Linked Questions

61
votes
4answers
56k views

Why does the Boeing 787 engine nacelle exhaust have such an unusual shape?

Why does the Boeing 787 nacelle have this unique shape at the exhaust: I haven't seen it on any other airplanes, does it serve an aerodynamic purpose or help engine efficiency or is it just to look ...
24
votes
5answers
7k views

Could the principle of owls' silent flight be used for stealth aircraft?

I was wondering about the ability of owls to fly so silently. Is it because they flap gently, they flap less often or do is their structure responsible? I was thinking their principle of stalking can ...
57
votes
4answers
28k views

Why can't jet engines operate with supersonic air and how do they slow it down?

Typically jets cannot operate when intake airflow is supersonic relative to the engine. Why is this so? Also, why are scramjets able to use supersonic air? To slow down the air to subsonic speeds, ...
24
votes
4answers
22k views

Why do turbofan blade tips exceed the speed of sound while prop tips should not?

It seems that the tips of the fan of a turbofan engine can and do break the sound barrier: The GE-90 has a fan diameter of 3124 mm and a rotational speed of 3475 RPM. Their circumferential velocity ...
29
votes
2answers
5k views

Are the fastest moving pieces of a jet engine supersonic?

A jet engine is composed of fast moving pieces. Those pieces are moving into an airmass different form the ambient airmass the aircraft is flying into. The turbine pieces are spinning quite fast, ...
14
votes
3answers
5k views

Did the XF-84H Thunderscreech really cause “900 sonic booms per minute”?

The Republic XF-84H, known as the "Thunderscreech" was an experimental version of the F-84F Thunderstreak. It was intended to be a supersonic turboprop fighter. Even at idle, the prop tips rotated at ...
16
votes
2answers
6k views

Why do jet engines sometimes spit out flames after ingesting birds?

After seeing this video of a 757's engine catching fire because of a bird, I wonder: What happens to the engine? Why does it periodically exhaust fire? Is this some safety feature?
9
votes
2answers
3k views

Why do engine cowl lips appear larger and more blunt on the sides than on the top and bottom?

I was looking into engine nacelles. I was not able to understand the design shape of it Why is it that in most aircraft, the engine cowl lips on the side are bigger (more blunt) than on the top and ...
14
votes
1answer
6k views

What is the purpose of the inlet doors of the Pratt & Whitney JT3D?

I have a question about the 707 Engine Inlet Doors, according to Wikipedia the Pratt & Whitney JT3D inlet doors purpose is to provide additional air. Is the thrust higher on more air intake? And ...
13
votes
2answers
760 views

Is there a surface of a commercial jet exposed to air flow at speed near Mach 1?

With commercial aircraft flying slightly above Mach 0.8, is there any surface exposed to speed of air significantly larger, e.g. near Mach 1? ignoring: The engine components, The boundary layer as ...
5
votes
2answers
978 views

What noise reduction measures were taken in the time between hush kits and chevrons?

In older jets such as 727 hush kits are used in the engines to reduce noise. In very modern jets such as 787 or 747-8F, chevrons are used for the same purpose. What happened in between? The switch to ...
6
votes
1answer
2k views

Why are podded engines preferred over engines fitted inside the fuselage or wing?

Given the fact that podded engines on the wings of airplanes cause much drag (and thereby contribute to a lot of loss of efficiency), why do airliners still prefer podded turbojet engines over ...
4
votes
4answers
203 views

Keeping the engine under the wings, doesn't hurt the lift as the airflow speed is higher under the wings?

To create a lift, the airflow speed on top of the wings should be higher than the airflow speed on the bottom of the wings. But when you keep the engine on the bottom of the wings, wouldn't it hurt ...
8
votes
3answers
2k views

What are these holes in the engine inlet?

In the next picture can be seen within the housing, near the inlet:
7
votes
1answer
739 views

Why does the chevron-shaped engine suffer losses in thrust performance?

From here I found out a lot about chevrons on the Boeing 787, but not enough to satisfy why it results in performance loss. My thinking was originally, if they are "cutting triangular holes" in the "...
3
votes
1answer
487 views

How does a wing mounted jet engine on a supersonic airplane prevent the interference in the flow due to Shock? [duplicate]

Wing mounted jet engines face the free stream at Mach number 1 or above, and they work perfectly for Mach numbers below 1 as well, even though the free stream characteristics change a lot after Mach 1....