High-Lift Devices for Models
IT'S SURPRISING that so few Radio Control model aircraft designers have adopted the high-lift devices that are commonplace in today's crop of full-scale lightplanes. Flaps and other high-lift devices can add a new dimension to RC flying. They're simple to design and build, and make a sport plane pure fun to fly. This first of two articles discusses the theory and application of high-lift devices (HLDs). Part Two will explain their design, construction, and actuation. One of the primary considerations in designing a plain, unflapped model airplane wing is that its area must be large enough to permit reasonable approach and landing speeds. This calls for wing loadings below 20 ounces per square foot of wing area (see Figure 1).
High-Lift Devices: For Models
ONE OFTEN overlooked solution to the quest for more realistic sport flying is to incorporate flaps or other high-lift devices in the model. Part One of this two-part article discussed the theory and application of HLDs for model airplanes. This concluding installment explains the design, construction, and actuation of these underappreciated devices. The high-lift devices that I have successfully used fall into two broad categories: (1) Trailing edge slotted flaps, either internally or externally hinged
Structural Design
A study of full scale aircraft structural design is fascinating. Take Bleriot's cross channel monoplane: its fuselage consisted of four wooden longerons, with wooden crossmembers, the whole thing being wire braced. Covering was fabric, and in fact, the aft fuselage was left uncovered. The wing had two wooden spars, with ribs and fabric covering. It was wire braced, which provided most of the strength, yet it had to be flexible in torsion, since lateral control was by wing warping.
Structural Design
IN THIS PART, actual structural designs will be illustrated, based on the engineering principle (outlined in Part I) of locating material as far from the neutral axis as possible. Consider the inflight forces involved for the various aircraft components: fuselage, wing, horizontal and vertical tail surfaces, and landing gear.
Glow Plug Heater
Top: Inverted engine installations can help to give models smooth lines and pleasing aesthetics as evidenced here on our author's Harrier II model. In the past the price for these nice lines was an engine that was hard to start and make it idle because the oil collecting in the inverted cylinder tended to extinguish the glow plug. Left: By simply using a switch connected to a battery and operated by a cam on the throttle servo, the glow plug no longer has to rely on the burning fuel to keep it lit. In the position shown here the throttle trim is full up for the engine to idle. Closing the switch energizes the glow plug so a reliable idle can be obtained. Right: Pulling the throttle trim back down closes off the carburetor and opens the microswitch, disconnecting the battery to conserve its charge and to extend the glow plug's life span.
