Workhorse of the Skies
By Awake! correspondent in South Africa
“WE HAD been flying for about two hours. Suddenly the engine revs started to drop—the first sign of engine trouble.* I immediately started to climb, using the remaining revs to gain as much altitude as possible before the engine stopped. As we reached the top of the climb, the clutch housing disintegrated, scattering fragments into the air all around us.
“Immediately I put the helicopter into a steep descent, keeping the forward speed constant at about 55 miles per hour [90 km/hr]. I had already checked out the terrain, and we were now heading for a small clearing within easy gliding distance.
“I flared out at 50 feet [15 m] above ground level so as to slow the aircraft down, and then we landed, skidding to a halt about 5 feet [1.5 m] from the edge of a donga [dry riverbed].”
All of this took barely a minute. True, helicopters have crashed in the final stages of an emergency landing, but as can be seen from this true experience, all is not lost if the engine fails. This pilot successfully completed a glide involving autorotation—practiced many times during training for just such an emergency.
Yet, as safe and as versatile as the helicopter is, many have still never ridden in one. Perhaps even you would be disinclined to take a short helicopter hop. You may, however, be interested in learning about these unusual flying machines.
Where Did It Start?
Leonardo da Vinci, in 1483, was the first to design a vertical flight machine, using an airscrew for lift. But, alas, aeronautical engineers say that the device he sketched is unflyable! Nevertheless, vertical flight has continued to fascinate inventors. Only relatively recently has this been successfully achieved.
It was in 1923 that the Spaniard Juan de la Cierva, at 27 years of age, successfully flew his autogiro at Getafe, Spain. The system he designed did much to advance helicopter theory. Later, a Russian-born designer, Igor Sikorsky, during the period from 1939 to 1941, made major advances toward the helicopter as we know it today. But what was the secret of getting the machine off the ground?
How Does It Fly?
A standard fixed-wing aircraft gets into the air by first accelerating down a runway. When it reaches the right speed, the air passing over the wing produces sufficient force to overcome the weight of the aircraft and lift the plane into the air. On a helicopter, however, the lift is generated by rotating the rotor blades, which are comparable to wings. Thus, a helicopter can obtain lift without forward movement. In order to do this, the blades must slice into the air at an angle, called the angle of attack, to produce any appreciable lifting force. And the pilot can vary the angle of attack, or pitch, of the blades by means of a control called the collective pitch lever. When the lift generated by the blades exceeds the weight of the helicopter, that is, overcomes the force of gravity, the helicopter will rise. A decrease in lift causes the machine to descend.
The helicopter can be made to go forward from the hovering position by tilting the rotor disc. This disc is the imaginary surface swept by the blades during their rotation. With the rotor disc tilted forward, air is forced not only downward to lift the helicopter but also slightly backward to push it forward. (See diagram below.) Thus, the helicopter can move in any direction, sideways, even backward, merely by tilting the rotor disc in the desired direction. The control that does this is held in the pilot’s right hand and is called the control column, or cyclic stick.
There is another problem that must be solved before we get off the ground—the torque reaction caused by the main rotor. What is “torque reaction”? Imagine yourself trying to tighten an overhead bolt with a large wrench while standing on roller skates. As you turn the wrench in one direction, your body will tend to turn in the opposite direction. This is according to a scientific law of motion that to every action there is an equal and opposite reaction. In the case of the helicopter, as the engine drives the rotor in one direction, the aircraft itself tends to rotate in the opposite direction. The most widely used method to compensate for this is an antitorque rotor, or small propeller, mounted on the tail. By means of two rudder pedals, the pilot is able to increase or decrease the tail rotor thrust and thus keep the helicopter’s movements under control.
The final control to consider is the throttle. The engine revs have to be constantly monitored by the pilot whenever he is using the controls, necessitating throttle adjustments. It was this constant monitoring of the rev counter that warned the pilot described at the outset of possible engine failure even before the engine had completely failed. In modern gas-turbine helicopters, much of this work has been reduced by the introduction of an engine speed governing system.
Saving Time—And Lives!
Helicopters have appropriately been called workhorses of the skies. In August 1979, for example, a violent storm disrupted the English Fastnet yachting race. Fifteen men were killed in what was described as “the worst disaster in the history of yachting.” This figure would have been worse had it not been for the work of helicopter crews. During one rescue, the pilot had to watch the surrounding waves and keep his aircraft moving up and down to avoid being hit by them. One news report described this as playing a “life-or-death leapfrog between the crests of 13m [40 ft] rogue waves.”
Huge oil tankers sailing around the Cape of Good Hope of southern Africa can receive fresh supplies, spare parts, and even a change of crew by helicopter, without calling into port. But it is a very tricky maneuver. The pilot brings the copter into a hover above the deck by matching the tanker’s reduced forward speed. Then he must match the roll of the ship so as to land as gently as possible.
What’s It Like Flying in a Helicopter?
For those who love flying, the helicopter’s maneuverability provides a thrill unmatched by other forms of powered flight. It is a fascinating experience to be able to hover, move slowly backward or sideways or rotate through 360 degrees at about two feet [half a meter] off the ground. The absence of forward movement at takeoff makes the helicopter feel much safer to fly, and in flight, one soon becomes absorbed in the countryside, especially when skimming along close to the ground.
The student pilot, however, will at first find the helicopter difficult to fly, since the controls are very sensitive and it is less stable than fixed-wing aircraft. Once mastered, it is fun to fly and easier, perhaps, than an airplane because of the simpler takeoff and landing techniques.
Today the helicopter is a highly developed machine—a real workhorse of the skies. True, compared with some of Jehovah’s flying creations, such as the dragonfly and the hummingbird, it may seem clumsy. Still, it is a rather marvelous machine. And now that you know a bit more about it, perhaps you’d like to take a ride in one!
[Footnotes]
revs = revolutions
[Picture on page 12]
Leonardo da Vinci’s design for a vertical flight machine
[Credit Line]
Bibliothèque de l’Institut de France, Paris
[Picture on page 12]
Airport commuter flight
[Picture on page 13]
Air sea rescue by the RAF
[Credit Line]
Courtesy of the Ministry of Defense, London
[Picture on page 13]
Police often use helicopters
[Diagrams/Pictures on page 13]
(For fully formatted text, see publication)
The control column controls the angle of the rotor disc, which in turn determines the direction of flight
Rotor disc
Helicopter hovering
Backward flight
Forward flight
Collective pitch lever
Control column
Rudder pedals