How do Airbus planes flare in normal operation? In reading the reports and Sully's comments regarding the flight that was ditched in the famous events of US Airways Flight 1549, I am wondering how the Airbus control system works to flare an airplane under normal flight conditions.

Sully stated that since the automated system did not let him flare as much as he wanted to, he was unable to reduce vertical speed further.

Is it that under normal flight, the aircraft has forward speed to generate lift, and the descent rate is thus less? I thought (I'm not a pilot) that it was desirable to basically stall by flaring at the last moment in normal powered landing, thus sticking it to the runway for traction, wheel spin-up, etc.

You don't do full stall landings in airliners.  You arrive over the threshold at reference speed (the full flaps approach speed), ease the thrust off (how soon depends on the airplane, but you need to be at idle before touchdown) and start to flare but only enough to reduce the sink rate to close to zero and then you tease the pitch to maintain a gentle sink until you touch.   If you wanted to do a full stall type landing, there is sufficient energy still available at reference speed that you would have to hold it off and float halfway down the runway, and you'd touch down with the stick shaker going.  Not a desirable outcome in a 150,000 lb soda can.

If you arrived over the threshold too much below reference speed, there is no energy reserve to save yourself if you are sinking too fast and there goes your tires, if you're lucky.

Water landings often don't go so well if the tail is too low (if the tail touches in too nose high an attitude, it tends to bounce upward and drive the nose over and things can go south).  So it's possible the FBW system actually protected them by limiting Sully's ability to pitch up.  They seemed to have touched down at an ideal attitude, getting a nice ski effect from the nacelles without the tail hitting too early.

In the famous Airbus airshow incident, the airplane descended gently into the trees as it struggled along way on the back side of the power curve (in that regime, the only option is to descend).  Had the crew more pitch up authority available to them, it is possible they would have semi-stalled into the trees at a much higher sink rate. That was Airbus's response to the criticism over the FBW's pitch limiting behaviour.


What is this INOP instrument and when is it safe to fly with INOP instruments? I flew ZRH->LHR on BA0711 today on G-EUOG. I noticed through the cabin door one of the instruments had a yellow INOP sticker across it (see photo). Which instrument was it? I am presuming the instrument has a backup, and the backup was operative, but I had thought the purpose of an backup was so that it could be used if the primary failed in flight? Or is the instrument just 'not important'? What are the rules re flying with INOP instruments?

It is a standby display, specifically a DDRMI (Digital Distance Radio Magnetic Indicator).

The aircraft can be dispatched with inoperative equipment. The process is controlled by a Minimum Equipment List (MEL). The operator will have an MEL for each type of aircraft in their fleet. The MEL is approved by the regulatory authority (FAA, CAA, etc.) and specifies what may be inop and associated restrictions.

I don't know what the BA MEL for the A319 is, but here's a snip from the FAA's Master MEL (MMEL), which is the guidance for each operator to use when creating their MEL.

Following this guidance, the MEL would say you can dispatch with the DDRMI INOP if the FAR equipment minimums are met. That (at least in the US) is along the lines of "navigational equipment necessary for the planned flight".


What type is this aircraft with "inverted" wings? A friend of mine saw this plane at Tampa Bay International Airport recently:

It has an odd combination of a negative dihedral and pylonless overwing engines, all traits I've seen individually but not together.

Does anyone know what this plane is, and what its purpose is?

If I am not horribly mistaken, it seems to be an Antonov 72 or 74, that were produced together, hence the similarity.

Another image (not included for copyright reasons) can be found here.

The wikipedia article classifies it as a "transport aircraft". It mentions a VIP transport variant and a maritime patrol one for the An72, several more variants are listed for the An74 version.

EDIT:

Flightradar24 lists only one An72 in the possession of CAVOK Air (thanks to bjelleklang for identifying the livery), registration UR-CKC.

The historical data indicates that this aircraft landed in Tampa on the 24th of May after a stop in St. John's on its way from Reykjavik.

  It has an odd combination of a negative dihedral and pylonless overwing engines, all traits I've seen individually but not together.

Concerning the anhedral (the name of "negative dihedral") angle, you can find more info here, but we can summarize here that it has more to do with the high wing mount rather than the engine one.

The overwing mount of the engine contributes to reducing the risk of foreign object ingestion on unpaved runways.

Update:

The aircraft has been damaged beyond repair in a runway overrun accident occurred on Jul 29th 2017.


How is the lift generated by a number of out-of-plane staggered wings calculated? I want to calculate the lift generated by a number of out-of-plane staggered wings but I don't think a valid approach is to simply use superposition and add the sum of the lift of all the wing's in isolation.

I have heard of Munk's stagger theorem but am unsure of it's implications.

I think the implication of Munk's theorem is that there is a limit to the amount of downwash and thus lift that can be generated by staggered wings.

Lets do an example:

I can calculate the lift force generated by a single planar wing as:

$$L=\frac{1}{2}\rho V^2SC_L$$

Where $\rho$ is air density, $V$ is free-stream velocity and $C_L$ is the finite wing lift coefficient, which is a function of the wing geometry.

Now, if I have say 5 staggered wings, is this statement:

$$L=5\times\frac{1}{2}\rho V^2SC_L$$

valid?

Now I know that the pressure distributions over the different wings will interact wing each other, but my question assumes that the wings are separated sufficiently far away from each other that this effect is negligible. Or is this interaction of pressure distribution a result of the stagger theorem?

I will appreciate any light being shed on this subject.

It depends on the vertical distance between the wings. Munk's theorem only covers the effect of their horizontal distance (in flow direction) and says it doesn't matter (in inviscid flow).

Your statement is correct if this distance is infinitely high (and the atmosphere has constant density over altitude). Only then there is no interference between the separate wings and their combined lift is the sum of the lift of every isolated wing.

On the other end of the scale, all wings together will just have the lift of a single wing if they are not separated at all. This is trivially easy to prove, but not practical.

For distances between the two extremes, lifting line theory gives you a good answer when the distance is not small. Below that, viscous effects will start to dominate the picture, and if the wings are separated only by something similar to the wing's thickness, they will impede the flow between the wings, making the combination appear as one blunt object to the outer flow, with consequences like flow separation and the collapse of lift.

Once you move the wings apart by more than their chord length, you will get practical solutions where the wings will produce more lift than a single one and even have lower induced drag than a single wing creating the same lift force. However, a distance sufficient to make interference negligible will mean that the struts between the wings will become long and heavy, so their mass cannot be neglected. I would expect that there is an optimum of lift minus mass which is somewhere around a vertical distance of one to three chord lengths.

Unfortunately, literature on the topic is more concerned with reducing drag, so the closest I could find is a work by Ilan Kroo on non-planar lifting systems. Using the solutions for biplanes will not give an answer to your question, because every wing interfers with every other, so adding a fourth and fifth wing to a triplane will reduce the lift of the triplane, but will in sum increase lift.


At KOAK, how can I get a passenger from the GA terminal to the commercial terminal? I want to land at the GA side of Oakland International (KOAK) in order to drop my passenger off for a commercial flight from the main terminal. I was told by a local guy that they do not allow a taxi on B over to the main terminal so I would need to park on the GA side and grab a shuttle/crew car/Uber over to the main terminal. I've contacted two FBO's and they tell me of about $50 in fees just to stop in. Has anyone done this and what is the best way?

This is a specific question but I think my advice applies to most FBOs.
I fly out of OAK and your best bet is to try signature. Buy some fuel, ask nicely and if they aren't too busy they might be able to accommodate you.
They have given me rides on the ramp before when my usual gate was closed due to a power outage.

If not, then call a rideshare/cab


What trade-offs are being made in the design of the planform alignment of stealth aircraft? Stealth technology uses angles in the aircraft shape, and homogeneous orientation of the surfaces. In the F-22A Raptor wing leading edges, tail surfaces, air intake bypass doors, refueling aperture, etc have the same orientation.

Incoming radar waves are deflected in a different direction, giving the enemy the impression that there is nothing there.

However, as mentionned in Wikipedia: "Shaping requirements detract greatly from an aircraft's aerodynamic properties. The F-117 has poor aerodynamics, is inherently unstable, and cannot be flown without a fly-by-wire control system."

I'd like to know what are the impacts of such planform alignment on planes capabilities, and how does a passive stealth shaping, using a small number of surface angles, compare to a "5th generation fighter"

This is a different question than Do similar angles on a plane make it more stealthy?" I'm looking for the advantages and disadvantages of using planform alignment.

To understand the functioning of planform alignment in befitting the fifth generation air-crafts in increasing their stealth, one first need to understand how Radars work:

Radar transmits a radio wave signal.
This signal when comes in contact with a surface (of an aircraft), it is reflected back. This reflection is a mixture of Specular and Diffused reflection.
The radar then after receiving the reflected signal, measures the speed (by computing the shift in the time period taken by the wave to be received over a period of time), and size (by computing the intensity of the reflected wave) of the air-craft.

But there is a problem, since the radar needs to get back its own transmitted wave back, if it is reflected off the surface of the plane only at a specific angle (specular reflection), then the receiver of the radar needs to be at specific places to receive the reflected wave.

Modern planes utilize this shortcoming of the radar by letting the incoming radar signal pass through them (using plan-form alignment), which then greatly reduces the reflected signal. The reduced reflected signal would be seen as an incoming signal of very low strength (intensity) by the radar, which then reads the size of the incoming air-craft as a very small object. This is called Stealth. The air-crafts also use special paints and composite coverings on the surface to again reduce the intensity of the reflected wave, to reduce the percieved size of the air-craft by the radar.

The shortcomings of such radars are removed by using radars such as AWACS, which is moving radar and can receive too directional signals (Specular reflection). Or, using radars such as AESA, which scans a large portion of area around it without having any moving parts.


Why does the Mitsubishi MU–2B have its own SFAR? The Mitsubishi MU-2B has a very long & detailed SFAR 108 that details the trained and currency requirements for anyone who wishes to manipulate the controls of the plane. I'm wondering what incidents or accidents and unusual handling characteristics required a Special SFR for this plane.

Since the MU-2 weighs less than 12,500 lb, a type rating is not required to fly the plane, so pilots only need a multi-engine rating. However, it is a high performance pressurized aircraft that requires more skill to fly. Mitsubishi Heavy Industries asked the FAA to create a type rating requirement for the MU-2, but the FAA decided on creating the SFAR instead, which is more strict than a type rating, especially in the amount of training specifically required.

Research showed that the accident rate of the MU-2 from 2001 to 2005 was not really exceptionally high compared to aircraft of similar size and performance. While the accident rate was higher than some, it was also lower than others. However, the FAA received a lot of pressure to create a rule for the MU-2.

Regardless, the accident rate has gone down significantly since the FAA created new regulations for the plane.


How does type ratings training work at the airlines? How does it work to get typed in a different aircraft at a carrier like United, American, and/or Delta? If you're a first officer on the A320, but want to be a first officer on a different aircraft? Is it seniority and bidding on a different aircraft? How long would that typically take to get to that point to change aircraft?

Getting ready to start at a regional, and was curious. I'm also wondering how you get selected for the aircraft you will fly once reaching a major

The carrier trains you for their aircraft.  If you don't already have a type rating for your new aircraft, then you'll get one as part of the checkride at the completion of Captain training. (Maybe you flew that aircraft at another carrier, or you were an International Relief Office -- a type-rated F.O., or maybe you simply got the type rating as part of F.O. training on that aircraft earlier.)  If the carrier needs you to have the type rating on your new aircraft as an FO, you'll get that as part of your training for that aircraft. If you don't need it, you probably won't.

Once you are in the system, everything is driven by seniority -- what do you have the seniority to hold -- and the rules of the contract.

Each fleet at each carrier, and more often than not, each domicile at each carrier, will have different dynamics.  In some cases, pilots "camp out" in one aircraft at a particular base for a long time; in other cases, after a couple of years, they're typically bidding (exercising seniority) to go back to training for the next step up the ladder (MD80 to 737 to 757 to 777 FO, then MD80 Captain to 737 to 757 to 777).  Different contracts have different rules; some allow a pilot to camp out as long as he wants -- perhaps he's enjoying the quality of life being a senior FO on a nice aircraft at a base close to home, and he isn't interested in upgrading to a bigger aircraft (where he'd be less senior) or the left seat of a smaller aircraft (where he'd also be rather junior) at a base far away. Other contracts (historically) have had provisions that once you can hold either your same seat on a bigger aircraft (or the left seat on any aircraft for an FO), your clock starts & within so many months, you have to upgrade (assuming one is still available) -- for whatever reason that contract was written to avoid having lots of pilots camping out in lieu of upgrading.  All very dependent on the contract in place where you work.

Also, the state of the economy and of the airline can drive a lot of this... with Delta retiring many, many senior captains over the next few years, there are lots of opportunities for progression.  When everything tanked after 9/11, forward progress stopped and in many cases people moved backwards... MD80 captains went back to being FO's, widebody FO's went back to being narrowbody FO's, junior FO's were furloughed, etc.  During the stagnation of the 2008+ recession coupled with the change to Age 65 retirements, nobody upgraded due to retirements (okay, very few retirements), and almost nobody was growing their fleets, so pilots stayed put much longer than they might have otherwise -- there was nothing available to bid FOR.  You can only exercise your seniority for a slot that is open.

  I'm also wondering how you get selected for the aircraft you will fly once reaching a major

It's essentially whatever aircraft/base needs the bodies that month.  One class may get a lot of 737's and a few A320's, another class gets all 767's.  Often, the vacancies in the 767 would be filled by pilots moving up from the smaller aircraft, but that doesn't always occur, and it's not at all unheard of for newhire FO's to sometimes go to much larger (read, better-paying) aircraft.  Of course, they'll be junior on that aircraft for a long time; they'd get a "more senior" schedule -- fewer weekends & holidays at work -- sooner on the smaller, more junior aircraft.

Likewise the domicile -- if JFK has the openings, you go to JFK (I'm so sorry). If JFK is full & ATL has the openings, you go to ATL (which is probably better, unless you live close to New York).  Easier to change domicile than to change aircraft, since no retraining is typically required. (Maybe an "international" course if your old domicile flew only domestic and your new one flies international -- but that's no big deal.)

Welcome to the airline industry!


How should Isopropyl Alcohol be used as an AvGas Fuel System Icing Inhibitor? I understand that 100% Isopropyl Alcohol (IPA) is used as a Fuel System Icing Inhibitor (FSII) additive in aviation gasoline systems—including 87 through 100LL fuel types—for cold weather operations. I know that IPA is, or can be, included as part of AvGas formulation. However, I am referring to operational use of IPA as an additive when fueling the aircraft. Pure IPA is also known as anhydrous isopropanol.

What documentation is available to support such use?
What is a proper treatment ratio for using IPA as an FSII (or what is the concentration limit)?

FAA Advisory Circular AC No: 23.1521-1B deals with use of IPA for Part 23 aircraft. It states:

  ASTM D 910, Standard Specification for Aviation Gasolines, allows the use of isopropyl alcohol conforming to the requirements of ASTM D 4171, specifications for Fuel System Icing Inhibitor, as a fuel system icing inhibitor. Accordingly, isopropyl alcohol conforming to ASTM D 4171 may be used in concentrations up to 1 percent by volume, to benefit safety, as an icing inhibitor in automobile gasoline.

However, it is left to the aircraft manufacturers (according to ASTM 910 too) to determine whether or not to use IPA as an additive. For example, in a letter regarding Lycoming engines in certain of their aircraft, Cessna says,

  Isopropyl alcohol in amounts not to exceed 1% by volume can be added only to aviation fuel  (not  automotive  fuel)  to  prevent  ice  formation  in  fuel  lines  and  tanks.  Although approved  for  use  in  Lycoming  engines,  do  not  use  isopropyl  alcohol  in  the  aircraft  fuel systems unless approved by the aircraft manufacturer.

Note that Cessna allows the addition of IPA only to aviation fuel for the applicable aircraft. In UK, the MoD Defense Standard 91-90 again leaves the matter to the individual manufacturers, saying,

  The concentration of Isopropyl Alcohol shall be recommended by the aircraft
  manufacturer at the time of delivery to the purchaser and typically not exceeding 1% v/v.

Though almost all these cap the IPA at 1%, the best way is to refer to the individual aircraft's appropriate manual as it would have the necessary details. But generally, I think that manufacturers (of large aircraft, atleast) prefer not using IPA these days due to environmental concerns.


Why are wind tunnel models sometimes placed upside down? Sometimes in wind tunnel tests, models are suspended upside-down:

Image obtained from DNW - Interference corrections

Image obtained from this Youtube video of testing at AEDC

Image obtained from UWAL - Model Support Effects

And sometimes they are in the normal flying position:

Image obtained from TRI models - wind tunnel testing

What is the specific reason for putting wind tunnel models upside-down?

I thought it had something to do with minimizing the influence of the support, but putting the plane upside down doesn't change much about the location of the support.

In the times before strain gauges and electronic transducers, the forces on the wind tunnel model were measured with scales. To avoid interference as much as possible, the model was hung on strings, the scales being mounted above the measurement area of the tunnel. Since the forces in upright flight were of the highest interest, gravity plus lift would make sure that the strings were always taut. If the model were hung upright, the lift might grow bigger than the weight, and the model would move towards the scales.

Today, the orientation of the model can be either way, and only in exceptional cases there is a strong reason for placing it upside down. This might be when unusual attitudes together with the supporting sting (the long spike on which the model sits) would block one part of the wind tunnel cross section too much, or if movement restrictions of the sting force a certain orientation.

Another reason is flow visualization techniques: Sometimes it helps to put a coat of a mixture of petroleum and pigments on the surface and to watch where the pigments are blown by the flow (this is called an Anstrichbild). Obviously, it helps to place the surface of interest on top.


Is there an "SR-72" under development? The Extreme Tech website reports that

  Lockheed Martin’s Skunk Works has confirmed that it is developing the SR-72 spy plane. The successor to the SR-71 Blackbird, which was capable of Mach 3.5, the SR-72 will be a hypersonic unmanned aircraft capable of Mach 6, or just over 4,500 mph.

The article goes on to say it will be unmanned, with the full scale vehicle built & tested by 2030.

It's not that I would ever doubt Extreme Tech or the author of this story (cough, cough), but it seems odd that news of an SR-72 project isn't being far more widely reported.

Are there any other sources reporting this new project, or is Extreme Tech the only one?

Yes, the SR-72 project has indeed been officially announced. Lockheed confirmed it to Aviation Week back in 2013. Apparently it actually did get quite a bit of attention at the time, enough to actually cause Aviation Week's servers to go down for a while after the announcement.

The source quoted in the question is correct that Lockheed's announcement did confirm that the SR-72 would be hypersonic:

  But now Lockheed Martin believes it has the answer. “The Skunk Works has been working with Aerojet Rocketdyne for the past seven years to develop a method to integrate an off-the-shelf turbine with a scramjet to power the aircraft from standstill to Mach 6 plus,” says Brad Leland, portfolio manager for air-breathing hypersonic technologies.

Also, from Lockheed Martin's own website, confirming both the Mach 6 capability and the intention for it having at least the option of flying unmanned:

  Envisioned as an unmanned aircraft, the SR-72 would fly at speeds up to Mach 6, or six times the speed of sound.

According to Lockheed, a technology demonstrator aircraft may be flying by 2018:

  Lockheed has run scaled tests on components. “The next step would be to put it through a series of tests or critical demonstrations,” Leland says. “We are ready for those critical demonstrations, and we could be ready to do such a demonstration aircraft in 2018. That would be the beginning of building and running complete critical demonstrations. As of now, there are no technologies to be invented. We are ready to proceed—the only thing holding us back is the perception that [hypersonics] is always expensive, large and exotic.”

Here's a rendering of the proposed design from the SR-72 Wikipedia page:

Source: Wikipedia, which apparently took it from Lockheed's website.

Lockheed was recently awarded a grant from NASA to study the viability of their proposed combination turbine/ramjet engine solution for the SR-72.

  Task Order No.NNC15TA03T provides for a parametric design study to establish the viability of a Turbine Based Combined Cycle (TBCC) Propulsion system consisting of integrating several combinations of near-term turbine engine solutions and a very low Mach ignition Dual Mode RamJet (DMRJ) in the SR-72 vehicle concept. Task Order NNC15TA03T is issued under Contract NNC10BA08B on a firm fixed price basis. Firm fixed price is $892,292.


Carb Heat and Lycoming Engines Why is Carb Heat less of an issue on Lycoming Engines? and if this is true, how much less of an issue is it?

It's because the spider duct that connects the carb to the intake runners going to the cylinders is cast into the oil sump and the carb mounts directly to that. So the carb gets a lot of engine heat that warms the carb body by conduction. Also, it's getting radiant heat from the sump directly above.

On Continentals the carb is insulated from the engine by its mounting and location relative to the sump.  Continentals without pressure cowls like J-3 Cubs are the worst for carb ice formation.

Carb icing is relatively rare on Lycomings but is still possible if the conditions are sufficiently favourable, so you still have to use normal carb heat protocols.


Who pays for the damages in this Asiana-Aeroflot collision? I just came across this article where an an Asiana 747 'collided' with an Aeroflot IL62 at the adjacent gate. As per the reports, IL62 had to be scrapped. From, what I read, it was like the Asiana pilot had a brain freeze.

I was wondering, in this case who payed for the damages and what happened to the pilots?

Here is the accident description from aviation-safety.net and here's a photo of the 747's wingtip embedded in the vertical stabilizer of the IL-62:

Short answer:
Someone's insurance company is writing a check.

Longer answer:
What usually happens in the insurance world is both insurance companies write checks to repair their respective clients' aircraft.  The insurance companies may then fight it out between themselves to determine who is responsible for what, if it makes financial sense to do so.

In cases where injuries or deaths result from an incident it almost always makes sense for the insurance companies to fight it out(those payouts can run in the millions of dollars).

In cases like this where there's only equipment damage the cost of the repair will determine how aggressively Aeroflot's insurance carrier pursues getting their money back from Asiana's carrier.  If we're talking about extensive and expensive structural repairs into the millions of dollars Aeroflot's insurance carrier will be motivated to get someone else to pay the bill. Conversely if the insurance company can make their money back through Aeroflot's premiums and pursuing Asiana for negligence or something along those lines to try to get them to pay for the repair would ultimately cost more (money and time pursuing the case) than just absorbing the loss the insurance carrier will just absorb the loss.


How much different are civilian and military aircraft autopilots? The requirements for military and civil aircraft are pretty different, so this possibly applies to their autopilots. Are they different in the way they function or capabilities that they are programmed with?

There is no civillian autopilot for an F-16, because there are no non-military F-16s. Ditto with the F-117 or or B-1 or B-2, so who knows what unique modes those autopilots have for their uniquely military missions (i.e. dropping bombs or low level terrain following). However, when the military aircraft has a non-military equivalent (KC-10/DC-10, KC-135/B707, C-40/T-43/B737, C-21/Learjet, T-44/C-12/KingAir, etc) then the autopilots are generally identical.

Any differences are more likely to be found in FMC software rather than in the Autopilot, and those differences would be very specific to each aircraft & its mission.


What would be the safest way to drop thousands of small, hard objects from a typical, high wing, GA airplane? The subject pretty much states my question, now I will provide a bit of background.

A family member, who lived on the west coast of Florida Manasota Key, collected tens of thousands of fossilized sharks teeth between the mid-1940s and the late 1970s. I have now become involved in deciding what to do with these sharks teeth. Here is one of the multitude of pictures available showing samples of these types of sharks teeth:

The vast majority of this collection ranges in size between a dime and a quarter and likely has the same level of hardness.

If you've visited one of the beaches in this part of Florida in the last 25+ years, you probably know that finding these treasures is no longer as easy as it used to be.  When I was a kid (late 1970s), I could usually come up with 10+ teeth in about a 2 hours stretch.  However, by the time my kids were of the age where this would be of interest (early 2000s), we were lucky if we found one a day.

What I'd like to do is return these teeth to the area just off shore of this beach thus giving future searchers a better chance of "re-finding" them.

Let's assume for the purposes of this question that the airplane involved would be a Cessna 172S. What would be a good way of doing such a drop without harming the aircraft itself?

I assume just dropping them out the window risks blow back that could damage the aluminum fuselage or tail assembly.

A couple of notes:

This is NOT a question about the legality of dropping items from an airplane in the United States. I am well versed with 14 CFR § 91.15 - Dropping objects, which states:

  No pilot in command of a civil aircraft may allow any object to be dropped from that aircraft in flight that creates a hazard to persons or property. However, this section does not prohibit the dropping of any object if reasonable precautions are taken to avoid injury or damage to persons or property.

I am not interested in a solution harmful to the environment. Thus dropping them in taped boxes or rolled up newspaper would not be warranted, because that would be littering.
I'm certainly aware that renting a boat and dropping them off the side would be an alternative. That said, for the purposes of this question, I am specifically asking how to achieve this using a Cessna 172 (or similar) high wing GA airplane.

Funeral homes sell gum bags for ashes. They dissolve in the ocean, releasing the ashes. You could make satchels and drop them in bundles with the teeth wrapped in kelp.


What is the purpose of the 787 engines extending on landing? As seen about 53 seconds into this video of the Qantas Dreamliner landing, the engine housings seem to extend upon landing. What specifically is the purpose of this? To balance? To help with air flow?

Those are the thrust reversers, which cause the engines to produce thrust "backwards" to help slow the aircraft during the landing.

You can see a close-up video of 787 thrust reversers in operation, including a look at the panels at the back of the engine which block the normal flow of air.

We also have a question How do thrust reversers work on a jet engine, and when should they be used?, which describes their operation in general.


Where can you find wind tunnel visualization data online? I was wondering if there was a repository of flow visualization results somewhere online, preferably of wing sections categorised in some manner.

The closest you will find to a comprehensive, freely accessible source of data on this is the NASA Technical Reports Server. It is a search tool that gives you access to many NACA reports on various airfoils.


Are centrifugal turbojets easier to make than axial ones? Looking at the history of jet engines, I noticed that the British first made centrifugal-types, but the Germans went straight into axial-types.

Which type is easier, if any? By that I mean, which type is easier to design and produce? As far as I can tell, they appear to be very similar pieces of rotating machinery, just the compressor blades are shaped differently and the airflow follows a different path.

Are the equations of centrifugal flow somehow much more complex than axial flow, or vice versa? Are the shaft bearings of one much different than the other? Are there tougher geometric problems of lubrication with one but not the other?

Note that I am not asking which is more efficient or the better choice. That would have to take into account much more than the cost to design and build something. For now, I'm only asking about which type of engine is easier to build, if any.

Centrifugal is easier to make.  It's just a big vacuum cleaner with a kerosene burning furnace behind it instead of an electric motor.  You have a one piece impeller, as opposed to numerous little blades and discs, and can be cast or machined from a block of metal.  It's not dependant on the aerodynamic lift of blades to force air from a large space into a small space. It just pulls it in and flings the air out into a small space, so it's more resistant to surge.  To get surge in a centrifugal compressor engine you have to really obstruct the inlet, whereas with an axial engine you just have to disrupt the flow enough to induce blade stall.

So in the 30s it was WAY easier, cheaper, and faster, development wise, to get a nice running engine using Whittle's design with the centrifugal compressor.  The big downside is that it is less efficient than axial. You can't get the compression ratio that you would get  with an axial because it's difficult to incorporate multiple stages, and the engine is quite large because of the need to fling air out to compress it.  The Germans went with legions of expense, grief and operational delicacy for the better efficiency and smaller profile of axial.

The most obvious example today is the fact that nobody uses axial compressors for turbochargers and most in fact use similar impellers as the turbine as well.  You won't see axial compressors on any of the little micro turbojets used in RC.  A lot of smaller turboprops also use centrifugal compressors, sometimes in combination with axial stages.
That should tell you something about how much easier and cheaper it is to make.


How do you choose engine placement for under wings engines? I'd like to know how you choose the location of the engines under the wings, in the case of a 4-engines aircraft with low wings (and therefore with engines under the wings).

Concerning the longitudinal location, what are the constraints? Nacelles are usually in front of the wing, but why? I know there is a security constraint, especially with high bypass ratio engines, but is that all?

Concerning the lateral position, you want to reduce the bending moment of the wings, and therefore have your engines close to the wing tips during flight. But one could also say you want the engines close to the CG to reduce bending moments on the ground... Which constraint is dominant? And why can't we have to engines close to each other? (far enough to avoid flow interactions)

After having read aeroalias' picture collection, I feel an urge to chime in.

Longitudinal position

The main reason to place them ahead of the wing is flutter suppression. Flutter is an oscillation caused by the interaction of elastic and aerodynamic forces. In case of the wing, it is an up-down bending motion. Since air takes its time to flow over the wing, at a certain airspeed the air pressure change on the wing is so much out of phase with the motion that it amplifies the elastic motion of the wing. By placing the center of gravity of the aircraft part ahead of its elastic axis, flutter can be suppressed. This is true of flaps (where a mass balance is added ahead of the hinge line) as of full wings (where engines take the part of the mass balance).

Imagine the wing bending up, and now add the inertial forces of an engine connected to this wing and also moving up. If it is placed ahead of the elastic axis, it will induce a torsion moment into the wing, such that the local angle of attack is reduced, which in turn will reduce lift and the forces which cause the wing to bend upwards. The same happens in opposite direction when the wing bends downwards. Since the biggest thickness of the wing is in its forward section (which shifts the elastic axis forward) and the heavy flap mechanism is in its rear section (which shifts the local center of gravity back), a wing without an engine mounted forward of it needs a much heavier structure or less heavy, but otherwise unproductive, balance weights.

Placing the engine ahead of the wing brings some more benefits:

Airflow at the intake is less influenced by the pressure field of the wing, so the variation in local flow direction is smaller, resulting in a better-performing intake.
An uncontained turbine failure is less likely to damage the wing.
The engine can be mounted higher relative to the wing, such that the landing gear can be shortened.

Why engines are not placed on top of the wing is discussed in this answer.

Lateral position

In two- and three-engined jets you put them at the wing station where the inner wing ends. The main reasons are:

There is a major rib anyway to support the wing's skin, so the structure for attaching an engine is easier to add.
There is a gap between inner and outer flaps (at least in Boeing designs), so the engine blast will not hit the flaps.
They are still relatively close to the center of the airplane to not require an excessively large vertical tail to cancel the yawing moment in single-engine flight.

Boeing 737 bottom view (picture by Adrian Pingstone). The inner wing section has an unswept trailing edge while the outer wing has less taper and a swept trailing edge. The engines are exactly where both meet.

Aircraft like the DC-8 had their inner engines at the wing rib which supported the inner flap tracks of the outer Fowler flap, because they had no gap between inner and outer flaps. On the DC-10, Douglas placed the wing engines at the break between inner and outer wing, however.

In four-engined jets the inner engines are placed like those on two-engined jets, while the outer engines are placed at the end (or slightly outside) of the outer Fowler flaps, about midway between the inner engine and the wing tip. Note that again a rib is needed where the aileron cutout starts - this rib doubles as the engine mount. There the engines can contribute a lot to bending relief, and since a single engine contributes only 25% of the total thrust, the yawing moment of the outer engine in the engine-out case is roughly equal to that of a single engine of a two-engined jet.

Airbus A340 bottom view (picture by Adrian Pingstone).

Why it is better to separate the engines and spread them out over the wing instead of collecting them in a single nacelle is explained in this answer.

In some cases, the engine location is dictated by other requirements. On the Antonov An-70 the inner engines need to be far enough out to allow to drop paratroopers from the front door, for example.


Where can I find pictures of "endplate"? Where can it possible to find pictures or drawings of "endplate"? (for "winglet" is much easier, but not endplate)

I'm asking what's written above, after I read the following text from Raymer and I need a better comprehension of it.

  The wing aspect ratio "$A$" is the geometric aspect ratio of the
  complete reference planform. the effective aspect ratio will be
  increased by wing endplates or winglets

  Endplate: $A_{effective} = A(1+1.9\frac{h}{b})$ - (12.10)   where $h$ = endplate height

  Winglet: $A_{effective} = \approx 1.2A$  -     (12.11)

  These effective aspect ratios should also be used in the induced drag
  calculations below. note that Eq. (12.11) for winglets is a crude
  approximation based upon limited data for wings of moderate aspect
  ratio

......................

  The extra drag due to non-elliptical lift distribution and the flow
  separation can be accounted for using e, the "Oswald span efficiency
  factor". This effectively reduces the aspect ratio, producing the
  following equation for $K$

  $K=\frac{1}{πAe}$ (12.48)

  If the wing has end-plates or winglets, the effective aspect ratio
  from Eq. (12.10) or (12.11) should be used in Eq. (12.48)

(Source: Daniel P. Raymer "Aircraft design . A conceptual approach" , Chapter 12 Aerodynamics)

I seem to remember that wing end plates were sometimes used on Short Take Off and Landing(STOL) aircraft in the 1960's.

I found a few photos while doing an internet search but they seem to be much more prevalent on race car wings these days.

Here is an explanation of why end plates are used on race cars: Analysis: Rear Wing Endplates

  The endplate has two functions, the primary reason for their shape is
  to control the wingtip vortices at the trailing edge of the wing as
  this reduces drag and also lift. The second reason is that they
  control how the airflow makes its way over, under or around the
  aerofoil device that is creating the downforce on the car, resulting
  in better airflow management and maximising the performance of the
  component.


Can I wear a helmet camera in an open cockpit? When flying an open-cockpit plane (specifically a Tiger Moth):

By Towpilot (Own work) [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/)], via Wikimedia Commons

Where helmets are worn, what precautions or certifications need to be observed to mount a small video camera (such as a GoPro) thereto, if it's even possible? Obviously it would be very bad if the camera were to come undone in flight, and there might be an effect on the helmet's impact protection, so my guess would be that it's simply not allowed, but perhaps it can be done if certain conditions are met.

It's certainly possible to use a GoPro in a Tiger Moth: there are plenty of videos online to prove it. That means the question is, is it legal and if so how to do it safely?

Legally, there isn't anything relevant that I could find on the UK's CAA site (your profile says you're in the UK), but in any case most discussions on cameras in GA aircraft have been about attaching a camera to the aircraft, not to the pilot (see this question, for example). For obvious reasons, it's difficult for any aviation authority to regulate what pilots wear or carry on their person and if there are no specific regulations that means that only the general don't do anything stupid or dangerous rule would apply. I assume that the UK has something equivalent to 14 CFR 91.13 in the US:

  No person may operate an aircraft in a careless or reckless manner so
  as to endanger the life or property of another.

(Note: I'm ignoring any contractual issues here, like what your insurance company or FBO allows.)

From a safety point of view, the main risk of a portable camera is that it comes loose and ends up blocking a control surface externally (e.g. wedging in the rudder or elevators) or a control internally (e.g. falling to the floor and getting stuck behind a rudder pedal).

One specific concern with a helmet-mounted camera is that if it does fall off then it's very close to your face and it could obstruct your vision or even just startle you, which would probably be bad news on short final with a gusting crosswind. (Pilot distraction from operating the camera controls is another potential issue but that's true of any gadget.)

Ultimately I would say it comes down to how confident you are that the camera is secure and not going to get in your way: if you are, then go for it. I don't think the attachment issues are significantly different from skiing, parachuting, driving sports cars etc. with a helmet camera, and that happens all the time. And cameras are a great tool for reviewing and improving your performance (especially if you have full audio too), which makes the 'risk' very worthwhile, in my opinion.


What is this? Multiple small cracks in passenger window I have seen this many times in typically older aircraft passenger windows and on a recent flight from Sydney to Melbourne I took the following pictures. It appears as if there are small cracks in the window or one of the laminate layers used to construct the windows. Could anyone shed some light on what is the cause and if there is any risk?

Airline pax windows are cast acrylic plastic (plexiglass) and when the panels age they can get little microcracks in the surface called crazing.  This can be formed from long term tension stress on the crazed surface as well as from degradation from chemicals (ammonia is one of the worst - NEVER use Windex or equivalent on plexiglass) or UV (acrylic cast for aircraft has a UV block in it that makes it relatively resistant to UV).

On airline windows it's mostly due to long term surface stress because the pressurization system is trying to blow the window out all the time and the outer layer is in tension.  Minor crazing is not a structural problem because it is in the outer couple thousandths of an inch of the plastic and doesn't reduce its strength significantly (1/4" thick acrylic sheet at 8ksi tensile strength, like you would typically find in a pressurized aircraft window, is roughly equivalent in tensile strength to .050" 2024 aluminum, so it's not that much different than the adjacent aluminum skin with minor abrasion surface scratches, structurally speaking).

Airlines restore windows with crazing and scratches by removing the outer crazed layer with abrasive products made for the purpose (like Micro Mesh https://micro-surface.com/).  There is an allowable minimum thickness of the acrylic and they can go down to that, and if crazing is still apparent at that point the window is scrap.


What's a metering fix? The Instrument Procedure Handbook says on page 3-18

  "Arrival delays typically are absorbed at a metering fix. This fix is
  established on a route prior to the terminal airspace, 10000 feet or
  more above the airport elevation. The metering fix facilitates profile
  descents, rather than controllers using delaying vectors or a holding
  patterns at low altitudes."

I cannot get my head around this concept. So how does a metering fix work to absorb arrival delays? What's exactly a profile descent and how is it related to the metering fix? What merits does it have as compared to delay vectors and holds?

Definitions from this page.

Metering:

  A method of time-regulating arrival traffic flow into a terminal area so as not to exceed a predetermined terminal acceptance rate.

Metering airport:

  Airport adapted for metering and for which optimum flight paths are defined.

Metering fix:

  A fix along an established route from over which aircraft will be metered prior to entering terminal airspace. Normally, this fix should
  be established at a distance from the airport which will facilitate a
  profile descent 10,000 feet above airport elevation [AAE] or above.

But behind these definitions, that's a whole domain under research and experimentation to shape the future of air traffic management.

Metering methods are currently designed to respond to traffic increase, resulting airports congestion, and requirement for fuel saving and less nuisances from aviation. Solutions are known collectively under AMAN acronym for Arrival Management.

As said, this fix is established on a route prior to the terminal airspace, 10,000 feet or more above the airport elevation. It can be the feeder fix.

The concept is to manage cruise speed to arrive at the metering fix in time, instead of holding/vectoring before (or in) the terminal area. ATC can determine in advance times aircraft will be allowed into the TMA, based on aircraft capabilities, traffic and weather). ATC is able to issue a "EXPECT descent in n minutes" to facilitate planning by crew using their FMS.

This allows for limited vectoring and holding prior to the TMA. When holding/vectoring is still needed, it happens at higher altitude, which is better for noise/emissions management.

Thales AMAN/DMAN concept in Europe,source

For example, there is such metering for arrival at Sydney. Sydney has a curfew at night, aircraft are descended in the order they arrive, which encourage crews of early flights to arrive before the end of the curfew and hold. But because many crews use this trick, waiting time increases. By using metered arrivals (ALOFT in-house system and MAESTRO AMAN from Thales), crews are provided with a narrow time window for crossing metering fixes, one at 160 NM from the airport, the other at 40 NM. Once you have the window, there is not need to hurry and then wait. The time crossing the first metering fix can be provided up to 1,000 NM before arriving at this fix.

  What's exactly a profile descent and how is it related to the metering
  fix?

The descent profile is the curve of altitudes followed for descent. The most efficient way to descent is the continuous descent without level segments. The aircraft just glides with idling engines and clean configuration (less noise, less fuel, reduced wake).

This profile is only possible if nothing prevents to descent at any point, e.g. a congestion in the terminal area. By ensuring a free descent after the metering fix, this portion of the descent can be optimized for fuel saving and noise reduction.

  So how does a metering fix work to absorbs arrival delays?
  What merits does it have as compared to delay vectors and holds?

The idea behind AMAN is to regulate traffic the most upstream possible, start sequencing early, and prevent wait time in flight. There is a complementary solution which is currently investigated too: DMAN for Departure Management, with transition fixes (also visible on the picture).

AMAN and DMAN systems can be coupled. As pointed out by @Lnafziger, metering fixes can be used more upstream than terminal area, up to departure. Such upstream fixes are visible on the picture. If we add Surface Management (SMAN), block-out times can be optimized effectively, minimizing taxi and airborne time, and at the same time minimizing delays and nuisances.

These systems tend to switch from distance sequencing to time sequencing. This field is currently actively experimented, both in the US, Europe (LFPG experimenting coupled AMAN/DMAN) and Australia and a few other locations.

Source

For more, see also: Accelerating Air Traffic Management Efficiency: A Call to Industry

I hope @DeltaLima will show and provide additional elements for Eurocontrol.


Question about federal airways in Class E airspace going from 5500 MSL(USA) Class E with a floor of 1,200 feet AGL is shown with the "fuzzy" side of the blue. And sometimes Class E has a floor higher than 1,200 feet. They will print the floor of the Class E altitude in the "fuzzy" side of the blue. I know the Class E with a floor of 1,200 feet AGL is usually the floor of an airway. It goes from 1,200 AGL to 18,000 MSL. But if there is a designated specific altitude higher than 1,200 AGL for Class E airspace floor covering a federal airway, at what altitude does the Federal Airway start?

Likely at the floor of the Class E airspace.  A Federal Airway coinciding with a Class E floor higher than 1200' AGL would normally only exist in mountainous terrain.

A definitive example could be found by looking in the FAA's "Airspace Designations And Reporting Points" document, available on-line.


How does fuel get to the engine during acrobatics? Given that during acrobatics, extreme G-forces may be impressed upon the fuel tank, wouldn't it make it somewhat difficult for fuel to get to the fuel pump while it's being pushed against a specific direction for the duration of the stunt? Is the solution just not to do the stunt long enough to starve the engine of fuel?

The basic problem is that no matter how the aircraft's fuel tanks are designed, if there is an air gap in the tank, then there is an attitude and/or a g-loading that puts that air gap over the inlet to the fuel line running to the engine.

There are a lot of solutions to this problem. The first is exactly as you say; don't sustain any maneuver that starves the fuel pump (and by extension the engine) for a longer period than you have fuel in the lines to feed the engine. You can actually do a lot without the fuel system seeing a single hiccup in supply; the fuel tanks are designed to feed while under positive G-load (otherwise you couldn't get any fuel to the engine just sitting on the tarmac), so hard turns, rolls, loops etc that keep a force on the aircraft and its contents acting downward towards the floor of the cockpit will keep the fuel flowing into the engine. Spins and high negative-G maneuvers tend to be the things that starve the engine; if the tanks are in the wings, a hard spin, snap roll or zero-g parabola will push the fuel out away from the inlets at the wing roots.

Most fuel systems except on the lightest aircraft have at least two fuel pumps per engine; one electric pump on the tank side to shove fuel into the line, and one crankshaft-powered pump that draws fuel out of the lines into the carb chamber or other fuel delivery system. The checklist often involves turning on the electric fuel pumps just before startup to prime the fuel lines, then turning them off once the engine is running smoothly, but you can keep the electric pump on if you plan on really twerking the aircraft in flight. The line between these two pumps actually holds a fair amount of fuel, plenty for a minute or more of sustained operation with the inlet at the tank totally starved, and coupled with a bleed valve on the engine side to release any air that's entered the line, the two pumps running together can usually keep an uninterrupted flow of fuel into the engine by having the electric pump shove fuel down the line as fast as it can whenever the inlet is under the liquid level.

For mild aerobatic maneuvers, a "flop tube" is put into the fuel tank. This is simply a flexible hose with a weight, that keeps the hose under the liquid level, no matter what forces are acting to move the mass of liquid around in the tank. This is a simple and very effective way to keep fuel flowing to the engine while the aircraft is under load in any direction, but because the flop tube requires a significant volume of fuel to sink underneath and draw from, flop tubes can increase the "unusable fuel" capacity of the aircraft (fuel that exists in the tank, but the fuel system can't draw out in some normal circumstance). However, there's a tradeoff; the heavier the weight on the end of the flop tube, the more reliably it will stay under the fuel level regardless of attitude, but the more force with which it will impact the sides of the tank in violent maneuvers (and padding the weight further increases unusable fuel).

For the real aerobatic nuts, though, the maneuvers are so violent and so long that even a flop tube, redundant fuel pumps and bleed valves might get starved as the fuel sloshes and churns and there isn't a real "liquid level" to draw from. Many of these aircraft go one step further; a bladder-style fuel container. Within the fuel tank is a flexible polymer vessel that actually holds the fuel (typically in either wingtip tanks or a fuselage tank; it's usually impractical to try this with in-wing tanks). This bladder keeps the liquid and gas in the tank shell separate as the tank empties, and may also keep the fuel under some static pressure. If there's no air to draw into the fuel lines, then no matter how the aircraft is oriented or how many Gs it's pulling in any direction, the fuel lines can't be starved.

Of course, the fuel lines are only one consideration. Most "normal"-rated aircraft have float-type carburetors, which hold a reservoir of fuel with another air gap, and the fuel level in the reservoir is controlled by a float that opens the inlet from the fuel pump (this system also deals with small hiccups in the fuel flow from the tanks; the air just forms part of the air gap and the float keeps the inlet open until fuel flows in to raise the level). This type of carb will starve the engine during any maneuvers involving less than 1g of force acting towards the "floor" of the float chamber, as the float will keep the inlet closed and the reservoir will starve the fuel feed tube that allows fuel to dribble into the throttle body at the throat. For aerobatics, either a diaphragm-chamber carb (which has a flexible wall on one side of the reservoir chamber that is connected to the fuel inlet) or a fuel injection system must be used to avoid dependence on gravity to get fuel into the engine. The downside of these systems are increased complexity, and in the case of the diaphragm-chamber carb, intolerance of air this far along the fuel system (requiring an air bleed to purge any bubbles in the line before the fuel enters the reservoir).


Is the life of pets considered when dealing with a cargo fire indication? In this event, the crew of a 777 responded to a spurious cargo fire indication by activating the fire suppression system, which suffocates the cargo area. Presumably any pets held there would have died as a result.

What are the SOPs for fire suppression when carrying pets in the cargo hold? Are they held in a separate compartment?

What happens to live animals in cargo depends on the type of airplane and the class of cargo compartment they're traveling in. For a typical passenger airliner, if you check your animal as baggage, they're going into the "lower lobe cargo compartment" under the cabin floor. This is classified as a Class C compartment, which essentially means that the crew have no access to it in flight, so it must contain fire detection and extinguishing systems. The applicable regulation is 14 CFR 25.857.

Quite simply, there are no considerations for live animals in Class C compartments. If you look in Boeing cargo fire checklists (copyrighted so can't post here, but you might get lucky with Google), the steps in the checklist deal with discharging the Halon into the cargo compartment and adjusting the pressurization system to minimize flow into the cargo compartment. This helps maintain the minimum required Halon concentration to provide the first big knockdown blast to stop the fire from spreading, and then maintain a low-level concentration to keep it suppressed for the length of the diversion to a landing. Unfortunately, that means any live animals will suffocate since Halon displaces oxygen.

For dedicated freighters such as the 747-400F/747-8F/777F etc., the main deck area is considered a Class E cargo compartment, which doesn't have a fire extinguishing system. If a fire is detected here, the procedure is to depressurize the entire cabin and minimize/cutoff air flow to the main deck area, and climb/descend to a mid-altitude (somewhere in the 24,000-28,000' range depending on the airplane) to minimize oxygen and help suppress the fire. If animals are transported here, rather than the Class C lower lobe compartments, they may survive. They may become hypoxic and lose consciousness, but there's no Halon to suffocate them. Depending on the length of time for the diversion to safe landing site, the lack of oxygen may be a serious issue for some animals just as it can be for humans, but that's a guess as I'm not a vet.

Bottom line is if you're taking your pet with you on a commercial flight, the safest, most comfortable, and least traumatic place for them is with you as a carry-on item.


Is it possible for a fighter jet to shoot itself down with an IR missile? In this answer, it's mentioned that

  However, IR missiles (AIM-9 Sidewinder, AA-11 Archer, MICA IR, ASRAAM) do not emit any EMR that indicates they're incoming; they use a passive FLIR sensor to identify and track the heat source they were told to kill (they don't even require a radar lock; the seeker can be cued to a pilot's helmet, or it can be "uncaged" and will lock on to the most significant heat source in front of it).

Emphasis added.

Given this, is it possible, given some very bad luck, for a fighter jet to fire an IR missile, only for it to get turned around somehow (for instance, by some sort of momentary combustion instability in its rocket motor, or by some very bad turbulence) and end up locking onto and shooting down the jet that fired it?

Not really, it would take any of these missiles so long to turn 235 degrees (way more than 6-10 secs), which is generally the maximum burn time of most of their rocket engines. Plus, if it did somehow, get turned around 235 degrees, the energy (airspeed) bleed from such a large turn would leave it without any energy to intercept the launch aircraft even if by some miracle it acquired an IR lock


How did the term PAN PAN originate? Where did  the phrase  " pan pan"  when declaring an emergency originate?

Wikipedia has an un-cited reference to the etymology being

  As with mayday (from venez m'aider, "come help me"), the urgency
  signal pan-pan derives from French. In French, a panne ([pan], "pahn")
  is a breakdown, such as a mechanical failure. In English, it is also
  sometimes[vague] pronounced as /pæn/ ("pan").

This article supports that history (and has many of the other emergency phrase histories as well).


What is the purpose of the shuttle valve in a Piper Arrow's landing gear system? This is the PA-28R-201 landing gear hydraulic system diagram.

I am wondering how this shuttle valve functions.  Research I have done indicates that a shuttle valve blocks one attachment to the valve while allowing another to run through.  Only one side or the other, not both or neither.

In the diagram below, everything beneath the shuttle valve is a closed system (other than the thermal relief).

Clearly, the valve cannot be closed on one side or the other or else the pump would be applying pressure through three pistons to a closed valve at the other end of the loop.

Is this shuttle valve different than what I have read them to be?  Is it perhaps in actuality that both sides are either open at the same time or both are closed at the same time but never one closed while one is open? If one remains closed, how could the pump move fluid through the complete circuit?

The shuttle valve is actuated by high or low pressure depending on what you select, gear up or down. It routes the hydraulic fluid to the bottom of the cylinders to raise the landing gear with high pressure, or to the top of the cylinder to lower them with low pressure and to allow the fluid to return to the reservoir.


Why is not every airplane equipped with 3 angle-of-attack sensors? For critical systems, redundancy is built into the system. It is common knowledge among designers/architects to have three different inputs so in case one is faulty, input from the remaining two can be used to find (and shut off possibly) the faulty one (two against one).

Why is not every airplane equipped with 3 angle-of-attack sensors and triple modular voting when these devices are critical for the safety?

Triple redundancy is necessary to detect a fault and exclude it. The system then continues to operate through the fault. Double redundancy is used to detect a fault but cannot exclude it, so the system stops operating. The important fact is that the faults they actually detect are identical.

Stall events are rare and are normally not expected in flight. There is no immediate hazard if handling augmentation or stall warnings are disabled. Therefore, there is no need for triple redundancy.

Simply put, if the system detects an AoA discrepancy, it can simply trip off and stay off until it is repaired on the ground.

If the double redundant system is ideally designed, then only a simultaneous fault will escape detection. Note too that if the same simultaneous fault occurs to two sensors in a triple redundant system, then it will also escape detection because it will outvote the correctly operating sensor. Therefore, both systems share the exact same failure mode.

Double and triple simultaneous faults can and do occur with common causes including environmental factors (AF 447), maintenance errors (XL 888), and birdstrikes (US 1549). It also allows faults in the voting logic (QF 72). Both recent AF and XL fatal accidents are signs of an overreliance of buying 3 of the same box and then calling it "safe".


How do KFm step airfoils work? I was looking for airfoils, and I came across an interesting design. It's called a KFm1 step airfoil. Those of you in model aircraft design might have heard of it. However, I've never really seen one of these in normal aviation.

My questions are:

Why don't they work for full sized aircraft?
Is there some way to make them work?
What gives this airfoil its properties?

The idea works but only with active automated re-configuration of the
  shape of the step(s) during flight. Further testing has shown that
  this airfoil is effective in low Reynolds number flow.

source: Wikipedia

The Reynolds number is indicative of the speed of the airflow over the wing. The higher the speed, the higher the Reynolds number and vice versa. This is why they would be more suited for model aircraft rather than large aircraft which would experience higher Reynolds numbers.


How does the wheel speed sensor in a Boeing 777-300ER work? I do have a maintenance manual that I found on Internet, but it doesn't have anything about the wheel speed transducer.

Any pics along with the information would be helpful.

From this Aviation Studies project report of group 2A2I at the University of applied Sciences in Amsterdam, for a Boeing 777-200:

  Every wheel is equipped with an anti-skid transducer (appendix VII),
  which is installed in the axle. The transducer consists of a rotor and
  stator. According to the speed of rotation, an electrical signal is
  send to the BSCU.

  This computer compares the rotation speed of all the
  wheels and detects when a wheel is rotating slower than the other
  wheels on the MLG. The BSCU will send a signal to reduce braking power
  when the rotation speed of one wheel reduces more in comparison to
  other wheels.

The principle is the wheel axle drives a permanent magnet within a 3-phase winding. The frequency of the signal generated is proportional to the wheel angular speed.

From B777 General Familiarization Manual:

Antiskid and Autobrake Diagram, source

Note: I initially believed the tacho-generator was a Socitec ST80, the same than on A320 (part number is C20105000). However when I wanted to provide a supporting document, I couldn't. So please take this as an assumption only until someone provides the part number from a Boeing document (I don't think there would be a big difference between B777 and A320 tacho-generator anyway).

Tacho-generator, part C20105000, source

More information: Bodet Aero. According to Bodet Aero, their tachometer equips A300, A310, A319, A320, A321, A330 and A340.

More about tachometers: TheAirlinePilots (section "Three Phase AC Electrical Tachometer").

This is a typical installation of the transducer (not a particular aircraft):

Source


Does an overhaul reset the 'life limit' of a turbine engine? I've come across a very unclear maintenance document.  It's often referred to as a "Hard Card" for an Engine Axial Compressor Turbine.  This specific part happens to come from a French manufacturer, so there may be a language barrier issue involved, but I'm trying to determine if anyone has clarified documentation that discusses this issue.

(Source: helisupportnz.com)

On this card, beneath a section translated as "Available Life", "Module Life Limited Parts", and "Usage Limited Parts", there is a section translated as "Time for the Calendar Limit".  Next to this is another section translated as "Date for First Entry into Service" and a logical third calculated section translated as "Limited Date for Usage".

These connect with each other very clearly and easily.  For example, one card marked with a 15 Year Calendar Limit is showing a Limited Date for Usage of 2020 when the Entry into Service was 2005.

I have a maintenance technician who is under the impression that this Calendar Limit is reset after every Overhaul of this Engine Module.  Unfortunately, no where in this card does it say that this is the case, and if this module gets reset when it is actually a Life Limit, then we will run into an overfly.

Has anyone come across this and received a clear answer from someone in authority over this?

All nations operate with very similar rules. For the US, the short answer is nearly all turbine powered aircraft operate under part 119/121 (air carriers) rules. Each company has maintenance and operations specifically tailored and tied to their operating certificate and so it depends on the approved procedures of that companies operating certificate.

In your example, no mention is made of the part being "rebuilt", therefor the use of the part will continue where the previous use left off. The card says it is a "life limited" part so it's use will run out according to operating hours, calendar time from first installation, or number of operating cycles, etc. The parts life span is set by the mfg or operating certificate rules.

For example if a part  has a 7yr calendar "life limit" (like some seat belts) and the part was installed January 1, 2015 then removed 10 days later, the part would become worthless Jan 1, 2022 even though it was used less than 1 month - the clock starts ticking from it's first use.

This card says the part has a 15yr calendar limit which will usually be in addition to other limits. It will either be limited from it's first date of use, or it's date of manufacture (whether the part is used or not). Once again, exactly how it should be interpreted will be based on the mfg or operating certificate rules.

Most life limited part life spans are TIS (time in service) and therefore expire after a certain number of hours of operation. If TIS for the turbine blade is 5000hrs and airplane "A" used it for 4000hrs, it could remain on the shelf indefinitely - be re-installed on airplane "B" and used for an additional 1000hrs. The card is designed to keep track of the dates and how long the part has been used - TIS, calendar, cycles, or whatever.

[I'm guessing for this particular part, but for many critical parts on helicopters and turbines a combination of TIS and calendar are used. So it would be something like 5000hrs TIS or 15yrs calendar from date of mfg - whichever comes first. Even if it sat on a shelf and was never used, it would have to be destroyed when the 15yr limit was up.]

NOTE: Due to a problem of expensive time limited parts being counterfeited, re-sold, or re-used, the FAA requires companies using life limited parts (once the service life is up) to make the part unusable by returning to a mfg, defacing, or destroying it.

Parts

On any US registered aircraft, "overhaul" and "rebuild" have very specific legal and maintenance meaning. "overhaul" per FAR 43.2(a) means "Disassemble, cleaned, inspected, repaired, reassembled, and tested to service limits", whereas Rebuild FAR 43(2)(b), 43(3)(j) means "disassemble, clean, inspect, repair, reassemble, and test to new part tolerances".

"Overhaul" means repair or fix the old part and does not change the wear or life of a part.

"Rebuild" means to make a "new" part out of the old one and the part's life is started over - "zero time". The part is treated as if it is a brand new part and many mfg even stamp a new serial number on the part.

Entire Engines

The above FAR's relates to "parts". For an entire engine, the FAA's AC-43-11 (Reciprocating Engine Overhaul Terminology and Standards) goes into great detail on what the terms mean and who may perform the work.

Why would AC-43-11 (entire engine) be limited to reciprocating engines? Because nearly all turbine engines are operated under Part 119/121 (not 91 or 135) operators. Part 119/121 receive FAA approval on a company by company basis and each company has maintenance and operations specifically tailored and tied to their operating certificate.

When a part 119/121 company has their operations approved, the FAA's standard practice is to hold them to all existing FAR's unless they show a "as good" or "better" way of maintaining the same level of safety. So, the spirit of AC-43-11 would be applicable unless some exception was given.


Does flying an airplane upside down imply negative AoA? Why? I saw the statement below in this answer:

  Note that for normal level unaccelerated flight $C_L$ is always > 0. The minimum $C_L$ is a negative value for negative AoA, and would mean that the aeroplane is flying upside down.

This would seem to me to imply that flying an airplane upside down implies a negative angle of attack.

But the typical illustration and explanation of angle of attack is that it is the angle between the airstream and a reference line, the latter of which in airplanes is normally the wing chord.

How can the two be reconciled? Alternatively, what am I missing?

Level flight (no change in altitude) upside down, with an airfoil with a zero-lift AoA of less than or equal to zero degrees, requires a negative AoA to get upwards lift.

This is assuming the AoA is measured in the body frame of the aircraft, aligned with the chord line of the airfoil.

Also this assumes there is no thrust/drag or thrust/drag do not meaningfully contribute to vertical net forces.


Why is a canard configuration more Structurally efficient for Rutan's Voyager? Firstly, I’d like to kindly request not to mark this question as a duplicate of previous SE question without first reading this, because the approach is different and the previously given answers are merely incorrect.

Background

I found this information in VoyagerEssay.pdf from Burt Rutans website.

EDIT: I am putting this possibly redundant info with the hope it might help better clarify the problem as suggested.

From Burt's own notes.

  The range of an aircraft is determined by three basic criteria: its
  propulsion efficiency, its weight and its aerodynamic efficiency. I
  had to make major improvements in one or more of these areas in order
  to build an aircraft that could fly more than twice as far as any
  previous flight.

Please see "breguet-range-equation" for more info. And this range equation suggests us the range of an airplane is exponentially sensitive to the initial and final weight ratios; and linearly sensitive to L/D and total propulsive efficiency eta.

And as the per the same source, this configuration was chosen to achieve higher structural efficiency.

  The primary reason we were able to double the old record related to
  our success in weight control. By using a new, unusual configuration
  we could place a large amount of fuel at three span-wise locations:
  the fuselage and two large booms at 30% of the distance out to the
  wing-tips. A very light main wing and canard wing provided just the
  amount of structural support for this large fuel mass. The two wings
  supported the fuel-laden booms via their bending stiffness without
  depending on the torsional stiffness of a single slender wing. This
  was Voyager’s secret to success. Its graphite composite structure
  weighed only nine percent of the take-off weight. The fuel consisted
  of 73% of the take-off weight. This phenomenal weight performance was
  the main reason we were able to achieve our goal of true global range.

And of course in return traded off aerodynamic efficiency.

  Regarding aerodynamic efficiency, I was unable to achieve a result as
  high as a typical sailplane since I was forced to use the unusual
  configuration

In this John Roncz presentation, he mentioned this configuration was to solve the problems of having high inertia fuel booms, [~18 mins] but without any specific note on how it resolves into a canard.
As per Mr. Roncz, he appears to suggest this minimizes the bending stresses of the booms. (Please correct me if Im wrong) and note from Burt appear to suggest the config was selected to minimize wing torsional loads.

Question

Can any of you please provide me with an explanation as to why the canard configuration ideally could be more beneficial for this design?

My argument is if he had chosen the second config shown below, he would have gained BOTH structural benefits of canard plus aerodynamic benefits of conventional config.

In my eyes, this is an even better win-win solution but most certainly too good to be true; hence my question.

If possible I would love to see some quantitative answer rather than qualitative but any constructive answer is more than very welcome.

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

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

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

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

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

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

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


What exactly is a BITE? I read that with each LRU or Module in the IMA it is associated a BITE, Built-in-test Equipment.

Can you describe more in detail what it is and which is its scope?

Built In Test Equipment is part of a system that monitors the correct functioning of that system. It produces an alert if part of the system fails to fulfil its function.

An example would be a system with two sets of memory chips; the BITE would copy all data to set 1, then test memory set 2 by writing and reading various test patterns. If the read pattern is different than pattern written, there is a memory error. If so, an alert is raised. If not, all data is copied to set 2, and set 1 will be tested. This is procedure is repeated at specific intervals.

Another example would be a watchdog timer which triggers a signal if a timer runs out. If the system is working correctly, it will reset the timer before it runs out. The signal from the watchdog can then for example reset the hardware, take some corrective action or raise an alert.


What happens to the high pressure below an airfoil when the angle of attack increases? I recently came across this question in a principles of flight exam:

When the angle of attack of an airfoil increases

the high pressure below the airfoil increases, the induced drag increases
the high pressure below the airfoil decreases
the induced drag decreases
can't remember this option

I chose 1. as the correct answer and it looks like I got it wrong. Although, I cannot tell for sure.

I know the induced drag will increase, but will the high pressure underneath the airfoil increase or decrease with an increase in angle of attack?

I'm pretty sure you were right. More angle of attack means more lift. More lift is caused by higher pressure under the wing and lower pressure on top. More lift causes more induced drag.


What prevents a Machmeter from being the standard airspeed indicator? Airspeed is more accurate when displayed by a Machmeter than when displayed by an airspeed indicator. It isn't affected by ambient temperature / density changes. It is still affected by position error, hence it must indicate something between IAS and CAS.

Source, source

What does prevent to have a Machmeter scale both in knots and Mach numbers, and use the Machmeter in place of the airspeed indicator, as the standard airspeed instrument?

Such instruments exist:

Source (From FAA Airplane Flying Handbook)

Machmeter-based tachometer would not indicate something between IAS and CAS, it would indicate TAS but for the same¹ instrument and position errors the normal airspeed indicator has.

However, airspeed indicator does not indicate true airspeed and this is intentional.

The EAS, that the airspeed indicator is aiming to show, is a measure of dynamic pressure. Since lift, which also includes effectiveness of control surfaces, is proportional to dynamic pressure and drag is also a function of dynamic pressure, most handling characteristics depend on the dynamic pressure. Therefore the value indicated by the airspeed indicator is exactly what the pilot wants to know.

The only effects that depend on other speeds are aeroelastic flutter, which depends on true airspeed, and compressibility effects, that depend on Mach number. Both limit the maximum safe speed. That is why fast aircraft also need Machmeter. But they still need the indicated² airspeed.

¹ Both instruments use the same two raw values obtained from the pitot-static system: total and static pressure. The airspeed indicator shows square root of the difference (because dynamic pressure is proportional to square of speed), the Machmeter shows the ratio to some fractional exponent. So all the errors affect both the same way, and in electronic instruments, they are compensated² to the same extent.

² Electronic systems in modern airliners say to show CAS, correcting all errors they can reasonably estimate.


What does it mean when ATC says "altitude indicates"? I've noticed that ATC sometimes calls out traffic (a traffic advisory?) to aircraft using the "altitude indicates" phraseology, and sometimes a specific altitude is given without the phrase "altitude indicates".

Is there a specific reason for when they use one over the other?

"Altitude indicates" means that the aircraft has a Mode C transponder but it isn't receiving radar service, i.e. it's VFR and not on flight following. In other words, the transponder is reporting an altitude, but because the aircraft isn't in contact with ATC, they can't be sure about its altimeter's integrity or the pilot's intentions.

See the ATC orders 2-1-21:

  For aircraft displaying Mode C, not radar
  identified, issue indicated altitude


Longitudinal stability of airships: How is the critical speed defined? Airships are unstable in pitch above a certain speed, called the critical speed. What causes the instability, how does it manifest itself for the pilot, and how is the critical speed defined and determined?

On page 43 of the Technical Manual of Airship Aerodynamics I found the following image:

Here $F_e$ is the resultant airforce on the hull, or the dynamical lift of the hull. As this is before the CoG, it is destabilizing.
This source mentions Munk's formula being:
$$ M_e = Volume \cdot 0.5 \rho V^2 (k_2-k_1) \sin{2\theta} $$
Where $k_2$ and $k_1$ indicate the effect of gas movement inside the airship.
I tried to trace the origin of this formula in Munk's paper, available here, but I can't immediately find a clear explanation.

The critical speed is reached when this resultant airforce equals the moment induced by the weight:
$$Wh\sin{(\alpha + \theta)}=Volume \cdot 0.5 \rho V^2 (k_2-k_1) \sin{2\theta}$$

In this sense, the critical speed is the maximum speed at which the gravity moment is able to compensate the moment induced by dynamical lift. As such, one should stay below the critical speed.


What degree is crosswind? I know that there are three type of wind, headwind, tailwind and crosswind.
What degree of wind direction can distinguish it? 30 or 45 degree?

Manu H has given what, to me, sounds like as close to a textbook answer as you can get.
Crosswind is always 90° to your direction of travel. You base crosswind off of your track instead of your heading. Regardless of your track or heading, or the wind direction, the crosswind intensity would be a percentage of the total wind intensity ranging from 0% to 100% coming from 90° to your direction of travel. You can find the numeric value of the crosswind using Pythagorean’s Theorem. The headwind/tailwind component and the crosswind  component make up two of the legs of the mathematical 90° triangle. The actual wind bearing from your direction of travel and its intensity make up the hypotenuse.
Or, you can use the graph, below:


Why is airflow forced to be speed up on the upper surface of an aerofoil? As the title says: Why is airflow compelled to flow further over the upper surface of an aerofoil? I understand because it has a larger distance to travel, but why can't the airflow travel at the same speed as the airflow underneath the lower surface?
I understand how the Bernoulli effect works but there is no constriction in an aerofoil, why does it speed up with the Bernoulli effect; without the constriction?
I also understand that the there is a wrong theory that airflow over the top of the wing wants to meet the airflow on the lower surface at the end of the aerofoil, at the same time.

Airflow isn't compelled to do that by some edict.  It just does it.  "Why" isn't all that meaningful, compared to a theory or formula with predictive power.
Bernoulli says that, under certain conditions, a fluid's speed and pressure have a certain relationship.
How a fluid flows past a obstruction, and what net forces and torques it exerts on that obstruction, aren't because of Bernoulli.
The closest we can come to a reason for the fluid's behavior is the Navier-Stokes equations.  But that's still a model, a simplification.

For an airfoil in conventional steady flight, it's actually more useful to say the reverse:  because the airfoil has been carefully chosen to generate lift under those conditions, the pressure above must be less than that below, so Bernoulli predicts that the flow above must be faster than that below.  And we can confirm that with CFD simulations or with onboard sensors.


Is it allowed to listen to music while piloting a plane? When I'm driving my car, I almost always put some music on. It's really relaxing for me.

I know that piloting a plane is nothing like driving a car, but it would be great, at least for me, to listen to some music while piloting.

So here is my question:

Is it allowed to listen to music while piloting a plane? Maybe with some device that mutes the music when someone is speaking in the radio?

Many aviation headsets either have an Aux-jack or a bluetooth connection, and listening to music is specifically mentioned as a feature.

(Link to headset)
(Link to adapter)

Some headsets even have a feature that detects radio-communications, and immediately silences the music.

The FAA has no problem with pilots listening to music provided its not distracting.   Individual company policies may differ.


Cruiser-Feeder Concept - feasible? The people from cruiser-feeder started a project called RECREATE.

  However, for the concept with fuel transfer from feeder to cruiser (civil air-to-air refuelling operations), the results of our collaborative research indicate a fuel burn reduction potential on isolated aircraft level between 11% and 23 % for a typical 6000 nautical miles flight with a payload of 250 passengers.

That sounds very good, doesn't it? I answered this question about civil air-to-air refuelling with the cruiser feeder concept. A User said:

  with the Breguet equation it is easy to see that the savings are modest.

And:

  This concept will never be certified

They even created a high-realistic simulation environment in which they tested the refuelling-process with real pilots as you can see in this video.

The feedback from the pilot is very good and promising that the concept might become real.

I'm curious why the savings are modest, because the planes can reduce the fuel burn from 11% to 23% and why this concept will never be certified.

Can the cruiser-feeder concept become real? That a feeder pumps fuel to a cruiser after he took of?

When does the use of the feeder burn more fuel than it saves?

What could stand in the way to make the RECREATE Project become real?

The system is highly impracticable for a number of reasons.

The referred paper acknowledges that the fuel savings due to existing tankers are negligible and a new design is required. I doubt anyone is going to develop this. Even the military uses modified civil airliners for its tankers needs. Development of the tanker as outlined in the paper will cost billions of dollars and no one is going to do that for a handful of tankers.
Even if such a tanker is built, the existing aircraft will require significant modifications for in flight refueling (assuming that the tanker is standardized from day one, which is practically not possible; even the US armed forces use two different type of tankers). Basically, the structural weight goes up,which reduces performance and increases fuel consumption.
Then the pilots have to be trained for operations of both the aircraft. In flight refuelling is potentially dangerous.See http://foxtrotalpha.jalopnik.com/aerial-refueling-hooking-up-is-hard-to-do-1559495801. Nobody's going to take that risk with civil operations.
The study is extremely simplistic. modern civil aircraft fly in a number of 'flight levels', separated by set altitude. So, for refueling, either the tanker or receiver should climb or descend the difference in altitude, and that burns up more fuel.
If carrying extra fuel in the aircraft is dead weight, it makes no sense to carry it in another aircraft and pay for its operations and maintenance.
It is not correct to compare the military and civil operations. Their priorities, methods and end goals are different. What looks good on paper may not work on real life. Remember Concorde?


What is the Function of Pressurization Light on Exit Doors for Commercial Airliners? I am well aware that the average human is unable to open plug doors in flight due to pressurization of the cabin. I've noticed, however, a "cabin pressure" warning light in the window of exit doors, and specific instructions to not try to open the door when the light is on. Is there an actual danger of someone outside the aircraft being able to release something in or around the door while the cabin is under pressure, or is the light simply to indicate why they would be unable to move the handle?

It is there to prevent "violent door openings":

(figure 1b source)

  In some abnormal cases, outflow valves can remain closed, when the
  aircraft is on the ground, causing the air pressure in the cabin to be
  higher than the ambient air pressure outside the aircraft (fig.1b). In
  this case, there is a risk that an aircraft door could violently open
  and injure the operator or damage the aircraft.

(fig 2 source)

  The Residual Pressure Warning Light (fig.2), part of the residual pressure
  warning function, warns anyone who wants to open a door if the
  aircraft is pressurized. This device is installed on all Airbus
  aircraft except for some A300, A310 and A300-600 where it was offered
  as an option. On these aircraft not fitted with the warning light, a
  caution placard located on the door reminds the operator of the risk
  that residual pressure may cause violent door opening.

This brief from Airbus has a lot of good info on residual cabin pressure as well.

Not to be confused with the "Slide Armed" light.


How to select and electric propulsion system for my experimental Ultralight? I've been trying to design and build, my experimental Ultralight using electric propulsion system, My plane designed base on Slaler and Gensis ultralight , following is the primary calculation

Empty weight 120KG

Wingspan 9.1

Length 2.8

cruise speed 120 Km/h

propulsion 20kw

I'm trying to select a pair of Brush-Less Direct Current motors (BLDC) for my airplane, but I have no experience using BLDC's before, whereas there is a lot of BLDC ambiguous options (mostly in Aliexpress) which claim to be a different KW.

My design goal is to find the best possible options for propulsion to have longest possible flight time duration.

Following is the 3D image of my design (located in my GrabCAD account)
any advice really appreciated

FLÜGEL World Directory Of Light Aviation 2019/2020 - English PDF could be a good starting point. On pages 278 - 281, a total of 71 lines of electric motors from 42 manufacturers are featured. Disclaimer 1: some data fields are incomplete for many of the entries. There are German, English French and Chinese versions in paper and pdf, starting at €8. Here's the paper version in German:
Welt-Index Ultraleicht und Flugzeug 2019/20 Wings of the World

In any version, the aircraft listings themselves may also be of interest, as aircraft models which are available with electric motors as the primary powerplant are highlighted with a green e icon. In browsing those, you may glean some emperical inspiration in terms of electric motor vs aircraft size. Disclaimer 2: the power-plant details for the aircraft listings are not always complete.

The free annual e-flight Journal by the same publisher includes motor manufacturer adverts which may be of some use.

Lastly, at the end of the online Kitplanes 2020 Engine Buyer’s Guide are four electric motors from one manufacturer.

Final Disclaimer: I have no vested interest in these magazines, publisher or any products listed or advertised.


What noises are considered worrying on a passenger flight? As a typical 'nervous flyer', I often find myself asking crew about a noise that they say is completely normal during flights. The thing is, I've flown a lot and still hear new sounds sometimes!

For example on a recent Easyjet Airbus flight, when the aircraft went into full throttle to take off, a loud whirring/buzzing sound started and lasted the whole flight (I was sat on the wing)... still no idea what that was.

So what is a general list of sounds that are to be expected vs a list that tells you that you are all but doomed :/

Let's keep this to an Airbus Easyjet might use to keep it a short(er) list.

The only noise (other than a clear and obvious explosion) that gets my complete and immediate attention is "This is the captain..."


Is there a way to avoid fuel loss caused by vaporization from engine heat? Concorde had engines directly attached to the wings, close to the fuel tanks. Some fuel was evaporated due to heat. What were the reasons to not use pylons or some cooling system to limit this effect?

According to this image of the locations of the Concorde's fuel tanks:
Borrowed from: ConcordeSST.com
and this image of the location of the Concorde's engines:
Also from ConcordeSST.com
It doesn't appear that there is a lot of room for direct transfer of heat from the engines to the fuel tanks.
Also of note, the Concorde's designers intentionally used the fuel for other cooling purposes:

The fuel is also used as a heat sink for cooling purposes. Surplus heat from the air conditioning and hydraulic systems from the constant speed drive and generator and also from the engine lubricating oil is rejected through heat exchangers to the fuel.
--ConcordeSST.com

Based on this, I would say that the amount of fuel vaporized by engine heat was minimal at best, and, therefore, of no concern.


What is a public airport? I know that ALL airports that have received federal funds are considered to be open to the public, however does that mean that every "public" airport was federally funded?

You can check out this info from the FAA

And the official FAA definition:

  Public use airport is an airport available for use by the general
  public without a requirement for prior approval of the airport owner
  or operator.

It should be noted that 4 airports in the US are considered "High Density" and have special rules about operations during certain times which require approval for use (arrival/departure) despite being public.

  §93.125   Arrival or departure reservation.

  Except between 12 Midnight and 6 a.m. local time, no person may
  operate an aircraft to or from an airport designated as a high density
  traffic airport unless he has received, for that operation, an arrival
  or departure reservation from ATC.

In answer to the question as its now worded,

No, there are public airports that are not federally funded. The airport I currently fly out of KDYL is owned and operated by the local government (Bucks County) and they are responsible for most things that go on there. I am not sure if they have received Federal funding in the past but I will ask around.

There is also such thing as "Privately Owned/Publicly Used" (elsewhere called POPS) airports like Trenton Robbonsville N87. These airports are owned privately, run privately, and generate their own income however you don't need to prior approval to land there and are open to general public use.