Q-talk 128 - Swing Bar Canopy Installation
- Category: Q-Talk Articles
- Published: Wednesday, 23 December 2009 16:24
- Written by Jim Masal
- Hits: 1263
Recently I had a chance to help Sam Kittle and Allen Thayer with the installation of their Q2 type canopies. These were of what I call the swinging bar type, i.e. 2 pivoting bars on each side of the canopy which lift it up and forward to allow ingress and egress. They got this setup from a proven installation currently being flown by Jim Patillo. I'm not sure how much of this has been covered previously in the newsletter, so here are some of the details.
On each side of the canopy the two bars must form a parallelogram with the canopy and fuselage side rails. Importantly, the attachment (pivot) points,
2 each per side on canopy and fuselage, must all be in the same plane geometrically. I measured the lower aft bar attachment at 13 inches from the seatback bulkhead and the top attachment about an inch from the end of the canopy. The forward bar is attached 12 inches from the rear one on both the fuse and the canopy. Both bars are 12 inches of %" aluminum stock about an inch wide. which gives you a 12 x 12 parallelogram.
For the 4 mount points on each side, I believe these guys started with a 1 inch phenolic doughnut, countersunk, to take a floxed flush head bolt. Probably an AN-3 and the threads stuck into the cockpit. The doughnut was spaced from the cockpit side with foam then glassed over with 2 BID. The doughnuts were hot glued into correct position before glassing.
Two considerations: the canopy has to swing forward enough to allow room for the pilot to easily get into the cockpit. This is not of concern with a forward hinged canopy. But forward hinging requires gas struts or some kind of support to keep it from slamming shut in windy ground conditions.
Secondly, when swung forward the forward 12" bars will contact the forward deck with the canopy fairly high off the deck. It is better if the canopy will sort of "kneel down" in front. I suggested that they keep the critical 12" spacing, but put a dogleg in the forward bars to allow the canopy to swing farther forward and lower down. In these 2 cases, a notch needed to be cut in the aft canopy rail to allow the rear bar to swing more forward.The way to test out the geometry before cutting expensive aluminum is to cut the bars out of cheap quarter inch plywood or scrap Masonite. The bars have to nest together nicely when the canopy is closed.
Also noted: Kittle's canopy had no rear crosswise support, it was only a half-moon "bulkhead" at the aft canopy perimeter. This might allow the canopy to "splay out" over time during the project and may make it a bitch to fit when the time comes.
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