Low max RPM

by Ricardo Urio in 912 / 914 Technical Questions 13 years ago

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Re: Low max RPM

by Roger Lee » 13 years ago

Roger Lee

125 5.12k 4.52k

Hi Ricardo,

First if you have a 912UL with a ground adjustable prop and get 5000 rpm on take off you may be about right. That most probably puts you in the 5500-5600 rpm range WOT.
There are two things to consider while setting up your engine/prop rpm. First if you have a in flight adjustable prop you can take advantage of the entire engine/prop rpm for climb and cruise. If you have only a ground adjustable prop then you are in the same boat as most of us. We have to find a balance between climb and cruise prop settings. First don't worry about a static rpm since this isn't a new prop for your engine as static just gets you in the ballpark for your specific engine/plane configuration and then it needs to be fine tuned anyway by flying it. If you get too much rpm at take off then you will have a good climb prop, but a poor cruise prop. If you get too little rpm on take off you may have a better cruise prop setup, but a bad climb prop and if the prop pitch is too course resulting in low rpm then that can cause excessive wear and tear on the engine and should be avoided at all cost.

Fly your plane and get to your every day normal cruise altitude. Apply full throttle to WOT flat and level for at least 30-60 seconds. See what the max rpm is and hopefully it is around 5500+ rpm. If it is lower i.e. 5200 rpm then the prop pitch is too course and this particular rpm and lower is overloading. A good place to be is between 5500-5600 rpm WOT for a ground adjustable prop. Everything else will take care of itself for rpm. Then just make sure the idle rpm is set and your good to go. This should give you a good balance between climb, cruise, top speed and fuel economy.

Balance and engine health are the key.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-349-7056 Cell

Thank you said by: Ricardo Urio

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Re: Low max RPM

by John Otter » 13 years ago

John Otter

2 55 0

Roger, isn't there a manufacturers recommended angle to set the prop blades at on a 912? Something like 16.5 deg.

John

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Re: Low max RPM

by Roger Lee » 13 years ago

Roger Lee

125 5.12k 4.52k

Hi John,

There are way too many prop variations out there (world wide) for a hard rule, that said it should be in the general ballpark. Everyone should do an adjustment for their plane and prop configuration.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-349-7056 Cell

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Re: Low max RPM

by Ricardo Urio » 13 years ago

Ricardo Urio

8 24 0

I will make the test this weekend, then I will come back to inform you.

Ricardo

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Re: Low max RPM

by John Otter » 13 years ago

John Otter

2 55 0

If you let us know what type of aircraft it is Ricardo, and the type of prop with how many blades, some research can be done. But as Roger says there's lost of variations out there and some minor adjustment for your configuration may be required.
John

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Low max RPM

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