Identification From Compressor Blades Question

In addition to FF systems and other BVR identification techniques a friend of mine told me US fighters with AESA radars can measure the compressor spin rate of distant fighters and determine from that if it's a foreign or hostile fighter. They do this by comparing the information they get with what's know about the compressor signature of US fighters. Anyone have more information on this? Or is it complete bull?

Its not unreasonable that you could get a doppler off of the fan blades (Compressors are a big source of radar return and thats why on stealth aircraft they are "hidden".

However, lets say the radar can resove and get a doppler shift off of the compressor. It may still not be enuf to fire off your BVR missiles. Why? Many airforces fly a variety of aircraft. Is that Mig an Iraninan AF or say a Afgan one?

I don't know if it would be used to fire a missile off but it could be helpful in giving the pilot an indication that the aircraft is a potential hostile (or non ally). Major Us allies don't fly Mig's and Flankers so at least you know it's not friendly.

It wouldn't be the only system used for IFF, you would expect, as FredT said. You may get the aircraft type, but no who's flying it.

The info would have to be used in conjuntion with other sources, like most systems today.

Yeap, apparently the APG-77 can recognise the engines of opposing aircraft by the radar return.


Of course, this would require a higher resolution than mere tracking, so the range it would be achievable at may not be that high (I don't know, but I'd imagine it would be significantly less than detection range!). It would also require the targetted fighter to be in a favourable attitude in comparison to the radar emitting aircraft.

Originally posted by WestPoint23
In addition to FF systems and other BVR identification techniques a friend of mine told me US fighters with AESA radars can measure the compressor spin rate of distant fighters and determine from that if it's a foreign or hostile fighter. They do this by comparing the information they get with what's know about the compressor signature of US fighters. Anyone have more information on this? Or is it complete bull?

Wouldn't the rpm - spin rate - levels change due to the engines are probably throttled back during cruise?

Or would they be looking at a wide open throttle situation as a means of identification during a potentially aggressive move by the distant fighter?

Good question there "Desert Dawg", and my answer is I don't know. I didn't even think it was real but apparently it can be done.

Originally posted by WestPoint23
Good question there "Desert Dawg", and my answer is I don't know. I didn't even think it was real but apparently it can be done.

I think . . . but don't know for sure, that differing designs of turbine blades can give off different pulses and perhaps what they're reading is that pulse moreso than the rpm levels.

Regardless, your initial post about reading a signature from an engine is right on the money and how they do it is probably information they're not gonna release for a while.

As a small matter of interest, I read several years back that fighters have an optical ID system in the cockpit that can tell the pilot just what he's looking at from about 50 miles out.
Gyroscopically stabilized I would imagine.

Gotta be tough to keep track of all the systems, threat warnings, radar etc. as well as navigate and fly the airplane....


(Edited for grammar.)

[edit on 16-9-2006 by Desert Dawg]

The F-14 had a camera under the nose. It wasn't very good in the early versions, and still nothing to write home about in the later ones, but it was a vast improvement.

Originally posted by Desert Dawg

Wouldn't the rpm - spin rate - levels change due to the engines are probably throttled back during cruise?

Or would they be looking at a wide open throttle situation as a means of identification during a potentially aggressive move by the distant fighter?

They'll probably count the number of blades then match that to an engine. Different blades will generate different signatures in their returns, these will be matched to a database.

Yep that's how its done.

N011M:

For aircraft N011M has a 350 km search range and a maximum 200 km tracking range, and 60 km in the rear hemisphere. A MiG-21 for instance can be detected at a distance of up to 135 km. Design maximum search range for an F-16 target was 140-160km. A Bars' earlier variant, fitted with a five-kilowatt transmitter, proved to be capable of detecting Su-27 fighters at a range of over 330 km. The radar can track 20 air targets and engage the 4 most threatening targets simultaneously (this capability was introduced in the Indian RC1 and RC2). These targets can include cruise/ballistic missiles and even motionless helicopters. For comparison, Phazotron-NIIR’s Zhuk-MS radar has a range of 150-180km against a fighter and over 300km against a warship. "We can count the number of blades in the engine of the aircraft in sight (by the NO11M) and by that determine its type," NIIP says.