Converting Inches-H2O to Airspeed at Sea Level

The dynamic pressure difference at the Pitot tube nozzle (assuming it is pointing exactly upwind), as measured by the manometer, is equal to 1/2, times the moving fluid density, times its velocity squared.

There's a bit of number crunching to get the required units, and these days any electronic abacus can do the grunt.

velocity pressure squared times 4005 = feet/min.

No!

√(velocity pressure) times 4005 = feet/min. Velocity pressure in inches water.

Cheers..........Codey

I apologize for the error I typed the formula improperly and thank you for the correction.

Make sure you correct for the pressure inside your transfer line. A pitot tube when used properly already does this. When dealing with these low pressures you have to use the correct "starting point" or your speed could be quite off. In your calculations you also have to start with the correct air density.

Great info. Thanks to all.

That's interesting dapts

The figures agree pretty well with calculated ΔP = 0.5*ρ*V² up to about 150 knot, but then fall off, to about 2/3 calculated at 1000 knot. Any idea why?

Cheers........Codey

The table generated by using the data from Honeywell Sensing and Control table labled "Pressure Sensors Conversion Factors" http://www.sensorica.ru/pdf/1_doc_4.pdf

OK thanks dapts.

It doesn't tell us much as it doesn't give a formula to get pressure from airspeed, just a table.

Also says 1 knot = 1.15 statute mile. It should of course be 1 nautical mile = 1.15 statute mile (or 1 knot = 1.15 statute mile/hour), which makes you wonder about their competence.

Cheers..........Codey