Avionics cooling capacity of fighter aircraft

[stealthflanker]

As in title. This is a topic i always wondering about, and the answer is not straightforward but i think it's interesting to brought.

Recently i got myself a good book titled "Radar Analysis and Modeling" 2005 edition by David K Barton. P-165 contain interesting equation which relates cooling capacity with maximum emitted average power of AESA radar. Plus example with air cooling which about 2 Kw/sqm. Other link i found however states air cooling capacity of 1-1.5 watt/sq inch or about 1.5-2.3 Kw / sqm.

http://www.militaryaerospace.com/articl ... iquid.html

Using 2.3 Kw/sqm as value (best case maybe) I tried working on possible range of new Chinese air cooled KLJ-7A. One should make assumption tho about the variables


-1000 TRM
-X band (0.032 m wavelength)
-Air cooling capacity of 2.3 Kw/sqm (air cooling capacity is between 1.5-2.3 KW/sqm) Liquid could be up to 155 KW but i wonder such capacity could be carried by fighter aircraft.
-Module efficiency (PAE) of 25% (A-class) Other classes could be used but for radar application this could compromise signal purity.

Working with the equation indicates the maximum average power that could be emitted from above spec is about 397 Watt. The peak power assuming 25% duty cycle (typical for pulse doppler radar) Is 1587.2 Watt or 1.5 KW. Each module's peak emitted power is then 1.6 Watt.

Calculated range would be 191 km with 50% detection probability for 5 sqm RCS target. However it's been revealed that the maximum range of KLJ-7A would be 170 km. Could be because my spreadsheet didn't take account of clutter Or the radar have lesser amount of modules or power rating than what i assume.


Now i wonder if there is any example value for say liquid cooling ? can a fighter jet carry 155 Kw/sqm cooling capacity ?

For me at least the equation is very helpful, especially when i tried to make educated guess on fighter aircraft radar range.

[garrya]

-Air cooling capacity of 2.3 Kw/sqm (air cooling capacity is between 1.5-2.3 KW/sqm) Liquid could be up to 155 KW but i wonder such capacity could be carried by fighter aircraft.

Liquid cooling as in using fuel?

[stealthflanker]

Liquid cooling as in using fuel?

Yes, basically the fuel is used as heatsink. The coolant medium would be PAO or other suitable liquid. The question is of course what's typical figure for fighter aircraft, can it carry 155 kW/sqm ?. Would love tho if relationship between fuel capacity vs cooling capacity can be established.

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Anyway I managed to discover this document (the link in ausairpower is dead so i have to use wayback machine) This document discuss milestones and figures of AN/APG-79 AESA Radar.

https://www.scribd.com/document/3664362 ... -AN-APG-79

The backup slide includes very interesting data namely the cooling loop. The threshold is 15.6 kW. The production appears to deliver liquid cooling capacity at 14.76 kW/sqm with 15.02 kW/sqm perhaps development. If we take those figure as cooling capacity. using similar assumption as above. Taking 15.6 kW threshold we could try guessing range of the AN/APG-79.

We know some information related to the radar :
-About 1100 TRM.

Assumption :
-15.6 kW/sqm cooling
-Class A/AB amplifier with PAE of about 30%
-Operating frequency of X-band with wavelength of 3.2 cm.

With such assumption, we could calculate that the maximum average power that can be emitted by the radar is 3765 Watt. Assuming 25% duty cycle, the peak power of the radar would be 15061.38 Watt or 15 Kilowatt. The TRM in turn would have peak power of 13.7 Watt.

Now we have enough data for attempt of calculating range. My calculation so far indicates range for 3 sqm target at 50% probability of detection would be 318 km. 90% it would be 197 km.

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I expect fighter aircrafts like F-22, Su-35S, PAKFA and JSF would have at least that capacity or more.