E-Flight Airliner Retract Project

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Page 2

       The retract mounts on both wing panels were now complete. A sanding bar helped true up the mounting faces on the blocks and clean up the shape of the balsa blocks.

       I used my Dremel tool to pilot drill the screw holes in the plywood blocks. I then mounted up both retracts for a test fit. Notice that the control linkage is on the inboard side.

       The next step in my build was to reconfigure the main landing gear trucks. As I mentioned before the airliner gets some of it’s appeal from it’s scale like gear. Unfortunately the monstrous triple trucks on the mains has to be sacrificed if I want to make my installation work. I do wish to keep some of that scale appearance though so I decided to lop off one set of wheels on the mains.

       I began the process by disassembling the mains into it’s basic components. I put the unused set of wheels and axles (2 axles and 4 wheels) away for replacements in the future if I need them.

       The next step was to shorten the wheel supports. These are the 100 mm horizontal tubes that the axles run through. I used a hack saw to cut the tubes to a length of 55 mm long. It does not mater what side you cut them from as they a symmetrical. This should leave a tube with a hole on either side.

       The wheel support tube is now ready to be drilled for the strut pivot screw. This hole will allow you to screw the shortened wheel tube to the existing strut assembly. I marked out the hole in the center of the two existing holes and drilled it out with a 7/64” drill bit. Notice the 3/32” drill bit in the existing hole below, it is used to align the old holes with the new one (keeps the tube from rolling around as well). You can use a drill press to do this operation if you wish, I was just lazy ;0)

       After some measurement and calculation I decided the main struts would need to be shortened 17 mm to maintain the original ride height of 134 mm from the wheels to the wing block.

       to do this I drilled a hole 17 mm above the existing hole in the strut before cutting off 17 mm from the end. This way there is no possibility of making the struts mechanically uneven. This hole was also made with a 7/64” drill bit. Notice the 3/32” bit in the end to hold the strut in place. When finished the hole should be about 86 mm center to the top of the strut.

       The last part to modify was the pivot spring that is used to keep the wheels from flopping around. I cut off 10 mm from each side of the spring and discarded the ends. I used a file to round off the sharp ends for safety.

       It was now time to assemble the trucks. To attach the wheel support tubes to the struts I used a set of 4-40 X 20 mm long cap screws with nylock nuts as seen below.

       I installed the pivot spring as it was originally and bent the arms upward to rest on the nylon wheel spacers as seen below. Some adjustment may be necessary to make the wheels level.

       Here is the finished product which still holds a little bit of the original scale appearance.

       It was now time to mount the struts to the retracts. I used one of the 1/8” main gear wire struts to fabricate two 46 mm long shafts that will join the struts and retracts. I used my Dremel tool with a cut off wheel to zip through the hardened steel rod.

       I used the Dremel tool to grind a flat spot on the shaft’s end to mate with the set screws of the retract units.

       I used “Blue” Permatex Thread Locker on the set screws to keep them from backing out. I am careful to only put the compound on the metal threads of the mechanism. *** Note: Loctite or any other thread locking compound can damage plastics over time. Glass-filled nylon is rarely affected by this compound but I though you should be warned as it will make some plastics crumble. ***

       I temporarily installed the wheel struts on the axles to see where the set screws would be contacting the shaft. I tightened the set screws to make a mark on the shafts so they can have a flat spot ground on them. This flat spot will keep the gear from moving on the shaft. The struts were reinstalled and blue threadlocker was used on the set screws.

       To lay out the holes where the wheels will go I reinstalled the gear on the wing. Notice that the trucks on the struts are offset to the inboard side of the gear. This is to help the gear ride higher in the belly of the plane while retracted.

       Using a coarse sand paper drum on my Dremel tool I started cutting out the holes where the wheels will retract into. This process takes patients and should be done in progressive steps or you will have big gaping holes to deal with. I set up my gear bays to have about 1/8” to 3”16 gaps between the wheels and the sides of the bay. Notice that the rear wheels are close to the wing mounting screw hole.

       The Dremel tool cuts the foam effectively without balling up the surface but care must be given to not accidentally scar the belly of the aircraft.

       Here is a closer view of the wing mount plywood below. This is the key reason the gear was moved forward as to miss the wing bolt. The plywood was trimmed a bit to clear the wheels. Take care not to cut too far into this block, about 1/4” max from the front edge.

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