Some gliders do not have compass deviation cards because they are not required instrumentation per the Type Certificate Data Sheets (TCDS). Most gliders are not considered powered aircraft as referenced in Title 14 of the Code of Federal Regulations (14 CFR) part 91, section 91.205, and are only subject to regulations specifying “civil aircraft.” Two examples that show these are 14 CFR part 91, section 91.209 and 91.211.
The most effective, yet least expensive, slip/skid indicator is made from a piece of yarn mounted in the free airstream in a place easily visible to the pilot, as shown in Figure 4-30. The yaw string indicates whether the pilot is using the rudder and aileron inputs together in a coordinated fashion. When the controls are properly coordinated, the yarn points straight back, aligned with the longitudinal axis of the glider. During a slipping turn, the tail of the yaw string is offset toward the outside of the turn. In flight, the rule to remember is simple: step on the head of the yaw string. If the head of the yaw string is to the right of the tail, then the pilot needs to apply right pedal. If the head of the yaw string is to the left of the tail, then the pilot should apply left pedal.
Another type of slip/skid indicator is the inclinometer. Like the magnetic compass, this instrument requires no electrical power or input from other aircraft systems. The inclinometer is influenced by centrifugal force and gravity. Mounted in the bottom of a turn-and-bank indicator or mounted separately in the instrument panel, the inclinometer consists of a metal ball in an oil-filled, curved glass tube. When the glider is flying in coordinated fashion, the ball remains centered at the bottom of the glass tube. The inclinometer differs from the yaw string during uncoordinated flight. The ball moves to the inside of the turn to indicate a slip and to the outside of the turn to indicate a skid. Remember the phrase, “step on the ball” in reference to the inclinometer; it helps coordinate the turn using rudder inputs. The long glider wing tends to increase the adverse yaw effects from the ailerons and requires more rudder control than many aircraft.
Gyroscopic instruments are found in virtually all modern airplanes but are infrequently found in gliders. Self-launching gliders often have one or more gyroscopic instruments on the panel. Gliders without power rarely have gyroscopic instruments installed. The three gyroscopic instruments found most frequently in a glider are the heading indicator, attitude indicator, and turn coordinator.
Another instrument that can be mounted in the instrument panel of a glider is a G-meter. G-meters register positive G forces from climbs and turns, as well as negative G forces when diving down or pushing over from a climb. The G-meter measures and displays the load imposed on the glider during flight. During straight, unaccelerated flight in calm air, a glider experiences a load factor of 1 G (1.0 times the force of gravity). During aerobatics or during flight in turbulent air, the glider and pilot experience G-loads greater than 1 G. These additional loads result from accelerations imposed on the glider. Some of these accelerations result from external sources, such as flying into updrafts or downdrafts. Other accelerations arise from pilot input on the controls, such as pulling back or pushing forward on the control stick. G-loads are classified as positive or negative.
Positive G is felt when increasing pitch rapidly for a climb. Negative G is felt when pushing over into a dive or during sustained inverted flight. Each glider type is designed to withstand a specified maximum positive G-load and a specified maximum negative G-load. The GFM/POH is the definitive source for this information. Exceeding the allowable limit loads may result in deformation of the glider structure. In extreme cases, exceeding permissible limit loads may cause structural failure of the glider. The G-meter allows the pilot to monitor G-loads from moment to moment. This is useful in aerobatic flight and during flight in rough air. Most G-meters also record and display the maximum positive G-load and the maximum negative G-load encountered during flight. The recorded maximum positive and negative G-loads can be reset by adjusting the control knob of the G-meter. [Figure 4-31]