Is there anything better than LiveATC to get accustomed with RT phraseology? I would like to "train my ear" for RT communications and I tried to listen to approach of Dublin's Airport. I simply can't understand more than 50% words because of loud background whistle and poor (quiet) sound quality, although the mp3 player shows 320 kbps. Do they sound just like that in real life too?

Is there anything else with better quality than LiveATC? I would like to get accustomed with ICAO phraseology, so US airports will not suit my needs.

Thanks for taking time to reply!

The loud whistling and popping has to do with the equipment that the person monitoring the frequency is using in addition to the range they are from the airport.

Depending on local law you could purchase a receiver capable of receiving those frequencies yourself directly. Under some conditions however transmissions may sound like that because they are AM and subject to whatever interference is on the air at the time.

When you are in an aircraft you are subject to less interference because there are no objects between you and the transmitter. The frequencies  you need to be able to receive are 118.000 Mhz to 136.975 Mhz AM mode for civil aviation.

Even if you are not directly near a major airport there is likely controlled airspace near you that you can check by looking at a sectional for your area. That will have the frequencies in use by your local airports. Then you can listen to controllers with your local accent. Once you know the words you'll be able to pick them out of the LiveATC feed better.


Is there a taxi turning radius requirement for normal category aircraft? Does anyone know if there is any requirement regarding turning radius during taxi for a normal category aircraft?

I searched both the Part 23 and Part 91 from cover to cover and couldn't find any. If there is no legal requirement but a recommendation from some Advisory Circular or any other document I also would like to know.

There is no legal requirement. In fact there is no stipulation that the aircraft be maneuverable on the ground.

Good examples of this are early aircraft (often biplanes) with tail skids. In the middle part of the last century there where gliders that had no wheels - just a center skid. Many current gliders have just one wheel and it is not steerable.

"The nose gear of a few aircraft with tricycle-type landing
gear is not controllable." FAA Airframe Handbook pg 13-4

These type of aircraft are usually steered using differential braking. Examples are: Grumman (AA1, AA5, AG5), Diamond (DA1, DA4), Rallye except the 235C, early "straight 35" Bonanza, Columbias, T-28, T-34C, Nanchang CJ-6A, HU-16 Albatross, IAR 823, etc.

The HU-16 Albatross does not have steerable gear

Aircraft without wheels

Glider without steerable gear


Steady-state simulation of pitching motion Is it possible to perform a simulation of 'steady-state' pitching motion of an aircraft/wing? Is there any method where we can analyse the effects through a steady-state simulation of a pitching motion? I have seen numerous papers/articles where the unsteady simulation has been carried out but none related to steady-state.

A "steady" rate of pitch condition is very rare because most aircraft are designed to be stable enough to avoid stalling themselves.  In other words, the more you pitch, the greater the control input you need to continue increasing AOA.
You can reach steady state in roll easily.  Here drag resistance to rolling will stabilize roll rate, provided the aircraft rolls smoothly around its axis.  Here, rudder and elevator inputs may be required.
So, for pitch, you could get a steady state pitch (relative to the horizon) in a loop.  Here, throttle inputs are definitely required (to get a perfect circle).
But for increasing AOA at a steady rate, this will lead to a stall.
There is also the analytical consideration of acceleration before reaching steady state.  Taking the easiest, the roll, roll rate goes from 0 degrees/second when ailerons are applied to steady degrees/second when drag force = rolling force (differences in AOA of rolling wings helps too).
Many early "video arcade" games do not simulate the acceleration (the deer is instantaneously in full gallop). To do an accurate simulation, acceleration to steady state must also be considered, so now you have a rate of acceleration to steady state.


During the holding procedure is it required that the pax must have the seat belt on? Imagine to have to hold at a busy airport before landing for a quite long time (let's say 20 plus minutes), does it requires that the pax must have the seat belt on during the whole holding procedure? Is it required by the Authority or just by the company?

There are no regulations which require passengers to be seated when the plane is flying a holding pattern, but there are a few practical advantages to keep the seat belt sign on during this phase:

The plane is flying at a lower altitude, where it is more likely to encounter turbulence and other unstable weather conditions. Up in FL330 it is usually clear skies all along.
The plane may need to get down quickly after an approach clearance is issued (after all, it is busy airspace). From that point onward the pilots may deploy the spoilers to lose altitude (which shakes up the plane a little), turn towards the approach course and without you noticing, landing gear is down and locked already. At the same time, we know it takes quite a few minutes after the seat belt sign has been turned on until everyone is seated (passengers won't just rush back to their seat after hearing the Ding Dong tune). If the seat belt sign is not illuminated in this period, there may not be enough time for the cabin crew to prepare the cabin for landing.
It reminds the passengers that if they wish to get out of their seat for whatever reason, they should make it quick.

If the flight deck tells the passengers it is going to be a delay, the cabin crew is usually a bit relaxed at enforcing the seat belt sign. E.g. if someone is going to the bathroom, they won't block unless that person is hanging around standing. When the approach clearance is given, another announcement will be made, and the cabin crew will now make sure everyone is seated because landing will commence shortly.


Why are jet engine nacelles, used on the same plane, so different? One thing that is plainly obvious about the design and configuration of jet airliners is how little they tend to differ.

It's surprising then that even on the same airliner, you will see two quite different-looking engines.

I've seen A330s with "fully-enclosed" engines, and "open" engines:

(Trent 700 with exhaust mixer, image from Wikipedia).

(PW4000 with unmixed exhaust, image from Wikipedia).

The fact that both designs are used suggests that one isn't simply better than the other, but the difference seems fairly significant.

Why would an engine designer or a customer opt for one design over the other, and why do they arrive at such apparently different solutions for the same use-case?

I assume, perhaps incorrectly, that each has its own advantages and that for whatever reasons different manufacturers and customers value different ones.

Sometimes manufacturers will certify with multiple engine types because their customers have their own power plant preferences (or manufacturer preferences, like say an airline's existing fleet is RR engines and they want to keep engine commonality for logistics benefits, or an airline feels one model engine is cheaper to run than another).  Providing different powerplant options for an airliner can therefore result in more sales.


How do Ram Air Turbines get deployed? I understand that most larger jets have a Ram Air Turbine (RAT) in case of total electrical failure (for instance, when you run out of fuel) in order to at least have some hydraulics and a couple of instruments. The RAT gets deployed automatically at the loss of electrical systems.

But how does it get deployed? I'm interested in the triggering mechanism, as, during a complete electrical failure, there can be no electrical trigger (computer or otherwise). So it must be something mechanical. Or are they relying on batteries?

I figured it'd have to be some failsafe mechanism, like stored (hydraulic or otherwise) pressure held back by something like an electromagnet or hydraulic pressure, cut the power and presto, the RAT deploys. However, I've never seen one deployed on an aircraft sitting on the ground with the power off, so that kind of shot down that idea.

The RAT is automatically deployed on many aircraft, including the CRJ and A320 series, but it can be manually released as well. In between the loss of power and the RAT spins up you have the batteries to fall back to which are normally fully charged.
The Airbus Manual has the following comment on the APU:

In case of total loss of all main generators, the RAT is automatically
extended and drives the emergency generator via a hydraulic motor. The
EMER GEN supplies the AC ESS BUS and the DC ESS BUS via the ESS TR.
The ECAM WD remains powered, with associated procedures presented.
Alternate law is operative through ELAC 1 and SEC 1
(Source)

While this is for the CRJ, who call it an Air Driven Generator (ADG):

In the event of a complete AC power failure in flight, the ADG will
automatically deploy and supply emergency AC power to the ADG bus and
to the AC essential bus. If the automatic deploy function fails, the
ADG can be deployed manually by pulling the ADG manual release handle
on the ADG CONTROL control panel at the rear of the center console.
(Source)

A RAT, with the spring loaded actuator visible:

I think most if not all are spring loaded, and have a little help from gravity on the way. You'll also notice that many are stored to be pushed into place by the jetstream.
Have a look at this video below around 0:20. The slow upwards motion suggests that it's having to reload the spring energy at 1:20. The doors are attached mechanically.
Taking a look at the Airbus Electrical System:

As can be seen, there's a hierarchy to electrical power use, and the battery feeds the essential busses, where the RAT deployment would be included. If I'm not mistaken, power is very limited: You loose some of the more fancy control computers along with the non-necessary stuff, like the copilot's displays, as can be seen in the following video.
Bear in mind that some aircraft, such as the 747 (up to -400), do not have a RAT on the aircraft, and rely on the windmilling engines to provide sufficient hydraulics to control the aircraft, and as such there's no deployment of sorts necessary.


What is this instrument that has "PACK" written on it and a temperature scale? All I know right now is that it’s made in 1973. Another instrument I have is from a b727 and is dated 1982. This one I have no clue. Serial number- H 2590. The brand is Amphenol. That’s all the info I can find. I have some pictures.

It looks like the pack temperature gauge for the air conditioning system on the 727

  To monitor the operation of the air cycle machines, each has a
  temperature transmitter at the outlet off  its compressor.  The
  temperature sensed is displayed on a pack temperature gauge for each
  pack.  As more air is directed through cycle machine to provide more
  cooling, more compression is  required from the compressor.  This
  results in a higher compressor outlet temperature.  Therefore, the
  pack temperature gauge monitors air cycle machine work load.  To
  protect the compressor from excessively high temperature an over
  temperature sensor at the outlet of the compressor will cause the pack
  to shut down if the temperature reaches the limiting value.  Another
  temperature limiting sensor located at the inlet to the turbine.

You can find a full video of how that section of the flight engineer panel works here.

Here it is on the flight engineer's panel (airliners.net).


How long does it take to restart a turbofan engine inflight? I'm especially interested how long it would take to restart a turbofan engine after a hypothetically erroneous shutdown of an engine immediately after takeoff i.e., at an altitude at which the air is reasonably dense. Is windmilling enough or would you need crossbleed and starters again?

It can take from a few seconds to eternity. If the core cools down, the engine might lock up.

Windmilling starts are only possible if the aircraft is flying fast and low enough. It will assist the startup process, but needs additional help from the starter or bleed air, typically below 300 knots and above 20,000 ft. Details vary from type to type. If everything works as designed, a windmilling assisted restart is faster than a regular engine start.

The ability to restart in flight must be proven as part of the certification process. However, right after takeoff the speed is too low for a pure windmilling start, and an additional energy source is needed.


Why is the stagnation point on the upper surface before the start of circulation? In many textbooks, such as Anderson (Fundamentals of Aerodynamics), Bertin (Aerodynamics for Engineers), and Houghton (Aerodynamics for Engineering Students), the authors present the idea that there is a starting vortex which is formed. This starting vortex and the bound vortex that form (due to Kelvin's Theorem) co-exist with lift (as Mclean puts it in Understanding Aerodynamics). However, I am unsure on why the starting vortex forms on the upper surface. Why does it not form on the lower surface and have clockwise rotation and lead to counter-clockwise bounded circulation at the airfoil?

While I know that this is not experimentally observed nor does it make intuitive sense, I would like to know why the starting vortex does not form on the bottom.

To shed more light, here are some instances of where authors state that the starting vortex starts on the upper surface, but never explain why it doesn't start on the lower one:
(taken from Bertin):
"At the instant of starting, the flow is a potential flow without circulation, and the streamlines are as shown in Figs. 6.3 a, with a stagnation point occurring on the rear upper surface"

(taken from Understanding Aerodynamics)
"It can be shown, based on starting the flow from rest, that in the absence of viscosity, the nonlifting flow pattern of Figure 7.1.3a is the one that would occur... "

So how can it be shown (mathematically) or using strong rigorous theoretical arguments that the stagnation point cannot be at the lower surface before circulation?

The illustrations under the time-invariant, inviscid, irrotational and incompressible (potential) description is a bit misleading, in my opinion. In the real world, assuming the airfoil starts from rest (no flow field) and you start accelerating it to some airspeed, viscosity should start generating vorticity as soon as airspeed becomes non-zero. Therefore, the non-lifting flow field would never exist in the first place.

The non-lifting flow field serves better as an illustration of the flow solution using uniform + doublet flows. In this case, there is a unique solution for a uniform flow past a cylinder with radius $R$:

Radial speed: $V_r=V_\infty cos\theta(1-\frac{R^2}{r^2})$
Tangential speed: $V_\theta=-V_\infty sin\theta(1+\frac{R^2}{r^2})$

Since we can conformally transform most airfoil geometries into a cylinder, flow solutions past a cylinder is a generalization to those past airfoils. The above result assumes zero angle of attack. But since cylinder is symmetrical, a non-zero AOA simply rotates the result by that AOA, and that's why you have the rear stagnation point on the upper airfoil surface.

For a lifting flow, we would need to model with uniform + doublet + vortex flows. In this case, a set of solutions can be obtained for a cylinder:

Radial speed: $V_r=V_\infty cos\theta(1-\frac{R^2}{r^2})$
Tangential speed: $V_\theta=-V_\infty sin\theta(1+\frac{R^2}{r^2})-\frac{\Gamma}{2\pi r}$

Notice that there is, at this point, no imposition on what the vortex strength ($\Gamma$) has to be. You can have an infinite number of lifting solutions with an arbitrary value of vortex strength (at the same AOA). I think that's what (b) and (c) of your second set of figures are trying to illustrate. We get around this by specifying the Kutta-Condition and impose the stagnation point at the trailing edge to get a unique solution.

Since the total flow field must have zero circulation, the starting vortex must have a counter-clockwise circulation.


What is a monitored approach? I've heard this term used to describe approaches into low weather (e.g. category 2 ILS), what is it?  How is this different than an ILS approach?

A monitored approach is a special kind of instrument approach involving added verbal call outs and increased monitoring of the airplane and is typically conducted when weather is below a certain threshold. For example, a crew may be required to fly a monitored approach if the weather is below 3/4 mile vis and the captain has less than 100 hours in type, or in any case with the weather below ILS Category I minimums. It is also specific to multi-crew aircraft and requires at least 2 pilots and in many cases an autopilot.

In a crew environment, the pilots are typically designated as Pilot Flying (PF) and Pilot Not Flying (PNF).  In general the PF is flying and making commands of the PNF, and the PNF mans the radios and operates gear and flaps the command of the PF.  More detail of this setup probably deserves its own question.

To illustrate a monitored approach, I'll describe on based on my companies procedures.  The specific requirements can vary between operators based on crew training, aircraft equipment and approved opspecs.

The monitored approach briefing

We have identified the arrival airport current weather is 1200 RVR and obscured ceilings and we plan to fly the ILS to category II minimums.  Myself and my first officer have both have current category 2 training, neither of us are high-minimums, and the aircraft has no MEL items effecting category 2 operations.  We are legal to fly the approach, but company operations require we fly it as a monitored approach.

Regardless of who has been PF and PNF up to this point, the first officer becomes the PF and the captain the PNF.  The PF briefs the approach as normal except for:

CAT II radar altitude minimums
Low vis taxi routes if applicable
The approach will be flown by the autopilot (company specific)
Special autopilot considerations
Required verbal call outs (see below)

The monitored approach

For my company, the autopilot had to be engaged in "CAT 2" mode before glideslope intercept.  This will vary by aircraft and company.  For the approach, as noted earlier, the first officer is PF, captain is PNF.

The PF duties are to monitor the autopilot and to execute the missed approach if the autopilot has problems.  The PNF also monitors the autopilot.  The pilots are monitoring the autopilot for performance and for indications it cannot meet required tolerances for the approach.

PF will call for gear and flaps as normal, except a non standard flap setting may be used for the approach (e.g. we flew flaps 22 instead of 45).

Once configured for landing, the PF will call for "Landing checklist - to the line" (company specific), this for us was the normal landing checklist with the caveat that the checklist is complete when the captain announces "Landing, I have the airplane" (more on this in a moment).

Nearing the Cat II decision height (typically 100 ft RA), the PNF will announce "Going heads up", discontinue monitoring the autopilot and look for the approach lighting system and the runway lights.

The PF will continue to monitor the autopilot.

The airplane will announce "Minimums" at the radar altitude DH and when the airplane reaches this height, the PNF will fly the missed approach.

If the captain sees the required lighting to continue the approach, they will announce "Landing, I have the airplane", and the FO will reply "you have the airplane, landing checklist complete.

The Captain must disconnect the autopilot (by 50 feet, no autoland for us), and would fly any aborted landing executed after taking control.

Caveats

Rules on autopilot usage, disconnect heights and autolanding will vary based on aircraft and company policies.  My example assumes an Embraer-145 certified for Cat 2 approaches and no autothrottles or autoland capability.  Checklist verbiage and flap configurations mentioned also would vary by aircraft and company.  And finally, the specific callouts will vary by company.

While it seems like there was a lot of Category II specific things in my example, the two concepts of reduced visibility ILS approaches and monitored approaches are intertwined, and you will almost always be flying a monitored approach because it is required to conduct the low weather approach by company policy.


Why were there pneumatic headphones on airliners in the 70's and 80's? I remember listening to the on-board program with headphones that consisted of hollow hoses as a kid. You plugged them into small holes in the arm-rests. The program was the same for everybody.

Why was the system in place? Why was it phased out?

Well, the rubber hoses themselves were used instead of traditional electromag transducer headphones for two main reasons; first, the hoses were much cheaper than a decent pair of traditional headphones at the time, and to an extent they're washable, so airlines could provide a pair for everyone at a much lower pricepoint than traditional headphones. Second, the hoses were more or less useless without the driving system aboard the aircraft, largely removing the incentive for passengers to walk off with them, again reducing costs of providing the system to passengers. The system was phased out in favor of simple 1/8" stereo jacks at each seat in the '80s and '90s as portable audio became mainstream, and as airlines looked to dramatically slash costs in the face of deregulation beginning in 1978. Economies of scale meant that buying cheapo Walkman-style headphones in bulk became cheaper than maintaining the aging pneumatic systems, and the electric-based system was more reliable and had several advantages (such as volume control for each passenger, and if standard 1/8" jacks were used, the ability for a savvy flyer to bring their own, nicer pair for use on the flight).

As an aside, this pneumatic audio system is still used today for a very different purpose; newborn hearing screenings. A pair of flaps with a mild adhesive are stuck to baby's ears, then hoses lead back to a finely-calibrated audio system coupled to an EEG. Audio is played and the EEG is monitored to detect the response to the sound in baby's brain. The hose system is used because it allows the expensive, fine-tolerance part of the audio system to be reused from test to test, while the hoses themselves are disposable and (as hospital equipment goes) fairly inexpensive.


On a 777 what would happen if the aft pressurization switch was accidentally left closed? The Boeing 777 has fore and aft pressurisation switches (see example here). If the aft switch was forgotten on takeoff, could this cause a loss of cabin pressurisation when the aircraft reaches altitude?

From my previous source in that incapacitation question:

  Two outflow valves are installed: one forward and one aft. Normally,
  most of the outflow is through the aft outflow valve. This improves
  ventilation and smoke removal. Cabin altitude and full ventilation
  rates can be maintained by either valve. Source


Is flying in ground effect dangerous? The stall angle  of a wing in ground effect reduces in comparison to the stall angle of a wing flying outside of ground effect. Doesn't this make soft field takeoff dangerous?

The decrease in stall AOA is more than offset by a decrease in the AOA required to achieve the same total lift and the result is indicated stall speed actually drops a little bit.  And pilots generally don't fly AOA itself as a parameter, but pitch and speed.

But the main thing is the power required to fly is less in ground effect so there is more power available to accelerate.  Normally when taking off you rotate and start right up because even though you are initially below best climb performance speed, there is ample reserve and you accelerate to it with no problem. Problem is in marginal conditions, where the airplane won't climb at all unless it's at its most efficient climb speed, you need to accelerate somehow without trying to climb, and you can't just roll along the ground faster, so you take advantage of the power bonus you get in ground effect.

Ground effect is much stronger the higher the aspect ratio.  How strong?  Watch this glider's L/D go through the roof:


Is a horizontal stabilizer necessary on an aircraft with a tandem wing? Let's say that there is an aircraft with more than one main wing and each of these wings have elevators. Would it be necessary to have a horizontal stabilizer? The figure below shows an example of what I'm thinking.

Is horizontal stabilizer necessary for tandem wing aircraft? not if the main wings are capable of carrying out the functions of the tailplane.

The main reasons for horizontal stabilizer are twofold:

To provide stability for the aircraft, as the wing alone configuration is unstable.
To provide pitching moment as the long moment arm enables enough moment to be produced by small changes in the lift (via the elevators).

It provides other benefits too (like damping), but these are the main ones.

For aircraft having tandem wings (i.e. having two wings one behind the another), horizontal stabilizer may or may not be present depending on various factors.

If the two wings are able to provide stability and provide pitch moment by differential control of the control surfaces (elevators) on them, the tandem wing has no horizontal stabilizer, like the Scaled Composites Proteus.

"Scaled Composites Proteus in flight 1". Licensed under Public Domain via Commons.

In some cases, the above objectives may not be met with the wings alone and a horizontal tail may be required, like the Scaled Composites Advanced Technology Tactical Transport. Interestingly, the aircraft was flown in two configurations. The initial configuration had a cruciform tail.

Image Courtesy of Scaled Composites, LLC

According to DARPA report AD-A227- 498,

  Analysis of the flight test results of the "Cruciform Tail" configuration disclosed a significant deficiency in the directional stability and engine-out minimum control speed of the airplane as well as some perceived loading difficulties due to low clearance of the aft cargo door.

As a result, the configuration was changed into a twin boom 'bronco' tail and flown.

Image Courtesy of Scaled Composites, LLC

There are some advantages with the tandem wing configuration, like:

For same weight, the tandem wings are more compact (i.e. have less wingspan) as both the wings produce lift (This was one of the reasons given by Burt Rutan). They have less frontal area and less parasite drag.
In case of tandem wings, both the wings produce lift, on either side of the center of gravity and produce moments about the c.g. in opposite directions. So, for stability, the c.g. is shifted forwards (for e.g. by having the power-plant forward). As the Angle of attack (aoa) increases, the lift force shift towards the rear and as the center of pressure shifts to the rear of c.g., the tail has to produce higher downward force to produce the required counteracting moment. As higher aoa is used mostly in landings, where more lift is required at lower speeds, this is not ideal. However, in case of tandem wings, at higher aoa, lift force of both the wings move to the rear, resulting in the rear wing having longer moment arm, and by extension, larger moment. So to compensate, the lift produced by the front wing has to be larger, which produces more lift, not less. For this reason, the front wing is set at a higher incidence (so as to produce higher lift) compared to the rear one.

Source: nurflugel.com

In general, the c.g. of a tandem wing aircraft is towards the main forward wing with the rear wing at a smaller incidence compared to the forward one. This means that the forward wing will have higher wing loading and stall first. However, as the rear wing is still producing lift, the nose drops and the front wing starts to produce lift again, giving the pilot some time to react and control the aircraft, unlike the conventional configuration.

As the wingspan is less, the induced drag is more though.


What is an "unsafe airline"? Question:
Is there any internationally accepted definition for what an "unsafe airline" is based on objective criteria (e.g. fatalities per million passengers) ?
Or is there an international standard or worldwide blacklist ?

All I was able to find are regional lists:

the list of air carriers banned in the EU, AKA the EU Air Safety List and
the International Aviation Safety Assessment for the US.

I'm hoping to receive answers in a similar vein as those for the question What is a “Major Airline”?.

There is no international blacklist of unsafe airlines. An airline can only exist if at least one country believes it is safe. Those regional blacklists are about the best you'll get.

In a formal sense, calling an airline "safe" is generally avoided. A regulator would use a term like "meets safety standards". This might be a small distinction but it helps make it clear that no airline flight is guaranteed to be safe. So the closest legal definition of a safe airline is one that has been certified as meeting safety standards by an ICAO compliant country. However this is not that helpful as different countries have different standards, as proven by the EU and FAA blacklists.

So to get an international comparison for airline safety you need to look at informal sources, which is subject to opinion. But this opinion can be formed by combining multiple official sources. A good example of how this can be done is on https://www.airlineratings.com/safety-rating-criteria/. This criteria is informal and doesn't consider the the most important behind the scenes information, but it is probably the best safety indicator we have.


What aircraft was used as Air Force One for the flight between Southampton and Shannon? On Wednesday 5th June 2019, The US President flew from Southampton Airport, UK to Shannon Airport, Ireland on Air Force One.

However, since SOU is more of a small regional airport, more used to seeing Dash-8s, the runway isn't very long so the aircraft used wasn't the usual B747-200, it was this much smaller aircraft.

Can anyone identify the type? My guess would be a B737-600?

As Bianfable mentioned, this is the C-32A, which is the U.S. Air Force's transport variant of the Boeing 757-200.

In this case, due to the shorter runway, they used the C-32A instead of the iconic VC-25, which is the Air Force's VIP transport variant of the Boeing 747-200 that is typically used for transporting the President of the United States.

U.S. Air Force C-32A. Image Source: Wikipedia

The C-32As are mostly used for transporting the Vice President of the United States as "Air Force Two" as well as members of the President's family and other high-level government officials.

However, the President may use the C-32As when flying to airfields that are too small to adequately support the monstrous VC-25s. The short-field performance of a 757 — especially a VIP-configured one — is quite good, so it can use runways that are relatively short for a plane of its size. It is also capable of making trans-Atlantic hops non-stop from the U.S. East Coast (indeed several airlines use the 757-200 to do that with much more dense passenger loads.)


Is the "Bay Tour" flight path documented, or is it a more informal route? Are there similar flight paths for other cities? During my Private Pilot's Licence days out in San Francisco, we often flew a "Bay Tour": a sightseeing flight northbound from San Jose through SFO's Class B , over the city and Golden Gate Bridge, then east to Oakland and south to return to SJC. Local approach controllers were familiar with this route, and a pilot could file a flight plan for a Bay Tour with everyone knowing what he was talking about. In addition, the tower at SFO would often go out of their way to give aircraft on a Bay Tour a better view of A380's and 787's out of SFO. However, I can't find any official information on it. Is it a published procedure, or just something that everyone out there has come to know about? Do similar flight plans exist for other cities and if so, where can I find information on them?

There certainly are similar routes - the Niagara Scenic Falls route, given in FAR 93.71 comes to mind.  (FAR 93 has plenty of these, by the way.)

  Comply with the following procedures when conducting flight over the
  area described in paragraph (a) of this section:

  (1) Fly a clockwise pattern;

  (2) Do not proceed north of the Rainbow Bridge;

  (3) Prior to joining the pattern, broadcast flight intentions on
  frequency 122.05 Mhz, giving altitude and position, and monitor the
  frequency while in the pattern;

  (4) Use the Niagara Falls airport altimeter setting. Contact Niagara
  Falls Airport Traffic Control Tower to obtain the current altimeter
  setting, to facilitate the exchange of traffic
  advisories/restrictions, and to reduce the risk of midair collisions
  between aircraft operating in the vicinity of the Falls. If the
  Control Tower is closed, use the appropriate Automatic Terminal
  Information Service (ATIS) Frequency;

  (5) Do not exceed 130 knots;

  (6) Anticipate heavy congestion of VFR traffic at or above 3,500 feet
  MSL; and

  (7) Use caution to avoid high-speed civil and military aircraft
  transiting the area to or from Niagara Falls Airport.


Which European (EASA, EU) regulation corresponds to US FAR 91.13 on "careless or reckless" operation of aircraft? The US has 14 CFR 91.13 about "careless or reckless" operation of aircraft, as a sort of catch-all for activities which are not explicitly prohibited by the regulations but which are still a bad idea and risks to, or actually, puts others in danger:

  § 91.13 Careless or reckless operation.

  (a) Aircraft operations for the purpose of air navigation. No person may operate an aircraft in a careless or reckless manner so as to endanger the life or property of another.

  (b) Aircraft operations other than for the purpose of air navigation. No person may operate an aircraft, other than for the purpose of air navigation, on any part of the surface of an airport used by aircraft for air commerce (including areas used by those aircraft for receiving or discharging persons or cargo), in a careless or reckless manner so as to endanger the life or property of another.

I have a hard time imagining that Europe doesn't have a similar statute, but I can't seem to find anything looking through Part-FCL or my local regulations.

What is the EASA or EU regulation corresponding to the US FAR 91.13?

This is covered by SERA.3101 (Page 19) for the UK:

  SERA.3101 Negligent or Reckless Operation of Aircraft
  An aircraft shall not be operated in a negligent or reckless manner so as to endanger life or property of others.


Do I need to use an airfield to take off or land a powered paraglider? Most aircraft require a runway to take off and land, however powered paragliders simply attach to the pilot's back, requiring the pilot to run a few metres to take off. The landing distance is also very short.

Due to this, why would I use an airfield with a runway to take off and land at, considering only the first few metres are needed, and the pilot would be required to walk along an active runway for a long distance. Why not just use an empty field where there is no nearby traffic and you are not causing delays to flights?

Should I land/takeoff from a runway in spite of this, or simply use a suitable field within reasonable distance of the airfield? What are the regulations or best practices for this in the UK?

NOTE: My answer is US specific
Not only is there no need to operate from an airport, it is recommended not to, if there are aircraft operating from the airport. Paramotors operate (in the US) under FAR Part 103.

103.13 Operation near aircraft; right-of-way rules.
(a) Each person operating an ultralight vehicle shall maintain vigilance so as to see and avoid aircraft and shall yield the right-of-way to all aircraft.
(b) No person may operate an ultralight vehicle in a manner that creates a collision hazard with respect to any aircraft.
(c) Powered ultralights shall yield the right-of-way to unpowered ultralights.

In addition to the above,

103.15 Operations over congested areas.
No person may operate an ultralight vehicle over any congested area of a city, town, or settlement, or over any open air assembly of persons.

as well as

103.17 Operations in certain airspace.
No person may operate an ultralight vehicle within Class A, Class B, Class C, or Class D airspace or within the lateral boundaries of the surface area of Class E airspace designated for an airport unless that person has prior authorization from the ATC facility having jurisdiction over that airspace.

It is common to operate a paramotor from (launch from and land on) a park or other cleared field, as long as you don't launch over a large number of people. In my area of Virginia, there are some paramotor pilots who use a public park and launch themselves along an edge, so as not to fly over on-going soccer games.


How is the centre of lift estimated for airplane models before they are being mounted in a wind tunnel? They mount the airplane models or parts of an airplane like just a wing, or a rudder in wind tunnels to test their drag and lift, stability, etc.

How do they know where to hang it from or mount it on. How do they estimate the lift center of a new design of a jetliner which has no predecessor to use as a reference.

I am guessing it is a process of trial and error. But there must be an algorithm or method to arrive from an estimate to actual lift center.

you mount it in a convenient way, and then with all the load sensors reporting, you use a spring gauge to apply known forces by hand to the object in known directions and record the load sensor outputs for each. this will tell you how to add and subtract the individual sensor outputs to yield the correct signals (pure lift, drag, pitching moment, etc.).


What is the largest and heaviest payload ever flown? Not counting the plane what is the largest or heaviest payload ever flown?

Source: Popular Mechanics

The Antonov-225 currently holds a number of records...

Heaviest maximum take-off weight at 710 tons (1.4 million pounds)
Total air lifted payload of 558,590 pounds
Single item payload of 418,830 pounds
Longest wingspan of 290 feet for any aircraft in service (Stratolaunch and H-4 Hercules had larger wingspans, but neither are currently in service)

The A380 by comparison has a maximum take-off weight of around 1.2 million pounds (600 tons) and is 260 feet wide.

For helicopters, the heaviest payload holder currently goes to the Mil Mi-26

Source: Wikimedia

It has the world record for a payload lifted to 2000 meters (about 6500 feet) of 125,153 pounds (about 62 tons).

As for the "largest" I'm not sure you can separate that. The Antonov 225 holds the largest single item payload referenced above, so that is held by weight. If you are asking about physical size, that could mean a number of things. Longest, widest, tallest, etc.

The Airbus Beluga held the world record for the most "voluminous" cargo ever lifted when it transported a chemical tank for a marine vessel.


For an airport to be designated as an IFR alternate, does it have to have a TAF? For an airport to be designated as an IFR alternate, does it have to have a terminal aerodrome forecast at the alternate airport to confirm that the forecast 600-2 and 800-2 will be in place at the time of arrival?

tl;dr You don’t need to have a TAF at the alternate and can use other sources of weather.

Keep in mind that there are two reasons that an alternate is required. First is to assure that the pilot has evaluated the weather at the destination and considered what to do if the destination is unavailable. Second is to let ATC know what the pilot intends to do if they lose communication. In the modern ATC system, with near universal radar coverage, that isn’t as much an issue as when the regulations were written.

In the US, the destination and alternates must comply with 91.169. It specifically says that there must be weather reports or weather forecasts for the airport. Normally when you flight plan you would rely on the Terminal Area Forecast to determine whether the weather one hour before and one hour after the estimated time of arrival at your destination is above the minimums. If that is not the case then an alternate is required. And again you would rely on the TAF for the forecast.

However, TAFs are not the only way to get a forecast. NOAA publishes Graphical Forecasts for Aviation and if the weather for the area is above minimums, you could use that as a means of satisfying the requirement.

Here is an example where the coastal forecast is below minimums but the airports inland will be VFR.

Or you could look at airports around the alternate and if they are above minimums, then your alternate would be as well. In the TAFs below, there are lots of airports that inland that do not have TAFs but that you can surmise that they will be VFR.

In practice, picking an airport with a TAF as an alternate is much easier. There is no requirement that you actually go to the alternate if you can’t make the destination. And with ADSB-In, you can monitor the weather while you fly, so you have a much better idea of what the weather is doing at your destination. You can divert to an alternate at any time it doesn’t look like the weather at your destination is below your personal minimums.

§91.169   IFR flight plan: Information required.

  2) Appropriate weather reports or weather forecasts, or a combination
  of them, indicate the following:

  (i) For aircraft other than helicopters. For at least 1 hour before
  and for 1 hour after the estimated time of arrival, the ceiling will
  be at least 2,000 feet above the airport elevation and the visibility
  will be at least 3 statute miles.

  (c) IFR alternate airport weather minima. Unless otherwise authorized
  by the Administrator, no person may include an alternate airport in an
  IFR flight plan unless appropriate weather reports or weather
  forecasts, or a combination of them, indicate that, at the estimated
  time of arrival at the alternate airport, the ceiling and visibility
  at that airport will be at or above the following weather minima:

  (1)
  If an instrument approach procedure has been published in part 97 of
  this chapter, or a special instrument approach procedure has been
  issued by the Administrator to the operator, for that airport, the
  following minima:

  (i) For aircraft other than helicopters: The
  alternate airport minima specified in that procedure, or if none are
  specified the following standard approach minima:

  (A) For a precision
  approach procedure. Ceiling 600 feet and visibility 2 statute miles.

  (B) For a nonprecision approach procedure. Ceiling 800 feet and
  visibility 2 statute miles.


Is there a daily list of diversions? Is there a way to find a daily list of commercial flight diversions that have occurred?  If not, is there any way to compile one from available data?  Extra points if you can also get the reason.

No. Diversions can happen for all sorts of reasons, and often on very short notice. Info about diversions is not communicated and compiled systematically. Generally speaking, only the crew, ATC, airline, original destination and actual destination airport will know, none of which have any interest in publishing the data.


How does an energy variometer work? In a comment to an answer regarding instrumentation complexity, an "energy variometer" was mentioned, labeled in knots. What does this dial actually show, and how does it work?

The image accompanying the answer in the linked comment was this, with the energy variometer shown at the top left. Don't get distracted by the legs. :)

As it is labeled with +- knots, I would assume it is showing rate of change in airspeed (i.e. acceleration), but calling it an "energy variometer" suggests that it is a combination of altitude and airspeed in which case it would show positive when entering updrafts (or when being towed) which is obviously useful for a glider. Either way it would be interesting to know how it works.

The energy variometer gives the rate change of total energy of the aircraft expressed in vertical knots.

A traditional variometer gives the vertical speed of the aircraft derived from the change in barometric pressure. This is very useful for gliding, especially when looking for thermals that lift you up. The problem with ordinary variometers is that they do not indicate why the glider is climbing; is it due to a thermal / ridge wind or is it because the pilot pulled up and the aircraft is losing speed.

When the aircraft is climbing in a thermal or ridge wind, the total energy is increasing. When the aircraft is climbing while it is exchanging speed for altitude the total energy is constant (neglecting drag).

Energy equations

Total energy is the sum of kinetic energy and potential energy:

$E_{tot} = E_{kin} + E_{pot}$

Kinetic energy is proportional to the velocity squared:

$E_{kin} = \tfrac{1}{2}mV^2 $

Potential energy is proportional to the height:

$E_{pot} = mgh$

So a change in total energy is the result of the changes in kinetic and potential energy.

$\Delta E_{tot} =\Delta  E_{kin} +\Delta  E_{pot}= \tfrac{1}{2}m\Delta(V^2)+mg\Delta h$

Differentiating with respect to time gives:

$\frac{\textrm{d}E_{tot}}{\textrm{d}t} =mV\frac{\textrm{d}V}{\textrm{d}t}+mg\frac{\textrm{d}h}{\textrm{d}t}$

The climbrate ($\frac{\textrm{d}h}{\textrm{d}t}$) resulting from exchange of kinetic energy to potential energy can be expressed by:

$\frac{\textrm{d}h}{\textrm{d}t} = -\frac{V}{g}\frac{\textrm{d}V}{\textrm{d}t}$

with $-\frac{\textrm{d}V}{\textrm{d}t}$ being the deceleration.

This is the correction that is applied to the ordinary variometer to obtain the energy variometer. This can be done in an electronic way but amazingly it can also be done by mechanical pressure measurement.

Total energy and pressure measurements

When we look at pressure measurements that are used to calculate the airspeed, there is a striking similarity to the energy equation.

A pitot tube facing the incoming airflow measures total pressure which is the sum of static pressure $P_s$ and the dynamic pressure $q_c$

The dynamics pressure, which is the measure for airspeed, is given by

$P_t =P_s+q_c =P_s + \tfrac{1}{2}\rho V^2 $

Note that $q_c$ scales proportionally with kinetic energy. The static pressure changes with height but it decrease while potential energy increases.

When mounting the pitot tube backwards with the total pressure port facing backwards, the total pressure measurement would change to:

$P_t =P_s-q_c =P_s - \tfrac{1}{2}\rho V^2 $

When the aircraft trades kinetic energy for height, the speed drops so the term

$-\tfrac{1}{2}\rho V^2$ would increase in value (becomes less negative).

At the same time, the static pressure $P_s$ decreases with the same amount due to the climb. The result is that the total pressure measurement from this aft facing port remains unchanged when the total energy of the aircraft is constant. That is why an aft facing pitot port is called a Total Energy probe (TE probe).

The rate of change of the $P_t$ is a direct measure of the rate of change of total energy. So while an ordinary variometer measures rate of change of static pressure, the energy variometer measures rate of change of the total pressure of an aft facing pitot port.

To work best, a TE probe must be in undisturbed air. This is difficult as the probe itself is ahead of the pressure port so there is always some turbulence affecting the measurement. A common approach is to have the probe stick out in front the vertical stabilizer.

The pressure port is at the end of the tube, facing the vertical tail plane:


Could the Boeing 787-9 near vertical takeoff demonstration be performed by Airbus A350 aircraft? I am an aviation enthusiast. A couple of months back I came to know about the difference between piloting Boeing and Airbus planes here.

What are the main differences piloting Boeing vs. Airbus aircraft?

The very first comparison says this:

  Boeing trusts more the pilots: they can supersede the autopilots
  commands by exerting enough force on the controls

  Airbus trusts more the autopilot: if the system is fully functional it
  will always have priority over the pilots (but they still have room
  for "non-standard" maneuvers, e.g. commanding bank angles beteween 33°
  and 60°)

Also another answer stated this:

  Airbus aircraft limit pilots' capabilities in situations that require
  extreme action to be taken; the computer may prevent the pilot from
  pushing the plane past its safe ranges, which could be necessary in
  case of an emergency.

  Boeing aircraft leave ultimate control mostly to the pilot.

Now relating the above points with the recent near vertical take off by Boeing 787-9 in the Paris air show 2015:

Is this near vertical take off is an example that "Boeing aircraft leave ultimate control mostly to the pilot"? If Airbus aircraft trust the autopilot more, would they allow this type of takeoff as it is done by pilot by pushing the engines to extreme? Also, is it some kind of mockery by Boeing to Airbus?

For those who haven't yet watched the video, here is the link:

No.

Firstly, as a comment noted, the takeoff was hardly "near vertical", the camera angle makes it look so. The takeoff angle in the video certainly is much steeper than a normal one, but Airbus aircraft are more than capable of doing the same - in fact an A350 did very much the same thing at the Paris Air Show.

The notion that an Airbus doesn't let the pilots have complete control is a little bit misleading. I'm not going to go into too much detail in this question, but what most people are referring to when they say that is the Alpha Protection system. This system kicks in when the aircraft is at extreme angles of attack. For example, if an aircraft is about to stall, it will not let the pilot pull the nose up. In any plausible situation the pilot would not want to raise the nose anyway, yet we have seen accidents such as Colgan 3407 where the pilot did exactly that (and, also AF447, however the system was disabled in that crash).

In summary, the Airbus system pretty much only prevents pilot actions that are dangerous (OK it is more complex than that, and the Boeing design has benefits too, but..). Back to your question, why does the Airbus system also allow such a steep takeoff? Because only the attitude was high, but the angle of attack was still within normal limits. These takeoffs are possible on lightly loaded aircraft with engines near full power.


Why hasn't anyone tried making two propellers facing upwards and the other two facing downwards? Within a quadcopter, I know usually it's all the propellers facing upwards or all of them facing downwards. Why hasn't anyone tried making two propellers facing upwards and the other two facing downwards? Do some forces cancel out and renders that method ineffective?

People have done that.

And it works.

They do it because it's one of the logical configuration for a quadcopter based VTOL plane.

Example:


What kind of balloons are these? I came across the following picture on a news site, in a series of 'this day in...' type items.

The accompanying text reads (in Dutch)

  22 juni 1975 - In Geldrop werd de Internationale Holland Ballonwedstrijd gehouden. Deelnemers uit zeven landen streden daar om de Trophee du ballon libre.

Which translates to

  22 June 1975 - The International Holland Balloon competition was held in Geldrop. Contestants from seven countries competed for the Trophee du ballon libre.

To my surprise, the balloons are round and are closed at the bottom. What type of balloons are these? They don't seem to be hot air balloons, are they?

These are gas balloons. Instead of heating the air to reduce its density and providing the buoyancy, these balloons use helium or hydrogen which is lighter than air. Before lifting off, the balloons are kept on the ground by extra weight hanging on the basket. Usually these bags, clearly visible on the picture, are filled with sand.
During the flights, the gas will slowly dissipate through the fabric of the balloon reducing the buoyancy of the balloon. By throwing more weight overboard, again sand, the balloon can maintain in the air.
Gas balloons have less control in height than hot air balloons. The balloons are more expensive to operate because of the price of helium and to a lesser extent hydrogen.
Although gas ballooning is less popular then hot air ballooning, there are a number of gas balloons operating in Europe and the USA.

Once a year the Gordon Bennett race  is held in which teams compete to fly the longest distance in their gas balloon.

After some more research into the Trophee du ballon libre I found this Polygoon Journaal item of 1976 (in Dutch). It mentions that the balloon is kept afloat by 630 cubic meters hydrogen gas.


What are good ways to gain experience and flying hours? As a pilot who has just graduated, what are the ways to gain experience and flight hours?

The first thing airline look at is your flight hours, they usually require 1200 hours.

Is there any chance for a fresh graduated pilot to get hired in an airline with only 250 hours of flying?

I'm graduated in the Philippines.

There are a few ways to do it.

As has been mentioned many people here in the US are flight instructors (my instructor is building hours to go commercial eventually).

As has also been mentioned you could build hours taking trips with friends and splitting the cost but even split 3 or 4 ways this can get expensive fast.

You could do things like tow gliders or banners if they have that kind of advertising near you. It's not glorious and I can't imagine it's that fun as far as flying goes but it will build you hours.

I'm not sure how to get into flying planes for sky diving tours but that is another option to just build hours.

Again your hours may be an issue but you could look into ferrying planes for people. This can be tough if you don't have a lot of experience in different planes.

These are just a few things that come to mind. There may be varying laws in your area so its worth checking up on that before trying any of these things.


How much efficiency gain can be attributed to aircraft handling? Since the beginning of commercial jets, constructors thrived to make planes more fuel efficient. I assume most gains since then come from cleaner aerodynamic design, weight savings, and engine design.

However, these are not the only factors to take into account.
For example, we have also became better at predicting meteo, or transmitting live information about airstreams so that planes can spend more time in the most favorable zones.
Traffic control can also improve fuel efficiency by optimizing the landings of planes or reducing taxi/idle time.

How much of the gain in efficiency can be attributed to this factors ?

Another way to phrase it would be: How much more fuel efficient would it be to fly an old plane with modern avionics today?

In a paper written in 2010 several factors are laid out in addition to aircraft design that have improved fuel efficiency and cost over the years and possible improvements in the future. Several areas were highlighted.

Routing

Opening up more airspace by more efficient usage increases efficiency.

  It is estimated that up to 8% of all aviation fuel is wasted as a result of the inefficient routes aircraft have to fly.

The paper cites flight management systems on newer aircraft as contributing toward efficiencies in routing.

  On certain oceanic routes, flight control computers are automatically plotting their own, most efficient routings with some impressive results. One airline, for example, has been working with Australian air traffic management to save almost 10 million litres of jet fuel and 772 hours of f light time in five years. It does this by exploiting the jet streams and tailwinds in the Indian Ocean.

The following charts show projected savings for implementation of NextGen air traffic systems in the US and SESAR in Europe.

Continuous climb

Being able to climb continuously to cruise altitude can save on fuel.

  A number of airports and airlines are trialling the use of so-called ‘green departures’, allowing pilots to take-off and climb to the optimal cruising altitude in one smooth, continuous ascent. This is   in contrast to the traditional method of climbing to the cruising altitude in several steps. By using this new departure method at one airport alone, some 10,000 tonnes of fuel and 32,000 tonnes of carbon dioxide were saved in one year alone.

Continuous descent

Similarly to climbing, fuel can be saved by avoiding stepped approaches.

  In trials, fuel savings of up to 40% during the approach phase have been demonstrated. This equates to between   CDO [continuous descent operations] vs stepped approach 50 and 150kg of fuel depending on the level at which CDO is commenced and the aircraft type. Up to 150,000 tonnes of fuel a year, or 500,000 tonnes of CO2, could be saved in Europe alone if CDO approaches were more widely adopted.

Satellite based approaches and departures

Using RNAV procedures help expedite aircraft through the airport environment.

  Using satellite-based and on-board precision navigation systems such as “Area Navigation” and “Required Navigation Performance” capabilities allows ANSPs [Air Navigation Service Providers] to re-design airspace and procedures so aircraft can fly automatic fuel-saving routes into and out of the busiest airports in the world. These new departure routes have reduced departure delays of more than 2.5 minutes per flight at one airport since their introduction. Annual fuel savings are estimated at $34 million, with cumulative savings of 105 million from 2006 through 2008.

Ground handling

Fuel is saved by using single engine taxi or tugs where appropriate.

Another place more efficiency can be garnered is by installing ground electrical power to reduce APU usage.

  studies suggest that up to 85% of APU use can be reduced if groundbased electrical power systems are available, cutting the fuel bill, per gate, by $100,000 a year.

Reducing delays

Another costly problem is flight delays. Aircraft end up sitting on the ramp or taxiway burning fuel waiting for clearances.

  In the United States alone, the cost of burning fuel on the ground as a result of delays to the airline schedule amounted to over $5 billion in 2008 alone.

Conclusion

The following graph represents the potential fuel savings projected into the future broken down by technological improvements in aircraft design and fuels, operational issues such as ground handling and delays, and infrastructure such as airspace availability and routing. Of course any future projection is speculative.


How does engine primer work? Does anyone have good resources on how piston-engine primers work?
Looking for literature, schematics, or better yet, videos.
I was told that in carburetor engines, it bypasses the carburetor and goes straight into one of the cylinders, but the I was told it goes through a different path in the carburetor.
Thanks in advance!

It's just a syringe pump that draws gasoline from the fuel lines where they pass through the cabin.  The outlet of the primer pump runs though plumbing that becomes a network of very small (usually copper) lines snaking around the engine to one or more cylinders, where it terminates at each cylinder in a small nozzle threaded into the intake port just upstream of the intake valve. This plumbing network is completely separate from the fuel system under the cowling with the gascolator, hoses and carb.
I couldn't find any handy schematics online, so I made a silly sketch.  My own airplane runs primer to 3 cylinders like this.  You can prime all 4 or sometimes you see primer line only to one cylinder (airplanes that don't see much cold weather).

When you stroke the primer, it's like you're a doctor injecting something into your patient, except instead of an unfortunate person, you are pumping fuel into those lines running to the cylinders and spraying a mist of raw fuel into the intake port just up from the intake valve.  The fuel spreads around and settles on the walls of the intake port and duct, and starts to evaporate.
The evaporating fuel provides the additional fuel needed, beyond the carburetor's supply, to make the mixture rich enough for starting and to keep the engine running for a bit while it warms up, and works for a number of seconds after starting before the excess fuel has evaporated (by that time the engine is able to sustain itself on the carb's fuel - aircraft carbs normally run a richer than necessary mixture for the idle circuit, to help them run better when cold).  In non-aviation engines, a choke is used on the carb, but aviation practice traditionally avoids adding potential intake blocking gadgets like choke plates.
The more strokes you pump, the more fuel coats the intake passage.  When it's cold outside, you need more fuel to give a longer evaporation time so that the rich mixture lasts longer, so more strokes are required, although obviously, not too much or you flood it.
The caburetor has an accelerator pump that squirts extra fuel when you pump the throttle as well, but this is to help an already running engine cope with sudden power demands when the throttle is opened quickly.  You can pump the throttle to get extra fuel for starting, they way you used to do in ye olden tymes with carbureted cars, but too much fuel just dribbles down into the airbox when you do that and it creates a fire hazard, so it's not a good practice.
Fuel injected engines are primed in a similar way but they just use the injection system itself to spray fuel in when you turn the boost pump on with the mixture rich.  In those engines you don't stroke a pump, but just put the boost pump on, put the mixture to rich, count a couple of seconds, then pull it back to idle cutoff and hit the starter.


Is there a legal requirement to tell your doctor you are a pilot? Specifically if I visit a doctor in Canada who is not a CAME for my regular aviation medical, do I have to tell him/her that I have a pilot's licence?

You can imagine why I'm asking.  I just explained to someone that I'm supposed to mention this to any doctor I see.  However, it's been ages since I've flown and I would no longer do this as I haven't even kept my medical up to date.

I've just searched the CARS and can't find any reference to this being a law.  Is it possible I was told this by mistake, or as something that's just recommended?  I do recall doing this once or twice and the doctor didn't just pat me on the back and say "good for you".  He nodded and just acted like it was a normal thing to be told.

Not sure what tags are available, but I'm interested in answers from other countries as well.

In the US, you are not required to inform a doctor that you are a pilot. However, on the application for a medical certificate (Form 8500-8) you must list all "visits to health professionals" in the last three years, including type of professional and the reason for the visit.

The medical examiner uses that information to guide questions to ask about your medical history: a yearly checkup with your family doctor will not be remarked on, while a visit to a specialist might invite scrutiny about that area of your medical status. Depending on any existing conditions, you may need a letter from your primary doctor explaining your condition, but you would specifically ask for this rather than expect it to be provided.


Are there different sub-types of a mayday call and do pilots use them when declaring emergencies? I was reading this pilot's quote from the Northwest Airlines Flight 85 incident:

  "This was a classic application of CRM. We were blessed and lucky that
  we had full flight crew augmentation. We had four pilots to work
  together in the cockpit. We had an excellent group of flight
  attendants on board; that became important later because we briefed
  this as a ‘red’ emergency, which means there’s at least a solid chance
  you’re going to have to evacuate. We weren’t sure we were going to be
  able to keep the airplane on the runway."

I'm aware of the Mayday call but does it have sub-categories?  He refers to a "red emergency". Do pilots always classify their emergency into sub-types when they declare it?

Any explanations on what the various sub-types are and how they are classified?

The simple answer is no, there are no "subclassifications" of emergency or urgency calls in standard aviation phraseology. In terms of priority, they are all the same; however, in terms of actions taken, there can be differences based on what caused the aircraft in question to make the emergency or urgency call.

There's mayday (emergency), pan-pan (urgency), and everything else (routine traffic). Mayday trumps pan-pan, and pan-pan trumps everything else.

Broadly speaking:

mayday is used when the safety of the flight has been compromised and the pilot(s) require immediate assistance to recover.
pan-pan is used when the pilot(s) require assistance beyond that normally offered by air traffic control, or require priority handling, but the safety of the flight itself has not been compromised.

Compare When should the term “pan-pan” be used instead of “Mayday”? which discusses the difference between the two in more depth.

Yes, there is a bit of overlap between the two: it's possible to come up with situations where it is not entirely clear whether "mayday" or "pan-pan" is more appropriate. When in doubt, it becomes a judgement call. A pan-pan can escalate into a mayday as the situation develops, and even a mayday can be terminated if the situation that called for the original mayday call no longer exists. (The latter could, for example, happen if a GA VFR pilot becomes uncertain of their position, and are then able to identify their position in such a way that the flight can proceed safely; or if a non-instrument-rated pilot flies into IMC, and are able to return to VMC and proceed safely.)

The broad classification of emergency or urgency is then further specified by describing the type of emergency or urgency situation, using either standard phraseology or plain language, as appropriate. The purpose of this, however, isn't to prioritize such calls, but to identify to ATC (and other aircraft) what types of assistance is required.

Compare How does ATC handle different kinds of emergencies?, though that question is somewhat US-specific and specific details can vary between countries.

To mention a few examples, without in any way intending for this to be an exhaustive list:

mayday, VFR into IMC, negative instrument qualified — this one likely requires immediate help in returning to VMC, whatever that entails
mayday, decompression, emergency descent to ten-thousand — no immediate assistance required for that flight, but get everyone else out of their way now, then figure out how and where to get them onto the ground
pan-pan, fuel — this one needs landing priority, and may require vectors to the nearest suitable airport, but not much more than that
pan-pan, passenger ill — this most likely requires notifying someone on the ground so that the situation can be handled when they land, and might require this one flight to divert, but other than that, not a big problem from an ATC standpoint


Why would one want to slow to V2 following an engine failure during takeoff? Reading about the crash of American Airlines Flight 191, the proximate cause of the final loss of control was the pilots' reduction of the aircraft's airspeed to V2, in compliance with the published procedures for a single engine failure after V1 during takeoff in a DC-10-10; unbeknownst to the pilots, the damage caused when the #1 engine separated from the aircraft had caused the left wing's outboard slats to retract, decreasing the left wing's stall angle, with the result that decelerating to V2 required the aircraft to fly at an angle of attack at which the left wing stalled.

But why would one even want to slow to V2 in the first place?  Even if we, like McDonnell Douglas, ignore the possibility of an engine separating from the airplane and damaging it to the process, there are still good reasons to go faster, not slower:1

If an engine has failed, there's no way to immediately know whether it's a contained or an uncontained failure; if it's an uncontained failure (which is, unfortunately, a common enough occurrence to demand consideration when designing an aircraft), there's a very good (or bad) chance that the exploding engine (especially if it's a wing-mounted engine, like the DC-10's #1 engine) has damaged the aircraft's flight control systems, in which case you'll want to be flying as fast as possible in order to maximise the control authority of the surviving controls.
If there's a chance that whatever caused the first engine to fail could also take out the remaining engines (for instance, contaminated fuel or a flock of birds), you'll want to get as much speed reserve as possible, so that, if the remaining engines do fail, you'll be able to zoom-climb and reach your best-glide speed at the highest possible altitude, thus giving you the most time and space to do something.

What good reason could there possibly be for eroding your already-degraded safety margins yet further by slowing to V2 following an engine failure?

1Not that doing so was justifiable of their part (it wasn't, as the NTSB accident report makes clear).

Simply put, V2 is the speed that guarantees the best angle of climb on one engine. Any slower or faster increases the risk of hitting an obstacle.

Drag

There are 2 main categories of drag - induced drag, and parasite drag. Induced drag is an unavoidable consequence from lift and largely shows itself in the form of wake vorticies. Induced drag is largest at high angles of attack - i.e low speed.

Parasite drag includes drag from things like skin friction, rough surfaces, wires, and so on. Parasite drag is largest at high speed.

If you plot both categories of drag together, you end up with a chart like this:

The aircraft must provide enough thrust to overcome the total drag, so this can be renamed the thrust required curve. If you picture a horizontal line across the top of the graph, that would represent the thrust available for a jet engine. The speed which provides the biggest gap between thrust required and thrust available, or excess thrust, is the speed at which the aircraft climbs at the steepest angle.

But if you lose 50% of the thrust available, then that horizontal line moves down a lot. If you are going too fast, the total drag might be more than the available thrust, forcing the aircraft to descend.

That's why V2 exists, to give the pilots a guarantee that at that speed, there will still be enough excess thrust to climb at the steepest possible angle.

It's true, slowing to V2 doomed this flight. But uncontained engine failures, especially ones that damage the wing, are extremely rare, and more rare than that is a dual engine failure for whatever reason. The powers that be decided it is safer to give pilots the V2 target so they don't mess up in an already high-workload scenario and hit a tree.


Would a drone strike be more dangerous than a bird strike? Let's say you have a seagull and a drone of a comparable size.  Pretend either one was going to be ingested by large turbo fan engine, like the one found on a 737 (eg., the CFM-56)

Which would cause more damage and why?  I'm particularly interested in how the fan blades and compressor stages will be affected by the difference in materials.

There is a numerical study on the topic at VirginiaTech, where they simulated a 5kg drone being ingested by a turbofan, some pictures related to the study below:

On the same  Aerospace America Article it can be read that:

FAA will begin testing of drone ingestion next year
The metric for danger is the density of the material, so metallic parts are more critical than the bird bones/tissues. Modern drones have more aluminum parts, but the most critical component of a Drone ingestion would be the batteries.

Comparing different sizes, a commercial quad copter is around 1.4kg, while the most frequent bird impact (from FAA database) is around 1.8kg.

This is not the worst case scenario since larger drones are commercially available, and a goose, which can weight up to 6kg.


Does a quadcopter have flight modes beyond traditional aircraft? Quadcopters, by virtue of software-piloting rather than human-piloting, are capable of new modes of flight. I've seen one in which the machine maintains altitude despite the loss of two rotors by spinning (yaw).

I wonder about a different mode, though; if a quadcopter could maintain a very high degree of pitch, then the flight is closer to a very short 4-engine X-wing aeroplane. This would be the advantage of a tiltrotor; after takeoff, rotate into the near-vertical position and permit much higher rates as we are no longer limited by usual helicopter dissymetry of lift arguments.

Is this possible? Are there other modes beyond the capacities of traditional aircraft? E.g. yaw spinning in the forward pitch position, coast-and-burn by varying the pitch periodically to switch between gaining altitude and gaining forward momentum, etc.

As DeltaLima noted, pretty much all flight modes of a quadcopter are "non-traditional" -- they're a relatively new aircraft design.

Most quadcopter designs lack anything resembling "wings", so they can't "fly" in an "X-Wing" orientation (with the rotors producing entirely lateral thrust) -- at least not as we traditionally define flight.

They can, as you surmised, do a climb-and-run maneuver in that orientation: Gain a lot of altitude by using vertical thrust, tilt the platform near-90-degrees in the direction you want to travel (so your thrust is pretty much lateral), and accelerate in that direction while rapidly losing altitude.

I've no idea if this is more or less efficient than the usual slight tilt they fly with, but it's certainly less stable since you're in vertical free-fall and would need to redirect thrust to be vertical again with enough time/altitude to arrest the descent before an ungraceful impact with the ground.

  X-Wings work so well because the microgravity environment of deep space isn't trying to drag you back to an impact with the ground - it wouldn't work well deep in a planet's gravity well, which is where most of our aircraft operate.
  Of course if you had access to a microgravity environment with an atmosphere you could configure a quadcopter to fly like an X-Wing fighter…

The quadcopter's thrust configuration does open up the option for some interesting maneuvers though.

It's theoretically possible to "flip" a quadcopter (around at least 8 axes) if you have sufficient altitude (especially if the rotors can be reversed in flight to assist in the maneuvers).

It's also possible to "rock the wings" (really rocking the whole platform) in many directions by alternating thrust on pairs of rotors.


what is the use and the locations of nacelle hinge bracket? i have seen on the webs about the additive manufacturing about this bracket here but I have no clues on where is it located and whats the purpose of it. Do give me any links if there are actually any if possible.

I'm assuming that you're talking about the part below. The part was changed from cast steel to titanium DMLS additive manufacturing technology.

Image from belement.co.il

The hinge is used to hold the engine nacelle cowling when opened. YOu can see four of them (older versions) on top of the open cowing in the image below:

Image from article.wn.com


How to calculate the variation of Z force with elevator deflection (Zδe) in Nelson for pitching dynamics? I have been trying to model the pitching dynamics of a General Aircraft (Nelson, "Flight Stability and Control").  I need to use the Zδe which uses CZδe parameter in the control matrix B, but Nelson provides no method to find it.  The state space equations are:

]2

There are a couple ways you can estimate control derivatives ($C_{L_{\delta e}}$ is a control derivative). You can then transform the coefficient from stability-axis to body-axis for use in the state space equations of motion.

Elevator is basically a full-span or part-span plain flap. Knowing that, you have several tools at your disposal:

USAF DATCOM: It contains semi-analytical equations to estimate 2D flap lift increment, and corrections to 3D with aspect ratio and taper ratio. Not the easiest to read resource, but it is free and forms the backbone of many conceptual design software and books.
ESDU: Items 70011 and 74011 contains semi-empirical relationships for estimating full-span 3D flap control derivative. ESDU contains step-by-step examples and is the authoritative source for all things aerospace in conceptual design and validation. Unfortunately, it isn't free.

Before going further, I should mention that tail experiences downwash from the wing. So converting from the tail stability-axis to aircraft body-axis requires converting the total tail incidence angle ($\alpha_t = \alpha+i_t-\epsilon$). Of course, you'll need to find downwash itself, which would be the topic of another question.

Vortex-Lattice Method: AVL is a reliable and free VLM, and is the go-to tool for conceptual low subsonic aerodynamics. Good thing about it is you don't necessarily need to estimate downwash; it directly outputs the control derivatives in aircraft stability-axis.

For conventional layout, all three tools should give you similar answers. Otherwise, you may not know the true value until you have access to wind-tunnel.


Why don't the ATR 42's propellers start/stop rotating simultaneously? Why is it that for the ATR 42 one of the propellers begins to rotate before of the other?

I've noticed that they also stop rotating at different times. Is there a reason for that or is it just for turning left or right?

Pilot only starts one engine at a time so the battery doesn't have to spin up both at once. At turnoff, one stop button is pressed before the other.


Dangers to the Engine if CHT goes below minimum in flight during descent? What are the dangers of CHT going below minimum in flight during descent since the power setting will be around 10inches in a power descent?

To my knowledge, the problem with running low CHT is mainly related to incomplete combustion, leading possibly to fouling of spark plugs and buildup of carbon and lead (if present in fuel) deposits in combustion chamber. How severe this actually is, I have not studied the subject any further, or looked inside an engine during such a condition ;)
However, from experience I can tell that after a prolonged descent, running the engine cool, the engine usually has some "difficulty" picking up the pace as the descent is stopped and power increased. Some sputtering and hesitation are present sometimes, but after a while the situation is normalized. During training, such descents were advised against, and I would say for a reason.
In extreme cases very low CHT might lead to stalling the engine, as it can no longer support combustion due to lack of heat and possibly the fouled spark plugs I mentioned earlier.


Why are commercial propeller aircraft smaller than commercial jet aircraft? I've read that turbo-prop aircraft are more efficient than jet-aircraft. Browsing this Wikipedia page it looks like in general, jet airliners burn less fuel per passenger. I imagine this is due to jet aircraft typically carrying more people, and flying longer in cruise. Is there some fundamental reason why traditional propeller designs couldn't be scaled up to 150+ passengers and trans-oceanic ranges? If it was possible, would air travel become substantially more efficient per passenger?

Edit: Perhaps a better phrased question would be: are turboprop aircraft always more efficient, regardless of airframe size? Or is there some regime where modern turbofans take over? I'm specifically asking about fuel efficiency (i.e. ignoring noise / speed).

There are a number of problems:

Speed

Traditional Propeller aircraft are much slower than jets. Propellers decline in efficiency as they increase in speed.

Noise

For the same thrust, propellers are noisier then jets.

Development Cost

There have been efforts for propellers but so far they have not been justified by economics.

GE36 Engine


Why was the DC-8-70 successful, but not the 707-700? The first high-bypass turbofan small enough to use on a narrowbody jetliner was the GE/SNECMA CFM56, which entered service in the late 1970s as an upgrade engine for the KC-135 tanker; Boeing almost immediately began working on a CFM56-powered 707 (the 707 and KC-135 are very close siblings), the 707-700, with a prototype flying in 1979.  Boeing offered the 707-700 for sale in 1979 and 1980 (the last 707 version in their product catalog), but got not a single order, and the prototype 707-700 was eventually converted back to a 707-320C and fobbed off on the Moroccan Air Force.

In contrast, when a CFM56-powered version of the DC-8 became available in 1982 (the DC-8-70), the airlines jumped in with both feet, even though the DC-8 had been out of production for a decade (unlike the 707, which was produced all the way up until 1979, and would have lasted longer still had the 707-700 caught on), and would thus be, except for the engines, years behind where the 707-700 would have been.

Why did the CFM56 fare so much better on the DC-8 than on the 707?

I think there is a bit of a misconception in your question.

The DC-8 was already out of production by the time the CFM56 was developed, so all of the DC-8 70 series are actually just retrofits of the 60 series aircraft already in use. So it’s really not correct to say “a CFM56-powered version of the DC-8 became available in 1982.” More like a CFM56 retrofit option for existing DC-8 60 series became available. They did not return to producing the DC-8. On the other hand, although the last civilian 707's were made in 1976, before the CFM56 was available, Boeing did manufacture new military versions of the 707 with CFM56 engines from 1986 to 1991.

As for why the civilian 707-700 was not pursued, the main reason is stated in the Wikipedia page:

  Boeing abandoned the retrofit program, since it felt it would be a
  threat to the Boeing 757 program.

The 757 and 767 programs were already in the works when the CFM56 became available.
The 707-700 was really more of a test program for retrofitting the fleet of military 707 aircraft with the new engines. They didn't pursue a retrofit for the civilian fleet of 707's so they could sell more of the new 757 narrow body aircraft.

If you consider how many DC-8's were upgraded to 70 series (110) vs the number of KC-135’s retrofitted (500) plus 39 more new CFM56 equipped 707 variants, then the new HBP engine was much more successful on the 707.


Efficiency of the Kuznetsov NK-88 or NK-89 engine burning hydrogen It's tough to find data about turbofan efficiency running on hydrogen.
The Tupolev Tu-155 has been used as a test bed for exotic fuels right before the fall of the soviet union, without much follow-up.
Is there any spec available on these engines? (like:)

Rated power
How much hydrogen used per second
Durability
Thermal efficiency

Matthieu Thomas of Airbus wrote an article stating an hydrogen turbofan could be more efficient than current kerosene ones because of:

Wide flammability range of hydrogen
High auto-ignition temperature

But as the piece is oriented pro-hydrogen, the author is probably not willing to admit any performance-wise downside of hydrogen when used in a turbofan. So a subsidiary question would be: Is there any foreseeable decrease of turbofan performance when switching to hydrogen?

Based on my reading, the biggest disadvantage of hydrogen as an engine fuel is its low density.  Even when stored as a cryogenic liquid, it take up more than ten times the space as the same mass of kerosene, which means the same size tanks will hold only about a third as much energy (even though hydrogen has about three times the energy content per kilogram as kerosene).
Given these qualities, an engine suitably redesigned to burn hydrogen ought to be able to run more efficiently in terms of specific power output (energy produced per mass of fuel) or specific fuel consumption (same thing only upside down -- fuel consumed per energy produced), but even ignoring the weight of insulation and the fuel cost of boil-off in flight (or before takeoff), an aircraft the same size would have roundly a third of the range.  This is usually taken to mean that hydrogen fueled aircraft would have the same issues as hydrogen fueled rockets: they have to be very large to carry an economically useful amount of fuel.
There are other methods of storing hydrogen (developed for automobile prototypes); as I recall, the highest density of storage (kilograms of usable hydrogen per volume) has been with metal hydrides; these require neither very high or very low temperatures, and operate at reasonable pressures (rather than hundreds of atmospheres as common pressure bottles do) -- but they barely exceed the density of liquid hydrogen, and there's a penalty in the weight of an "empty" tank, which is still filled with a solid material when no more hydrogen can be drawn from it.
Beyond qustions of range, hydrogen is difficult to work with in terms of materials (it causes most metals to become brittle just from being in contact with hydrogen), it leaks through almost everything, and is so flammable that these unavoidable leaks are very prone to become invisible conflagrations (because a hydrogen fire contains nothing that glows from heat, the flame is practically invisible -- the bright flames of the Hindenburg were due to the envelope and its coating, not the hydrogen).  This is obviously irrelevant to engine efficiency, but very relevant to whether such an engine can last long enough in service to be economical to operate.


Why does "no aircraft cross directly over the pole"? This is from the last paragraph here:

  ... no aircraft crosses directly over the pole – the closest route is
  60 nautical miles (nm) away.

User Michael Shen of York University asked this originally under the article.

This article from AA (titled "Over the Top" by Gerard J. Arpey) says,

  By the way, because of the limitations of older navigation systems, none of the polar routes we fly crosses exactly over the North Pole. At the Pole, an airplane’s compass changes from a due-north heading to due south, and that change of course could potentially lead to problems with earlier-generation autopilot systems. Fortunately, that is not an issue with the latest generation of long-haul aircraft, such as the Boeing 777s we fly, whose source of navigation is the extremely precise Global Positioning System (GPS). Nonetheless, to make polar flying equally effortless for both the new generation and the previous generations of aircraft, none of the approved civil polar routes comes closer than about 60 nautical miles from the Pole.


When to turn from crosswind to downwind to base in a circuit? I was told by my instructor that my circuit spacing is inconsistent. I do not know how to look at the runway and use it to judge when to turn downwind and base. As a result, my base leg is sometime high and sometime low.

How do you determine when to turn at different leg in a circuit?

Like almost everything (aviation or otherwise), this is just something you learn with practice!

I was taught to turn downwind to base when the threshold was between 4 & 5 o'clock (in a RH circuit).

Here's a good graphical representation in a LH circuit.

]

  At the end of your downwind leg, when you once again reach a 45° angle to the runway, do a medium 30° turn onto base.

(Image & Text source: http://www.ppl-flight-training.com/circuits-briefing.html)

As for the base leg being high or low - it shouldn't be a problem. You can easily correct this.

Too high:reduce power 50-100rpm, lower the nose slightly to maintain speed
Too low: Increase the power slightly.

As was commented, it is also worth considering the wind direction before you depart. On a perfect day, the wind will be directly down the runway towards you on final. Consider the effect of this on your circuit? I find it useful to draw the circuit, and an arrow with the wind direction. Then consider when to turn early/late as appropriate.

Finally remember the GOLDEN rule: You can ALWAYS go around. (Assuming you have a fan up front!)


Would a wingtip stall still be bad if there was no aileron there? If there was no aileron on the wing tip, would a tip stall still be bad compared to a root stall?

Short answer: yes.
Control effectiveness: We do care about ailerons
The fact that there is an aileron at the wingtip implies that flow separation (stall) at the wingtip results in significant decrease or complete loss of aileron effectiveness during a tip stall.  As a result, as you imply by your question, designing aircraft to begin their stall at the wing root (or, otherwise, to implement some device such that control effectiveness is maintained at high angles of attack) is a typical practice.  Peter Kämpf has a very detailed answer about this (and other topics related to stalls in swept-wing aircraft) here, and there's another answer from AEhere Supports Monica and another one JohnK that gives a summary as well.
But what if the aileron wasn't there?
However, if the aileron did not exist, loss of lift (and increase in drag) at the wingtips is still of great concern.  Insofar as the stall itself goes, when I think of the dangers of losing lift at my wingtips, I think of spins, which look like the below.  This "classic" spin entry is caused by a sideslip (in this case, to the left wing) with the stick pulling back to put the aircraft into a stall.  In this case, the left wing is operating at a higher angle of attack than the right and stalls first, creating the conditions for a spin.

When I did spin training in a Grob 103 sailplane (with your typical control setup of elevators, rudder, and ailerons), the mantra was put the stick neutral, push the rudder opposite the spin, then recover in pitch.  The ailerons were not a part of the recovery (until, perhaps the very very end once the airplane has started flying again and you find yourself not quite level).  This is not the case for all stalls: forward stalls (stalls with near-zero sideslip and coordinated controls) are relatively simple to recover from, and I've held Grob 103s in a forward stall for extended periods of time (though they also have pretty benign stall characteristics).
Turning stalls or stalls in uncoordinated flight are where you get get in trouble with spins, and the more your airplane wants to stall at the wingtip first, the more dramatic (and interesting) will be the aircraft's departure from controlled flight.  This is, in part, because of the yawing and rolling moment caused by the lift and drag differentials between wings -- and, if those differentials are between wingtips, the moment arm for those forces is that much more.  Note: you are not usually using ailerons during this maneuver--in fact, if ailerons are deflected counter to the direction of the spin (per intuition), it can make the spin worse.  That said, Peter Kämpf pointed out that using the ailerons to point the aircraft in the direction of the spin can make it easier to recover from.
However, more to the point: regardless of if ailerons are present or not, rolling an airplane usually produces a restoring roll moment.  As I move a wing upward, per the diagram below, the wing "sees" air coming from above the wing, which decreases the angle of attack (relative wind coming from above the chord line is a negative angle of attack).  The converse occurs for a wing that is descending.  A negative angle of attack corresponds to a decreasing lift coefficient and vice versa: hence, the lift of the wing with change with the wing's motion and, in some way, "damp" the wing's heaving motion.

However, keep in mind that we are talking about something a little more nuanced.
If we go back to the picture of an airplane entering a spin (above--1st picture), the right wing is close to stall and is operating at a very high angle of attack and a relatively large lift coefficient.  The left wing is stalled (operating at an even higher angle of attack than the right wing): it's lift coefficient is much lower than that of the right wing: the airplane wants to roll.  However, if we reference the chart of angle of attack vs. lift coefficient below (stall is denoted by the first peak of lift coefficient around 10 or 12 degrees angle of attack), the stalled wing is operating "post-stall" or, potentially, somewhere in the 15-20 degree range where an increase in angle of of attack no longer corresponds to an increase in lift coefficient--but, rather, a decrease.  Even if the stalled wing if past this range, the lift coefficient increases relatively slowly, and drag increases much faster, slowing the wing down and rapidly decreasing the wing's lift production (lift is directly proportional to the lift coefficient, but changes with the square of velocity).

In short, the aircraft already wants to roll towards the stalled wing and the lift coefficient of the stalled wing is, potentially, decreasing as the wing drops (which increases the local angle of attack).  Now, the opposite wing is moving upward and, as such, its angle of attack is decreasing and it's lift coefficient (which is already higher than the stalled wing) is also decreasing.  However, drag is also decreasing as well, so the wing can travel a little faster - and, thus, produce even more lift.  If the lift production of the stalled wing remains less than that of the other wing, the aircraft will continue to roll.  Which, as you might imagine, is a $Bad \hspace{1ex}Day^{TM}$ (unless you can get both wings flying again).
Peter does mention some issues with tip stalls in the answer I linked earlier as well, specifically in swept-wing aircraft.  In swept-wing designs, lack of aerodynamic or geometric washout resulted in substantial nose-up moments at stall (when the wingtips stalled first) due to the physical geometry of the aircraft.  The tip of the wing, which was no longer producing significant amounts of lift, is probably located behind the aircraft's center of gravity.  As a result, loss of lift at that location would decrease the nose-down moment generated by the wings, which is exactly the opposite of what you want to be produced when in a stall.  A stall at the root would obviate this.  In short, how bad the results of a wingtip stall will be are tied to the design of the aircraft -- and swept wings, in most cases, are a design choice tied to lateral stability or design for high speed flight.  A design choice for one characteristic influences others.
But what if we didn't use ailerons at all?
The most complete answer would speak to how tailerons or elevons (or a horizontal tail whose surfaces can be actuated independently of each other) change spin recovery technique.  For example, I was reading this document on F/A-18C/D spin recovery technique, and it notes that proper spin recovery in the F/A-18 is accomplished by a lateral stick movement.  The Hornet, apparently (can't say I've flown one, but I know there are folks on here who have), has a very violent stall/spin departure mode in which the stick should be kept neutral, but, once the spin is established, the stick is moved laterally to recover.  Examples I've seen go into the direction of the spin, which would match with the prior note about turning into the spin with ailerons.  I anticipate that this leverages the sheer size of those horizontal surfaces and that they have some degree of effectiveness (as opposed to the rudders, whose effectiveness may be reduced due to the wake from the other vertical tail).
Regardless, with reference to the question of "would a tip stall be bad if I was using tailerons anyway", the earlier points about how the severity of the stall is tied to aircraft design still stand.  How bad it is depends on the design of the aircraft, how the CG is located relative to the wing, how pitching moments are produced and balanced in the aircraft's design, and so on -- all factors that are not necessarily tied to the selection of roll control surface.


What is the non-projected cross-hair for on the F-18 HUD? Top right, there's a little cross-hair - it looks like it's for lining something up, since on the second pane there's a little dot.

I haven't seen this on any other HUDs. Appears to be present on all variants including Super Hornet.

source

simulated - source

It is a "Standby Reticle":

  A fixed standby reticle (Figure 7–151) is available in the upper right side of the HUD for use in performing visual designations in the event of a HUD failure. The reticle is fixed at a 15-mil depression angle from the gun boresight. If the HUD fails, the HUD symbology is available by selecting HUD via the menu on the left or right DDI [Digital Display Indicator]. To perform a HUD designation in the NAV or A/G [Air/Ground] mode when the HUD is inoperative, the pilot first places TDC [Target Designator Control] priority to the HUD (either by placing the sensor switch to the normal HUD position, or to the left or right DDI displaying the HUD symbology). The mission computer slaves the radar in AGR mode to the LOS [line of sight] of the HUD standby reticle. The pilot maneuvers the aircraft to position the standby reticle over the aim point and actuates the TDC to perform the designation. The aim point position at the LOS of the standby reticle is computed. The pilot may use the HUD display on the left or right DDI to null the steering error when automatic weapon delivery is being conducted.

Source: ED Forums

The standby reticle is used when the HUD fails for designating targets. The pilot must lean to the right and line up the cross-hairs with the dot so that the bore-sight is accurate.