Engine/prop noise at startup and shutdown

George was taking a friend up yesterday and when the engine caught, there was a metallic 'screeching' noise and the same noise occurred on shutdown, only seemingly louder. He said he didn't notice anything but it was very pronounced to me, standing out to the side. Anyone with similar experiences? I'd rather not fly it anymore until I/we get it resolved.
thanks
Meade and George
612RV

What RPM are you shutting the engine down at?

And what oil are you running?

rotax noise

HI it could be the slipper clutch on the rotax if you shut it down when it is idleing too slow it will make a noise check the rotax manual for the recommended revs at shut down

Know of another one

I have a friend that had one a year or so ago, and I heard that one myself. Really squealed when it was shut down. I think it did it on start up also if I remember right. He sent the gear box in, and they told him it was the clutch, and he just lived with it.

John Bender

Read your rotax operating manual!

Gearboxes engines are different than direct drive, then the Rotax 912 has a slipper clutch as well.

PS: in addition the worst thing you can do to a Rotax is idle it too low! Gear Chatter is an awful sound!

Regards
Rudi

Prop Noise

Thanks for the suggestions and information guys. Steve called me last night and made some suggestions, one of which was to lower my idle speed. We've been shutting down while the engine was at idle of about 2200 rpm. He suggested that was too high and should be around 14-1600 rpm. I'll check with George about the engine oil, but I'm pretty sure it was a grade prescribed by Rotax; I'll check out the owner's manual when we go back up to check out the plane this morning.
Thanks again for all the information.
Meade

meadeduck said:

Thanks for the suggestions and information guys. Steve called me last night and made some suggestions, one of which was to lower my idle speed. We've been shutting down while the engine was at idle of about 2200 rpm. He suggested that was too high and should be around 14-1600 rpm. I'll check with George about the engine oil, but I'm pretty sure it was a grade prescribed by Rotax; I'll check out the owner's manual when we go back up to check out the plane this morning.
Thanks again for all the information.
Meade

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Meade, 2200 RPM is too fast for a "normal shut down" of the Rotax 912S. As you have found out these engines are a tad touchy about that. In a nut shell what happens is the gear box wants to stop right away, the engine wants to coast a little, but the inertia from the prop tries to keep both spinning. The gear box loads and unloads energy causing a "backlash" effect which it engaging the gearbox friction clutch and the squealing you are hearing.

Get the idle down to 1400 when you pull the throttle back all the way. If the engine idles rough add enough throttle until it smooths out. Do not let it run rough at idle, as the same effect of the engine and prop working against each other will result.

To properly shut down the 912, pull the throttle back to the "new" idle. As the engine slows down from say 2,000 rpm to around 1,400 RPM kill one mag, then the other. All of this takes place in just a second or two. You want to catch the engine slowing down and use that trend to kill the mags and stop the engine. There should be no "shaking" when the engine shuts down.

Now when you go flying pull the idle back all the way without worry. The force of the air will keep the prop spinning smoothly until you land. Your approach and final will be MUCH easier to slow down now that the idle has been lowered.

Just trying to help. Good luck!

Geico266 said:

<SNIP>

Get the idle down to 1400 when you pull the throttle back all the way. If the engine idles rough add enough throttle until it smooths out. Do not let it run rough at idle, as the same effect of the engine and prop working against each other will result.

<SNIP>

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Ditto, but clarification, Never never let the 912 run rough at low RPM's Gear Chatter will result. Typically you always want a positive prop load and those gearbox teeth. To low RPM and the engine and prop hunts against each other resulting positive and negative loading on the teeth. I ensure it always 'idle' on the ground with a bit of throttle at +/- 2,000 RPM unless you want to shut it down, then you pull the throttle all the way back and catch it with the mags to kill it, before it goes rough.

Prop Noise

We went back up to the hangar yesterday and checked out the noise from the plane again, with George outside the cockpit. It seemed to help by reducing the throttle to around 1800-2000 rpm then quickly shutting off the 'mags' sequentially, quickly followed by the master. George said he still heard a little noise at shutoff but I didn't hear anything.
Thanks to all for the suggestions.
Meade
612RV
...and if I had to do it over again, I would've sprung for the 496 over the 495...

meadeduck said:

We went back up to the hangar yesterday and checked out the noise from the plane again, with George outside the cockpit. It seemed to help by reducing the throttle to around 1800-2000 rpm then quickly shutting off the 'mags' sequentially, quickly followed by the master. George said he still heard a little noise at shutoff but I didn't hear anything.
Thanks to all for the suggestions.
Meade
612RV
...and if I had to do it over again, I would've sprung for the 496 over the 495...

Click to expand...

Still a little high on the RPM if you are hearing the clutch squeeling. It will only take so much before wearing out. Try resetting the throttle cables to get a lower RPM.

Also, as the engine breaks in you'll need to adjust the RPM lower anyway.

Geico266 said:

Still a little high on the RPM if you are hearing the clutch squeeling. It will only take so much before wearing out. Try resetting the throttle cables to get a lower RPM.

Also, as the engine breaks in you'll need to adjust the RPM lower anyway.

Click to expand...

1800 to 2000 rpm at shutdown is fine - the main thing is to let it idle for at least 2 mins after any high power operation.

The squeaking seems to be normal as virtually every 912 equipped with a clutch I've ever heard does this at shutdown. The only one I heard that didn't do it was a pretty high time engine swinging an enormous prop (IVO medium 3-blade), which likely needed new springs in the box. Mine makes a loud squeak right as it comes to a stop (regardless of the RPM it was at when I killed it); I just measured my friction torque at about 450 in/lbs so the box appears to be in order.

I wouldn't worry about it...

LS

RudiGreyling said:

Ditto, but clarification, Never never let the 912 run rough at low RPM's Gear Chatter will result. Typically you always want a positive prop load and those gearbox teeth. To low RPM and the engine and prop hunts against each other resulting positive and negative loading on the teeth. I ensure it always 'idle' on the ground with a bit of throttle at +/- 2,000 RPM unless you want to shut it down, then you pull the throttle all the way back and catch it with the mags to kill it, before it goes rough.

Click to expand...

I'll second this. 1400 rpm and then only one mag will yeild a whole lotta' shakin' goin on, even if only for a few seconds. Best to have the gearbox chattering for zero seconds and shut down all at once with both mags from a smooth high idle (1800-2000).
With a light prop like the Sensenitch it's not as hard on the box to idle that low but still not a good idea. 1400 is the absolute minimum idle RPM recommended by Rotax, IIRC and they really want you up around 1600 at least....

LS

I've never heard mine squeal in the -12, or in the other 3 912s I've own and operated.

LS, you need to read my instructions a little closer.

Geico266 said:

I've never heard mine squeal in the -12, or in the other 3 912s I've own and operated.

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Yours would be the first I've heard of that didn't, but it could vary with the prop used. Mine is on its 3rd prop now (don't ask ) and it has always emitted a squeak right as it comes to a stop. All but one other clutch-equipped 912 I've heard has done the same thing.

LS, you need to read my instructions a little closer.

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I have, and I don't see what advantage your procedure offers. If anything, you're more likely than not to stress the box trying to run it through such low RPM's as you shut the first mag down, etc.
Just kill the motor altogether from a normal 1800 to 2000 rpm idle and you avoid that possibility altogether. There's no problem doing it that way and the engine/gearbox will last their normal lifetime.

LS

lucien said:

Yours would be the first I've heard of that didn't, but it could vary with the prop used. Mine is on its 3rd prop now (don't ask ) and it has always emitted a squeak right as it comes to a stop. All but one other clutch-equipped 912 I've heard has done the same thing.

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Maybe, if you tried my proceedure yours would be #2.

I have, and I don't see what advantage your procedure offers. If anything, you're more likely than not to stress the box trying to run it through such low RPM's as you shut the first mag down, etc.
Just kill the motor altogether from a normal 1800 to 2000 rpm idle and you avoid that possibility altogether. There's no problem doing it that way and the engine/gearbox will last their normal lifetime.

LS

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I never stated to idle the plane at 1400, and I clearly stated not to idle the plane at any RPM where is it running rough.

There are two reasons for having the ability to get the RPM's lower in the RV-12. You want to have the ability to kill the mags as the RPM is falling. If you are idling at 1800 RPM smoothly, pull the throttle back and as the engine falls to around 1600 you kill one mag, then as the engine falls further kill the second mag. This all happens in 1-2 seconds at the most, and the entire time the engine is dragging the entire drive train lower. The "Rotax shake" does not have time to develope.

The second reason is the -12 is a good glider. Being able to pull the throttle all the way back to in the pattern will allow much better short feild landings, and more accurate landings in general, IMHO. On the ground if you have the idle set at 1400 and you pull it to idle in the air the RPM is still 2,000 and smooth as silk as the air is now pushing the prop. With this additional drag the plane can be slowed down much easier on final.

Granted, not everyone will understand this proceedure so it is not for everybody. It's your engine, set it up any way you want.

JMHO.

What SN RV-12 are you flying?

Geico266 said:

Maybe, if you tried my proceedure yours would be #2.

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I did, in fact, the other day as I was curious to see if it had any value but I couldn't discern any. It had no effect on the squeak as I suspected it wouldn't. The squeak I'm referring to in my engine and in all the others I've observed occurs at an rpm far below any sustainable idle speed, so there's really no way what you do with the engine above that could affect its occurrence. Seems to be a brief resonance right before the engine comes to a stop. This could also affect whether it occurs or not, but that's just a guess.

So again I'm dubious that this really buys you anything. If it makes you feel comfortable, sure I'd say keep doing it. But OTOH, I don't see many reports of reduced TBO from the field, for example, from others who've never heard of this. And like I said, unlike the normal procedure of killing the motor at once from a normal idle speed, it introduces the hazard of chattering the box if it's not done just so every time. So it seems to be of low/no value to me.

I never stated to idle the plane at 1400, and I clearly stated not to idle the plane at any RPM where is it running rough.

There are two reasons for having the ability to get the RPM's lower in the RV-12. You want to have the ability to kill the mags as the RPM is falling. If you are idling at 1800 RPM you can pull the throttle back and as the engine falls to around 1600 you kill one mag, then as the engine falls further kill the second mag. This all happens in 1-2 seconds at the most.

The second reason is the -12 is a good glider.Being able to pull the throttle all the way back to in the pattern will allow much better short feild landings, and more accurate landings in general. On the ground if you have the idle set at 1400 and you pull it to idle in the air the RPM is still 2,000 and smooth as silk as the air is now pushing the prop. With this additional drag the plane can be slowed down much easier on final.

JMHO, You can set your plane up anyway you want.

What SN RV-12 are you flying?

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Not sure what the relevance of this discussion of idle speed vs. use in the air is, this isn't really the topic. Again, I will say:
a) 1400 rpm is the very lowest rpm Rotax wants to see on the ground (what it is in the air is irrelevant) and generally they want to see 1600 or more.
b) the shutdown procedure you're advocating offers no visible advantage over a normal shutdown from a normal idle speed, and in fact increases the hazard of running the engine in an abnormal manner, even if only for a moment (which a normal shutdown doesn't).

Maybe if engines not operated the way you're advocating weren't making TBO or something like that I'd be inclined to believe you, but absent that I remain skeptical that it's of any value. Sorry.

But it's your engine, so knock yourself out

LS

lucien said:

I did, in fact, the other day as I was curious to see if it had any value but I couldn't discern any. It had no effect on the squeak as I suspected it wouldn't. The squeak I'm referring to in my engine and in all the others I've observed occurs at an rpm far below any sustainable idle speed, so there's really no way what you do with the engine above that could affect its occurrence. Seems to be a brief resonance right before the engine comes to a stop. This could also affect whether it occurs or not, but that's just a guess.


LS

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I see you are flying a Titan Tornado with a Rotax 912S. I assume you have a 3 blade prop or have you switched to the ground adjustable 2 blade Sensenich? I don't see how comparing your set up to the RV-12 would be a fair comparison.

Geico266 said:

Granted, not everyone will understand this proceedure so it is not for everybody.

Click to expand...

Sorry, blaming the victim is not an effective support strategy for your proposal . What you really need to do instead is support it with some kind of evidence for its efficacy. I don't mean to be quarrelsome, but the problem here is you're advocating an unusual shutdown procedure without also showing how/why it's better than the normal procedure that's been in use on these engines for decades already with no known ill effects.

If you can provide that support or even show how the normal procedure is defective compared to it, I'll be more inclined to look at it. But until then I continue to express skepticism that it's of any additional value.

The other problem is that it clearly introduces additional hazards that a normal shutdown doesn't, due to the skill and good timing with the throttle and ignition switch that seems to be required to carry it out. If it weren't for that, I wouldn't really be too concerned about it and probably wouldn't have ever typed anything.

But at 20 grand a pop, we need to experiment with our 912's only very carefully

Good luck with it tho. I'd be interested in what results you're getting 1500-2000 hours or more down the road....

LS

Geico266 said:

I see you are flying a Titan Tornado with a Rotax 912S. I assume you have a 3 blade prop or have you switched to the ground adjustable 2 blade Sensenich? I don't see how comparing your set up to the RV-12 would be a fair comparison.

Click to expand...

Good point - showing exactly what it is that's special about the RV-12 installation that requires the shutdown procedure you're advocating would help you a great deal as well.

LS

Throttle detent

The type of propeller probably has a lot to do with the noise as it stops turning.
I like Larry's suggestion of idling at a lower RPM while approaching for landing. It is hard to make short landings with the engine pulling the plane. How about a detent in the throttle position for 1800 RPM idle on the ground. The throttle could be out pulled past the detent for approach to landing.
Larry, figure out a way to get reverse thrust to make really short landings.
Joe

lucien said:

Sorry, blaming the victim is not an effective support strategy for your proposal . What you really need to do instead is support it with some kind of evidence for its efficacy. I don't mean to be quarrelsome, but the problem here is you're advocating an unusual shutdown procedure without also showing how/why it's better than the normal procedure that's been in use on these engines for decades already with no known ill effects.

If you can provide that support or even show how the normal procedure is defective compared to it, I'll be more inclined to look at it. But until then I continue to express skepticism that it's of any additional value.

The other problem is that it clearly introduces additional hazards that a normal shutdown doesn't, due to the skill and good timing with the throttle and ignition switch that seems to be required to carry it out. If it weren't for that, I wouldn't really be too concerned about it and probably wouldn't have ever typed anything.

But at 20 grand a pop, we need to experiment with our 912's only very carefully

Good luck with it tho. I'd be interested in what results you're getting 1500-2000 hours or more down the road.
LS

Click to expand...

According to Rotax Maintainance Procedures Section #12, Chapter #4, the engine idle can be set to as low as 1,400 RPM, but it is recommended to idle at 1,800 - 2,200 RPM for warm up. We are talking about shutting down the engine. Following my shut down proceedure by idling at 1,800 and pulling the throttle back does not violate Rotax maintance instruction, and actually reduces wear & tear on engine compents including avoid the clutch to squeal.

http://www.lightsportaircraft.ca/volume2-issue16/webcast-3/

http://www.conairsports.co.uk/downloads/912 maintenance article - inc carb bal.pdf

Larry,
Thanks for posting your engine shut-down procedure. I intend to take your advice. Since you start shutting off the mags at 1600 RPM, your procedure is not unusual and is within the Rotax recommendations of not idling below 1400 RPM. The Rotax operator's manual does not specify shutting off the mags at a certain RPM, so 1600 should be fine. I understand that even though your engine can be idled as low as 1400 RPM if desired, you never operate at that RPM, but rather at 1800 on the ground and 2000 in the air. Even if the pilot is slow shutting down the mags and the RPM drops to 1400 for a couple of seconds, no harm will be done to the engine or reduction gears because 1400 RPM is allowed for up to one minute at a time. You are still operating it within Rotax's guidelines. If the clutch does not squeal at shutdown, that is good enough for me. Using less runway on landing is an added benefit. I hate running into the fence at the end.
Joe

0.1.1) Operating speeds and limits (912 UL / A / F)
1. Speed:
Take-off speed............................5800 1/min (5min.)
Max. continuous speed...............55001/min
Idle speed ...................................approx. 1400 1/min

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Roberta

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