Tip Up Canopy Woes

It was another night of trimming plexi in the garage. I'm still having great difficulty with the plexi making contact to the aluminum just aft of the ears. I must put a fair amount of pressure (guessing 10 + lbs.) on the plexi in this area to make contact. The left is worse than the right, but both are too resistant. Under advice of Van's and in reading other posts from builders struggling with this dilemma, I have trimmed the front curve more and more for a possible resolution. The plexi is now slightly aft of the forward mark on the aluminum skin, and the aft of the plexi is within 1/16" of the center-line of the rollbar. I can't take anymore material off and maintain the overall fore and aft prescribed dimensions. I still have the issue of outward tension in that area of the plexi. I will use Sika to bond and this seems to have stopped all progress. Very frustrated and not sure what to do next. Take a chance and heat that area while it's clamped with the side skirts? Put extra Sika thickness in the area with slight clamping pressure, then try to fair it in with fiberglass later? Start again from scratch? Ughhhh!!!! Anyone have an idea for resolution? Thanks!

Pics:
http://www.mykitlog.com/users/display_log.php?user=sblair&project=2420&category=0&log=225389&row=1

In the picture in Kitlog, it seems that the plexi is OUTSIDE the ear?
If so put it inside - as in plexi between the ear and the rest. I usually cut off the ears completely. This is if you are going to use sika to bond the plexi.

Not always clear in the pictures, but have a look here. http://www.mykitlog.com/users/category.php?user=jan&project=2437&category=3233

Hope it helps.

Hi Jan,

Thanks, you are correct. I do not have the plexi under the ears in those pics. I can get the plexi under them on both sides. It does help some, but there remains a lot of outward force and no contact to the aluminum aft of the ears for several inches along the side rails. It takes enough force that it makes me nervous of cracking the canopy now....or eventually.

Sean: I leaned on these two sites for "help" in working the canopy. They both seemed to get it right as did I following their methods. For sure working the canopy can become very frustrating. I became paralyzed with fear of ruining the canopy and as a result accomplished nothing for several months. Set that task aside and work in another area until you feel ready to get back into it.

http://www.europa.com/~swayze/RV-7A/Finishing/20120420.html

http://www.overthehills.com/RV-9A-Project/Finish-Kit/Canopy/i-72B4GTW

I bet I almost have those two sites memorized by now. Very thankful for the detailed information from these and other builders!

Beyond helpful

Thanks for a great help in the canopy.

I am there now and wondering on all these points. Unfortunately, I have made my front portion of the canopy a little shy of enough plexi to comfortably get a screw hole to take so i am looking at the use of Sika there and this was undoubtably a great help.

Terrible how one can take so much care and yet a mistake happens but the edge of my plexi near the "ears" misses forming a screw hole by an 1/8 inch so Sika it is there, otherwise I have made about seven Good screw holes along the 745.

Nice advice here!

This is one of many critical steps that can go awry. I think it was B Swazye (sp?) that made come U shaped clamps that were 1/8" thick and would fit around the side rails and clamp the canopy to the rails. This is important. The bulging deformation of the canopy will balance the deformation of the flimsy rails and cause the whole structure to reach a new (possibly unhappy) geometry. And - and - the more the sides are pulled in the more the front puckers UP. This will create a larger gap. So, be careful all these are taken into account right up to the time you drill the canopy to the side rails.

Scott,

The canopy skirts fit well with the fuselage. The frame was a bear, too, but I feel it is the proper width and relates pretty well to the rest of the airframe. The problem with the plexi seems to reside just aft the aluminum ears for about three inches. All other areas of plexi fit well.

Thanks.

SeanB said:

Scott,

The canopy skirts fit well with the fuselage. The frame was a bear, too, but I feel it is the proper width and relates pretty well to the rest of the airframe. The problem with the plexi seems to reside just aft the aluminum ears for about three inches. All other areas of plexi fit well.

Thanks.

Click to expand...

Yes, it all looks good until you clamp the plexi to the rails, then it won't look so good. Mine was within .010 then attached the canopy to the rails. Waaay off , again. I made an overhead lift system to pick the canopy and frame up, then lower to a table with a shrinker/stretcher to get it re fitted with the canopy influence on the rails. Maybe you will get lucky, but don't bet on it.

sahrens said:

Sean
When you cleco the side skirts on the rails are they flush with the fuselage side skin? If so, ignore my question. If not your frame may not be wide enough.

The U clamps BillL is writing about were made by BruceH, I bought them and someone bought them from me. They were very useful in fitting the frame and the canopy, but I did not use them when I attached the canopy to the frame with Sikaflex. Bruceh describes them on his build log.

I also cut a slight filet on the forward edge of the canopy which allowed some inward movement of the sides. I also had to widen the frame at the ears to get the fit I wanted.

Click to expand...

Scott, how did you widen the frame at the ears. That is the only location I am not happy wit (I am about 1/8-3/16" narrow on both sides; 1/4-3/8" total width).

My 2 cents

I cut off the ears. I could not get them to lay flat
And I knew this would create a high spot in the glass.
I also used Silka and used the side skins as clamps with clecos.

I used Sika with great success and also trimmed the ears to get a good fit. A little flox and it all fits and looks great.