Home > Control Cables, Cowling, Exhaust, Lower Cowl Brace > Cowl, Oil Door, Exhaust, etc. – 9 hrs

Cowl, Oil Door, Exhaust, etc. – 9 hrs

Sunday Feb 17, 2013

It’s been a very busy weekend. I didn’t have as much time as I wanted to work on the airplane because I had to replace and paint some base molding that was damaged by a water leak recently but I got quite a bit done anyway. First, I trimmed and sanded out the epoxy and microlight filler layups I placed a few days ago in the outer nostrils of the air intakes to make flanges. As you can see it turned out pretty well. Not ready for paint but good for a first cut. The rest is just making it prettier.

DSC_2572

I also sanded the epoxy layer I added to the inside of the oil door. This is ready to prime and seal, then I will rivet in the latches.

DSC_2574

Another recent mini-project has been the lower cowl brace which I primed and assembled yesterday. Here are the parts ready for installation.

DSC_2577

I called Clint at Vetterman Exhaust last week and asked him about the unused heat muff in the exhaust system. Since I plan to use only one heat muff the other will not have forced air. I read somewhere that if left uncooled it will get very hot and could damage the cowl. Clint recommended three options; 1) duct air to the muff to cool it, 2) take the outer shell off the muff to allow air flow around the muffler, or 3) replace the muff with a bent sheet of aluminum alclad that wraps only half way around the muffler. I chose option 3 as you see in the photo below. With half the shell open the muffler should not overheat and the aluminum shell will act as a thermal shield to protect the mixture cable which is right behind it.

DSC_2590

Installing the lower cowl brace was a pain in the neck but as you can see in this picture I got it in. I also bent and fitted the final hinge wires for the lower hinges. These wires have long “handle” extensions that overlap the center brace and then poke through holes in the lower brace to retain them. You can see them if you look carefully on either side of the brace. Something else I did was rivet the cowl hinges to the sides and bottom of the fuselage.

DSC_2589

With the lower cowl and cowl brace installed I was ready to finalize the positions of the exhaust pipes. As you can see above, the pipes come fairly close to the cowl, engine mount tubes, and the edge of the fuselage. Each exhaust pipe has a slip joint right in front of the muffler that allows the aft section of the pipe to be rotated to “aim” the joggle for best fit and clearance. I tweaked the pipe alignment about as much as I could and when I thought I could get it no better I decided it was time to lock it down. The aft section of each pipe is locked to the front section with a split collar with  1/4 inch diameter internal pin. You have to drill a 1/4 inch hole through the joint for the pin and then clamp it together with an AN3 bolts and lock nut. I mustered my courage and drilled. In this next photo you can see the clamp installed one of the slip joints.

DSC_2613

The next few photos are just to illustrate the exhaust pipe supports and clearances to various critical components like control cables and fuel lines. It is hard to see in two dimensional pictures but everything seems to have reasonable clearances. The forward supports for the exhaust pipes connect to engine sump bolts. There is also a horizontal support that ties the two pipes together.

DSC_2579

In this view you can see the right side.

DSC_2596

I recently ordered a longer fuel line (part number VA-139) because the “standard” one that came with the kit would not reach to the AFP fuel servo inlet. As it is, the VA-139 is just barely long enough.

DSC_2595

This photo gives you an idea how much clearance the throttle cable has to the engine mount and exhaust. I also ordered a 46.5 inch long throttle cable from Vans because the standard 44.5 inch cable was a little tighter than I liked under the panel. The 46.5 inch cable allows for a more slack routing.

DSC_2600

This photo gives a good view of the mixture cable and it’s clearance from the exhaust. I may put a fire sleeve around the mixture cable to further protect the rubber seals from the heat.

DSC_2607

Back on the cowl I drilled holes in the hinges for bonding. These holes will improve the strength of the bond according to Vans. I used a 3/16 drill because the 1/4 inch holes recommended in the plans looked too big to me. Since the extra holes are called “optional” in the plans I figure I have some latitude here.

DSC_2599

Finally, I started work on hinge pin covers for the horizontal cowl hinges. I sketched six round patches on a piece of 8 oz Rutan cloth. These sketches are about 2.5 inches in diameter which will give some margin for 2-inch cover plates.

DSC_2608

I placed this between two pieces of plastic drop cloth, poured in some epoxy, and rolled it out to make prepreg cloth. After I cut the round patterns out with a roller knife I applied packing tape over the hinge pin access area and laid up three layers of prepreg on each side. I will let this cure to make stock for 2-inch access covers.

DSC_2611

Advertisements
  1. No comments yet.
  1. No trackbacks yet.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

%d bloggers like this: