Aerodynamics of Flight

of equal weight. Instead, do a full computation of all items 240 knots R = V2 to be loaded on the aircraft, including baggage, as well as 11.26 x tangent of bank angle the pilot and passenger. It is recommended that all bags be 2402 weighed to make a precise computation of how the aircraft R = 11.26 x tangent of 30° CG is positioned. 57,600 R = 11.26 x 0.57735 The importance of the CG was stressed in the discussion R = 8,861 feet of stability, controllability, and performance. Unequal load (four times the radius at 120 knots) distribution causes accidents. A competent pilot understands The radius of a turn required by an aircraft traveling at 240 knots and respects the effects of CG on an aircraft. using the same bank angle in Figure 4-51 is 8,861 feet. Speed is a major factor in a turn. Weight and balance are critical components in the utilization Figure 5-60. Radius at 240 knots. of an aircraft to its fullest potential. The pilot must know how much fuel can be loaded onto the aircraft without be converted to fps by multiplying it by a constant of 1.69. violating CG limits, as well as weight limits to conduct Therefore, an aircraft traveling at 120 knots (TAS) travels long or short flights with or without a full complement of at 202.8 fps. Knowing the speed in fps (202.8) multiplied by allowable passengers. For example, an aircraft has four seats the time an aircraft takes to complete a circle (68.6 seconds) and can carry 60 gallons of fuel. How many passengers can can determine the size of the circle; 202.8 times 68.6 equals the aircraft safely carry? Can all those seats be occupied at 13,912 feet. Dividing by π yields a diameter of 4,428 feet, all times with the varying fuel loads? Four people who each which when divided by 2 equals a radius of 2,214 feet weigh 150 pounds leads to a different weight and balance [Figure 5-61], a foot within that determined through use of computation than four people who each weigh 200 pounds. the formula in Figure 5-59. The second scenario loads an additional 200 pounds onto the aircraft and is equal to about 30 gallons of fuel. In Figure 5-62, the pilot enters a canyon and decides to turn 180° to exit. The pilot uses a 30° bank angle in his turn. The additional weight may or may not place the CG outside of the CG envelope, but the maximum gross weight could Weight and Balance be exceeded. The excess weight can overstress the aircraft and degrade the performance. The aircraft’s weight and balance data is important information for a pilot that must be frequently reevaluated. Aircraft are certificated for weight and balance for two Although the aircraft was weighed during the certification principal reasons: process, this information is not valid indefinitely. Equipment changes or modifications affect the weight and balance data. 1. The effect of the weight on the aircraft’s primary Too often pilots reduce the aircraft weight and balance into structure and its performance characteristics a rule of thumb, such as: “If I have three passengers, I can 2. The effect of the location of this weight on flight load only 100 gallons of fuel; four passengers, 70 gallons.” characteristics, particularly in stall and spin recovery and stability Weight and balance computations should be part of every preflight briefing. Never assume three passengers are always Aircraft, such as balloons and weight-shift control, do not require weight and balance computations because the load is suspended below the lifting mechanism. The CG range 360 r = speed (fps) x ROT in these types of aircraft is such that it is difficult to exceed Pi (π) loading limits. For example, the rear seat position and fuel 2 of a weight-shift control aircraft are as close as possible to 202.8 x 68.6 the hang point with the aircraft in a suspended attitude. Thus, r = π load variations have little effect on the CG. This also holds 2 true for the balloon basket or gondola. While it is difficult 13,912 to exceed CG limits in these aircraft, pilots should never r = π overload an aircraft because overloading causes structural 2 damage and failures. Weight and balance computations are 4,428 r = = 2,214 feet not required, but pilots should calculate weight and remain 2 within the manufacturer’s established limit. Figure 5-61. Another formula that can be used for radius. 5-40