Howard wrote:

Paul:
    I was daydreaming on the way home about prop thrust and horsepower and
realized that horsepower is directly translatable into thrust using the
horsepower = torque * RPM / 5252 formula.

If one looks at 100 hp you will have 100 foot lbs of torque @ 5252 RPM
less at higher RPM, more at lower RPM....

Torque being measured in foot lbs represents a circle of 24" diameter or a
circumfrence of 6.28 feet which in this case is rotating at 5252 RPM
bringing the resulting distance traveled to 32982.56 feet per minute or
roughly 375 mph.

This means that at 375 mph with a prop which is 100% efficient, a 100 hp
engine will produce 100 lbs thrust.

This also means that at half that speed or about 187 mph it would produce
200 lbs thrust

If we take a realistic peak efficiency of 80% we find that it is not
unrealistic that thrust should equal horsepower at 300 mph.     Thus the
formula:

horsepower = thrust * speed / 300
thrust = horsepower / speed * 300

This would be an obtimised prop for the speed.

An interesting exercise..... How close to correct is it??

               H.W.

Right on Howard.
I am amazed Howard. With out learning this in formal physics class you have
intuitively
derived and realized the basic formula for HP. Namely: HP = Drag * FPS / 550.
No offense intended. 375 MPH is 550 FPS. One HP is 550 pounds moving at 1 FPS.

I taught simple physics to race car wantabe engineers for awhile back in
the early 70's
and that is the way I presented it. All sorts of things now become clear,
easy and obvious.

HP is a force (drag) times a speed.

Paul Lamar

Good job! (seriously)   It's good to see the lightbulb come on for someone.
All this will help understand how all this stuff really works.  Paul and some
others of us try to help with this informal education process, hoping to
make someone's life easier (avoid error$) and SAFER.

Knowledge is power!

Bill

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