What is the minimum altitude for dumping fuel?

The altitude appears to be above ground level. From FAA Order JO 7110.65W Air Traffic Control:

Section 4. Fuel Dumping
9−4−3. ALTITUDE ASSIGNMENT
If an aircraft is dumping fuel in IFR conditions, assign an altitude at least 2,000 feet above the highest obstacle within 5 miles of the route or pattern being flown.

The wording says 'above the highest obstacle', indicating AGL. The CAA Manual of Air Traffic Services is much more explicit:

13.3 Controllers are to recommend to flight crew that jettisoning of fuel should be carried out above 10,000 feet agl. Exceptionally, if fuel dumping at this level, or over water, is operationally impracticable or inconsistent with safety, fuel may be jettisoned above 7000 feet agl in winter and above 4000 feet agl in summer.

This indicates that the altitude requirement of dumping fuel is from the from the first consideration i.e. it takes x feet for the fuel to fall before it evaporates. Swiss regulations go into this at a little bit of detail.

Generally, air masses are only moved vertically very slowly, usually at a settling rate of approximately 60 centimetres per second. In addition the upper limit of the planetary boundary layer (PBL) at the altitude of
approximately 3000 ft over ground renders the air flow from the upper to the lower layers more difficult. Therefore the chance that even a small quantity of fuel reaches the ground is estimated to be unlikely.

Again, it says 'above ground' indicating AGL.


What's the relationship between aileron deflection and roll moment?

Using a linear theory, the roll moment coefficient can be expressed as:

$$
C_l =C_{l0}+C_{l\beta}\beta+C_{l\delta_{\alpha}}\delta_{\alpha}+C_{l\delta_{r}}\delta_{r}
$$

, where:
$\beta$ : slip angle
$\delta_{\alpha}$ : aileron deflection
$\delta_{r}$ : rudder deflection

This doesn´t really say much, as we are simply defining this coefficient in a way that is convenient. This equation just says that $C_l$ is equal to a linear composition of the effects of assymetry, slip angle, and aileron and ruder deflections, each weighed by a stability derivative.
Some of these stability derivatives have proper names or are trivially discarded:

$C_{l0}=(C_l)_{\beta=\delta_{\alpha}=\delta_r=0}=0$ , for symmetric aircraft without engine torques
$C_{l\beta}$ is the dihedral effect, or the effect of slip on roll. It is the sum of contributions from the wing-body assembly, the HTP and the VTP. The wing-body effect can be further split into: the geometric dihedral of the wing, wing sweep and vertical position (high or low).

$C_{l\beta} =(C_{l\beta})_{WB}+(C_{l\beta})_{HTP}+(C_{l\beta})_{VTP}$

$C_{l\beta}=-\frac{a_w \Gamma}{4}-\frac{C_L}{4}sin(2\Lambda)+(C_{l\beta})_{\text{wing height}}+(C_{l\beta})_{HTP}-a_v\eta_v\frac{S_v}{S}(1+\frac{\partial\sigma}{\partial\beta})\frac{h_v}{b}$

$(C_{l\beta})_{HTP}$ is obtained the same way as the WB contribution, although with different adimensionalizers.
For general reference, wingtips above the root are stabilizing, positive sweep is stabilizing and the wing height effect depends on the fuselage fraction ahead and behind the wing, but usually a high wing should be stabilizing.

$C_{l\delta_{\alpha}}$ is the roll control power or the effect of ailerons on roll. Is is calculated directly from the Prandtl wing theory by considering the impact of aileron deflection on the lift distribution
$C_{l\delta_{r}}$ is the effect of rudder on roll

$C_{l\delta_{r}}=C_{Y\delta_r}\frac{h_v}{b}=-a_v\eta_v\frac{S_vh_v}{Sh}\tau_r$

Your original question asked for the roll rate, and Peter Kämpf does indeed provide an answer, but it is probably no more useful to your particular need than my very first equation.

If you are interested in the roll rate, you will need to solve the lateral-directional system. You can simplify it somewhat by allowing fixed controls and level fight, thus obtaining a stability cuartic. This has, for most configurations, two real and two complex conjugate solutions,  corresponding to the three lateral-directional eigenmodes: Roll Subsidience (large negative real root), Spiral Divergence (small real root, sometimes even >0) and Dutch Roll (complex conjugate root). Since the large negative real eigenvalue has a much greater modulus than the rest, its mode (Roll Subsidience) will dominate for short periods, and you can obtain a good approximation of the roll transfer function by doing $\Delta\beta=\Delta\hat{r}=\Delta\delta_r=0$ and $C_{l\hat{\dot{\delta}}_\alpha}\cong0$:

$$
G_{\hat{p}\delta_\alpha}=\frac{\Delta\hat{p}(s)}{\Delta\delta_\alpha(s)}=\frac{C_{l\delta_\alpha}}{\hat{I_x}}\frac{1}{s-(C_{l\hat{p}}/\hat{I_x})}
$$

...in the Laplace plane. Keep in mind the parameters are non-dimensional.


Is it legal to use a home-made Airband radio receiver in the United States?

FYI, the runway is supposed to be closed XXX with NOTAM when it is mowed.

There is no FAA or FCC limit on constructing homemade airband receivers in the United States.

You can also construct transceivers. As long as you do not sell a transmitter you are allowed to make and operate up to 5 of them.

The exemptions covering low power transmitters are covered in Part 15 of Title 47 in FCC regulations.

The maximum unlicensed radiated output power for airband is 500 μV/m @ 3 m. Typical commercial airband handheld transmitters go up to about 1 Watt and base stations up to 50 Watts. For your purposes a 1 Watt transceiver would probably be reasonable.

Note that typical receiver/scanner designs have an oscillator in their mixer that can generate a small amount of RF noise. Normally the signal is so weak it is completely undetectable. Nevertheless, there are specialized receivers that have no oscillator that some people use to listen to airband with zero chance of interference.


What are hydraulically powered and electrically controlled actuators?

As wikipedia mentions, "Electro-Hydrostatic actuators" (EHA) are self contained, the only input they need is electrical power and commands.

The electricity powers up the hydraulic pump that is used to move the actuator piston, while the electrical commands are used to select what the actuator does through the use of a valve.

  What does electrically controlled means?

Means that the position (and thus the action) of the valve is controlled via a solenoid. The following scheme shows a valve with two solenoids. The valve has three positions, indicated by the three squares. Depending on the electrical control signal, the current in the solenoids changes and thus moves the selector (the block with the three squares) laterally.

Image source

  How does hydraulics power the actuator?

Through a pump. Where the fluid goes is selected by the electrically controled valve, but the piston of the actuator is moved by the hydraulic fluid.

In the image below, if the valve of the image above is in the central position, the actuator does not move.
If it is in the left position, the actuator retracts.
If it is in the right position (with the two arrows crossing) the actuator extends.

Image source


How are further structural failures prevented if an aft pressure bulkhead fails?

If what's escaping a compromised bulkhead is cabin pressure, not an explosion; the airframe structure aft of the pressure vessel is wide open for air to escape.  The structure is hollow from one component to the next with "lightening holes" wherever possible designed to minimize weight (nothing to do with thunderstorm lightning).  Additionally, the lightening holes provide for plumbing, wiring, maintenance, inspection access, and ventilation.

Unless there's an explosion or some catastrophic failure of the pressure vessel, escaping cabin pressure by itself cannot pressurize the open empennage.  Pressurized aircraft also have a safety valve to protect the pressure vessel from structural damage in the event of outflow valve failure.  The prospect of aft pressure bulkhead failure before other skin fracture is unlikely.

If you are able to peer in between the rudder and vertical stabilizer of an aircraft, you will likely see the openings.


Why would a jet engine that runs at temps excess of 2000°C burn when it crashes?

How The Jet Engine Works:

Inside the typical commercial jet engine, the fuel burns in the combustion chamber at up to 2000 degrees Celsius. The temperature at which metals in this part of the engine start to melt is 1300 degrees Celsius, so advanced cooling techniques must be used.

You can read more about some of those cooling mechanisms in How are temperature differences handled in a jet engine?
See also, How do you stop a jet engine melting?:

Neil - The normal melting point of the nickel blade alloys that we use in the turbine is typically about 12-1400 degrees. But what you do, and this is the clever bit, is you actually cool these blades. You have internal cooling passages, which effectively has air that flows through and it's about 7-800 degrees. And this cooling air then exits from small little minute holes that have been drilled on the surface of the blade and this air then forms a kind of a film on the surface of the blade, and this technology is typically called a 'film cooling.'
What you also do - you coat these blades and typically use something called a thermal barrier coating. The thermal barrier coating, effectively, is ceramic, typically about quarter of a millimeter in thickness, but they have got very, very low thermal conductivity. So, effectively, even though the gas stream is at a much higher air temperature, the effective metal that exists beneath the thermal barrier coating is much colder, and you get thermal grade of the order of about 100 degrees C between the hot and the cold surface. So all of this put together - this whole cooling technology effectively helps to keep the blade below its melting temperature.

The engine is designed to manage the intense heat in a controlled way, by restricting it to certain components, injecting cool air around the hot parts, and choosing different materials for different parts of the engine. If the engine is severely damaged, doused in jet fuel, and set on fire, none of those mechanisms function; the entire engine (or whatever is left of it), as opposed to just the portions intended to manage heat, will be hot, and none of the cooling mechanisms will be working.


Why did my flight climb so sharply on takeoff?

Your flight took off during a storm. During a storm, the wind speed close to the surface of the earth is much lower than the wind speed a bit higher up. This variation of wind speed over a short vertical distance is called wind shear. The aircraft is taking off into the wind, so during the initial climb the headwind increases. Increasing headwind during climb does miracles to the climb rate.

Suppose you want to climb from sea level to 2000 feet while increasing the true airspeed from 140 to 160 knots (70 m/s to 80 m/s).  In steady wind conditions that means the aircraft needs to accelerate 20 knots during that climb, which consumes part of the energy available from the engines.

But if there is a windshear and the headwind is increasing by 30 knots during that climb (not unreasonable in stormy conditions), the ground speed will reduce by 10 knots. Instead of needing to add kinetic energy, the aircraft needs to reduce it by converting it into potential energy (altitude). This means more energy is available for climbing and thus the climb rate is higher.

The wind reports from the airport at the time of take-off showed a wind of 29 knots (39 knots gusts), almost straight down the runway.

If you look at the wind profile this morning (I could not access yesterday's data anymore) you see that the wind increases from 20 kts at the surface to 51 knots at 3000 ft. That's a lot of free airspeed the aircraft gets during climb!

 source: screenshot from windy.com

 source: screenshot from windy.com

In addition, the effect of a stormy headwind is that the ground speed is relatively low. This makes the climb much steeper than in the no-wind condition.

Looking a bit closer at the raw data from FR24, the aircraft took off at 131 knots groundspeed (the first airborne report is 25 ft above the runway). 6 seconds after the first airborne ADS-B report, the altitude had increased by 525 ft. Even if we conservatively assume it took 7 seconds to climb to 500 ft (round-off errors), it requires a vertical acceleration over 1.6 g to achieve that. That must have felt very aggressive!

The first 2000 ft of climb took only 25 seconds, an average of 4800 ft per minute. The ground speed reduced to 119 knots by the time the aircraft had climbed 2800 ft, 37 seconds after take-off.

After that, the aircraft had climbed through most of the boundary layer of the earth and the windshear reduced. The rest of the climb was fairly typical.

It was not only your perception; by all means it was an impressive take-off performance for a B738


ETOPS 330 vs ETOPS 370 etc; how are the exact minute ratings derived?

If there is a formula currently used to generate an ETOPS time, no regulatory agency has made it public that I can tell. ETOPS originally grew out of a "60-minute rule" that was the result of earlier distance-based rules (see this report for a thorough history). My guess is that 60 minutes was a case of  "well, that sounds good" rather than the result of any rigorous analysis. From there, it's mostly been manufacturers slowly pushing and getting approved for longer and longer extensions (usually just a percentage increase that results in round-ish numbers—again, this is policymaking, not engineering).

However, take a look at the formulas on pages 9–11 of this report. I hesitate to declare them the way to generate an ETOPS number because the report is thirty years old and a lot of it is critical of the methodology, so the regulators may have changed their approach between then and now. In fact, the report does not explicitly state that the formulas within were in use at the time, either. Nevertheless, if there is a formula in modern use, it likely uses a similar approach of quantifying the probabilities of failure and using a factor to convert them into a do-not-exceed diversion time.

The difference between certification at 330 minutes (777) and 370 minutes (A350) may be due to FAA vs. EASA methodologies and/or decreases in inherent failure probabilities as technology matures. With that, I doubt there is much difference in maintenance of a 777 vs. an A350 (at least as far as ETOPS goes—obviously their construction necessitates very different maintenance programs), as that 40-minute increase for the A350 was approved without any in-service maintenance data. It may be different for the 787, which was not initially certified at 330 minutes.

Going forward, I have no doubt we'll see ETOPS 430 and above. Airbus already toyed with 420 minutes for the A350, and perhaps we'll see that after some time in service. At 420 minutes, there are only a few non-compliant routes; I expect that, eventually, any new twin will be able to fly unrestricted between any two points within its endurance.


Do I need AFSP TSA approval once I get my PPL?

Merely to exercise the privileges of your PPL, no. Even to take additional training with a CFI for proficiency or endorsements such as complex/tailwheel, no.
To train for an additional rating (e.g. Instrument or Multi-Engine) or certificate (e.g. Airline Transport Pilot, but not Commercial Pilot), yes.


What are the advantages of a geared contrarotating turbofan?

what problems are stopping us from doing this?

In some sense, it's business reasons. Developing a brand new jet engine from scratch costs a lot of money. Usually the pricetag runs into the billions. It will often take 10 years from the time you start to develop a new engine until you see a single dime of profit. If you are the board of directors of an engine manufacturer, and you give the greenlight to develop a new product, you might be literally betting the entire company on the success of that new product. So, you have a tendency to be conservative. If you can get a 10% performance improvement from some new never-tried-before fancy contra-rotating fan thingy, or you can get a 5% performance improvement by keeping the same basic tried-and-true design but just tweaking the aerodynamics a bit here and there, you are probably going to go with tried-and-true. Eventually, a limit will be reached where the basic turbofan architecture cannot be tweaked anymore, and then you may see some new thing like this tried, but I don't think we are quite there yet right now.


A "sterile runway" indicates that all traffic has been cleared from the runway.

This can include both traffic currently active on the runway as well as potentially other inbound traffic on approach, or even elsewhere on the tarmac - if it is deemed disruptive.

A sterile runway is often used in emergency situations, such as when an airplane is coming in for an emergency landing. For the safety of both that plane as well as the others, the runway is cleared of any traffic.

That said, this term is not exclusive to emergencies. For example, the FAA requires 250 feet on either side of a runway to be clear of airplanes when a Commercial Airplane lands. An airport that is smaller and has tight taxiways might have an aircraft taxiing closer than that. To be within FAA compliance, they would need to ensure that the runway was sterile and that there were no active planes taxiing within that 250 feet at the time of the commercial plane landing. An example of this rule being observed includes this notice posted by Friedman Memorial Airport in Hailey, ID, where they adjusted their procedures in response to FAA determinations in order to accommodate commercial traffic and maintain a "sterile runway".


How are Max Brake Energy Speed & Weight affected by other factors?

The factors you mention will affect how much energy the aircraft has that's going to be transferred into the brakes, and how much will be lost otherwise.  The more energy you have, the slower you can go before the brakes are overwhelmed -- thus, reducing your VMBE.

With more flaps, energy will be dissipated in aerodynamic drag, although probably not all that much (though going from the least possible to the greatest possible flaps may make some difference -- or it may be sufficiently slight that the charts are published with a worst-case scenario & if you have greater flaps then your situation will be slightly better than what's charted).  With runway gradient, you'll dissipate some energy rolling uphill, while you'll have more energy (potential energy becomes kinetic energy) rolling downhill.

The really significant factor is aircraft weight, as your formula makes clear... an aircraft stopping at 100,000# will have 2/3 of the energy of an aircraft stopping at 150,000#, all else being equal.  So, in those two cases VMBE would be much higher for the 100k case... if Limit = 0.5 * wt * V-squared, you can have a higher V-squared to reach the same limit with a lower weight.

Contamination probably wouldn't matter much: while you would be transferring energy more slowly into the brakes stopping on a slick runway than on a dry one, the total energy absorbed into the brakes would be the same.  So unless the rate that the energy is absorbed changes the maximum energy that the brakes can absorb (seems like it would be unlikely, although in some cases... who knows), contamination wouldn't affect VMBE.  (Unless the charts take stopping credit for the deceleration due to "plowing through" contamination -- which would actually help out to some extent.

The most likely effect would be to make the stopping distance more limiting in the contaminated case than it would be otherwise -- so you might be limited by the ability to stop before the end of the runway in a contaminated case, where you'd be limited by brake energy in a dry runway case.

The effect of weight, flaps, and slope on the actual VMBE would be that things which give the aircraft more energy (more weight, less flaps, downhill slope) would reduce the VMBE.  Think of it in an extreme case... if you had the brakes of a bicycle, a one-pound vehicle could go insanely fast before you could put enough energy into the brakes to cause a problem, but if your vehicle were, say, the Space Shuttle, even at slight speed, the brakes would be overwhelmed by the KE of that much mass.  Consider likewise, a 45 degree downslope vs a 45 degree upslope, or the drag caused by a huge drag chute vs the drag of a pencil flying through the air.


Because some people like new things... Thats how salesmen stay in business.

There are however some practical aspects to this question and on the tail end of my instrument rating I've been getting serious about buying something, here is what I have found. For the purposes of this answer I'm only going to talk about aircraft that are still in production like the 172 and have been for some time. The only other comparable aircraft is the Piper Archer. Mooney no longer makes the lower power stuff, the early low power PA-28 variants have been out of production for some time and are thus out of scope. In the end it depend s on what you, the pilot/owner/operator really wants out of the aircraft.

While a 1956 172 will share a lot in common with ones rolling off the line now a G1000 cockpit is not a steam gauge cockpit. A G1000 unit, or any of the various glass options for retrofit are NOT cheap to buy and install. Thus if you get a decent, low time 172SP and replace the panel to make it just like a new one, you have already spend about what a new one costs and there may very well be 2000 hours on the airframe already.
The older the plane (generally), the more engines its been through. A well flown early era 172 may very well be on its 2nd, 3rd or 4th engine. These engines could have been overhauled, rebuilt, swapped by various different entities in various ways. There may or may not be a warranty on them anymore and you may have little protection against it blowing out on you. Meanwhile a new plane may come with a warranty which represents real tangible value especially considering the first hundred hours or so of an engines life are quite critical. You can find all of Textron/Cessna warranty info here.
You are buying effectively a 0 time engine (or as low as practical) again you can buy a nice 172 then go spend another 20K, 30K, 40K... putting a fresh engine in it to get a "new" airplane.
The paint and interior are new and clean. There is nothing quite like the tired velour interiors of rental aircraft but even second hand planes often have tired 80's fabric that have seen a lot in their time. A fresh paint job and new interior is not cheap, especially when you realize you need fireproof fabric, may need to take a lot of the plane apart to paint it and dealing with the downtime. We come back to the 80's 172 that needs paint and a costly interior example...
Finally, old planes are just tired. Even planes that look to be in good shape, pass inspections, and fly great dont last forever. Some times you are just taxing along and your gear gives out...

Buying an old plane and making it a new plane may just cost as much as a new plane.


Would this be a dangerous impeller to use for a drone?

I know those things as squirrel cage blowers. As the video says, they are a good choice if you want to move a moderate amount of air without exposing rotating blades.

Impeller, by the way, was initially the word for a sort of airscrew that is moved by the flow. The small thingy in the nose of the Me-163 rocket interceptor was an impeller and needed for driving the plane's electric generator. Unfortunately, this word has recently been abused to mean shrouded propellers.

The proper name for those blowers is "centrifugal fan", and I will continue to use this word for the remainder of this answer.

As @pericynthion says in the comment, air pressure is less of a concern than centrifugal loads. Basically, the blades spin air around and hurl it to the inner housing of the blower, increasing pressure when the kinetic energy of the swirling air is converted to pressure as the air slows down. If we assume that air comes to a total standstill at the housing (which it doesn't, otherwise the blower would choke), the maximum attainable pressure is determined by the radius of the cage $r$ (in meters) and the rotational speed $\omega$ (in rad/sec) of the blades.
$$∆p = \rho\cdot r\cdot\frac{\omega^2}{2}$$
For a 20 cm blower spinning at 3000 RPM this would be 5.9 bar. The centrifugal acceleration $a$ on the blade would be
$$a = r\cdot\omega^2$$
which produces 1000 g with the same parameters.

To give you an idea about the efficiency: It is generally desirable to accelerate a large volume of air a bit rather than to accelerate a small amount of air by a lot. Therefore, helicopters use the largest practical rotor diameter, so they can capture as much air as possible for lift creation. Centrifugal fans cannot enjoy the same luxury and can only use the air which enters them from the side. As you can see from the two formulas above, your ideal centrifugal fan runs at a low speed but has a large diameter for the best ratio of pressure over centrifugal loads.

If you build them without regards to the loads, yes, those centrifugal fans can indeed be dangerous.


What methods are used for calculating maximum takeoff windspeed of a helicopter?

The simple (and probably unsatisfying) answer would be:
The maximum headwind into which a helicopter can land will be somewhat less than it’s listed maximum operating speed.
Flying at Vmo into a headwind of equal speed should lead to a stationary velocity relative to the ground. In theory, the aircraft could gently lower itself all the way the ground like this (although, I certainly wouldn’t try it). The problem is, most helicopters will be in a very pitch-forward attitude at this point and the skids or landing gear may not be in the proper orientation to safely put the aircraft on the ground. This will vary from model to model and would need to be tested on a case-by-case basis.
It should be noted that landing and shutting the engine down are 2 separate problems. Many helis have a maximum wind speed for startup/shutdown, like this BK117 which has a listed limit of 50 knots in its POH.


What is this substance on these pipe fittings?

That is called "torque seal" or "torque putty".

It is used by mechanics to mark a part after it has been properly torqued, and thereafter to serve as an indication if loosening has taken place. The torque seal hardens after application and serves as a marking mechanism that will show—by cracking and/or flaking of the putty—if the part has loosened resulting in rotation.

The photo below shows torque seal as initially applied (left), and then with the seal broken following loosening an rotation of the nut (right).

Image courtesy of theleanwarehouse

Just to be clear, the torque seal does nothing to secure the part or otherwise serve any locking function. It serves only as an indication.

Dykem is one manufacturer of torque seal.

Here is a page with additional information about torque seal from a retailer.


Why are jet aircraft never designed with a slower cruise speed?

There is indeed a benefit in flying more slowly, but the aircraft needs to be designed that way to profit from slower speeds. You can see that wing sweep has been slightly reduced in the more modern airliners, but this is also due to better airfoils with higher Mach drag rise onset.

But some things will also cost more when you slow down: You have to pay the crew for more hours, and the aircraft cannot be utilized as often. To transport the same number of passengers requires more aircraft when they fly at a lower speed. The cost versus speed relationship is not linear, but it should have a minimum somewhere below today's operating points. Aircraft with a slower design cruise speed can be lighter and smaller for the same payload, but for now airlines don't have a choice of slow or fast jets; all manufacturers try to design their long-range airplanes for at least Mach 0.83.

This has a lot to do with marketing: The aircraft with the higher speed will show a shorter travel time for the same distance, so it will show up first in the booking systems of travel agents. Of course, now you will argue that most people book on the internet and will try to get the lowest cost, regardless of travel time. True. But this is not the sort of customer the airlines are after. Their profit comes from people in First and Business class, and these still book predominantly via travel agents. Therefore, Airbus and Boeing try to market their planes as the ones which come first on the Amadeus and Sabre screens.

If you would single-mindedly optimize a configuration for the best fuel efficiency, you would arrive at something close to the MIT D8 design or Boeing's SUGAR study. Note that both are designed to fly quite a bit slower than current airliners at Mach 0.72. These designs are for a world in which fuel costs 200 USD per barrel or more, while the current designs are based on the expected prices at the time of their design start.

When fuel prices were low, the optimum speed for the best transport performance was indeed above Mach 1. The Vickers VC-10 of 1964 sported a maximum cruise Mach number of 0.886 and still holds the record for the fastest commercial Atlantic crossing. When Concorde was developed, the general consensus was that future air travel would be supersonic. Only the jump in oil prices after the 1973 oil crisis put those plans to rest. Large business jets today can cruise at up to Mach 0.935 because their owners are less concerned with saving money by flying more slowly. Technically, there is still room for cruising above Mach 0.85; it's economics that keeps airliners back.

If airplane companies were free to pick the optimum Mach number, they would today choose a speed between Mach 0.78 and 0.82 with fuel prices around 50 USD per barrel. Note that this is the design Mach number range for regional jets which fly short hops in which the increase in trip time from the reduced speed is insignificant. Also, especially in times of high fuel prices airlines operate their gear at lower speeds in order to conserve fuel. But if you follow this link, you will learn that airplane companies don't have that freedom.

Regarding drag:

Drag does not go up with the square of speed. When plotted over speed, the drag of an airplane will first go down, reach a minimum and only then go up. Airliners fly close to this minimum, and they fly high to shift this minimum to the highest possible flight Mach number. They do this by flying in less dense air, which requires to fly at an altitude around 30.000 - 40.000 ft. An additional benefit to flying this high is the lower air temperature which makes the engines more efficient.


Are Air Traffic Flow Management Algorithms mostly based on linear programming techniques?

Linear programming (LP) is an optimization method that finds the highest (or lowest) possible value of a set of linear equations given a number of linear constraints.

There are a number of objectives in Air Traffic Management that may be described by linear equations. Runway throughput for example: twice as many aircraft can be seen as "twice as good". Or delay: one minute of delay of a passenger aircraft with 400 passengers is as bad as 2 minutes of delay for a passenger aircraft with 200 passengers (both have 400 passenger-minutes-of-delay). Mathematical models based on these linear relationship can help to make decisions for air traffic controllers/planners.

There are obvious limitations to linear programming. Not everything can be modeled as a linear relationship. Often the relations are more complex and linear models will be a poor fit because the relationship is not linear at all. In ATFM modelling, usually binary integer variables are used that can only take values of zero or one, thus a Binary Integer Linear Program is solved (BIP). And is 40 minutes of delay of a 10 passenger aircraft as bad as 1 minute of delay of a 400 passenger aircraft? These kind of relationships tend to prevent the small aircraft from ever taking off: it always pays off to let a bigger aircraft jump the queue. Perhaps a quadratic component in the  'cost-function' would bring a solution here.

Therefore more advanced models are needed. Methods like Integer Linear Programming (ILP), Mixed Integer Linear Programming, Mixed Integer Quadratic Programming and more advance optimization algorithms are used as well.

Another problem is that while these optimization methods may be able to find a best possible strategy, they are not necessarily easy to understand. Air traffic controllers don't like to be just told what to do, they need to understand why a strategy is proposed so they can think ahead and create what-if scenarios. It is impossible to program every what-if scenario in the optimization model, so at times the controller will need to deviate from the proposed solution. Without understanding what the algorithm had planned, it is difficult for a controller to predict the knock-on effects of his deviation from the proposed plan.

Early arrival management software worked reasonably well when the weather was nicely playing along, but gave hopelessly wrong suggestions when a couple of thunderstorms would render the normal approach routes unusable. Flexibility and two way communication between the system and the controller is essential to make a good product, there is much more to it than choosing the right optimization algorithm.


Would a 50 mph aircraft holding a ground pattern in a 20 mph cross wind risk stalling by abruptly rolling away from a crosswind?

Your question is flawed because it is creating a link between two different things.  Let's deal with them one at a time:

In the title question you ask whether a plane holding a crosswind correction in a landing pattern risks stalling by rolling abruptly away from a crosswind.  Ignoring for a minute that doing anything "abruptly" imposes some additional level of risk, (depending of course on the severity) the answer is no.  Turning into, or away from the wind in a "uniformly moving airmass" does not alter the airspeed of the aircraft.  You said as much yourself.  When ready for downwind you simply turn to a new heading for that leg as you would normally.  (in this case 090 because you will now have a tailwind.)

The very concept of "wind" only matters when you consider the surface of the earth.  The airplane doesn't recognize or care what the ground is doing, only the airmass matters.

Now to the second part; would flying near stall speed and then abruptly rolling and yawing the aircraft risk a stall?  Yes, absolutely yes!  As well as a spin...  Those are the main two ingredients of a spin, and every pilot is taught to avoid them, especially down low.  Statistically this is probably one of the main GA pilot killers.

So, let's further unlink the two concepts.  You seem to be espousing an unbalanced slip approach to maintaining heading and ground track in the crosswind turn, furthermore, doing it right around stall speed!  (Sorry, that wasn't you, it was pilot Bob...) This is improper and unsafe technique.  You should not attempt to maintain aircraft heading of 180 on the crosswind, you should fly 190, or 195, or whatever heading will allow you to maintain a consistent ground track.  You should do it wings level, in balanced flight, at a safe and appropriate airspeed for your aircraft in the pattern.  The same airspeed you fly when the airmass is not moving relative to the ground.  This wind correction technique is called "crabbing".

Bottom line, it isn't the wind creating any additional risk, it is pilot Bob's improper technique.


Is there a way to avoid exhaust fumes when landing?

Smelling exhaust in the cockpit is not normal.  Tell your instructor and squawk the problem.  Bonus - turn it into a learning experience by arranging to be with the A&P when he decowls and inspects.  You can learn a lot about the engine that way.

If you are getting a headache from this you may have mild CO poisoning.  This does need to be checked out.


What measures can the aerospace industry take to deal with changes in the electronic industry that are incompatible with its own conservatism?

The aviation industry is strongly cognisant of these risks.

At least one research programme has attempted to analyse them in depth, the Aerospace Vehicle Systems Institute (AVSI) Consortium Project #17 Methods to Account for Accelerated Semiconductor Device Wear Out.

The project ran for six years until 2007 with a budget of ~US$1.2 million.

However, the project's scope was analysis, development of guidelines, testing methods and so on, and did not include ways of addressing the fundamental problem.

A paper from the project Microelectronics Reliability: Physics-of-Failure Based Modeling and Lifetime Evaluation discusses some of the issues in depth.


Can the maximum thrust of a turbofan engine be estimated by its intake diameter?

No.

You need to know one more parameter: How much fuel will be consumed per unit of time. In the end, thrust is created from heating some of the air entering that engine, and only if you know what proportion of air will be used for combustion can you make valid estimates of the thrust than can be generated.

What you can calculate from the intake diameter is how much air flows through the engine per time. The flow speed at the engine face is about Mach 0.5, almost regardless of aircraft speed, so the mass flow is strongly correlated with engine size. The plot below is from NASA TM-X 73,199 which lists statistical data on weight and dimensions of turbofan engines. Unfortunately, it is now more than 40 years old, but the laws of physics have not changed since then.

Correlation of intake diameter with the square root of mass flow from NASA TM-X 73,199. Wa is the air mass flow and h/t is the hub-to-tip ratio of the fan. $\left(1-\left(\frac{h}{t}\right)^2\right)$ is proportional to the effective fan area.

Now this uses fan diameter, not intake diameter, as the basis for the correlation, but those two dimensions are closely correlated, too. For a first order estimate, you can assume $D_F\cdot\sqrt{1-\left(\frac{h}{t}\right)^2}$ to be equal to the intake diameter.

The next step is to get a grasp on the ratio between core flow (which is available for combustion) and secondary flow (which only goes through the fan and exits the engine without being heated by combustion). This ratio is called bypass ratio (BPR) and has grown over time from 0.25 for the RR Conway, the first operational turbofan from the late Fifties, to 11 for the newest version of the CFM LEAP-1A engine on the A320 NEO. Core flow is Wa/BPR.

The fuel-to-air ratio of turbofans is roughly constant at 0.03. Given the bypass ratio you can now calculate the fuel flow and then continue to the thrust by using the specific thrust (thrust per unit of fuel) from sources like Wikibooks or statistical analysis. Note that specific thrust changes with aircraft speed, altitude and bypass ratio!

Thrust specific fuel consumption over Mach for different engine types. Page 29 from Jack Mattingly: Elements of Gas Turbine Propulsion. McGraw-Hill, 1996


During VTOL landings, do Harrier pilots cut power before touching the ground?

The Harrier's NATOPS flight manual (A1-AV8BB-NFM-000) is available online.

Both the text and the diagram in Part III Normal Procedures confirm the opposite. Thrust is idled when "positively down". And not before. Which agrees with the dozens of soft landing videos on YouTube (base and shipboard alike). And as with shipborne helicopters, in rough seas the pilots wait for the pitching deck to catch up to them. Anything else would be an unlucky situation the pilot has found themselves in, but is not standard procedure.

  7.6.4 Vertical Landing

  (...)

  When positively down:

  Throttle — IDLE.
  Brakes — APPLY.
  Nozzles — AFT.
  Trim — 4° ND.
  Water — OFF (if selected).

Moreover, before step 5 there is this note:

  If strakes or gun pods are not installed some suck-down effect is present.
  A power increase may be required near touchdown to prevent excessive sink rate.

The only mention of idling (i.e., cutting/chopping) is step 5 and the diagram.


How do I renew/revalidate my lapsed JAR PPL?

I'll have a go at answering this.  It's confused by the UK's transition from the JAA to EASA licensing.

My JAR-PPL(A), issued in 2011, is valid for 5 years so yes, I assume yours will have expired.  My FRTOL is valid for 10 years so presumably yours will have expired too.

The requirements are hidden in CAP 804 ([Deep breath] Section 7, Part B (Schedule 7) Part C, Section 2, Paragraph 9-(1)(c)).  Renewing an expired licence (single-engined/single pilot aeroplane) seems to require meeting FCL.740.A of Part-FCL (type rating) and Appendix 9 to Part–FCL (skills test).

I believe this effectively means you'll have to undertake training to ensure you can pass the skills test, pass it and pay to have your licence reissued.  (Not forgetting the medical.)   You will end-up with a part-FCL PPL (which do not expire).

I'm not sure about having to retake the FRTOL tests, I think you may just have to re-sit the theory (PPL comms), fill out a form and pay but the answer is probably in CAP 804 somewhere!

The easiest/best thing to do would be to pop-in to your local friendly FTO and discuss with them...


What is the power generating capacity for an airport GPU?

Power requirements are dependent on airframe and configuration (see this question for a general idea). GPU's come in varying sizes for varying aircraft types. For example this GPU (arbitrarily chosen) can deliver: 800 amps continuous, 2500 amps peak. While this GPU can only drive 70Amps continuous. Others may be able to drive more and some may drive less. Are you asking about a particular application? The GPU's at the tiny airport I fly out of that we use to bump start the occasional Piper are no where near the capacity of what you may find at JFK for starting up a 747.

  Would it by possible to power GPUs entirely by solar power?

Depends on the application but it would be unlikely to chose such a medium for powering a GPU the way things stand now (in terms of power requirements). You may be able to have a battery powered GPU that is charged by solar cells but that would only work well in the smaller scenario. Having a solar powered airport that can provide ground power is a whole different question.


What is the heat signature of a piston engine, relative to a jet engine?

Here is a color IR image of what I believe to be another F6F, on the tarmac shortly after landing:

As you can see, the engine cowling is very noticeable, as are the tires (from touchdown and braking).

Here's a similar image of an F/A-18 performing a runup test prior to takeoff. This jet is longer and larger than the F6F (though if you've ever stood under a Hellcat you'll notice they're not exactly small planes), and as you can plainly see, the entire back half of the aircraft glows white-hot:

So clearly jets are more visible targets for an IR missile, though a prop plane wouldn't be that hard for an IR seeker to find.

The biggest issue relating to getting a good IR lock and track is contrast. Against a blue sky, almost any airplane is readily visible to the missile's seeker. The biggest problem for combat aircraft in early engagements was firing at a target below the horizon (so-called "look-down, shoot-down"). This was a problem for both radar and IR technologies. For IR, solar heating of the ground produced high enough temperatures that the aircraft could not be distinguished unless it had turned its tail to the shooting aircraft and was showing its 600-degree exhaust plume. Nothing on the ground underneath it would be that hot. Prop planes, while operating at lower temperatures, would still be warmer than the ground, and unlike a jet the aspect angles at which this heat is most noticeable is around the front half of the aircraft.


IFR Currency with a safety pilot who has a BasicMed

FAR 61.113(i) authorizes flight as PIC when using BasicMed. Therefore, your buddy can act as safety pilot if he is also acting as PIC.

If you were acting as PIC, that would make your buddy SIC (as a required crew member), which still requires a traditional medical certificate.


Simple explanation for static and dynamic pressure?

Static pressure is a force per unit of area due to fluid molecular motion leading to some statistical collisions with its environment (a solid submerged or another fluid for instance). Pressure gives an information of the fluid state (in a thermodynamics sense) and is a « measure » of the force apply by molecules as a whole. Wikipedia could be helpful on that topic.
Dynamic pressure is a bit confusing term as it is the kinetic energy of a fluid parcel (a unit of volume). This parcel has different form of energy (internal, pressure, potential) and this one is energy due to its motion. But it is not a pressure at all and does not act on the solid. However, disturbance created by the body (the flat plate on the picture) will slow down the flow in front, increasing pressure near surfaces. But this is still that pressure difference between front and back which is « felt » by the plate.
In fact, I believe this is the reason why we call it dynamic pressure. It is an energy form (known as kinetic energy) which is easily changed into pressure (or inversely pressure changing to kinetic energy) during fluid dynamics process: drag and lift are created like this on a flow around a body, gas expanding inside jet engine nozzle for thrust generation, etc..


Pay for training (PFT) is a bad thing.  I am specifically referring to operations in which you pay to go through initial aircraft training and fly right seat.  Yes, you not only pay for 121 initial (BAD!), you also pay to fly from the right seat.  The bottom line is you are occupying a seat that the company should be paying you to be in!

Part 121 pilots are in a constant struggle over wages.  Companies paint a picture that the only reason they take quarterly losses is that they pay the flight crews too much.  Negotiating capital has to be spent to combat this.  These pay for job (PFJ) operations hurt our negotiating positions on wages, as do the pilots that come out of these programs who some might argue are more likely to support concessions (after all, they'll fly for free!).

It is hard to combat these kind of programs because flying is more than a job for a lot of people. It is a dream and a passion and some of these people are more than happy to pay for the "privilege" of flying a beech 1900 from the right seat.

You asked for Pros and Cons, so:

Pros

You learn an aircraft and log some SIC and TT, maybe even turbine.

Cons

You are helping depress wages across the industry.
You are enabling the company to avoid paying a wage to half of its pilots.
You will probably carry a stigma when you move up in the 121 world, at least at the regional level (FO's I flew with were very reluctant to name their former operation if it happened to be [REDACTED])

Don't go the PFJ route.  Find something to do that will pay you a wage to fly and build hours to get into a regional 121 seat.  Once you have your commercial (and cfi) certificates, you shouldn't be paying to fly any more.  You'll also find once you get into the 121 world that paying to accelerate your way there  perhaps wasn't worth it.


Is implementation of CPDLC mandated by EASA?

according to eurocontrol, http://www.eurocontrol.int/services/link-2000-programme:

  The LINK 2000+ Programme started in 2001 and is now in the full scale
  implementation phase governed by the DLS IR which requires:

  • All newly delivered aircraft operating above FL285 to be equipped as
  of 2011,

  • Core European ANSPs to be operational by 7 February  2013,

  • The rest of European ANSPs to be operational by 5 February 2015,

  • All existing aircraft operating above FL295 to be retroffited by 5
  Feb 2015 (unless exempt).

What aircraft are exempt? See page 4 of this pdf: http://ec.europa.eu/transport/modes/air/single_european_sky/doc/implementing_rules/2014_01_22_2nd_exemption_under_29_2009.pdf


Why is a canard configuration more Structurally efficient for Rutan's Voyager?

I listened to John Roncz explanation more than a couple of times and figured the reason he was explaining.

The first thing to understand is any aerodynamic surface placed in front of the CG is a DE-stabilizer. The aft wing is the stabilizing surface.

The high inertia of the fuel filled booms demand either a very torsionally stiff wing structure or else a very big stabilizing power characterized by higher tail volume. But torsional strength is very expensive in terms of wing weight because higher torsional loads imply a bigger secondary spar and thicker wing skins.

Considering the fact that the Breguet range equation favors higher structural efficiency over the other parameters, It appears that Burt chose the second approach. This adds to the second benefit that wing and canard both subjects almost only to the bending loads.

Quick number-crunching shows that with 10% static margin canard configuration leads to ~7 Times statically stable airplane than the conventionally configured one.

EDIT:
As of why GlobalFlyer with very similar mission requirements used conventional configuration could be tracked down to the following reasons.

Due to the nature of the Voyager project, Burt's responsibility was only to design the airplane. The materialization of the design was on Dick and Jeana, he opted for the most simple structural solution with the minimal analysis he could come up with at the time.
As per the previous analysis on tail volume comparison, it is clear that conventional configuration provides only minimal "P" gain for the longitudinal transfer function; meaning that dampening out a gust response, for example, could result in diverging oscillations or even a stall. At the time, I believe completely failsafe autopilot is not a feasible solution given the additional weight it put and/or risks it brings onboard.
Also, Global Flyer demands even a higher fuel fraction due to fuel thirst jet engines, so losing the aerodynamic benefits of conventional configuration was not a feasible one. Instead, they ended up utilizing a fulltime autopilot.


Are the airport "taxi" plans available online?

A great site to download airport diagrams and other charts is charts.aero. As of April 2015, however, the site seems gone.

Airport diagrams show all the taxiways and ramps, which is what you are looking for.

Keep in mind that this is an unofficial website. The charts should not be used for actual navigation.


Are transponders required for hot-air balloons in the US when operating within a Mode C Veil?

I've gotten this question enough times to look up the regulations and answer my own question :)

14 CFR 91.215 lays it out quite nicely.  Particularly section B(3):

  (3) Notwithstanding paragraph (b)(2) of this section, any aircraft
  which was not originally certificated with an engine-driven electrical
  system or which has not subsequently been certified with such a system
  installed, balloon or glider may conduct operations in the airspace
  within 30 nautical miles of an airport listed in appendix D, section 1
  of this part provided such operations are conducted -

  (i) Outside any Class A, Class B, or Class C airspace area; and

  (ii) Below the altitude of the ceiling of a Class B or Class C
  airspace area designated for an airport or 10,000 feet MSL, whichever
  is lower; and

Where I see the balloons is definitely outside of the Class B airspace and below 10,000 feet MSL, so the answer is, no, they don't need a transponder.


In a tailwheel plane, which design elements affect the propensity for a ground loop?

CG Fore/Aft Location
The further forward the main wheels are in front of the CG, the greater the propensity for ground looping.
Main wheel separation
The closer together the main wheels, the greater the propensity for ground looping.
Main wheel Toe-in and Toe-out
The following text and images come from the book "Landing Gear Design For Light Aircraft" by Ladislao Pazmany, obtained on-line via this web page on www.vincesrocket.com:

The "toe-in" and "toe-out" of a wheel is measured either in degrees or
in inches as shown in Figure 3-9.

How the "toe-in" or "toe-out" affects the directional stability and
control of an aircraft is a controversial subject.  The author
consulted with a number of aeronautical engineers and landing gear
experts.  The answers were mixed.  Some indicated that with "toed-out"
wheels as shown in Fig 3-10, the wheel on the outside of the turn
tends to run straight and counteract the ground loop.

Other opinions were that the "toed-in" wheels result in more drag (due
to skidding) in the outside wheel than in the inside wheel, therefore
counteract the ground loop as shown in Fig 3-11.

The recommendations in some Service Manuals are that a very small
amount of "Toe-in" (0 to 1/8 inch) measured at empty weight, is
desirable.  Essentially the wheels should run straight (zero toe-in)
at normal operating weight.  The PL-4A (Figure 1-11) designed by the
author has 0 degree toe angle and exhibits excellent ground handling.
Any tendency to ground loop initiation is easily countered with the
rudder and steerable tail wheel.  The same comments apply to tricycle
gear airplanes.

Here's a post from an on-line discussion forum for rc airplanes where the author describes a particular plane where the landing gear can be quickly removed and re-attached to convert toe-in to toe-out or vice versa.  The author notes that any toe-out seems to greatly increase the difficulty of keeping the aircraft going straight when the aircraft is rolling at high speed on the main wheels with the tail in the air.
The entire thread from which the above post was taken may be of interest-- the opening question is very similar to the question here: "What design aspects affect ground handling?"
Here's another post from another related thread on the same forum where the author-- a very experienced builder and flier of rc planes-- advocates some toe-in.
Camber
Camber is a significant factor.  If the bottoms of the main wheels are closer together than the tops, the wheels have positive camber.  If the tops of the wheels are closer together than the bottoms (like on a Me-109 or Spitfire), the wheels have negative camber.  Note that if a tailwheel aircraft has zero toe-in but positive camber when it is an a fuselage-level attitude, then the camber will automatically create toe-in when the tailwheel is on the ground.  If a tailwheel aircraft has zero toe-in but negative camber when it is in a fuselage-level attitude, then the camber will automatically create toe-out when the tailwheel is on the ground.  This may be part of the reason why negative camber has generally been found to contribute to an increased propensity towards ground looping, and positive camber has generally found to contribute to a decreased propensity toward ground looping.  Note also that when a ground loop begins and the "leading" or outside wheel starts to get more heavily loaded than the "trailing" or inside wheel as the plane starts to tip over toward the outside wingtip, negative camber will make the "leading wheel" tend to "dig in" or experience an increase in traction, exacerbating the process, while positive camber will tend to reduce this tendency.
Tire traction
Tailwheel aircraft show much less propensity towards ground-looping when landing on grass or wet pavement, than when landing on dry pavement.  This might seem to suggest that any tread on the tires of the main wheels--or at any circumferential grooves -- should increase an aircraft's propensity for ground looping, by increasing traction.  However this related ASE answer indicates that tread or circumferential grooves don't actually increase a tire's grip on dry pavement.
It would seem that anything that increases a main wheel's "contact patch" -- which would include decreasing the tire pressure-- would increase the ground-looping tendency on dry pavement.
CG height
A high CG location increases an aircraft's tendency to tip over and drag the outside wingtip during a ground loop.  Even before the wingtip touches, any tipping will load up the "leading" wheel and unload the "trailing" wheel, which will exacerbate the developing ground loop.
Fuselage length
An aircraft with a relatively short fuselage is called "short-coupled", and will experience a greater propensity for ground-looping than an aircraft with a relatively long fuselage.1  If the mass of the aircraft is concentrated near the CG so that the moment of rotational inertia is low, the aircraft will have less tendency to ground loop than if the mass of the aircraft is distributed far from the CG.
Annex
Here is a PDF from a course on landing gear design.  Note however that it doesn't go into a great deal of detail.  Toe-in/out and camber are not discussed.
Footnotes:

This sentence naturally begs the question-- exactly how might we quantify how "short-coupled" an aircraft is?  Probably not by comparing the fuselage length to the width of the landing gear tread, as this would seem to imply that increasing the distance between the main wheels is not helpful.  There may be some room for further refinement of this part of this answer--


Are airliner flight plans/routes preset?

Airlines have an own department that is solely responsible for their flights and flight plans: Dispatch. Since single airways can have different availability or just direction for different days or even times of the day, there will be a preset pool of routes for recurring flights, which can then be adapted for anything out of the ordinary, like NOTAMS, weather forecasts, operational requirements like airspace closure, etc...

The flight plan is usually submitted by the dispatchers and not the aircrew.


The MMEL and MEL list items that can be inop while still dispatching the aircraft, it also lists any required restrictions of that system being inop.

I think FAA Policy Letter 34, which is the preamble for all MMELs, gives some of the best information:

First they set the basis of an MEL, that every system/function of the aircraft must be operation to dispatch. This restriction can be superseded by the MEL:

  The following is applicable for authorized certificate holders operating under  Title 14 Code of Federal Regulations (14 CFR) Parts 121, 125, 129, 135:  14 CFR  require that all equipment installed on an aircraft in compliance with the Airworthiness Standards and the Operating Rules must be operative. However, the Rules also permit the publication of a Minimum Equipment List (MEL) where compliance with certain equipment requirements is not necessary in the interests of safety under all operating conditions.

Then they tell you that MEL includes items that are allowed to be inoperative along with any limitations:

  The FAA approved MMEL includes those items of equipment related to airworthiness and operating regulations and other items of equipment which the Administrator finds may be inoperative and yet maintain an acceptable level of safety by appropriate conditions and limitations

  The individual operator's MEL, when approved and authorized, permits
  operation of the aircraft with inoperative equipment. Equipment not required by the operation being conducted and equipment in excess of  14 CFR requirements are included in the MEL with appropriate conditions and limitations.  The MEL must not deviate from the Aircraft Flight Manual Limitations, Emergency Procedures or with Airworthiness Directives.  It is important to remember that all equipment related to the airworthiness and the operating regulations of the aircraft not listed on the MMEL must be
  operative.

The image below is from the 767 MMEL, as you can see it lists items that can be inoperative and the limitation. Some items carry many restrictions, such as anti-skid or a pack, others carry none, such as reading lights. The MMELs are available on the FAA's website, so it can be an interesting read.

I do not know why the terminology is backwards, I assume it comes from a time aircraft were much less complex and an list of required items was realistic. But if it only listed items that were required for flight, you could end up with hundreds of systems inop, with no direct requirement to repair them. PL-34 addresses this a little bit:

  The MEL is intended to permit operation with inoperative items of equipment for a period of time until repairs can be accomplished.  It is important that repairs be accomplished at the earliest opportunity. In order to maintain an acceptable level of safety and reliability the MMEL establishes limitations on the duration of and conditions for operation with inoperative equipment.

and

  Operators are responsible for exercising the necessary operational control to ensure that an acceptable level of safety is maintained. When operating with multiple inoperative items, the interrelationships between those items and the effect on aircraft operation and crew workload will be considered.

Basically the take away from this is that an operator can not issue every MEL in the book and dispatch the aircraft. For example, it may be okay to MEL one AC pack or one AC pack temp control valve, but it would not be okay to MEL one pack and the temp control valve on the other pack.


What repair can be done on this wingtip? (777)

What action need to be taken towards this kind of damage?

The aircraft will be grounded immediately and damage like this needs to be repaired in a timely fashion to get the plane back in the air and making money once again. Its worth noting as well (under FAA regulations) that you would also be in breach of § 23.1385 Position light system installation as the position lights are usually installed in the wing tip.

For damage like this Boeings AOG team will be brought in to repair it

  The Boeing team isn’t called in for everything. Airlines have
  incidents every day, Testin says, and most airport ground crews can
  handle routine repairs—a window cracked by a bird, a component failing
  calibration. An AOG intervention is required for the big things: an
  airplane off the end of a runway, landing gear accidentally retracted,
  a flaming tail drag, two 150-ton behemoths kissing wingtips on the
  ramp.

Since it's Boeing themselves coming in, they may use a variety of reference material to fix the damage and it really will vary case by case depending on what needs to be replaced. In this case the damaged metal will be removed until they get to an area at which they can begin to joint on a new wing tip.

I cant find any great examples of wing repair being done on jumbos as its most likely done behind closed doors but here is a great video of it being done to a small aircraft generally speaking the fundamentals are the same as the designs only change in size. Remove the damaged skin, get the wing down to the ribs/spars, repair/replace ribs if necessary, re-skin wing.


What could the fuel pump failure have been that my flight experienced?

The conversation may have been about fuel pumps or fuel transfer valves but the flight attendant was probably told that as a simple explanation - it would not have been the real cause.

Aircraft have multiple systems to pump fuel, transfer, and pipe it so no single failure will affect normal operation.

For example, pumps have automatic bypass valves so that other pumps will continue the normal flow past the failed pump. No single transfer valve obstructs fuel flow. There are multiple paths to get the fuel to the engines; either directly or by transferring through a completely different set of pipes to another tank then on to the engines.

What likely happened was there was one or more FILTERS that became obstructed. Both ice particles and algae often obstruct filters. But once again all the filters have automatic emergency bypass valves and pipes. However, it is not unheard of for polluted jet fuel containing large amounts of algae to overwhelm the filters.

[ In my 10 years with Continental Airlines, we had one aircraft engine obstructed by ice particles, but numerous occurrences of algae contamination. ]

  If the filters and/or bypasses either obstructed engine filters, made
  one or more tanks unusable, or reduced the fuel flow, the Captain
  would have chosen an altitude and speed that gave best fuel economy;
  and would have arrived late.

It is worth noting that algae contamination is quite severe in some parts of the world such as Asia and Pacific Island nations. It is common practice for American airliners to carry more fuel than necessary when headed abroad to help "dilute" the bad fuel in other parts of the world.

Simplified Airbus diagram of a typical fuel system showing multiple pumps, transfer valves, and paths to each engine.

B737 diagram (one of the simplest airliners) showing multiple pumps, transfer valves, and paths to each engine.


As the face says, it's a "G meter", aka "accelerometer". It measures vertical acceleration in units of "G" (i.e. acceleration due to gravity, 9.8 m/s^2 or 32 f/s^2).
Price would vary, but here's a site with a similar instrument which sold for $75 when it was in stock: https://aeroantique.com/products/accelerometer-g-meter-1?variant=39681371274


In helicopter's forward motion, how is the forward pitching moment taken care off?

It's a complicated answer, with many contributing factors in a multi-dimensional matrix. In a helicopter flying at forward speed, there are several stabilising stability factors and several de-stabilising ones.

Before the helicopter can fly at speed, it needs to take off in a hover.

The rotor provides the lift force to climb.
Gravity applies down force in the Centre of Gravity.
The rotor hub is hinged - one could picture the fuselage as hanging off of the rotor hub, like a pendulum.

From this answer, own work

In this situation, hinging freely, the CoG would move directly underneath the rotor hub without re-aligning the rotor - the helicopter would stay in place, and only the fuselage would tilt until the CoG is underneath the lift vector. There is a range of allowable horizontal CoG positions, which would result in a range of fuselage angles when climbing up in a straight hover. Of course, if the CoG is chosen excessively forward or rearward, this scenario would result in an impossible fuselage angle.
But the rotor hub hinge does transfer torque, from rotor to the mast and vice versa. The fuselage is not free to dangle underneath the hub. From Prouty, Helicopter Performance, Stability and Control:, describing behaviour in a vacuum:

The teetering rotor in a vacuum has no tendency to align the rotor and mast perpendicular to each other, while the very common hinge offset rotor does. And in the atmosphere, the teetering rotor also wants to align the mast perpendicular tp itself via the torque of the flapping effect described here.

So a helicopter taking off in a hover with the rotor horizontal, aligns both the fuselage and the rotor until the CoG is underneath the lift vector. If the CoG was not exactly underneath the hub centre, the fuselage rotation tilts the lift vector and the helicopter starts to drift, which needs to be compensated by cyclic stick input from the pilot. From FAA Rotorcraft Flying Handbook, Chapter 7 Weight and Balance:

  CG FORWARD OF FORWARD LIMIT. You can recognize this condition when coming to a hover following a vertical take-off. The helicopter will have a nose-low attitude, and you will need excessive rearward displacement of the cyclic control to maintain a hover in a no-wind condition.

Note that the above means that the rotor wants to align to the forward lean of the fuselage, which tendency must be compensated for by rearward cyclic.
In order to fly forward the pilot moves cyclic longitudinal forward, effectively tilting the rotor disk forward. As seen above, this also tilts the fuselage forward, moving the CoG to a new position further aft - this creates a nose-up moment, compensating for the nose-down moment of the thrust/drag torque.

When the helicopter picks up forward speed, air pushes at the fuselage: there is parasitic drag. This wants to tilt both the fuselage and the rotor further forward.

At increased airspeed, the rotor flapping provides an increased nose-up torque: the forward moving blade experiences higher lift at higher speed, and reaches a higher tip position when pointing forward. As explained in 2. above, this results in a fuselage nose-up moment as well due to the hinge coupling between rotor disk and fuselage.
The helicopter trim angle at speed can be further influenced by incorporating a horizontal tail, which applies a nose-up torque at speed. The horizontal tail incidence is often variable, in order to provide a wide range of stabilising moments at cruise speed, high angle descent etc.

The horizontal tail in cruise usually has a negative angle of attack, and is designed to make optimal use of the rotor downwash upon it. Horizontal tails are not required but highly desirable, for positive cyclic speed stability.
But a horizontal tail is ineffective in the hover, and a rotor on top has negative speed stability, as explained in this answer - the main reason for the instability in the hover of conventional helicopters, requiring constant stick inputs to maintain position.

Summarising, the nose-down pitching moment at forward speed is compensated by:

The flapping angle of the rotor disk.
The hinge moment coupling, either from hinge offset or from aerodynamic coupling in case of a teetering rotor. This effect wants to keep the rotor mast aligned perpendicular to the rotor.
The horizontal tail.
The useable horizontal range of CoG location.
And not mentioned above: in some cases canting of the tail rotor.


How can using split throttles help when landing twins in crosswinds?

The use of asymmetric thrust when landing a twin in a crosswind effectively accomplishes the same thing that rudder input does.  It induces a yawing moment about the aircraft’s vertical axis, the same as pushing on the rudder pedals does.  It helps to alleviate excess rudder pressure on the flight controls during the approach, making it a little more comfortable for the pilot to fly the approach. You are still required to apply aileron input into the wind in order to hold the runway centerline.   Using asymmetric thrust during a Crosswind Landing does not alleviate aileron pressure or required bank angle to track the runway centerline.


How close is this Su-27 to the aircraft recording the pass?

It looks like it's maybe 50-75 ft away from the camera, but you would have to know whether the camera's focal length is neutral, magnifying or wide angle, so it's really a wild guess.  There's not enough detail on the host aircraft to be able to scale it that way.


What is the Dimension of Equilibrium Space in Longitudinal Space?

I never heard of the term "Equilibirum Space" in flight dynamics and I can't find references in a quick google search.

However, I assume you are talking about describing the flight dynamics of an aircraft as a linear state-space model. When linearising, you can indeed separate the equations of motion in the plane symmetry (longitudinal) from the assymetric (lateral) motions.

$\dot{ \vec{x}}=\mathbf{A} \vec{x} + \mathbf{B} \vec{u} $

The dimension of the state vector $\vec{x}$ is usually 4 (velocity, flight path angle, pitch angle and pitch rate), in your case the dimension of the control vector  $\vec{u}$ is 2 (thrust and elevator deflection).

You linearise the equations of motion around an equilibrium point; the state and control vectors describe the deviation from that equilibrium point. The dimension of the equilibrium points is 6 (4 state variable, 2 control variables).

One could say that the equilibrium point is in the space spanned by the 6 independent state and control variables. If that is what you mean, then dimension of the equilibrium space is 6.


How to announce in an ATIS message that two parallel runways are in use?

By simply stating that both runways are in use.

For example, "arriving and departing runway 16 left and 16 right."


How tight should passengers wear the seat belt?

According to this document published by the FAA (about smaller GA planes but the topic is applicable)

  Tests have shown that slack in the restraint system should be minimal.
  In an impact, your body keeps moving until the slack is taken out of
  the restraint, but then must be abruptly stopped to “catch up” with
  the airplane. The restraint should be adjusted as tightly as your
  comfort will permit to minimize potential injuries.

Here is a video of them testing the seats. You can see the waist lines of the dummies does not move very much.

Here is an interesting research paper on the topic, may be worth checking out.

A study was conducted by the DOT "Human Factors Associated With the Certification of Airplane Passenger Seats: Seat Belt Adjustment and Release" on the difference between belt tension (as applied by a passenger) in both a cruise and emergency setting. This looks like the most conclusive numbers I can find on measured tension.

  An analysis of results indicate that most passengers (90%) tighten
  the lap belt to a tension less than 7 lb. during normal flight
  conditions and less than 10 lb. for an anticipated emergency.


Why doesn't the flight path angle increase beyond a certain angle even if the angle of attack is increased?

If you keep increasing your angle of attack, your drag will increase and combined with the increasing along trajectory component (your path angle will increase) of the weight vector will slow you down (assuming your thrust does not exceed your weight + drag). Because you slow down, your lift will decrease. The lift will now be less than the across trajectory component of the weight vector and the flight path will become less steep.
I don't understand your second point.
The critical angle of attack is where the maximum lift coefficient occurs. If you increase the angle of attack further, the wing will stall and the lift will decrease. This does not occur at Vx


What do we hear, on the ground, from a helicopter in flight?

Rotor noise is relatively complicated, and is very highly dependent on the design of that particular aircraft. Here are at least a few components to consider:

Ultimately what you're "hearing" is of course pressure waves in the air, which in a helicopter are almost entirely caused by the rotors passing through said air[1].  If you're head-on and a fair distance away, you're primarily hearing the pressure wave that's generated as the rotor passes the point where it directly points at you, because that's where you get the strongest component of pressure "pointed" in your direction.

As the aircraft moves, your orientation to the sound profile changes: you get both the doppler effect which changes the pitch, but you also get a very different sound profile because the pressure waves from the main rotor are interacting with both the body of the aircraft and more importantly the pressure waves from the tail rotor in different ways.  I don't remember the exact percentage, but a very large part of the sound generated by helicopters is the interaction of the main and tail rotors - this is a main reason that you see a lot of modern helicopters with a "shrouded" tail rotor. If you're truly head-on, it's reasonable to assume that you're getting very little of the interference with the tail rotor, and as you get more side-on with the aircraft you get far more interference noise.

[1] You also, of course, get noise from the engine-- but that's usually drowned out unless you're quite close, OR if you happen to be sitting near a chopper with the rotor at zero-lift... in this case the noise from the rotor is actually pretty low and you can hear the engines and the tail rotor a lot more clearly...


Do NOT worry about getting an unsatisfactory result!!  It just does not matter.  There will be no record of it anywhere but in your memory.  It's not noted on your certificate and, really, nobody will care.  The PPL is a license to learn and that is what you'll be expected to do after you pass.  The checkride merely assesses basic requirements.  Now, if you want to be a professional pilot...it still doesn't matter.  Nobody will care if you made a dumb mistake on a PPL ride and had to go back and demonstrate a maneuver again.  Anyone who does is not worth working for anyway!

Think about it, worst case you have to go flying again (that's a pretty good "worst case").  The only downside I see is having to pay the examiner fee again.

Ok, but real advice...
1.) Get sleep the night before.  You'll be nervous, but sleep anyway.  You already know everything you need to know to pass, a few more hours of studying won't make or break the ride.

2.) It's ok to say "I don't know the answer, but I know where to find it," and then look it up.  You can't say it for every answer, but it's not a deal breaker to not know something.

3.) At least one experienced pilot (your CFI) thinks you're ready to be a PPL.  If you took a stage check with an evaluators at a flight school, two experienced pilots think you've got what it takes.  CFIs don't sign off on a checkride if they think the student will fail.

4.) Be able to explain why the plane is legal to fly.  One of the examiners I used loved to ask the students to prove that the plane was legal.

5.) Be able to explain why you're qualified to take the exam.  The same examiner would routinely ask students to prove that they were qualified to take the exam.

The only way this ends is with you earning a PPL.  If it takes two rides, so what?  You've already done the hard work.  Just go flying with the examiner and show him/her what you've been showing your instructor for the past few hours.

Good luck.  Don't sweat it.


Is a magnetic compass required for VFR (day) flight in powered aircraft?

The phrase "magnetic direction indictor" is interpreted as "magnetic direction-indicator", not "magnetic-direction indicator".
You need a device based on magnetism that indicates your direction. That could be a floating-card type compass, or a fluxgate compass, for example.
Some interpretation of this phrase is given in AC 23.1311-1C section 8.8:

Under VFR operation, part 91, § 91.205, requires a magnetic direction indicator (that is normally intended to be a compass) for heading information.
[...]
Section 23.1303(c), Amendment 23-62, amended the requirement from “A direction indicator (non-stabilized magnetic compass)” to “A magnetic direction indicator.” As new technology becomes more affordable for part 23 airplanes, many electronic flight instrument systems will use magnetically stabilized direction indicators (or electric compass systems) to measure and indicate the airplane heading to provide better performance.
[...]
Part 23 does not prescribe specific accuracy requirements for magnetic gyroscopically stabilized heading systems. Specific accuracy requirements for avionics may be found in the related TSO and, as acceptable means of compliance to § 23.1301, in ACs, notices, or policy statements/letters.

Further, installation of the magnetic direction indicator is regulated by §23.1327:

Each magnetic direction indicator must be installed so that its accuracy is not excessively affected by the airplane’s vibration or magnetic fields.


I'll use the following diagram for illustration:

Intuitively, a hard surface resists fluid flow via shear stresses; these shear stresses tend to rotate fluid elements (i.e. vorticity). Therefore, we can regard a hard surface as filled with vortex sources.

In actual fact, only the boundary layer contains vorticity, and there is usually no fluid element rotation outside of it. Since the boundary layer does not affect lift [much] in attached flows at high Reynolds number, we can ignore it and call the entire flow irrotational. This leads to the concept of potential flow. Furthermore, we can model the hard surface as a vortex sheet. The vortex sheet is called singularities and does not affect the irrotational assumption because it is a boundary and not part of the flow itself.

We can simplify the picture further. If the body is thin (like a wing), we can model the entire wing as a single vortex sheet (collapsing both upper and bottom surfaces into one). To simplify further, we can break the vortex sheet into individual vortex filaments running parallel to the wing (in the y-direction in the picture). These vortex filaments are called bound vortices. For high aspect ratio wings, we can simplify even further by considering the entire wing as a single filament, which leads to the Lifting Line Theory.

Since a vortex filament cannot end in a fluid, it must shed and end in the far field at infinity. This is a horseshoe vortex; the shed vortex filaments are called trailing vortices. A filament does not only shed at wingtips; in fact, it's shed everywhere along its length.

Image ref: https://history.nasa.gov/SP-367/f53.htm

Circulation is the total vorticity within a given closed loop. If you draw a closed loop from leading edge to trailing edge at a given span location, the total vorticity passing through this loop is the circulation at the given span location. Note that trailing vortices would be parallel to the said loop and will not partake in the circulation.

Lastly to complete the picture, acccording to Kutta-Joukowski Theorem, lift at unit span ($L'$) is directly proportional to the circulation ($\Gamma$) at the location:

$$L'=\rho_\infty V_\infty \Gamma$$


What are the advantages of a variable-incidence wing as used in the F-8?

The main reason for having variable incidence wing in the F-8 was that it allowed the production of increased lift due to a greater angle of attack without reducing pilot visibility as the fuselage stayed level.

For aircraft with high angle of attack TO/landings (like delta winged aircraft), pilot visibility is a problem in low speed landings, as the nose will obstruct the runway (or carrier, for that matter) in extreme cases. There are two ways to solve this problem:

Droop the nose, like the Concorde or
Make the wings variable incidence, like the F-8.

The first option is usually preferred (same thing was done in Tu-144) as the weight penalty is (significantly) less. However, this wasn't possible in the F-8 as the engine air intake was in the nose; so the incidence of wings was changed. The variable incidence wing had the added advantage of reducing the length of landing gear required and improved the low speed characteristics.

In case of Martin XB-51, the variable incidence wings were used to reduce take off distance as it was expected to be operated from forward airfields.


Can an instructor sign off for my check ride if I didn't fly with him since a year?

No.  Instructor A needs to provide at least three hours of training in preparation of the practical test within two calendar months of the checkride.

  §61.39   Prerequisites for practical tests.

  (6) Have an endorsement, if required by this part, in the applicant's logbook or training record that has been signed by an authorized instructor who certifies that the applicant—

    (i) Has received and logged training time within 2 calendar months preceding the month of application in preparation for the practical test;

    (ii) Is prepared for the required practical test; and

    (iii) Has demonstrated satisfactory knowledge of the subject areas in which the applicant was deficient on the airman knowledge test;

  §61.109   Aeronautical experience.

  (a)  For an airplane single-engine rating...

    (4) 3 hours of flight training with an authorized instructor in a single-engine airplane in preparation for the practical test, which must have been performed within the preceding 2 calendar months from the month of the test

  §61.103   Eligibility requirements: General.

    (f) Receive flight training and a logbook endorsement from an authorized instructor who:

    (1) Conducted the training in the areas of operation listed in §61.107(b) of this part that apply to the aircraft rating sought; and

    (2) Certified that the person is prepared for the required practical test.

Instructor A has to provide the required training to the applicant before signing him off for the practical test.  I would agree it doesn't have to be within two calendar months... but three hours are required from an authorized instructor with two calendar months.  However, I would not, under any circumstance, sign off an applicant without at least three hours of training within the preceeding two calendar months.  How else would I know they are prepared for the practical test?


Is a weak battery a valid reason to reject a rented aircraft?

First off, you absolutely made the correct decision. As PIC/pilot you have not only the ability, but the duty to call off any flight you don't feel comfortable regardless of the reason. Your go/no go decision can be based off of anything and you should always be comfortable making that decision.

Now as far as the battery goes I can tell you I was in exactly this situation a couple years ago with a rented Piper Comanche. It was cold out and the start attempts completely killed the battery. The FBO (also the owner) decided to jump it using a start cart and got it going. They comp'd me about .25 hours since they wanted me to sit on the tarmac at 1200 RPM until the oil temp gauge came up (something that I would have done anyway).

I made the decision to go, but I also made (a rather poor) decision to board a passenger while the aircraft was running (at the direction of the FBO and because I was at an unattended airport to pick that passenger up). I don't regret taking the aircraft but I never felt comfortable boarding somebody with the engine running.

In this situation you probably would have been fine had you left, provided you were making a VFR flight in good conditions. If this were IFR I would say that it would be better to say "no-go". The only thing you would probably have noticed would have been the ammeter showing the battery charging, but it would probably have recharged the battery in about 30-45 minutes of flying.

The other question is if the owner should have comp'd you for this and that is a little harder. You probably didn't burn all that much fuel or put much time on the engine tach so I'm guessing that while it would have been inconvenient to the owner, you didn't make a lot of difference financially (maybe $20 at most).


How do I differentiate between different types of installed wire lock/safety wire on planes?

Monel is more expensive than stainless steel so it's use is limited to where it is an advantage, mainly in high temperature applications such as securing engine accessories, piping etc.  If the locking application is not in a high temperature, high humidity, high oxidisation area, then it's probably stainless steel.

There are chemical tests you can do on small samples using acids and reagents but you asked about an installed lock. The only way I know for testing an installed lock is to  polish it. Monel is duller than stainless steel and does not polish to a shine so  the quick way to tell is to try to polish a piece of it with a cloth.  If it shines up, it's stainless steel.  If it doesn't, it's monel.


What are torque events and are they very common when flying a rotorcraft?

Most western made helicopters have limitations on the amount of engine torque to which the transmission and drive dynamic components may be subjected. Exceeding the rated torque either transiently or for a specific length of time can trigger the need for special inspections or worse, an actual maintenance evolution. Depending on make and model, short transient excursions may be allowable under certain conditions. Many, if not all, Russian made equipment have well overbuilt transmissions / dynamic components and I have heard that some don't even have torque indicating instruments. Just keep pulling collective till max engine temp or engine droop. This comes at the expense of heavier transmissions though. Hope this helps.


Why do airlines follow these routes between Barcelona and Düsseldorf?

Large parts of France's airspace are designated military training areas. If there is military flight training going on, the choice of routing over France is very limited. The only option is to fly around these areas, which  results in the routes you found.

Higher altitude route map of France courtesy of EUROCONTROL[PDF, 8MB]

Since the PDF seems to be giving problems on some computers, I've combined several screenshots and drew the approximate route of your westerly flight (in yellow), the planned flight of GWI 9525 (blue) and Temporary Segregated Airspaces (TSA's) in red onto the map. The crash location of GWI 9525 is marked by a red/yellow star.

Note that not all the TSA's in the map are actively used at all times and that in some cases crossing is allowed but altitude restrictions apply.

In addition to active TSA's there are other considerations that come into play such as weather and airway capacity & demand. If you have to wait 15 minutes longer for a slot on the shortest route, you might as well fly a slightly longer route if that allows you to depart earlier.


Could the Concorde reliably land with all engines out?

In theory yes.  The loss of the engines will mean you also lose the generators and hydraulic pumps, but Concorde was equipped with a RAT which drove it's secondary and emergency hydraulic systems, so control would be possible.

Having never flown Concorde, but familiar with the flight characteristics of supersonic, high performance aircraft, I would guess such a forced landing would be flown at a steep angle of descent and at higher speeds say around 220-230 kts with leveling out in a shallow descent and roundout at or very near the threshold, placing the aircraft down at Vref in 1000-1500 feet thereafter.


How are flaps sized in order to give necessary delta CLmax?

This is to answer your follow-on question in the comment;

  That answer did not cover the analytical method of determining CL change. I'm unsure what this iterative method is. Is the only method using CFD or wind tunnel testing? How were they sized before these technologies were available?

I feel the main question has been answered already here.

Flaps, especially the ones with gaps between the wing and the flap, depend a lot on how the boundary layer forms and when separation occurs. Therefore, CFD is still struggling to get everything right and wind tunnel testing is still needed at least to verify the computational simulation.

Before CFD, the average aircraft engineer would experience a number of designs in his (rarely her) lifetime which gave him a feeling what works and what not. Still, surprises were not uncommon and late fixes were needed to arrive at the desired performance.

If you desire to use a simple formula which precisely predicts the maximum lift coefficient, including size, speed, temperature, airfoil shape and manufacturing imprecisions: It does not exist.


What is this aircraft that has flown over my house all day?

Looks to me like a Boeing C-17, if you live near a military base or airport that may explain it.


How do airports charge airlines for using their gates?

Gates are usually not charged to airlines separately. Gate fee is usually part of the landing fee package. Landing fees are an important part of the airport revenue, with passenger fees.

Airport pricing is subject to recommendations from ICAO, IATA, and other organizations, as regard scope of costs to be taken into consideration, and non-discrimination of airlines. Pricing is determined by the organization managing the airport and/or State or local administration.

Single till vs dual till: Distinguishes between aeronautical and non-aeronautical (commercial) charges. Airport schedule pricing may use single or dual till. See: Single till - IATA.

ICAO Policies on Charges for Airports and Air Navigation Service. ICAO guidelines tries to maintain some principles for airport business across all countries:

Landing charges: Should be based on the aircraft weight formula. The maximum certificated take-off weight as indicated in the certificate of airworthiness (or other prescribed document) should be used, while considering local restrictions that may affect aircraft maximum take-off weight. Allowance should be made for the use of a fixed charge per aircraft or a combination of a fixed charge with a weight-related element, in certain circumstances, such as at congested airports and during peak periods.
Parking and hangar charges: For the determination of charges associated with use of parking, hangar and long-term storage of aircraft, maximum permissible take-off weight and/or aircraft dimensions (area occupied) and length of stay should be used so far as possible as the basis.Any period of free parking time for aircraft immediately following landing should be determined locally by considering aircraft scheduling, space availability and other pertinent factors.
Other charges:

-- Passenger service charges
-- Security charges
-- Noise-related charges
-- Emissions-related aircraft charges

Albeit a bit old, The Airport Business by Rigas Doganis has a chapter on Aeronautical charges and pricing policies which discusses this topic in depth. Extracts:

Landing fees: Charged per aircraft, usually based on MTOW (maximum takeoff weight). On most airports covers ATC, runways, taxiways, parking at stand or apron for a certain time (e.g. 2 hours), use of gates / fingers / terminal for disembarking (use for departure may be paying), take-off.
Surcharges or rebates in addition of landing fees: For noise, peak-hour operations,
Parking and hangar: Beyond the free-parking period covered by the landing fees. Usually based on weight.
Passenger charges: per departing passenger, sometime per arriving passenger too.

It is easy to find pricing for airports online.

Adelaïde airport (2015)

Rates are different for domestic and international flights.
Charges per passenger for landing and passenger facility.
For domestic flights, additional landing charges per ton of MTOW.
Charges for diversion.
Parking charges beyond 2 hours, paid per arrangement with airport.

New York LaGuardia (2015)

Charge for aircraft landing, per thousand pounds of MGLW (maximum gross landing weight).
Additional charge for day landing or takeoff (not for schedule airlines).
Charge for using public passenger ramp and apron area (in some cases, when congestion).
Charge for parking and storage, per 8-hour slot, based on MGTOW (maximum gross takeoff weight). Agreement possible for operators of aircrafts.
No charge for air terminal use.
Charge for each passenger departing.

Los Angeles Intl (2013)

Landing fee, based on MGLW, different between permitted and non-permitted air carriers.
No charge for remote gates bussing service.
Charge for using ramp, apron and remote area, (in some cases, when congestion).
Charge for parking, per 1000 lbs of MGLW, per day, after 3 hours.


What is the purpose of this helicopter fin antenna?

It can be quite difficult to see as the big fin in the first photo is a wire cutter and it seems that the arrow points to that.

The second photo shows it a little more clearly.  It is a wire cutter.


Why were the space shuttle’s flight controls only certified for low airspeeds?

From what I understand the limits seem to be related to contingency maneuvers such as RTLS or TAL where the external tank was still attached. These were only possible after the solid rocket boosters had been jettisoned, but while the external tank was still attached.

I couldn't find any altitude references for RTLS, but according to this
TAL required the shuttle to fly to around 350.000 feet. RTLS would have been at a lower altitude and required a 180 degree turnaround. Doing these maneuvers with the ET places a higher stress on the vehicle resulting in black zones. Wayne Hale also mentions this in an old blog post, but doesn't go into specifics.


Why would an airplane's nosewheel bounce during landing?

Sounds most like the pilot released back pressure  on the control stick abruptly once the main wheels touchdown. The idea here is that you gently lower the nose wheel to the pavement once the mains are on the ground in order to prevent that kind of a bounce.   As I recall the Cessna 162 has a tendency to bounce on the nose wheel as well as to porpoise if the landing attitude is not done correctly it's just a quirk of that airplane.


When is a CFII required to provide instrument training?

No, you cannot provide

  instrument training for the issuance of an instrument rating, a type rating not limited to VFR, or the instrument training required for commercial pilot and airline transport pilot certificates

Unless you hold

  (1) Except as provided in paragraph (c)(2) of this section, the flight instructor must hold an instrument rating appropriate to the aircraft used for the instrument training on his or her flight instructor certificate,

Having an instrument rating on your CFI makes you a CFII.

You are confusing a CFII, who is a CFI with an instrument rating on his / her flight instructor certificate, with

someone that has an instrument rating on his / her pilot certificate and who also might hold their CFI.

You must be a CFII to give instrument training, the exception to that would be for private pilot candidates from 61.109

  (3) 3 hours of flight training in a single-engine airplane on the control and maneuvering of an airplane solely by reference to instruments, including straight and level flight, constant airspeed climbs and descents, turns to a heading, recovery from unusual flight attitudes, radio communications, and the use of navigation systems/facilities and radar services appropriate to instrument flight;

a CFI is able to give those 3 hours of instruction.  Anything beyond private pilot is the realm of the CFII.