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Old 03-01-2011, 05:59 PM
KayS KayS is offline
Join Date: Jul 2009
Location: lake constance
Posts: 434
Default distance between top cowling and baffles

Hi, i'm about to cut/shape the upper parts of the baffle. the manual says to keep the distance between the bottom surface of the top cowling and the top edge of the baffles between 3/8 and 1/2.

the procedure is to fit the baffles to the cowling in an very iterative and time consuming process. taking off the cowling and baffles a zillion times.

is there an "smarter", more time efficient, alternitive way to do this?

help's very appreciated...

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Old 03-01-2011, 06:08 PM
pmccoy's Avatar
pmccoy pmccoy is offline
Join Date: Jan 2006
Location: Orange County CA
Posts: 646
Default Baffling

I just finished up my baffles. I learned a couple of things along the way.
- Trim the front air ramp about 1/2 to 3/4" clear of the front lower cowling. That extra room is required to get the baffle material through the area as you take the cowling on and off later.
- When trimming the front air ramp back, leave the inboard and outboard sides longer. They still need to fill the area around the front opening of the cowling
- To set the proper 3/8" to 1/2" height, use the paper clip trick. Trim the top of the baffling just enough to clear the top cowl. Then put a bunch of paper clips around the top of the baffles. Carefully place the top cowl on, then take it off and measure down 1/2 inch from the top of each paper clip. Trim to that line and it should be pretty close to what you want.

That what I did, and it seems to have worked out ok.

Peter McCoy
RV9A N35PM S/N:91335
First Flight: April 2013
Hobbs: 400 hours after Oshkosh 2017
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Old 03-01-2011, 08:45 PM
KayS KayS is offline
Join Date: Jul 2009
Location: lake constance
Posts: 434


aha, paper clips... cool thank you very much for the infos! why i didn't get that idea by myself?

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Old 03-01-2011, 10:46 PM
Flying Scotsman Flying Scotsman is offline
Join Date: Nov 2005
Posts: 1,256

I don't know who first thought of the paper clips, or where I read it, but I owe them a cold beer . That's what I've been doing (not quite done yet, but nearly there...still have to do the forward inlet ramp stuff), and it's worked out beautifully so far.

Thanks to whomever first came up with this idea...
Steve "Flying Scotsman"
Santa Clarita, CA
PP-ASEL, ASES, Instrument Airplane

RV-7A N660WS flying!
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Old 03-01-2011, 11:03 PM
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Greg Arehart Greg Arehart is offline
Join Date: Jul 2007
Location: Delta, CO/Atlin, BC
Posts: 2,439

I suggest that you will be better off in the long run with a half-inch gap, maybe even a bit more, rather than the 3/8-inch gap. Those engines can twist around a lot on startup (I have a tiny crack in my cowl paint to prove it). The baffle material (rubber) is generally stiff enough to seal effectively at even 3/4 or one-inch gaps.

Greg Arehart
RV-9B (Big tires) Tipup @AJZ or CYSQ
N 7965A
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Old 03-02-2011, 11:32 AM
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fl-mike fl-mike is offline
Join Date: Jul 2005
Posts: 1,631

Another method:
  1. Mount bottom cowl.
  2. Clamp some paint stirring sticks to the outside of the bottom cowling sides, two on each side.
  3. Clamp the top cowl to the vertical sticks leaving three or four inches of gap between the two cowl halves (depending on how fat your arms are (see step 6)). Make the gap even all around.
  4. Tape a Sharpie to another stick (at a right angle to the stick) so the marking end just extends past the (side) edge of the stick. (popsicle stick is fine).
  5. Cut the Sharpie stick so the distance from the Sharpie marking tip to the end of the stick is the distance in step 3 plus the desired baffle to cowl gap.
  6. Reach into the cowl inlets and while holding the Sharpie stick vertical, run it around the inside wall of the baffles.
  7. You now have an almost perfect cut line on the baffles.
I really wish I had taken pictures of this process, as it is dirt simple, quick, and very accurate. Much better than the paper clip process.
Mike W
Venice, FL
RV-6A. Mattituck TMX O-360, FP, GRT Sport EFIS, L3 Lynx NGT-9000
N184WM reserved (RV-8)....finishing kit in progress. Titan IOX-370
N184P reserved (RV-8QB)
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Old 03-17-2011, 12:59 PM
KayS KayS is offline
Join Date: Jul 2009
Location: lake constance
Posts: 434

I just finished up my baffles. I learned a couple of things along the way.
- Trim the front air ramp about 1/2 to 3/4" clear of the front lower cowling. That extra room is required to get the baffle material through the area as you take the cowling on and off later.

one question left... the drawing/manual says to cut the forward edge of the ramps so that they are even with the edge of the bottom cowling. i understand that it's better to have a small gap here for putting on/removing the lower cowling. but is 1/2" to 3/4" not a bit to much?

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Old 03-17-2011, 02:10 PM
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pierre smith pierre smith is offline
Join Date: Jan 2005
Location: Louisville, Ga
Posts: 7,912
Default No's not too much.

We had at least 3/4" of an inch from the lip of the lower cowl to the lower ramp. That gap is filled with baffling material anyway and a tight fit makes getting the lower cowl off and on a real bear. With the gap around 3/4" you can easily fold the baffling material up when you raise the lower cowl and your fingers have room to fit in between.

Rv10 Sold
46 years ag pilot/CFI
Air Tractor 502/PT-6
Building RV-12, Wings, fuse, emp complete. FWF in progress.
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Old 03-18-2011, 05:53 AM
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rzbill rzbill is offline
Join Date: Nov 2005
Location: Asheville, NC
Posts: 2,755
Default I just finished doing this

Keep the iterative cuts to less than 1/2" each time and it will be hard to miss.

First cut can be eyeballed. The raw baffles have steps at the joints. Place the top cowl roughly in place (no jigging) and look through the inlets to see the gaps. Goal is to remove the gross steps.

Remove top cowl and roughly mark memorized spots for a 1/2 inch cut. Execute cuts.

Maybe do this eyeball one more time (since it is quick) if you still have locallized big gaps.

Like Mark said above, make a marking stick. I used a medium sharpie (not the fine one) with a 1" grommet taped to the tip so that I had a 1/2" offset no matter how I held the sharpie. Tape that to a stick to reach into the cowl. Mark the areas you can. Remove cowl and join marks by eye or straightedge. Cut.

It took about 3 iterations of this to get to a perfect fitting 1/2" cowl gap. On the last marking iteration, the cowl should fit fully in place before the final marking. Again, if you keep the initial cuts below 1/2" each time, and then start following the sharpie marks this should happen automatically.


I was lucky. I did cut the left ramp just enough to get the lower cowl on. Just before whacking it again per the baffle instructions, I whipped out the filter and plopped it in place. Yikes! My cut marks would leave a ramp smaller than the filter! The cowl inlet must be cut instead. Be careful.

CLARIFICATION: The marking stick method worked best through the spinner hole in the cowl. I did not have the starter ring gear or the front center baffle sections in place during the procedure.
Bill Pendergrass
ME/AE '82
RV-7A: Flying since April 15, 2012. 850 hrs
YIO-360-M1B, mags, CS, GRT EX and WS H1s & A/P, Navworx
Unpainted, polished....kinda'... Eyeballin' vinyl really hard.
Yeah. The boss got a Silhouette Cameo 4 Xmas 2019.

Last edited by rzbill : 03-21-2011 at 05:25 AM. Reason: Clarification
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