[ARC5] An Interesting Failure Mode

[Robert Eleazer]

Well, even though typically it is -12F outside at 20,000 ft that does not mean that inside the Oboe box it was not too warm and toasty.  

I have not seen cooling fans used on very many avionics.  The ARC-27 has a fan that circulates air between the inner and outer cases, and that was a radio used mainly in air conditioned aircraft.  Of course, it is sealed, and the wind can't get in and out so the fan needs to cool the case.  

My AVQ-55 radar has a fan to blow air into the electronics, and I think it was mainly used in unpressurized non-air conditioned fairly light aircraft.

Interesting item on a radar range calibrator I have.  It uses a lot of sub-miniature tubes and has a cooling fan.  The equipment works on 115VAC 60 cycles but the fan runs on 90 VDC; a selenium rectifier turns the AC line voltage into DC.  I assume they did that so that the rotating field from an AC motor did not cause interference to the calibrator.

Also, I wonder about that "Hoover vacuum cleaner motor" used in the Oboe fan.  I assume that was an AC motor?  Where did they get the AC?  From the same power supply that supplied the radar equipment?  And why did they not use a DC motor?     

By the way, the Oboe system was called that because of the sound it made if you tuned the signal. 

Wayne
WB5WSV

   

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