Newbie Engine Question part2  
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Newbie Engine Question part2 - 5/15/2008 10:12:10 PM   
solace67


 

Posts: 16
Joined: 5/5/2008
From: Rochester, NY, USA
Status: offline 		yup, here we go again ;D I'm in the process of trying to tune my new engine (Tower .46) And when its at idle its vibrating, and quite a bit, tailfeathers and all. I'm just wondering what would cause this? I'm assuming it isn't normal. could it be set too rich on idle? Thanks for all the help

Cheers,
Derek

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The Day I learn to fly, Im never coming down, On perfect wings Ill rise, through the layers of the clouds.
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RE: Newbie Engine Question part2 - 5/15/2008 10:20:17 PM   
TedMo


 

Posts: 70
Joined: 6/11/2006
From: , FL, USA
Status: offline 		possibly due to too rich is one. Out of balance prop another.Unsecure motor mount. Try adjusting the idle screw.
They will vibrate quite a bit at idle though.

(in reply to solace67)
       Post #: 2

RE: Newbie Engine Question part2 - 5/16/2008 12:24:47 AM   
Jester241



Posts: 315
Joined: 8/25/2007
From: , PA, USA
Status: offline 		Wouldnt think vibration from that engine would be THAT noticable. Make sure your prop is balanced very well,and make sure theres not something wrong with your spinner that would throw it out of balance or something. Other than that,everything should be normal and maybe thats just the way it is. It could be really rich,but I wouldnt even think that would be so noticable on that size engine,but anything is possible.

(in reply to solace67)
       Post #: 3

RE: Newbie Engine Question part2 - 5/16/2008 3:05:49 AM   
downunder



Posts: 3097
Joined: 10/10/2002
From: Adelaide, AUSTRALIA
Status: offline 		It's quite possible it's just a reaction from the model to the firing impulses from the engine. Every time the engine fires the torque reaction feeds back into the model and maybe the wing or tailplane is acting like a tuning fork and resonating. Sometimes just using a different prop can cure it by making the engine run at a different speed at idle.

(in reply to Jester241)
       Post #: 4

RE: Newbie Engine Question part2 - 5/16/2008 3:18:13 PM   
MinnFlyer



Posts: 19094
Joined: 4/22/2002
From: Willmar, MN, USA
Status: offline
quote:

ORIGINAL: downunder

It's quite possible it's just a reaction from the model to the firing impulses from the engine. Every time the engine fires the torque reaction feeds back into the model and maybe the wing or tailplane is acting like a tuning fork and resonating. Sometimes just using a different prop can cure it by making the engine run at a different speed at idle.

Downunder is correct.

This is known as "Harmonic Vibration"

Everything in the world wants to vibrate at a certain frequency - This is how a Microwave oven works. The magnatron sends radio waves at the same frequency at which water molecules vibrate. The molecules vibrate and create heat and your food cooks.

Or look at Downunder's analogy to a tuning fork - If you have a tuning fork which is tuned to an "A", and you play an "A" on an instrument, the tuning fork will vibrate because it is getting hit with vibrations that are the same frequency at which it is designed to vibrate.

So what's happening is your engine is vibrating at the same frequency that your tail wants to vibrate. Now this can be caused by only one thing - the vibrations put out by your engine.

Being rich has nothing to do with it. An unbalanced prop MIGHT be the culprit, so try checking it's balance first.

Otherwise, your only options are:

1) Idle at a different RPM
2) Redesign your tail so it vibrates at a different frequency
3) If the prop is balanced, try unbalancing it slightly and put the heavier end opposite the piston at Top Dead Center.

_____________________________

Mike B.
AMA# 42400 www.gettingairborne.com

"Those are my principles. If you don't like them, I have others." - Groucho Marx

(in reply to downunder)
       Post #: 5

RE: Newbie Engine Question part2 - 5/16/2008 4:38:10 PM   
jetmech05


 

Posts: 1372
Joined: 7/12/2005
From: Jacksonville, FL, USA
Status: offline 		Have you broke in your new engine? you aren't doing yourself or your engine any favors tuning it before you have broke it in....

(in reply to MinnFlyer)
       Post #: 6

RE: Newbie Engine Question part2 - 5/16/2008 5:22:04 PM   
opjose



Posts: 5275
Joined: 11/26/2005
From: Poolesville, MD, USA
Status: offline 		Seconding (???), Downunder's and MinnFlyer's posts...

The T.H. is no more prone to vibration than any other engine.

As indicated, balance your prop & spinner.

You may also need or want to re-do your engine mount. It may be contributing to this.

At worst you can also utilize a Dubro anti-vibration mount.

When I put these on planes, almost no harmonic vibrations get translated back into the fuse.

If you put your hand on the fuse you can barely feel the engine running at any speed. This will make your plane last longer too.



_____________________________

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Build em'', fly em'', crash em'' and build more.

(in reply to jetmech05)
       Post #: 7

RE: Newbie Engine Question part2 - 5/16/2008 5:24:40 PM   
gaRCfield


 

Posts: 642
Joined: 5/20/2008
From: Burlington, VT, USA
Status: offline
quote:

ORIGINAL: opjose

Seconding (???), Downunder's and MinnFlyer's posts...

The T.H. is no more prone to vibration than any other engine.

As indicated, balance your prop & spinner.

You may also need or want to re-do your engine mount. It may be contributing to this.

At worst you can also utilize a Dubro anti-vibration mount.

When I put these on planes, almost no harmonic vibrations get translated back into the fuse.

If you put your hand on the fuse you can barely feel the engine running at any speed. This will make your plane last longer too.




If this is anything like what's on the Nexstar it works like a charm! My plane has much less vibration than every other plane I've seen so far (of course I DO balance my props)

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...because flaps are cool.

(in reply to opjose)
       Post #: 8

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