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Guidelines for Trimming Tip-up Canopy

T

tx_jayhawk

Well Known Member
Before I get too crazy trimming the canopy, I was hoping I could find some guidelines on about how much past the clamp marks the canopy will get trimmed on the front, sides, and rear.

Based on what I see so far, it looks like:

front - Trim all the "flat" portion of the canopy
rear - Remove just a little (?) past the clamp marks
sides - ??

I know the exact amount will be established on final trimming, but it would be very helpful to have some general guidelines (I wish Vans would put this in the manual).

THanks,
Scott
7A Finishing
 
Trimming the conopy

Scott,

When you start trimming the canopy the first thing you do is cut the front rim off as you mentioned. Then you can start trimming more off the front so that the canopy will sit closer to the roll frame. Make sure you have the rear top skin off while doing the initial trimming prior to the "big" cut (separating the front from the rear glass).

If I recall I had to take about 1 1/4" off the vertical portion of the front to get the canopy to sit close to the roll frame prior to the "big" cut. The distance from the inside of the canopy to the roll bar was about 1/4" prior to the "big" cut. You don't have to get it that close but if you are within 1/2" I would make the cut. You will have to trim the rear edge later anyway.

Once the front is cut down you can trim the sides (leave them long for final trimming once you have made the "big" cut.

Install the main canopy glass first, leave it a bit long in the back (which I didn't though I wished I did) and then install the rear glass. Keep in mind that once the gas springs are installed the canopy may move a little forward.

In addition like many I removed the ears from the canopy top skin. I did this after I completed trimming and fitting the canopy. If I had cut them off to start with I would have saved a bit of time.

Currently I am painting the canopy frame today and permanently installing the canopy glass. I have Thanksgiving week off from work and hope to start and finish the front fiberglass fairing during this time.

You can search on my posts to find more detailed "trials and tribulations" on my quest for a perfect canopy installation.

I hope this helps,

Paul Merems
RV-7A Finishing kit, Canopy installation
 
THanks Paul. Good feedback as always...I've been following your recent threads.

Given my rear top skin is already on, I hope that is not a problem with fitting.
 
Keep Trimming?

Okay Guys (Paul, Radomir, others?),

I've completed the initial trimming where the canopy now "roughly" fits the frame. On the front, I started by tracing and cutting right along the "gulley" where the plexi transitions from vertical to horizontal (all of the horizontal portion was then cut off). The contour matched the skin remarkedly well after that first cut, but there was a significant gap between the rollbar and plexi. I then cut back another 1/2" along the front edge. The contour of the plexi then did not match quite as well (maybe I did not cut as straight?), and I did not observe a noticeable closure of the canopy gap over the roll frame.

If I understand others, should I continue to be cutting on the front edge until the gap closes on the roll frame? Right now it is around 1 - 1.25" I would estimate. I do have the rear top skin, so I assume it is contributing some to the extra height (although I don't believe that much).

Also, are there any tricks for cutting the canopy lip so that the contour lines up? I assume I should just be removing portions that touch the canopy skin (until it all lies flat).

Thanks,
Scott
7A Finishing
 
Scott, I'd remove that rear top skin. You can also trim just a little on the back.. just the clamping flange. However, in my opinion, following the instructions is the best way to go. Trim forward side until you get a good fit between canopy and skin.

Now, the tricky part is that you want to somehow clamp canopy sides to the side rails.. as that's the final position.. IIRC, this is printed in capital letters in the manual.. (for a good reason). When you're checking the fit, you really want to ensure that the canopy is in its final position (clamped to 725 side rails etc..).. doing any trimming w/o observing this will change things.. there's SO much "dyanamics" in that whole thing..

Also, since it's just an airplane you're building, don't worry if there's a little bit of a gap here and there inbetween skin and canopy up front.. it gets filled anyways.. :)


Sounds like you're doing great so far.

PS.. I wouldn't worry too much about the gap between rollbar and canopy for now.. try to get it a bit less if you can.. eg. 1/2" or so would be great.. I can't now remember what I ended up with just prior to making the big cut but there was some gap there.
 
Thanks Radomir. I unfortunately have the rear top skin riveted, so it would be non-trivial to remove it.

I guess I'm just apprehensive about taking too much off of the front. It sounds like Paul took 1.25" of the vertical portion off, but I did not see that others took as much (when searching the web).

Thanks,
Scott
 
Scott,

I'm about to start cutting (today). I'm presuming you've finished cutting and was wondering if you could give an "after action report"?
- how much did you cut off the front before the first fit test
- describe those enigma "clamp marks!!!" - the grooved portion around the canopy?!
- in the end how much would you say you trimmed total (front, back, sides) compare to stock?
- what techniques for clamping canopy securely when fitting, marking. ie. clamping to 725's?

Thanks for your input.
 
Finding a way to clamp the plexiglas to the side frames is one of the harder things to do. I tried tape and straps before I finally came up with some homemade clamps that really work well for keeping everything aligned during the trimming and fitting process. You can find a description of how to make the clamps and pictures at

http://www.matronics.com/wiki/index.php/Gluing_Your_Canopy#Jim_Ellis

I used eight clamps (four per side). The clamps sit under the frame on the sill and the bolts press the plexiglas against the frame. I put vinyl thread protectors over the threaded end of each bolt to protect the plexiglas.

Jim Ellis
N155T
RV-9A, flying
 
Gsuit,

I'm not completely done yet, but I'll tell you what I think works and what good advice I have gotten from others.

1) Start by cutting off all the way around the canopy on just the inside edge of the mold clamp marks.
2) Draw a line around the front edge along the "gulley" where the front canopy transitions from horizontal to vertical. Cut the horizontal piece off.
3) Place the canopy on the fuse and check the fit. begin trimming the front edge until the canopy gets close to touching the roll bar. I think I ended up cutting around 1" off of the vertical portion of the front edge until I got the glass within aroun 5/8" from the roll bar.
4) Make the big split. The closer you get the plexi to the rollframe before splitting, the more true that the cut will be. It will likely vee out at the bottom, so cut a little ahead of the split if ou need to cheat.
5) On the advice of Jeff B., I began fitting the rear window first. At first I was very worried that I did not have enough edge distance at the rear, but it was much better once I get the plexi under the reat skin (I had to cut more off the back to get rid of all the ducktail).
6) When preparing to get the rear window under the skin (my skin was already riveted), I slightly beveled the rear-most edge. This was tremendously helpful, and I think the kits should have you do this as part of the standard instructions.
7) Slowly keep trimming the rear until it will all fit under the skin and you can drill it. I probably ended up trimming around 3/5" - 1" from the rear clamp marks.
8) I haven't trimmed any more off of the sides or front so I can't help much there....

Scott
 
When it comes time to fiber glass the thing in, the instructions for doing it all at one time work great, having just done it this past Saturday.
 
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