Introduction
This chapter discusses the weight and balance procedures
for light sport aircraft (LSA) that differ from conventional
aircraft, specifically weight-shift control (WSC) aircraft
(also called trikes), powered parachutes, and amateur-built
LSA. [Figure 4-1]
Light Sport Aircraft Weight
and Balance Control
Chapter 4
Figure 4-1. Examples of light sport aircraft (from top left, clockwise): weight-shift control, powered parachute, glider, airplanes, hot
air balloon, and amateur-built LSA.
LSA Definition of Term
LSA is a category of simple, very basic, small, light-weight,
low-performance aircraft, other than a helicopter or powered-
lift, and a classification of aircraft specific to the United
States. The Federal Aviation Administration (FAA) defines
LSA as an aircraft with a maximum gross takeoff weight of
not more than 1,320 pounds (600 kg) for aircraft not intended
for operation over water, or 1,430 pounds (650 kg) for aircraft
intended for operation over water; a maximum airspeed in
level flight of 120 knots (220 kilometers per hour (km/h); 140
miles per hour (mph)); a maximum stall speed of 45 knots
(83 km/h; 52 mph); a maximum seating capacity of no more
than two persons (including the pilot); fixed undercarriage
and fixed-pitch or ground-adjustable propeller; and a single
reciprocating engine (if powered).
An aircraft that qualifies as LSA may be operated by the
holder of a sport pilot certificate, whether registered as LSA
or not. Pilots with a private, recreational, or higher pilot
certificate may also fly LSA, even if their medical certificate
have expired, as long as they have a valid driver’s license to
prove that they are in good enough health to fly. LSA also
have less restrictive maintenance requirements and may be
maintained and inspected by traditionally certificated aircraft
maintenance technicians (AMTs) or by individuals holding
Figure 4-2. CG of a trike.
CG
Aircraft CG
• CG is under wing hang point for level flight.
• Center of lift is directly above CG, above the
wing hang point for level flight.
Thrust line is typically
designed to be at vertical
CG.
Fuel tank
a Repairman: Light Sport certificate, and (in some cases) by
their pilots and/or owners.
Weight and Balance
Aircraft such as balloons, powered parachutes, and WSC do
not require weight and balance computations because the load
is suspended below the lifting mechanism. The CG range in
these types of aircraft is such that it is difficult to exceed CG
limits. For example, the rear seat position and fuel of a WSC
aircraft are as close as possible to the hang point with the
aircraft in a suspended attitude. Thus, load variations have
little effect on the CG. This also holds true for lighter-than-
air aircraft, such as a balloon basket or gondola. While it is
difficult to exceed CG limits in these aircraft, pilots should
never overload an aircraft, as doing so may cause structural
damage and/or failures.
Weight affects performance; therefore, pilots should calculate
weight and remain within the manufacturer’s established
limits at all times.
WSC Aircraft
WSC aircraft are one- and two-place aircraft that exceed the
criteria of an ultra-light vehicle but do meet the criteria of an
LSA. The definition for WSC can be found in 14 CFR part 1.
A WSC aircraft used for sport and private pilot flying must
be registered with an FAA N-number, have an airworthiness
certificate, a pilot’s operating handbook (POH), and/or
limitations with a weight and loading document aboard.
As mentioned earlier, WSC aircraft are commonly called
trikes. These aircraft have few options for loading because
they lack places to put useful load items. One-place trikes
have only one seat and a fuel tank, which means the only
variables for a flight are amount of fuel and weight of the
pilot. Two-place trikes can accommodate a pilot and a
passenger. This version may have 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 and, if the aircraft has two
seats, the weight of the passenger. The trike acts somewhat
like a single, main-rotor helicopter because the weight of the
aircraft hangs like a pendulum under the wing. Figure 4-2
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 hangs 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 is moved slightly forward
or slightly aft, depending on the weight of the occupants. For