Margie O’Connor

When asked how helicopter flying is different from flying an airplane, my response has always been the same: it’s much more difficult to eat a sandwich while flying a helicopter, whereas, in a well-trimmed airplane, light finger pressure on the yoke is enough to hold the aircraft straight and level while eating a sandwich with the other.

Why is this? Well, helicopter flying, although an adrenalin mounting endeavor (and the one I prefer), requires the use of both hands simultaneously on the controls. Does this mandate a white-knuckle grip, through all phases of flight, to keep the helicopter flying? Quite the contrary. Helicopter pilots are typically taught to place their hands and feet on the controls and then simply “think” about flying the helicopter or applying very small, smooth movements via the flight controls. But both hands are still occupied.

Aerodynamic Forces

Helicopter and fixed-wing flying use the same aerodynamic principles – just applied in slightly different ways. Lift, weight, thrust and drag play a role in the movement of both aircraft.

Thrust must be greater than drag to cause forward movement in an airplane in flight. In helicopter flying, these same forces act as vectors to accommodate the condition of flight (i.e., left, right, up, down, etc.). For example, in forward helicopter flight, lift acts as the vertical component of the Total Aerodynamic Force (TAF) and drag takes up the position opposite and perpendicular to the TAF. Or using a different visual, lift makes up the vertical component of the total lift vector with thrust acting perpendicular and opposite to lift in the same vector – thrust either acting forward (in forward flight) or left, right or to the rear (in the corresponding direction).

In steady state, un-accelerated flight in an airplane, lift equals weight and thrust equals drag. In a hover (in a no wind condition) lift and thrust combine into one force and are equal to and act opposite the sum of weight and drag.

Airflow

While these same forces come into play in both helicopter and airplane flying, the airflow is slightly different. In an airplane, the air flow over the wing speeds up as the aircraft’s speed increases. Helicopter flying incorporates both the helicopter’s speed and the speed at which the rotor blades move through the air.

How do we manipulate all these forces? Well, in an airplane, the pilot uses the control yoke or column and rudder pedals. In helicopter flying, the collective, cyclic and antitorque pedals control the forces in flight.

Controlling the Forces

In helicopter flying, the pilot’s left hand controls the collective and sometimes a throttle, depending on the aircraft. The collective is a bar or stick, if you will, parallel to the floor of the helicopter, when in the down position. As the pilot lifts the collective, the corresponding change in the rotor blade’s pitch angle increases lift and thus helps “lift” the helicopter up. The collective controls the up and down of the entire helicopter.

The pilot’s right hand controls the cyclic, positioned between the pilot’s legs. The cyclic runs somewhat perpendicular to the floor of the helicopter and provides pitch and roll about the lateral and longitudinal axes, respectively. The cyclic essentially works by changing the tip path plane of the rotor allowing you to maneuver in directions impossible for the fixed-wing pilot. So, yes, you can actually fly backward (without help from an excessively strong headwind) or hover over a fixed location!

While collective and cyclic keep your hands busy, the antitorque pedals demand your feet participate, as well. In a single rotor system, like those found on many trainer helicopters, pushing on the right pedal, turns the helicopter to the right while pressure on the left pedal, rotates the aircraft left. But that’s not the primary function of these two pedals on the floor. Their main purpose in life is not to add yet another required movement to flying a helicopter but rather to counteract torque.

Torque is the force that causes rotation and is countering the main rotation of the rotor blades. In aircraft flown in the United States, rotor blades rotate counter-clockwise, as viewed from above the rotors. Based on Newton’s third law of motion, torque imparts the tendency for the nose of the helicopter to move right. Antitorque pedals exist then, to counter torque.

So there you have it. Flying helicopters differs from flying airplanes mainly in the controls you will use… and that it may be slightly more difficult to eat a sandwich. But I’m still partial to helicopter flying: there’s nothing quite as awesome as hovering.

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References:

Center, U. S. (1996, July). Theory of Rotary Wing Flight. Fort Rucker, Alabama, United States of America.

Dole, C. E. (1994). Flight Theory for Pilots. Redlands: Jeppesen Sanderson.

Harp, P. (1996). Pilot’s Desk Reference for the UH-60 Helicopter. In P. Harp, Aerodynamics (pp. 6-18, 6-21, 6-32). Enterprise: Presentation’s Plus.

Michael J. Kroes, J. R. (1993). Aircraft Basic Science. Westerville: Glencoe Division of Macmillan/McGraw-Hill.

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