Does Smeaton's coefficient have a modern accepted value or it is dependent of the air density? Does Smeaton's coefficient, k, have a modern value or it is
dependent of the air density?
Why is the accepted value of k so high?

In various texts about the Wright brothers (see 1 and 2) one can read about Smeaton's coefficient that troubled them a lot and that they finally discovered the parameter had a much lower value reaching the conclusion $k = 0.0033 lbf/ft^2/mph^2 = 0.79 kg/m^3$ (instead of $k = 0.005$), a fact also noticed by others before them.

"the Wright brothers calculated a new average value of 0.0033.
Modern aerodynamicists have confirmed this figure to be accurate
within a few percent." Source: Correcting Smeaton's
Coefficient
$L = k \cdot  S \cdot V^2 \cdot C_L$

$L$ = lift in pounds

$k$ = coefficient of air pressure (Smeaton coefficient)

$S$ = total area of lifting surface in square feet

$V$ = velocity (headwind plus ground speed) in miles per hour

$C_L$ = coefficient of lift (varies with wing shape)"

Source: The Wiki page of the Wright brothers

However, knowing that the modern formula for lift is
$$L = 0.5 \cdot \rho \cdot S \cdot V^2 \cdot C_L$$
Where $\rho$ = the air density.

It appears that $k = 0.5 \cdot \rho$ and so it does not have a standard average value. Also a $k = 0.0033 lbf/ft^2/mph^2 = 0.79 kg/m^3$ leads to a $\rho = k/0.5 = 1.58 kg/m^3$ that corresponds to a sea level air temperature well below -25 C, which is unusual.

If the two relations for lift are correct, the Smeaton's coefficient can not be 0.0033 but closer to 0.0025 a value corresponding to a standard air density at $20 ^\circ C$ close to $1.2 kg/m^3$.

There is no modern equivalent to the Smeaton coefficient, therefore it has no "modern" value.

The Smeaton coefficient is supposed to represent a "coefficient of air pressure" (and thus indirectly density), but it is a false constant: There is no single value because air pressure is not a constant value, but rather a variable (depending on altitude, temperature, etc.).

As you noted lift is calculated by a different formula today, using actual density of the fluid (air) you're moving through in place of the Smeaton coefficient.

$ L = Cl \cdot \frac{(A \cdot \rho)}{2} \cdot V^2$

You can calculate the Smeaton coefficient at any given location/altitude with simple algebra if you know the air density: Solve the modern lift equation, plug the values into the "old" Wright Brothers era equation, and solve for $k$.

The density-based calculation also has the benefit of working in other fluids besides air. (The same equation can give you hydrodynamic lift for boats and submarines by plugging in the density of water - itself a dynamic value depending on temperature, salinity, etc.)


Do pilots land a helicopter sideways for improved visibility of the landing area? When flying helicopters in the PC-based game Arma 3 (not a flight simulator), some of the cockpit have a large instrument panel directly in front of the pilot, obscuring the view of the ground ahead when flying low. However, the cockpit has excellent visibility to the sides.

One of the technique to achieve a precise landing is to land not forward, but sideways. For example, let's assume the pilot is seated on the right, and the helicopter is heading North and approaching a landing target from the South. When the helicopter is approximately 50 feet from the landing target, the pilot swings the helicopter to the left by applying left pedal, pointing the nose to West while keeping the helicopter travelling North. The pilot then completes the landing by looking to the right.

Is this technique valid in real world helicopters?

No.  Often helos use windows on the floor of the cockpit near the anti torque pedals, which allow a pilot to look directly down at the landing area, as this example of a EC130 shows.

Helicopter pilots seldom land at a sideways angle, save for landing on slopes terrain or a situation required to fit the helicopter into a space.


What's inside the packs? (Airbus a320) I have some questions about ATA 21, how packs works?... I mean, what's inside them?, what are their mechanims? And How the warm air becomes into cold air?. (On a airbus A320)

I'm starting my major at aeronatics and i don't have any idea about ATAs.
I couldn´t find clear information about it on my lenguage, But found this forum and i hope that somebody can help me.

Thanks.

Here's an answer for the B737, from own work compiled from several public sources. The A320 and other airliners are very similar.

The air conditioning packs are Air Cycle Machines (ACM) which remove heat from air through a reverse Brayton cycle. Hot compressed air is cooled and then expanded, which drops the outflow temperature to a temperature cold enough to provide cooling in hot environmental conditions.

The ACMs in the Boeing 737 are 3-wheel units consisting of a compressor, two heat exchangers, a turbine and an impeller fan. Bleed air is cooled in the primary heat exchanger, enters the ACM, is compressed further and cooled again in the secondary heat exchanger. The ACM compressor’s further temperature rise allows for more efficient cooling by the heat exchangers.

Cooling air for the heat exchanger is provided by ram air, via inlets underneath the fuselage, in front of the body/wing intersection. Water is extracted from the cool air, and sprayed into the ram air stream for more efficient cooling via the heat exchangers.

The impeller fan creates cooling air flow when airspeed is low. The impeller fan speed can be controlled independently from the ACM turbine/compressor axis, by the Turbofan Control Valve.


How is cloud height measured? In general, cloud height is measured from ground or AMSL (above mean sea level)?

If they measure from AMSL, how are low level clouds' height measured in higher terrain?

Cloud ceiling is measured from ground:

  height of the base of the lowest clouds ... that cover more than half
  of the sky ... relative to the ground

Cloud base is measured from sea level:

  ... the lowest altitude of the visible portion of the cloud. It is
  traditionally expressed either in m or feet above mean sea level


What is the story of this aircraft? From this page about nuclear bombers:

It seems out of Wild Wild West. What is this (Russian?) aircraft from another era? and what has been its use?

Update:We know now the image has been created using CG software, based on a real aircraft, that seems interesting and is by itself quite a mystery and technical feat that deserve explanations.
Why this design? gondolas, size, holes in wings, angular panels...? for apparently not so many people on-board.
Images of actual aircraft are found in answers. Also this one:

Source.
Thanks to @user52723a and @RonBeyer for providing details.

It is in fact fake but its most likely loosely based on a real plane. The Russian Kalinin K-7 contains a lot of the same design elements.

(source)

It appears that the real plane was also boarded from the landing gear area.

(source)

On a bit of a funny note this article mis-uses the photo you have linked in reference to the Kalinin K-7


How to calculate the Gust Envelope? I am trying to draw the V-n Diagram for a small aircraft I built, but I am stuck in the gust envelope part. I know how it is supposed to look. However, I am having a hard time calculating it. I would like to know (1) why it's composed of four lines; and (2) how to find the slope of each line. So far, I have these three equations:

Also, (3) why do these equations describe the gust envelope, and (4) what each variable in the equations stands for?

The gust envelope is four lines overlaid on the flight envelope, usually the plus/minus of maximum gust at design cruising speed (Vc) and half maximum gust at maximum speed (Vd) as required by the certifying authority. This is usually +-50ft/sec (15.2m/sec) and +-25ft/sec (7.6m/sec).

n is the normal acceleration in a sharp edged gust
K is the tailplane gust alleviation factor. In a canard this is an aggravation factor.
u is the airplane mass ratio

The source contains examples of how the lines are calculated. The following information (defined) is required:


Why does Thrust Reverser need to be operative during the cargo door operation? It is stated that when the Electric Pump push button is depressed, the electric pump is automatically running as long as the cargo door selector valve is set to either OPEN or CLOSE position.

During this period, the operation of other systems powered by the Yellow Hydraulic system is inhibited except Alternate Brake and Thrust Reverser of ENG #2.

The Alternate Braking is understandably essential as it stops aircraft from moving, and cargo door operation is considered that aircraft is in parking, not landing phase when the thrust reversers are only being used.

My question here is why thrust reverser ENG#2 needs to be operative during cargo door operation.

Thanks for your answers.

(Source: Training Manual A320 Family)

“It is stated that when the Electric Pump push button is depressed, the electric pump is automatically running as long as the cargo door selector valve is set to either OPEN or CLOSE position”

This is not correct. Cargo door operation will automatically energize the Elec Pump while it is in the OFF position. (not depressed)

“My question here is why thrust reverser ENG#2 needs to be operative during cargo door operation”

It doesn’t need to be operative. It needs to be Not Inhibited,  in case there is a malfunction.

The cargo door uses the Yellow system. It is designed to be used on the ground even with the Electric Pump in the OFF position. The pump will come on automatically in this case to supply hydraulic power to the cargo door. It will inhibit all the  other items on the yellow system to insure adequate hydraulic power to the cargo door.

BUT......If there was a malfunction in the Cargo Door system while in flight, it could possibly cause the Yellow Elec Pump to engergize while it is in the OFF position. If that were to happen, it is designed to inhibit all items on the Yellow system. That would be bad, so they designed the switch to inhibit everything except Alt Brakes and #2 Reverse.

This situation could only happen if the Yellow Elec Pump was automatically commanded ON while in the OFF position.


What are the rules in the UK about attaching a GoPro camera to the outside of an aircraft? Is it fully legal to have a GoPro attached to the outside of the aircraft during flight, in the UK? I've heard mixed answers, but I don't want to try it until I've got confirmation.

Flyer magazine had an article on this recently. I've not been able to find the full article on their website, but I have found this which at least partially answers your question.

https://www.flyer.co.uk/gopro-camera-mounts-to-be-approved-by-engineer/

From the article, which was published in Feb 2016:

Mounting a camera is a modification, and requires either inspection from a Part66 licensed aircraft engineer, or via the CAA as a minor modification.
To approve any installation the engineer will need to complete a maintenance release checklist and complete the aircraft logbook entry.
If your aircraft is overseen by the British Microlight Aircraft Association or Light Aircraft Association, then their restrictions apply (but it doesn't say what those are).

It also references CAP1369, which is the CAA document covering mounted cameras. I'm including a link to that here.

CAA CAP1369


In a spin, are both wings stalled? I missed a test question which asked that if an airplane was spinning to the left which wing was stalled.  The supposed correct answer was that both wings are stalled (I had answered that the left wing only was stalled).  However after looking at the this article on Wikipedia it seems to indicate that only one wing needs to be stalled to spin:

In a normal spin, the wing on the inside of the turn stalls while the outside wing remains flying. It is possible for both wings to stall, but the angle of attack of each wing, and consequently its lift and drag, are different. Either situation causes the aircraft to autorotate toward the stalled wing due to its higher drag and loss of lift.

So my question is was it fair for me to have missed that test question since according to Wikipedia a spin can occur with only one wing stalled?

Yes, both are stalled.

I guess a nit-pick is on "what is stalled"? I adopt that you are at or beyond the point that an increase in AOA results in an increase in lift (critical AOA). That's the top of the blue curve in the plot below.

Also, a stalled wing does not mean every point on the wing has unattached flow. It means the wing is operating at an AOA where an increase in AOA results in a decrease in lift.

At low angles of attack (AOA) planes are naturally stable in roll. The downgoing wing sees a higher AOA which results in more lift, and a restoring force. The upgoing wings sees a lower AOA, and less lift, so it is stabilizing too.

At a high AOA, though, you are operating on the backside of the wing lift diagram. In the picture below, this would be at and beyond 20 degrees AOA.

Now, the upgoing wing sees more lift, which leads to positively reinforcing going up. Same but opposite on the downgoing. It sees less lift.

Also, the red line shows drag. That downgoing wing (on inside of the spin) sees a great increase in drag, which will lead to a yaw towards that wing, i.e., pro-spin.

So to get in the situation where a roll/yaw movement is positively reinforcing, you need to be in stalled AOA. You might start with just one wing, you'll get to both.

JMHO!

EDIT

Here’s a NASA video of a wing with tufts when it is both on the inside of the spin and outside. Stalled in both (but different airflow).


How are go-arounds safe with close parallel runways? Some airports operate simultaneous take off and landing on parallel but close runways. By close, I mean like the pairs of runways at LAX.

What if a landing aircraft makes a go-around at the same time as another aircraft takes off? How is separation maintained? Would it be enough for the missed approach procedure to specify turning away from the departure runway?

The first thing I would point out is that LAX isn't going to be running simultaneous approaches on 24L and 24R or 25L and 25R. They'll select one of each of the parallel sets for the landing runways (typically the outer runways), and one of each for departing runways (typically the inner runways). For example, they might be landing on 25L and 24R and departing 25R and 24L. So, there's quite a bit of distance between those runways, and very little risk in a go around situation.

Here's a diagram illustrating LAX's typical arrival/departure runway usage to make it more visually apparent what I mean:

The second part of your question about an aircraft taking off at the same time as a go-around certainly happens, and when it does, ATC needs to take action to ensure safety and separation. ATC separation requirements can be satisfied by altitude, distance, or divergence (and, in some cases, visual contact). In the situation you described, divergence is the quickest and safest way to achieve separation. I believe the requirement is 30°, so tower would typically order a go-around and order a new heading at least 30° off of runway heading. The geography of the area, layout of the airspace, and the approach patterns would likely dictate the exact procedure used at each airport since their two primary goals, in order, are going to be 1. safety, and 2. getting them back in the approach sequence.

In the LAX example, a go-around on 24R would most likely get a right turn, and 25L would most likely get  left turn (away from the airport) so as not to conflict with other departing or arriving traffic. This is one of a few reasons the outer runways are preferred for landing.


Why this P-51 limitations placard for diving? I noticed that this placard has different diving speeds related to altitud. My guess is that those values are a safety speed to prevent going into regions close to Mach 1. I know that the speed of sound is related to temperature. I did some calculation: 260 mph (IAS) is about 525 kts (TAS) @ -56.6ºC which is standard temperature at 40000ft, that's pretty close to the speed of sound. Am I guessing wrong or those limitations have another purpose?

That's correct.  The limitations are to stay below the critical Mach Number, and altitude is used because it's easier for the pilot to monitor and reference to than temperature.  The numbers are based on the standard atmosphere's temperature profile and I imagine there is some fudge factor or safety margin to allow for normal deviations from ISA.
The chart below is from the P-38 training manual which shows more or less the same thing as your placard in graphic form.  The lines become vertical near the top because at about 36000 feet you are in the stratosphere in the mid latitudes and temperature stops decreasing (The Mustang's placard is a bit odd because you would expect the limit speed at 35000 and 40000 ft to be the nearly the same, but there is a 30 mph difference.  Not sure why that is).
The P-38 suffered from a lower critical Mach Number than the P-51 (.68 vs .7) limiting its dive speed at 30000 ft to 290 indicated vs 325 for the Mustang (a major combat limitation until dive recovery brakes were developed - until then, P-38s couldn't chase aircraft in power dives because of the pitch control problems when going transonic).


Can the "G" and "VRB" wind conditions be combined in METARs? I have never seen the "VRB" (for wind direction variations < 60°; e.g. VRB12003KT) and "G" annotation (for gusts > 10KT wind speed difference; e.g. 12003GT30KT) being combined in a METAR.

Until now I have just seen:

VRB03KT (so "VRB" without gusts)
12003G30KT 090V150 (so "G" with wind direction variation > 60°)

Why does this never happen? Is there a rule and is it not possible or does it just never happen?

Yes, it is possible for a METAR to contain both VRB and G. VRB10G25KT is valid.

The reason it rarely happens is because, as wind speed increases, major variations in wind directions tend to disappear.


Has the Beechcraft company considered building a single-engine turboprop? I was passing a stack of magazines at a friend's office and I could have sworn I saw a cover article about a single-engine King Air. I went looking for that article and haven't been able to find it, but it got me thinking. Has the Beechcraft company ever released any information in any form that might indicate that they've considered building a single-engine turboprop?

I'm curious more on airplanes comparable to the King Air. I believe I remember reading that they played with the idea of a turboprop Bonanza, not to be confused with any STC modifications that make a Bonanza or Baron a turboprop.

I also realize that now Textron owns Cessna and Beechcraft, so if you consider the question in the larger frame of reference it looks a bit different as well.

Yes.
https://www.google.com/search?q=single+engine+king+air
Top result:
http://www.flyingmag.com/aircraft/beechcraft-reborn

Perhaps the most intriguing product floated by HBC at its NBAA press conference was a single-engine turboprop. The company says the airplane has no public name or designation but will “absolutely,” said Holcombe, be “called a King Air.” That name, of course, has never been bestowed upon a single-engine airplane before.
This King Air, however, will be no scaled-back PT-6 single. Like the remarkably roomy and powerful Pilatus PC-12, the Beechcraft single will be big. Its fuselage will be — get this — based on that of the Premier 1A, which, HBC claims, has the best cabin of any bizjet in its class. It will certainly be huge for a single. In addition to the voluminous cabin, the single would feature a large side loading door, room for eight to 11 occupants and industry-leading pressurization. The composite fuselage allows for efficient pressurization. HBC says it will build the fuselage in the same way it builds the Premier 1A today, using state-of-the-art winding technology for extremely light and strong composite structures.


What would be the challenges to taking off and landing a typical passenger jet at FL300? Suppose it was somehow possible build a runway at FL300. Yes, doing so would be incredibly expensive, and it would be a mammoth civil engineering task, and the downsides would probably by far outweigh its advantages in practice; but for the time being, let's say that the desire to do it exists, and the issue of money has been resolved (as if by magic).

Let's also ignore the issue of getting the passengers, cargo, etc., to and from the actual aircraft, and focus on the aircraft operation itself.

Having constructed this runway-in-the-sky, what difficulties, compared to a similar runway built at ground level, would pilots and airplanes face when using it to "land" (if we can even use that term here) and take off, respectively, with a typical passenger jet (turbofan) aircraft?

It has been suggested that this is a duplicate of Would building an airport at 30,000 ft save money? (which also, in the question body, allows for one at 10,000 ft). I believe that this question is not a duplicate of that one because that question focuses on the cost of building such an airport and the savings in fuel expenditures because airplanes would already be near cruising altitude, while this question focuses on the challenges of landing at and taking off from an extremely-high-altitude airport while specifically ignoring the economic aspects.

These are the main challenges I can think of:

High takeoff and landing speed: To generate enough lift for takeoff in the thinner air at FL300 (gravity has almost not decreased, so required lift stays almost the same), very high speeds are required. Combine this with less thrust from the engines available and you need very long runways. It should still be possible to accelerate and takeoff eventually since FL300 is still below the maximum altitude most jet airliners can climb to (coffin corner).
Tires: The tires used on aircraft have a maximum speed which would be exceeded when taking off or landing. Other tires could be developed, but it is a major challenge to make these work in the cold temperatures (rubber does not like freezing temperatures, that is why Mars rovers do not use rubber tires).
Cold Temperature: It is cold at FL300, around 220K on average or around -50°C. This is not only problematic for the tires, but also for fuel, which would be constantly close to its freezing point. A heat exchanger between e.g. engine oil and fuel would be mandatory to operate an aircraft from here.
Wind: Wind speeds can easily reach 150kt at FL300. The runway would have to be perfectly aligned with the wind to have a pure headwind component. Otherwise, the crosswind would quickly exceed the limits for the aircraft.
Engine Failure: FL300 is above the maximum altitude for OEI (One Engine Inoperative) flight, which implies one cannot return to this airport after an engine failure. An aircraft would be forced to drift down to a normal airport for landing.


Which airports have the highest fuel upload? Which airports consume the most fuel for aircraft refueling, and how much fuel do they use?   I was able to find that "Heathrow uses about 20m litres of fuel a day", but it isn't easy to find figures for other airports.

The best data I could find is in this paper about biofuels, which has data for US airports in 2014. Based on my reading of the chart on page 14 and some conversion:

Airport  Millions of barrels per year
KLAX     48.6
KJFK     43.5
KATL     30.8
KORD     30.5
KSFO     28.3
KMIA     26.0
KDFW     25.4
PANC     19.0

Comparing this to the top US airports in 2013, it is interesting to note that LAX and JFK use significantly more fuel than KATL, despite passenger traffic figures ranked the other way. Also notable is Anchorage showing up here right after DFW, while MIA and ANC are the only ones not in the top 10 by passengers, showing up at 11th and 58th, respectively.

Figures for other countries have been harder to find. This article from 2004 estimates the Dubai International usage at 24.2 million barrels that year, which has certainly grown since then. The 2012-2013 environmental report from Emirates Group lists their consumption at 73.9 million barrels, and half of this figure would be in line with the other numbers available.

I found a similar figure for Heathrow, listing it at 20-25 million liters per day, depending on season, which gives a range of 61.2 to 76.5 million barrels per year, well ahead of the US airports.

Becoming even fuzzier, the pipeline to Narita Airport in Tokyo transported 130 billion liters in its first 30 years of operation, which averages out to 36.3 million barrels per year.


Can a jet cruise with asymmetric thrust? If a twin turbojet aircraft has an engine failure during takeoff, does it return for landing or does it continue to cruise with asymmetric thrust?

As a practical matter, the aircraft will probably land ASAP. Having lost an engine pretty clearly qualifies as an emergency for twin-engine aircraft!

That said, the aircraft would be capable of cruising with asymetric thrust. Rudder is applied to keep the aircraft flying straight.


How does a circulation control helicopter work This essay describes that this helicopter uses circulation control of the rotor for cyclic and collective control, but not how circulation control works.
https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19810017584.pdf

A quick scan of the linked document suggests that they're referring to controlling the relative amount of engine exhaust directed into each rotor, which (due to the downward direction of the exhaust jet that drives the rotor) controls how much downward deflection each blade gives its airflow.  By making this differ from one blade to the other, the rotor can be tilted without twisting the blades at the root as would usually be the case with large, heavy lift rotor designs (the effect is somewhat like the Bell-Hiller paddle system often seen on small helicopters).

The resultant rotor tilt gives pitch and roll control, which are used (directly, or by mixing rudder effect) to move forward, aft, or sidewise in hover, and to control speed and climb/dive, plus turn, when in forward flight.


Are flight attendants paid in the same way pilots are paid? I understand that airline pilots are generally paid for their time "in flight", which means the clock starts when the aircraft begins to move away from the gate. Are flight attendants paid in the same way?

It mightn't be a bad idea to specify which country you are talking about, as practices can vary throughout the world, and potentially even amongst individual airlines within the same country.

Last year I looked into becoming a FA for a smaller Australian airline. The pay arrangements were:

A guaranteed minimum annual salary (which was about $45k)
On top of that,  flying wages based on scheduled flight times (4.20 per hour, a bit extra per hour for the hours worked above an agreed number of hours in a month). Note that even if a flight is delayed it is still issued with adjusted scheduled times. The 'padding' applied to regular scheduling works in favour for the employees here.

However, I believe the US  works completely differently. And as I said, this is an example from only one airline.


What happened with flight AC692 to St John's? Yesterday, 2nd of March 2020, I was on board of Air Canada flight AC692 from Toronto (YYZ) to St. Johns (YYT). 40 minutes before landing, the plane turned around and flew back to Toronto. The flight time was supposed to be 2:20 hours, instead we flew a round of ~4 hours. The pilot announced that it "unsafe to land" in St John's. But this sounds rather ambiguous to me.

I have a colleague in St John's. He says the there was quite a bit of snow in the morning, but by the time we were in the air, all the roads were clean. This mean they easily could have cleared the runway? Overall conditions weren't too bad and the sky was clear with sun.

Wind would be another condition, but this was a Boeing 777. Those can handle a bit of wind conditions, as opposed to the smaller aircraft types?

Why all the way back to Toronto? Why not divert to Halifax or Montreal and wait until the conditions get better?
I was in the understanding planes don't over-fuel for safety reasons. How did we make it back to Toronto without refueling? If we wouldn't have turned back, would the plane have had too much fuel to land?

I would like to add during the landing in Toronto, flaps were pulled down rather late to my experience. The approach was rather short (in time) and spoilers were used during descend. Also, (almost) no reverse thrust was used used during braking. Does this tell me the plane was running on fumes?

Why return to Toronto and not stop on the way:

Generally speaking the most probable cause for reverting back to an airport that seems an unlikely choice is that the airline has a base there. From a base airport the aircraft is readily available for other use, and crew rotations are easily managed. In addition to that, if the "unsafe to land" condition was due to a technical issue with the plane, maintenance is secured at a base airport, but not necessarily elsewhere.
As Verandaguy pointed out in his comment, Air Canada does have a base at Montreal, which would have been closer to the aircraft at the time of diverting. This being the case, the reason for returning to Toronto is very likely to get the plane and crew to a position that best suits  the following rotation of each.
We do not know about the flight hours the crew had on them, so diverting to a non-base or non-scheduled airport might have caused serious trouble with continuation of the flight: You might have to fly (or if diverted to a base, call up) a relief crew to the divert airport  to fly the plane onward, and the crew with rest period limitation would have to be flown to their "home" base airport. This situation might have arisen at St. Johns after a stopover enroute.
While I at first did not think that weather was the reason (ref. METAR posted by Federico), it turned out that runway conditions were not suitable for landing in high and gusting crosswind (comment below by Mike Sowsun, kudos for that). We do not know the weather trend, so flying to, say, Halifax might prove problematic if the weather and/or runway conditions did not get better fast enough (see previous bullet point)

Fuel: too much to land at destination, too little on arrival at Toronto?

The reason for not carrying extra fuel is pretty much solely economical: it's a huge waste of money to fly fuel around instead of cargo or passengers. However, while it is true that airlines do not like to ferry extra fuel, an aircraft has all sorts of reserve fuel on board: you carry extra juice for trip to alternate airport, holding at destination or alternate and so on. When a crew decides to divert to an alternate airport, they make sure they choose one that does not result in fuel emergency.
It is therefore extremely unlikely that the plane was running on fumes when it arrived at Toronto.
Nor is it likely at all that the plane would have been over fueled by mistake. If it had been so, you would most probably just have circled at St. Johns for a while to burn the excess off, or dumped on the way there.
The observed use of flaps and/or speed brakes cannot be used to determine the fuel situation of the plane. These are more likely dictated by traffic situation.

As for the reasons for not landing at intended destination: As Mike Sowsun commented below, runway conditions were less than satisfactory, and the captain made the only possible judgement call: high gusty crosswind + slippery runway is a big no-no. A roadside observation cannot be used as a reference when judging what conditions are at an airport, even nearby. I know by experience that local variations in weather can be huge at places such as St. Johns. Also, changes in weather at these latitudes in coastal regions are very hard to predict, sometimes even for such short periods of time as the duration of this flight.


Can an Autogyro with wings survive a rotor mechanical failure? Will it be safer? I'm not an expert but as I understand autogyro sustentation relies on the rotor. If the rotor breaks, the aircraft will fall as a rock to the ground... But If the autogyro was built as a tractor design and had wings as the first cierva autogyros did: Would it survive to a rotor destruction? In case of rotor breaking the pilot maybe has a chance to glide and do an emergency landing. Is it safe to build an autogyro with wings? Does it have an increased operational cost?
Note that having wings add the  incovenience of being afected more by the turbulences and wind.

That is a very broad question and covers many topics, but I will try to answer as best I can and not miss anything.

A quick note on the wings.  Adding wings as a safety aspect to the aircraft kinda defeats the purpose of an autogyro.

Would it survive to a rotor destruction? The likelihood of an autogyro surviving rotor destruction is extremely remote. Best case scenario would be the entire rotor assembly detaches from the mast and flies away from the aircraft.  Worst case scenario only 1 or 2 blades fly off. (Honestly would be more likely to happen IF rotor destruction were to take place.)  In this situation the imbalance in the rotor would be so violent that surviving, let alone actually flying, an autogyro in such a configuration would be truly "Hand of God" type miracle.  If you want to see something similar try removing a blade or two from a fan and you will see this imbalance in action.

Taking the best case scenario could the pilot make an emergency landing? Yes, but their options would be limited, assuming you can recover AND get into the best glide configuration by 5,000' AGL you would likely have less than 8.3 minutes to find a field and get ready before landing. Lower altitudes will provide even less time before contacting the ground.  (This number is only approximate for a 9.3:1 glide ratio and it would be unlikely for wings on an autogyro to even do that well.)

Is it safe to build an autogyro with wings? Yes, as your picture shows it does work.  A few companies today, such as Carter Aviation Technologies, use that design albeit with much shorter wings designed to work in conjunction with the rotor.

Does it have an increased operational cost? Possibly.  Those smaller wings mentioned in the paragraph above actually increase the efficiency and reduce the operational cost.  The problem is that those types of wings are almost entirely useless without the rotor.  Wings big enough to provide a decent glide ratio and time for the pilot to react to rotor destruction would end up providing more drag and require a larger engine to overcome it thereby increasing the operational cost.

As far as turbulence goes, you could see more turbulence with larger wings but with small wings like on the CarterCopter, the additional turbulence added to the aircraft because of the stiff wings would be minimal.


What is the bag for on a passenger oxygen mask? We may all be familiar with the part of the cabin safety briefing where they say that, in the event of a reduction in cabin pressure, oxygen masks will drop from a compartment above our heads, yadda yadda, the bag may not inflate. What is the purpose of the bag?

Oxygen in passenger masks is either generated by oxygen generator or released from pressurized container via reduction valve. In either case it is released at fixed rate. But human breath is discontinous. So the bag acts as a buffer. You inhale the oxygen accumulated in it and then it slowly refills while you are exhaling.


Can an outside observer tell if an aircraft is flying through turbulence? As a passenger, when I look out of the window, I can see the wings shaking. What would another plane (not in turbulence) see if they were observing the same plane (in turbulence)?

The wings are flexing because there is a change in lift.
The wings are more aerodynamic than the body of the aircraft. I.e. the wings are more "responsive", they respond to changed aerodynamic forces more rapidly.
As a result of the change in lift in the wings, the body (being connected to the wings) follow the change.

Therefore, to an observer who is immune to turbulence, the wings would flex first, followed by the aircraft as a whole. If the turbulence is causing the wings to flex up and down repeatedly (e.g. imagine sine wave), the body of the aircraft can be observed lagging behind the wings and smaller in amplitude.


Does contra-rotating vs regular propellers, have any effect on icing? I am trying to understand whether can there be any correlation between the contra-rotating propellers and the ice accretion over the wing ? For instance, is there any evidence that ice accretion is more in regular propellers when compared to a contra-rotating propeller ?

What are the parameters for icing on the wing?

temperature
air humidity
airspeed / pressure

The rotation direction of the propeller does not effect any of this parameters. Therefore the propellers rotation direction does not affect icing.


Do I need to get a new AFSP approval if I change my instructor or aircraft? I plan to remain with the same provider though.

An AFSP application is valid for one provider, one aircraft category (TSA category, not FAA category), and one training event (single-engine, IR or multi-engine). If you change any of those things, you need to submit a new application.

If you're at a part 61 or 141 school that has multiple instructors, the approved provider is usually the school, not the individual instructor. So you can receive training from any instructor there without an issue.

If you're getting training directly from a freelance part 61 instructor, then it's possible that the instructor himself is the approved provider. In that case, you would need to submit a new application to get training from a different instructor or school.

In either case, your school or instructor should know exactly who's registered with the TSA as the provider.

As for the aircraft, you only need to submit a new request if you want to train in a different aircraft category. Initial training is usually done in category 3 aircraft (maximum MTOW of 12,500lbs) and you can train in one or many physical aircraft, as long as they're all in the same category. But remember that SEL and MEL are different training events so if your current approval is for SEL training you can't receive MEL training, even if the aircraft is under 12,500lbs.

Links to specific pages on the AFSP website don't work properly, but their FAQ is reasonably clear and you can email their helpdesk at AFSP.Help@dhs.gov if you need more information. AOPA has a useful guide, and the regulations (including category definitions) are in 49 CFR 1552.


Why do multiple planes arrive from the same airport at the same time? I'm looking at the Arriving flights page of the Vancouver Airport and in many cases there are several planes coming from the same airport, arriving at the same time, all at the same gate.

Does it count for only one plane and they are affiliated companies?

Here are some screenshots:

This has to do with codesharing or codeshare. Two or more airlines can agree to share the same route and operate it with only one aircraft to reduce cost of operation.
See the WikiPedia article on codeshare
Here an excerpt:

A codeshare agreement, sometimes simply codeshare, is an aviation business arrangement where two or more airlines share the same flight. A seat can be purchased on one airline but is actually operated by a cooperating airline under a different flight number or code

In the case where multiple flights are listed arriving at the same time from the same departure airports, there will only be one physical airplane serving the connection but under different flight numbers and operators. The different flight numbers and operators are listed to make it easier for passengers to identify their flight if codeshares are being used.
On busy airports or where there is not enough space on the information displays to show all flights of a codeshare, the relation is only shown once with rotating flight numbers.


What stops an international private airplane from landing outside of airports with a customs zone? Let's say somebody charters a small airplane from Canada and flies into the US (after receiving clearance from the US ATC). After crossing the border, they land on a small airstrip in the middle of nowhere instead of going to an airport with a customs facility.

Would anything stop them from doing so? Would the police be notified immediately by the ATC? Is all international air traffic closely monitored until they pass through customs?

It is usually required to file a flight plan for international flights (with very few exceptions), and I'll assume this is the case for Canada/US as well, but I'm not 100% sure of this. In this case you have two options

You close your flight plan and let ATC or FSS know where you are, they'll note it's an international flight that landed somewhere without customs, and you're likely to end up in trouble.
You don't close your flight plan, and you'll trigger a search-and-rescue operation as you'll eventually be overdue, drawing attention to yourself, and you're equally likely to end up in trouble. Not to mention that you'll probably be liable for the cost of the search-and-rescue.

You could of course file a plan with a drastically reduced TAS, do a very quick stop, and arrive at the original destination within the grace period. I don't know if that will trigger any surveillance systems though.

If you don't file a flight plan and cross the border anyway, I'm guessing that you will indeed trigger some alerts though.


Has anyone considered putting a hydrofoil on a sea plane? One of the main problems with water landings is that you need a bigger engine to counter the various drags caused by the pontoons. The specific case of "run[ing] across our own wake to be able to get up on the step on glassy water" brings some interesting thoughts.

  [B]asically a floatplane has to break the suction of the water - kind of like pulling your boot out of mud - and if the water isn't moving at all then it has to do that all by itself. If there are some waves, or a wake, or any kind of discontinuity in the water, then that gives the aircraft the momentary break it needs to overcome that initial suction. "The step" in this context refers to the step-up shape you see partway down the float (or hull); when you're "on the step" then you're using the part of the float forward of that step to hydroplane.

It is well known that water's significantly higher density makes high speeds difficult. A solution to that problem is the hydrofoil - a small underwater wing that raises some or all of a boat's hull out of water to reduce friction and increase speed.

So here is my dumb question: would placing a hydrofoil under a pontoon save fuel on takeoff? And how likely would the increased drag during flight cancel that advantage on a typical flight?

Yes. I mean, sort of. Nobody's ever built a production hydrofoilplane.

It's not a bad idea, but seaplanes are a relatively niche product these days and there doesn't seem to be a lot of innovation in the field. Back when there was, there was innovation everywhere so the idea of hydrofoils didn't stick.

The Convair F2Y Sea Dart, a 1950s prototype jet-powered fighter, used two 'hydro-skis' for takeoff and landing. It was more or less awful compared to the crop of land-based aircraft coming along and after a prototype disintegrated they (probably wisely) chose to shut the program down.

There are some other prototype aircraft that used actual hydrofoils that I found after some quick googling. A company called Lisa Airplanes seems to have an LSA - the Akoya - that's under development using tech similar to the Sea Dart.

The 1929 Piaggio P.7 used hydrofoils, and was intended to compete for the Schneider Trophy, but never made it airborne. Interestingly enough it had a screw (marine propeller) at the tail and a proper aviation propeller up front, and the pilot would've had to do some juggling between the two.

It's likely there were others, but I'm running low on sleep.


Why are some fuel-injected engines started with the mixture at idle cut-off? The POH for a C172N with a carbureted Lycoming O-320 says:

  STARTING ENGINE

  Mixture -- RICH
  Carburetor Heat -- COLD
  Master Switch -- ON
  Prime -- AS REQUIRED
  Throttle -- OPEN 1/8 INCH
  Propeller Area -- CLEAR
  Ignition Switch -- START

The POH for a C172S with a fuel-injected Lycoming IO-360 says:

  STARTING ENGINE (With Battery)

  Throttle -- OPEN 1/4 INCH.
  Mixture -- IDLE CUTOFF.
  Propeller Area -- CLEAR.
  Master Switch -- ON.

  [Beacon and priming steps omitted]
  Ignition Switch -- START (release when engine starts).
  Mixture -- ADVANCE smoothly to RICH when engine starts.

Why is the fuel-injected engine started at idle cut-off?

Often times fuel injected engines can be difficult to start with the mixture rich, particularly if run recently and still hot.  Following a priming procedure with the electric boost pump then cranking with the mixture at idle cutoff allows the engine to flush out fuel from the injector manifold until an optimal fuel air mixture is reached and the engine starts up.  Quickly moving the mixture to full rich at this point will stabilize the engine at idle with an appropriate throttle setting.


Why is the Cumulonimbus cloud formation so dangerous? I once heard my pilot friend say that it's really dangerous to fly near any Cumulonimbus cloud formations... Something about that it could drag the plane into it.

Cumulonimbus :

Why is it so dangerous?
How is it created?

A cumulonimbus cloud (CB) is dangerous because of the processes occurring in them.  At a minimum you will have an updraft and a downdraft containing rain.  The particular CB you posted in your picture is typical of severe convection.  The anvil is spreading out along the tropopause and there is significant overshooting tops over the anvil.  This indicates the updraft in this cloud is very strong and there is a lot of energy in this storm.  A storm like this likely has hail near the updraft, very strong winds both up and down and severe turbulence within the interface between and around the strong up/down drafts.  There can also be very active in-cloud lightning as well as cloud-to-ground discharges.

Threats near the storm are turbulence, lightning, large hail and significant downdrafts (e.g. microbursts).  Threats within the cloud are severe turbulence, very strong updrafts (some as high as 100 m/s or more) and downdrafts containing torrential rain, hail and lightning.

To better illustrate the magnitude of vertical winds, here is a quick plot from a modeled storm I am working with.

In this plot the reds are updraft and blues are downdraft with the scale on the right in meters/second.  The plot covers 20 km x 20 km area at a height of 5.4 km, which is close to 18,000 ft or 500 mb.  This corresponds to the main updraft in a supercell and you can find areas where less than 5 km cover a vertical wind gradient of 50 m/s.  If you were penetrating this at any decent airspeed you would be in for a very rough ride.
 This storm only had 1800 J/kg CAPE and updrafts can be much faster than this.

CB clouds are (typically) realized from a release of convective available potential energy (CAPE), which is simply a measure of how much warmer a parcel rising from the surface is than its surroundings as it rises.  In an environment that is favorable for convection (CAPE, vertical windshear) where there is ample moisture and a mechanism to force parcels to rise to their level of free convection you can end up with a CB cloud.  A CB is simply a cumulus cloud with rain falling out of it and whether this is a small rainshower or a severe rotating supercell is determined by the environment the storm occurs in.


How does the spoiler actuation mechanism work on the Airbus A340? How does the servo control spoiler actuation mechanism on the Airbus A340 work?

Most aircraft utilize a weight on wheels switch. When the landing strut is compressed when ground contact is made, the weight on wheels switch is activated. The signal is distributed to various systems in the aircraft, including the spoiler system.
The spoiler is activated as soon as the aircraft touches the ground to "scrub off" any lift and to make sure the aircraft doesn't become airborne as the jet engines spool down.


Has anyone compiled all the NTSB accident reports and broke down the percentages for cause of accident and fatalities? I am not talking the typical breakdown such as Pilot/Mechanical/Other, but rather, more specific things such as, engine failure, Stall/Spin on approach, controlled flight into terrain... etc

There's a book called "The Killing Zone - How and Why Pilots Die" by Paul A. Craig which has a great deal of statistical work in it around aircraft accidents which may be useful to you. It's an alarming title which might make you think it's some sort of sky is falling mentality, but it's actually very sensible, statistics-based information about aviation accidents.


Should I report my cured mild PTSD in the FAA medical certification application? I am a combat veteran who was diagnosed with moderate Posttraumatic stress disorder (PTSD) after getting out last year. I  decided to seek treatment and, upon reevaluation, am now at a very mild rating for PTSD with no personality disorders, and no use of medications ever. I am not even eligible for disability compensation that is how NOT severe my PTSD is or ever was. I am currently in the process of trying to get my FAA Medical Certificate for a student pilot and the FAA came back wanting these extreme and expensive tests that were never conducted by my psychologist because they were deemed unnecessary. My psychologist is writing the report they requested, but I have a feeling they will dismiss it and cancel/deny my application because I only have my medical records and my psychological report and cannot afford the psychiatric evaluations and the VA cannot do them for me because they are not medically needed.

Now to my question, if they deny it, then I will reapply again, however as I am as close to 'cured' as possible when it comes to PTSD and it does not affect my reactions to stressful situations or anything that could come up in flying (I've been in a helicopter during the healing process so I know), do I just NOT put anything in the mental disorders box? And if so will they hit me back with "hey we know you applied last time with this, so you're a liar"? PTSD is a curable thing and I feel even more normal than before I even joined the military. Thanks for your time.

Unfortunately, you have to report it.  It even says so right on the medical application (emphasis added by me):

  18) Medical History - HAVE YOU EVER IN YOUR LIFE BEEN DIAGNOSED WITH, HAD, OR DO YOU PRESENTLY HAVE ANY OF THE FOLLOWING? Answer
  "yes" or "no" for every condition listed below (All "yes" answers
  require a comment. Click Add Comments to add or edit a comment).

  ...

  Mental disorders of any sort: depression, anxiety, etc.

  ...

Based on your own admission, you had it at one point and are now cured.  This means that you have "at some point in your life" been diagnosed with it.

Unfortunately, the FAA takes a very hard line on this kind of thing and it does not surprise me in the least that they are now requiring a battery of expensive tests in order to prove that you are fit to fly.  I don't like it either, but it does keep the people out who "say" that they are cured when they aren't, either because they don't realize it or because they just want to fly anyway.

If it is denied, then you can appeal it, but I would suggest getting good professional help.  As voretaq7 mentioned, AOPA has a very good medical service that helps their members for free.  Membership is pretty inexpensive, and more than worth it just for this service, plus they have many many other benefits as well.

A couple of other questions on the site that may help you:

FAA Class 3 Medical re-examination
Can a private pilot receive recurring training while waiting for a special-issuance medical approval?


From this reference:

$$c_f=K_1\cdot \frac {t}{c} + K_2(\frac {t}{c})^2 +  K_3(\frac {t}{c})^3 + K_4(\frac {t}{c})^4$$

For the 64A series:

$K_1$ = 8.2125018
$K_2$ = 0.7685596
$K_3$ = 1.4922345
$K_4$ = 3.6130133

$c_f$ is the particular scale factor for this profile. And then the reference continues with this head spinning further explanation:

  Now, for a specified family and thickness, the thickness distribution may be determined without iteration. From the thickness, the scale factor is computed from the polynomial function shown above. Then, the scale factor is used to multiply the basic values of the psi and epsilon functions for this airfoil family. These scaled psi and epsilon functions are used in mapping the z-plane to the z'-plane shown in Figure 1. The Joukowski function zeta = z' + 1/z' then maps the z'-plane into the zeta-plane and these results are normalized so that the leading edge is at x=0 and the trailing edge is at x=1.

Hope this helps, my head hurts after reading that.


What is the reference chord for AoA measurement or calculation in a twisted wing? Let us assume we have a rectangular, unswept wing with no dihedral and a given wing twist and we want to measure in flight or calculate its $c_L$ vs $\alpha$ (angle of attack) diagram. Of course each airfoil along the span will have a different local angle of attack at every flight attitude. Which y-coordinate along the span must (or should?) be used as a reference?

In short: it’s up to the designer to pick any definition as long as the design and analysis always obeys that definition.

Usually, it’s a general practice to define a root chord and then calculate the rest of the local aoa‘s in relation to the root chord. This makes wing-strip calculations simpler. It’s also used in helicopter rotor blades and propellers.

On the other hand, there are numerous simplified calculations (that calculate wing or aircraft level properties) that may consider the mean aerodynamic chord. In this case, of course, the mac location would be used.


Would mechanical indicators have helped in the Air France 447 incident? NB I am not an aviation professional.

I saw a documentary about the terrible Air France 447 disaster the other day.

I was struck, as were the experts in it, including David Learmount, who's known as a great aviation expert here in the UK, by the way all 3 pilots were completely unable to grasp what was really happening because of their fatal inability to trust the electronic instruments.

I had a thought: is it not the case when flying any aircraft, whatever its size, that you always need to know, particularly in an emergency, two things?

air speed
attitude

I know this is VERY VERY obvious, but please bear with me.

The fact of the matter is that you can obtain totally reliable information about both these aspects, regardless of darkness, regardless of electronics, regardless of Pitot tubes, at all times:

air speed: by having an incredibly robust, small structure outside the front of the cabin window which would flex visibly according to windspeed, thereby making the invisible (air flow) slightly less invisible: at 0 knots this would be inclined downwards; at over 150 knots the windspeed would cause this to become fully horizontal.  Lack of horizontality would therefore indicate a low speed. One thing I have appreciated since posting this question is the intensely hostile environment this structure would be facing: freezing temperatures, high windspeeds, sometimes containing ice, etc. No doubt one of the reasons why during the development of aviation this has not been considered possible. But materials are being developed now which are much stronger than ever previously known.  One candidate might be carbyne.  It would also presumably have to be heated.
attitude: by having one of those completely mechanical floating compasses (as used on ships) in a prominent position in the cabin. Much confusion has been created in some of the comments about apparent gravity. But apparent gravity has effect only when acceleration other than gravity (down!) and lift equal to 1G (up!) is present. The fact of the plane accelerating/decelerating (in any or all of the 3 dimensions) could be indicated by a system of calibrated inertial accelerometers in all 3 dimensions, with lights varying in intensity according to acceleration.

Obviously such a bendy thingy would have to be very tough to withstand the speeds, battering, temperatures, etc. But it is at least conceivable that this is not beyond the wit of humanity.  Designed carefully, a change in the way it was flexed would then indicate without any possible doubt when an aircraft was in or near a dangerously low speed.

Wouldn't these two measures have had a good chance of providing the pilots of AF 447 with a true and totally irrefutable mental picture of what was actually going on?

PS it has been objected that such a system, even if feasible, would be redundant. But redundancy in critical systems is a desirable thing: what's worrying is if you don't have redundancy, and the aviation industry has made gaffes in the past over insufficient redundancy: Boeing 737 rudder issues; MD80 horizontal stabiliser: "The absence on the McDonnell Douglas MD-80 of a fail-safe mechanism to prevent the catastrophic effects of total acme nut loss" (Alaska Airlines 261, NTSB report quoted).

Unfortunately, if there had been a jazz band in the cockpit singing "The plane is stalling" it wouldn't have helped. If Moses had been in there carrying a stone tablet newly-carved by God himself inscribed "Pitch down" with a host of angels to help announce it, that would have made no difference.

The unrecoverable problems were in the pilots' brains and in the communication between them, not in the aircraft or the technology.

Once in that state, only a fresh perspective (for example stepping back from the problem, bringing in a fresh person to look at it, using a checklist) is likely to snap those trapped in it out of their spiral: of alarming events, inappropriate reaction, unexpected result of the new inputs, and mounting panic.

It's a common experience in many crafts and disciplines, though in some - like computer programming - it's easier to find the new perspective than in others, such as piloting or surgery.

Anyone who has found themselves in that spiral will be able to tell you that adding more data or new sources of data to the mix rarely help.

It seems reasonable to think that a clear, simple and apparently unarguable piece of evidence would be the way out of such a situation. Unfortunately, in practice, it rarely if ever is, and there is nothing to suggest that in this case it would have been any different - despite compelling intuitions to the contrary.


What should I do to become a pilot for skydivers, in France? What are the steps needed to become a pilot that can transport skydivers?
I'm more specifically interested in the situation in Europe, France.

I would expect lessons / certifications, then more certification to accept passengers, then more certifications to be allowed to carry skydivers and let them jump. Also, medical examination, books, insurance, fees...

How much would it cost?
I'm more interested in the money amount spent usually observed than the theoretical price. I have a day job so I won't be able to easily spend all days of the week at the airport.

How long should I expect until I'm certificated?

Then, how often should I fly to stay current.
Obviously, there is the issue of practicing enough to be safe and the legal requirements to be allowed to fly with passengers.

I also expect to be required to be certificated with a specific level for the skydiving. Bonus points if you can answer that too.

I have seen this question about how much it cost to learn to fly, but it is less specific than my case. Still, many interesting points in its answers.

Short answer: you need a commercial pilot's license. The drop zone will provide the extra training, it takes about a day (I worked at a skydive center for 10 years)

However, since you seem to not have any kind of pilot's license right now (or you would know this already) I will add that it isn't a full-time job at any except the busiest drop zones. Our pilots usually worked for a couple of years to build time and then went on to other aviation jobs. During those 1-2 years they had other income - flying for us was mainly a way to log flying hours without having to rent aircraft.


Why is the pitching moment of this symmetric aerofoil non-zero? As I understand it, the pitching moment coefficient of a symmetric aerofoil should be zero, under potential flow assumptions. Obviously, approaching stall and post-stall, these assumptions are invalid and the pitching moment coefficient would no longer be zero.

However, looking at this graph of pitching moment coefficient against angle of attack, for a NACA0009 aerofoil at Re = 1e+6, it seems like Cm does actually vary considerably at low and moderate angle of attack.

Why?

Under incompressible potential flow and at small angles of attack, one of the most celebrated results of Thin Airfoil Theory is that all airfoils have their aerodynamic centre at 1/4 chord; and for symmetrical airfoils, the centre of pressure coincides exactly with aerodynamic centre.

If you look at the plot in the OP, the variation of Cm between -3 and 3 deg are relatively small, indicating that the linearized theory agrees well with the nonlinearized simulation.

Beyond 3 deg, however, the viscous effects present in the simulation but absent from Thin Airfoil Theory begin to alter the results. This manifests primarily in the boundary layer, which alters the apparent shape of the airfoil, thereby making it non-symmetrical. The next graph shows the XFOIL simulation at 7deg AOA; notice that the boundary layer at upper surface thickens near the trailing edge.


Did the twin engined Lazair ultralight have a throttle for each engine? Did the twin engined Lazair ultralight have a throttle for each engine?

I know larger aircraft have dual throttles.

What about the smaller aircraft like ultralights?

It would be so much easier just to have a single throttle, much like a motorcycle throttle which splits into 2 on a 2 cylinder, 2 carb bike.

I've examined a Lazair, and actually taxied one around on the ground once, and yes there are two throttles.

Two reasons:

In any twin engine airplane you want to minimize or eliminate single-points-of-failure (especially with engines as unreliable as little 2-stroke water pump motors) and this means you want the keep each power plant completely mechanically independent all the way up to the throttle.

You need to be able to adjust power independently to synchronize motor RPM (because the wowowowowow of out of sync motors will drive you bonkers), as well as control each engine independently for starting etc.

So, a single throttle to control both engines is a very bad idea.


Other than a swing wing, what types of variable geometry have flown? We're well familiar with swing wings, on small and large aircraft from both the east and west.

What other types of variable geometry have been tried?

Extending wings

The idea is to have a larger wing area at takeoff for more lift and a smaller wing area in flight for more efficiency.

The NIAI RK and followup RK-I used two tandem wings that served as rails for an extendable panel that could be rolled out between them.

The project failed because Stalin was so enthusiastic about it he had it use the most powerful engine available which was too unreliable. I can't find a reason why the concept was not tried again.

The German FS-29 glider of 1972 had a different arrangement. It had an outer wing that fit over an inner wing and could unsheathe like a sword. Only one was built.


Is the Bede BD5 actually a tandem wing airplane, and not a mono wing? Is the Bede BD5 a tandem wing airplane, and not a mono wing?
The following picture (Source: Wikipedia.org) shows a Bede BD5 with a high angle of incidence on the horizontal tail, estimated at about 5 deg.
Being a rear engined airplane ( estimated fuel and engine north of 150 lbs) and with the main wing close to the pilot(150 lbs+), it seems the CG would be aft of the main wing.
Does this mean the vertical tail was used to generate some of the total lift (estimated at about 30%),in straight and level flight, thus making the BD5 a tandem wing, and not a mono plane?

No. The BD-5 uses a stabilator for the horizontal tail with a single wing. When parked and the gust locks are in place the stabilator is in the 'pitch down' position you see in the picture. As the whole surface moves, the apparent incidence is not present when in normal flight.


How are folding wings managed? There exist several aircraft - especially carrier-based ones - that have folding wings, to save space.

How is this structure strong, taking into account the considerable amount of force on the hinge-based system (is it?) from the wing loading? How are they prevented from just snapping mid-air?

 Photo by Petty Officer 3rd Class Jason Johnston, U.S. Navy: Public Domain

The same question regarding helicopter rotors too.

 Photo by Lt. Col. Kevin Gross: Public Domain

The wing folding mechanisms (in aircraft) and rotor folding mechanisms (in helicopters) are different. The V-22 Osprey falls somewhere in the middle.

In case of aircraft, the wing folding mechanism is usually made of high grade steel (or titanium in some cases) and actuated either hydraulically (or in recent cases) electrically. The outer wing rotates about a hinge, to which the two parts (inboard and outboard) of the wings are locked. For example, the F/A 18 wing folding mechanism looks something like this:

Image from US Patent Wing fold push-pin locking assembly US 5558299 A

In general, once the wings are either folded (or unfolded), they are locked using very hefty sliding pins which provide a secure mechanical connection once (they) slid into place in sockets in the outer wing.

However, incidents do happen, usually because the pins have not locked and not because of failure. A number of incidents have happened where aircraft have taken off with wings folded (and landed safely, surprisingly).

Source : reddit.com/theaviationist.com

In case of helicopters, the blade folding method is more or less the same with some variations- pull the pin that holds the blade (on one side) and fold the blades, which is done manually for small helicopters and hydraulically for large ones.

Source: reddit.com

They are then held either by hydraulic pressure or mechanical attachments.

Source: adf-messageboard.com.au

At-least in helicopters, there is little chance of a takeoff with the wings folded.

The V-22 Osprey is a special case- The propellers (or rotors) is folded first, then the engines are rotated, followed by the wings themselves.


What is the encoding difference between ARINC 429 BNR and BCD formats? I think I have an understanding of the differences between the types of ARINC word formats, but would just like to get some input to see if my understanding is correct. In the ARINC 429 specification, it is discussed that there are some differences in how messages are handled between the two formats.

Data Field

This one just seems like basic arithmetic concepts and doesn't concern me as much. From what I understand, the BCD data-field works the following way:

Data-Field = 0x12340, means that the data is actually 12,340 (twelve thousand, three-hundred-forty) in base-10.

Then, BNR data-field would work like:

Data-Field = 0x7FD1C, means that the data is actually -740 (based on two's complement arithmetic).

Sign-Status Matrix Field

The operational codes just mean different things. Or in other words, the code numbers are the same, but the codes themselves have different meanings for BCD messages than BNR ones. Now, if there aren't any other differences, I would also like to know why the op-code schemes are slightly different.

My Question

So, I guess in a single sentence my question would be: are these the only differences between the types of ARINC messages?

Your basic decoding strategy looks correct -I didn't double-check the values, but the logic is sound. Note, however, that the difference of BCD vs two's-complement is not the only difference between BNR and BCD (and Discrete labels, which are also common). Binary-coded decimal (BCD) and binary (BNR) labels generally do decode as you have shown, but the Sign-Status Matrix (SSM) plays a large part in interpreting that data and using it is not optional.

For BCD labels, the SSM informs whether the data is positive or negative (or what direction is points), hence "Plus, North, East, Right, To, Above" vs "Minus, South, West, From, Below". It also informs if the data is invalid ("No Computed Data"). BNR labels include sign information already in the two's-complement encoding, so duplicating that information into the SSM would waste valuable bandwidth. The SSM still informs you of invalid data, but can also inform of (non-)operation in reversionary mode ("Failure Warning") or correct behavior ("Normal Operation").

What that of that means for a given LRU (line-replacable unit)1 can be completely different from any other LRU. To have any confidence in your interpretation of a label, you must obtain a hardware integration guide for the specific LRU in question to determine what format data is or must be provided in and what the SSM values imply. This integration guide is a separate document from any user or maintenance manual you may have received with an LRU for installation into an aircraft. It is usually only provided to original equipment manufacturers of other LRUs.

For example, a BNR label might still contain a readable value when the SSM is set to "Failure Warning", but whether or not you can still use that data depends on what the failure implies for the particular LRU. I once encountered an LRU that provided a label for barometric altitude that reverted to GPS height above ellipsoid when failure mode was set. This change in represented value was not appreciated at the time, but did teach me to always inspect the SSM first before believing any particular value. Furthermore, many BNR labels are also scaled by some arbitrary factor to provide a wider range of representable values. The scale factor is provided in the integration guide, and is usually a fixed value, but I have encountered some labels with values scaled by values from other labels.

The format for Discrete labels is always specific to the LRU. To know what this encoding is, you must have the integration guide.

Ultimately the difference between each particular ARINC429 label will depend on the specific equipment to which you are interfacing. The standard data types (BNR/BCD/Discrete) provide a rough idea of how the data is packaged, but the integration guide is the authoritative source for data encoding.

1: I use LRU as shorthand to mean any ARINC429 node. In practice, many ARINC429-compatible devices are not necessarily line-replacable.


Why do helicopters not roll over when flying forwards? Related to this answer: with velocities so different at forward going and rearward going blade, why does the helicopter not roll over? The higher airspeed at the forward going blade should cause more lift, shouldn't it?

Juan de la Cierva's first autogiro did roll over, twice, and he then applied the principle of blade flapping, a stroke of genius. Flapping is created by allowing the blade to move up and down. Depending on rotor head design this is done in different ways:

By a flapping hinge at the hub, allowing vertical rotation.
By a teetering hinge on two-blade designs, where both blades together are hinged so they can teeter-totter, one flapping up while the other flaps down.

The lift stays equal at both sides because of blade flapping. If the blades can freely travel up- and downwards, the forward going blade indeed experiences more lift, but as an effect of this starts to travel upwards and reduces its angle of attack. The rearward going blade experiences the reverse, less lift makes the blade descend and increases angle of attack. The lift distribution with and without flapping is depicted in this figure from Prouty, Helicopter Performance, Stability and Control:

The local angle of attack distribution of an example helicopter travelling at 115 kts looks like this:

The rearward going blade has a local AoA of 9°, not very far from stall. Increasing airspeed will at one point result in retreating blade stall, with associated loss of lift and increase of drag, and then the helicopter will start to roll over.

Notice that the reverse flow region is not really a big problem in lift creation:

It is close to the disk centre, where lift creation is minimal anyhow.
The loss of lift is reduced because of the increased AoA
Not only lift reverses, drag is negative as well: in this region the airstream actually helps to propel the blade, reducing the required profile power a bit.


What's the technical name of the side window on Boeing and on Embraer? On Airbus, the window beside the Captain and the First Officer has the technical name of SIDE WINDOW.
What's the name on other aircraft, or they have the same specification?

The windows to the side of the pilots on the Embraer airplanes are called "Direct Vision" (DV) windows.   They are named as such because they can be opened and removed both during normal ops on the ground and emergency ops while airborne to provide forward vision when the main windscreens are obscured.


Do I have to prove my flight training time abroad when applying for a standalone FAA license? I have done flight training in Germany and hence hold a German EASA Private Pilot License. For this I did the appropriate flight training which is documented in my logbook. But in Germany these logbook entries are not endorsed by an Instructor, it is the flight school sending the paperwork to the CAA that confirms you fulfilled all requirements.

Now I am in the situation, that I want to get a stand-alone FAA license. The two Part 61 flight schools I enquired so far both stated, that without logbook endorsement, non of the flown hours could be credited for the requirements of 61.109. But I also have German pilot friends that claim they also had no endorsements and that this was no problem while getting the license.

Is there maybe an official position paper of the FAA or something that states in more detail, what a foreign pilot needs to bring to prove being eligible?

And of course I know, that I will need additional training, but hopefully not 45 hours again. Therefore if the assumption of StephenS in the first answer is correct and I can use my logbook to prove part of the 20h DUAL (later night training is endorsed and 2.5h flying with CFIs in the US), then maybe I can reduce the requirement to about 15h. But where does the interpretation of only the 20h DUAL must be endorsed come from and not the SOLO or the rest to 40h? And what about the specific requirements in the section below in 61.109? If I have a cross country which is not endorsed, does it fulfill the requirement or not?

To keep this topic straight on this point, I am aware of all the necessities to start flight training:  Regarding medical, I have a Class 3. Regarding student license, I have a 61.75 validation of my German license with ASEL and Instrument. Regarding Visa I am already staying in the US and working legally on a visa, the flight training is just part time.

You can find the detailed requirements for a FAA PPL in Part 61 Subpart E.

The total time of 40 hours can be met by any flight time you have logged, either DUAL or PIC.  (In theory, SIC should qualify too, but I can't think of any legal way for a student pilot to have that.)

DUAL time can only be logged when you are receiving "training" from a CFI, who must endorse each such log entry along with a description of said training (maneuvers, procedures, etc.) in the remarks.  This endorsement is what allows those hours to count toward the 20 hours of "flight training" required for your PPL.

The "solo" time of 10 hours can only be met by flight time where you are the only person in the plane, meaning that it can only be logged as PIC time. PIC time does not need to be endorsed--ever.

Where I think you're getting hung up is that a student pilot cannot legally act as PIC without getting an endorsement before the flight, and those endorsements have limitations.  For instance, my first endorsement only allowed me to fly around the pattern at my home airport, the second allowed me to fly between my home airport and a neighboring airport, and the third was for a specific cross-country trip that I'd previously flown with my CFI.  However, the resulting PIC time was not endorsed by my CFI after those dozen or so flights.

In your specific (and unusual) case, you were able to legally meet the solo time and cross-country time requirements without an endorsement before those flights.  Still, like me, you don't need any endorsements after the flights.  Just logging the PIC time yourself was enough for it to count.

Your records and history will undoubtedly look strange to your CFI (and eventually your DPE), so it's best that you make it easy for them to see which specific log entries you're using to meet each requirement.  I'd suggest marking those entries with sticky flags, noting which FAR(s) they fulfill, and including a translation of the remarks if they're not in English.  Don't note or translate your entire logbook, though; they don't care about anything beyond seeing that you've met the minimum requirements.  And, while it shouldn't matter according to a literal reading of the regs, common sense suggests a preference for time logged in US aircraft (N reg) at US airports (Kxxx).

Finally, FAR 61.103(j) says that any applicant for a US PPL must "Hold a U.S. student pilot certificate, sport pilot certificate, or recreational pilot certificate." There's nothing in the regs that says a validated foreign PPL qualifies, so you'll need to discuss with your local FSDO; if they say it does, it's best to get that in writing so there's no paperwork problems with the DPE on the day of your checkride.


Brace position - Why hands atop head in the UK, but on ankles or atop seat in front in the US? Source: Does the brace position save lives?,  By Oliver Smith, 2013 Mar 13, telegraph.co.uk

"To adopt the brace position passengers should place their feet and knees together with their feet firmly on the floor,” added [Steve Allright, a British Airways training captain] .... “Feet should be flat or on the balls of their feet, and further back than the knees. In the event of an impact, this position helps prevent shins and legs being broken against the base of the seat in front, which would obviously hinder evacuation.
"Passengers should bend as far forward as possible, if it's in reach, they should rest their head against the seat in front, with hands placed on the back of their head. Hands should be placed on top of one another (not with fingers interlocked) [emphasis mine; this seems a critical fact], elbows should be tucked in to their sides. The head should be as far below the top of the seats as possible. This position prevents flailing of the arms, minimises the risk of broken fingers and protects the head from moving objects.”
The position varies slightly in the US. Rather than placing hands on the back of the head, passengers are advised to place them on top of the seat in front, or to hold their ankles.

1. Why the difference in the hands' position? Which is more protective?
2. What does it mean to 'hold their ankles' with the hands? Simply place your hands atop your ankles?

The difference is just because there are often disputed methods on which technique is best. To be brutally honest, many accidents are so severe and can't really be analysed, so this is still a point of contention.

I would hypothesize that the UK version is safer as the hand position protects the skull and face from direct impact with the seat in front; instead colliding with the inside forearm. This will naturally reduce impulse (strengthy plastic vs. fleshy skin) and should thus reduce injuries.

The concept of holding ankles stems from the position your body is put in when holding your ankles. Any kind of "holding" is fine, touching on top or sides. It puts your body into a position that ducks your head and should (because of close seat proximity) rest your head against the seat infront anyway.


Why do small jets usually have one low flap setting? For example, the CRJ has a flap setting of 0, 8, 20, 30, and 45 degrees.

The Learjet has similar features across their models, as far as I can see which is 0, 8, 20, and 40 degrees

Why do smaller jets have one low flap setting? Why not have 0, 8, 15, 20, 40? Comparing to larger aircraft like the 737, they have a flap setting that captures just about every degree you can imagine.

The provision of lots of flaps settings is motivated in part by the desire to provide as many profile optimizations as possible. Generally, the less the flap extension for takeoff, the more efficiency you have in a departure plus better engine failure performance, but you need the longest runway, so you would use the least extension allowable for a given runway.

The CRJ was originally certified without an 8 degree flaps setting, and it was added as an option a year or so into production.  In general, you will always use Flaps 8, unless conditions require Flaps 20 (shorter runway).

It can create a trap for the CRJ because if you are departing an airport where 20 is required to meet departure performace requirements, and you set Flaps 8 by mistake, there is no Takeoff Configuration Warning mode to warn you you're at the wrong takeoff flap setting (only a warning for 0, 30 and 45... it can't know which 8/20 TO setting you actually want) and you can take off with insufficient flap extension and get into a bit of trouble when you rotate at the Flaps 20 Vr and you don't lift off.  When departing a short field that required Flaps 20, you had to be extra careful to make sure Flaps 20 was selected.


With today's technology, why can't we find crashed planes How can a plane just go missing? It's mad surely with the technology these days they could at least pin point the location of a plane. We have the technology to transmit pictures of Pluto back to Earth million miles but a plane goes missing and can't be found?! Even if my iPhone got lost, I'll be able to have an app locate it for me.

Having a technology and using it are two different things. As already noted, you are able to get pictures from Pluto because your tracking station knows where it is.

Similarly, the aircraft position is determined by Primary Radar, which literally scans the sky, but its effective range is limited and they are costly to operate. The secondary Radar locates the aircraft by interrogating its transponder, which provides the ATC with its location and speed. However, if the transponder is not working, there is no way for to detect the aircraft locations.

The aircraft can also communicate with the ground station using ACARS, but it depends on on board electrical system. The same goes for the ADS-B, which depends on onboard systems for determining its location and speed.

Its a bit like trying to find your mobile after switching it off. No app is going to work.

Assuming that the aircraft is involved in a crash, the Emergency Locator Transmitter (ELT) can be used to trace the aircraft. However, these are not mandatory in scheduled flights(though ULB is mandatory).

Satellites could help, but again, they should know where to look for.

The wifi or working mobile phones onboard could help, but these are yet to be implemented in any big way.

The next generation technologies under development will allow  real time tracking of the aircraft, but these are still under development.


What special training is required to fly in the Washington DC area? I remember hearing that special training was required to fly into the Washington DC area and that it didn't really apply to me (maybe it was VFR only?).  What is the requirement and what must you do when flying in the area?

There is a training course on FAASafety.gov that all pilots operating VFR flight within 60nmi of Washington DC must take.

Since I assume you are flying IFR, you would not be required to take it.

From AOPA:

  All of the following operations are exempt from the training
  requirement:

  Pilots operating under instrument flight rules (IFR);
  Law enforcement, military, and aeromedical operations; and
  A pilot who must deviate to the extent necessary to address an emergency situation.


Do modern aircrafts like 747/787/A320/A380 have some Plug and Play subsystems/sensors? Do modern passenger aircafts like 747/787/A320/A380 have some sub-system or sensors which are plug and play that might include some kind of sensors or radars which comes as optional and can be used plug-play as and when needed as per the requirement?

It wouldn't make much sense.

By definition "plug and play" would means that the avionics automatically and silently adapts to whether whether the optional device is present or not.

This would mean that if the device is physically fitted, but not in contact with the main avionics -- say, a wire might have broken or shaken loose recently -- then the cockpit instrumentation would look exactly as if it had never been there. This is not desirable: when something the pilot thinks will be available for the flight isn't actually available you want to tell him explicitly so he can decide whether the problem needs to be planned around or reacted to.

Of course there are limits to how much the plane can itself verify that it is whole and in working order -- that's why there are preflight checklists. But to spend engineering effort specifically on allowing it to fail silently when communication with one of the sensors is lost, that would be counterproductive.


How can the F-16 remain stable when there is a loss of hydraulic power? Edit for justification:

This question is different from If the EPU (Emergency Power Unit) on a modern fighter jet fails, will the aircraft drop out of the sky? for the following reasons:

The question in If the EPU (Emergency Power Unit) on a modern fighter jet fails, will the aircraft drop out of the sky? asks if an aircraft drops out of the sky if the EPU (Emergency Power Unit) fails, for a generic aircraft. The accepted answer only briefly touches on the F-16, and certainly not in a way to answer this question. This question is specifically about an aircraft with RSS (Relaxed Static Stability), and how this relates to loss of hydraulics and power.

Question:

The F-16 has Relaxed Static Stability (RSS) to enable a high degree of maneuverability.

This causes the aircraft to be inherently unstable and RSS is corrected for by the on-board computer in real time, as part of the fly-by-wire system.

In the event of loss of hydraulic power, the ailerons cannot be operated, the on-board computer/avionics will also fail, if there is no power. The EPU (Emergency Power Unit) will re-establish hydraulic and electrical power, but this doesn't happen instantaneously. It takes some seconds.

During this critical window, what allows the F-16 to remain in stable flight in the context of RSS?

Reading this PDF it seems that the F-16 can be unresponsive to pilot input, yet remain in stable flight.

My question is, how is this achieved? How is it possible?

My own reasoning:

Either the F-16 is not as inherently unstable as I'm given the impression it is, or, there is enough hydraulic power and electrical power left in the interim between power from main hydraulics to switching to the EPU to allow the fly-by-wire system to keep the aircraft stable.

As I understand it (I'm neither an F-16 pilot nor an F-16 mechanic), Relaxed Static Stability doesn't mean the aircraft is unstable, just that it's less stable than the long-established standard.

To put it another way, if you build a free flight model airplane scaled from an F-16, you'll have to put the center of mass significantly further forward than its location in the full size, piloted F-16, in order for the model to have static stability.  The same is true of many radio control models intended to be flown by an experience model pilot -- they're what's call "neutrally stable".  The primary characteristic here is that these models will "go where you point them" and require that you "fly them all the time" -- unlike a trainer, or many/most scale models of piloted aircraft, you can't just set the throttle to cruise and take your eyes off the airplane, and expect to find it in a predictable location a minute later.

The same is (mostly) true of the F-16, in that, in most flight regimes, it's stable enough that as long as a violent maneuver wasn't in process when the flight computer restarts, the aircraft won't be badly out of shape by the time the computer returns to full function.  Back in the 1980s, however, it wasn't unheard of for a pilot to have to eject due to a fly-by-wire system failure; my parents lived near Hill AFB and would hear by local rumor mill and newspaper of "another F-16 crash" every so often.

Bottom line (again, based on my understanding as an "interested bystander") is that the F-16 is just about stable enough that it can remain recoverable through a control system restart, if it was in a steady state flight condition beforehand.


ATC calling out regional airlines in traffic advisories: phonetic or "aircraft paint" airline used? When ATC points out traffic that is a regional airline (e.g. Compass, Envoy, SkyWest, etc.), do they use the phonetic callsign of the airline, or do they use the callsign of the airline that they are operating as (how the plane is painted)?

The plane that a regional airline flies might be painted differently, depending on which airline they are flying for.

My thinking:

1) Pros of using the "aircraft paint": aircraft who are flying in VMC can spot each other more easily.

2) Pros of using the phonetic callsign: aircraft are on the same frequency in the same phase of flight, so they are more situationally aware if you use their phonetic callsign because they have probably already heard it in another transmission.

The call-sign is not used – it's as useful as saying the tail number if it's a GA plane ;)

The information given to the pilot is in FAA JO 7110.65 – section 2-1-21. TRAFFIC ADVISORIES.

Azimuth (o'clock position), or cardinal position (e.g., northeast) if moving rapidly
Distance
Direction and/or relative motion (e.g., southwest bound, converging)
If known, type and altitude.

Example:

ATC: [You], traffic, 12 o'clock, 10 miles, opposite direction, Boeing 737, one thousand above.

A comment by @user71659 remarked that Cockpit Display of Traffic Information (CDTI) can be used to follow traffic, and hence a call-sign/tail number would be given. This notice was cancelled in May of 2016 and was only to authorized users.


What is the performance of a flat plate wing? By flat plate I mean this:

Source: Physics.SE

Low performance indeed, but how much low? How would:

The angle of attack,
The speed range,
The turn capability,
The fuel consumption,
Or other significant characteristic

compare to the ones of some reference foil, e.g. a NACA 00xx?

Link to related benchmarks appreciated.

I cannot answer all your questions, but maybe point you to some facts to come closer to an answer.

Most important is the thickness of your parallelepiped - more than a few percent will just increase drag, without benefiting performance. It should be as thin as structurally possible. There are lots of model airplanes using flat plates for lift. The most popular are flying discs like that below:

(picture source)

Lift

The lift curve slope of a flat plate is the same as that of regular airfoils, complete with stall. They have a zero-lift angle of attack of 0° (obviously) and separated flow on the suction side. The maximum lift coefficient of 0.7 to 0.8 is reached at moderate angles of attack - details depend on the aspect ratio.

Your typical four-digit NACA airfoil will have a maximum lift coefficient of 1.2 to 1.6, depending on camber and Reynolds number (picture source).

Drag

Due to the missing nose thrust, the aerodynamic force vector will stand almost perpendicular to the plate's plane. It will be slanted slightly backwards due to friction, but the separated flow on the suction side means that friction will mostly happen on the pressure side. As a rough approximation, the drag coefficient of the flat plate is $$ c_D = c_L \cdot \sin\alpha + \frac{0.43}{log\left(\frac{100}{R}\right)^{2.56}} + 0.3 \cdot\delta\cdot\cos\alpha$$
with $R$ the relative surface roughness, $\delta$ the relative thickness and $\alpha$ the angle of attack. The first part is caused by the direction of the lift vector, the second part is the friction contribution and will be dwarfed by the pressure part, and the third part is an approximation for the suction along the thick trailing edge. At $\alpha$ = 5° and a lift coefficient of 0.5, the drag coefficient will already be around 0.05.

Regular NACA airfoils will have a $c_{D0}$ of 0.004 to 0.01, depending on Reynolds number, and their $c_D$ at stall is normally between 0.02 and 0.025.

Performance

From the above it is fair to assume that drag in cruise condition will easily be 4 times higher (induced drag is not affected), and the optimum cruise condition will be at a lower speed due to the higher zero-lift drag. On top, the airplane will need a bigger engine to stay airborne, which will reduce its useful load. Expect fuel consumption to increase in line with the drag increase.

The stall speed of an aircraft with a flat plate wing will be approx. 50% higher than with a proper airfoil on the wing, and drag will increase much more at high lift coefficients than usual, which translates into very low sustained turn rates and load factors.

Only the angle of attack range will stay similar. All other parameters will be markedly affected.


Can a Boeing 767-200 fly at 510 knots at a height of 400 metres? Can a Boeing 767-200 physically fly at 510 knots at around 400 metres altitude?

If it did manage that speed, how likely would a structure failure be?

Also, if those measurements were achieved, how difficult - relatively - would it be to control?

The speed is secondary - what determines the physical limits of the Boeing 767 is Mach number and dynamic pressure.

510 kts at 400 m in standard atmospheric conditions equals Mach 0.775. This is well within the limits of the Boeing 767. But at 400 m it produces a dynamic pressure of 40,567 N/m², and that is too much. The maximum dive speed $v_D$ of the 767 is 420 kts.

This only means that flying at 510 kts is illegal, but it is still possible. If the airplane dove down to those 400m from enough altitude, it would entirely be capable to reach this speed, but would slow down once it stops diving.

There are several effects which can cause a catastrophic failure when flying too fast:

When the aircraft flies into a gust, the resulting load factor can overstress the structure.
When the pilot commands large control inputs, he will also overstress the structure.
Flutter might also cause structural damage.

The maximum Mach number of the 767 is 0.91 (0.05 above the maximum cruise Mach number, which is 0.86), and this corresponds to 523 kts in 11,000 m.  Thankfully, certification requirements demand a margin of 20% between the maximum speeds and flutter onset speeds, so flutter might be close, but is still tens of miles per hour away when diving to 510 kts. Remember, to experience flutter you need also to excite the motion first. Here is a good discussion of this topic.

In short, flying a Boeing 767 in 400 m at 510 kts is not recommended, but is entirely possible and most likely even safe when done in calm air and by a calm pilot. It only won't last long, because the engines will not produce enough thrust to maintain that speed. Flying this dive requires guts, but no special skills.


Aircraft fuselages being shipped on a boat Earlier this morning, my wife and I were down by the docks in Southampton (UK), watching cruise-liners move about with our binoculars. Whilst panning around, we noticed two old aircraft bodies (/fuselages - are the terms interchangeable?) on a large trailer, looking like they were waiting to be loaded onto a cargo vessel.

They had the wings, tail & nose removed, but the cavities that this exposes had been covered by yellow maintenance covers. I can't imagine they are simply being scrapped if the innards were protected like this.

So, I imagine they are being shipped somewhere for spares, is this trade a regular thing, and we just don't normally see it?

The aircraft you saw was N733UK (not Z733UK). It's a Boeing 737-300, most recently operated by European Aviation Group, and before that by easyJet  and bmibaby. It was stored at Bournemouth Airport in 2015 and subsequently dismantled.
This site suggests it's on its way to China to be used for training.
https://www.planespotters.net/airframe/boeing-737-300-n733uk-european-aviation-group/rovlz3


Is this a good or a bad propeller? I want to see if a propeller is bad or good for generating static thrust. This is what I know about the propeller and the engine used to turn it during a test:

Engine shaft power, $P$ = 0.58 hp

Propeller diameter, $D$ = 8.5 ft

Revolutions per minute, $RPM$ = 245

Static thrust, $T$ = 18.75 lbf

Can I calculate the efficiency of the propeller? What is the maximum achievable efficiency?

Additional explanations

The formula I was suggested to use could be exactly what I need. However, using it, I do not get some reported experimental results like:

Engine shaft power, $P$ = 6 hp

Propeller diameter, $D$ = 8.5 ft

Static thrust, $T$ = 66 lbf

Propeller efficiency, $\eta_{prop} \geq 66\%$

Gear efficiency, $\eta_{gears} \geq 85\%$

Doing the calculations: $\eta_{prop} = \sqrt{\frac{T^3}{(P^2 \cdot \pi \cdot \eta_{gears} \cdot \frac{D^2}{2} \cdot \rho )}} = 37.2\%$ which is well below 66%.

Engine shaft power: P = 0.58 hp, Propeller diameter: D = 8.5 ft, RPM = 245, Static thrust: T = 18.75 lbf

$\eta_{prop} = \sqrt{\frac{T^3}{(P^2 \cdot \pi \cdot \frac{D^2}{2} \cdot \rho )}} = 49.5\%$

where $\rho=1.2 \frac{kg}{m^3}$

So at an efficiency of 49.5% that propeller is rather poor.

Note: I used the formula that relates static thrust to efficiency, power and propeller diameter from here.


Can anyone identify this plane? Can anyone please help me identify this biplane? The photo was taken in Newcastle, NSW, Australia. I can’t seem to find anything.

Looks very much like a de Havilland DH.82 Tiger Moth.

This webpage lists all Tiger Moths used by the RAAF.