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Spinner fouling cowling

TroyBranch

TroyBranch

Well Known Member
Friend
I am helping a new RV10 owner get the annual done on a recently purchase US built RV10 so he can pass the MDRA inspection for a canadian C of A. One of the concerns is the builder has the cowling built to close to the spinner that it is actually touching on the bottom right side.:eek: The cowling has a groove wore into it from the near 300 hrs of flying it has.

I sent this question in to vans and never got a response. Hopefully you folks can give some suggestions.

On the RV10 the first thing I noticed is the back plate of the spinner is rubbing on the cowling. The plane has close to 300hrs but I really do not like the idea of leaving it as it is.

The first thing that came to mind was placing a large washer between the engine and the rubber mount to push it ahead 1/16 or so.

The other choice would be to trim the back of the back plate down of there was room to the nut plates.

And the last choice would be to take the washers out of the forward side of the spinner back plate that are between it and the prop, requiring the back plate to be trimmed on the inside to clear parts of the prop hub.

What is the best fix beside redoing the cowling?

Thanks
 
suggestions

Might I suggest you take various pics and post them? Let others see the issue so that responses are fitting to the issue. Just always helped me get good answers.
 
Troy shimming is the easiest.
Might affect your engine mount bolt length to the point where you may need a longer bolt, depending on how much thread you have left for the cotter key.
 
If you move the engine forward you may have to re-trim the baffle fronts & FAB inlet. If not, the mount washers would be really easy.
 
My thoughts: a 1/16" shim won't be enough. If it's rubbing, you want about 1/8". Shimming on the face of it sounds easy but - moving the engine forward in the cowl may cause fit problems at the scoop, inlet ramps, and other places.

Then I think about your description and you say it is rubbing in one quadrant (lower right). How close is it in the other quadrants? What I'm thinking about is how the cowling is aligned with the prop back-plate. Sounds like the cowling needs to be reworked.

However, I come bearing good news. You don't have to buy a new cowling and start all over. Here's how you fix this: Using the prop back-plate as a guide (by the way, you didn't mention if the spinner or back-plate was damaged but you should be sure to replace those first if they were) mark around the cowling ring where you'd like the spinner clearance to be. Now, remove the cowling and use a flox/epoxy mix to build up behind the cowling ring. You've got room, so make it thick. It wouldn't hurt to put in a layer or two of bidirectional glass in there, too. Once the epoxy has cured, file the ring back to your mark, trying to make it even across the diameter of the ring. You were going to have to repair and repaint the damage anyway and this is not much worse and takes care of the problem. Best of all, the engine does not have to move, nor is the rest of the cowling affected.
 
The fact the rubbing is located on the bottom, leads me to consider sagging motor mount bushings.

Is the spinner still lined up correctly with the cowling, or is it apparent that things have sagged a bit???

I seem to remember something about occasionally this being caused by installing the top mounts in the bottom, and vise-versa.

If it comes to having to modify either the spinner, or the cowl, I find fiberglass pretty easy to work with, so I would be looking at the cowling.

In addition, if the area it is rubbing is only on a part of the whole circle, then it would give you a chance to make an equal gap all the way around.
 
Why would you tinker with structure (bolts, washers, backplates) to compensate for poor craftsmanship? Refit/rework the cowl.
 
Sagging

The rubbing is from the sagging. The top is about 3/32 clear at best. If it wasn't touching prior to the sagging it was just clear. Deffinately built to tight. It is just the bottom right quadrant of the spinner that is touching. The 10 cowling line up pretty good compaired to the 7 & 9 from stock so the amount out of square is very little, just to tight all around. Spinner and back plate has no damage.

I was thinking that just shimming the bottom mount might be enough to do it but the top could just get tighter. Easy to try I guess. I have no trouble doing the fiberglass work to make it perfect, just planned for this to be a simple annual for the guy. This is all being done as a favor to help out a new RV guy. That is what we RV people do right:rolleyes: I just thought that the prebuy inspector would have noticed things like this, so I did not expect my favor to be any more than an annual, making sure everything is up to date and adding the gascolator. Not sure why I thought that;) It is an airplane.:D
 
You say it is sagging

I would address the known sagging condition first to get the as built thrust line back where it was. Taking the gravity load off and retorquing the bolts is a start. Then there is the shimming with the engine mount washers that can be done. Then there is the spinner assembly to consider. When I went from the old Hartzell 7666 bladed constant speed prop to the blended airfoil prop there was a change in position of the mounting plane at the rear of the hub and the information from Hartzell warned me of that. I changed the washer stacks used to mount the bulkheads to reposition the spinner back to the original fuselage station (forward & aft location) and all went well. I hesitate to mention it ... well I just will not. Be carefull.

Bob Axsom
 
Also you should check the isomount orientation.
This would not be the first builder to have installed them backwards.
There is a front and back to them that requires proper orientation to engine loads.
If installed improperly, early sagging is to be expected.
 
Bob Axsom said:
I would address the known sagging condition first to get the as built thrust line back where it was. Bob Axsom
Click to expand...

Why would one adjust this? Both of my RV's dropped about 1/8" of an inch within a year of first flight at the spinner. No different on this plane. If you look at the mounts, the front lower ones are generally more compressed than the top which create the slight nose drop of the engine. Is there any benifit in trying to change this? I know my RV10 is remaining as is, that is why I set the spinner a bit high and now it aligns perfectly.
 
Not top vs. bottom

Kahuna said:
Also you should check the isomount orientation.
This would not be the first builder to have installed them backwards.
There is a front and back to them that requires proper orientation to engine loads.
If installed improperly, early sagging is to be expected.
Click to expand...

Thanks Mike, that is what I was trying to remember.....
 
Kahuna said:
Also you should check the isomount orientation.
This would not be the first builder to have installed them backwards.
There is a front and back to them that requires proper orientation to engine loads.
If installed improperly, early sagging is to be expected.
Click to expand...

If these are in backwards, how much sagging would be expected over the normal? I will look at this on the weekend, even if they are wrong, there will still need to be some changes.
 
I thought the front/back orientation was different between the two different brands that Van's has supplied. I seem to recall that the Lord version didn't have this issue.
 
rleffler said:
I thought the front/back orientation was different between the two different brands that Van's has supplied. I seem to recall that the Lord version didn't have this issue.
Click to expand...

Im no expert on Lords. Im sure they make all kinds possible.
My lords however do have the splits that require proper orientation.
 
Sorry to send this thread down a lord mount rat hole.
My 540 lords are Lord J-9613-12.
I do not know what Vans ships for the 10.
As mentioned, Im sure lord makes all kinds for all things.
 
I agree with Kahuna on shimming. First correct the sag. I did this with an extra washer (thin) under the bottom engine mount points at the firewall. Then to move the whole engine out just a little, put an extra washer on the Lord mount. Consider using high temp stop nuts (AN363-720, I beliieve) on your engine mount bolts rather than castelated nuts, then you don't need to be concerned with cotter pin holes lining up. You just need to make sure the bolts are long enough to have a couple threads showing beyond the nut. You can get these nuts at ACS. If the bolts are too short, just get longer ones - AN-7, I think.....
 
Saturday I will put the cowling back on to check the alignment. I think it was pretty good. I have seen some that were way off, so I will decide if change is needed vertically. I don't think the sag is any more than the usual. After that i will let the owner decide which route to take. Cowl or washers. Each solution is pretty easy and each has their pros and cons. Sure wish you all gave the same answer;)

This might be my last favor of this kind:rolleyes:
 
flion said:
However, I come bearing good news. You don't have to buy a new cowling and start all over. Here's how you fix this: Using the prop back-plate as a guide (by the way, you didn't mention if the spinner or back-plate was damaged but you should be sure to replace those first if they were) mark around the cowling ring where you'd like the spinner clearance to be. Now, remove the cowling and use a flox/epoxy mix to build up behind the cowling ring. You've got room, so make it thick. It wouldn't hurt to put in a layer or two of bidirectional glass in there, too. Once the epoxy has cured, file the ring back to your mark, trying to make it even across the diameter of the ring. You were going to have to repair and repaint the damage anyway and this is not much worse and takes care of the problem. Best of all, the engine does not have to move, nor is the rest of the cowling affected.
Click to expand...

We used this method before first flight, when I was not happy with the clearance. It worked great. 370 hours with no apparent engine sagging. I expected to see some by now.
 
Siimalar Problem

I have a similar problem for a different reason. After setting the cowl and the camlock fasteners for a fixed pitch prop on the RV9A I am building, I changed to a Hartzel constant speed prop and ended up with about 1/32 inch clearance between the spinner back plate and the cowl. I trimmed 3/32 inch off the spinner and back plate, which provided 1/8 inch clearance except a three inch long section. It turns out that the back plate, which has already been fitted and drilled to the spinner, is slightly warped; the too small gap move with the rotation of the prop. To fix this, I will sand 1/32 off the cowl flange if during phase ! testing there is evidence that the plate is touching the flange. If necessary I will put additional layers of cloth behind the flange as suggested above. I had to do this when fitting the fix pitch prop and it worked out well. In that case I remove 1/16 form the flange on the upper cowl.

I also have a problem with the spinner being lower than desired relative to the cowl with no allowance for future engine sag. To adjust this, I plan on shimming the lower four engine mount attachments to the firewall up to 1/4 inch using 4 AN970 washers and longer bolts at each attachment point. This will raise the engine and spinner relative to the cowl. I tried this with temporary shims and it appears that it will work. I have a note into Vans to see if there is concern related to shimming the engine mount to firewall attachment points.
 
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