Adjusting Main Rotor Blade Pitch
Main rotor blade pitch on Lite Machines helicopters is adjusted by interchanging the
blade grips that hold the blades to the rotor head. Blade grips are available in even
numbered two-degree increments from two degrees to six degrees and are called
two-grips, four-grips and six-grips. Odd-numbered grips are not available.
Six-grips increase natural blade pitch by six degrees, and are identified by six raised
dots on the top of the grips. To change blade pitch from six degrees to five degrees,
remove
ONE
six-grip and install a four-grip (four raised dots). After adjusting the
mixing-arm/swashplate pushrods so that the blades have equal pitch (that is, after
re-tracking the blades), each blade will be pitched five degrees. Note that re-tracking
the blades usually requires two complete turns of the pushrod ball-links for a one
degree change in blade pitch.
Warning!
Be careful not to reduce blade pitch so much that the main rotor exceeds its maximum
rated speed since excessive speed could damage the main rotor or engine.
Stability and Climb Performance
Helicopter flight stability and control power is affected by the rotational speed of the
main rotor. At high rotor speeds, the main rotor blades generate high gyroscopic
forces that stabilize the main rotor, and minimize the effects of disturbances such as
wind gusts. The rotor blades can also generate the high aerodynamic (air) forces
needed to forcefully push the helicopter around when the pilot moves the controls.
On fixed-pitch helicopters, helicopter weight and the pitch of the main rotor blades
determines the operating speed of the main rotor, and directly affect stability, control
power and climb performance. High blade pitch generally improves climb
performance, but reduces stability and control power in hover.
This is because rotor blades operating at a high pitch angle produce lift at a relatively
low rotor speed. They do not generate the gyroscopic forces needed for solid
stability, or the aerodynamic forces needed for snappy control. Low blade pitch, on
the other hand, increases rotor speed and stability but reduces climb performance.
The main rotors on Lite Machines helicopters are designed to generate high lift with
very little engine power. High lift is required to fly on hot days and at high elevations
where air density is low. When flying at low elevations (especially near sea level
where air density is high) and with high blade pitch, some helicopters may leave the
ground without adequate rotor speed for acceptable stability and control power.
The usual solution to this problem is to add weight in order to increase rotor speed.
Generally, main rotor blade pitch should be set to the highest value that provides
acceptable stability (usually five degrees when flying near sea level, and six degrees
at higher elevations).
Op er a tor's Guide
Main Rotor Stability and Control
5-4
LITE MA CHINES
