Chapter 9 - Section 4

Landing Gear Cover

 

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  Landing Gear Cover   Axles, Brakes & Brake Lines   Landing Brake  

 

I did not follow the plan method for making the landing gear cover because of the dreaded joggle in Chapter 7. On the other hand, I really liked Wayne Hicks approach, therefore I decided to follow. This entire section is my interpretation of his ingenuity and is extracted from his web site.  

 

Preparing the Foam Block

I gathered 3 blocks of 2" thick urethane foam and trimmed them to size. The bottom one (green) is 8"x14" while the other two (yellow) are 8"x11". I trial fit them in place and traced the joining surfaces on the sides of the foam, such that I can fit them back onto the same place (note the lines on the sides of the foam). I made them a bit tight so that I can force them into the space between the LG bulkheads. Then I microed them together as shown.

 

 

 

 

 

 

 

Once the micro was cured, I force fit the foam block back into the bulkhead slot for sanding. Note the sanding blocks I used for sanding.

 

 

 

 

 

 

 

 

 

Once I got the outer contour close to the surface of the fuselage, I dug out the original NACA scoop paper template and traced out the inner contours. Note I used my laser for alignment and my tracing wheel (red) for transferring the outline onto the foam.

 

 

    

 

 

 

 

 

With the shaping of the contour completed, I applied 2" packing tape along the seam of the cover and the fuselage. Roughly 1" over the cover and 1" over the fuselage. Ready for glassing!

 

 

 

 

Referencing the method I used for the first part of the NACA scoop in Chapter 7 page 2, I first glassed the inside of the cover with 2 layers of BID and allowed to cure overnight.

 

 

 

 

Once cured, I trimmed off the excess glass along the top edge of the NACA scoop. Then I used my Dremel and dug a V groove along the sides of the newly glassed cover. I packed in some relative dry flox into the groove. This step is necessary to ensure a sharp corner along the bottom edge of the NACA scoop (per plan). Note the packing tape for mold release as mentioned above.  

 

 

 

Before the flox is cured, I applied 2 layers of BID onto the rest of the cover and allowed to cure. Right before I lay down the BID, I brushed pure epoxy on top of the flox to get a smooth flox surface. Again, I trimmed off the excess glass after cure.

Top surface of main gear cover completed...

 

 

 

The next step is to trim the ends of the cover to accommodate the main landing gear. I mounted the landing gear back in place and used the carpenter's widget and traced out the profile of the landing gear surface. Then I transferred the profile onto the left and right ends of the cover and trimmed with my FEIN tool and sand paper. Note the uniformity of the cover edge to the strut surface. Eventually, an external cover will be made to cover them all up and nobody will see this - you'll be the only person that appreciates this work...

 

 

Here's a picture with the gear mounted and the cover in place. It is gratifying to see various parts you build are fitting together!    

 

 

 

 

Murphy Strikes

After I glassed the underside of the landing gear cover, I sat it on its back for cure - that was a big mistake. The vertical walls spread a little and the middle of the cover sagged a little. By the time the cover was cured, I got a stiff cover that won't fit in the landing gear slot. After I force fit it, I got a 3/16" gap right at the middle of the NACA scoop. The cover was stiff enough that there is a good chance that I will not be able to pull it down flat even with the holding screws. I was debating whether to re-make the part or repair it.

 

 

 

 

 

I decided to take the repair route because it probably will take less time. I sanded down the edges of the cover and trimmed off the entire foam and glass at the middle of the cover. The undesirable bow was gone, but now I need to build it back up. I cut a 1/4" foam piece and microed it onto the back of the landing gear cover. This time, I put a lot of weight on top of it during cure to make sure it is flat. It turned out OK... but it set me back a couple of days!

 

[Lesson learned here: don't expect a part to cure to a certain shape unless you hold or clamp it down in place throughout the cure. Otherwise it will move on you and it could be costly... ]

 

The next step is to add a lip to the under side of the cover so that I can have some means to hold the cover down. However, this requires turning the fuselage over (for ease of making the lip). I decided to wait until I finish the axle installation and landing brake because they both require an upside-down fuselage position.

 

Making the Cover Lip

Now that I have completed the installation of the axle and landing brake, I turned the fuselage over for the long awaited lip. The landing gear lips are made out of two 6-ply BID strips, conformed to a 90o angle along the entire length of the landing brake cover.

 

I roughed up about a 1.5" wide surface strip along the LG bulkheads (forward & aft) with 36 grit sandpaper in preparation for the BID tapes. I put packing tape along the 1" edge at the underside of the landing cover. I should have put a wider strip and I sweated over that later. Note that if the cover ever gets epoxied to the lip, you would have a heck of the time separating the two... 

 

I placed the cover over the strut opening, making sure its nice and straight, weighed it down and hot glued the cover in place. I put enough hot glue to make sure nothing moves or any chance of falling off when the fuselage is turned over.

 

I made 6, 2x38", 2-ply BID tapes for the cover lips because I was concerned that a single 6 ply BID may not want to conform well around the bends of the landing cover. Its more work, but the results should be better.

 

It was a challenge to lay the 2 ply BID tapes nicely and I ended up with ~3/4" over the under side of the cover edges (now covered with packing tape) and then the 90o bend along the face of the LG bulkheads. It took me a good 6 hours to perform this entire task. After cure, I trimmed them out and they are stiff and strong. It also provides a very nice snug fit for my cover.

 

Nut Plates & Rivets

I marked out 16 locations for nut plates and screws for the cover and drilled them out with appropriate holes & countersinks. I used the same screws that were called out by the plans and selected the matching nut plates (MS21069-L3) for them. It is advisable to buy a rivet squeezer for the job. I ended up using two flat squeeze heads due to limited access space, but it worked out OK.

 

The most difficult part of the task was to keep the nut plate alignment while squeezing the rivets. First, I put a smaller size (one size smaller), short screw through the nut plate and pulled it against the under side of the lip. Secondly, I slipped the 2 rivets through the nut plate ears. Then I used the squeezer to anchor the rivets. After few trial fits and refinement, the landing gear cover is finally secured in place. With the 16 anchored screws and the snug fit, I think my landing gear cover is staying put for good. Note the notches I cut out of the lips - they provide clearance for the strut to 'drop' into place.

 

 

 

 

 

 

Here's the completed landing gear cover with gear strut in place - no interference plus a snug fit throughout!

 

This would be a good place to thank Wayne Hicks for his alternate Landing Gear Cover approach!  

      

 

  LG Bulkhead Reinforcement   Preparing Strut   Attach Tab 

 

  Landing Gear Cover   Axles, Brakes & Brake Lines   Landing Brake