University of Southern California

Innovative Aviation Technology of the F-35B

William Blair

Phone: (510)499-6691

Email: wblair@usc.edu

05/04/2013

My name is William Blair, and I am an undergraduate Junior from Castro Valley,

California. I am studying Industrial & Systems Engineering, and hope to be a Naval

Aviator after graduation.

Abstract

Jet aircraft were first built in the late 1940s, and since then the technology has

continuously evolved. One such development is the F-35B’s turbofan engine. Unlike its

predecessors, it is designed to allow for aircraft to hover in mid-air, as well as take off

and land vertically. This article will outline how traditional turbofan engines work, as

well as give insight to the differences in the F-35B’s engine that give it these new

capabilities.

Introduction

Throughout history, military technology advancements have often been found to

also have civilian applications. For example, many civilian medical technologies have

arisen out of the need for emergency battlefield wound treatment. The aviation field has

been particularly impacted by military demand for advanced technology. For example,

ever since the military realized potential uses of aircraft in battle, military-funded

research and development has largely contributed to advancing aviation technology.

Specifically, ever since a member of the Royal Air Force created the first design for a jet

engine in 1930 [8], the military has been constantly seeking new and inventive designs

for jet engines. The latest innovation to aircraft engines is a feature of the F-35B Joint

Strike Fighter that allows the turbofan engine’s thrust to be redirected downward, giving

the plane the ability to take off and land vertically as well as hover in place. Though this

technology is very new, it could find civilian application in the future to change the

design of aircraft.

How Traditional Turbofan Engines Work

The term “jet engine” encompasses a variety of air breathing engines, including

turbojet, turbofan, turboprop, turboshaft, and propfan. The most commonly used of these

is the turbofan engine, named after the fan mechanism from which the main forward

thrust comes. This is the engine type used in most military and civilian jet-powered

aircraft, due to its high efficiency (energy produced per unit fuel) and power (force that

the engine is able to produce). The engine is particularly efficient because minimal

energy is lost through the engine’s processes, as the energy produced by the combustion

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of gasoline within the engine is mostly transferred into rotational energy that pushes the

engine forward.

Figure 1, Cross-section of a standard turbofan engine, with fan extending past combustion chamber. (Picture taken from popsci.com)

The main components of turbofan engines are the fan, compressor, combustor,

turbine, and nozzle [9]. The front of the engine (where the fan is in the figure above) is

open to allow for the intake of air into the compressor, where a spinning shaft with blades

attached forces the air to the outer edge of itself, causing the air to become very dense.

This dense air then travels into the combustor, where it is mixed with jet fuel and ignited,

causing heat to be released and forced further rearward. The amount of fuel injected into

the combustion chamber is what determines the amount of thrust generated by the engine,

which can be controlled by the pilot within the cockpit of the airplane [7]. The dense air/

fuel mixture’s combustion creates a very large amount of force, and expands further into

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the turbine, which consists of angled blades resembling a windmill connected to a freely

rotating shaft, which is then connected to the fan at the front of the engine. Similar to a

windmill, the turbine converts this rearward moving air into rotational energy in the form

of spinning the high-pressure shaft attached to it. The air that passes through the turbine

then exits out of the engine’s nozzle, adding extra forward thrust.

Figure 2, showing the main components of a standard turbofan engine, and their positions relative to one another. (Taken from dcradio.org.uk)

In the turbine, the high velocity air causes the turbine to rotate at an extremely fast

rate, and as a result the fan at the front of the engine is rotated as well since it is

connected to the turbine by a shaft. This fan extends out past the outer edge of the

compressor/ combustor, and forces air out through the rear of the engine. Then, this force

directed backward propels the engine (and attached airplane, of course) forward [7]. All

of the individual sections of the engine work to compress intake air, ignite it so it

becomes very hot and expands, and then transform this thermal energy into rotational

energy that causes a fan to act as a very fast propeller and force the plane forward.

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Using a fan rather than just allowing all of the engine’s thrust to be generated by

the exhausted air (i.e turbojet engines) is what gives the engine more power and

efficiency. Because of their improved efficiency, engines can be more compact while still

giving the same amount of thrust as a larger engine, reducing the weight of the aircraft.

Also, this makes the engine much quieter, which gives it an advantage to commercial

airlines that have to minimize noise pollution in crowded city areas.

How the F-35’s Engine Differs from Standard Turbofan Engines

The reason for the F-35’s development was to replace aging aviation technology

at a lower cost than previously used jet aircraft such as the F/A-18, which is becoming

too expensive to maintain and outdated [11]. It is intended to replace all military jet

aircraft, in all branches of the U.S. military, with specific models tailored to the needs of

each branch [10]. There are three variants of the plane’s design: F-35A (intended for the

Air Force), F-35B (Marine Corps), and F-35C (Navy) [3]. Each of these has the same

engine, avionics (electronic components), and structural components [5], but each has

specific features that optimize it for its specific branch’s use. One such feature is the F-

35B’s STOVL (Short Take-Off/ Vertical Landing) capability, which is made possible by

its engine’s thrust-vectoring nozzle. This is among the most innovative of the aircraft’s

features, and is not seen in any other aircraft engine in production. The need for an

aircraft that has this ability to take off and land using short distances arises from the

Marine Corps’ operating procedures. Marine Corps aircraft often land and take off on

Naval ships called amphibious assault ships (as seen below), which have much smaller

landing areas than what is needed for conventional aircraft operations. This creates a need

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for aircraft that do not require long runways to take off and land, and the F-35B is a

solution to this problem.

Figure 3, Amphibious Assault Ship (taken from Wikipedia.org)

The “thrust-vectoring nozzle” is unique to the F-35B’s Pratt & Whitney F135

Turbofan engine, and is the first of its kind. “The engine exhausts through a three-bearing

swivel nozzle that can deflect the thrust from horizontal to just forward of vertical” [6],

which means that the engine’s force can be diverted downward rather than rearward like

conventional turbofan engines. This gives the aircraft upward force rather than forward

force, allowing it to hover in midair.

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Figure 4, F-35B in hover (taken from http://juliantheaviator.files.wordpress.com)

The nozzle allows the pilots to be able to control the direction of thrust, allowing

the plane to also rotate its heading (direction) by 360°, as well as move side to side/ front

and back parallel to the ground (similar to how a helicopter would) as the nozzle is

redirected [4]. The engine’s main propulsion is also diverted into a lift fan near the front

of the plane (to counterbalance the downward force of the main engine at the rear of the

plane) so that the aircraft does not flip forward, as well as at the end of the wings to give

the pilot control over the roll (lateral stability) of the plane [1].

The F-35 program is still in the end stages of testing and production, and is

scheduled to be implemented into the military in 2016. Currently, this vertical lift

technology is unique to the F-35B, however has potential to have other applications.

Future Applications

As a result of this capability, aircraft can more easily take off and land on aircraft

carrier decks and smaller landing areas, reducing the area needed for safe operation of

jet-powered aviation. Because this technology is so new, it has not been applied to any

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civilian applications yet. However, it has potential to make its way into the civilian

aviation community similar to the way other military has transferred over to non-military

applications.

In the future, this technology could possibly be implemented in civilian aircraft,

enabling airplane landings in small areas such as rooftops or areas without otherwise

suitable airports. This would widen the capabilities of airplanes to now be able to land in

areas that could only previously be reached by helicopter (which have speed and distance

limitations that airplanes do not have). This technology could also be implemented in

spacecraft, enabling shuttles (which currently use engines more similar to traditional

airplanes) to land on the rough, uneven terrain of foreign planets that they cannot

currently land on. Though these are just hypothetical applications of the technology, it is

very likely that we will see this technology applied to non-military aircraft in the future.

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Terms and Definitions

Avionics: Electronic equipment fitted in an aircraft.

Compressor: A machine used to supply air or other gas at increased pressure, e.g., to power a gas turbine.

Turbofan Engine: fanjet: a jet engine in which a fan driven by a turbine provides extra air to the burner and gives extra thrust.

Vectoring: Direct (an aircraft in flight) to a desired point.

Suggested Websites

Lockheed Martin F-35 website: https://www.f35.com

Site giving specifications and project history: http://www.fas.org/man/dod-101/sys/ac/f-35.htm

Suggested Multimedia Applications

http://www.youtube.com/watch?v=ZD-J1KksHUQ, video by Lockheed Martin showing

how thrust-vectoring nozzle works to give the F-35B vertical lift.

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Bibliography

[1] Bevilaqua, Paul. "Joint Strike Fighter Dual-Cycle Propulsion System." Journalof Propulsion and Power 21.5 (2005): 778-83. Print.1

[2] Craig, David. "The Thrust of the Matter: Inside a Jet Engine." USA Today 14June 1994, Final ed., Bonus sec.: 12E. LexisNexis. Web. 23 Feb. 2013.

[3] "F-35 Lightning II Joint Strike Fighter (JSF), United States of America."Airforce Technology.com. N.p., n.d. Web. 19 Feb. 2013.

[4] Kandebo, Stanley W. "New Nozzle Eyed For Stovl F-35." Aviation Week & SpaceTechnology 156.14 (2002): 41. LexisNexis. Web. 18 Feb. 2013.

[5] Lawson, Chris. "The Joint Strike Fighter." Leatherneck 81.5 (1998): 14-19.Proquest. Web. 18 Feb. 2013.

[6] "’Lift Fan Spherical Thrust Vectoring Nozzle’ in Patent Application ApprovalProcess." Defense & Aerospace Week. N.p., 21 Nov. 2012. Web. 18 Feb. 2013.

[7] Patrício, Pedro, and José M. Tavares. "Simple Thermodynamics of Jet Engines."American Journal of Physics 78.8 (2010): 809. Print.

[8] Scott, Phil. "Birth of the Jet Engine." Mechanical Engineering 117.1 (1995): 66.ProQuest. Web. 20 Feb. 2013.

[9] Shaw, Robert J. "Engines." Engines. NASA, 13 Sept. 2010. Web. 23 Feb. 2013.

[10] Thompson, Mark. "The Most Expensive Weapon Ever Built." Time Magazine.N.p., 18 Feb. 2013. Web. 18 Feb. 2013.

[11] Wilson, Jim. "America's F-35 Joint Strike Fighter Plane." Popular Mechanics.N.p., 07 Dec. 2004. Web. 18 Feb. 2013.

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