[prkaye]

OK, so to prevent long-term cracking, it's been recommended to me to drill holes 30% bigger than the screw being used. The screws for the canopy are #6, right? I'm not sure of the diameter of these screws, or how much bigger the 5/32 drill is than this.
Instead of the 5/32, has anyone gone up to a 3/16 plastic drill, and then used #6 Tinnerman washers (A3236-012-935) to center the screws in these holes and distribute some of the stress fromt he head of the screw?
Or is 3/16 too big for these holes?

 

[Brantel]

Have seen this done on a slider on an RV6A local.

 

[Greg Arehart]

I think if your holes are nicely centered the 5/32 should be large enough to take up any expansion. I bet there are a lot of airplanes out there that have done this and had no problems for years. IMHO, if your holes are too large, then you have less of the (countersunk) screw head grabbing the plexi and it will put more stress on the edge of the hole, i.e., make it more likely to crack.

greg

 

[prkaye]

interesting thought Greg, I hadn't thought of it that way. What about the Tinnerman washers (in 5/32 holes)? Is this a commnon practice?

 

[Amit]

Plexiglass expansion calculations.

Read this:
http://tinyurl.com/5jxu3h

and the correction here:
http://tinyurl.com/5ewpvv

for information about how I did my canopy.
I have 4 years and 270 flying hours on it (I know, not enough) and it is holding up fine.

 

[BillSchlatterer]

Here is another idea. I might worry a little about the tinnermans not sealing good under the windshield overlap.



Not to hard, just takes a little time. It is also prosealed down to seal and keep it from moving.

Bill S
7a finishing

 

[andrewbutler]

Scratched my head too.

I am trying to find out the the anwwer to the same question. Reviewed the plans ad nauseam and still coudln't confirm for myself whether or not the 5/32 holes would be big enough for the #6 screws. What is the verdict? Will be drilling in a couple of weeks...