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Getting a correct Big Cut trim line

Draker

Well Known Member
Well, the weather in NorCal this weekend isn't going to get very hot, so I'm going to put off the big cut. This gives me another week to agonize over the cut line on my (tipper) canopy. I can't seem to get the top of the canopy less than an inch or so from the roll bar. I've trimmed and trimmed and trimmed (probably trimmed too much) and it still doesn't rest close to the roll bar. Van's says to draw the line "when you have gotten the fit to be somewhat close". Does 1 inch count as somewhat?



I'm worried that after the cut, when the canopy pivots down such that it can touch the roll bar, the cut line will no longer be aligned with the roll bar centerline:

Before cut:
i-vWgXDww-L.png


After cut:
i-hmrrCKg-L.png


Am I overthinking this? I'm not sure I want to trim too much more since the existing trimming I've done has not really helped. I also don't want to put pressure on the top of the canopy to "force" it down onto the roll bar.
 
Canopy fit

I share your concerns. It?s been 8 years since I dealt with this on my 7A tipper, and yes, it?s a time to slow down. My advice is to eliminate any stress points on the plexiglass around the front and forward sides of the canopy so that it comfortably rests on the tip up frame. Then secure (tape) the plexi to the tip up frame. I believe the slightly elevated plexi over the roll bar will not be a factor in the offset as it drops down a bit after the cut.
Good luck and take your time

Jim Diehl 7A
Based at KLHV
 
I would cleco the turtle deck on to insure there is sufficient overlap at the back to insure the plexi can be screwed to the skin all around. Maybe leave the side clecos loose so the plexi can slip under the forward sides.
I would continue trimming the front of the plexi (w/s area) back till the plexi dome lies very close (vertically) to the rear canopy frame/roll when the bubble is draped over the fuselage structure.
Then you can mark the plexi for the big cut.
After the cut, trim the sides of the canopy plexi to their final shape.

Bringing the dome height down dictates your plexi front/back positioning, which locks the big cut location.
 
I would cleco the turtle deck on to insure there is sufficient overlap at the back to insure the plexi can be screwed to the skin all around. Maybe leave the side clecos loose so the plexi can slip under the forward sides.
I would continue trimming the front of the plexi (w/s area) back till the plexi dome lies very close (vertically) to the rear canopy frame/roll when the bubble is draped over the fuselage structure.

Thanks, Yea. I still have plenty of overlap in back to attach to the turtle deck skin. After a little more work, I'm about 3/8" to 1/2" from the top of the roll bar. I don't think I'm going to be able to get closer than that. Another builder suggested I make the big cut line a little farther aft on the roll bar and then square it to the roll bar centerline later. That also sounds like a good idea.
 
Trim it close, make the cut, then finish the trimming. The canopy will rest on the roll bar and then finish trimming the side skirts and the joint between front and aft pieces. Cut the front a bit long and trim it to set nicely on the roll bar. Then trim the aft section to set about 1/8" from the front section aft edge and also set well into the aft upper fuselage sections.

It's best not to get too aggressive before the cut, because you will still have a lot of trimming after the cut. Just get it close and I think you are there. We all anguish during this part of the build. Once it is done, it seems to go a lot easier.

Roberta:)
 
Thanks for everyone's advice -- again! The big cut went smoothly. I decided to mark the trim line 1/8" aft from the center of the roll bar. This resulted in the post-cut sides matching the centerline exactly, and 1/8" too far aft on the top, which can be easily sanded away.



Obligatory "Larry pose" with the Saw Max:

 
Last edited:
Hey Ryan,
Nice job!! I have made cuts on several canopies over the years, and the last one I did was with the tool I see in your hand. To me, that is the best tool ever for the job. Quick, easy, and a smooth cut - which is very important. Congratulations on an important part of your build!! A hangar neighbor borrowed my tool to make his cuts on his RV7A and they all came out beautiful. Good luck going forward.
 
Yea, the Saw Max worked great on the canopy. Used it for the initial trimming and the "big cut". Great for straight lines and very shallow curves. It leaves pretty gnarly tool marks on the plexi, so you need to follow up with a good thorough sanding after each cut to smooth it out. Also, a minor complaint: It is VERY easy to engage accidentally, so you need to be careful how you pick it up when it's plugged in. After a near disaster, I now have a policy of not having the thing in my hand until I am 100% ready to cut.

Ray, you're welcome to borrow it when you're ready to start cutting your canopy.
 
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