The snap roll: do it right!

Apr 28, 2014 2 Comments by

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.

Make sure that you have enough altitude to allow mistakes! Now take the airplane to a comfortable altitude at least 100 yards in front of you, parallel to the runway. Enter the aerobatic zone and fly to the center of the box at mid throttle (not full throttle). From level flight, perform an inside left snap by simultaneously applying up-elevator, left rudder and left aileron for 1 to 2 seconds.

Recover from the maneuver by neutralizing the sticks and immediately adding right rudder to correct your loss of heading. Maintain the mid-throttle setting throughout the maneuver.

FINESSING THE MANEUVER
There are several places where a little finesse will go a long way. Most pilots bury their sticks in the corners of their transmitters to snap their planes. This typically creates a stall in which too much energy is depleted, and recovery is very difficult. This condition is known as “snapping too deep.” Your goal is to fly through the maneuver with enough inertia to allow the airflow to re-attach to the stalled wing on demand. To accomplish this, you will need to decrease the elevator and/or rudder input until your plane just barely snaps. The only way to find this point is to practice it. When you find the perfect combination of elevator, rudder and aileron, practice it over and over until you can easily duplicate it. BY DAN WOLANSKI

Fixed-Wing Flight School

About the author

Executive editor About me: I’m a publishing professional who has a passion for aviation and RC, and I love creating issues, books and a website that help RC pilots to enjoy this sport even more. I admire scale aircraft and enjoy the convenience of flying smaller electrics.

2 Responses to “The snap roll: do it right!”

  1. Alan_In_Pgh says:

    I may be one guilty of “snapping too deep”

    How does one distinguish between “barely snaps” and “does not snap”?

  2. 50+AirYears. says:

    I’ve never used aileron in a snap. In fact, I’ve even done snaps, inside and out, with 3 channel planes, that is, rudder, elevator, and throttle. You get what in effect is a is a horizontal spin, with the plane rotating about th apparent CG, not about the longitudinal axis.

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