Bristol Brownie
Bristol Brownie. Radio control scale model, for electric power with geared KP-00 motor. All-sheet design. Wingspan 14.4 in, wing area 41 sq in.
Quote: "The Bristol Brownie is one of a number of very light and low-powered aircraft that were designed and built to compete in the efficiency trials at Lympne, England, in the mid-1920s. I have long been attracted to the Brownie as a scale model, and I have built several larger versions. The Brownie is one of those full-scale airplanes that seems to have been designed with modelers in mind. Very little needs to be changed to make a nice flying scale model. That said, the tiny size of this version required that I make several changes. The wing airfoil on the original plane would be a very poor performer on this little guy, so I elected to use a curved, single-surface airfoil. I also lengthened the landing gear slightly to ensure adequate prop clearance.
To achieve satisfactory flight performance from such a tiny model, strict weight control is a must. The airframe is all balsa, so light, warp-free wood is required. My sheets of 1/32 x 3 x 36-inch balsa weigh 6 grams each. If you can’t find wood of this grade at a local hobby shop, Lone Star Balsa and Superior Balsa & Hobby Supply can supply it.
The adequate control and lightness provided by the RFFS-100 radio system make it the best choice for the Bristol. To save even more weight, I used a 3.7-gram, 170mAh lithium-polymer (li-poly) cell.
The RFFS-100 actuators would usually be mounted directly on the tail, but because I used such a light battery, mounting them there would cause a serious balance problem. My solution was to use a few bits of sheet aluminum and a piece of wire to modify the RFFS-100 actuators so that they could be mounted in the cabin and connected with pushrods. This works very well, and it is reasonably simple to do. Another alternative is to use the Gary Jones actuators sold by Bob Selman and Dynamic Web Enterprises.
For power, I decided to use a KP-00 motor with Didel 6:1 gears (available from Dynamic Web Enterprises). I mounted a couple of 1mm-internal-diameter ball bearings on the propeller shaft, which is made out of 1mm wire. Please note that the large gear is mounted on the rear of the drive unit to ensure it has enough clearance. This power system works well with a GWS 5x4.3 propeller.
To streamline the aircraft, the spokes on the wheels of the full-size Brownie were covered, but I had bought a set of spoked wheels from Peck-Polymers, and they were just too charming to resist. If you decide to use the scale wheels, Peck-Polymers offers several lines of 'realistic' wheels at acceptable weights.
The finish on these tiny models is another area in which weight can quickly get out of hand. The original Brownie was all silver with black lettering, but I felt that this would be difficult to see in flight, so I rewrote history and painted mine yellow with black markings. To achieve a bright finish while keeping the weight low, I use thin automobile touch-up spray paint diluted by 50 percent with auto paint thinner. I use DupliColor paints, but Krylon paints also work well. I sprayed a thin coat of color directly to the bare balsa; this created an effect that looks more like a stain than a coat of paint. I cut the letters out of black tissue paper and attached them with Elmer’s white glue. The trim colors are model enamels. The entire finish on my Brownie added only 0.4 gram..."
