sound barrier

As a rough guess I think my fan would need to do 9000 rpm. I dare say my motor would be everywhere before that happened!

I just tried a rough calculation and got about 15000rpm based on a 44cm diameter fan which is about what my car has.

But I have probably buggered my calcs up somewhere.


Speed of sound at ground level at 20degC is 343 meters/sec (Wikipedia)
Thats 20580 meters per minute.

Pi x Diameter of fan = circumference of the fan. ie distance travelled per revolution.

RPM revs per minute x 3.14 x Fan diameter = meters/minute
RPM x 3.14 x Fan Diameter = 20580m/min
RPM = 6554 / Fan diameter in meters
RPM = 6554 / 0.44
RPM = 14895

That would give a speed at the tip of the blade at the sound barrier.

Please correct me if I have made a mistake.

D

G'day Muzbury, there is a bloke here with me who says "The Washerwoman" would know.

Dave

Heres a link to a Cessna 210 at take off I use to fly these things from time to time there 3 blade prop hits the speed of sound at around 2700 RPM on take off.

Turn the sound up and enjoy, But the prop won't last long at that rate let
alone a fan

C 210 prop hitting the speed of sound.

Cheers

Heater fan, air con fan or radiator fan? Just wondering..................

WHY?

The velocity= radius X revs. Only catch is you have to make sure all the units are the same. So if the revs are rev per minute and radius is in cm then the velocity will be cm per minute. The radius never changes and velocity of sound is fixed so the revs required will be speed of sound in cm per minute divided by the radius of the fan in cm.....I think....it's been 40 years since I used that equation. My head is now spinning as well...

Muzbry

At what altitude, as the speed of sounds varies with altitude.

Cruiser

Presumably a lawnmower wont get to any significant altitude.

Except of course if he lives in the Snowy area



LOL