Helicopter Human Factors
Bruce E. Hamilton Johnson Engineering Corporation
Helicopters are just like fixed-wing aircraft except that helicopters are different. The differences are not in the men and women who fly helicopters, for they can be, and sometimes are, the same men and women who fly fixed-wing aircraft. Their abilities and limitations are the same regardless of the kind of aircraft they fly. Helicopters and fixed-wing aircraft differ in how the crew makes flight control inputs, the information required to decide what control movements are necessary, and the missions assigned to the crew. There are many areas of similarity, such as in navigation, communication, subsystem management, monitoring vehicle status, coordination between crew members, and interaction between the helicopter and other aircraft. Helicopters and fixed- wing aircraft follow, for the most part, the same flight rules and procedures. Minor differences exist in the flight rules, mostly about minimum visual ranges and decision heights. Although rotary- and fixed-wing flight is mostly the same, the differences are important and often overshadow the similarities.
One difference is in how helicopters fly. Fixed- and rotary-wing aircraft all obey the same laws of physics and use the same principle of differential pressure caused by air flowing across and under a shaped surface to generate lift. The difference is that the rotary wing, as the name implies, rotates the wing about a mast to generate airflow while the fixed wing moves forward through the air. The difference in method of generating lift accounts for the helicopter's ability to hover and move at slow speeds in any direction. Figure 17.1 illustrates the method by which the helicopter balances opposing forces in order to fly. In short, the rotating blades (rotor disk) generate lift. Tilting the rotor disk provides thrust, with the resultant vector a function of how much lift (pitch of the blades) and thrust (degree of tilt) are commanded. This resultant vector counters the force of gravity acting on the mass of the helicopter and payload, and the drag of the fuselage as it moves through the air. Increasing the pitch of the blades (more lift) without tilting the rotor disk (thrust constant) causes the helicopter to rise, whereas increasing pitch and tilting the disk causes movement in the direction of the tilt. When hovering, the resulting vector is vertical (without thrust) to balance the force