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First flight with new (to me) engine - possible detonation event?

A key area to check on the baffles and cowl are the diffuser ramps that are attached to the inside of the upper cowl.

Is is surprising how often I find an airplane that has those with the ends open, creating a HUGE leak tunnel through to the low-pressure side.

I have seen some installations where there are baffle seals on both the inboard and outboard ends of the difffusers, so being open wouldn't matter in that case, but it is much more common to just have baffle seals on the outboard end and the inboard end is inside the upper plenum. If the ends are open, forming a tube, it is a big leak.

If your diffuser tunnels are open on the ends, tape over them with duck tape and and flight test to see the difference.
 
scsmith said:
A key area to check on the baffles and cowl are the diffuser ramps that are attached to the inside of the upper cowl.

Is is surprising how often I find an airplane that has those with the ends open, creating a HUGE leak tunnel through to the low-pressure side.

I have seen some installations where there are baffle seals on both the inboard and outboard ends of the difffusers, so being open wouldn't matter in that case, but it is much more common to just have baffle seals on the outboard end and the inboard end is inside the upper plenum. If the ends are open, forming a tube, it is a big leak.

If your diffuser tunnels are open on the ends, tape over them with duck tape and and flight test to see the difference.
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Here’s a picture of my upper cowl, for reference.
 

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Two things I noted.

1) Is there an open 2” flange for Scat on the aft baffle? Closing that will help a lot.

2) How much overlap is there between adjacent pieces of baffle material? You want an inch or so.

3) OK… 3 things. Near the inlets, but on the vertical aluminum portions of the baffles, I believe your baffle material is overlapped the wrong way. You want the forward pieces overlapped on the inside of the pieces behind them. That way, airflow won’t open up the seam.
 
Upper Cowl

I can not see the depth in that white inlet. It's almost looks like the guide ducts were installed upside down. Maybe an illusion, or the 3/4 is not at all like the 6 and later. Attached is the guide Steve was talking about. A diffuser function is required in the inlet for good cooling.

Screenshot 2023-04-03 at 4.13.51 PM.png
 
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I wonder if your scat tube for the oil cooler should be a larger diameter or have two of those to feed to the oil cooler?
 
BillL said:
I can not see the depth in that white inlet. It's almost looks like the guide ducts were installed upside down. Maybe an illusion, or the 3/4 is not at all like the 6 and later. Attached is the guide Steve was talking about. A diffuser function is required in the inlet for good cooling.

View attachment 40491
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Here’s a different angle to show the depth.
 

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I worked the baffles some to fix the overlap issue that was brought up earlier. On test fitting the cowl everything appears to fit up tightly with two possible exceptions along the front. The outside corner transition and then right at the inlet both seem like they could be improved but I’m not entirely sure how to deal with the geometry after test fitting a couple different shaped pieces. The inlet looks like it may be a “blow open” potential, while the corner is just a bad place to fully seal around - the two pieces overlap as is but with the side making the turn sticking out. Maybe it blows shut or maybe it provides an escape route; I’m not sure.
 

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Methinks you need someone who knows how to properly do baffling to help sort out this rather odd looking setup.

Is there an EAA chapter anywhere close to you?
 
00Dan said:
I worked the baffles some to fix the overlap issue that was brought up earlier. On test fitting the cowl everything appears to fit up tightly with two possible exceptions along the front. The outside corner transition and then right at the inlet both seem like they could be improved but I’m not entirely sure how to deal with the geometry after test fitting a couple different shaped pieces. The inlet looks like it may be a “blow open” potential, while the corner is just a bad place to fully seal around - the two pieces overlap as is but with the side making the turn sticking out. Maybe it blows shut or maybe it provides an escape route; I’m not sure.
Click to expand...

That area around the cowl inlet is tricky. I found looking at the RV-7 and RV-14 plans very helpful. I used very flexible silicone rubber baffles which have good overlap, and get tighter with pressure. The flexibility makes it easier to get the cowl on and off.

My cooling is excellent - but I have no idea if it's because of the baffles, or something else. I only have one data point, since this is the only aircraft I've built.

I have some photos like the one below here:

http://www.rv8.ch/silicone-rubber-baffle-seals/

IMG_6916.jpg
 
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