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  #1  
Old 11-17-2015, 12:28 PM
macrafic's Avatar
macrafic macrafic is offline
 
Join Date: May 2006
Location: Rochester, MN
Posts: 431
Default Shimming the Canopy Skin

Like so many others, my canopy skin catches the front top skin a bit in the center. I see others have put shims in here to raise the front of the canopy skin equal to, or slightly above, the front top skin.

My question is, how/where did you put the shim? Did you rivet the shim between the canopy skin and frame, along the front row of rivets that attach the two, leaving the edge of the shim back from the front of the canopy skin so that the shim itself doesn't become a problem? Does this hold up over time?

If not, what have others done?

I am holding off riveting the center brace between the skin and frame until I know what to do here. Appreciate your help.
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  #2  
Old 11-17-2015, 12:37 PM
BillL BillL is offline
 
Join Date: Sep 2007
Location: Central IL
Posts: 6,313
Default

Quote:
Originally Posted by macrafic View Post
Like so many others, my canopy skin catches the front top skin a bit in the center. I see others have put shims in here to raise the front of the canopy skin equal to, or slightly above, the front top skin.

My question is, how/where did you put the shim? Did you rivet the shim between the canopy skin and frame, along the front row of rivets that attach the two, leaving the edge of the shim back from the front of the canopy skin so that the shim itself doesn't become a problem? Does this hold up over time?

If not, what have others done?

I am holding off riveting the center brace between the skin and frame until I know what to do here. Appreciate your help.
Do you mean the center frame splice?

The way of pulling all very tight down over the frame, adversely depresses the center of the frame, just between the hinges. The time to fix that problem is now, or it will cascade to other issues on the portions of the frame outboard of the hinges.

Push up on the center of the frame until you can put a straight edge fore/aft across the intersection of canopy skin and forward skin with NO DEPRESSION aft of that line.

I found this a bit late in the process and after many restless nights, I decided to just bend the frame across the splice. I put mine in a hydraulic press and bent it until it fit. It was my second frame, and almost became the third. After just following directions, I finally learned what made this part work. It is complicated.
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  #3  
Old 11-17-2015, 08:00 PM
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chrishalfman chrishalfman is offline
 
Join Date: Jan 2005
Location: LaVista, NE
Posts: 62
Default This sounds kinda thrown together..... but.....

I did the exact same thing. I?m assuming you?ve discovered this after riveting the two halves together and wish you could go back a step. This is one area of the airplane the directions were just wrong (in my opinion). Sometimes I follow directions too blindly. BillL has it right-the frame should be assembled straight across the top, but a lot of people end up in the same?. Boat, so to speak. I followed the lead of a local guy that was already flying his -7. Details below.

I cut thin strips basically the width of the frame and layered them between the frame and skin until it was pretty much level across the top. The bottom strips were shorter and the top ones were longer-an upside-down pyramid stack. The ends of the top layer were thinned out to prevent making a crease in the skin. I did _not_ extend them to the front of the skin. And, yes, I just sandwiched them in there. Obviously, use length appropriate rivets. Does it hold up? Has for me and the guy that advised me of his mods.

It ended up making the left side of the front frame kick out on the left (pilot?s) side a ?? or something (for both our planes). It?s really noticeable if you look for it. I actually gently bent it back along the whole bent length in a vice and being realllllly careful to not kink the frame.

The skin probably won?t lay flat on the back part of the frame (the tubes) either. Just fill in the gaps with washers (to prevent wrinkling) and long enough blind rivets. I filled the gap with a slurry of microbubbles and epoxy to give it a finished look. It seems a bit hodge-podged, but I?ll bet you?ll find a lot of otherwise well-built planes with the same mods.

Don't worry, you'll get it perfect on the second plane.
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-7A, 360+ hours on the Hobbs, ECi O-360 185 hp, GA200L Whirlwind prop
Anything I post on here may not be the best way, the right way, the only way, or even an accepted way to do something, but it's how I did it. Use the information accordingly.
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  #4  
Old 11-27-2015, 12:26 PM
jj_jetmech jj_jetmech is offline
 
Join Date: Aug 2013
Location: Klgb
Posts: 125
Default Shimming the Frame

In my opinion this is a battle won slowly. Manipulating and clamping the frame in position prior to drilling in the 614 splice plate is just the first step. Problem as I see it, the 716 frame is provided semi complete for all airplanes yet all,airplanes vary slightly.

I was very unhappy with the alignment of the 771 and 702 skins when letting the frame guide the shape of the 702 skin. This causes highs and lows of The 702 skin when compared to the 771 fwd fuse skin and ultimately affects the gap and fit between the two.

I tried a couple metal shims (strips) these improved the fit some but the shape still followed the frame shape. Frustrating. I abandoned the aluminum strips.

My solution was to use a liquid shim (WS epoxy and flox) between the canopy frame and 702 skin. The result is near perfect with no waves and a symmetrical gap.

Use mold release or tape on the frame and skin mix up some flox and resin and spread on forward frame, top and sides. I then placed the 702 skin in position with clecos on only the sides and rear tube. Note the forward deck and 771 skin are in position and will help guide our new canopy frame shape. I then taped about an 8" wide strip of aluminum in position over the 702, 771 skins where they mate and extending down the sides of the fuse.

This created a varying thickness shim across the frame and sides and solved my frame fit issues.

I also used a flox filet in the big gap between the rear frame tube and 702 skin as many other have.

Couple other things that helped:

Make sure you install the shock struts before trimming or fitting the 702 skin fwd and bottoms edges. I actually waited until the frame was riveted.

Use/fabricate adjustable fwd canopy stops. I was trying to avoid this but the shock struts pull the frame forward affecting fit. Stops solve this.

I also made new/longer 725 side skirts. Trimming / shortening the trailing edge of the 702 skin sides, this moves the joint between the 702 and 725's forward and improves the fit to the canopy deck. I made these last after the frame was already painted, riveted and canopy glued, I Sika flexed.

The canopy and frame took way more time that I expected, on and off and on and off. When started looking at time spent by other builders on builder sites and accepted that this could take a couple hundred hours I stopped worrying about it just keep working it until it your happy.

Good luck!

http://a67.tinypic.com/30wt5hi.jpg
http://a68.tinypic.com/14allag.jpg
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Last edited by jj_jetmech : 11-29-2015 at 11:37 AM. Reason: Add pic
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  #5  
Old 11-27-2015, 07:26 PM
BillL BillL is offline
 
Join Date: Sep 2007
Location: Central IL
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Quote:
Originally Posted by jj_jetmech View Post
<snip>

Couple other things that helped:

Use/fabricate adjustable fwd canopy stops. I was trying to avoid this but the shock struts pull the frame forward affecting fit. Stops solve this.

<snip>

Good luck!
Do you have any pictures of the adjustable stops? I have been considering, but if the forward skin is riveted before deciding, it is done.

Thanks
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  #6  
Old 11-29-2015, 11:43 AM
jj_jetmech jj_jetmech is offline
 
Join Date: Aug 2013
Location: Klgb
Posts: 125
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Quote:
Originally Posted by BillL View Post
Do you have any pictures of the adjustable stops? I have been considering, but if the forward skin is riveted before deciding, it is done.

Thanks
Hi Bill

I don't have a pic of mine at hand right now but will post one when I get back home after TG. In the mean time google RV-7 canopy stops you'll see many examples of what others have done..

Good luck!
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  #7  
Old 11-29-2015, 08:00 PM
Rupester Rupester is offline
 
Join Date: Dec 2005
Location: Mahomet, Illinois
Posts: 2,195
Default

I installed adjustable canopy stops and they saved my bacon ... Not to mention my sanity. Without them it seemed like the hydraulic struts distorted the frame slightly differently after every iteration. The stops stabilized everything. I can send pics of the stops but not until 12/1 when I'll have access to my laptop.
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  #8  
Old 11-30-2015, 10:41 PM
jj_jetmech jj_jetmech is offline
 
Join Date: Aug 2013
Location: Klgb
Posts: 125
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Quote:
Originally Posted by BillL View Post
Do you have any pictures of the adjustable stops? I have been considering, but if the forward skin is riveted before deciding, it is done.

Thanks
Hi Bill

Here's mine. Note I bonded a strip of UHMH (Mc Master Carr) to the canopy frame (not pictured)for the Acorn nut on the end of my stop to glide on.





Good Luck
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Last edited by jj_jetmech : 11-30-2015 at 10:42 PM. Reason: Repair pic link
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  #9  
Old 12-01-2015, 12:50 AM
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BSwayze BSwayze is offline
 
Join Date: Jul 2007
Location: Molalla, Oregon
Posts: 955
Default

For what it's worth, here are some pictures of my canopy stops. I found them necessary as well, since the pressure from the air struts push the canopy forward if you don't have them.







You can see that I put some UMHW tape on top of the stop, but later on I found that it doesn't stay put very well. It wants to slide off. I'm going to put a larger piece on the canopy frame instead, and see if that works better.

For more pictures and discussion, you can visit the page on my website where I documented this in more detail, here:

Forward Canopy Stops
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  #10  
Old 12-01-2015, 07:00 AM
BillL BillL is offline
 
Join Date: Sep 2007
Location: Central IL
Posts: 6,313
Default Nice options!

Thanks guys. Two considerations, first bucking the rivets on the forward skin - you got that, second - self locking of the reaction screw (without climbing under the panel) - - is that an inverted plate nut? That is the only way I could think to (1) take the force in that direction and still (2) get a bolt that would not come loose, and (3) have it adjustable from the cabin side. A steel angle with a tig tacked steel self locking but did come to mind, but welding/locking experimentation would be in order. The nut plate seems more straight forward.

Bruce, I found yours in the search, a hidden work of art, and like the large flat face of the stop. I was thinking about a HDPE contact plate too, or a bolt head cover. The stick on UMHW sounds like a light, elegant (available) solution.
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Last edited by BillL : 12-01-2015 at 07:52 AM.
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