The source shows the rudder on player two X-axis. And something called the "collective" on player two Y-axis.
Introduction to helicopter flight (from the C64 game gunship):
BASIC CONCEPT'S: The two main flight controls are the cyclic joystick
and the collective. The cyclic joystick controls the pitch ("nosing"
up and down) and roll ("leaning" left or right) of the helicopter. The
collective changes the angle of attack of the rotor blades (see
"Aerodynamics" for details). This changes the lifting force of the
blades.
The cyclic joystick is controlled with your joystick
The collective is controlled from the keyboard. On computers with a
mouse, the mouse can be used to move the collective up and down as
desired.
Pushing the cyclic joystick forward pitches the helicopter downward
("nose down"). This causes the helicopter to gain forward speed. The
helicopter will NOT dive until it reaches a steep pitch downward, then
it dives like a normal aircraft.
Pulling the cyclic joystick back pitches the helicopter upward. If the
helicopter's pitch is upwards (the crosshairs are above the horizon)
the helicopter will go backwards. Pitching upward does not necessarily
mean you will climb!
A common mistake of novices is to assume that the harder they pull
back on the cyclic, the faster they will climb. Instead of climbing
fast they end up flying backwards! Watch the crosshair/horizon
position to avoid this error.
Pushing the cyclic joystick left or right rolls the helicopter in that
direction. At low speeds (under 40 knots) the helicopter skids
sideways. At faster speeds it performs a banking turn like an
aircraft. In either case, the further you roll, the more your lift
decreases. Novices in level flight are often surprised by the loss in
altitude as they roll left or right.
Moving the collective up increases the amount of lift in the rotor. If
you are in level flight the higher collective causes you to ascend.
The torque will increase as you raise the collective. When torque
reaches the maximum value on the gauge you are at maximum lift.
Moving the collective down decreases the amount of lift in the rotor.
If you are in level flight, the lower collective causes you to
descend. The torque decreases as you lower the collective. Except in
unusual conditions, you cannot maintain level flight, much less
ascend, if torque is below 50%.
Anti-torque (tail) Rotor Controls (rudder pedals): These controls function only if the
helicopter is moving very slowly (just a few knots) or hovering Each
tap on rotate left speeds up the tail rotor and causes the nose to
swing left Each tap on rotate right slows down the rotor and causes
the nose to swing right. Tap stop rotation to return the tail rotor to
normal speed, ending all rotation.
From
http://www.devili.iki.fi/pub/Commodore/docs/Project64/games/gunshi10.txt