A tiltrotor is an
aircraft which generates
lift and
propulsion by way of one or more powered
rotors (sometimes called ''proprotors'') mounted on rotating
shaft
Shaft may refer to:
Rotating machine elements
* Shaft (mechanical engineering), a rotating machine element used to transmit power
* Line shaft, a power transmission system
* Drive shaft, a shaft for transferring torque
* Axle, a shaft around whi ...
s or
nacelles usually at the ends of a fixed
wing. Almost all tiltrotors use a
transverse rotor
Transverse rotor aircraft have two large horizontal rotor assemblies mounted side by side.
Single-rotor helicopters (unicopters) need an additional tail rotor or tail exhaust to neutralize the reactional angular momentum produced by the mai ...
design, with a few exceptions that use other
multirotor layouts.
Tiltrotor design combines the
VTOL capability of a
helicopter with the speed and
range
Range may refer to:
Geography
* Range (geographic), a chain of hills or mountains; a somewhat linear, complex mountainous or hilly area (cordillera, sierra)
** Mountain range, a group of mountains bordered by lowlands
* Range, a term used to i ...
of a conventional
fixed-wing aircraft
A fixed-wing aircraft is a heavier-than-air flying machine, such as an airplane, which is capable of flight using wings that generate lift caused by the aircraft's forward airspeed and the shape of the wings. Fixed-wing aircraft are distinc ...
. For vertical flight, the rotors are angled so the
plane of rotation is horizontal, generating lift the way a normal
helicopter rotor
A helicopter main rotor or rotor system is the combination of several rotary wings (rotor blades) with a control system, that generates the aerodynamic lift force that supports the weight of the helicopter, and the thrust that counteracts aerody ...
does. As the aircraft gains speed, the rotors are progressively tilted forward, with the plane of rotation eventually becoming vertical. In this mode the rotors provide
thrust as a
propeller
A propeller (colloquially often called a screw if on a ship or an airscrew if on an aircraft) is a device with a rotating hub and radiating blades that are set at a pitch to form a helical spiral which, when rotated, exerts linear thrust upon ...
, and the
airfoil
An airfoil (American English) or aerofoil (British English) is the cross-sectional shape of an object whose motion through a gas is capable of generating significant lift, such as a wing, a sail, or the blades of propeller, rotor, or turbine.
...
of the fixed wings takes over providing the lift via the forward motion of the entire aircraft. Since the rotors can be configured to be more efficient for propulsion (e.g. with root-tip twist) and it avoids a helicopter's issues of
retreating blade stall, the tiltrotor can achieve higher
cruise speed
Cruise is the phase of aircraft flight that starts when the aircraft levels off after a climb, until it begins to descend for landing. Cruising usually consumes the majority of a flight, and it may include changes in heading (direction of flight ...
s and
takeoff weights than helicopters.
A tiltrotor aircraft differs from a
tiltwing in that only the rotor pivots rather than the entire wing. This method trades off efficiency in vertical flight for efficiency in
STOL
A short takeoff and landing (STOL) aircraft is a conventional fixed-wing aircraft that has short runway requirements for takeoff and landing. Many STOL-designed aircraft also feature various arrangements for use on airstrips with harsh conditio ...
/
STOVL operations.
History
![XV-15 N703NA USCG](https://upload.wikimedia.org/wikipedia/commons/9/9a/XV-15_N703NA_USCG.jpg)
The first work in the direction of a tilt-rotor (French "Convertible") seems to have originated ca. 1902 by the French-Swiss brothers Henri and Armand Dufaux, for which they got a patent in February 1904, and made their work public in April 1905.
Concrete ideas of constructing
vertical take-off and landing (VTOL) aircraft using helicopter-like rotors were pushed further in the 1930s. The first design resembling modern tiltrotors was patented by George Lehberger in May 1930, but he did not further develop the concept. In
World War II, Weserflug in Germany came up with the concept of their P.1003/1 around 1938, which was tilting to the top with part of the wings but not the full wings, so it may be in between tilt-rotor and tilt-planes. Shortly after a
German
German(s) may refer to:
* Germany (of or related to)
**Germania (historical use)
* Germans, citizens of Germany, people of German ancestry, or native speakers of the German language
** For citizens of Germany, see also German nationality law
**Ger ...
prototype
A prototype is an early sample, model, or release of a product built to test a concept or process. It is a term used in a variety of contexts, including semantics, design, electronics, and Software prototyping, software programming. A prototyp ...
, the
Focke-Achgelis Fa 269, was developed starting in 1942, which was tilting to the ground, but never flew.
Platt and LePage patented the PL-16, the first American tiltrotor aircraft. However, the company shut down in August 1946 due to lack of capital.
Two prototypes which made it to flight were the one-seat
Transcendental Model 1-G
The Transcendental Model 1-G was an experimental American tiltrotor prototype of the 1950s. It was a single-seat aircraft powered by a single piston engine, and was the first tiltrotor to fly.Norton ''Air Enthusiast'' 2005, p. 49. A single exampl ...
and two seat Transcendental Model 2, each powered by a single reciprocating engine. Development started on the Model 1-G in 1947, though it did not fly until 1954. The Model 1-G flew for about a year until a crash in
Chesapeake Bay on July 20, 1955, destroying the prototype aircraft but not seriously injuring the pilot. The Model 2 was developed and flew shortly afterwards, but the
US Air Force withdrew funding in favor of the Bell XV-3 and it did not fly much beyond hover tests. The Transcendental 1-G is the first tiltrotor aircraft to have flown and accomplished most of a helicopter to aircraft transition in flight (to within 10 degrees of true horizontal aircraft flight).
Built in 1953, the experimental
Bell XV-3 flew until 1966, proving the fundamental soundness of the tiltrotor concept and gathering data about technical improvements needed for future designs.
![VTOL DiscLoad-LiftEfficiency](https://upload.wikimedia.org/wikipedia/commons/e/e5/VTOL_DiscLoad-LiftEfficiency.svg)
A related technology development is the
tiltwing. Although two designs, the
Canadair CL-84 Dynavert
The Canadair CL-84 "Dynavert", designated by the Canadian Forces as the CX-131, was a V/STOL turbine tiltwing monoplane designed and manufactured by Canadair between 1964 and 1972. Only four of these experimental aircraft were built with three ...
and the
LTV XC-142
The Ling-Temco-Vought (LTV) XC-142 was a tri-service tiltwing experimental aircraft designed to investigate the operational suitability of vertical/short takeoff and landing (V/STOL) transports. An XC-142A first flew conventionally on 29 Septemb ...
, were technical successes, neither entered production due to other issues. Tiltrotors generally have better hover efficiency than tiltwings, but less than helicopters.
In 1968, Westland Aircraft displayed their own designs—a small experimental craft (We 01C) and a 68-seater transport We 028—at the
SBAC Farnborough Airshow.
In 1972, with funding from
NASA and the
U.S. Army,
Bell Helicopter Textron started development of the
XV-15
The Bell XV-15 is an American tiltrotor VTOL aircraft. It was the second successful experimental tiltrotor aircraft and the first to demonstrate the concept's high speed performance relative to conventional helicopters.
Development Early VTOL ...
, a twin-engine tiltrotor research aircraft. Two aircraft were built to prove the tiltrotor design and explore the operational flight envelope for military and civil applications.
["History of tiltrotor technology", NASA Ames Research Center](_blank)
In 1981, using experience gained from the XV-3 and XV-15, Bell and
Boeing Helicopters began developing the
V-22 Osprey
The Bell Boeing V-22 Osprey is an American multi-mission, tiltrotor military aircraft with both vertical takeoff and landing (VTOL) and short takeoff and landing (STOL) capabilities. It is designed to combine the functionality of a convention ...
, a twin-turboshaft military tiltrotor aircraft for the
U.S. Air Force and the
U.S. Marine Corps
The United States Marine Corps (USMC), also referred to as the United States Marines, is the maritime land force service branch of the United States Armed Forces responsible for conducting expeditionary and amphibious operations through comb ...
.
Bell teamed with Boeing in developing a commercial tiltrotor, but Boeing went out in 1998 and Agusta came in for the
Bell/Agusta BA609.
[ This aircraft was redesignated as the ]AW609
The AgustaWestland (now Leonardo) AW609, formerly the Bell/Agusta BA609, is a twin-engined tiltrotor VTOL aircraft with a configuration similar to that of the Bell Boeing V-22 Osprey. It is capable of landing vertically like a helicopter while ...
following the transfer of full ownership to AgustaWestland in 2011. Bell has also developed a tiltrotor unmanned aerial vehicle (UAV), the TR918 Eagle Eye.
Russia has had a few tiltrotor projects, mostly unmanned such as the Mil Mi-30
__NOTOC__
The Mil Mi-30 (also known as the Vintoplan) was a Russian tiltrotor STOL/VTOL concept that originated in 1972. The Mil Mi-30 Vintoplan would have been a transport aircraft for up to 19 passengers or two tons of cargo. Its purpose was to ...
, and has started another in 2015.
Around 2005["Bell-Boeing's QTR selected for Heavy Lift study"](_blank)
. Boeing, 22 September 2005.–2010, Bell and Boeing teamed up again to perform a conceptual study of a larger Quad TiltRotor (QTR) for the US Army's Joint Heavy Lift (JHL) program. The QTR is a larger, four rotor version of the V-22 with two tandem wings sets of fixed wings and four tilting rotors.
In January 2013, the FAA defined US tiltrotor noise rules to comply with ICAO
The International Civil Aviation Organization (ICAO, ) is a specialized agency of the United Nations that coordinates the principles and techniques of international air navigation, and fosters the planning and development of international a ...
rules. A noise certification will cost $588,000, same as for a large helicopter.
AgustaWestland says they have free-flown a manned electric tiltrotor in 2013 called Project Zero
Project Zero is a team of security analysts employed by Google tasked with finding zero-day vulnerabilities. It was announced on 15 July 2014.
History
After finding a number of flaws in software used by many end-users while researching other p ...
, with its rotors inside the wingspan.
In 2013, Bell Helicopter CEO John Garrison responded to Boeing's taking a different airframe partner for the US Army's future lift requirements by indicating that Bell would take the lead itself in developing the Bell V-280 Valor, with Lockheed Martin.
In 2014, the Clean Sky 2 program (by the European Union and industry) awarded AgustaWestland and its partners $328 million to develop a "next-generation civil tiltrotor" design for the offshore market, with Critical Design Review near the end of 2016. The goals are tilting wing sections, 11 metric tons Maximum takeoff weight, seating for 19 to 22 passengers, first flight in 2021, a cruise speed of 300 knots, a top speed of 330 knots, a ceiling of 25,000 feet, and a range of 500 nautical miles.[8.6 Next Generation Civil Tiltrotor (NextGenCTR) Project – WP1]
pages 254-301. Size: 747 pages, 23 MB. '' Clean Sky 2'', 27 June 2014. Accessed: 7 October 2014.
Technical considerations
Controls
In vertical flight, the tiltrotor uses controls very similar to a twin or tandem-rotor helicopter. Yaw is controlled by tilting its rotors in opposite directions. Roll is provided through differential power or thrust. Pitch is provided through rotor blades cyclic-, or nacelle, tilt. Vertical motion is controlled with conventional rotor blade pitch
Blade pitch or simply pitch refers to the angle of a blade in a fluid. The term has applications in aeronautics, shipping, and other fields.
Aeronautics
In aeronautics, blade pitch refers to the angle of the blades of an aircraft propeller or ...
and either a conventional helicopter collective control lever (as in the Bell/Agusta BA609) or a unique control similar to a fixed-wing engine control called a thrust control lever (TCL) (as in the Bell-Boeing V-22 Osprey
The Bell Boeing V-22 Osprey is an American multi-mission, tiltrotor military aircraft with both vertical takeoff and landing (VTOL) and short takeoff and landing (STOL) capabilities. It is designed to combine the functionality of a convention ...
).[Norton, Bill. ''Bell Boeing V-22 Osprey, Tiltrotor Tactical Transport''. Midland Publishing, 2004. .]
Speed and payload issues
The tiltrotor's advantage is significantly greater speed than a helicopter. In a helicopter the maximum forward speed is defined by the turn speed of the rotor; at some point the helicopter will be moving forward at the same speed as the spinning of the backwards-moving side of the rotor, so that side of the rotor sees zero or negative airspeed, and begins to stall. This limits modern helicopters to cruise speeds of about 150 knots / 277 km/h. However, with the tiltrotor this problem is avoided, because the proprotors are perpendicular to the motion in the high-speed portions of the flight regime (and thus not subject to this reverse flow condition), so the tiltrotor has relatively high maximum speed—over 300 knots / 560 km/h has been demonstrated in the two types of tiltrotors flown so far, and cruise speeds of 250 knots / 460 km/h are achieved.
This speed is achieved somewhat at the expense of payload
Payload is the object or the entity which is being carried by an aircraft or launch vehicle. Sometimes payload also refers to the carrying capacity of an aircraft or launch vehicle, usually measured in terms of weight. Depending on the nature of ...
. As a result of this reduced payload, some estimate that a tiltrotor does not exceed the transport efficiency (speed times payload) of a helicopter, while others conclude the opposite.[ Additionally, the tiltrotor propulsion system is more complex than a conventional helicopter due to the large, articulated nacelles and the added wing; however, the improved cruise efficiency and speed improvement over helicopters is significant in certain uses. Speed and, more importantly, the benefit to overall response time is the principal virtue sought by the military forces that are using the tiltrotor. Tiltrotors are inherently less noisy in forward flight (airplane mode) than helicopters. This, combined with their increased speed, is expected to improve their utility in populated areas for commercial uses and reduce the threat of detection for military uses. Tiltrotors, however, are typically as loud as equally sized helicopters in hovering flight. Noise simulations for a 90-passenger tiltrotor indicate lower cruise noise inside the cabin than a Bombardier Dash 8 airplane, although low-frequency vibrations may be higher.][Grosveld, Ferdinand W. et al.]
Interior Noise Predictions in the Preliminary Design of the Large Civil Tiltrotor (LCTR2)
20130013992 '' NASA'', 21 May 2013. Accessed: 9 June 2014.
Tiltrotors also provide substantially greater cruise altitude capability than helicopters. Tiltrotors can easily reach 6,000 m / 20,000 ft or more whereas helicopters typically do not exceed 3,000 m / 10,000 ft altitude. This feature will mean that some uses that have been commonly considered only for fixed-wing aircraft can now be supported with tiltrotors without need of a runway. A drawback however is that a tiltrotor suffers considerably reduced payload when taking off from high altitude.
Mono tiltrotor
A mono tiltrotor aircraft uses a tiltable rotating propeller
A propeller (colloquially often called a screw if on a ship or an airscrew if on an aircraft) is a device with a rotating hub and radiating blades that are set at a pitch to form a helical spiral which, when rotated, exerts linear thrust upon ...
, or '' coaxial proprotor'', for lift and propulsion. For vertical flight the proprotor is angled to direct its thrust downwards, providing lift. In this mode of operation the craft is essentially identical to a helicopter. As the craft gains speed, the coaxial proprotor is slowly tilted forward, with the blades eventually becoming perpendicular to the ground. In this mode the wing provides the lift, and the wing's greater efficiency helps the tiltrotor achieve its high speed. In this mode, the craft is essentially a turboprop aircraft.
A mono tiltrotor aircraft is different from a conventional tiltrotor in which the proprotors are mounted to the wing tips, in that the ''coaxial proprotor'' is mounted to the aircraft's fuselage. As a result of this structural efficiency, a mono tiltrotor exceeds the transport efficiency (speed times payload) of both a helicopter and a conventional tiltrotor. One design study concluded that if the mono tiltrotor could be technically realized, it would be half the size, one-third the weight, and nearly twice as fast as a helicopter.[Article title]
Leishman, J. G., Preator, R., Baldwin, G. D.,Conceptual Design Studies of a Mono Tiltrotor (MTR) Architecture, U.S. Navy Contract Number: N00014-03-C-0531, 2004.
In vertical flight, the mono tiltrotor uses controls very similar to a coaxial helicopter, such as the Kamov Ka-50. Yaw is controlled for instance by increasing the lift on the upper proprotor while decreasing the lift on the lower proprotor. Roll and pitch are provided through rotor cyclic. Vertical motion is controlled with conventional rotor blade blade pitch
Blade pitch or simply pitch refers to the angle of a blade in a fluid. The term has applications in aeronautics, shipping, and other fields.
Aeronautics
In aeronautics, blade pitch refers to the angle of the blades of an aircraft propeller or ...
.[ Baldwin, G. D., 'Preliminary Design Studies of a Mono Tiltrotor (MTR) with Demonstrations of Aerodynamic Wing Deployment', AHS International Specialists Meeting, Chandler, Arizona, January 23–25, 2007.]
List of tiltrotor aircraft
* AgustaWestland AW609
* AgustaWestland Project Zero
* American Dynamics AD-150
__NOTOC__
The AD-150 is a high-speed VTOL tilting ducted fan unmanned aerial vehicle that is being developed by American Dynamics Flight Systems as a future competitor for the United States Marine Corps' Tier III VUAS program as well as other c ...
* Bell XV-3
* Bell XV-15
The Bell XV-15 is an American tiltrotor VTOL aircraft. It was the second successful experimental tiltrotor aircraft and the first to demonstrate the concept's high speed performance relative to conventional helicopters.
Development Early VTOL ...
* Bell Eagle Eye
* Bell V-280 Valor
* Bell Boeing V-22 Osprey
* Curtiss-Wright X-19
* Focke-Achgelis Fa 269
* IAI Panther
* Transcendental Model 1-G
The Transcendental Model 1-G was an experimental American tiltrotor prototype of the 1950s. It was a single-seat aircraft powered by a single piston engine, and was the first tiltrotor to fly.Norton ''Air Enthusiast'' 2005, p. 49. A single exampl ...
See also
* Pitch drop-back
Pitch drop-back is the phenomena by which an aircraft which is perturbed in flight path angle from its trim position by a step input exhibits an output which is indicative of a second order system.
A pilot who actuates an elevator input may find ...
* Tiltjet
A tiltjet is an aircraft propulsion configuration that was historically tested for proposed VTOL, Vertical Take-off and Landing (VTOL)-capable fighters.
The tiltjet arrangement is, in concept, broadly similar to that of the tiltrotor; whereas a t ...
* Tiltwing
* Tailsitter
* VTOL
* Thrust vectoring
References
External links
*
*
* Archived a
Ghostarchive
and th
Wayback Machine
*
{{Aircraft types (by method of thrust and lift)
Aircraft configurations