Static thrust on ground

I measured the static thrust on ground with a normal digital scale. The measured result was 10.1kg with the 30" propeller and unbelievable 14.9kg with the 40" propeller.

From the photo you can see that the axis has a inclination of about 25º. That means the real thrust in propeller direction is about 10% higher: 11kg for the 30" and 16,5kg for the 40".

That is far more than I expected for the 40".

Measurement setup with a sand bag to avoid the movement of the housing on the scale: