[AntiGravity]

Hi Guys, this issue has been mulling around in my brain for several days and I'd like some advice on how best to proceed. I'm building a Tom Clark fastback and have a Todd canopy for it. I',m part way through the fitting of the canopy and have the following issue. Please bear with my somewhat rembling description.

The curve of the canopy does not match the modified canopy frame at the rear. The photo is looking up at the edge of the canopy from underneath. The canopy itself is also a little short in height as it sits. I need to push the canopy in to match the frame. In doing so the bottom edge also gets moved downwards to give me the correct fitting along the bottom tube (at the moment it is ?" short of teh required distance). The gap you are looking at is approximately 7/8" between the canopy and the frame. The garden hose spacer for the sikaflex is a fraction over 1/8". So I need to close the gap by ?" or so. This is easy to do with moderate pressure from thumb and one finger, so it doesn't take much.

I am concerned that squeezing the canopy this way might cause issues. Such as, perhaps, the sikaflex bond failing some time into the future, or stresses being setup in the canopy that causes other issues. My initial plan would be to clamp the gap against some 1/8" spacers (which I would fabricate). I would rivet through the spacers *and* sikaflex between the spacers, but just in the affected area on each side of the canopy. Once dry, sika around the spacers if necessary. To my mind, this would aleviate the issue of the bond failing in the future, though perhaps not the 'other stresses' issue.

Problem is, if this is not a suitable way forward then I either need to get a better fitting canopy or modify the canopy frame again. The current modified frame took considerable work and pretty closely matches the lines of the fuselage bulkhead upper; it is the canopy that does't match. This canopy fitting has caused considerable work and many issues, this just being the latest. Hence why progress and motivation are at an all time low at the moment :-(

EDIT: note that this only occurs on each side at the rear of the canopy and is around 8" long, tapering from ok near the bottom edge to 7/8" in the 'middle' of the upsweep to ok again at the top rear. The photo is the left hand side looking up. The front of the canopy still needs trimming some more to bring it down further to meet the frame at the front.

Thoughts?

Picture:

 

[AntiGravity]

Bump...

anybody?...

 

[N62XS]

Wrong canopy!

Jeff:

Tom is very clear in his instructions that you need to use the LP Plastics canopy specially formed for this kit. I'm not sure that Todd's is formed to the same shape.

 

[rvbuilder2002]

anybody?...

Jeff,
I need to start off by saying I haven't installed a canopy on a fastback RV-8 nor have I bonded one on, but I have installed probably a dozen canopy's on side by side and tandem model RV's.
My opinion would be that you would be fine just forcing the canopy to the shape you need at this location. With the back part of the canopy trimmed off, I am sure it is pretty floppy at the back already. A standard canopy install on an RV-8 also requires some pulling of the canopy into position. This is because when the canopy's are made they are free blown (not molded in a mold like the side by side canopy's are). To get them to blow to the proper height, the base shape does not exactly match what the normal canopy frame shape is.

 

[AntiGravity]

Jeff:
Tom is very clear in his instructions that you need to use the LP Plastics canopy specially formed for this kit. I'm not sure that Todd's is formed to the same shape.

Hi Robbie. I am aware that Tom recommends Airplane Plastics. I tried in vain to get a hold of them when ordering the canopy about 18 months ago. After a while I started talking with Todd and they advised me the canopy sold would be suitable. I'm finding that may not be the case...

 

[AntiGravity]

Thanks

Jeff,
I need to start off by saying I haven't installed a canopy on a fastback RV-8 nor have I bonded one on, but I have installed probably a dozen canopy's on side by side and tandem model RV's.
My opinion would be that you would be fine just forcing the canopy to the shape you need at this location. With the back part of the canopy trimmed off, I am sure it is pretty floppy at the back already. A standard canopy install on an RV-8 also requires some pulling of the canopy into position. This is because when the canopy's are made they are free blown (not molded in a mold like the side by side canopy's are). To get them to blow to the proper height, the base shape does not exactly match what the normal canopy frame shape is.

Thanks. I've also emailed Todd and await his reply. The good deal I received may not turn out as good as I thought, though I hope it does. It doesn't take much to pull the canopy in; as you surmise, it is rather floppy back there. If I do need to purchase the 'correct' canopy (assuming I can get hold of them this time!) then it would be a rather expensive affair, especially considering the current [ouch] exchange rate :-(

Cheers

 

[N62XS]

In any case, let us know what you determine and mostly, good luck.

 

[AntiGravity]

Gonna try it!

Had a reply from Todd who believes it should be ok to proceed since the amount of 'squeeze' is small (in terms of both distance and pressure required). I plan to sika the whole frame but additionally rivet that area that doesn't quite conform. Either way, at this stage I have nothing really to lose by giving it a whirl.

 

[deene]

Hi Jeff. I have mounted a "Todd's canopy" to my Tom Clark fastback canopy frame. The frame was a modified Van's frame with a new rear section.

I had similar problems and just went ahead and clamped the canopy down to the frame at the spacer locations with spring clamps. As you said forcing the canopy down to the frame shape will cause some movement elsewhere.

I used a bunch of clamps and applied the sikaflex as described elsewhere in the forums. After the stuff setup, I don't think the canopy is ever coming off without destruction. I didn't use any rivets and doubt any are required if the sikaflex is properly installed, which turned out to be a messy job, but went quickly. I used 1/4" square pieces of heater hose as spacers and found that they will not move or come off if glued with "superglue" CA adhesive. I put the clamps over the canopy at the spacer locations.

The only problems I had in the results were where I allowed to clamp to slip and form a slight dip in the shape...as I mentioned earlier, whatever the shape of the canopy is when clamped and glued will be the shape forever. Also I had some problems getting the sikaflex joint to look nice, even after two passes. I don't know if the smoothing liquid from Sika would have helped, but I didn't have any to try.

I also found that the (metal) rear skirt easily covered the small variations in the shape of the canopy/frame relative to the fuselage.

Another hint is that if you have the standard RV8 turtledeck skin available, you can cut nice side skirt pieces from the standard skins. I had the skin leftover after removing the standard turtledeck from my QB fuselage. I formed the joint between the skirt and the canopy from fiberglass. The rearmost section of the skirt (across the top of the turtledeck) was made from 0.032 flat aluminum handformed and riveted to the side pieces. All in all, the skirt was an easier job than I anticipated.

 

[AntiGravity]

Thanks!

Hi Jeff. I have mounted a "Todd's canopy" to my Tom Clark fastback canopy frame. ...<snipped>

Hi Deene, many many thanks for your reply; that is exactly what I'm am pushing ahead with so it is nice to see that someone has been there and done that. Todd emailed me back and advised to push ahead and gave some additional hints on how to proceed. Thanks for your report on your own TC FB, much appreciated.