Does anybody know the formula for propellers that I'm tryig to remember? It was talked about either here or on the old yahoo site, had to do with the relationship of propeller pitch/rpm/airspeed. I kinda remember the number 1156 being part of the formula but don't know how I dredged that up.
It'd be useful if you wanted to estimate the airspeed at a certain rpm using various propeller pitch figues,like if you were gonna repitch & were trying to decide how much.
Eric
formula for propellers
Moderators: GAHorn, Karl Towle, Bruce Fenstermacher
The pitch is how far the airplane moves per rprop evolution. If it is 53 inches the plane moves forward 53 inches per prop revolution.
mph= pitch *rpm/1056 pitch in inches, rpm in rev/minute
The formula is approximate and depends on the condition of the propr, for standard conditions, and a "clean" airframe in cruise configuration
mph= pitch *rpm/1056 pitch in inches, rpm in rev/minute
The formula is approximate and depends on the condition of the propr, for standard conditions, and a "clean" airframe in cruise configuration
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zero.one.victor
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- Joined: Tue Apr 23, 2002 12:11 am
PROP FORMULA
ERIC:
THE PREVIOUS POST IS CORRECT FOR AIRSPEED COMPUTATIONS. IF YOU WANT TO KNOW WHAT THE PROP TIP SPEED WILL BE AT A GIVEN RPM, (SO YOU DON'T EXCEED THE SPEED OF SOUND),:
PROP DIAMETER IN INCHES DIVIDED BY 24 TIMES (RPM DIVIDED BY 60) X(2 X 3.1416) = FT PER SECOND. (1116 FT PER SECOND = MACH I AT SEA LEVEL).
ERNIE JARVIS
THE PREVIOUS POST IS CORRECT FOR AIRSPEED COMPUTATIONS. IF YOU WANT TO KNOW WHAT THE PROP TIP SPEED WILL BE AT A GIVEN RPM, (SO YOU DON'T EXCEED THE SPEED OF SOUND),:
PROP DIAMETER IN INCHES DIVIDED BY 24 TIMES (RPM DIVIDED BY 60) X(2 X 3.1416) = FT PER SECOND. (1116 FT PER SECOND = MACH I AT SEA LEVEL).
ERNIE JARVIS
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Dave Clark
- Posts: 894
- Joined: Mon Apr 22, 2002 6:25 pm
Prop formula
Actually, I meant the speed of his prop tips exceeding Mach I, but his 170 may be faster than most.
Ernie J.
Ernie J.
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zero.one.victor
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P-ponk has a website-based calculator to determine tip-speed:
http://www.pponk.com/HTML%20PAGES/propcalc.html
The April, 2003 issue of Sport Aviation (The EAA magazine) has an article about how to calculate how a pitch-change of your prop will affect cruising speeds. As soon as I can locate my copy, I'll try to post the info.
http://www.pponk.com/HTML%20PAGES/propcalc.html
The April, 2003 issue of Sport Aviation (The EAA magazine) has an article about how to calculate how a pitch-change of your prop will affect cruising speeds. As soon as I can locate my copy, I'll try to post the info.
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons.
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons.
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zero.one.victor
- Posts: 2271
- Joined: Tue Apr 23, 2002 12:11 am
Like I said,I'm not too worried about tip speed with a 145-horse 170! The formula we've been discussing (rpm X pitch / 1056 = mph) is actually a pretty darn good one for calculating cruise speed with various pitch propellers.Of course it assumes 100% efficiency (no "slippage") after stabilizing in cruise. The 1056 figure is to convert from inches of forward travel (pitch) per minute (rpm) into miles & hours.
I'll try to hunt up that article in Sport Aviation. I'm sure it'll be very interesting but it's pretty hard to beat this little formula for simplicity.
Eric
I'll try to hunt up that article in Sport Aviation. I'm sure it'll be very interesting but it's pretty hard to beat this little formula for simplicity.
Eric