Trivia

[Bob Vic]

Agreed Dave - prop slippage is a variable in the calculation. I would have thought that allowing 2% slippage would be unrealistsic - props rarely that efficient.

What I'm seeking is the formula with the known factors taken into account; being pitch, engine rpm and gear ratio. and then converting that to MPH .... and then you can deduct the slippage factor of your choice.

Any takers?

Bob

[bootlegger]

Revs (in 1000,s) x prop pitch x step up x .76.
The .76 assumes you have 80% efficiency (you will not have a completely efficient prop).
To work out step up
3% equals 1.03
9% equals 1.09
19% equals 1.19

If underdriven
3% .03
9% .09
19% .019

Direct drive is 1

Hope this works for you Bob

[Jeff]

RPM*Prop Pitch*60*Setup then divided by 63360.

Jeff

[Darren]

Guys,
Interesting......We can do the Maths, but were does Hull efficiency come into it.
All the calculations wont be worth diddly if the hulls a brick!
Wetted area, displacement, Friction Coefficient.........
Hang on my brains exploded.

Darren

[Jeff]

Darren
Bob only asked for an engineering equation on props, hulls are another part to the equation.
Four bees should do 62MPH why is it doing 70MPH


Jeff

[Darren]

Jeff,
Isn't 8 mph equivalent to the reputation coefficient!

Darren

[Ricshaw]

(RPM+20%)xprop pitch
___________________ x60=MPH
63360
Prop pitch in inches.
Theroetical speed with no encombering influrences.

[Bob Vic]

Bingo - that's correct. Then once you have the theoretical maximum speed, you need to deduct slippage. The use of this calculation is to prove that you can't for example be doing 60 mph when with a given pitch and rpm the maths says the best you can do is say 50 mph. Also handy to know the maximum theoretical speed, compare it to the actual speed off a GPS and see how much slip is occuring. It's a useful formula to know.

Your question Rick.

Bob

[Ricshaw]

The term GO FAST-TURN RIGHT !
In what year and at which meeting did the APBA change this in Victoria ?
.....Ric

[Bob Vic]

Good question - I'm guessing a bit here but how does 1969 sound?

Bob