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Author Topic: I ain't sure???  (Read 3709 times)

Offline Bootlegger

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I ain't sure???
« on: October 14, 2013, 10:23:12 AM »

  Where this goes, but what are you fellow's doing to prevent profile front ends fron shaking when the engine runs?

  I have a P T 19 from H-9 that I believe has this problem. I am trying to get a more stable engine run, so any suggestions that you fellow's have will be appreciated.

  The model is equipped with an OS 32 ball bearing engine.
 Again thanks for all help...
8th Air Force Veteran
Gil Causey
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Offline john e. holliday

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Re: I ain't sure???
« Reply #1 on: October 14, 2013, 10:30:29 AM »
Balanced props for one thing.   But, I have also added a cheek cowl on inboard side of the fuse.   Even a triangle like piece like on the P-51 Mustangs help.
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Offline Randy Ryan

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Re: I ain't sure???
« Reply #2 on: October 14, 2013, 10:33:35 AM »
Balanced props for one thing.   But, I have also added a cheek cowl on inboard side of the fuse.   Even a triangle like piece like on the P-51 Mustangs help.




Sometime rotating the prop 180 degrees on the shaft will help a bit. Not ideal, but sometimes helps some.
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ChrisSarnowski

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Re: I ain't sure???
« Reply #3 on: October 14, 2013, 10:58:48 AM »
If the problem is fuel foaming, then put some Armorall in the fuel. Try a quart or so first. Shake the quart of fuel up and note how much foaming you get. The add a squirt and try again. A few squirts should be all it needs.

Also mount fuel tank on foam pad to isolate vibrations some. Works best when mounting with rubber bands and hooks.

-Chris

Offline tom hampshire

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Re: I ain't sure???
« Reply #4 on: October 14, 2013, 11:31:41 AM »
     Try a ply tee brace like so:


Offline Juan Valentin

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Re: I ain't sure???
« Reply #5 on: October 14, 2013, 11:51:18 AM »
Hello Gil
                   I add a 1/2 balsa cheek in my profile and it works real good,no shaking of the nose with an OS.40FP using a Xoar 11x6 prop.Here is a pic.
                                                         
                                                                 Juan

Offline Paul Taylor

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Re: I ain't sure???
« Reply #6 on: October 14, 2013, 12:19:14 PM »
Could also had a hub issue with the prop. Seen some of the APCs with a off set hole.

Swap the prop.
Paul
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Offline proparc

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Re: I ain't sure???
« Reply #7 on: October 14, 2013, 12:55:37 PM »
Could also had a hub issue with the prop. Seen some of the APCs with a off set hole.

Swap the prop.

This is a VERY serious problem with the Saito 72. The prop MUST be trashed. Ask me how I know. LL~
Milton "Proparc" Graham

Offline Dave_Trible

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Re: I ain't sure???
« Reply #8 on: October 14, 2013, 01:45:18 PM »
I've had few problems with this by running the motor mounts well back to the wing leading edge area.  These act like train tracks to conduct the vibration back into the rest of the airplane where it can be absorbed.  When the mounts are short the vibration concentrates in the nose area with no place to go.   Also a layer of heavy carbon tissue, .5 ounce and dope clear back to the wing spar would help lots.  Try to fill the carbon- not sand it all off.  Don't worry much about weight.  Profile fuselages are generally lighter than built up anyway.

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Offline Howard Rush

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Re: I ain't sure???
« Reply #9 on: October 14, 2013, 02:39:22 PM »
What I've seen is that sometimes a resonant frequency of the forward fuselage with motor and stuff on it is close to the engine RPM.  This was a problem with a B-17 with which I had an acquaintance.  You can either change the resonant frequency of the forward fuselage by changing its stiffness or mass distribution (heavier or lighter engine) or change the engine operating RPM.  Stiffening the Bomber engine mounts didn't work.  They had to be made softer, and the RPM had to be held down to keep from getting another resonance.
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Offline Brett Buck

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Re: I ain't sure???
« Reply #10 on: October 14, 2013, 02:42:52 PM »
What I've seen is that sometimes a resonant frequency of the forward fuselage with motor and stuff on it is close to the engine RPM.  This was a problem with a B-17 with which I had an acquaintance.  You can either change the resonant frequency of the forward fuselage by changing its stiffness or mass distribution (heavier or lighter engine) or change the engine operating RPM.  Stiffening the Bomber engine mounts didn't work.  They had to be made softer, and the RPM had to be held down to keep from getting another resonance.

   That had 4 graphite tuning forks interconnected by a fifth, as I recall.

   That was a fun afternoon. Howard and Paul both called me at work one afternoon. Howard called to lobby me to tell Paul not to cut off his carbon engine bearers, and then Paul called me telling me that he was going to do it.

    Brett

Offline Bootlegger

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Re: I ain't sure???
« Reply #11 on: October 14, 2013, 04:12:28 PM »

 Dave Trible & Ty Marcucci, I am working with an ARF so all the construction is already done, and the model is covered in Iron Paint (iron on film), so it would take quite a bit of work to add another cheek doubler.

 Today I made a 3/32" triangle and joined the wing L/E to the fuse in hopes that this will help.
 Paul Taylor I also remember that problem about APC hubs being out of "kilter" so I plan to check that also.

  Being that this is a one cylinder engine I can balance the prop, but that doesn't mean that it won't "shake".

  I thank every one for their suggestions/advice, as always this forum has fellow's that like to help, that is what makes being a modeler so much fun..Again I can't say thanks loud enough...
8th Air Force Veteran
Gil Causey
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Offline Balsa Butcher

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Re: I ain't sure???
« Reply #12 on: October 14, 2013, 05:32:13 PM »
Just for curiosities sake do you have another engine you could try? It could be that particular engine just doesn't want to work in that fuselage...it happens. OS-32 is interchangeble with Evo 36, Magnum 36, TT 36, AT-36, Webra 32 and possibly a few others. 8)
Pete Cunha
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Offline Steve Helmick

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Re: I ain't sure???
« Reply #13 on: October 15, 2013, 06:41:35 PM »
Gil, just peel that crap off athe front end, glue on a slab of firm balsa, shape it and recover or sand and dope it.  H^^

BINGO! And check the prop.  y1 Steve
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Offline Garf

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Re: I ain't sure???
« Reply #14 on: October 20, 2013, 03:35:10 PM »
Try this:



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