Weight and Balance— Weight-Shift Control Aircraft and Powered Parachutes
The terminology, theory, and concepts of weight and balance that applies to airplanes also applies to weightshift aircraft and powered parachutes. Weight is still weight, and the balance point is still the balance point. There are, however, a few differences that need to be discussed. Before reading about the specifics of weight and balance on weight-shift control and powered parachute aircraft, be sure to read about their aerodynamic characteristics in Chapter 3, Physics.
Weight-shift control aircraft and powered parachutes do not fall under the same Code of Federal Regulations that govern certified airplanes and helicopters and, therefore, do not have Type Certificate Data Sheets or the same type of FAA mandated weight and balance reports. Weight and balance information and guidelines are left to the individual owners and the companies with which they work in acquiring this type of aircraft. Overall, the industry that is supplying these aircraft is regulating itself well, and the safety record is good for those aircraft being operated by experienced pilots.
The FAA has recently (2005) accepted a new classification of aircraft, known as Light Sport Aircraft (LSA). A new set of standards is being developed which will have an impact on the weight-shift control and powered parachute aircraft and how their weight and balance is handled.
Weight-Shift Control Aircraft
Weight-shift control aircraft, commonly known by the name “trikes," have very few options for loading because they have very few places to put useful load items. Some trikes have only one seat and a fuel tank, so the only variables for a flight are amount of fuel and weight of the pilot. Some trikes have two seats and a small storage bin, in addition to the fuel tank.
The most significant factor affecting the weight and balance of a trike is the weight of the pilot; if the aircraft has two seats, the weight of the passenger must be considered. The trike acts somewhat like a single main rotor helicopter because the weight of the aircraft is hanging like a pendulum under the wing. Figure 4-37 shows a two-place trike, in which the mast and the nose strut come together slightly below the wing attach point. When the trike is in flight, the weight of the aircraft is hanging from the wing attach point. The weight of the engine and fuel is behind this point, the passenger is almost directly below this point, and the pilot is forward of this point. The balance of the aircraft is determined by how all these weights compare.
The wing attach point, with respect to the wing keel, is an adjustable location. The attach point can be loosened and moved slightly forward or slightly aft, depending on the weight of the occupants. For example, if the aircraft is flown by a heavy person, the attach point can be moved a little farther aft, bringing the wing forward, to compensate for the change in center of gravity.
Figure 4-38 shows a close-up of the wing attach point, and the small amount of forward and aft movement that is available.
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