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Home✈️Aircraft🚁HelicopterHelicopter Main Discussion › Nitro engine RPM question
03-30-2010 09:36 PM  10 years ago
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Nitro engine RPM question
Perhaps im thinking wrong here, please help me out..

Take a OS .91hz, peak HP is at 15000rpm, according to O.S.
Most 3D guys run a headspeed of around 1900-2000 on a 90 size bird.
T-rex 700 gear ratio is 8.2, that make 15000/8.2 = 1829 rpm.
So to get 2000rpm on the head you need to spin the engine 16400rpm.
I heard that the RPM "red zone" of a O.S 91hz is 17000rpm.
Why is the the gear ratio so "far" off stock?
Or is everyting between 15000 and 17000rpm "ok" ?
Wount keeping the eninge at that unnecessary high RPM just shorten its life?

Wount a better gear ratio be 7.5, 15000/7.5 = 2000rpm..?

Just something i reflected over..
JR Vibe Ito Edition, JR Nex E8, JR E550, TAGS01 FBL system, JR XG8 radio
03-30-2010 11:56 PM  10 years ago



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This is so the engine loads down into it's peak HP rpm."I'm a dirt torpedo!"
03-31-2010 12:55 AM  10 years ago

rrKey Veteran

Jenison, MI

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If you look further into the engine specs it should tell you the amount of horse power and and what rpm that is, Then it will tell you the min and max rpm range the engine is capable of running. Ideally you want to set the head speed so that under load the engine is at the rpm specified to make the optimal horse power for that motor. Think of it as a pro mod drag car. they set the shift points so the engine stay near the rated horse power/rpm's for the motor to get the best performance out of the engine. A torque curve rises and then falls at the highest point that the engine can produce power,that is the rpm you want to run at.
03-31-2010 01:07 AM  10 years ago


UK. Herts

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Many seem to massage the figures. I prefer to take the streightforward view whereby if an engine has a peak performance at say 17000rpm, then with a gear ratio of 8.5, the optimal head speed is 2000rpm. Has allways worked well for me.Vegetable rights and Peace
03-31-2010 01:43 AM  10 years ago

rrKey Veteran

noblesville IN United States

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there is no right head speed, there is a range, but you need to run a gallon or two and play with the head speed and find what you like. pending on your pitch, cyclic, and style of flying only you can figure what you like by the feel. as long as you are not over reving and you have a good tune you are aint crashin you aint learnin
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