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Top cowl

DeltaVee47

Active Member
Despite my best efforts it appears that my top cowl is 1/4-3/8 inch high in relation to the spinner. My EAA counselor brushed this off saying I just needed a shim or two under the lower engine mounts. However it would seem to me that this would change the angle of thrust. What say the assembled?
Thanks
Greg Beckner
N557GB
140366
 
Unfortunately, if anything, you want the cowl to be low in association to the spinner because your Lord mounts are going to break in and your engine will sag up to 1/4". Search for threads on this, there are many, for the other model RV's at least. I used washers behind the top engine mount and firewall to bring the spinner down until my engine sagged after the first year of flying and then took them out.
 
Cowl

Thanks for replies.
Multiple mistakes were made, probably the worst of which was doing things out of order. For what seemed like good reasons at the time I did the baffles with rubber parts prior to starting on the cowl. Getting a proper fit of the upper cowl was difficult but I thought I did it right in the end. But obviously not. So the question is whether to try to shim the engine up or modify/redo the upper cowl. I am leaning toward the latter. I would have move the spinner more than 1/2 inch in relation to the cowl in order to account for further sag.
Greg Beckner
N557GB
Dues paid
 
It is much easier to adjust a top cowling that is too high then one that is too low. First make sure that the cowling has the proper gap between the spinner and the front face of the cowling, this may effect how much you have to remove at the back. Remove the baffle pieces if you have not already done so.
Then it is a matter of shaving a small amount off the sides of the top cowling to allow it to drop to the proper spot. Essentially you will be sanding off a long triangular piece on each side. For example you may end up sanding off 1/8" from the bottom aft corners tapering up to nothing at the top centre of the cowling. You will have to fill any drilled holes, and drill again. This will all take much less time then you imagine.
Do not remove too much. It should take very little sanding at the aft end of the upper cowling to allow it to drop to its proper position.
After the top and bottom cowlings are in place then fit the baffles and adjust them to the cowlings.
 
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I also did the baffles out of order, but I taped the rubber seals down with a generous amount of masking tape before fitting the top cowl ... you don't necessarily have to remove the baffles.
 
Do what Bill said, you need the rubber out of the way. I fit mine with baffles but no rubber so there was no interference from them. Fit the entire cowling first, then add the rubber. Once I put the rubber parts on, the top cowling took a lot of pressure to get pushed down into place where it belonged and then attached. I can't imagine how difficult it would be to try and fit the top cowling from scratch with the rubber baffles on.
 
Thanks for great advice. Unfortunately I have final riveted the vertical hinges on the aft lower cowl. As I see it I will need to drill out the hinges on the lower cowl, glass in the holes, refit the cowl properly with sanding as advised, redrill and rivet the hinges. The whole cowl assembly should pivot downward. I still prefer this to the idea of shimming the engine unless the general consensus is that this would be acceptable.
Greg Beckner
N557GB
 
Thanks for great advice. Unfortunately I have final riveted the vertical hinges on the aft lower cowl. As I see it I will need to drill out the hinges on the lower cowl, glass in the holes, refit the cowl properly with sanding as advised, redrill and rivet the hinges. The whole cowl assembly should pivot downward. I still prefer this to the idea of shimming the engine unless the general consensus is that this would be acceptable.
Greg Beckner
N557GB

You may not have to fill the rivet holes in the cowl. Start with new hinges and see where the rivet holes will be. A very small amount of hole movement at the hinge can translate into a rather large movement in the cowl at the fwd end ,because the distance ratio is so large.
 
I know of several RVs that have washers between the FW and motor mount to adjust for engine sag with no issues.
 
I know of several RVs that have washers between the FW and motor mount to adjust for engine sag with no issues.

That is to put the engine back to it's optimal angle relative to the fuse centerline, not to raise it a degree or so from it designed angle. I would not recommend changing the designed angle to addess a problem that can be resolved with fiberglass work.

The prop's axial centerline relative to the fuse's centerline (both horizontal and vertical) is an airframe design element and should not be adjusted without understanding the effects that it has on flight characteristics. The angle absolutely effects certain flight characteristics when the prop is spinning.

I am not an aero Eng so can't say whether the considered change is within the tolerance range.

Larry
 
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Good discussion, my spinner is 1/2" larger diameter than the cowling. Had to be to accommodate counter balance on prop. I haven't mounted anything yet so before I start, is there a problem with the spinner being 1/4" larger on each side?
 
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