Originally Posted by
hllywdb
It's got to be a porting issue. Has anyone compared the cylinder ports on a .010 and .020? It looks like I should get to 25K though if I can get to 20500 with the 4" prop looking at the chart, no?
If the smaller prop requires 35 watts to spin at 25k then I would say yes. Who knows, maybe the power drops off more quickly than indicated.
Since for speed you want maximum hp, with stock porting/intake configuration, and assuming the data is correct, the goal would be to run at 23k in the air with the appropriate prop load. I doubt reviews that provided the data are based on reams of test results.. the graph was generated from old Aeromodeller reviews and the like, with some extrapolation and curve fitting applied I'm sure. As to the test procedures.. run it on an .049 prop, run it on stock Cox .020 props, clip the Cox prop, measure rpm, use rule of thumb calcs to determine power, repeat, extrapolate, etc. Or so I tend to think. I doubt any magazine reviewer was using a dynamometer to record torque on a TD .020 in the late '60's.