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Pilot's Handbook of Aeronautical Knowledge
Aerodynamics of Flight
Load Factors

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Pilot's Handbook of Aeronautical Knowledge



Table of Contents

Chapter 1, Introduction To Flying
Chapter 2, Aircraft Structure
Chapter 3, Principles of Flight
Chapter 4, Aerodynamics of Flight
Chapter 5, Flight Controls
Chapter 6, Aircraft Systems
Chapter 7, Flight Instruments
Chapter 8, Flight Manuals and Other Documents
Chapter 9, Weight and Balance
Chapter 10, Aircraft Performance
Chapter 11, Weather Theory
Chapter 12, Aviation Weather Services
Chapter 13, Airport Operation
Chapter 14, Airspace
Chapter 15, Navigation
Chapter 16, Aeromedical Factors
Chapter 17, Aeronautical Decision Making




An entirely different situation exists in aircraft design with
maneuvering load factors. It is necessary to discuss this matter
separately with respect to: (1) aircraft designed in accordance
with the category system (i.e., normal, utility, acrobatic); and
(2) older designs built according to requirements which did
not provide for operational categories.

Aircraft designed under the category system are readily
identified by a placard in the flight deck, which states the
operational category (or categories) in which the aircraft
is certificated. The maximum safe load factors (limit load
factors) specified for aircraft in the various categories are:
Normal1 3.8 to –1.52
Utility (mild acrobatics, including spins) 4.4 to –1.76
Acrobatic 6.0 to –3.00

For aircraft with gross weight of more than 4,000 pounds,
the limit load factor is reduced. To the limit loads given above,
a safety factor of 50 percent is added.

There is an upward graduation in load factor with the
increasing severity of maneuvers. The category system
provides for maximum utility of an aircraft. If normal
operation alone is intended, the required load factor (and
consequently the weight of the aircraft) is less than if the
aircraft is to be employed in training or acrobatic maneuvers
as they result in higher maneuvering loads.

Aircraft that do not have the category placard are designs that
were constructed under earlier engineering requirements in
which no operational restrictions were specifically given to
the pilots. For aircraft of this type (up to weights of about
4,000 pounds), the required strength is comparable to present day
utility category aircraft, and the same types of operation
are permissible. For aircraft of this type over 4,000 pounds,
the load factors decrease with weight. These aircraft should
be regarded as being comparable to the normal category
aircraft designed under the category system, and they should
be operated accordingly.

Load Factors in Steep Turns
In a constant altitude, coordinated turn in any aircraft, the
load factor is the result of two forces: centrifugal force and
gravity. [Figure 4-44] For any given bank angle, the ROT
varies with the airspeed—the higher the speed, the slower the
ROT. This compensates for added centrifugal force, allowing
the load factor to remain the same.

Two forces cause load factor during turns.
Figure 4-44. Two forces cause load factor during turns.

Figure 4-45 reveals an important fact about turns—the load
factor increases at a terrific rate after a bank has reached
45° or 50°. The load factor for any aircraft in acoordinated
level turn at 60° bank is 2 Gs. The load factor in an 80° bank is
5.76 Gs. The wing must produce lift equal to these load factors if
altitude is to be maintained.

It should be noted how rapidly the line denoting load factor
rises as it approaches the 90° bank line, which it never quite
reaches because a 90° banked, constant altitude turn is not
mathematically possible. An aircraft may be banked to 90°,
but not in a coordinated turn. An aircraft which can be held in
a 90° banked slipping turn is capable of straight knife-edged
flight At slightly more than 80°, the load factor exceeds the
limit of 6 Gs, the limit load factor of an acrobatic aircraft.