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  #1  
Old 10-16-2018, 07:23 PM
rzbill's Avatar
rzbill rzbill is offline
 
Join Date: Nov 2005
Location: Asheville, NC
Posts: 2,541
Default Front Page - Baffle Stiffeners

My dim memory recalls failures of either push rod tubes or injection lines when extra mass or loads over and above the injection line masses are imposed.
The additions change the resonant frequency of the tube/line system and can cause fractures.
I'm sorry I cannot supply documents to support the assertion or remember the detail of whether it was tubes or injection lines that failed. It was too long ago that I read the report.

They are experimentals of course. Just be aware and keep an eye on them.
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  #2  
Old 10-16-2018, 07:48 PM
David Paule David Paule is offline
 
Join Date: Dec 2009
Location: Boulder, CO
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Default Do-Nothings

Good catch, Bill.

This photo from the Front Page today, Tuesday, shows that the brace is supported at the right end by an Adel clamp. As shown, this support does nothing.



What happens is that if the brace has a forward load, the Adel clamp can rotate. This is because the force from the brace creates a torque about the pushrod. The pushrod, being round, can do nothing to prevent the Adel clamp from rotating. So the brace doesn't brace the baffle.

The pushrod can’t even prevent the brace from sliding towards the center of the engine. All there is, is friction. And especially with vibration, friction is very unreliable. It’ll hurt you if it can and leave you with zip if it gets a chance. In between those things, it'll tease you and pretend to be good.

The net result is that the brace DOES NOTHING.

Do-nothings, as I call them, are worse than dead weight. They give the illusion of doing something useful while actually doing nothing at all.

Dave
[ed. Intersting observations and input.

My data point to add to the convos:

I've been putzing around in RVs for about two decades now, and have flown in a few dozen solo, and this particular RV-8 is by far the smoothest flying one I've been in. Almost everyone else who has flown in it ends up describing it with the same word....'Turbine'. I'm told the purpose of the braces is to keep the baffle rigid while putting the cowl back on. I do know that the pilot can control the oil temp within a single degree (highly mod'd cowl flap). I'm not an expert my any means and don't profess to know much about harmonic resonances, but I do know this RV is the smoothest I've ever experienced.

There are many little mods that have been added over the last decade, from oil cooler to baffles, to exit area, etc.

He's worked on a few hundred RVs over the decade, so he has a better idea than me where they tend to wear.

I think the continual little tweeks just add to the enjoyment....this plane gets a lot of love.

my .02. v/r,dr]

Last edited by DeltaRomeo : 10-17-2018 at 04:44 PM.
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  #3  
Old 10-17-2018, 09:26 AM
Ralph Inkster Ralph Inkster is offline
 
Join Date: Feb 2008
Location: Calgary, Alberta
Posts: 418
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I agree with Paul about the Adell clamp rotation. The builder could shorten the struts a inch or so & flip the Adeleís around making the connection more in line, this would make the desired support a bit more effective.
Personally I have not seen a reason to support the rear baffle, in the many planes Iíve seen I have never observed cracks form in this area. Most common condition Iíve run into is rubber seals folding back caused by too great a gap between metal baffle and cowling. If the intent is to support the oil cooler area of the baffle, than a diagonal brace to the case would be more effective.
I note the double AN960 washers under the 1/4Ē bolts holding the side panels to the cylinders. I have not built up a baffle set for angle valve engines yet, always played with parallel valve engines to this point. Should there be a doubler plate riveted to the side panels at these areas (as is used on parallel engines), or at least change out one AN960 washer for a AN970 washer?
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  #4  
Old 10-17-2018, 10:15 AM
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vlittle vlittle is offline
 
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Location: Victoria, Canada
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Why not just use the stock angle brace?:

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Last edited by vlittle : 10-17-2018 at 10:28 AM.
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  #5  
Old 10-17-2018, 07:35 PM
Ralph Inkster Ralph Inkster is offline
 
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Location: Calgary, Alberta
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He has one. Note the single bolt top center rear, there is a bracket behind there that goes to the accessory cover.
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