The Simpleton 40 biplane is a rugged sport plane that flies great. The design is based on a mostly forgotten airplane published in RCM magazine in the 1970s known as the RCM Basic Bipe Mk II. The Simpleton is an even more simplified version that’s engineered to be an easy, practical project for a first time balsa builder who already knows how to fly.
Wingspan: 47″ top, 44″ bottom
Wing area: 780 square inches
Weight: 5 pounds
Wing loading: 15 oz/square foot
Engine: 40-50
It’s designed for 40 size glow engines, and rubber bands to hold the wings on. I’m an old fashioned guy who likes glow engines. Since I’m the one producing the kit I’ve done it the way I know how, and I flew the prototypes with various glow engines from 40 to 46 size. It works well, it’s a lot of fun, and the majority of the exhaust oil goes between the wings and flies right past the airplane instead of making a huge mess. The rubber band wing attachment is intended to be easier for beginners. One of the prototypes had a take-off mishap and cartwheeled on its wing tips. The rubber bands 100% protected the plane from damage. Are rubber bands old fashioned? Certainly. But they do protect the airplane.
Those with more experience are welcome to skip the instructions and build the plane with bolt-on wings, flaps, electric power, or any other modification that comes to mind. If you want to do that I’ll assume that you know what you’re doing and don’t need me to tell you how. Send me a photo when it’s finished.
To mitigate the cost of printing a construction manual, the complete instructions are posted here.
Tools needed: Screwdrivers; Drill with an assortment of bits; Pins; Thin and medium CA glue; Titebond wood glue or 30 minute epoxy; Sanding block with coarse and fine sand paper; Hobby knife and #11 blades; Masking tape; A bunch of small clamps or a bag of clothes pins. A razor saw is handy for cutting spars and sticks. A hobby size planer is handy for shaving down balsa to reduce sanding time. It’s also nice to have a utility knife with a long blade that you snap the end off of when it gets dull.
You could build the whole plane with Titebond or Elmer’s white glue, or build the whole thing with CA. I prefer a mix, and the instructions tell when and why to use various types. If you’re going to mostly use CA, a 1/2 oz bottle will probably leave you lacking, so maybe you should go for 1 oz.
150 grit sand paper is good for quickly chewing through balsa, and 200 or 220 will produce a baby’s bottom smooth surface ready for covering, but you can use whatever you have in the house. How smooth you want your finish is up to you. I always keep one block with 150 grit and another with 180. The most important point about sand paper is that you shouldn’t waste time fooling around with old worn out paper. Keep fresh sharp sand paper on your block and you’ll be a lot happier, and your parts will probably look better, too. When your sand paper is dull you tend to push harder, and the wood will deform rather than being cut. For instance, when you sand the front of the wing in preparation for putting the leading edge stick on, if you’re pushing hard on crappy sand paper the sheeting in between the ribs will deflect and your wing sheeting will have a noticeable ripple along the front edge. It’s much better to use good sand paper and let it do the hard work.
In addition to the laser cut balsa parts the following items are included:
HARDWARE
machine screw 4-40 x 3/4 4pc engine mount
Blind Nut 4-40 4pc engine mount
machine screw 6-32 x 1/2 4pc landing gear
blind nut 6-32 4pc landing gear
nylon bolt 1/4-20 x 1/2 4pc landing gear
self tap screw #2 x 3/8 2pc tail wheel
self tap screw #2 x 1/4 2pc hatch
self tap screw #4 x 1/2 4pc servo rails
Machine screw 8-32 x 1 1/2 2pc axles
nylock nut 8-32 4pc wheel retainers
control horn 4pc
machine screw 2-56 9pc control horns, tailwheel strap
nut 2-56 1pc tailwheel strap
throttle cable assembly dubro 1pc
steel in nylon pushrod dubro 2pc tail
2-56 rod 12″ 2pc ailerons
2-56 nylon clevis 4pc ailerons, optional for tail
landing gear 325-400-1200
tailwheel bracket
HARD WOOD
1/4 x 1/4 x 48 bass 4pc spars
1/4 x 1/4 x 3 bass 1pc elevator
3/16 x 9 dowel 1pc struts, alignment holes
5/16 x 12 dowel 1pc wing rubber band dowels
1 x 36 triangle 1pc tips
14 x 36 triangle 1pc bulkhead gussets
BALSA STICKS
1/4 x 3/8 x 48 2pc TE
3/16 x 5/8 x 48 2pc LE
3/16 x 1/2 x 48 2pc LE
3/16 x 3/16 x 18 1pc head rest
1/4 x 1/4 x 48 1pc shim
BALSA SHEETS
1/16 x 1 x 48 4pc TE sheeting
1/16 x 2 x 48 2pc LE sheeting, bottom wing
1/16 x 2.35 x 48 2pc LE sheeting, top wing
1/16 x 5/16 x 48 5pc cap strips
1/16 x 4 x 36 2pc top and bottom fuselage sheeting
1/8 x 3 x 12 1pc fuselage top deck, windshield
Click below to start building.