[Davepar]

I'm working on a -7A, but this applies to 9's as well and maybe 6's.

I have the fit of the plastic canopy bubble to the frame looking pretty good. However, when I push in on the sides of the bubble, there's quite a bit of pressure right at the front ends of the sides. The plastic wants to pull in, but the frame is pushing it out. As the instructions mention, I did some massaging of the joint between the front and sides of the frame. Is some pressure at that point expected? Or should I bend the frame joint even further inboard? I'm worried about future potential cracks from the stress on the plastic at that location.

Thanks,
Dave

 

[Scott Will]

Just worked on this and I am open to suggestions, too. but what I did, like you say, is massage the corners. Then I went about fitting and trimming the canopy. I think once you trim the canopy to its final shape the fit will be alot better there. I also took my scotchbrite roloc and went to town in that area smoothing it as best I can.

 

[sf3543]

Have you cut the bubble in half yet to separate the windscreen from the canopy?
If not, when you do I think that your problem will disappear.
If you have alerady done this and still have a tight fit, try to manipulate the frame until it fits better. I did a lot of banging and bending on my canopy frame to get a better overall fit. ( I know of some folks who have actually cut and rewelded them to get a better fit.) You'd be surprised how much pressure you have to use to get a slight change in the frame shape. The more you work on making it fit right now, though the more you will appreciate it later since it will make the side skirts much easier to fit, as well.

 

[dan]

A little pressure is normal

Having some pressure toward the front corners is normal. We're not taking about a buttload of force, but enough to bring the sides in. As you secure the bubble to the sides of the frame (later, via screws/nuts), it pulls right in.

The only thing to be cautious of is that as the sides pull in, it may cause the front edge to bow a little bit. So even if you absolutely nail the contour when you're initially fitting the bubble to the glareshield/front skirt, as the sides pull in it will change the fit a bit. Any gap you have at that point can easily be filled with filler and then the whole thing gets covered with layers of glass -- as per plans. But if you can anticipate that effect and plan for it, all the better.

What you don't want is a pressure point on the plexi. Massage the canopy frame (joint of the sides to the front), which it sounds like you've already done, and smooth out the transition there so that the plexi rests against a surface instead of a point...as best you can. I figure if the plexi rests against a pressure point it's more likely to fatigue and possibly crack.

I hate to even say this, but after 600+ hours I don't have so much as a hairline crack anywhere. There goes, now I need to go check my canopy because it's probably cracked...

Anyway, sounds like you're on track. Keep doing what you're doing!

)_( Dan
RV-7 N714D (608 hours)
http://www.rvproject.com

 

[Davepar]

Thanks for the suggestions guys. I did bend the front corners of the frame a little more. I think it's as good as it's going to get. As Dan said, there is some pressure on the bubble, but it's spread over an area rather than at just one point. That does seem reasonable. I just want to avoid any potential crack location.

As I drilled and pulled in the sides, the front of the bubble did lift a little bit. It's only about 1/16" mainly along the left side. I'm going to try a tiny bit more sanding, but I can certainly live with the fit.

I'm just happy that I did (I hope) the last plexiglass cut. I'll probably do a little more sanding, but the messing cutting is over. Woo hoo! As my daughter said, it's starting to look more like a plane.