<<On the 8, the front end of the slider will be under the fairing of the windscreen and not exposed to wind stress. That would leave the back of the canopy as the primary area of concern.>>
The issue under discussion is stress created by differential thermal expansion, not air loads.
<<How much would you figure the canopy will move in the area around the side fasteners?>>
If you assume an oversize hole at every fastener, and that the fasteners do not firmly clamp the plexiglass to the frame, a rough estimate of relative displacement can be found as outlined previously. Instead of 36, substitute the distance from canopy midpoint to the fastener in question.
Example; fastener is 12 inches aft of midpoint (or about 48 inches from the front).
12" x .000035 x 60 degrees = .0252" growth in the length of the plexiglass
12" x .000005 x 60 degrees = .0036" growth in the steel frame
.0252 - .0036 = .0216 difference in thermal expansion
Let's say you want to eliminate stress at the hole in the plexiglass due to thermal expansion pushing the plexi against this fixed fastener. You might enlarge the hole in the plexiglass enough that when at 0F or 120F, the thermal displacement shifts fastener position just to the edge of the hole. In this case you would add .0216" to the radius of the fastener, ie, if using an 1/8" diameter rivet, you would drill a .1682 hole in the plexiglass.
Doesn't take much thought to see this method has some serious practical limitations, as the required hole size gets larger as you get further from the midpoint. You would need almost a 7/16" hole at the far end fasteners on an RV8 canopy.
Are to starting to see why chicken fasteners are kinda dumb here? Unless you use large holes and unclamped fasteners, you'll have all the point stress of the standard riveted attachment and its potential for cracking from the holes. The whole purpose of the bonding method was to eliminate these stress points. If you're gonna drill holes and use fasteners, forget bonding, as you gain nothing.
The issue under discussion is stress created by differential thermal expansion, not air loads.
<<How much would you figure the canopy will move in the area around the side fasteners?>>
If you assume an oversize hole at every fastener, and that the fasteners do not firmly clamp the plexiglass to the frame, a rough estimate of relative displacement can be found as outlined previously. Instead of 36, substitute the distance from canopy midpoint to the fastener in question.
Example; fastener is 12 inches aft of midpoint (or about 48 inches from the front).
12" x .000035 x 60 degrees = .0252" growth in the length of the plexiglass
12" x .000005 x 60 degrees = .0036" growth in the steel frame
.0252 - .0036 = .0216 difference in thermal expansion
Let's say you want to eliminate stress at the hole in the plexiglass due to thermal expansion pushing the plexi against this fixed fastener. You might enlarge the hole in the plexiglass enough that when at 0F or 120F, the thermal displacement shifts fastener position just to the edge of the hole. In this case you would add .0216" to the radius of the fastener, ie, if using an 1/8" diameter rivet, you would drill a .1682 hole in the plexiglass.
Doesn't take much thought to see this method has some serious practical limitations, as the required hole size gets larger as you get further from the midpoint. You would need almost a 7/16" hole at the far end fasteners on an RV8 canopy.
Are to starting to see why chicken fasteners are kinda dumb here? Unless you use large holes and unclamped fasteners, you'll have all the point stress of the standard riveted attachment and its potential for cracking from the holes. The whole purpose of the bonding method was to eliminate these stress points. If you're gonna drill holes and use fasteners, forget bonding, as you gain nothing.
