Does weight and balance of an airplane matter more on takeoff? On a few international flights with non-full cabin, the crew has asked no one to move to open seats until the plane has finished take-off. I assumed this was just to force people to sit down during take-off and not cause problems, but when I asked I was told it was because of weight. The claim is, the airplane is balanced by where people are sitting. The next claim is by the end of the flight, there is less fuel, so if people have switched seats there is less of a problem. This weight balance apparently uses all information, people, baggage, and fuel.

I believed this, until recently a plane had lost at least 30 peoples baggage, some people had more than 1 bag. The bags were left at the previous airport, and on arrival no one knew that the bags were not on the plane.

If the lack of knowledge for bags not being on the plane (which seems logical, why would they depart without the bags), how did this change in weight not show in the take-off, or was this a dangerous occurrence?

By regulation, a "weight & balance" must be computed before departure to ensure that the weight is within the weight limits for a number of different conditions and that the weight is distributed such that the c.g. (center of gravity) of the airplane is also within the longitudinal c.g. limits for those conditions. That c.g. is typically computed assuming the the passengers are in the seats they have been assigned. If the passengers are seated elsewhere, the computed c.g. is not accurate. In other words, the pilots wouldn't know where the c.g. is or whether it is even within limits.

The takeoff trim setting is affected by the c.g. If the pilots set the trim according to the computed value, and the c.g. is considerably aft of that, on liftoff the nose is going to want to pitch up more than the pilots expect. If the c.g. is so far aft that it is well beyond the aft limits, serious control problems can occur. If the c.g. is far forward of what the pilots are expecting, they're going to have to pull harder on the elevator control than expected to get the aircraft to rotate, and that is going to extend the takeoff roll.

Different makes of aircraft vary widely in c.g. limitations and how tolerant they are limit wise of passenger placement in aircraft that are not full. For example, when I was flying Metroliners, if you had few passengers, you had to ask them to sit toward the rear. I once got a strange look from Rosey Grier (Google him if you don't know who he is) when I had to ask him to sit in the back of the aircraft.

Once you're in the air, the movement of passengers is of lesser concern balance wise. You're at speed, the elevator is fully effective, and the pilots or the autopilot keep the airplane in trim. In other words, the trim is what it is rather than a computed value that might not reflect reality.

Also, on large aircraft, once you're in the air in level flight and if you're so inclined, you can work out your weight by using your fuel flow, pressure altitude, and airspeed. Then with the weight and your trim setting you can come up with your c.g. I would guess that most of the glass cockpit aircraft probably do that for you automatically if you request it. My experience stopped with the 747-200, which is now a near relic.

The c.g. limits are defined conservatively, and usually in terms of the percent of the mean aerodynamic chord. It's not a case of that if the aft c.g. limit is 33% mac (a common value for 747s) and you're at 33.1% you're going to crash. It's just a case that you're beginning to move into an area that gives you a lesser degree of controllability than is deemed necessary for some situations. Continued movement to an extreme value would eventually make the aircraft uncontrollable.

Insofar as the bags-left-behind part of the question, I don't think their absence would cause a problem. If the computed c.g. including the bags was right right up against the aft c.g. limit, their absence could conceivably put the c.g. beyond the aft limit. The pilots might notice it, but handling it would not be difficult. However, aircraft are typically not loaded such that their c.g. is close to a limit. A preferred aiming point for 747-100s, -200s, and -400s is 26.6% mac.

Just for the heck of it, I did a weight & balance for a 747-400, loading it so that the takeoff c.g. was 26.6% mac. I then took 5000 lbs (100 bags x 50 lbs each) out of the most forward baggage area. This changed the the c.g. to 28.0% mac, still within limits. On the 747, a given weight of baggage misplacement has less potential to affect the c.g. than the same weight of passenger misplacement because the passenger seating extends over 20 feet forward of the most forward baggage compartment and over 17 feet aft of the most aft baggage compartment.


Are there any specific weight or structural reasons to choose low vs. high wings for a cargo aircraft? I have a large cargo aircraft concept and I am debating between a high or low wing.  It seems like both are viable, but intuitively it seems structurally harder to support a high wing.  Alternatively though I like the idea of a high wing to raise the engines and provide better field landing abilities.  Can anyone comment on the weight penalties associated with one concept or the other?  Is there a structural advantage to one configuration?

@Ron Beyer has pointed you in the right direction.  Study existing designs going all the way back to the Gigant.

The wing is by far the strongest part of the aircraft as it must carry leveraged aerodynamic loads and the weight of the aircraft while flying. A low wing may be slightly stronger to positive G loads as the fuselage forms an arch over the middle of the wing.  However, for cargo transport the high wing offers the advantage of a lower set, roll through cargo bay and more stability in flight.

As far as landing gear, the low wing offers placement
of gear on wings for wider track. High wings mount theirs in the fuselage, but the high wing offers the opportunity for greater ground clearance of obstacles on "unfinished" landing strips.

As you can see both are made and both are in service worldwide.  Commercial freight would favor the 747 type, military the C-17.  And let's not forget turboprops for fuel efficiency!

Both high and low wings will fulfill the requirements for cargo hauling, what about both on one plane to get wingspan back under 150 feet!.


What are the conditions for the percentage power vs fuel consumption figures in the engine operator manual? For the Lycoming O-160-A4A, the operator manual says in Economy Cruise, which is 75% Rated power and 2450 RPM, the engine produces 135 HP and burns 9.5 GPH.

How were these figures determined? Were they in standard conditions at sea level, or on the ground at the factory?

It is true that if you assume a power setting to be constant at 65% power and the aircraft is leaned at peak, the aircraft will consume 9.5 GPH, or is this figure not reliable?

The correct source for burn data is not the Lycoming operator manual, but the aircraft manufacturer's manual.

All modern POH have the consumption data qualified (in tables) relative to altitude and temperature.

When adding a new plane to our fleet, we enter that data in and do a linear regression on the data, so that we have a generalized equation for flight planning purposes.

You need to look at the aircraft documentation, not the engine documentation, because the same engine in different planes will have different performance. The POH will have figures which were established empirically, by the manufacturer's test pilots. Fuel burn tests are conducted at various altitudes, and temperatures.

Please note that to answer your fuel burn questions, it is essential to know the aircraft, configuration, and really, have that specific POH.  Then the questions you pose are readily answered.


Why do (some) aircraft shake at low speeds with flaps, slats extended? I landed a couple of times as a passenger with the Embraer 190 (I like Embraer very much) on runways with a length below 2 km.

I noticed that the plane started to shake or vibrate quite strongly once reducing its speed prior to landing. The flaps during this time were fully extended. How can one explain these vibrations? I have to note though, that I often sit in the back of the fuselage, where vibrations tend to be more pronounced.

There are many phenomena which can cause vibrations. Without knowing further details like the frequency, starting moment or the weather conditions on landing it is difficult say. Common causes are:

Stall buffet/ self induced turbulence Normally when a plane lands it flies with low velocity and a high lift coefficient, near to stall. The flow detaches much earlier and there is more turbulence behind the main wing. The tailplane has to fly through this turbulent zone and hence you feel the vibrations. Sometimes deploying the spoilers, even if you're not flying at stall speed is enough to create turbulence which will hit the tailplane. T-tail airplanes are less affected because they're further away from the air zone influenced by the main wing.

Atmospheric turbulence Can be created due to thermals (in that case it should be sunny) or wind hitting ground structures. If you have landed a couple of times and always felt the vibration it probably isn't the answer.

Wake turbulence Shouldn't be your case either, separation minima exist to avoid this problem and it would probably feel different every time you land.


Is there a time limit for a line-up and wait? So this was from a barrage of History Channel documentaries celebrating the century of flight, some 13 years ago. In one of the shows, I recall it being said that an airliner has a time limit for a line-up and wait, else an asphalt runway would start melting behind the jet engines.

Update:

Maybe, it was the case in the early jet age. For those good at finding historic regulations, etc.

We can get some idea of what temperature the pavement would be subjected to by looking at some data on different jet aircraft.

Older low-bypass turbofans produced higher exhaust temperatures over a larger area than new high-bypass turbofans. This is due to the high-bypass engines having more of the cooler bypass air mixing with the hotter core exhaust.

Manufacturers provide various data about their aircraft that can be useful for planning operations at airports. Included in the data are figures showing exhaust velocity and temperature for different throttle settings.

It should be noted that aircraft holding for takeoff clearance will be at idle power. The power will be increased only when cleared for takeoff, so the takeoff temperatures will be experienced only briefly.

Although hot air tends to rise, the 737 analysis notes that:

  The buoyancy effects are considered to be small relative to the exhaust velocity and therefore are not included.

The figures for the 707 show the exhaust contours starting at the engines. The highest temperature labeled is 200°F (93°C), though higher temperatures would be expected closer to the engines. At idle power the 150°F (66°C) contour barely reaches the tail and stays above the ground. At takeoff power, the 200°F contour reaches bast the tail, but the highest temperature in contact with the ground would be the 150°F. These figures do note "data not verified by test".

The figures for the 737 note that the contours were produced by computer analysis. These contours only start at the aft end of the aircraft. The engines on the 737 are located closer to the ground than the 707. The original 737-100 and -200 models have the highest temperatures. At idle thrust, the 150°F contour barely reaches the tail of the plane, though it may reach the ground closer to the engines. At takeoff, the 200°F contour extends past the tail, and definitely reaches the ground.

The DC-8 is similar to the 707. At idle power, only small contours are shown for 125°F (52°C). At takeoff power, temperature contours reach 200°F but only the 150°F contour reaches the ground.

Based on these temperatures, it does not seem that an aircraft sitting on the runway with engines at idle would cause issues with the pavement. On a hot sunny day, asphalt could easily reach 150°F or more.


How does induction ice form in and affect jet engines? Recently someone talked to me about the possibility of induction ice on the engine:

He told me that because of conditions around fan and compressor blades (mainly because of pressure and temperature) some ice may form, under certain exterior conditions, and destruct the engine by ingestion or by stall of boundary layer.

My question: It is really possible? If yes, can someone explain to me how it works?

I don't find proper explanation on Google.

I raised this question after this hypothesis:

  Icing inside jet engines can become a hazard at high altitude near large thunderstorms, when moisture turns into tiny ice crystals that can be sucked inside an engine. If the ice melts but then freezes again on metal surfaces, accumulating ice can either break into chunks that damage turbine blades, or melt and douse the ignition system.

source

Induction ice can be a problem for jet engines. Other answers have explained how the ice forms. The air expands and cools in the inlet before entering the engine. The first stages of the compressor do not compress the air enough yet to warm it enough to prevent ice from forming. Low power settings can also make it easier for ice to form. Certain atmospheric conditions make ice more likely to form.

The FAA released AC 20-147, which "provides guidance and acceptable methods, but not the only methods, for demonstrating compliance with the applicable engine induction system icing and engine ice ingestion requirements." This describes different types of icing, and the effects it can have on engines. It also describes how engines should be tested to conform to the regulations for these conditions. Ice can form in various places:

The fan or compressor blades themselves
Vanes
Sensors
Bleed ducts

This ice can cause various problems:

The ice can come off and damage engine components downstream
The ice will reduce the effectiveness of blades, making it harder for the engine to compress the air
The ice can impede the flow of air in the engine
The ice can block sensors, preventing the control system from correctly monitoring the engine, which can lead to power loss or instability

One form of icing that has been an issue lately is ice crystal icing. This is caused by small ice crystals in the upper atmosphere, particularly above convective clouds. The FAA has issued an AD (Airworthiness Directive) recently about this.

  This type of icing does not appear on radar due to its low reflectivity, and neither the airplane ice detector nor visual indications reliably indicate the presence of icing conditions. Therefore, it is often undetected by the flight crew. Flight in these conditions can cause ice crystals to accumulate in the core gas flow path of the engine.

There were previous events on GE CF6-80 engines (used on 747, 767, A310, A330, and others) that the FAA looked into.

  In the events leading to those prior ADs, the ice has shed during throttle transients and in the descent phase of flight, causing temporary thrust loss.

However, there have been incidents with the newer GEnx engines on 747-8 and 787 aircraft which have been more serious.

  The new events that prompted this AD, however, have occurred during the cruise phase of flight and caused permanent damage (beyond maintenance manual limits) to the engine compressor. In all thrust loss events, data indicate that ice crystals entered and collected in the initial stages of the compressor. Engine temperature data indicate small ice accretions were shed through the core of the engine.

The engine manufacturers are working to resolve the issues on the aircraft currently affected, and in the meantime flight crews are advised to avoid weather conditions where ice crystals tend to form.

  More definitively, the AD includes immediate mitigating procedures for the affected aircraft which prohibit flight within 50nm of amber and red radar returns that are displayed below the aircraft’s flight path during operations at or above 30,000 ft, when approaching, or in, IMC or visible moisture.

  Note: Boeing has also published an updated Flight Crew Operations Manual Bulletin with specific operating procedures for flight crews.


Can airline ignore or get exception from V1 and other safety rules? In this famous video with not to good quality now

             I don't believe this IL76 was able to takeoof if the engine failed. Are the rules ignored? Or it's possible to get permit takeoff without V1 and any consideration for engine failure on multi engine airliner?

Update:Ok V1 maybe is not a rule. It's a number that you get after application of certain rules. But MEP aircraft doesn't have V1 and single engine aircraft as well. They all operate and even can carry people.
Maybe it's possible get an exception to operate ME turbine aircraft without consideration of an engine failure? For example runway is very short or you are heavily leaded and aircraft will not climb at all with -1 engine.

I was not asking about the V1.

Maybe there is an airport somewhere very high with 40 degrees outside, short runway and down slope. Guys have IL76 fully loaded. They see that there is no way they can takeoff applying standard safety rules. But they run calculation and they see that if they use 100% of runway for take off run they will get 1% climb gradient with all engines on full power. If you want to depart very much maybe it's possible to go to aviation authority and ask for a special permit?

To answer the question as asked, no I've never heard of an airline "ignoring" V1.

To address the implicit question, I have no idea what the story is behind that IL-76 operation shown in the video, but I could creatively come up with all sorts of possible explanations for the takeoff roll that essentially matched the available runway: power not set correctly, takeoff data computed incorrectly, poor pilot technique, unexpected tailwind, aircraft loaded heavier than expected, or maybe that crew DID decide that it was so important to get home that they were willing to accept an absurd risk.  But I wouldn't take ONE video without explanation of "what really happened there" as any indication of what airlines in general will do.

At its most basic, V1 is simply the point at which you transition from a "stop" mentality to a "go" mentality: if something goes wrong PRIOR to V1, we'll stop; if something goes wrong AFTER V1, then we'll go.  Now, there are LOTS of things that complicate that discussion... not everything that can "go wrong" is the same: at 80 knots, getting an "anti-skid fail" light is probably not worth aborting for; at 80 knots, getting a loss of all generators probably IS worth aborting for (assuming that V1 is well above 80 knots).  Just below V1, losing an engine IS something you'll stop for; losing one generator or one hydraulic system might not be.  And this is all dependent on the aircraft... in the C-130, we were pretty stop-oriented, and we'd stop for all sorts of things immediately prior to V1 that in the 737 -- a much more go-oriented aircraft -- we'd take airborne.  The difference being, you can stop the Herk pretty quickly & with a comparatively low risk of problems; a high-speed abort in the 737 (as in many jet aircraft) is much more of a big deal.

All that said, though, there is always a speed below which you'll stop, and above which you'll go.  If an engine flames out at 20 knots, you'll stop in nearly any scenario I can think of (that doesn't involve bad guys storming the airport).  In the Herk, it was common that your accelerate-stop speed was above your rotation speed, so V1 was essentially at rotation.  But there was always some speed where your default choice between stop/go changed over.

You might "ignore V1" by simply saying that once takeoff power is set, we're going to continue regardless, but that's just bad decisionmaking by the crew, and not the sort of policy that I could envision ANY airline ever making.  (Again, the case of mortar shells falling closer & closer to the aircraft & bad guys overrunning the airport might be an exception to this... take our chances with the ground rather than with the bayonets.  But the outlandish nature of this exception illustrates how rare it would be to "ignore V1" in any considered scenario.)

Airlines tend to accept far fewer risks than other forms of aviation.  The mission of an airline is to make money, and nothing interferes with that mission like the bad publicity & loss of assets (and potentially, certification) that comes from a crash.  In the military, there can be a mindset of accepting lots of risks because troops are counting on us completing this mission. In general aviation, there tend to be individual decisionmakers, with little institutional guidance & corporate wisdom to back them up.  But the airlines tend to be entirely willing to postpone a flight if it can't be performed safely, so for "airlines" to ignore V1 or other safety rules seems highly unlikely.  (Which isn't to say that an individual crew might not do so, although at least at US carriers, they aren't likely to continue to be employed if they're found out.)

--- EDIT, added in response to updates/edits in the original question:

What you're asking is, in essence, can "they" get permission to take off knowing that takeoff roll = available runway, and if anything goes wrong after the point at which stopping takes all of the remaining runway, then they're dead.  If takeoff roll = available runway, using all engines, after you've reached the speed at which you can no longer abort the takeoff within the remaining runway, and then you lose a motor, you now

Don't have enough runway left to stop, but also
You don't have enough runway left to accelerate to takeoff speed with the remaining thrust (less than the original case)

That's more or less the "bad guys storming the airfield" scenario, where you know that you're dead if you stay, so it makes sense to take off & hope that the motors keep running through the takeoff roll.  Given that the risk of staying is so high, the risk of losing an engine during those seconds of the takeoff roll is the lesser of the two evils.  And yes, in Viet Nam there certainly were times when C-130's would accept those sorts of risks to get the badly wounded out of dirt strips in combat.

Now, is that a reasonable thing to do in peacetime?  Not in my simple mind.  If we are assuming that the IL-76 crew did their performance computations correctly & their long roll was a known & accepted risk, then maybe they reached the opposite conclusion.  It's not something that I'd expect an airline to ever approve with passengers on board, and we'd have to get creative to find a scenario where they'd approve it for a ferry.

Can a crew make that sort of choice on their own?  Well, yeah, at least once.  Would an airline approve that option?  Hard to imagine.


What are the disadvantages of using just rudder to roll an airplane? Ultralights with slight dihedral will roll and yaw on rudder input (e.g the Bloop 3, Maxair Hummer) so some don't have ailerons for the sake of simplicity. Is this kind of control input advisable, or are there disadvantages?

It works in a half-assed way but the key word is half-assed. You'll always be skidding around the sky since sideslip is required to obtain and maintain any rolling moment.  Control response can be somewhat laggy, since you have to induce a skid and wait for the roll, depending on how much dihedral you have.  So to have something approaching snappy control response, you need way more dihedral than is necessary for normal lateral stability.  The inability to cross control limits the ability to handle crosswinds and prevents you from using sideslip to increase descent rate.

So it works after a fashion, but will never be as good as full 3 axis.  The thing with ultralights is that because of the really low mass/large surface area, they are really strongly affected by turbulence, and when close to the ground, half-assed control authority is the LAST thing you want.

Control authority is not a place I would cut corners in the interest of simplicity.  I think that the attraction of 2 axis control for ultralight designers was in the idea that non-pilots getting into ULs would think "Hey that must be only 2/3rds as difficult to learn as 3 axis.  Must be better."


Are there any pitfalls to be wary of when purchasing an "umbrella" insurance policy? Typically, a pilot will have airplane insurance (or renter's insurance, if flying un-owned aircraft), car insurance, home insurance, life insurance and then for good measure purchase an "umbrella"-type insurance (usually up to $1MM). Have there been cases where this wasn't enough insurance, or the pilot thought he or she was insured but there was something unforeseen that rendered his insurance policies ineffective of shielding him or her from liability?

This question is specific towards American pilots, in this case if would be for an "average" person, owning/flying a small single-engine piston airplane and a net worth of less than $1MM.

An umbrella policy is insurance on top of insurance in case your primary insurance is not enough. For this reason it is usually inexpensive relative to to other insurance policies.

Using your example, a million dollars beyond what you are already insured for is a pretty good amount of coverage. It would take a really catastrophic event for a small plane to do more than a million dollars worth of damage beyond the limits of an owner's or renter's insurance policy.

If you're considering an umbrella policy be sure that it does not specifically exclude aircraft because many do. If you purchase a policy through an agent who knows that you are a pilot, you're probably fine but don't assume that your commercial umbrella policy covers you because many commercial umbrella polices specifically exclude aircraft.
I would be more worried about the umbrella policy excluding aircraft (like you mentioned unforeseen things rendering the policy ineffective in the last sentence of the first paragraph) rather than a million dollars on top the normal coverage not being enough.

I'm also assuming that by typical pilot you mean small aircraft not a corporate jet or something that has a lot more potential liability.


Is drag coefficient lowest at zero angle of attack? The drag coefficient of a symmetric airfoil is lowest when its angle of attack is zero. I'm not sure if this is true in general.

Obviously, drag should be smallest for symmetrical airfoils at zero angle of attack.

However, most airfoils have camber, and then the lowest drag is at positive lift coefficients in case of positive camber. Where that point is exactly depends on many parameters; in case of laminar airfoils even local imperfections can have a noticeable effect. Generally, the lowest drag can be found at the angle of attack where the stagnation point is exactly at the center of the leading edge, where the local curvature is highest. A deviation from this point will force the flow on one side to negotiate this point of highest curvature all by itself, resulting in a suction peak which will increase the losses in the boundary layer.

This is a theoretical drag polar (calculated with XFOIL) of an airfoil with a 20% camber flap at different settings and a Reynolds number of 1.5 million. The laminar bucket is clearly visible and produces a range of lift coefficients with nearly identical drag. The small waviness at the lower end of the laminar bucket is an artificial result of smoothing the plot.

What is obvious is how camber shifts the area of minimum drag up and down. If you use the right side of the plot to find the angle of attack of minimum drag, you will find that this is not constant but goes down as flap angles go up. For the 0° flap polar it is at about -2° AoA. This is caused by the induced angle of attack which increases with the lift coefficient.

The 6-series NACA airfoils were the first to be systematically designed with the pressure distribution in mind, and the design lift coefficient is where the condition of the ideal stagnation point location is met. This is indicated by the digit right after the hyphen in the airfoil name: Divide this digit by 10 and you have the lift coefficient of minimum drag.

Example: The $63_1-412$ airfoil has its lowest drag at a lift coefficient of 0.4.

If you want to know the angle of attack with the lowest drag of a whole airplane, this is a very different matter and needs to include the drag due to lift, which is of course smallest at the zero lift polar point.


What is the correct term for the type of performance chart where curved lines are followed? What is the correct term for the type of performance chart where, from a starting location, curved lines are followed to various reference points to eventually find a solution?
For a specific example, the type of chart I'm asking about can be found in the Pilot's Handbook of Aeronautical Knowledge as Figure 11-23:

Background to the question: I would like to reverse-engineer a performance chart in order to use it in a spreadsheet. I have no idea how to do this but if I can discover the name of the type of chart it is, I can begin by looking for notes from other people who have attempted the same.

The correct term is nomograph or nomogram. Thanks Gerry!
Also, thank you to Peter Kämpf and Dean F. for helping to answer my actual question, instead of the one I asked.


Can hang glider hover straight into wind and keep same position? Isnt resultant force allways  pointing slighlty backward at every wing,so why hang glider is not push downwind by the wind?
From theory that cant be possible,so does wind somehow coming at him at angle from below? ground seems flat,maybe slightly angled..
(Is it easy what his doing or that can do only very very skilled pilots?)
Can he penetrate continusly forward into wind direction in zag-zag motion,first straigt up and then down-forward or maybe with dynamic soaring like birds do?

The ground is not flat, and indeed slightly angled. This is enough to "hover".
Specifically, the ground slope should be equal or more than the max L/D ratio of the hang glider at the current wind speed. The wind should go 'up' as much as the glider goes 'down' per unit of distance. The ground seems to go up about 2m over a distance of maybe 10m, which is a slope of one in five. An L/D of 5 seems perfectly reasonable for a hang glider.


What does a higher pitching moment mean? (ie -0.095 vs -0.0022) I've found that as the angle of attack increases, the moment becomes more negative. I wanted to know what does that negative value say about the characteristics of the airfoil, and what is its importance.

A negative pitching moment is stabilising: it is a nose down pitching moment, which is what is required for static stability.

If the stabilising moment of the wing profile increases with AoA, the horizontal tail volume can be smaller - less resistance.


Electric Airplane - Hybrid / dual type engines how would that work? If you have an airplane with electric propellers for take off and landing and you have a turbofan/jet to reach higher speeds for cruise.
For example, electric propellers can go to 250mph and turbofan to 550mph

Do you switch off the electric propellers or leave them on ?
Do they work in conjunction ?
What is the effect on the propellers when the turbofan reaches 550mph ?
Is the thrust added if both engines are working ?

The B-36 Peacemaker had 6 radial engines, driving 6 propellers, AND 4 jet engines in 2 nacelles.  The jet engines were used for takeoff and for "dash" over a target.  The jets were turned off during cruise because they used considerably more fuel than the piston engines.

As such, they HAVE made propeller/jet hybrid aircraft in the past, though not electric.

To answer your questions:

You probably want to feather the propellers and kill the electric motors.  If the props can only drive you to 250 MPH, leaving them windmilling in the slipstream when the jets are running will add drag, which will only serve to hurt your cruise speed and/or increase your fuel consumption.
They only work in conjunction as speed BELOW what your props can drive (eg 250 MPH, in your example).  Beyond that, if it's speed you're after, you're better off without the props.
At speeds above what the props can deliver, they're essentially small windmills.  And not very efficient ones at that.
See 2.

Now, what WOULD be helpful as a "hybrid" aircraft would be a gasoline engine, turning a prop, with an electric motor added between the engine and the prop.  The electric motor could supply extra power during takeoff and function as a generator/dive brake on the prop during descent.  In the event the gasoline engine failed, the prop/electric motor assembly could be declutched from the gasoline engine, providing you with temporary power to maneuver around and land safely.  Gasoline engines in aircraft tend to be very reliable, but when they DO fail during take-off or landing, the most vulnerable parts of the flight, the results tend to be catastrophic.  As such, the gasoline/electric hybrid would be of no use during cruise but it MIGHT improve the safety factor during the most vulnerable parts of the flight.


Is it legal to carry medical oxygen on an aircraft for a passenger? If a passenger shows up with an oxygen tank, can they bring it with them on the flight if their doctor says that it is medically necessary, or is a compressed tank of air considered hazardous material?

What are the regulations that cover this for flights operated under Part 91 and Part 135?

FAR Part 135.91 notes that medical oxygen containers - whether for the storage, generation, or dispensing of oxygen - must be:

135.91.a.1.i Of an approved type or in conformity with the manufacturing, packaging, marking, labeling, and maintenance requirements of title 49 CFR parts 171, 172, and 173, except §173.24(a)(1)
135.91.a.1.ii When owned by the certificate holder, maintained under the certificate holder's approved maintenance program;
135.91.a.1.iii Free of flammable contaminants on all exterior surfaces; and
135.91.a.1.iv Appropriately secured.
135.91.a.2 When the oxygen is stored in the form of a liquid, the equipment must have been under the certificate holder's approved maintenance program since its purchase new or since the storage container was last purged.
135.91.a.3.i-ii When the oxygen is stored in the form of a compressed gas as defined in title 49 CFR 173.300(a) When owned by the certificate holder, it must be maintained under its approved maintenance program; and The pressure in any oxygen cylinder must not exceed the rated cylinder pressure.
135.91.a.4 The pilot in command must be advised when the equipment is on board, and when it is intended to be used.
135.91.a.5 The equipment must be stowed, and each person using the equipment must be seated, so as not to restrict access to or use of any required emergency or regular exit, or of the aisle in the passenger compartment.
135.91.b No person may smoke and no certificate holder may allow any person to smoke within 10 feet of oxygen storage and dispensing equipment carried under paragraph (a) of this section.
135.91.c No certificate holder may allow any person other than a person trained in the use of medical oxygen equipment to connect or disconnect oxygen bottles or any other ancillary component while any passenger is aboard the aircraft
135.91.d Paragraph (a)(1)(i) of this section does not apply when that equipment is furnished by a professional or medical emergency service for use on board an aircraft in a medical emergency when no other practical means of transportation (including any other properly equipped certificate holder) is reasonably available and the person carried under the medical emergency is accompanied by a person trained in the use of medical oxygen.

Part 91 does not seem to speak to medical oxygen
Additionally, a page on the FAA website notes that:

In the DOT final rule, section 382.133 generally requires that air carriers conducting passenger service must permit someone with a disability to use an FAA-approved portable oxygen concentrator (POC) on all flights (on aircraft originally designed to have a maximum passenger capacity of more than 19 seats) unless the device does not meet applicable FAA requirements for medical portable electronic devices (M-PED) and does not display a manufacturer’s label that indicates the device meets those FAA requirements.

The page goes on to list approved oxygen containers. So, it seems that the FAA does not consider POCs to be hazardous, so long as they meet certain FAA approval standards. (If you are asking about General Aviation requirements, I would assume an FAA-certified POC is okay to bring on a GA flight as well)


What caused the Belgian aircraft mechanic who stole an F-16 to crash? This is the story, from the late 80s:

https://apnews.com/3b2ba1c5735b3817a3e7ae3562780e9b

Why did he crash? Why would anyone crash in this scenario?

I'd like to ideally hear from someone who is either an F-16 pilot or has been lucky enough to be able to try flying the F-16. Even if this has been ruled a suicide I'm still curious what beyond landing are the main challenges with flying the F-16 for someone untrained.

As someone who will never get that chance myself but likes flight simulators, I'm curious exactly where the big difference from the simulation to reality lies. I'm quite certain many others who fly flight simulators are also curious what the difference actually is. What stops someone that knows what all of the functions of the controls are, and is intimately familiar with the startup procedure for the engine of the F-16 (like a mechanic), from actually flying an F-16? Yes, landing, but what else? Do you need to remember to change some engine settings, fuel settings, after taking off, otherwise the engine stalls? Can you easily exceed EGT, or otherwise damage the engine, if you don't know what you're doing? Do you need to change some settings for the battery, internal power? I'm just guessing blindly here.

Forgive me for the hand waving like arguments I'm using, but, how hard can it be to keep an F-16 in level flight, if you are able to climb to 2,000 feet in the first place?

For the particular cited story above, it seems strange that the mechanic was able to take off and climb to 2,000 feet, and only then crashed. Does this point strongly to suicide?

Unauthorized flights of military jets by mechanics have happened in the past.  Some of the aircraft landed successfully after the ordeal others resulted in fatal accidents.  The two successful cases which I’m aware of, the mechanics had previous flight training.  We still cannot determine whether this F-16 went down as a result of inability of the pilot to control the aircraft or whether it was an intentional suicide by airplane.

There is nothing outrageous or unusual about an F-16, save that it is a high performance fighter, with a high thrust to weight ratio, (relatively) high wing loading and low aspect ratio wings and handles accordingly.  The sidestick controller combined with the fly by wire flight controls and nimble handling requires a light touch on the controls - some pilots describe it as almost a ‘kissing’ sensation - to properly fly, which possibly could get away from a neophyte.  Like most high performance airplanes, it needs to be flown by the numbers and can be demanding to land, though not as difficult as some other military jets eg T-38, etc.

The physical act of flying seminal maneuvers is very easy in these jets with a little flying knowledge.  Most fighter pilots describe their jets as easier to fly than say a Cessna.  Flight control laws eliminate a lot of the babysitting and grunt work one has to do in an aircraft with conventional controls.  The pilot has an unobstructed view from the canopy of the environments, offering very good situational awareness.  All primary flight data is displayed prominently in the HUD and easy to decipher.  More complex flying will start to become demanding and potentially lead to trouble.

Aviation has a lot of scenarios which seem benign but turn into death traps if you don’t fully understand what’s happening.  There are plenty of sad tales such as stall spin accidents, low level aerobatics, etc. where people thought they could handle a situation but their reach quickly exceeded their grasp.  This is compounded by untrained human psychological responses to stress and fear.  Some of the lethal gotchas I’ve seen are inability to understand aerodynamic concepts like stall speed to load factor, density altitude, aircraft system interactions, emergency procedures, operation in adverse weather or IMC, jet engine thrust response time to throttle commands, etc.  You also have the unusual quirks specific to each aircraft.  The F-16, for instance, can enter a deep stalled condition lethal at low altitudes if not properly flown.  These kinds of phenomena exist on other fighters with neutral or negative dynamic stability as well.

The exact cause of the accident in question is not totally clear, so anything specifics would be speculative.  If someone can find the Norwegian AF accident investigation report on this, we can read it and see what their conclusions were.


At a constant power setting, does TAS change with altitude? I found a lot of references to the question but no definite simple answer.
What would be the influence on true airspeed (TAS) for same airplane at same throttle setting flying straight and level at higher altitude?
Would it change for Jet engine vs internal combustion engine?

The answer to your question largely depends on what you mean by "constant throttle setting".

For propeller propulsion, if "constant throttle setting" means "constant power setting" as in a fixed output BHP, TAS will increase almost linearly with altitude (up to the altitude where constant power output can no longer be maintained).

For a normally aspirated reciprocating engine with a fixed pitch propeller, a constant throttle position will mean a decreased manifold pressure with increased altitude resulting in less power output, less thrust (T), and thus decreasing TAS (assuming the decrease in thrust is larger than the decrease in drag (D) resulting from the decreased density at higher altitude, this generally holds true). For a supercharged engine, depending on how the supercharger is controlled, "constant throttle setting" can have the charge control maintain a constant manifold pressure. In this case, the power setting will be maintained (up to the maximum altitude where the supercharger can maintain the manifold pressure), and TAS will increase.

For a jet propulsion engine, once again it depends on what is implied with "constant thrust setting". For example, for low/no bypass engines, a constant EPR should roughly correspond to constant T with altitude, hence with D decreasing with altitude, TAS will be higher before T = D. If "constant thrust" means "constant N1", thrust will actually decrease with altitude, how quickly it decreases with altitude will determine the effect on TAS (once again, where T = D).

If "constant throttle setting" simply implies "constant thrust". Resulting TAS will always be higher (as for a given TAS, T remains constant and D once again decreases).


What operations during preflight and pre-takeoff engine run-up cause a change in engine rpm? In a Cessna 182, during certain preflight check procedures with the engine running, RPM drops. What are these procedures and why does rpm change?

You will get a change in engine speed doing a mag check, cycling the carburetor heat, if equipped, and cycling the propeller governor.  You will also see a drop in oil pressure and a rise in manifold pressure when cycling the propeller governor as well.

The reasons?

Carburetor heat increases temperature of the mixture passing through the carburetor, thereby decreasing its density.  Consequently, as the same amount of fuel is being metered into the air steam in the Venturi throat as before, this causes the mixture to become richer and the engine to produce less power and run slower than before.

Mag checks involve turning off individual magnetos, causing the combustion in the cylinders to become less uniform, resulting in a power loss and slower engine speeds.

Cycling the propeller governor causes the governor to slow the engine by increasing the angle of attack of the propeller blades.  This creates a greater workload on the engine.  Lower engine speeds also cause the engine driven oil pump to turn slower, decreasing the oil pressure. And, as manifold pressure measures the pressure of the intake air at the cylinder head, an increase in the workload increases the air pressure at the manifold, causing the spike in indicated manifold pressure with the prop governor set to its lowest speed setting.

Cowl flaps are simply moveable panels which can alter the flow of cooling air around the engine to better maintain engine cooling at low speeds when ram air flow through the cowling is limited.  I’ve never heard of a situation where cowl flap position causes an engine to run slower or faster, though the cylinder head temperatures will change quite a bit and there is a risk of overheating and damaging an engine if you are running at high power settings at low air speeds for extended periods.


How does helicopter mustering make financial sense? I've seen and know that helicopter mustering is popular in Australia and what I do not understand is why this works from a business perspective.
Helicopters are expensive and dangerous machines so it does not seem cost effective to round up cattle and livestock when it could be done, not as quickly, by people on the ground with ATVs and other wheeled vehicles. Not to mention the low-level flying is very demanding and tough on the machines and maintenance.
Surely it would be cheaper to employ extra people than pay the expensive hourly rate of a helicopter?

Two reasons:

It is way faster and allows one person with a relatively cheap-to-run R-22 to do the work of several cowboys.  You're paying for the cowboy 24-7 if they are on staff, which is usually the case on a sprawling and remote ranch/station where you have to keep them on full time (and the horse if using them); you're only paying for the machine (direct hourly operating costs at least) while it's running.
It almost eliminates losses from stragglers that get missed and later become dinner for predators.  This feature was a welcome surprise when gyrocopters and helicopters were first tried out. Originally, gyrocopters were used to help out with the cowboys, mainly to hunt for strays that couldn't be seen from ground level. When the R22 came out, being able to hover and maneuver in confined areas, it became feasible to do both the mustering and overwatch role from the air.

Between the two, the business case starts to favour the helicopter.  If it didn't, they wouldn't do it. Granted, it is pretty dangerous flying, not for the faint of heart, but there are lots of young pilots keen for a thrill.


During inverted banking, what happens to heading? In normal flight, a plane that banks will turn and change heading.

What happens if the plane is inverted?
If the plane rolled 180° to wings-level inverted flight, then it will not be turning.

But if the plane rolled 135°-- 45 degrees beyond wings-level inverted flight-- what would happen?

Will the aircraft's heading tend to change toward the earthward wingtip, or toward the skyward wingtip?

Does it matter if the wing is positively loaded (e.g. the aircraft is performing a barrel roll) or negatively loaded (e.g. during a "slow" roll, or while performing a banked turn during sustained inverted flight?)

During sustained inverted flight, would the pilot be pushing the stick forward to maintain altitude?

Would a plane in 135° roll be using stick-forward to retain altitude? And thus bank in the direction the wheels are pointing?

Yes and yes.

Let's say you're flying North.  You roll inverted, then lift your left wing 45 degrees above the horizon (this is the wing that pointing East, now that you're upside down).

You'll experience the usual G forces pushing into your head (it hurts), and the plane will start turning to the West.

I once saw a great diagram that explained which controls do what when inverted - it showed the outline of the plane with one cartoon pilot sitting in the normal position, and another "phantom" pilot sitting in the same seat with feet on the rudder pedals, holding an extension of the stick, but with his head pointed the opposite direction - head towards wheels instead of away from wheels.

When the plane's inverted, the "phantom pilot" is upright, and all the controls would behave normally from his point of view.


Where can I rent a float plane? Is it possible to rent a float plane with a private pilot's license?

Flying floats is one of the main attractions for me to learn to fly.  However, after some searching on the internet I can only find wheeled aircraft that are available for rent in my area.  Am I missing something?  Are there flying clubs or partnerships that have float planes available?  I would love to fly floats but owning a seaplane is not in the cards for me at this point in my life.

The Seaplane Pilot's Association publishes a Water Landing Directory that includes seaplane facilities and flight planning maps for cross countries. This lists facilities that offer seaplane rental's. There is a discounted price on the directory for SPA members.


What is the difference between a private and a commercial flight according to the US Customs and Border Protection? From what I understand, whether or not a flight is classified as private or commercial in the eyes of US Customs and Border Protection (CBP) has nothing to do with the Federal Aviation Regulations (FAR) flight rules that they are operating under. For instance, I understand that I can legally be operating under FAR Part 91 and still be a commercial flight in the eyes of CBP. What then is the determining factor?

According to the CBP eAPIS FAQ, this definition is in 19 CFR 122.1:

  (d) Commercial aircraft. A “commercial aircraft” is any aircraft
  transporting passengers and/or cargo for some payment or other
  consideration, including money or services rendered.

  [...]

  (h) Private aircraft. A “private aircraft” is any aircraft engaged in
  a personal or business flight to or from the U.S. which is not:

  (1) Carrying passengers and/or cargo for commercial purposes;

  (2) Leaving the U.S. carrying neither passengers nor cargo in order to
  lade passengers and/or cargo in a foreign area for commercial
  purposes; or

  (3) Returning to the U.S. carrying neither passengers nor cargo in
  ballast after leaving with passengers and/or cargo for commercial
  purposes;


Does burning fuel to get to your max landing weight violate any regulations? Consider a hypothetical situation where where an unexpected tailwind will cause a flight to arrive at its destination above maximum landing weight. After reviewing all reasonable changes to altitude and airspeed, it is clear that on the flight plan route nothing short of a hold or delay vector would allow for a landing within the weight limits.

The SIC suggests including the dispatcher in the decision, and asking for a delay vector or or hold that adds 8 minutes to the flight.

The PIC elects to land overweight, citing a regulation in FAR 121 that precludes any undue delay to burn fuel. Not a specific regulation, just that there is something like this in there.

Is there a regulation in FAR 121 (or any of the other 14 CFR/FAA regulations that govern the flight) that would be violated by adding distance to the route or a hold in order to facilitate additional fuel burn and a landing within the limitations?

This scenario isn't common but it isn't exactly rare, either. You take off with a full plane & lots of fuel for holding & an alternate, planning to arrive just at max landing weight. Then, due to shortcuts and/or better than forecast tailwinds, you under-burn & see that you'll arrive above max landing weight.

First, the hypothesized rule in Part 121 doesn't exist. Absent the Captain's use of his emergency authority (which does NOT require declaring an emergency to invoke, but which DOES have to be reported after the fact), what you can't do is "just go ahead and land overweight." That would be deliberately violating an operating limitation on the aircraft, and that's bad.

Second, there's typically no need to involve the dispatcher... just burn the gas. Holding, or extended vectors, or an early descent, or extending the gear way early... take your pick of what works best in your situation & then make it happen. Not a big deal.

Burning extra gas (really, just burning all the gas you'd planned to burn with the flight plan) is NOT a violation of anything in Part 121. On the contrary, intentionally landing overweight - in the absence of a circumstance making that the safest option - would be a violation.

Listen to ATC long enough, and you'll occasionally hear somebody ask for a delay to burn the extra gas. ATC can easily accommodate that; I've never heard it treated as if the crew is asking for something strange or suspect. Sometimes winds or shortcuts put you in that situation; it's nobody's fault, and it isn't a problem to burn the planned fuel.


Hypothetical aircraft drag reduction What would happen if I mounted a system dumping hydrogen (sound velocity 1310 m/s) at the leading edges of an aircraft flying at i.e. mach 2 (ignore all practicality issues)? What would happen at the hydrogen/air interface? Would the aircraft experience wave drag?

Consider that, without any hydrogen, the surface of the wing is coated in aluminum, a material with a sound velocity of 6,300 m/s. It's not the speed of sound on the surface of the wing that matters. It's the speed of sound in the medium it's passing through.

You are proposing a wing coated in hydrogen, but even if that could be made, it would still have to move the surrounding air out of the way. It is the "moving the air out of the way" that creates the mach effects.


Which are the requirements for the water supply on board? Which are the requirements for the water supply on board of a commercial airplane? I know that there are minumum mandatory requirements, but I don't know where to find them and how they can change with the category of the aircraft. Surely there are different requirements from a small turboprop without a toilet to a A320.

The IATA standards as per the IATA Drinking Water Quality Pool are based on

  ISO 17775, WHO requirements or EU/98/83/EC or those set by the civil aviation authorities of the participating airlines

Source

Airlines and operators will periodically test their water in aircraft, ground service vehicles, and filling stations for bacteria contamination (E-coli, coliform, etc).

Some aircraft may not actually have potable water tanks or may have removed them. Horizon Air operates their Q400 Dash 8 aircraft without potable water.


Why is UTC activation time referred to 30W in NAT-OTS? I am reading the NORTH ATLANTIC OPERATIONS AND AIRSPACE MANUAL and I came across the following statement more than once during my reading:

  The activation time of the westbound OTS shall be published as 1130z
  to 1900z at 30W.

  The activation time of the eastbound OTS shall be published as 0100z to
  0800z at 30W.

You can find this quotes at page 175 of the link provided above.

Here is my question: if the activation times are expressed as ZULU time (therefore as UTC), why is it specified at 30W? As far as I know a ZULU time is referred to the Greenwich meridian and therefore at 0W. To me it sounds quite contradictory to express an UTC time by specifying a longitude different than 0.

What am I misinterpreting? What is the right interpretation of the quotes presented above?

Think of 30W as a kind of traffic marker for flight planning.
If your planned route is going to cross 30W before the tracks activate (that is, ahead of the traffic flow), then you can file "random route." If you're crossing 30W during the active period, then you have to file on one of the tracks unless you can climb above them before crossing the entry fix.
This also works going against the flow: if you're crossing 30W in the opposite direction during the active period, you'll have to route either north or south of the tracks unless you can get above the NAT FL's before your entry fix.
As far as Zulu goes, it's just the common reference everyone uses (therefore, "Universal Coordinated Time").


Why do some Canadian Class E airspaces have no ATC frequency on VFR maps? PPL student here, studying airspace. Looking at the airspace around Vancouver, BC (see Vancouver VTA) I see that most of the lower mainland is class E controlled airspace. "No Contact" tells me that there is no ATC unit to ask for permission. Why is it class E then in the first place? Why isn't it class G?

In class E airspace, ATC service is provided to IFR flights, but not to VFR flights. The "NO CONTACT" note most likely refers to VFR flights, since you are looking at a chart designed for VFR flight planning. The airspace is class E, and not G, because whoever designed it wanted IFR flights to be controlled within in.

See this related answer for a brief description of the different airspace classes.


Why does lower atmospheric pressure produce higher EPR (thrust)? Recently, I read manual about engine, PW JT8D-217A/C, and there is a chart making me so confused.

Manual show the reference table tells you what number, EPR, is normal in specific temperature and atmospheric pressure.

(Click to enlarge)

We all know EPR can be related to engine thrust.

I thought higher Atmospheric Pressure meaning higher air mass density, so EPR should be higher.

At lower temperature making higher efficiency (Higher EPR) is quite easy to understand.

But according to the manual, lower Atmospheric Pressure can produce higher thrust when temperature is constant.

Also when temperature is higher than 102.2F, the EPR doesn't change anymore in different atmospheric pressure.

Why is that?

You can also notice that for one atmospheric pressure, the EPR remains constant until it starts to get really hot.

That's a flat rated engine (or an engine that is not easily temperature limited).

The three limits for a jet engine are: pressure limit, temperature limit, and N1 RPM limit.

How can a lower atmospheric pressure produce higher thrust when temperature is constant?

Cold weather—high EPR is as you said is straight forward.

Normally a decrease in pressure would decrease the EPR. However, engine manufacturers are willing to push the pressure limit when the ambient pressure decreases (altitude rises).

This allows more thrust for a takeoff from a high airport, which otherwise would significantly limit the engine/airplane. This increased tolerance comes at the cost of more frequent checks for the engine, i.e., more money.

  We are frequently asked why this is the case. The engine manufacturers,
  recognizing that good takeoff performance may be critically important on the more challenging
  routes, allow some increase in the pressure-limited takeoff thrust setting at altitudes above sea
  level.

  Jet Transport Performance Methods - Chapter 15


Which companies develop software for airplane systems? I am wondering which companies develop software for systems on airplanes?

I am a software engineer major and I would love to work with planes in some way. I am not sure if that would be more of an electrical engineering position or not, any input would be greatly appreciated.

This entire branch is known as  avionics (aviation electronics). Limited work is generally done by the aircraft producers themselves, and the majority is subcontracted to specialist companies. A name which does come to mind is Thales group, who are behind much of the Airbus A380 avionics. Other ones are Rockwell Collins, Honeywell and Garmin. These are however though often at the top of an iceberg of various subsystems and controls.

A huge increase in this field (particularly in small aircraft but now also coming to larger ones) has been in tablet computers and the like in the past few years, and while I'm not a pilot I think it's hardly at the limit of what is possible. An iPad has more processing power than most if not virtually all aircraft flying today. Many customers today are disappointed if they don't get WiFi and inflight entertainment onboard.

With the increase in drones and unmanned aircraft, it's certainly not a shrinking field. A large area of this includes complex calculations and plenty of sensors. And more drones and unmanned aircraft require advanced communication and control systems. I've even heard about dynamic models of aircraft who adapt the plane's control to maintain control in the event of structural failure or serious damage. Only having scratched the field personally it's a very broad field with plenty.


What's the use of so much torque on propellers? (This question is closely related to this question)

A typical Cessna 172 has a 180 hp engine, with a max. rotational velocity of 2700 RPM. Even small 1 hp electrical motors can achieve that RPM, and therefore, I guess the rest of the power is converted into torque.

What's the use of so much torque, and what happens if there is less torque at the same RPM - i.e.

Can an electric motor perform similar to the Lycoming IO-360 with the same max. RPM, but with just half the torque of the latter?

Even small 1 hp electrical motors can achieve that RPM

Yes, but can it sustain that RPM when something tries to stop it, that is the question. 1 hp combustion engines can get to 2700 rpm as well, but you cannot attach a propeller to it, stick it in the air, and expect it to maintain the RPM. It takes a lot of torque to create aerodynamic thrust.

It is a fact that electric motors are way better at producing torque than combustion engines. An electric motor produces almost maximum torque at the get-go, with the rotor standing still. The combustion engine needs to make RPM in order to make torque. This article compares electric motors with combustion engines for powering a hydraulic pump: a 20 hp electric motor can do the job that a 50 hp combustion engine can do.

Electric motor:

Combustion engine: intermittent torque means torque pulse from combustion.

But wait, is that even possible? Power is power, kilowatt is kilowatt, and it should not matter which engine we use to generate the kilowatts, they should all equate to equal amounts says the first law of thermodynamics, the conservation of energy. But it does matter, since with a combustion engine torque is a function of RPM. So increase RPM, and power increases due to increased RPM and increased torque. At lower RPM the combustion engine may simply lack the torque to speed up, while the electric motor has an almost flat torque curve.

This same happens with outboard motors, when comparing 2-stroke with 4-stroke. 2-stroke has way more torque at lower revs, the 4-stroke may have the same horsepower but may never get to the high revs because it lacks the ability to get the boat planing.

But I digress. To get back to your questions:

  What's the use of so much torque, and what happens if there is less torque at the same RPM

To keep the output shaft at this RPM while the propeller is pushing all that air backwards. That requires a serious amount of torque. If there is less torque at the same RPM, there will be less thrust produced and the aeroplane won't fly as fast.

  Can an electric motor perform similar to the Lycoming IO-360 with the same max. RPM, but with just half the torque of the latter?

Well, the surprising thing is that a horsepower is not a horsepower. Part of the problem lies in the horsepower output functions, so maybe an electric motor with a lower hp rating can be used. But one thing is very clear: at the RPM of the propeller, a certain torque is required at a certain speed to keep the propeller turning. This amount of torque will always be the same, no matter what kind of engine produces it.


Do all airports have the authority to impound aircraft for overdue fees? In the 'Collapse' section of the Thomas Cook Wiki, it states that

  At around midnight on 23 September, airports in the UK began to impound Thomas Cook aircraft upon arrival, citing "default in payment of airport charges"

Do all airports have authority to do this? If I refuse to pay a $15 landing fee in a Cessna, can they impound the aircraft?

Yes, at least if the airport is city owned (or owned by a municipality). For example Philadelphia's airports are city owned and they have landing fees as well as default repercussions

  1.05. Payments

  Non-tenant Air Carriers and Operators not providing adequate surety or
  security in form and amount satisfactory to the Department of
  Commerce, to ensure payment of fees and charges, shall be required to
  pay all incurred fees and charges prior to aircraft departure.

  ...

  If any charges remain unpaid for a period of twenty (20) days after the due date,

  the City may:

  a. Bar operator from the Airport and
  the use thereof; and/or

  b. Deny operator the use of Airport
  facilities; and/or

  c. Commence such actions at law or in equity as are
  deemed in the best interests of the City.

I see no reason impound would not be covered under section C there. Privately owned airports are a different situation but I imagine they have some kind of legal recourse.


What does the letter J mean at the start of an FAA instrument approach chart identifier? To identify a specific Instrument Approach Chart in either the FAA Terminal Procedures Publication (TPP), or the Department of Defense (DoD) Terminal Low Altitude (TLA) Charts, the FAA uses what they refer to as an internal numbering system.

This identifier on any given approach chart is found in the center of the top margin information area and includes two letters, A and L, followed by three or four numbers, followed by the approval authority for the chart, i.e.: AL-571 (FAA).

Found in the FAA Terminal Procedures Chart Users Guide and the general information legend in both the TPP & TLA, the "AL" stands for "Approach and Landing", however, on a high altitude approach chart, the AL is proceeded by a "J", i.e.: JAL-685 (FAA).

Does anyone know what the "J" stands for?

The chart users guide does not identify its meaning nor can I find any reference that addresses it. My assumption is Jet...but I would prefer to confirm what it stands for.

According to JO 7340.2J - Contractions p. 2-2-15 you're correct. It stands for "jet approach landing charts".


What determines spanwise placement of spoilers for roll control? Specific application of spoilers was discussed in What is the benefit of spoilerons compared to ailerons? As I remember it, 40yrs ago gliders had spoilers close to the wing tips - perhaps slightly inboard of the normal aileron position.

Current aircraft design places them mid-wing or even next to the wing root. What design principles favor a particular span-wise location.

To be specific; I am interested in roll control not drag.

On airliners, spoilers serve three purposes, roll enhancement (assist the ailerons when greater roll rate is commanded), speed brakes (help slow down and descend faster), and ground spoilers (kill lift in order to transfer weight from the wings to the wheels for more effective braking). Spoiler span-wise location is a compromise to accomplish all three goals. Also, the outboard spoilers are primary for roll control and the most inboard spoilers may only be used on the ground. Spoilers are not placed in front of the ailerons because they would interfere with roll control. The chord-wise location leaves the wing box clear for fuel tanks.


Why would a stretch variant need a larger horizontal stabilizer? With the 787-10 stretch, Vedad Mahmulyin (a Boeing engineer) saved the company millions by implementing a software solution that negated the need to enlarge the horizontal stabilizer.

Software again proved useful with the sizing of the horizontal tails. As a stretch of the 787-9, textbook aircraft design would suggest the 787-10 would need larger horizontal stabilisers, offsetting the effect of the longer fuselage on pitch control. Instead, Boeing engineer Vedad Mahmulyin used software to increase the effectiveness of the existing stabilisers. Boeing gave Mahmulyin an internal engineering award for solving the problem.
Flight International (27 Mar 2018)

When a plane is shrunk, that is usually the case because of the reduced moment arm. When it is stretched, the tail volume is retained if I understand this comment about the DC-10/MD-11 stretch correctly:

Isn't the tail of the MD-11 smaller because it has a longer lever arm? The tail volume of both aircraft should be quite the same. Also, any FCS cannot help to trim the aircraft over a wide range of cg positions, and it is this trim range which drives tail surface volume. @PeterKämpf

So why would a stretch variant need a larger horizontal stabilizer?
Also, from an interview with Mahmulyin:

Mahmulyin figured out he could use software to tell the wings and the stabilizers how to fly together, "As opposed to having to produce all new horizontal and vertical stabilizers," he said.

What does "flying together" mean? (This is an optional question and does not involve proprietary information.)
Update and accept reason
The reason for asking why would as opposed to why does is I was not aware of any previous [jetliner] stretch requiring a larger horizontal stabilizer. For example, all the DC-8's from shortest to longest (almost the same stretch as the 787-10) retained the horizontal stabilizer throughout:

Source: Great Airliners; click to view

But then I finally recalled a situation where it has happened, the 737 Classic, and the reason given is the "fore-and-aft loading flexibility", in other words the cg range, and that's why I'm accepting @jwzumwalt's answer.

When the fuselage is stretched, the arm of the horizontal stabiliser is increased, and hence it's effectiveness increases linearly with the fuselage length.

However, because the mass is distributed further away from the centre of gravity, the pitch moment of inertia increases too.

If the fuselage would be modelled as a uniform rod, the moment of inertia in pitch would be $\frac{1}{12}mL^2$, with mass $m$ and length $L$.

source: hyperphysics.phy-astr.gsu.edu

You see that the moment of inertia increase with the square of the fuselage length, while the effectiveness of the elevator increase linearly with fuselage length. The nett result is that the pitch response of a longer fuselage with the same horizontal stabiliser/elevator is reduced.

In addition to the change of inertia, the heavier aircraft needs more powerful flaps (double-slotter vs single slot before) which causes a bigger pitch moment change.

Therefore a stretched aircraft needs a more effective elevator.

As for the meaning of "flying together" I assume that this means that the software solution for the 787-10 controls the pitch moment of the aircraft not only by changing the elevator angle, but also uses control surfaces on the wing.


What is the type of a SID that is neither RNAV nor RNP? I am studying FAA's Order 8260.46F and I have noticed that, as far as the different types of SIDs are concerned, it states:

  [3-5] (1) “RNAV 1” will be the default designation for RNAV DPs. Annotate procedures with a standard note: “RNAV 1” on Form 8260-15B [see appendix E].
  (2) “RNP 1” (in-lieu-of RNAV 1) will be used when a DP that contains an RF leg or when surveillance (Radar) monitoring is not desired for when DME/DME/IRU will be used. Annotate the procedure with a standard note: “RNP 1” on Form 8260-15B [see appendix E].
  (3) All RNAV DPs will contain a note that describes the equipment sensor limitations.

However, I have trouble figuring out what type of SID is the La Guardia Five Departure ( route description and take-off minimums ) of La Guardia airport. It is does not have the indication "RNAV" and, as far as I can tell, it is not an RNP departure procedure either.

Could someone point me in the right direction?

That SID is not an RNAV SID since it uses VOR/DME and headings for navigation. The FAA Aeronautical Chart User’s Guide simply refers to them as “non-RNAV SID’s”


what are the ways to avoid skidding off the runway apart from thrust reversers? what are the different ways to avoid skidding off the runway apart from thrust reversers?

Do crew have any option if thrust reversers are not available and the ground is too slippery which is making the vessel skids off the runways sideways?

Your question appears to assume that thrust reversers are an acceptable way of keeping an aircraft from sliding off a slippery runway. While this may be true in rare cases, generally speaking you would NOT want to use reverse thrust to avoid skidding off a runway as that typically would exacerbate the problem.

Consider the following scenario: you have an icy runway and a strong crosswind from the right. As you start the takeoff roll, the airplane begins drifting left. You apply right rudder to correct, and the aircraft heading moves to the right of the runway direction. If you resolve the engines thrust vector into it's components relative to the runway centerline, you have most of the thrust propelling you down the runway, a much lesser amount propelling you toward the right side of the runway.

Lets say the left drift continues in spite of the engine thrust vector driving the aircraft to the right side of the runway, and you decide to abort the takeoff using reverse thrust. Thus, the thrust vector relative to the runway centerline will slow the aircraft. However the thrust vector 90° to the runway centerline will be toward the left side of the runway, which when added to your leftward drift will likely put you off the left side of the runway.

If you Google "tower air 747 crash" you'll see a number of entries concerning just such a scenario and the result. I found http://flightsafety.org/ap/ap_mar97.pdf to be the most instructive, although I do not wholly agree with the conclusions or with the narrative of what happened (a friend of mine was in the jumpseat right behind the captain, and I flew as a f.o. with that captain).

An obvious answer to your question is to never get yourself into such a serious situation. Can you wait for better conditions? Is another runway available? But if you MUST use a slippery runway for either takeoff or landing (or have already foolishly committed yourself), remember that if a runway is that slippery, it's feasible to continue down the runway in a manner that your course (the runway direction) doesn't match your heading. If the captain of the Tower Air flight had elected to do that, he might not have had the accident he did, or he might have had a much more serious accident. Tough call!


Where is the generator in a large turbofan of a commercial airliner? So, where do you put the electrical generator?

If it's gonna be coaxial, the only place is the rear (it will be burnt) or the front (it will get in the way of intake).

If it's gonna be coupled to a gear, I can't see how to mesh a gear onto the spinning parts, because the bypass air surrounds the entire engine.

Note: I'm interested in large turbofans of large airliners like the A380 or Boeing 787, basically anything with turbofans carrying 200+ passengers.

(P.S., does the generator spin from the LP turbine or the HP one?)

Image source

The generators are usually driven from the Accessory Gearbox. This CAD drawing is from the company that makes accessory gearboxes for the Rolls Royce Trent engines driving the A330 and A350, and it shows the connection of the accessory gearbox to the high pressure rotor.

This picture from the book The Jet Engine by Rolls Royce shows the same arrangement: a bevel gear drives off of the HP spool, then drives another bevel gear connected to the crescent shaped Accessory Gearbox underneath the engine.

The gearbox itself is shown above (from the same book), with the accessories connected to the LP spool:

The Engine Driven hydraulic Pump
Fuel pump
Oil pump
Pneumatic starter, requiring the highest loads and therefore dimensioning the gear strength.
The IDG: Integrated Drive Generator which provides the AC power.

The accessory gearbox contains the engine starter as well, pneumatic for older types and electrical for bleedless engines. The engines are started by turning the HP rotor, and the accessory gearbox must be connected to the HP rotor for this purpose. For this reason, the HP rotor drives the generator and other accessories, although it would be more beneficial for fuel economy to use the LP compressor. Source: The Jet Engine issue 5 by Rolls Royce.


What is the guy in green showing to the F/A-18E pilot before catapult launch? In the following frames, you can see a guy in green showing a panel-like device with numbers on it to the pilot of the Super-Hornet that is about to launch from the carrier USS John C. Stennis.

What is this panel for?
What information is the pilot given?
Why just before takeoff and not while boarding/briefing?

(YouTube)

Edit:
I won't accept this question as a duplicate. It may contain the answer

  Taxiing up to the catapult, a green shirt will hold up the weight board. If the weight on the board matches the weight on the weight chit, acknowledge ...

but the question isn't really about that part and quite "hidden".

That's a weight check. The sign has the weight of the aircraft in pounds. The catapult crew guy first shows the presumed weight to the PIC who must give a thumbs up, agreeing, "Yes, that is the weight I believe my aircraft to have."

The crew guy must then show the same exact set of numbers to the catapult chief operator, who must also approve it: "Yes, the catapult is set to launch that weight.

You can actually see both verifications happening in the two photographs above, the first one is to the PIC, the second to the catapult operator. Only when both verifications have occurred will a launch be permitted.


What is it exactly about flying a Flyboard across the English channel that made Zapata's thighs burn? CNN's French inventor makes 'beautiful' flight across Channel on hoverboard reports that:

  "French inventor Franky Zapata has successfully crossed the Channel on a jet-powered hoverboard for the first time, after a failed attempt last month.

Later in the article it says:

  The inventor said that he tried to "take pleasure in not thinking about the pain," even though "his thighs were burning."

What is it exactly about flying a Flyboard across the English channel that made Zapata's thighs burn? 20 minutes of standing shouldn't be that stressing, what is it exactly about flying this board that requires so much muscle activity that it would be painful?

He's using the angle of his legs to control the attitude of the platform (and as a result, the direction he's flying in). So he can't take a relaxed pose, he's standing with his knees slightly bent the whole time.


Is the Boeing 737 MAX 8 MCAS exceptional in operating when autopilot is off? To the uneducated reader it seems strange the Boeing 737 MAX 8 MCAS system only operates when autopilot is off. I understand the reasoning behind why it was implemented to operate when autopilot is off. My question is, is the operation of MCAS automated system when autopilot is off an exception for the 737 line, or are there other automated systems providing direct control surface actuator inputs when autopilot is off on the Boeing 737s? If so, what are these?

Are there other automated systems providing direct control surface actuator inputs when autopilot is off on the Boeing 737s?

One such system on the 737 Classic and NG is the Speed Trim System:

As you can see above, when certain conditions are met, of which 5 seconds has passed since a pilot trim input is made, the STS trims the plane if required.

The system's classification would be stability augmentation system. When light, rear loaded, and with plenty of power (during the climb phase of the takeoff or during a go-around), the 737 has a tendency to pitch (nose) up (since the engines are below the wing and below the center of mass); the STS would limit that.


What effect does downwash have on the horizontal stabilizer Fighter aircrafts usually have their horizontal stabilizers in lined with the main wing which would subject it to downwash. How does this effect the stability of the aircrafts and the effectiveness of the elevator?

First, the downwash extends over a wide height, so moving the tail up or down will change the local downwash angle only a little (first order approximation: By the cosine of the elevation angle at which the tail is positioned).

Next, downwash at the tail is a good thing: Since the downwash angle increases with angle of attack, the angle of attack range at the tail is smaller by the downwash effect than it is for the wing. This keeps the tail in a narrower band of angles and allows it to still stay firmly in the linear range when the wing is about to leave it (which happens when the wing stalls).

What you don't want to happen is that the wing wake hits the tail. The wake contains the wing's boundary layer and produces an undesirable drop in dynamic pressure at the tail. Initially, tails were moved up to avoid the wing wake impinging on the tail (think MiG-15 or F-101 Voodoo), but that only shifted the eventual point where the wing would blanket the tail to higher angles of attack. With the reduction in aspect ratio and the increase in wing sweep made possible by more powerful engines, the upper angle of attack limit went up and the tail could not be moved up enough. Therefore, all modern designs try to put the tail as low as practical and even add some anhedral. Here the limit is of course a tail strike, so you might get the impression that the tail is in line with the wing. At practical angles of attack it isn't.


How serious is an impact like the 10/2017 Delta Airlines suspected bird strike? Recently, there was an incident where a Delta Airlines charter flight carrying the Oklahoma City Thunder basketball team was struck by an "unidentified object". Delta's official statement claims that

  Delta flight 8935, operating from Minneapolis to Chicago-Midway as a charter flight for the Oklahoma City Thunder, likely encountered a bird while on descent into Chicago. The aircraft, a Boeing 757-200, landed safely without incident; customers have since deplaned and maintenance teams are evaluating.

While I do not agree with the UFO label that this story seems to have run with, I am shocked that a bird (especially at such an altitude) could cause such severe damage to the nose cone (even at such speeds).

Is this characteristic of a bird strike and how severe would this incident have been had the collision been with the windshield?

Bird strike happens all the time - almost on a daily basis. See avherald : there are 9 instances of bird strike in the past 7 days at the time this answer is written. Usually it is ingested into the engine (which usually turns out to be a non-issue), other times it impacts the cone or leading edge of the wings or knocks off a pitot tube.

While a few incidents make it to mainstream news from time to time, bird strikes are a common occurrence in the aviation industry. It is an unusual situation, but not a dangerous situation if the pilots handle it properly.

How severe if it collided with the windshield? The windshield is tested against this type of impact during certification. At worst the outer layers will crack, and the pilot will execute the landing using the "cracked windshield" procedure (Yes there is a procedure written for this scenario).

A note about the UFO: technically it is an UFO, an Unidentified Flying Object. It could be a bird, a drone, weather balloon etc. Examination of the impact area might reveal what the object was.


Why is the horizontal stabilizer root interface designed this way? Most large aircraft have a similar design for their trimmable horizontal stabilizer: they connect to the tail cone on a flattened area which allows them to be rotated within some range:

From left to right: A319 (source), A320 (source, B787 (source)

But the THS of the A330 is different, it looks like a frog eye... What is the purpose of this flexible wall?

Source

It is a seal- to prevent entry of air into the stabilizer mounting area. For aircraft with trimmable horizontal stabilizers (THS), there is an opening to the rear of the aft bulkhead to allow for the movement of the THS. It can be seen in the following image for Boeing 787.

Boeing 787 aft fuselage structure; image from aero-news.net

Now, as the opening will be there while the THS moves, a seal has to be present to prevent entry of air (and FoD etc.). Boeing went ahead and put a hinge aperture sealing plate over that area, with only a small opening where the actuated area of the THS moves, with the seal inside the structure, as can be seen below.

777 THS area; image from deicinginnovations.com

Without cover, the are will look something like this:

Trimmable horizontal stabilizer region without cover, ; image from skysoftairlines.blogspot.in

Airbus, on the other hand went ahead and put a tailplane sealing plate outside the opening. This was used in the A330 and initial versions of A340 (which shared the fuselage with A330), before Airbus changed its mind and made the THS region similar to the other aircraft in A340-500 and -600 versions, where the horizontal stabilizer was redesigned.

Also, see these (1 & 2) patents and this discussion.


Can I use the autoland mode if the airport is unknown to the FMC database? Can I use the autoland if I have to land on an airport which is not known to my FMC database? Is it possible to insert the coordinates to get the autoland mode?

Autoland is an autopilot mode.
AUTOLAND could be « armed » while the autopilot is receiving FMS inputs, but once it is « active » it doesn’t use FMS data but the ILS receivers or the ILS and GPS receivers.

No need of the FMS neither for the approach, nor for AUTOLAND


Can we change light aircraft skin from aluminum to foam and fiberglass? Can we change the skin and wings of light aircraft from aluminum to foam and fiberglass composite in zenith ch 750 ?

Yes. No. A little bit of yes, but overwhelmingly a NO.

It's possible to design and build an aircraft like the CH-750 with fiberglass instead of aluminum, but it's so far above the skill and qualifications of anyone who would ask the question on the web - as opposed to starting by modeling it in ANSYS - that the only realistic answer is "no".

Not because of any intrinsic properties of fiberglass, but simply because of the level of knowledge involved in redesigning an aircraft of this scale, and the fatal consequences of getting it wrong.


What is the difference between ARINC 429 labels 025 and 102 for Selected Altitude? What is the difference between ARINC 429 labels 025 and 102 for Selected Altitude?

According to A429, the difference is the type of data coding. Label 025 is BCD. Label 102 is BNR.

Label 025 by being a Binary Coded Decimal codes each character of the altitude value in binary. With a range of 0 to 50000 feet, the first digit uses 3 bits and the remaining use 4 bits each for total of 19 data bits.

Label 102 is a Binary number. The range is 0 to 65535. There are 16 data bits (2^16 = 65536).

Both are transmitted. Receivers will use the version most appropriate for the application.  BCD is normally used for display. BNR is normally used in computations.


When is a control tower required? I know there are busy airports without control towers, and the converse is also true. There is a process for an airport to acquire a control tower. Sometimes, airports want to have their own control tower.

Is there some activity level where an airport would require a control tower for safe operation? Or does air traffic control exist simply to reduce risk?

As far as I'm aware there's no specific regulation that requires a control tower to be established. FAR 170 and the regs referenced therein set out when an airport becomes eligible for a tower, but nothing requires an eligible field to have a control tower (in fact the FAA won't establish a tower unless someone gives them the land).

That said it would probably be a Bad Ideatm for certain airports to operate without a control tower (Atlanta, Kennedy, O'Hare, LAX...) - in fact those airports are busy enough that they have additional traffic management procedures in place beyond what a control tower can provide.

Control towers exist to improve safety (improve risk) as you alluded to. There are procedures and rules established to allow pilots to self-sequence at untowered fields (you'll find those in section 4-1-9 of the AIM), and they work very well when everyone follows them.
The catch is everybody doesn't follow those procedures - or more accurately they're followed with varying degrees of precision (my personal favorite example of sloppy procedure is when you hear someone say "any traffic in the area please advise" at an uncontrolled field). These procedures also don't cover other movements on the airport surface very well: Some pilots will announce their taxi plan at an uncontrolled field, but there are plenty of pilots who taxi from point A to point B with their head up and their mouth shut so as not to tie up the frequency for aircraft in the air.

As the number of operations increases at an airport the various degrees of precision and adherence to the uncontrolled-field procedures in the AIM  becomes more of an issue, and a control tower may be established by the FAA or the local airport authority to safely and efficiently coordinate aircraft movements.


How good is the ground visibility by a moonless night In the Grand Canyon? My night flying experience is limited to light-polluted coastal southern California.

When flying over low-population countryside on a clear, moonless night, do the stars provide enough light to identify the contour of the ground or is it completely dark?

If anyone has specific knowledge of flying over the Grand Canyon at lowish altitude under those conditions, I would appreciate your impressions.

Background - I'm writing a fiction novel where characters make that flight and want to accurately describe what they can see if anything.

No, in a remote area on a moonless night, it’s a black hole.  It’s the blackest darkness you can imagine with a few pinpricks of light from remote settlements on the ground or vehicles.  I have heard a few stories from pilots flying at higher altitudes on moonless nights, such as Maj Brian Shul who did this over the Arctic Ocean in an SR-71, where they shut down cockpit lighting and found that starlight was intense enough to illuminate their instruments.  I also know of tales from Navy pilots who have flown fighters in dark night over water who can’t see anything out in front of them.

These conditions require total reliance on instruments to know which way is up and plenty of people have become spatially disoriented flying like this and crashed.  I have heard some hairraising tales from drug runners like Barry Seal, Carlos Lehder, etc., who used to fly airplanes low level over the ocean at night in order to avoid detection, remaining about 50ft or so off the deck.  One guy they interviewed for the MSNBC documentary Cocaine Cowboys used to do this approaching the Keyes south of Miami for a drop off.  He used to say if he could see the light glow of Miami off his nose he was fine but if he could see the glow from both Miami and Tampa, he was too high and risked detection.  God help you if you had a bad altimeter setting in these conditions.

I will make my own comment, as a professional pilot, that dark night conditions over remote areas or open water are downright eerie and there’s is always an uncomfortable feeling in myself when doing PIC operations in these condition.


How could I match the surrounding traffics displayed with their radio communication If I have a traffic display I could see the traffics in proximity of my aircraft and meanwhile I could listen to their voice communication. So how could I match the traffic shown in the display with the corresponding voice communication? My understanding is that if I have a ADS B in system and the other aircrafts have mode-s transponder, I could know their call sign thru the ADS-B data, is that right? But how about I just have a TCAS or I have the ADS-B in transponder but other aircrafts do not have a Mode-S transponder?

Several approaches, currently impractical for GA:

Your radio receiver would need to be directional, to estimate the
sender's bearing and maybe distance, and from that derive the
sender's identity.
Voice broadcasts would need to be augmented with a digital squawk
indicating the sender's call sign, like some automated speech
broadcast weather reports do.
Onboard automatic speech
recognition
trained particularly for call signs could try to infer the sender's.

But we're a long way from duplicating how videoconfering software highlights whoever's speaking.


What are the regulations on flying UAVs over people on the ground? We are considering a project related to drones and in my discussions with people I heard that flying UAVs overhead people (crowds or otherwise) is banned. I also heard this is the case for the USA and EU. I searched and couldn't find the related detailed explanations anywhere.

I would be grateful if somebody could shed some light and point me in the right direction.

The general rule of thumb is "don't do anything hazardous for people or property on the ground".

In the US, do not intentionally fly over unprotected persons or moving vehicles, and remain at least 25 feet away from individuals and vulnerable property.

Based on whether your project is for recreation or not, how heavy the drone is,... you may not be able to do the same things. The FAA website has a page titled ``What Can You Do With Your Unmanned Aircraft?'' that gives details on what you can and can't do based on these parameters.

A document published by EASA states that for low-risk drone operations:

  Flights above crowds are prohibited, but flights above people not related to the operation in cities or populated areas is allowed.

Refer also to local laws. A number of states and municipalities have passed or are considering limitations on unmanned aircraft.


What is this ring-shaped device behind this DC-8's jet engine? What is this ring-shaped device behind this Douglas DC-8's jet engine?

(YouTube)

(airliners.net) Ejector on the Rolls-Royce Conway of a DC-8.
It's called an ejector.
Introduced in c. 1958 by Douglas for their DC-8, it is extended during takeoff and landing, and stowed during the flight because it increases the drag at high-speed flight.
In the extended position it acts as a noise suppressor, and it also reclaims thrust that has been lost due to the corrugated exhaust nozzle. Doors within the ejector also close to provide thrust reversal.
(Flight—PDF)

Two views of the device developed by Douglas to suppress the sound and reverse the thrust of the DC-8. The corrugated exhaust nozzle is combined with a cylinder which extends beyond the nozzle during take-off. This "ejector" is claimed to reduce the sound level by 3-4 decibels and increase the thrust sufficient to offset the loss caused by the nozzle. The indentation near the forward lip of the ejector is one of the two doors which close to form a thrust brake. Noise level with the ejector ring and nozzle combined is said to be reduced by 9-12 decibels.

(Images from aamalebourget.fr and flightglobal.com)
The image on the right shows a similar installation on the BAC One-Eleven with the positioning screw-jack mechanism.
(YouTube) Factory testing of the ejector on the DC-8.


How to estimate blade interference in a propeller or fan? The ideal propeller has one blade. For obvious reasons, that would be impractical.
However, adding more blades causes each blade to operate in each others slipstream/downwash.

How to quantitatively estimate this interference?In other words, what is the real angle of attack and airflow speed seen by each blade

For a simple 2D approximation, you can do it in a similar way to how you would analyze the effect of wake on a tailplane or any other body, i.e. by solving the flow field around both at the same time.
Since the movement of the  blades is cyclical and the flow is subsonic, each blade affects both the ones ahead and the ones behind it. Therefore, you would would need to solve for an infinite number of blades simultaneously so that the one in the middle would have a realistic airflow, but since the effect of the N-th blade will tend to nill, a good approximation can be had with just a few blades on either side of the studied one.

The process would look like this:

Choose the spanwise station of the blade you are interested in and the operating point (rpm and forward velocity) you want to study. These will give you the effective angle of attack for the blade station.
Knowing the angular blade spacing around the hub, the spanwise station you selected, the rpm and the forward velocity, find out where the first airfoil will be relative to the second one in a 2D representation.
Solve the flow field for an effectively infinite number of airfoils spaced this way. In practice solving for a relatively small number of blade instances will provide a good approximation of the real flow on the central blades in the series, as the ones on the edges are only used to provide boundary conditions resembling the real world case:


What is this G1000 Flight Plan Symbol? What does the horizontal flag on the G1000 flight plan page mean?

Thanks

Those are METAR flags. From the G1000 manual:

  METAR flags and their associated text are displayed on the Active Flight Plan Page on the MFD. METAR flags appears next to waypoints in the flight plan with an associated METAR. A solid light blue METAR flag indicates the METAR observations are available for a specific waypoint; a hollow light blue METAR flag indicates an off-route METAR near the waypoint is available. When off-route METAR text is displayed, the system provides additional information as to the origin, distance, and direction of the report in relation to the selected flight plan waypoint.

The ones you have are the 'hollow light blue'.