In 1967 Sikorsky investigated new light-weight dual-hardness aircraft armor. The tilt-rotor has two counter-rotating main rotors or propellers that are mounted on engine nacelles at the ends of a short wing. Two P&WA PT-6 engines were used to power the rotors. At takeoff, this means the aircraft can lift off and move away quickly without needing to tilt forward. Design studies showed that four-bladed rotors would dramatically reduce the rotors vibratory characteristics. The data and discussions lead us to believe the proposals were not consistently evaluated to deliver the best value in the interest of the Army, our soldiers and American taxpayers, Sikorsky said in a statement. Also, the Invictus has a wing. S-70A-1 Desert Hawk; variant for Saudi Arabian military S-70A-1L Saudi Desert Hawk Medevac variant S-70A-5 Variant for Philippine Air Force S-70A-9 Sikorskyis developing plans to design and build a civilian X2 Technology helicopterthat would satisfy operators? This was a major breakthrough in helicopter technology. That's in an assault configuration; there will also be an attack variant that shares a common fly-by-wire drivetrain and many other systems, but has a different composite fuselage and is much more heavily armed. The helicopter has a small rotor at the end of a tail boom (Sikorsky) Or a fan instead of the propellor (Fenestron Aerospatiale) Or a jet thrust output (Cierva W.9, NOTAR) 4. Military Potential of the ABC, George Price, American Helicopter Society Vertiflight magazine, November/December, 1982. Update: In an email, an Army spokesperson says the service plans to make a decision for one FARA aircraft in fiscal year 2025, which for the US government begins Oct. 1, 2024. When Black Marxist Angela Davis found out her ancestors owned slaves. They will likely sell it in the commercial market as well. The mainadvantage of helicopters? Rival contractors Bell and Sikorsky (part of Lockheed Martin) both say they have transcended those limits to build dramatically faster rotorcraft, but they have taken very different paths. Its just $1 per month . Here are more target drones for your ne In a separate project, Sikorsky is working with Boeing on an X2-based helicopter called the SB-1 Defiant in a precursor program to the the Army-led Future Vertical Lift initiative, which aims to find a next-generation medium-lift helicopter for use across all the military branches. Independent control for upper and lower rotor of a rotary wing aircraft Patent number: 11440650 Abstract: An aircraft is provide including an airframe, an extending tail, and a counter rotating, coaxial main rotor assembly including an upper rotor assembly and a lower rotor assembly. The rotor system was destroyed. In phase 1 of the contract manufacturing techniques, including methods for cutting, joining, forming and finishing the material, were evaluated. One month later the first XH-59A aircraft experienced a low speed accident on the flight field. Here's how the machine is coming together right now. This used two very rigid counter-rotating rotors, allowing rotor lift at high speeds to migrate off the rotor centerline to the advancing sides of the rotor discs, thus eliminating retreating blade stall which limits the speed of conventional helicopters. Vertipedia provides high-quality information on current and historical aircraft, as well as notable milestones in the history of vertical flight and biographical information on the people who made them happen. The Containerized Flight Training Device (CFTD) is a full-mission flight simulator that will allow flight crews to train on the full scope of Marine Corps heavy lift missions, including external lift operations, and executing degraded visual environment take-offs and landings. Transmission for a coaxial counter rotating rotor system Abstract A transmission system for a hybrid aircraft is driven by a plurality of driveshafts and drives a translational propulsion. With this rotor configuration, the rotors capability to generate lift would not drop off with speed, or with altitude. That feat has since been eclipsed -- by a slim margin -- by the Eurocopter X3. Lockheed Sikorsky-Boeings SB Defiant has taken flight more recently than Textron-Bells 280 Valor, however both appear to be showing early promise. The spar tubes were then hot formed into an elliptical shape, while twisted, in ceramic hot-forming dies. This was phased out at speeds from 40 to 80 knots and yaw control was provided by rudders. The result was a prototype that could fly at 290 mph (460 km/h, 250 kn). The demonstrated agility, stability, and increased speed would provide tactical flight crews with additional capabilities to fight and win on the modern battlefield. The team gave the aircraft the best rating possible for hover out-of-ground-effect (HOGE) handling qualities. in large part because of the two counter-rotating rotors. That depends on who you believe and what the mission is. That required changing how the rotors flap, improving materials, and, above all, increasing the size of the rotors relative to the aircraft. Bell Boeing V-22 Osprey. The SB>1 Defiant is a joint multi-role medium-class Future Vertical Lift technology demonstrator built around Sikorsky's X2 platform, which uses two counter-rotating rigid blades on the top of the aircraft to eliminate the retreating blade stall problem that puts a ~150 mph (~240 kmh) speed limit on helicopters with a single top rotor. Learn More. The advancing blades are effectively going faster, relative to the air, because they add the helicopters forward movement to their own, so they generate more lift. This human and technical feat has given rise to a family of aircraft that have been entered into the history of aviation. In late May, Sikorsky first turned on power to its S-97 prototype, which at the time was about halfway through assembly. The extra lift from each rotors advancing blade balances out the diminished lift from the opposite sides retreating blade, which gets rid of retreating blade stall. Sikorsky's technology puts two main rotors on top of each other, rotating in opposite directions, which balances out the lift profile on either side and allows the craft to fly much faster up to twice the airspeed of a regular helicopter while maintaining excellent handling and agility. Watch later. When it comes to the fastest helicopters, the V-22 is by far the fastest- except it isn't really a helicopter at all. Part 1 of a narrative series illustrating how Americas armed forces might use technology to accomplish their most demanding missions. This successful R&D program demonstrated the promised speed and altitude performance. Thirty years later, with advances in the available technologies in the areas of blade construction, shape and airfoil design, vibration control, propulsion system integration, advanced composite material application and fly-by-wire-control system design, Sikorsky went back to the ABC concept in the development on the X-2 high speed aircraft. But all of these were two conventional rotors mounted in a coaxial counter-rotational configuration. The rotor diameter was therefore reduced to 36 ft. Blade construction was similar to that of the wind tunnel rotor. - four smaller disks have a smaller effective lifting area than a single large disk, all things being equal. The rotor system is typically of the fully-articulated design. All Rights Reserved. : The Future Vertical Lift program aims to create revolutionary replacements for todays military helicopters. The XH-59A is currently in storage at the U.S. Army Aviation Museum at Ft. Rucker, Alabama. Five years in the US Army as a translator (German and Polish). The answers lie in the speed limits built into the physics of how a helicopter flies. At high speeds, Gehler claimed, tiltrotors are far and away more maneuverable than compound helicopters: Right now, compound coax is having challenges turning at high speed., Thats true of less sophisticated compound helicopter designs, said Van Buiten, but not of theirs, in large part because of the two counter-rotating rotors. Other American helicopter pioneers like Larry Bell, Stanley Hiller, and Frank Piasecki subsequently employed this convention. These useful machines handle everything from tourism to search and rescue. Built in Connecticut, the Sikorsky CH-53K is the latest in the Companys proud helicopter legacy. At the helicopters tail will also someday be a propeller that can help the aircraft accelerate or decelerate. Igor Sikorsky's helicopter patent sketch, 1930. New York, This issue of the newsletter is devoted to the aircraft designs and paintings by Andy Whyte, who had a 40 year career at Sikorsky Aircraft. (Each propeller may have an electric motor & electricity could be provided by a central gas turbine engine (that also provides extra forward thrust)!). But how? However, the counter-rotating blades also brings a sound advantage by virtue of enabling quieter, stealthier flight trajectories generating a much smaller acoustic signature. The tailcone and empennage would be conventional aluminum structure. Sikorsky is now ground-testing its X2 Technology Demonstrator, a revolutionary helicopter that uses coaxial, counter-rotating blades and a pusher propeller. Want the latest defense industry news? With a composite airframe, the 36-foot-long single-engine S-97 prototype has a maximum gross weight of just over 11,000 pounds. The Containerized Flight Training Device (CFTD) is a full-mission flight simulator that will allow flight crews to train on the full scope of Marine Corps heavy lift missions, including external lift operations, and executing degraded visual environment take-offs and landings. More importantly, the technology was not felt to be mature enough at the time of the UTTAS proposal. Published Jun 30, 2022 3:03 PM EDT. At the aircrafts nose is a simulated weapona 3D-printed substitute for the actual 20mm cannon that would someday hang from under the aircraft in the same spot. In an unconventional approach, a concept was proposed to build a helicopter fuselage with this armor, rather that simply adding the armor parasitically around sensitive areas of the vehicle. They were refined in the S-97 Raider and now the SB>1. Two companies are competing against one another in a program called FARA (Future Attack Reconnaissance Aircraft) to create the whirlybird that will fill that role. Whats visible is a simulated version of a system called the modular effects launcher, which someday could carry missiles, rockets, or other kinetic objects, like drones or other sensors. The X2 won the 2010 Collier Award for demonstrating a revolutionary 250 knot helicopter, which marks a proven departure point for the future development of helicopters by greatly increasing their speed, maneuverability and utility. The Collier Award is given out once each year for the greatest achievement in aeronautics or astronautics in America, with respect to improving the performance. ?The X2Technology Demonstrator is an integrated suite of technologies intended toadvance the state-of-the-art, counter-rotating coaxial rotor helicopter. These advancements will prove critical for Army operations in a theater like the Indo-Pacific where the dominant geographical feature is water and yet land forces remain the predominant military force in the majority of nations in the region, Army Chief of Staff Gen. James McConville said following the flight demo, according to anArmy report. The rigid rotors provided high control power. We remain confident Defiant X is the transformational aircraft the Army requires to accomplish its complex missions today and well into the future, Sikorsky said in its protest. Kamov has been making dual contrarotating rotor helicopters since the 1940-s. The FVL competitors havent flown yet, but the Bell V-280 is designed to go 280 knots (320 mph), while the Sikorsky-Boeing SB>1 is derived from the Collier Trophy-winning X2 demonstrator, which reached 250 knots (287 mph). It never went beyond the concept stage. In general, tiltrotors dont offer the kind of agility and maneuverability that a compound design does, said Richard Aboulafia, aviation analyst at the Teal Group. The following reference has great detail of information on the full ABC program, including manufacturing technology used, aircraft description, and ground and flight test results: American Helicopter Society paper The ABC Rotor A Historical Perspective, Robert K. Burgess. Sikorsky, a Lockheed Martin company, today delivered its 5,000th "Hawk" variant helicopter, a U.S. Army UH-60M Black Hawk. Osborn previously served at the Pentagon as a Highly Qualified Expert with the Office of the Assistant Secretary of the ArmyAcquisition, Logistics & Technology. The. Some balance is needed in order to keep the machine stable usually either another, counter-rotating rotor or a small vertically-mounted tail rotor. There are two main ways to overcome this inherent speed limit of helicopters: tilt-rotors, like Bells V-280, or compound helicopters, like the Boeing-Sikorsky SB>1. Copyright 2023 Center for the National Interest All Rights Reserved. Taking action to help you protect what matters most. The Drive reports that that FLRAA decision could happen in September. Rob Verger [Edit #1] My initial answer wasn't very clear so here are some expanded details: A rigid rotor design. The Army set up the Utility Tactical Transport Aircraft System (UTTAS) program to develop this new transport helicopter. Aviation Week & Space Technology, October 12, 1970, page 65, Armor Used as Airframe for Helicopter. Joining the team as a motorcycle specialist, he's covered just about everything for New Atlas, concentrating lately on eVTOLs, hydrogen, energy, aviation, audiovisual, weird stuff and things that go fast. The Army plans to publish new requirements for the helicopter by 2021 based upon data gathered and lessons learned through ongoing experiments,weapons developmentand test flights, the report added. When it enters service, the Defiant will carry a crew of four and a cabin equipped for up to 12 combat-ready troops or eight medevac litters. (The X2 demonstrator had a gross weight of 6,000 pounds.) On June 6,2005, Sikorsky announced that it would build and test a technology demonstratorthat would maneuver like a conventional helicopter and cruise at 250 knots (288mph), which is at least 60 percent faster than conventional helicopters. Been watching the x2 program progress for the last few years. We have invested in developing and demonstrating hypersonic technology for over 30 years. One of the concerns with the coaxial rotor arrangement was how to provide aircraft yaw control. The development of the next-generation rotary wing technology allowed Sikorsky to select suppliers for the high speed X2 prototype aircraft intended for flight test and evaluation by the US Army. And lifting payload is a biggie for the mission profile. The aircraft is the first S-100 Helicopter. Oct 26, 1972 : Igor Sikorsky dies due a heart attack at the age of 83. Sikorsky Delivers 5,000th "Hawk," Highlights Versatility and Future of Iconic Helicopter. High-power engines are necessary to drive rotating blades, which . The rotors of the S-97 are designed based on the "Advancing Blade Concept"only the blades moving forward are pitched, while retreating blades are "unloaded" to reduce drag. Sikorsky hopes that the sleek, speedy design of the S-97, unveiled Thursday, will win the favor of the US Army as a potential replacement for OH-58D Kiowa Warrior helicopter, an airframe whose history dates back to the Vietnam War era, and as an aerial platform for special operations units. The helicopter model has Sikorsky configuration, i.e., main rotor in perpendicular combination with a tail rotor. Both helicopters, Raider and Defiant, have similar design elements: two counter-rotating top rotors, and a propeller in back. The hubs spin in opposite directions, whicheliminates the torque effect. In 1972, both Boeing and Sikorsky were contracted to develop prototypes for this new breed of combat helicopter. Sikorsky Aircraft Corporation: Counter-rotating rotor system with stationary standpipe US20150139799A1 (en) * 2013-11-15: 2015-05-21: Sikorsky Aircraft Corporation . The subject of this newsletter is in response to an archive members question, How Are Sikorsky Helicopters Named?. He writes occasionally, on topics from GPS to James Bond. Join PopSci+ to read sciences greatest stories. Its significantly smaller than Defiant.. The X2 demonstrator will feature a coaxial design (two rotors on . American helicopters manufactured by companies like Sikorsky, Boeing Vertol, Bell, and MD Helicopters all appear to rotate counter-clockwise [when viewed from above] In 1972 when the XH-59A design was initiated, Sikorsky was interested in an Aerial Armored Reconnaissance Vehicle, or AARV, which was a smaller size. 80 years ago, Russian-born inventor-engineer and pilot Igor Sikorsky made the first flight of his self-designed single-rotor helicopter, the VS-300. Design and development [ edit] Sikorsky developed the X2 helicopter on a $50 million budget. Presented at the 37th AHS Annual Forum, New Orleans, LA, May, 1981. here for reprint permission. The body shape of the aircraft does appear to blend somewhat gradually up to the rotor blades, as if to decrease sharp angles and engineer a gradual incline or slope from the front end of the aircraft up through the body to the rotor blades. The coaxial design is uncommon, but not unprecedented -- it's long been a distinguishing characteristic of helicopters from Russian manufacturer Kamov. The Sikorsky S-97 Raider has an unusual configuration, with two coaxial main rotors on top and a pusher propeller in the rear. Up to twice as fast as a regular helicopter. An extensive flight test program of about 170 flight hours was accomplished through 1981. The downside of a tilt-rotor is the mechanical complexity and weight of the mechanisms needed to do the tilting as well as the need to switch modes in flight. "Extensivetest instrumentation is also being installed as preparation for its firstflight.". When you purchase through links on our site, we may earn an affiliate commission. The ABC had the additional advantages of not requiring a tail rotor, and a design where the control swashplates for the two rotors were buried below the rotors, both further reducing the vulnerable area of the aircraft against ballistic threats. Two J-60 engines and their North American Saberliner pods (which were previously used on Sikorskys S-61F experimental compound helicopter) were used for auxiliary propulsion. We develop laser weapon systems, radio frequency and other directed energy technologies for air, ground and sea platforms to provide an affordable countermeasure alternative. Helicopters dont really fly, they just beat the air into submission. This type of configuration does not need a tail rotor because the main rotors are counter rotating. Mosthelicopters have a ?disc? The S-97 prototypes, Sikorsky has said, will go beyond the X2 aircraft in several ways, demonstrating precision maneuvers in low flight speed, high G turning maneuvers at over 200 knots, and hot-day hover performance at altitudes up to 10,000 feet. Space is part of Future US Inc, an international media group and leading digital publisher. Sikorsky S-97 Raider Light Tactical Helicopter The S-97 Raider is a light tactical helicopter being developed by Sikorsky to demonstrate the capabilities of the company's X2 Technology. That might require different designs for different missions and different services, Aboulafia told me, with the military ending up with a mix of tiltrotors, compound helicopters, and traditional helicopters. My team strives to advance aircraft engine capability through prioritization, definition, and execution of technology maturation programs. Two aircraft were fabricated. Sikorsky, a Lockheed Martin company, filed a formal protest this week asking the U.S. Government Accountability Office (GAO) to review the Armys decision for what the service has called the Future Long-Range Assault Aircraft (FLRAA). Groundtesting of the X2 Technology Demonstrator is still underway and Sikorsky hasn'tyet scheduled a date for the aircraft's first flight, said company spokesmanPaul Jackson. It was a small toy powered by rubber bands, but it would turn out to be his life's work. Stability and control proved to be excellent. Where a standard helicopter uses a side-facing tail rotor to offset the torque of the main rotor in front, the pusher propeller of the S-97 will assist in high-speed acceleration and deceleration. "Experimentalaircraft have minds of their own ? Tail Rotors. The counter-rotating blade is basedupon innovative engineering methods that combines airplane-like speeds with the hovering and maneuvering capabilities unique to helicopters. This had the integrated propulsion system with twin General Electric T700-GE-700 engines driving both the rotor system and a ducted pusher propeller. When vertical, they act like giant propellers, allowing fast and fuel-efficient flight with no risk of retreating blade stall (because of the angle at which they meet the air). Sikorsky would attend schools in Paris and Ukraine, studying the sciences. This proved the basic advancing blade concept and led to a contract in 1972 with the U.S. Army for the design, fabrication, and flight testing of the XH-59A advancing blade concept demonstrator aircraft. | Whichever helicopter becomes the Armys choice for the FARA role will be powered by a single engine, which is General Electrics T901. Mike Glenn can be reached at mglenn@washingtontimes.com. Composite materials technology would soon appear which could produce a better blade, with almost infinite options in geometry, at a substantially reduced cost and lighter weight. Missions Armed reconnaissance Length 37ft Width 16ft Rotor Diameter 34ft Speed 220k Expand The Washington Times The contract is worth $1.3 billion and could accelerate as additional helicopters are bought by the U.S. and other countries. A 40 ft. diameter test rotor was fabricated in 1970 and tested in the NASA Ames 40 x 80 ft. wind tunnel. The conclusion was that the control system gains were too low to cover all flight modes. collectivelycalled "X2 Technology" ?that would significantly change helicopter flight. However,the new Sikorsky aircraft will have one or more aft-mounted ?pusher? We are testing the limitsand pioneering this exciting innovation.". (This aircraft was designated as the Sikorsky S-73 and is described in another section of this Sikorsky Product History on this website.) advance ratios, the potential for greater tion for applications of HHC to a counter-interharmonic coupling exists, rotating aircraft at very high speed in the 12000 ib range of gross weight. When the job is hot, high, dirty or dangerous, the K-MAX is ready performing multiple missions. Designs were prepared for the rotor, drive system, and controls, and preliminary designs of mission aircraft were studied. The Advancing Blade Concept exhibited excellent potential for application to tactical Army aircraft. The main fuselage of the AARV was to be constructed from half-inch thick dual hardness armor. The Sikorsky S-97 Raider is a high-speed scout and attack compound helicopter [2] based on the Advancing Blade Concept (ABC) with a coaxial rotor system [3] under development by Sikorsky Aircraft. Contact the author here. Although designed in to the gearbox, this feature was not found to be required during the development flight test program. Copyright 2023 Breaking Media, Inc. All rights reserved. Helicopter with counter-rotating coaxial rotors without cyclic variation of pitch. It is not at all unusual for weapons system requirements to be refined throughout the developmental process of a new platform, given that new things are learned on an ongoing basis. TheCH-53K King Stallionadvances Sikorskys 50 years of manufacturing and operational success with its CH-53A, CH-53D/G, and CH-53E predecessors. The aircraft has been assigned the registration N100FV. "Certainlycivilian travel appears to be a promising market. And civilian uses are already being considered. To replace the Apache gunships, an aircraft needs to fly low and slow over the battlefield, ducking behind cover when enemy anti-aircraft units appear, then popping up again to fire guns and missiles. In September 2010, Sikorsky's similarly designed X2 technology demonstrator reached a speed of 250 knots (287 mph), a feat that the longtime rotorcraft maker at the time said "unofficially shattered the helicopter world speed record." At higher speeds, moreover, helicopters run into a problem called retreating blade stall. You dont want to wait for your rotors to tilt from vertical to horizontal flight mode like a V-22 or V-280, Van Buiten argued. Source: Sikorsky ?Customers aredemanding greater speed but without sacrificing any of the unique capabilitiesthat make helicopters theideal platform for countless civil and military missions.? For fb36 wondering why not a quad? in the industry,? The Sikorsky-Boeing SB-1 Defiant concept for the Joint Multi-Role demonstrator, a predecessor to the Future Vertical Lift aircraft. CSSCustPortalSuppt@sikorsky.com. It has already committed heavily to the V-22 Osprey tiltrotor jointly built by Bell and Boeing. Boeing-Sikorsky RAH-66 Comanche. (Bells partner on the V-22, Boeing, switched sides on FVL). Do Not Sell or Share My Personal Information. But that unconventional rotor placement will help drive the S-97's exceptional speed. Bring back the COMANCHE ! The retreating blades are going slower relative to the air, because they subtract the helicopters speed from their own, so they generate less lift. Sikorskys compound-helicopter experiments also started in the 1970s with the experimental XH-59, then were revived in the X2 demonstrator now in the Smithsonian. Raider X is one of two candidates in the Army's Future Attack Reconnaissance Aircraft competition. Some balance is needed in order to keep the machine stable--usually either another, counter-rotating rotor or a small vertically-mounted tail rotor. SpaceX Crew-6 astronaut launch: Live updates, Heli-Skiing: Winter Thrills in Remote Areas, Marvel's 'Star Wars' comics celebrate Women's History Month with Peach Momoko covers. Pitch change was accomplished with conventional stack bearings. American Helicopter Society paper An ABC Status Report, Arthur W. Linden and Andrew J. Ruddell. Part 2 of a narrative series illustrating how Elbit Americas USA-manufactured products enable customers to successfully accomplish their most demanding missions. X2Technology aircraft will take-off and land vertically, hover, maneuver at lowspeeds, and transition from hover to forward flight like regular helicopters. Whilerotor bladesare, quite naturally, likely to generate some kind of radar signal to enemy systems, depending upon range and the fidelity of a given air defense platform. +1 (800) WINGED-S (946-4337) It is similar to a tandem rotor system when in helicopter mode. Nelson Hyde Chick - this will likely be used for more then just war. June 6, 2005 Sikorsky Aircraft today announced plans to build and test a demonstrator for a new class of coaxial X2 Technology helicopters that maintain or improve on all the vertical flight capabilities of rotorcraft and whose high speed configuration will cruise at 250 knots. The counter-rotating blades are engineered toreduce high-speed vibrations, steady the aircraft and best optimize massive amounts of thrust coming from a pusher prop mechanism in the rear of the aircraft. Terms of Use / Privacy Policy / Manage Newsletters, - Do not sell my information, IAI eyes Heron MK 2 for Aussie armed drone sale, US Army picks 5 companies to compete for RQ-7B Shadow replacement, Boeing awarded $1.2 billion for E-7A Wedgetail production deal, Despite Saudi statement, KSA not joining UK-led FCAS program at least not yet, All new Apache helicopters will have Australian components, Some F-35s will require engine hardware fix, Pratt exec says, BAE unwraps Strix VTOL strike drone with 800km range at Avalon, In the era of Great Power competition, state-of-the-art technologies are needed, Russia turning to N. Korea, Iran for more weapons ahead of spring offensive, NATO head warns, Sovereignty a vexing problem for Australian defense, Eye on exports, Lockheed Australia targets all domain AIR 6500, US State Department clears $500 million in anti-radiation missiles for Australia, Unmanned drones take too many humans to operate, says top Army aviator, Biggest-ever Avalon Air Show draws a dozen key US officials. Spice up your small talk with the latest tech news, products and reviews. Privacy Terms of Use EU and UK Data Protection Notice Cookies. This can get so unbalanced that it threatens to tip the helicopter over altogether if you don't stay beneath a defined maximum airspeed. Sikorsky hopes the X2 will fly nearly twice as fast as today's helicopters. However, UnitedTechnologies Corp. subsidiary Sikorsky Aircraft, the oldest name in helicoptermanufacturing, is working to change that by developing a helicopter that willfly almost as fast as a conventional aircraft ? The advancing blade concept had been shown in a textbook in the 1930s, but the structural requirements for the blades were well beyond the technology of the day. However, they each claim their aircraft is more agile a crucial consideration when landing troops in tight spaces or ducking behind hills and trees to hide from radar. Yaw control was achieved by using differential collective pitch in hover. The two main rotors of the S-97 are coaxial, and they rotate in opposite directions, driving both lift and forward flight. Born in Kiev, Ukraine, in 1889 to a family of physicians, Igor Sikorsky actually built his first helicopter at the age of 12. That cannon is attached to a turret. A compound helicopter has no wings and two separate sets of blades, a rotor that stays a rotor and a propeller that stays a propeller.