Prop Overspeed On Takeoff?

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iflyc77
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Prop Overspeed On Takeoff?

Post iflyc77 »

Hello,

On takeoff in P3Dv4.5 - my engines over-rev the redline by 150 or so RPM to 2650 or so when I am handling the RPM, with the 4 prop levers all the way 'up' fwd/high RPM.

I have never heard of an airplane that would have the high RPM limit of the governor set above red-line and it is kind of annoying to have to manually set 2500 RPM during the takeoff roll.

Is this normal and can I fix it? To make sure it wasn't some weird B-17 'feature' that I had never heard of I asked my two B-17 pilot friends if there was anything they knew about it and they said no - but the B-17 they fly also has the turbos removed so maybe that has something to do with it.

Any ideas or is this how it is?

Thanks

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Gypsy Baron
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Re: Prop Overspeed On Takeoff?

Post Gypsy Baron »

Have you calibrated the turbo boost control? See the manual pg 69 & 70.

Setting the throttle to max and RPM to the takeoff value adjust the setting to achieve 46" MP. Then your RPM should
be limited to that take off setting. That should get you closer to the proper setting.

Paul

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Jacques
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Re: Prop Overspeed On Takeoff?

Post Jacques »

Hi Curt, it is possible to take the props over 2500 with full throttle but I think you need the turbo selector set to “10”. Is this where you have your turbo selector or do you have it limited at “8”?

“... For short field takeoff, the manifold pressure may be set to the maximum war emergency setting of 55" (manifold pressure selector 10) and the propeller governor control may be set to 2760 RPM. These represent the maximum possible propeller and throttle settings. Use 1/3 flaps and use a three point takeoff technique, climbing at full war emergency power. Do not use war emergency power for more than two minutes.”

Edit - Paul is right on it! 😀

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iflyc77
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Re: Prop Overspeed On Takeoff?

Post iflyc77 »

Gypsy Baron wrote:
06 Jan 2021, 20:23
Have you calibrated the turbo boost control? See the manual pg 69 & 70.

Setting the throttle to max and RPM to the takeoff value adjust the setting to achieve 46" MP. Then your RPM should
be limited to that take off setting. That should get you closer to the proper setting.

Paul

Image
Ahh. Yeah I have not messed with that. I figured that it was only to keep all 4 engines in sync as they are adjusted with the boost selector. I will go experiment with that.

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iflyc77
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Re: Prop Overspeed On Takeoff?

Post iflyc77 »

Jacques wrote:
06 Jan 2021, 20:33
Hi Curt, it is possible to take the props over 2500 with full throttle but I think you need the turbo selector set to “10”. Is this where you have your turbo selector or do you have it limited at “8”?

“... For short field takeoff, the manifold pressure may be set to the maximum war emergency setting of 55" (manifold pressure selector 10) and the propeller governor control may be set to 2760 RPM. These represent the maximum possible propeller and throttle settings. Use 1/3 flaps and use a three point takeoff technique, climbing at full war emergency power. Do not use war emergency power for more than two minutes.”

Edit - Paul is right on it! 😀
I have it at 8" but have not done the calibration steps yet.

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Masterius
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Re: Prop Overspeed On Takeoff?

Post Masterius »

Gypsy Baron wrote:
06 Jan 2021, 20:23
Have you calibrated the turbo boost control? See the manual pg 69 & 70.

Setting the throttle to max and RPM to the takeoff value adjust the setting to achieve 46" MP. Then your RPM should
be limited to that take off setting. That should get you closer to the proper setting.

Paul

Image
Is 46" correct? The manual says within an inch of 45".
Image

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iflyc77
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Re: Prop Overspeed On Takeoff?

Post iflyc77 »

The two present day B-17s I know about use 41 - but that is without the turbos and per the people that built the engines.

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Paughco
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Re: Prop Overspeed On Takeoff?

Post Paughco »

We've got the Shift+7 free parts hangar! Fly that machine like it's 1943! By the book, but the book as it was written in '43.

Seeya
ATB
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