RCM Basic Bipe

I made  a lot of modifications to this design, but it’s nothing complicated.  In fact, it’s a lot more simple than the original.  The chin block allows you to make up a typical wire landing gear and attach it with nylon straps.

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Or if you prefer a sheet metal landing gear, that’s even easier.  The hatch shown on the plan is not needed, as the hole in the bulkhead is big enough to allow easy access for battery and tank installation.  And you can leave the big chunk of wood off the bottom of the lower wing, which saves a fair amount of weight.

Laminate all of your plywood parts.  The wing bolt plate, the firewall, the pylon, and the two 1/8″ plywood wing ribs should be laminated with epoxy or some kind of wood glue. If using Titebond, Elmers, or other water based glues, weigh the parts down with heavy objects and leave them there until they are totally dry, to prevent warping.  On critical parts such as these I prefer epoxy for this reason.

Make a right and a left fuselage side by adding the lite ply nose compartment doubler and the wing saddle doubler to each fuselage side.  Assemble the fuselage and make sure it’s square, but don’t add the plywood chin block until after you drill for the wing mounting dowel.

Build the wings according to the plan, with three exceptions.  The first difference is that the ribs are cut for 3/16″ square spruce or basswood spars, because I think they are superior to balsa spars.  Another difference is the 1/4″ plywood rib in the center of the top wing.  Make sure that it is absolutely straight.  If it’s crooked, your wing will be crooked.  The other difference is that the outboard wing strut locations will have 1/32″ ply doublers on the ribs.  Note that the wing ribs in the top wing do not line up with the ones in the bottom wing, so your outboard strut will have bends in it to line up with the tabs.  Figure out where you want your struts to be, based on aesthetics.  Place your reinforced ribs in these locations.

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You will need a chunk of circuit board, phenolic board, or similar.  Make eight tabs about an inch long and a half inch wide.  They can be longer, wider, narrower, etc.  That’s just a ballpark figure.  Drill 1/16″ holes in one end of half of these tabs, and 1/8″ holes in the other half of the tabs.  They should look something like this:

tabs

Scuff the indicated area of each tab with sand paper to assure a good bond.  The ones with the small holes go in the outboard wing panels.  One of them should stick up from the bottom wing on each side, and one should stick down from the top wing on each side.

The pylon is a really easy thing to build.  Make sure that your fuselage sides and bulkheads are all square to each other.  The pylon keys into the top of the fuselage very easily.  Install a cockpit floor made of firm sheet balsa and mark a center line on it to help you align the pylon.

Don’t glue the tabs into your top wing yet.  When you are ready to mount the top wing, place a temporary spacer on top of the pylon to allow your top wing to float above the pylon a bit.  Use a piece of 1/8″ balsa sheeting.  Attach it with two dots of medium CA glue.  Sand each side of the pylon to eliminate any overhang of the balsa spacer.  When you assemble the wing, it should look kind of like this.

pylon

Now glue two tabs into your top wing, but glue them on only one side of the center wing rib!!!  If you do the left side first, glue the front tab on the left and the rear tab on the left.  Do not glue the ones on the right side of the rib yet!!!  I used medium CA to glue mine.  You can use CA or epoxy, etc.  Note that CA will allow you to work a lot more quickly.  But if you’re not confident that it will turn out right, use epoxy so you have more time to get everything the way you like it.

Align the top wing where it belongs, on top of the spacer.  Use a pencil or a center punch to mark the pylon in the exact location of the hole in the front mounting tab.  Remove the wing and drill a hole at this location.  Now replace the wing in its proper location and pin this tab in place with a 1/8″ music wire or brass pin.  Now mark the location of the rear hole and drill it.  If you have a long drill bit that will allow you to drill right through the hole in the tab while the wing is in place, that’s even better because it will be very accurate.

After you have both holes drilled place the other two mounting tabs where they belong, on the opposite side of the pylon.  Thread the pins through the holes in the unmounted tabs.  Align the wing and glue the tabs in place on the plywood wing rib.  In summary, the first tab determines where you will put the hole in the pylon, which in turn determines where you will put the other tab.

Once your glue has cured, remove the pins and set the top wing aside.  Remove the temporary balsa spacer from the top of the pylon and sand the glue off.

dsc_0544Now mount the bottom wing.  Drill the hole for the front wing mounting dowel through Bulkhead #2, and then mount the 1/8″ plywood chin block.  I like to put some triangle stock around the inside edges along the two fuselage sides and the firewall, sand it flush, then mount the chin.

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Glue the strut tabs to the ribs.  Add some balsa sheeting around the tabs for the covering film to have something to attach to.

dsc_0545  Mount the bottom and top wings in place.  Adjust the top wing until it’s square to the rest of the plane, and figure out how long your struts need to be.  I used a 2-56 threaded rod with a solder clevis on one end and a screw clevis on the other.  Once you get it mounted, it’s surprisingly sturdy.

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That’s pretty much all there is to it.  The rest of this project is just like any other airplane building project.  If you have any questions, just ask.