Exhaust support system

Bubblehead · #1 04-23-2011, 05:58 AM

I think the Larry Vetterman system of hose and end fittings for suspending the exhaust collector and pipe works really well with his system but a couple years ago I changed to an AWI 4 into 1 system and did not like their cable system so adapted Larry's system to the AWI exhaust.

Every time I have the cowling off I look at the hoses and generally one is loose and not supporting the pipe at all. The adel clamps also work back and forth on the motor mounts a bit and I never felt they had a location where they would stay. In fairness to Larry, that problem is caused not by his system but because I did not add the 3rd hose and fittings that keep the spacing right.

Here's the original setup I had. Sorry it is a little fuzzy but it shows the system "as was."

I am trying something different now that will maintain some upward bias to the system and still allow for differential movement between the engine, motor mount and exhaust.

The springs came from a local farm and ranch focused hardware store. I used the self-bonding tape to protect the motor mount from the clamps. The whole system seems more stable. The clamps want to stay at the base of the tubes.

In looking at the exhaust system once the slip joints and swivel joints lock up a little the system is rigid to the cylinders. While I don't like the cylinders having to take loads when some vertical g's try to move the collector down, it's really a rigid system that is probably unaffected by either Larry's system or mine or the cable system.

Any thoughts on pros and cons of each system?

BTW the springs were carefully chosen by the "BR" engineering system. BR = "'bout right."

Kevin Horton · #2 04-23-2011, 06:32 AM

I am using springs on my RV-8. The Vetterman four into two exhaust had his original hanger design that supported the pipes from the engine mount, similar to yours. Various hanger parts broke twice. I discovered that Larry had updated the design to support the exhaust from the back end of the oil sump, which makes a lot more sense, as now the whole exhaust system is hung from the engine. But, I already had too much stuff in the way, and there is no straight shot from the exhaust system to the oil sump.

So, I looked at one of the Mooneys in the same hangar I'm in. The back end of the exhaust is supported by springs from the bottom of the firewall. So, I bought springs from the local farm supply shop, and they've worked fine for over 85 hours now.

Pictures

Lycosaurus · #3 04-23-2011, 07:07 AM

My exhaust system was originally from AWI and the support system they provided did not work for my RV-9A. I used Larry Vetterman's support system and it worked just great. I have 270 hours and the pipes stay where they should.

I did apply a modification to the metal support pipes by grinding grooves. These fit in the rubber hoses and the grooves allow for more friction.

DanH · #4 04-23-2011, 07:48 AM

I'm curious regarding the two comments about the AWI cable hanger. What didn't you like and what didn't work?

(Photo so others have an idea of what we speak, coiled loops of 1/8" steel cable with nico'ed ends):

Toobuilder · #5 04-23-2011, 08:41 AM

I use a solid link from the accessory case bolt to one of the pipes on my 4 into 1. The only relative movement between these points is cause by heating and cooling of the pipe. A simple bloted connection allows this slight slippage. Anyway, it is this single pipe which supports the collector and other pipes. In several hundred hours, it works fine. You might look to see if there are good places to attach the rear supports to a solid part of the engine. Just eliminate connection to the airframe (and the problem of relative movement).

BTW, the collector is also welded solidly to this single pipe, with the remaining 3 pipes as a slip fit to the collector. There are NO other slip joints in the system.

Sometimes, I think we over think the needs of an aircraft exhaust. Certainly, you want to reduce any cantilevered, overhung loads, but trying to provide all kinds of articulation to a lightweight system does not seem to be required.

Bubblehead · #6 04-23-2011, 09:00 AM

Quote:

Originally Posted by DanH

I'm curious regarding the two comments about the AWI cable hanger. What didn't you like and what didn't work?

(Photo so others have an idea of what we speak, coiled loops of 1/8" steel cable with nico'ed ends):

DanH - If I remember correctly the plate is riveted to the tunnel. Because my -8 is already built I did not know how I would be able to rivet it into place. Other than that no real problem. It allows everything to move yet supports the collector. My original statement may have been overly strong.

Toolbuilder - I agree that we sometimes over-think exhaust system needs (and other things). The cantilevered, unsuspended load was my concern.

Kevin - good info and I'd forgotten that Mooney's used springs.

I appreciate the feedback.

Lycosaurus · #7 04-23-2011, 10:44 AM

Quote:

Originally Posted by DanH

I'm curious regarding the two comments about the AWI cable hanger. What didn't you like and what didn't work?

This was about 4 years ago ... Ordered exhaust and mufflers (Vetterman did not have mufflers available back then) from AWI for an RV9A. AWI told me that they had the kit for the 9A. It subsequently turned out that they had never done one for a 9A and they thought it would be the same as the 7A. Unfortunately the engine mounts for the two are quite different and the geometry of the hanger mechanism provided would not work. Following several unsuccessful attempts and discussions to find a solution, I finally called Vetterman and he provided me with his exhaust hanger system for 50 bucks. The combination seems to have worked well for us.

jsharkey · #8 04-23-2011, 11:19 AM

I have a Vetterman cross over system suspended from the back of the sump on my RV-6 O360-A1A.

The tail pipes seem to drift to the left over a few hours of flight. When I push them back they drift left again.

Anyone else noticed this?

Jim Sharkey

DanH · #9 04-23-2011, 11:24 AM

Duh on me Alfio....you said you had an 'A" and I missed it.

John, I attached the mount plate to the tunnel lip with AN3's up through the flange of the firewall angle.

I'll keep an eye on things. Can't make any durability claims for the AWI hanger yet; not quite to 100 hours.

Kevin and John; Rotax two-stroke flyers run a bead of silicone along the length of the spring in order to damp any resonant coils. Different exciting frequency range here, but still a good idea.