I can't seem to find it on the net, but the Mythbusters tv series set up an experiment to see if bullets fired vertically came back to earth with lethal force. They set up a vertical wind tunnel using about 50mm plastic tube and airspeeds of around 130mph. Bullets dropped into the tube were supported by the airstream, leading to the conclusion that the bullets terminal falling velocity was about 130mph.

I have a hazy memory that they used a shop compressor to generate the air velocity in the tube with a hand held airspeed meter to measure the speed.

Paul,

At those speeds, I think you should be able to use a Pitot tube

This paper is worth a read.

MichaelG.

It's easy enough to make a water manometer and pitot head to measure airspeeds in the range specified. It shouldn't need calibrating. If one wants to be precise one can take into account the variation in dynamic pressure with density, but unless one is half way up a mountain I doubt it'll make much difference. There are also errors at higher airspeeds from assuming that the dynamic pressure is exactly 1/2 rho V squared, but at 130kts these are less than 1%.

I've used a home made water manometer to calibrate aircraft ASIs for full size gliders.

Regards,

Andrew

Hi Windy

Have you looked at using a reversed domestic vacuum cleaner or cleaners if you need more flow (some are around 1500 watts) maybe with a speed control that works with brush type universal motors. Maybe an electric router or hand drill controller will do.

I tried in vain on the net to get the typical air speed…. Hmm

The pipework may need to be designed carefully to smooth out the turbulence from both the machine and the pipework if your experiment requires it.

Regards
John

Many years ago, when I did an industrial placement at RAE Farnborough, we were investigating the efficacy of various fire suppression systems in aircraft wing fuel tanks. In order to test these we fired canon shells (from a captured soviet gun) at a full size mock up of a wing section with a tank of fuel in it. In order to simulate the airflow over the wing we used the exhaust from a RR Avon engine (which for some historical reason was mounted on a coach chassis). The exhaust was directed into a venturi that induced an airflow down some ducting. One of my jobs was to measure the air speed over the wing using a pitot tube on a stick- with 2 other guys holding on to me. Usually about 120mph. Sometimes the fire suppression systems worked but it was much more fun when they didn't!

Sorry, this doesn't help at all – unless you have an Avon handy.

Rod

This idea is probably to crude for your usage, but it might be of interest– some years ago I needed to measure wind speed and asked my brother, who was working for the met office then, if he had a wind speed indicator. He didn't but gave me a method. Hang a suitable sized flat plate from a "goalpost " structure. Calibrate by driving a car and stick the thing out of the window, mark the inclination at a few speeds. interpolate for intermediate speeds. This worked for my needs but have no idea how accurate it was.