Why does the B-29 have eight oil needles? In the image above, quiet flyer and I realized that there are 2 needles in every oil gauge, and there are 4 oil gauges. Well, why in the world are there 8 needles in total? And the optimal range arcs and redlines of each oil gauge is different. Why would that be? Oil is oil, I can't see how the optimal range arc for some oil in one gauge is different from the optimal range arc for some oil (same oil, oil is oil, the B-29 does NOT run on multiple oils. It isn't an eco-plane and it drops bombs. It has no need for more than one oil) Any thoughts would be great. Solving questions concerning something like dials and maximum speed with flaps extended for such an old plane have answers that are hard to come by, since they would have had to note this stuff down on paper and not electronically, and the people who built them are either very, very old; or unfortunately dead.

Each of the four engines is represented by two needles, one in each row. The top gauges are for the nose oil; the bottom gauges are for the rear oil.
Nose and rear here refer to two sections (remember that's a twin-row radial engine). The nose case oil is also used by the propeller's governor, feathering mechanism, and reduction gear – those would explain the lower pressure range of the nose section.
During development the nose case was troublesome:

Reduction gear failures started to occur during extended climbs, forcing the addition of external oil lines from the accessory case to the nose case to shore up low nose case oil pressure (enginehistory.org; PDF).

B-29 commander training manual

More on Google Books: United States. Army Air Forces (1950). Technical Data Digest. p. 26.


Why does the auto brake panel on an A320 use "lo", rather than "low"? Is there a specific reason that Airbus chose to shorten "LOW" to "LO" for the lowest autobrake setting?

Wouldn't it be more consistent to use three letters for each setting?

Boeing 747 wiper knob showing LO; source: alamy.com

As shown above, it's not unique to Airbus, or to just airliners, so from that perspective:

Keeping the same standard as on-screen messages$^1$

Example A320 ECAM messages:

  CAB PR LO DIFF PR
  ELEC IDG 1 OIL LO PR
  FUEL CTR TK PUMP 1 LO PR
  FUEL L WING TK LO LVL
  HYD B RSVR LO LVL

Note: Messages on displays are abbreviated to save space, and are in all caps for readability (see: Why do aircraft cockpit displays use uppercase fonts?).

It wouldn't make sense to deviate just for the auto brake (its ECAM indication is also LO).

That labeling is also typically electroluminescent, so the fewer the letters the cheaper (not just for LO, not just for airliners).

$^1$: FAA AC 20-175 - Controls for Flight Deck Systems

  Labels are the most common means used to identify and describe controls and other devices in the flight deck. They can be full text (e.g., "Standby"), abbreviated text (e.g., "STBY"), acronyms (e.g., "AGL" for "Above Ground Level"), as well as icons (e.g., [icon example] for "On/Off").

  Control labels must be visible, legible, and understandable for the population of pilots that will use the controls, per § 2X.1555(a).

  Use only one abbreviation and/or one icon for labeling a function. This is to prevent confusion when a label appears in multiple locations. [emphasis added]

The AC also references SAE standard ARP 4105B Abbreviations, Acronyms, and Terms for Use on the Flight Deck (paywall), and ICAO Doc 8400.


Can quadcopters still fly with propellers at an angle? Can quadcopters still fly with propellers at an angle? By this I mean like the whole motor mounts will be situated along a certain slope (so as to be neither horizontal nor vertical).

UPDATE
I meant something like this (I know it's a crude diagram, but I hope it gets my meaning across better):

I don't think that's how most drones fly, if the surfaces the motors are on are folded in a way that resembles a flying motion of birds or butterflies.

Yes, you can. But it very depend with the angle (as in your drawing). If it is "folded) to make V-shape (that will make divergent thrust), then will reduce the lift compared to if the angle is opposite direction (inverted V-shape), which will make the thrust become convergent, it will produce more thrust. Both will work, but one is better than another. See this Akagi Helicopter. But the angle should not be high enough.

There is research that researching eagle and bird shape. There are two kind of bird or eagle's shapes. The 1st is the wing feathers trailing edge is divergent, which is make it look like V seen from the head. The 2nd is, the wing feathers trailing edge is convergent (closing to the tail, so it look like V seen from the tail, not from the head). From the research, the 2nd is better than the 1st in maneuvering and speed. But in slow move (like surveillance), the 1st is better as the flaps are produce less speed and power for the same amount of flapping (power). Another thing, the power of the flapping of the 1st is divergent, leaving the bird/eagle body, while the power of the flapping of the 2nd eagle is concentrated beneath the body (convergent) that make amount of lifting power.  Unfortunately I can not find the video in Youtube. Maybe later.


Can I display the route which I have created with skyvector.com on google maps? I really appreciate skyvector.com as a tool for initial route planning and providing me with a good lookout to the upcoming VFR flight, but honestly I'm not very satisfied with the FAA Sectional charts.

Using these charts navigation in some more congested areas is tough work especially as I'm not very familiar with the area yet. Its often useful to have a satellite picture of these areas to identify some helpfull landmarks, which might not be shown on the sectional.

Does anyone know how to transfer the skyvector route to Google Maps, or know an alternative to achieve a similar result?

It's not web based, but you can use Google Earth for this — There are overlays for aeronautical charts available, and you can do all your flight planning by entering routes in Google Earth. Then just turn off the sectional and you'll have the Google Earth satellite imagery to work with.

As an added bonus (relating to your comment about mainly using an Android tabled): Google Earth is available as an Android application (and the plugin version of the chart overlay should work in the tablet app — I know it works in the iOS version of Earth)

BIG SCARY IMPORTANT DISCLAIMER

As the folks who publish that collection of charts will tell you, the charts are not always current and thus should not be used for navigational purposes (much like SkyVector).  You can of course replace the chart graphics with current ones (or locate a chart collection that is current) if you want to, but as you're only using this as a pre-flight planning aid and will be doing your real flight planning with current charts and data the ones provided in the Google Earth Library are probably "good enough" for your purposes.


Are there laws about how close military aircraft can fly to passenger jets, and are they enforced? Yesterday I was on a passenger plane flying at 35000 feet from Denver to JFK on a fairly clear day. Just west of Sioux City, we made a relatively sharp, but short, right turn for whatever reason (may be unrelated). I happened to be looking out my window and caught what appeared to be a military fighter jet (presumably from the Air Force base there) flying in the opposite direction. It blew past my field of vision in a fraction of a second, slightly below us and off to the right, close and fast enough to startle me. It left a beautiful set of trails but, while my distance judgments aren't very good from a plane, appeared to be no more than ~1000 feet away from us (based on its size, I imagined it to be about 4-5 NYC city blocks away, that's my only reference). The passing aircraft's trails were dead straight at least as far back as they extended before dissipating. I didn't get a chance to ask the pilot about it after the flight.

My only knowledge of separation laws is from wikipedia, which seems to state a 2000 foot limit above 29000 feet.  I absolutely might be misjudging distance, but this aircraft seemed to be well under a half a mile away. So my question is: Are there a different set of separation laws for military aircraft, or perhaps are existing laws just not as strictly followed / enforced by the military? Would the pilot of one of the aircraft expect some sort of reprimand later? Was this a normal occurrence or was it a close call?

This is somewhat speculation, but here's what I think happened:

You were flying at around 35,000 feet, in RSVSM airspace. The fighter jet was correctly on track 1000 feet below you. Without any other guides of distance, you tried to judge its distance by apparent size compared to real size. You might have underestimated the size of a fighter jet; they're typically about 50 feet long. I know I, for one, always thought they were much smaller. Thus what looked like "slightly below" was actually 1000 feet below you.

As for the more general question you posted: the military can get as close to other aircraft as they damn well please, through a procedure called Military Assumes Responsibility for Seperation of Aircraft, or MARSA (thanks to fooot for pointing this out!). Generally this only happens with a civilian aircraft during an interception. I don't know the specific procedures that are followed, but I know that in the past intercepting pilots have gotten close enough to pick out individuals in the cockpit.

As for enforcement, the question is kind of null. Generally, if civilian pilots violate separation without putting anyone in danger, the air traffic controller will just yell at them for a bit, but it does depend on the case. The FAA doesn't have much authority over the military, however. If the air traffic controller passed the information on to the military, perhaps there could be some sort of corrective action, but at this point I'm just guessing.


Do aircraft cabins have suspension? On cars, we have 'shock absorber' suspension that decouples the passengers and loads from the road vibrations, bumps etc.

On planes do we have any form of suspension that decouples the passengers & loads from the turbulence, and vibrations induced by 'bumps' in the air?

I imagine even if it doesn't use a spring damper system, whatever attaches the cabin to the outer shell of the plane will have some finite stiffness. If so, has damping of this spring been considered to avoid oscillations?

The cabin is rigidly attached to the fuselage, with bolts. But in a way the cabins do have suspension: from the wings riding on air.

Elasticity of the wing construction material acts like a spring. Load it with a vertical gust, and it will bend upwards, then spring back.
The wing bending experiences damping forces from the surrounding air, proportional to bending velocity.
The wing sweep angle spreads out the gust: not all of the wing is accelerated upwards immediately.

Modern subsonic airliners with swept wings, flying with near transsonic speeds, experience much less turbulence than the olden days DC-3 type aircraft. So far, so good.

OPs proposal to provide suspension between fuselage and cabin may not be very effective. Notice that car suspensions work best when the unsprung mass is low: independent suspension is able to follow the un-evenness in the road much more effectively than rigid axle suspension, due to the much lower unsprung mass of only the wheel+tyre.

The unsprung mass of the suspended-cabin would be the whole fuselage-plus-wing structure, engines, fuel etc. Considerably more than that of the cabin plus payload. A lot of extra complexity for not much gain.


When calculating the lift coefficient,should I use only the lift provided by wings, or also the net upward forces of the entire aircraft? I'm preparing a wall force analysis from an aircraft at different angles of attack that resulted from a cfd simulation, so I can plot the lift & drag polars. For the lift coefficient, should I only pick the wing surfaces to obtain the lift and drag forces or all the airplane's surfaces for the net forces? The fuselage and the wing fairings have positive lift, so I'm a bit confused if I need take them into account.

If you want the lift for the whole airplane, of course you add the contributions for each part. While the fuselage might indeed contribute a positive lift, its presence will lower the lift of the wing. In the end, all parts of the aircraft will stick together when it flies and need to create just enough lift to keep its mass airborne, so it makes sense to look at the sum of all parts.

Since the wing will dominate lift, it is common for first-order calculations to consider the wing only. However, if you have data for all parts, you should include all their contributions, too, for a more precise result.


Do additional passengers impact on weight and balance of a domestic airliner? Recently my kids and I were denied access to our flight because we missed the check in window.  We were informed that new calculations would have had to have been made by the pilot, despite not having had any check in luggage.  When are these calculations made?  Before or after the passengers board?  Apparently, our names did not make the manifest in time, despite nobody having boarded the plane yet.  We were left stranded at the gate.  Can anybody explain the procedures regarding these calculations, because I cannot understand why we were not permitted to fly?

You're really asking two questions here

1) What is the procedure (ie when are the calculations made)?

2) Do additional passengers affect the weight?

What is the procedure

As soon as check in closes, the numbers for passengers and bags is finalized - nothing else can be added to the plane, otherwise it could potentially run out of fuel. Passengers can be removed, but the captain must be informed in case it affects balance.

At this point the captain calculates the required information for weight, fuel, and balance. It's done shortly after check in closes as there is a limited window in which to add extra fuel etc - remember that the tanker needs to be long clear before the engines can be started and other departure checklists can be run.

This is done so early because the pilot needs time to prepare the aircraft for departure, he doesn't have time to mess about later on adjusting the numbers, and if he has to re-calculate later it adds a whole extra area where mistakes can be made - especially since later on the pilot is likely to be more distracted. Doing it once is fairly easy, you plug the number of passengers into a set of sums along with temperature and other related factors, and it works fuel load out for you. If you try adding passengers you have to re-calculate this, then work out how much extra to add... it's just a whole bunch of extra things that can go wrong.

Do extra passengers affect the weight/balance of the aircraft

Short answer: yes

Take an A319 as an example aircraft: empty, it weighs 40,000 kg, up to a maximum of around 60,000kg

Now I have no idea what you and your family and bags weigh, but let's produce a range. Please don't be insulted by the range: the airline aren't judging your weight when deciding if you can board late: they have to have a single rule regardless of whether it's a skinny teenager travelling alone or a party of 15 obese people

You're an adult, so you presumably weigh anywhere between 50 and 150kg
You said children but don't state an age, so they could be newborns or adults: weight anywhere between 2kg and 150kg
I don't know how many children you have, but for the sake of argument I'll guess it's between 2 and 5 (as you said "children") - that's somewhere between 4 and 750kg

So your total weight for a single family is anywhere between 54kg and 900kg. Chances are most families are more like 250-300kg (a couple of adults at 60-100kg each, and a couple of kids at 20-40kg), but airlines have to assume worst case, otherwise their check in staff have the impossible job of deciding who's too fat to board late.

So take that worst-case scenario (6 obese people) and add a 7kg carry-on bag each, that's nearly 1000kg of weight which the pilot doesn't know on the plane. Or over 2% of the aircraft's empty weight and nearly 1.5% of the maximum takeoff weight. This is assuming they have no hold bags.

Even if your family only weighs 250kg between you and your bags, that's still nearly 0.5% of the aircraft's empty weight - a not insignificant number.

And finally you have to remember that by carrying the extra 0.5% of weight in people, the aircraft needs some extra fuel. And a bit more fuel to carry that extra fuel, and both of those extra amounts of fuel change the balance of the aircraft.

In most "normal" flights you aren't going to make a huge enough difference to balance to cause a crash, or change the fuel requirement enough to cause an issue, but if the aircraft had to divert, you could be the difference between running out of fuel or not, and in some worst-case circumstances a really big family could upset a small aircraft.


How can a pitot tube freeze when it's heated? Reading Why turn off pitot tube heating?, it appears that the pitot tube heat can be switched off to extent its lifetime and also in case of short-circuit.

(Thales pitot-static probe, source BEA)

On airliners the probes seem to be heated during the whole flight. This makes me ask myself different but related questions:

Accidents occurred due to probes freezing. How can a heated pitot probe freeze?
Extending the life of the tube seems a questionable choice, I'd rather expect the technology to be improved and be able to sustain permanent heat. Heating a small metal device from -56°C to 5°C (or maybe more, say 100°C, taking into account comments) looks like feasible (not taking into account air friction) ⇢ The problem seems to be how to transfer enough heat from the metal (which is very hot) to the ice accretion.
A short-circuit is easily terminated by a fuse or a circuit breaker. Why does the crew have to worry about switching the heat manually, adding a possibility to have it OFF unintentionally?

Captain Bill Palmer, in his book "Understanding Air France 447" has a section dedicated to answering that very question as it pertains to AF447. Although there is no way to know for certain he puts forward some possibilities.

He quotes a commenter on a website:

  One commenter on the Weather Graphics website’s AF447 article provided this interesting observation: “I'm an aircraft icing specialist and wanted to point out a factor that hasn't been discussed much … high ice crystal concentrations. I've seen flight test data from power rollbacks due to flight in high ice crystal environments … In our case, the crystals collected within heated, aspirated Ram Air Temperature sensors, forming a 0 ° C slush…”

He notes that just before the pilot tubes clogged, the sound of ice crystals hitting the windshield could be heard on the CVR.

  Ice crystals bounce off the exterior of an airplane and cause no visible ice accretion, but they can enter the probe inlets. When highly specific climatic conditions exist in combination with certain combinations of altitude, temperature, and Mach, the concentration of ice crystals entering a probe can exceed its capacity to melt and evacuate the moisture through its drain holes. The result is that the ice crystals form a physical barrier within the probe that disrupts the measurement of total pressure.

The particular type of ice that may have been responsible was a substance called graupel.

  Graupel forms when tiny supercooled water droplets adhere to snow crystals to the point that they engulf the snow crystal itself.

Graupel. Photo from Wikimedia commons

Capt. Palmer notes factors that make graupel a possible suspect:

  No airframe icing. The supercooled water theory is discounted by the fact that the A330's icing detectors were not triggered.
  Graupel has large enough particles to be audible on the voice recorder. It takes a particle with enough mass and inertia (a given density) to hit the fuselage with a sound, instead of flowing around it with the relative wind, like snow.
  Graupel has enough mass to temporarily overwhelm pitot anti-icing when concentrations are high enough. The pitot tubes are hot. But even if you put a snowball on a hot skillet it does not melt instantaneously. If there is enough mass in the blockage, and in combination with new particles being added to the blockage as the first ones melt, it may exceed the pitot tubes capability to melt the obstruction as fast as it is introduced. Graupel is of significantly higher density than snow.
  Graupel has sufficient blocking properties to prevent efficient transmission of dynamic pressure within the pitot tube.For example, water can flow and transmit pressure within the pitot tube, though it too can alter pitot-static readings, a physical non-fluid blockage could shield the pressure sensing port.
  The likely presence of snow or similar form, as evidenced by the St. Elmo's fire discussed by the crew. The accident report stated that the sound of ice crystals hitting the aircraft can be heard about 20 seconds before the airspeed loss and autopilot disconnect.

It must be noted that the exact cause of icing problems on the A330 was never completely identified but it was specific to the particular brand of pitot tubes originally installed. Airbus was in the process of replacing them all with pilot tubes from a different manufacturer.


Can rotorcraft pick up a dangerous electric charge? So, I was re-watching The Hunt For Red October, (in light of current Russian shenanigans with Sweden), and there was a scene in which a crew-member on the ground was electrocuted by making contact (and presumably grounding) the helicopter, which had picked up a charge in the stormy weather. Can anyone explain more of what is going on here?

In the same way than an aircraft will build static charge on the wings from friction with the air, the same thing can happen with helicopters from fast moving blades.
From a 1962 US Army document:

Any aircraft flying in the atmosphere can be considered as a conductive body located in a highly electrically insulated environment. In such a body, electrostatic charge is generated by three principal mechanisms:

Charge transfer created by a triboelectric effect between the aircraft and the atmospheric particles, such as dust, water, water vapor, snow, etc.
Unbalance of the ionic content of the exhaust gases produced by the aircraft engine(s).
Induction charge due to high electrostatic
field gradients which are found occasionally in the aircraft flight path.

Source

Here's a more detailed photo of the US army discharging a helicopter while wearing insulating gloves:

 SGT Nathan Rodeheaven uses a static probe to discharge static electricity from a UH-60 Black Hawk before his teammate, PV2 Danny Browning, hooks up the cargo to the helicopter. The safety measure prevents the hook-up man from being electrocuted in the event there is accumulated static electricity. Photo: Kristin Molinaro


Is there a best-practice method to work through a checklist? I've noticed that there appear to be many ways to read of a checklist between aircraft types and operators. The task and work division confuse me:

In some cases it appears to be entirely managed by the Pilot Not Flying [PNF], while in some cases the Pilot Flying [PF] is involved.
For the latter case, the response from PF seems to be 'checked' some of the time while in others there is a verbal feedback on the state of that control.

I guess this is a question between Standard Operating Procedures, but is there a best-practice to reading off checklists that is suggested to be followed as suggested by EASA or the FAA for instance?

Extra Thing: It would be great if somebody could elaborate on how a checklist actually would be worked through in practice like the one below with who says and does what.

The current FAA Advisory Circular dealing with SOPs in general, but only lightly touching upon checklists, is AC 120-71a. It is primarily aimed at Part 119 certificate holders who conduct operations under part 121, but is also recommended for operations under Parts 91, 125, and 135. It also changes the wording from Pilot Not Flying (PNF) to Pilot Monitoring (PM) in order to reinforce the idea that he or she is not just a passenger with a better view, but an integral part of the flight crew.

With respect to actual checklist usage, to the best that I've been able to find, the FAA does not issue a hard recommendation (air carrier checklists and procedures have to be approved by the FAA prior to certificate issuance anyways), but it does identify two primary methods of checklist usage: Challenge-Do-Verify (often used for abnormal and certain emergency procedures) and Do-Verify (often used for normal and time-critical emergency procedures), which relies on memorized flows followed by verification with the use of a checklist.

A 1995 Study issued by the FAA weighs in on the pros and cons of the two methods and surmises that, when used properly, the CDV method is less likely to result in missed items, but does allow for the fact that, in operational usage, pilots may batch items together, thus defeating the purpose of the systematic, step-by-step approach of the method.

Stepping aside from the multi-crew environment, where having someone with the checklist in their hand and reading things off one by one can work quite well, my personal observation has been that, in a single-crew environment, pilots who rely on a CDV-like method (sometimes known as Read-Do) are more likely to end up falling behind in configuring their aircraft than those who use DV-like methods, assuming of course that the pilots actually know their flows and perform the verification properly (as in actually verify that everything is as it should be rather merely reading items off the list and trying to remember if they've accomplished them).

Lastly, with respect to the 'checked' vs. verbal confirmation of status, this is usually dependent on how critical and laborious the status confirmation is. An example would be with altitude setting verification, where it is not uncommon for the procedure to call for the PF to set the new altitude in the Mode Control Panel and, while pointing to it, call out the new altitude, which is then verbally confirmed by the PM. Every operator's experience and demands will be different here, but a number of best practices are recognized and the folks at the FAA, NBAA, FSF, AOPA, and many others are doing their best to publicize and promote them.

See here for the FAA's Industry Best Practices Reference List.

The checklist you've provided appears to be intended for multicrew operations. In this particular case, what would happen if the CDV method was to be used is that the Pilot Monitoring would read the items off one by one and the Pilot Flying would execute accordingly, verbally acknowledge doing so, the PM would quickly verify compliance and move on to the next line item.

In a DV environment, the Pilot Flying would go through the flow, and call for the checklist, at which point the Pilot Monitoring would begin to read off the items, and the Pilot Flying would verify that they have been complied with.

The line items that have BOTH in them are meant to be a special emphasis case in that both crew members are required to verify that the line item has been complied with, regardless of method used.


What mode is the Boeing 777's autothrottle in right after touch down? This question came to my mind when I saw the Emirates B773 (Dubai on Aug 3rd 2016) accident.

I saw a couple of 777 cockpit videos and I saw that autothrottle (A/T) is widely used during landing and they just turning the autothrottle knob left or right to set the speed. Question. Does anyone know what mode is the 777 in right after touch down? Especially the A/T? As far as I know the aircraft goes to roll out mode (whatever that means). Lets assume they initiated a go around right after touch down for whatever reason. The pilot assisting just turned the knob again (as usual) instead of pushing TO/GA but it was ineffective as A/T was disengaged automatically. So yes, it is guessing without any knowledge so lets focus on my question. What mode is the A/T in right after touch down?

During the flare somewhere between 25' and 50', the A/T retards the thrust levers to idle. They remain in idle mode until reverse thrust is selected which automatically disconnects the A/T.

In the case of Emirates 521, eyewitnesses observed the aircraft do a bounced landing and then attempt a go-around reaching a max altitude of about 150'.

Because the aircraft had touched down, it can be assumed the A/T had automatically gone to idle, and it appears the thrust levers were not manually advanced. The aircraft then settled back on the runway as the gear was being retracted.

More speculation here:  Emirates B777 crash was accident waiting to happen

  a pilot colleague observed exactly what happened as he was there, waiting in his aircraft to cross runway 12L. The B777 bounced and
  began a go-around. The aircraft reached about 150 feet (45 metres)
  with its landing gear retracting, then began to sink to the runway.

  This suggests that the pilots had initiated a go-around as they had
  been trained to do and had practised hundreds of times in simulators,
  but the engines failed to respond in time to the pilot-commanded
  thrust. Why?

  Bounces are not uncommon. They happen to all pilots occasionally. What
  was different with the Emirates B777 bounce was that the pilot elected
  to go around. This should not have been a problem as pilots are
  trained to apply power, pitch up (raise the nose) and climb away.
  However pilots are not really trained for go-arounds after a bounce;
  we practise go-arounds from a low approach attitude.

  Modern jets have autothrottles as part of the autoflight system. They
  have small TOGA (take off/go-around) switches on the throttle levers
  they click to command autothrottles to control the engines, to deliver
  the required thrust. Pilots do not physically push up the levers by
  themselves but trust the autothrottles to do that, although it is
  common to rest your hand on the top of the levers. So, on a go-around,
  all the pilot does is click the TOGA switches, pull back on the
  control column to raise the nose and — when the other pilot, after
  observing positive climb, announces it — calls “gear up” and away we
  go!

  But in the Dubai case, because the wheels had touched the runway, the
  landing gear sensors told the autoflight system computers that the
  aircraft was landed. So when the pilot clicked TOGA, the computers —
  without him initially realising it — inhibited TOGA as part of their
  design protocols and refused to spool up the engines as the pilot
  commanded.


How much thrust is applied in a 737 to achieve taxi speeds? I'd imagine not much, but maybe none? I wouldn't be surprised if the plane moves forward without brakes alone.

From the 737 (Classic and NG) normal procedures section of the flight manual:

Aircraft response to thrust change is slow, particularly at high gross weights. Idle thrust is adequate for taxiing under most conditions. A slightly higher thrust setting is required to start taxiing. Allow time for aircraft response to each thrust change.
To initiate taxi, release brakes, smoothly increase thrust to minimum required for the aircraft to roll forward and reduce thrust to idle. Under normal conditions, 45% N1 should be considered the maximum N1 for breakaway thrust. Do not start a turn until sufficient forward speed has been attained to carry the aircraft through the turn at idle thrust.

In short, advance the levers a little, achieve breakaway, then back to idle.
Smaller jets with higher thrust-to-weight ratios, such as business jets, often taxi with one of the engines in idle reverse, instead of having to ride the brakes.


Can a drone travel beyond the range of its remote control signal? In a hobby drone, is it possible to set up the autopilot so that the drone travels to a distance far beyond the range of the remote control device and then comes back to the starting point? When I see hobbyists flying drones , it seems the drone always hovers within the boundaries of the field.

Is it possible for a drone to reach a friend's house on the other side of town and then come back to the start point?

If the controlling software allows it then yes. There's at least one drone available where autonomous flight is possible; the Vision 2 FAQ says that the drone will continue its "mission" even if you lose the signal to it, although the overall length of the flight path is limited to 5km and the drone will not fly close to airports. Other drones stop and hover or land if they lose the connection to the controller.

Whether doing this is actually a good idea (or legal in whichever jurisdiction you want to operate in) or not is a whole other question.


How can the required wing area for climb be calculated, given aspect ratio? I'm currently working on problem 3.20 from the picture above. In order to find the rate of climb, I'm using the formula Rate of Climb= (Power available - power required)/weight. Doing this, I need to find the power required, which the formula I'm using is Pr=sqrt((2*W^3*Cd^2)/(densitywing areaCl^2)). Now I have everything but the wing area needed for this climb. Given the aspect ratio of 12 and a Cd of .01, how do I calculate this. Also, please let me know if there is a simpler way of going about this problem. Thanks

Let's start with 3.19, since you need the result for 3.20. The parameters given suggest that we should calculate drag $D$ with the parabolic formula $$D = \frac{\rho}{2}\cdot v^2\cdot S\cdot\left(c_{D0} + \frac{c_L^2}{\pi\cdot AR\cdot e} \right)$$
I haven't seen the symbol $R_A$ before, but its magnitude suggests it is the aspect ratio (normally $AR$ in the US, $\Lambda$ elsewhere). Since the whole is an optimisation problem (we look for flight with minimum power consumption), we can determine the lift coefficient $c_L$ already. For propeller aircraft the point of minimum power is when the lift coefficient is $$c_L = \sqrt{3 \cdot \pi \cdot AR \cdot e\cdot c_{D0}}$$
Hey, you know all terms already! This allows you to proceed to the wing area once the needed lift is known. My next heroic assumption is that $W$ actually denotes a mass (the unit seems to say it is pound-force). The power plant should weigh 100 - 150 lbs already, so 200 lbs for the whole aircraft seems reasonable. So you can proceed:
$$L = 200 lbs \cdot g = \frac{\rho}{2}\cdot v^2\cdot S\cdot c_L$$
Plug in what we know, use sea level density ($\rho = 1.225 \frac{kg}{m^3}$) and the previously calculated lift coefficient:
$$S\cdot v^2 = 1527 \frac{m^4}{s^2}$$
This gives you pairs of wing area and speed squared which together fulfil the requirement. Some pairs, though, make more sense than others. Generally, the biggest wing will need the lowest power but will become increasingly fragile as wing area increases.

But there is still one requirement left: We cannot use more power than those 0.33HP:
$$P = 0.33\cdot0.7 HP = 172 W = D\cdot v = S\cdot v^3\cdot\frac{\rho}{2}\cdot0.04$$
$$\rightarrow S\cdot v^3 = 7094.8 \frac{m^5}{s^3}$$

Both conditions can be fulfilled when the flight speed $v$ is 4.646 m/s. This makes the wing area $S$ = 70.735 m².

Solving this for Denver, CO and finding the climb speed with 0.6 HP of power should be easy now. Just calculate the SEP and you know the climb speed.


What's the difference between ATIS and D-ATIS? What's the difference between the two? Do you need a special digital VHF radio to receive D-ATIS broadcasts?

ATIS is traditionally a voice recording of someone reading the weather. D-ATIS is a way to deliver the information digitally so onboard equipment can interact with it. From the requirements

  Digital ATIS is an enhancement of the Tower Data Link Service (TDLS)
  and uses the Pre-Departure Clearance (PDC) System microcomputer to
  automate the delivery of airport and terminal area operational and
  meteorological information to aircraft flightcrews.
  Two phases of development are planned. The first phase will provide,
  via data link, a digital version of the ATIS /4 to flightcrews. Voice
  recording will continue to be utilized in the preparation of the ATIS
  broadcast. The second phase will add automated voice generation for
  the ATIS broadcasts.

Its part of a larger data link system that allows aircrafts and controllers to communicate certain things (weather info, clearances etc) with out clogging the radio channel.

Some ATIS systems now have a voice synthesizer reading out the reports so that no one needs to manually update the recording every hour.


Is medical evacuation aircraft D-AIGZ "Robert Koch" protected against decompression? In 2014, Lufthansa engineers converted a A340 into a medical evacuation aircraft specially equipped to carry contagious patients, e.g. with Ebola fever (D-AIGZ, "Robert Koch", msn 347). This aircraft was at the time the property of the German Government (as of today, 2020, it is back to Lufthansa).

Source.

The patient is in an isolation unit surrounded by an airtight tent with negative pressure:

Source.

I was wondering about how this isolation system would react in case of in-flight decompression and how the cruise altitude would be selected. Is it common to have negative pressure tents in civil medical aircraft? Is it safe? Is it regulated?

More:

Inside the flying quarantine used to transport Ebola patients, on Wired
It seems this airplane has been recently converted back to commercial transport.

I'll try to answer in a general sense. It appears that the Lufthansa engineers have changed only the interiors- basically they've changed the passenger fittings with the containment unit. As such, the effect of decompression will be the same as in commercial aircraft- in case of negative pressure containment unit, the air will tend to leak from it. In general, there are some safeguards in such cases:

By sucking air out through the filters, a negative pressure is created within the unit, so that while fresh air may leak in, contaminated air will not leak out. An alarm sounds if negative pressure is lost.
...  in case the negative pressure protection failed, the air inlet at the front (crew-facing) side of the tent is also fitted with a filter to prevent airborne contamination of the main cabin. As a further protection for the crew, Phoenix Air’s mechanics have reversed the airflow in the whole aircraft, so that now it flows fore to aft (instead of aft to fore as it comes from the factory); the pilots and medical crew are in effect located ‘upwind’ of the patient.

However, as @abelenky already noted, in flight decompression is quite rare and the people on board have to worry more about the patient they are transporting than decompression.
Negative Pressure tents with HEPA filters are usually used only in medivac cases where the diseases are highly infectious. In other civil medivacs, the patients are usually exposed to the cabin.
There is a FAA approved Aeromedical Biological Containment System (ABCS) devised by CDC and used in US, which uses the same negative pressure principle- so I'd say that it is safe to operate.
For medical aircraft, the cruise altitude is usually set lower- FL200 or so to enable having the cabin pressure altitude at a lower level (for military aircraft, it is maintained at 4000', though it can vary depending on the circumstances). One thing to note is that most medivac aircraft are business jets like Gulfstream and Learjet, which can maintain sea level cabin pressure upto FL200.
Also, any interior modification will have to be approved by the corresponding regulatory body (here its EASA, though I'm not able to find anything about this particular aircraft). Other manufacturers have obtained EASA certification for negative pressure tents and as already seen, FAA certification too.
European Air Ambulance explains the EASA certification process for medical aircraft, which basically involves:

Type certificate for the original aircraft

Supplement Type Certificate for the medical configuration and

Air Operator Certificate for the aircraft equipped with the approved medical configuration.

Image from European Air Ambulance


How can an airplane descend faster than a free-falling roll of toilet paper? Watching this video, I was wondering, does the Toilet paper have this much lift, because I think the descent speed of the Airplane is not that much?

I don't think that a parachute-plane can catch up with a person in
free-fall?
Can somebody explain me physical how this maneuver works?

"I think the descent speed of the airplane is not that much"

I think you are wrong.  Airplanes can descend very rapidly when needed.

The airplane is aerodynamic, meaning it slices through the air nicely, whether it is flying straight-and-level, or aiming straight for the ground.  So its free-fall speed is much higher than that of a roll of paper, which will have considerable wind resistance.

In addition, the airplane has a propeller, which adds force.  When in a dive, the airplane has gravity plus the force of the propeller taking down.  But the roll of paper only has gravity.

I expect that in a full dive, the airplane could probably exceed a 10,000 FPM descent, or around 120MPH, which is around the terminal velocity of a skydiver.
(pulling out of a full dive safely is not easy, however).

The roll of paper will obviously and intuitively be slower than a skydiver.
I estimate it to be no more than 2,000 FPM, or about 20 MPH. (and probably a bit less)

  (edit: In the comments, Henning Makholm suggests that a paper roll may only fall at 200 FPM. That is less than 3 MPH, which seems a bit slow to me.   A slow descent rate for a Cessna when approaching an airport is 500 FPM.)

The airplane does not even need to enter a full dive to be faster than the paper. It could probably catch the paper with a nice, gentle 2,500 or 3,000 FPM descent.


What happens if a plane breaks down away from a maintenance facility? I am curious about what happens when a large plane, such as a commercial passenger jet, has an equipment problem at an airport where the company does not have a maintenance facility.

For instance, do airlines have mechanics at every airport that they serve? And do those airports have a supply of spare parts?

Even if those answers are no, I imagine it's easy enough for an airline to fly in parts and staff. What happens if the repair requires some large piece of equipment to complete?

I’ve done it both in the military and the civilian world. At major airlines, it’s pretty rare that you’ll fly into a place without mechanics. That said, there are odd circumstances as pointed out in other answers. In those cases, we do our best to coordinate with the pilots to get a very good idea of what the problem is.

Usually Maintenance Operations Center techs will try to find a local mechanic or even someone from another airline to get it going. Generally speaking, if the problem was that simple, the pilots probably didn’t need to divert anyway. Other airlines don’t mind helping with parts, but manning is another story. There are labor contract issues, payroll problems, etc... It gets complicated quickly. That’s usually when they call The Mothership and decide to bring a few mechanics in to fix it.

From there, we brainstorm most likely scenarios and also the most outlandish. We try to bring everything including the kitchen sink. From experience, no matter how easy you thought it was on the phone, and no matter what you bring, there is a guaranteed monkey wrench lurking in the midst. After all, if this was just any ordinary problem, the plane would have been off the ground already.

We usually dispatch to the plane by other commercial flights, or we drive to the location ourselves. Most guys prefer to drive because we’re usually on overtime for the majority of the trip... Might as well drive 8 hours on OT too...

Once we arrive, the mess we’re in quickly becomes apparent. We usually hem and haw in gaped astonishment at what went wrong. Then we realize that nothing we are looking at is what we were told over the phone. Then we call The Mothership and explain that we need some outlandish piece of equipment. It then becomes MOC job to get us that equipment somehow or some way. Still on OT, we make our way back to the hotel and wait for the call that our stuff is on the way.

I have changed engines with skyscraper cranes, performed wire splaces with two terminals, a bolt, a nut, and a piece of tape, and made adjustments to “non-adjustable” equipment to get a plane off the ground and into a better location. Sometimes you have to be creative but judicious in the repair process.

Usually, after days of lack of sleep and suffering from overexposure to cold, heat and/or other intolerable elements, we get the airplane up and go home. After our arrival, we fill out our travel paperwork, are summarily haggled to death by bean counters who have no idea what we have  just done, and find that the 47 hours of OT we were billing the company for gets knocked down to about 12 hours plus a few denied receipts. In the end, you break even, go home, lie to the wife why there is a $2000 charge for “The Dollhouse” on the credit card and go to bed. Later that evening, you’re called to go on another trip and the cycle continues.


Which books should I study to understand more about Supercritical airfoils? I want to understand the theory behind supercritical airfoils and all the details about them. It would be nice if I could get a standard supercritical airfoil, its experimental Cl, Cd data in the transonic region and its verification from theory. I haven't been able to find anything concrete on the internet.

Introduction to Transonic Aerodynamics

Roelof Vos, Saeed Farokhi (more)

  Written to teach students the nature of transonic flow and its
  mathematical foundation, this book offers a much-needed introduction
  to transonic aerodynamics. The authors present a quantitative and
  qualitative assessment of subsonic, supersonic and transonic flow
  around bodies in two and three dimensions. The book reviews the
  governing equations and explores their applications and limitations as
  employed in modeling and computational fluid dynamics.

Transonic Aerodynamics of Airfoils and Wings

W.H. Mason (more)

  Professor emeritus by the Virginia Tech, expert in aerospace
  engineering who worked at Grumman Aerospace where he served in the
  structural mechanics section and later in aerodynamics and worked on a
  number of high-profile projects, including the Grumman X-29. Has
  taught classes — including his "famous" Configuration Aerodynamics
  course.

Review of NASA Supercritical Airfoils

Richard T. Whitcomb (more)

  NASA supercritical airfoils are characterized by a substantially
  reduced curvature of the midcord region of the upper surface together
  with increased camber near the trailing edge. The basic aerodynamic
  phenomena associated with the airfoils and representative wind tunnel
  results are discussed. The results indicate that the drag rise Mach
  numbers for NASA supercritical airfoils are 0.1 higher than for
  comparable NACA 6-series airfoils. A recent analytic method for
  predicting the aerodynamic characteristics of supercritical airfoils
  is described. The flight demonstration programs of three applications
  of supercritical airfoils utilizing the F-8, T-2C and F-111 as test
  beds are summarized.

Richard T. Whitcomb on Wikipedia.

NASA Supercritical Airfoils, A Matrix of Family-Related Airfoils

Charles D. Harris (more)

  The NASA supercritical airfoil development program is summarized in a
  chronological fashion. Some of the airfoil design guidelines are
  discussed, and coordinates of a matrix of family related supercritical
  airfoils ranging from thicknesses of 2 to 18 percent and over a design
  lift coefficient range from 0 to 1.0 are presented.

Supercritical Airfoil Design for Future HALE Concepts

Kasim Biber, Carl P. Tilmann (more)

  This paper presents design and analysis of a new airfoil for future
  High-Altitude Long-Endurance (HALE) aircraft that has an operational
  condition at supercritical speeds. The XFOIL and MSES computational
  codes were used to design, modify and analyze the airfoil.

Design of Laminar Supercritical Airfoils Based on Navier-Stokes Equations

Zhong-Hua HAN, Jie DENG, Jun LIU,  Ke-Shi, ZHANG, Wen-Ping SONG (more)

  This paper aims to develop a suit of design methods and
  tools for laminar supercritical airfoils, based on
  high-fidelity computational fluid dynamics (CFD). The reliable
  transition perdition method, efficient inverse design and
  global optimization design methods are regarded as
  three key issues, which are addressed in this paper. The automatic
  transition prediction method coupling Navier-Stokes equations
  flow solver and eN linear
  stability analysis method is applied to the design and analysis of the
  laminar supercritical airfoils; inverse design and optimization design
  methods based on kriging surrogate model is developed to
  attain favorable pressure gradient while reducing wave
  drag; efficient optimization based on kriging model and an
  improved EI (expected improvement) method is developed for finding
  the global optimum.

NASA Technical Memorandum 103933 An Experimental Investigation of a Supercritical Airfoil at Transonic Speeds

George G. Mateer, H. Lee Seegmiller, Lawrence A. Hand and Joachim Szodruch (more)

  Benchmark experimental data obtained in the two-dimensional, transonic
  flow field surrounding a supercritical airfoil are presented. Airfoil
  surface and tunnel wall pressure and LDV measurements are used to
  describe the flow on the model, above the wing and in the wake.
  Comparisons are made with calculations using the Reynolds-averaged
  Navier-Stokes equations. The results illustrate the performance of two
  turbulence models in both separated and attached flows. The largest
  differences between theory and experiment occurred in separated flows
  with the Johnson and King turbulence model providing the best
  estimates.

Analysis of Aerodynamic Characteristics of a Supercritical Airfoil for Low Speed Aircraft

P.Sethunathan, M.Niventhran, V.Siva, R.Sadhan Kumar (more)

  The main goal of the proposed paper is the analysis of aerodynamic
  characteristics of an various supercritical airfoils like 0406, 0412,
  0706 and 1006 influence on the  dramatic improvement in lift and
  reduction of drag in low speed aircraft. In a precedent work,  a  cusp
  like  structure  at  the  trailing  edge  of  an  unsymmetrical
  airfoil  produces a  very  high  improvement  in  climbing performance
  of an aircraft.

Two-dimensional Wind-tunnel Tests of a NASA Supercritical Airfoil with Various High-lift Systems

E. Omar et Al. (more)

  Three high lift systems for a 9.3 percent blunt based, supercritical
  airfoil were designed, fabricated, and wind tunnel tested. A method
  for calculating the viscous flow about two dimensional multicomponent
  airfoils was evaluated by comparing its predictions with test data. A
  comparison of high lift systems derived from supercritical airfoils
  with high lift systems derived from conventional airfoils is
  presented. The high lift systems for the supercritical airfoil were
  designed to achieve maximum lift and consisted of: (1) a single
  slotted flap, (2) a double slotted flap and a leading edge slat, and
  (3) a triple slotted flap and a leading edge slat.

Aerodynamic Characteristics of an 11-percent-thick Symmetrical Supercritical Airfoil at Mach Numbers Between 0.30 and 0.85

Blackwell, J. A., Jr. (more)

  Abstract: The aerodynamic characteristics of an 11 percent thick
  symmetrical supercritical airfoil were determined in an 8 foot
  transonic pressure tunnel over a Mach number range of 0.30 to 0.85.
  The Reynolds number of the tests, based on the airfoil chord, varied
  with Mach number over a range of 360 million to 774 million. The
  geometric angle of attack varied from -0.5 to 10.5 deg. The abrupt
  drag rise for the supercritical airfoil at zero normal force
  conditions occurs at a Mach number just above 0.82. The corresponding
  drag rise Mach number for a conventional NACA 0012 airfoil is
  approximately 0.70. At zero normal force conditions, the level of
  supervelocity over the supercritical airfoil is considerably reduced
  from that for the NACA 0012 airfoil. Also, the shock wave for the
  supercritical airfoil is substantially weaker than that for the NACA
  0012 airfoil.


Why do X-wing configurations missile/guide bombs use symmetric airfoils? From all the missiles/guide bombs I have come across, I've always observed that a symmetric airfoil is used for both the wing and tail.

Why not have a cambered airfoil for the wing and a symmetric airfoil for the tail? It would provide a better range for the missile/guide bomb.

If an airfoil were to be selected for X-tail missile/guide bomb configurations, what is the selection criteria? I'm trying to better understand the reason for this generally accepted design decision.

Any answers/suggestions would be appreciated.

Assymetrical wings on missiles/guided bombs do exist. However the goal of all missiles/guided bombs is to hit or come close to its target, which mean different things for various missiles. This drives their design:

Symmetrical airfoils on missiles are used in order to guarantee uniform turning capability. This enables the missile to immediately turn in either direction, therefore not losing time to first roll the entire missile before turning, therefore making the missile more maneuvrable. This is especially needed for air-to-air missiles like the R73-Wympel or the Diel IRIS-T. Cruise Missiles, on the other hand, can be less maneuverable (ground targets seldomly move), which is why they do not necessarily have symmetrical wings. For example, if you look closely at the image of the Tomahawk missile, you will notice the unsymmetrical wingshape.  Such missiles use the bank-to-turn control strategy. *.

I do not know too much about this, but the main design goals for these again are good turn capabilities (aka, pull a lot of gs), and supersonic performance. Therefore basically the same considerations you have as for any other airfoil with the exception that the requirements are a bit more extreme.

* An interesting mix is the MBDA Meteor. It uses bank-to-turn because it has underbelly intakes. I cannot find the source, but apparently in the endgame the control mode is switched to skid-to-turn as it is more important to hit the target, then to keep the motor running


How do I achieve a lower stall speed, and capture potential CLmax without enough elevator control authority? I am running some analysis on a uav, and the results I have found show that with proposed modifications I am unable to trim at my previous $c_{L\:max}$ and thus originally designed stall speed (experimentally determined).  Ideally I want to decrease my stall speed as much as possible (for obvious reasons).  Theoretically with a new flap design I can achieve higher lift coefficients however the elevator does not have enough control authority to obtain steady level flight at these conditions.  Varying my cg location somewhat will allow me to capture my original $c_{L\:max}$ but it doesn't have enough range to reach the new potential $c_{L\:max}$.

What am I over looking that can help me achieve a lower stall speed?  How does the propeller/power, glide slope etc effect this problem?

It depends, partially on what you precisely mean with "trim".

Pilots use a rather narrow definition where trimming means to zero the control forces for a specific control surface deflection and speed. This is achieved by tabs or springs in the control linkage.

Engineers use it more broadly and include the ability to deflect control surfaces such that the desired attitude can be stabilized. I guess that you refer to this line of thought.

Long before the lift coefficient of a stalling airplane peaks, the flow over part of the wing will start to separate. Ideally it will do so near the trailing edge of the wing root, and the separation will slowly progress forward and outward as angle of attack increases. This separation will shift the local center of pressure back, such that the aircraft will experience an increasing nose-down moment as it approaches stall. To stabilize it at higher angles of attack will, therefore, need nonlinearly increasing elevator deflections. Depending on the position of the center of gravity, the installed elevator authority might not be sufficient to trim the aircraft all the way into the fully developed stall.

If you mean the first interpretation of "trim", then yes, most aircraft will not allow you to zero stick forces into the stationary stall. The trim range should cover the speed for steepest climb, not more. However, if the center of gravity range is wide enough, you should be able to trim an aircraft with rear c.o.g. all the way into the stall. After all, with neutral stability you can ideally trim (second interpretation) any angle of attack with the same elevator deflection angle (note that the nonlinearity explained above will require more negative elevator deflections as you approach stall even in a statically neutral aircraft).

I would rule out that the control forces are too high - after all, when stalling in level flight at 1g the aircraft will fly as slowly as possible, so stick forces should be small.

The effects of thrust depend on the engine installation. With a propeller, more power will add torque and increase the dynamic pressure at the tail. Now it depends whether the prop blast will hit the empennage - if it doesn't, the effect of adding power will at best be be an asymmetric stall.

In case you have a configuration change where the older configuration is known and the new should give the same flight characteristics, use tail volume as a sizing parameter. Horizontal tails of the same volume should give the same control power. Volume is the product of area and the lever arm between tail neutral point and the center of gravity. If the new tail has a different dihedral angle, don't forget to add the cosine of the dihedral angle.

When comparing elevators of the same size but of different flap chords, use the square root of the relative flap chord for comparison. Say the old elevator has a 20% flap and the new one 30%. The new one will have 22.5% more control power for the same deflection ($\sqrt\frac{0.3}{0.2}$).

Depending on elevator chord, at some point more deflection will not help much (typically 20° for a 25% elevator - going higher will add little control power). Now several options can be employed to increase control power:

Change the incidence of the stabilizer. That is what airliners do to compensate the massive trim changes caused by Fowler flaps.
Add leading edge devices on the stabilizer to make the elevator more effective. This adds a lot of complexity for a small gain, however.
Use slotted flaps and double flaps to eke more control power and higher useful deflection angles from an existing elevator. Again, airliners with their wing flaps should point the way.

In damping, both the dihedral angle and the lever arm have a quadratic influence while they have a linear influence on control power. This way one can adjust damping and control characteristics individually.


Do aircraft tyres have inner tubes? Do aircraft tyres have inner tubes? Modern small single-engine turboprops to the largest Jumbos. If not, did they ever have inner tubes? And if so, why were they discontinued?

From this Goodyear document on aircraft tires, both types exist. For the 747, they are all tube-type.

  Tires are tube-type unless otherwise indicated.

The listed 747 civilian variants do not indicate otherwise (page 18).

(Source: wikimedia.org) Cross section of a 747 tire. Full resolution via link is a must see. You can make out the inner tube (flap) from this image.

But that document is from 2002, nowadays tubeless tires are also available for the 747 and many commercial types, for example the 49X19.0-20 Flight Leader by Goodyear (thanks @user71659).


What are the advantages of the NASA LEAPTech propeller on wing technology? NASA has detailed experiments with a new type of parallel array of small electric propellers on the leading edge of the wing technology that they are calling LEAPTech.

The press release notes that the benefits include: "Each motor can be operated independently at different speeds for optimized performance. Key potential benefits of LEAPTech include decreased reliance on fossil fuels, improved aircraft performance and ride quality, and aircraft noise reduction."

A Popular Science article notes that: "When complete, LEAPTech’s planned cruising speed will be 200 miles per hour, with a range of 230 miles on electric power and 460 miles when running as a hybrid. The tremendous and immediate lift generated by this octodecaprop plane and its mere 31-foot wingspan means it should be able to take off from runways as short as 2,000 feet, which is a good 700 feet shorter than the FAA recommends for small passenger aircraft."

Is  this related to a spinning wing (Magnus effect) or do the benefits accrue from some other aerodynamic effect? This appears to be a technology that would only benefit very small aircraft and would not be scalable, is this correct?

[Photo credit: NASA]

The lift augmentation has nothing to do with Magnus lift (or the Coanda effect).  It is simply an increase in the dynamic pressure across the entire streamtube of the wing.

At the low takeoff and landing speeds (slightly above a 61 knot stall speed), the induced velocity of the propeller almost doubles the velocity that the wing sees; and the lift is a function of the effective velocity squared.  But due to swirl and other effects the wing doesn't experience a 4x increase in lift, but about 2 to 3 times.

The objective of the inboard propellers is not to achieve a high propulsive efficiency, instead we want those inboard props to achieve high induced velocities - think of them as part of the high lift system (which happens to also provide thrust redundancy).

In fact landing is the critical case, and having lower propulsive efficiency (and a poorer spanwise lift distribution because of the swirl effects) is helpful in creating sufficient drag.  The inboard props are not active in cruise flight, but simply fold against the nacelle (many motorgliders already do this type of folding on the nose).

By only using the wingtip propeller at cruise, we're able to achieve a ~95% propulsive efficiency (versus 75 to 85% with a typical fuselage nose propeller installation).  The reason for this is because we have lower blockage and scrubbing drag, as well as being able to take advantage of the strong wingtip vortex by rotating against it.  Since electric motors don't experience a power lapse with altitude (because it's non airbreathing) we have far too much power at altitude anyway so by only using the wingtip motor it doesn't cause much penalty in motor weight (and electric motors achieve ~6x lower weight per horsepower than a reciprocating engine).

In terms of batteries and range, the key is to achieve high efficiency cruise flight and it looks like with current batteries a 200 mile range is achievable.  By adding a small <50 hp range extender motor, the aircraft will be able to achieve ~400 mile range.  We're currently designing an X-plane that will fly in 2017 to substantiate all these numbers, with the ground test rig (wing and truck) providing an aerodynamic database to validate our analysis.

Please note that I'm the NASA Principal Investigator of the LEAPTech Distributed Electric Propulsion integration approach, and the Convergent Electric Propulsion Technology (CEPT) X-Plane demonstrator.  We have a team across NASA Langley and Armstrong, as well as two great small companies, Joby Aviation and ESAero who are retrofitting a Tecnam P2006T with a Distributed Electric Propulsion wing system.


Can a commercial airliner sink to the bottom of the ocean? Is it possible that a commercial airliner could hit the ocean surface at such an angle that it made a deep dive intact, got filled with water, sank, and got stuck in mud at the floor of the ocean?

Can a large modern jet airliner plunge intact underwater from flight?

No.

Large airliners are not desgned for this and are not even strong enough to make a landing on water in less than perfect conditions.

E.g. 961

striking the surface at a larger angle would certainly lead to widespread disintegration.

Is it possible for a large modern jet airliner to sink intact?

Yes (as near as makes no difference)

Almost all large aircraft impacting the sea surface in an emergency or uncontrolled will break up immediately and catastrophically.

One notable exception was US1549, an A320, which was landed on water without breaking up. It was described as "still virtually intact though partially submerged and slowly sinking". The left engine detached and sank.

So a controlled landing on water is possible under extremely favourable circumstances. It would then be possible for the aircraft to sink in more-or-less one piece without creating a large amount of floating debris.


Can a "Destroyed" Helicopter be repaired and flown? If a helicopter is reported by the NTSB as Destroyed in their Accident report, and as they make no disposal recommendation in their reports, can the aircraft be legally rebuilt by an authorized and approved FAA and Bell Repair facility and flown again?

Follow up:

The aircraft in question, after using Bell referenced repairs, carried out by a Bell Licensed Repair facility, in a Bell Certified Jig, now has its Certificate of Airworthiness and is again Supported by Bell and has a handsome price tag.

The NTSB defines Destroyed as

  Damaged due to impact, fire, or in-flight failures to an extent not economically repairable.

Another common definition is:

  The estimated or likely cost of repairs would have exceeded 50
  percent of the new value of the airplane had it still been in
  production at the time of the accident.

This fact that the costs of repairing are estimated to be exceed the economical value of the aircraft does technically not prevent the aircraft to be repaired and made flyable again. It can be recertified on the original airworthiness certificate. See FAA order 8130.2H.
Special attention needs to be given to the identification plate (serial numbers etc.) of the aircraft; the original plates of the aircraft have to be installed.

Do not expect any support from Bell as on their website they state:

  There are some aircraft that have been destroyed in an accident or
  retired from service that are no longer considered to be genuine Bell
  Helicopter Aircraft. These aircraft will not be supported by Bell
  Helicopter.

This makes resurrected Bell helicopters very difficult to sell in the future.


What system populates the Flight Stats? Which system is in place which gets data from all the flights on a terminal and display them every where like Airport Screens, Websites, different Apps etc?

The same system which populates all the data on displays in a Railway Terminal.
For a standalone airport, this data can be mined from ATC of that airport (Which has all the data regarding incoming/outbound flights ).
On an International scale, the data has to be mined from various different agencies. According to a data provider FlightStats:
It gets data from:

Complete, accurate data is the cornerstone of our business and what
sets us apart from competitive solutions:
Geographic Coverage - FlightStats provides definitive information for approximately 99.5% of U.S. flights, and better than 86% of
flights worldwide.
Completeness - FlightStats queries multiple sources to create a record for each flight enabling us to offer a broader range of
information (for example, gate information).
Accuracy - We have invested heavily in the areas of parsing, interpretation and error checking and developed the logic that enables
handling of difficult issues such as cancellations, diversions and
changing schedules.
Codeshare Support - Our codeshare logic enables us to deliver flight information for both the operating and the marketing carriers,
filling what is often a major gap in coverage.
Real-time data sources include:
FAA ASDI Data Feed
European Data Feed
GDS (Sabre, Amadeus, Apollo, Galileo)
Direct Airport / Airline Data Feeds

Batch data sources include:
Innovata Schedules
TSA Security Wait Times
Security Information
Health Information
Consular Information

For the system which gets all this data from various different sources, its the central computer database of the airport, which gets data from ATC and the a fore mentioned sources, and this database is accessed by many other end users, including the Screens in the airport


What is an airliner's "green dot speed", and how does it vary with weight, and why? A related question told us, quoting from an Airbus performance manual,

  Green dot speed (minimum gradient) is a function of weight.

Comments under the question stated that the "green dot speed" increased as weight increased.

So-- what is "green dot" speed?  Does it reference some fixed, optimal angle-of-attack?  Perhaps the one that gives the best L/D ratio (glide ratio)?  If so, it would obviously increase with weight, generally being proportional to the square root of the wing loading.  If this interpretation of how green dot speed varies with weight is not the correct one, then what is?

Green Dot (GD) speed is a term used by Airbus. It is named after the symbol on the speed tape. It refers to the speed that results in the best climb gradient in case of an engine failure, but it is close the speed resulting in best L/D ratio with all engines operating.

Airbus defines it as follows:

  Definition

  GD speed is the engine-out operating speed in clean configuration. In
  other words, it corresponds to the
  speed that allows the highest climb
  gradient with one engine inoperative
  in clean configuration.
  In all cases (all engines operative),
  the GD speed gives an estimate of
  the speed for best lift-to-drag ratio. It
  is also the final take-off speed and it
  represents the operational speed of
  the clean configuration and the recommended speed in holding in clean
  configuration.
  It is represented by a green dot on the
  PFD speed scale and displayed only
  when the slats / flaps control lever is in
  the ‘0’ (CLEAN) position and landing
  gears are not compressed

  How is GD determined?

  GD speed is computed by the Autoflight systems and is based on the
  aircraft weight. The GD formula has
  been set up so that the resulting airspeed provides the best lift-to-drag
  ratio for a given altitude, air temperature and aircraft weight, in clean configuration with one engine out.
  In some phases of flight, GD is computed to minimize drag and thus, the
  fuel consumption (for example during
  the HOLD phase).

(Airbus Safety First Magazine)

The GD speed is increasing linearly with aircraft weight and slightly increases with altitude above FL200:

(Airbus A320 QRH - 4.01 In Flight Performance - Speeds)

Here is a plot of the GD speed as a function of weight for different altitudes:


Does a dual-rotor helicoptor like the Chinook transition from hover to forward flight differently than a single rotor helicopter? I watched this video of an RAF Chinook taking off vertically and transitioning to forward flight.

I'm curious if the method for increasing lift to move forward, controlled by the cyclic in a single rotor if I'm not mistaken, is different when you have two rotors along the length of the aircraft. My untrained assumption is that to lift the rear of the helicopter and start moving forward, you would increase power or the collective on only the rear rotor.

The cyclic (dubbed control stick for the CH-47) takes care of that, not separate collectives (there's only one collective for both rotors per seat).

For forward flight, the pilot moves the control stick forward; the thrust of the aft rotary wing is increased while the thrust of the forward rotary wing is decreased, causing the helicopter to move forward. Since there is a large range of longitudinal control, high forward speed and extremes in center-of-gravity travel are inherent.

Source: CH-47 familiarization manual (see pages 55-56; PDF; 40 MB)


Why did this pilot have his single-engine license revoked? 5 minutes into this video, a commercial Indonesian pilot is shown performing a very tame version of a parabolic flight path as performed by zero-gravity flights, in a Cessna 172.

This video has over 11 million views currently and due to the 'wrong' people presumably having seen this footage, the pilot has had his single-engine license revoked. There is currently a petition to have his license re-instated and the coverage in Indonesia is widespread.

What actual laws or regulations did he break? Seems like he performed the maneuveur safely to me.

Link to news story (translated to English)

Lets break this down as best we can.

For starters you've made an error in your assertion. The pilot hasn't had their license revoked, just simply their SEP rating. There's a difference. The person in question can still do their day job as a pilot, on a type-rated aircraft. They have accepted a suspension of their Single Engine rating.

On some finer points mentioned in the linked news article:

  [...] both pilots and passengers do not use shoulder harnesses

The Indonesian Aviation Regulations specify

  For small civil airplanes manufactured after [27 December 1993], an
  approved shoulder harness for each front seat.

If we make an assumption that this flight was carried out in an aircraft manufactured after 27th December 1993, then both front seats should have been equipped with shoulder harnesses which should have been worn. Hardly the crime of the century, but there you go.

  Second, Vincent gives flying control to unauthorized people

This one is a bit tenuous, unless the PiC has an instructor rating he is "officially" not supposed to allow someone else to manipulate the controls. Finding exact wording to back this up is not easy. I think most pilots (of light aircraft) have let their passengers have a go at the controls.

  Third, he was deliberately maneuvering zero gravity

This in and of itself isn't the problem, I suspect the problem was whether he was doing so in an entirely safe manner. He gave no warning to his passengers that I could see, and I'm not convinced he performed the checks suggested before such a manoeuvre that would make it safe.

They could easily just cite the following:

  No person shall operate an aircraft for the purpose of air navigation or for operations on
  any part of an airport (including areas used by those aircraft for receiving or discharging
  persons or cargo), in a reckless or reckless manner so as to endanger or be likely to
  endanger the life or property of any person.

The wording of this regulation is fairly similar across many aviation regulators, and is often cited for "You did something against regulations".

Sources:

CIVIL AVIATION SAFETY REGULATION - Republic of Indonesia


May aerobatics be performed over a controlled airport without getting a waiver? CFR 14 Part 91.303 states:

Aerobatic flight.
No person may operate an aircraft in aerobatic flight--
(a) Over any congested area of a city, town, or settlement;
(b) Over an open air assembly of persons;
(c) Within the lateral boundaries of the surface areas of Class B, Class C, Class D, or Class E airspace designated for an airport;
(d) Within 4 nautical miles of the center line of any Federal airway;
(e) Below an altitude of 1,500 feet above the surface; or.
(f) When flight visibility is less than 3 statute miles.
For the purposes of this section, aerobatic flight means an intentional maneuver involving an abrupt change in an aircraft's attitude, an abnormal attitude, or abnormal acceleration, not necessary for normal flight.

For the purposes of this question I want to focus on paragraph (c). Assuming we don't have any other specific permission (waiver), may aerobatics be performed above class B, C, D, or E surface airspace?
I know aerobatics may be performed under the outer rings of class B and C airspace.
There also doesn't appear to be anything preventing aerobatics above the outer rings of class B or C airspace.
So the question is focusing on the center core (the surface area) of class B and C as well as the typical cylinder of a class D airspace and whatever shape a class E surface area happens to be.
Paragraph (c) simply states "Within the lateral boundaries of the surface areas" but makes no mention of altitude (other than the 1500' AGL reference in paragraph (e)).
Obviously we are talking about surface areas that go to the ground so clearly you may not fly in or below these surface areas. But may you fly above them as long as you are 1500' AGL?
"within the lateral boundaries of" has no implied altitude restriction. That term, in English, implies surface to outer space. So it would seem that aerobatics may not be performed above a class B, C, D, or E surface area at any altitude.
But you may perform aerobatics above the outer rings of class B and C. So why restrict doing them over the surface area?
Is there an official answer? May I legally do aerobatics above class B, C, D, or E surface airspace?
I have searched and looked at many related topics but none address this specific question. Even the Hucker discussion leaves this unanswered (to me at least) which only clarifies being able to do aerobatics under (no mention of over) the outer rings of class B and C airspace.

Actually "within the lateral boundaries of the surface areas of any Class D, Class C, or Class B airpace" DOES imply that you are not permitted to do aerobatics over these areas without special permits from the FAA or if there is a designated aerobatic box at that airport and said pilot remains within that airspace.  Even if you are not in the actual airspace itself, if you're above it, you're not allowed to fly acro over it.

Now, note the term "surface areas" could imply that you could fly aerobatics above or below Class C or Class B airspace SHELVES, that is a section of Class C or Class B airspace which does not touch the ground,  provided you don't enter those areas and and said airspace meets all the other requirements of FAR 91.303.

Also, some elements of the question may be interpreted in a way that would lose sight of the distinction between Class-E-to-surface areas "designated for an airport"-- i.e. actually surrounding the airport whose approaches they protect -- versus Class-E-to-surface "extensions".   Or perhaps the questioner was fully cognizant of, and following the example of, the language used in the AIM, as well as in the section headings of FAA Order 7400.11B, "Airspace Designations And Reporting Points".  In these places the phrase "Surface Area" is used ONLY to refer to Class-E-to-surface areas that surrounding the airports whose approaches they protect, and not to refer to Class-E-to-surface "extensions".  At any rate, the Class-E-to-surface "extensions" do not fall within the meaning of "Within the lateral boundaries of the surface areas of... Class E airspace designated for an airport".  One clear way to refer only to those Class-E-to-surface airspaces that actually surround the airport whose approaches they protect, is to include the phrase "designated for an airport".  For much more on the meaning of "Within the lateral boundaries of the surface area of... Class E airspace designated for an airport", please see this answer to the question "Which parts of class E airspace can an ultralight (part 103) fly in without prior ATC authorization?", as well as this answer to the question "Does FAR 91.155c apply to class E surface extensions?"


What would have happened if the jet engine on my aircraft had ingested caulk from the pavement? I was recently on a flight - the aircraft was a 737-800 - where I had a good view of the front of the left engine. The situation in the title did not occur, but it seemed awfully close.

After pushback, while the plane was waiting to start taxiing under its own power, I looked at the tiny waterspouts sporadically forming in front of the engine (it'd been raining all morning). And then I noticed a piece of caulk (or tar or whatever it is) was being lifted from between two concrete slabs of pavement.

The strip of caulk looked like it might have been 30cm long and 2cm in "diameter" (it had a more rectangular cross-section, but you get the idea). It was still attached at one end, but it was directly in front of the engine, and its free end was being "tugged" up toward the intake in fits and starts, sometimes standing straight up.

Thankfully, it never went further than that. I considered alerting the cabin crew, but everyone was already buckled in, and I really didn't want to cry wolf on a airplane (so to speak). Still, I was very much considering it just as the plane started moving without any further drama.

As soon as we were in the air, I discreetly told a flight attendant, and she told the pilots. She came back a little later asking for a few specifics, so I imagine the pilots were radioing the airport we'd just left.

And I got a free cup of coffee (yay...)

My question is: What might have happened if that piece of debris had come loose and been ingested by the engine?

I wouldn't expect it to be catastrophic or anything (which is also why I hesitated in informing anyone while it was going on), but I would expect it to be expensive. I.e. it might ground the plane, at least for a short while. Probably some flames out the back. Maybe it'd even mess up the engine by gumming up the works.

I was never worried for my safety or anyone else's. I know engines are tough, and can eat all manner of crap. And even if they tear themselves apart in the process, they contain it. Not that I'd expect something like that happening at low power anyway.

But really: I don't know for sure what would happen. I'm not a pilot or mechanic, just a nerd with a nerd's interest in engines and airplanes.

Edit: Checking the airline's website, it seems the engine would be a CFM 56-7B26, if that's at all relevant.

Well, not an expert on caulking, but birds go through plane engines sometimes, and they seem to be roughly the same consistency overall (if you account for the dirt and pebbles that are sometimes stuck to caulking.) So it possible they would have the same effect.

If you're curious about what would happen if it's like a birdstrike you can take a look at the Miracle on the Hudson, or this 757 that had a birdstrike on takeoff.  With the 757, they simply went around and landed the plane since they only lost one engine...

Anyway, you folks were still on the ground, so all that would have happened is that the engine would have flamed out while you were sitting there and the plane would need to be taken to service to check for damage.  It would have been annoying to have to switch planes, but it wouldn't have been dangerous to any of the passengers or crew.

Nice of them to give you a free coffee though, considering you may have saved them a few hundred thousand in engine repairs if the next jet in that slot had managed to actually ingest the caulking ;).


What kind of flaps are used in gliders? I'm estimating some wing parameters for an imaginary airplane (simple college project). We are allowed to use coefficients for any basic types of flaps (plain/split/slotted/Fowler etc), but since I'm doing a glider I'd like to go with the one that's really used.

tl;dr - What kind of flaps are used in modern gliders (preferably training ones)?

As Timothy already mentioned, most trainers do not have flaps, but when a glider is equipped with flaps, it would be most commonly in form of flaperons where full-span ailerons are coupled with flap control allowing common-mode motion both upwards and downwards. In contrast to the powered airplanes, flaps in gliders are used not only for landing, but also (maybe more importantly) to adjust optimal glide ratio for the speed currently flown. Thus upward turned flaps are common configuration during fast gliding between thermals for example.

Finding information for particular gliders, especially such mentioning flaperons explicitly turned to be quite hard. Pilot operating manuals usually just describe how to manipulate flaps handle without going into the details on actual construction. Typical placecard for flaps handle (from DG-400 manual) does look like this. Ranging from landing configuration to negative flaps.

Particular gliders equiped with flaperons include (maybe not the most modern ones, but those I was able to find some more info about, good enough as examples IMO):

DG-800 and LS-10 has full-span flapperons. Mentioned explicitly in the flight manual: The wings feature single piece flaperons, which are driven at two places. The mixing of aileron and flap deflections takes place in the fuselage. (The same formulation exists in LS-10 flight manual.)
DG-600 -- according to the wiki.
ASW-20 (and probably some other Schleicher gliders too) -- there are two distinct surfaces on each wing, sometimes referred as "flap" and "aileron", but both of them actually moves according to the mixed inputs of both controls, the ASW-20 flight manual contains nice table of deflections:

Eta has three flaperon sections on each wing, each with different mix ratio between control inputs
... and many others, I believe


What is the most recent turbofan engine that used steel for its bypass fan blades? I haven't been able to locate any engines that use steel for the bypass fan. All sources suggest Ti and composites are used for blade construction. Apart from the weight steel could partially make up for it by offering a thinner blade, cost/ease of construction and more resistance to foreign objects.
The reason I ask is that I am trying to design a large ducted fan (800mm) that will be as cheap as possible to manufacture by using a thin sheet of stainless steel for the blade material. The cut to shape sheet will be pressed in a mold to achieve the designed AoA across the blade length and then a 3D printed airfoil will slide over it.

The tickness of the Fan blade is not only defined by the structural requirement but rather for aerodynamic purpose, thus the geometry of the blade won't change much depending on the material used. Most of the metallic blades in use are hollow.
The price of the blade is quite irrelevent in modern engines. If you can decrease the wheight of the fan by 10% for double the price you'll do it as it will ensure so much fuel saving over the life of the engine. Thus I don't see the advantage of using steel over titanium for a fan blade.
Looking at other comments I understand it is for prototyping and needs to remain cheap. I would then recommend to build the core with 3D printed material which will give you the airfoil shape for aerodynamic and then enclose it with a metal sheets in order to obtain a sandwich like structure. This could greatly increase the stiffness and strength without much added weight.


How often are slats used on airliners? Are slats only used when there is a short runway or on all occasions?

On all occasions when flaps are deployed.

Slats are a necessity when the wing uses slotted flaps or Fowler flaps for maximum lift. Those flaps cannot reach over the whole span of the wing to leave room near the wingtips for ailerons.

Once the flaps are extended, they increase the incidence of the wing along the flap span. This leaves the outer wing at a lower incidence, but in the vortex field of the inner wing. This vortex field induces a high local angle of attack over the whole wingspan, which would produce a local stall at the wingtip, where the ailerons prevent the use of slotted flaps. This stall would in most cases be asymmetric: One wing tip loses lift while the other barely manages to get along with the high angle of attack. The result is a strong rolling moment which will even increase once the aircraft starts to roll, because the local angle of attack at the down-moving wing will increase further. At this condition, the ailerons are of little help, so the roll cannot be controlled.

Angle of attack change due to movement (own work)

Now consider when flaps are used most often: Close to the ground, during take-off and landing. Then imagine what happens when the airplane rolls over one wing uncontrollably. To avoid this, slats are very helpful: They give the wing an extra stall margin by shifting the stall angle up.

While the Airbus in your picture uses slats over the whole wing, they are strictly needed only at the outer wing. Adding them ahead of the slotted flaps will increase the maximum lift and reduce the minimum speed over what is possible with flaps alone, so full-span slats (sometimes combined with Krüger flaps on the inner part of the wing) are now standard.


Does EASA have access to medical records outside of the EU? When registering for the Class 1 Part-MED Medical Certificate can/will the EASA have access to your medical records that's outside of the EU?

No, EASA cannot access anything.

You will be asked to bring your medical records to the exams. Neither EASA nor your examining doctor is able to access any of your medical records without your consent. It's restricted personal information.

Some countries already have medical records in digital (computerized) form, but many still rely on written data. In any case, EU institutions have no jurisdiction outside of EU.

You will also be given a questionnaire that will include a checkbox for any known medical conditions you have (or had in the past). I don't know what your condition is/was, but it might be a good idea to consult a private examiner first before checking anything on the list that might prevent you from getting a certificate issued.


Are aircraft accidents more frequent in specific countries? In the past months I heard about several aircraft accidents that happened to occur in Russia, Indonesia, Malaysia... and I was wondering if some countries are actually more connected to accidents than other.

Is there some statistics on this topic? and if so, do they confirm this alleged over-representation, and do we know the reasons behind?

Crashes, meaning accidents with significant number of fatalities, are so rare, even in places with least attention to safety, that it is not possible to conclude the risk is higher in some countries with statistics.

And if you wanted to judge from the number of incidents, that is including events that were dangerous, but ended well, you would be stopped by the fact that quality of incident reporting varies wildly. In this interview Simon Hradecky, the editor of The Aviation Herald, explains that Canadian TSB reports many, many incidents, but that is is not because the safety would be poor in Canada – quite to the contrary – but because they have particularly good system of reporting them. So many incident reports can actually be taken as a sign of good safety in that country, but you can't make any statistics from that.

Regarding the countries you mention:

Indonesia is widely believed to have poor safety. The EU Air Safety List says:

  All air carriers certified by
  the authorities with
  responsibility for regulatory
  oversight of Indonesia, with
  the exception of Garuda
  Indonesia, Airfast Indonesia,
  Ekspres Transportasi
  Antarbenua, Indonesia Air
  Asia, Citilink, Lion Air and
  Batik Air, including …

clearly indicating that EASA does not believe the aviation authority of Indonesia oversees operators registered under them sufficiently.

Together with high incidence of severe weather and a lot of mountainous terrain this creates environment where the risk might be elevated. As mentioned above, even there accidents are not that common to allow firm statistical conclusion.

The excepted airlines however proved to EASA that they have a safety management system in place and that it works according to industry best practice. With them, the risk probably isn't significantly higher than with any other decent airline.
Malaysia and Russia: I have not noticed any specific concerns about safety in those two countries. If you seem to have noticed accidents in those two countries in particular, it is likely just bad luck.


Why is the fatality rate in the Diamond DA40 so remarkably lower than the SR20/22? I assume it has a lot to do with the stall characteristics, but with the SR20/22 having a combined 1.6/100,000 Fatal rate and the DA40 having .35/100,000 Fatal, it seems like a very stark difference. Additionally, the SR-- has a ballistic parachute and the DA40 does not.

Not sure how true it is, but one theory I've heard about the high accident rate of the SR22 is the parachute. Every added safety feature tends to make people more careless. Was the same when airbags were first introduced in cars, accident rates shot up for a while before slowly trending down again.
Also, the DA40 is used more often as a trainer, while the SR22 is more often used by relatively inexperienced pilots who do have a license. Might well make a difference (student pilots tend to be more aware of the limits of their skill and knowledge than cocky fresh graduates who think that now that they are certified to know it all they really do know it all). And often that student will have an experienced instructor in the cockpit with him as well.


What are the qualifications for a small airport manager? I live in a small city in the Southeastern United States and the county's airport has an opening for the manager. The airport is paved but no control tower, serves general aviation as well as company jets for regional businesses. They sell aviation gasoline as well as jet a, oil, etc.

What are the qualification for being a good candidate for this job? Are there certifications that would be needed? Would one need to be a pilot?

There are no formal qualifications required to be an airport manager -- it's not a "regulated professional field" in the same way as Doctors, Lawyers, or Professional Engineers.  If a person had the money they could purchase an airport and name themselves "airport manager" of their own facility.

That said, managing an airport has an interesting set of challenges and could probably be described as like being the mayor of a small city with its own road infrastructure (runways, taxiways, and ramp areas), snow removal services, business districts (FBOs, restaurants, & other tenants), municipal services (ARFF), and utilities (airport lighting, fuel farms, drainage systems). The airport manager will also have to interface with federal agencies: The FAA/DOT at a minimum, and likely also the EPA and Homeland Security (TSA/CBP). Working with the local municipality and dealing with local residents on matters like noise abatement is also usually part of the job.
In many ways "airport manager" is as much a political position as an operational one.

Because of the unique challenges involved in managing an airport there are degree programs specifically focused on airport management, and preference will probably be given to applicants with those degrees. Alternatively relevant operational experience (either from running an airport elsewhere or from working in other municipal departments within the county) might be enough to deem a candidate qualified.
There are also professional organizations for airport executives/managers which offer independent certification for individuals.

As a pilot I would say it's advantageous for an airport manager to be a pilot (and in the case of a small airport like the one you describe it would be helpful if they were an active pilot), but being a pilot doesn't really qualify a person in any of the other key operational areas - snow removal, runway maintenance, emergency response, etc. - so while experience as a pilot or controller might be helpful in that it imparts a greater understanding of the operational impact of certain decisions it would likely be viewed as a secondary qualification.


When there is a holding pattern assigned by a civilian airports ATC, do military aircraft get first priority over landing? When a military aircraft is landing at a civilian airport, and a holding pattern is in place, do military aircraft get to skip the que, or join in earlier in the holding pattern?

Do military aircraft get landing priority?

If the government so wishes, yes. ICAO Doc 4444 says:

  7.6.3 Priority for landing

  7.6.3.1 If an aircraft enters an aerodrome traffic circuit without proper authorization, it shall be permitted to land if its actions indicate that it so desires. If circumstances warrant, aircraft which are in contact with the controller may be instructed by the controller to give way so as to remove as soon as possible the hazard introduced by such unauthorized operation. In no case shall permission to land be withheld indefinitely.

  7.6.3.2 In cases of emergency it may be necessary, in the interests of safety, for an aircraft to enter a traffic circuit and effect a landing without proper authorization. Controllers should recognize the possibilities of emergency action and render all assistance possible.

  7.6.3.3 Priority shall be given to:

    a) an aircraft which anticipates being compelled to land because of factors affecting the safe operation of the aircraft (engine failure, shortage of fuel, etc.);

    b) hospital aircraft or aircraft carrying any sick or seriously injured persons requiring urgent medical attention;

    c) aircraft engaged in search and rescue operations; and

    d) other aircraft as may be determined by the appropriate authority

Or c), if by military it's a search and rescue C-130 (for example) wanting to land to refuel and be on alert ASAP.

Now is it wise to put d) ahead of a)? Of course not. So if there is a prioritized government VIP, they will have to wait for the low-on-fuel emergency or the rogue-in-distress (first two paragraphs).

If it's a fighter, say an F-35, why would it land in Heathrow for example among civilian Jumbos? Unless of course it's been coordinated beforehand, or there is an emergency, then yes it will land first.

In the documentary Jetstream, RCAF F/A-18's flew from Canada to KLAX and landed there during heavy traffic, they were treated as normal planes when it came to the sequencing. It was part of their training to manage the complex aircraft in the heavy traffic environment of the civilian world.

You can watch it here. The narrator says (around 3:40):

  In Cold Lake an F-18 coming in to land is top priority, but here you are just another plane in a long queue.