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Captain Avgas

Well Known Member
I have an RV7A with Larry Vetterman's standard RV cross-over exhaust system.

The Vetterman installation instructions call for the horizontal brace joining the exhaust support brackets to run behind the nose gear mount. However I do not believe there is enough space in that area to run a horizontal brace and provide any clearance whatsoever between the moving brace (attached to moving exhaust system) and the stationary nose gear.

The following is a photo from another thread that shows clearly that this chap has experienced the same problem (disregard the arrows). He not only has no clearance but his horizontal brace actually bends around the nose gear. This detail must eventually fail.

Some people have recommended using "spacers" at the horizontal brace to gain clearance in this area but I cannot see that installing spacers will provide any meaningful clearance.:confused:

Does anybody out there who has run the horizontal exhaust brace behind the nose gear on any RV7A and achieved reasonable clearance have a photo of their installation. I'd love to see what magic they used. :)

 
Bob,
I believe there's an alternate way to install those horizontal braces, one which is included in the newer kits from Vetterman, and that is to brace outward from each pipe to an adel clamp installed on the lower outboard down tube on the motor mount. To use this method, you would reverse the position of the SS band clamp you show so that it's "ear" is on the outboard side rather than the inboard side as shown in your picture.
I originally had my pipes braced as you show in the picture, but now have them braced to an adel clamp on the motor mount, outboard from each pipe. I'll look around and see if I can find a picture of my install, but I'd suggest you call Larry and talk to him about it, he's always real helpful, maybe he can email you an illustration of this alternate install. My point is, there is an alternative...
 
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This picture was intended to show the fuel servo brackets for my Airflow Performance injection, but it also shows the exhaust brackets:
DSC01254.jpg


Note that the horizontal brace has been spaced upward significantly. The angle of the shot is poor but it has about 1/2" clearance in front of the nose gear and, at 60 hours, is not showing signs of hitting the engine mount. My -6A uses the -7A FWF kit from Vans.
 
Exhaust hangers

Bob
I too used the "V" brace that Mr Brown refers to. FWIW I have not flown yet but have run the engine. This system appears to be much stiffer under a side load. It does require a different clamp or modification of the one shown in the photo. Mine has ear tabs welded on at 3 and 9 oclock.

Matt
 
No problem here, 900hrs +, no spacers.
Have switched to AFP FI with no changes to the exhaust.

IMG_4388b.jpg
 
Walt said:
No problem here, 900hrs +, no spacers.
Have switched to AFP FI with no changes to the exhaust.
Click to expand...

Hi there Walt, I see you've installed your bracket and cross brace forward of the bend in the pipe (and forward of the nose gear). Have you had any cracking at all anywhere in the exhaust system during the 900 hours.
 
Bob,

On my Vetterman x/over system fitted to an IOF-360 i was able to move the brackets forward and hence up, effectively clearing the nose strut member. Orientation of the bracket around the tail pipe is the same as you have it just have the whole thing moved closer to the engine.

Cheers, Greg:)
 
Exhaust

Bob,

Mounted mine almost identical to Walt's setup. Just remember that the rods inside the rubber tubing should not meet. That way the rubber acts as shocks and allows 3D movement independent of the other exhaust, thus reducing the fretting that induces cracking or splits in the exhaust. The idea is a free floating system that stabilizes the exhaust run but touches nothing directly.

Mike H 9A/8A SOLD
 
Captain Avgas said:
Hi there Walt, I see you've installed your bracket and cross brace forward of the bend in the pipe (and forward of the nose gear). Have you had any cracking at all anywhere in the exhaust system during the 900 hours.
Click to expand...

No cracks, no problems at all to date, replaced the rubber tubing once.
 
Walt said:
No cracks, no problems at all to date, replaced the rubber tubing once.
Click to expand...

Thanks for that Walt...you've convinced me. I'll instal the brackets so that the cross brace is just forward of the nose gear as you did.

And thanks to everyone else who responded with advice. Much appreciated.

Incidentally Larry Vetterman does not give any dimension on his drawings of the gap inside the rubber hose between the stainless tubes. So I asked him this and he said 1/4". I mention this for the record because I'll bet there are a lot of builders with much bigger gaps that this.

My guess is that if the gap is too big the braces will not work well in compression (the hose will tend to "snake"). Larry says that if the vertical braces in particular do not act effectively in compression (presumably due to either poor construction and/or placement) the exhaust pipes often ride up at high speeds due to wind force and hit the bottom of the fuselage.
 
I am unfamiliar with these exhaust mounts but they look like someithing I can duplicate.

Two questions -

1. What holds the stainless tubes in the rubber tubing - is there anything more than the hose clamp friction?

2. What type of rubber tubing is used? '300psi flame proof' does not sound like anything I am familiar with.

Thanks,
Doug
 
You shouldn't have to duplicate them; they come with the Vetterman exhaust. For that reason, I'm not sure of the rubber hose source. Clamp pressure is all that's used to keep the tubing inside the hose. I was tempted to flare the tubing slightly or bead it but was afraid it would make it impossible to insert them into the hose. So far, no sign of slipping.
 
flion said:
You shouldn't have to duplicate them; they come with the Vetterman exhaust. For that reason, I'm not sure of the rubber hose source. Clamp pressure is all that's used to keep the tubing inside the hose. I was tempted to flare the tubing slightly or bead it but was afraid it would make it impossible to insert them into the hose. So far, no sign of slipping.
Click to expand...

I believe the rubber tube is fuel line hose. I was also thinking about slightly flaring the ss tube but on further consideration I decided it would create a high stress wear point on the rubber hose given the type of forces being transmitted. Instead I'm going to knurl the ss tube to improve grip...and completely degrease the inside of the rubber hose which seems to be quite "greasy" as supplied.
 
I had this same concern and questioned Vetterman about it. He said not to worry - the grip of the tubing improves afer they experience a few heating cycles. He was right.

erich
 
flion said:
This picture.......also shows the exhaust brackets:
DSC01254.jpg


Note that the horizontal brace has been spaced upward significantly.
Click to expand...

Patrick, rework the horizontal brace install. If it hasn't broken yet, it will.
 
Here's my setup

Had the cowl off today, took this pic of how I set it up. I like this setup much better than across the nosegear area, it probably also cleans up the airflow in that area, it's certainly much better to service and inspect. Larry advised me to try to move the clamps as far aft of the ball joints as possible to reduce stress on the exhaust system. I lube the ball joints with mouse milk every time I have the cowl off, as you can see in the picture. Those mice sure are hard to milk...

280vaj7.jpg
 
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flion said:
You shouldn't have to duplicate them; they come with the Vetterman exhaust.
Click to expand...

Yes they do now! Unfortunately mine did not come with the 'hangers'. I have sent a message to LV to get a set, hopefully while I am at Osh. this year.

Doug Gray
 
1/4"? Yikes. I worked on this today. I guess I'll move the bracket up along the pipe a little more. I had moved it farther back. I thought I read the bracket should be as close to the firewall as possible.

One other question. Is there a thin-walled socket or something that people use to get at the inboard exhaust studs on $2,3 and 4 cylinder? I can't get a standard socket in there.
 
Bob Collins said:
1/4"? Yikes. I worked on this today. I guess I'll move the bracket up along the pipe a little more. I had moved it farther back. I thought I read the bracket should be as close to the firewall as possible.

One other question. Is there a thin-walled socket or something that people use to get at the inboard exhaust studs on $2,3 and 4 cylinder? I can't get a standard socket in there.
Click to expand...

Bob, I have a 1/4" drive socket with 6" extension that works fine for those nuts, don't think it is "thin-wall" per se.
 
DanH said:
Patrick, rework the horizontal brace install. If it hasn't broken yet, it will.
Click to expand...

Just working on this this weekend, but I haven't seen anything in the thread to indicate (a) why it will fail and (b) how it should be reworked.

I've seen the methods whereby it's attached to the engine mount, but I'm with Tony Bingelis and he says not to do it that way, so I'd like to avoid that if I could.

Also are most people finding that the bracket should mount BEFORE the bend in the Vetterman tubing or after?
 
Bob,

Your exhaust hangar photos don't look all that different from mine (on a 6A). I agree with you, it does not look like the side to side brace can go behind the nose gear mount......no way, no how! :)

Not sure if you have fit the cowl yet. If not, don't get too tied up in where the pipes hang for now. It becomes much clearer where the pipes need to go once the cowl is on and you see where the pipes can't go. There is only so much clearence between the bottom of the firewall above, the fiberglass outside and below, and the nose gear mount inside.
 
Bob Collins said:
Also are most people finding that the bracket should mount BEFORE the bend in the Vetterman tubing or after?
Click to expand...

Hi Bob, here's a photo of how I set mine up with the exhaust cross brace in front of the nose gear leg. I opted for this after messing around on this detail for days and after talking on the phone to Larry Vetterman. If you have the cross brace in front of the nose gear leg it stands to reason that the pipe clamps will be forward of the bend in the exhaust.



I also found that I needed to make 0.016" thick stainless shims to go under the pipe clamps as the pipe clamps would not pull up tightly on the exhaust. You can just seem them protruding from under the clamps in the photo. They go right around the circumfrence of the exhaust.

Incidentally my friend had the same access problem as you with the exhaust nut. He simply bought a cheap 1/2" socket and ground away the wall to make it a bit thinner just at the opening. It didn't need much grinding and it fits nicely now.
 
Stevea said:
Not sure if you have fit the cowl yet. If not, don't get too tied up in where the pipes hang for now. It becomes much clearer where the pipes need to go once the cowl is on and you see where the pipes can't go.
Click to expand...

Good advice... my exhaust pipes are currently held up by a bungie cord around the engine mount. Until I get the lower cowl fitted, I'm not too worried about the exhaust hangers! :)

mcb
 
Good deal, guys. I finished fitting everything and attaching the brackets and braces tonight.

One more question. I ran the horizontal cross piece as I indicated across te forward side of the nose gear fork. The horizontal tabs on the brackets on the pipe angle slightly to the rear since I have the bracket right at the beginning of the bend.

Anyway, how much clearance do you figure there should be between the hose (horizontal brace) and the nose gear fork? I've got between 3.8" and 1/2" as things stand now. I could add a spacer to get a little bit more, but since the horizontal tabs are angled backward just bit, it probably won't give me THAT much additional clearance (since the nose gear fork is also angling up).

Temperature was a high of 53 here today so I declared the end of fiberglassing season (good thing, too, as I just finished the last of the emp fairings yesterday) and will be working on engine stuff 'til spring.
 
Bob Collins said:
DanH said:
Patrick, rework the horizontal brace install. If it hasn't broken yet, it will.
Click to expand...
Just working on this this weekend, but I haven't seen anything in the thread to indicate (a) why it will fail and (b) how it should be reworked.
Click to expand...

Sorry I didn't spot your question earlier. Dan is pointing out that the long stand-off is subject to a lot of side load. I'm inclined to agree but it's showing no signs of problems yet (only 80+ hours); I'm thinking the hose will take up a lot of the load. However, rather than rely on wishful thinking, I am planning to replace the horizontal brace with another, located farther back on the pipes just after they exit the cowl. This will require an extra set of clamps but should not weigh anymore than the current setup. In the meantime, I'm keeping an eye on it.
 
Pilottonny said:
Bob, what is that wire for, running down the gear leg?

Regards, Tonny.
Click to expand...

Very observant Tonny. Actually it is my mixture cable which was not running through the firewall when this photo was taken. It's attached to the throttle body in the picture but the other end is passing through the engine mount and simply hanging on the floor.
 
Different wire

Bob,

I mean the white wire running down, attached to the engine mount with the black ty-rap.

Regards, Tonny.
 
Pilottonny said:
Bob,

I mean the white wire running down, attached to the engine mount with the black ty-rap.

Regards, Tonny.
Click to expand...

Aaaah Tonny, I see what you mean. Actually you are referring to a photo that I posted in the opening email of this thread. If you read that email you will see that the aircraft is not mine.....I lifted the photo from another thread for illustrative purposes (to show the problems others have had with running the exhaust horizontal brace behind the nose gear).

So, in short, I have no idea what that wire is for.
 
How I installed the crosswise hangers

I just finished up installing my exhaust hangers on my 9A and here are a couple of pictures:

cimg2396x.jpg


cimg2402s.jpg


I kind of did what I needed to do to make it work so you'll see that I have attached to different points on the clamps. It just seemed to fit better this way. I also determined that installing the crosswise hangers were not an option since the nose gear was in the way.

So, I attached to Adel clamps at another portion of the engine mount as somebody suggested in an earlier post. It seems pretty secure.

There were only 6 pieces of tubes in the kit. I made two more using the scrap that I had cut off of the existing tubes.
 
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Reservations about proposal

ArVeeNiner said:
So, I attached to Adel clamps at another portion of the engine mount as somebody suggested in an earlier post. It seems pretty secure.
Click to expand...

The Vetterman bracket design provides for the exhaust to be supported only off the engine so that there is no differential movement placing stresses on the exhaust support componentry, on the exhaust system, AND on the engine mount.

In respect of the latter, it is relevant that the tubular members in Vans engine mount will only be designed for axial loads whereas you are inducing lateral loads by connecting in the centre of a member span. Over time and many cycles it is possible that this member could fail.

A friend of mine recently used proper calibration techniques to measure the amount of engine movement at start-up and shut-down on his O-320. He found that he had rotational engine movement around the crankshaft of 3/4" at start-up and 5/8" at shut-down.

You say that your set-up seems "pretty secure". I'd say that is the problem with it.

If I was going to support an exhaust system from the airframe I'd be wanting something with much more flexibility.....like springs. And I wouldn't be connecting anything to the span of an engine mount tube.

You might be safer sticking to Vettermans support design but moving everything forward a little so that the horizontal brace is in front of the nose gear.
 
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Captain Avgas said:
You might be safer sticking to Vettermans support design but moving everything forward a little so that the horizontal brace is in front of the nose gear.
Click to expand...

Thanks Bob. I spoke with a friend of mine at work today, who is sometimes an RV builder, about this. We put our heads together and quickly came to the same conclusion as you. The engine moves, the mount doesn't and that's not a good thing. I didn't realize that it moved so much during start up! WOW!

So, a few minutes ago, I went out to see just how "secure" it was. I thought there would be a little side to side slop since I've tied it off at an angle to the sideways motion of the engine. Not so. It is as I said, pretty secure.

So, I'll make the stock crosswise support work. In fact, I think I'll copy what you did. :D

Thanks for being my second set of eyes!
 
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Connecting only to the engine......but how??

I have a Vetterman with Mufflers on my O-320 RV9A. The instructions and sketch say to attach one bracket, on each side, to the Engine Oil pan bolts and one, on each side, to the lower engine mount tubes. The Adel Clamps to do so are in the package and the brackets on the pipes are pointing in the correct ways to connect as described. There is ball-joints forward of the mufflers, but I can hardly move them as they are at the moment. Maybe they have to work in during the first hours of engine running.

I can see what you guys are saying, about movement, but how can I support it only off the engine? The system with the mufflers is a lot heavier than the straight pipes also. I was going to cut off as much as possible from the pipes to reduce this weight, but I am not doing this now, because people have warned me about heat, vibration and noise under the floor, with short pipes.

Regards, Tonny.
 
Pilottonny said:
I can see what you guys are saying, about movement, but how can I support it only off the engine?
Regards, Tonny.
Click to expand...


Tonny, why can't you set it up as I did in my Post #25 (see pix). I have a cabin heat muff on one side in front of the bracket (but not shown in my pix)....plenty of room for the muff between the ball joint and the bracket.
 
Very crowded in that area !!

Bob,

This is what it looks like, now, as per Vetterman instructions.

f_usrr588fm_d9a87fa.jpg


This is a picture looking from one side to the other, through the top of the front gear mount (bottom of the engine mount). Although the picture is a bit hazy, you can see there is not a lot of room, three fuel lines and the starter cable living in that area as well! The mounting bolt on the exhaust tube, is right in the middle of the picture.

f_usrr5899m_e09552b.jpg


This is the view from the bottom, quite crowded as it is. Because Vetterman has the two connections to the engine mount on the outside, I did not consider the cross brace (going where the fuel lines are now).

f_usrr589cm_43f81fe.jpg


I will need to thinker about this a bit more. I guess you are right when saying that the connection to the engine mount is not preferred, but that is how Vetterman has got it in his manual!

Any suggestions?

Regards, Tonny.
 
Exhaust hanger

Tonny
I have the same exhaust as you. I understand the problem of the exhaust hangers fighting against each other. One is mounted to the engine and the other to the engine mount. I decided to use Vettermans suggested design but tried to make the hanger attached to the engine mount more flexible than the other. I did this by making a larger gap between the steel end tubes. With a larger gap there is more rubber hose to flex. Suggestions are qualified by saying that its not flying yet so I dont know how long it will last.

Matt
 
Pilottonny said:
I will need to thinker about this a bit more. I guess you are right when saying that the connection to the engine mount is not preferred, but that is how Vetterman has got it in his manual!

Any suggestions?

Regards, Tonny.
Click to expand...

Hi Tonny, you might be paying a price for not installing things in the most optimum sequence. Certainly the "fixed hardware" should be installed before the "flex hardware". In other words the exhaust system should be installed first and the fuel lines routed to suit (not the other way around).

However it's obvious from your pix that the configuration of the exhaust system for the RV9A is slightly different from the RV7A that I have.

If I was going to connect to the engine mount I'd do it at a nodal area (where the struts converge) rather than mid span of a strut. Vetterman may approve of it but I'd be worried that oscillating lateral loads mid strut could eventually cause failure of the strut (probably adjacent to a weld at one end). As I've said previously those struts will only be designed to accept axial loads (loads in compression and tension along the axis of the strut).

If in doubt about a design detail I often go to the maintenence shop at the local airport and check out a few of the certificated aircraft in for service to see how the pros are doing it.
 
The plot thickens

I spoke with the man himself today, Larry Vetterman. He said:

-There are many ways to secure your pipes.

-It's perfectly fine to tie to the engine mount.

-There is a ball joint in the exhaust precisely to allow for movement.

Just passing the word. Now I need to sleep on it.
 
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