Thrust Vectoring

Aero 2360

Aerospace Propulsion

Research Report

Thrust Vectoring

Jared PocockS3234813

Abstract

Thrust vectoring is the ability for an engine to change the direction that the thrust acts in. This capability gives aircraft much greater control over a wider range of conditions giving the increased maneuverability that military aircraft are primarily concerned with. The various different types of Thrust Vectoring will be discussed including nozzle vectoring, Tilt Rotor/Tilt Wing and Exhaust deflection. A number of aircraft on which thrust vectoring is a major characteristic are explored. The possible future advances and opportunities for thrust vectoring are also examined.

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Jared Pocock S3234813

ContentsAbstract.......................................................................................................................................................1

Introduction.................................................................................................................................................3

Current Designs...........................................................................................................................................4

Current Platforms........................................................................................................................................5

AV-8 Harrier.............................................................................................................................................5

C-17 Globemaster III................................................................................................................................5

V-22 Osprey.............................................................................................................................................6

F-22 Raptor..............................................................................................................................................7

F-35 Lightning II.......................................................................................................................................8

Future designs...........................................................................................................................................10

X-36.......................................................................................................................................................10

Conclusion.................................................................................................................................................12

References.................................................................................................................................................13

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IntroductionIn this day and age, the push for each military forces to be able to obtain air supremacy is of utmost importance. To achieve this, they need their fighter aircraft to be more maneuverable, faster and undetectable than their counterparts. Thrust vectoring is one way in which the aircraft are able to increase their maneuverability giving them an edge against their counterparts.

Thrust vectoring is the ability for an aircraft engine to change the direction in which the thrust is acting. This ability to change the direction of the thrust created by the engine on aircraft effectively gives the aircraft an additional means other than control surfaces with which to give the aircraft control. This gives an aircraft the ability to have extremely good handling and maneuverability characteristics especially at high angle of attack and low speed flight where standard aircraft would be uncontrollable.

Thrust vectoring can be used on both turbofan and turboprop engines. Turboprop engines achieve thrust vectoring by rotating the entire engine and prop or rotating the entire wing. This creates extra concerns for the structures ability to cope with the addition of loads from the engine and wing loads not acting primarily in one direction. Turbofan engines achieve thrust vectoring by altering the direction that the exhaust is expelled. This is done by deflecting the exhaust flow at an angle either by using a variable nozzle of by obstructing the path of the exhaust flow after it has left the engine.

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Current DesignsThrust vectoring is achieved in two ways, either by deflecting the airflow of the exhaust coming from the engine or by rotating the engine so as to change the direction of the thrust. The prime example of an aircraft that rotates the engines to change the direction of the thrust is the Osprey V-22. The ability to deflect the exhaust downward can also be used to increase lift, one aircraft that utilizes this ability is the C-17 Globe master.

The nozzle of an engine has a great effect on the thrust of the engine. Nozzle design is especially important in supersonic flight where convergent-divergent nozzles are used to control the speed of the airflow coming from the engine. (Braeunig, 1998) The ability to change the diameter of the nozzle enables greater efficiency of the engine over a much larger speed range. As such changing the diameter of the nozzle of an engine is incorporated into the design of all military jet engines. Adding the ability to change the direction of the nozzle as well has been a complication engineers have recently been able overcome.

Jets with thrust vectoring via the use of exhaust nozzles on the rear of the aircraft are split into two different classes. 2D Thrust Vectoring and 3D Thrust vectoring. (Soni, 2009) 2D thrust vectoring is the ability of the nozzle to vector the thrust along one axis ie the nozzle can vector the thrust up or down giving the aircraft greater pitch control. The picture below shows the change in the direction of thrust achievable by this particular engine in the pitch axis.

Figure 1 "2D Thrust Vectoring showing the up/down thrust vectoring" (Pratt & Whitney, 2011)

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Figure 2 "3D Thrust Vectoring showing nozzles both facing down and inward" (Airliners.net)

A nozzle capable of 3D thrust vectoring is able to direct thrust on two axis ie. left and right and up and down effectively giving the aircraft increased pitch and yaw control.

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Current Platforms

AV-8 Harrier

Figure 3 " AV-8 Harrier II" (worldwide-military.com, 2010)

The first aircraft to extensively use thrust vectoring was the AV-8 Harrier. (Pike, 2011) The Harrier was the first jet with the capability to take off vertically. This was achieved by directing the thrust downward through four vents. The Harrier could then transfer from hover to forward flight by changing the direction of the thrust from downward to horizontal. The reverse was also possible where transition from forward to stationary flight is easily achievable. The front two nozzles discharge air compressed by the engine whilst the two rear nozzles discharge the engines hot jet exhaust gasses.

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C-17 Globemaster III

Figure 4 "C-17 Globemaster III" (DOD Media, 2005)

The C-17 Globemaster III is a large military transport aircraft. The C-17 has the ability to take off and land on very short runways whilst carrying very large loads. (Pike, 2011) This is made possible by the aircrafts ability to direct engine exhaust onto its flaps which deflect the exhaust stream downward increasing lift. The C-17 also utilizes thrust reversing in which the exhaust from the engine is directed forward dramatically reducing the landing distance of the aircraft. These combined allow the C-17 to land with loads up to 160,000lbs on a runway just 3000ft long.

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V-22 Osprey

Figure 5 " V-22 Osprey" (Military-Today.com, 2006)

The V-22 is a tiltrotor aircraft that uses two turboprop engines that can rotate 90 degrees from horizontal to directly vertical. The aircraft acts like a helicopter when the engine is rotated up whilst when in their forward position they act like normal turbo prop engine and the aircraft is controlled with the conventional aircraft control surfaces. This gives the V-22 the bonuses of being able to fly like a helicopter with stationary and vertical flight. All the while having a fuel efficient high cruise speeds giving the V-22 a much larger range of 1,940nmi when compared to 1216nmi for the CH-47 Chinook while still being able to lift very large weights. (Wikipedia.org 2011)

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F-22 Raptor

Figure 6 "F-22 Raptor" (Rexwallpapers.com)

The United States current air superiority fighter the F-22 Raptor utilizes 2D thrust vectoring. The Raptor is able to vector the thrust with an articulating nozzle which is capable of directing the thrust by up to 20 degrees in the up and down or pitch axis. (howstuffworks.com) The diagram below illustrates the difference in the pitch up and down ability of the F-22 raptor vs. a typical jet fighter without thrust vectoring, note the much larger angle of attack of the F-22. This greater maneuverability is one of the many characteristics that arguably makes the F-22 the most superior fighter to date.

Figure 7 "The difference thrust vectoring has on maneuverability in pitch axis for F-22" (Wollenhaupt, 2011)

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F-35 Lightning II

Figure 8 "F-35B Lightning II" (Haines, 2011)

F-35 Lightning II is an aircraft that is currently under development in the United States. The aircraft uses thrust vectoring extensively. The F-35B variant has the capability for Short take off and vertical landing. The F-35B has an innovative system to provide the aircraft with vertical lift. The nozzle on the main turbofan is able to deflect up to 95 degrees in just 2.5 seconds providing vertical lift from the tail exhaust stream. (AviationWeek.com) To rotate the nozzle down the engine uses what is known as a three-bearing swivel module. The three-bearing swivel module is made of three titanium casings with ring bearing at 45 degrees, these casings are able to rotate relative to the other thus allowing the nozzle to deflect 95 degrees. Changing the direction of the flow of exhaust gasses is an engineering challenge. Not only does the nozzle have to be able to withstand the very hot and corrosive exhaust gasses but it must be able to support the 18000lbf of thrust that is being generated and then transmit that forces through to the engine mountings. GlobalSecurity.org The very high heats alone are very trying on the materials, the combination of both heat and large forces requires specifically engineered materials to be able to withstand the pressure and the heat without failing. (Zolfagharifard, 2011)

To supplement the vertical lift from the tail nozzle the F-35B also utilizes a lift fan to produce 20,000lbf vertical thrust. The vertical lift fan is connected to the engine via a drive shaft that takes 28,000 hp from the engine and transmits it to the lift fans. The vertical lift fan consists of two counter-rotating bladed disks. The blades are made from titanium, are hollow and are manufactured individually. The blades are

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then welded to the disk with a welding process known as linear friction welding. The lift fan sucks air from above the fuselage of the aircraft and forces the air through the variable area vane box nozzle. The variable area vane box nozzle is able to direct the thrust from the lift fan. Above and below the Lift fan are doors that open when the fan is in operation and will close for normal flight. This enables the aircraft to have stealth capabilities whilst in normal flight. Another engineering complexity of the system is for the lift fan to have the ability to operate effectively under the flight conditions of hovering up to the speed of 250kts where the aircraft is then able to transition to forward flight.

Figure 9 "F-35b Thrust Vectoring system" (Tosaka, 2008)

For lateral and roll control the F-35B utilizes roll-post nozzles that direct bypass air from the engine downward through ducts to two nozzles, one on the lower surface of each wing. These nozzles are capable of providing 1950lbf thrust each. The power from each of the roll posts can be modulated to give lateral and roll capabilities. The nozzles have a door that closes when they are not in use to once again maintain the stealth characteristics of the aircraft. (Rolls-Royce, 2011)

These three thrust vectoring systems combine to give the F-35B exceptional control in hovering and low speed flight, allows the aircraft to take off either vertically or on extremely short runways giving it a major advantage in its capabilities as compared to aircraft without thrust vectoring.

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http://upload.wikimedia.org/wikipedia/commons/5/55/F-35B_Joint_Strike_Fighter_(thrust_vectoring_nozzle_and_lift_fan).PNG

Future designsThrust vectoring is a design criteria that will be incorporated extensively on future aircraft designs. The push for increased stealth capability is also pushing the development for thrust vectoring. Being able to remove or supplement control surfaces has the ability to reduce the radar cross section. The removal of the tail is one such way in which removal of a control surface can reduce the radar cross section of an aircraft. Some tailless concept aircraft have been flown which require thrust vectoring engines to provide additional control and stability to compensate for the loss of the control and stability usually provided by the tail. The ability to asymmetrically change the direction of thrust from two nozzles on an aircraft has the capability to give the aircraft control in roll, yaw and pitch.

X-36

Figure 10 "X-36 experimental Aircraft" (NASA, 1997)

The X-36 was a joint venture between NASA and Boeing to develop an agile tailless fighter aircraft. The aircraft was built to a 28 percent scale representation of an expected configuration. The aircraft being designed to fly without a tail utilized a canard wing, split ailerons and thrust vectoring system to provide control. (NASA, 2002)

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ConclusionThe benefits from having thrust vectoring have become increasingly significant since thrust vectoring was first implemented in aircraft designs. Thrust vectoring has since become an extremely desirable characteristic in all new military aircraft designs. The ability for an aircraft to behave favorably under adverse conditions where previously they were unable to be controlled gives the aircraft a significant advantage over its counterparts.

From its origin, thrust vectoring enabling the Harrier to take off vertically and now the ability to design tailless aircraft which utilize thrust vectoring to give added control, thrust vectoring will play a very significant role in the future. The ever increasing demand from the military for this increase in the agility and stealth characteristics of their aircraft will continue to push the advancement of thrust vectoring technology.

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References

Airliners.net, viewed 24 August 2011, Airliners.net, <http://cdn-www.airliners.net/aviation-photos/middle/5/1/5/1314515.jpg>

Braeunig, R 1998, Rocket Nozzle Design: Optimizing Expansion for Maximum Thrust, Rocket & Space Technology, viewed 24 August 2011, <http://www.braeunig.us/space/sup1.htm>

DOD Media, 2005, DOD Media, viewed 24 August 2011, <http://www.dodmedia.osd.mil/Assets/Still/2006/Air_Force/DF-SD-06-03299.JPEG>

Haines, L 2011, US Air Force in serious stealthless state, The Register, viewed 24 August 2011, <http://www.theregister.co.uk/2011/08/10/stealth_grounded/print.html>

Military-Today.com, 2006, BellBoeing V-22 Osprey, viewed 24 August 2011, <http://www.military-today.com/helicopters/bellboeing_v_22_osprey.htm>

NASA, 1997, X-36 on Ramp Viewed from Above, NASA, viewed 24 August 2011, <http://www.dfrc.nasa.gov/gallery/photo/X-36/HTML/EC97-44165-151.html>

NASA, 2002, X-36 Tailless Fighter Agility Research Aircraft, NASA, viewed 24 August 2011, <http://www.nasa.gov/centers/dryden/news/FactSheets/FS-065-DFRC.html>

Pike, J 2011, AV-8B Harrier, Global Security, viewed 20 August 2011, <http://www.globalsecurity.org/military/systems/aircraft/av-8.htm>

Pike, J 2011, C-17 Globemaster III, Global Security, viewed 20 August 2011, http://www.globalsecurity.org/military/systems/aircraft/c-17.htm

Pratt & Whitney, 2011, Military Engines - F119 , Pratt & Whitney Military Engines, viewed 24 August 2011, <http://www.pratt-whitney.com/products/military/f119.asp>

Rexwallpapers.com, F-22 raptor wallpaper 3, viewed 24 August 2011, <http://www.rexwallpapers.com/wallpaper/F-22-raptor-3/>

Rolls-Royce, 2011, Rolls-Royce LiftSystem, Rolls-Royce Group, viewed 20 August 2011, <http://www.rolls-royce.com/defence/products/combat_jets/rr_liftsystem.jsp>

Soni, R 2009, Sukhoi Su-30 MKI - Purpose of Thrust Vectoring, viewed 24 August 2011, <http://soni2006.hubpages.com/hub/Thrust-Vectoring-Sukhoi>

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Tosaka, 2008, F-35B Joint Fighter's thrust vectoring nozzle and lift fan, Wikipedia, viewed 24 August 2011, <http://en.wikipedia.org/wiki/File:F-35B_Joint_Strike_Fighter_(thrust_vectoring_nozzle_and_lift_fan).PNG>

Warwick, G 2011, STOVL- IN WORK, Aviation Week, viewed 15 August 2011, <http://www.aviationweek.com/aw/blogs/defense/index.jsp?plckController=Blog&plckScript=blogScript&plckElementId=blogDest&plckBlogPage=BlogViewPost&plckPostId=Blog:27ec4a53-dcc8-42d0-bd3a-01329aef79a7Post:c6b42472-184d-4c6d-80ba-4936e6d986ed>

Wikipedia.org, 2011, Bell-Boeing V-22 Osprey, Wikipedia, viewed 19 August 2011, <http://en.wikipedia.org/wiki/Bell-Boeing_V-22_Osprey>

Wollenhaupt, G 2011, How F/A-22 Raptor Work, HowStuffWorks Inc, viewed 24 August 2011, <http://science.howstuffworks.com/f-22-raptor5.htm>

worldwide-military.com, 2010, AV-8 B Harrier II, World Wide Military, viewed 24 August 2011, <http://www.worldwide-military.com/Military%20Aircraft/Attack/AV-8B%20Harrier_algemene_info_english.htm>

Zolfagharifard, E 2011, Rolls-Royce's LiftSystem for the Joint Strike Fighter, The Engineer, viewed 20 August 2011, <http://www.theengineer.co.uk/in-depth/rolls-royces-liftsystem-for-the-joint-strike-fighter/1008008.article>

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Thrust Vectoring

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