minimum temperature an IR missile can lock onto

[Adam Chapman]

Hi,
is there a threshold temperature that a heat-seeking missile like the
stinger identifies as a target?

I am trying to design a stealth UAV at university, and I want to keep
the exhaust temperature as low as possible. However, as I reduce the
temperature, I reduce the thrust force.

What is the maximum temperature that I could use without risk of being
shot down by a stinger?

Adam

[150flivver]

"Heat seeking" is an oversimplification for the benefit of the general
public. Specific thresholds for seeker functionality and what it
actually is looking for is most probably classified.

[Jim Yanik]

Post by Adam Chapman
Hi,
is there a threshold temperature that a heat-seeking missile like the
stinger identifies as a target?
I am trying to design a stealth UAV at university, and I want to keep
the exhaust temperature as low as possible. However, as I reduce the
temperature, I reduce the thrust force.
What is the maximum temperature that I could use without risk of being
shot down by a stinger?
Adam

Using a turbine or a piston engine?
(sounds like a turbine.)

1.Mix your exhaust output with cold air.
2.Use a diffuser on the exhaust output from the airframe.

[Adam Chapman]

Thanks guys.

Jim, yes we do have a turbine. We are making a nozzle with increasing
cross-sectional area so the flow can expand and cool down (like in the
pipes behind a refridgerator, but much faster).

As the flow slows down, the thrust force decreases. This means we need
a more powerful engine than we would need if the exhaust was
convergent.

Ijust wondered if anybody knew exactly how coolthe exhaust will need to
be.

Adam

[Ragnar]

Post by Adam Chapman
Hi,
is there a threshold temperature that a heat-seeking missile like the
stinger identifies as a target?
I am trying to design a stealth UAV at university, and I want to keep
the exhaust temperature as low as possible. However, as I reduce the
temperature, I reduce the thrust force.
What is the maximum temperature that I could use without risk of being
shot down by a stinger?
Adam

IIRC, the temp will be dependent on the wavelength of the detector.
Shouldn't be too hard to look that up.

[WaltBJ]

FWIW modern IR-seeking missiles with cooled seeker heads can detect and
track skin temperatures - temperatures above ambient caused by ram air
impact. Low altitude flight at high true airspeeds give the steepest
rise. Forex, STP at sea level, TAS 300 knots, the Q or ram pressure
rise is about 2.12 PSI. This will also involve a stagnation point
temperature rise. The faster you go, the higher the rise; it is not a
linear but an exponential function. It's been far too many years since
I dealt with this but I do know that in the 70s uncooled IR seekers
could detect and track skin temperatures at M2.0 at high altitude. If
you intend to operate your vehicle at speeds over 300 KIAS you may have
problems concerning skin temps. If however you are content with slower
speeds and lower altitudes a propeller or ducted fan might be better.
There are other methods of detection and tracking not involving
vehicle-emitted IR, however. A search should discover some of them,
methods now in service in certain MANPADS. Defeating these may involve
some serious design problems.
Walt BJ.

[Jim Yanik]

Post by WaltBJ
FWIW modern IR-seeking missiles with cooled seeker heads can detect and
track skin temperatures - temperatures above ambient caused by ram air
impact. Low altitude flight at high true airspeeds give the steepest
rise. Forex, STP at sea level, TAS 300 knots, the Q or ram pressure
rise is about 2.12 PSI. This will also involve a stagnation point
temperature rise. The faster you go, the higher the rise; it is not a
linear but an exponential function. It's been far too many years since
I dealt with this but I do know that in the 70s uncooled IR seekers
could detect and track skin temperatures at M2.0 at high altitude. If
you intend to operate your vehicle at speeds over 300 KIAS you may have
problems concerning skin temps. If however you are content with slower
speeds and lower altitudes a propeller or ducted fan might be better.
There are other methods of detection and tracking not involving
vehicle-emitted IR, however. A search should discover some of them,
methods now in service in certain MANPADS. Defeating these may involve
some serious design problems.
Walt BJ.

They also are dual band IR;3-5um and 8-12um,to help in discrimination
betweeen decoys and the real target. Perhaps UV band too.

[Ancient_Hacker]

Post by Adam Chapman
What is the maximum temperature that I could use without risk of being
shot down by a stinger?
Adam

Just a wild guess, but looking at what's available:


You can go to any hardware store and for $6 buy an IR motion-detecting
light-switch, capable of detecting body temperature against a
background of room-temperature.

I assume any ground to air missile can afford the same or better. Plus
it has a much colder background for contrast.

Also consider the two elements the hot exhaust nozzle versus the hot
gases. For the nozzle you can shield it somewhat with cooler baffles.
The exhaust gases you can spread out to minimize the peak temperature,
at the expense of a wider plume. You might consider a SR-71
configuration, designed for more net thrust derived from suck than blow.

[weasel]

The goal is to reduce the temperature of the nozzle parts that the IR
seeker can see.

The exhaust gas itself is a very inefficient radiator.
The nozzle can be cooled by bypass or ambient air.
beware of engine parts that can be seen up the nozzle duct.

Also, don't use afterburner when your missile warning goes off...

BT,DT (...got the T-shirt)

Wes