Quote:
Originally Posted by SteveC  I was curious so I did a little Googling:
The first chart I looked at was for a IO-360. It shows 55% and 65% power settings at 2100 and 2400 RPMs. The MP change varied from 2.3" to 3.0" for a 300 RPM change. This equates to 0.77" to 1.0" per 100 RPM.
The second chart is for an O-320. This one shows 2450, 2500, and 2550 RPM. Searching through the chart it appears that 100 RPM changes in this engine (2450 - 2550) require 0.5" or less change in MP to hold the same horsepower.
I'm not yet convinced of your contention that 1" = 100 RPM. Do you have more charts available that support your thesis? |
Well you are only looking at half of the problem here. If you reduce the power 1" that yields a certain decrease in power and no change in propeller effeciency. If you reduce the power by 100 rpm you reduce the power, as you pointed out by a greater margin, but you increase the propeller effeciencies leaving the resulting performance change negligable.
The only way to do this on paper that I am familiar with is to calculate for each new propeller effeciency. The charts you have will only give you the engine bhp percentage and leaves the prop out of the mix.
It will not hold 100 percent true for any given situation, it is a baseline. But go ahead and test it out, in every aircraft I have flown thus far there was no appreciable difference between the in speed/rate of descent when comparing 1" to 100 RPM.
Sorry webster not riddle, I felt I would flunk out with a beach nearby, Same thing just a different state.