a.s.elliott(at)cox.net
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 Posted: Sun Feb 18, 2007 9:15 am Post subject: Heated pitot tubes |
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Folks:
Since I do fly in the clouds sometimes, I have been looking for heated pitot tubes. New ones run between $500-$900. Used 12V units usually go for $150-$300 on EBay. I often saw 24V units much cheaper and wondered how they would work on my 12V airplane. Since a heated pitot tube is designed to melt off ice when it's -56°C, I figured that running it at 1/4 power might be OK for an occasional trip into clouds below the freezing level.
I purchased a very nice 24V unit on eBay for $43 (including mounting bracket and shipping!) and here are the two results of my not-too-scientific testing:
[1] Hooked up to my 13.8V bench power supply, the unit reached a temperature that burned my finger in less than 1 minute. I turned it off then.
[2] Room temperature resistance was about 2.7 Ohms, meaning the start-up draw should be about 13.8/2.7 = 5.1 amps.
This makes it about a 70-watt heater, which I am going to say is fine for my purposes. Complete testing would actually measure both the tip temperature and resistance as a function of time and environment temperature, but I'm pretty happy as is. Of course, you should make your own decisions about that for your own planned flight profiles.
Note that this is a pitot tube only, and a source for static air has to be installed. I plan on using the $20 static air kit from Van's and placing the ports on the fuselage sides about 1/2 way back, much as they are placed in the certified aircraft.
FWIW,
Andy Elliott, Mesa, AZ
N601GE (reserved)
601XL/TD/QB, Corvair, building...
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