Avionics cooling?

[shouldbworking]

Idle wonderings.. how do you cool avionics on an aircraft? is it done using the fuel or a system like cars air conditioning with refrigerant? How does the heat get dissipated on a stealth aircraft in such a way that it doesn't compromise the radar or heat signatures? If the cooling system(s) were to fail how long would a (for the sake of argument) aerodynamically unstable aircraft have to get on the ground the avionics became inoperable?
yes, my idle wonderings can get quite detailed at times..

[tegwin]

The Eurofigher typhoon's engine ECU and MFMU are housed in alloy cases with a hollow jacket around them... the fuel is pumped through the cases before being burned in the engine.. I cant imagine that all of the avionics are cooled this way though.. you would end up with superheated fuel

Seemed quite a dodgy thing to do but apparently its common place...

[shouldbworking]

tegwin said:

The Eurofigher typhoon's engine ECU and MFMU are housed in alloy cases with a hollow jacket around them... the fuel is pumped through the cases before being burned in the engine.. I cant imagine that all of the avionics are cooled this way though.. you would end up with superheated fuel

Seemed quite a dodgy thing to do but apparently its common place...

I know a fair few aircraft systems are cooled with fuel but then I was thinking what about things like the f-22 - presumably you'll need to dump the fuel heat to air at some point and I can't imagine a honking great radiator would be particularly stealthy

Edited by shouldbworking on Monday 12th April 14:41

[eccles]

Tornados used to use ram air, or fans on the ground. Apaches use refrigerant (R134a)to cool everything as there's not much ram air whilst you're hovering!

[bulb763]

Fuel is certainly used. It's chilled in many cases before being pumped onboard so it's effectively one giant heat sink and used to move the heat to somewhere it can be removed. Some avionics are cooled directly by the fuel and in other cases it is used as a heat sink for other fluids which are pumped around the aircraft. Of course it won't stay cool forever (imagine for example a black F-22 / F-35 with a relatively high surface-area : volume ratio in 100F heat) but various devices are used to help - including what are effectively just giant computer fans. In flight there are ram air scoops through which fuel is pumped to remvoe the heat.

[S7Paul]

Some avionic boxes have hollow walls through which cooling air passes. This means that the heat path is through the PCB guides into the box itself. In other cases the air is just blown through a stack of PCB's.

We used to build an ECM Pod (for Tornado) whose electronic units were bolted onto a large hollow "cold plate" through which Coolanol was circulated. Obviously this also needed all the other paraphernalia like pumps & heat exchangers.

[Bosshogg76]

Tornado uses engine bleed air for the avionic boxes. The air is ducted from HP4 and is cooled using the Pre-cooler and the inter-cooler. The coolers work by air flowing through them like a car radiator or turbo intercooler. When on the deck air flow is induced through the coolers using ejectors on the ground, in the air obviously airflow is not a problem.

Radar is cooled with a combination of coolanol and ducted pre-cooled air.

As has been mentioned before the avionics boxes sit on hollow based trays, through which the cooling air is ducted. The fans in the forward and belly avionics bay help with the flow of air through the bays whilst on the floor. All this for the Air Display Variant, and my memory is horrendous so there will be some miss-information.

[john_p]

Bosshogg76 said:

Air Display Variant

I've never heard that one before, nice

[Simpo Two]

eccles said:

Apaches use refrigerant (R134a)to cool everything as there's not much ram air whilst you're hovering!

A small scoop pointing upwards?! If there's no downdraught from the rotor you're either parked or about to run out of sky...

Edited by Simpo Two on Monday 12th April 21:34

[eccles]

Simpo Two said:

eccles said:

Apaches use refrigerant (R134a)to cool everything as there's not much ram air whilst you're hovering!

A small scoop pointing upwards?! If there's no downdraught from the rotor you're either parked or about to run out of sky...

Edited by Simpo Two on Monday 12th April 21:34

There's not that much down draft over the fuselage, lots more as you move out of the rotor disc!

[strudel]

Which bits exactly need cooling? I've never really thought about it at all, just assumed it's all solid state like my pc!

[Mojocvh]

john_p said:

Bosshogg76 said:

Air Display Variant

I've never heard that one before, nice

Sound like a right pair of II (AC) homs.......

[tank slapper]

strudel said:

Which bits exactly need cooling? I've never really thought about it at all, just assumed it's all solid state like my pc!

Most PCs have cooling fans, even laptops. Electronics produce a fair bit of heat, and in aircraft they tend to be packed in to small volumes which would allow heat to build up unless measures were taken to remove it.

[Mr Dave]

On the old russian aircraft with valved electronics, it was often cooled with ethanol which was drunk quite a lot by the groundcrews so it ended up having to be poisoned. So ive heard anyway.

[shouldbworking]

Interesting stuff... so how long would the electrickery last if the cooling system went kaput? does it ever happen?

[Bosshogg76]

Mojocvh said:

john_p said:

Bosshogg76 said:

Air Display Variant

I've never heard that one before, nice

Sound like a right pair of II (AC) homs.......

And the meaning of this is?

After spending entire career spent on F3's checking into hotels, having nicer accommodation in the Gulf, not having to clamber into zone 19 to change bits, and having panels somewhere near the components I want to change etc. I'm pretty used to my manliness being questioned by the mud moving tent dwellers. However they tend not to post pretty pics.

shouldbworking said:

Interesting stuff... so how long would the electrickery last if the cooling system went kaput? does it ever happen?

Things like radar times out, ie over heats and switches itself off after 20mins. ECS systems frequently go U/S for things like Shut Off valve or PRV failures, amongst other things.

Edited by Bosshogg76 on Tuesday 13th April 09:31

Edited by Bosshogg76 on Tuesday 13th April 10:19

[Tango13]

When Lockheed started test flying the A12 they had intermitant generator failures that could never be replicated on the ground. It turned out to be the lead solder was melting due to the heat generated by the sustained Mach 3+ flight then becoming solid once the aircraft had landed. Switching to silver solder cured the problem

[Mojocvh]

Tango13 said:

When Lockheed started test flying the A12 they had intermitant generator failures that could never be replicated on the ground. It turned out to be the lead solder was melting due to the heat generated by the sustained Mach 3+ flight then becoming solid once the aircraft had landed. Switching to silver solder cured the problem

Had a similar fault on a F3 once at Andøya, turned out the cab was a F3 cobbled together from a bent F2 back and F3 front. Somehow (??) the snow column was forcing the water layer through a path in the structure onto the mid point marry up electrical connectors.
This manifested as a shorting out of the perm magnet generator return from the gcu back to the gennys field coils. It had been apparently an intermittent ongoing fault with the owner sqn but the severe (LOL) conditions at Andøya had finally forced a solid fault. Pity for the crew on an operational launch whose electric jet just lost half it's electrics over the middle of the Arctic Ocean, still thats what fly pay is for I was told.

Happy days, them and us. Simples.

[Bosshogg76]

Mojocvh said:

Tango13 said:

When Lockheed started test flying the A12 they had intermitant generator failures that could never be replicated on the ground. It turned out to be the lead solder was melting due to the heat generated by the sustained Mach 3+ flight then becoming solid once the aircraft had landed. Switching to silver solder cured the problem

Had a similar fault on a F3 once at Andøya, turned out the cab was a F3 cobbled together from a bent F2 back and F3 front.

There are a fair few F3's made up of F2 centre sections with F3 front and rear ends. These jets are the result of the RAF's desire to penny pinch and employ contractors at St Athan who had no aircraft engineering experience. It's amazing how much damage can be done to frames by a determined welshman and a windy chisel.

[Mojocvh]

Bosshogg76 said:

Mojocvh said:

Tango13 said:

When Lockheed started test flying the A12 they had intermitant generator failures that could never be replicated on the ground. It turned out to be the lead solder was melting due to the heat generated by the sustained Mach 3+ flight then becoming solid once the aircraft had landed. Switching to silver solder cured the problem

Had a similar fault on a F3 once at Andøya, turned out the cab was a F3 cobbled together from a bent F2 back and F3 front.

There are a fair few F3's made up of F2 centre sections with F3 front and rear ends. These jets are the result of the RAF's desire to penny pinch and employ contractors at St Athan who had no aircraft engineering experience. It's amazing how much damage can be done to frames by a determined welshman and a windy chisel.

Was it Airworks? can't remember??