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Engine/Prop Vibration

gblwy

gblwy

Well Known Member
Hi,

I've just got back from my first 6-hour return trip - no squawks.

However, I have noticed a high-frequency vibration. I first spotted it on the canopy side frame, but I then touched the panel, and the vibration is quite noticeable.

I can also detect a vibration when warming up on the ground at 2500rpm. At first I thought this was a cross-wind through the prop, but now I'm not so sure.

Is this normal?

Cheers...Keith
 
I would double check and eliminate possibilities for vibration. Is the choke fully opening? Any vibration on mag check? Carbs synced correctly? Are the blades set correctly? Have you checked both sides to make sure they are even? Is the blade tracking to within an 1/16"?

After you have eliminated all other possibilities IMHO, it is critical to have the prop / engine dynamically balanced.

Keep us posted on your results.
 
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Larry -

With the gearbox on the Rotax, the relationship of the prop to the engine is constantly changing, so can they be dynamically balanced together ? Or did you balance the engine and prop separately somehow ? or am I missing something ?
 
Granted the engine runs pretty smooth, but you still have the prop swinging out there. Any weight difference between the two, paint thickness, spinner offset, hardware differences, etc. are going to make a difference.

There was a noticeable difference after I dynamically balanced mine. ;) In fact the difference is measurable. If I remember right it went from .25 IPS (inches per second) down to .04 IPS... much smoother. Any airplane can benifit from a dynamic prop balance. I have only seen two that did not need it, but it was good to verify it. Most planes are WAY out of spec.
 
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I have some vibration too. Dynamic balance?

I have only 5 hours on the airplane so far, but have noticed that there is more vibration at certain RPM's than at others. Not enough to be scary , but enough to get my attention. This being my first experience with a Rotax I have no idea if this is nomal.

I checked the prop pitch and the blades were about 1 degree out. Corrected this and noticed no change in vibration level. I plan to recheck the carb sync when I get a warmer day, but it was near perfect after I set them the first time.

Larry, I like the idea of a dynamic balance, but I have no experience with this. How does one go about getting this done?
 
BigJohn said:
Larry, I like the idea of a dynamic balance, but I have no experience with this. How does one go about getting this done?
Click to expand...

There should be a local A&P that can get it done for you, just ask around. If not, buy one and start your own business dynamically balancing experimentals. Cost should be around $150. Do 10 planes and it pays for itself! Gravey after that, except the 10% you will need to send me for giving you the idea. ;)

Sometimes a good EAA chapter will have one you can rent, or one of their members does it. Just ask around.

http://www.rpxtech.com/rpxweb/Dynavibe.asp
 
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Larry,

Thanks for the link. Interesting! The website however is not real clear on how and where the weights are added to the prop. Could you elaborate on that?

John
 
How to correct imbalance?

Larry,
That balancing tool will tell you if the engine / prop are balanced or not. I assume that the instrument will tell which half of the prop is heavy. Do you add paint to one prop blade or file a little off from the other one or what? I suppose that a little counterbalance weight could even be placed inside of the spinner. How exactly does one go about correcting the imbalance?
Thanks, Joe
 
After a run, temporary weights (metal washers of different sizes) are added to the spinner screws on the aft spinner bulkhead. With the model I use it will tell you where to add the temporary weights, but not how much weight. The more expensive units like Walt (Great web Site BTW!) uses give you a "solution" of how much weight, ect. The Dynavibe unit uses the trial and error method based on experience, and then add weight to the spinner bulkhead (drill a hole) with a bolt & washers based on a formula for a reduced diameter circle, then retest. I can get pretty much the same results as the more expensive units, it just takes more run ups (time). The more you balance the better you get.

It is a lot of fun too, I like working with precision equipment.
 
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Mich48041 said:
Larry,
That balancing tool will tell you if the engine / prop are balanced or not. I assume that the instrument will tell which half of the prop is heavy. Do you add paint to one prop blade or file a little off from the other one or what? I suppose that a little counterbalance weight could even be placed inside of the spinner. How exactly does one go about correcting the imbalance?
Thanks, Joe
Click to expand...

It is much more precise than that. It will tell you where to add the weight based on a 360 degree circle of the spinner. Interestingly, after you add weight the angle can move, so there is some trial and error. It does not take too much to nail it down.

Walt's web site has a ton of good info in it. Check it out.

http://www.expaircraft.com/PropBalance.htm
 
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Walt, I have always wondered why a professional does not balance props at SnF or OSH, ect. I'm sure there are TONS of planes that need it, and many pilots / owners who would want to have it done. I think you could talk the show people into it if you could find an out of the way place to to the work for engine run ups and provide insurance proof, and liability forms, etc.

I do it as a hobby, not a business. Any thoughts?
 
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Geico266 said:
Walt, I have always wondered why a professional does not balance props at SnF or OSH, ect. I'm sure there are TONS of planes that need it, and many pilots / owners who would want to have it done. I think you could talk the show people into it if you could find an out of the way place to to the work for engine run ups and provide insurance proof, and liability forms, etc.

I do it as a hobby, not a business. Any thoughts?
Click to expand...

Larry,
Thats a good idea actually, I always figured the "hassle factor" would be to high to make it worthwhile but it does merit at least an inquiry to find out what it would take to do something like that. Dynamic Solution Systems had a booth as Oshkosh last year, maybe I can talk them into supporting a "hands on" forum where we could actually perform balance jobs rather than just talk about it :D
 
Walt said:
Larry,
Thats a good idea actually, I always figured the "hassle factor" would be to high to make it worthwhile but it does merit at least an inquiry to find out what it would take to do something like that. Dynamic Solution Systems had a booth as Oshkosh last year, maybe I can talk them into supporting a "hands on" forum where we could actually perform balance jobs rather than just talk about it :D
Click to expand...

I would think with the backing of a paying vendor, the proper insurance, ect., it would be providing a valuable service for airplane owners.... and gold mine to the guys doing it! Even if you scheduled 3 in the am and 4 or 5 in the pm. Maybe get a couple of balancers going? Once the word spread, you would have more worth that you could handle. :D

If they would not let you do it say at SnF, I'm pretty sure you could talk the Winter Haven FBO into it. Planes could fly over there and have it done, get fuel, buy stuff, ect. Just a thought.

Where there is a will, there is a way.
 
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Geico266 said:
I would think with the backing of a paying vendor, the proper insurance, ect., it would be providing a valuable service for airplane owners.... and gold mine to the guys doing it! Even if you scheduled 3 in the am and 4 or 5 in the pm. Maybe get a couple of balancers going? Once the word spread, you would have more worth that you could handle. :D

If they would not let you do it say at SnF, I'm pretty sure you could talk the Winter Haven FBO into it. Planes could fly over there and have it done, get fuel, buy stuff, ect. Just a thought.

Where there is a will, there is a way.
Click to expand...

Guess I have some homework to do now, it definately merits some investigation as to what exactly it would take to make it happen..

Mabe I could work the show circuit and spend the rest of the year in the Bahamas :rolleyes:
 
Re-check your carb balance. Is it still on at 3500-4000 RPM?

Mine has a little more vibration between 4200-4800 the colder it gets and it is probably the carb balance. Rotax 912 is affected most by improper carb balance in that range.
 
Carbs?

Thanks John, for readdressing the original problem after the thread morphed into an interesting business opportunity.

No-one has said that vibration is normal, so I guess I need to investigate further. My suspicion is that the situation has changed over 15 hours, so I'd be inclined to look at the carb balance before the prop. I cannot see any inherent imbalance in the prop getting worse - I haven't lost a chunk off the end ;-)

I know it's subjective but can anyone confirm whether they feel any significant vibration when touching the panel, so that I know I have a definite problem.

Cheers...Keith
 
Keith,

My old engine developed a very strange vibration; enough that it would shake the oil dipstick lose.

It took me some time to figure it out and the cause was two mud dabber tubes on the back of the flywheel, out of sight.
 
Another possibility...

gblwy said:
Hi,

I've just got back from my first 6-hour return trip - no squawks.

However, I have noticed a high-frequency vibration. I first spotted it on the canopy side frame, but I then touched the panel, and the vibration is quite noticeable.

I can also detect a vibration when warming up on the ground at 2500rpm. At first I thought this was a cross-wind through the prop, but now I'm not so sure.

Is this normal?

Cheers...Keith
Click to expand...

Hi Keith,
I probably don't need to ask this because of all the previous public discussion of the issue; but did you loc-tite the M10 engine mount to crankcase screws? If not, have you checked them for tightness after the first few hours of running? Especially the lower right.

Your symptoms are similar to those I experienced when the bolts loosened.

Tony
 
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Keith,

I have a perceptable vibration at all RPM's, but it feels worse in some ranges. I can feel it and see it in the top of the stick. I am at the same point as you - trying to determine if this is "normal". I have heard a lot of people say the Rotax is a smooth running engine - so maybe I am expecting too much.

Tomorrow I plan to check the prop blade angles once again, and possibly do another carb sync run. If I pull the upper cowl I will get out my mirror and check those upper mounting bolts too - although it is hard to believe they would have come loose in 6 hours - after the loctite and retorquing.

John
 
Thanks

Thanks all, for your input. I'll investigate further. I have loctited (is that a verb?) the engine bolts so would be surprised if this was the root of the problem, if indeed there is a problem.

Cheers..Keith
 
John.....or you can fly that puppy down here to KLRP ('bout 20 min away from me) and have Sensenich do it for perfectly....they've been doing my props for 25 years and are the best! Make a nice little X-cntry for ya.....and of course let me know if ur ever in the SE PA area.....otherwise maybe we can get up there in the Spring.
Wing kit gets delivered on Fri...
best,
den
 
Smooth and noisy

After about 28 hours I rechecked my props and found them about 1 deg. apart. After resetting the props the engine now runs very smooth. Im wondering if this didn't contribute to the loosening of the engine mount bolts. The interior noise during cruise power, with out a head set is extreme. :eek:

The engine sounds solid and great from the outside. No strange noises.

I'm waiting on getting the plane painted before installing the canopy seals. Could seals make that much difference? Although its not a problem with the headset on I'm just wondering what every body else is experiencing.

Gary
 
Hey Gary - -

I have mine sealed about as well as can be done. Don't think seals change the noise at all. With good headsets, it is ok. The interior kit might help, I do have floor mats.

John Bender
 
Back to the vibration issue.....

I'm still trying to reduce the vibration. Might have discovered at least a partial cause today. See today's log entry.
 
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