Airframe Vibration

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Postby russell » Wed May 31, 2006 8:42 am

The material that the Lazair is made from has a life expectancy of about forever except for one problem, and that 's vibration. There is no way to describe the amount of vibration with words but the Pioneer engines in my opinion transmit a good bit. It's not hand numbing by any means but it does concern me as to the effect it has on the airframe pieces. One engine alone doesn't have much vibration, but when the two are syncronized it can be a good bit. It's actually more of a shutter that runs through the plane. I normally run the engines out of sync so as to lessen this.

Just curious, but do the rotax engines transmit much vibration to the airfame?

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Postby ozzie » Wed May 31, 2006 4:36 pm

check the balance and tracking of the props. normally out of sync engines will cause more vibration. ozzie
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Postby russell » Thu Jun 01, 2006 6:33 am

Tracking I can check but balance would be a little difficult. What's a good method?

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Postby russell » Fri Jun 02, 2006 12:05 pm

Well, I guess I'm on some sorta Lazair.com black list, because I know that there is a lot of members that are knowledgeable about props and some that even have the capability to make them, so how about some suggestions on how to check the balance and just how much out of balance is acceptible.

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Postby ozzie » Fri Jun 02, 2006 5:14 pm

tracking is pretty simple. you can tape a piece of timber (2x1 ect) on the wing leading edge and run it out close to the tip of the prop mark the position of the blade and then rotate the prop and check the other blade. take the spark plug out first. alternativly use a lazar pointer and tape it to the back blade and mark on wall. then do other blade.
it is a bit harder to check the balance on the plastic prop as most don't have a hole in the centre so you can just drill a 1'4 hole or go thru the motions of making a mount plate to pick up the two mount bolts. i went the drill hole way. so drill a quarter hole using a bench drill to mack sure it goes straight thru and in center. (no slop) find two small bearings that have a 1/4 centre fit one two each side of the prop. two V blocks come in handy here as you sit the two bearings in the v blocks so as you can rotate the prop. if it is sensitive enough the prop should move when you put a drop or two of oil on a blade tip. spin the prop gently and observe how it stops. play with it a bit and you will work out if it is in balnce. visuall check each blade for straghtness twists ect. on timber props if they are out of balance you can drill a small hole at the hub a put some lead in it and then some epoxy over it to balnce it. may be a bit harder to work this out. do you run spinners? if so take them off and test. hope this helps lots of tips possibly out on the web as well. try a googal you may find something easier. ozzzie
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Postby russell » Fri Jun 02, 2006 6:02 pm

I can always count on Ozzie. Thanks for the input. With that info in hand I think I can work something out. As for balance, I was considering the possibility of useing a lawn mower blade balancer perhaps. The method you suggested I had forgotten about, but it's one I have used in the past to balance the props on a small hydroplane racing boat I once had. Getting the hole in the exact center might be a little tricky for someone as shakey as I am, but I can probably work something around that idea, maybe.

Thanks again Ozzie,
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Postby JPXman » Fri Jun 02, 2006 7:56 pm

just thinking out loud here, but if there is no hole in the centre, couldn't you just put a nail in a 2x4 with the sharp end sticking out, put the 2x4 on the bench, then put the prop balanced on the nail head? is there any kind of hollow in the back of the nylon props? i am unfamiliar with them, i've only seen the wood props on JPX's....

if you can balance it on the head of a nail, at least you can find the centre, if not completely balance it.

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Postby russell » Sat Jun 03, 2006 4:40 pm

Yeah, Tyler, I sorta jumped the gun here. I started this thread before I removed the prop. Now that I have I see that there is a 3/8" dia. hole in the center on the back side that goes within about 1/8" inch of penetrating the other side. Maybe with some sort of device using a possible combination of your and Ozzie's suggestion might could be devised. This hole is gonna make things a lot easier.

Thanks,
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