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10-10-2008 | 10:47 AM

#26

DarZeelon

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From: Rosh-HaAyin, ISRAEL

RE: Overloading an engine

Quote:

ORIGINAL: Juice

...I have some RPM numbers at various pitch settings. Can anything be determined from these numbers?...

Juice,

I will, using the Pé Reivers Prop-Power, give the the output on each of these props and find the RPM with the highest torque...

Output (in HP) times 5,252.1 and divided by RPM, equals torque (in lbs.ft.).
So, to simplify the calculation and since were not actually interested in the exact numerical value of the torque, I will only divide all HP numbers by the RPM at which it was achieved, to get a 'torque factor'... I used APC's and Bolly's 1.2 constant...

18x13, 3,840 RPM = 0.48 HP; torque factor .000125 (This is definitely too large...)
18x11, 4,400 RPM = 0.62 HP; torque factor .000141 (HP and torque)
18x10, 4,450 RPM = 0.58 HP; torque factor .000130

16x13, 4,760 RPM = 0.57 HP; torque factor .000120
16x12, 4,960 RPM = 0.59 HP; torque factor .000119
16x11, 5,200 RPM = 0.63 HP; torque factor .000121(HP only)

Peak torque seems to be somewhat below 4,400 RPM... because just over this number there is a rather sharp drop in both torque and in HP, despite the rise in RPM, but another HP peak is apparent (local absolute...) at 5,200 RPM.

It would be interesting to see what an 18x12 would show, since the gain from the 18x13 to the 18x11 is very pronounced.

This engine has an HP curve with very a pronounced 'bog' and a torque curve with a very pronounced 'peak'...

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