Canopy attach

[fly.more.work.less]

I've recently imported a flying RV-3A into Australia, and am working to get it in the air over here. Removed the canopy yesterday to ease re-attaching the wings, and found that the canopy piano hinge attached to the fuse had a lot of play, with a couple of rivets just about pulled through.

My impression was that this was a weak point, but the plans suggest that the intention is to keep the number of rivets low to ease removal in an emergency,

Wondering if there are any stories / experiences of canopies departing during flight using this attachment method? If so, are there suggested alternatives for the attachment that people are using?

Alexis

 

[David Paule]

A guy I know has an RV-4 with a similar arrangement. He told me that while flying once he noticed that his canopy latch was not secure, but that before he could get it secure, the canopy disappeared.

It didn't hit him or any part of the plane upon departure and in fact, landed mostly intact.

The plane flew okay but the wind made it hard to see. He landed successfully, put the plane away, and went looking for the canopy. He found it and reused the frame. He now pays more attention to the latch.

He said that this set-up was designed to allow for escaping the plane if necessary.

Dave

 

[highflight42x]

I doubled the number of rivets on my canopy attach when I noticed the same thing. Upon jettison, I'm guessing that the hinge eye's will tear out before the rivets do, so the thing to be concerned with is keeping those rivets at the extreme fwd and aft attach points tight. And don't use pops - they'll work loose. Squeeze some AN-426's on there. (IMHO)

 

[Ironflight]

The design calls for Pop rivets to attach the hinge to the longeron specifically so that the soft heads will tear away if you have to open the canopy and get out. If you want to keep canopy jettison capability, I would be very hesitant to change the number or types of rivets given in the plans. But make sure that you have a good canopy latch, and a foolproof way of remembering to latch it before flight!

Paul

 

[danbenua]

Hi Alexis,
I have never heard of a tip-over canopy loss due to hinge failure
without the latch side being released first. The loose rivets
you see are probably from damage on the ground with the
canopy open; maybe on a windy day! If it were my plane
I would replace the hinge section and/or the pop rivets, but
not modify the design.

- Dan Benua
EAA Tech Counselor
Repeat Offender

 

[highflight42x]

The plans do indeed call for pop-rivets in the canopy-hinge-to-longeron attach. However, the specified pops *will* work loose in this area (voice of experience). That's why I replaced them with an426's - no problem since.

Now regarding canopy jettison: one day I was warming up the engine, 1000rpm, canopy cracked open for ventilation. I neglected to hold onto it, and over it went, hitting the stop. The hinge-eyes started opening up immediately, before I could pull it back. The repair was simple: just bend the hinges back. But if I had been at speed, or in a full run-up, that hinge would have come undone like a zipper, and the canopy would have been long gone

- Steven

 

[rph142]

I used AN426's as well. If the piano hinge doesnt tear away like a zipper at first then ill be sure to help it out with some right rudder.
I did sort of a back of the hand calc to estimate the loads on the canopy.

F = (air density * Velocity ^2 * drag coefficient * Frontal Area)/2

for rho = 1.2 kg/m^3
V = 55 m^2
drag coefficient = 0.5
Area = .3m^2

F comes out to around 600 pounds, and of course the hinge must hold back that force on a 12" moment arm.