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Great Vibration Mystery - Solved

J

JBPILOT

Well Known Member
For a few weeks I have been 'occassionally' having vibrations at high speeds, and high power settings.

Sequence of events :

1. Plane flew great all winter.
2. Installed wheel pants when available - picked up speed as indicated. No problems.
3. Weather got warmer ( KEY NOTE ) 'sometimes' would have a vibration in the front, but not always, at higher speeds and RPM's.

This morning, I finally figured out what it was. ( warm today again ) The front wheel bearings are sealed, and in warmer weather ( and wheel pants ), the front wheel was spinning up to high enough RPM's it caused vibration because I had not gotten as good a balance as I needed while I was still building. It was cool then, and the wheel would not self-center the heavy spot on the bottom due to more rolling resistance in the bearings. With the warm weather today, the wheel would let me know exactly where it was heavier. I put on enough weights so I can not find a 'heavy' spot now, and the vibration went away. The tire is still spinning a bunch likely when flying, but not causing vibration. Sorry - long story, but it might save someone else a 'mystery' someday.

John Bender
 
Last edited:
John,
Thank you for sharing - Tips received from you and others have been invaluable and I really appreciate them. Great timing for me on this tip as I was planning to assemble my wheels this weekend. Its very very hot in Las Vegas, so hopefully I'll get a good balance the first time.
 
JBPILOT said:
For a few weeks I have been 'occassionally' having vibrations at high speeds, and high power settings.

Sequence of events :

1. Plane flew great all winter.
2. Installed wheel pants when available - picked up speed as indicated. No problems.
3. Weather got warmer ( KEY NOTE ) 'sometimes' would have a viration in the front, but not always, at higher speeds and RPM's.

This morning, I finally figured out what it was. ( warm today again ) The front wheel bearings are sealed, and in warmer weather ( and wheel pants ), the front wheel was spinning up to high enough RPM's it caused vibration because I had not gotten as good a balance as I needed while I was still building. It was cool then, and the wheel would not self-center the heavy spot on the bottom due to more rolling resistance in the bearings. With the warm weather today, the wheel would let me know exactly where it was heavier. I put on enough weights so I can not find a 'heavy' spot now, and the vibration went away. The tire is still spinning a bunch likely when flying, but not causing vibration. Sorry - long story, but it might save someone else a 'mystery' someday.

John Bender
Click to expand...

Thanks for this info John. Where in the plans does it advice to balance wheels? Scott Lane
 
Hey Scott

It doesn't. I did, due to past experience, but did not do a good enough job during the build. Once you get some hours on the front wheel, and the sealed ball-bearings get loosened up some, and then it gets warm enough, you'll find out if you have wheel pants. I would say it should be added to the instructions. TODAY is the first time I can make that statement however. Until today, my original balance was enough to get a decent vibration control. If the nose wheel is a long ways out of balance, you will know it someday likely. It really concerned me until I finally figured it out this morning. Like most things in life, looking back now, it makes lots of sense.

John Bender
 
More info please,

Hey John,
Very interesting, I had not considered that the wheel pants would cause the wheel to spin. Makes sense, tho. Can you describe the setup you use to balance the front wheel? From what you said I assume you are just leaving it on the axle and spinning it until it stops, looking for a consistent stop point?

Also, I am wondering if those tight Matco main wheel bearings will keep the mains from spinning in flight? You can't hardly spin those by hand.

Tony
 
Tony

The mains use conventional packed bearings, and with brake drag, I don't think they would ever spin. The nose wheel is free to roll. Once you have some time on the bearings, and it is very warm, then they turn VERY easy. I just used my scissor jack, and jacked it up and the wheel turned so easy it let me know right away it was out of balance. It would rotate so easily, it showed me exactly where I need to add weigh, without taking it off. Just had to remove the rear of the pant. I had/have some of the self-adhesive type wheel weights, and I also put RTV around the edges once I get them in place. I added 1/4 oz at a time and rechecked until I did not have a 'heavy' spot.

John Bender
 
3. Weather got warmer ( KEY NOTE ) 'sometimes' would have a vibration in the front, but not always, at higher speeds and RPM's

John,
...and those "higher speeds" would be higher than what? lol the sound barrier will cause a vibration too.
 
Petie -

I found the vibration started about 105 kts. I tried speeding up, and it stayed the same, and took a while after slowing down to may 90 kts for it too stop. This morning, when it was warm ( for Iowa ), the nose wheel could have been turned with a feather ( seriously ). If you moved the wheel, it would cycle back and forth very slowly for 5 - 6 cycles before 'settling'. That really helped in balancing, but it is hard to get the same results with new bearings, and lower temps.

( mach 1.1 is the answer ! ! ! )

John Bender
 
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