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Tell me why I can’t pop rivet my windscreen to the rollbar…(slider)
- Thread starter nohoflyer
- Start date
PaulvS
Well Known Member
Typically the windshield will need shimming between the roll bar and the plexi in order to align it with the slider. Shim thickness will vary from nothing to 1/16" or 1/8" or maybe even 1/4", depending on the individual parts. Screws can easily accommodate the varying thicknesses, but pulled rivets will have their specified grip range, so there would be some effort involved with obtaining extra rivets to match the rivet length to the hole. I used screws on the windshield, per the plans, and it wasn't difficult. The #6 tap I used was high quality whereas a cheap tap might snap off and that would create complexity!
PilotjohnS
Well Known Member
Please, Please look into using sikaflex to glue the canopy onto the frame. It is much better and lessens the chance to have canopy cracks. And I think is far easier. JMHO. YMMV
Is there date to prove this with certainty at this point?
Sika installed canopies have cracked.
I agree, probably not near as many as have cracked with the traditional installation, but in the entire fleet, probably only one in every 100 RV’s currently flying has a Sika bonded canopy so by percentage, there would be much fewer, even if the cracking rate is the same.
rockyfatcat
Member
I wouldn’t use pulled rivets. I used to work at the Robinson Helicopter factory. (A&P) They used screws just barely torqued with a torque screwdriver to just a few inch pounds. The two issues were distorting the windscreen and cracking the glass.
I glued, so far so good, but between screws properly installed as the plans instruct, and pop rivets, I'd follow the plans. Preparing the holes for screws will take a few hours, but replacing a cracked canopy in a couple of years will take a lot more time and cost a lot more money.
There are a lot of threads discussing canopy installation, and most come down to this - if you do it right, your chances of a crack are greatly reduced. If you do it wrong, a crack is almost guaranteed. The challenge is that there are lots of things that need to be done right, mainly how to drill the holes, how to smooth all the edges, temperature, frame preparation, etc. Good luck!
There are a lot of threads discussing canopy installation, and most come down to this - if you do it right, your chances of a crack are greatly reduced. If you do it wrong, a crack is almost guaranteed. The challenge is that there are lots of things that need to be done right, mainly how to drill the holes, how to smooth all the edges, temperature, frame preparation, etc. Good luck!
Dan 57
Well Known Member
Thread bound for jolly popcorn time 
FWIW, my 6.9i has been flying for 20 years and close to 2K hours, in freezing cold to scorching hot environmental settings. Fingers crossed, no cracks but for minute star like minis at the rearward canopy corners, where the plexi is attached with the screws.
The roll bar canopy bow did require some shimming (Im not the builder) as described by PaulvS above, but is fixed using the pop rivets, all according to plans.
FWIW, my 6.9i has been flying for 20 years and close to 2K hours, in freezing cold to scorching hot environmental settings. Fingers crossed, no cracks but for minute star like minis at the rearward canopy corners, where the plexi is attached with the screws.
The roll bar canopy bow did require some shimming (Im not the builder) as described by PaulvS above, but is fixed using the pop rivets, all according to plans.
I did some work with a gent who's business was acrylic.
Basically you want to locate the bubble in place but not "pull it tight". If it looks like a wet spot around the screw, you've applied too much tension and it will crack. That indicates to me that a pulled rivet will apply too much tension.
I installed a bubble on a Pitts S2B (those that have and those that will) and used screws to locate with a flexible auto window adhesive that I was not convinced would hold and added MarineTex as a fillet and that canopy is still flying some 20+ yrs later.
I intend to do the same process on the canopy I'm building for my biplane now.
Mark
Basically you want to locate the bubble in place but not "pull it tight". If it looks like a wet spot around the screw, you've applied too much tension and it will crack. That indicates to me that a pulled rivet will apply too much tension.
I installed a bubble on a Pitts S2B (those that have and those that will) and used screws to locate with a flexible auto window adhesive that I was not convinced would hold and added MarineTex as a fillet and that canopy is still flying some 20+ yrs later.
I intend to do the same process on the canopy I'm building for my biplane now.
Mark
Going from memory, I seem to remember that screws with flat washers and oversized holes in the plexiglass were desired. I believe the reasoning was that with just snugging the bolts, the oversized holes would allow for contraction of the plexiglass in the cold at altitude. A rivet will totally fill the hole and negate the ability to contract without causing cracking. This is worth exactly what you paid for it.
At least two people have already given you the answer.
It provides a simple means of shimming the windscreen, so that it exactly matches the profile of the main canopy where they come together when the canopy is closed.
This would be rather difficult, if blind rivets were used. Particularly since in some instances, a rather thick spacer is needed in a few locations.
It’s starting to sink in. Thanks gents.
