Hot answers tagged

118

The reason is the large spinning thing on the front. Residual fuel in the engine has been known to auto-ignite (i.e. combust without a spark), causing the prop to spin, causing serious injuries and deaths. A lean cutoff reduces the risk that someone handling the prop will get maimed or killed. In a car when you turn the engine off usually it is in park or ...


82

No. Not a useful propulsion engine. The first problem is power. The air stream from Dyson's fans is weaker than what you can get from a conventional fan the same size, and jet engines need a very powerful stream. You'll notice they're quite heavy as well; Dyson AM-06 has a thrust-to-weight ratio of just 0.06, 100 times less than a jet engine. The second ...


80

Both engines use a turbine for power. This is where the "turbo" part of the name comes from. In a turbine engine, air is compressed and then fuel is ignited in this compressed air. The energy produced by the ignition turns the turbine. The turbine is then able to drive both the compressor at the front of the engine and also some useful load. In airplanes, it ...


76

Broadly speaking, there are three families of motor fuel that you're probably interested in: Diesels, Kerosenes, and Gasolines. The difference between the families mainly has to do with the molecular weight (and thus boiling point / vapor pressure) of the fuel components - in order above from heaviest to lightest. The differences within each family are ...


54

GE Aviation Clue 1. Parts designed at the Lynn MA plant have part numbers of the form xxxxTxxPxx, where x is a digit. 4922T12P01 fits that pattern. The gr.in is another clue. That refers to a weight that would be used in balancing the fan. GE uses units of gr.in. I'm fairly sure that Pratt uses oz.in, snecma uses gr.cm. I'm not sure what RR uses. But ...


47

Some do (or have in the past) but very high altitudes present their own issues. Historically the Concorde cruised anywhere from FL550 to FL600 and was actually allowed to climb and descend at its discretion up there since they were well clear of any traffic. However the increase in pressure differential on the airframe as well as supersonic flight meant the ...


46

In a word, the tropopause. Gas turbine engine efficiency improves with colder & denser air. As an airplane climbs through the troposphere, the density & temperature both drop, and the loss of density is more than offset by the lower temperature. Above the tropopause, however, the density continues to drop while the temperature holds (approximately) ...


44

This happens when the maximum output was changed after design. 100% is simply a reference to a certain value. In the space shuttle's case, the engine output was increased after the initial design. Instead of updating the engine value everywhere, they decided to simply keep the initial value constant. The same goes for N1 in turbo engines. 100% N1 is simply ...


42

A rubber engine is not to be confused with a rubber motor (a rubber band which is twisted in order to store energy which can be released when the rubber band untwists. This type of engine is good for short energy bursts in small model airplanes). A rubber engine is an engine deck (tables of engine data) which can be scaled according to your needs. In a way, ...


41

Today, most GA aircraft in Europe do have mufflers so they can pass the ever more stringent noise requirements. Here is one mounted to a Cessna 172 (picture source): Historically, mufflers were considered as a disadvantage because they reduce engine performance by increasing back pressure. By partially blocking the exhaust flow, the muffler increases ...


41

You won't see it done in the fixed wing world unless the aircraft is tied down or otherwise securely restrained (like when you tie off the tail to something when hand starting your no-starter taildragger; some pilots just use chocks or parking brakes to hand bomb their airplane, but it's a terrible idea). However, it's common in the helicopter world ...


36

Yes, and it has been demonstrated 30 years ago on the Tupolev 155. This is/was a hydrogen-powered version of the Russian Tu-154B tri-jet. Only one has been built and has since been retired after demonstrating the use of liquid hydrogen in 5 experimental flights. In total, the Tu-155 performed about 100 flights with several fuels, among them hydrogen and ...


35

Combustion in a gasoline internal combustion engine for most aircraft, requires four things: fuel, oxygen, compression and ignition. If the engine is starved of fuel, accidental combustion (and an accidental spinning prop) will not happen. So shutting off the fuel is one way to prevent accidental "start" if even for one stroke. Oxygen is ubiquitous and ...


34

Short answer It's the vastly different flow conditions from static to cruise which demand a separate placing of high-bypass-ratio jet engines. They would produce less thrust and more drag when paired. Why were there paired engines at all? The early jets had their engines mounted directly beneath or in the wing, and comparisons between separately mounted ...


34

Those are known as "Mach diamonds" or "Shock diamonds" (and a number of other names) and are not a characteristic of the afterburner per se but are formed by standing waves in the exhaust when the pressure of the expanded exhaust gases do not exactly match external ambient pressure. They can be formed by either over-expansion or under-expansion of the ...


33

Simply, more engines = more power, and power is needed for several things, the first of which is, taking off. At max takeoff weight, a multi-engine aircraft has to be able to lose one engine (after reaching the go/no-go speed) and safely continue the takeoff, which means that if you could just barely fly on 3 motors, you're going to have to have 4 to meet ...


32

There are multiple factors that affect an aircraft based on its cruise altitude. The cruise altitude directly affects the aircraft pressurization and aerodynamics. In order to keep the cabin altitude around 6000 to 8000 feet, the fuselage would have to withstand a higher pressure differential. This would require more material, and make the plane heavier. ...


32

The engine inlet lip is bare metal to facilitate anti-icing. The area is heated from within using hot engine bleed air. This partial schematic (from Boeing AERO QTR_01.12) shows the engine anti-ice valve, which controls the air supply to the inlet lip: Interesting side note: Even the 787 "no-bleed" system architecture uses bleed air for engine anti-ice.


30

Generally yes, but not always. If you include the APU as an engine, the answer would need to be different, but I understand your question concerns just the engines used for propulsion. For jets, the direction of rotation doesn't make much of a difference, so the same engines can be used on all stations. However, with propellers the swirl does influence ...


28

That looks very much like a TF-34 fan blade. The TF-34 is used on the A-10 Thunderbolt and S-3B Viking. The root style is known as "pinned" or "clevis". You can see a blade being pinned into the rotor hub in this photo: And there is a clear view of the blade root in this photo: U.S. Air Force Senior Airman Steven Valencia, 18th Component Maintenance ...


28

This airplane is based on the Airbus A300-600. The maximum take-off weight of the aircraft is 155 tonne as published in the wikipedia. In addition, the the manufacturer has published the Aircraft Characteristics for the base aircraft. If we assume that the aircraft low-aerodynamic aerodynamic characteristics has not been changed for the take-off phase (...


28

Engines don't fail, on average. And if they do, it's a very low probability that two engines will fail at the same time. Modern jet engines are extremely reliable, with failure rates on the order of 0.01/1000hrs. And if you do have a failure, you have redundancy, as you have two (or more) engines. A plane can stay aloft and land with a single engine. It ...


28

The bleed will be tapped from one or two of the 3rd, 4th, 5th or 6th High Pressure Compressor stages. Usually there are two bleed ports. The highest pressure port will supply really hot air for things like anti-icing. The lower pressure port farther upstream will supply air for air conditioning/pressurization and other pneumatics. Some systems combine ...


27

They are flaps or doors on the engine cowling that open up in order to provide increased cooling airflow for the engine. They look like this when open. They are generally controlled by a handle in the cockpit (some aircraft have electric cowl flaps with an open/close switch). The disadvantage is that the open flaps also increase drag. So on airplanes ...


27

The A-10 uses a GAU-8/A. According to Wikipedia: The average recoil force of the GAU-8/A is 10,000 pounds-force (45 kN), which is slightly more than the output of one of the A-10's two TF34 engines (9,065 lbf / 40.3 kN each). While this recoil force is significant, in practice a cannon fire burst only slows the aircraft a few miles per hour in ...


26

Both Bo-102 and 103 were experimental aircraft, with Bo-102 more of a jig than an actual aircraft. They were used a testbed for various technologies and the single blade rotor is only one of them , with the main thrust being in the development of (hinge-less) rigid rotor and (glass fiber reinforced) composite blades. The single blade rotor offers some ...


26

The air is compressed in the compressor section of the engine and heats up. Hot air is able to hold disproportionally more water in gaseous form than cold air, so all that water will vaporize and enter the combustion process together with the air. Since it is already vaporized, it will not absorb that evaporation enthalpy again that makes water such a good ...


25

Flying with only one of two engines will not increase range, but reduce it. A gas turbine consumes fuel in proportion to the mass of air moving through it, so with increasing altitude consumption decreases proportional with air density. Thrust goes down with density as well, so thrust-specific fuel consumption is roughly constant (actually, the engine ...


25

I know there is already an accepted answer, but some key facts are missing. Mainly, the optimum cruise altitude is where thrust and lift requirements for both take-off and cruise balance well. An additional benefit is the cooler air which increases the efficiency of heat engines. With increasing flight altitude, the airliner needs: Bigger engines to ...


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