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mprather(at)spro.net
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 Posted: Sun Dec 10, 2006 9:13 am Post subject: Pitot Current Draw |
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Hey Chuck,
One more idea (I think I've read all of the other messages on this topic
- I haven't seen this idea before)... How about modifying the heating
element in the heater. Possibly a heating element from a more modest
pitot tube could be installed...
Matt-
Chuck Jensen wrote:
[quote] Craig/Matt/Bob/Bob again/et al
Thanks for the technical responses which transcends the proclamation
that only dummies fly in ice. And Stein, you have a point if I was
only trying to use some reject hand-me-down pitot and I was too cheap
to get one of Gretz's very elegantly functional pitots. This isn't
about functionality, this is about aesthetics. I have a sharkfin pitot
off an old warbird that I use at the tippy-point of the Velocity. The
sharkfin perfectly picks up the lines of the winglets, yadda,
yadda.....trust me, it's just a personal preference.
Unfortunately, the heating elements in it were obviously designed for
use in cold weather areas. In the winters, when they saw this sucker
coming in, the ramp and line crews left the warmth of their burning
trash barrels to comeover and stand by the pitot where there was some
real heat!!!
My conclusion is if I want to keep the pitot (which I do), I either
live with the current draw, which is really not a serious problem for
the 60amp alternator and just hope I don't need it at the same time
that I start suddenly have a shortage of electrons. While the resistor
fix may work, because of the loss to the resistor, the overall
amperage reduction is minimal.....kind of like having to spend a $100
to get a $20 tax reduction.
The more attractive alternative is duty cycle--assuming it doesn't put
me in electron hell. Anyhow, I appreciate the many responses and the
many tangents engaged. As to those who thought the thread went on too
long and contain too much irrelevant material, just remember--that's
why we sort through the pile of straw and horse s--t that was shoveled
out of the horse barn with our bare hands---on the oft chance there
might be a pony in there somewhere.
Chuck Jensen
* *
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cjensen(at)dts9000.com
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| Posted: Sun Dec 10, 2006 9:35 am Post subject: Pitot Current Draw |
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Matt,
I considered modifying the heating element but this thing is put
together with a special Fort Knox Silver Solder that resists removal. I
had a pitot exactly like it earlier and tried to dissect it. My final
adjustments were with a claw hammer and pipe wrench, so a modification
of the element, like shortening it, is probably not going to work.
I have a handheld, thermo temp gun that I'm going to 'shoot' the pitot
today after it get up to temp--that's assuming the composite nose of the
Velo doesn't melt first and the whole thing falls to the ramp.
I probably should put a porcupine heater shroud around it and route the
heat into the cabin...a pusher can always use the extra heat!
Chuck Jensen
Do Not Archive
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MLAS(at)cox.net
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| Posted: Sun Dec 10, 2006 9:44 am Post subject: Pitot Current Draw |
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Stan,
You are correct, I was having some fun expressing my view that in my opinion this issue as a builder or flyer is not something worth pursuing. For the real down and dirty instrument flyer this issue just over complicates the business of flying safe to save a few amps. A simple point, a pitot heat system is a safety item much like a fire extinguisher (KISS).
I have a different philosophy then many on this site but not all. I answer questions using a strait forward set of rules meeting My basic philosophy. I work towards putting things into the field that work and can be maintained buy the builder. My work goes directly to the builder who is working to get a complete project into the air that is safe, maintainable, reliable, and cost effective both in time and money. But I do respect the more micro of you folks on this board. Without your work and ideas we would not have the wonderful opportunities we have today. So we coexist.
My main focus in aviation is safety of operation, both in maintenance and flight.
Mike Larkin
[quote] ---
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bob(at)bob-white.com
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| Posted: Sun Dec 10, 2006 12:11 pm Post subject: Pitot Current Draw |
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On Sun, 10 Dec 2006 12:36:14 -0500
"Chuck Jensen" <cjensen(at)dts9000.com> wrote:
| Quote: |
Matt,
I considered modifying the heating element but this thing is put
together with a special Fort Knox Silver Solder that resists removal. I
had a pitot exactly like it earlier and tried to dissect it. My final
adjustments were with a claw hammer and pipe wrench, so a modification
of the element, like shortening it, is probably not going to work.
|
Hi Chuck,
Shorten the element if you would like MORE heat, lesson I learned as a
teenager. I had a piece of nichrome wire that I wanted to get red hot.
(I have no memory of what I was trying to do other than that.) I
stretched the wire out and clamped on an electric cord I could plug
into the wall. It got a little hotter than I wanted. Well, I knew
ohms law and I knew P=I^2*R so the obvious solution was to cut R in
half to get half power. When I plugged it in, that sucker got white
hot so fast I didn't have time to blink. Haven't had much trouble
keeping ohms law straight since. 
Bob W.
Do not archive
--
N93BD - Rotary Powered BD-4 - http://www.bob-white.com
First Flight: 11/23/2006 7:50AM - 0.7 Hours Total Time
Cables for your rotary installation - http://www.roblinphoto.com/shop/
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Speedy11(at)aol.com
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| Posted: Sun Dec 10, 2006 2:41 pm Post subject: Pitot Current Draw |
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Thanks, Bob. I'd never heard that term before. Didn't know about the Tripacers either and I owned one!
Stan Sutterfield
| Quote: | "Cockpit referenced" is a specific term for "vented to
cockpit atmosphere" . . . which is what the vast majority
of alternate static sources do.
The piper Pacer and Tri-Pacer didn't have static systems.
The altimeter was simply mounted to the panel and vented
to cockpit as was any VSI and/or altitude encoders added
at later dates.
Bob |
[quote][b]
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cjensen(at)dts9000.com
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| Posted: Sun Dec 10, 2006 3:16 pm Post subject: Pitot Current Draw |
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Geeez, I guess that's why I ask electrical questions. Now that I think
about it, it makes sense...size does matter.
Chuck Jensen
Bob W. wrote...
Shorten the element if you would like MORE heat, lesson I learned as a
teenager. I had a piece of nichrome wire that I wanted to get red hot.
(I have no memory of what I was trying to do other than that.) I
stretched the wire out and clamped on an electric cord I could plug into
the wall. It got a little hotter than I wanted. Well, I knew ohms law
and I knew P=I^2*R so the obvious solution was to cut R in half to get
half power. When I plugged it in, that sucker got white hot so fast I
didn't have time to blink. Haven't had much trouble keeping ohms law
straight since.
Do not archive
--
N93BD - Rotary Powered BD-4 - http://www.bob-white.com
First Flight: 11/23/2006 7:50AM - 0.7 Hours Total Time
Cables for your rotary installation - http://www.roblinphoto.com/shop/
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cjensen(at)dts9000.com
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| Posted: Mon Dec 11, 2006 5:54 am Post subject: Pitot Current Draw |
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I had a TriPacer for a long time. It definitely had a static system...unfortunately it was in the radios.
Chuck Jensen
Do Not Archive
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nuckollsr(at)cox.net
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| Posted: Tue Dec 12, 2006 5:09 am Post subject: Pitot Current Draw |
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At 06:16 PM 12/10/2006 -0500, you wrote:
| Quote: |
Geeez, I guess that's why I ask electrical questions. Now that I think
about it, it makes sense...size does matter.
Chuck Jensen
Bob W. wrote...
Shorten the element if you would like MORE heat, lesson I learned as a
teenager. I had a piece of nichrome wire that I wanted to get red hot.
(I have no memory of what I was trying to do other than that.) I
stretched the wire out and clamped on an electric cord I could plug into
the wall. It got a little hotter than I wanted. Well, I knew ohms law
and I knew P=I^2*R so the obvious solution was to cut R in half to get
half power. When I plugged it in, that sucker got white hot so fast I
didn't have time to blink. Haven't had much trouble keeping ohms law
straight since.
|
Pitot tube heaters are not like those used in your toaster.
See:
http://tinyurl.com/yyuted
The heater wires are wound on a flexible mandrel contained within
the "tube" visible in these pictures. The winding pitch is varied so
as to put optimized heat sources at various places throughout the
pitot-tube structure. Lots of heat in the probe, not so much around
the corner, lots more in the mast.
Bob . . .
---------------------------------------------------------
< What is so wonderful about scientific truth...is that >
< the authority which determines whether there can be >
< debate or not does not reside in some fraternity of >
< scientists; nor is it divine. The authority rests >
< with experiment. >
< --Lawrence M. Krauss >
---------------------------------------------------------
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