Monday, January 21, 2008

Robbing my gumption

I need help from you engineering types out there -- especially you Minnesota engineering types (and you know who you are). I'm at wit's end on the canopy frame.

Last week, I installed the tip-up canopy frame struts on the project and although my old pal Kevin Faris warned me it would pull the frame forward, I was shocked by how much it pulled the frame forward. My nice 1/4" gap between the rear channel and the rollbar was now more than 1/2". And everything was slamming into the front skin, inviting a disaster of another type. That 3/32" gap I filed in per the instructions months ago? I needn't have bothered.

I wasn't sure what to do. My e-mail to Van's support for guidance went unanswered. But a gentleman of the Yahoogroup list mentioned the reinforcing kit. When I looked, to my surprise, I hadn't riveted in the reinforcing kit yet. I thought I had but I had removed them for painting and I'd never gotten to them.

I had previously fit things with the reinforcing kit clecoed in place and while things weren't perfect -- this is the canopy frame for a Van's aircraft, after all -- they were acceptable. And while the left side was a little higher than I would've liked (because I slightly misdrilled the left hinge ear way back when), the right side has been pretty darned good through all of the fitting and cutting and bending and drilling and riveting since I started this part of the project last February.

So imagine my surprise when I refit the canopy frame yesterday afternoon (I'd gotten frustrated when Tom Brady threw an interception during the Patriots-Chargers game that I shut the game off and went out to the garage where things, I thought, would be far less frustrating. Wrong!).



What you may be able to see there is what appears to be some sort of a twist. The whole right side is sitting way off the 1/8" spacer atop the side canopy rails. What the heck?



The only thing that has changed, it seems to me, is riveting on the reinforcing kit. But it fit fine when clecoed, and there's no obvious mess up there.



The one thing I did notice this morning, however, is that the angle on the right side (the one extending from the front of the frame to the rear tube "spar" is sitting atop the curved angle clecoed onto the instrument panel. That, it seems to me, would account for some of the problem.



I had backriveted on the reinforcing kit. Is it possible that somehow the rear tube got bent? Has anyone see this problem before?

I really don't want to drill off the reinforcing kit, because there's nothing there I can fix, is there? The holes are where they're going to be and perhaps the only question now is maybe getting rid of the reinforcing kit altogether.

Or should I try to bang on that rear tube somehow? I'm not sure how I'd do this because it has to get higher in that one spot.

All of this reminds me of a message on the RV list a year and a half ago from John McDonnell, who was frustrated as he whacked away on his canopy frame.

I'm no engineer, but I'm reasonably intelligent, so can somebody tell me why Vans couldn't put the welded canopy frame (and roll bar) in some kind of factory jig to make it fit the rest of the airframe? I can visualize such an apparatus but I have neither the skill, means, nor would it be practical for me to build such a jig for a "one time" application. If you can match drill skins and ribs surely you can match drill this section too. Just tell me what it costs and I'll pay it.


I've thought about John's exasperation a lot while working on this part of the project, partly because I don't recall hearing from him since and I wonder if he gave up or plugged ahead in more anonymity.

The Van's instructions say the canopy can be "gumption robbing." Man, they at least got that right.

Update: I have located the culprit. I took the instrument panel off and, voila! The side rails rested (roughly) where they're supposed to.

So what's causing the problem? The weldment that attaches at the rear tube on the right side is hitting the top of the instrument panel, thus propping it up slighly.

You can click on this image to see a larger one:



So, what to do now? I'm thinking of cutting the angle that reinforces the panel in that spot and filing the top of the panel in that, perhaps, 1/2" to 1" swath to allow the weldment to nest and the canopy frame to come down properly. Does anyone see a problem with that solution?

As to the problem of the struts pulling the canopy frame too far forward, I'm completely digging this tip from Mark Phillips in Tennessee. He created a "stop" to keep the frame from going past a certain point. This seems like a fabulous idea.

Read about it here.

1 comment:

  1. Bob do you have the front boot cowl skin riveted on yet? If not don't get too worried. When the struts are put on it will actually shift the whole frame forward. Those hinge points are not solid and move a lot till they are riveted down. I have built five of these darn things so far and I am arguing with the forward skin right now because it catches the boot cowl when you go to lift it up. Everyone of them has been a major challenge. Good luck. If I was closer I would drop in to give you a hand but being on the west coast it is a bit far for a short flight.

    ReplyDelete