not handling metals here. Composites have the advantage of being able to be made stronger by adding on a few layers around high-stress area like windows. This was difficult with metals since this needed some sort of fasteners or adhesives to do. This reinforcement is seen in the photo below.
The windows are designed to keep an even pressure all around in the context of the fuselage shape at that point. You'll notice the flange design which keeps the fuselage shape and stop it from popping open. This is a little like the thicker part of a bottle neck. This is very difficult (if possible) to do well in a metal fuselage to this extent.

(source: msn.com)

The usage is completely different. Concorde was a commercial aircraft, intended for many years of operation. This is a very low-cycle aircraft which will see a fraction of that flying. The number of pressurisation cycles is a lot lower, putting much less force on the windows.
As for safety, the style of flying is completely different. Probably flown by test pilots, the aircraft might never even experience rain and will fly under very predictable conditions, with very few flight cycles.
Periods of elevated temperatures gradually degrades many materials, this is much less a concern with short flights. If I gather correctly this is the main issue with sustained high-speed flight, as seen on Concorde and SR-71 and other aircraft.

(source: guardian.co.uk)

Composites have a lot lower thermal expansion (CFRP vs. Aluminium is an order of magnitude lower) which reduces issues with expansion in the fuselage.
Concorde was a commercial aircraft with weight and operating price in mind. This aircraft is built for this purpose, with the windows considered as a main feature from the start. You could probably have been able to make the windows a lot larger on Concorde, at the unacceptable price of weight, production and operating cost.
Needless to say that knowledge of materials and structures has advanced substantially, all our these features can be modelled in detail on computers, not necessitating the traditional conservative approach.
As for redundancy, predecessor SpaceShipOne had double pane windows and double seals everywhere. For the passengers without suits, if a window were to blow entirely, you're most probably out of luck.


What is the purpose of a freewheeling unit in an helicopter, if a centrifugal clutch is already present? Some helicopters such as the Bell 47 are fitted with a centrifugal clutch.
Centrifugal clutch will engage only at certain engine RPM. If the engine fails, the engine RPM will reduce and the centrifugal clutch will disengage the rotor from the engine. So, why is an additional freewheeling unit needed?

the centrifugal clutch will only disengage after its rotating speed falls to the disengagement point. The over-running clutch disengages the engine from the rotor at the very instant that the engine's rpm falls below that of the rotor.

In this way, the rotor is never wasting kinetic energy by trying to turn over a dead engine and the vehicle stands a better chance of achieving successful autorotation.


Are there differences between the runway lighting on a land runway and on an aircraft carrier? How are the lights on aircraft carriers placed and are there differences to the color/position/number of lights at normal airports?

Yes, basically just (dim) Edge and Centerline lights plus the IFLOLS


Human-powered flight in vs. out of ground effect? There is an impressive flight (figure-of-eight) with a human-powered aircraft shown here:

Given the long wings of the Aerocycle 3, can it be considered to fly in ground effect for the whole flight?

Nothing wrong with that - the Ecranoplans are fascinating creations - but how much more power will be needed to lift it out of the ground effect, should it be desired?

Also, this thing is just screaming to be fitted with an e-bike powertrain...

Ground effect plays a role when the aircraft is within one wingspan of the ground, so the aerocycle is getting the benefit of lowered induced drag. It looks to be flying about a quarter of a span above the ground, so using the graph that is about two thirds of normal induced drag. Flying out of ground effect would therefore require about 50% more power.


What are the details of opening a cockpit door from the outside? Can one pilot lock the other out of the cockpit?

It is mentioned in the answer to the question I linked that a person inside the cockpit can stop a person outside from opening the door by "canceling the unlock process". This leads to several further questions:

How exactly does the person on the inside "cancel the unlock process" (Press a button, flip a switch, enter "counter code", etc...)
It seems there is a delay before the door opens. Is this correct? What's the duration of the delay?
What are the "authority levels" of codes? Which levels exist, what do they mean?
What is the confidentiality policy regarding those codes in theory and practice? (Who gets what authority level code officially? If stewards/stewardesses are not allowed to have the codes do pilots usually pass them on anyways?)

I'm going to explain this for the Airbus (also known as the Cockpit Door Locking System or CDLS):

  How exactly does the person on the inside "cancel the unlock
      process" (Press a button, flip a switch, enter "counter code",
      etc...)

If the code is entered for an emergency external opening, the pilot has 30 seconds after the request period to toggle the door button to lock to deny the request or the door will unlock. It pops back the the 'Norm' position automatically.

  It seems there is a delay before the door opens. Is this
      correct? What's the duration of the delay?

30 seconds, unless the lock button is pushed, in which case the request is inhibited for 5 minutes.

  What are the "authority levels" of codes? Which levels exist, what do
  they mean? What is the confidentiality policy regarding those codes in
  theory and practice? (Who gets what authority level code officially?
  If
      stewards/stewardesses are not allowed to have the codes do pilots
      usually pass them on anyways?)

There are indeed two codes, but I believe the normal access one is optional. The (optional) normal code just chimes the cockpit for an opening request, while a secret code to the best of my knowledge is shared among the crew to request emergency access. "There are two different access request types : “Routine” and “Emergency” access request." These are however internal airline policies and differ from airline to airline, and I've read in some cases that they might even have the same emergency code across the fleet. In any case, the pilot(s) can still decline access.

Here is a video about cockpit door as well.

Source, Page 37 onwards. While the source suggests that the time can be changed, most sources I've read refer to 5 minutes and 30 seconds as the standard times.


How can hang gliders and paraglider pilots prevent stall? Aircraft and gliders usually have instruments to measure air speed and angle of attack, which should be monitored to prevent stalling the aircraft.

However, it seems that most paragliders and hang-gliders lack such kind of tools.

How do the pilots avoid stalling without these kinds of instruments?

Paraglider pilots learn "active flying", whereby you use feedback from the wing to determine what's going on. You monitor the tension in both controls (the "brakes"), and the wing's attitude (if the wing pitches forwards then you feel like you are swinging backwards).

In bumpy air (such as on the edges of thermals, or in wave) active flying is used to keep the wing more or less above your head. If the wing surges forwards then you risk a collapse; if the wing falls back then you risk a stall.

In smooth air a stall is only likely if you are pulling the brakes down too far. This can happen accidentally, especially in nil-wind landings if you mistake your ground speed for airspeed.


Are passengers allowed to travel seatless(on the floor)? I was told that a flight in Europe carried two passengers on the floor, because their purchased seats didn't exist. BBC.

Is that allowed?

For example, in Greece, a bus is not allowed to travel with any passenger on the floor (or equivalently standing), so allowing a flight to do so seems surprising!

Passengers on commercial airliners (US, EU, Canada, most of the world) aren't allowed to sit on the floor because 1) they could block the aisles and emergency exits and 2) they cannot be buckled up, putting their and others lives at risk.

That does not mean it could not have happened, just if it did it was against regulation.

There are cases where commercial passengers may sit on the floor but they are rare, for instance parachuting.

EDIT: In the BBC article cited after the original post says that the passengers were given spare crew flip-up seats for take-off and landing, but had to sit on the floor the rest of the time so the crew could do their service. This is against regs as they would not have been secured against unexpected turbulence. The article says the following which proves my point:

  The Civil Aviation Authority says while passengers are allowed to sit
  in crew seats under certain conditions, they must not be left unseated
  during any stage of the flight.


What is minimal altitude that aircraft (rocket?) can fly above any country without any permission? What is minimal altitude that aircraft (rocket?) can fly above any country without any permission? I mean, at what altitude ends country's airspace?

Actually, what you're asking are two different questions- According to ICAO ( ICAO Annex 11: Air Traffic Services), Class G airspace is uncontrolled and aircraft can fly in the without ATC permission. The definition if Class G is left to the regulatory authorities of individual countries (in US, it is where the other airspace classes are undefined).

Where does the airspace of the country end is a completely different one and as of now, there is no agreed definition. The United Nations General Assembly Committe on Peaceful Uses of Outer space is still in the process of defining what exactly an outer space is.


What can ground personnel do in the event of in-flight depressurization? If the pilots, crew and passengers had all passed out from an unexplained result of gradual de-pressurization, and ground personnel were somehow aware of this scenario, would there have been anything that could of been done to save the plane and people before the fuel ran out?

No.  If the crew and passengers have all passed out due to lack of oxygen and the plane has not been commanded for a descent, they will never wake up.  This has happened before, e.g. the Payne Stewart fatal accident.  In cruise flight an autopilot is only commanded to perform lateral navigation and absent instructions from the crew to initiate a descent it will fly to its last fix and then maintain its current heading, all the while maintaining altitude.  When fuel is exhausted it will maintain altitude at the expense of airspeed until the stick shaker activates, disconnecting the autopilot.  Absent the pilots input, the stick pusher should next activate to forcefully prevent a stall.  You'll probably get some oscillations in pitch but ultimately a steep descent that even if the (literally) brain dead crew could somehow wake would not give them time to act.

While ground crews can get data from the airplane and can attempt to contact the crew, they cannot remotely control the airplane so the best they could do, if aware, is watch.  They could perhaps get a fighter scrambles to intercept and visually inspect the cockpit, but that still would not allow them to alter the outcome (just verify the scenario).

Note that this scenario is much more likely to happen in an extreme depressurization event in which the crew is unable to don O2 masks in time.  A slow gradual depressurization will give plenty of warning as the cabin begins to climb and automated sensors start complaining.  In the EMB-145 you'll start getting aural warnings when the cabin exceeds 10,000 ft pressure altitude and somewhere shortly above that you'll get master caution alarms and automatic pax 02 deployment.  These altitudes should give the crew ample warning before becoming hypoxic (you can reach these altitudes for limited time with no supplemental O2 in a Cessna 172 for example).  Even at cruise, it only takes a few minutes to get the plane back down to 10,000 ft and as such a slow gradual depressurization should not pose a threat unless multiple warning systems are malfunctioning.


Who has the authority between captain and first officer in emergencies? Yes I know, Captain has authority over First Officer.

I was reading about Airblue Flight 202 and according to the investigation, First Officer said these words 40 seconds before crash:

  Sir turn left, Pull Up Sir. Sir pull Up.

Although many sources have questioned the investigation and its subsequent report, because of several facts including how the captain with over 25,000 hours and an unblemished flight safety record could make such mistake when he is so much familiar with the terrain etc., my question isn't about that.

What I want to know is that in case of an emergency or a similar incident of an imminent crash (as mentioned above), can a captain order the First Officer not to touch anything, or ignores his warnings or simply not listen to him at all? What the First Officer has to do or can do?

Authority in the cockpit, especially in emergency, is very important in a principle called Crew Resource Managment, or CRM. A number of incidents similar to your example led to the formulation of this concept to enhance the coordination between the crew. The idea is that all crew members should be working together as effectively as possible to solve the problems at hand.

In emergencies, the crew need to be able to communicate. This means that the first officer should be willing to question the Captain, like they did in your example. They should also be willing to take action if they feel it necessary. However, communicating this action is also important, as evidenced in the crash of Air France 447, where the pilots were commanding different inputs.

Neither of the pilots should be ordering the other to do anything unless absolutely necessary. They need to get the attention of the other pilot, state the problem, say why it's a problem, and suggest a solution to the problem. Then they need to agree on a plan of action, and be clear about who is in control.

In your example, the captain's negative attitude may have prevented the first officer from saying anything more.  A better response from the first officer would have been to say something more along the lines of, "Sir, we are flying towards high terrain, we are not flying high enough to clear it. We need to either climb over it or turn left to avoid it. Do you agree?" This makes it clear to the captain what problem the first officer sees, and is clear about how the first officer thinks they should respond. It also includes a direct question for the captain to answer. Both pilots should be ready to communicate like this if necessary, and should also be making sure that they aren't creating an environment where the other pilot isn't comfortable with doing so. If the first officer still got no response, he should have been willing to take control, and should communicate to the captain that he is doing so, including the previously stated information about what actions he intends to take.


Is it possible to bluff one's way to the flightdeck like in Catch Me If You Can? I was watching some clips from Catch Me If You Can starring Leonardo DeCaprio as Frank Abagnale.

I was wondering- If brought a ticket on an airline today, came dressed up like a pilot, would you, be able to sit in the cockpit? (assuming pilots are normally allowed to jumpseat in that jurisdiction) Say you come onboard the plane and present them a fake ID at the door. Is there anything to prevent this from happening, or are we still as vulnerable to this type of trick like in the movie?

A lot has changed since the Frank Abagnale / "Catch Me If You Can" days, and riding as a non-revenue passenger (particularly in the cockpit jump seat) is no longer not as simple as grabbing a passable captain's uniform, polishing your shoes up, and smooth-talking the flight crew.

Someone seeking a ride in an airplane jump seat would still have to pass through airport security and prove their identity & authorization to occupy such a seat to the satisfaction of the crew operating the flight, which would likely include checking credentials that are at lease somewhat difficult to forge.

So in short it's possible – if someone is particularly adept at social engineering, forgery, and has at least a working knowledge of airport & airline security procedures they might get away with it – but it's extremely unlikely, and as has been pointed out the consequences if and when you get caught are particularly unpleasant these days.


Is this a glitchy ADS-B signal? I was looking through my virtual radar logs one of the days and found this "glitchy" ADS-B behavior.  I am almost 100% sure that this is not due to my antenna or setup since two independent different radars confirmed this weird behavior from FlightRadar24.  Also A/C before and after this one did not exhibit this behavior.

Does anybody have any thoughts as to what may be happening???
Why is the "skew" at seemingly same angle?  Is that anything?
In light of MH370, does this happen often, how reliable is that GPS data?

Tail # N657UA
Boeing 767-300
Typical route between EGLL and KORD

Time of occurrence is approximately: 3/16/2014 6:09pm CST

I have also verified FlightAware is ALSO showing the same weird glitch.

See below "yellow" highlighted airplane:

Same A/C from FlightRadar24:

UPDATE:

This seems to be related to THIS aircraft.  The explanations given (GPS->INS->GPS switching) still applies in my opinion, but wanted to give another screen shot.  Here it is today (3/30/2014) and again displaying this behavior - should their maintenance department be alerted to adjust their GPS antenna??

This is a classic example of fallback to INS. Most of the track data is coming from GPS. For some reason the GPS signal is lost momentarily causing a fall back to INS. The INS is offset by about 1km to the Northeast, which appears as a jump. Next position report is from the GPS again, in line with the original track. This happens several times.

In the transmitted data these spikes will be flagged as data of low integrity. This allows for filtering them out.


How does ATC handle tv coverage of police pursuits in the US? On YouTube there's a lot of aerial footage of US police pursuits to be found, usually filmed from news helicopters, flying around and doing a lot of maneuvering in the same small area, sometimes in the immediate vicinity of big airports.

Almost always there are more helicopters involved: Police and tv stations, you can sometimes see them crossing the camera view. And all of this time, essentially no one knows where things are going. The whole thing seems to me quite hazardous from an aviation point of view, maybe even more so than the proceedings on the ground.

How are these operations kept safe? Under what rules or procedures does ATC handle this kind of situations?

I know about the operations of police in South Pacific Area so I will answer from that point of view not the USA as is queried.

The Air Traffic Controllers have an agreement set up between the various Police Forces and themselves. This agreement allows them to operate in a covert capacity if required. When they do this special phrases and/or special call signs are used to give them higher priority.

When something like a chase or surveillance is being carried out the police helicopters are usually operating below the control steps. If not they will talking with ATC to obtain a clearance for either to operate in an area or for particular headings. I have seen clearances be issued that say Stay North of Road X Operate Below 1500 AGL.

If Police operations bring them near an airport, the Terminal Area Controllers or Tower Controllers will separate them from the other traffic. In fact this is very safe operations.

As to do with TV helicopters they have to follow the same rules as all the other helicopters. If in controlled airspace obtain a clearance and if not operate VFR under the VFR Rules. The TV choppers would be told to get lost if they were interfering with Police choppers (Yes I have heard it happen).


Do Alaskan bush pilots generate a Clmax of 5 with 90° flaps? I understand the Alaskan bush pilots use 90° flaps in the Valdez STOL competition. I think this would stall the flaps. And if so, it wouldn't increase lift and reduce stall speed, but Javafoil says the opposite.

Perhaps this is more for lift/lower stall speed than drag. Since they land flat halfway down a long runway they don't need drag to slow down.

Just to do a test, I input a NACA 2415 foil in javafoil, 25% chord flap, 90 deg flaps deflection. And as expected, lots of drag, but Clmax jumps from 1.5 to 5 at about 0 deg AOA.

Is this realistic? If not, what is the real Clmax?

The following graph is from Cahill, Summary of Section Data on Trailing-Edge High-Lift Devices. As you can see, for a plain flap, with gaps fully sealed, the $C_{L_{max}}$ maxes out at around 60deg.

When I played around with xfoil, things became unreasonable beyond 40deg. Probably some assumptions in the boundary-layer equations broke down. Since Javafoil utilizes the same computational approach as xfoil, I would expect the same behavior.

On the Alaskan Bush pilots, are we sure they are 90deg deflection, and not just some high deflection that looks almost vertical? With multi-element, slotted flaps, you can do better than plain flaps.


Is it considered good or bad practice to raise the flaps right after touchdown? This question is about light, tricycle, single engine aircraft.

I have made it a habit to raise the flaps right after touchdown (when the nosewheel is on the ground). My instructor used to do that every time during initial training so I took over the habit.

It makes sense to do this for the following reasons:

better braking performance because lift is reduced while rolling out
less crosswind effect, reducing the risk of loss of directional control after landing
(less important) it's part of the after landing checklist, so when it's done, it's done

However, I was recently checked out on a C182 that I wanted to rent in Florida and when I raised the flaps right after touchdown the instructor shouted "what the < beep > are you doing? You should never raise the flaps until you've turned off the runway". He couldn't provide a good reason though, so when I told him about the things I listed above he simple mumbled something about keeping my attention on the runway instead of fiddling with the flaps lever (which is a something I don't even have to think about)

My question is: Is it really a bad idea to raise the flaps that soon after landing? Or is it actually a good habit?

(I noticed that most airliners also wait until they're clear of the runway, but these jets have spoilers to get rid of all the lift)

You should wait until clearing the runway before performing any non-essential checklist items because you are still in a critical phase of flight and at a relatively high risk while still on the runway.  You should focus 100% of your attention to controlling the airplane (don't stop flying the airplane until you come to a complete stop) and watching for other traffic (or someone crossing the runway in front of you) that might be a hazard.
There is also the possibility that in a retractable gear airplane you could accidently retract the gear if you are moving things while still preoccupied with landing.  Once you exit the runway and come to a complete stop, you can devote the proper attention to the after landing checklist so will be more likely to complete it correctly without missing any items that may become an issue on your next flight.
That being said, follow the guidance in your POH.  Sometimes there are abnormal situations that actually call for this, like voretaq7 mentions in his answer, the Cherokee POH references it as a short field landing technique.
FAA Guidance
The FAA also covers this in AC 91-73B - Parts 91 and 135 Single Pilot, Flight
School Procedures During Taxi Operations.   It says (in part):

7. SINGLE-PILOT PROCEDURES.
a. General.
...
In addition, upon  landing, no items should be changed or moved until
the entire aircraft has crossed the respective  runway’s hold short
line.
...
NOTE: After the entire aircraft crosses over the landing runway’s hold  short line, conduct after-landing checklist items, based upon
company  procedures, before contacting ATC for taxi instructions.

You could also fail a checkride for doing this
The PTS also repeatedly stresses the  objective:

Utilizes after landing runway incursion avoidance procedures.

To figure out what they mean by that, we can look at their Runway Incursion Avoidance material, which says:

Finally, after landing and upon exiting  the runway, ensure your
aircraft has completely crossed over  the runway hold markings. Once
all parts of the aircraft have  crossed the runway holding position
markings, you must hold  unless further instructions have been issued
by ATC. Do not  initiate non-essential communications or actions until
the  aircraft has stopped and the brakes set.


Why isn't testing fuel flow from both tanks a run-up checklist item? On most single engine GA aircraft, testing both mags is always on the checklist. For a plane (like a Mooney M20) that doesn't have a "both" selector, it would seem prudent to throw the switch to verify there is not a flow issue from either tank.

Is there any good reason why not to run this test, or is it just not considered worth the effort?

There is a very good reason not to run this test: If it is not done perfectly your engine can become starved of fuel during takeoff.

For simplicity let's assume your fuel selector only has two positions (Left and Right) and think about what's involved in the test and a few things that can go wrong:

What are we testing?

One of the points of an engine Runup is to verify that the fuel system can deliver a fuel flow sufficient to allow the engine to develop takeoff power. There are other things we're verifying but let's stick with that item for this discussion.

How can we verify this?

We verify that the fuel system has adequate flow by running the engine up to something resembling takeoff power (most runup checklists don't have you go to full throttle, but you advance the throttle enough that the engine is demanding a significant fuel flow compared to idling and taxiing around).
To verify that your fuel system is allowing sufficient fuel flow from each tank you would have to switch tanks during the engine run-up (with the engine at runup power) and wait long enough to exhaust any fuel that might be in the system between the fuel selector and the engine.
If the fuel selector handle comes off in your hand or the engine quits you found the problem on the ground, so you can get a tow back to the ramp and get the fuel system fixed.

What can go wrong?

The test above sounds innocent enough, but it's deceptively dangerous.
Here are two possible failure modes that may make you rethink it:

The second tank doesn't have adequate fuel flow.
This could be a complete obstruction of the tank pickup or just a restriction in one of the lines, but for some reason the second tank will not supply a fuel flow sufficient for takeoff and climb out at full power.
You may miss this if you don't wait long enough at runup power after switching tanks to drain the fuel from the system forward of the fuel selector, and now your engine suddenly got quiet as you're rolling down the runway - or worse it quits 100 feet off the ground and now you're having a Really Bad Day!
You missed the fuel selector detent.
Easy enough to do, especially if fuel selector maintenance has been lacking and the positions are not really distinct (when is the last time you *really, critically, felt the clicks on your plane?). It could happen in the initial switch, or when switching back to the first tank if that's your procedure.
A fuel selector not in a specific tank position may still allow enough fuel flow to complete a runup when combined with the fuel left forward of the fuel selector, but it may be too restricted to allow a takeoff. The fuel selector may also vibrate into an OFF position during takeoff.
In this scenario maybe your engine stops at 200-300 feet, but you're still having a Really Bad Day.

In both of these scenarios the engine is still running because there is fuel in the system between the fuel selector and the engine (the two big reservoirs are the fuel strainer / gascolator & the carburetor float bowl, but there are also fuel lines that will need to drain before the engine dies).
To get an idea how long these reserves last try setting your engine to Runup power and turning off the fuel selector. You may be surprised how long the engine will run before the fuel after the selector is exhausted. Also remember the time will vary based on power setting, mixture setting, and even aircraft attitude sitting on the ground allowing more or less fuel to get to the carburetor from the lines (a nose-high attitude during takeoff may starve your engine more quickly than sitting level on the runup pad).

How can we safely conduct this test?

Making sure your fuel tanks all work is kind of important, especially if you are going to be making a flight near the endurance limit of your fuel.
There is no 100% safe way to conduct this test, but the way I was taught seems to have the fewest possible failure modes:

Start, taxi, Runup, and takeoff should be conducted on one tank.
Typically this is "the fullest tank", but if they're all equally full then either the one the fuel system return flows to if your airplane has such a thing, or just pick one.
By using the one tank for all your ground operations and your Runup you are pretty much guaranteeing that it flows sufficient fuel to allow a takeoff, and that at least this position on the fuel selector works.
After takeoff switch tanks after reaching a safe altitude.
Do this with enough fuel left in the tank you took off on to turn around and get back to where you started in case you discover the tank you switched to doesn't work, and as with any tank switch be prepared for the fuel selector handle to come off in your hand: Know where you'll put the plane if that happens!
If your engine stops a few minutes after you switch tanks…
…you now have a good reason to suspect that the tank you switched to doesn't work.
Per the first rule of troubleshooting, undo the last change you made (switch back to the working tank you took off on) and wait for the engine to get fuel again. When the engine restarts go home: You have a fuel system problem and need to get it fixed.

If after switching back to the working tank your engine doesn't restart…
…make sure you've waited long enough (it doesn't take long, but it FEELS like a long time when the engine is quiet).
If you waited long enough you may have a fuel selector failure. These don't happen often, but they do happen (and this is why you do the test at a safe altitude with a landing spot picked out).
In this unfortunate case run your engine failure checklist and expect to be making that dead-stick landing: Fixing a fuel selector in flight is probably beyond the skills and daring of most pilots.
(Of course you expected this because every time you touch that fuel selector handle you expect it to come off in your hand like I said before, right? Your CFI was like mine and a few minutes after you switched tanks they pulled the throttle on you al the time, so you got this landing made, Right?)

The test process I use and have outlined above is obviously not free of risk, but the risk level is reduced to be the same as any other fuel tank change: You can be reasonably sure that you won't have an engine failure on takeoff when you're close to the ground, trees, people, and other things we try not to hit with our airplanes, and you can pick when you take on the risk of an engine failure to be sure you can safely recover from the situation.


What is the purpose of the translucent tube and dial on JU 52 engine nacelle? Mounted on top of each JU 52 engine is a translucent tube and a dial (see images).

What is the purpose of the tube and what does it measure?
Does the dial measure (oil or fuel) flow or quantity?
Are these indicators visible at night?

This is the Fuel Gauge.

Direkt auf der Triebwerksgondel sind bei der Ju 52/3m die Treibstoffanzeigen montiert
The fuel guage is mounted directly on the engine pylons on the Ju 52/3m.
AustrianWings

It is suggested that the indicator gives a reading in hundreds of liters (Liter x 100 written underneath).

Source
Visible on the illustration below as Kraftstoffuhr ('Fuel Clock').


Why can Boeing V-22 Osprey carry more cargo internally than externally? According to the Wikipedia, V-22 Osprey can lift 20,000lb of internal cargo, whereas it is able to carry only 15,000lb externally by dual hook.
I wonder why there is a difference between external and internal cargo capacity.
Is it due to the aerodynamics effect of the cargo?

The difference is because when the cargo is inside the aircraft the weight is spread across the cargo compartment floor, whereas when it is carried externally, the weight is concentrated entirely on one or both cargo hooks. The cargo hook attachment points are reinforced, but they still have a weight limit. When the cargo is inside the aircraft the weight limit is the MTOW of the aircraft.


During takeoff, why throttle forward then raise hand from throttle to push a button, instead of pushing button then throttling? Preface: The comments assert the video to have been horizontally flipped, probably because (I am divining) the original belonged to someone else (user 'Jb380' if I remember)?

At 4 mins 3 secs of this video, the captain (who appears in the video on the right, but per the preface above, should be on the left) pushes forward the throttle, but from which he then removes his hand to use this same hand to push a button that changes an instrument display,

from showing the tail view (camera) of the aircraft (to assist with taxiing???),
to the primary flight display.

Afterward he replaces this hand back atop the throttle.

Why doesn't he instead push the button before deciding to takeoff and set takeoff thrust: this is safer than the above? For example, if abortion is decided exactly when nobody's hand is handling the throttle, then previous seconds needed to stop would be wasted?

Actually he does push the button before selecting takeoff thrust.

Often1 the procedure on jets during take-off is to move the thrust levers about half way, wait for the engines to spool up and only then select TO/GA or Flex thrust as desired. In the video the pilot switches the display during this intermediate step. So the engines are not even spooled up yet and the aircraft is still moving slow. Plenty of time to stop if anything fails.

In fact even when nearing v₁ the reaction does not need to be that fast. The calculation of v₁ includes 2 s reaction time and correct response is more important. Look e.g. on this training video (it's A330, not A380, but the procedure is the same). The reaction is not that fast; they only retard the throttle after checking and calling the fault ("engine fire").

1It used to be that the engines could flame out if you added fuel too quickly, but that's no longer the case now when engines are managed by FADEC (full authority digital engine computer). Some manufacturers/airlines/pilots maintain the procedure, most likely to avoid applying full power if one of the engines manifests some problem early. Or at least the pilot in this video does it.


How much thrust could a 400 mm EDF produce? There's a 195mm EDF from Schübeler that produces 25 kg of thrust at a peak power consumption of 15 kW: https://www.schuebeler-jets.de/de/produkte/hst

Now, my question is: How much thrust could you approximately get if the diameter was 400 mm instead of 200 and how much more power would you need ?

Thanks for your answers !

It can be safely assumed that thrust $L$ is a function of the input power $P$, the diameter $D$ of the gas jet and the air density $\rho$.

Thus, $L = f(P,D,\rho)$

where $f$ is a function to be determined.

From dimensional analysis, the thrust $L$ can be easily derived:

The variables are Thrust $L$, dimensions $MLT^{–2}$; Power $P$, dimensions    $ML^2T^{–3}$; Gas jet diameter $D$, dimensions $L$ and air density $\rho$, dimensions $ML^{–3}$

The variables form a non-dimensional product $k$

$k = L^a\cdot P^b\cdot D^c\cdot \rho^d$  where $a,b,c,d$ are numbers to be determined.

Let’s form now a parallel product $k^*$ with the dimensions:

$k^* = (MLT^{–2})^a  (ML^2T^{–3})^b  (L)^c (ML^{–3})^d$

Clearly, $k^* = M^0 L^0 T^0$... We now take the exponents for each dimension:

$a  + b + d = 0 \\
a + 2b + c – 3d = 0 \\
–2a – 3b = 0$

We make $a = 1$, since $L$ is the variable we’re going to solve for.

$b = –2/3 \\
d = –1/3 \\
c = –2/3$

Then,

$k = L^a\cdot P^b\cdot D^c\cdot \rho^d \rightarrow  k = L\cdot P^{–2/3}\cdot D^{–2/3}\cdot \rho^{–1/3}$

Solving for $L$

$L = k\cdot P^{2/3}\cdot D^{2/3}\cdot \rho^{1/3}$

where $k$ is a constant

Hence, for gas jet diameters $D_1$ and $D_2$, and for the same power and air density, the corresponding values of thrust $L_1$ and $L_2$ are:

$L_1/L_2 = (D_1/D_2)^{2/3}$

For the case of $D_1 = 400 mm$ and $D_2 = 200 mm$, $L_1/L_2 = (400/200)^{2/3} = 1,59$

In other words, the larger (400 mm) gas jet gives you, for the same absorbed power and air density, 59% more thrust than that attained with the smaller (200 mm) jet.

Of course, this is an approximation valid for not too high aircraft speeds, based upon momentum theory, but gives you an idea...  For different values of power and gas jet diameter, you can derive the constant k from the data of thrust, power and diameter you already have,  $k = L\cdot P^{–2/3}\cdot D^{–2/3}\cdot \rho^{–1/3}$  and then use that constant in your calculations.


What happens if a helicopter engine fails at 20,000 feet? A fixed wing aircraft is able to glide in case of an engine failure and potentially land safely.

What would happen if a helicopter engine fails at high altitude?

Is it possibly to land it safely?

Yes. See the Wikipedia's article on autorotation!, which mentions a real-world example of the case you are describing:

  The longest autorotation in history was performed by Jean Boulet in 1972 when he reached a record altitude of 12,440 m (40,814 ft) in an Aérospatiale Lama. Because of a −63 °C (−81.4 °F) temperature at that altitude, as soon as he reduced power the engine flamed out and could not be restarted. By using autorotation he was able to land the aircraft safely.

The biggest concern here is the disk loading of the helicopter's rotor - the greater the disk loading (the mass of the aircraft related to the rotor's area) the worse the autorotation capabilities. See this Google Books link for an in-depth discussion of the autorotation capabilities of different aircraft based on their characteristics.

The weight of the very rotor also plays a significant role here - the heavier the rotor, the more kinetic energy it stores, and the greater the probability of a successful entry into the autorotation state. See the Osprey's design, for example - it has light propellers on each wing which are practically unable to autorotate because of their small mass.

As you can see, the aforementioned helicopter - Aérospatiale Lama - is a light aircraft which is geared towards high altitudes - it has three propeller blades, which translates to low disk loading, and sufficiently heavy blades to allow easy entry and execution of the autorotation stage.


Do vortex generators increase Re of a wing? Do vortex generators (VGs) increase Re of a wing?

I understand that VGs re-energize the boundary layer on a wing.

I understand it turns laminar flow into attached turbulent flow.
Doesn't that mean the Re increases substantially?

If so, wouldn't that increase it's cl/cd, which means lower drag in the 600-900k Re range?

Reynolds number depends on the free-stream speed, the chord length, fluid density and viscosity. So vortex generator does not modify the Reynolds number. However, it trips the flow aft of the device into turbulent flow. Turbulent flow, in fact, has higher drag than a laminar flow (at the same Re). Therefore, on top of the additional skin friction drag introduced by the VGs, the aerodynamic surface would also have higher drag.


Why can't we extract more from exhaust gases in gas turbines? It is seen that EGT are of the order of 600°C (What is a normal EGT range of a jet engine?) for aviation turbines and nearly the same for stationary turbines. Why can't high temperature exhaust gases are further harnessed like adding another stage in turbine section that extracts more energy?

In aviation turbines can't we just add another turbine stage like another low-pressure turbine mounted on another spool? For land-based gas turbines we can somewhat utilize these high temperature exhaust gases in Combined cycle but what about aviation engines?

It can be done, but the better specific fuel consumption does not compensate for the extra weight. We all know that aero engines have to be as light as possible. In land, stationary installations, where weight matters but little, regeneration, intercooling, and even combined-cycle (in electricity generation, using a gas turbine that drives an alternator, but with the exhaust gases generating steam for a steam turboalternator, for example...). The efficiency is very, very high, but the weight and bulk are considerable, too...

But it has been tried: https://airandspace.si.edu/collection-objects/allison-t78-2-turboprop-engine

https://www.flightglobal.com/pdfarchive/view/1963/1963%20-%201880.html


Lost radio communication after take-off in IMC - what are my options? This might be "yet another lost comms questions", but I've tried to read a lot and there are different answers everywhere. Here's the scenario:

(The flight plan as filed is - KSSI SSI V441 MONIA GNV OCF V581 DADES KTPA)

I'm taking off from an uncontrolled airport - KSSI to fly to KTPA (ICAO IDs). The current weather at KSSI is 003 OVC and 2 SM. I call MACON FSS for my clearance on 121.5, and here's what I get -

MACON FSS: "ATC clears N123CW to KTPA Direct SSI and then as filed, climb and maintain 4000 expect 8000 two-zero minutes after departure, departure control will be 126.75, squawk 1234. Released for departure, clearance void if not off by 20:45, time now 20:30, frequency change to advisory approved."

After read back, I take off exactly at 20:35 and after a couple minutes I contact Jax Center on 126.75 as I'm crossing 1300ft. I hear no other traffic on the frequency, and I try to contact them 2 more times while I'm heading direct to the SSI VOR. I try to contact MACON FSS with whom I'd just spoken a few minutes ago - and I hear nothing back. I try a couple of other frequencies that I can get from charts - no luck anywhere. I'm in complete IMC.

Now, I know that I've lost my radio communications capabilities and hence squawk 7600, and figure out my route and altitude to fly.

I was cleared direct to the SSI VOR, and then as filed. Looking at "AVEF", ATC expects me to fly the route I filed. Looks good - no problems here.

I was asked to climb and maintain 4000ft, and expect 8000ft 20mins after departure.

Looking at "MEA", ATC expects me to be at 8000ft since it's the highest amongst the Minimum En-route Altitude, the expected altitude (which is n/a) and the assigned altitude).

I'm still at 2400ft, climbing to 4000ft.

My questions are:

1) When should I start my climb to 8000ft? Should I level off at 4000ft and wait until 20:55 (which is 20 minutes after my departure time) before initiating my climb, or does ATC expect me to be at 8000ft by 20:55?

2) Along my route (not immediately after departure, but after a while), for e.g. at the GNV VOR, if I briefly enter VMC, should I go ahead and land at the nearest airport as practicable or should I still continue through my route? I do know that the regulations advise to land as practicable when you're in VMC, but if the airspace ahead is being cleared for you when you're under IFR, is it advised to try and land into VFR traffic who have no idea that you're coming-in out of nowhere?

Appreciate all the answers. Thank you!

PS - Here's the Low-Enroute chart for quick reference:

The answers to these questions can be found in the AIM in section 6-4-1. All quotes are from that page.
To the first question, you should expect to receive a clearance to 8,000 feet twenty minutes after departure; therefore, don't climb above 4,000 until that time. If you are still in radio contact after 20:55, the "expect" portion of the clearance expires:

If the pilot received an “expect further clearance” containing a higher altitude to expect at a specified time or fix, maintain the highest of the following altitudes until that time/fix:
(1)   the last assigned altitude; or
(2)  the minimum altitude/flight level for IFR operations.
Upon reaching the time/fix specified, the pilot should commence climbing to the altitude advised to expect. If the radio failure occurs after the time/fix specified, the altitude to be expected is not applicable and the pilot should maintain an altitude consistent with 1 or 2 above.

For the second question, the answer comes down to the definition of "briefly". Is your hole big enough for you to get under the clouds, and is the ceiling high enough that you can remain VMC to land? If so, you should do so. But if you just briefly see the ground, or aren't confident that you could safely fly VFR to a suitable airport, then you should maintain IFR and continue flying your clearance. You may inconvenience a few controllers, but if you leave your cleared route only to discover that your intended airport is socked in, getting back to your route to resume your original destination puts you potentially low to the ground, and not along the route that ATC is expecting you:

Pilots should recognize that operation under these conditions may unnecessarily as well as adversely affect other users of the airspace,
since ATC may be required to reroute or delay other users in order to
protect the failure aircraft. However, it is not intended that the requirement to “land as soon as practicable” be construed to mean “as soon as possible.” Pilots retain the prerogative of exercising their best judgment and are not required to land at an unauthorized airport, at an airport unsuitable for the type of aircraft flown, or to land only minutes short of their intended destination.

That said, VFR traffic should always be looking for other aircraft - with and without radio contact. Radios are not required equipment, at least at non-towered airports, so landing among VFR traffic without a radio should not be a big deal.


How do single GA pilots prevent boredom during long flights? My question somehow relates to this question asking about how pilots cope with boredom, but now the scenario is not the typical airliner configuaration with two pilots, but with only one. I'm thinking of single pilot operated business jets with flights over, say, 4 hours. What does the single pilot do to prevent boredom and associated problems such as vigilance loss and fatigue? They've got no one to chat with as stated in the first answer to above cited question... of course, they will continue to check and monitor systems, occasionally report and talk to ATC, but there is plenty of scientific evidence (i.e. see this book) a simple monitoring task can easily lead to fatigue - so are there any methods pilots use to prevent boredom and vigilance decrement?

Not long ago, I had my longest flight as a PPL: about 4 hours from Dallas, TX to Kansas City, MO, in a 172, facing a steady headwind the whole way, so making a ground speed of less than 90kts.

I ran checklists about twice as often as normal, and re-did my fuel calculations very regularly (in part because of the extremely slow progress).

I listened to the ATC frequency, and tried to build a good mental picture of all the planes around me.

I went through every single setting and option on my MFD glass cockpit and iPad.

I watched the scenery, both for visual navigation (despite my GPS), and just to admire the view.

Even after all this, the flight was pretty boring near the end, and I'm glad I don't do flights that long very often.


What happens if a seat belt is found broken, before flight take off? What happens in a commercial airliner, when a passenger finds the seat belt to be broken. Does the crew de-plane the passenger or do they provide him something like a child/infant seat belt?

I'm also curious as to FAA's regulation on this area, if any.

Options would be to either move the passenger to another seat & placard that seat as unusable, or go back to the gate and have maintenance fix what's broken. In the former case, the seat would most likely be fixed by a mechanic at the next station.

The seatbelts used in the F/A demos are seatbelt extensions, which still need the installed seatbelt itself to be intact. They are fully functional as such, though, unlike the demo life vests & O2 masks, which indeed are "demo only" and of no use at all in a real emergency.

For a mechanic, the seatbelt is quick & easy to replace, although without needle-nose pliers (and a spare male or female belt), rather difficult for the crew -- who wouldn't be allowed to anyway.

The FAA requires that every passenger has a seatbelt and has been told how & when to use it, and that the crew has verified that they have it on before takeoff.


What are the definitions of elevator angle of attack and critical angle of attack? Angle of attack is the angle between the chord line of the wing to the direction of relative wind. So angle of attack helps the aircraft climb.

Then what is the angle between the chord line of the elevator and relative wind? Because if I am not wrong, by pitching the elevator up, the wing of an aircraft is subjected to the 'angle of attack'.
When you say angle of attack exceeds the critical angle of attack, is it because the elevator is pitched up thus creating wider angle between the chord line and the relative direction of the wind?
In the Air France 447 accident, the PF kept saying, keeps the wings level. What does it mean? How can the wings be leveled when the angle of attack is so high? Does keeping the wings level mean reducing the angle of attack to zero?

Angle of Attack is the angle between the chord line of the airfoil and the relative wind. The elevator is also a "wing" in the effect that it is an airfoil.

  1) Then what is the angle between the chord line of the elevator and relative wind? Because if I am not wrong, by pitching the elevator up, the wing of an aircraft is subjected to the 'angle of attack'.

It's also called "Angle Of Attack". Pitching the elevator up also changes the angle of attack of the elevator. There are such conditions as elevator stall, although much less common than wing stall.

  2) When you say angle of attack exceed critical angle of attack, is it because the elevator is pitched up thus creating wider angle between the chord line and the relative direction of the wind?

The "Critical AoA" is the angle at which the airfoil is generating the most lift.

  [Wikipedia Article on AoA]: The critical angle of attack is the angle of attack which produces maximum lift coefficient. This is also called the "stall angle of attack". Below the critical angle of attack, as the angle of attack increases, the coefficient of lift (Cl) increases. At the same time, above the critical angle of attack, as angle of attack increases, the air begins to flow less smoothly over the upper surface of the airfoil and begins to separate from the upper surface

Usually when you exceed the critical AoA, the air on the upper surface of the airfoil de-laminates and becomes turbulent. This results in a loss of lift (stall).

Source: FlightSimBooks.com

  3)In the Air France 447 accident, the PF kept saying, keeps the wings level. What does it mean? How can the wings be leveled when the angle of attack is so high? Does keeping the wings level means reducing the angle of attack to zero?

I'm not sure what context you are talking about. I've read the transcripts pretty carefully and I don't recall the PF saying to keep the wings level. The Captain said to descend, while the PF was trying to climb. The SIC was pushing the stick forward while the PF was pulling back, causing the wings to remain level (or at a slight climb).

Keeping the wings level (avoiding an un-coordinated turn) in a stall condition is the best way to avoid putting the aircraft into a spin. This is possibly what they meant, although they didn't know that they were in a stall (or if they did, they were not reacting to it appropriately).

Yes, leveling the wings would be making the AoA at zero (zero meaning where the airfoil is developing lift, and depending on the bank angle), but only if there were positive airspeed to make the relative wind parallel with the chord. In the case of AF447, the aircraft was falling out of the sky at a spectacular 15,000 FPM, which means that the relative wind to the airfoil was basically perpendicular. They didn't have the forward airspeed to change the AoA, so they should have lowered the nose to gain airspeed and decrease the AoA.

The important thing to remember is that the pitch angle of the aircraft is not the same as the AoA. You can take an aircraft at zero forward speed and drop it straight down, the pitch angle will be zero but the AoA will be perpendicular.


How can the Perlan II glider climb to 90,000 feet? I've been reading material about the Perlan II experimental glider. They hope to take it up to 90,000 feet  -- higher even than an SR-71 BlackBird.

But the Perlan II is just a glider. Can it really just climb thermals up to that level? Is there something special about its aerodynamic design that lets it do that -- or are all gliders capable of climbing as high as possible, with only the  heat and oxygen needs of the human occupants being the limiting factor? Or is it just me that finds it odd that a glider can climb higher than  a powered aircraft?

Perlan II will climb to extreme altitudes on wave lift, not thermal lift. Wave lift is created when strong winds blow approximately perpendicular to a mountain range, and the wind speed increases steadily with altitude. This creates a standing wave in the atmosphere, kind of like the ripple behind a rock in a fast moving stream of water. On the leading edge of the wave, air is moving up, and that's where gliders fly. Standing waves can reach very high into the atomosphere, which is why Perlan II is expected to reach 90,000 feet.

Perlan II is different from normal gliders in that its wing is optimized for minimum sink, instead of best glide ratio. It's meant to float along while losing a minimum of altitude, which makes sense if it's going to fly in nothing but wave. Normal gliders are usually optimized more for gliding long distances, for which glide ratio is more important than minimum sink. Interestingly, Perlan II's wing looks a lot like RC model glider wings, which are also optimized for minimum sink, since RC gliders don't typically fly cross country.


If I fly both Part 135 and Part 91 in a 24 hr period, which regulations apply? I was wondering if there is a regulation if you fly both part 135 and part 91 in the same day which regulations do you follow?

Part 91 contains the General Operating and Flight Rules. These rules apply to almost every civil flight within the USA.

Part 135 contains the Operating Requirements for Commuter and on-demand operations and the rules governing persons on board such aircraft.

So when you fly the "Part 91 flight", you follow the regulations of Part 91.

When you fly the "Part 135 flight", you follow the regulations of both Part 91 and Part 135. If Part 135 is more strict in some regard, the more stricter rule of 135 applies.


Does wearing glasses mean you automatically meet the first class medical requirements? I have been wearing glasses for a very long time. If you wear permanent eyeglasses do you automatically meet the FAA first class medical vision requirements?

Certainly not.  Eyeglasses can't fix everything.  Some people have very poor vision even after correction with glasses.  One example out of many, would be someone suffering from macular degeneration.


How do pilots in the US identify the circuit (pattern) height? In the UK, aerodrome weather information includes not only QNH (the air pressure at mean sea level), but also QFE, the air pressure at runway level. To arrive at an aerodrome, normally one obtains and sets the altimeter to QFE, so that it reads height above aerodrome level. Then if the circuit (traffic pattern) height is 1000 ft (which it usually is), you just read 1000 ft on the altimeter all the way around the circuit; for a standard overhead join it says 2000 ft; and so on. At any aerodrome the altimeter reads the same thing, because you always set QFE.

I've heard that QFE is not used in the US. Do you just have to work out the circuit height in your head by adding 1000 ft to the published aerodrome level? Or are circuit heights given amsl?

The Airport/Facility Directory (AFD) has that info. It lists the Traffic Pattern Altitude (TPA) in both MSL and AGL, as well as circuit direction.

QFE is not used in the US. So yes, you have to make the correction for field elevation. For example, an airport at 1200 MSL would have a pattern altitude of 2200 ft. (1000 AGL for props. 1500 AGL for Jets) and would be flown using that altitude on the altimeter.


Under what conditions do airliners retire aircraft and sell them to other airlines? How often (and under what conditions) are airliners resold to another organization with...less stringent qualifications?  Is there a certain number of hours after which an airliner has to be retired or something?  Or is it just that airlines like to buy new and shinier airplanes on occasion?

Further, when an aircraft is being resold, are there any particular procedures that have to be followed?  And are there different levels of airworthiness involved (ie., you have a lower litmus test if you are just selling it off to be used as a cargo plane or private plane?)

Some reasons for an airline to sell some of its fleet:

they need quick cash (as ratchet freak points out). This usually means the company is in serious trouble
they're changing their route network and there's no more need for it (e.g. KLM dropped a lot of very short flights in the 1990s and early 2000s, and got rid of the aircraft that were operating them as they were inappropriate for the longer routes that replaced them)
they bought out another airline and have no need for (all) its aircraft, or want to replace them with other types to keep their fleet homogenous (operating many similar types is less economical than operating a smaller number of types)
they're splitting part of their operations to a new company set up for the purpose (the new company becoming the new owner of the aircraft, usually for a symbolic fee), for example a regional affiliate or a charter operation
it may be more economical to replace the aircraft then to keep them. When NWA decided to replace their DC9 fleet with A320s this was for economic reasons (lower maintenance and fuel cost for example), not because the aircraft had run out of fatigue life. The aircraft were old so most probably were scrapped, but some may well have ended up with airlines in other countries, replacing even older aircraft or expanding existing DC9 fleets there.
and some airlines just want to portray a public image of always flying shiny new aircraft. I believe Singapore Airlines used to have a policy like that and replace everything it bought relatively quickly (more so than most other airlines at least). PanAm was like that as well. If you have a reputation of exclusivity, this may add to customers' willingness to pay premium to fly with you


Helicopter aerodynamics The formula in Prouty's book shows

the blade inertia unit is slung-feet squared
rotor kinetic energy unit is foot-pounds

if blade's inertia is high, the rotor kinetic energy should be high.

In other words, blade inertia and rotor kinetic energy are two different terms for the same thing.

am I right?

Blade inertia and rotor kinetic energy are NOT the same thing, but they are related.

Blade inertia is a characteristic of the blade. It is a quantity that shows how difficult it is to change the blade speed (either by acceleration or deceleration) The bigger the inertia of the blade, the harder it is to make it move or make it stop once it's moving. It has nothing to do with the speed/RPM of the blade, it has the same value regardless if the rotor is turning or not. It depends on the way the blade is built (how heavy it is and how is its weight distributed).

Rotor kinetic energy depends on inertia AND rotor speed (RPM). So, a rotor when it's stopped has inertia but has no kinetic energy.

Once you start turning the rotor you start building kinetic energy in it using power from the engine. If rotor inertia is big, the engine will work harder to accelerate the rotor BUT, if the engine fails in flight the bigger inertia will oppose RPM decay giving the pilot more time to perform the proper actions.


Do hot air balloon pilots file flight plans? Are hot-air balloon pilots ever required to file flight plans? (can they file?)

As a balloon pilot: no we do not.  We do fly regularly in classes G, D, and E and will occasionally wander into class C; but it is very frowned upon...and you better have an aircraft radio or at least call the tower to let them know you are there.   Of course balloons always have right-of-way so if you see us get out of the way; we can't control where we're going.


Calculating thrust and required propeller size for a given engine power I am looking to build an Airplane, the weight of Airplane will be around 20 to 25 kg and I am going to use a 70cc motorcycle engine as an Airplane engine.

I want to know how I can calculate the engine thrust. The 70cc engine is an air-cooled, four-stroke, single cylinder, OHC petrol engine generating a maximum power of 5.19Ps at 7500 rpm and a maximum torque of 0.519kgm at 5500 rpm.

So will it work as a plane engine or not, and can you give me any rough idea about how much thrust will it produce and how big propeller do I need for this engine.

This that follows isn't an accurate calculation, but may be useful as a starting point: let's say the mass of your plane is 23kg. That's a weight of 225 newton. You have to add 830 N for the pilot, so the total weight is 1055 N. Let's assume, also, that the best L/D of your airplane is 9 at 36 km/h = 10 m/s. In a glide, that would mean a sink speed of 10/9 = 1,11 m/s. The implied 'gravitational power' would be 1055 x 1,11 = 1171 watt. That would be the minimum power required for s/l flight at best L/D and for a 100% prop efficiency. In the real world you might need at least three times that power, around 3500 watt.

Now, concerning the relationship between prop size, power, and thrust, at 100% prop efficiency, you may use this formula for the stationary case (airspeed = 0):

(From Wikipedia entry https://en.wikipedia.org/wiki/Disk_loading). Where P is the power in watts, T the thrust in newton, A the disk area of the propeller in sq. meters, and rho the air density in Kg/m3, around 1,22...


Can wing sweep decrease total drag force at low-subsonic speeds? From  experience everybody knows if you put your arm out of car window at high speed(150km/h), it's a lot easier to hold arm angled backward then hold arm straight out(prependicular to airlfow).So conclusion will be that drag force is reduced..
Can wing sweep in same manner reduce total drag force at speeds up to 250km/h?

Pulling angled "beam" with rope in water will be easier than if "beam" is prependicular to flow.Right beam has smaller lift force but also less total drag force.Is this correct?

Sweeping back a wing of fixed spar length and area does decrease form drag. However due to both its lower aspect ratio (span/chord) and sideways flow effects, it increases induced drag and decreases lift, so that the net L/D ratio or efficiency of the wing falls.
Whether the absolute amount of drag goes up or down depends on other factors, such as wing loading and angle of incidence. In most situations drag would be higher. Where it is less, other design optimisations such as reduced spar length would offer greater improvement.


How is rotor airfoil analysis different than fixed wing airfoil analysis? What the is difference between rotor airfoil analysis and fixed-wing airfoil analysis?

Intuitively, it seems that the airspeed at the tip of a rotor blade would be more than that at its root. Wouldn't this result in irregular torsion along the blade? Subsequently, wouldn't this affect the airfoil analysis as compared to a fixed wing?

If this is the case, then what software (hopefully free) can carry out this analysis?

You are correct on many fronts.  Rotor blades see a varied load along their length, resulting in twisting, bending, and lagging (e.g., the blade being bent against its direction of rotation) loads.  It's a mess.  And, yes, all those effects feed back into blade aerodynamics, but that's a much more complicated answer that you might be looking for.

What you are describing is the foundation of blade element theory.

Let's consider a helicopter rotor, independent of the helicopter fuselage, and look at one annular ring of it while the rotor is in hover (so we have an axisymmetric flow field):

If we look at that annular ring, it would "cut" through a section of the rotor, which, in 2D, would look something like an airfoil.  If we drew a bunch of vectors on it to represent the forces acting on the airfoil and the direction of the relative wind, it does look a heck of a lot like our 2D airfoil free body diagram from fixed-wing aerodynamics.  And, truly, blade element theory (BET) considers it as such.

In BET, elements of the blade (such as the 2D airfoil above) operate without impact on the other blade elements.  If you can determine the inflow at a particular blade section, you can determine the sectional lift and drag, and, integrating those properties across the blade, you can determine the thrust production and torque requirements that correspond to a particular operating condition.  That said, while most of the labels on that diagram are familiar from fixed-wing flight, there are a few that should be different, namely: the induced velocity, inflow angle, and tangential velocity.

As you stated, the horizontal speed of the blade is going to change based on where you are on the blade, radially speaking--which is absolutely correct.  If we look at a distribution of elemental velocities around the rotor, it's going to vary as shown here, in a plot from Leishman's Principles of Helicopter Aerodynamics (which has a great description of how to implement all of this, as well as some basic corrections for going into some rudimentary higher-order approximations).  Note the hover case on the left hand side, where the velocities are axisymmetric, versus the forward flight case on the left hand side, where the velocities are asymmetric.  That second case is a whole 'nother can of worms, and we'll get there in a minute.  Stick with the hover case for now.

So knowing your radial location can get you the element's velocity, and knowing your climb rate and help you get how fast flow is moving vertically through the rotor, but flow has to be moving vertically through the rotor even when the aircraft's not climbing -- else our analogy of a rotor being a big fan (which it is) doesn't correspond with reality.  Hence, there's some inflow speed, and it makes sense that that inflow speed is correlated to the amount of thrust being produced by a given element of the rotor...and this is the crux of the problem for us, since it has to capacity to dramatically change the angle of attack of the blade section (and thus our lift and drag predictions).  So: how do we estimate the inflow velocity?

A simple approximation uses momentum theory (i.e., a quasi-1D analysis on fluid moving through the rotor disk, treating the rotor as a device that simply adds momentum to the flow) to determine the inflow on the rotor along that annular section, assuming that the inflow is axisymmetric.  For what it's worth, it's a simple way to capture inflow velocity variation (and thus angle of attack variation as well) across the rotor disk, which is something that momentum theory cannot do alone, and it's decent at what it does.  It has been the de-facto standard of the wind energy industry for awhile as more complex CFD computations have caught up to the industry's analysis needs and desires.

However, when flow is no longer axisymmetric, we get into a big mess of approximations to determine what that inflow does look like, since the wake will start to interact with the inflow as well and that, somehow, needs to be accounted for.  It is here that we start to depart from analytical expressions and look to computational models using free-wake theory or higher-order models.  Where fixed-wing models advance in similarity by modeling the wing's wake, viscous effects, etc, rotary wing models model a rotating wake that is being convected and recirculated by both rotor effects and the freestream.

That said, the expressions for a rotor in hover are relatively easy to code up, depending on how much fidelity you want (e.g., how much you know about the airfoils used on the blade as well as how the blade tapers and twists along its length).  Googling around, I found a MATLAB code that might be useful, again, depending on your problem: https://www.mathworks.com/matlabcentral/fileexchange/21994-analysis-of-a-rotor-blade-system-using-blade-element-momentum-theory


Why does Airbus continue with the A330-800neo despite only having 6 orders? Airbus rolled out the first Airbus A330-800neo out of the paint shop last week (see press release).

Until now, this type has only six orders by one airline (U.S. Hawaiian Airlines, who switched orders from the A350-800 to the A330-800neo), with no new orders in the past months. According to various sources, even those six orders by Hawaiian seem to be questionable (see Hawaiian seeking A330-800neo alternatives).

Update 02/22/2018: The only customer, Hawaiian, has canceled their six orders.

Given these circumstances, why does Airbus continue to develop, produce and flight test the smallest A330neo variant? What is the business case for Airbus with one single customer?

There used to be a bit more demand. Hawaiian committed to 6 orders plus 6 options, and Transasia also ordered 4, coming to 16. Unfortunately, Transasia ceased operations and canceled their orders, and Hawaiian hasn't exercised any of their options yet. That leaves the -800neo at only 6 planes on order.

Update: Hawaiian Airlines announced they would cancel their orders for the A330-800neo and instead opt for the 787-9, signing a letter of intent to order 10 with purchase rights for 10 more.

Airbus was probably hoping for more orders and continuing development of the -800neo somewhat "at risk". Of the 1368 currently delivered A330ceo, 615 of them are the -200. This would suggest there may eventually be demand to replace those with the -800neo. Almost all of the A330 fleet is less than 20 years old at this point. There's still time for more orders as the A330neo only recently made its first flight.

As the first -800neo has now been built, most of the overhead in developing it has already been spent. There will of course be more as it must also be flight tested and certified, but evidently Airbus still sees value in going through with that. It will be a balance between Airbus recouping costs of development or avoiding costs of further development and support, and the needs of the customer.

Airbus probably also sees value in keeping Hawaiian happy. Hawaiian has not ordered any -900neos and they currently have 24 -200s in their fleet, suggesting that even if no other -200 operator orders the -800neo, Hawaiian might order more. Airbus may prefer that Hawaiian takes the only 6 -800neos they ever build than for them to go and order the 787 instead.

The 737-7 MAX is in a very similar situation. Boeing only has 58 orders for the type, which is 1.4% of the total orders for the MAX (the 6 -800neos account for 2.7% of the total A330neo orders). To compound this, the launch customer, Southwest, recently announced that they're delaying 23 of their 30 orders, possibly to covert them to a different version. Yet Boeing recently rolled out the first -7 and seems to plan on going ahead with it.

Since these planes have already been built, the manufacturers probably see some value in keeping the orders around so they can still sell the planes, and avoid the bad PR of going through the trouble to develop, sell, and build the plane only to cancel it. It remains to be seen if the airlines will continue to see value in taking delivery of types that no one seems to want.