Bill Crawford’s Flightlab Blog

You’d think that an aerobatic maneuver as apparently straightforward as a loop would be a cinch to perform: Dive for speed, haul back on the stick, and then be patient until the world appears more or less as it was before. That’s certainly the core idea, but it’s not by itself a sufficient plan. We want a round loop, something Euclidian. And we want a loop in which the wings remain level with the horizon throughout the maneuver.

Roundness isn’t easy. It comes from flying a constant radius, which itself isn’t easy because the aircraft is busy changing speed and also its relationship to the pull of gravity. If you could hold your speed constant during a loop, roundness would be a matter of staring at the G-meter and adjusting your stick force to maintain a constant G value. The trouble is that speed doesn’t stay constant, but decreases in the climbing part and increases as you come back down. (Your exit speed, by the way, is always a bit lower than your entrance speed, due to the induced drag those Gs cost.) Because of the change in airspeed during the loop, you have to vary the G-force to maintain a constant radius. In practice, you pull pretty hard at the start because you’re going fast, ease up over the top because you’re slowing down, then start pulling hard again as the nose passes through vertical and comes back up to the horizon.

The problem with roundness is that as a pilot you can learn to infer it, but can’t actually see it. You are yourself within the phenomenon you’re trying to observe. To remove this epistemological roadblock you need help from an aerobatic coach on the ground, to see the loop for you and keep you apprised on the hand-held. If your coach radios “flat spot,” your pitch rate (thus G) was too low for your airspeed. If your coach says “pinched,” you pulled too hard—your pitch rate was too great for your airspeed. Eventually, if you have a good coach and aren’t a complete dullard, you learn to associate each part of the loop with its appropriate pitch rate—at least from a given starting speed, and at least in calm winds. When the wind is blowing you have to compensate by increasing your pitch rate if the wind is behind you in the loop, and by decreasing it if the wind is ahead. Windy conditions are a pain.

In an aerobatic competition, big loops tend to score badly because the judges can easily see variations in radii (flat spots and pinches). If you’ve got a fast airplane, you’ll have to pull pretty hard initially to keep the loop from getting too big. When I had my little Giles G-200, which was fast, I was pulling 6-G loop entries in an effort to keep them small. That was during my irresponsible period, but at least I slept well. Training in the Flightlab Zlin or Air Wolf, we pull about 3 G entering a loop, and maybe 0.5 G floating over the top.

Keeping the wings level with the horizon isn’t easy, either. Imagine you’re beginning a loop from a slight bank angle. Model this with your hand. As a banked aircraft pulls from level flight to vertical, one wing will end up lower than the other. In other words, after ninety degrees of pitch-up, an initial roll error becomes an error in yaw. If you just continue merrily along, that yaw error will again become a roll error, ninety degrees later, at the top of the loop. That roll error, in turn, becomes a yaw error as you head through vertical on the backside. Finally, as the nose returns to the horizon, the aircraft is again banked and you’re no longer headed in the direction in which you started.

All aerobatic maneuvers are extremely sensitive to initial conditions. In other words, if you screw things up at the start you have to work extra hard to make things come out happily in the end. Most beginning aerobatics students have a tough time keeping the wings level on the initial pull into a loop. With the right hand on the stick, there’s often a tendency to pull slightly to the right when pulling back. Sometimes it’s hard to track the resulting bank error, because the nose rises quickly above the horizon and the familiar roll references pass from view. In a loop, once you lose the horizon ahead, you look at the wingtip in order to judge attitude and position in the maneuver. If a wing is up or down when you hit vertical, a quick jab on the rudder can make things right. But it takes practice to learn where to look to identify errors, to recognize them, and then quickly to make the fix. Eventually, you pick up errors right as they begin. Then small, easy corrections are all you need.

I like to remind my sometimes-frustrated aerobatics students that you can’t learn to see errors unless you make errors. So lighten up. It’s all data, and it’s all useful if you’re willing to persist. I’ve noticed that good aerobatic learners take their mistakes more or less in stride. They don’t hurl a fit or have smoke come out of their ears. There’s no ego to nurse. They understand the relationship between making errors and making it to the next level.