Why should isobars be aligned with the leading edge of the main wing for a transonic cruiser? When designing an airplane meant to cruise at transonic speeds (or supersonic speeds), I heard that one should look at the isobars on the main wing in order to assess if the shape, sweep angle and other airfoil parameters are suitably chosen. I also read that the better configuration yields isobars that are parallel to the leading edge. I already know that there are several techniques to get the isobars aligned with the leading edge (area ruling, adapting the sweep angle, extra care in the design of the junction between the fuselage and the wing), but why is this configuration better than another one? What does it improve?

I finally found several arguments to answer this question from different sources.

Sweep and Mach Number from Airbus

This argument is developed in an Airbus magazine from 1985. To grasp it it is important to understand the purpose of swept wing. By sweeping the main wings one introduces an angle between the leading edge of the wing and a line perpendicular to the fuselage axis. Let's consider two airplanes, one with swept wings (A) and one with straight wings (B).

One of the most important parameters is the Mach Number experienced by the wings. It is measured normal to the leading edge of the wing which means that for the two airplanes flying at the same Mach Number, the Mach Number seen by wings of (B) is larger than the one seen by the wings of (A). This allows to fly at higher speed because it delays the large increase in drag (drag divergence) and other effects linked to the Mach Number around the airfoil.

However, if the isobars on the wing are not aligned with the leading edge, they are following a less swept pattern which tends to reduce the benefits from the sweep angle of the main wing because the effective sweep angle is smaller and the Mach Number around the wing should not be computed normal to the leading edge but normal to the isobars close to the leading edge.

From a theoretical point of view it would even be better to have isobars not aligned with the leading edge but having a larger sweep angle. However this never happens due to boundary conditions at the root and the tip of the wing.

Other sources

All this is also explained here.

Finally, this last source deals also with the matters but does not justify the need for the isobars to be parallel to the leading edge. It deals more with the shock on the wing and the ways to weaken it and thus reduce the drag.


Could a flight engineer fly a jet solo? In modern two-engine planes, if one pilot is disabled, it's my understanding that the remaining pilot can safely fly and land the plane. But what about in aircraft like the 727, which had two pilots and a flight engineer? Assuming the FE had flight training, could they land the plane if the two pilots up front were incapacitated? More generally, what is the minimum number of pilots required to safely land a jet with a three-person cockpit?

You've asked a question the answer to which is in large part a matter of opinion. Also, which three-person cockpit aircraft you're talking about also enters in, as does the stage of flight, as do the conditions at the airport of intended landing. All this, in my opinion, means the answer is "maybe" insofar as an FE who had had flight training be able to get the airplane down safely, and the currency of the FEs piloting would be important as well.

As far as the minimum number of pilots required to safely land a jet with a three-person cockpit (a separate question really), one pilot and the FE can safely land the airplane. In a normal landing, the flying pilot is doing most of the pilot work. The non-flying pilot typically is doing the radio work and manipulating the gear and flap levers at the command of the flying pilot. Since pilots usually trade legs, both are used to doing all that needs to be done. If a non-flying pilot is not there, the flying pilot can easily reach the flap and gear controls, and he's used to manipulating them when acting as the non-flying pilot.

In the scenario of an FE leaving his seat and sitting in a pilot seat and performing the piloting, there is the problem that the FE panel generally cannot be reached from a pilot seat. To a degree, depending on the stage of flight, the FE could pre-set his panel for the landing.

Some years ago I wrote a novel (unpublished) in which I had a single pilot fly a 747. In the novel the pilot had fashioned a wooden pole long enough to reach the FE panel from the captain's seat. The pole had at one end an arrangement that allowed the pilot of manipulate the necessary switches and dials on the FE panel.


How is the climb gradient calculated? I was part of a discussion about the differences between all engine climb gradients and one engine inoperative (OEI) climb gradients, and a colleague suggested that climb gradient can be calculated as

$G = \frac{T-D}{W}$

Where

$G$ is Climb Gradient as a percent,
$T$ is Thrust,
$D$ is Drag, and
$W$ is Weight.

This derivation was never really explained, and it doesn't really make sense to me.  He continues by stating that lift can be assumed to equal weight for small climb angles, so that his equation becomes

$G = \frac{T}{W} -\frac{D}{L}$

Where $L$ is Lift.

For some analyses, I can see using the approximation $W = L$, but since that is essentially assuming your climb gradient is 0, it doesn't seem prudent to use that assumption to calculate the climb gradient itself.

Has anyone seen these equations before?  Or is there a piece to this that I'm missing that someone could explain to me?

Assuming that thrust is entirely in the direction of travel and the flight path angle is constant, the Lift is equal to the weight times the cosine of the flight path angle:

$L = W\cos(\gamma)$

For small $\gamma$, $\cos(\gamma) \approx 1$

E.g. for a flight path angle of 10 degrees, the error introduced by the approximation is ~ 1.5%

For unaccelerated climb, the sum of all forces in the along path direction cancel each other out:

$ T-D-W\sin(\gamma) = 0$

The gradient is $\tan (\gamma)$.

Again, for small angles, $\sin(\gamma)\approx\tan(\gamma)$

From there it is a small step to see that the calculation suggested by your colleague is acceptable for unaccelerated climbs at small flight path angles.


Can a transonic airfoil have two shock waves? I am currently running CFD cases on a transonic airfoil at Mach 0.75 and performing an angle-of-attack sweep to evaluate its performance. When I reached the angle of attack of 4.5 degrees (which I appreciate is very high for transonic flight, but tested nonetheless), a dual shock was formed on the suction side. Is this physically possible?

I understand how the suction-side flow may reaccelerate after a shock with favourable pressure gradient and possibly exceed sonic again, leading to a second shock, but wouldn't it just produce a single, stronger shock downstream?

I attached the two flowfields, colored by Mach number, with the first image representing the angle of attack of 4.5 and the second at 3.5 degrees.

Following jayS answer, I plotted the Cp for the two airfoils seen above, for comparison to the chart found.

Very Interesting results. I must say I have never before seen such a peculiar case. Yes, theoretically it seems possible to have this situation, but it's difficult to say if this is possible in reality or not. I found another similar behavior mentioned here:

One of the three aerofoils has dual shock.
It's difficult to say whether it's a physically correct situation or a mere artifact of CFD, especially without data on type of solver, type of simulation, numerical methods employed, mesh details etc. It would be advisable to simulate the same case in another code and see what results are seen.


Should a pre-flight inspection spot snakes on a plane? In January 2013, a python hitched a ride on plane, unfortunately exposed on the wing after getting sucked out of its hiding place.

Qantas 191 is a Cairns → Port Moresby flight on a DHC-8-400, probably the first of the day.

Having done walk-arounds for a Cherokee, I would like to think that I wouldn't allow such an event to happen on a small plane.  On the other hand, I realize that it would be impossible to do a thorough inspection on, say, an Airbus A380.

What is a typical preflight inspection checklist for a Dash 8 or similar plane?  Would it have included, for example, a visual inspection of the flaps that would have allowed the snake to have been spotted?

Given the location of the snake from the photos/video in the article and the height of the wing/engine assembly (as shown below) I think it's entirely possible to miss this critter in preflight.  A visual inspection of the control surfaces is certainly a part of the preflight, but unlike on a small aircraft (say a Piper Cherokee or Cessna 172) you will probably not be getting "up close and personal" with the control surfaces - you would need a ladder to to so, and the sort of in-depth examinations that would require getting up on that ladder would probably normally be performed by maintenance personnel.

A pilot doing a preflight might get up on a ladder if they noticed something amiss (say a snake obviously hanging from the wing), but on a simple pre-filght visual inspection from the ground this unfortunate critter could easily be missed - particularly if it was curled up tightly in a small space as snakes are wont to do, and didn't have its body hanging out where it could be seen.


Fan power for 3x3m wind tunnel? How much power do I need  for 3x3m wind tunnel,with airspeed up to 200km/h?
Some formula for calculation?

200 km/h = 55,6 m/s
The density of air is taken as 1,23 kg/m3
You have a mass flow rate of 55,6 x 3 x 3 x 1,23 = 615 kg/s
In other words, in every second, you're moving a mass of air of 615 kg. The kinetic energy of that moving mass is 0,5 x 615 x 55,6^2 = 951 kilojoule. In a second, that's 951 kilowatt.
A lot of power, and that, assuming your fan has an efficiency of 100% and friction losses are zero...


How do I determine holding pattern entry and direction in this example? I need help with this question for the IFR written test: "A pilot receives this ATC clearance: '...CLEARED TO THE XYZ VORTAC. HOLD NORTH ON THE THREE SIX ZERO RADIAL, LEFT TURNS...' What is the recommended procedure to enter the holding pattern?"
Why is the answer on the left the correct visualization? It doesn't say if I should hold left or right of the radial. Both answers are left turns. Both answers are holding north. What am I missing?

Thank you all for your help. My 150 arrow was wrong and I was confusing myself. Also, it's helpful to know that the inbound leg terminates at the fix (which entirely makes sense now). So, my new answer is direct entry and here is my new visualization:

Neither of the two representations show holding North if the arrow depicted in the corner is truly pointing towards 150°. If this is the case, North is at the bottom of the page and South is at the top. Therefore, both representations are showing holding South of the fix.
If the dot depicted is the fix, the representation on the left is not a holding pattern. Holding patterns have their inbound leg terminating at the fix. Your turn towards the outbound leg would then begin when crossing the fix on the outbound leg.
Furthermore, your HSI is showing that you are on the 150°  To-Radial of the fix, on a 155° Heading, and a 16.5 DME. This would put your aircraft inbound, 16.5 Nautical Miles North of the fix, roughly on the 330° From-Radial (or just Radial). You should intercept the inbound leg 360° Radial of the fix well before crossing it. Then effect a Direct Entry, Performing your 5Ts Once you hit the fix with wings level.
You could, however, continue direct to the fix, inbound on the 330° Radial, and still perform a Direct Entry. I just, personally, think it’s easier to intercept the inbound (360° Radial) leg first.
Research AIM 5-3-8 for further details.


Do overland long-haul flights have something similar to SELCAL? This question will be regarding airlines, flying high altitudes.

As with short flights, you are in contact with local controllers, then get passed off to enroute and local again.

I am familiar with SELCAL, where you do not have to listen to HF Radio jumble for your 7 hour oceanic flight.

However, what if you are flying for example Dublin to Hong Kong, not crossing oceans. Will you be in contact with ATC the whole time, and the pilots on duty always having to wear headsets just in case if ATC wants to find them? Or would there be a system similar to SELCAL where they will buzz the aircraft only when they need them?

(skyvector.com)

Yes SELCAL is provided over land in remote areas.

I checked the Russian AIP, and shown above is an example.

I'm not sure which FIRs the flight from Dublin to Hong Kong will pass through, mainly because the routing near China is not always consistent. Nevertheless, in remote Northern areas as shown SELCAL is provided.

According to ICAO Annex 10 it will be the operator's responsibility to arrange its use if they want to (or if it is mandated). For example:

  5.2.4.2.1 PANS.— It is the responsibility of the aircraft
  operating agency and the aircraft to ensure that all
  aeronautical stations, with which the aircraft would normally
  communicate during a particular flight, know the SELCAL
  code associated with its radiotelephony call sign.

Regarding the headset, the crew doesn't have to wear it unless mandated by the airline. During long cruise it's not uncommon to remove the headset and turn up the volume of the loud speaker in the cockpit.


Are there big differences between Douglas Commercial 3 and Douglas Commercial 4? I always thought of the DC-4 as a DC-3 with two added engines and somewhat improved hydros.

What are the actual differences between them?

The DC-4 was a totally new design in all respects, as can be seen from the planform diagrams (wiki)

The DC-4 was larger, and structurally totally different:

Straight tapered wing (no sweepback)
Straight tubular fuselage, not the aerodynamic teardrop shape
Round fuselage cross-section. The original DC-4E was going to have a pressurised cabin. The later DC-4A did not implement this but retained the circular cross section necessary for pressurisation.
MTOW = 33,100 kg for the DC-4, 11,430 kg for the DC-3
Four engines of 1,081 kW each, while DC-3 had 2 engines of 890 kW each.
Tricycle landing gear instead of a tail dragger, as @Gerry points out.

All in all a larger aircraft, designed from scratch, implementing more modern features of a later age.


Can the dome gunner on a B-17 Flying Fortress shoot the plane's tail off? I was at the California Capital Airshow on Mather AFB over the weekend, and came across a beautifully maintained B-17 Flying Fortress. The crew were kind enough to allow people to go inside and take a look - what a magnificent machine!

While inside, I noticed the dome gunner seems to be in a position to accidentally shoot the tail off the plane!

Are there any confirmed instances of this happening? Was there some way to prevent it - either be it training or some mechanism that stopped the guns while in this position? I can imagine, in the heat of battle, sweeping an enemy fighter and nicking your own tail in the process!

There's a profile cam in the turret track ring that operates a mechanism that interrupts the guns when the barrels are pointed at parts of the aircraft.  Waist gunners were the only ones who had to worry about hitting their own plane.

The bigger problem was gunners hitting adjacent aircraft.  The "box" formation design attempted to provide as much of an open field as possible to each gunner.


Relation between altimeter setting (QNH) formula and the barometric formula I'm searching for a reliable source for a formulization of the QNH adjustment to the barometric altitude. I found this document from weather.gov that gives a formula for the Altimeter Setting, which is QNH if I'm correct. If I replace the formula's values with the appropriate constant names, it becomes this:
$Altimeter Setting (QNH?) = \left ( P - 0.3 \right )\left ( 1 + \left ( \left ( \frac{P_{0}^{\frac{L.R}{g}} L}{T_{0}} \right ) \left (  \frac{H}{\left ( P - 0.3 \right )^{\frac{L.R}{g}}}\right ) \right ) \right )^{\frac{g}{LR}}$
I also know the following formula from the US Standard atmosphere (which is identical to the ISA standard atmosphere up to 50 km):

Which can be expresses like this (for troposphere):
$P = P_{0} \left [ \frac{T_{0}}{T} \right ]^{\frac{g.M}{R.L}}$
Symbols and their meanings for extra information:

$P$: Pressure at the airport
$H$: Altitude at the airport
$P_{0}$: Standart pressure (1013.25 $hPa$)
$T_{0}$: Standart temperature (288.15 $K$)
$L$: Temperature lapse rate
$R^{*}$: Universal/ideal gas constant
$R$: Characteristic gas constant
$g$: Gravitational acceleration of Earth.
$M$: Molar mass of dry air

So, my questions are twofold:

Are these formulas actually different reperesentations of the same formula? I tried but I haven't been able to acquire the second formula from the first one.

What is the $-0.3$ for in $(P-0.3)$ in the first formula? Why is it there?

Formula 33a (from the US Standard Atmosphere 1976 document you quote) gives you the pressure at a specific altitude in the U.S. Standard Atmosphere, and corresponds closely to airport/station level pressure in met reports (it corresponds exactly when the real atmosphere has the same characteristics as the Standard Atmosphere). An altimeter setting/QNH is essentially a pressure at sea level (and will be 29.92"Hg/1013.2HPa when the real atmosphere matches the Standard Atmosphere, no matter what elevation the airport is).
see the weather.gov definitions here
So the two formulas (33a, and the weather.gov formula you quote) do not give the same thing.
It would be interesting to know why you need to calculate an altimeter setting, as opposed to getting it from met reports. The setting provided in met reports is a value calculated from the measured station level pressure, and this calculation is actually non-trivial.
Beware the frequently-used rule-of-thumb of 27 feet being equal to 1 HPa on an altimeter is only an approximation, and one which only "works" for low elevations/altitudes.


Why does the helicopter's nose go down when the cyclic is pressed forward (in a hover)? Helicopters have hinges on top of the rotor mast, allowing the rotor to be tilted longitudinally (forward/aft) or laterally (sideways).

Why does the helicopter fuselage tilt up/down when the cyclic stick is moved longitudinally? It should not be influenced by what the rotor does due to the hinge, right?

I think you might be confused by what the hinges do.  In the example you show, the teetering hinge, which is only present in 2 blade rotors, causes both blades to tilt, or "teeter" or see-saw, together.  It is not possible for both blades to rise or fall in normal operations.  The feathering hinge is not really a hinge at all.  It is a bearing in the blade cuff which enables to blade pitch angle to change, caused by the position of the swash plate, by rotating the blade within it's cuff.

Consider a helicopter hovering in a no wind situation - simply because adding wind needlessly complicates the explanation.  I will also assume a counter-clockwise rotating rotor.  Simply reverse the explanation for a clockwise rotor.

The total thrust vector of the rotor is vertical, perpendicular to the centre axis of the disc.  It has a zero horizontal component so no force is applied longitudinally or laterally to the helicopter and it remains in a fixed position.

When you push the cyclic forward, the pitch of the blade at the leftmost position is increased, increasing the angle of attack and therefore the lift.  Due to precession, the blade rises at the back of the disc and falls at the front, tilting the entire disc forwards.

The total thrust vector remains perpendicular to the disc and since the disc is tilted with respect to the fuselage, is now comprised of horizontal and vertical components.  It is the horizontal component which accelerates the helicopter in the direction of the tilt.

So there is a force (lift) lifting the rear of the disc and lowering the front.  This force is transmitted through the rigid rotor drive shaft and pushes the nose down and pulls the tail up. Another way to think about this is that you are applying a force at the top of a lever, the drive shaft, which is above the centre of gravity and therefore causes the fuselage to rotate in pitch. The helicopter will continue to accelerate until the additional drag equals the horizontal component.

Helicopters also employ horizontal stabilisers which produce lift to push the tail down with increasing airspeed so the nose down pitch in cruise is reduced.

Therefore, pushing the stick forward and holding it at some attitude (when flying VFR you select a speed by adopting the nose down attitude for that speed which is learned from experience and practice followed by small trimming to hit the desired speed) will cause the nose to pitch down and the aircraft to accelerate until the trimmed speed is attained.


Does an AQP line check conducted by a part 121 carrier count as a flight review and instrument proficiency check for part 91 operations? If a pilot completes an AQP program with a part 121 airline, does completion of all training and passing the line evaluation also qualify as a flight review and instrument proficiency check for continued part 91 operations?

It depends if the AQP qualifies as a pilot proficiency check.  Most likely the the outcome will be a pilot proficiency check.

  §61.56   Flight review.

    ...

    (d) A person who has, within the period specified in paragraph (c) of this section, passed any of the following need not accomplish the flight review required by this section:

      (1) A pilot proficiency check or practical test conducted by an examiner, an approved pilot check airman, or a U.S. Armed Force, for a pilot certificate, rating, or operating privilege.


Can a F/O declare "My plane" to the Captain? Let's presume an airline flight piloted by 2 people: the Captain (assuming PIC role) and the F/O.

Is the F/O allowed to take manual control over the Captain actions?
Under what circumstances?
Could this create safety issues, for instance, the Captain trying to recover control from the F/O?
What does CRM suggest about this matter?

Pretty much every FO struggles with this.  Technically yes, in the extreme case.  If the actions of the capt are about to get everybody killed or otherwise endanger the aircraft, the FO is supposed to have the authority and an obligation, after a suitable verbal interchange, to intervene by saying "I have control" and take over.  Generally there needs to be a trigger such as a situation where the capt does something that deviates outside normal operating limits, procedures, or protocols.

If the capt declines to hand over control, because, say, the capt has gone off the deep end, well you have a problem.  But in most cases of suspected suicide by plane for example, the suicidee waits for the other crew member to use the rest room and locks the cockpit door - one unintended consequence of reinforced cockpit doors.

The more likely case is a capt that is disoriented or fixated, and in theory an FO who intervenes with proper procedure and with enough "authority" should be able to do it and a capt is expected to relinquish control in such a situation.

But however well trained the crew is, they are two humans and you can't predict what's going to happen.  Different airline cultures apply this kind of thinking more strongly than others. At some airlines the FOs are encouraged to be maybe a little too forceful for most captains' tastes, questioning everything, and others, it's the old fashioned "shut-up-and-pull-gear" culture.  This is still a serious problem outside of "western" operators, in countries that have strong patriarchal cultures, which is partly why you see so many "expat" American, Australian/NZ, Canadian, British, or European captains at far east airlines.

But even in up-to-date places like Canada, FO inassertiveness can be a problem. First Air 6560, pretty much the only major crash of a heavy in North America in almost 20 years (excluding runway excursions and Sully's adventure), is a classic case of an FO failing to intervene to thwart an incompetent captain who develops fixation tunnel vision and breaks the most basic rules of the book.  Every FO needs to read the Transportation Safety Board report.


Can balloons be stacked in a climable daisy chain to the edge of space? How high can a balloon/s be and still be tethered to the ground?

The most common problem was finding the calmest place on Earth.

The longest balloon chain is 20 km

Pictures below are basic balloon chains.

As you go higher the pressure decreases which means that the density of both the air and the lifting gas goes down.

That means that the higher you want to go the bigger the balloon you need for a given lifting force. Eventually you reach a point where it is not not practical to make the structure light enough to go any higher. The highest altitude reached by a balloon is considerably lower than the lowest altitude at which orbit is practical.

It also means that as you go higher the wind-area of your balloon increases which will put more force on the tether. The loading from the tether, both from it's weight and from winds at various altitudes will further reduce the practical maximum altitude compared to a free floating balloon.

There is also the issue that in low orbit you need a considerable sideways movement relative to the ground. Most of the delta-v in a launch rocket is spent on gaining the sideways velocity, not in gaining the altitude.


Why do the stabiliser trim wheels not move exactly in sync? I've watched a few videos about the Boeing 737, and in particular because it's a bit of a current topic, about the stabiliser wheels in the cockpit.

On some of these videos, which are often in commercial flight simulators, we see the stabiliser wheels rotating backwards and forwards automatically. On the wheels there are white marks. However these white marks are often not synchronised and level with each other, for example this video, or this GIF below from here:

There are other videos where these marks are sometimes nearly 160 degrees out from each other. From my naive expectations, shouldn't these marks be within a a few degrees of each other to accurately represent that the stabilisers are at the same level?

Or, are stabilisers individually independent such that the left stabiliser may need a more acute angle of attack whereas the other may not?

The rear wing (horizontal stabilizer) of a 737 is effectively one piece. There is no separate left and right trim control. Both sides during assembly are attached as one.

This is just a visual illusion because the white marks are not aligned. If you manually move one wheel, both wheels will move.

It's worth noting that the white marks do not represent the position. For the full stabilizer travel, the wheels would make many, many revolutions.

The stab trim position indicators would show the position, not the wheels:

(source)


Help Identifying a LEGO plane I need some help identifying a LEGO plane.

The LEGO set 7292, Propeller Adventures, features a twin engine airplane, with conventional landing gear, and a bubble canopy.  There are no pontoons on the wings

Assuming it's based on a real plane, does anyone have any ideas?

There are a few which are similar on some points, although all have at least one issue. In the end I suspect in the end it's just a "generic mid-wing, twin engined WWII fast bomber"

Other than the radial engines, it looks a lot like a de Havilland Mosquito

Or perhaps a Junkers Ju88

Or a CAC Woomera, at a stretch


Are commercial aircraft required to have the model number painted on them? On a lot of aircraft, the model number / aircraft name is clearly marked somewhere on the fuselage, e.g. "Airbus A320". Is there any rule or mandate, that all aircraft must bear the model number at some designated place on its body, to help others identify them?

Every aircraft I have flown had a data plate mounted somewhere in the outside, showing the make, model, serial number, and the year of manufacture. You probably can't see it unless you're 3 feet away, but it's there.
The relevant regulation in the US is:

§ 45.11 Marking of products.
(a) Aircraft. A manufacturer of aircraft
covered under § 21.182 of this chapter must mark each aircraft by
attaching a fireproof identification plate that—
(1) Includes the
information specified in § 45.13 using an approved method of fireproof
marking;
(2) Must be secured in such a manner that it will not likely
be defaced or removed during normal service, or lost or destroyed in
an accident; and
(3) Except as provided in paragraphs (d) through (h)
of this section, must be secured to the aircraft fuselage exterior so
that it is legible to a person on the ground, and must be either
adjacent to and aft of the rear-most entrance door or on the fuselage
surface near the tail surfaces.

and

§ 45.13 Identification data.
(a) The identification required by § 45.11 (a) through (c) must
include the following information:
(1) Builder's name.
(2) Model designation.
(3) Builder's serial number.
(4) Type certificate number, if any.
(5) Production certificate number, if any.

Here's an example from a Stinson 108:


What is this aircraft with wings seemingly fixed the wrong way? In this page there is this image:

Is it a concept model or a real model?
If this is the latter, then are there real aircraft with such wings?

It looks like the Cessna Citation II of which hundreds were built.

By Adrian Pingstone - Own work, Public Domain, https://commons.wikimedia.org/w/index.php?curid=2971403

The wing profile is trapezoidal, as can be seen in the image below.

Image from avistar.org

This kind of wing design is found in a number of aircraft, for example the other Cessna Citation series aircraft and the Embraer Phenom 100.

By Josh Beasley from USA - Private - Embraer Phenom 100 - N629AS (26/365)Uploaded by tm, CC BY 2.0, https://commons.wikimedia.org/w/index.php?curid=25761759


How does lowering altitude conserve energy in Solar Impulse 2? In this article the author explains that the aircraft flies at a lower altitude to conserve energy.

  During the day, it climbs to its maximum cruising altitude of 8,500 metres to capture the most rays. To conserve energy, it works its way down to 1,500 metres in the evening, and stays there overnight.

How is this possible?

Generally, best range is at high altitude(thin air, less drag), and best endurance is at low attitude(thick air, more lift) and low power.

It makes sense that at night they would have to descend to a best endurance altitude to conserve battery power.

Source: solarimpulse.com


What would happen if a hot air ballooon was punctured in mid-air? I am writing a script for a film where a hot air balloon is punctured and it falls to the ground. There are two teenagers in the balloon when it is in the air. What I would like to know is how fast the balloon would fall the ground. Would it glide down or would it drop? This might be a dumb question but it would really help me out in the story. If it helps at all, the balloon is supposed to crash land on top of a canopy tree. Would the balloon go down like an airplane and crash landed, nosediving towards the earth at a fast speed or would the rest of the balloon slows its velocity down?
I need the characters to survive the crash and the tear will be about 4 inches. Would it need to be longer for the balloon to start descending for a crash landing?

Hot-air Balloons are already made with large holes in them. They are called vents. They can be located in the balloon’s top or sides. They tend to be much much larger than the 4-inch diameter you described in your question. But, their opening and closing are controlled by the pilots. Research the FAA Balloon Flying Handbook. It will give you much more insight than I can.


ETH 409: Was the most obvious sign of fatigue being a factor due to one of the pilots calling out “go around” when they were climbing after T/O? One of the pilots yelled out “go around” x6. It looks like they were making a right turn when they should have been making a left turn. The controller informed them for the second time to turn left, and that’s when the callout happened. Is this the most obvious reason for fatigue being a contributor to the accident?

The "Go Around" call was a call for a particular power setting (TOGA) because the aircraft was in a stall condition (rapidly decreasing airspeed, high AoA and stick-shaker). This was not fatigue by the aircrew thinking that they were actually performing a "go around", the captain wanted full-power out of the engines and there is a button that does that.


Is this a Hurricane or Spitfire? Can anyone identify the fighter here in this picture taken from a Dornier-do17?

From: https://stukablr.tumblr.com/post/145040185970/a-pic-took-it-from-a-donier-do17-a-hurricane

Relative thickness of the airfoil, thickness repartition over span, and low dihedral angle of the entire wing, tells it's a Hurricane.


Landing in very high winds A few weeks ago, a storm passed through my area with winds reported at 55kt and gusting to 68kt.  Many light planes managed to break their tie-down ropes and were flung around the ramp area, which isn't surprising given the storm's winds were definitely above a typical light plane's VS0, VS1 and VR, possibly above VREF, VX and even VY.  Pilots being pilots, though, there were soon jokes about being able to take off and land vertically.

I understand that actually trying this would be a very bad idea, even before one considers the other aspects of the storm, e.g. lightning, rain, hail, low visibility, etc. that would make flying unsafe anyway.  I would never even think of trying it.  Still, it seems like an interesting theoretical question.

Is it even theoretically possible to "land" or "take off" in such winds, at least within the usual meaning of those words?  I can see that you could fly to touchdown easily enough, but how would you stop flying?  How could you taxi and secure an aircraft when you need significant power just to not go flying up (and probably backward) off the ramp?

It can be done. Some bushplane action...


What could cause an irregular climbing pattern on takeoff? Yesterday (Dec 21, 2015), I was on board Ryanair flight FR4966 from London Stansted (STN) to Lamezia Terme (SUF). The aircraft was a Boeing 737-800, registration EI-EFW.

On takeoff, the climbing pattern didn’t seem very regular to me. It was clear that the engines were first running at full power, but then decreased their thrust and our altitude seemed not to increase as it would regularly do. I was certain we were about to return to STN due to some kind of malfunctioning. However, we reached our destination flawlessly.

Later, I checked the climbing pattern, and my impression was confirmed. You can see below that the climbing pattern was initially steep, but at an altitude of approximately 5,700 feet, the aircraft stopped climbing and proceeded at the same altitude for about 5 minutes.

My question: what caused this steady situation? Did the aircraft undergo a malfunctioning that the cabin crew was able to cope with? Or was it just due to the fact that we were overflying London — a congested airspace — and that was our assigned altitude?

The brief period of leveling off is not unique to the flight on that day. Looking at track logs for previous days, it always levels off at around 7,000 feet for some period.
As Terry commented, this is most likely to deal with the congested airspace. Other routes coming into and out of the London area probably pass through the same space, and keeping flights departing Stansted at a lower altitude prevents them from interfering with other traffic.
Looking at a standard departure chart, there is a warning box:

WARNING
Due to interaction with other routes, do not climb above 5000 until instructed by ATC.

This looks to be the route followed by this flight, at least to the DETLING VOR, so it would be expected that ATC will need to limit the flight's climb until clear of other traffic.


In what ways is color blindness an issue in modern jet airliners? What are the specific problems in modern jet airliner cockpits or in piloting operations that would prevent a person with any type or severity of color blindness from completing his/her job to the same degree as a pilot without color blindness?

As a follow up, are modern airliners designed to allow for pilots who have any type or severity of color blindness in case regulations change to allow them to work?

There are lots of problems.

Sight is just generally important when flying. Even in airliners, most approaches are still flown manually and often visually. Any significant degradation of sight is going to be a problem when flying any type of airplane.
Red/Green/White light signals are used by air traffic control in the event of a radio failure. The inability to differentiate red from green in this case would be an enormous safety hazard (e.g. did tower just clear me to land or tell me to keep circling?)
PAPI/VASI lights use colors to indicate whether you're above, below, or on the proper glide slope for a runway. While it's possible to land without them, it's a significant reduction in safety.
Lights at airports are color-coded to indicate whether a particular road is a runway or taxiway, how close you are to the end of the runway, that a runway is in use, etc. Landing on a taxiway is usually a bad idea, so it's best if you can tell the difference.
The navigation lights on airplanes themselves are color-coded. The right wingtip has a green light, the left wingtip has a red light, and the back has a white light. This lets other pilots easily determine which way you're going and, in case of conflict, who should yield (seeing a red light on another aircraft means that they're to your right and, therefore, you should yield to [i.e. divert around] them.)
Colors are used on aviation charts to indicate all kinds of things, including class of airspace, type of special-use airspace, whether a field is controlled or not, type of route, elevation of terrain, where you should expect to see city lights at night, etc. You need to be able to distinguish these things quickly and accurately, even in low-light conditions.
Some cockpit instruments use colors to indicate various things. These include color bands on airspeed indicators, color of annunciator lights or their on-screen equivalents (i.e. red for warning, amber for caution, green for gear down, etc.,) echo intensity on a weather radar display, etc.


If the Quadcopter is a MIMO Nonlinear System, How Can it be Controlled using PID? I know that it is very common to control quadcopters using PID algorithms. I'm just wondering if it isn't a problem that the system is highly nonlinear as well as having multiple inputs and outputs. Does the model need to be linearized so that PID algorithms can be used?

Thanks in advance!

If the Quadcopter is a MIMO Nonlinear System, How Can it be Controlled using PID?

Exactly as you mention later:

  Does the model need to be linearized so that PID algorithms can be used?

Yes, that's correct.

To be a little more explicit, you need two things:

linearise the system (usually around a so-called "working point", e.g. cruise conditions)
de-couple the system (because a linearised MIMO is still a MIMO, you need a set of 4 SISOs)

Achieving the first is fairly simple, as I mentioned, you "only" have to select a working point. The second is instead a little more elaborate, and requires making assumptions on the flight conditions that will be encountered, plus it is not always possible, some vehicles have their dynamics so coupled that de-coupling is not an option (and thus simple PIDs tend to be not a viable option if you have to tune them manually).


How are range and frequency related in HF communications? How does the range of HF communications differ with frequency used? Is it less frequency more range, or more frequency less range?

Neither or both, depending.
Unlike VHF and higher bands, which travel mostly via line of sight and therefore have limited range depending on altitude, HF radio relies on skywave propagation. This means the radio waves travel up, bounce off a layer in the upper atmosphere and then travel back down to the receiver. They may even bounce up and down between layers several times, allowing one to receive signals from the other side of the planet. You may be able to talk to stations far away but not nearby, or the bounces may not work the same in both directions. It’s unpredictable.
All of this odd bouncing depends on atmospheric conditions, which vary from place to place and even from hour to hour. Worse, different parts of the HF band will behave differently at the same time and place, so it has been broken up into several sub-bands of frequencies that tend to behave similarly.
That is why oceanic flights are given two HF frequencies in different sub-bands: at least one of them will probably work. Probably. And which one (if any) may change over the course of a long flight!
Worst of all, because of this long-range behavior, every station on the planet needs a unique frequency, and there isn’t a lot of bandwidth to go around, which is why it is chopped up into very narrow channels that give horrible sound quality. So, HF is only used when absolutely nothing else will work (or is available).


Do pilots need to know how to use a sextant? Can a sextant be used while flying? How accurate/reliable is a sextant, both standing still and at 500+ mph? Are sextants found in any cockpits today?

Ooh, a celestial navigation question...about airplanes... I never thought I'd see one of these in the 21st century!

To answer the basic question: Pilot training doesn't cover sextant use, but there is still a "Flight Navigator" certificate (you'll find it in Part 63 of the FARs), and an associated Flight Navigator Handbook (FAA-H-8083-18), last updated in 2011. The written test question bank is also available if you want an idea of what the FAA expects you to know in order to earn that certificate.

  Can a sextant be used while flying?

Yes, if you have a clear view of the sky overhead.
Aircraft used to be designed with "sextant ports" as shown in Stelios' answer, and special aircraft sextants (indirect-sighting, with a bubble to provide a horizon, and usually some kind of averaging mechanism and timer).

  How accurate/reliable is a sextant, both standing still and at 500+ mph?

A sextant is a pretty accurate tool under the right conditions, if you know how to use it.
Stationary on the ground you can do a surprisingly good job with a sextant, see for example the US/Canada border monuments. I'm out of practice, but on calm water I used to be able to fix my position to within about 1 minute of arc (1 nautical mile) on any given line.
To put that in perspective, that's slightly better navigational performance than a VOR provides at distance (2-4 nautical miles), but substantially worse performance than GPS (within a few feet).

As far as reliability, the reliability of a ship's sextant is pretty good: much like a mechanical E6B flight computer it'll work fine unless you abuse it (drop, step on, etc.).
Reliability of an aircraft sextant (or any other bubble sextant with an averaging timer) is not quite as good because there are more moving parts involved, but properly maintained they could be trusted to work when you needed them (and most failures could be compensated for by a decent navigator).

The problems with sextants that make them impractical for modern air travel are:

Speed
Sextants don't tell you where you are, they tell you where you were when you made the observation. The averaging mechanisms I mentioned earlier allow aircraft sextant to partially account for the fact that the aircraft was moving (both vertically and horizontally), but at modern speeds you cover a minute of arc pretty quickly. Radio navigation systems and GPS provide much faster position updates than you could get with a sextant.
Complexity of the instrument
Aircraft sextants are precision instruments. They need to be maintained and calibrated or they won't be accurate when you need them, and as I mentioned there are a lot more moving parts to an aircraft bubble sextant than a basic ship's sextant.
Complexity of the process
Using a sextant also require an operator (navigator) who knows what they're doing in order to take the sighting and compute the position, compared to radio navigation (VORs, VOR/DME, or GPS).
Most pilots don't have any training in using a sextant (my experience comes from sailing), so having one would be useless to them.
Weather
While the sextant is a reliable instrument the stars are not reliable: They're always there, but sometimes they're not visible. You can't see most of the stars & constellations you would take a sighting of during the day (usually only one star is visible), and clouds can obscure them when you want to take a sighting, delaying or preventing your position fix.

  Are sextants found in any cockpits today?

Certainly not in any light GA cockpit I can think of, and probably not in any single-crewmember cockpit: Even if you held both a pilot certificate and a flight navigator certificate a pilot with their head buried in the sextant is rather useless for actually flying the plane.

I would assume that most commercial cockpits also no longer have a sextant as modern jets don't include a sextant port, so there's no way to take a sighting.

There might be a few restored vintage aircraft that have a working sextant onboard, but I doubt those are used for practical navigation (they're probably not used at all, except possibly to demonstrate how it was done).


How does hovering in ground effect (IGE) reduce drag? I understand that when IGE the induced velocity and thus the induced angle is reduced, rotating the total aerodynamic force (TAF) closer to the vertical and hence increasing the vertical component of lift (for the same power).
What I don't understand is why drag is reduced (some texts refer to a reduction in induced drag, others to rotor drag). Diagrammatically, the horizontal component of drag (parallel to the tip path plane and that which opposes rotor RPM) actually appears to increase.
I've concocted this diagram which may itself be incorrect and the source of confusion, or maybe its just semantics?

The inflow becomes less vertical and also reduces in velocity since the pressure under the disk increases.  The rotor airspeed is therefore reduced and induced drag reduces in proportion to the square of the reduced airspeed.

The tip vortices (recirculation) are also reduced meaning that the outer portion of the blade, where most of the lift is generated, becomes more efficient.

Since the angle of attack has reduced, because the inflow is more horizontal and the lift vector is now more vertical, you get more lift for the same pitch angle and therefore require less power.

Less power into the rotor = reduced induced drag.

This image, from Copters.com, may help.

To add some clarifications.

Why does the rotor effective airspeed reduce?

Imagine a helicopter in a zero wind, ideal conditions out of ground effect hover.  The rotor, to produce lift, accelerates air downwards. Since there is no wind and the helicopter is not moving, the air is drawn into the disc from around it and mainly from above it.  Ignoring side effects, the air is drawn down equally all around the disc.  The airflow drawn into the disc has a horizontal component and a vertical component.  The vertical component is large as there is little to stop the disc from pulling air down and accelerating it downwards.  The speed of the rotor plus the horizontal component of the inflow co-incident with the average chord of the blade can be thought of as the "relative airflow".

Now imagine the same except hovering in ground effect.  The cushion (increased pressure) below the disc reduces the inflow (imagine a fan partially blocked, the fan draws in less air) and thus the horizontal component of the inflow is reduced.  Therefore, the relative wind airspeed is reduced.  As you can see from the diagram solving the triangle of vectors, the angle of attack is also reduced.  The collective could actually be reduced to accelerate the same amount of air.  This power reduction results in a decrease in the induced drag.

Why does the same pitch angle produce more lift when hovering in ground effect?

The biggest "drain" of power when hovering, and the main reason why hovering uses more power than any other flight phase, is the vortices around the rotor tips and the outer third of the rotor where most of the lift is produced.

When hovering out of ground effect, there is nothing to stop the accelerating column of air under the disc from "escaping" and being drawn back up into the in-flowing air leading to re circulation and significant vortices.  When hovering in ground effect, the air is forced to move out laterally from under the helicopter which effectively increases the radius of the vortices.  There is a significant reduction in the turbulence around the tips and the outer third with a corresponding large increase in efficiency.  Therefore, more lift is generated in ground effect than out of ground effect for the same angle of attack.

This can be seen practically by hovering over a hard surface and measuring power required then comparing this when hovering over long grass or worse, hovering over a dense standing crop.  Since the long grass or crops reduce the ability of the air to escape further out laterally, the vortex radii are not increased as much as when hovering out of ground effect and more power is required.

It is possible, when there is little power in reserve, to be unable to take off vertically from long grass but be able to do so from the adjacent hard standing.

I think this video helps to visualise the vortices.


What's required for a plane certified to fly to Antarctica? What special features besides the obvious long range does a plane have to have to fly to and land in Antarctica?  I know not just any plane can make the trip, but I couldn't find many relevant regulations or certification requirements.

It seems like the C-17 and LC-130 are some of the most popular for these flights, based on the "US Antarctic Program Inter-agency Air Operations Manual" and this site. The manual does list other aircraft that can use Pegasus White Ice Runway: "C-5, KC-135, C-17, C-130, LC-130, P-3, A-319, and smaller aircraft".  I also know the Basler Turbo BT-67, DeHavilland DHC-6 "Twin Otter" aircraft, and C-141 are traditional polar operations planes.

The only applicable regulations I could find were:

In VOLUME 3   GENERAL TECHNICAL ADMINISTRATION, CHAPTER 29   PROVING
AND VALIDATION TESTS, 3-2438       CLASS II NAVIGATION AUTHORIZATIONS
D.4) North Polar (OpSpec/MSpec B055) and Antarctic Airspace
(OpSpec/MSpec B050). Applicants proposing to conduct terminal area
operations within these areas must conduct validation flights. No
requirement exists for validation flights for those applicants
conducting overflights if previously authorized in OpSpec/MSpec B036
and B040. During validation for approval of overflights of these
areas, test teams should include in-flight planning, contingencies,
CNS requirements, “fuel freeze” procedures, cold weather altimetry,
applicant’s reaction and passenger recovery plan, and emergency
airfield procedures.
Airplanes must have enough fuel to reach an off-continent alternate
if they arrive and cannot land.
I also remember reading somewhere that these aircraft had to have
fuel temperature and/or manual fuel level indicators to help prevent
fuel freeze.

So what special features or parts does a plane need to make an antarctic trip besides long range?  Why are c-130's and DHC-6's perfect for this kind of mission?

Note: Obviously pilots also have to have very specific and special training for Antarctic missions, but I'm focusing on the planes themselves in this question.

Image source

I'm not aware of any specific 'certification' for aircraft operating to/from Antarctica. The air operations to/from Antarctica varies greatly depending on the location of the airstrip and season.

Actually, there are airports in Antarctica that can handle 'conventional' aircraft (atleast seasonally), like the Union Glacier Blue Ice Runway, which has been certified to handle commercial flights. US Army CRREL Report 93-14, Notes on Antarctic Aviation identifies three broad flight categories:

  Long trans-ocean flights to and from well developed Antarctic airports.
  Medium-range flights to and from short substandard Antarctic runways with limited facilities.
  Long trans-ocean flights to and from expedient runways that are rough or soft.

According to the type, the aircraft requirement can vary significantly. For example, for the first case, (long range) civilian and military aircraft maybe more than enough. From the same report:

  For flights of the first category, exemplified by Christchurch to McMurdo in springtime, any conventional trans-oceanic transports, civilian or military, should be satisfactory as long as they have adequate useful range, with the ability to reach an alternate or to return to the point of departure, arriving with standard IFR fuel reserves.

  For medium-range flights to and from short substandard Antarctic runways with limited facilities, the aircraft can be smaller, but it has to be capable of safe over-ocean journeys, with appropriate range and engine-out performance.

  For long trans-ocean flights to and from expedient runways that are rough or soft, the aircraft requires both long range and robust, high-flotation landing gear.

The report also lists the desirable characteristics of aircraft for operations in Antarctica, which should explain why aircraft like C-130 and DHC-6 are used the most:

  General configuration: High wing; high engines; tee-tail or high tail; low belly; spacious flat-floor fuselage; large doors (tail ramp,side hatch, swing nose).
  Engines: Multi-engine; gas turbine (free turbine turboprop; turbojet or turbofan).
  Landing gear: Wide stance; short legs; low ACN/LCN; large tires; soft tires; multi-wheel, multi-unit assemblies; large wheel-well fair ings (for big wheels or ski retract).
  Speeds: Reasonable cruise speed; slow approach; low stall and landing speed.
  Robustness: Strong airframe, tolerant to vibrations; reliable engines and fuel system; rough-field landing gear; good hydraulics; instruments, avionics and electrical systems resistant to vibration.
  Maintainability: Easy access to problem areas and parts that need frequent changes; spares inventories based on failure probability, easy troubleshooting; access to additional spares at reasonable speed and cost

You can see where this is going. The aircraft used in Antarctica are varied, with anything from C-17 Globemaster IIIs to re-manufactured DC-3s in service, De Havilland Twin Otter being one of the most popular. You can see that most of the aircraft operating from there are high wing aircraft with excellent STOL capability. The report also lists some of the aircraft most suited for operations in Antarctica.

Aircraft with characteristics that are appropriate for Antarctic internal operations; Image from CRREL Report 93-14, Notes on Antarctic Aviation by Malcom Mellor

Most of the aircraft look similar with high wing with wide, short landing gear and multi-engined. Quite a few of these are excellent STOL aircraft too. Obviously, they will be modified with the required navigation equipment and long range fuel tanks (for example, with long range fuel tanks, the range of Basler BT-67 is extended to ~4000 km).

Operating in semi prepared fields require the aircraft to be equipped with skis- like the Lockheed Martin LC-130J. These aircraft have the provision for carrying out JATO operations. A number of smaller aircraft (like the Basler BT-67) are equipped with skis as well.

LC-130 skis, By NSF Contractor - US Antarctica Program Common Share Servers, Public Domain, https://commons.wikimedia.org/w/index.php?curid=5883002

Aircraft operating in Antarctica should also consider the effect of air operations on the fragile and unique environment. The long range of aircraft come in handy as this limits the need for holding fuel reserves at the Antarctic airport, reducing infrastructure requirements and ecological impact.

The aircraft operating to/from Antarctica have, in addition to the usual requirements, items like onboard stairs:

  The A319CJ is designed with ultra-long range tanks, enabling the aircraft to return safely to its original port without the need to land and refuel. .... Skytraders limit the need for extensive ground support infrastructure by equipping its aircraft with specialist remote field functions such as its onboard stairs.

Though quite a few types of aircraft can (and have been) operated in Antarctica, it should be noted that not all of them are equal. A good example would be the conclusion of the inquiry into RNZAF Boeing 757 that landed below published minima at Pegasus Field in 2003:

  ... a whiteout landing. However, in the event of this occurring the likelihood of injury was significantly greater for the Boeing 757, with its long landing gear supporting low-slung engines on a low wing, than it was for the Hercules with its rough-field landing capabilities

This, in addition to the additional navigational aids (TACAN) fitted in the C-13Js. It should be noted that RNZAF still flies 757s to Antarctica.


Is a complex airplane endorsement required to act as PIC of a plane without all three elements of the "complex airplane" definition? Is an endorsement required to fly act as pilot-in-command of an airplane equipped with a constant-speed propeller, adjustable flaps, and fixed-gear?

This does not meet the complex airplane definition because it is not equipped with retractable landing gear.

No, you do not need a complex airplane endorsement for this airplane because it doesn't have retractable gear, unless it is a seaplane.

All three elements are required for that endorsement to be necessary for landplanes.

A jet-engine is not a controllable-pitch propeller, therefore it would not require a complex endorsement even if it has retractable gear and flaps.

However, the above would require a type-rating because it is a jet.

An airplane with a controllable-pitch propeller and retractable landing gear that isn't equipped with flaps would also not fit the definition of complex, so you are absolutely right.

See §61.31(e) Additional training required for operating complex airplanes

The definition for complex is in the Airplane Flying Handbook Ch 11,

  “A complex airplane is defined as an airplane equipped with a
  retractable landing gear, wing flaps, and a controllable-pitch
  propeller. For a seaplane to be considered complex, it is required to
  have wing flaps and a controllable-pitch propeller.”

The definition for complex as shown in 14 CFR §61.1(b)(iii):

  "Complex airplane means an airplane that has a retractable landing
  gear, flaps, and a controllable pitch propeller, including airplanes
  equipped with an engine control system consisting of a digital
  computer and associated accessories for controlling the engine and
  propeller, such as a full authority digital engine control; or, in the
  case of a seaplane, flaps and a controllable pitch propeller,
  including seaplanes equipped with an engine control system consisting
  of a digital computer and associated accessories for controlling the
  engine and propeller, such as a full authority digital engine
  control."


How do you calculate minimum runway lengths for Part 135 operations using the 60% rule? FAR 135.385 requires that at your destination airport your flight planning shows that you could make a full-stop landing "within 60 percent of the effective length" of the runway when flying transport-category turbine-powered aircraft.

For piston-powered aircraft FAR 135.377 has a similar 70% rule.

How do you calculate minimum runway lengths under these rules?
Can you use 80% of the runway? What if the runway is wet?

Required runway length for landing
The minimum runway length required for landing under Part 135 operations is, believe it or not, the same as Part 91: You need to be able to land and stop within the available runway length specified in the AFM.   This is what you use when you are getting ready to land.
That being said, since you reference the "60%/80% rules", there is a more stringent requirement that is required as part of your preflight planning and specified in 14 CFR 135.385
60% Rule for Large Turbine Transport Category Airplanes
This rule is specified in 14 CFR 135.385(b), and says (in part):

no person operating a turbine engine powered large transport category airplane may take off that airplane unless its weight on arrival ... would allow a full stop landing at the intended destination airport within 60 percent of the effective length of each runway

So to follow the regulation by the letter, you need to take 60% of the runway length and compare it to your actual landing distance.
Example
We want to land on a 6,000 ft. runway, so our max allowable landing distance is 3,600 ft.:
$$6,000ft\times60\%=3,600ft$$
Determining minimum runway length
Sometimes pilots prefer to ask the question in a different way, and ask "what is the minimum runway distance needed for the current conditions" instead of "what can my maximum landing distance be.  To calculate this, we simply re-arrange our formula above like this:
$$Minimum~Runway=\frac{Actual~Landing~Distance}{60\%}$$
If our actual landing distance is 3,000 ft. then we would need a minimum field length of 5,000 ft.:
$$\frac{3,000ft}{60\%}=5,000ft$$
80% Rule
The 80% rule specified in 14 CFR 135.385(f) works exactly the same way, but can only be used by an "An eligible on-demand operator" if approved in accordance with their Operations Specifications (A057 and C049) and the procedures listed in their Flight Operations Manual.
You would then replace the 60% with 80% in the above calculations.
Wet Runways
14 CFR 135.385(d) says:

(d) Unless, based on a showing of actual operating landing techniques on wet runways, a shorter landing distance (but never less than that required by paragraph (b) of this section) has been approved for a specific type and model airplane and included in the Airplane Flight Manual, no person may take off a turbojet airplane when the appropriate weather reports or forecasts, or any combination of them, indicate that the runways at the destination airport may be wet or slippery at the estimated time of arrival unless the effective runway length at the destination airport is at least 115 percent of the runway length required under paragraph (b) of this section.

So basically, you use the information from your AFM for wet runway landing distance, or if it isn't provided (since it isn't required), you do the same calculation that you did before but include an additional 15%.
Example:
Taking the example from the 60% rule and assuming that it is wet, we have a max landing distance of 3,130 ft.:
$$\frac{6,000ft\times60\%}{115\%}=3,130ft$$
Minimum Runway Length When Wet
The minimum runway distance with a 3,000 ft. actual landing distance would be 5,750 ft.:
$$\frac{3,000 ft\times115\%}{60\%}=5,750ft$$


Can a pilot over the age of 65 exercise the privileges of a commercial pilot license under FAA Part 91 in the Bahamas? I am hearing there may be a problem with flying in the Bahamas over the age of 65 as a commercial pilot, even under 14 CFR 91. Because the pilots are being compensated they may consider this a commercial operation which then would be age limited to 65 as per ICAO regulations. Is there gray area here or is there no problem flying under 14 CFR 91 over the age of 65 in the Bahamas?

There should not be a problem as long as you are flying under Part 91 because the age restriction which you refer to does not apply to all commercial pilot operations.

14 CFR 61.3 is consistent with the ICAO rule which you refer to and covers a US pilot, flying a US registered aircraft internationally and states:

  (j) Age limitation for certain operations

  (1) Age limitation. No person who holds a pilot certificate issued
  under this part may serve as a pilot on a civil airplane of U.S.
  registry in the following operations if the person has reached his or
  her 60th birthday or, in the case of operations with more than one
  pilot, his or her 65th birthday:

  (i) Scheduled international air services carrying passengers in
  turbojet-powered airplanes;

  (ii) Scheduled international air services carrying passengers in
  airplanes having a passenger-seat configuration of more than nine
  passenger seats, excluding each crewmember seat;

  (iii) Nonscheduled international air transportation for compensation
  or hire in airplanes having a passenger-seat configuration of more
  than 30 passenger seats, excluding each crewmember seat; or

  (iv) Scheduled international air services, or nonscheduled
  international air transportation for compensation or hire, in
  airplanes having a payload capacity of more than 7,500 pounds.

  (2) Definitions.

  (i) "International air service," as used in this paragraph (j), means
  scheduled air service performed in airplanes for the public transport
  of passengers, mail, or cargo, in which the service passes through the
  airspace over the territory of more than one country.

  (ii) "International air transportation," as used in this paragraph
  (j), means air transportation performed in airplanes for the public
  transport of passengers, mail, or cargo, in which the service passes
  through the airspace over the territory of more than one country.

Each of the bolded sections (added by me) show how each part is ruled out for a Part 91 operation as you describe.

Along the same lines, the ICAO SARP that you are referring to governs "commercial air transport operations," and not all commercial operations.  Part 91 flights do not fall under the annex with these requirements.

That being said, it is a foreign country and they can make their own laws which do not necessarily have to agree with any of this.  To be sure, you can always contact the FBO that you intend to use and ask them, or obtain a copy of the Bahamas AIP (I wasn't able to find a free copy) and see what it says.

Being based in South Florida and doing lots of flying to the Bahamas, I haven't heard of a problem with this (although I haven't specifically been looking for it either).


Is (L/D)max achieved at a specific speed or AOA? I'm little bit confused about the (L/D)max.

So I've read this blog: https://joeclarksblog.com/?p=4155
and the author shows this graph:

So if I understand it correctly the (L/D)max is at the intersection of parasitical drag and lift-induced drag. Thus, at the point which has the minimum total amount of drag. Which is achieved at a specific speed.

Skybrary states the following:

  The maximum lift/drag ratio occurs at one specific CL (Lift
  Coefficient) and AOA (Angle of Attack (AOA))

https://www.skybrary.aero/index.php/AP4ATCO_-_Lift/Drag_Ratio,_Forces_Interaction_and_Use

Here is is the lift coefficient:

Source: https://en.wikipedia.org/wiki/Lift_coefficient

The graph shows that the airfoil is the most efficient at a specific AOA. Thus in the ranges between 15° and 18°.

sciencedirect.com states the following:

  The L/D is not constant for a given wing, however, but changes with
  the angle of attack. Researchers thus normally use the maximum
  lift-to-drag ratio, L/Dmax, to characterize a given wing.

https://www.sciencedirect.com/topics/earth-and-planetary-sciences/angle-of-attack

I'm confused because one source tells me that (L/D)max is achieved at a specific speed. The other source tells me that (L/D)max is influenced by the AOA.

Can you clarify this thought twist?

I'm confused because one source tells me that (L/D)max is achieved at a specific speed. The other source tells me that (L/D)max is influenced by the AOA.

The speed is only correct for a specific wing loading and straight flight at 1g. Only then will the optimum lift coefficient be reached in level flight at that speed.

The angle of attack version is the more generic and better way. Actually, optimum L/D is achieved at a specific lift coefficient, which is closely related to the angle of attack via the lift curve slope.

  The graph shows that the airfoil is the most efficient at a specific AOA. Thus in the ranges between 15° and 18°.

No, it only achieves the highest lift coefficient in that range. This is right before stall and certainly not the position of optimum L/D. Drag will have grown disproportionally over the previous angle of attack range. Without a drag polar it is impossible to say where that specific airfoil has its best L/D.


Why is IndiGo adding A320NEOs more aggressively than any other airline? Currently there are about 45 NEOs with PW engines and 6E operates 17 of them. These PW engines have notoriously reported many engine issues and 48 of them have been replaced so far. IndiGo itself has faced 6 engine replacements so far.

Usually, we see that when an Aircraft type reports so many problems, airlines usually halt deliveries until the manufacturers fix them. Even with A320Neo, Qatar Airways has cancelled their order for PW NEOs and Lufthansa is deferring the deliveries.

Why is it then IndiGo is adding them so aggressively? It plans to add 4 NEOs in March 2017 only.

It's quite common for the first customer(s) to serve as a proving ground.
Memorandums of understanding (MoU's) are signed that detail the specifics, which in 99% of the cases are not revealed to the public.
If IndiGo was upset, it would have been loud, but it hasn't been so:

IndiGo did not comment when approached by FlightGlobal.
In a statement to FlightGlobal, P&W says that it is supporting GoAir and IndiGo “to assess the situation and minimise any disruption”. However, the engine maker adds that the issues “are still under review so it would be premature to speculate on the cause(s)”.
"We are working closely with our customers and our suppliers in order to address and resolve these issues quickly," it adds.
— FlightGlobal

Not commenting hints at a non-disclosure agreement (NDA) in place and quite possibly discounts.


Is it okay to take off with weight more than the POH max gross weight? I wonder if I could take off with weight more than the gross weight stated in the POH of my aircraft as long as I take off with a higher speed?

I think I have done it once by mistake.

Can you take off over gross weight? Yes, it's possible on any airplane, dependent on how far over the weight limit you are, the density altitude, how much runway you have, what obstacles are in the area and other factors. It's very easy to go above gross in a Cessna 152 with full fuel and 2 passengers, and probably happens more often than people realize or own up to. That doesn't make it a good idea, which is why pilots are trained to do weight and balance plus performance calculations before every flight.

Besides the safety angle, taking off over gross weight could land you in trouble with the FAA even if nothing goes wrong, you can lose your ticket for that. If there was an incident your insurance may not cover damage or litigation costs.


Where is it documented an airport is military? On sectional charts (at least in the US) military airports appear with the same symbols as public airports, eg. KBKF.  Some military bases are within restricted airspace.  I would assume all military airports are restricted to public use.

Is there a way to see this on the sectional chart?  Would this information be found in the A/FD?  Is it just assumed that AFB, NAS, etc. indicates military?

AFB, MCAS, NAS, CGAS/CGS, and AAF would always be military, yes. BUT the lack of that in the name doesn't mean it's not military... Outside the US especially there's often no such thing to indicate a military base from a civilian field (though AB (for AirBase) is at times used).
How do you know? You're supposed to know where you're going when you're flying, and that includes what's off limits to you.
http://www.post8.org/images/secchart.jpg shows the legend of a sectional (can't inline the image, SO refuses to), which says clearly "All military airports are indicated by abbreviations AFB, NAS, AAF, etc. For complete airport information consult DOD FLIP". So how do you know? The chart tells you by the name of the facility. It also shows a double ring instead of runway icons as indicating military, but on some charts I looked at that appears to not be consistently applied.


F-16 low speed SAM avoidance tactics? After having watched the rather horrible yet fascinating F-16 avoiding multiple SAM launches:

I'm left wondering why he doesn't increase his speed? There are, however, some moments when he's pulling rather high G's where he must have given it some more throttle to sustain any speed at all. Does he need to preserve fuel to get back? Or is it better to maintain somewhat lower speed to have a better turning radius when avoiding SAMs in an F-16?

I understand this is basically asking for an entire lecture in how to avoid SAMs, and I'm trying my best to refrain from doing so. I will keep it to a few specific questions:

Assuming he has the fuel to do so, should he have increased his speed, full afterburner?
Is it possible to see in the video, if chaff/flares are deployed?
Was it wise of him to reduce his altitude by as much as he did, or would he have been safer higher up?

The missile works by predicting where the airplane will be. If you maneuver, it has to re-adjust, wasting energy.

When the missile has lost enough energy, it'll eventually fail to re-adjust.

Now you can try to beat the missile by being far away and fast
or
you can try to make the missile lose a lot of his energy by doing turns, at low speed. (You can even nodge the missile into the ground by making some close-range, low altitude dives)

In this instance, the pilot was probably already low. Or needed more energy for maneuvering and traded his altitude for energy by descending.


Does the jet blast from a large aircraft pose any risk for other aircraft nearby? We know that the jet blast of jetliners - A320, B737 and bigger - are dangerous for people passing by, airport vehicles and even small planes, and we must always maintain a huge distance to avoid receiving this jet.

So, is there any risk or damage to other similar sized aircraft queuing for takeoff or whatever?

The airplanes in the photo are quite far apart, at least 1-2 lengths between each (it's just the long lens making them look cheek by jowl), and while in line going straight, they are only using a little over idle thrust to get rolling when required, so the jet blast effects are negligible.  The main factor is FOD (foreign object damage) kicked up, and at that distance that would mean sand/dust particles, but the effects of that would be too subtle to measure over the long term in any reasonably clean environment.

That being said, if I was in a desert area where there was drifting sand on the taxiway, I would probably increase my spacing a bit behind the guy ahead.  And you can bet that the guy in the (what looks to be a) King Air that is second in line in the pic - walking with the elephants - is keeping a little bit more distance from the elephant in front as well, owing to the size differential. If I was in the King Air I would be worried about the plane adding a big shot of thrust in both engines to start the turn (hopefully they'll just use the left engine), and the inside engine would be pointing straight at me part way through the turn, and I would be staying  well back.   Airmanship and all that...


What do we mean by taking the lowest of ZFW; TOW and LW to determine the maximum takeoff weight of the day? Firstly, I understand that the maximum permissible takeoff weight can be limited by landing weight because landing weight plus trip fuel gives us one take off weight. We obviously do not want to be taking off with any extra fuel which we can not burn to allow us to be under the MLW upon reaching the destination.
Secondly, I understand there is a structural limitation which can not be exceeded.
I can not get my head around how we are limited by the Zero fuel weight to determine how much should be the maximum takeoff weight for a given day?
I am specifically asking with regards to Airbus 320 wherein MTOW is 77t, MLW is 65t and MZFW is 62.5t

If you know how much fuel you'll need for the flight, then the things that can limit your load (which is really what you're interested in -- how much weight can I put on the airplane today, in terms of passengers + cargo) are:

Empty weight + Payload (ZFW) may not exceed Max ZFW
ZFW + fuel for the flight (TOW) may not exceed MTOW
TOW - fuel burned during flight (i.e. ZFW + fuel reserves) may not exceed MLW

Depending on how much fuel you expect to burn and how much fuel you expect to land with (i.e. reserves), any of these may be the most limiting.
Max ZFW will be limiting for a short flight with minimal reserves required... you're taking off with minimal fuel and landing with minimal fuel, but if you loaded up to max TOW or max LW you'd be well over MZFW.
Max TOW will be limiting with lots of fuel burn planned: if you loaded the pax/cargo to MZFW, the fuel load would put you over MTOW.
Max Landing Weight tends to be most limiting when you need lots of fuel at landing for reserves.  (If you envision an extreme case where you need 5 hours of fuel still in the tanks at landing, if you were close to MZFW you'd be way, way over max landing weight, so the latter rather than the former is most limiting.)
Modern airliners tend to have a range of landing fuel that tends to suggest when MTOW or MLW will be the more limiting.  If you're planning to land with min reserves, you can load to MZFW easily enough (max ZFW + min reserve gas will be < max landing weight); you'll probably be limited by either MZFW or MTOW.  If you need to land with significant reserves, MLW will probably be most limiting for how much cargo/pax you can have.
If you can find a typical empty A-320 weight and typical "good weather" and "bad weather" fuel reserve values (maybe 3t and 7t for the latter), as well as some "short haul" and "long haul" burns (guessing, maybe 3t short haul and 20-25t long haul), you can work out various cases of what load you can accept in each scenario of good/bad wx and short/long haul flight using the equations I described above.
EDIT: The discussion above treats MTOW as a constant, although in reality that isn't necessarily the case: the max takeoff weight on a high, hot, and short runway can be significantly less than the structural max takeoff weight.  The basic math doesn't change, but it's fair to note that MTOW is the lesser of structural MTOW or the performance-limited takeoff weight.  (The various performance limits can be any of a number of things: accelerate-stop, accelerate-go, climb performance, etc.)  For some jets, you can also have a performance limitation of Enroute performance, i.e. being able to clear enroute terrain if an engine fails.  Most modern jets, however, have sufficient performance that this isn't often (or ever) an issue.  But it is the stuff of ground-eval orals.


What is the way to calculate the required twist of a flying wing? I am interested in flying wings and a couple of weeks ago I started researching them. I found mh-aerotools.de website and think it's a great source.

The website stated that flying wings need twist to stabilize, but I don't know how to do this or even is it required at all.

Is a twist needed and if so how do I to calculate it?

Note: I chose airfoil EH 1.0-9.0 for this purpose.

Twist is closely coupled to the wing's sweep angle, airfoil camber, taper ratio and the desired level of static longitudinal stability. Other factors are the desired spanwise lift distribution and maneuverability. There is no simple, general formula: In the end twist, or, more precisely, local reflex camber, is the consequence of your selection of the parameters mentioned above.

Background

Static longitudinal stability means that the aircraft will return to the trimmed angle of attack after a disturbance. This is made possible by producing proportionally more lift in the forward part of the wing than in the rear part. Reflex airfoils do it all by themselves and unswept flying wings do not need washout, but a proper reflex airfoil.

The Horten flying wings had highly tapered wings and used a bell-shaped lift distribution over span which produced a small downforce at the tips. This helped a lot to reduce adverse yaw and allowed them to do away with a vertical tail. Also this made stall chararcteristics benign. This lift distribution was reached by extensive washout (as much as 8°).

If you add stability by computer control, washout will not be needed and you can use an elliptical planform for best performance. This will, however, have unfavorable stall characteristics and needs wing fences when the wing is swept. Moderate sweep adds stability and damping, but above a critical combination of aspect ratio and sweep angle it is hard to achieve satisfactory stall characteristics.

Critical angle of sweep for swept wings, from Chapter 16 of S. Hoerner's Fluid Dynamic Lift. Too much aspect ratio and sweep will result in a strong pitch-up when the wing stalls.

By adding some chord at the outer wing you can twist the local incidence by the amount of chord added. This will lower the local lift coefficient and produce reserves at stall which will improve stall characteristics a lot. Karl Nickel has published a method for calculating the optimum planform for a given static stability with nearly elliptic lift distribution over a wide range of speeds. The key is his insight that by trimming the wing for a particular angle of attack the pilot will adjust local washout by moving the elevons trailing edge up. Ideally, the wing uses several elevons with increasing trim deflection towards the wingtip. (By "trimming" I do not only mean the reduction of stick forces, but also the adjustment of local lift to cancel any pitching moments.)

Note that now the planform is tightly coupled to the static margin and, consequently, to the location of the center of gravity (cg). Flying with a more forward location of cg than ideal means more negative elevon deflection angles and lower local lift at the tips than ideal, and vice versa.

The SB-13 flying wing glider uses this technique and has a taper ratio (ratio of tip to root chord) of 0.8. It uses two elevons over the outer 50% of span, the inner of which travels 1/3 of the trim deflection of the outer elevon. Twist is zero for the inner half of the wing, changes from 0° to -1.5° over the 0.15 m section where the root airfoil (HQ 34 N) changes over to the tip airfoil (HQ 36 K) to adjust for their difference in zero-lift angle and increases again linearly towards the tip to +0.5° (I hope I got that detail right, typing all this from memory). The negative washout was chosen to allow the elevons to have 4° twist themselves, so in sum (fixed wing and elevons) the wing has increasing twist towards the tips. In flight, the elevons will always have a slightly negative deflection, so the effective washout is even stronger.

SB-13 in flight (picture source)

To answer your questions directly:

  Is (a) twist needed?

Not necessarily. An unswept flying wing does not benefit much from twist. It will only help to add some stall margin at the tips. A positively swept flying wing can also get away without twist if the airfoil is changed over span from positive camber at the root to negative camber at the tip. If the same airfoil is used over the whole span, twist/reflex camber is necessary and cannot be avoided as soon as the cg is ahead of the neutral point: It will result from trimming the wing for the desired angle of attack.

  How do I to calculate it?

Select your desired static margin.
Select your desired lift distribution over span. An elliptic distribution will result in the lowest induced drag, and a bell-shaped distribution will give better maneuverability.
Select the planform that results in the desired lift distribution when trim changes over speed are considered. Use several elevons over span to be able to adjust the local incidence independently.
Twist is then a necessary consequence of trimming the aircraft.


Where to find the aircraft maintenance manual for the Falcon 2000? How can I find a Falcon 2000 aircraft maintenance  manual (AMM)?

You can get the latest AMM through the Falcon Interactive Electronic Library by Dassault (FIELD). Contact the manufacturer through their website for pricing and information on how to setup an account.


What does happen when a supersonic aircraft passes another supersonic aircraft, regarding sonic booms? I wonder about sonic boom existence and effects when two fast aircraft interact, for example:

When supersonic aircraft flying opposite routes cross each other, do pilots hear a sonic boom?
If they fly in the same direction, with the appropriate offset, does one hear a permanent sonic boom?
If two aircraft fly in opposite directions at Mach 0.6, can they create a sonic boom by adding their individual shockwave speeds?

Two Sukhoi Su-30MKI maneuvering, Wikipedia

Further than the sound aspect:

What are the effects on the aircraft?
Is there a distance after which the effects become insignificant?

When supersonic aircraft flying opposite routes cross each other, do pilots hear a sonic boom?

If the aircraft are near enough, yes.

  If they fly in the same direction, with the appropriate offset, does one hear a permanent sonic boom?

The boom will not be permanent i.e. static, but yes, it will be persistent. However, it should be noted that the shocks from various parts of the aircraft body will interact nonlinearly (mostly coalsce), resulting in unpredictable results.

  If two aircraft fly in opposite directions at Mach 0.6, can they create a sonic boom by adding their individual shockwave speeds?

No, sonic boom is caused by the object travelling faster than sound while the disturbances travel in the medium with speed of sound and get 'bunched up'. So, the aircraft has to fly supersonic with respect to the medium

  What are the effects on the aircraft?

Shock wave is basically a pressure discontinuity. So the effect will be similar to that of an impact, whose strength depends on the shock wave.

  Is there a distance after which the effects become insignificant?

Yes, but it depends on the aircraft size and the speed. The shock wave produced by the bullet loses its strength in a short distance, while the Concorde has to be flown over sea and Tu-144 at over 35000' to mitigate the effects.


What are the costs and labour hours for converting a B767 airliner to an aerial refueling aircraft? To win the tender of RAF Future Strategic Tanker Aircraft, Boeing, BAE systems and British Airways formed Tanker Transport Services Consortium to offer air-to-air refuelling to military jets, using converted aircraft based on the B767 passenger jet. BA would provide the aircraft, Boeing would provide the conversion technology, and BAE systems would perform the majority of the aircraft modifications.

Roughly speaking, how much does it cost and how much labour hour is needed to convert a B767 airliner to military aerial refueling and strategic transport aircraft?

It's very difficult to answer this question directly, mostly because that the costs you or I would face when undertaking such an endeavour are primarily capital in nature. For a large airline (or other organisation), they'd have staff and equipment on hand already, and the price an organisation like BA or BAE pay for parts is almost certainly different to the list price.

That being said, the deal in question is notoriously bad value for money. From that source, the taxpayer will be paying around £10.5 billion for 14 Airbus A330 troop transport/tanker jets with a capital value of only about £1 billion, although the deal also includes maintenance. Although converted to military specification, the converted passenger jets will not be flying into a war zone any time soon.

Interestingly, it appears that the government itself didn't really know the answer to 'how much will this cost', even as they were signing the contract to provide new aircraft. Specifically, a critical report from the National Audit Office concluded that there was 'poor access to full cost data – the Department never gained visibility of detailed sub-contractor costs and margins for the aircraft and their modification'.

In other words, nobody knows!


What is this fuselage-side aerial used for? (instagram.com)

I have seen this picture, and this feature on the port fuselage called my attention. Does anybody know the purpose of this?

One of the features on this American Airlines Airbus A319 is the Gogo Inflight Internet.

  The A319 will be the first aircraft type in American’s fleet to use Gogo’s ATG-4 Wi-Fi solution. ATG-4 uses more antennas and better data compression technology to provide more robust and reliable service (August 15, 2013).

There's another one on the other side. It's part of the air-to-ground (ATG) internet setup that utilizes Gogo's cellular towers in the US and Canada, as opposed to satellite internet.

(Left; Right) Click to view.

Related external links:

Inside a Gogo ATG4 installation
How Does In-Flight Wi-Fi Really Work?

Thanks to @mins for their help on the answer.


How to identify different pipes / hoses on aircraft engines? When looking at an aircraft engine (without any cowlings) is there an easy way of identifying what pipes are for fuel, air, oil, hydraulics etc..? Maybe certain fluid pipes are different size diameters or do you just have to know the engine system and components they are providing to be able to tell?

You can guess what most of the tubing goes to if you know a few of the parts under the cowl and have a general understanding of how engines work. You can also get a good idea of what each part is by studying the parts catalog for the aircraft. You can view the Parts Manual for my Cherokee and an Arrow that I fly.

Piper Arrow Six Cylinder Continental

Let’s start with easy ones to identify. You should be able to find the tailpipe rather easily.  Notice in the picture of the Arrow that there are a lot of big orange tubes. That’s called scat tubing and it is used to move air around the engine compartment. In most singles, there is a shroud around the muffler that has orange hoses coming out of it. The ones going into the firewall provide cabin heat and defrost. The ones going to the carburetor provide carb heat to prevent icing.

Notice the rusty pipes coming out of the bottom of the engine. Those are the exhaust pipes and it’s hard to see in this picture, but they connect to the muffler. The big black pipe at the top of the engine is connected to the air filter and is the air intake. The clean pipes along the top of the engine are the air intake tubes. Most fuel-injected engines have the air intakes on the top of the engine.

Fuel injected engines also have small lines that put fuel directly into each cylinder. The line entering the "spider" at the top is a fuel line and you can trace it back to the fuel pump.

The brown hose in the picture below going to the spider is a fuel line.

Cherokee Lycoming Four Cylinder Engine

Compare this to the carbureted engine in the Cherokee. The more rusty pipes are the exhaust and the cleaner blueish pipes come from the carburetor with air and fuel.

If you can find the vacuum pump (the dark item to the right of the oil filter with the red bands) you can identify the hose going to the attitude indicator and heading indicator. There’s usually a filter attached to the hoses and a line leading to the vacuum gauge—although sometimes that is inside the cabin. The big open-ended hose is the exhaust for the pump.

Here’s another four cylinder where you can see the intake and exhaust. Notice the silver lines with the blue fitting. Those are primer lines. At the bottom left is an oil cooler. There is scat tubing bringing air to the cooler and two lines going in and out.

Oil coolers are often in the front of the cowl like this one. If there are lines attached to something that looks like this, they are oil lines.

This is a different method of plumbing carb heat. Rather than coming off the muffler hot air comes directly from the engine.

Here’s a picture with lots of hoses.

The two small hoses at the bottom of the picture are attached to the oil cooler. If you follow them back you’ll find the oil pump.

You can see the carburetor with a scat tube coming from the air filter and one on the back side coming from the muffler shroud. The two small hoses going into the carb are fuel lines.

The vertical silver tube running from the top of the picture, down past the muffler, and out the bottom is the crankcase breather line.

The box in the bottom right-hand corner has the electric fuel pump (boost pump). The line coming out of it is a fuel line. The silver tube in the box goes to the gascolator.

You should also see an oil line going through the firewall that measures oil pressure and one for fuel pressure but I don’t have pictures that show them.


Are there regulations for water skiing in a ASEL aircraft? What are the regulations regarding water skiing with ASEL aircraft, as in touching your tires down in a particular body of water such as a lake or river? Sometimes referred to hydroplaning.

(bush-air.com)

I couldn't find any regulations for it. But the closest thing to an official mention of it I found was in a 2009 piece on Anchorage Daily News, where an unlicensed pilot water skied, hit a sandbar, and it didn't end nicely for his Super Cub.

The FAA regional counsel said:

  The practice is called water-skiing, and it is not encouraged. It was developed for landing in tight quarters, like sand bars where space is short, but doing it wrong can be disastrous.


How practical might it be, to carry military tanks by helicopter(s) to remote areas? How practical might it be, to carry military tanks by helicopter(s) to remote areas?

Wikipedia lists the M1 A2 Abrams tank at 65 metric tons.
HeliPress lists the Russian-made Mi 26 copter as being able to carry 56 tons; it’s unspecified as to which type of tons.
Might it be practical to carry in by helicopter a crane of sufficient lifting capacity to assemble “reasonably quickly”, a tank that had been disassembled to weights that could be carried by helicopter(s)? I believe it would be practical to carry in such a crane, & assemble it reasonably quickly.

Then there’s the aspect of what sort of areas might tanks need to be flown to: High elevations permit smaller payloads, as do hotter temperatures. Presuming the helicopter(s) would take off from an aircraft carrier, how far would the flight likely need to be?
Thank you for your attention to this.

Feasibility
The maximum payload of Mi-26 is:

20,000 kg Internal or external load.

The same page lists the following as possible payload for Mi-26:

2x BRDM-2 scout cars, or 2x BMDs, or
1x BMP or,
1x BTR-60/70/80 or,
1x MT-LB

All of the above are armoured vehicles and not classical tanks.
The 2S25 Sprut-SD is a self-propelled tank destroyer or light tank with a weight of 18 tons. So theoretically it could be carried by the Mi-26.
Other similar light tanks could also be carried. Or heavier tanks disassembled and carried (but as mentioned by Ralph J, that may not be very practical). The Mi-26 is routinely used to ferry heavy earth moving equipment to remote location.
With an C-17 or Il-76, main battle tanks can be (and are) easily carried and would be strategically preferable/more practical (see end of answer for more on same). Light tanks/armoured vehicles are also airdropped from the C-17/Il-76 (as mentioned by Ralph J).
Actual Practicality
However, locations where a tank could be practically employed (predominantly plains) would generally make transport by air and (then as required) by road possible. An example which comes to mind, is use of tanks by the Indian Army in Ladakh with induction by air using Il-76/C-17 and then further movement by road (of interest, that Leh airfield from where they are inducted is at 3,256m/10,682ft!, making it no easy feat).
In areas so remote that tanks need to be moved by helicopter, the use of the tanks (and note tanks are tactically best utilised only in more numbers and never in ones/twos) itself may not be feasibly/practical, so making the exercise futile/uneconomic.
Also, just getting the tanks would not be enough as you also need to move the large amount of fuel, ammunition and spares. These are no lesser of a payload in themselves.
So overall most probably not a very practical exercise.

C-17 ferrying Abrams Tank

Video on YouTube
Source: http://armedforcesweekly.com/c-17-globemaster-iii-loading-m1a1-abrams-tank/
Il-76 ferrying T-72 Tank

Source: https://defense-studies.blogspot.in/2016/07/main-battle-tanks-will-stengthen.html?m=1