Canopy drilling - hey, look, it breaks!
It's 57 and rainy in Minnesota today so I fired up the Buddy Heater in the garage to see how hot I could get it. By late afternoon, it was up to 74, so I put the canopy back on the fuselage and lined it up with an idea that maybe -- maybe -- I would drill it. Working with the plexi these last few months, I've gotten a little more confident that maybe this idea was wrong that if I so much as look at it the wrong way, it'll crack.
I thought I was happy with the aft edge but I'm really not. It lines up fine on the pilot side, but I took a little too much off the passenger side and it's slightly forward of the line I drew in the middle of the rollbar. So I'm thinking a little more about this and what to do. But that's not my problem.
You know those builder sites that show a builder drilling some scrap plexi and noting that, try as they might, they couldn't get it to crack? I had no such "problem." And now I'm way too spooked to drill this thing.
Using an Avery plexiglass bit in the cordless drill, I put a little pressure on this scrap piece -- not a lot but I'll bet it's not much more than I'd put on pushing in the side of the canopy as I drill it.
This first time, I drilled at a normally speed, and just before the bit broke through, snap! The piece flew about 4 inches.
Here you can see that it broke just as it was about to break through.
Next, I didn't put any pressure on it, but drilled at the same speed. As you can see -- hopefully -- cracks developed:
I experimented a little more, not with putting less stress on the plexi, but slowing down the drill speed. I got it down to where it was turning very slowly, and while it took a long time to drill through it, it didn't snap this time, even when I put on a fair amount of pressure.
Obviously, there'll be no canopy drilling today. And if I can get the garage up to 90 degrees sometime this week (supposed to get hot again), I'll run these tests again.
But, boy, am I scared to death now.
(If you get Yahoogroups by email, you should see these pictures, if not, go to the blog here:
- RonLooks like you have trimmed the winscreen level with the top of the fuselage skin, mine overlaps about 1/2 inch, is is supposed to be level (did not see this in the plans). Maybe that is why mine bulges a little?Dave----- Original Message ----
From: "colfearnow@..." <colfearnow@...>
Sent: Wednesday, August 29, 2007 10:19:47 AM
Subject: Re: [RV Builders] Re: Canopy drilling - hey, look, it breaks!Hello Dave F.Just completed my slider and windscreen (-7A). Well....need to do some fine sanding, but is looking good.I used little alum clips to help hold the windscreen down per the plans (about 12 each). Covering them with epoxy/fiber glass is not a problem. In the attached photo, you can see them protruding from the first layer of epoxy/fiber glass (used the West System kit available at AC Spruce...resin and hardener-slow) .Ron F., FWF, baffling, prop----- Original Message -----From: Dave FigginsSent: Monday, 27 August, 2007 8:50 AMSubject: RE: [RV Builders] Re: Canopy drilling - hey, look, it breaks!Interesting thread as I am in the same place on canopy construction, ended up following Van's instructions and so far everything is OK. One quick question is on the forward windscreen the two bottom sides that run straight back to the roll bar both bulge out a little, the drawing suggest the small clips to hold it in place but these would show inside the skin under the glare shield. Two suggestions I have had is to Sitka flex or micro balloon/epoxy this area which will be covered by the fiberglass strip.Is this a common problem as the rest of the glass site perfectly on the top skin and what did other people do?BTW this is a sliderThanksDave
From: RV7A@yahoogroups. com [mailto:RV7A@ yahoogroups. com] On Behalf Of littlebobbyau
Sent: Friday, August 24, 2007 6:36 PM
To: RV7A@yahoogroups. com
Subject: [RV Builders] Re: Canopy drilling - hey, look, it breaks!
--- In RV7A@yahoogroups. com, "Bob Collins" <bcollinsrv7a@ ...> wrote:
> Using a Unibit, I enlarged the #30 holes to 5/32". Will this be
Bob, probably not....but it's what Vans calls for...and it seems to
have worked OK for some buiders.
When Jon Johanson flew to the North Pole with his stock Vans canopy it
developed a large and very sudden crack so he replaced the canopy and
used oversize holes and grommets...no further problems (even when he
went to the South Pole some time later).
I followed up on his idea after discussions with him and went to 1/4"
holes with silicon bushings. Effectively my whole canopy can float. I
used the expertise I developed in one of my former roles performing
research and development into polymeric glazing systems.
Initially I researched Sikflex when I saw that a number of builders
were opting for it but in the end I felt that there were numerous
technical deficiencies with that approach.
If I were to do my bushing mods again I could do them quite quickly but
first up the canopy project ended up taking me 6 months.
I believe it should be an improvement over the standard Vans design
(which frankly also seems to have severe limitations from a mechanical
engineering perspective) but it may not be. Ultimately the floating
system may have it's own problems and I will not document it or
recommend it until I have at least 300 hours or more on it.
My only consolation at this stage is that if my fastening mods fail I
feel cofident that the worse that can happen is that the canopy will
develop a crack(s). There is no concern that there might be a
catastrophic loss of the canopy.