Cracked canopy

[Rickadler]

Noticed our canopy had about 6 cracks in it yesterday. Ran up the engine on the ground and saw the cracks afterwards. Possibly were there before but don't know for sure. This is now going to be our 3rd canopy because of cracking and we only had 1 short 1st flight on the plane. Any thoughts? This is getting expensive having not flown the plane for any real time. Tim and RIck - Waiex 0146

[fastj22]

Two potential issues. Too tight on the screws or chemical contaminant. Doubtful on the second, unless you used something. Instead of tapping the frame, drill through and use a screw/nut combo. Tighten only to the point you can still rotate the screws by hand. Takes the stress out. My first canopy I over torqued the screws and got cracks. My second, I drilled through the frame and used screws and nuts. Zero cracks for 4 years.

[DCASonex]

Every cracked canopy i have seen (Including mine) the cracks originated along the lower edges of the sides. The standard Sonex "A" model canopy is curved on the sides and when pressed into shape along the straight edges, the inside surface is under tension. Any tiny scratches or nicks along those lower edges, especially if on the inside will result in cracks. Unfortunately the Todd's canopies that had nice straight sides are no longer available. Folks that have had the best success with Sonex canopies seem to install them on very warm days.

David A.

[jerryhain]

Have you balanced your propeller? You may as well get rid of as much vibration as you can.

[fastj22]

Every cracked canopy i have seen (Including mine) the cracks originated along the lower edges of the sides. The standard Sonex "A" model canopy is curved on the sides and when pressed into shape along the straight edges, the inside surface is under tension. Any tiny scratches or nicks along those lower edges, especially if on the inside will result in cracks. Unfortunately the Todd's canopies that had nice straight sides are no longer available. Folks that have had the best success with Sonex canopies seem to install them on very warm days.

David A.

Yeah, I didn't go the plans route on the bottom. Instead I took a piece of thin angle aluminum to capture the outside edge and screwed the angle to the bottom of the frame. Nothing penetrates the plastic there.

[andrewp]

I still have an original canopy on N618PE and it had not a crack in it until I had to put the poor thing on the ramp in the last two years. Cold feels like is what did it in, not heat or anything else, but I am finally starting to get cracks in the hinge side which I am having to stop drill. Makes me feel like a bad parent and I super super hate it. Hell I got a crack in the front plexi windscreen (I didn't think that would be possible). Having said that, the little girl puts up with being on the ramp fairly well. Alas there is only room for one airplane in a hangar and I have to keep that one I can fix more cheaply outside. Still hurts. This is the old material (circa 2003), not the newer easier one so no one should panic about this.

This has all been said before, but sticking a heater in the plane and making sure canopy was toasty warm worked pretty well for me and just going really slow. The canopy was for me one of the tougher items to get through, along with everything else.

If it was easy, none of us would be doing it. We will never admit this and I personally will whine about all parts of it, but that is what makes it great.

I took the little thing up to the wash ramp and gave her a good clean this past weekend. A Sonex is still an adorable object that stands out at an airport. And she is such a fun thing to fly. Doesn't wear off... but I digress!

AP
#618

[Rickadler]

John Gillis- Can you send us photos what you did with the angle on the bottom. Thanks in advance.
Screws and nuts were used and not more than finger tight and oversized holes through the plastic.

[N418SX]

Cracks used to be a problem in the RV canopies until some of us decided to use Sika primer and adhesive rather than mechanical fasteners. It is fool proof and if you use a rotary tool to cut the lexan, no potential for cracks from a stressed edge.

[fastj22]

John Gillis- Can you send us photos what you did with the angle on the bottom. Thanks in advance.
Screws and nuts were used and not more than finger tight and oversized holes through the plastic.

Unfortunately, I sold the canopy to another builder. Did you use stainless rivets or softer aluminum? I think the stainless pull much harder than the aluminum.

[sonex892.]

There are a couple of things I don't like about the A model canopy. Rivets in perspex, yuk! and lack of a reasonable edge distance from the holes where it attaches on hinge and and latch side of the frame. I bought a bit more edge distance by using 4 strips of 025" aluminium to support with a 1/8" aluminium spacer where I tapped 3mm threads into the canopy tubes and screws 3mm screws and nuts which are all slightly loose to support the perspex. Almost 10 years, 390 hrs and no cracks.

My preferred method to cut and trim is a small angle grinder with a cutting disc for the cutting and a flap disc for trimming. Unlike using a bandsaw, using an angle grinder can be a one man job. I like using proper persex drills, compared to the cost of a cracked canopy they are cheap and last a lifetime