I have the 'Airspeed Indicator Calibration Record' for my full size glider's
pot pitot based instrument. It appears that the tests are done with a
manometer and the ideal values are given here. This is probably a standard.
The pitot pot on the nose of the aircraft is about 1 inch dia. I don't know
if the area of it makes a difference to the readings. I could measure it
accurately if you want. Incidentally, just putting your hand over the pitot
causes a speed reading due to the increase in pressure from warmth of the
hand. Airspeed indicators under read as altitude increases.

Inches of Water (Gauge) /Speed.
0.26 /20
0.39 /30
1.04 /40
1.63 /50
2.35 /60
3.19 /70
4.18 /80
5.28 /90
6.52 /100
7.89 /110
9.40 /120
11.02/130
12.78/140
14.68/150

I found this information because I am building a PIC based airspeed
telemetry link to be used between the glider and the launching winch so that
the winch driver has feedback of the gliders speed during the launch. This
will allow optimum launches. The PIC will do the A/D conversion, modulate
the RF carrier and control the power to the unit automatically. It will turn
itself on when the airspeed goes above 25 Knots (ground run). It will remain
on for one minute (launch in progress). It will then turn off (in free
flight). It will not turn on again until the airspeed has gone below 25
knots for a minute (landed)and then goes above (relaunched). This should
ensure that the battery life is maximised and that one carrier frequency can
be used by all gliders so that the winch driver doesn't have to change
channels on the receiver. The system is completely automatic and can be
forgotten by the pilot. The display should be easy to read by the winch
driver using peripheral vision as he should be looking at the glider all the
time.

Launch speeds are typically 30 to 80 knots allowing a 5inches of water
pressure sensor to be used.

Gerry Cox
Weymouth U.K.

-----Original Message-----
From: Roland Andrag [mailto:randrag@ICON.CO.ZA]
Sent: 07 May 1999 16:50
To: PICLIST@MITVMA.MIT.EDU
Subject: Re: Airspeed


>  I've been thinking about calibration;  Borrow time at a campus wind
>tunnel, for higher speeds?  (Borrow a friend with an airplane?  <G>)


What happened to the car window? Or get up on the back of a truck.. Assuming
you can hold the plane, that is... Take off the wings - use only the
fuselage...

Cheers

Roland