What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Lower Cowl Heat Damage

A

ArlingtonRV

Well Known Member
I am experiencing problems with the lower cowl and the #2 exhaust pipe. Pictures can be seen here: http://www.hangara13.com/Cowl.html.

I first noticed this after the engine was run on the ground for about 15 minutes (third time it was run). At the time the exhaust tube was in contact with the cooling duct, so naturally I figured that was the problem.

After repairing the cowl and moving the muffler to the right about 1 1/7" I had between 1/16 and 1/8 clearance between the tube and the duct. I can't figure out how to get any more. I thought it would be adequate. After about 15 minutes again I had heat damage to the duct.

Engine temperatures (oil, CHT, EGT) are well within the green and both CHT and EGT on the left side are slightly lower than the right. I'm a little confused and concerned.

I was a little concerned about ground runs so I asked Van's whether they should be made with the bottom cowl on or off, I didn't like the idea of the oil cooler just laying on the muffler. They confirmed bottom cowl on.

I wonder if it has anything to do with the top cowl being off? It might be that the airflow just isn't right with the top cowl off.

What have those of you that didn't have problems do? I also have a question in to Van's on the same topic.

Thanks
 
IMHO there is no good reason to run the engine on the ground for 15 mins. What is your purpose for doing this? I'm not trying to be difficult, I'm trying to understand why you would run an aircooled engine on the ground for that long?
 
Last edited:
"At the time the exhaust tube was in contact with the cooling duct, so naturally I figured that was the problem."


You should not have contact here. Something is not correct!
 
thoughts

My front #2 exhaust spring contacted the cooling shroud so I made a 1/4 dent in it where the spring contacted the shroud and glassed it, as well as adding the aluminum sticker.

A bit off topic but related. My air cooling shroud over the cylinders shows a bit of discoloration after 25 hours. If its really hot out, I would leave the oil door open on landing.

Also, it is possible bubbles develop in the 2 carb hoses from the main fuel line. I have got a drop in rpm and a brief gas smell twice after letting it sit on a hot day after a cross country, but I didn't leave the oil door open.

What EGT's do people get on hot days? Mine are about 1100-1200 and I might be a bit rich.

John
 
Repairing the cooling duct

Cut a 5" diameter circle (or 4 x 5 oval) out of the cooling duct centered below the exhaust pipe. Sand the top edges around the cutout so that the new fiberglass patch will stick. In order to make the bottom transition smoother between old and new fiberglass for better air flow, sand the TOP edge of the hole so that it is as thin as a knife edge. Clean the sanded area with acetone. Paint the sanded edge with resin. Prepare 3 layers of glass cloth and resin by sandwiching between sheets of plastic and rolling with a cylindrical object to remove excess resin. Apply the patch to the hole. If desired, peel-ply can be placed on both sides of the patch to make the repair smoother. Use one hand inside of the cooling duct and one hand outside to apply pressure to the peel-ply to wet it and make the bottom peel-ply stick without falling off. The patch can be slid inward or outward to increase or decrease the tightness of the cloth and thus the amount of sag in the center. Gravity will pull the center of the patch downward to provide clearance between the patch and the exhaust pipe. A half inch of clearance should be adequate. More will help to prevent scorching the fiberglass but will restrict airflow to the water radiator. When cured, remove peel-ply and apply aluminum heat shield to top surface of patch.
Joe
 
You must log in or register to reply here.
Back
Top