- 6 months ago
For educational purposes
From Cierva's breakthrough in autogyro design, to the state-of-the-art BK-117, the heart of the helicopter story has been the rotorhead.
Early helicopters were complex, dangerous flying machines, prone to failure.
For the men and women who took the controls, concentration and daring were essential.
Featured Aircraft:
- Pitcairn PCA-2 autogyro
- MBB/Kawasaki BK 117
- Sikorsky SH-60 Seahawk
From Cierva's breakthrough in autogyro design, to the state-of-the-art BK-117, the heart of the helicopter story has been the rotorhead.
Early helicopters were complex, dangerous flying machines, prone to failure.
For the men and women who took the controls, concentration and daring were essential.
Featured Aircraft:
- Pitcairn PCA-2 autogyro
- MBB/Kawasaki BK 117
- Sikorsky SH-60 Seahawk
Category
📚
LearningTranscript
00:01Hi, I'm Neil Armstrong. Join me for an adventure through time.
00:56The Aerodynamic Principles
00:59that lift a rotorcraft have been known for centuries. Chinese children played with toys like this one in the 4th
01:07century BC.
01:11A young Leonardo da Vinci could well have played with the same traditional toy in 15th century Italy.
01:20Da Vinci's sketches revealed his dream of helicopter flight.
01:25It was not until the 20th century that a light, practical engine combined with a working rotor head could make
01:34the dream come true.
01:37The Aerodynamic Principles
01:45The Aerodynamic Principles
01:46The Aerodynamic Principles
02:00The Aerodynamic Principles
02:01The Aerodynamic Principles
02:19The helicopter is a rotary wing aircraft.
02:23The basic aerodynamic principles of lift that apply to fixed wing aircraft also apply to rotocraft.
02:29Nevertheless, rotocraft development has always been a world of its own.
02:34In the early part of the 20th century, aeronautics wasn't yet an industry or even a science.
02:40It was an art and a passion.
02:46Many aviation pioneers tried to build helicopters, but the mechanical problems of rotary wing
02:52flight seemed insurmountable.
02:54Even when flying machines were built with engines powerful enough, they didn't have
02:58the necessary control.
03:02In September 1907, in Douay, France, a Breguet-Régé No. 1 became the world's first manned helicopter
03:09to become airborne.
03:10It achieved a height of about two feet.
03:13The ground crew provided control with ropes.
03:17In November of the same year, also in France, a Cornu tandem rotor helicopter achieved the
03:22first unrestrained free flight.
03:25Whatever provisions he made for control didn't prevent the helicopter from crash landing.
03:34Many aviation designers in the early part of the 20th century gave up helicopter research
03:39for the relative safety of the fixed wing aircraft.
03:42aircraft.
03:42By 1924, fixed wing aircraft had flown the Atlantic nonstop, while the world helicopter
03:49distance record had been increased to a mere 2,600 feet.
03:53At the heart of the problem was the evolution of the rotating mechanical assembly called the
03:58rotor head.
03:59When a fixed wing aircraft flies, the flow of air over the wing creates lift.
04:04The craft must move forward to provide a sufficient flow of air.
04:08But the wings of a helicopter are rotating.
04:10So they create lift even when the craft is standing still.
04:14The rotating blades act as a propeller, creating tremendous torque and spinning the fuselage
04:20in the opposite direction of their rotation.
04:22Another problem is created as the helicopter moves forward.
04:26Each individual blade creates lift, but the lift varies depending on whether the blade
04:31is advancing into the wind or retreating.
04:34This lift asymmetry and torque cause a rotorcraft to be extremely unstable.
04:40The breakthrough in rotating wing design was achieved by an engineer who refused to build
04:46helicopters because he considered them too dangerous.
04:49The Spaniard Juan de la Sierva invented the autogyro.
04:54Sierva mathematically analyzed other rotorcraft designs to overcome the stability problems.
05:00He called the phenomenon autorotation.
05:03Sierva's autogyro had its rotor shaft slightly angled so that the disk of rotation was
05:08upward and forward.
05:10The blades advanced into and against the airflow so that the air gave solid support.
05:15It also meant that when the motor was cut, the aircraft did not stall, but descended
05:20gently downwards.
05:22Sierva's other innovation was to hinge the rotor blades to even out the lift.
05:26The advancing blade could droop to lose some of its bite, and the retreating blade
05:31regained some of its lift.
05:32Harold Pitcairn was the foremost American pioneer of Sierva's autogyro.
05:37His son, Steve, discusses Sierva's pioneering work.
05:41Sierva came up with the idea of hinging each rotor blade at the rotor hub, and this did
05:47away with the gyroscopic action which was causing control problems.
05:52My dad visited Sierva several times, and he finally worked out an arrangement with Sierva,
05:58where my dad would have all the patent rights and development rights to the autogyro in the
06:02United States.
06:03The autogyro here, as you see, has ailerons on the wings and has elevators.
06:08This is because you needed something to control the autogyro on flight since you had no control
06:12on the rotor head itself.
06:13The idea of direct control, where you had control of the rotor head for control of the autogyro
06:20in flight, came to Sierva, as the story goes, in an opera house somewhere in Europe where
06:27he had gone to the opera on a rainy night.
06:31While Sierva was sitting in the opera house, he had an umbrella, and the idea came to him,
06:37if he hooked it to the rotor head, if he pushed the umbrella forward, the rotor head would
06:41tilt back, and if it was in an autogyro, the autogyro would climb.
06:45And if he pulled the umbrella towards him, it would tilt the rotor head forward, and the
06:49autogyro would go down.
06:50He also figured the same way with moving it side to side, he could bank the autogyro.
06:57Although they were never able to hover, Sierva's autogyros provided the design theory that became
07:03the foundation of the helicopter industry.
07:06Ironically, the man whose rotary wing work was intended to make fixed wing flights safer
07:10while the helicopter was killed in an airliner crash in 1936.
07:17Armed with Sierva's discoveries of the nature of the rotary wing, pioneer helicopter designers
07:23focused their attention on the rotor head.
07:27Powered rotor heads had to be much stronger so they wouldn't be pulled apart by the drag
07:33and torque forces they were subjected to.
07:37Like the autogyro, the helicopter rotor head included flapping hinges to allow the blades
07:43to move up and down as they rotated, but there were also drag lengths to allow the blades some
07:49fore and aft leeway, as well as controls to change the pitch of the blades.
07:56Helicopters were complex, even dangerous flying machines, prone to failure.
08:01But the men and women who took the controls of early helicopters, concentration and daring were equally important.
08:15By the late 1930s, several pioneer helicopters had begun to attract the interest of the military.
08:21The main attraction was the ability to hover.
08:24This was essential if the helicopter were to have potential as a reconnaissance aircraft
08:28that could also swiftly deliver ground forces.
08:31Military sponsorship has, to this day, remained the major factor in the evolution of the helicopter.
08:39The German FW-61 was essentially two rotors mounted on outriggers over an old biplane.
08:45The rotors spun in opposite directions, and this eliminated torque.
08:50German pilot Hannah Reich dramatically demonstrated hovering capability
08:54when she piloted the FW-61 indoors for Adolf Hitler at Deutschlandhalle Exhibition Center.
09:01But control was still a problem.
09:04During one pre-show practice, it landed upside down.
09:07In the United States, helicopter pioneer Igor Sikorsky provided a solution to the long-standing problem of control
09:14by equipping his VS-300 with a vertical tail rotor.
09:18When the main rotor of a helicopter spins, it creates tremendous torque, turning the fuselage in the opposite direction.
09:26The addition of a tail rotor provides a force to counteract this torque.
09:30This became the classic configuration for successful helicopters.
09:34Neil spoke with Sergei Sikorsky about the early helicopters his father designed and flew.
09:39I remember very distinctly the first trainer that my father built, which was swiveled on a post.
09:49He used that to train himself on the controls of the machine.
09:54And then in September of 1939, the first very brief hops.
10:01I think it was a fairly well-held secret that the machine was very erratic, very nervous on the controls.
10:11And in fact, when Dad had to make the first report to the board of directors of United Aircraft, he
10:23chose to show films of the flight.
10:29But a minor technical detail that wasn't revealed to the board of directors was that the films were taken in
10:38slow motion,
10:39which changed all of this weird wobbling into a fairly slow and graceful ballet.
10:45I would say the first free flights took place and the first crash when the aircraft was hit by a
10:54gust of wind and rolled over.
10:56Then it was rebuilt with a slightly different configuration.
11:00And the tests continued with two long ropes from the wheels.
11:06And the two long ropes led to two gentlemen, very athletic gentlemen who kept running back across the airfield, holding
11:14the machine down.
11:15They were out of camera range to the right and to the left, but they were necessary.
11:20And it took approximately maybe six months.
11:24I think you as a professional will appreciate the fact that Dad said to him it was a unique challenge
11:30to design a machine that no one really had designed.
11:34To build it without really being able to pinpoint the stress loads and the nodes and everything else like that.
11:40And then the equally great challenge of climbing into the pilot's seat, firing up the engine, and trying to bring
11:47it into a hover to test fly it while you teach yourself to fly this new machine.
11:51It's the true experimental test pilot.
11:54Yes, sir.
11:55I think many people will remember the famous early flights of the VS 300 and your father wearing the test
12:08pilot wearing a most unusual test pilot hat.
12:11This is the actual hat that Dad wore on the first liftoff with the VS 300.
12:19It became sort of a legend.
12:21Pilots that would come from Korea would ask to put this hat on because somewheres the legend grew, especially among
12:27the Marine Corps pilots,
12:28that if you ever put this hat on, it would mean that you would be lucky and you would never
12:34be hurt by helicopter through the rest of your career.
12:36Oh, may I?
12:38Please do.
12:42Looks good.
12:42I feel a lot better now.
12:47By the beginning of the Korean War, the primary mission of the helicopter was rescue.
12:53Without the need for landing strips, helicopters saved thousands of soldiers wounded or stranded behind enemy lines.
13:00The military was quick to realize that if the helicopter could infiltrate enemy lines to remove soldiers, it could deliver
13:08them as well, along with weapons and supplies.
13:11So helicopters were asked to carry more weight and for longer distances.
13:15As the mission demands of the helicopter increased, so did the stress and strain on the rotor head.
13:23This slow motion footage of an early helicopter blade clearly shows the stresses exerted during flight.
13:34Neil spoke with Dr. Dave Jenny of Sikorsky Aircraft about the evolution of the rotor head.
13:41Dave, this is a restoration?
13:44Quite a major project.
13:46They're just starting the restoration of an S-51, one of the earlier helicopters built in the 40s.
13:51The rotor, of course, provides not just the lift but the control as well.
13:55No wings, no flaps, no rudders on a helicopter.
14:00So each blade is connected to one of these arms on what's called a swash plate.
14:05This one rotates, this one does not.
14:09And they're both mounted on a ball so the whole thing can be tilted.
14:13So if you tilt it and then rotate it, one horn runs up and down as it goes around and
14:19changes the pitch once each time it goes around.
14:21And the blades respond to that and flap and you get controlled motion in the direction you want to go.
14:27The Sikorsky S-51 had aluminum hinges in the 1940s.
14:31The craft could barely carry four people.
14:34Bigger helicopters required larger or more rotors.
14:38So steel was used for stronger hinges.
14:41In the mid-1960s, the development of titanium hinges offered the strength of steel without the weight.
14:51Helicopter manufacturers are striving for simple, less expensive and easy to maintain flying machines.
14:59They're safer and more reliable.
15:02Many of the traditional design problems that make helicopters so complex are being solved today using simplified rotor head designs.
15:13These so-called rigid rotor helicopters, such as this BK-117, might be better described as hingeless rotor machines because
15:24the hinges are replaced with flexible parts.
15:29Experiments with rigid rotor craft began as early as 1946.
15:34Then McDonnell Aircraft Corporation developed, rotor tested and flight tested a ramjet unit on the rotor blade tip.
15:42The rotors had to be rigid to tolerate the high rotation speed.
15:45Called Little Henry Ramjet, this prototype for the Air Force was the first jet propelled rigid rotor helicopter.
15:52Although the rigid rotor concept survives until today, power plants for the helicopter would take another direction.
16:00From the mid-50s on, the development of the turbine engine would give helicopter designers more power.
16:06Bigger and faster helicopters became practical.
16:10By the 1970s, the quest was for rotor heads that could meet the demands of this new generation of helicopters.
16:16The objective was a rotor head that would be easier to maintain, as well as simpler, cheaper and quieter.
16:24One way to do this was to get rid of the numerous bearings and hinges that had allowed the blades
16:29to flap and bend since the days of the auto gyro.
16:32Oil lubricated rotor heads with bearings evolved first into elastomeric bearings, which used layers of steel and rubber to allow
16:40the blades to flap.
16:41The direction today is towards bearingless rotor heads.
16:45In these rigid rotor helicopters, the flexible blades themselves allow the bending and flapping that hinges gave Sierva's auto gyro.
16:54Today, exotic materials like graphite and epoxy composites are being used in the rotor head and the blades.
17:01Neil checked out the flight characteristics of a modern helicopter flying a Navy Seahawk.
17:06In production since the late 1970s, the Seahawk uses titanium hinges and elastomeric bearings.
17:14It has been improved over the years and remains state-of-the-art for helicopters produced in large numbers.
17:20The Seahawk and related models, such as the Black Hawk and Jayhawk, are used in a variety of military missions,
17:27from troop transport and weapons delivery to search and rescue.
17:31The Black Hawk is used extensively for anti-submarine warfare, surveillance, mine delivery and target acquisition.
17:39Now the purpose here in Pension is to make an automatic approach to the water.
17:46This approach will be used more for search and rescue type stuff.
17:50But we're in the hover mode now, it's switched over automatically.
17:53See, I brought up the hover bars and that'll tell me that these hover bars, as long as they stay
17:56centered and I'm not drifting anywhere.
17:58And that's a Doppler radar?
17:59That's a Doppler radar, right?
18:01And that'll just sit here and keep us hovering.
18:02And this is as comfortable as, you know, at night I'm plenty comfortable sitting in here.
18:07Also, you just press a button and it departs on its own.
18:10It'll fly you back.
18:11This airplane will fly you back to 500 feet and I think it's 70 knots or 90 knots.
18:19Companies around the world are moving toward hingeless, bearingless rotor heads with few moving parts.
18:25The number of rotor head parts in these state-of-the-art designs is a fraction of what it was
18:30a decade ago.
18:32The French company Aerospatiale, with its Starflex rigid rotor,
18:36manufactures helicopters that are faster, have a higher payload and use less fuel.
18:42The combination of composite rotor heads and blades means that parts are stronger and corrosion resistant.
18:48Maintenance is easier because there's no more lubrication.
18:56Another rigid rotor helicopter, the German BK-117, is the result of design and development cooperation between MBB and Kawasaki.
19:10It is designed for a variety of civil missions, such as air ambulance and law enforcement.
19:23The main rotor head is titanium and has four blades made from fiber reinforced composite materials.
19:30The strength and flexibility of these materials eliminates the need for the hinges that made earlier helicopter rotors so complex.
19:38Flapping motions are absorbed by the inherent elasticity of the blades.
19:48With this rotor head simplicity comes an amazing level of maneuverability.
20:03Flight control is achieved by changes in blade pitch angle on both the main and tail rotors.
20:09The BK has a semi-rigid two-blade tail rotor system.
20:21The next generation of helicopters will be even quieter, more comfortable and more maneuverable.
20:27Some of this maneuverability will come from developments in the tail rotor, like the fan and fin design.
20:33The Boeing Sikorsky H-76B has a fan tail anti-torque system that gives the aircraft unusual agility and maneuverability
20:42at air speeds up to 80 knots.
20:44This helicopter is demonstrated sideward and rearward flight of 70 knots.
20:49It's interesting that the most recent advance in rotor head design, the rigid rotor, was first used in vertical tail
20:57rotors.
20:58Rotor craft design has made great strides since the first fitful attempts at vertical flight.
21:05Manufacturers worldwide are continuing to make progress towards simpler, safer and more efficient rotor craft.
21:13Join me again for First Flights.
21:56First Flights, the flagship team, tour will be headed into
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