RV 8 Aerobatic engine mounts

Merry Christmas! I had some downtime so I thought I would put this out there. My RV8 spinner seems to be hitting the lower cowling when I pull g's. It doesn't hit it very hard but the tracks are there. I have the extra washer in the lower engine mounts to jack it up for sag. I needed it. I have the stock Van's rubber engine mounts. Does anybody know of an aerobatic mount (part numbers please) and what are the tradeoffs if I jump to it. I have the whirlwind spinner which is fiberglass. I could sand it down about 1/32" and it would probably fix it. I have access to a dynamic balancer so I would then have to redo that project, but that seems excessive. I think a stiffer mount might solve the problem easier and more permanent. The current mounts and airplane are only 3 years old. Any suggestions? Thanks in advance

BluSkyRidr said:

Merry Christmas! I had some downtime so I thought I would put this out there. My RV8 spinner seems to be hitting the lower cowling when I pull g's. It doesn't hit it very hard but the tracks are there. I have the extra washer in the lower engine mounts to jack it up for sag. I needed it. I have the stock Van's rubber engine mounts. Does anybody know of an aerobatic mount (part numbers please) and what are the tradeoffs if I jump to it. I have the whirlwind spinner which is fiberglass. I could sand it down about 1/32" and it would probably fix it. I have access to a dynamic balancer so I would then have to redo that project, but that seems excessive. I think a stiffer mount might solve the problem easier and more permanent. Any suggestions? Thanks in advance

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I’m interested in the responses that you receive. I have a similar problem, but it’s the top of my cowling when I fly sustained inverted. I also have a whirlwind spinner, and it appears that the overlap on the back of the spinner is what’s rubbing.

I’ve had good results with my Barry mounts for my IO360 with Hartzell CS prop. Routinely do aerobatics and inverted flight. Part # 94011- 20. Pretty sure I got them through Aircraft Spruce. 5 years now, 420+ hours, with no issues.

Thanks for the reply on the Barry's mount. That is a good data point. How much vibration are you now feeling since installing the mounts. More or less? Is the motor more or less rigid when dancing around during the wet dog dance during startup and shutdown?

So here is what I found out this weekend and today after talking to Whirlwind.

On the weekend I called a gentleman who was on the EAA homebuilt committee for a while and is now on the EAA safety committee. He is familiar with my airplane. He indicated to me that sanding the spinner and backplate would be OK, but it will have to be done very carefully. If I go that route I will have to dynamically rebalance the prop. So not that big a deal. 1/16" should be enough.

Today I had a good conversation with the Whirlwind people (I have a RV74 prop and spinner). They also indicated that I could sand the spinner and the backplate. Both the items are fiberglass. I probably will go this route . . . but I still think I need to replace the motor mounts if I want to use this airplane to compete in some IAC competitions. I hope I hear from some people who regularly fly acro and have different motor mounts than the stock Van's mounts

BluSkyRidr said:

Thanks for the reply on the Barry's mount. That is a good data point. How much vibration are you now feeling since installing the mounts. More or less? Is the motor more or less rigid when dancing around during the wet dog dance during startup and shutdown?

So here is what I found out this weekend and today after talking to Whirlwind.

On the weekend I called a gentleman who was on the EAA homebuilt committee for a while and is now on the EAA safety committee. He is familiar with my airplane. He indicated to me that sanding the spinner and backplate would be OK, but it will have to be done very carefully. If I go that route I will have to dynamically rebalance the prop. So not that big a deal. 1/16" should be enough.

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These are the mounts I have used from day one so I cannot comment on more or less vibration compared to other mounts. I can tell you that it feels smooth as butter from 800 RPM through 2700 RPM. I had the prop balanced and it required less than 1/2 ounce to make it perfect. Spinner to cowling spacing on mine is 1/4”. The only change I had to make was to use a slightly shorter alternator belt for my B&C alternator because it was rubbing on the bottom cowl so obviously it is shifting when pulling G’s. No contact whatsoever with the spinner backplate though from +6 to -2 G’s. Vibration during start and shutdown is comparable to any other Lycoming. I know quite a few RV’s have cracks on the exhaust ramp caused by engine vibration and I have no evidence of that on my aircraft. No evidence of sag that I can tell either.

I don’t see why sanding the back side of the spinner and mounting plate would be a problem as long as you maintain the proper edge distance for the rivets or whatever fasteners you have on your fiberglass backplate.

Barry does have an aerobatic mount listed on the application list for the RV8, PN 94016-08, if you want to go even firmer.

I’m in the market for new engine mounts. The aerobatic Barry mounts (94016-08) are 3x the price of the standard mounts (94011-20). At what point should the aerobatic mounts be considered?

What is the cowl to spinner gap?

I have no idea. The engine is currently in the shop. I just figured it would be a good time to replace the mounts since I don’t know when they were last replaced. It’s more of a preventative exercise.

Pilot8 said:

What is the cowl to spinner gap?

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Check out all of DanH's posts in this thread. He did some research on different engine mounts, including stiffer 'aerobatic' mounts.

I tried so-called aerobatic mounts and found that Van's mounts were just as stiff and much, much less expensive. I ended up putting a big washer under the lower engine mount. Problem solved.

RV8JD said:

Check out all of DanH's posts in this thread. He did some research on different engine mounts, including stiffer 'aerobatic' mounts.

Failed Mount Isolators

Engine seemed a bit shaky recently, so today the cowl came off for a look. Problem wasn't hard to find: The liquid was squeezing from an isolator: Bring out the wrenches... These are the bottom isolators. Don't have the top pair out yet. Lord J9613-40, about 830 hours on a 390 with...

www.vansairforce.net

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FWIW, the standard, non-acro, VIP set (four part #50011-20 and four #50016-08) is still in there, doing fine. I typically max out at a little over 3.5G. More G with a 390 or 540 may require eight 50016-08's and spacers.

Anyone have issues with Lord mounts?

N82VM said:

Anyone have issues with Lord mounts?

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They’ll sag more than the standard VIP mounts mentioned above. This was verified with alternator pulley marks on the bottom cowl. I was routinely pulling 5-6 g.

Thanks for all the replies. I went to the Van’s store and cannot find the VIP mounts. At ACS, both the VIP aerobatic and standard mounts are on indefinite backorder. Does anyone have any intel on the situation?