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'pitot tubes'
1999\04\15@175953 by Andy Kunz

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Anybody know of small (3-5mm dia) pitot tubes for a PIC-based project?

Thanks.

Andy

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Montana Design - http://www.montanadesign.com - Electronics & Model Boats
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1999\04\15@190040 by goflo

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Hi Andy,

http://www.dwyer-inst.com/index.html

Pitot tubes in there somewhere. Unless the OT sturmtruppen
decide you don't need to know, of course.

Jack

Andy Kunz wrote:
>
> Anybody know of small (3-5mm dia) pitot tubes for a PIC-based project?


'pitot tubes'
1999\05\04@171553 by Andy Kunz
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At 04:06 PM 4/15/99 -0700, you wrote:
>Hi Andy,
>
>http://www.dwyer-inst.com/index.html
>
>Pitot tubes in there somewhere. Unless the OT sturmtruppen
>decide you don't need to know, of course.
>
>Jack
>
>Andy Kunz wrote:
>>
>> Anybody know of small (3-5mm dia) pitot tubes for a PIC-based project?

They have pitot tubes alright, but I'm looking for small ones in the 2-3"
long range.  I would like to mount it to a model airplane to determine
airspeed.

Does anybody have an alternative idea?

Thanks.

Andy


==================================================================
  Montana Design Tech Support - http://www.montanadesign.com
==================================================================

1999\05\04@181432 by Adam Bryant

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Andy,
I have thought about this too.  The only feasible idea I came up with was
a small paddle wheel mounted inside the fuselage or wing with half the
paddles sticking out into the airflow.  Count the RPM's over a period of
time and calculate airspeed based on the circumference of the paddles.
Placement would be important, and thinking about it, you probably
wouldn't want it on the fuselage so you don't have the effect of the prop
blast throwing off your readings.  It might be kind of draggy depending
on the install, but should give you a reasonable approximation of the
speed.

On Tue, 4 May 1999 11:50:14 -0400 Andy Kunz <spam_OUTsupportTakeThisOuTspamMONTANADESIGN.COM>
writes:
{Quote hidden}

Adam Bryant (age 0x23)
.....abryantKILLspamspam@spam@peaktech.com (work)
adamdbspamKILLspamjuno.com (home)
Parker, CO, USA
Robotics, RC Airplanes, anything using a PIC

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1999\05\04@211512 by Peter van Hoof

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how about measuring different

glue 2 thermistors to 2 resistors
put the two resistors in series on a constant current source (constant
output heater)
put the one pair in the airflow
the other pair inside the plane

measure resistance of both thermistors
the heatloss from airspeed should be a good indication of airspeed
(needs small mass so reaction speed is sufficient)
use  the pair inside the plane to compensate for air temperature
use a 2 dimensional lookup table for windspeed

Peter

{Original Message removed}

1999\05\04@214052 by Dennis Plunkett

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At 21:13 4/05/99 -0400, you wrote:
>how about measuring different
>
>glue 2 thermistors to 2 resistors
>put the two resistors in series on a constant current source (constant
>output heater)
>put the one pair in the airflow
>the other pair inside the plane
>
>measure resistance of both thermistors
>the heatloss from airspeed should be a good indication of airspeed
>(needs small mass so reaction speed is sufficient)
>use  the pair inside the plane to compensate for air temperature
>use a 2 dimensional lookup table for windspeed
>
>Peter

<SNIP>
Do you think that it will work well at temperatures around -45C? :-) I
guess that an altimeter would also be required, or another set of
thermistors outside to measure air temp.

Perhaps we should look into rocket control, as there are some methods of
placing holes in the body, and measuring and calculating the disturbance to
airflow-> speed and direction etc. Dunno much about it but. I guess that it
would take more than a PIC to do the complex calculations.

Dennis

1999\05\04@214640 by Sean Breheny

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What about just the force on a vane placed in the airstream? RC models
almost never go above 1500 ft AGL in normal usage so pressure differences
would be small. I once saw an article on doing this very thing for
ultralights. It was in one of the free electronics magazines (but I can't
remember which :( I think it may have been the one that Bob Pease has a
column in.

Sean

At 11:45 AM 5/5/99 +1000, you wrote:
{Quote hidden}

| Sean Breheny
| Amateur Radio Callsign: KA3YXM
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Save lives, please look at http://www.all.org
Personal page: http://www.people.cornell.edu/pages/shb7
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1999\05\04@220421 by Mark Willis

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Andy, consider making your own with a piece of 3-5mm Brass tubing
swaged down to 1mm or so, a differential pressure transducer, and a bit
of elbow grease?  (Vent the transducer into a 'pore' on the side of the
body of the airplane, same as larger aircraft do it.)

 At www.instrumentation2000.com/catalog/pressure/09/020958a.html
they have a micro-manometer that measures either -14" H2O..+14" H2O, OR,
velocities up to 15,000 fpm.  Seems to me that you could start off by
making your own system, "wind tunnel" test the system (read: Drive
around like a madman, with the rig stuck on a pole sticking up off the
front bumper of your car, to give you some good velocity calibrations),
and call it good.  I'm suspecting a lower pressure range might do you,
though <G>  Start out guessing that 1" H2O = 1,071 fpm, roughly <G>

 (Under constant velocities, the reading will be accurate, smaller
pitot tube will just make the system read a little "laggier", is all.)

 Mark

Andy Kunz wrote:
{Quote hidden}

1999\05\04@232449 by Brian Kraut

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A lot of homebuilt aircraft use two aluminum tubes.  One facing forward and
one pluged in the front and small holes drilled in te side.  Hook one up to
each side of a differential pressure transducer.  Should be pretty acccurate
and easy to build.

Mark Willis wrote:

{Quote hidden}

1999\05\05@041632 by Windows-1252?Q?Sebasti=E1n_Dols?=

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have pitot tubes alright, but I'm looking for small ones in the 2-3"
long range.  I would like to mount it to a model airplane to determine
airspeed.

Does anybody have an alternative idea?
-----------
When I was young, I resolved these trouble through heating a NiCr wire and
measuring how the wire was not so hot when in air flow compared to a static
heated wire. In fact, some anemometers work this way..

1999\05\05@074456 by Michael Rigby-Jones

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>  have pitot tubes alright, but I'm looking for small ones in the 2-3"
> long range.  I would like to mount it to a model airplane to determine
> airspeed.
>
> Does anybody have an alternative idea?
> -----------
> When I was young, I resolved these trouble through heating a NiCr wire and
> measuring how the wire was not so hot when in air flow compared to a
> static
> heated wire. In fact, some anemometers work this way..
>
Mass Air Flow meters for fuel injection work like this.  However, you have
to have a reference wire that is not exposed to the air flow in order to
account for ambient temperature variations.

Regards

Mike Rigby-Jones

1999\05\05@104237 by Sebastián Dols

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>>  have pitot tubes alright, but I'm looking for small ones in the 2-3"
>> long range.  I would like to mount it to a model airplane to determine
>> airspeed.
>>
>> Does anybody have an alternative idea?
>> -----------
>> When I was young, I resolved these trouble through heating a NiCr wire
and
>> measuring how the wire was not so hot when in air flow compared to a
>> static
>> heated wire. In fact, some anemometers work this way..
>>
>Mass Air Flow meters for fuel injection work like this.  However, you have
>to have a reference wire that is not exposed to the air flow in order to
>account for ambient temperature variations.

Of course, thats rigth, and that is the correct way to read 'compared to a
static heated wire' in my text. Maybe the quick answer was a bit obscure.
BTW, the 'static heated wire' was not so static, because traveled in the
belly of the airplane model, but was not exposed to the air flow.

Keep on PICing.

Regards

Mike Rigby-Jones

1999\05\05@124609 by Andy Kunz

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>Placement would be important, and thinking about it, you probably
>wouldn't want it on the fuselage so you don't have the effect of the prop
>blast throwing off your readings.  It might be kind of draggy depending
>on the install, but should give you a reasonable approximation of the
>speed.

It doesn't have a prop.  It's a jet.  And it doesn't have much room inside.

Andy
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  Montana Design Tech Support - http://www.montanadesign.com
==================================================================

1999\05\05@134056 by Alan.King

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 As someone else suggested, a small pinwheel type of setup would be
cheaper and easier if this is a one-off kind of thing.  First hacker
thing that comes to mind is one encoder axis of a mouse.  Course you
only need one half of the encoder since you only need rate, not
direction.  This with a small fan blade should be pretty accurate once
calibrated, probably better than a pitot tube.  Look for a real Mouse
Systems mouse.  They had both supports for the shaft on one side, so you
could have only the contact point sticking out with a fan on it.  And
you can select the pitch of the fan to give best accuracy at the speed
you need.  Heck, send me your address and I'll send you one of mine, not
like I'm really going to run out of all the old mice I've collected..
Alan


Andy Kunz wrote:
{Quote hidden}

1999\05\05@153457 by MEDICINTEKNIK KB

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I would measure airpressure in a pitot tube. You can ask a hospital for a used (well cleaned) diposable pressure transducer from the Intensive care unit. They form a bridge, that need to be amplified a fair bit, but you have a cheap linear pressure transducer that way. The bridge would probably give you 30 - 40 microvolts or so, at a high speed.

Mail me if you are interested, but have difficulties obtaining the X-ducer.

Sven
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FrŒn: Adam Bryant <EraseMEadamdbspam_OUTspamTakeThisOuTJUNO.COM>
Till: PICLISTspamspam_OUTMITVMA.MIT.EDU <@spam@PICLISTKILLspamspamMITVMA.MIT.EDU>
Datum: den 5 maj 1999 00:15
€mne: Re: pitot tubes


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