The snap roll is an advanced maneuver that you’ll first encounter in the IMAC Sportsman sequence. It evolves into more difficult variations in the upper classes of competition. It is one of the most difficult maneuvers in which to consistently achieve a high score because it requires a keen sense of timing, throttle management and exit correction. In addition, every plane seems to snap differently owing to its CG location and wing placement, i.e., low wing, mid wing, or high wing.
If you want to achieve a good snap roll, practice is mandatory. The snap roll is an autorotation maneuver in a stalled condition. During a snap, one wing is stalled while the other is accelerated about the roll axis. This creates a sudden roll-rate acceleration that you can’t obtain by simply inputting aileron. To achieve this condition in a model, several inputs must be given, including elevator, rudder and aileron. Pilots of full-scale planes will scoff at the idea of adding aileron because it is not required when they deal with wing loadings in the range of 35 pounds per square foot. Our models, however, typically carry a wing loading of from 20 to 40 ounces per square foot, so their flight dynamics are different from those of full-scale planes.
FLYING THE MANUEVER
The simplest snap is known as the “inside snap” (see Figure 1). This maneuver is performed from the upright position and is induced by adding elevator, rudder and aileron. Before you try this maneuver, be prepared for your plane to rotate at least twice as fast as it does during a typical aileron roll. You probably won’t even see your plane perform the maneuver because it happens so quickly. Instead, you will barely have started your control inputs when you’ll immediately have to think about recovery.
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