A proprotor is a spinning

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 turbin ...

that function as both an airplane-style

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 a helicopter-style

rotor Rotor may refer to: Science and technology Engineering * Rotor (electric), the non-stationary part of an alternator or electric motor, operating with a stationary element so called the stator *Helicopter rotor, the rotary wing(s) of a rotorcraft ...

. Several proprotor-equipped

convertiplane A convertiplane is defined by the Fédération Aéronautique Internationale (FAI or World Air Sports Federation) as an aircraft which uses rotor power for vertical takeoff and landing ( VTOL) and converts to fixed-wing lift in normal flight. In th ...

s, such as 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 conventio ...

tiltrotor A tiltrotor is an aircraft which generates lift and propulsion by way of one or more powered rotors (sometimes called ''proprotors'') mounted on rotating shafts or nacelles usually at the ends of a fixed wing. Almost all tiltrotors use a trans ...

, are capable of switching back and forth between flying akin to both helicopters and fixed-wing aircraft. Accordingly this type of airfoil has been predominantly applied to vertical takeoff and landing (

VTOL A vertical take-off and landing (VTOL) aircraft is one that can take off and land vertically without relying on a runway. This classification can include a variety of types of aircraft including helicopters as well as thrust-vectoring fixed-wi ...

) aircraft. The dual-role airfoil is accomplished by one of several design approaches: :*changing the

angle of attack In fluid dynamics, angle of attack (AOA, α, or \alpha) is the angle between a reference line on a body (often the chord line of an airfoil) and the vector representing the relative motion between the body and the fluid through which it is m ...

of the wing that the proprotor is attached to, from approximately zero degrees to around ninety degrees: a

tiltwing A tiltwing aircraft features a wing that is horizontal for conventional forward flight and rotates up for vertical takeoff and landing. It is similar to the tiltrotor design where only the propeller and engine rotate. Tiltwing aircraft are typical ...

aircraft, :*changing the angle of attack of only the rotor hub, and possibly the engine that drives it, as on a

, :*changing the angle of attack of the entire aircraft, as on a tailsitter, which launches and lands on its tail.

Application details

On several aerial vehicles such as the

AgustaWestland 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 whil ...

and V-22 Osprey, a pair of three-bladed proprotors have been used.Croft, John
"Tilters."Alternate link
'

Air & Space/Smithsonian ''Air & Space/Smithsonian'' is a quarterly magazine published by the National Air and Space Museum The National Air and Space Museum of the Smithsonian Institution, also called the Air and Space Museum, is a museum in Washington, D.C., in the ...

'', 1 September 2007. Accessed on 6 May 2015. Both the proprotors and engines are mounted on load-bearing rotatable pylon at the wingtips, allowing the proprotors to be positioned at various angles. In the case of the AW609's, while flown in helicopter mode, the proprotors can be positioned between a 75- and 95-degree angle from the horizontal, with 87 degrees being the typical selection for hovering vertically; and in airplane mode, the proprotors are rotated forward and locked in position at a zero-degree angle, spinning at 84% RPM.

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 condi ...

rolling-takeoff and landing capability is achieved by having the nacelles tilted forward up to 45°."V-22 Osprey Guidebook, 2013/2014."
''Bell-Boeing'', 2013. Retrieved: 6 February 2014
Archived
in 2014. Typically, flight control software would perform much of the complex transition between the distinct helicopter and airplane modes; while automated systems are usually provided to inform crews on the optimal tilt angle and air speed to pursue. Furthermore, it is typical for flight controls, such as blade pitch, to both resemble and function akin to their counterparts on conventional rotorcraft, easing the transition of conventional helicopter pilots to such vehicles. Proprotors can be designed to fold for storage purposes.Currie, Major Tom P., Jr., USAF
"A Research Report Submitted to the Faculty, In Partial Fulfillment of the Graduation Requirements: The CV-22 'Osprey' and the Impact on Air Force Combat Search and Rescue" (PDF).
''Air Command and Staff College,'' April 1999. However, in the case of the V-22, in order to facilitate proprotor folding, the proprotor's diameter had to be constrained to a diameter of 38-foot (11.6 m), five feet (1.5 m) less than optimal for vertical takeoff; this difference has been attributed for causing relatively high

disk loading In fluid dynamics, disk loading or disc loading is the average pressure change across an actuator disk, such as an airscrew. Airscrews with a relatively low disk loading are typically called rotors, including helicopter main rotors and tail rot ...

.Whittle, Richard.
Flying The Osprey Is Not Dangerous, Just Different: Veteran Pilots
" '' defense.aol.com'', 5 September 2012. Retrieved: 16 September 2012
Archived
on 3 October 2013. In a typical implementation, both proprotors must be rotating in order to maintain flight in helicopter mode. To guard against instances of single engine failure, on both the V-22 and AW609, both engines are connected by

drive shaft A drive shaft, driveshaft, driving shaft, tailshaft ( Australian English), propeller shaft (prop shaft), or Cardan shaft (after Girolamo Cardano) is a component for transmitting mechanical power and torque and rotation, usually used to conne ...

s to a common central

gearbox Propulsion transmission is the mode of transmitting and controlling propulsion power of a machine. The term ''transmission'' properly refers to the whole drivetrain, including clutch, gearbox, prop shaft (for rear-wheel drive vehicles), diff ...

so that one engine can power both proprotors if such a failure occurs.Norton 2004, pp. 98–99. Despite this provision, the V-22 is generally not capable of hovering on a single engine.Whittle, Richard.
Fatal Crash Prompts Marines To Change Osprey Flight Rules
". ''Breaking Defense'', 16 July 2015. If a proprotor gearbox fails, that proprotor cannot be feathered, and both engines must be stopped prior to an

emergency landing An emergency landing is a premature landing made by an aircraft in response to an emergency involving an imminent or ongoing threat to the safety and operation of the aircraft, or involving a sudden need for a passenger or crew on board to term ...

. The

autorotation Autorotation is a state of flight in which the main rotor system of a helicopter or other rotary-wing aircraft turns by the action of air moving up through the rotor, as with an autogyro, rather than engine power driving the rotor. Bensen, Ig ...

characteristics are poor partly due to the rotors' low

inertia Inertia is the idea that an object will continue its current motion until some force causes its speed or direction to change. The term is properly understood as shorthand for "the principle of inertia" as described by Newton in his first law ...

.McKinney, Mike
"Flying the V-22"
'' Vertical (magazine)'', 28 March 2012
Archived
on 30 April 2014.

Aircraft

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 The Bell V-280 Valor is a tiltrotor aircraft being developed by Bell and Lockheed Martin for the United States Army's Future Vertical Lift (FVL) program.

NASA Puffin The Puffin is a 2010 concept for a hover-capable, electric-powered, personal vertical takeoff and landing (VTOL) technology-concept proprotor aircraft. The concept design was projected to be capable of flying a single person at a speed of 150 m ...

Leonardo Next-Generation Civil Tiltrotor The Leonardo Next-Generation Civil Tiltrotor (NextGenCTR or NGCTR) is a tiltrotor aircraft demonstrator designed and developed by the Italian aerospace company Leonardo S.p.A. Studies for a two times larger tiltrotor than the AgustaWestland AW6 ...

References

Citations

Bibliography

* Norton, Bill. ''Bell Boeing V-22 Osprey, Tiltrotor Tactical Transport''. Earl Shilton, Leicester, UK: Midland Publishing, 2004. . * Whittle, Richard
''The Dream Machine: The Untold History of the Notorious V-22 Osprey''.
New York: Simon & Schuster, 2010. . {{Aircraft gas turbine engine components Aircraft configurations