Cowl inlet ramp ends sealing--any CHT data? Worth the effort?

Gash · #1 06-21-2013, 02:26 AM

After doing a search on VAF, I have been unable to find any good CHT data to show the results of closing off the ends of the cowl inlet ramps. I found a few pictures, but haven't found much data.

I am considering plugging the ends of my inlet ramps to avoid turbulent or decreased airflow caused by the little openings on the sides of the ramps. My baffles don't do a good job of covering the ends, and it seems a lot easier to simply fabricate my own fiberglass ends. Has anyone else plugged their ramp ends? Is it worth the effort, and if so, do you have any supporting data?

Bob Axsom · #2 06-21-2013, 04:19 AM

The metal ramp at the lower part of the cooling air inlet is already sealed by metal at the inboard out board and aft (cylinders 1 & 2) ends. On the front I have three pieces of baffle seal rubber overlapping in a way that seals off that opening. I had that configuration from the beginning so no differential operation data is possible. There are two curved fiberglass panels added to the upper cowl from the top of the cooling air inlet up to the inside of the upper cowl several inches back. I flew for a while with those inboard and outboard ends open. I later foamed and fiberglassed those openings closed. I believe I achieved no change in speed and at that time I had not installed my CHT probes and instrument yet so again no data. On the ends of the vertical members of the baffling I extended the rubber baffle sealing material forward so that it seals against the internal unexposed cowl surface inboard and outboard of the cooling air inlet opening. Again, i did this with the original build so no differential data.

From your description, it sounds like what you intend to do is a good idea - one that I would do if I visualized a condition that involved an opening that might (will) cause disturbance or undesirable routing of the air flow.

Bob Axsom

Kahuna · #3 06-21-2013, 04:29 AM

I have sealed off ramps and the before and after was not material in temps.

Brantel · #4 06-21-2013, 04:40 AM

Quote:

Originally Posted by Kahuna

I have sealed off ramps and the before and after was not material in temps.

Same here....made no real measurable difference.

rzbill · #5 06-21-2013, 06:00 AM

Quote:

Originally Posted by Gash

My baffles don't do a good job of covering the ends,

If your baffles DO seal against the ramps, then closing them will make no difference. If they do NOT seal against the ramps, then closing the ramps can make a difference if that is the only issue with your baffle installation.

My baffles seal well. I ran with the ramps open and later closed. No measurable dif.
If memory serves, Walter Tondu had a big improvement in performance when he blocked off his ramps.

Gash · #6 06-21-2013, 08:49 AM

Okay guys, thanks for the replies. You're right Bob, I was referring to the upper curved ramps--I should have been more specific. My baffles seal well on the outboard ends, but the inboard ends (next to the prop) don't seal well. It's a tough shape on that side to get sealed well with a flat piece of rubber material.

I figure it can't hurt, so what the heck. I'm going to head over to the hangar this morning and make a couple of fiberglass covers for the inboard ramp end openings. I'll snap a couple pics and post before/after CHT data when complete.

BTW Bob, I don't have any foam laying around the shop to put behind the glass when forming the complex shape. So I'm going to form a mold with duct tape over the openings, cover those with mold release wax, and then glass them over. When cured, I'll pop them off, remove duct tape, trim, and then epoxy those babies right back in there. We'll see how that holds up.

It's on days like this that I'm very happy to be flying an experimental aircraft!

aerhed · #7 06-21-2013, 09:10 AM

Couldn't you use masking tape instead and just glass it closed in one step? No need to remove and glue.

rzbill · #8 06-21-2013, 12:45 PM

Quote:

Originally Posted by Gash

It's a tough shape on that side to get sealed well with a flat piece of rubber material.

Karl,
If you are going to do some glassing, take a look at how I added some shape to the ramps near the spinner. I think this good sealing surface is why I got no improvement when I blocked under the ramps.

Inlet ramp construction

Gash · #9 06-22-2013, 04:29 PM

Thanks for the suggestions and ideas guys. I glassed over the upper inlet ramp inboard openings yesterday. Today I flew 4 times. I must say that my data collection shows no real improvement in CHTs. I still have #2 and #4 running hot, with #2 sometimes 40 to 50 degrees higher than the other cylinders. This was the same problem before and after I glassed the inlet ramp ends.

Next step will be to start trimming away the inlet dam in front of #2.

Jesse · #10 06-22-2013, 05:10 PM

Before trimming, may I recommend that you swap CHT probes from #2 to #4, keeping wires connected, and see if the higher temp now reads on 4 (really cyl 2) or 2 (same probe and wire as before). It's an easy way to verify if it is really a hotter cylinder before trimming dams. Then, if you just drill the 3 rivets holding the dam in place, that will show if it will make more than the required difference before taking steps to sneak up on a good balance. You may find that removing the whole dam is necessary.