Chapter 24 - Section 7

Landing Brake and Battery Covers


Battery Cover

The exact size and curvature of the battery cover took a bit of effort to determine. Since the location of the cover is a bit forward of the firewall, it will be a bit larger than the firewall. However, I can use the firewall dimension as a rough guide. Fortunately, I still have the wood template of the firewall from Chapter 6, therefore, I traced out the top edge of the firewall onto a thin white board (shown left). If you look close, I made a series of marks (at 1" intervals) radiating from the bottom of the center line to the top edge of the board. I cut out the template for the next step. I also added an extra 1" at the bottom for temporary clamping onto the center section spar.







Determining the Battery Cover Curvature 

I clamped the white board (template) onto the openings of the center section spar. With a ruler aligned along the radiating line, I measured the width of the gap between the roof of the turtle back and the top edge of the template. I took 20 measurements on each side, totaling 40.


I removed the template and lay it on top of a sheet of 1/8" PVC foam. I projected the gap dimensions from the edge of the template onto the underlying foam. Once completed, I connected the dots with a thin metal strip, thus forming a curvature that mirrors the roof of the turtle back. After trimming the foam and with just a slight touch of sanding, I got a perfect match line.


I glassed both sides of the battery cover with 2 layers of BID. Though I used 1/8" foam, the 2 layers of BID made it plenty stiff for a cover. 


My next step was to find a way to hold the cover in place. I made 4 tabs (4 layers of BID each) and glassed them at specific locations on the center section spar and the turtle back respectively. Make sure you provide set back spacing to accommodate the thickness of the cover. I marked the planned bolt locations on the cover, butt it up against the 4 BID tabs, then match-drilled a through hole (both cover and tab) for an AN3 bolt. Then I removed the cover and riveted a nut plate on the back side of the tab.


After the trial fit, I drew out a half moon shaped paper template (2" width x 1" height) and traced its outline on all 4 tabs. A bit of trimming and sanding made it reasonably pleasing. The picture shows the tab at the top of the turtle back.










'Loud Speaker' Covers

I was not able to find any instruction in the Plans for the 'loud speaker covers'. So I used the remaining 1/8" foam and made two covers to fit. Sanding down the covers to fit took a lot more effort than expected. Because of the uneven bevel edges of the speaker holes, I had a tough time making the covers to sit flush. After 2 1/2 hours of sanding...fitting...sanding...fitting - they still looked ugly!


I decided to take a different approach - fit the cover from inside out. Here's a picture of the two different approaches. The right one shows gaps along the edges, while the other does not. 






Since I messed up the right cover, I ended up making a new cover set. At the far ends of the cover, I embedded a 1" x 1" x 1/8" hard point. Then I drilled and tapped the hard points. I drilled the 4 holes to accommodate the AN3 bolts at the longitudinal center of the covers, 1/2" from the opening edges. After I tightened the AN3 bolts to the hard points, I traced out the opening onto the cover, then removed and trimmed to shape. Here's a picture of my covers.


Note: you do have to find a way to hold the covers forward (in place) in order to screw them in. I tried using a piece of duct tape and a GPS suction cup - they both worked.   





Here's a picture of the completed battery and loud speaker covers. If you look close, you can see the bolt locations - 2 for each loud speaker cover and 4 for the battery cover.










Landing Brake Cover

The landing brake cover consists of 3 sides. Instead of making a mold out of 1" foam (per Plan), I used a few pieces of left over foam from the strakes and made a mock up cover. I have yet to round off the edges before glassing.


I traced the outline of the brake cover onto the fuselage, seat back and floor, then removed the brake cover and applied packing tape over the outline. 


With the brake cover on the work bench, I taped it over with packing tape. I applied 2 layers of BID over the outside surface of the brake cover, leaving ~1" of glass overhang (without epoxy).




I carefully sat the brake cover (with 2 layers of BID) back over the landing brake and wetted out the overhung glass - which is now laying over the packing tape. I used a couple of sticks to keep the landing brake cover tight against the fuselage and let it cure over night.   










After curing, I popped the cover off the mock up, trimmed, did a bit of sanding and held it in place with 4 metal screws per Plan. I may trim the edges down some more later on...