How does the aspect ratio of a wing impact its lift? The wing lift formula shows that lift of a wing is proportional to its area.

$
L = {\dfrac 1 2 \times \rho V^2 \color{magenta}S C_L}
{\small
\begin{align}
&{} &&\text{where:} &&L = \text{lift,} &&\rho = \text{density of air,} \\
&{} &&{} &&V = \text{velocity,} &&\color{magenta}S = \text{wing area,}\\
&{} &&{} &&{}&&C_L = \text{coefficient of lift.}
\end{align}}
$

So why are most conventional wings shaped the same (swept back rectangles)?

Imagine a conventional airplane but with the wings shaped as 2 thin long rectangles attached to a fuselage from the cockpit until the tail with the same area as the original wing.

With all other things (like angle of attack, etc) being equal will the same lift be generated as the original wing?

"The wing lift formula shows that lift of a wing is proportional to its area".

That's absolutely true. However a wing generates both lift and drag. Drag is of two natures: Parasitic drag and lift-induced drag. The sum of all drag is the total drag:

Source: Wikipedia

Induced drag decreases with speed, and has its origin in wing tip vortices. Vortices actually increase the velocity of the downwash, and changes the effective angle of attack. Which in turn changes the direction of the aerodynamic force, creating a force opposing to the direction of flight:

Induced drag, source: Wikipedia

Induced drag being due to tip vortices, if we can make vortices less efficient, then we also reduce induced drag. The way to do that is to have long wings, so the the downwash from the vortices affects only a part of the wing:

Tip vortices, source: Wikipedia

Research demonstrated that the induced drag is dependent on the wing aspect ratio, not only on the wing span. This can be understood easily: The quantity of air in a tip vortex is larger when the chord is large.

So the answer to your question is: Yes lift is proportional to the wing area, but the lift/drag ratio is proportional to the wing aspect ratio. That's why longer wings are preferred, they minimize energy lost in fighting drag.

"Why are most conventional wings shaped the same (swept back rectangles)?"

Longer wings are better for fuel efficiency, but we have other problems in the designer queue, and some can be solved by selecting the wing planform, e.g.:

We want to prevent the stall to be abrupt (at the expense of creating less lift though):

We want to delay the creation of a local supersonic flow in supercritical wings used in commercial airliners. When flying at M 0.8, airflow is accelerated to produce lift, some areas of the wing reach supersonic speed (Mach > 1). The associated shock wave creates an additional drag. By sweeping the wing we add a spanwise component to the airflow which decreases the chordwise velocity, so the shock wave appears only to a higher aircraft airspeed:

On the other hand, the sweptback wing tends to stall at the tip first, which is not good at all, as when a stall appears we need ailerons to prevent it from worsening, and ailerons are located at the tips to increase their effectiveness. So swept wings are also twisted so that the tip angle of attack is smaller than the root one, forcing the stall to start at wing root.

Wings planforms are multiple, each type of wing, or sometimes subcomponent, can improve a particular issue (possibly creating another that will be less important for the designer). See this very interesting article on Wikipedia: Wing configuration


Why is luggage required to be loaded in containers? Luggage is loaded into containers, in Wide Body airliners (as mentioned here). Why is this required to be done? Why don't they simply keep the luggage in the luggage compartment? Why is loading the luggage piece-by-piece time consuming, and at the end, in second photo mentioned there, the luggage is being loaded piece-by-piece. What is that?

The central cargo hold is usually pretty big and open, if cargo was placed in loosely then it might shift in flight which can cause the center of mass to shift or damage the walls of the hold. Putting them in containers and fixing those down will prevent that.

The containers can also be weighed before hand and their position set to ensure the center of mass ends up where it should be. With loose cargo the pilot would need to rely on the intuition and experience of the loaders to ensure that they don't put all the heavy stuff on one side.

Loading loose luggage requires that the loader in the cargo hold handles each bag while stacking them. The hold also needs to be full enough that the luggage can't shift around.

The smaller forward and rear cargo holds (or on smaller planes) can still accommodate loose luggage (or more precisely they are too small for the containers to fit). They will also have netting to provide barriers against shifting.


Why would 2 aircraft fitted with the P&W PT6 Engine have different top speed? Why can the Quest Kodiac and Cessna Caravan not exceed 200 knots?

PT6 from Pratt and Whitney in other implementations like Epic E1000 and Pilatus PC12 can cruise at over 300 knots.

The Kodiac and Caravan are advertised at only ~180 knots. Why is there such a difference?

Is the fixed landing gear the problem for such a limitation on speed?

The P&W PT6 comes in many different varieties. The smallest PT have 500hp while the largest have 1700hp.  It is not the "same engine" as you state in your question.

The standard Caravan has 675hp while the other aircraft you mention have 1,200hp. That alone can account for the major difference in performance. Fixed gear and struts also add to an increase in drag and a reduction in speed.

The bottom line is they are different aircraft, with different engines, designed for different roles. There is no reason to expect similar speed or performance.


How do jet engines work? I was doing research about jet engines, and they seem really difficult to fully understand. So, can anyone explain it in a simple way?

An afterburner glows on an F-15 Eagle engine, source: Wikimedia.

How do jet engines work?

In the simplest of terms:

Suck - Air is sucked into the turbine. For efficiency reasons, most aircraft let some of that just pass through the outer part of the fan, rather than through the whole engine.
Squeeze - The compressor squeezes that air together to a high pressure. This helps with ignition.
Boom - Fuel is injected and ignited. As the air gets hot, it expands.
Blow - The hot air drives the low-pressure turbine (driving the whole shaft holding the engine together), sucking new air in, and is itself blown out the back.


Is it possible to buy a retired Boeing 747 aircraft? American airline companies landed their last passenger 747 jet into retirement last year citing higher costs of flying this aircraft in comparison to modern widebody twin-engine aircraft designed for the same purpose.

Is it possible to buy a passenger version of the Queen of the Skies (747-8) for use elsewhere if the costs of flying are not a problem and profitability in light of buying second hand compared to much expensive new aircraft? Will the FAA allow this if the aircraft is airworthy and for how long will Boeing keep maintaining its aircraft in terms of manufacturing spare parts and supporting it?

Sure, the 747 is a Type Certified and airworthy aircraft, the FAA does not really care who owns it so long as they play by the rules. Boeing even sells them directly to the private market via their BBJ line.

There are even a few used ones listed for sale right now.

Some people even buy them for other purposes than flying them...

  for how long will boeing keep maintaining its aircraft in light of
  manufacturing spare parts and innovating it

this is impossible to speculate on as its their decision ultimately but considering how many 747's there are you will be flying it long into the future.


Why aren't airports built identically (like aircraft)? Considering the delays and mishaps in super-projects (e.g. the new airport in Berlin), wouldn't it be rational to standardize airports in the same ways aircraft are: Building them all according to the same designs and not in a "one-off" fashion? Why is this not done?

1. Terrain and land use

Several new airports are build on landfill island or coast next to mountains, their shape is influenced by the terrain and their size.

Hong Kong International Airport runways and shape are influenced by the terrain. Its curved east bank looks like the Chek Lap Kok island, which the airport is built on there. Both HKIA runways are parallel to the hill of Lantau island, south of the airport island.

HKIA is on the north of Lantau island (largest green shape), the grey colour stands for reclamation land and the green colour is the originally Chek Lap Kok island.

2. Prevailing wind

Prevailing winds influence the runway heading. Since takeoffs and landings are usually done as close to headwind as possible, wind direction generally determines the active runway. If the prevailing wind is uncertain, multiple runways with different directions will be built, Boston Logan airport is a extreme example.

3. Terminal building and bargaining power of airport management

This factor largely influences the terminal layout. In USA the airport management is largely influenced by the airlines, sometimes the terminal buildings are managed by airlines themselves, like New York JFK. The airlines prefer the terminal building which can minimize the taxiing time, passengers transfer time and maximize the perimeter (and hence the number of gates), Atlanta Hartsfield airport is one good example. Its linear shape can minimize the taxiing time and increase the number of gates available.

On the other hand, for main airports outside USA and Europe, the airport owner has strong marginal power of the airport management. They will choose the terminal building which can best fit for their strategy. Some airports owned by the government prefer a massive size of airport as an image of the country/cities; and some airports prefer large commons which can maximize the shopping experience (and hence rental income). Pictured below is Beijing Capital International Airport.

4. Historical factor

Several airports were built before World War II and some even existed before World War I. At that time the airport was just a new concept. A full development and operation methodology for airport had not been developed. Many full airport layouts, which nowadays seem to be "inefficient", were developed. And since the layout with the buildings were built, it is costly and time-consuming for reconstruction, especially at the busiest airports. Airport managers tends to expand the existing building with new gates and other facilities, rather than total reconstruction. Pictured below is a master plan for O'Hare International Airport from 1948.

Heathrow airport is reconstructing Terminals 1-3, replaced by linear buildings like Terminal 5. It will take 5 years to destroy the old Terminal 2 and phase one was just completed last year. Terminal 3 will be rebuilt after 2019 and the whole project will take more than a decade.

5. Airport operation

Operations of the airport are influencing the airport layout. For airports have more flights for both general aviation and airlines, they tend to have more runways, like Dallas DFW and Amsterdam Schiphol. On the other hand, in most parts of the world there are only 1 or 2 runways even for the most busiest airports where most of the flights are from airliners, like Dubai and Hong Kong, ranking for 6th and 10th busiest airport in terms of total passengers.

6. Reversal: Experience

On the other hand, huge number of airports has been built in the half century, several airport design has been well developed. We can see the latest airport may share similar terminal shape, runway plan and airport layout.

Hong Kong international airport and Hamad International airport

Chongqing airport (Far future) and New Lisbon airport proposal

Conclusion

To sum up, there is not one optimal conclusion of airport layout. The airports are built related to physical limitation, historical constraints, stakeholders opinions, and, of course, the architects' designs. No airport will be identical, regardless the layout, terminal shape and style. On the other hand, the experience from airport planner will create a similar airport.


What is the purpose of having contra-rotating props on an aircraft? Why do planes, like the famous XF-11 and the Tu-95, have contra-rotating props? What is their purpose?

Image credit: Mike Freer / Touchdown-Aviation / Wikimedia

According to my experience, you have two problems with props:

Torque
Exhaust Speed

If you use contra-rotating propellers, you eliminate the torque reaction problem because you now have two contra-rotating propellers each cancelling out the opposite's torque.

Also you increase the speed of air accelerated by the propellers, thus the aircraft’s efficiency at relatively high travelling speeds is increased.

Normally, the propeller can only be operated effectively at low Mach numbers and increasing the RPM above a certain point will only cause the air behind the propeller to compress but not accelerate. Using a second propeller with higher pitch angles can generate high enough airspeed without the problem of compression because the second propeller is rotating inside the airstream generated by the first propeller.

Correction
However, having a different speed and pitch WILL induce a torque effect.


Why would a runway friction measurement improve over time? Why would a runway friction measurement that I've just made (with a SARSYS friction tester) give better (condition improved) results than a measurement that I made 6 months ago? The runway has been in use in the interim and no repairs have been made in the interim.

The runway is asphalt and 15 years old. For both measurements, the runway was dry.

There could be a number of reasons. Temperature affects asphalt significantly or calibration could be off.

But if higher friction is measured in the touchdown area after significant use I would look to rubber deposited by landing aircraft tires, which is stickier than asphalt. Dragsters do burnouts before their runs to put rubber on their lane. It is just like glue.


Under 3rd Class Medical Reform, When Do I Need To See My Doctor? Lets say I'm a 35 year old pilot who just had a medical renewed so that it doesn't expire until 2021. 3rd class medical reform (although not law yet) requires that I visit my regular physician once every 4 years.

When do I need to see my doctor?

Anytime prior to the expiration of my 3rd class medical?
Do I surrender my 3rd class medical and go to the doctor immediately (after regulations pass of course)?
Do I go to my doctor in 2020? 2019?
Do I wait until my 3rd class medical expires (or within a month or two)?
4 years after the expiration of my 3rd class medical?

And a bonus question:

Does the 4 year clock start ticking when my medical expires, when regulations are enacted, or some other time?

114th Congress Senate Bill 571 - Pilots Bill of Rights 2

The FAA hasn't written the regs yet so who knows. All that has happened is congress has told the FAA to write the refs

Personally I think it's foolish to use your personal doc. You're waving all your HIPPA rights and obligating your personal doc to report anything to the FAA without your consent.

-Robert


What is this large engine doing on a B52? In this YouTube video, discussing plans to use the 747 as an aircraft carrier, there is a brief sequence starting at 4 min 14 s, showing images of a B52:

What is the explanation for the very different inboard engine pod on the starboard wing? There is a current call for proposals to re-engine the B52 with eight modern engines. Was this an earlier test of moving to four larger engines instead?

Testbed Aircraft Cameos

  As a young engineer in the 1960s at Pratt & Whitney Aircraft (now
  UTC’s Pratt & Whitney) in East Hartford, Connecticut, I was involved
  (along with many others) in the development of their 44,000 pound
  thrust (lbt) JT9D turbojet, which powered the first Boeing 747 jumbo
  jet aircraft[ Display footnote number: 2 ]. Because of its then
  ground-breaking large fan diameter (new for the 1960s), P&WA had to
  use a U.S. Air Force Boeing B-52 as a testbed. The Stratofortress,
  with its high wing, allowed the JT9D to be mounted with adequate
  ground clearance for takeoff and landing. In Figure 1, the P&WA
  testbed aircraft is shown landing at the Windsor Locks, Bradley
  International Airport, after a test flight, with a JT9D engine
  replacing two TF-33 inboard engines on the right wing of the
  eight-engined B-52.

  The B-52 continued as a P&WA testbed aircraft until 1981, even after
  being damaged in its hangar by a violent tornado that raced through
  Windsor Locks in 1979. Pratt & Whitney more recently used two Boeing
  747SP aircraft for testbeds, to flight test their new geared fan jet
  engines.


What causes 'wing rock' and how does it work? Currently studying for a course on fighter aircraft. I came across the phenomenon of 'wing rock', which occurs at very high angles of attack, but I couldn't find any good sources that explain how this phenomenon works in detail. Could anyone give me an explanation of the mechanics of this phenomenon?

It occurs on aircraft that have triangular or arrow-like wing shape.

Let's say at a high angle of attack, the left wing begins stalling first. The aircraft will turn slightly to the left. Immediately, there are two forces counteracting this:

when the left wing goes down, it stops stalling and the shadowed wing on the right begins stalling;
if the aircraft is laterally stable, the aircraft has a tendency to revert to the center position when turning left or right.

Therefore the aircraft will turn slightly to the right, and the same process repeats again.


Can someone please help me identify this? I apologize for the image quality as it is a picture of an image on a television screen.  I was watching an episode of American pickers at the time and the model of the plane was not discussed.  Can anyone identify this aircraft?  I am not sure I have seen a configuration like it before.

It looks a lot like a Curtiss Model D to me.


How do ER models store more fuel? The whole purpose of an ER model is to increase range and by doing that you need to increase the amount of fuel stored in the wings. EX: Boeing 737-900, Boeing 737-900ER. Is the wing area increased or is their another way to increase fuel capacity.Source:(https://en.wikipedia.org/wiki/Boeing_737_Next_Generation#/media/File:Lionair_737-900_ER_first_flight.jpg)

Not all fuel is stored in the wings. Some is also stored in the fuselage. The ER variants have a larger, or additional, centre (fuselage) tanks at the expense of cargo bays volume.

The centre tank is located between the wings to minimize the change in centre of gravity as the fuel is consumed. The wing spar, which must go through to provide sufficient structural strength, does not allow the cargo bay to be continuous in most designs anyway.

The ER models may be also fitted with more powerful engines to increase the maximum take-off weight (engine out performance is usually the limiting factor), so the plane can still take reasonable amount of payload when the tanks are full.


Am I expected to stay on glide slope for landing in a light aircraft? When I land the airplane (Cessna 172, 182, 152) I notice that I come in pretty far above glide slope (four white lights on the PAPI).  I pick an aiming spot on the runway (like the second center line stripe) and maintain my approach airspeed while flying towards that point.  I'm able to reach that aiming point with quite good accuracy and land the plane smoothly and softly, but I'm above glide slope for most of the approach, and then on short final the white lights start to turn red.  Clearly my approach is steeper than the usual 3 degree glide slope.  I thought that's what flaps were for - to allow for a steeper approach.  Am I doing this wrong?  Should I focus on staying on glide slope, or should I focus on my aiming point?  I've had several flight instructors and most of them have never said anything about this.  I kinda like being a little higher, and approaching exactly on glide slope usually means I have to add power on short final because I start getting too low.

It is more important that your approach is stabilized and safe than you are strictly on slope (i.e. two red/two white). But let's discuss a few things before extending this answer.
ATC is not terribly concerned with where exactly you touch down (especially in a light aircraft) so long as you don't run off the end of the runway. When cleared to land the whole length of the runway is yours to work with:

If receiving “cleared to land” instructions from ATC, you are
authorized to use the entire landing length of the runway and should
disregard any LAHSO holding position markings located on the runway.
If you receive and accept LAHSO instructions, you must stop short of
the intersecting runway prior to the LAHSO signs and markings.

Different runways will call for different touchdown situations which is why it's important in preflight to understand what your landing distance and roll out will be.
In any aircraft you fly you should be proficient (or learning to be proficient) in various landing techniques than includes standard approaches as well as no flap approaches and short field landing maneuvers. If you have all these things in your toolkit you will be fine. If you are proficient in an aircraft you should be able to put it down on the numbers or the 1000 foot markers or any other spot your instructor asks you to demonstrate so long as there is sufficient distance to roll out and stop. You should focus on being able to deliberately put the aircraft down on a spot of your choosing rather than thinking of it in terms of "i always end up touching down on the mid point of the runway" as the latter statement means a very different thing on a 2000 ft runway than it does on a 10,000ft runway. This can generally be controlled with small pitch and power changes on final.
Generally speaking you should fly the glide path if it is available to you as this will guarantee obstacle clearance and keep you safe. While it is never bad to be a bit above glide path (three white, one red) it can be problematic to be very high (all white). The issue with 4 white lights on a PAPI is there is no further indication of how far above glide path you actually are. Making the assumption that you are anywhere near the glide path if you see 4 white lights is dangerous and can lead to a fast, unstable, slam dunk approach. Slope adjustments can be a bit delayed on approach and a power increase will generally bring you back up to slope if you are low while chopping the power will bring you down to slope but remember it will take some time to settle in so you need to think ahead of the airplane.
If you put it all together you will see that staying on slope brings you down to the 1000 'footers, keeps you clear of obstacles, and allows you to make small final adjustments to control your touch down if you want to land a bit short or a bit long.
It is not a question of focusing on one OR the other but focusing on both and realizing how they play together. If you come in on slope you can make small power changes to adjust your aiming point and suit your desired maneuver.
The FAA's Approach And Landing Chapter of the Airplane Flying Handbook has lots of good info on the matter and is worth the read.

Stabilized Approach Concept
A stabilized approach is one in which the pilot establishes and maintains a constant angle glide path
towards a predetermined point on the landing runway. It is based on
the pilot’s judgment of certain visual clues and depends on the
maintenance of a constant final descent airspeed and configuration.
An airplane descending on final approach at a constant rate and
airspeed is traveling in a straight line toward a spot on the ground
ahead. This spot is not the spot on which the airplane touches down
because some float occurs during the round out (flare). [Figure 8-9]
Neither is it the spot toward which the airplane’s nose is pointed
because the airplane is flying at a fairly high AOA, and the component
of lift exerted parallel to the Earth’s surface by the wings tends to
carry the airplane forward horizontally.

To address some points of your directly:

I thought that's what flaps were for - to allow for a steeper approach.

Flaps allow you to fly a steeper decent angle at a given airspeed, this is not a blanket security measure to fly arbitrarily steep approaches at 80Kts in a 172. They also help you to generate more lift at a given airspeed so you can fly a standard approach at a slower than normal speed (think short field landing).

...and approaching exactly on glide
slope usually means I have to add power on short final because I start
getting too low.

If you are on glide slope on short final you are not too low (thats the point of a glide slope). If you are high for most of the approach, cross the slope, then find your self sinking below slope your approach is not stabilized and you are likely coming in hot then cutting power and diving for the runway.

I kinda like being a little higher

While there is no strict regulation on flying above glide slope flying arbitrarily high is typically an indication of an unstable approach that will result in a slam dunk dive final. The glide slope exists for many reasons and should be followed for those reasons.
If you are student pilot (you dont mention here) work on flying stable, on slope approaches. If you already have your ticket I would start some Instrument training and understand what its like to fly the slope in the soup (or foggles) and how being high can be a real issue when you break out, it might help put it all into perspective.


Why does centre of pressure (drag?) move forward when transitioning from transonic to supersonic? I am studying aerospace engineering at college and I am wondering why the centre of pressure moves forward when the aircraft changes from transonic flight to supersonic flight?

Also, is centre of pressure the same as centre of drag? I can't find anything on centre of drag but I've found loads on centre of pressure.

The center of pressure does not move forward when transitioning into supersonic flight, but back. Let me compare the pressure distribution around a sub- and a supersonic airfoil, and the reason should be obvious:

First subsonic flow, showing an Eppler 502 at a moderate angle of attack (3°):

And here is a rhombic airfoil in supersonic flow, copied from this answer:

While the pressure difference between upper and lower side is highest near the leading edge in subsonic flow and tapers off the more you move backward, the pressure difference between both sides is constant over chord in case of the supersonic airfoil. An uncambered rhombic airfoil is the simplest case: The pressure jumps up when the air passes through a shock and jumps down when it passes trough an expansion fan. In between, pressure is constant because the local inclination of the surface does not change.

As a consequence, the center of pressure is near the quarter point in subsonic flow and at mid-chord in supersonic flow (when tip effects are neglected).

Even in transsonic flight, when the local supersonic flow delays the pressure rise, the center of pressure starts to move back. This is the reason for the pitch-down experienced when accelerating above the critical Mach number which is called Mach tuck.

OK, now I forgot to mention the center of drag so far. It is of minor importance because the drag force is so much smaller than the lift force. The concept is the same: Sum up all drag contributions and find the point where a discrete force applied in the direction of drag has the same effect. While the center of pressure just sums up all pressure (and includes the portions which contribute to drag), the center of drag mixes both shear and pressure effects and looks at the fraction which acts in flow direction.


How is one's hypoxia resistance affected by the time of day? I am doing my PPL course in the Czech Republic and here they have the following question in tests: when during a day is the resistance of a human organism to hypoxia the best? There are 3 possible answers:

3 am
12 am
5 pm

What is the correct answer and why? Is a human's ability to resist hypoxia connected somehow with the time of day? FAA book doesn't have a word about it.

As noted by others here, PPL course questions might not be designed according to pure deductive or inductive reasoning. My approach would have been the following:

Medical-related aviation questions tend to base their background on "old" studies, so let's have a look at Van Liere, E. J. (1964). Resistance to Hypoxia. Archives of Internal Medicine, 113(3), 418.:

  As a corollary, it would be anticipated that if the metabolic rate of
  an animal were elevated, the ability to withstand hypoxia would be
  decreased. Zarrowetal in 1951 demonstrated that hyperthyroid states
  decrease tolerance to hypoxia. The thyroid-stimulating hormone (TSH),
  thyroxin, and dinitrophenol all decrease hypoxic resistance.

TSH has a circadian rhythm (24 hour cycle) and levels peak between midnight and 6am (refer to https://medicalsciences.stackexchange.com/a/4034/15791). Therefore, 3am and 12am are not an option, which leaves us with 5pm.

I'm aware that you stated that the correct answer is 3am, and I'll definitely check back with my medical colleagues on that, but the question in itself is clearly not well-defined within the visible context on this platform.

As others mentioned, one measure of gauging the depression of cellular oxidation is metabolic rate, for which in 2014 according to Examining Variations of Resting Metabolic Rate of Adults: A Public Health Perspective no single value for RMR is appropriate for all adults.

Last but not least, if we talk about hypobaric hypoxia, conclusions change again.


What happens when two different control inputs are commanded in an aircraft with two control columns? For example, the captain starts pulling back and to the right to turn right. First officer initiates a left diving turn. What happens?

It depends on the aircraft. In any aircraft where the two control columns are linked, there's only one input to command the control surfaces. While most smaller aircraft are connected directly through the control surfaces, Boeing publicizes that on the 787 - a fly-by-wire aircraft - the control columns "[a]re cross-linked between pilots to reduce potential confusion."

On Airbus aircraft (and probably others), the controls are not linked: there is no indication on one pilot's controls of the other's position. The computer handles this by adding the two inputs: opposite commands will cancel each other out, while both pilots commanding the same input will increase the total commanded input. Some Airbus aircraft have a feature which makes an announcement of "DUAL INPUT" when there is input on both sidesticks simultaneously. As of January 30, 1997, this was "an installation" (optional feature, I believe) on the A320 and under development for the A340.

Airbus aircraft also have a Priority Takeover button, which lets one pilot take control and have the airplane ignore inputs from the other sidestick. As Farhan noted, good CRM (Crew Resource Management) is also very important to ensure that only one command is given at once.

Some aircraft have linked controls, which can be separated if necessary. On the 767, if sufficient force is applied, the elevators will "split": each control column will control one of the elevators. The pilot who is stronger or better prepared will have more control over the aircraft. There's also the EMB-145 and -135:

  The roll input is ... linked at the control column[.] Each yoke independently controls its own aileron -- the CA yoke only flies the left aileron and the FO yoke the right aileron. It is only through the control column linkage that each yoke can control the whole airplane. It is done this way so that if there is a problem with a cable jamming, the control interlock can be disconnected and at least half control regained.


What is the reason for the T- shaped rudder trim tab on the DA42? Why does the rudder trim tab on the DA42 have a T-shape?

The feature was added to reduce undesirable flutter discovered during flight test.  It appears on the rudder trim tab of the DA-62 as well.


On crosswind landings, is it preferable to side slip or crab on final approach? I've seen several instructional videos on crosswind landing techniques.  Some advise the pilot to crab the aircraft until just before touchdown when he/she should kick the rudder over to align the aircraft with the runway centerline.  Others advise the pilot to slip the aircraft all the way down so that no other cross control maneuver is needed.  Many of these videos also acknowledge the other way of doing things but say that their method is superior.

Is there an accepted "safer" method for flying a final approach with a crosswind or is it an entirely personal preference?

Neither technique is "preferable" - the assumption that one is superior to the other is one of the most common false dichotomies (and over-simplifications) in aviation.
With some notable exceptions (like the Ercoupe which is incapable of a slip and lands crabbed) a proper crosswind landing should involve elements of both techniques.

Crabbing
Crabbing involves turning the nose into the wind so that some component of the aircraft's thrust is counteracting the crosswind, allowing the aircraft's ground track to align with the runway.
Advantages
Flying on final it is advantageous to crab into the wind: It is aerodynamically more favorable than a slip, and as the aircraft is kept coordinated it is more comfortable for passengers than a slip.
Pilots often find a crab subjectively "easier" to maintain for extended periods of time compared to a slip: It does not require the pilot to maintain "crossed controls", and it's similar to how we maintain our course in other phases of flight (you were probably crabbing into the wind on downwind just a few seconds ago, and on instrument approaches flying the localizer in a crab is analogous to tracking a VOR on the enroute portion of your flight).
Disadvantages
On touchdown however landing in a crab will put a side-load on the landing gear (the aircraft is traveling along the runway centerline, but the gear is not aligned with that direction of travel). In extreme cases this can damage the tires, cause difficulty controlling the aircraft, and possibly even damage the landing gear assembly itself.
"Kicking out the crab" to align the landing gear with the runway requires an abrupt control movement at low altitude (generally not a good thing), and if done too early the crosswind will begin to blow the aircraft across the runway (leading to a landing that's not on the centerline, a side-load on the gear, and in the worst case an unintended departure from the runway surface.

Slipping
Slipping involves banking the aircraft so that some portion of the wing's lift is counteracting the crosswind. Ordinarily the aircraft would tend to turn in the direction of the bank, so opposite rudder is applied to prevent the aircraft from turning and maintain the ground track parallel to the runway.
Advantages
Touching down on the runway a slip has the advantage of allowing you to align your landing gear with your direction of travel (down the runway) and avoid side-loading the gear. It also allows you to touch down on the upwind landing gear first which helps to stabilize the early roll-out, and positions your ailerons appropriately for taxiing with the crosswind.
Disadvantages
Slipping down final however is likely to make your passengers uncomfortable - the plane is slanted in one direction, the rudder is pushing the nose around in the other direction, and folks start to feel like their butt is sliding out of the seat.
Aside from passenger comfort a slip is a terribly inefficient aerodynamic arrangement (you're essentially trying to fly sideways), and not a "normal" way to fly in other phases of flight. You may have difficulty estimating the aircraft's performance and require power to maintain your glide path in this configuration.

Combining the techniques
So a crab is advantageous on final (and flying an instrument approach), and a slip is advantageous on touchdown. It logically follows that the two techniques can be combined to provide the advantages of both:

Crab down final (or on the localizer).
At some point transition into a slip.
Exactly where you make this transition is pilot preference, but the transition should be smooth, simultaneously bringing the nose around to align with the runway while banking into the wind to counteract the crosswind component.
Touch down in the slip.
Complete your rollout with the appropriate crosswind aileron deflection, controlling your ground track with the rudder as needed to prevent weathervaning.


What is the minimum number of engines required for taxiing an airliner? What is the minimum number of engines required for taxiing for jet airlines from a fuel savings perspective, for 4 engine configurations and 2 engine configurations?

Is using fewer engines counter productive, given that if fewer engines are used more throttle would be required and hence more fuel?

Finally can jumbos like the boeing 747-800 and the airbus A380 taxi with just one engine?

Whether it's a twin-, tri-, or quad-jet, it very much depends on the aircraft design, airline policy, and conditions such as taxiway slope, contamination, weight, etc.
Read the below example for the Airbus A320 to get an idea:

An example of what can go wrong when taxiing on two out of four engines (or 1 out of 2) is having the aircraft in the wrong configuration. Like what happened on August 23, 2001 when the ground engineer had no steering or braking and they ended up in a ditch:

For the Airbus A380:

The minimum is a symmetrical two on the A380 (likewise for the 747).
777
In the 777 it is not allowed. That's an example of how it depends on the aircraft design.

Taxi – One Engine
Because of additional operational procedural requirements and crew workload, taxiing with an engine shut down is not allowed. High bypass engines require warm up prior to applying takeoff thrust and cool down prior to shutting down. If the engine has been shut down for several hours, it is desirable to operate at as low a thrust setting as practicable for several minutes prior to takeoff.
Note: Single engine taxi with an inoperative engine is authorized consistent with good judgement.
(Boeing 777 FCOM)

Fuel saving
According to this Eurocontrol document, the saving is about 4-8 kg of fuel per minute.


How should I establish initial contact with ATC after being handed off by another controller? What is the proper way to contact a new air traffic control facility after you have be instructed to do so by the controller you are currently interacting with?

As a practical example: Here in Northern California, I will typically contact NorCal Approach on 125.4 to get flight following. If I travel ~50 miles north, approach will tell me to contact Oakland Center on 132.2. When I contact Oakland Center, what is the proper way to announce myself?

My original CFI instructed me to say:

  Oakland Center, Tail Number, with you on 132.2

However my new CFI, says that is incorrect and in fact alluded to the idea that perhaps it was ridiculous. His instructions were:

  Oakland Center, Tail Number

However, the two times I had used the more abbreviated version above, the controller seemed unsure of my intentions and I had to state (in plain english because I was not sure how to communicate this) "NorCal Approach just sent me over to you".

What is the proper way to handle this situation?

In your situation:

Oakland Center, Aircraft Identification, Altitude

For example:

Oakland Center, Cessna 123AB, Level four thousand fife hundred.

See Aeronautical Information Manual, 5-3-1: ARTCC Communications.

b. ATC Frequency Change Procedures.
2. The following phraseology should be utilized by pilots for establishing contact with the designated facility:
(a) When operating in a radar environment: On initial contact, the pilot should inform the controller of the aircraft’s assigned altitude preceded by the words “level,” or “climbing to,” or “descending to,” as appropriate; and the aircraft’s present vacating altitude, if applicable.
EXAMPLE-
1. (Name) CENTER, (aircraft identification), LEVEL (altitude or flight level).
2. (Name) CENTER, (aircraft identification), LEAVING (exact altitude or flight level), CLIMBING TO OR DESCENDING TO (altitude of flight level).
NOTE-
Exact altitude or flight level means to the nearest 100 foot increment. Exact altitude or flight level reports on initial contact provide ATC with information required prior to using Mode C altitude information for separation purposes.
(b) When operating in a nonradar environment:
(1) On initial contact, the pilot should inform the controller of the aircraft’s present position, altitude and time estimate for the next reporting point.
EXAMPLE-
(Name) CENTER, (aircraft identification), (position), (altitude), ESTIMATING (reporting point) AT (time).
(2) After initial contact, when a position report will be made, the pilot should give the controller a complete position report.
EXAMPLE-
(Name) CENTER, (aircraft identification), (position), (time), (altitude), (type of flight plan), (ETA and name of next reporting point), (the name of the next succeeding reporting point), AND (remarks).
REFERENCE-
AIM, Position Reporting, Paragraph 5-3-2.


Airliner speed when descending through 10,000 feet How do airliners get to 250 kts when descending through 10,000 feet as required by the FAA? Do you level off at 10,500 feet until speed is less than 250 and then descend further? Must pilots ask ATC permission to temporarily level off slightly above 10,000 feet to decelerate and then get further permission to continue descent? I’ve wondered for years how this works. On a 787 into SFO, we had the screens on the headrest that showed us GPS and speed etc. I remember looking at it on descent and noticing we were leveled off traveling around 145. Also, considering 250 is the maximum, do you travel around 240/245 above 10,000 feet to be sure you do not accelerate beyond 250? Thank you for the explanations.

Note that the speed you saw would have been ground speed not air speed. But in any case, you generally descend with the autopilot in a mode that pitches to hold an airspeed, called "Speed Mode" or something similar.  The other option is to descend in a mode that pitches to a vertical speed, called "VS" mode.  Speed  Mode is used most of the time.  You set the target speed the AP will maintain with a dial on the autopilot panel that moves a bug on the speed tape.

When you start a descent you will usually dial the speed you want to descend at, engage speed mode, then pull the thrust to idle, and over you go. Say you are descending with the bug at 290, which means the bug is set to 290 on the tape and the airplane will nose up or down as required to hold that speed, and in this case you are in some kind of dive.

As 10000 ft approaches, say passing through 12000, you just dial the bug down the speed tape to 250.  The airplane will pitch up a bit and start decelerating, then start pitching down again to maintain 250.  You try to time it so you are hitting 250 just as you are passing 10000.

ATC doesn't know your indicated airspeed, only your ground speed, so a controller has to estimate your airspeed based on the wind and ground speed.  This means being a few knots over the limit won't get you busted.

If you screw it up and are still too fast by more than say 10-20kt passing 10000 (or maybe because of some other imperative), then you'll dump some speed brakes to slow down faster.  But like I said, 10kts too fast passing 10 is not a big deal.


How does a ring paper airplane fly for a long distance? My friend showed me something which he called the glider. At a first look, it looks like it will crash, but it flew quite well:

I was surprised to see it go about 25 meters (82 feet), as it was nothing but a big ring made out of paper. I thought of how it could fly, but I had no idea. I knew that it could go through air with least resistance, but it wasn't supposed to fly.

Can someone explain me the logic of how this flies?

No takers? Then I'll bite.

This question addresses how paper airplanes generate lift. This lift is caused by higher pressure on the lower side and lower pressure (suction) on the upper side, and if both are added up, the chordwise pressure distribution is shown below:

Flat plate pressure distribution (picture source)

If you collect all the local forces in one point, the lift acts at a quarter of the wing's chord. That is why the forward half of the paper which in the end will be bent into the ring needs to be folded onto itself: The center of gravity of the wing is also at one quarter of chord. Thus, the lift and the weight will act a the same station and no pitching moment results.

To achieve a flight distance of 25 m, your friend threw the ring with some force to give it a high initial speed. This speed would allow it to create enough lift with very little angle of attack, so it did not suffer from flow separation initially. This resulted in low drag and the high launch speed gave the ring some kinetic energy.

Friction slowed the ring down gradually, but the decrease in lift at lower speed was compensated by a gradual increase of the ring's angle of attack. Why would the angle be just right to prevent the ring both from rising and dropping, you might ask? Any imbalance between lift and weight would add a vertical acceleration which would immediately change the angle at which the ring hits the flow. Its chord length and inertia would prevent it from rotating nose up or down, so it would pretty much stay on its initial path until most of the speed was eaten up and the angle of attack was so high that separation sets in. At this point, the drag would go up and speed up the deceleration process, and the ring would sink to the ground.


Why is there no numbering system for more than three parallel runways? If an airport has three parallel runways - a good example being Schiphol (EHAM/AMS) - the parallels are usually labeled "left", "center", and "right", and in case of Schiphol they are 18/36 L/C/R.

However, if there are four or more parallel runways, one or more have to be given a different number. For instance, ORD has five parallel runways heading 93.6-273.6 and their designations are 9/27 L/R and 10/28 L/C/R.

Why couldn't these runways all have the same number and add a second letter - I, M, or O (for Inboard, Midboard, or Outboard) so the number can accurately indicate the runway's heading? Under this system, ORD's 10R/28L could become 9LO/27RO.

Is it because the I and O could easily be mistaken for a 1 and 0?

"Because those are rules."

ICAO Annex 14 (volume 1) provides the following guidance:

  5.2.2.4 A runway designation marking shall consist of a two-digit number and on parallel runways shall be supplemented with a letter. On a single runway, dual parallel runways and triple parallel runways the two-digit number shall be the whole number nearest the one-tenth of the magnetic North when viewed from the direction of approach. On four or more parallel runways, one set of adjacent runways shall be numbered to the nearest one-tenth magnetic azimuth and the other set of adjacent runways numbered to the next nearest one-tenth of the magnetic azimuth. When the above rule would give a single digit number, it shall be preceded by a zero.

and

  5.2.2.5 In the case of parallel runways, each runway designation number shall be supplemented by a letter as follows, in the order shown from left to right when viewed from the direction of approach:

  for two parallel runways: “L” “R”;
  for three parallel runways: “L” “C” “R”;
  for four parallel runways: “L” “R” “L” “R”;
  for five parallel runways: “L” “C” “R” “L” “R” or “L” “R” “L” “C” “R”; and
  for six parallel runways: “L” “C” “R” “L” “C” “R”.

Presumably, the rules for runway designation were created before anyone had the fantasy to imagine mega airports with 4 or 5 parallel runways like we have today. They have then later been adopted to accommodate such airports, without changing the core principles, since doing so would potentially require thousands of airports worldwide to rename their runways and change associated procedures. Not to mention the changes that would be required to aircraft and ATC software, meteorological reporting formats, training and certification of various personnel and so on. Simply put, the disadvantages of using a slightly flawed system are significantly smaller than the cost of redesigning it completely.


How can I tell how far I am from a cloud? So the other day as I was flying, I started to wonder:

All pilots should be familiar with basic VFR cloud clearance requirements in 14 CFR 91.155 (and if not, then go study now!).  When flying piston airplanes, we probably spend most of our time in the Class E below 10,000 ft. arena:

This is great and all, but how can we actually determine how far away we are (especially vertically)?

I thought about using a sextant and some "simple math":

Unfortunately, I need to know my actual distance TO the cloud as well as my angle...  A quick Google search found one of these, but I'm not so sure how it will work with a cloud:

In all seriousness though, how can we stay legal and safe when operating VFR in the vicinity of clouds?

The answer, as best I can discern it from my training & my own experience, is "You can't!" -- every instructor I've flown with has said that cloud clearances are the most inadvertently-busted regulation, even when pilots are doing their best to obey the requirements.
Our eyes and brain are really good at judging distance relative to landmarks and objects of known size (that's how we can tell we're on a "3 mile final" or "8 miles out"), but without known references our ability to estimate distance quickly falls apart, and there simply aren't that many useful landmarks in the sky.

Judging lateral distance to clouds is, at least in my experience, generally easier than vertical distance - as long as you're a fair distance away from the cloud anyway.
You can roughly estimate the ground position of a cloud pretty easily (and if you can't you can always use its shadow and be pretty close). You can also usually find features on the ground of known size (runways, for example: You can get the length of the longest runway at a field from your handy VFR sectional), and figure out how many of those are between you and the cloud's ground position.
Also if you're doing this whole pilotage-and-navigation thing right you know where you are on the chart, and you can visually estimate the ground position of a cloud pretty easily (again if all else fails use its shadow and you'll be close). Break out your plotter and you can figure out how many miles away you are from the cloud (but inside about 3 miles this is going to get pretty difficult, and with your head in the cockpit mucking about with the chart and plotter you may wind up inside the cloud by the time you're done working up your estimate!).

A final close-in technique for clouds at your altitude is to use your wing. You know your aircraft's wingspan, and you can also say that roughly half that value is the length of one wing. Figure out how many "wings away" the cloud is, and do the math -- of course if you're at a distance where you can do that kind of visual estimation you're likely to be close to the cloud clearance limits.

Judging vertical distance is harder.  The usual advice if you're below the clouds is to get the cloud heights from a local airports ATIS or AWOS and use that as a guide.  If you're above the clouds PIREPs for cloud tops serve the same purpose.

Visually if you're above the cloud the same skills you use to judge your height above a runway will work. The catch is those skills really only work when you're within about 1000 to 2000 feet (i.e. "By the time you can really judge the distance you may already be too close!").
Coming up from below a cloud you're basically relying on judging your closing speed to an object of unknown / nebulous size: As you approach the cloud it's going to get bigger, but you don't really know how big it's going to get before you wind up inside it.

As a final visual cue in any direction, remember that clouds aren't clearly-defined boundaries - Often you'll see little wispy streaks of cloud around you as you're getting closer to the cloud you're trying to avoid (particularly when approaching from below). This is a pretty definitive indication that you're probably closer to the cloud than you should be, and you should start heading away from the cloud before you wind up inside it.

I think the best bottom-line practical advice I've ever gotten on cloud clearances, loosely paraphrased from a couple of the local CFIs: "Just stay way the heck away from clouds until you're instrument rated and on an IFR flight plan." and "If you think you might be too close to a cloud, get further away!" -- the latter probably being what the FAA is getting at with their statutory distance requirements.


What will be in 'radiotelephony privileges' part of EASA PPL without practical RT examination? My question is addressed to pilots who recently obtained PPL in Europe (preferably in Czech Republic, but not so important).

As I understand, EASA itself does not require separate radiotelephony license (FRTOL, RT etc.), but some EU states does.

Does anybody have any recent experience in obtaining EASA PPL in Europe (especially if it is not your domestic country)? What do you have in the 'radiotelephony privileges' part of your license? Have you had to pass a separate practical RT exam?

NOTE: I do not consider UK.

what do you mean "radiotelephony privileges"? The PPL itself doesn't allow you to use radio at all (legally - you shouldn't be even listening to the traffic).

You have to get a separate "Flight Radiotelephony Operator's Licence" issued by any member state (usually issued by the telecommunication regulator).

For each state - you should contact any aviation school / club and they should help you at least pointing out the direction (or giving out some training). This way I got my radio license (aviation RT operator) even in non-domestic country.


Is there any ATS into the Special Use Airpaces (SUA)? The SUA has its own characteristics and limitations. Is there any unit responsible for providing separation, control or information, for pilots flying into or across any SUA?

In many cases, there are controllers dedicated to providing ATC services to the aircraft that are USING the SUA.  Callsigns such as "Nellis Range" or "Eglin Mission" are used for the controllers working with aircraft within the SUA, be it MOA or Restricted or Warning areas or whatever.  What looks like one big chunk of airspace on the chart may likely be divided into separate areas for training or testing purposes that the aircraft flying into it will know about, and it's useful (sometimes, vital) to have a controller monitoring the various missions and keeping the various aircraft apart.

These controllers may work in a dedicated facility that only deals with military aircraft, or they may work within a larger facility that includes "regular" ATC functions as well.  For instance, the controllers who work the off-shore warning areas south of Eglin AFB as well as the on-shore restricted areas east and west of Eglin are physically located in the same RAPCON that is Eglin approach.  So civilian aircraft inbound to Crestview or Destin or Eglin/Ft Walton Beach are talking to controllers working one set of scopes, but across the room are the controllers for Eglin Mission who are watching the various SUA.  An aircraft that departs Eglin (or Hurlburt, or Duke Field) would probably be talking to one of the former initially, then when they head into one of the restricted or warning areas, they'd be handed off from "Eglin Approach" to "Eglin Mission."  Essentially it's like being handed off from one Approach sector to another, just that the Mission controllers have slightly different roles in keeping the airspace safe.

It's far better to clear an aircraft transiting a particular sector of SUA to fly through it ABOVE the aircraft in it that is employing air-to-ground ordinance, for instance, than clearing him through the airspace BELOW the bomb-dropper!  Or, if necessary -- maybe it's a helo with an emergency that needs a straight line return to base and isn't going to climb up very high -- at least you have the bomb-dropper go cold and hold up high until the transiting aircraft is out of the way!  That's the sort of ATC that Eglin Mission does that Eglin Approach doesn't... along with confirming that this callsign is in fact scheduled for this range at this time, and the last aircraft has departed, so "you're cleared in to Range XYZ to work surface to 15,000', advise 5 minutes prior to departing."

Fun times!


What's the reason for this frog finger shaped parking lots at Köln/Bonn airport (CGN)? Most aprons of international airports are vast areas paved with asphalt or concrete. However, I noticed this structures in the south of Köln/Bonn airport (CGN) (Google maps link):

Does anyone know what's the reason behind this unusual shapes?

EDIT:

Just found the Royal Airforce Base Brüggen with lots of dispersal areas. Some with hangars, some with banks of earth like in the black/white picture in aeroalias' answer. It's also a perfect example for the conceptional layout. (And between the areas in the south, there are even typical bunkers for explosives)

@Simon is right. The 'parking lots' are actually dispersal areas in the (previous) military airfield at that place.

The Cologne Bonn Airport started out as an airfield for Luftwaffe in 1938 in what was a former artillery shooting range. After war, RAF took over the airfield, with the first civilian flights in September 1950. The airfield was converted for full civilian use only in 1957.

"Koeln-Bonn-Airport14" by Borsi112 - Own work. Licensed under CC BY-SA 3.0 via Commons.

The original 1886m (32L/14R) runway is near the bottom of the image (near the dispersal area). The top runway, 3800m in length (32R/14L), was opened in 1961.

In military sirfileds, the parked aircrafts are usually dispersed in order to reduce vulnerability in case of an air raid. According to US Army Field Manual 5-430-00-2 (accessed via globalsecurity.org)

  If dispersal of aircraft is possible and consistent with active defense measures, varied parking patterns provide fewer lucrative targets for indirect-fire weapons.

It also gives some (conceptual) layouts for aircraft dispersal:

Source: globalsecurity.org

The aircraft are parked in such a way as to reduce the probability that more than one aircraft is hit simultaneously. These dispersal areas have banks of earth or small walls around them to reduce the aircrafts’ susceptibility to the effects of bombs landing nearby and to reduce collateral damage in case one of them blow up. It might've looked like this:

Source: portalnews.gq


How to use wind currents for constant elevation in gliding? I am using X-Plane learning some basics in aviation. Currently, I'm using the glider so I can focus on flying and not engines.

I've heard of gliders being able to catch drafts so as to keep continuous flight. Is there a rule to be able to do this? I thought by riding with the wind and occasionally intersecting I might keep up the energy, but it does not seem to work that way.

You need some inhomogeneity to extract energy. For gliders there are three basic ways to do that:

Thermals: The sun heats up the ground which in turn heats up the air above it. Hotter air is lighter and rises up. It keeps rising as long as the lapse rate of the atmosphere is above the adiabatic rate. This means that three conditions must be met for thermals to occur:
1.1 Sunshine
1.2 Sufficient atmospheric lability
1.3 Ground that easily heats up, such as forest or sand.
Ridge lift: Air streams across a hill and rises up on the windward side. Behind mountain ranges you might also find lee waves, an atmospheric oscillation caused by wind blowing across a mountain.
Dynamic soaring: Here the wind gradient in the atmospheric boundary layer is exploited by flying turns while pulling up when turning into a headwind and diving down when turning into a tailwind. This is currently only used by Albatrosses and has been experimented with by Ingo Renner, but is much too stressful for human pilots if done for extended periods.

Look at the variometer in your glider and try to fly circles when you see an indication of rising air. Tighten the circle when climb rate decreases and flatten it when it increases in order to center the glider in the thermal.


Is thermal expansion/contraction a major design problem for large subsonic airplanes? Most large airplanes flying today are mostly metal, which has a relatively big coefficient of thermal expansion. Cruising altitudes of commercial jets can reach 10 km or more, where the air gets down to about -50 Celsius. Room temperature is more like +25 Celsius, and I would not be surprised if that large fuselage, sitting under the sun, gets up near +50 C.

This is quite a range of temperatures to handle. It would cause some contraction/expansion of metals. The larger the piece of metal, such as a wing spar or long airframe beam, the greater the contraction/expansion.

Is this a major design problem for large aircraft, and how is it handled?

EDIT: only interested in subsonic designs. I'm concerned about the cold high altitude air cooling most of the fuselage and making it contract. The nose and leading wing edges might not suffer from this, but I expect the rest of the aircraft will.

Not thermal contraction but condensation of vapor is a problem.

Immediately, fuselage pressurization is the far bigger problem that comes with the altitude changes. But if you operate in hot and moist weather, the moisture in all the air carried inside the fuselage will condense when this air cools down at altitude and will collect somewhere. If no proper drains are included (remember, drain valves and fuselage pressurization do not mix well) and maintenance is sloppy, this accumulated water can weigh several tons.

A special case are foam sandwich structures. PVC foam is the standard in composite gliders, but airliners use honeycomb sandwich structures. When fairings made from PVC foam were tried on airliners, it was found that pressure and temperature cycles damaged the sandwich core pretty quickly. The moisture inside the cells would condense, the cells themselves would crack and bacteria would munch up the soggy remains. Only with honeycomb cores could the sandwich be made durable enough for airliner use.


What is the optimal bank angle to accomplish a given turn in a glide? For an aircraft in a glide, what—if any—is the optimal bank angle to make a given turn while maximizing glide distance and maintaining published best glide speed?

In other words, at a constant airspeed, which bank angle will produce the greatest turn rate with the smallest loss in altitude. Assume a constant airspeed turn that is already established. I am not asking which bank angle will produce the least reduction in the vertical component of lift.

In envisioning this scenario, I specifically have in mind a single engine aircraft experiencing an engine failure at low altitude. However, the aerodynamic theory may apply to any fixed wing scenario.

Edit: let me emphasize that this question assumes the pilot is maintaining the aircraft's nominal published best glide speed throughout the turn, not adjusting airspeed to some variable theoretical best glide speed. Airspeed should not be a variable.

The best bank angle is indeed 45°.

It can be shown relatively easily that that gives the tightest turn for constant angle of attack, where we assume that constant angle of attack results in constant angle of descent too. It would be pretty hard to show for constant speed, and it might not even be exactly true in that case.

However, this can't really be separated from the best speed. And the surprising answer is that the stall speed (which is ~19% ($\sqrt[4]{2}$) higher than in straight flight) gives smallest loss of altitude for turning given number of degrees.

The reason is that the drag (near the stall speed) is proportional to $\frac{1}{v}$, but the turn radius is proportional to $v^2$, so as you slow down, the radius decreases faster then the drag (and therefore vertical speed) increases.

References:

http://www.nar-associates.com/technical-flying/impossible/possible.html
Is it even remotely feasible to turnback a single engine aircraft with an engine failure?


What is a stabilized approach? Most (all?) airlines require the use of a stabilized approach, and it is constantly referred to as a safer way to land an airplane.

What are the criteria for an approach to be considered stabilized?

What makes it safer than a "normal" (unstabilized?) approach?

When you look at FAA publications the criteria for a "stabilized approach" is pretty simple:

  A stabilized approach is one in which the pilot establishes and maintains a constant angle glidepath towards a predetermined point on the landing runway.

When pilots talk about stabilized approaches we generally mean a little more than that though - for example the SKYbrary description of a stabilized approach, the Flight Safety Foundation, and Airbus all include more than just the constant-angle glide path in their recommendations for what makes an approach "stabilized".

Criteria that are commonly included in a "stabilized approach" are:

Maintaining a constant-angle glidepath toward a predetermined aiming point on the runway.
Maintaining a specified descent rate
Maintaining a specified airspeed (Vapp)
(Generally being slightly above Vapp is OK, but below is unacceptable.)
Having the aircraft configured for landing (gear, flaps, etc.)
All required checklists completed
The approach can be maintained with only "small corrections" to pitch, heading, or power.

An approach is "stabilized" if all the required criteria are met by a specific altitude (Airbus calls them "Stabilization Heights", and recommends 500 feet for approaches in VMC, and 1000 feet for approaches in IMC).
If the approach is not stabilized by the appropriate stabilization height (or conditions cause the approach to become "destabilized" - a sudden change in winds for example) the approach is abandoned (a "go-around").

So what makes stabilized approaches safer?
The theory is that a stabilized approach reduces the pilot's workload as they're getting closer to the ground: If the aircraft is configured for landing and all the checklists have been completed all the pilot has to do is gently nudge the controls to keep the plane going where they want it, and they can concentrate all of their attention on a nice, safe, (hopefully) smooth landing.

Are stabilized approaches always safer?
From a workload perspective, yes. It's hard to argue with "The pilot has less work to do".
From a "What if my one-and-only engine dies?" perspective, maybe not.

Stabilized approaches generally require partial power to be maintained throughout the approach, and although the engines in modern single-engine piston/jet aircraft have a pretty good track record of reliability there are good arguments for "non-stabilized" approaches (or approaches that are effectively "stabilized" at idle power) in single-engine aircraft.

Even if you're not flying a "stabilized approach" the way the airline folks define it you're well-served by incorporating some of the elements though - going around if your checklists aren't completed by a certain altitude, abandoning the approach if you have to manhandle the controls to try to keep things together, etc.


Is it possible to fly a tandem-rotor helicopter after a single rotor failure? Tandem-rotor helicopters, such as the Boeing CH-46 Sea Knight and CH-47 Chinook, are helicopters with rotors distant by more than 10 m.

Photo by Cpl. Ryan Carpenter on SNAFU

It seems unlikely a single rotor could sustain the force moment created by the failure of the other rotor. On the other hand it seems to me it would be difficult to have one rotor in autorotation and one powered.

If this is possible, how would the pilot fly the helicopter? If it's not possible, why?

It's been a few decades since I crewed CH-46s, but the situation you're describing is  called a de-sync and it's a catastrophic failure. The forward and aft rotors are linked by a driveshaft that drives the forward transmission and synchronizes the rotors. In a de-sync the intermeshed rotors will collide and the aircraft will tear itself to pieces.

Also, setting aside for a moment the consequences of a de-sync, the flight controls for both rotors are linked so it would be impossible to flatten the pitch to autorotate just the front rotor head. I suppose it would be mathematically possible to keep the rotors in sync and match the rate of deterioration in the rotor speed, but the odds would be extremely low, and the chances of recovering from any altitude beyond a few feet would be near nil.


Can an FAA-certified pilot rent/fly a GA aircraft in England? I am a U.S. certificated pilot in the U.S.A. I have about 1200 hrs flying mostly general aviation.

I will be traveling to England with family in March 2019 for a personal vacation. I would like to know if anyone on StackExchange has rented an airplane in Englad before and what their experience in doing this was.

In addition, it looks like it would be pretty easy to qualify for an EASA license in England. Any advice/insight on how to go about this?

You can rent a G-registration aircraft but your license will be treated as a UK private pilot ticket with day VFR privileges without any additional paperwork so long as you stay in UK airspace. There is a basic requirement to file one form, and you must get a signoff on simple theoretical knowledge, but that is it for now. See this CAA Information Notice for additional details.


Why pull up on the rollout after landing, after the nose wheel is down? I'm a student pilot learning on a Piper Cherokee 180.  When I land and the nose wheel touches down my instructor wants me to keep pulling back on the stick through the landing roll.

For soft field landings this makes sense as you don't want the nose wheel to dig into the ground and tumble over.  However we are landing at an airport with hard surface runways which routinely experiences gusty wind conditions.  It seems to me that if I keep pulling up and a gust of headwind hit us shortly after the nose wheel touches down that the gust would lift the nose wheel back off the ground.  This of course would not be a good thing.  So in my mind I think it would be better to ease off the back pressure once the nose wheel touches down.  What are your thoughts?

Note:  My instructor was a crop duster so I think he just carried over the soft field landing technique and is just teaching this because this is what he learned.

It is a soft field technique but is generally applied on hard surfaces for the sake of the aircraft. There are a few main reasons;

Take stress of the nose wheel and nose gear assembly which is a bit more fragile than the main gear assembly. This is particularly true in aircraft equipped with a steerable nose wheel like the Cherokee (or in retracts).
Provide adequate clearance for the propellor. If you look really closely the Cherokee has a low enough clearance such that, excess low pressure on the nose wheel and a sufficiently hard landing can cause a prop strike. This is one of the reasons its so important to check tire pressure in your preflight.
It also helps to reduce the risk of the fated nose wheel bounce which can collapse the assembly.
Generally it also helps to prevent you from simply releasing the controls after the mains touch down or potentially even pushing forward on the column which would drive the nose down and potentially cause damage.

During training this also helps to build habits that lead to a good landing attitude and speed bleed off especially if you start out landing flat.


Do ANR headsets affect pilots' perception of engine problems? ANR (Active Noise Reduction) headsets reduce the sound level to a pilot's ears by creating an interference wave that cancels out some of the environmental noise in the cabin. Some say that this reduces the pilot's ability to hear minor changes in the engine's sound, thus delaying the point when the pilot would take action to diagnose the problem or land the aircraft.

Are there any conditions of engine malfunction or suboptimal performance which a pilot wearing an ANR headset would not be able to detect, but one wearing a passive headset would?

Although its possible to detect engine problems audibly, I don't think that's the primary mechanism (except for engine out) by which pilots are expected to detect engine anomalies. Part 91.205 requires that every aircraft be equipped with the following instrumentation, and these should be the primary mechanism by which engine malfunctions are detected.

  (4) Tachometer for each engine.

  (5) Oil pressure gauge for each engine using pressure system.

  (6) Temperature gauge for each liquid-cooled engine.

  (7) Oil temperature gauge for each air-cooled engine.

  (8) Manifold pressure gauge for each altitude engine.

  (9) Fuel gauge indicating the quantity of fuel in each tank.

That being said, ANR headsets attenuate sound, but don't eliminate it entirely. Having flown with an ANR headset for most of my flying career, I can certainly hear variations in engine noise in the mag check and prop exercise during the runup, as well as during throttle and prop changes. I can also hear a fouled plug during runup, as well as verifying it visually on the gauges.


Why is a procedure turn required if you are more or less on the final approach course? From this question.  I am not instrument rated.  The answers to the question explain, from the point of view of the plate instructions, if a PT is required or not.  The OP was failed for not performing a hold.

However, I can't see why a turn or hold is required at all.  If you are approaching within say 30 degrees, why would you not simply turn onto the final approach course and fly the approach (assuming that you are cleared of course)?

  If you were simply cleared direct to BEJCY and cleared for the approach, then your instructor is correct and you should have completed the procedure turn as charted.

The OP was approaching from SSW from AUGIE so continuing to BEJCY puts him 21 degrees to the South.  Why not just turn right onto 007?

I am assuming no ATC instructions to do anything other than the published approach.

Read that other question again.  He was approaching from the SSW and made an assumption based on the approach segment from AUGIE.  He wasn't actually on the AUGIE-BEJCY leg as it would be impossible to be there if he were approaching from the SSW.

His clearance was "Direct BEJCY cleared for the GPS 01 approach".  That clearance, in lieu of any specific instructions about the procedure turn, requires that the procedure turn be flown.  He assumed that because he was roughly on the extended centerline of the runway SSW of the airport that he was exempt.  However, there is no charted course there labelled "NoPT", so his assumption was incorrect.

Back to your question of why someone flying from that location would have to fly the PT, and the answer generally boils down to "TERPS".  The leg from AUGIE can be flown at 3000 ft while the area minimum safe altitude is 3100 ft.  It is very likely the minimum enroute altitude over that area is higher than 3100 feet.  This means a pilot that is using BEJCY as the IAF may be considerably higher altitude than 3000 ft.  On this approach you ideally want to be at 2500 ft by the FAF at CUCTO.  If you are approaching BEJCY from any direction other than AUGIE this means you cannot start your descent from whatever altitude you are at down to 2500' until passing BEJCY.  The procedure turn is not only for course alignment but also to descend to the procedure altitude from the enroute environment.


Why is the trailing edge sweep angle smaller at the wing root? Many airliners have a distinct unswept part at the wing root at the trailing edge. See for example this image from Wikimedia of a B737-400.

Other examples include the B777, A320, Embrear 145, and many more. Virtually all airliners have at least some degree of less sweep at the wing root.

Why is there a part of less sweep at the wing root (to facilitate engine mount; Aerodynamic reasons)? Why does a completely unswept part seem to be a preferred choice for this part of less sweep, as opposed to any other sweep angle than zero?

There are two main reasons:

Swept wings suffer from interference at the center of the wing. If wing taper and sweep remain constant over the full span, the lift distribution will show a distinct drop at the center. This is called the "Mitteneffekt". The remedy is to locally increase the wing chord near the root and to decrease the wing's sweep angle. This, together with a change in airfoils and local incidence, "fills up" the dimple in the lift distribution and reduces induced drag.
Large aircraft need heavy wing spars, and increasing chord near the root gives the spar more height while the relative thickness of the airfoil can remain unchanged. A higher spar is structurally more efficient, so increasing its height at the root saves weight. Since the relative thickness determines the maximum operating Mach number, it cannot be increased locally without hurting the whole wing. The better alternative is to disproportionally increase wing chord at the root.

The unswept trailing edge near the root is a consequence of Boeing's flap track mechanism. Boeing Fowler flaps move perpendicular to the hinge line, and an unswept hinge line avoids lateral movement of the flap. Another consequence is a gap between the inner and outer flaps in order to allow both to move back without colliding. Boeing fills the gap with a high-speed aileron. Also, this gap avoids that the flaps protrude into the hot, turbulent exhaust stream of the jet engine.
Airbus flaps move in flight direction and leave the sweep angle of the trailing edge free. Also, they don't need a gap between the flap segments left and right of a sweep change of the hinge line.


How stable is the "customer" power on a commercial aircraft? This question on Travel.SE got me thinking... Just how stable is the power that's available via the outlets in the passenger cabin on a modern, commercial aircraft?

My assumption in my answer that it's probably quite clean was based on these things, but I'm not sure if or how accurate these assumptions are:

Power for avionics needs to be clean to ensure there are no spikes or dips that would cause avionic failures as this could lead to otherwise avoidable emergency declarations.
Since the plane is already providing clean power to the avionics, the power coming out of the transformers to step it down to 110V, 60Hz for the outlets should also be pretty clean.

Are these accurate assumptions, or is the effort to provide nice, super clean power to the cabin outlets too much work/too expensive to bother with getting it any nicer than the sketchy quality stuff the power company provides to your house?

There is a pretty great article on the design of the 777 electrical system here.

  Power for avionics needs to be clean to ensure there are no spikes or
  dips that would cause avionic failures as this could lead to otherwise
  avoidable emergency declarations.

The avionics and passenger power systems are two completely different systems. The 28V instrument power system is pulled right from the source,

  Flight instruments on the 777 are primarily powered by 28 Volts DC.
  Direct current power is supplied by three-phase transformer-rectifier
  units. There are four such units each rated at 120 Amperes.

This pulls right from the generator/alternator output of the plane. Everything ranging from your classic Cessna 152 all the way up through a 777 regulates their alternators/generators with voltage regulators and fuses to protect against current overloads. These things work in tandem to protect the avionics and internal power systems of the plane. The 28VDC system for the avionics is also connected to the battery system which prevents dips should the generators have issues outputting enough power or quit all together.

The rest of the plane is powered by 110/200V 400Hz system.

  The primary electrical system is a 3-phase, 4-wire, constant frequency
  400 Hz, 115/200 Volt system, which has been the industry standard on
  commercial jet transports since the Boeing 707

Interestingly it's 400Hz, I'm still looking to see how they get that to 60Hz.

  Since the plane is already providing clean power to the avionics, the
  power coming out of the transformers to step it down to 110V, 60Hz for
  the outlets should also be pretty clean.

The power is quite "clean" but you have some incorrect assumptions here. The power is not really stepped down. That is something that occurs on the power grid since most power lines on the street carry a significantly higher voltage than what you have in your house plugs. In this case we have the luxury of choosing an alternator/generator system that is close to (most likely slightly above) our required voltage. Slide 4 from this presentation from Boeing alludes to the fact that the system outputs 115V (and is presumably conditioned) and is then split to the cabin as well as the 28V DC bus. Power does not come out of the transformers it comes out of the generator/alternators it then is conditioned and transformed as needed. Stability is achieved though numerous conditioners and regulators, see the article I linked for more details on them.

Don't worry, it's safe to charge your laptop on a jet.


Can a UAV over 55lbs legally fly 20 miles off the US coast? For US aerospace companies that are developing UAVs heavier than 55lbs for application for the DOD, is it possible to test UAVs over the ocean outside what we would normally consider US controlled airspace legally without a FAA specific exemption?

I should add that in this particular case the UAV can be launched and recovered from Sea.

Thoughts?

The United States does not own or control airspace outside its territorial limits, but there is an exception; our government has extended Class A airspace out to twelve miles from the coast of the contiguous 48 states and Alaska. If you launch the UAV at sea and stay out of US airspace, there's no need to ask for an exemption.


What is a "frozen ATPL"? I've heard the term "frozen ATPL" and it seems to be some kind of limited EASA ATP certificate. What exactly is a frozen ATPL? What privileges does it give the holder? How is it unfrozen to become - presumably - a regular ATPL?

A frozen ATPL holder is somebody who has passed all the required (14) exams for the issue of an ATPL but does not have the required flying hours. Strictly speaking, there is no such thing as a 'frozen' ATPL, though a number of training schools do use the term:

A Frozen ATPL holder refers to somebody who has passed all the required theoretical exams but does not qualify him to be issued with a full ATPL until he has logged a total of 1500 hours.
A student from a flying school will normally graduate with a CPL (Commercial Pilot Licence) and IR (Instrumental Rating) (CPL+IR). This Licence is known as the Frozen ATPL.

In order to 'unfreeze' the ATPL, the candidate has to complete a flight time of 1500 hours subject to certain conditions:

... ATPL will remain frozen until you have reached 1500 hours of flying time, which is made up of the following criteria:

500 hrs multi-pilot in transport or commuter aircraft
250 hrs PIC (or 100 Pilot in Command and 150 PIC under supervision)*
200 hrs cross country flights (100 as Pilot in Command)
75 hrs instrument time
100 hrs night flight as PIC or co-pilot


TFR based on an invisible VOR? A new TFR was recently published, which references the Riverside (RIS) VOR/DME.

When I look at the relevant chart in SkyVector, I don't see such a VOR in that area.

When I put the ID "RIS" into SkyVector, it takes me to an intersection outside London, UK.

PilotNav has the info, but that took a lot of searching.

How is one meant to interpret this TFR if the nav aid is so hard to find?
Why didn't they use bigger and easier NavAids like MCI or ANX, which are not far away, and clearly depicted on the charts?

Update!After I brought this to the attention of the local offices, they canceled the TFR and issued a new one expressed in terms of the MCI VOR, which makes a lot more sense.    The FAA was incredibly responsive and helpful!

After I brought this to the attention of the local offices, they canceled the TFR and issued a new one expressed in terms of the MCI VOR, which makes a lot more sense. The FAA was incredibly responsive and helpful!

They didn't explicitly say it was a mistake, but I think they decided it was better to use an operational VOR.

(however, a couple weeks later, they referenced the RIS VOR again in a NOTAM.)


Why do lavatories in modern planes still have ash trays? Last week I flew on a modern B737-700. I noticed that the lavatory was equipped with ashtrays  (both on the inside as on the outside) even with the smoking sign on it. Smoking on airplanes has been banned from quite some time now, so why are lavatories still built where ash trays are provided?

Because in the US (where Boeings are made) it's required by law. 14 CFR 25.853(g) says:

  (g) Regardless of whether smoking is allowed in any other part of the
  airplane, lavatories must have self-contained, removable ashtrays
  located conspicuously on or near the entry side of each lavatory door,
  except that one ashtray may serve more than one lavatory door if the
  ashtray can be seen readily from the cabin side of each lavatory
  served.

The law may be different in other jurisdictions, of course. Why the law still exists is another question, but either no one found the time to change it (laws are often very difficult to change once passed) or it was a deliberate decision to keep requiring ashtrays in case someone tries to smoke anyway.

EDIT: As commenters have noted, the law I quoted requires ashtrays outside the lavatories but it's still common to find them inside. My guess here is that the ones outside comply with the letter of the law, whereas the ones inside comply with the intent, i.e. they're there because if someone does light up, it will be inside the lavatory and not outside in plain view. This 2012 article quotes an anonymous FAA source as saying that people continue to smoke on aircraft so it still makes sense to have them for safety reasons. That raises the question (again) of why the law doesn't fully reflect reality, but that's neither unusual nor unique to aviation.


Does having a halo effect after LASIK disqualify you from being a pilot for the Air Force or commercial pilot? I had LASIK a while ago and I have some halo effects when I look at lights at night, and was wondering if that alone is something that would disqualify me from being a pilot for the Air Force or an airline?

FAA doesn't allow airmen with complications like halos. etc. From FAA Guide for Aviation Medical Examiners:

  The FAA expects that airmen will not resume airman duties until their treating health care professional determines that their post-operative vision has stabilized, there are no significant adverse effects or complications (such as halos, rings, haze, impaired night vision and glare)...

A medical examiner should certify that the applicant (for pilot) is not suffering from any such complications:

  An applicant treated with a refractive procedure may be issued  a medical
  certificate by the Examiner if the applicant meets the visual acuity standards and the Report of Eye Evaluation (FAA Form 8500-7) indicates that healing is complete; visual acuity remains stable; and the applicant does not suffer sequela such as; glare intolerance, halos, rings, impaired night vision, or any other complications.

USAF doesn't allow individuals with cases where the surgical outcome affects one's performance of duties; having a halo effect would be a disqualifier.


What is the radius of a VOR compass rose on a VFR sectional chart? I thought I read somewhere that it was 10 nautical miles. Does anyone have a reference on whether that's the case or not?

I'd like to use the measurement of a compass rose to aid in my estimation of how far away I might be from something else.

I measured one on a sectional and it came out to approximately 19.4 NM. However, as mentioned, I'm not sure it has a fixed size. Symbols on a map can be resized by the cartographers (map makers) for ease of reading. I would not rely on this for anything other than trivia.


Are exoskeleton wings technically possible? While there have been a robot simulating a bird, could be there also an exoskeleton wing system for a human?

Main design considerations:

a) only human powered

b) using an additional, or exclusive source of power

I consider b) is more trivial because it's near to more or less attaching a human to a big bionic bird similar to mentioned above.

So we concentrate here on a).

Yes, and it has been done.
In 2010, the first human-powered ornithopter recorded its first flight.

It took a very light aircraft and a lot of power from the pilot, about 650 W, so the flight only lasted 20 seconds. It only sustained level flight, requiring assistance to take off.

To put this into perspective, a good power target for cyclists is 250 W. A top competitor will put out 300 W over a race and 400 W over 10-15 minutes, and over 1000 W for 10-20 seconds. So it's possible (not certain) that a top Tour de France cyclist could hold it in the air for a couple minutes, or even have the stamina for a takeoff. But it's still more power than any human can sustain long enough to cover a mile.

Meanwhile, the record for propeller-driven human powered aircraft, without flapping wings, currently holds at 115 km. This was achieved with autonomous launch.

The ornithopter in question isn't exactly an "exoskeleton", though, because an exoskeleton is not optimal for the job. Human arms are unsuitable for flying or sustaining high power output in general, so all successful human-powered aircraft derive power from the pilot's legs. Typically it's a cycling motion, but a straight leg press machine motion is used in this particular case.


Is the "confirmed allocation" string in "A Scandal in Belgravia" a real airline practice? (This is a repost of this question on Movies SE. I hope to get better answers here.)

Irene Adler shows the following text to Sherlock:

007 Confirmed allocation
4C12C45F13E13G60A60B61F34G34J60D12H33K34K

He immediately guesses that "these are seat allocations on a passenger jet", claims it must be a Boeing 747 and then recalls a specific flight which takes off at 6:30 PM the next day. Note that only 14 seats are listed. A Boeing 747 can carry about four hundred passengers. The flight takes off tomorrow evening.

Do airlines really document or communicate seating allocations in this way? Shouldn't there be more seats "confirmed" (whatever that means)?

No

Based on my research for string confirmed allocation, there were no references found related to airlines or their practice.

However, the background scenario about the conversation Sherlock was having, something like the following had happened (references: this and this and this and this and this):

(my paraphrasing, not actually a quote)

  Sherlock knows that 007 is a flight of Bond Air which is leaving for
  Baltimore tomorrow at 6:30pm. He is aware of a terrorist plot of
  having dead bodies on an airplane (14 seats allocations) so that no one actually dies. The
  first 0 in flight number indicates that zero causalities will happen.

P.S.: This question is not about aviation but movies.


Are airline pilots worn out at an age of 55? Lufthansa's pilot union is calling for a strike to defend pilot's right to retire at the age of 55. They argue that the stressful job of flying is too much for older people. This provokes two questions:

What fraction of pilots takes advantage of such a rule (if it is available to them)?
Is there really a steep decline in the capabilities of older pilots?

I would expect that many pilots continue to fly, so I wonder whether it makes sense for Lufthansa to risk full confrontation. Also, if the reasoning of the union is right, it would be prudent for airlines to retire older pilots before they are a safety risk.

My experience, speaking as a pilot who had to retire in 1999 from a small 747 carrier when the US age 60 rule was in effect, was that NONE of us close to retirement wanted to retire. More often than not, the attitude was, "It's hard to believe they actually pay us for this." We didn't want to quit; we were at the top of our game; the world was our playground. The money was also very good!

Insofar as worries of a "steep decline in capabilities of older pilots," there is no statistical evidence that I am aware of to support this, although whether there is at least some decline has been a matter of controversy. You can Google "age 60 rule" and find reams (screen loads?) of info on this. A particularly good link IMO is http://www.avweb.com/news/aeromed/181875-1.html

What makes a good air carrier captain is not so much being a good stick or quick reactions, but being situationally aware, learning what to avoid, being able to read the politics of a situation (especially in third world countries), and other things that come to one primarily through experience.

For example, when I hired on to my second 747 carrier as an f.o., I was paired with a relatively young, fresh captain. I was older, had been a 747 captain at a previous carrier, and had more hours in the airplane. We landed in Harare, Zimbabwe to pick up a charter. Our APU was inop, so as per standard procedure, we left #4 engine running to supply the pneumatic air we would need to start the other engines. However, when the ground handlers told us there would be a delay of a couple of hours, the captain ordered the engines shut down, saying that we would use a huffer to start. Both the f.e. and I simultaneously objected, both saying in so many words that we couldn't depend on there being a usable huffer in Harare. The captain ignored us and shut down the engines, believing that the capital of a country would surely have such. The fun started when he asked for a huffer to be hooked up for our start. Long story short, what would have been but a two hour delay turned into something like a 10 hour delay. It included hooking up 4 different beat up old huffers to the airplane, but even using the two best at once (the 747 can accommodate 2 hookups) failed. Finally, a mechanic worked on those two best units and managed to get enough pressure to start us.

The captain was a good stick; he just hadn't had enough experience.


Why did the Bede Bd5 have strakes on the horizontal tail? Why did the Bede Bd5 have strakes on the horizontal tail?

Is it a sexy way of adding horizontal tail volume or reducing the span of the horizontal tail by increasing it's chord?

They work like large vortex generators to delay flow separation on the underside when the stabilator is at high (leading edge down) angles at low speed.  IIRC, the BD-5 had stabilator stalling issues during development.  That's one way of doing it.  Another way is to put VGs along the underside leading edge.

The Cessna Cardinal had a similar problem when it first entered service and Cessna's fix was to put LE slots in (a famous Service Bulletin known as the Cardinal Rule, with a comprehensive fleet mod campaign for the initial 500 or so aircraft), more or less for the same effect.


At which angle tiltrotor's rotors generates more lift? [Tiltrotor 1]

                        [Tiltrotor 2]

I can't name these tiltrotors. I just want to know which of the tiltrotors generate more lift considering aerodynamics and based upon the rotors horizontally tilted or vertically. I used these images just to show an orientation of rotary wings at which angle they are tilted not for differentiating these two models. And what happens to the lift generated by the rotors tilted 45 degree to the axes.

Note: Only concerned with the rotary wing either horizontal or vertical inclined but not whole aircraft design.

Technically, if the tilt rotor flies forwards with vertical rotors, the lift is produced by the wings and forward thrust by the rotors. So let's regard the rotor thrust, whether in horizontal or vertical rotor position. Tilt of the rotor does not affect the amount of thrust produced. The following factors do:

Rotor speed. This would remain pretty constant over the tilt range, with tip speed as close as possible to drag divergence speed. At top speed with vertical rotors, rotor speed must be lower than in the hover because of the velocity triangle tip speed = rotor speed + air speed.
Blade Angle of Attack. A function of blade angle and of airstream inflow.
Airstream inflow. With the rotors in a vertical position and flying forwards, air flows into the rotor disk and requires less acceleration to provide the same amount of thrust. Or: a given thrust requires less engine power in forward flight than in vertical take-off.

Therefore, for a given amount of engine power the vertical rotor at speed would be able to provide the highest thrust - but depending on the max. speed of the craft, rotor speed must be reduced, which also reduces the ability of the rotor to convert power into thrust.

The picture above from Leishman, also used in this answer, shows the amount of engine power required vs. airspeed for helicopters. Note that a helicopter rotor must always provide more thrust than its weight. In order to gain airspeed, the main rotor is tilted as well, and the effect or airflow at higher speed can be seen from the reduced amount of induced power.

For a tiltrotor, the rotors will be dimensioned for vertical take-off: they must provide thrust > weight in this situation. In horizontal flight the wings provide the vertical force for weight compensation, and the rotors only need to overcome drag. Which increases quadratically with speed, so at top speed thrust will be the same as TO weight again.