[arpbrs]

We completed the canopy last summer with what we thought was a perfect fit. When we reassembled this February and started flying we found air entering the back and a gap of 1/8 inch between the rear of the skirt and the fuselage. We decided we would work on the fit after flying the test hours off. As temperatures warmed the canopy laid down nicely and became a perfect fit again. Unfortunately, when a cold snap occurred the canopy gap came back. A few more cycles and it is clear the gap is directly related to temperature.

Our assumption is that the Plexiglas is contracting (shrinking) when cold and pulling the frame and skirt with it creating the gap at the rear. We have a Todd?s canopy and are otherwise very satisfied with it. I could not find a thread on this specific subject and wondered if anyone else was experiencing this and if any solutions have been found.

 

[DanH]

Your observation agrees with the materials properties....plexiglass has a very large coefficient of thermal expansion. Don't recall the exact value right now, but you can look it up easy enough if you're curious.

No way to beat Mother Nature, so I can only sugggest soft seals of some kind.

 

[Guy Prevost]

It can vary somewhat by manufacturer, processing of the material, etc, but the Coefficient of Thermal Expansion of acrylic is about .000041 in/in/?F.

Since your canopy can easily be warmer than ambient air it is not unexpected for it to see temperature swings of 100?F. Assuming it is about 60" from the top front of the canopy to the aft center, that little bit of CTE turns into .246" of canopy length change over 100?F. As Dan has already said, a soft seal or a total (and drastic) redesign are your only real options.

Guy

 

[jthocker]

Such is life with an RV8(non fastback of course). We cut and build the canopy in warm temps(70+), get the perfect fit for warm temps(when we least need the perfect fit), and then much to our chagrin, the gap opens up in the winter!


The solution is: take a nice wool scarf with you in the winter. When solo, wrap the scarf around your neck. When you have a passenger, pass the scarf to them, then have them stuff the scarf in the back of the canopy!