34
votes
Why are turboprop intakes placed below the propeller?
Inertial separators are augmented by gravity when located under the engine. It is easier to discharge ingested ice and debris downward, rather than some other direction, so that is where they go if ...
- 21k
28
votes
What is this F-18 Hornet "air intake" for?
It's for keeping the boundary layer flow from entering the intake, it's called a splitter plate. I think it's done to prevent turbulence inside the turbine (prevent compressor stall) and to make sure ...
- 2,544
28
votes
Accepted
What are those half-vanes in the engine inlet of a 707-328?
You have a very interesting find there! It is in fact not an engine from a B707, but a Kuznetsov NK-8 from Russia.
It was used in Ilyushin Il-62 and Tupolev Tu-154 aircraft.
As for the intermediate ...
- 30.5k
25
votes
Accepted
If the intake of a running jet engine is blocked for some short duration what would be the sequence of events following it?
This explanation is for a subsonic aircraft, a similar process occurs at higher speeds.
Causes
A bird, an object or ice can disturb the flow of air entering the engine. Another source of compressor ...
- 80.9k
23
votes
Accepted
What are these small engine inlets on the Super Hornet?
These are the auxiliary air inlets for the ECS (Environmental Control System):
(image source)
They provide air to the primary heat exchanger (A18), which is then exhausted via the ram air exhaust (...
- 58.3k
16
votes
What is the difference between side-by-side vs under-cockpit engine intakes?
I wouldn't call the Su-27 small, but that is another issue.
The main difference is the wing planform. The Su-27 wing is optimised to work over all angles of attack up to 120° with very little pitch ...
- 237k
16
votes
Accepted
What is this tube in a jet engine's air intake?
That's the EPR inlet pressure sensor (there's another one located aft of the engine in the exhaust).
EPR = Engine Pressure Ratio, one way to measure thrust.
(source)
See also:
What is the ...
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13
votes
What is this F-18 Hornet "air intake" for?
EDIT: I'd just finished writing out my own answer when I stumbled across this answer to a different question, which nevertheless explains the function of the small intake in greater detail. I've ...
- 2,365
13
votes
Why is the S-duct intake on the Tu-154 uniquely oblong?
This doesn't fully answer the question, but the B727-100 also had an oval engine intake.
AIRLINERS magazine Sept/Oct 99 edition:
"The oval shape inlet on the 727-100 series was changed to a ...
- 37.9k
11
votes
Accepted
Why does the cross sectional area of the air going into the inlet of a turbo fan changes during take off and cruise?
why [is] the area of the streamtube of air going into the inlet [] much larger than the inlet during take off than during cruise?
Because at low speed the engine has to suck in air while at high ...
- 237k
10
votes
If the intake of a running jet engine is blocked for some short duration what would be the sequence of events following it?
The compressor would stall. This will cause a sudden rise in turbine temperature, which could damage the turbine(s). In the end, with no air intake, the flame will die out and the engine would stop.
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9
votes
Accepted
How is the jet engine inlet danger area affected when airborne?
Let's assume the A320 is powered by V2500 engines, one of the options for it. This engine has an air mass flow of 355 kg/s. At sea level, air density is 1.225kg per cubic m. Hence, 355 kg/s = 355/1....
- 4,533
9
votes
Accepted
Why is the inlet cone on some subsonic engines conical (sharp)?
This is not an inlet cone as found on supersonic aircraft engines. This is a spinner used on subsonic turbofan engines, both the rounded and pointed one. Older engines used rounded ones; the JT8D in ...
- 21k
8
votes
Accepted
How does a long inlet affect a jet engine's performance?
Long, winding intake ducts can increase the drag on the airflow moving through them, reducing the amount of air which the engine can ingest as opposed to a traditional diffuser design on a nacelle. ...
- 75k
8
votes
Accepted
What is the function of the holes in splitter plates?
Do the holes in splitter plates reduce the boundary layer?
Yes. Suction is applied to remove the slow-moving layer of air close to the surface, so the air entering the intake has as uniform a speed ...
- 237k
8
votes
How can an F-22 Raptor reach supersonic speeds without having supersonic inlets?
The jet uses a fixed, rhombohedral shaped jet intake combined with a serpentine intake duct. It allows for speeds just north of Mach 2 without the need for a variable geometry inlet to prevent ...
- 75k
7
votes
What is this F-18 Hornet "air intake" for?
The intake is for the primary heat exchanger. secondary is on the other side, Same location. The ambient air flows across a large rectangular heat exchanger. Basically a air to air radiator for the ...
- 71
7
votes
Accepted
Why do the intake of some helicopters have a bump body?
I don't know of the Apache, but the Russian helicopters have a dust separator there. This link shows how the dust protection system works on the Mi-17. The Mi-28 and Ka-52 have the same engines, so ...
- 1,189
6
votes
Why are the intakes of some fighters not attached to the fuselage?
The problem which this gap is solving has to do with boundary layer air as @ymb1 suggested but performance is not the only complication.
Boundary layer is not only slower, in some regimes of flight ...
- 315
6
votes
Why are turboprop intakes placed below the propeller?
I believe the main reason is simply mechanical practicalities.
The bulk of the engine core is mounted overlapping the structural members of the wing, either below or above the wing spars.
The ...
6
votes
What is the purpose of the vertical splitter and the NACA duct at the MQ-9 Reaper engine scoop?
Went to do some research after @niels nielsen's answer; the engine being used on the MQ-9 is the Honeywell TPE331-10. As Niels has rightly pointed out, the turboprop engine has its inlet facing the ...
- 141
6
votes
What is the purpose of a movable inlet on a jet engine?
Jet engines require the air that flows into them to be subsonic. Supersonic air hitting the front fan would cause shockwaves inside the engine, with undesirable results.
So the job of the intake on a ...
- 10.3k
6
votes
Accepted
Why should the dust protection on the Mi-17 helicopter not be used above 3000m?
Anything that blocks or restricts flow to the engines will hamper performance.
At low altitude, the aircraft has sufficient performance margin that this is acceptable. However, engine performance ...
- 16.9k
5
votes
Accepted
What drives the shape of an engine's intake on a fighter jet?
Are the design drivers solely based on supersonic pressure loss improvement?
Yes. And sometimes a few more considerations need to be taken into account.
We have covered the reason for intake shapes ...
- 237k
5
votes
What is this F-18 Hornet "air intake" for?
The rectangle in the center is the housing for the primary heat exchange. There is another heat exchange on the right side. The two "ramps" on top and bottom is to bleed off air during transonic/ ...
- 51
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