Finish Kit

I am delighted with the way the canopy is coming together. Like so many things with this project, I think I would be able to do a much better job the second time, having learned the first time. My reservations relate to cosmetic and work efficiency issues only.

First of all I have to say once you have glued your canopy on you become very confident this stuff is not going too let go. It is very strong. The only residual concern I have, is how will it hold up after perhaps 10 years? I doubt there will be a problem, but who knows? There are many advantages that I see for gluing the canopy on:
- the likelihood of cracks I see as much reduced.
- there will be no 'working' between the canopy and frame. The joint should be completely quiet.
- the joint will be 100% waterproof.


There was a Sikaflex thread sometime ago on Vansairforce which was full of posts pointing out that the force to extend a tear in the Sikaflex was quite low. What these doom mongers missed was that before the product tears it has to extend by 500%. Since the strength is 160psi it is hard for the canopy to move.
I had read the instructions from Sikaflex many times (and everything they say should overide anything I write here), but until you work with a product it is hard to fully understand it. So much of what we work with comes in two parts; epoxy paints, Proseal etc. Although you require 3 items to make a Sikaflex glue joint is is essentially a one part glue joint.

Cleaner 226
This is fairly amazing stuff. It manages to find dirt on apparently clean surfaces. It evaporates very quickly. It is unclear if it leaves any magic residue behind once it has evaporated, but it certainly leaves the surface VERY clean. The 10 minutes that you are required to leave it for are, I think, just to ensure it has completely evaporated.

Primer 209N
This is quite a watery black liquid that is brushed on. It can 'flick' off the bristles of the brush so make sure everything near by is masked. As I understand the instructions, thin is better. The purpose of this layer is to provide a bond between the 'glue' and the metal or Plexiglas. The instructions say to leave this layer for 30 minutes minimum before adding the glue. I suspect this is quite important. When you have finished priming CLEAN THE BRUSH. I put it into the same fluid that I use to clean the spray gun. It cleans quite easily. If you leave it to harden I know of no solvent to soften it again.

Sikaflex 295UV
This is the 'glue'. Before I had used it I was quite concerned as to how runny it is. Perhaps the answer to that is, slightly thicker than toothpaste. If you squirt it into a 1/4" wide joint it does not sag back out, even if gravity is working against you. It has amazing power to stick to the primer, but in fact peels off bare metal or Plexiglas quite easily.

I used about one and a half tubes for the RV4 canopy, though most of what I used has been thrown away with the masking tape, or sanded off.

Where I learned a lot was about how to make a tidy looking joint. What I wish I had really understood before I started was this:

1. Decide where you want the Sikaflex to end up.

2. Mask all the places you do NOT want it, with electrical tape. Push the edges down hard.

3. Abrade the ali/Plexiglas with Scotchbright, and wipe the dust away.

4. Clean it with the Sikaflex cleaner.

5. Once this is dry, put a layer of masking tape on top of the electrical tape. (I found that if you put the tape on before the cleaner, the paper of the tape tried to 'hold' the cleaner beyond 10 minutes.) Wait for the cleaner to dry.

6. Prime it. Remove the masking tape. You now have a nice edge to the primer. Wait the period as defined by Sikalex. My understanding is this period is a min of 30 minutes and a max of 2 hours. The max time might only be defined because Sika are concerned about dust contamination. I do not know what the true upper limit is if you can keep the primer free of dust.

7. After the necessary time for the primer to cure, add the Sika 295UV. (If you are good at grouting bathroom tiles, you will find it easy to make a tidy job. I am not!)

8. Quite quickly, you will find the Sika is setting, or at least skinning on the outside. It does this by taking water from the air.

9. Most of the time I removed the electrical tape within an hour, though I now think it is better to leave it at least 24. Have a razor blade to hand as you remove the tape.

10. If some Sika goes where it should not, don't worry, it will peel/sand off if you leave it a couple of days, as long as there is no primer.

11. Leave it a couple of days, then tidy up with razor blades and sand paper.

Because of the difficulty of working inside the RV4 canopy I am working in a 2 stage fashion. First I apply Sika to bond it on, but don't worry about the cosmetics. Then I return after 48 hours for a cosmetic coat. If you are good at grouting you may not find this necessary.

I haven't got this far yet, but I understand that after a week or so, it will sand quite nicely. I intend to complete the fairing around the front of the canopy entirely of Sika.

If you have read this far you are obviously interested in the Sikaflex approach. Go for it! You wont regret it.

With the canopy attached to the frame my time has been spent fitting the skins. Because of the space - 1/8"- between the canopy and frame and a similar space between the canopy and exterior skins I think the whole structure is slightly larger than the typical -4 canopy. Apart from the fact that there was little trimming of the skins to do at the rear, this does not seem to present a problem.

In these pictures the skins are fitted, the spacers for the glue installed. I Would like to find sacrificial spacers that can be left inside the finished article but, to date, have not been able to find anything appropriate for sale in Europe.

The fit of the canopy over the rear fuselage is crucial and if I can get it glued and stable as it currently is, I will be pretty happy.

I look forward to getting rid of all the various layers of tape, masking tape, giving it a good clean and recovering it with a new sheet of plastic. It will be a while yet.

It will finish up as a very strong structure. I would think it is several ounces heavier than the riveted equivalent, but that is a price worth paying if I avoid cracks. It will also be waterproof!