Bill Crawford’s Flightlab Blog

We looped last month, and contended with the usual errors. We should roll this month, and try out a new set of mistakes. Usually, pilots learn the simple “aileron roll” first; then learn the additional inputs necessary to transform the aileron roll into a “slow roll,” which is in turn the foundation maneuver in both unusual-attitude training and aerobatic competition. (Oh-oh. My personal sylph, the grease-stained, litigation-conscious muse of aviation prose, whom apparently no one else can see, just blew into the hangar, fluttered to earth, and is now whispering in my ear. “Remind your readers that they shouldn’t try this rolling nonsense without parachutes, and then only in an approved aircraft with an instructor who actually knows what she’s doing. Cover yourself—you live in a litigious dimension. And by the way, you might want to start working on your column earlier in the month. I’m getting a little tired providing your filler on deadline day.” Wow, what a crummy mood on her! At least I think she’s a sylph. Maybe she’s a nymph. That would explain a lot.)

Whatever she is, she’s right—on both counts. Procrastination is a very bad habit, and the problem with rolling an aircraft is the real possibility of hitting the dirt but missing an attorney. I like to demonstrate the latter possibility to students by doing a couple of lousy (within reason) rolls to show what happens. Starting from level flight, all I ask is that the student apply full aileron, while leaving the rudder and elevator alone. As the aircraft rolls, the nose begins to drop below the horizon. It can be well below the horizon at the completion of 360 degrees. The slower the roll rate, the lower the nose at the end, thus the faster you’ll be going, and consequently the more thrilling the next couple of seconds.

The nose heads south because the aircraft is simply doing what its inherent stability is telling it to do. At 90 degrees of bank (knife-edge flight), the aircraft wants to yaw its nose downward to align itself with the relative wind, which now has a vertical component due to the fact that the aircraft is sinking. That’s directional stability. At inverted, the aircraft’s longitudinal stability, meaning its tendency to returned to trimmed angle of attack, pitches the nose toward the earth (and gravity gives a boost). As the aircraft then rolls upright, passing through the second knife-edge, directional stability again sends the nose down.

Roll rate is a function of how fast you’re flying (double the speed, double the rate) and also how far you’ve deflected the ailerons. If you don’t have full deflection, you’re missing the roll rate the aircraft has to offer, and you’re prolonging the time the aircraft is subject to the stability characteristics described above, which are designed for upright flight, not for excursions to knife-edge or inverted.

In an aileron roll, you solve the nose-going-down problem by starting the maneuver nose-high. Dive for speed, remembering that airspeed equals roll rate, then bring the nose up maybe 20 degrees or more above the horizon. Release any aft pressure on the stick, and apply full aileron. Hold full aileron until the wings roll back level with the horizon, and then return the stick to neutral. The nose will again be below the horizon, most likely, but not nearly as much as when you start the maneuver with the nose in normal flight attitude, rather than up.

The aileron roll provides the basis for the more complicated slow roll, in which you use rudder and elevator, separately and in combination, to hold the nose up throughout the maneuver. Briefly, you push forward on the stick a bit when inverted, and use “top” rudder at each knife-edge. Sometimes you use a combination of rudder and elevator, blending one in while blending the other out—whatever works best to hold the nose up.

The transition from aileron roll to slow roll is where mistakes typically appear. As an instructor, you welcome them. You want the aerobatic beginner to make the mistakes necessary to clarify technique. Learning aerobatics is not like learning to land, for instance. You don’t want students to screw up overmuch during landing practice, because a: they secretly blame their mistakes on you; and b: it’s hard on airplanes. But you want people to screw up—a bit, under supervision—in aerobatics, because the screw-ups contain so much information.

The almost universal screw-up is for the student to release some aileron deflection as he attempts to hold the nose up with forward pressure when inverted. Releasing aileron deflection, of course, causes the roll rate to go down. The student may not perceive this as it occurs, and not correct for it. The nose goes down as a result, for the reasons we’ve described. Or the student may be spooked by the reduction in roll rate (or just plain confused in general) and start pulling back on the stick in response. Now the nose can really go down, and the student might begin to pull into a split-s, as if flying the second half of a loop—except at much higher speed and maybe not enough altitude. That’s why the instructor’s hand is guarding the stick, ready to take over.