rpm fluctuations

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Zacke
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rpm fluctuations

Post Zacke »

Hey guys,

the rpm fluctuations (most noticeable with the P-40 when idling cold): Does actually the engine oscillate that much or is it just the gauge?

Regards,
Zacke

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MkIV Hvd
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Re: rpm fluctuations

Post MkIV Hvd »

It’s just the gauge.
Rob Wilkinson
A2A Harvard, Mustangs Civ & Mil, Spitfire, P-40, P-47, Comanche, Bonanza, Cub, VATSIM P2 and some other stuff...

Zacke
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Re: rpm fluctuations

Post Zacke »

Thanks!

Is it caused by the vibrations or by gauge internal physics?
Last edited by Zacke on 13 May 2020, 10:28, edited 1 time in total.

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MkIV Hvd
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Re: rpm fluctuations

Post MkIV Hvd »

No doubt, both...
Rob Wilkinson
A2A Harvard, Mustangs Civ & Mil, Spitfire, P-40, P-47, Comanche, Bonanza, Cub, VATSIM P2 and some other stuff...

Zacke
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Re: rpm fluctuations

Post Zacke »

Allright, thanks.

Hook
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Re: rpm fluctuations

Post Hook »

Somehow I doubt that the RPM gauge is a direct mechanical linkage.

Given the amount of inertia on internal engine parts the RPM could not fluctuate as fast as the gauge would indicate. Other gauges also fluctuate which would point to vibration causing most of the fluctuation. The gauges in my car don't fluctuate like that, but then my car doesn't vibrate much either. :) It's been a couple of decades but I remember some fluctuation in the needles on my motorcycle.

After flying the P-40, flying a vanilla aircraft that has rock-steady gauges makes the panels in those aircraft feel dead, and by extension the entire aircraft.

Hook

Zacke
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Re: rpm fluctuations

Post Zacke »

So true, Hook! I seriously can't fly sim aircrafts anymore which don't shake and vibrate like the Accu-simmed. It's impossible to me. :wink:

Another observation concerning the P-40 gauges: ASI and VSI seem to be rock steady. Is this correct and why is that the case? In the Spit and P-51 (even the civ) they always are dancing a little bit.

Zacke
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Re: rpm fluctuations

Post Zacke »

Meanwhile I eventually have problems with the absolutely wonderfull Comanche because it's not shaking and rumbling enough...It's crazy! :P

Hook
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Re: rpm fluctuations

Post Hook »

Zacke wrote:
13 May 2020, 11:25
Meanwhile I eventually have problems with the absolutely wonderfull Comanche because it's not shaking and rumbling enough...It's crazy! :P
Given the fact that the Comanche is modeled after Scott's personal aircraft I'm pretty sure they got every detail on it right. :D I suspect the Aerostar will be the same way.

Hook

Zacke
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Re: rpm fluctuations

Post Zacke »

Absolutely no doubt the Comanche is simulated very, very good. But it doesn't rumble and shake like the warbirds... :wink:

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MkIV Hvd
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Re: rpm fluctuations

Post MkIV Hvd »

Hook wrote:
13 May 2020, 10:48
Somehow I doubt that the RPM gauge is a direct mechanical linkage.

Hook
I'd be willing to bet that's exactly what it is..,.speedo cable... :wink:
Rob Wilkinson
A2A Harvard, Mustangs Civ & Mil, Spitfire, P-40, P-47, Comanche, Bonanza, Cub, VATSIM P2 and some other stuff...

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Scott - A2A
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Re: rpm fluctuations

Post Scott - A2A »

MkIV Hvd wrote:
13 May 2020, 12:18
I'd be willing to bet that's exactly what it is..,.speedo cable... :wink:
Yes, this is what most of these old airplanes have (and cars from the 70's and 60's). The cable develops a sort of "out of round" friction where it accelerates and slows down on each revolution. It's basically just cable wear. My old Trans Am had a cable driven speedometer and it was useless for doing acceleration tests as it just could not keep up, oscillating +/- 30 mph.

Scott.
A2A Simulations Inc.

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Skycat
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Re: rpm fluctuations

Post Skycat »

I like Thunderbolts! (Click on "Photos")

Hook
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Re: rpm fluctuations

Post Hook »

The chronometric tachometer was connected mechanically and directly to the engine via flexible cable shaft, which was eventually replaced in later aircraft with electrical tachometers.
"Is it mechanical or electrical?"
"Yes."

Hook

Zacke
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Re: rpm fluctuations

Post Zacke »

:D :D :D

Coming up with an older question: Why are the ASI and the VSI so steady with the P-40 even when the other gauges vibrate like crazy?

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