Stealth Aircraft Inlet Question!

As much as I appear to know about stealth aircraft, I have one thing I can't figure out: Inlet Placement

For the longest time, I was of the oppinion that the inlets on a stealth aircraft had to be above the wing/fusalage in order to hide them from radar. However, now we are seeing stealthy designs like the F-22, YF-23, A-12 Avenger, and F-35, which have underwing inlets on them.

How dose the location of an aircraft engine inet/s really affect its stealthyness? Does it really make a signifigant difference in terms of RCS?

I would appreacieat any help or insight into this issue that folks are willing to share!

Tim

Originally posted by Ghost01
How dose the location of an aircraft engine inet/s really affect its stealthyness? Does it really make a signifigant difference in terms of RCS?

The placement decision depends on a whole load of things, first of which is - what is the aircraft gonna do?

High altitude penetration?
Low altitude penetration?
Need to be manouverable?

then there are other details like engine placement, weapons bay placement, engine mass flow rate, undercarriage etc etc. Everything has knock on effects.


The B-2 was (originally) designed for high alt penetration of Soviet airspace - hence shield the inlets from the ground. Same with the F-117.

The F-22 needs to be manouverable, you need engine power at high AoA, so you need a good supply of airflow - thus get them intakes under the wings where the air is cleanest.


Of course, with all of the above, most important thing in an inlet is not letting any radar waves get in and get out after hitting the fan face [at least - not get out in any useful manner]. So all intake ducts are twisted/bent/whatever to ensure no clean path (i.e. without bouncing off a wall or two) for waves (within a range of wavelengths) to the fan/compressor first row.

During the gulf war part 1 I was involved with fixing "special" tiles to the insides of the intakes of the Tornado F3's and GR 1's which were to be used in the war.

They were to soak up any radar waves which reflected back off the blades as the Tornado's have a fairly straight internal intake path with no s-bends as they were designed before stealth and RCS became the watch words they are today.

So as that was quite a while ago I would imagine that with S bends and composite materials being used in intake construction the position of the intakes on a modern stealth A/C can be anywhere the designer dictates.

Sv....Out!