Canopy trimming question

[Mark Henderson]

The plans call for a 1/32" gap between the canopy and the rear window. When I called Van's to ask about how my canopy fit, I was told that the red one had a gap far larger than 1/32". The issue seemed to be the need for expansion of the canopy when it sits in the sun. This raises the question, how much gap at what temp is best? It was 82 degrees in my hanger today when I was fitting it. Where I fly I can expect temps well over 100 degrees. The canopy would be even hotter I would suspect. Any thoughts, or am I worrying too much. Thanks

 

[Geico266]

I think the gap has more to do with expanding from forces in flight. 1/32 is what you can shoot for and see what you end up with.

IMHO, the rear window is the last thing you want to install before inspection. You'll be very glad you left it out.

 

[gasman]

The plans call for a 1/32" gap between the canopy and the rear window. When I called Van's to ask about how my canopy fit, I was told that the red one had a gap far larger than 1/32". The issue seemed to be the need for expansion of the canopy when it sits in the sun. This raises the question, how much gap at what temp is best? It was 82 degrees in my hanger today when I was fitting it. Where I fly I can expect temps well over 100 degrees. The canopy would be even hotter I would suspect. Any thoughts, or am I worrying too much. Thanks

COPPERSTATE 1998................. Owner was locked out of his tlit up 6 because the canopy had expanded and pinched the canopy against the rear plexi.


I vote 1/4" gap................. but then I also used a TARGA STRIP.

 

[Mich48041]

Expansion of Acrylic

From http://www.chemcastacrylics.com/acrygp2.htm#VIII
Plastics are organic materials which naturally expand and contract more than inorganic materials. CHEMCAST GP sheet will expand 3 times as much as metals, and 8 times as much as glass, and therefore the coefficient of expansion and contraction must be considered by architects and designers. A 48" panel will expand and contract approximately .002" for each degree F change in temperature. Another quick calculation is CHEMCAST GP will expand (or contract) 1/8" per running foot per 100 degrees F. In outdoor use, where summer and winter temperatures differ as much 100 degrees F, a 48" sheet will expand and contract approximately 1/4".

The canopy on the RV-12 is 44 inches measured front to back. So it could expand almost 1/4" with 100 degree temp change. Temperatures can be below zero at altitude in northern climates and above 100 in the desert. Of course each end of the canopy does not move 1/4". Each end could move 1/8". And because the canopy is curved, some of the expansion will bow out the middle instead of increasing the length or width.
All of the above is theory. The best bet is to follow the guidance of previous RV builders. Perhaps other builders will tell what works for them. I think that a larger gap will not hurt anything as long as it is uniform and straight.
Joe

 

[Rupester]

I just passed this point with my Nine-A canopy. I called Vans for guidance and got essentially no help. At one point I said, "I have heard some say that 1/16" is the recommended gap. Is that correct?" Builders' Help responded tentatively, "That sounds OK." Hardly a confidence builder. After talking to other owners and calling back Vans to talk to Gus, I concluded 1/16" to 1/8" works for most people. any less than 1/16 and you risk it jamming when sitting closed in the hot sun with the interior rising to 140F. Any more than 1/8" and you risk a B-I-G gap in a 10F hangar in mid-winter. Mine is 1/16"+.

 

[rvbuilder2002]

I just passed this point with my Nine-A canopy. I called Vans for guidance and got essentially no help. At one point I said, "I have heard some say that 1/16" is the recommended gap. Is that correct?" Builders' Help responded tentatively, "That sounds OK." Hardly a confidence builder. After talking to other owners and calling back Vans to talk to Gus, I concluded 1/16" to 1/8" works for most people. any less than 1/16 and you risk it jamming when sitting closed in the hot sun with the interior rising to 140F. Any more than 1/8" and you risk a B-I-G gap in a 10F hangar in mid-winter. Mine is 1/16"+.

We need to be careful lumping all RV's together though. There are differences.
One difference is that most builders of models other than the RV-12 use fiberglass to mold a targa strip to cover any gap that exists. This is not part of the RV-12 canopy installation because it doesn't work well with the different hinging geometry.
Without the targa strip, the bigger the gap...the louder your whistle will blow.