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pmather
Joined: 17 Sep 2009
Posts: 33
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 Posted: Sat Feb 05, 2011 10:37 am Post subject: Heated pitot Question |
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I’ve got a heated pitot off a C182 (28V) that I want to use on a Tailwind I’m building (www.tailwindbuild.blogspot.com). Originally I assumed that I would not bother with the heater as the aircraft will not be used for IFR (not allowed for experimentals in the UK) and will have a 14V electrical system. But, as an experiment, I wired the pitot up to my bench supply and at 14V it pulls 4amps and gets too hot to touch. Is there any reason not to just wire it off the 14V supply? At 50W+ of heat it presumably is better than nothing?
Thanks
Peter
[quote][b]
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nuckolls.bob(at)aeroelect
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| Posted: Sat Feb 05, 2011 11:12 am Post subject: Heated pitot Question |
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At 01:32 PM 2/5/2011, you wrote:
| Quote: | | I’ve got a heated pitot off a C182 (28V) that I want to use on a Tailwind I’m building ( www.tailwindbuild.blogspot..com). Originally I assumed that I would not bother with the heater as the aircraft will not be used for IFR (not allowed for experimentals in the UK) and will have a 14V electrical system. But, as an experiment, I wired the pitot up to my bench supply and at 14V it pulls 4amps and gets too hot to touch. Is there any reason not to just wire it off the 14V supply? At 50W+ of heat it presumably is better than nothing? |
Having a heated pitot tube was always an
option on Cessna single engine airplanes . . .
and not a cheap option either.
But if one watches some certification
programs for flight into known icing,
the idea that dumping few hundred watts of heat
into a pitot tube is a good and useful
thing to do becomes problematic.
The kind of ice that plugs a pitot tube
is also the kind of ice that covers
windshields, gathers on prop roots, leading
edges of wings. and any other sticky-out
thing like landing gear.
Any time you even THINK you've gathered
some ice, the prudent action is to take
immediate measures to get out . . . 180
turn, change altitude, etc. This (or a similar)
philosophy for icing encounters should have
you breathing easier in a much shorter
period of time . . . and probably before
the pitot tube ices over.
The pitot tube is but one of MANY potential
victims for ice accretion. Knowing the
true value of IAS is of little value when
the airplane wont fly well at any achievable
IAS.
Hooking your heater up to provide 1/4th the
design value for deicing energy is a whistle
in the dark when you need a good flashlight!
Bob . . . [quote][b]
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Bob McC
Joined: 09 Jan 2006
Posts: 258
Location: Toronto, ON
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| Posted: Sat Feb 05, 2011 11:57 am Post subject: Heated pitot Question |
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Peter;
You could do that if you wish but you will be generating only ¼ of the designed wattage. While this low level of heat might provide some protection you must remember that the wind-chill effect is considerable and that while it may be too hot to touch on the bench, when flying it may only be slightly warm. True values of 4 amps (at) 14 volts provides just under 60 watts of heat (56) whereas on 28 volts you will get close to 230 watts , a significant difference. The manufacturer obviously considered it prudent to provide over 200 watts and ¼ of that may not be adequate to accomplish much of anything. It would be your call to decide if it’s worth it. A properly functioning pitot tube heating on the bench is not only too hot to touch, but will come close to branding you.
Bob McC
From: owner-aeroelectric-list-server(at)matronics.com [mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of Peter Mather
Sent: Saturday, February 05, 2011 1:32 PM
To: aeroelectric-list(at)matronics.com
Subject: Heated pitot Question
I’ve got a heated pitot off a C182 (28V) that I want to use on a Tailwind I’m building (www.tailwindbuild.blogspot.com). Originally I assumed that I would not bother with the heater as the aircraft will not be used for IFR (not allowed for experimentals in the UK) and will have a 14V electrical system. But, as an experiment, I wired the pitot up to my bench supply and at 14V it pulls 4amps and gets too hot to touch. Is there any reason not to just wire it off the 14V supply? At 50W+ of heat it presumably is better than nothing?
Thanks
Peter 01234567890123
[quote][b]
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_________________
Bob McC
Falco #908
(just starting) |
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