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HelicopterMain Discussion › RPM´S engine equation
12-29-2009 05:44 AM  7 years agoPost 1
wreckless

rrApprentice

Colombia S.A.

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-Gear ratio 8.25:1 (99T / 12T)
-head speed=1950
-So the engine is sopoussed to be at 16.087 Rpm´s
-that´s to much rpm´s for a O.S.91.... am I missing something?
Thanks
wreckless

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12-29-2009 07:44 AM  7 years agoPost 2
Dood

rrProfessor

Wescanson

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The practical RPM of an OS91 is 2000 to 16000 RPM's.
According to the OS website, your peak horsepower is closer to 15,000 RPM.

1950 headspeed is fast for a 90. I would turn it down.

Personally, I wouldn't be running my engine that hard.

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12-29-2009 07:48 AM  7 years agoPost 3
GC1

rrNovice

Manchester, UK

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I would agree with your calculation and technically you are 87RPM over the OS recommended limit. In reality I doubt if 87RPM (Just over 0.5%) would be the difference between breaking the engine or not, but I'm no expert.

For peace of mind why not run at 1939 as 11 RPM on the ehad will not make any difference?

I recently purchased a Trex 700 and OS91HZ. I wondered what people had the headspeead set at so I searched these forums.1950 seemed to be the top end anyway and the max power is actually developed a little below this.

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12-29-2009 01:17 PM  7 years agoPost 4
holzback

rrKey Veteran

noblesville IN United States

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i would run 1850-1900, remember though there is no set number. play with it until you have found the rpm were power is peaking

you aint crashin you aint learnin

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12-29-2009 01:28 PM  7 years agoPost 5
ErichF

rrElite Veteran

Sutton, NH

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Remember that RPM drop is expected when loading the head. Flying a little above peak power RPM is good, provided you aren't above redline. When the system loads, the RPM will drop into the peak power band, and the RPM should stabilize and hold...unless the load is too much of course.

Erich

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12-29-2009 07:33 PM  7 years agoPost 6
wreckless

rrApprentice

Colombia S.A.

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Hello :
I forgot to ask, if the revlimiter(AR7100R)is limiting the engine at 80% value..I don´t
think the engine can be at the top rpm´s, even do the head speed
is at 1950....any comment´s please?
wreckless

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