 Helicopters, the most versatile equipment to appear on the scene in recent years, are making possible new concepts in transportation for both military and civilian use. The helicopter has earned a place of importance in aviation because in small confined areas it can take off or land vertically. It can move forward. It can move sideways in either direction. It can move backwards. And if the engine should fail in midair, it can make a safe emergency landing. Although the helicopter has only recently become a practical means of transportation, its idea has occupied man's thought for centuries. Leonardo da Vinci expressed his idea for a flying machine in the 15th century. Others followed da Vinci in dreaming of vertical flight for man. In 1783, a French scholar, Lenoy, and a French mechanic named Bienvenue demonstrated to the French Academy of Science a flying top made of feathers, sticks, and string, like this model you see here. It was the first heavier-than-air device ever to fly on its own power. Half a century later, an English schoolboy, George Cayley, heard about Lenoy's flying top. In 1843 he designed a four-rotor model helicopter, but having only heavy steam engines available for power, he never tried to build a full-size machine. In 1878, Enrico Forlunini of Italy built a model powered by a midget steam engine which actually hovered at 40 feet for 20 seconds. The advent of the gasoline engine marked a turning point in the development of the helicopter. Inspired by the success of a pilotless machine built by Charles Renault, his student Louis Briget built this helicopter in 1907. It carried him to an altitude of five feet. This flying octopus was built by Dr. Georges de Botezac for the United States Army Air Service and test flown in 1922. It rose to a height of five feet and stayed aloft for one minute and 43 seconds, but was too complicated and proved impossible to control in flight. In that same period, the American Amil Berliner and his son Henry built two machines. This, his second, proved fairly successful. Experiments continued throughout the world and in 1923 came a significant development. A Spanish inventor, Juan de la Sierra, developed the autogyro. It was a cross between a helicopter and an airplane. It had fixed wings and a standard propeller to raise it off the ground, a free spinning rotor on top gave additional lift. He was able to cross the English Channel on this machine and his principles of design were to lead to a successful, true helicopter. In 1934, the Frenchman Louis Briget tried again. This time he achieved real stability and control. In fact, his machine is generally considered the first practical helicopter. In 1937, the German Heinrich Falka built this FW61. It could hover, go straight up or down, and move forward or backward. It set new records for endurance, speed, distance and altitude. Other inventors, of course, were hard at work developing different ideas in helicopter configuration. Here in America, Igor Sikorsky, who had been carrying on rotary wing experiments for years, made his first free flight with this VS-300 in 1940. Although the army had already commissioned the Platt-LePage Company to build a helicopter, it followed Sikorsky's progress with keen interest. As a result of Sikorsky's success with the VS-300, that model was used as a prototype for the first helicopter design for military use, the Sikorsky XH-4. From this basic design came Sikorsky's later models, the H-19, then later the much larger and greatly improved H-34. Other designs by American inventors were being developed. In the late 1940s, two more models were accepted by the United States Army. One produced by Bell was the forerunner of this H-13. The other was the H-23 manufactured by Hiller. By a second designed the H-25, a small compact utility helicopter, employing the principle of two rotors driven by a single engine. He also devised another tandem rotor machine, the H-21, known as the Workhorse. Cayman built machines such as the H-OK series, using two rotors mounted side by side and so synchronized that the revolving blades intermeshed. Even though these present helicopters are satisfactory, research continues to explore new fields. The search for a practical small helicopter has resulted in this experimental two-place model powered by ram jets on the blade tips. In the one man class is this simple compact version of the conventional helicopter. Developed by Hiller, it has the advantage of being collapsible and easily carried. A distinct departure is the flying platform, with its rotor blades mounted on a frame under the pilot. Directional control is accomplished by the pilot's body movements. Seeking engines with higher horsepower and more efficient operation, designers have turned to turbine engines. One designed by like-homing is used in this Cayman H-OK. Bell's latest utility helicopter designed for the Army, the X-H-40, also uses the like-homing turbine engine. In reaching out for greater and greater capacity, Sikorsky uses two engines to drive one main rotor in the H-37. Although we have accomplished a great deal in the development of the helicopter, we have even more to accomplish in the future, and the task is not without its difficulties. Rotary wing was man's first idea of flight, but practical helicopters were not produced until long after fixed wing craft filled the air. This was because helicopter pioneers had to solve so many additional problems. Consider some of the problems and the solutions which made rotary wing flight possible. Take a bird's eye view of the two types, fixed wing and rotary wing aircraft. There is a resemblance. Rotor blades are really wings. That's why helicopters are called rotary wing aircraft. So first let's see how a fixed wing aircraft flies. Then go on to the helicopter. In flight, two basic forces must be overcome. Weight and drag. The forces which overcome these two factors are lift and thrust in fixed wing aircraft. Lift is obtained from the velocity of airflow over the airfoil or wing and is about equal to the square of the velocity. Thrust is obtained from the propeller which drives the aircraft through the air. So the greater the thrust, the greater the velocity of the airflow and the greater the lift. Another factor which affects lift is a change in the angle of attack of the wing, as shown here. The angle of attack is the angle formed between the chord line of the airfoil and the relative wind. Increasing the angle of attack up to the stalling point will increase lift within the limits of airfoil design. Now any increase in the flow of air or in the angle of attack or both will increase lift. A conventional fixed wing aircraft gets most of its lift from its wing. The helicopter gets enough velocity of airflow by rotating its blades at speeds up to 350 miles per hour while standing in one place. To increase the angle of attack, the pitch of the rotor blades themselves is changed. In all helicopter rotor blades, two types of pitch changes are possible. The first, called collective pitch, gives a change in the angle of attack which is constant and equal on all blades. By changing this collective pitch, the helicopter can make vertical movements up or down or it can hover. The other type of pitch change is called cyclic pitch change. In it, the pitch or angle of attack of each separate blade is being constantly changed as it revolves. This means that during each revolution, there is a constantly changing increase and decrease of pitch put into each blade. One effect of this changing is to tilt the plane of the tip path in the direction of flight, causing the helicopter to move in the direction in which the rotor is tilted. One reason for cyclic pitch change is to overcome a symmetry of lift. This term, the symmetry of lift, simply means the difference in lift between the advancing blade and the retreating blade in the rotor system in forward flight. However, the cyclic pitch change tends to balance out this difference. By decreasing lift on the advancing blade and increasing lift on the retreating blade, the symmetrical lift is restored and the rotor system is balanced in flight. To fly forward, the rotor disc must be tipped forward. To do this, we introduce low pitch to the pilot's right. Following the laws of physics, the effect will take place 90 degrees later and will tend to tip the rotor disc directly to the front where there is less lift. At the same time, rising pitch is applied at the pilot's left and it takes place 90 degrees later directly behind. In actual operation, cyclic pitch is gradually changed throughout the rotation. But its effect is to tilt the rotor forward, making the helicopter move forward. This cyclic pitch change applied independently to each blade in the rotor system governs horizontal movement. Now there's another point to be considered in helicopter flight principles. The problem is that of torque. In most single rotor helicopters, the blades turn counterclockwise. Under Newton's law of equal and opposite reactions, the force of the turning rotor tends to make the fuselage turn around the rotor axis in the opposite or clockwise direction. If there were no means of controlling torque, helicopter flight in any direction at all would be impossible. Torque, however, can be controlled by an anti-torque rotor mounted on the tail boom. By changing the pitch of these anti-torque rotor blades, the helicopter can be turned in any desired direction. In tandem rotor designs, torque is no problem. As the rotors turn in opposite directions, the torque of one cancels out the other. This is true if two rotors are mounted separately or if both are mounted on the same mast. So much for the principles of rotary wing flight. Now let's take a look inside the cockpit at the flight controls by which the helicopter is operated. Alongside the pilot is the collective pitch stick which changes the collective pitch of the rotor blades and causes the helicopter to move up, down, or to hover. A motorcycle-type throttle is mounted on this stick. The cyclic control stick tilts the rotor and causes the helicopter to move forward, backwards, or sideways. These anti-torque pedals are coupled to the tail rotor. By varying the pitch of the rotor blades, the helicopter is turned to the left or right when hovering. With the development of the helicopter into a practical reality, new uses are being found for it every day by private industry, government agencies, and military services. For example, oil companies find that helicopters earn their pay in running preliminary surveys and in patrolling their pipelines. Even the farmer is found to use for the helicopter in croc dusting. The low and fairly slow flying helicopter can put the spray where it is needed in a hurry. Inexcessible areas are opened up for on-the-spot news coverage by airborne television cameras. The postal department also is found to use for helicopters. It has become quite commonplace now to carry mail from a downtown post office to a nearby airport for direct transfer to a cross-country airliner. Traffic police use helicopters to patrol the highways and prevent dangerous traffic conditions from developing. Conservation officials find it useful in counting elk and other wild animals in game surveys. Game can be herded toward better feeding areas or have food delivered to them in bad winter weather. In time of civil emergencies such as flood, the helicopter is called upon to carry medical supplies and food to isolated victims or to evacuate them to places of safety. Today the military services are among the more important users of helicopters. Commanders find they can get to advance units quickly to keep themselves abreast of tactical situations. Official messages and personal mail delivered from headquarters to isolated units can speed up communications and strengthen troop morale. Telephone wire on speed reels can be laid over rough terrain in a matter of minutes, a job which otherwise would require hours of work by the usual ground team. March control is handled more efficiently when a helicopter is aloft to spot traffic delays and to find possible alternate routes. For artillery units firing at concealed targets, helicopters serve as mobile aerial platforms for the forward observer. Cargo transport craft can support military operations by delivering heavy equipment such as artillery, or a quarter-ton truck, or even sections of a pontoon bridge. Combat troops isolated by difficult terrain conditions can receive quick delivery of ammunition, medical supplies, gasoline, or other needed equipment. During the Korean conflict this machine gained respect from fighting men by its ability to evacuate wounded from battlefields under conditions in which other means of transportation were almost useless. However, this vehicle's greatest value to the Army lies in the fact that a commander can plan on going over as well as around an enemy. Knowing that troops and equipment can be delivered to virtually any point when needed, he can proceed with confidence. The helicopter then can well be considered a new weapon in the hands of the field commander. Through its versatility, it provides the commander with the ability to maneuver and gives him the shock action necessary to assure success on tomorrow's battlefield.