OLD_SLOW and in the WAY

hi ya guys
i do race modifications on zenoah engines the 231/260/g62 etc. a dyno is financially out of the question.
but there is a formula to convert thrust and rpm to hp. i have made a test cell with a sliding mount and a scale in concert with my tach. if any of you have the formula i'd certainly appreciate it

THanx

BRO

Mike Connor

My Feedback: (5)

http://www.bmaps.net/

Under goodies there is a ThrustHP calculator to download.

DipStick

Fastrat,

Here are the formulas for Thrust and Power:

If you are measuring the thrust then it would be better to figure the Ct:

Ct=Thrust/(q*n^2*D^4)

Thrust= Ct * q * n^2 * D^4
Horse Power = Cp*q*n^3*D^5

Ct is the Coeff of thrust
Cp is the Coeff of power
q is the mass density of air
n is the rev per sec
D is the diameter

The Cp can be roughly calculated with the following equation:

Cp= (pitch/diam)*.0819-.00726 (liner eq. based on a clark Y type foil and rp378)

(Word of warning: as your pitch to diam ratio gets higher (like a speed prop) the less predictiable the Cp becomes because the prop may or may not be stalled or parts of the prop can be stalled so the Coeff of power can very a lot...so you would be best to use props that have a pitch/diam ratio of .6 or less to try and figure the power) There are a few dino test that I have seen published for different engines and these calculated results agree with the dino information alot better than the results that ThrustHP gives. This information is roughly based on [link]http://naca.larc.nasa.gov/reports/1932/naca-report-378/[/link]) If you go to the report and have figured the Ct you can also find the approx Cp. Or you can figure the 75% blade angle of attack and use this to find the information in the report.


Hope this Helps

Steve

Ducted Fan Dan

My Feedback: (2)

Check out www.lcrcc.net. Nothing to download, just click on thrust calculator, enter prop diam, pitch and rpm and you get thrust.