Lessons from a snap roll

Beyond the excitement of seeing an airplane in every possible attitude, the ground training deepened my understanding of aerodynamics. Once a pilot completes an aileron roll, she has seen that any bank angle with respect to the horizon is not only possible, but the acceleration with which she’s pulled into the seat feels the same as it does during cruise flight. When she performs a loop, she sees the airplane pass through every pitch attitude and remains seated with no tendency to float toward the ceiling of the airplane. The loop also teaches that, when done correctly, the wings never stall. And, if she pulls too hard and the stall warning horn sounds, pushing forward on the yoke or stick will solve the problem no matter what the pitch angle is with respect to the horizon (see “Lessons from a Loop,” March 2025 AOPA Pilot). The spin is the third basic aerobatic maneuver and thorough training in stalls and spins should be part of every aerobatic course.

My own course finished with emergency and unusual attitude training. Learning the basic and combination aerobatic maneuvers first proved helpful as I was able to identify, and already felt comfortable in, unusual attitudes so that I could complete recovery checklist items naturally. Each of the basic aerobatic maneuvers provides a lesson or a tool that can be used in an emergency. I use the same syllabus in the courses I offer today.

Every so often, a student asks to see a snap roll and I cringe because I’m loath to teach them. The snap roll is a variation on a spin in which the airplane gyrates around an axis parallel to the ground. As opposed to more gentle spin entries, the pilot pulls back on the yoke abruptly at an airspeed often well above stall speed. The resulting load can be high, and the fact that it’s applied instantly is more stressful than, say, the gradually applied load in a loop.

There is no sticky situation in which a snap roll is the answer, so it doesn’t serve as an emergency maneuver. Still, considering the mathematics behind minimizing the stress on an airplane during a snap roll is interesting and those ideas can be applied to everyday flying. If I do teach a snap roll, we thoroughly discuss aircraft loads so that my student understands how critical choosing the correct entry speed is.

During the snap roll entry, the pilot pulls back abruptly at V airspeed and the load factor rapidly increases from 1 to n=V²/V_stall² quickly. Once the wings are stalled, the pilot then gives full rudder in the direction of the desired rotation so the airplane experiences loads in more than one axis. For these reasons, the International Aerobatic Club recommends limiting the load factor to 4.5 during snap roll entry instead of the acrobatic category limit load factor of 6.The snap roll is a variation on a spin in which the airplane gyrates around an axis parallel to the ground.

My personal rule for the load factor during a snap roll in my Cessna 152 Aerobat, Wilbur, is a more conservative value of 3. With my student, we calculate the desired entry speed as follows. Wilbur has a mid-CG stall speed of 47 KCAS (all these calculations should be done with calibrated airspeed). Flying at 1,525 pounds, instead of its maximum gross of 1,650 pounds, reduces the stall speed to 45 KCAS. Because we want to pull exactly 3 Gs, set 3=V²/45² and solve to see that V=78 KCAS. Finally, the POH tells us that 78 KCAS=80 KIAS.

Sure, the snap roll itself is fun, but my favorite part of the maneuver is that, after completing one with an entry speed of 80 KIAS, I point to the accelerometer to find that we pulled exactly 3 Gs. The load factor model is very accurate and, with a little care, we can use it to ensure Wilbur stays in good shape for a long time.

Catherine Cavagnaro teaches aerobatics at UOS and is the Gaston Swindell Bruton Professor of Mathematics at Sewanee: The University of the South.