Aerodynamics of Flight

Effect of Weight on Flight Performance a load of 3.8 times the approved gross weight of the aircraft The takeoff/climb and landing performance of an aircraft are without structural failure occurring. If this is accepted as determined on the basis of its maximum allowable takeoff and indicative of the load factors that may be imposed during landing weights. A heavier gross weight results in a longer operations for which the aircraft is intended, a 100-pound takeoff run and shallower climb, and a faster touchdown overload imposes a potential structural overload of 380 speed and longer landing roll. Even a minor overload may pounds. The same consideration is even more impressive make it impossible for the aircraft to clear an obstacle that in the case of utility and acrobatic category aircraft, which normally would not be a problem during takeoff under more have load factor requirements of 4.4 and 6.0, respectively. favorable conditions. Structural failures that result from overloading may be The detrimental effects of overloading on performance are dramatic and catastrophic, but more often they affect not limited to the immediate hazards involved with takeoffs structural components progressively in a manner that and landings. Overloading has an adverse effect on all is difficult to detect and expensive to repair. Habitual climb and cruise performance, which leads to overheating overloading tends to cause cumulative stress and damage during climbs, added wear on engine parts, increased fuel that may not be detected during preflight inspections and consumption, slower cruising speeds, and reduced range. result in structural failure later during completely normal operations. The additional stress placed on structural parts The manufacturers of modern aircraft furnish weight and by overloading is believed to accelerate the occurrence of balance data with each aircraft produced. Generally, this metallic fatigue failures. information may be found in the FAA-approved AFM/POH and easy-to-read charts for determining weight and balance A knowledge of load factors imposed by flight maneuvers data are now provided. Increased performance and load- and gusts emphasizes the consequences of an increase in the carrying capability of these aircraft require strict adherence gross weight of an aircraft. The structure of an aircraft about to to the operating limitations prescribed by the manufacturer. undergo a load factor of 3 Gs, as in recovery from a steep dive, Deviations from the recommendations can result in structural must be prepared to withstand an added load of 300 pounds damage or complete failure of the aircraft’s structure. Even for each 100-pound increase in weight. It should be noted that if an aircraft is loaded well within the maximum weight this would be imposed by the addition of about 16 gallons limitations, it is imperative that weight distribution be of unneeded fuel in a particular aircraft. FAA-certificated within the limits of CG location. The preceding brief study civil aircraft have been analyzed structurally and tested for of aerodynamics and load factors points out the reasons for flight at the maximum gross weight authorized and within the this precaution. The following discussion is background speeds posted for the type of flights to be performed. Flights at information into some of the reasons why weight and balance weights in excess of this amount are quite possible and often conditions are important to the safe flight of an aircraft. are well within the performance capabilities of an aircraft. This fact should not mislead the pilot, as the pilot may not In some aircraft, it is not possible to fill all seats, baggage realize that loads for which the aircraft was not designed are compartments, and fuel tanks, and still remain within being imposed on all or some part of the structure. approved weight or balance limits. For example, in several popular four-place aircraft, the fuel tanks may not be filled to In loading an aircraft with either passengers or cargo, the capacity when four occupants and their baggage are carried. structure must be considered. Seats, baggage compartments, In a certain two-place aircraft, no baggage may be carried and cabin floors are designed for a certain load or in the compartment aft of the seats when spins are to be concentration of load and no more. For example, a light practiced. It is important for a pilot to be aware of the weight plane baggage compartment may be placarded for 20 pounds and balance limitations of the aircraft being flown and the because of the limited strength of its supporting structure reasons for these limitations. even though the aircraft may not be overloaded or out of CG limits with more weight at that location. Effect of Weight on Aircraft Structure The effect of additional weight on the wing structure of an Effect of Weight on Stability and Controllability aircraft is not readily apparent. Airworthiness requirements Overloading also affects stability. An aircraft that is stable prescribe that the structure of an aircraft certificated in the and controllable when loaded normally may have very normal category (in which acrobatics are prohibited) must different flight characteristics when overloaded. Although be strong enough to withstand a load factor of 3.8 Gs to take the distribution of weight has the most direct effect on this, care of dynamic loads caused by maneuvering and gusts. This an increase in the aircraft’s gross weight may be expected means that the primary structure of the aircraft can withstand to have an adverse effect on stability, regardless of location 5-42