What are the lowest authorized minimums for each ILS category? I have been recently told that ILS minimums were changed some time ago. Could anyone tell me what the lowest authorized ILS minimums are for CAT I, CAT II, CAT IIIa, CAT IIIb and CAT IIIc? I'm interested in FAA, EASA and ICAO standards.

As Carlo mentioned in the comments, the minimums may vary from place to place to place. Here in the US you can find all that information here. Or you can buy a printed copy from a variety of aviation suppliers.

This order published in 2012 sets some minimum performance guide lines for minimums as well. For example,

  (2) The following is the minimum class of performance (refer to
  Appendix B) required for an ILS to support a published Title 14 of the
  Code of Federal Regulations (14 CFR) part 97 CAT II or III SIAP:

  Class II/T/2 for operations not less than RVR 1200.
  Class II/D/2
  for operations not less than RVR 1000.
  Class III/D/3 for
  operations not less than RVR 700.
  Class III/E/3 for operations not
  less than RVR 600.
  Class III/E/4 for operations less than RVR 600.

See appendix B in that order for more information.

This may also be of some interest.


Do aircraft at cruise bob and/or skip? Recently I started flying a model aircraft, admittedly a kindness for a motor stuck onto a piece of foam, and have noticed that it either bobs, for lack of a better term, like something afloat on water might when depressed or that it skips, for lack of a better term, like a stone thrown across the surface of a pond might.
In the first case the motorized foam is at cruise at constant speed at some height when I force it into a dive it seems to "bob" back up to it's original height when I stop giving it the input to dive. I suspect I'm observing a little Newtonian mechanics here trading potential energy for kinetic energy during the dive and that this gets converted back as it "bobs" up again.
In the second case when the motorized foam is at cruise at constant speed at some height it tends to undulate. This is exacerbated if I increase the angle of attack(?) such that in the extreme, where it stalls, the motorized foam goes into a cycloidal "swoop". Each "swoop" starts with a stall where it'll "flip over" and dive down and gaining speed as it does so, the gain in speed results in the nose "picking up" resulting in a "swoop" back into a near vertical "climb", at roughly the same height as when it first stalled it'll stall again and repeat the process.
Do larger scale aircraft, that is anything with at least a human on board, behave in this manner as well? In the case of "bobbing" do pilots use this in any way to their advantage e.g. does it help them maintain altitude or is it helpful in some way during dire situations? (My imagination can't help but wonder if there was ever a pilot who forgot to throttle down on decent, intending to land, who found they simply "bobbed" back up to their pre-decent altitude?)
In the case of "skipping" I can't imagine passengers being very agreeable to such a motion, especially not the stalling swoop variant, but I'm fairly certain I've felt a plane undulating slightly on a flight before. Do pilots have to constantly fight such undulations or do they reduces/eliminate this through proper trim?
Note:
I'm not talking about wing in ground effect, I observe this when the motorized foam is at roughly tree top height. The veldt I fly in comprises of knee high grass so I doubt I'll observe this until I fly over a lawn or something.
Note:
If it's relevant motorized foam is shaped like a flying wing; in case aircraft with tails behave differently.
Note:
I've certainly observed that the wing tends to "pitch up" in proportion to its speed above a certain speed; this is most noticeable in the cycloidal "swooping". Initially I thought this was a CG thing or that the motor was off center and generated a moment force but I see this is already discussed. It's more likely my trim is off.
Update

Update :
I phugoid it out, I believe, stuck a coin under the battery (rotating it made it poke out like an Adam’s apple) and I trimmed the trim to something slim. Did the glide test and she stays level as a lake wafting gracefully from the skies like Dumbo with his trunk out, tail tucked and his C.G. Is under his chin ! Thanks all for the helpful hints and the epoxy related non-confessions. (When the coin is worth more then the model I’ll fork out for an upgrade. Till then I’ll wait for the back of this cold front)

It sounds very much what you're experiencing is a Phugoid cycle

Image License info
To put simply, your aircraft is not trimmed correctly. As it descends slightly it gains speed, which increases lift over the wing making it climb. This has the effect of it losing some speed, reducing the lift over the wing causing a descent, increasing the speed - and on it goes.
Full scale aircraft from light to airliner can and do experience the same thing. One notable case which comes to mind is the accident sequence of United Airlines 232 which lost all hydraulic pressure and thus had no control surfaces operational. They were controlling pitch (and roll) somewhat using engine power only, and thus did not have exact control of pitch and experienced significant Phugoid cycles.
Side note: You're unlikely to be experiencing ground effect at treetop height unless you have very tiny trees or very large wings.

When an aircraft flies at a ground level approximately at or below the half length of the aircraft's wingspan there occurs, depending on airfoil and aircraft design, an often noticeable ground effect
source


Is possible to do a private pilot license training and check-ride on a Light Sport Aircraft? I am planning to do my Private Pilot License. Is it acceptable to do all my training and Check-ride on a LSA?

The answer is yes. The regulations make no reference to the TYPE of aircraft. Just to the Category and Class. You will need to have at least 3 hours of dual instruction under actual or simulated instrument conditions, flying solely by reference to instruments. As long as this can be done in the particular LSA you are flying, or you achieve it in a different aircraft, it counts.

LSA is neither a Category nor is it a Class of aircraft.

You will have to get a type rating to fly passengers (even not for compensation or hire) if one is required for that aircraft.


Do the ICAO and IATA codes for an airport ever change? Do ICAO and IATA codes ever change for airports in time? If they do, how often does it occur? I am developing an app for airports and I am thinking of setting the uniqueness of an airport through ICAO or IATA codes.

Yes it does happen.

A city can build a new airport, in which case it will usually get a new ICAO code, but will get the original IATA (city) code. For example, Oslo changed from Fornebu to Gardemoen - Fornebu is ENFB, Gardemoen is ENGM; the OSL code was Fornebu but uis now Gardemoen.
A city can rename its airport for political reasons, so again the codes are liable to change.
Example 1 is New York - Idlewild KIDL was change to John F Kennedy KJFK
Example 2 is Johannesburg - Jan Smuts International was FAJS, then renamed to Oliver Tambo International FAOR.


How can the Antonov AN 225 only have 2 nose wheels? I was watching the video of the AN 225 unloading at Perth airport this weekend, and it suddenly occurred to me that there are about a zillion rear wheels on the aircraft, yet only 2 nose wheels?

This might make sense in a normal airliner, but in this one, the whole weight of the 117 Tonne generator is passed over the front wheels, as it is unloading?

The reason An 225 has only two nose landing gears (for a total of four wheels) is that it was developed from An 124 Ruslan, which had pretty much the same arrangement. This works during normal operations as the MLG take up most of the load.

However, for loading/unloading, the wheels are not loaded- the nose landing gear is folded, while a support strut comes out, which provides the necessary support and load carrying capacity, as shown below (thanks to @Federico for finding the image).

Image from airliners.net

In this image, you can clearly see that the NLG is folded and the weight is supported by the struts.

Image from news.yahoo.com


Flight Control Weight limitations Does anybody know any limitations of flight control weights?
For instance elevators must have same weight? What is the acceptabld difference/limits and what would be the reason of overweighting? (Paint, bushings, repairs etc).
Please consider A320s and B737s for giving example

Flight control mass balance weights are used primarily to prevent things like flutter. Most airline manufacturers are able to perform analysis of their designs to determine the exact weight to introduce, and where to place it. The rest use static balancing. This article from the Experimental Aircraft Association is not an airliner example, but it provides a good explanation of the why and how of flight control balancing.


Do large commercial aircraft have keys? Do the likes of 737 or a320 or 777 or a380 as examples have keys to the aircraft or to initiate the flight deck? Or are aircraft unlocked and to start the engines it's just a flick of a switch or switches?

There are no keys to anything on a modern airliner. You just get in, hit the switches and go.


Is there some technology which will help in stall recovery? Although rare, it seems that there has been a number of cases where airliners have crashed as a result of a high altitude stall. I tend to picture this as entailing a long, uncontrolled descent where the plane never has proper flow over control surfaces to re-establish flight.

Is there any type of deployable technology that could force a plane into an attitude from which it could re-establish control? I am thinking of something like a drogue system that would force the nose down and dampen spin that could be jettisoned later.

On modern airliners we have audible stall warnings (ranging in complexity from a blaring horn to a voice saying "STALL. STALL. STALL."), stick shakers, stick pushers, and in some aircraft sophisticated flight envelope protection systems (control software that simply won't allow the pilot to stall the aircraft).

When everything is working as designed these systems either make it very difficult to stall an aircraft (you would have to ignore the audible warning, ignore the stick shaker, and either override or overpower the stick pusher), or impossible to do so (flight-envelope protection).

When things are not working as designed - e.g. if the pitot (airspeed) and angle-of-attack systems malfunction these protective systems can become ineffective, however in such a scenario any other automated protection system that we would seek to implement would have similar challenges to overcome (if the flight-envelope protection system can't determine that the aircraft is in a stall how would the hypothetical "stall recovery" system know that it should do its thing?)

The idea of airframe parachutes - even a "spin recovery drogue" - for airliners has its own problems and is a largely impractical solution. (I won't rehash the reasons here, but they are well covered in the linked question.)


What is Waterline and why is it called so? What is waterline and why is it called so?  Is it same as fuselage reference line?

Water lines (WL) designate location in the height of the aircraft, from ground up.

This is explained more in this question


What is the bypass air in a turbofan engine actually for? I'm planning on building a small model turbofan engine for a bit of fun but I thought I'd better get a better understanding of how they work first. I understand the majority of it at the moment but I'm struggling to see what the bypass air actually does, to my mind it seems like a waste of air and energy if its just going straight out of the engine without compression...could someone explain this to me?

On modern turbojets the bypass air provides (at least) two things

Thrust

The air does bypass the engine core, but it is accelerated by the N1 fan and provides thrust as it is expelled rearward out of the engine.  Thrust from the bypass air can contribute more than half of the total thrust produced by the engine (upwards of 80% of the total thrust for some engines in certain phases of flight).  Part of the reason the bypass air is so efficient is that much energy is extracted from the core exhaust to spin the high and low pressure turbines (dual spool) that drive the N1 fan and the N2 compressor stages.
Engine cooling and noise reduction

Cool bypass air can be mixed with the hot air that went through the core at the rear of the engine.  This mixing cools the engine exhaust and reduces the jet engine noise resulting from the rapid expansion of that air once it leaves the engine.  The cool bypass air flowing around the engine core can also be used for general engine cooling.


What military aeroplane seen at Prestwick is this? I saw this plane flying out from Prestwick airport yesterday but what is it?

Based on the fact that this looks like a 4-engined jet, with a T-tail, and winglets. I think it is a C-17.

(wikimedia.org)


Is this ferry flight route possible for a B737-800 WL? Recently a new aircraft, B737-86X (tail AP-BNA) was delivered to a new airline in Pakistan.

The ferry flight as reported by planespotters is BFI - BGO - KHI but this seems like a large stretch given the performance of the aircraft (range of 3,115 nm); so I am trying to find the exact ferry route taken.

However, flightware only shows the test flight when I search by the tail number.

Is there a way to find out what the actual flight plan was?

To clarify based on comments:

I am aware that additional modifications can be done on ferry flights (since these are not normal passenger flights) - such as adding of additional fuel tanks - however, due to the facilities available at KHI I doubt this was the case.

Further I understand that it may be possible that the plane was flown BFI-BGO-KHI - even without any further modifications (favorable winds, etc); so I am trying to find a way to confirm what was the actual flight plan; or if crew-only 737-8 WL can fly that route without modifications.

(737-800 Payload/Range chart) The winglet version has increased range compared to the chart above, per the airport planning manual.

The variant with the 31.7-tonne fuel capacity has a max ferry range of ~5,500 NM. The biggest leg in your question is ~4,400 NM, it's doable even without any tailwind.

In case the 737 in question has the basic fuel capacity (20.9 tonnes), flying eastbound usually cuts the distance due to flying in tailwind. For example, a distance of 4,400 NM at a true airspeed of 450 knots is reduced to 3,600 NM (air distance) with an average tailwind of 100 knots. And down to 3,300 NM with average tailwind of 150 knots.

  The wind may provide a head- or tailwind component, which in turn will increase or decrease the fuel consumption by increasing or decreasing the air distance to be flown.— Wikipedia

It could be down to choosing the best day to fly with the best jet streams.


What happens to incoming flights when the airport shuts down? In Die Hard 2 terrorists take over an airport's ILS and landing lights on a snowy night (visual landing is impossible) and start making threats essentially holding the planes hostage.

The tower immediately sends incoming flights away to the diversion airports and "rack and stack" those already in the landing holding patterns. They also notify the pilots what happened mentioning that after the crisis is over they will start landing planes in order of fuel emergency and that radio may go dead later. Later in the movie the planes in the air actually start running out of fuel and one actually tries to land in the fog.

What is the protocol when you are a pilot in that situation? Do you just turn to your alternate when you have been circling around for 30 minutes (the "Final reserve fuel" for commercial jets).

If a "terrorist takeover" like this were to happen in the real world...

...and the tower still had communication capability:

The tower controllers would advise pilots of the situation, and likely instruct them to return to the Approach frequency to coordinate their next steps (probably a landing at an alternate airport).
Presumably the tower would still have telephone communication as well, and be able to let Approach know to expect the planes to come back because of the emergency, otherwise the pilots would certainly inform the approach controllers of what's going on when they switch back to that frequency.

...and the tower has no communication capability:

With no response from the tower the usual thing for pilots to do is return to the Approach frequency to find out what's going on. The pilots could elect to attempt a landing anyway, treating the airport as an untowered field (this somewhat famously happened at KDCA, for somewhat different reasons), or proceed to an alternate airport.
If the weather required an instrument approach and the ILS radio signals are not transmitting this would be something the pilots could detect pretty easily (similarly if they were turned off while flying the approach there would be indications in the cockpit that the signal was lost and the pilot would execute the missed-approach procedure), and they would proceed to an alternate airport, again coordinating with the approach controllers.

...in any case:

No matter what the situation the aircraft would divert to their alternate airports long before they were in danger of running out of fuel. They would notify ATC of the situation and proceed to an alternate airport. (If not cleared by ATC to proceed to an alternate at some point any sane pilot will declare an emergency for low fuel and proceed on their emergency authority to make a safe landing somewhere.)

So basically there's some "artistic liberties" taken in Die Hard 2 in the interest of making it a movie you'd want to sit through.
A movie where a bunch of terrorists take over an airport and a bunch of flights divert to alternate airports (mildly inconveniencing the passengers) while the National Guard surrounds the airport and deals with the terrorists wouldn't sell nearly as many tickets!


Why do aircraft have an unusable amount of fuel? I learned from this question that a Cessna 152 holds 5.6 litres of fuel that it can't use.

Why would it be designed to hold fuel that it cannot burn, especially since water contamination of fuel is a concern?

Pilot here (with Cessna 152 hours) as well as an engineer who made it most of the way to an Airframe and Powerplant technician license at one point in life.

There are several reasons that conspire to produce 'unusable fuel':

Fuel tanks on airplanes have complex shapes - they include baffles and other walls (with holes in them) to prevent oscillations from building up during in-flight movement. Sometimes these baffles are even engineered into the tanks late in the design cycle as testing finds oscillation issues. These baffles result in 'geometric trapping' of fuel in nooks and crannies.
Drawing fuel from a fuel tank is more complicated in a plane - cars are pretty much flat with minor tilts while airframes can have all sorts of odd and sustained directions that the fuel wants to go due to acceleration. Imagine an extended tilted spiral while descending - that fuel experiences far more lateral acceleration over a longer time period that a car would have. Getting the fuel system to pull fuel out from these different angles is challenging (note that I've picked a non-aerobatic maneuver for which the Cessna 152 of your question is qualified here).
All of this is a cost/complexity tradeoff - solutions exist for 1 and 2 above - fighter jets use fuel bladders that have pressure bladders arranged to squeeze the fuel out so that they can get almost all the fuel even at high G-forces and unusual angles. Aerobatic planes have similarly more expensive and complicated systems than the old and cheap Cessna 152.

There are other considerations as well, but mostly it comes down to whether the plane in question can justify the cost and effort to get every last drop of fuel.

Things get even more complicated in rockets - the moon rockets (properly the Saturn 5 although it was an upper stage specifically) had special extra engines called ullage motors whose only job was to give the stage a little boost in space to push the fuel towards the rear of the rocket so that the main motors could draw fuel and start.

Addendum edit: @supercat below - the definition of unusable fuel is set by federal aviation regulation part 23, section 959 (FAR 23.959) and basically is the worst case under "intended operation" for the particular plane. Since the Cessna 152 is not aerobatically rated, for example, the unused fuel is defined as the fuel level where SOME intended maneuver would be capable of causing a fuel system error. In practice, especially in flat level flight, some of that unusable fuel would be available for use although you are not supposed to plan to use it in your flight planning.


Why do pilots use airways instead of just "flying direct" every time? These days, on larger/newer aircraft at least, GPS navigation is ubiquitous.  So VORs and Non-directional Beacons (NDBs) are used less.  Wasn't the reason for airways because they were the connection points between VORs and NDBs?

It seems like a pilot could easily "fly direct" from one airport to another without using any intermediary checkpoints.  And yet I've been told on several occasions that most pilots use airways.

Why do pilots still use airways instead of flying direct?

Airways simply allow for better management of traffic.
Imagine for a moment that everyone had an off-road capable car, if all the drivers were going "GPS Direct" to their destination how would drivers ensure separation? How would you avoid hitting other cars if there were no roads?

Airways are the aviation solution to this problem: Defined routes between navaids (VORs, NDBs, and the like). Airways can also be defined using "fixes" defined by GPS coordinates which can provide something closer to "GPS Direct" routing while still providing a defined route.

Airways also provide a bunch of other benefits, including:

Traffic Flow Management

Flightplans in Europe are validated by the CFMU (Central Flow Management Unit) and checked for criteria such as direction of airways (which can change during the day, e.g. one airway being for eastbound traffic only between 1000 UTC and 1400 UTC), correct flight level ranges and airways correctly connecting waypoints, such as fixes, VORs or NDBs. The bottleneck in all flight operations is understanding airport capacity (how many operations/hour) and sector capacity (how many aircraft handled per sector/per controller). The goal is sometimes to distribute traffic between two sectors, although having the same destination. Below you will find two routings to Düsseldorf - EDDL, one departing from Leipzig - EDDP and one from Berlin-Tegel - EDDT (click on links to see visual representation):

EDDP - EDDL
ORTAG Q230 WRB T854 DOMUX

EDDT - EDDL
BRANE Y200 HLZ T851 XAMOD

The routing from EDDP to EDDL is going via WRB - TINSA - ADEMI - INBAX - DOMUX, which is within the boundaries of a sector called "Paderborn High" or PADH.

The routing from EDDT to EDDL is going via PIROL - DENOT - HMM - XAMOD, which is within the boundaries of a sector called "Hamm High/Medium" or HMMH/HMMM.

During peak hours, both sectors are separate and deal with traffic only within their sector, which uses the full capacity of each controller handling the sector. Outside peak hours, the sectors can be combined and worked by one controller. This allows a granular usage of controller resources and airspace.

Separation between Traffic

From the example above we have seen that there is 2 routing endpoints at Düsseldorf - EDDL for traffic arriving from the North-East and South-East, XAMOD and DOMUX. Both waypoints or fixes are respective STAR or transition entry-points for arrivals into Düsseldorf. By using a standardized routing to and from airports, we can now expect traffic to always arrive via these two points from the east, unless other coordination has been achieved by the ATC units involved. Looking at the reverse routing for both airports, we will see these routes:

EDDL - EDDP
NUDGO Z858 BERDI Z21 BIRKA T233 LUKOP

EDDL - EDDT
MEVEL L179 OSN L980 DLE T207 BATEL

MEVEL and NUDGO are two of the SID exit waypoints out of Düsseldorf, MEVEL being 10nm north of XAMOD and NUDGO being 26nm east of DOMUX, however the relevant fix here is ELBAL, which is one of the fixes on the SID23L from Düsseldorf to NUDGO, which is 16nm south of NUDGO. With something simple as using standardized entry and exit fixes to and from an airport, we have managed to maintain a traffic flow with ensured separation between departing and arriving traffic, something which would not be possible with GPS direct routing or would require constant ATC vectors.

Handoffs from ATC Unit to ATC Unit

The above examples show different routings and sometimes different sectors handling traffic on these routes. How is traffic handed off to other controllers and where? A handoff consists of moving the radar track of the aircraft from one controller to another and thereafter instructing the aircraft to change the frequency to the next sector controller. Handoffs are initiated at sector boundaries, at specific fixes, which have been agreed on between different ACC (Area Control Centers) or sometimes even within one ACC between single sectors. Since we are already familiar with Düsseldorf airspace, let's use the below routing from München to Düsseldorf.

EDDM - EDDL
GIVMI Y101 TEKTU Z850 ADEMI T854 DOMUX

From the graphical represenation you will see that traffic from EDDM to EDDL will pass the waypoint ARPEG, which is close to the destination airport. Before reaching the waypoint ARPEG, aircraft will be under control of either the Hersfeld (HEF) or Gedern (GED) sector (page 5) and need to descend towards the destination airport. The next sector for arriving traffic into Düsseldorf via ARPEG would be Paderborn High Sector (PADH). The agreements between HEF/GED and PADH are that arriving traffic to Düsseldorf via ARPEG is to be expected at FL240 level at ARPEG and released after handoff for further descent through PADH, even if the aircraft has not yet crossed the sector boundary and is not in PADH airspace. These coordination waypoints and handoff procedures are documented in Letters of Agreement between or within an ACC.

Weather

When weather (wrong-way lows, strong jetstreams, storms, etc) affects the Direct route, flight dispatchers will pro-actively suggest routes around it. It's not unusual for NYC-SFO traffic to be routed over Canada or over Kentucky when the Midwest is storming.

Exceptions - Free Route Airspace

Where airport and air traffic density allows, the use of airways is not mandatory or in some cases, not even expected or provisioned for. One example is the Free Route Airspace overhead Scandinavia, where a portion of airspace can be freely used between defined entry and exit points. Similar systems are also being discussed by NATS UK and the  FAA NextGen Air Transportation System.

For more information on airways and their use, see also the related question:
Is there a difference between how commercial jets and GA aircraft use airways?

  Some material courtesy of VATSIM or VATSIM Germany. While only for simulation use, the material used is as accurate and close to the real sectorisation or procedures as possible, so should be sufficient to explain the concepts presented here.


What is the pilot's obligation to verify a registration has not expired? Old registrations had no expiration date, so a pilot could get in a plane that is owned by someone else and verify the airworthiness and registration by inspecting the documents. But that registration might be expired, and without going to the FAA site to verify it is active could find themselves flying an unregistered aircraft. Has the FAA addressed this situation since they started expiring registrations that didn't originally expire? What would the pilot's liability be in this situation?

You verify new (expiring) registrations the same way you verified the old ("for life") registrations -- by looking at the document. You just have to pay attention now (it's not just "It's there", you need to check the expiration date too).
New-style registration certificates (issued some time after October 2010) are supposed to have the expiration date clearly printed on the certificate (In the lower-left corner, under the date of issue).
For certificates without an expiration date printed on them (registered prior to October 2010) the FAA established a table of expiration dates back when the re-registration requirement was initiated.
ALL of the old certificates have expired by now: The last ones expired December 31, 2013.

As regards the pilot's liability, an unregistered aircraft (or one with an expired airworthiness certificate) is de facto unairworthy:

Does expiration of registration affect an aircraft's airworthiness certificate?
Because an aircraft with an expired registration is not registered, its airworthiness certification would be considered ineffective. Without registration the aircraft is not authorized for flight.
…

From The FAA's registration FAQ.
Aside from being a violation of the FARs to fly the aircraft with an expired registration (because it's "not airworthy") this triggers other implications, for example most aircraft insurance is invalid if the aircraft is "not airworthy" .


Why is the main landing gear of the Cessna Caravan placed so far forward? Why is it that the rear landing gear of the Caravan is placed so far forward?
I understand that the center of gravity must lie somewhere in the middle between the nose gear and the  rear gear but wouldn't it be more convenient to have positioned it a little more towards the rear, giving it (to my opinion) more stability?

This would avoid the need of placing the support on the the tail of the aircraft when it is parked.

Image shows clearly the support.

I suppose that this would not compromise stability during flight.

You're right, placing the gear more aft would make ground handling much easier and not affect flight stability. But it would make taking off harder.

When the aircraft has accelerated to a speed just below lift-off speed, the wing's angle of attack is too low to create enough lift when that speed is reached, so the pilot will lift the nose while the main gear is still on the ground. This maneuver is called "rotation", and the speed at which the pilot pulls the stick or yoke back to lift up the nose is called rotation speed. By the time the aircraft has the right angle of attack, the lift-off speed is reached and the aircraft takes off.

If the gear is further aft, the downforce on the elevator needed to push the nose up needs to be bigger, and more drag is created during rotation. If the gear is still further aft, the maximum possible downforce at that speed would not be sufficient to get the nose up, and rotation must be delayed. The acceleration up to rotation speed is done with horizontal ground attitude because then the wing creates less lift and also less drag during the take-off run. Therefore, the pilot has to get the nose up to get the plane into the air, or he would need to accelerate to a much higher speed, at which the airplane flies even with its ground attitude. This all helps to minimize the airfield requirements.

To strike the right compromise between ground handling and elevator downforce during rotation, it is recommended to position the main gear along a line from the center of gravity down to the ground which is slanted 10°-15° back. The drawing below shows limits between 6° and 20°, but this is quite a wide range. Details depend on the desired angle of attack at liftoff and the maximum range of the center of gravity.

Side view of the recommended tricycle gear layout (Picture source).


Does Airforce one carry missiles to protect itself and its passengers? Do the VC-25 aircraft used for Air Force One carry missiles to protect itself and its passengers?

If so, can these missiles be fired at potential threats?

Near as is know outside of a security clearance the answer is no, a Boeing VC-25 does not carry missiles or offensive weaponry.  During times of crisis, VC-25s are often escorted by armed jet fighters which can attack potential threats to the VC-25 if need be.


Why doesn't GA aircraft use the JASC/ATA document standard? By international law large aircraft are required to categorize aircraft information using a standard called the ATA document numbering system (Air Transport Association).

The ATA document chapters allow a pilot or mechanic to find the same information for any airplane under the same chapter/sub-chapter number. Thus a chapter number for a Boeing 747, B737, or Airbus 380 will be the same. Examples of this include Oxygen (Chapter 35), Electrical Power (Chapter 24) and Doors (Chapter 52).

A few examples of ATA chapter numbers...

ATA No. ATA Chapter name
ATA 00  GENERAL
ATA 01  MAINTENANCE POLICY
ATA 02  OPERATIONS
ATA 03  SUPPORT
ATA 04  AIRLINE USE Aircraft Handling
ATA 05  TIME LIMITS/MAINTENANCE CHECKS
ATA 06  DIMENSIONS AND AREAS
ATA 07  LIFTING AND SHORING
ATA 08  LEVELING AND WEIGHING
ATA 09  TOWING AND TAXIING
ATA 10  PARKING, MOORING, STORAGE AND RETURN TO SERVICE
ATA 11  PLACARDS AND MARKINGS
ATA 12  SERVICING
ATA 14  HARDWARE AND GENERAL TOOLS
ATA 18  VIBRATION AND NOISE ANALYSIS (HELICOPTER ONLY)

About 20years ago the FAA strongly urged GA aircraft to follow the standard with the anticipation that it would soon become law - it never did.

Why has the International community not mandated GA aircraft use the JASC/ATA document standard.

Newer GA aircraft do generally follow this format like the SR22 service manual. As jamesqf mentioned in the comments many of the popular GA aircraft were designed upwards of 50 years ago and their airworthiness and maintenance procedures have not really changed a whole lot thus the manuals are sill what they were when published 50 years ago.

14 CFR § 23.1529 requires that instructions be drafted (or in the process of being drafted) during certification. Like anything in aviation once its certified, why rock the boat by re-writing the manual just to comply with a format.
More reading...


What can I do if I cancel IFR when I shouldn't have? Standard procedure for T-38 training is to cancel IFR in the MOA and fly back to the base VFR.

A couple days ago I canceled in the MOA out of habit and instantly realized that I was above a broken layer between my and the base.

Luckily the other side of the MOA was clear, and I used the extra distance for a more shallow descent than I'd have otherwise done.

But it got me thinking, could I have asked ATC to get me back on my previous clearance?  Being a military training flight, and military controllers I'm sure they would have been super chill and helped me out regardless.  But in the civilian world what would be the best way to handle this situation (other than "don't cancel IFR")?

Since you used the term MOA, I assume you're in the US.

Within the FAA ATC software (not sure about DOD's), the only data difference between IFR and VFR Flight Following is the flight plan altitude. For instance, IFR might have a filed altitude of "060" (6000ft) while VFR FF might have a "filed" altitude of "VFR/065" (6500ft). When you cancel IFR, the controller amends your altitude and leaves the rest of the data unchanged. They don't actually delete your flight plan unless you cancel radar service. Therefore, to resume IFR, all they have to do is amend your altitude again.

Obviously, IFR and VFR are very different procedurally. When you canceled IFR, your existing clearance was invalidated, so you'll need to get a new one. However, since they should still have all your previous data available, it'll probably be similar. But it's less work for them than a normal pop-up IFR.


Why are there no stealth helicopters? There aren't exactly an abundance of stealth planes, but most highly developed countries own one. Why are there no stealth helicopters? If there are, why are they so obscure?

The closest question to this currently is Why aren't modern helicopters quieter?, which one should read first. That regards sonic stealth.

As for radar stealth, any rotating part, visible from the outside, is a major source of unavoidable radar reflections. In 4th generation jet fighters, the engine faces generally contribute more than half of the total RCS (radar cross-sections). Very simple tweaks like installing radar blockers into the intakes can reduce the RCS several-fold.

The rotor is a very large rotating part. Even if made completely radar-transparent, the rotor will accumulate dirt and grime from the air, which have some reflectivity. On a properly stealth-shaped surface, this will be deflected away from the mainlobe. But a rotor, constantly rotating and flexing, has an uncontrollable shape.

This means helicopters can never reach B-2 or F-22 level of stealth. They can get lesser RCS reduction, along the lines of the Silent Eagle proposal. This could be useful, but helicopters fight at much shorter ranges than fighters or bombers.

The F-15 is expected to be visible to high-end opposition fighters out to 300-350 km, and the F-22's stealth reduces that to about 40-50 km against most fighters. At that range, radar stealth is defeated by more powerful or longer-wavelength radars, and even an aircraft with no radar cross-section could be detected by IRST/FLIR systems (correspondingly, high-end opposition fighters use all of these). The F-22's weapons have some hit probability at ranges up to ~80 km against fighters and up to twice that against other aircraft, creating useful room to shoot first. Helicopter radars top out around 50 km and their weapons even closer.

The Comanche could never hope to be as stealthy as the F-22. It's hard to guess its best-case scenario, but something like 60-100 km would've been pretty good. Operationally, for a helicopter, such detection range doesn't make much difference.

Helicopters can already hide from THAAD (theater area air defenses, mostly networked long-range SAM such as the Patriot or S-400) by nap-of-the-earth flying, placing surface features between them and the radar, and hiding among the ground clutter. It's only at 15-40 km that a helicopter would come in direct view of short-range air defenses (highly mobile "all in one" transporter, launcher and radar vehicles). A Comanche would still be visible and targetable by radar at this range.

Essentially, a helicopter's stealth would help protect it from enemy fighters. But there's more than one way to protect your aircraft from enemy fighters.

For the US, it's air superiority. The US maintains an air force that, including the USN, is a match for the rest of the world combined for air-to-air combat. It's not by happenstance - US military doctrine prioritizes air superiority, so resources were spent on it.

With air superiority, a helicopter doesn't need to hide from enemy fighters; the risk they face in every mission won't be worth it for such a low-priority target. The Comanche project was started in a wave of excitement with stealth, with an assumption that stealth could be an easy add-on to it. Without stealth considered, it was underwhelming. Radar-stealthing a helicopter proved difficult and expensive, and there just wasn't much to be gained by it.


Can air to air refueling can be done in the rocket engines as done in the Aircraft jet engines? Can air to air refuelling can be done with rocket engines as is done with conventional aircraft jet engines? If no then what are the possible hazards or conditions preventing this?

It depends if you are asking about rocket ships or rocket planes. On any note, its unlikely in the lower atmosphere, but in orbit, quite possibly.

There are a few issues you may encounter,

Some rockets use solid fuel which cant be pumped from one tank to the next so you would not be able to refuel on the go.
As @TomMcW mentions in the comments most rocket engines also carry oxidizer which you would need to pass over as well, doubling the volume you normally need to pass
Most rockets use liquid oxygen which is stored at very high pressures, you would need to not only have another craft carrying a specialized tank but a way to transfer the oxygen in the proper state.
You would need to transfer the fuel with out causing a pressure issue that lead to cavitation in the engine. During the design of the Saturn V Engines pressure variances in fuel flow caused serious cavitation issues and even lead to the loss of a test bed engine. While this problem was inevitably solved, the solution (as far as I know) does not account for pumping into the tank during operation.
Rockets move fairly fast and also roll on takeoff so some sort of connection mechanism would need be quite complex. Matching speeds is less of an issue than having something revolve around another object that is rotating on an axis.
Most rocket planes operate above the celling of practical refueling aircraft.

Frankly there is little practical reason as most rocket planes don't really need to refuel. Historically rocket planes like the Bell X-1 or the X-15 were built as test beds to push speed and altitude limits they carried the fuel they needed, burned it, broke the record, and glided home using histories oldest engine, gravity.

Refueling spacecraft has not proved to be a need yet as we have been able to successfully escape earth orbit on a single tank of gas. Building a rocket in space and sending it off has been theorized but there no examples of that yet and in that case you could ferry fuel up in small loads and deal with the docking in orbit.

Once in orbit docking two craft is fairly straight forward, then just connect the fuel lines and pump (presumably with out the engines running)...


Why does the ATIS say "read back all instructions"? Whenever I'm at a class D, I'm always confused as to why the ATIS says "read back all runway assignments and hold short instructions." Isn't that just a given? It seems redundant and it takes up valuable time in the ATIS broadcast. If I tune in half way through the reading, I don't want to have to sit there for 5 minutes just to hear the whole thing.

Due to the ongoing runway incursion epidemic, US ATC must hear every aircraft read back certain instructions, including callsign. If you don’t read them back correctly, they’re required to repeat the instruction until you do. No matter how many times it takes.
When this rule was first adopted (or at least enforced), a shocking number of pilots couldn’t give proper readbacks. This caused a lot of frequency congestion and other issues, such as making an aircraft on final go around or holding departures just because someone taxiing toward that runway wouldn’t properly confirm they’d hold short of it.
Things have gotten somewhat better as pilots have learned, but it is still common enough of an issue in practice that they won’t take the reminder off the ATIS. And since some other countries either don’t have or don’t enforce this rule, it may never go away.


Who can sign off the aircraft after completion of 100-Hour Inspection? Can the mechanic who performed 100-hour inspection sign off the aircraft?

Yes.
In the United States, annual inspections must be signed off by an IA, but 100-hour inspections may be signed off by the A&P that performed the inspection.


Can tower clear aircraft for take off with traffic still on the runway? How much separation is required after an aircraft lands before ATC can clear another aircraft to take off from the same runway? On longer runways are small aircraft allowed to commence take off roll or be cleared for take off while the preceding landing aircraft is still on the runway? I looked and was unable to find any ATC instruction requiring separation between landing and departing traffic on the same runway.

While this would be unsafe, it seems to me that I have been cleared to take off while there was still an aircraft finishing its landing roll. By the time I had lined up for take off the preceding traffic is alway clear but is this still a "legal" practice to be cleared for take off before the preceding air craft calls "clear of the active"

According to the ATC orders controllers can indeed clear an aircraft for takeoff 'early':

  3−9−5. ANTICIPATING SEPARATION

  Takeoff clearance needs [sic] not be withheld until prescribed separation
  exists if there is a reasonable assurance it will exist when the
  aircraft starts [sic] takeoff roll.

A common scenario would be clearing an aircraft that's holding off the runway to take off while the landing aircraft is still on the runway. If the controller expects that the landing aircraft will be off the runway by the time the holding one turns onto it, then it would be allowed.

Section 3-9-6 lists the conditions for allowing an aircraft to start its takeoff roll. It's too long to quote here and you can read it yourself but the two main  conditions seem to be:

The other aircraft has departed and crossed the runway end or turned to avert any conflict
A preceding landing aircraft is clear of the runway


Stalls: which flight control surface is effective last? In an aerodynamic stall, which flight control surface (limited to ailerons, elevators and rudder) remains effective for the longest period of time during the stalling condition? In other words, which of the three loses its effectiveness last?

It depends on the type of stall and the loading configuration of the aircraft. The short answer is that the rudder typically stalls last because the angle of attack of the wings is independent of the AOA of the vertical stabilizer. However it's usually among the least effective control surfaces in getting out of a straight dive (very useful for recovering from spins and spiral dives though).

Of the horizontal surfaces, it depends on which one has a higher AOA at the time the wings stall, which is dependent on how the plane entered the stall, and how the aircraft is configured. A sudden pitch-up in an airframe with an aft CG will cause the horizontal stabilizers and thus the elevators to depart first. In most other situations especially when the CG is forward of the CL, the wings will have the higher AOA as the nose pitches downward, so the elevators will remain useful as long as the tail isn't caught in the turbulent airflow off the wing. T-tails have this disadvantage; the higher tail location normally puts the tail in cleaner air, but in a stall the turbulent air off the wing shelters the tail making it less effective.


What are the differences between top and bottom mounted airbrakes? What are the differences between airbrakes on the top side of jet aircraft (like on the F-15) compared to those on the lower side (like on the A-7), in terms of effectiveness and pitching when they are deployed?

From Wikipedia.

From Reddit.

Would pitch authority be better in one than the other?

Since airbrakes are frequently used during landing, putting them underneath the fuselage could create a ground clearance problem.

Putting brakes on the top only would create a pitch-up tendency when they are deployed. This is countered automatically by the Fly-By-Wire flight controls, so no correction is necessary for the pilot.


What is the most fuel efficient climb speed for a C172 SP? Assuming ISA, sea level, no wind, max gross weight, what speed would be most fuel efficient per 1,000 ft of climb?

Alternatively, if that converges to the most fuel efficient cruise speed, when there's no time and/or distance limitation for completing such a climb, please explain why this is so.

First consider the four forces on the airplane in the cruise:

          ⇧
        Lift
⇦ Drag    .  Thrust ⇨
       Gravity
          ⇩

Drag is a function of the airframe, attitude, and airspeed. If the airplane can fly, then drag is more then offset by thrust. The lift is generated by a component of the forward motion when the flying surfaces convert the horizontal force to vertical force. And finally, the lift force is equal to the force exerted by gravity.

Now let's talk about fuel efficiency. That is how much you can do with a quantity of fuel, and you didn't specify whether you're interested in fuel for time (endurance) or fuel for distance, or something else. But let's discuss the major components of fuel usage:

Engine motion. The engine is more efficient in terms of power at its higher rated power setting. So, you would think efficiency would be gained by selecting a higher power (assuming you could also climb with less than 100% power).
Heat. I guess a typical heat engine like a piston engine consumes about 50% of fuel energy to heat (rough guess, it's prob. in the range 35% - 65%). But the heat engine is more powerful the greater the difference between inlet temperature and exhaust temperature. So, the greater time you can spend at higher altitude is probably more efficient in fuel for power.
Cooling. Sometimes you need extra unburnt fuel for engine cooling. For example during climb, when the engine is at higher power and the airflow is reduced.

Now let's discus climbing. During a climb the aircraft has (in theory) to produce all the power necessary for level flight, plus a little extra for the change in elevation. I would posit, without any evidence, that the fuel spent on the elevation change is insignificant compared to the fuel required to stay aloft. (I will gladly accept a reference or metrics if someone has them). But think about it, if you put the aircraft in an elevator powered by a similar motor, it would take a few drops of fuel to raise a few feet. That's a thousand drops for a thousand feet - it is nothing versus constantly offsetting the the weight constantly as it does in flight.

So what is the more fuel efficient climb procedure? It is the technique using:

Higher engine power
Maximizing time at higher altitude; minimizing time at lower altitude
Balancing the mixture to keep the engine as hot as its design will allow. (you said fuel-efficient. You didn't say cost-efficient. Don't violate your POH!)

In summary, to expend the least fuel, climb as early as possible, as quickly as possible (e.g. Vy) and with minimum acceptable richness.

And as long as we are talking efficiency, please also run the tanks dry at your final cruise altitude. This will maximize the most fuel efficient part of the cruise, when you are carrying less fuel.


Could the Grumman G-21 Goose be started by punching the instruments? In the 1985 movie "Commando", John Matrix (played by Arnold Schwarzenegger) initiates engine ignition simply by punching the cockpit dials after several failed standard attempts.

Could this ever result in the engines starting in reality?

No, punching would not cause engines to start because you'd need to hold the starter button down (or twist the key depending on the airplane) until the engine catches. It's possible that if there was bad wiring on the panel that punching it could make it work again, but that would likely be temporary.

It's just Hollywood.


How does a helicopter hover? Technically, unless a helicopter's centre of gravity and centre of lift (centre of the rotor) are in perfect alignment, it would generate a pitching moment which would make it unstable.

So, how does a helicopter manage to solve this issue. (I'm assuming it's impossible to perfectly align the CG and the centre of lift due to practical loading conditions.)

A helicopter can hover without the CoG being directly underneath the rotor hub, because the rotor hub can apply hinge moments:

Fully articulated hubs with a hinge offset and fixed hubs apply direct mechanical moments to the fuselage, which line them up with the rotor angle.

The rotating blades are subject to centrifugal forces, which pull the rotor hub in the plane of the rotor deflection. As soon as the rotor plane changes as a result of cyclic stick input, the resulting rotor hinge moment will change fuselage angle accordingly, providing the desired feedback cue.
Any helicopter, regardless of the type of rotor hub, has an aerodynamic coupling between fuselage attitude and rotor attitude. A teetering rotor such as on Bell 212 and R-22 does not produce above mechanical rotor hinge moment. In flight, a helicopter is suspended from its rotor, with the Centre of Gravity underneath the centre of lift, unless the rotor can apply a hinge moment to the fuselage. With a rearward CoG and no hinge offset, the following could happen:

The helicopter has taken off vertically, nose tipped up first, and cyclic forward was input. If the rotor had a hinge offset the fuselage would tilt forward, but with a teetering hinge like in the question there is no centrifugal force acting on the hub, and fuselage position now depends only on CoG location. The upward nose angle has consumed some of the useful forward tilt of the cyclic stick. Visibility is impeded. Fuselage tilt provides no direct feedback of the cyclic position.

Fortunately there is an aerodynamic rotor hinge moment, created by the aerodynamics of flapping. The picture is from Helicopter Performance, Stability and Control by Raymond Prouty. It shows that at first, the rotor acts as a gyroscope and stays in its plane. But the blade feathering is referenced to the shaft, and angle of attack of the right hand blade is increased, left hand blade decreased. The rotor will then flap until it is perpendicular to the shaft. With teetering rotors, there is an indirect aerodynamic coupling between fuselage and rotor shaft: the fuselage attitude still follows the rotor attitude but at a slower rate.

The CoG cannot be placed anywhere, it must remain in the area where the moment caused by gravity pulling on the CoG is lower than the maximum hinge moment. But with all helicopters, there is a region of useful CoG.


What regulations are in place for ultralight vehicles flying over US national parks? A flight instructor i met with recently said that flying ultralight over national parks is a crime. The law section of the powered paragliders bible has nothing on parks.

One would think that commercial vehicles wouldn't be needing to  plan around parks above a certain altitude.  But ultralight vehicles may have different regulations.

After further reading into the book,  it says "almost all state and federal parks prohibit launching aircraft and ultralights except at airports." Nothing about flying though

The use of mechanized items, which UAS, ultralights and other aircraft are considered are prohibited from Congressionally Designated Wilderness areas.

That designation does not appear on a sectional chart, but can be queried from the supervisor for the park or forest.  As far as I know, overflights, particularly those by manned aircraft are not prohibited, but launch, recovery or operation from the wilderness area is prohibited.


Why did the RAAF procure the F/A-18 despite being purpose-built for carriers? Why did the Royal Australian Air Force (and others) procure the F/A-18 despite being purpose-built for carriers?

Two reasons:

The airplane is extremely versatile, while having adequate performance, and is a good choice when a small airforce needs a do-everything airplane to replace multiple types.

Being designed for carriers, it's overbuilt for normal land operations in many key areas, which means a longer airframe structural life in its much easier life landing on runways.  For an air force with a limited budget and the need to run the airplane a long time, it's worth giving up some of the speed/payload/range that was sacrificed by the structural needs of carrier ops.


Can hood time in a glider be logged as simulated instrument time for FAA IR purposes? I need to build my simulated instrument time toward IR. Can flying under the hood in a glider (with an instructor/safety pilot...) be legally counted as simulated instrument time in the same way would be the case had it been an ASEL?

In the US, yes. According to the FARs you only need to have three hours in an airplane in preparation for the flight test and you must fly the cross country in an airplane so that’s probably another 3 hours.

It looks like you can log hours under the hood in a glider, but it would have to be with an airplane CFII. However, I don’t know that you would be able to train in any of the areas of operation except for (4) Flight by reference to instruments; so it probably wouldn’t be worth your time. I don’t know how you would fly an approach or fly a course by reference to navigation systems.

So as a practical matter, the answer is no.

  §61.65   Instrument rating requirements.

  (c) Flight proficiency. A person who applies for an instrument rating
  must receive and log training from an authorized instructor in an
  aircraft, or in a full flight simulator or flight training device, in accordance with paragraph (g) of this section, that includes the
  following areas of operation:

  (1) Preflight preparation;

  (2) Preflight procedures;

  (3) Air traffic control clearances and procedures;

  (4) Flight by reference to instruments;

  (5) Navigation systems;

  (6) Instrument approach procedures;

  (7) Emergency operations; and

  (8) Postflight procedures.

As an aside, I used to rent out my Cherokee to helicopter commercial students who needed instrument training

  (i) Five hours on the control and maneuvering of a helicopter solely
  by reference to instruments using a view-limiting device including
  attitude instrument flying, partial panel skills, recovery from
  unusual flight attitudes, and intercepting and tracking navigational
  systems. This aeronautical experience may be performed in an aircraft,
  full flight simulator, flight training device, or an aviation training
  device;


How is minimum runway length related to V1? 1) Is $V_1$ used to determine minimum runway length? How is $V_1$ calculated?

2) If it is used to determine the minimum runway length, and for example we have a runway of 8000 ft and my airplane's accelerate stop distance required (ASDR) is 4000 ft and takeoff distance required (TODR) is 5000 ft, can my $V_1$ be as low as 15 kts? Since (let's say) below 15 kts, of course you will have the 4000 ft required to stop and also have enough distance to takeoff with 1 engine inoperative.

3) Let's say we have a very long runway so an airplane can make a rejected takeoff even at rotation speed ($V_R$). Can $V_1$ be the same as $V_R$?

Takeoff Field Length
The “FAR” Takeoff Field Length determined from the FAA Approved Airplane Flight Manual (AFM) considers the most limiting of each of the following three criteria:
1) All-Engine Go Distance:
115% of the actual distance required to accelerate, liftoff and reach a point 35 feet above the runway with all engines operating:

2) Engine-Out Accelerate-Go Distance:
The distance required to accelerate with all engines operating, have one engine fail at $V_{EF}$ at least one second before $V_1$, continue the takeoff, liftoff and reach a point 35 feet above the runway surface at $V_2$ speed:

3) Accelerate-Stop Distance:
The distance required to accelerate with all engines operating, have an engine failure or some other event at $V_{EVENT}$ at least one second before $V_1$, recognize the event, reconfigure for stopping and bring the airplane to a stop using maximum wheel braking with the speed brakes extended.

$V_1$ Speed
$V_1$ is the speed chosen by the manufacturer as "the pilot’s initiation of the first action to stop the airplane during the accelerate-stop tests."  Note that this is particularly important in that it is not a takeoff decision speed as some pilots like to think of it.  The decision must have been made prior to $V_1$ so that there is time to react by $V_1$.
This speed is chosen by the manufacturer and must be between the engine failure speed1 and rotation speed.  Within this range, they could choose any speed, but typically they choose the speed which gives a balanced field length (see next section).
There are also other factors to consider such as the maximum brake energy limit ($V_{MBE}$) which will prevent $V_1$ from being too high.

Balanced Field Length
If we takeoff from a fixed length runway (like, say one that matches the Takeoff Field Length from above), changing the $V_1$ speed will affect the weight that we can successfully continue the takeoff or abort within the available runway.
At a particular weight, a lower $V_1$ will enable us to stop sooner if we abort but will take more distance to continue the takeoff.  A higher $V_1$ will require more distance to stop but will take less distance to continue.  If we graph these values, there will be a point where the $V_1$ speeds for the abort/continue lines meet, and this is known as the balanced field length.  It is the value typically given in the AFM:

This is nice because it gives the pilot one important number to remember instead of different stop/continue $V_1$'s.
If they were to choose an extremely low $V_1$ as in your question, then it would require considerably more runway in order to continue the takeoff than if it were higher, and it would not be balanced.  Some AFM's do include separate charts for accelerate-go and accelerate-stop though so you could figure out exactly how much runway that you would need if the engine failed at a lower airspeed.

Rotation Speed
$V_R$ is determined independently from $V_1$, and if it is ever less than $V_1$ then it must be raised to be equal to $V_1$.

References
The regulatory information for takeoff performance on transport category aircraft is listed in 14 CFR Part 25, Subpart B, Performance, 25.101 - 25.113.
Of particular interest for this question would be 14 CFR 25.107 - Takeoff speeds and  14 CFR 25.113 - Takeoff distance and takeoff run
An easier to read document is the FAA's Pilot Guide to Takeoff Safety which covers this and a lot more.  Much of my answer was taken directly from this document, and I would highly recommend anyone that is flying a multi-engine aircraft to read the entire thing.

1 $V_{EF}$ itself must be above the minimum controllable airspeed on the ground plus acceleration while the pilot reacts to the engine failure.


How are compressor maps drawn? I've always thought they are empirically derived: once you have your axial compressor phisically in a bench, you set both a rotational speed and a mass flow throught the turbomachine then you measure the pressure ratio so you can fix a point on the map. After, It will be made for several mass flows therefore defining a particular constant speed line.

It is correct?

(image source: Wikimedia)

From my textbook, Fluid Mechanics and Thermodynamics of Turbo-machinery by Dixon, it is explained that they find the results for the working line empirically. This corresponds to the line with the black dots on the diagram you provided.

Essentially, your test rig is made up of a compressor that is connected to a downstream throttle. It is the size of the throttle (in a real engine, this corresponds to the size of the nozzle) that is going to determine the test working line (called an operating line if it does not pass by the Design Operation Point). In other words, a different operating line corresponds to a different size throttle.

Then you vary the speed and measure the obtained pressure ratio. Connecting the dots will give you the working line.

ADDED DETAIL:
You have to know the size of the throttle because it will give you valuable information regarding your exit configuration. This has to do with the fact that the nozzle will usually be chocked, which will fix your non-dimensional mass flow through the nozzle. But that's a whole other topic in itself!

I did my best to answer your question, sorry if it does not help, I am only a student! If you want details of the calculations for compressor maps, you should check out chapter 5 of Dixon.


Why is the Beluga chartered out for oddball missions, but not the Dreamlifter? Both Airbus and Boeing have special outsize-cargo freighters for transporting large pieces of airliner; Airbus has five Belugas (derived from the A300), while Boeing uses four Dreamlifters (extensively-rebuilt 747s).  The Beluga fleet is primarily used for moving pieces of Airbus aircraft around, but Airbus also charters them out for moving various other very large things from place to place, making a tidy profit on the side.  Not so with the Dreamlifters, which are used exclusively in the airliner-transport role.

Why is it that Airbus charters out spare Beluga capacity, but Boeing keeps their Dreamlifters all to themselves?

The 747LCF cannot haul any cargo except Boeing’s own cargo as its type certificate only allows it to carry Boeing’s own cargo.

Whereas A300 Beluga’s type certificate limitation section only refers to Airplane Flight Manual. It may allows to carry other cargo with some conditions met.

—————————

Page 28 of A20WE, type certificate of 747, states

  XIV - 747-400 Large Cargo Freighter (LCF) Major Design Change (Approved June, 2, 2007 ) Transport Category

  Allowable cargo

  These airplanes are not approved for commercial freight hauling operations of material other than that approved per Exemptions 8769, 8769A and 8769B. Only cargo that supports Boeing corporate lines of business is allowed for carriage. All items intended for carriage must conform to the standards found in Document D926U013-44, “747-400 LCF Flammability Acceptance Criteria for Cargo Carriage,” or be accepted by the FAA once a safe method of transport has been established. A summary of all items allowed for carriage is identified in Document D451U742-01, “Allowable Cargo – 747-400 Large Cargo Freighter.” Document D451U742-01 is considered part of the Weight and Balance Manual/Airplane Flight Manual. In addition, a listing of the FAA-approved shipping mechanical equipment (SME) fixtures that are approved for installation on the 747-400 LCF aircraft are contained in the Weight and Balance Control and Loading Manual (Document D043U545-BHC1).


Would a roll cage plus a safety harness make a small GA aircraft accident more survivable? It seems to me that race cars (like Formula 1 and NASCAR) and small GA aircraft (like a Cessna 172 or Piper Cherokee) travel at generally the same speeds, roughly between 70 and 200 mph. Yet, if an accident happens, you appear to be more likely to die in a small plane than a race car.**

I figure this may have to do with some of the safety features of race cars versus the safety features of GA aircraft. The main features being the racing harness and the roll cage.  (And also, as Freeman pointed out in a comment, the HANS device and the helmet help quite a lot as well, especially in frontal impacts.)

I know roll cages weight about 80lbs and that they aren't cheap, and I know a safety harness can be difficult to put on and people might not like using them, and I know a HANS device can be cumbersome, as also a helmet can be. But forget all of that for a moment. I'm not asking about why we don't use them from an economic/utility perspective.

What I really want to know is if putting these in a small airplane would be of any benefit to begin with. It's true that they are massively helpful in racing vehicles, but I wonder if the forces racing vehicles face during a crash are markedly different than what you would find in your typical GA crash (e.g., perhaps aircraft accidents happen at less predictable angles, or involve more torsion, etc.). And if perhaps those differences in forces make the use of a roll cage and a safety harness kind of pointless in a small plane because they can't actually help in that kind of accident.

So, would all of these racing safety devices actually make a GA crash more survivable, or does the nature of GA accidents make their use less effective than they are in a race car?

** Try as I might, I couldn't find hard stats on "deaths per accident" in either area.  So this is mostly an impression I've gained from reading a lot of NTSB reports and watching a lot of racing. The fact may be debatable, but shouldn't detract from the main question.

Short answer: Yes, a better harness would help in some cases, but will achieve little all by itself. A roll cage might help in a few cases, too, but would be much less effective per pound.

Your observation is correct: Race car drivers enjoy a lot more protection than GA pilots. This is a rather recent development; 30 years ago the chances of surviving a crash were equally low for both.

There are two factors which stand out in a GA crash:

Peak accelerations which will lead to internal lesions like the rupture of the coronary blood vessels, and
Physical injury by sharp objects entering the occupant's space, including flailing limbs being hurt by sharp objects in the cabin.

Both factors were also killers for race car drivers, and they were defused with improved design methods. A safety cage is not just a frame around the driver: Any structural failure must occur in such a way that the structure fails away from the driver. In addition, the whole car body is designed to crumple at roughly the same force over its length in order to use the available crumpling zone as well as possible. This allows to decelerate the safety cage at a constant rate, so that peak loads can be avoided. A third factor is a much better restraint system, of which the HANS device is only one aspect. Using five-point harnesses would already help to avoid "submarining", a process where the pelvis slides under the lower restraint, causing the harness to press against the intestines. The image below shows the regular pelvis location and body contours as a dashed outline and the displaced pelvis and spine as a solid line. The displaced body is the shaded area.

None of this was considered at the time when today's GA aircraft were developed and the regulations were set up. At that time the prevailing opinion was that nothing could be done in a crash, so all efforts focussed on avoiding crashes in the first place. Adding only parts of the whole protection packet will be of little help - only their combination can effectively protect the race car driver. Even the 5-point harness needs an adequate seat and properly located mounting points to be effective.

The US army has collected all research up to the early Eighties in a five volume work called the Army Aircraft Crash Survival Guide (pdf!). It's intention is to improve the crash survivability for helicopter occupants and Army aviators, and much can be transferred to General Aviation. If you look for hard stats, you will find at least lots of citations there. I remember in particular a study from the Fifties where statistics showed that J-3 pilots would mostly be killed in a crash, while the rear occupant would show only minor injuries. In the study, Pipers filled with test dummies were put on rails and crashed into an earth wall. Funny stuff.

A J-3 in Army livery. Then it was called O-59 or L-4.


What reasons exist for not designing airplanes with breakaway wings for crash safety? As most crashes are on takeoff and landing, and fire is the real killer, most often. Why not have breakaway wings? That's where the gas is. Let's assume a plane has to make a hard landing..upon touchdown/contact jettison the wings. They serve no purpose at that point and they definitely kill people. Breakaway parts/modules are employed in many arenas, so why not wings?

I can't think of an accident scenario where this might help. If you're hitting the ground hard enough to crash but have survivors, you're looking at an accident like TK 1951, where not only was the wreckage all in pretty much the same area, but it didn't even catch on fire. Aviation fuel is not as volatile as movies make it seem.

Maybe you are thinking of something like AF 358 which overran the end of the runway and burst into flames? Despite that fire everyone survived, but what if they realised it was going to overrun and jettisoned the wings whilst still on the runway?

Well the biggest problem to me is how to slow the aircraft down without wings. At higher speeds, the wheel brakes are ineffective without the use of ground spoilers. Without the reverse thrust from the engines you are guaranteeing that the aircraft will be going faster when it leaves the runway, leading to a much higher chance of casualties.

No piece of engineering is perfect either - what happens when it fails and the wings accidentally detach when everything is going well? What if they are flying in severe turbulence and the sensors detect high G forces and confuses that for a hard landing? Or if it a manual jettison, what if the pilots accidentally pull it, or a suicidal pilot does it while the other is looking the other way?

There are many other problems too, such as how some aircraft are designed with the gear support in the wings, that some have large fuel tanks in the fuselage, and the extra weight and cost of getting such a system certified. Ultimately this suggestion falls into the same bucket as every other drastic safety idea - in trying to fix a problem that barely exists, it creates a lot more in its place.


What is the transient bleed valve in a gas turbine engine? What is a transient bleed valve and what's its purpose ? Also, can you explain the purpose of bleed valves in general?

The high pressure compressor in a typical engine has many stages (e.g. GE90-115 has 9) all running on the same shaft, and thus all at the same speed. The problem is that sometimes the flow/pressure that the front stages are producing does not match the flow/pressure that the back stages are able to accept. When this happens, the compressor will stall (this is bad).

This can happen in several different situations, and one of them is a quick transient.  For example a very quick acceleration from idle to full power.

During this quick transient, the front stages might be trying to pump too much air versus what the back stages are able to accept. Eventually, everything will even out, but for a few seconds there may be a mismatch.

There are several different ways that engine designers can accommodate this situation.  One is a transient bleed valve.

When the engine performs a very quick acceleration, the transient bleed valve is opened and some of the air from the compressor is just dumped overboard.  When the engine reaches a steady operating condition, the valve is closed.


What are the advantages of more than 4 propeller blades? I have heard that propellers with more than four blades are not as efficient as 4 or less blades because of lower thrust which may result from interfering prop-streams. But I see the ATR-42/72 and they have 6 blades. What is the reasoning and the advantages to that prop layout?

You are right, more blades are bad for efficiency (follow the link for the definition). Ideally, a propeller should have only one blade. Every additional blade will cause disturbances which interfere with the flow on the other blades.

When engine power increases, the propeller disc area should also grow, but this growth is limited by the resulting speed of the blade tips. Once the flow speed there becomes supersonic, the drag at this section of the blade increases without a corresponding increase in thrust. To avoid that, the next best option is to increase the solidity ratio of the propeller, called also the activity ratio. This is done by either increasing blade chord or the number of blades.

Make no mistake, this is bad for efficiency. But if there is enough power available, adding more blades is the best way to transform that engine power into thrust.

Take the Supermarine Spitfire:

The prototype, powered by the 1,030 hp Rolls-Royce PV-12, had a two-bladed propeller
From the Mk II, a three-bladed propeller was fitted to accommodate the increasing power of the RR Merlin (1,470 hp for the Spitfire Mk V).
With the Mk IX, a four-bladed propeller was needed for the 1,575 hp of the supercharged Merlin 61.
From the Mk XII, the more powerful Rolls-Royce Griffon made a five-bladed propeller necessary. Engine power was raised from 1,735 hp to 2,300 hp for the last variant, the Mk XXIV.

Rolls-Royce Griffon-powered Supermarine Spitfire (picture source)

A lower prop speed allows to increase its diameter, but while tip speed will drop by less than the reduction in prop speed (after all, flight speed should not change), the available thrust from this propeller will drop by the square of the speed reduction, since thrust is proportional to the dynamic pressure on the blades. And thrust you get only from the circumferential fraction of the local speed at the blade; flight speed does not count here and does not help to mitigate the reduction. Consequence: You cannot make the propeller bigger and spin it more slowly for a given power.

An extreme example for a propeller with a high activity ratio is the Aerosila SV-27 contra-rotating propeller of the D-27 propfan engine powering the Antonov An-70:

SV-27 propellers on the An-70 (picture source). Eight blades in the forward disc and six in the rear, running at only 1200 RPM. In order to reduce Mach effects, all blades have a swept tip and deep chord.

This can only be topped by something like an ungeared turbofan with a ducted propeller. A turbofan, in other words.


What does the Airbus A340 Primary Flight Display look like during startup? I'm developing a simulator addon and I'd like to accurately show what the A340 Primary Flight Display (PFD) shows during its startup sequence.

I'm looking for any images, photos, documents or movies that show the display from a cold and dark start until it's fully operative. That might include different states like a boot screen, self test and so on.

I can easily find information on what the PFD looks like once startup is complete, but what is displayed before that point?

Initially, I would like to apologize for the not-so-good quality of the pictures (there were taken into a busy enviroment).

I tried to find some vector photos from the respective manuals but I couldn't, that's why I took them by myself.

I am going to provide you with some information on each photo. It is very synoptic description in order to get the help you need for the development of your stuff, and to cover this question.

In case that you need any further technical information please open another question.

  1) Immediately after provide the a/c with power.

  2) After 40s

  3) After approximately 50s and before initialization of the ADIRS (which is taking place at cockpit preparation after the preliminary cockpit preparation checklist.)

  4) Approximately 15s after the startup of the ADIRS, and during the "IR alignment in progress." (info* on ECAM)

  5) During IR alignment in progress. (Only here the FDs are by default ON when the a/c is powering up, and the red FD symbol on the PFD during alignment is flashing, then manually FDs are switched off.)

  6) After IR alignment and before FMGS PERF PAGE preparation, (and FDs still are OFF).

  7) FDs are ON, FMGS preparation at PERF PAGE not completed yet, and ENGINES are OFF.

  8) FMGS PERF PAGE data inserted, FDs ON, ENGINES OFF.


What could reasonably be done in case 7,500 airplanes must be landed quickly? I read 5,000 to 10,000 aircraft are flying at a given time. There are several very unexpected but plausible reasons to land all planes quickly, e.g: a war / terrorism event; a giant volcano eruption); or a major meteorite impact

Whatever, in case there is a sudden need to stop flying, what would happen:

From an ATC standpoint, is there any impossibility to conduct such massive landing?
Is there enough runway throughput to allow planes to land quickly?
Is there enough room to park all aircraft?

Is there any preparation for this kind of operation in some countries?

There's roundabout 400 paved runways over 2438 m (8000 ft) in the USA and EU, respectively, and about 200 or so in China and Russia, respectively, so that's about 1200. They are long enough to deal with most aircraft. Some might be untowered or unavailable, but then there are other countries, too. Estimates for "commercial" airports worldwide run around 4000 (there are about 9000 IATA codes, apparently).

So, every suitable runway would have to accommodate around 2 to 10 aircraft.

You can have around 50 to 70 movements per runway per hour, though you need separation of up to 3 minutes to avoid wake turbulence if a smaller jet arrives after a heavy. Let's say 30 landings per hour, and we're talking about 20 minutes, just in terms of pure runway capacity.

Now, to get all those planes lined up nicely... Parking might get crowded, too, but I'd think it would be doable - just fill up taxi ways progressively (presumably you don't care about take-offs for a while). See this diagram of aircraft parking prior to the Tenerife disaster (where many planes diverted to the small Tenerife airport due to a bomb in Las Palmas).

At any rate, the practicalities would be daunting. Would be interesting to see a proper feasibility study.


Pilot passed out in a small GA plane. What can a passenger do? There is another question about airliners and if someone not qualified could land them. My question is about the steps I should take to stay alive in a small GA plane.

Let say a friend of mine invites me aboard a small aircraft (like Cessna 172 or equivalent).
At some point my pilot friend passes out for some reason. What should I do considering the following:

I'm not a pilot.
I'm seated in the co-pilot seat.
I spent hundreds of hours on Flight Simulator (a few years ago).
I've been initiated to fly a small aircraft (1 session covering the very basics), but no take-off/landing exercises.
The weather is good.
Aircraft is in good condition.
The tank is full.
Area has ATC and I know how to operate the radio.

This is my guess:

Hold the plane's level and heading
Slap my friend to try to wake him up
Send "Mayday" asking for assistance and technical guidance
Try to follow ATC instructions as well as I can

Does this look good? What should be done differently?

Best case scenario: You're straight and level, on frequency with some form of human being, there's no immediate danger and you have the know-how to transmit. In that case, that human will provide you with everything they possibly can to help you. Most important thing for you to do is keep the aircraft away from clouds, away from terrain and not panic. You'll probably be in an aircraft that is more-or-less easy to fly in this situation. Most GA aircraft are quite stable and will not be a beast to control.

Once talking to ATC they will tell you to set your transponder to a number. You should find somewhere a 4-digit readout with a knob below/above each digit. Set the number indicated to help ATC identify you easily.

Otherwise, look around you for big landmarks (Mountains, Lakes, even a large Church/Cathedral) as one of the first things ATC will want to do is work out where you are.

That's best case; let's look at some alternatives.

You're out of range of the tuned frequency on the radio, or there is no response:

Tune 121.5MHz, this is the emergency frequency. Someone will be monitoring this channel and be able to give you further advice - if nothing else a local ATC channel to tune. Failing this see if your pilot has a chart handy, he may have drawn his intended route on it - look along that route for anything that looks like a frequency to tune into the radio.

Aircraft is climbing, or descending:

Get the aircraft into safe, level flight. Remember controls work in the opposite sense to what you might expect (probably not if you've ever played any flight simulator). If the engine is roaring reduce power slightly. If you appear to be losing altitude with the nose on the horizon increase power slightly. Do everything with tiny incremental changes. Try not to fiddle too much with controls, only what is necessary.

Aircraft is heading directly for a cloud/out to the sea/towards a heavily built up area/a big airport:

Turn 180 degrees - don't try to turn too quickly, it should take roughly 30 seconds to 1 minute to complete this turn.

There are courses which are aimed at non-pilots who regularly fly in the right hand seat. Here's some interesting reading:

http://www.avweb.com/news/safety/183023-1.html


Why are some seemingly major waypoints nowhere to be found on sectionals (including enroutes)? I'm looking at the BNTLY.CAVLR3 arrival at KIAD:

Almost none of the waypoints (BNTLY, CAVLR, COINZ, etc.) are on a single sectional or chart, enroute or otherwise. Considering this is such a major route into such a major airport, why would these waypoints not appear? How would one ever hope of finding their location?

The CAVLR3 is an example of an RNAV procedure. A requirement to fly an RNAV procedure is for the aircraft to have navigation equipment capable of finding all of those points. There are many thousands of those waypoints, and it would create way too much clutter to show them all on a chart.

For a pilot planning on flying the CAVLR3, the Enroute H-10 chart can help them find the transition waypoints DORRN, THHMP, and TRSSK. Once they reach a transition, the approach chart covers the remaining route.

If the aircraft does not have the equipment to fly an RNAV approach, they would use a non-RNAV procedure like the COATT4. This follows fixes and VOR's, which are all included on the Enroute L-36 chart.


What is the meaning of these Lido abbreviations? Can someone help with the abbreviations and meaning from Lido flight planning:

RCONT 5 MIN
HLDDST
ADDT

For each of these abbreviations, the flight plan has fuel and time:

I placed a red rectangle around the abbreviations; I Hold Distance is ok, however I still o not understand RCONT

RCONT is route reserve / contingency fuel:

SKYbrary Fuel - Flight Planning Definitions

  Contingency fuel is carried to account for additional enroute fuel consumption caused by wind, routing changes or ATM: ATM/CNS restrictions. According to ICAO Annex 6, the recommended minimum contingency fuel is the greater of 5% of the trip fuel or 5 minutes holding consumption at 1500' above destination airfield elevation computed based on calculated arrival weight.

In this case the 5 minute holding consumption is greater than the 5% of trip fuel, so it is the one considered in calculation.


What is the purpose of the small wheel at the end of the F-14’s launch bar? At the end of the launch bar (catapult strop link) on the F-14 airplane, there is a small wheel. Does anyone know what this is used for?

https://siregar3d.com/category/grumman-f-14-wip/page/3/

Above is a 3D modelling of the nose landing gear (NLG) well looking forward. The tiny wheel during retraction would slide forward to aft on the curved guide rail I circled, so the launch bar can be stowed with its tip near the top of the NLG. Otherwise there would be no space for it with it vertical (as the NLG swings forward for retraction).

http://www.primeportal.net/hangar/howard_mason2/f-14d/index.php?Page=3

Above is a real photo. The declassified F-14 manual shows the wheel, but it is unlabeled and unexplained. The above is my proposal. Other carrier-borne fighters of the USN I checked lack this wheel, such as the F/A-18 (shown below).

Like my proposal, the F/A-18 launch bar also slides aft during retraction (YouTube), but instead of the wheel and rail, perhaps it actuates into position.

http://www.navy.mil/view_image.asp?id=13836


Where to find a 1983 NTSB report of a R-22 clutch failure? Why can't I find the incident report I had to file after my death defying landing at John Wayne Airport in Costa Mesa Ca. around 1983?
They found the clutch with 4 belts to have malfunctioned and grounded all Robinsons in service, until a better configuration was developed.

I don't think your "death-defying experience" was classified as an incident or accident. Checking the list of occurrences the NTSB classifies as an incident does not show that what happened to you needs to be reported as one. Mechanical failures of all kinds happen on aircraft all the time. Very few of them are required to be reported to the NTSB.


Why is the ICAO prefix for Alaskan airports "P"? Mainland US airports all (to the best of my knowledge) have ICAO codes beginning with "K", however Alaskan airports all (from a couple of minutes rummaging about on FlightRadar24 and Flight Aware) seem to be prefixed with "P"?

Additional searching seems to indicate that Hawaiian airports are also prefixed with "P".

Definition from wikipedia:

The ICAO (/ˌaɪˌkeɪˈoʊ/, eye-KAY-oh) airport code or location indicator is a four-letter code designating aerodromes around the world. These codes are defined by the International Civil Aviation Organization, and published in ICAO Document 7910: Location Indicators are used by air traffic control and airline operations such as flight planning.

https://upload.wikimedia.org/wikipedia/commons/thumb/a/ab/ICAO_FirstLetter.svg/1200px-ICAO_FirstLetter.svg.png

This is a map of every ICAO airport code wordwide.

Alaska has PA, PF, PO and PP as airport codes. P = Eastern North Pacific.
PA=USA (Alaska) (also PF, PO and PP)

There is no special meaning behind the letter P and these codes, it's just a classification!!


Will this diagnosis from my cardiologist prevent me from getting a Class 1 JAA medical? In 3 days I will have my Class 1 JAA medical test for the first time. However I said let's do a heart checkup before I go there and when I did this suddenly my cardiologist wrote that I have:

  Anterior mitral leaflet is slightly redundant and shows mild systolic prolapse. Trivial mitral regurgitation present.

He did for me a TMT and my performance was 97% as I'm 23 years old my heart rate increased to 195 bpm.

He told me this will not affect your pilot studies and nothing to worry about because it is normal and if you want to check it again, check it after 4 years, however no need to check it again.

Now I'm worried, will they stop me if they found out about this or what will happen?

i passed my medical exam and it was good, this issue wasn't a big problem at all even its not a problem.


What would be the ideal plane specs that minimizes consumption for 1000 kg of cargo payload (slow speed, wing span, whatever..)? Speaking of electric planes, I wonder what'd be the optimal specs if the only variable that we'd try to optimize was consumption (assuming a 1000 kg payload and 600 mile legs, unrestricted runway)?

The most fuel-efficient configuration would be one having a very high L/D. The best examples are modern sailplanes, aerodynamically clean, and with very long, slender wings.


What exactly is the meaning of "detent" in aviation? I come across it in many different situations e.g. "settings changed to flight detent" or "landing altitude changes at first detent". There are other scenarios which I came across in the past, but I don't remember them.

Could someone explain me all the different scenarios and what it really means?

A detent is usually a discontinuity in force at a certain position: the control likes to move into that position, and moving it away takes more than average force.

Image source

In the image above, the flap detents are clearly identifiable as the notches in the guide rail: in order to move the lever away from a notch, it needs to be lifted first and can only then be positioned in a different detent.

The flight control sticks often have a detent that indicates force trim position: on either side of stick travel is a preloaded spring, and the stick can only be moved once the breakout force is exceeded. The rest of the stick travel will then simply increase force proportional with the spring gradient - if released to neutral, the force will gradually decrease until the stick falls into the breakout position.


How to calculate CL with the use of MTOW? I have a problem that it gives us the MTOW of a UAV (200 kg), the speed and the reference area.
So its probably easy to find the CL knowing that it flights at steady level flight (L = W). I'm confused about the use of MTOW. Should we multiply it by the g? (gravity acceleration)

I've done some exercises in the past using lbs as the unit of MTOW and we didnt multiply it with the g. (John Anderson. Aicraft performance and design)
Is it different when using lbs and kgs? I'm confused with the different metric/imperial systems.

For every equation the left and right side should have the the same units.
For example:

$$ Speed  = \frac{distance \:[m]}{time \: [s]}$$

Or in units:

$$[\frac{m}{s}] = \frac{[m]}{[s]} $$

The same so with the lift equation:

$$L = C_L \cdot \frac{1}{2} \rho V^2 S$$

With units:

$$L [N] = C_L [-] \cdot \frac{1}{2} \: \rho \: \left[ \frac{kg}{m^3} \right] V\left[\frac{m}{s} \right]^2 S [m²]$$

Units only:
$$\require{cancel} [N] = [-] \cdot \left[ \frac{kg}{m^3} \right] \: \left[\frac{m^2}{s^2} \right][ {m^2}] $$
Simplifying:
$$\require{cancel} [N] =  \left[ \frac{kg}{{\cancel{m^3}}} \right] \: \left[\frac{m^\cancel{2}}{s^2} \right][\cancel{ {m^2}}] = \frac{[kg][m]}{[s^2]}$$

Which is correct, link to Wikipedia.

So if you want to use the equation:

$$ L = W $$

Both have to be in $[N]$. You have two options, either have it given to you in Newton, or convert a weight (in $[kg]$) to $[N]$ by using the gravitational acceleration g (in unit $[\frac{m}{s^2}]$ )

I think that the confusion stems from the fact that the unit pound is used in two ways.

for weight called pound (mass)
$$1 [lb] = 0.45359237 [kg]$$
for force called pound (force)
$$1 [\mathbf{lbf}] = 1 [lb] \cdot g
   = 4.44 [N] $$

So if somebody is unspecific and asks what the lift is needed to carry 400 pounds, we don't know if it's way 1. or 2.


What is the purpose of this aileron trailing edge strip? See the following photos of the LH aileron of a Beechcraft King Air B200:

Source: own work

Source: own work

As seen in the above photos, the Beechcraft King Air B200 has what I would describe as a bulged trailing edge strip on both ailerons. These strips are roughly centered in the span of the aileron, and in the case of the LH aileron are located outboard of the trim tab.

In figure 57-50-00-06, the Beechcraft B200 IPC lists these as -320 and -325, calling them the LH and RH trailing edge strips:

The King Air 200 has the same trailing edge strips, which are listed as -70 in fig  57-70-10 of its IPC with the same part number as on the B200.

I do believe the King Air 300 series also has these strips, though I am not certain. I don't believe the King Air 90 has these, but again, I could be wrong.

I have asked many King Air pilots and maintenance crew if they knew what the purpose was, with no definite answer. The best answer I have recieved was a tentative suggestion that they might be for something like dampening control buffet.

Does anyone know the purpose for these bulged aileron trailing edge strips? Does anyone know of any documentation for their purpose? Do similar control surface design feature appear on other aircraft?

Mr. Tom Clements—the Tom Clements—told me the following in answer to my inquiries on this matter.1 While I cannot yet offer any documentation on this in the form of a Beechcraft publication, this comes pretty close, and is—I think—definitive enough.

According to Mr. Clements, the aileron trailing edge strip serves to re-center the aileron after control surface deflection.

In the early 1970's, Mr. Clements was the first Beechcraft factory instructor in King Air 200. The Project Engineer for development of the King Air 200 was a Mr. Leroy Clay. Prior to achieving FAA type certification for the 200, Mr. Clay was discussing the prototype aircraft with Mr. Clements—Serial Number BB-1—and revealed the following, which I paraphrase from Mr. Clements.

BB-1 borrowed wingtip and aileron design from the late model King Air 90s, including the wingtip which extended beyond the outboard end of the relatively short ailerons. After its first test flight, it was decided that BB-1—with its more powerful engines, greater wingspan, different roll inertia, etc—was lacking in aileron roll authority. The design solution was to extend the ailerons outboard to the wingtips, for a greater overall aileron span.

This change proved to solve the control authority concerns, but revealed a new problem: the ailerons lacked sufficient aerodynamic centering tendency, and now tended to remain partially deflected after a roll control input. The initial solution was the bulged trailing edge strip in question. The idea was that the bulge would cause a small amount of drag, especially when deflected, which would tend to streamline and center the aileron.

I say the initial solution, because, Mr. Clements recalls that Mr. Clay, the Project Engineer, stated that the bulge was a temporary fix added to the aileron, with the intention of a complete aileron redesign to follow prior to certification. I will point out the obvious: it has been over 40 years since the King Air 200 was certified with that bulged trailing edge strip.

Mr. Clements goes on to confirm that this trailing edge strip has remained a feature of King Air models through all the 200 and 300 series.

1This exchange took place and is available on BeechTalk.com, though the content is only accessible to members. BeechTalk.com terms of service do not allow copying and reproducing member content outside the site.