Small Unmanned Aircraft Loading Part 2

Small Unmanned Aircraft Loading Part 2

In aerodynamics, the maximum load factor at given bank angle is a proportion between lift and weight and has a trigonometric relationship. The load factor is measured in Gs (acceleration of gravity), a unit of force equal to the force exerted by gravity on a body at rest and indicates the force to which a body is subjected when it is accelerated.

Any force applied to an aircraft to deflect its flight from a straight line produces a stress on its structure. The amount of this force is the load factor. While a course in aerodynamics is not a prerequisite for obtaining a remote pilot certificate, the competent pilot should have a solid understanding of the forces that act on the aircraft, the advantageous use of these forces, and the operating limitations of the aircraft being flown.

For example, a load factor of three means the total load on an aircraft’s structure is three times its weight. Since load factors are expressed in terms of Gs, a load factor of three may be spoken of as 3 Gs, or a load factor of four as 4 Gs. With the structural design of aircraft planned to withstand only a certain amount of overload, a knowledge of load factors has become essential for all pilots.

Load factors are important for two reasons. 1. It is possible for a pilot to impose a dangerous overload on the aircraft structures. 2. An increased load factor increases the stalling speed and makes stalls possible at seemingly safe flight speeds.

At a constant altitude during a coordinated turn in any aircraft, the load factor is the result of two forces: centrifugal force and weight. For any given bank angle, the rate of turn varies with the airspeed. The higher the speed, the slower the rate of turn.

Small Unmanned Aircraft Loading Part 2

This compensates for added centrifugal force, allowing the load factor to remain the same. The load factor increases at a terrific rate after a bank has reach 45° or 50°.

The load factor for any aircraft in a coordinated 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 angle, which it never quite reaches because a 90° banked, constant altitude turn is mathematically possible.

An aircraft may be banked at 90° in a coordinated turn if not trying to hold altitude. An aircraft that can be held at 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.

Small Unmanned Aircraft Loading Part 2

Any aircraft, within the limits of its structure, may be stalled at any airspeed. When a sufficiently high angle of attack is imposed, the smooth flow of air over an airfoil breaks up and separates, producing an abrupt change of flight characteristics and a sudden loss of lift which results in a stall.

A study of this effect has revealed that an aircraft’s stalling speed increases in proportion to the square root of the load factor. This means that an aircraft with a normal un-accelerated stalling speed of 50 knots can be stalled at 100 knots by introducing a load factor of 4 Gs. If it were possible for this aircraft to withstand a load factor of nine, it could be stalled at a speed of 150 knots.

A pilot should be aware of the danger of inadvertently stalling the aircraft by increasing the load factor, as in a steep turn or spiral. Banking an aircraft greater than 72° in steep turns produces a load factor of three, and the stalling speed is increased significantly.

If this is made in an aircraft with a normal unaccelerated stalling speed of 45 knots, the airspeed must be kept greater than 75 knots to prevent inducing a stall.

A similar effect is experienced in a quick pull up or any maneuver producing load factors above 1 G. This sudden, unexpected loss of control, particularly in a steep turn or abrupt application of the back elevator control near the ground, has caused many accidents. Since the load factor is squared as the stalling speed doubles, tremendous loads may be imposed on the structures by stalling an aircraft at relatively high airspeeds.

Small Unmanned Aircraft Loading Part 2