**4.4 Aerobatics:**

Special nature of aerial application flying

Flight profile (G exposure, push-pull effect)

Spatial disorientation

Thermal stress

Crash survival and crash worthiness

Aerobatic flying, is a specialized form of flight, where the aircraft\'s
performance and attitudes change rapidly. Aerobatics are governed by
special aspect of FAR 91.303, which requires aerobatics to be performed
in a specified box of air space, and requires that the aircraft be
certified for acrobatic flight and a utility rating and that the
pilot(s) wear parachutes. The flight profile is beyond normal operations
for whatever class of aircraft and may involve rolls, loops, stalls and
generation of smoke trails. Acrobatic flight has special hazards due to
acceleration affects and orientation problems for the pilots as well as
avoidable hazards for spectators. You will understand the risks involved
in this aspect of aviation and be able to counsel pilots and airshow
participants for safety issues.

Aerobatic flight is an intentional maneuver involving abrupt change in
an aircraft\'s

attitude, an abnormal attitude, or abnormal acceleration, not necessary
for normal flight. FAA Regulation Part 91 (General Operation and Flight
Rules), Subpart D, section 303 regarding flight over inhabited areas or
over people, requiring flight more than 1,500 feet above ground and
governs acrobatic flight operations limiting flight to visual flight
rule (VFR) conditions. Section 51 also requires the use of parachutes,
and defines aerobatics as banks over 60^o^, pitch attitudes over 30^o^
and prohibits carrying passengers. Aerobatics vary by aircraft type. A
glider can perform aerobatics by a simple loop or roll, while a steep
nose-high pitch-up constitutes acrobatics in a helicopter. Aerobatic
maneuvers constitute normal operations in agricultural (Utility)
aircraft but are virtually unknown in passenger jets (although a Boeing
707 was rolled in a 1959 flyby).

Basic maneuvers include the loop, roll and stall. A loop is simply
flight where the nose of the aircraft is pitched up (or down in an
outside loop) until the aircraft has completed 360^o^ of rotation. Basic
physics dictate that the aircraft will experience at least 2 Gz of
acceleration on the bottom of the loop. Entrance speed must be
significantly above stall speed so that as speed is lost during the
climb, it does not drop below stall speed and maneuverability is
maintained. In theory, the acceleration level can drop to 0 Gz at the
apex of the loop, but no pilot does this in practice and normally a
pilot will maintain excess speed and positive Gz will be experienced
through the entire maneuver. Performed at high speed, the accelerations
can be much higher in all aspects of the maneuver, pitch-up,
over-the-top, pitch-over and pullout. If the speed is too high, the Gz
can be excessive anywhere in the loop, but particularly during pullout
with the possibility of loss of consciousness due to G-LOC (see
Sustained Acceleration). The maneuver is accomplished entirely with
horizontal elevator control changes and when performed properly, the
entrance and exit altitudes are the same. In the outside loop, the nose
is pitched down and negative Gz is maintained throughout; this is
uncomfortable for the pilot and potentially dangerous if Gz forces are
high enough.

![](media/image3.wmf)

**The Loop-360^o^ of pitch change**

The roll is an aileron maneuver. The ailerons are deflected to start the
aircraft into a bank as in a turn, but no elevator or rudder is applied.
The aircraft will roll about its longitudinal axis. However, there is
always loss of altitude during this maneuver, as lift is lost when the
wing is not parallel to the ground. Therefore the maneuver is started
slightly nose high and ends slightly nose low. Use of rudder during the
maneuver to keep the nose up also reduces loss of altitude. There is
minimal speed change and accelerations vary from slightly above 1 Gx
when horizontal to +1 Gz while at 90 ^o^ to -1 Gz while inverted and -1
Gz at 270^o^. However, the roll itself induces Gy accelertations. The
direction of flight does not change.

![](media/image2.wmf)

**The Roll-360^o^ of Bank Attitude Change**

The Barrel Roll is a variation of the basic Roll. Here the pitch of the
aircraft does change and nose describes an arc around a point. The pilot
will initiate a roll with ailerons, but also pulls up the nose and
maintains elevator pressure, resulting in nearly constant acceleration,
typically +1.5 Gx, through the maneuver. The result is a full roll of
360^o^ while describing a spiral path through space. No altitude is
lost. Other variations on the Roll include 8-point or 16-point Rolls,
where the pilot will pause the maneuver every 45^o^ or 22^o^
respectively. Snap Rolls are simply a roll performed very rapidly, and
Slow Rolls are where the maneuver is drawn out.

Other maneuvers combine the Roll with a Loop to form figures in space
such as an "8" or a cloverleaf. Still another acrobatic maneuver is the
Stall, where the aircraft speed is slowed enough that lift is lost,
usually by performing a near-vertical climb. The aircraft stops flying
and falls, usually pitching nose over. This causes airspeed to increase
to above stall speed and flight resumes. Obviously all these maneuvers
require considerable skill and training, as failure to perform or
recover from the maneuver will result in a crash. While the maneuvers
described above can be performed with modest G profiles, most pilots
vary this considerably. Their flight profile causes significant
variation in G exposure, usually to high G during pullouts, as high as 6
Gs during some civilian maneuvers, although military aerobatics jets are
capable of over 9 G maneuvers (see Sustained Acceleration).

Keep in mind, that this compares to a standard 30 degree bank turn of
about 1.3 Gz, and a "steep" 60^o^ level turn yields only +2 Gz. Maneuver
variations can induce additional yaw with Gy loads, particularly during
Snap Rolls, and a pilot who is not stabilized in the seat can strike
their head against the canopy during these maneuvers. The high G
exposure may cause stasis of blood flow and G-induced loss of
consciousness (G-LOC). There is also a "push-pull effect", where the
pilot rapidly changes the loading from positive to negative Gs. This may
induce spatial orientation problems which are inherent to aerobatics, as
well as slowing the cardiovascular response to high G loads when
returning from zero or negative Gs (See Spatial Orientation). Aerobatics
training is required by a certified instructor, and rolls in
performances during air shows are extremely strict.

In addition to spatial disorientation, thermal stress may occur, as many
aerobatic aircraft have large glass canopies, and performances are often
on hot summer days. The combination of greenhouse effect with the
vigorous physical activity from flying and straining can produce a
significant heat load, which in turn may produce mild dehydration and
reduce G tolerance.

Aerobatics may not be performed over inhabited areas. During air shows
acrobatics may not be performed over a crowd or flown towards a crowd.
Failure to follow these rules led to massive spectator casualties during
an air shows at Ramstein, Germany in 1989 and in the Ukraine in 2002
(below).

![](media/image3.png){width="3.6458333333333335in" height="2.71875in"}

There has never been as fatality in an aerobatic competition, although
accidents during air shows are unfortunately frequent, usually due to
the tendency of a pilot to "over perform", and misjudge their height
above ground, or location relative to another aircraft. Additional
permission must be obtained to use smoke generators. Some colored smokes
include oils and volatiles that can drift down, coating buildings and
onlookers, and cause skin and respiratory irritation.

![](media/image4.png){width="5.55in" height="3.6166666666666667in"}

Aircraft and their engines must have certifications to withstand the
increased loads and unusual attitude induced by aerobatic maneuvers.
Certified acrobatic aircraft include Citabria, Cessna C150 Aerobat,
Decathlon, and Pitts S-2A/B. Specialized acrobatic aircraft used for
performances and competitions include the Extra and Sukhoi. Pilots only
need appropriate certificates and medical certification for the aircraft
they are flying. Performance for remuneration is usually a commercial
activity and would require a commercial pilot's license and a
second-class medical certificate.

![](media/image5.png){width="5.25in" height="3.65625in"}

WORLD CHAMPION PATTY WAGSTAFF PERFORMING IN HER

**EXTRA 300S**

One characteristic of all aerobatic aircraft is a low wing load. This
means that the weight per square foot of aircraft wing area is quite
low, sometimes, on the order of 2 pounds per square foot, and often
one-tenth that of a standard non-aerobatic aircraft. This effect permits
the aircraft to make "sharp turns", and greatly enhances performance.

In order to reduce the weight of the aircraft to meet some of these
standards, however, some other safety features, such as a protective
cage for the pilots is reduced to minimum. Due to the possibility of
accidents during aerobatic flight, pilots are not only required to wear
a parachute, but will frequently wear fire protective garments made of
Nomex to enhance post crash survivability.

Reference: International Aerobatic Club and Experimental Aircraft
Association.