basic figures: let's loop, turn & roll
All aerobatic figures, however complicated they may look when flown, are comprised of a only few basic elements. It is well worth one's time to master each basic figure, before moving onto more complicated, combined maneuvers. A lack of understanding and expertise in the most basic elements will be revealed as one progresses through the competition levels where technique and energy-management become key.
Let's look at some of these basic elements.
There are three types of lines flown in competition: horizontal, vertical and 45 degrees.
Horizontal lines are judged on flight path, which should show level flight – not climbing or descending – across the box. In the cockpit, you will want to develop a sight reference to the horizon for your particular aircraft that will help you stay level. When inverted, this sight picture will change due to a more nose-up attitude and it is helpful to use the altimeter to maintain your altitude as you are more likely to climb on an inverted line. An area to watch for altitude loss is when capping off from a 45 or vertical line into a spin. You will most likely be slow, so there is a tendency for the plane to "settle" and descend before you enter the spin.
Vertical lines are judged on the aircraft's "zero-lift axis." This is the attitude where the wing is producing no lift and the flight path is exactly 90° to the horizon up or down. This is complicated to judge, however, because often the wing and its relationship to the longitudinal axis, or body, of the aircraft are not square and the zero-lift axis doesn't line up with the tail. An example would be a Decathlon. Sighting devices on your wings can help you with alignment (if they themselves aligned) as well as a ground observer. The common errors here are being slightly pitched forward, called "positive," or being slightly on your back, called "negative." If you are too negative on a hammerhead or very slow and add control inputs, it is possible to fall backwards into an inverted spin. And if you try to add a roll to a vertical line that isn't exactly vertical, the wingtip will not scribe a perfect circle, rather a scallop.
Forty-five degree lines are also judged on the zero-left axis. In theory, these lines should be a perfect 45° angle to horizontal. In practice, winds will cause these lines to appear more shallow if downwind, or more steep if flying upwind. This wind effect should be ignored by the judge, who may fold a piece of paper and hold it up as a device by which to verify the 45° angle. Rolls are introduced earlier here than on vertical lines, for example on a Half Cuban, and the challenge is to keep the line the same before and after the roll. It is common for a line to "steepen" or "shallow" after the roll if correct inputs are not applied.
All lines should be flown parallel to the x- or y-axis on which they are located.
Is there a better description for aerobatics than doing "loop de loops"?
The loop is, of course, a circle flown in the vertical plane. But flying a perfect loop is more difficult than it first appears. The airspeed at the bottom is much greater than the airspeed over the top, which can require you to "float" in an almost 0g arc as you let momentum carry you over. The amount of back stick used varies, and a common error is to "pinch" part of the loop because of too much pull. And, like lines, the wind can have an effect on the shape, causing the circle to narrow into an "L-shape" or widen into an oval. The loop judging criteria states that the entry and exit altitudes be the same, so another common error is to fly an "E-shape" loop that is "out low" or "out high."
Partial loops are found everywhere. The transition between a horizontal line to a vertical is a 90° segment of a loop. A Half Cuban has a 3/4 loop and the Humpty Bump, a half loop. The concept of flying a round circle still applies with the partial loops – the radius must be consistent. Some figures such as a Square Loop, which is really four equal lines, require that the corner radii be the same.
A look at flying a loop from Gordon Penner, IAC Chapter 34.
Loops and lines would get pretty boring without rolls. There are four types of rolls: aileron, barrel, slow and snap. Only the latter two are used in competition.
An aileron roll is initiated by pulling the nose up and then rolling with aileron, while a competition slow roll does not allow the nose to rise before the roll and requires the aircraft to fly a straight line. Judging criteria for a slow roll require a constant rate of rotation and a straight flight path (except on a loop). Common errors include "barreling" the flight path, which means the nose rose or dropped away from the straight line, or changing the roll rate, often in the last half when transitioning from inverted to upright. A slow roll requires a myriad of control inputs – you use both stick and rudder – and the figure is quite uncoordinated.
A barrel roll is a gentle corkscrew maneuver that combines a loop and a roll and is often seen flown in formation at airshows. We don't fly it in competition.
A snap roll isn't really a roll, it is an accelerated horizontal spin. One wing is momentarily stalled and the plane rotates aggressively around its longitudinal axis. A snap is stopped just like a spin, with opposite rudder. These do not appear in IAC competition sequences until the Intermediate level, and some aircraft are not certified to perform them. Snaps are the one maneuver flown below the aerobatic maneuvering speed as they can require full deflection of multiple control surfaces. They can be both "positive" or "inside" if initiated with a pull, or "negative' or "outside" if initiated with a push. They can also be flown as partial full-rolls, i.e. 1/2, 3/4 , 1 1/4.
Slow rolls may be further divided into hesitation or "point" rolls. A full roll could be thought of as 1-point. A 2-point roll means that you fly half a roll or 180°, pause, then fly the other half. A 4-point roll would be 90° segments separated by pauses and a 8-point roll, 45° segments. These look like the hands of a clock stopping on the way around a circle. These full point rolls can be divided even further into partial rolls such as 2x4, which is two 90° segments and if started upright, would end inverted. The common error on point rolls is to not pause and hold the point long enough, which is referred to as a "soft" point. Or you can just miss a point entirely, which is scored as a hard zero.
All about rolls from Gordon Penner, IAC Chapter 34.
To most pilots, a steep turn has a 45° to 60° bank. They are practiced as maneuvers for practical flight tests and not flown that often afterwards I'd hazard to guess. To aerobatic pilots, a competition turn requires a minimum of 60° bank and will likely be much greater. If you recall your flight lessons, there is an overbanking tendency in steep turns whereby the plane wants to keep rolling into the bank, and, if your instructor happened to know their stuff, you'd have learned that it is the elevator, thus a pull, that causes the plane to turn. In aerobatics, this knowledge is incredibly useful to understanding the competition turn.
A competition turn requires that you bank the plane, pause, pull it around in the turn, pause, and unbank to level flight. There is no blended entry like as is taught in private and commercial maneuvers. Because the plane wants to overbank at such a steep angle, you will probably require some rudder to hold it level during the pause. Then, once you start pulling, it is just like the normal steep turn in that a point over the nose should be kept on the horizon. A competition turn is not a coordinated maneuver and the ball will not be centered. Airspeed will increase the radius of the turn, and the very steep bank will require sustained Gs. Common errors are the blending of bank and pull, and climbing or descending in the turn.
Turns may be flown as 90°, 180°, 270° or the rarely seen 360°. They may be upright, positive-g, or inverted, negative-g, where you push around the outside of the turn. They may also be combined with rolls to create the rolling turn, which is possibly the most confusing figure to learn how to fly! The rolling turn, or "roller," can be "inside" – meaning a positive-g pulled turn – or "outside," a negative-g pushed turn. The rolls can be in the same or opposite direction as the turn itself.
The spin is not only a competition maneuver, but it is also a hazard that can result from a botched maneuver. Competency in spin recovery, both upright and inverted, is an absolute requirement for both recreational and competition aerobatic flying. There are many spin/upset recovery courses taught in the U.S. and internationally – run, don't walk, and complete one of the courses before trying any aerobatic maneuvers.
The competition spin is a highly-choreographed figure and has little besides autorotation in common with a spin recovery situation. The competition spin requires that the aircraft stall and rotate about all 3-axes at the same time. This means the nose drops, the wings roll and the body yaws in the direction of the spin. Spins may be one-turn or add quarter-turn segments, such as 1 1/4 or 1 1/2. At the prescribed turn exit, the aircraft must stop the spin and assume a vertical down line with wings level. Spins may be entered upright or inverted, and are one of greater altitude-losing figures in a sequence. Common errors included "forcing" the spin to occur, which usually results in the nose popping up and a snap-like entry, and rotating past the exit point and rolling back to the exit heading, which is called "over and back."
There are some unique figures that are classified on their own. The two most seen in competition are the hammerhead and the tailslide.
The hammerhead is a vertical up with a pivot near stalling (but not stalling, despite the British term "stall turn") at the apex, followed by a descending vertical line. The "hammer" requires that the aircraft rotate in the vertical plane so that it looks like someone stuck a pin in the wing and turned the aircraft to point downward. There can be considerable technique involved with rudder and stick, but once learned it is a enjoyable figure to fly well, and it can be combined with rolls on the up and down lines.
The tailslide is an advanced maneuver that is not usually seen in competition until the Unlimited level. Unlike the hammerhead, the tailslide is flown until the plane has no upward momentum left, then it falls/slides backwards, flops over – either canopy or wheels up – and does a pendulum-type swing at the bottom before setting a down line. Like the snap roll, some aircraft should not perform tailslides as damage to the elevator may occur.
Overall, these are the elements and maneuvers are the base of all aerobatic figures. Loops may be combined with lines. Rolls and spins added to increase complexity. Get good at the basics (well, maybe not tailslides just yet), and you'll be starting off right.
by Susan Bell, IAC #438132