About this Plan
Whistler. Multi R/C model. Wing area 732 sq in, for Veco 45 power.
Quote: "Newest member of America's International Radio Control Competition team brings you his famed Multi Class aerobatic aircraft, reveals design secrets that can be of very great help to all would-be R/C flyers. Balsa importers should be happy, too! Whistler, by Dr Ralph Brooke.
While searching for a smooth-flying, stable multi R/C model, I experimented with a number of different designs, the latest and best being 'Whistler'. Inspiration came from a design of Milt Boone's which I built a year ago. During several long bull sessions, Milt sketched out what he considered to be the 'ideal' multi design, which I proceeded to build. The distinguishing feature of this model was that the wing was set up deep into the bottom of the fuselage, approaching true mid-wing conformation. This model showed great promise, but unfortunately was short-lived (only one week!) due to an intermittent power pack plug. (This same trouble also struck down the Whistler that I flew at the '62 Nats.)
Construction of Milt's design was somewhat more difficult than the average multi job and I could not quite muster up the courage for another go at it. His provided the spark, however, and Whistler uses the same basic moments in its concept. A number of unique design features distinguish Whistler from previous multi designs.
First, the wing has generous area (732 sq in) to give the model smooth low-speed and aerobatic handling characteristics. The particular airfoil used is one by Glenn Spickler, with a thick semi-symmetrical section and blunt leading edge for good low-speed characteristics. Both a large vertical stabilizer and ventral fin are used to give smooth rolls. The ventral fin provides a good distribution of tail area above and below the fuselage, and it also helps to reduce corkscrewing in inside loops where the vertical stabilizer is less effective due to wing wake.
Large-chord, top-hinged ailerons are used to give positive and snappy roll response, which is important in four-point rolls and other similar maneuv-ers. There has been a trend lately to-ward full-span ailerons, the excuse being that a stronger wing can be had, easier to build, etc. However, I find them mushy in some flight conditions, making precise rolls more difficult.
The installation of the radio gear in Whistler was also inspired by Milt Boone (and constructed by him to boot). Rudder, elevator, trim and throttle servos all mount on a 1/16 epoxy printed circuit board, which is installed as a unit in the fuselage. The servo wiring is all soldered to the obard, eliminating the usual servo plugs, with their 48 flexing soldered connections.
Another innovation is the use of Dzus fasteners to hold the wing, rather than the dowel and rubber band method. (Nowadays I really have to search high and low in my tool box for rubber bands to use in vibration checks!) Dzus fasteners give a very neat installation and, contrary to popular opinion, the solid mounting of the wing prevents damage in cartwheels and hard landings. In many dowel and rubber band set-ups, the stretched rubber bands bite into leading and trailing edges, weakening the wing at the center section, where 'wing-folding' stresses are greatest! With the solid mounting the overloads are taken up by the Dzus fasteners and dowels, which can be easily reinforced with plywood gussets.
Whistler was designed to have quick but accurate construction along with the best combinations of strength and light weight. Since the plans are fairly well detailed most comments will deal with those points which differ from usual practice.
In building the wing, the most important thing to have is a flat building board, 6 feet long and supported well enough to prevent warping. The thickness should approximate 3/4 in. A good grade of plywood will most often be your best bet in this department, as the wing construction makes the difference between average performance and consistent winning. A flat section is incorporated in the wing ribs to facilitate accurate construction. I prefer templates of galvanized iron (aluminum is too soft). Note that two rib shapes are needed. I rough-cut my ribs, employing two locator dowels through the stack to line them up. Then a template at each side of the stack (dowel locator holes in same spots as on ribs) and I'm ready to go at it with a long-bladed X-Acto knife. Don't overlook the 3/4 in center rib and the 1/4 in false ribs. All ribs must be uniform. Trim the 3/32 x 4 in LE and TE sheets with the aid of a straight edge (a mighty important tool, often overlooked by many hobbyists). Cement or glue the 1/8 x 1/4 spars in place.
Note the webbing used between the ribs and spars. Size must be exact on these, as they act as rib spacers and must bridge the gap between spars. Note the vertical grain direction. Construction should be proceeding quickly now, with the flat section (rear) of the wing pinned to the workboard and the front of the wing shimmed up. Ribs and web pieces are cemented alternately in place, working from the center rib to the tips..."
Whistler, American Aircraft Modeler, July/August 1963.
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Supplementary file notes
Article pages, thanks to RFJ.
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