Dear All,
First i would like to thank one of the forumer here who open this thread, http://www.rcuniverse.com/forum/m_10...m.htm#10907244
Because of the problem posed, the calculation of actual thrust of the prop for a given rpm is critical.

No doubt that there are many thrust calculator out there, but trust me, many are way off from actual figure. Currently there are iteration solution suggested by University of Sydney which can be viewed here - http://www-mdp.eng.cam.ac.uk/web/lib...ler/prop1.html

To me that is a very good technique for estimation. I did draft-out the equations and the iterations are difficult to converge. So you'll end up ashtray...

In view of the proposed idea, i came out with a similar iteration technique, however the basic changeable variables holds a different unit value. No worries if one doesn't understand it, the target is to have a very close to life reading of actual THRUST per propeller dimension with certain rpm.

The inputs are all the yellow colored cells in the spreadsheet. The major output are in red. In using this, one has to get the 'SOLVER' plug-in for excel. Activate also macro for the file usage.

Check any of my posts where I have stated static thrust measurements for my engine / prop combinations. All of these figures I have accurately measured with my test setup. My results have proven to be repeatable, and also correlate with what I experience in the air. They all have shown Thrust HP to be optimistic. The degree varies, but seem to get worse as pitch goes down and diameter goes up.
Here are a few examples:

Mejzlik 20x6 @ 8800 RPM - Measures 20 lbs, 4 oz thrust. THP says 37.17 (used APC airfoil)

Zinger 20x6 @ 8300 - Measures 19 lbs, 14 oz. THP says 31.19.

APC 17x6 @ 9400 - Measures 17 lbs, 12 oz. THP says 22.14.

APC 13x4W @ 11,800 - Measures 8 lbs, 12 oz. TP says 11.93.

You get the picture

Above was posted by Aerosplat in this thread http://www.rcuniverse.com/forum/m_608127/tm.htm We have to extend our gratitude to his work because i managed to simulate the result obtain by him physically via my spreadsheet by a very close margin of within 5 to 7%.

There are few variables that maybe different from actual production propellers. In my spreadsheet i utilized 'CLARK Y' airfoil data both for Cl and Cd. Both parameters have been manipulated to produce a function in terms of actual angle of attack. I do not actually know what type of airfoil being used to produce Mejzlik, Zinger or APC nor did i actually know the hub diameter, the root chord and the tip chord. And the worst unknown is the actual profile of the each blade when you view from front; on this juncture most prop blade will have a slight curvature at the root, grow a bit and taper down at the tip. In the spreadsheet however I modeled the blade to be a straight taper from root to tip.

The equations being derived as such a way that, this spreadsheet is usable even when the forward velocity is zero. You'll have actual static thrust reading. When you add in some forward speed, you'll see a reduction in thrust. You may continually adding speed until it reaches the 'pitch speed', because of the nature of the airfoil, even at pitch speed, it'll still produce a small amount of thrust.

The button "CALCULATE" is for the SOLVER program to work-out the quantity required for 2 variables in order to satisfy a few equations. At times it may not converge, this can be viewed via the green solver cells which is not 'zeroed'. Most of the times this may be caused by illogical value being inserted such as more forward speed than the pitch speed itself.

The inputs are,

Prop Diameter (inch)
Hub Diameter (inch)
Pitch (inch)
Forward Velocity (inches/sec)
Root Chord (inch)
Tip Chord (inch)
Revolutions Per Minute (rpm)
Number of Blades
Altitude of airport (ft) - this is to determine the average air density.


And for example, i uploaded the file with example data for mejzlik 20 x6 spinning at 8800 rpm. The result can be seen on it...

The solver may take a few seconds to work-out the solutions, so be patience a bit...Especially when one is using a relatively slow computer.

One other point, this is my work for my thesis, use it as you please, but please take note the original developer of this.

I hope many will find this useful, and if there are any question, i'll be glad to answer them. And for those who are actually testing propellers, your outputs are most welcome in this thread.

And here is the link to download this file http://www.mae.my/download/ThrustEstimator.xlsm

Thanks