Gap appears between canopy frame and longeron when flying

During my test flights after annual inspection, I discovered that when flying above 100 kts, a gap starts to appear between the bottom of the canopy and the skin covering the longeron. It can reach up to 1/4 inch on the aft part of the passenger side. On one flight the gap was up to 1 inch but I found after the flight that the canopy was not locked completely. Still with the lock in the correct position although there is no gap on the ground, it appears at high speed in flight. I disassembled the lock and checked that nothing was amiss. I could not check if this happens too on the pilot side (I would need to fly from the right seat!). I suspect that there is too much play in the lock and I am curious to find out if anyone faced the same problem and how it can be fixed.

Do you have any type of gap seal installed?

BigJohn said:

Do you have any type of gap seal installed?

Click to expand...

Yes, John the seal provided by VANs is installed at the bottom of the frame. I did some tests today, adding a shim (as thick as a skin) under the Teflon block on which the handle pushes. This decreased the gap to about 1/8" from previously 1/4" but coming back from the test flight I could not turn the handle to open the canopy! Luckily I had a copilot with a strong arm! I also noticed during the flight that closing the vents decreased the size of the gap to almost nothing although you can still see some light through the little gap left.
I do not think that this appeared after my annual as I did not do anything to the canopy. My feeling is that it has always been there but I did not noticed it. It might be that many other fellow RV-12 builders have the same problem as it is not that much noticeable, especially when you have a passenger. Also flying full speed with both vents open is not very common. During today's flight I asked my passenger to check if there was a gap on my side and there was.
I am expecting this thread to have some legs after people do some testing and observation on their own. We will soon get an S-LSA RV-12 in our area and as the owner is a good friend, I will definitely carry the same test on it.

My first 12 did the same thing. I noticed it on the first flight. I made a simple device to stop it from moving. I don't have any pictures though. Maybe Big John cold snap a picture of it as the airplane is up in his neck of the woods now?

I think that's pretty much normal

Had that on both sides of my canopy (can't see pilot's side when flying_ and adding some extra canopy seal (the square strip) at the break in the canopy lower frame helped. Add too much and you can't unlatch the canopy! as many of us has discovered the canopy will lift in flight-- several inches if you don't have it latched completely. Several had the canopy come open and lift up several inches; I had mine pop open and catch on the flat part of the handle. I COULD NOT pull it back down in flight even after slowing to 70 knots. Left it alone and landed nearest field with no problem other than lots of noise/wind.

Wayne 120241 143WM

I checked mine today and noticed about a 1/4" gap between the rail and frame. I don't use any gap seal. I had my vents full open. I wonder if that pressurized the cockpit a little forcing the canopy up along with the Venturi effect.

RFSchaller said:

I checked mine today and noticed about a 1/4" gap between the rail and frame. I don't use any gap seal. I had my vents full open. I wonder if that pressurized the cockpit a little forcing the canopy up along with the Venturi effect.

Click to expand...

You are in the situation I was before I put the shim, Rich. The seal provided by Vans does not help and I don't think the solution is to stuff foam at the bottom of the canopy frame because in time the foam's elasticity will change. The issue is that the frame is moving under air pressure and the solution is to prevent it to move. The frame is moving because the locking mechanism is subject to play and deformation (if you twist the handle when the canopy is open, you see the frame bend). The shim under the Teflon block helps by creating a stronger pull in the locked position. This makes the unlocking harder but today I solved the problem by shaving a little bit of Teflon to decrease the little step that keeps the lock in the closed position.
I love the concept of E-LSA because it produces planes that are supposed to be identical. This is true for this canopy problem and what would be nice is that VAN's provide the value of the minimum pull required to keep the gap from forming at "high" speed. For structural and safety reason there should be a maximum pull force not to exceed. Of course the issue of how we measure this pull would have to be solved too.

My canopy latch is pretty tight. The gap is not a big enough deal for me worry about, but I'll keep an eye on it.

Just one persons uneducated opinion...

Vent (pressurized) air into the cabin is going to find the path of least resistance in an attempt to get out. Want the same amount of vent air AND the canopy to stay in place?... add an exit vent. Doing so will keep the canopy in place and increase the available volume of vent air; but it will also add some drag and most likely the loss of precious knots. All things are a trade-off and the talent of Van's engineering to find optimum solutions continues to amaze me.

Special Delivery said:

Want the same amount of vent air AND the canopy to stay in place?... add an exit vent. Doing so will keep the canopy in place and increase the available volume of vent air; but it will also add some drag and most likely the loss of precious knots.

Click to expand...

There is actually an exit path already.... the gaps in the congregations of the removable baggage bulkhead cover.
If a upholstered interior panel is installed that fully covers it, it is likely blocking an outflow path, requiring the air to find another route.

I did not have the baggage upholstery and still had the canopy spreading in flight. It was not lifting up, but spreading at the bottom of the frame. In looking back, I should have cut a slot in the canopy sill and used another set of guides like we install at the rear of the lower canopy. Maybe you could consider another set of guides Scott?

I originally thought about adding additional vents, but even in the Phoenix summer the stock vents are more than adequate.

New flight test. Observing more attentively I noticed that as Dave said the gap that appears at high speed is due to the canopy getting slightly wider, not lifting. The gap is more visible just in the middle where the frame bottom makes an angle. Before adding the shim under the lock I had both a lifting and a spreading which caused the gap to appear all the way from the middle to the back. I don't think that anything can be done to suppress this gap caused by the aerodynamic pressure on the canopy at "high" speed and due to the flexibility of the frame. The gap is not very large anyway, it is just annoying to see the light filtering at the bottom of the canopy as the speed is increasing. Now that I understand what's going on it's just fine with me.

The tip-up canopy on my -6 does this as well. I believe the issue is less that of pressurization within the cabin, but lift generated by the bubble. The lift pulls on the canopy, the gaps appear where it can flex.

Adding an exit vent may decrease the pressure inside and counteract this, I agree.

Canopy Gap

I noticed that the gap is even greater when the heater is open even partially. Was hoping some one had an easy fix, Guess I will have to devise one. Am open for any suggestions.
Thanks

Spreading

I think the shape of the canopy is causing low pressure on the top and the sides.

This would cause the lifting and widening of the canopy

I am not sure if the gap is from lifting or spreading

Spreading would appear as lifting

I think if I put a pin in the center of the rail of the canopy it should minimize the problem

I think the canopy is harder to bend vertically the horizontally.

My view

joedallas said:

I think the shape of the canopy is causing low pressure on the top and the sides.

This would cause the lifting and widening of the canopy

I am not sure if the gap is from lifting or spreading

Spreading would appear as lifting

I think if I put a pin in the center of the rail of the canopy it should minimize the problem

I think the canopy is harder to bend vertically the horizontally.

My view

Click to expand...

Your view is correct Joe. I used this mod several years ago and it worked. I am going to do it to my new 12 as it is doing the same thing.

Dave12 said:

Your view is correct Joe. I used this mod several years ago and it worked. I am going to do it to my new 12 as it is doing the same thing.

Click to expand...

It has been my experience and conclusion too and I am concerned that the cycles of expanding and retracting the canopy might create fatigue stress in the long run. I have been reluctant so far to introduce a restricting device similar to the tabs located in the aft part of the canopy frame by fear of creating a source of cracks in the middle of the frame (welding would be the best option but it is excluded once the plastic bubble is in place). Feel free to share the details of your solution when you have one.
Scott might also have some valuable input about why VANs has not done anything about it so far.

If it can't go out it can't go up.

The pin would be working in sheer 3/16 to 1/4 should be more than enough.
If this concerns you a clip on the inside of the canopy fame should also work

I will probably use a 5/16 aluminum pin with the end rounded and only down by about 5/8"
about 33% from the front, just inside of the longeron.

I don't want to hit it getting in or out

If it can't go out it can't go up.

My View

WingedFrog said:

It has been my experience and conclusion too and I am concerned that the cycles of expanding and retracting the canopy might create fatigue stress in the long run. I have been reluctant so far to introduce a restricting device similar to the tabs located in the aft part of the canopy frame by fear of creating a source of cracks in the middle of the frame (welding would be the best option but it is excluded once the plastic bubble is in place). Feel free to share the details of your solution when you have one.
Scott might also have some valuable input about why VANs has not done anything about it so far.

Click to expand...

In Phoenix I'm happy to take the extra ventilation in summer!