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Pat Stewart

Well Known Member
I just wanted to pass on the results of the latest modifications to my 8A. The first mod was changing the nose wheel from the stock Van's wheel to the Grove RV wheel. Very simple and reduced the shimmy in the nose wheel.

The second mod was adding the exhaust tips from Larry Vetterman. What a difference. This mod significantly reduced the noise and vibration in the forward floor pan. I also believe it will reduce the possibility of cracks in the lower skin aft of the exhaust. I have already stop drilled two small cracks in that area. The installation turned the exhaust down into the airstream about and inch but well worth any impact to speed which I doubt can be measured.

Thanks Larry, now if I can just remember to send you a check.;)

Pat Stewart
RV8A
 
Both Changes should affect the speed of the airplane

Around a year ago I cut the turned down exhaust off to eliminate the turndown and there was a slight increase in speed. The change was less than a knot I believe but if you are struggling for every fraction of a knot that is significant. If not I guess it doesn't make any difference. I cannot imagine a crack starting in a parallel flat piece of aluminum with no unfinished edges due to Lycoming exhaust pulses.

I made subfairings for my main and nose wheel fairings. The Mains are the large new pressure recovery design from Van's and the nose gear wheel fairing is the older, smaller and flat sided design from Vans. The main landing gear change contributed no measurable change in speed. The nose wheel fairing change made a STRIKING increase in speed. In my testing this is a very sensitive drag area and any change will probably impact the speed of the airplane. Just a speed comment.

Bob Axsom
 
Floor Cracks

Bob,

The cracking starts at the rivets. I have seen several 8 and 8A's with this problem some with less than 50 hours. One with less than 25 with a stacked doubler repair already in place. This is a known RV8 problem and most believe the exhaust vibration is the problem. From my experience there are only two types of RV8 aircraft, those that have cracked and those that will. The tips turning the exhaust down made a huge difference in noise and vibration. I can't help but believe this will improve the cracking problem.

Pat
 
I seem to recall that the turned down exhaust became "stock" at some point. Can anyone confirm if and when that happened? Also, does anyone have a side-by-side picture showing the non-turned down and the turned down pipes? It would be nice to visually see how much difference there is between the two.

Thanks,
 
RV8 belly mod

Pat Stewart said:
Bob,

The cracking starts at the rivets. I have seen several 8 and 8A's with this problem some with less than 50 hours. One with less than 25 with a stacked doubler repair already in place. This is a known RV8 problem and most believe the exhaust vibration is the problem. From my experience there are only two types of RV8 aircraft, those that have cracked and those that will. The tips turning the exhaust down made a huge difference in noise and vibration. I can't help but believe this will improve the cracking problem.

Pat
Click to expand...

Listers,
The 8s and 8As do indeed crack in this area. I had read about this years ago on the Matronics List. Vans original intent was to make the exhaust area ramp a variable outlet, to reduce drag. It became complicated, so Vans dropped the idea. However, they left the original design "as is" (note the hinge attach at the rear of this panel). I felt that the design could be easily and cheaply improved. If interested in what I did, contact me off list. I'll send emails with photos.
Charlie Kuss
PS I've just added photos of my mod to the thread below. (4/20/09) See
http://www.vansairforce.com/community/showthread.php?t=29475&page=2
 
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This is a stress area

Even on my RV-6A where the bottom cowl attachment was designed to be made with hinges. I had rivet heads popping off in the first year. In increased the rivet diameter but they started "Working" in the cowl. I drilled them out and replaced the aft hinge half with an 0.032 2024T3 flange extending forward inside the cowl and modified the cowl rivet holes (enlarged to 3/8") to be attachment points for dimpled washers and #8 flathead SS screws. Several hundred hours now and no more problems. Good luck with the "8" problem though I am still skeptical about the Exhaust vibration as the source of the problem. If I had one I would certainly be working on the skin vulnerability issue but I just really am bothered by drag additions.

Bob Axsom
 
a little off the topic but....

I notice some curved angle on the rt of the fuselage Carl - what function does that serve? Some sort of Vortex generator, or trim device?

Thanks
 
turn downs here

Hi.

Here's pics of the turndowns I've just installled on my -7.
You can easily see where the Vetterman exhaust tubes ends because of the thicker part of the turndowns.

I've only from two trips with them so far, but it seems to me like the drumming is reduced to 50-75%.

They're probably adding drag to the plane and I'm planning to fly some tests with and without them and see how much (if any) added drag they make.
Anyone else done this so I can save me the trouble?

Link: http://aviationtechproducts.com/html/shopping.html

Bt the way; they also have a nice tailwheel fork.






 
<<Vans original intent was to make the exhaust area ramp a variable outlet, to reduce drag. It became complicated, so Vans dropped the idea. However, they left the original design "as is" (note the hinge attach at the rear of this panel).>>

Ahhhhhhhh! So that's the deal! Never could understand why the hinge was there, and now I do. Thanks Charlie.
 
<<<Here's pics of the turndowns I've just installled on my -7.
You can easily see where the Vetterman exhaust tubes ends because of the thicker part of the turndowns.

I've only from two trips with them so far, but it seems to me like the drumming is reduced to 50-75%.

They're probably adding drag to the plane and I'm planning to fly some tests with and without them and see how much (if any) added drag they make.
Anyone else done this so I can save me the trouble?>>>>

There are several ways to reduce the drumming on your belly. One is to cut the pipes at a relatively horizontal angle. Here's pic that explains what I mean http://www.vincesrocket.com/exhaust trim 2.jpg It made a noticeable difference in exhaust tone on my Rocket, and it's certainly less drag than having the extra pipes sticking out in the breeze.

Another way is to visit my web store (http://www.flyboyaccessories.com/) and get some of the ThumpKiller to put inside your forward floorboards. It also reduces the drumming noticeably. It's cheap too.

If you've not visited my web store, please do. There are over 60 items directly related to RVing. And many of them are exactly what your wife wants for Christmas! ;-)
 
rv 8a vetterman exhaust

I need help on installing the exhaust on an 8a. Does anyone have pictures of how they secured the exhaust on an a model. Larry v. drawing is not very helpful.
 
Pat Patton said:
I need help on installing the exhaust on an 8a. Does anyone have pictures of how they secured the exhaust on an a model. Larry v. drawing is not very helpful.
Click to expand...

This has worked for me for 300+ hours.

361781276_FnveS-L.jpg


361781287_5QscB-M.jpg
 
Although I'm not flying yet, I was thinking the Vetterman fairing under the fuselage would be the way to attenuate floor vibration and increase speed at the same time.
http://www.vettermanexhaust.com/ go to the bottom of his page for pics etc.
I realize it has only been tested on side-by-side RV's to date.
But I have a deeper cowl exit scoop due to having a chin radiator for a liquid cooled enigne. I'm ground running, and seem to have mastered the cooling problem. I can run over 25% power on the ground without overheating. There will be high cooling drag, but that's a small price to pay for the first flights. Overheating would be much worse.
Later come reductions in radiator and scoop size, vetterman style fairing, alternate exhaust tips etc.
Oh! I just had a thought. Those super quiet Swiss Mufflers wouldn't pose such a drag penalty if they were incorporated with the vetterman fairing....
 
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