WHIRLING WINGS

"The idea of a vehicle that could lift itself vertically from the ground
and hover motionless in the air

was probably born at the same time that man first dreamed of flying."

 

                                                                       Igor Sikorsky, helicopter pioneer.

Leonardo da Vinci (born in Italy in 1452) was blessed with an encyclopedic knowledge of invention, science, music, engineering and many other areas, including human-powered flight. Also an accomplished artist (Mona Lisa comes to mind), da Vinci drew sketches of human-powered flying machines, one of which was an "aerial screw" operated by four men running on a turntable.

 

Long before Sir Isaac Newton propounded his laws of motion, Leonardo's intellect may have led him to conclude that the surfaces of his spiral flyer would produce the reactive force that was eventually labeled "lift." Considering the very low density of the atmosphere, there was no way those four athletes could move enough air to lift men and machine off the ground; nevertheless, da Vinci's aerial screw was a logical, if not practical, step in the right direction.
 

In the years that followed da Vinci's drawings there were numerous attempts to achieve vertical flight, none of which met with success. The use of rotating wings (rotors) to generate lift was the primary requirement for vertical flight but inventors encountered three major problems; the engines were underpowered, the rotor blades were inefficient and the control systems were woefully inadequate.

An innovative Frenchman named Paul Cornu got a leg up on his fellow inventors when he rolled out his flying machine in 1907. A 24-hp engine turned two 20-foot rotors in opposite directions to counteract torque and the flat rotor blades were angled somewhat to generate lift. The rectangular panels at the fore and aft extremities of the machine were intended to control the aircraft in flight.
 

Cornu's flying machine -1907

In November 1907 with Cornu at the helm, the problems of power, lift and control were overcome for a short time; his helicopter climbed to five feet and held that altitude for a full minute. Although subsequent flights got no higher than seven feet and flew less than a minute, Cornu was given credit for conducting the first flight of a rotary-wing aircraft carrying a man.

 

Enter Raul Pescara, an Argentine engineer who made a quantum leap in vertical-flight technology in the early 1920s. He not only built a sturdy helicopter with 16 contra-rotating blades mounted on a coaxial shaft, he applied wing warping (twisting) to the rotor blades to produce additional lift…and he invented the basic helicopter control system that is still in use today.

 

Pescara's helicopter - 1922

 Pescara's invention of the collective and cyclic pitch controls was a momentous contribution to helicopter development. The collective pitch control warped all the rotor blades simultaneously, resulting in climb or descent. The cyclic pitch control warped the blades individually as they moved through the rotation cycle and provided movement of the helicopter forward and backward, right and left.

Most of today's helicopters have a collective pitch lever on the left side of the pilot's seat and a cyclic pitch stick between the pilot's knees. A twist-grip throttle on the collective lever changes engine power as required to maintain the proper rotor speed (turbine-powered helicopters are equipped with automatic power control systems). Anti-torque foot pedals on the cockpit floor control yaw by changing the pitch of the tail-rotor. A helicopter pilot is a very busy aviator.

Three dimensions of flight and the controls that manage them.



 

IGOR SIKORSKY ARRIVES ON THE ROTARY-WING SCENE

Born in Russia in 1889, Igor Sikorsky studied engineering in general and aeronautics in particular at several institutions in Russia, Germany and France. In 1908, upon learning of the Wright brothers' accomplishments, he said "Within twenty-four hours, I decided to change my life's work…I would study aviation." And so he did.

Seeing little opportunity for aircraft designers in war-torn Europe, Sikorsky emigrated to the United States in 1919 and founded the Sikorsky Aircraft Corporation.

 

A number of transoceanic flying boats were launched from the Sikorsky plant in the 1930s but when the flying boat era came to an end, Sikorsky turned his attention to vertical flight and the result—designed and flown by Igor himself—was the VS-300, the aircraft that pioneered the two-rotor configuration used in most of today's helicopters.

 

Igor Sikorsky in the cockpit of the VS-300

 

Having experienced Russian winters as a child, Igor was accustomed to steering snow sleds by pushing on the right side of the steering bar to turn left and vice versa. This steering arrangement developed a habit so strong that Igor rigged the anti-torque pedals in reverse on his personal helicopter…suffice it to say no one else could fly this aircraft safely.

The VS-300 evolved into the R-4, a modified design with two seats and an enclosed airframe. In response to military contracts 131 of these helicopters were built during WW II and in 1944, a U.S. Army pilot flying a Sikorsky YR-4B accomplished the first-ever combat rescue mission with a helicopter.

Sikorsky R-4 helicopter

THE UBIQUITOUS BELL 47 HELICOPTER

Lawrence Bell founded the Bell Aircraft Corporation in Buffalo, New York in 1935. During WW II the Bell emphasis was on fighters, notably the P-39, P-63 and the P-59 Airacomet, America's first jet-powered aircraft. After the war the company produced the Bell X-1, the first aircraft to break the sound barrier in level flight. 

The Bell company began developing helicopters in 1941 and two years later the prototype Model 30 conducted its first flight. This early version evolved into the Bell 47 with the bubble cockpit that made it one of the most recognizable aircraft in history.



                          Bell Model 30                            Bell Model 47                  

The Bell 47 (H-13 Sioux for the Army folks) was delivered to the U.S. Army Air Forces in 1946 and provided outstanding service during the Korean War. Perhaps most significant among the many roles it played, medical evacuation saved untold lives by transporting wounded warriors quickly from combat zones to  mobile army surgical hospitals (MASH). Post-war, the Bell 47 was also a frequent choice for civilian helicopter flight instruction, including yours truly.

In 1949 a Bell 47 set an altitude record of 18,550 feet and three years later a company pilot flew a Bell 47 1,217 miles non-stop from Texas to New York, a world distance record for piston-powered helicopters. When production ceased in 1973 the Bell Company had built 5,600 Model 47s.

THERE'S MORE THAN ONE WAY TO FLY STRAIGHT UP         

Igor Sikorsky and Lawrence Bell made profound contributions to the progress of rotary-wing aircraft and both companies have since focused on turbine-powered helicopters. But over the years other manufacturers built helicopters that were departures from traditional designs.

Kaman Huskie

A good example is the Kaman Huskie (HH-43 in Air Force lingo) that employed an intermeshing twin-rotor arrangement, each rotor mounted at a slight angle to assure the blades would not come together. It looked weird, but it worked. The contra-rotating design eliminated the need for a tail rotor, which made room for a wide rear door with easy access to the cabin. Huskies flew more rescue missions during the Viet Nam war than all other aircraft combined.

Piasecki H-21 Workhorse

The Piasecki H-21 Workhorse was sold to the U.S. Navy in 1944 and promptly acquired the nicknames Flying Banana or Sagging Sausage because of its unusual fuselage profile...and also because the Coast Guard decided to paint its H-21s bright yellow. The rear rotor was elevated to make sure the overlapping blades didn't hit each other in flight.

Ryan X-13 Vertijet

 

The X-13 Vertijet was obviously not a helicopter but was a true VTOL (Vertical Take Off and Landing) jet airplane that could translate from vertical to horizontal flight. Its turbojet engine delivered 10,000 pounds of thrust, some of which was diverted for attitude control. A hook in the airplane's nose engaged a cable on the launch pad and the pilot's seat could be tilted forward 45 degrees to provide adequate visual clues during the landing procedure. Hanging the airplane on the cable proved to be an exceptionally difficult pilot task and the project was cancelled in the mid-1950s.

THE BEST OF BOTH WORLDS



Helicopter mode                                Airplane mode

It was in the development process for a long time but the V-22 Osprey was accepted by the Marine Corps in 2007 and the Air Force in 2009. Known as a tilt-rotor aircraft, the V-22 can land and takeoff like a helicopter and fly like an airplane. The wingtip nacelles house the turbine engine/rotor combination and rotate 90 degrees for takeoff, landing and hovering; in the airplane mode the nacelles are rotated downward as required and the V-22 can fly at any airspeed between zero and 241 knots.

In consideration of its flight capabilities and offensive weaponry, Cassius Clay might have said the Osprey could "float like a butterfly and sting like a bee."