S

Stephen Lindberg

Well Known Member
Eddycurrent1


Recently during a pre-flight inspection I noticed a missing rivet head in the line of pop rivets holding the canopy hinge to the longeron. So I went back home, got some tools, and replaced the headless pop rivet with a solid rivet. Then I noticed that the vibration of driving the rivet had caused an adjacent rivet to lose its head, too. So I put in a bunch of solid rivets and now I feel better.

I realize that Van designed the canopy to tear off the airplane if it opened in flight, hence the pop rivets. On the other hand, my 13 year old, 350 hour pop rivets are failing and I don't want the canopy to leave on its own, which I understand has happened, so I think driven rivets are in order. Pay close attention to the condition of these canopy hinge pop rivets. There isn't much to them.

If I am successful in posting a picture it will show the aft end of the hinge with two new rivets and a smoking rear pop rivet. The rivet that initially failed was the third from the front.
 
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Hi Steve,

Why not just replace with new pops?

I don't know if it is customary in the -4 world to replace those with solid rivets, but I don't know that I would make it my first fix - I'd go back in with new pop rivets and get another 13 years of service if it was me. I would be nervous about defeating a safety feature such as the tear-away canopy unless I had thought it through carefully, which maybe you have. For instance, if you don't own a parachute, then you're never going to open it in flight to jettison....

This is more thinking out loud so that folks understand that altering the design of a feature like that should be approached with care.
 
Thanks, Paul, but I'm sticking with the extra solids rivets.

My thinking is as follows: These pop rivets are unexpectedly popping their heads off and putting the integrity of my canopy in question. The only reason I would want the canopy to leave the airplane in flight is if the latch failed (it looks solid) and the canopy opened AND if the open canopy made the airplane uncontrollable. The parachute angle is irrelevant to me. I don't own one, I probably couldn't fit into the airplane wearing a parachute, and even if I did, and if I jettisoned the canopy with the intention of bailing out, it wouldn't much matter to me what the canopy did after I opened it, 'cause I would be leaving anyway.

The most likely scenario in my opinion, and the one best addressed with additional solid rivets, is the canopy coming unzipped at the hinge, whacking me on the head on its way off, and then me facing a 180 mph wind blast sans glasses and headset. And I really need my glasses. The rear seat passenger (often it's the Nice Lady Who Feeds Me) might be more at risk for a head whack.

After the hinge failed, the canopy would remain attached by any lanyard or gas cylinder or whatever keeps the canopy from going too far over center. That element would have to be evaluated for breaking strength in keeping with the break-away philosophy. I'll wager that most haven't. Mine is fairly stout and I like it that way, having opened my canopy on the ground in some fairly strong winds.

That's my thinking and the reason I increased the strength of the hinge. In the absence of testing, which to my knowledge has not been done, nobody knows much for sure.

If anyone disagrees, fire away.
 
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