Canopy Bow Frame Screw Spacing and tab

[drone_pilot]

Okay. These questions have probably been asked 900 times on this forum but I'm going 901 as my search criteria magic is not working for me tonight.

I'm laying out the screw spacing along the canopy bow of my tip up. The plans call for 2-1/2" spacing on the screws but I keep hitting top dead center of a rivet with that spacing. 2-7/8" spacing works great but is there anyone out there with data that says my canopy will blow off for using one less screw on each side? Actually, I believe I counted 22 screw locations along the bow.

Is there anything folks use on the screw threads to lock them in along the bow? I realize lots of things aren't compatible with the acrylic canopy. I'd like to be able to see out of the plane when I'm done.

Where the front of the canopy passes thru the skin, has anyone out there just cut the tabs off and glassed it in? If the tab is a transistion area, wouldn't fiberglass accomplish the same thing? I just need a better understanding of the purpose of these tabs. If I keep the tabs, should they be epoxied down on the canopy?

Lastly, has anyone put anything between the canopy and the skins as a sealant?

 

[sahrens]

I can not answer your question on screws as I used Sikaflex. As for the tabs, or ears, on each side many folks have cut them off. I spent the time enlarging the gap to accommodate the canopy. When I actually mounted the canopy I wished I had cut them off.

Once you start glassing the fairing on the front of the canopy you will need to pick the point where you transition from glass back to aluminum. I picked the seam between the canopy frame and the side skirts. That included the area of those tabs in the fiberglass work.

Here is what mine looked like as I trimmed for canopy fit

Part way through the glassing work for the fairing you can see the tab is enclosed.

I added black dye to the epoxy during the layout, the white areas are a micro-balloon slurry. I hope this answer your question. Other folks will have different approaches to the same area.

 

[drone_pilot]

Is there any downside to chopping the tabs off? I don't really see the point of having them.

 

[sahrens]

You will lose the metal over plexiglass aspect of securing the canopy in that location, but you will have the fiberglass layup. It is really your choice.

 

[RV7Guy]

No

Is there any downside to chopping the tabs off? I don't really see the point of having them.

No downside. I cut mine off and then glassed. Unless you get that tab perfect, this is a very easy area to develop a stress point and crack when you drill. Frankly the tab makes no sense at a all.

 

[macrafic]

How did you guys cut the tab off? Did you cut horizontally from the bottom of the slot? Or did you just continue the slot all the way vertically down and cut the tap off that way?

 

[drone_pilot]

Well, I cut the tabs off a few days ago. I had jumped the gun and had riveted the skin onto the frame, so I started by drilling some of the rivets out along the sides to free the tabs enough to get at them with shears. Before drilling the rivets out, I just took a straight edge and aligned it with the joggle in the canopy frame and transposed the line across aluminum tab to the bottom of the "transition" slot. I extended the line 1/4" forward of the slot then made a diagonal line back to the top of the slot. I cut the tab off with standard sheers with no problem. I then shaped the forward portion of the slot with a Dremel tool and carbide cutting bit. It came out really nice. I made one minor trim to the front of the canopy and everything fit up great. I finally drilled the canopy to the frame this afternoon!

One thing I did that helped a lot with the final canopy trim was this....

I had used regular masking tape on the canopy bow frame to mark the split line. After splitting the canopy, I was having a hard time registering/seeing the canopy split line when fitting the canopy. I took some blue painters tape and taped one edge along the forward edge of the canopy split line drawn on the white tape. I also took the blue tape and taped the edge along the joggle in the canopy frame. This made registering the canopy and trimming to dimension much easier as the color of the tape gave me a good definition of the cut line. I'm very pleased with the way it all came out.

 

[dr cooper]

Hi Ben

Could you please post a couple of pictures of your trimmed C702 skin ears / tabs removed? I'm at the point of doing the plexi work.

Thanks.
Cliff
RV9A

 

[pazmanyflyer]

I cut the tabs off

I’m doing this now. I trimmed them off completely. I think with the canopy side skirt and glass fairing this will hold the canopy in good. If been referring to Mike bullock (http://www.rvplane.com/?categoryid=5&dayid=575) and Jason Beavers (http://www.jasonbeaver.com/rv7/2010/10/final-fitting-of-canopy.html) build sites. I like the approach Jason came up with the best and followed suite.

Here’s my pic’s for show and tell. My thumb is at the first screw location. I’ve read cracks start here so as many others I’m not drilling for a screw there either. The canopy skirt will be there and the glassed windshield too. You can see that I cut a slit along the canopy line. This allows the skin to flex in when the canopy is secured. It will all be covered by the fiberglass windscreen so it won’t be visible either.

 

[drone_pilot]

Sorry Cliff, I've been out of pocket the last couple of days but I did pretty much the same as Carlos with the exception that I did not need to cut slits in the skin like he did. My canopy is a little wide in that area and possibly sits a tiny bit forward of where his does and the split would not benefit me.

Don't make the mistake on the rear window as I did. Clamp the rear glass to the rollbar at the top along the split line first (maybe even slightly forward). Don't clamp the sides down tight. I drilled mine along the roll bar perfectly along the split line (not good) first. When you cleco the forward aft skin over the rear window, it pulls it down a little more than what I noticed during the test fit. Let the skin pull it down but the rear window may tend to buldge out a little at the roll bar. You can gently massage that buldge out and get it to lay down nicely and maybe with a little trim at the roll bar where it lies along the top of the angles where the rollbar mounts but that pull down will affect where that window lays along the split line. After that is done, I'd then drill it according to the plans and then mark the forward edge along the split line and trim/sand to get it just right. I went from a near perfect split line to a little better than a 1/16" split because I was hurrying and did not engage my brain during the process. I think I could have achieved near perfection if I would have waited to drill it to the roll bar. It doesn't look too bad and the untrained eye probably won't notice, but I'll need to think up some good one liners when other builders approach. ) I was really hoping to forgo the targa strip but I'll wait and see as things get riveted. I'll keep the option on the table for now.