Micromaster (oz14603)

About this Plan

Micromaster. Radio control sport model for electric power. Wingspan 18 in, wing area 114 sq in. For DC5-2.4 motor with 5:1 gearing.

Quote: "Lightweight classic micro bipe. Aeromaster, by Roger Carignan.

The Micromaster is an attractive model of a biplane. I used several weight-saving construction methods that resulted in a low weight, given the complexity of the model. The Micromaster has enough speed to handle light outdoor breezes. It performs loops easily and flies inverted very comfortably. The addition of a rudder servo would increase aerobatic capability and only increase the weight to a bit more than 2.5 ounces.

Among classic biplane models, the Lou Andrews Aeromaster (oz1971) is one of the all-time favorites. And since the Aeromaster is no longer available in its original size, any remaining kits are fast becoming collectors' items.

My first scale model of the Aeromaster was powered by a Cox 020 engine and had an 18-inch span. It had 3 channels of control: ailerons, elevator and rudder; the engine ran at full speed until the fuel ran out. This model weighed 6 oz and was very fast and extremely aerobatic. I decided to build a lighter, electric-powered version of this model with the same wingspan. My objective was to achieve a weight of 3 oz -half the weight of my first model. It would have at least 3 channels of control including ailerons, elevator, and throttle, and it would use as many weight-saving methods as I could devise.

The result is the 2.4 oz Micromaster. Its wing area is 114 square inches, and the wing loading is 3 oz/sq ft. Even if you aren't interested in building this model, read on; I describe several weight-saving construction techniques that could easily be applied to other models of this type.

Construction: Use contest-grade balsa for most of this model's parts. The structure mainly uses 1/32-inch balsa, but the wing spars and empennage use 1/16 inch.

Cut out all of the ribs and fuselage bulkheads. Note: do not cut slots in the cabane and landing-gear formers F2B, F3B and F8B at this time. Cut the motor mount from two laminations of 1/32-inch cross-grain balsa, but do not cut out the center yet. Stiffen the fuselage bulkheads with 1/32 x 1/8 strips. I used carpenters' wood glue for as much of the assembly as possible, carefully removing any excess glue. I found that due to its wicking action and its penetration of the surrounding wood, thin CA made the model heavier.

Fuselage: Cut out two fuselage sides following the outline indicated by the black triangles on the plan, but do not cut out the lightening openings at this time. Glue the 1/32 x 1/8 stiffeners into place, making left and right fuselage sides. Be sure to accurately position these, as they determine the alignment of the cabane formers. Mark the positions of the cabane formers F2 and F3 on the horizontal stiffeners, as well as the position of former F6. Cut the elevator pushrod slot in the left fuselage side.

Glue 1/16 x 1/8 corner-filler strips to the rear bottom edges and 1/16 square strips at the stabilizer location. Glue 1/8 triangle stock to the forward bottom edge and then cut these in sections to form the lower nose curve. Sand any excess to match the fuselage sides. Glue doublers D1 at the wing locations.

Glue formers F2B, F3B and F8B to F2C, F3C and F8C, respectively. Cut slots 1/32 inch deep (per the drawing) in F2B, F3B and F8B. Complete these formers by gluing their respective formers F2A, F3A and F8A. These three formers now have 1/32 square channels that will be used to hold the cabane and landing-gear struts. Check that these are clear by running a small wire or pin through each channel. Note that F2 and F3 are not the same because of the fuselage forward deck's taper; mark these to ensure correct installation.

Assemble formers F1 through F5 and F8 to one fuselage side and assemble the cockpit floor at F5 to ensure square alignment of the bulkhead. Taper the filler strips at the tail and glue the fuselage sides together. Be sure to check for proper alignment before the glue sets. Glue formers F6 and F7 into position, making sure that the pushrod guide holes are on the left side.

Wet the outside surfaces of the upper fuselage sides, then roll over the formers and glue them into place. This forms the forward and turtle decks. Install the motor mount, and make a note of the proper side-thrust orientation. Clamp and glue the fuselage sides to the motor mount. Cover the bottom from the motor mount to the wing leading edge and from the wing trailing edge to the tail using 1/32 balsa with the grain perpendicular to the fuselage. Glue the 1/16 bottom doubler piece between F8 and the wing leading edge. Cut out the motor-mount opening and the six lightening openings in the fuselage.

I made a cowl for my model with an opening that simulates the engine compartment of the Aeromaster. This is made from soft balsa and is hollowed to a thickness of at least 1/16 inch.

Shape the fuselage bottom corners and sand the entire structure. Cover the fuselage, cowl and tail-filler blocks. At this stage, the fuselage should weigh less than 6.5 grams..."

Direct submission to Outerzone.

Update 7/6/2023: Added article, thanks to theshadow.

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