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yankee-flyer

Well Known Member
After trimming to the scribe lines I fitted the lower cowling. The right side seemed perfect, with 1/8 to 1/4 clearance between the spinner backplate and the circular flat on the cowl. The left side was up tight against the back plate. I'll have to take almost 1/4 inch more (forward of of the scribe lines) off the right side ( the vertical part that meets the fuselage side) to get an even gap all the way around. Has anyone else run into what looks like assymetric scribe lines?

THANKS

Wayne 120241
 
It sounds like you are figuring it out, but I would be very leary of cutting forward of the scribe lines at this point. It's a trial and error process. The scribe lines were extremely accurate on mine, and I did the cowl before the engine per the plans.
 
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Wayne,

I had a similar issue about a week ago... I was carefully sanding the lower cowl to get a perfect fit at the spinner (I attached a nice spacer to the back of the spinner plate)... the right side was spot on but the left side was snug. I kept sanding the left and finally got the same spinner clearance on both sides and the bottom. Then I put the top cowl back on and found that I really over sanded the left by 3/16 or a little more.

Looking back I believed the left side was dipping down and I never noticed it. Putting the top cowl back on pulled the cowl back into place and on the center line of the spinner. I never thought about the scribe lines being asymmetric. Make sure you test the fit with the cowl top and don't make my mistake.

The bottom line... I had to add fiberglass strips to left side to build it back out... I plan to start over today... see the pictures of the patch work.

-Ron

http://picasaweb.google.com/ronedmark/Cowl#
 
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I is important to have both the bottom and top cowl pieces attached to one another when you are fitting the cowling to the firewall. The top cowl pulls the bottom cowl into position.
 
Thanks for photos

John, your cowling looks about like mine (assuming you'd cut to the scribe marks already) so in spite of what Van's tells me (The scribe marks are correct!) it looks like at least a couple of us have the same problem. The add-back photos aren't mine, they're ron's-- and I too hope he'll add some detail just in case.

I've fitted the top cowling a couple of times with no apparent effect but I'll put it all together with tape tomorrow and take another shot at it.. Spinner seems to line up at the top OK, it's just that the cowl seems to need to come left.

Thanks guys

Wayne 120241
 
My experience ........

yankee-flyer said:
.....Spinner seems to line up at the top OK, it's just that the cowl seems to need to come left.
Click to expand...

With the cowl trimmed to the scribe lines the front was about 3/8' or so to the left, and low. I ended up taking about a 1/4" off the back of the left side, top and bottom, and tapering that down to nothing on the right side. This brought it into near perfect left/right alignment, and very close vertically. Took me several days on this darn cowling - I am definately ready to move on!

Others are correct when they say you have to put the two halves together to get the final fit. Drill out and cleco all 6 holes in the front end, and go ahead and install the side hinges too. Then you have a stable unit to play with your final trimming. Otherwise the lower piece just keeps flopping around.

Once you have the top and bottom firmly connected to each other, you can use duct tape strips for temporary positioning. Plan on taking it on and off many times, because you don't want to sand too much at a time and end up overdoing it, like I did in one or two places. This is one of those areas that seems to take waaaay too long - mostly because it is a learn by doing operation. I think I could do it again in 1/2 the time, or less.

John
 
Old topic, but.....

I also have to trim the cowl on the left side aft of the scribe line. When I measure the difference (sanded to the scribe line) it will give an offset angle of about 1 degree to the right. So instead of sanding aft of the scribe line I can also ad a washer of about 1/16" at the two left engine donuts giving the thrust line an angle of 1 degree to the right.
Anyone tried that before?
 
:eek:I don't think it's a good idea to play around with the engine alignment. For one thing, it is a departure from the plans. Perhaps more importantly you might end up with an airplane that you can't get rigged to fly straight! JMHO.
 
Most off the planes end up with a big trim tab. The other RV models have an offset to the right of about 2 degrees. The 1 degree ofsett I was looking for gives a bettter trimmed plane.
But I already decided not to do it and just follow the plans. The cowling is more work than expected.
Thanks for the input!
 
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