Widening canopy frame

[ymc9]

Hello folks,

I'm working on the initial fitting of the canopy frame. The KAI requests the frame to have a 1/32'' overhang with respect to the fuselage skins. My frame's rear side is about flush with the fuselage, so I need to open it up by about 1/16''.

I've tried Van's method of squeezing the square tube with a wood block, but haven't been able to change its shape by even a tiny bit. Also tried using a spread bar to open up the rear side directly, but no success either.

Any trick to get this done?

 

[ymc9]

Just wondering, since the purpose of the extra width is for the canopy skirt's clearance, wouldn't it be easier to shim below the skirt instead of forcing the canopy frame to fit?

 

[N8DAV8R]

Just wondering, since the purpose of the extra width is for the canopy skirt's clearance, wouldn't it be easier to shim below the skirt instead of forcing the canopy frame to fit?

I would suggest that it's better to keep working on a way to secure the forward portion while applying force to the rear in order to get the frame to bend a little. I might even go out on a limb and say it's ok to be on the proud side of 1/32. This comes from looking at a number of examples in the field. The rear portion of the canopy skirt is kind of an achilles heel and it's common for it to end up tweaked a little bit.

Also, in my opinion, it's more important to be thinking about the overall fit of the canopy frame than focusing on that skirt dimension. One of your checks at this step could be to cleco the catch tabs into place and screw in the inserts. Open and close the canopy frame a few times and look closely at the fit of those tabs. You can manage the final skirt clearance easier than you can fix a poor fit of the tabs, and this is one of your last opportunities to tune this up. Presumably, when the frame is sitting in the right place based on the skirt clearance dimension those tabs will be centered in the slot.

I was lucky to have a neighbor who is an engineer and also crews with some auto racing teams and has done a bunch of chassis tuning. He wandered into the garage and was quietly watching us mess with the blocks as described in the KAI, trying spreaders and various tricks to get this dialed in. After 20 or 30 minutes he kind of pointed and said 'support here and push there'. I recall his recommendation not really making sense to me but we gave it a shot. It worked perfectly. I guess it's the kind of experience you get fixing bent chassis components under pressure. Point being, I would encourage to noodle around your bending methods a bit more and don't be afraid to apply some force.

 

[ymc9]

I would suggest that it's better to keep working on a way to secure the forward portion while applying force to the rear in order to get the frame to bend a little. I might even go out on a limb and say it's ok to be on the proud side of 1/32. This comes from looking at a number of examples in the field. The rear portion of the canopy skirt is kind of an achilles heel and it's common for it to end up tweaked a little bit.

Also, in my opinion, it's more important to be thinking about the overall fit of the canopy frame than focusing on that skirt dimension. One of your checks at this step could be to cleco the catch tabs into place and screw in the inserts. Open and close the canopy frame a few times and look closely at the fit of those tabs. You can manage the final skirt clearance easier than you can fix a poor fit of the tabs, and this is one of your last opportunities to tune this up. Presumably, when the frame is sitting in the right place based on the skirt clearance dimension those tabs will be centered in the slot.

I was lucky to have a neighbor who is an engineer and also crews with some auto racing teams and has done a bunch of chassis tuning. He wandered into the garage and was quietly watching us mess with the blocks as described in the KAI, trying spreaders and various tricks to get this dialed in. After 20 or 30 minutes he kind of pointed and said 'support here and push there'. I recall his recommendation not really making sense to me but we gave it a shot. It worked perfectly. I guess it's the kind of experience you get fixing bent chassis components under pressure. Point being, I would encourage to noodle around your bending methods a bit more and don't be afraid to apply some force.

Thanks, Nate!

I've also searched and read earlier posts and build logs; tweaking this thing feels like an art . I'll wait for my helper to come in during the weekend, give it a harder massage and see how things go. Good idea to put the tabs on to help understand the positioning.

 

[Blain]

Thanks, Nate!

I've also searched and read earlier posts and build logs; tweaking this thing feels like an art . I'll wait for my helper to come in during the weekend, give it a harder massage and see how things go. Good idea to put the tabs on to help understand the positioning.

Just in this stage now. I can tell you that trying to spread the frame will wrinkle the hoop before anything else happens. I think the root of the problem is forming the longerons. Seems like we should have a finished width to shoot for.

 

[ymc9]

Just in this stage now. I can tell you that trying to spread the frame will wrinkle the hoop before anything else happens. I think the root of the problem is forming the longerons. Seems like we should have a finished width to shoot for.

I guess so, otherwise I don’t know how the bow is gonna accommodate the shape change …

Have you finally successfully made the adjustments?

 

[Blain]

I guess so, otherwise I don’t know how the bow is gonna accommodate the shape change …

Have you finally successfully made the adjustments?

I expect the skirts to wear on the rails. A friend has an -7 with the same problem. He formed skirts from fiberglass.

 

[ymc9]

Just to report back, I finally broke the frame while giving it a massage today ... time to get a new one.

 

[jsalley]

Just to report back, I finally broke the frame while giving it a massage today ... time to get a new one.

Any chance of having it welded (in a jig to hold the correct alignment)?

 

[ymc9]

Any chance of having it welded (in a jig to hold the correct alignment)?

So the entire thing started with the goal of widening the rear side a bit . It took quite some back and forth. With the last attempt, I used too much force and distorted the front side of the arm's aluminum, and broke one side of the rear bow welding. The rear bow itself also had some distortion. I guess it's pretty hard to get it perfectly back in shape, and even so, I'm worried whether the other welding points are still strong enough ...

Lesson learnt, sometimes good enough is good enough I guess ...

 

[N8DAV8R]

Really sorry to hear that this went south for you, especially since I was a voice encouraging you to press-on with trying to get the spacing correct.

I don't think I have heard of anyone else breaking the canopy frame. If you can stomach sharing some pics, I'd like to see it.

 

[ymc9]

Really sorry to hear that this went south for you, especially since I was a voice encouraging you to press-on with trying to get the spacing correct.

I don't think I have heard of anyone else breaking the canopy frame. If you can stomach sharing some pics, I'd like to see it.

Hey Nate, no hard feelings, please. And I really appreciate your advice. It's entirely my own fault. With a bit more patience, the result would probably be different. I'll share some pictures later.

It's still a lot better than having a bad fit, getting the canopy riveted, and then end up needing to replace both .

 

[ymc9]

I'm new to bending metals, and the challenge I had was that, if you don't use enough force, it all springs back and nothing changes; and if you pass the threshold, the metal suddenly complies, and it's easy to overdo, and then you need to make an opposite adjustment - all putting more load to the welding points.

 

[ymc9]

Really sorry to hear that this went south for you, especially since I was a voice encouraging you to press-on with trying to get the spacing correct.

I don't think I have heard of anyone else breaking the canopy frame. If you can stomach sharing some pics, I'd like to see it.

Here's the wreckage - bent forward arms and broken rear welding.