Thanks Gordon,

I appreciate your comments and the link. Good stuff.
Although I did not follow Doug's question, but the above are all good
tools.

PS: As a side note, I trust the pitot tube works by narrowing the air
passage through it, thereby increasing the air velocity which equals a
reduction in air pressure, and this reduced pressure is read by the
needle. It is not a positive dynamic (impact) pressure that is being
read. Is this right?

Regards
Rolf

I think you are speaking of a venturi Rolf.
A pito tube measures impact pressure.

For a simple minded example:
If one holds a one square flat plate out the window of one's
car at 100 MPH at sea level one will measure a force of
26 pounds or 26/144 = .18 psi. Pito tubes work on this simple
principle. There is no airflow into the pito tube.
One could stick the pressure sensor out the window and get
the same result.

The simple equation I use is force (drag) = .0026 times MPH squared
times the area of the flat plate.

The .0026 constant is related to the air density. It is
not the air density per se.

The same equation is used when calculating  drag on a streamlined
object where C sub d is the drag coeff. of that object. In that
case the formula is Drag = C sub d X Frontal Area X .0026 X
MPH squared.

The term C sub d X Frontal Area is frequently called the flat
plate equivalent drag number.

The terms impact pressure and dynamic pressure are interchangeable.

Paul Lamar ...No rotor no motor.

Thanks Paul,

You are right, of course.
I had a "venturi" in mind, sorry.
This must be signs of getting old. :)

Rolf


I just had a problem with pressure. Our house is in a valley
and there is a reservoir up the valley that is several hundred
feet higher than the house. The toilet valves and the pressure
relief valve on the water heater would spew hot water. My wife
said she turned the supply valves to the hot water tank and the
toilet almost off and could not understand why that did not work.
I had to explain to her that  would not help when no water was
flowing. Pressure is pressure whether it goes through a pin hole
or a sewer pipe. It took two pressure regulators in series to
solve the problems. We probably had 75 to 100 psi water pressure.

The flat plate is at the end of the pitot tube hose.
Same goes for thick radiators at the end of a duct. The
less porous the radiator the more the scoop looks like a flat
plate.

Paul Lamar ...No rotor no motor.

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