Dear Pe,
We'll discuss further on that.

Yesterday's file that i uploaded, by changing the cell for inputs i missed out the pitch speed calculation... sorry... anyway it has been corrected.

Prop Size Rpm Thrust (kg) Thrust Estimate (kg) Diff (%)
11 x 7 13000 3.08 3.49 11.747851
11 x 7 12000 2.72 2.98 8.724832215
11 x 8 12500 3.12 3.50 10.85714286
11 x 8 11400 2.74 2.91 5.841924399
12 x 6 12400 3.65 3.84 4.947916667
12 x 6 11300 3.25 3.19 -1.880877743
12 x 8 10800 3.3 3.52 6.25
12 x 8 10500 2.99 3.33 10.21021021
13 x 6 11200 3.64 4.10 11.2195122
13 x 6 10600 3.32 3.67 9.536784741

Average Variance (%) 7.745529654 on over prediction.


To progress further, above table was included in the latest file (same 2nd link as before). It shows the different between calculated and actual measurement done by ROSSI engine. No i'm not promoting rossi or any other manufacturer, but the way the measurement being taken and the way the data being presented seems sound and good. There are a few things which were unknown to me, they were the plan form of those props that they used and the average air density during the testing. This may account for another 1 or 2% variance.

Looking at this, for an average RC hobbyist who wanted to have a close estimate of required thrust for estimating take-off distant, hovering or just for fun of it may be able to use this file. For a serious propeller designer/developer, this tool will be their friend. By changing the dimension, pitch and profile, one may predict the actual behavior of their designed propeller.

Attached also the actual file produced by them (rossi).

rgds
umran