[RudiGreyling]

Hi Guys,

Busy with the Canopy Forward skin, got a problem. I am sorry if it has been disccused before, but I am at home on leave to do the canopy and only have dialup, low bandwidth at home, so searching the net is not realy an option, VERY SLOW. I posted this in the general discussion since it is not applicable to only one model.

My forward canopy skin bulges AWAY from the forward fuse skin around the bends.

HOW DO I FIX IT?? I was thinking to EDGE roll/seam the canopy skin edge Down the whole raduis of the bend and the forward fuselage skin UP. I have a cleaveland edge tool.

Did you guys see the same thing and how did you fix it.

I really like to finish this work in the next day or so, so quick replies appreciated.

Thank you very much in advance.

Kind Regards
Rudi

 

[gbataller]

Rudi,

I'm at the same point you are and have the same problem. What I did last night is to take a ratchet-strap around the area in question and tighten it up. It totally got rid of the misalignment. My holes are #40 and I will drill them out to #30 with this configuration. I plan on doing this tomorrow and expect it will take care of the problem.

Gary B

 

[JimP]

Shims

Just one word. Shims. Almost everyone seems to have this problem ane even when using a strap to pull the forward skin down, you'll still have the issue. Use some shims under the aft edge of the forward skin and you'll be fine.

Jim

 

[Gsuit]

Rudi -

Jim's right. Shims. Mine bulged at the "10" and "2" o'clock positions. And at the "12" on the forward skin. I used .040 shims the width of the subpanel flange and match drilled them to the skin-flange. No sweat.

I think every -7 builder has this issue.

 

[trib]

Leave it till later

I would leave it at this point because when you install your gas struts, you're going to find out it bulges in all directions! Keep what you have now and do not rivet it yet. Finish the installation of the struts and latch assembly and then align. I had to install a spacer to prevent the forward end of the canopy structure from distorting the skin due to the pressure from the struts in the closed position. I'm still planning on some sort of bayonet/hole assembly to align the skin when the canopy is closing and prevent the bulge. I'm also thinking of glassing over the seam and fairing in to give a smooth transition, then cut the glass at the canopy/foward skin joint.

Bottom line is leave the final alignment with shims or whatever until you have the struts installed.

Tim Ribble

 

[Gsuit]

Tim -

I'm just finishing the Big Cut and haven't read ahead that far, but it seems I'll need to rivet the 706 canopy frame skin on before I begin any glass work at the fwd canopy edge. Would you recommend doing the struts now, then fit, then glass?

 

[hevansrv7a]

Fill it later?

I still have it at the 10 & 2 positions and I'm flying. My painter says he will bring the forward skin up to the level of the tip-up skin with lightweight filler. He says most of the RV's he sees have this issue. My friend who is building a nearly identical airplane is working with metal shims, but even with the shims it looks like the gap will still be there. He's still at the Cleco stage, though.

 

[frankh]

Shims will work a bit

But they seems to be more effective at pushing the flange down rather than the skin up.

Assuming your painting then a couple of skims of filler will be in order and it will be perfect.

Frank

 

[dwilson]

Just one word. Shims. Almost everyone seems to have this problem ane even when using a strap to pull the forward skin down, you'll still have the issue. Use some shims under the aft edge of the forward skin and you'll be fine.

Jim

I have a different take on the situation. I believe that the radius of the underlying rib on the canopy is slightly too small. I put shims under the midline ends of the canopy ribs to flatten out the radius a little bit. This allowed the outboard ends of the ribs to match up with the width of the fuselage and the curve of the canopy skin to match the curve of the foreward deck skin.

Worked out pretty good in my case.

Duane

 

[Harold Lanfear]

Shims & Epoxy

I had a similiar problem on my QB-8 where the lower body was about 3/16" wider than the bulkhead that the forward deck skin riveted too. I used some shims to gradually ease the skin radius to meet the body and then a friend told me a neat trick to make the final riveting very easy.

Use shims as needed to get the fit you nee and then use 3M 2216 Epoxy to glue the skins in place while cleos hold everything exactly where you want it. Since the epoxy has a good working time, there is plenty of time to 'adjust' the fit. The next day, you remove the clecos, clean up the holes if needed, and rivet. The epoxy holds everything exactly in place and shims any low spots so the rivets don't pull metal where its not supposed to be. I just wouldn't use only a thick layer of epoxy without a shim in place as it does have some pliability.

If you do the baggage door the same way, the skin and door will match perfectly. I just finished the baggage door recently and this worked like a charm.

Hope this is useful.

 

[n5lp]

I used a shrinker to bring the front edge of the tip-up skin down and in on the sides a bit.

 

[RudiGreyling]

Hi Guys,

Thanks, I am going to give the shims idea a try, I'll try it under the low skin to try and push it a bit up i.e. the back of the forward fuse skin

I'll report back my findings later.

If you have more ideas please add them below.

Regards
Rudi

 

[trib]

There are a number of ways to fix this, as discussed, but my point is to install the hydraulic lift cylinders before you do, otherwise you'll be doing this incrementally! If you are going to shim, then you need to do this before you drill and cleco, as the shims will end up causing your rivet holes, particularly on the sides, to not line up as the forward skin position changes due to the shims. That's why I decided to glass and bring the level up (instead of filler). I was surprised how much the cylinders distorted the canopy, even with the stiffening kit it was at least 3/16" on each side. By providing a stop at the forward end, it took up much of the stress and corrected a large amount.

Do the best you can getting a good fit, then install the lift and latch components and make any adjustments at that point.

Tim Ribble

 

[az_gila]

A hard stop

....
By providing a stop at the forward end, it took up much of the stress and corrected a large amount.

Do the best you can getting a good fit, then install the lift and latch components and make any adjustments at that point.

Tim Ribble

Tim .. did you provide a separate hard stop?

I've seen a RV with a UHMW plastic block providing a forward stop to the push of the gas springs, and was wondering if anyone else had done this...
The block was attached to the F-668 instrument sub panel...

gil in Tucson

 

[trib]

Gil,

That's the same thing I did. I fitted a UMHW block on the subpanel and sanded it until the fit was tight without the struts installed. That way, with the struts installed the block prevents the stress from pushing the canopy frame forward and distorting it. I'm still planning on installing some type of bayonet on the frame which will fit into a hole in the UMHW block. The block took 90% of the distortion out, but I figure the bayonet will be more reliable in the long term.

Tim Ribble

 

[RudiGreyling]

Thanks for the shim idea it worked...

Hi Guys, just came back to update this thread with what I did, since I asked the question and it can help someone else in the future?

I don?t know about the hard stop idea, sounds good, but maybe someone can post some pictures or a better description of it.

In the absence of the above hard stop recommendation (I was without internet for a while) this is what I did:

I had drilled and dimpled my skins already, as seen in the pictures above, before I noticed the bulge. So I made 2 shims each for left and right, long one and a short one out of .025. Remember to thin out the outer edges for a good transistion.

I just shoved them on the rounding between the skin and the rib, then drilled and dimpled one hole at a time, to get a nice fit around the bend. I did not have any problems with refitting the clecko's on the side as Tim eluded to, they still seem to fit perfectly, after pulling a little on the skin.

It came out pretty good, the shorter one fits where the bulge was the biggest, as depicted by the sharpie marks on the skin.

After fitting the gas struts, things got pushed around a bit, but not to bad, my bulge fit was still pretty good. Or should I say good enough NOT to consider using glass any more. I just had to trim a little of the side corners of the Canopy Skin off, since it pushed up against the top forward skin.

I would still like to see some pictures of the hard front stop, since I think it is a good idea...

Now to figure out a GOOD way to seal the canopy all around, cause the gas struts changed the shape a bit around the base. But I will explore that question in another thread...

Thank you, Kind Regards
Rudi