Aerial Acrobatics FAQs

What types of airplanes are approved for aerobatics?

First I want to emphasize that you should do aerobatics only in airplanes that are approved for aerobatics. It is potential suicide to try aerobatics in any other airplane. Other planes are not stressed for this type of maneuvering and they WILL break. Please don't do it!

A list of aerobatic airplanes is available at http://acro.harvard.edu/IAC/acro_planes.html with a summary of their features. If you know any of the numbers that are missing, or know of any other aerobatic airplane (not one-of-a-kind planes though) please let me know about it.

Which aerobatic plane to use is almost a religious question, but here are somepointers: The most common aerobatic planes for beginners are probably:

• Citabria
• Decathlon
• C-150 Aerobat

For more advanced aerobatics the most popular trainer is probably the Pitts S-2A or Pitts S-2B. Most other higher performance aerobatic planes are experimental and cannot be used for regular flight instruction.

Now on which trainer should you get started? It depends on various things, not the least on the amount of money that you want to spend. Here are some rough figures for hourly rates:

• Citabria: $60 - $90
• Decathlon: $70 - $120
• C-150 Aerobat: $50 - $80
• Pitts S-2A: $130 - $200
• Pitts S-2B: $160 - $220

It obviously is much less costly to get started in a Citabria or a Decathlon than in a Pitts. And both are good enough to teach the basics of aerobatics. The C-150 Aerobat is very limited in the type of aerobatics it can do. It seems to be a consensus on the IAC e-mail list that it makes sense to get started in one of these trainers and then move up to a Pitts to work on more advanced aerobatics.

What types of rolls are there?

There are four different types of rolls:

• Aileron Roll
• Slow Roll
• Snap Roll or Flick Roll
• Barrel Roll

What is an Aileron Rolls?

During an aileron roll, the airplane rotates 360 degrees around its longitudinal axis while the nose remains pointed at a specific reference straight ahead. In other words, the airplane "twirls" around a line drawn from the tip of the nose to the tail, as if you held your outstretched arm straight and rotated your wrist and elbow.

Throughout this maneuver, look straight ahead at a cloud, mountain peak, or other reference that I point out.

As the aileron roll begins, I pull the nose up 20–30 degrees above the horizon. I then stop the pitch-up and move the stick to the left or right, depending on the direction of the roll. As the wings bank, I keep the nose pointed at the reference and let the airplane fly through a smooth arc. The maneuver ends with the wings level and the nose still pointed at the reference, but about 20 degrees below the horizon. We start with "half-stick-deflection" rolls and then, if you're up for it, we'll do faster rolls (the Extra can roll at about 400 degrees/second—i.e., a complete rotation in less than a second) later in the ride.

What is a Slow Roll?

Slow rolls have to be flown normally on a straight line (exception is the avalanche). The roll rate has to be constant and the longitudinal axis of the plane has to go straight. This requires constantly changing rudder and elevator control inputs throughout the roll. Hesitation or point rolls include stops at certain roll angles. The number on the base of the roll symbol describes the number of points the roll would have if it were a 360 degree roll. Allowed are 2 point, 4 point and 8 point rolls. The fraction on the arrow of the roll symbol describes what fraction of a full roll is to be executed. If no points are specified, rolling is done without hesitations. If no fraction is specified, a roll symbol that starts at the line specifies a half roll (see description of the Immelman). A roll symbol that crosses the line specifies a full roll (first figure). The second figure shows the symbol for 2 points of a 4 point roll (adding up to half a roll) from upright to inverted flight.

What is a Snap Roll?

Snap or flick rolls also have to be flown normally on a straight line. A snap roll is similar to a horizontal spin. It is an autorotation with one wing stalled. In the regular snap, the plane has to be stalled by applying positive g forces. In an outside snap, the plane is stalled by applying negative g. In both cases rudder is then used to start autorotation just like in a spin.

What is a Barrel Roll?

A barrel roll is a combination of a loop and a roll (often confused with the aileron roll, the barrel roll is a different animal). There are several ways to fly a barrel roll, but during an aerobatic ride, we'll use the following procedure:

From level flight, I pull the nose up smoothly but quickly to 45 degrees above the horizon. As the nose reaches the 45-degree point, I start a smooth roll (usually to the left) while gradually increasing the pull to start a loop. I continue the maneuver by using aileron, elevator, and rudder inputs to maintain a constant, smooth rate of change in both pitch and roll. As we reach the inverted position at the top of the "loop," the wings should be level and the nose should be on the horizon, with our heading 90 degrees from our original direction. The maneuver continues with the nose falling through the horizon as the airplane rolls back toward wings level. The barrel roll ends, like a loop, with the airplane returning to level flight on its original altitude and heading.

You should look around during a barrel roll, which ideally is a smooth, graceful maneuver. Enjoy the view as the world goes upside down, but make sure you look straight ahead as we fly through the top (inverted) portion of the maneuver. It's always cool to see "the earth above and the sky below."

What is a Wing Over?

The Wing-Over is a competition maneuver in glider aerobatics. You pull up and at the same time bank the plane. When the bank increases past 45 degrees, the nose will start to drop while the bank keeps increasing and the plane keeps turning. Halfway through the maneuver, the plane has turned 90 degrees, the fuselage is level with the horizon and the bank is 90 degrees. The plane is above the original flight path. The nose then keeps dropping below the horizon and the plane keeps turning, while the bank is shallowed. When the bank drops below 45 degrees, the nose is pulled up towards the horizon and the plane reaches horizontal flight with wings level after 180 degrees of turn. At the completion of the maneuver, the plane is at the same altitude as on entry and flying in the opposite direction.

What is a Hammerhead?

It starts with a quarter loop into a vertical climb. When the plane stops climbing, it pivots around its vertical axis (which is now horizontal).The nose moves in a vertical circle from pointing up through the horizon to pointing down. After moving vertically down to pick up speed again, the maneuver is finished with the last quarter of a loop to horizontal flight. This figure can have optionally rolls on both the up-line and the down-line.

The quarter loop is flown just like the first part of a loop. When the plane is vertical, the elevator backpressure is released completely. During the vertical line up, some right aileron and right rudder is needed to maintain the vertical attitude because of the engine torque and p-factor. When the plane has slowed enough, full rudder initiates the turnaround. It is followed by right-forward stick (right aileron and forward elevator) to keep the plane from torquing off. The pivot is stopped with opposite rudder when the nose points straight down. When the pivot is completed, the ailerons and rudder are neutralized. Elevator and rudder are used to keep the nose pointing straight down. Thee pivot must be completed within one wingspan. Rolls on the downline require only aileron input if the plane is trimmed correctly.

This maneuver is sometimes called a hammerhead stall. This is not an accurate name because the airplane never stalls. The airspeed may be very low, close to zero, but since there is now wingloading during the turn-around, there is no stall (at zero g wing loading, a wing does not stall). The plane is flying throughout the maneuver with all the control surfaces effective (even sometimes only marginally so).

The previous paragraph is true even for gliders that don't have the support of the propeller slip stream. The missing slip stream makes it much more difficult to keep some flow over the control surfaces during the turn-around in a glider.

What is the Aerobatics Box?

The aerobatics box is the area in which aerobatics competitions take place. The competitor has to stay within the lateral limits of the box and within the height limits. During competition there are boundary judges in place that determine when a competitor leaves the box. Boundary infringement penalties subtracted from the score in such cases. The dimensions of the aerobatics box are as follows:

Lower limits:

1500' AGL: Basic and Sportsman Categories
1200' AGL: Intermediate
800' AGL: Advanced
328' (100m) AGL: Unlimited

Upper limits:

3280' (1000m) AGL: Unlimited
3500' AGL: All Others

Lateral dimensions:

3300' x 3300' centered on the judges line.

The lower limits of the box are, for safety reasons, strictly enforced.

How do I find an instructor?

The IAC maintains the most comprehensive list of aerobatics schools. If you have a World Wide Web browser, you can access the list at http://acro.harvard.edu/IAC/schools.html. It is also periodically published in the IAC magazine, Sport Aerobatics. You can also call IAC at (414) 426-4800 and ask for a list of local schools. In addition to names, locations and phone numbers, the IAC list also includes aircraft types and rates used by each school. Note that inclusion or exclusion from the list does not constitute any sort of endorsement or qualification by IAC.

If you don't find what you're looking for on the IAC list, the next step might be to contact a nearby IAC chapter and ask for recommendations. A list of IAC chapters is on the World Wide Web at http://acro.harvard.edu/IAC/chapters.html, or you can call IAC at the number listed above.

Of course, you can always ask around at your local airport, or put out a request on the rec.aviation newsgroups.

Once you've found a school, check them out! This can't be stressed enough. Get references from pilots who have taken instruction with them. Find out how long they've been in business, and how much and what type of aerobatics experience they have. What kind of a reputation do they have? Are they self-taught weekend warriors who recently bought an aerobatic airplane, or are they Unlimited-level competition pilots with 20 years of experience? What kind of airplanes do they fly? What condition are they in? Have they had any accidents? Will they rent the airplane to you (solo) after you've completed the course?

Will I feel sick?

Aerobatics entail forces and visual situations that are new to just about everyone. Each person will respond differently to these. Typically, on your first few flights you may feel queasy after some number of maneuvers. With each flight, your tolerance will build and you will feel a bit better and better, until you eventually find that you feel perfectly fine at the end of a flight. Don't let the initial discomfort discourage you. It's natural, and the end result is well worth it! The more often you practice, the higher your tolerance will become.

There are a few ways to minimize the discomfort. The first is to know when to quit. Once you start feeling queasy, flying one or two more maneuvers is a great way to get yourself sick. Instead, take the controls. This will help take your mind off of how you're feeling, and will also help your brain resolve what it's feeling with what it's seeing. Fly straight and level for a few minutes. Open the vents wide, and keep your eyes looking outside the cockpit. If you continue to feel sick, you may want to think about landing.

You'll probably also find that when you fly the maneuvers yourself, you won't feel bad as quickly as if someone else (i.e.- your instructor) is flying. This is probably because when you're handling the controls, you have a better idea of what to expect. Seating position is also a factor. For example, people seem to do better in the front seat of a Decathlon than in the rear.

Do I have to wear a parachute when I do aerobatics?

Wearing parachutes for aerobatics flying is regulated in FAR 91.307. It specifies that whenever you carry a passenger, you may not exceed 60 degrees of bank or 30 degrees of pitch up or pitch down unless both occupants wear an approved parachute. This means that you do not have to wear a parachute when you fly alone. It does not say anything about aerobatics, it just specifies the bank and pitch limits. So any maneuver that exceeds these limits falls under this rule and requires you and your passenger to wear a parachute.

The rules for aerobatics differs from country to country. In Sweden for example an aerobatic pilot is requred to complete a ten hour training course and parachute is mandatory for every flight.

About G's

Aerobatics look graceful from the ground, but when you fly or ride through the maneuvers, you experience positive and negative Gs—multiples of the force of gravity. If you've ridden a roller-coaster or been pressed back in your seat during a rapid acceleration in a car, you've experienced Gs, albeit relatively mild, generally positive-only Gs.

During a typical aerobatic ride, you'll experience a maximum of 3–4 positive Gs (i.e., 3–4 times the normal force of gravity) and a minimum of about –1G.

Unlike jet fighter pilots, who have the engine power to sustain high G for extended periods, those of us who fly small piston-engine aerobatic airplanes can't maintain high-G loads for more than a few seconds. The airplane runs out of energy when it is highly loaded. By the way, that's one reason we don't wear G-suits. The other is that those suits require complicated sensors, air compressors, and other gizmos that aren't practical in the types of aircraft we fly. Aerobatic pilots must stay in reasonably good physical condition and gradually develop (and then fly regularly to maintain) G tolerance. To learn more about Gs while flying aerobatics, see the following Advisory Circulars from the FAA:

Acrobatics—Precision Flying with a Purpose (AC 91-48) G Effects on the Pilot During Aerobatics (FAA-72-AM-28) A Hazard in Aerobatics: Effects of G-Forces of Pilots (AC 91-61)

How safe is aerobatics?

Many (most?) people contemplating getting involved in aerobatics feel a bit apprehensive at first. By it's very nature, aerobatics involves risks that are not involved in non-aerobatic flight. But as with most anything else in aviation, it is only as safe or dangerous as the pilot makes it. Discipline, planning, common sense, and knowledge are basic prerequisites to safety. Aerobatics can be quite safe if certain safety rules are followed religiously.

Examples include:

• Get proper training, especially in all types of spins and botche maneuvers.
• Fly at a safe and conservative altitude.
• Know your equipment and yourself, and keep both well maintained.
• Don't overstress the airplane (and never fly aerobatics in non-aerobatic aircraft).
• Always perform a proper, thorough aerobatic preflight.
• Set and observe strict personal limits (altitude, g-limits, flight duration, health, etc).
• Stay current and take recurrency check rides.
• Don't run out of fuel! (should be obvious, but it happens a lot)
• Stay clear of conflicting traffic, either with regular clearing turns or an observer on the ground.
• Know how to handle emergency situations.
• Always leave yourself a way out.
• Always wear a parachute. Know how to bail out and use it.
• Learn by others' mistakes, not your own.

An example of how safe aerobatics can be is that there has never been a fatality in IAC-sanctioned competition, where strict safety rules are always followed.

The penalty for ignoring safety procedures can be quite high. A review of NTSB accident data for the 8KCAB Decathlon (probably the most common aerobatic trainer) from 1983 through 1993 shows 14 accidents related to aerobatics. Eight of them involved attempting aerobatics at low altitudes. One was caused by lack of training, one by lots of unsecured loose baggage (ie- lawn chairs and more) floating around the cockpit, and one by structural failure. Causes of the remaining three are less clear from the reports, but two appear to have been due to low level aerobatics, and the third by failure to recover from a spin. So, of the 14 accidents in ten years, all but one (structural failure) could have been prevented by following the few simple rules listed above. The structural failure was in a known problem area and *might* have been avoidable if the pilot was more familiar with his equipment.

With higher performance aircraft and more advanced aerobatics, there are additional risks. The airplanes are less forgiving, the forces on plane and pilot are higher, some of the equipment is newer and less proven, and much of the flying is done at lower altitudes. Also as skills and experience build, complacency and bad habits can begin to creep into the picture. By the time you get to this level, you won't need this FAQ to learn how to manage these risks.

One thing is for certain. Once you have learned to fly aerobatics, your increased knowledge will make all the rest of your flying safer.