126
votes
Accepted
Why do we need to starve the engine before turning it off?
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 ...
- 49.5k
91
votes
Accepted
What is the difference between a turbofan and a turboprop engine?
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 ...
- 69.7k
84
votes
Accepted
Could a Dyson fan scale up to be used as a bladeless aircraft engine?
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 ...
- 17.7k
77
votes
Accepted
What are the differences between fuel types (comparing with vehicles)?
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 ...
- 67.2k
76
votes
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Should the helicopter be washed after any sea mission?
The helicopter shown is an Anti-Submarine Warfare Helicopter. ASW helicopters generally have the ability to detect submarines either Passively or Actively. Passively, sonar-buoys are dropped into the ...
- 1,166
60
votes
Accepted
What's wrong in this engine test cell picture from the book 'Ignition'?
I think there's a mix-up in the labeling of the photo.
Here's the photo and caption from a copy of "Ignition" that I just downloaded:
Here's the photo and caption from the next page:
Seen together, ...
- 616
55
votes
Why are many jet aircraft designed to cruise around FL350-370?
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 ...
- 898
54
votes
Which manufacturer produced this fan blade?
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 ...
- 5,228
51
votes
What are the least powerful airplanes that ever flew?
There are a number of human-powered aircraft (list here). For the Gossamer Albatross, we have
In still air, the required power was on the order of 300 W (0.40 hp),
though even mild turbulence ...
- 2,839
49
votes
What is the rationale for single engine military aircraft?
Because single engine fighters are substantially cheaper to purchase and operate. Exact figures are hard to obtain, but as an example, an F-15 squadron will spend about 25,000 USD per flight hour ...
- 65.5k
47
votes
Why don't airplane piston engines have mufflers?
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 ...
- 218k
47
votes
Why then don't aircraft fly even higher, for even greater efficiency?
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 ...
- 96k
44
votes
Accepted
Why does afterburner exhaust have "pulses"?
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 ...
- 1,432
44
votes
Accepted
What is the significance of 104% for throttle power and rotor speed?
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. ...
- 39.2k
41
votes
What is a rubber engine?
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 ...
- 218k
41
votes
Accepted
Is it allowed to let the engine of an aircraft idle without a pilot in the plane. (For both helicopters and aeroplanes)
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 ...
- 104k
41
votes
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What are the most powerful airplanes that ever flew?
Most thrust overall?
Well the most powerful aviation gas turbine to date is the GE90-115B, producing a whopping 115,000 lbs of thrust per engine at maximum static thrust settings.
Overall the ...
- 65.5k
39
votes
Accepted
Why are many jet aircraft designed to cruise around FL350-370?
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 ...
- 69.7k
38
votes
Why do we need to starve the engine before turning it off?
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 ...
- 17.4k
37
votes
Accepted
Can hydrogen gas be an alternative fuel source for a gas turbine engine?
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 ...
- 218k
36
votes
Why does the 747 have 4 engines instead of 2?
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 ...
- 41.9k
36
votes
Accepted
What is the rationale for single engine military aircraft?
Fighters don't carry passengers.
The figure of merit for combat aircraft isn't passenger-miles flown between accidents, it's objectives completed (like enemy targets destroyed) per billion dollars ...
- 17.7k
35
votes
Accepted
Why do new engines have a case with a triangular tiling pattern?
This type of structure is called isogrid structure. Solid walls are usually very heavy and therefore engineers use more weight-efficient structures such as sandwich structures or stiffened structures ...
- 4,098
34
votes
Accepted
Why do we never see high-bypass turbofan engines sharing the same nacelle on large airliners and similar aircraft?
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....
- 218k
33
votes
Accepted
Can you identify this engine?
It appears to be a Rolls Royce Viper turbo jet engine made in 1966. The maker's mark (BSB) derives from Bristol Siddeley, formed from Armstrong Siddeley (the company that originally developed the ...
- 3,026
32
votes
Accepted
Are all the engines on a multi-engine plane the same?
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 ...
- 218k
32
votes
Accepted
Why is the front part of the engine not painted?
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 ...
- 3,113
31
votes
Accepted
What are cowl flaps?
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 ...
- 10.5k
31
votes
Why are all engines identical in typical commercial airplanes?
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 ...
- 1,506
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