Giovanni Propersi6/6/2013Professor Warford, Writ 340

Flying Wings: Creating the Aircraft of the Future

Abstract

Flying wings have consistently been an optimal airframe for reducing drag, increasing fuel

economy, and reducing noise created by aircraft. Yet inherent issues with stability and control,

along with lack of materials that can pressurize a non-cylindrical cabin, have prevented many

experimental flying wings from reaching production. The B-2 Stealth Bomber is the single

exception. Its flying wing shape gives it a stealthy advantage, yet making it a stable airframe

was difficult. Today’s technology has been able to solve many of the problems associated with

earlier flying wing concepts. There is a high possibility of future flying wings, as NASA and

Boeing have teamed up to determine whether the X-48 is a capable aircraft, with highly

successful results.

Introduction

When the word “airplane” is mentioned in conversation, what image do you see in your

head? Typically, it would have a cylindrical body, with a vertical tail on the rear, and two wings

on either side, as shown in Figure 1. These aircraft, known as monoplanes for their one set of

wings, have been ingrained into our head as to how an airplane looks. Yet is it the most efficient

design possible? The answer is no. The fuselage and vertical tail increase the aerodynamic drag

and require strong structural integrity, especially at the joints, which means a lower fuel

efficiency [1]. The cylindrical shape limits the amount of passengers that can be carried [2]. And

finally, the placement of the engines increases the noise of the aircraft.

Figure 1 – A conventional aircraft design used almost exclusively today. This aircraft is a Boeing 767 – note the cylindrical fuselage and vertical tail

http://www.aerospaceweb.org/aircraft/jetliner/b767/b767_02.jpg

The answer to this problem has already been developed. Flying wings, as depicted in

Figure 2, remove the necessity of the central fuselage and tail, and allow for various engine

configurations to reduce noise. While their usage in passenger aircraft is still being developed,

the advantages of a flying wing over conventional monoplane aircraft outweigh its

disadvantages. To understand and appreciate the flying wing design, and why it was not used

immediately in the beginning of the 19th century, we must look at the history, design

characteristics, and its possible future usage in aviation.

Figure 2 – YB-49 flying wing, developed by Northrop Grumman after World War 2. Note the lack of center fuselage and vertical tail.

http://4.bp.blogspot.com/_lWjaeTyaIY8/TPOWltgymPI/AAAAAAAAABY/Wm3xkDv5-hY/s1600/YB-49_titel.jpg

History of Flying Wings

Flying wings have been in the background of aviation for almost a century. Much of the

inspiration for flying wings came from nature, such as from birds or seeds. The first attempt at

mass production was designed by Igo Etrich in 1909, and was based on the seeds of the Zanonia

macrocarpa, which looked like a single flat wing [3]. The design was too unstable, and as shown

in Figure 3, a more conventional design incorporating a tail was used. A true flying wing would

require the removal of the tail, which caused inherent stability problems that technology in the

early 20th century could not compensate for.

Figure 3 – The Etrich Taube, using the conventional aircraft design.http://www.the-blueprints.com/blueprints-depot/modernplanes/modern-e/etrich-taube.gif

It was the outbreak of World War 2 that spurred research into the flying wing concept

[4]. All governments, especially the United States and Germany, were willing to spend funds on

any aircraft that would give them the advantage in the war[4]. The Germans, known for their

intensive military research during the war, were the first to use employ flying wings in their

arsenal [4]. The Horten brothers were two prominent aircraft designers in Germany at the time

who took the flying wing design very seriously [4]. They produced countless powered and

unpowered variants, and even created the first turbo-jet powered flying wing in January 1945,

known as the Ho 229, as shown in Figure 4 [4]. Many of their designs were captured by the

Allies, and vague similarities can be found between the Hortens’ designs and the B-2 Stealth

Bomber.

Figure 4 – The Ho 229, the first jet powered flying wing.http://2.bp.blogspot.com/-xV_pf-gCO6A/Ua7WJbP-EJI/AAAAAAAACyQ/W1BDDMIbYVU/s400/

ho229B.jpg

After World War 2, there was some general interest in applying the flying wing concept

to long distance bombers and reconnaissance planes. Northrop Grumman developed two

experimental flying wings, the XB-35 and YB-49. The pilots who test flew these planes

complained of constant stability and control issues, and by 1953 the idea of a flying wing as a

bomber was scrapped [5].

It was not until the development of the B-2 Stealth Bomber in 1989 that the flying wing

concept returned [6]. Engineers at Northrop Grumman had discovered the advantages of the

flying wing shape in concealing its radar signature (although the aircraft’s paint also plays an

important role), and now the B-2, shown in Figure 5 is the only operational flying wing, with

many successful missions.

Features of the Flying Wing

The main difference between flying wings and conventional aircraft is the lack of a

fuselage and vertical tail in the flying wings, as seen in Figure 4. A cylindrical fuselage and a tail

add to the overall drag of an aircraft, and their removal provides less overall drag [7]. Normally,

a tail, otherwise known as a vertical stabilizer, is used to keep a plane swinging from side to

side. The lack of a tail causes inherent stability issues, observed during the test flights of the XB-

35 and YB-49.To solve this problem, engineers have developed a method of integrating the tail

into the ends of the wings (see split rudder in Fig 5). These control surfaces allow the plane to

stabilize itself from swinging to the left or right. Since the airframe would not need the

structural strength of conventional aircraft, it could be made out of plastics instead of

aluminum. This, along with the removal of the tail and cylindrical fuselage, would reduce weight

and drag, and increase the overall fuel economy. These reductions may lead environmental

enthusiasts to appreciate the capabilities of flying wings.

Figure 5 – The rudder, which generally goes on the tail of an aircraft, is placed on the wingtips of the B-2.

http://static.ddmcdn.com/gif/stealth-bomber-1.jpg

The airframe moreover allows for varied placement of the engines, in comparison to

their standard position under the wings. The B-2 and the experimental X-48C, seen in Figure 6,

have engines on top of the airframe. This reduces the heat signature, giving greater stealth

capabilities, and also lowers noise output. The sound waves hit the top of the airplane and

bounce off upwards, almost completely avoiding the ground [9]. Drag is also reduced if the

engines are embedded in the airframe, as seen in the B-2 in Figure 5, or Figure 6.

Figure 6 – The X-48C. Since the engines are on top of the aircraft, the noise has nowhere to go but up. This is only a scale model used for flight tests.

http://www.aviationweek.com/media/images/fullsize/Defense/Miscellaneous/X-48C_Blended_Wing_Body-RobertWall.jpg

Flying wings are also capable of a much greater cargo load due to a larger amount of

internal storage space. Therefore a flying wing could have the same wing span (distance from

wing tip to wing tip) and be more efficient in carrying passengers or cargo.

Modern Flying Wings and Future Implementations

In addition to the B-2, Boeing and NASA have created a scaled down, unmanned version

of a flying wing so as to determine how to solve the issues that may arise in such a design. The

X-48C, shown in Figure 6, is called a Blended Wing Body, in that two flattened fuselages were

attached to wings, and then the airframe was smoothed out in order to attain the flying wing

shape. The research team has already concluded that such a plane would have a much greater

fuel efficiency ,and reduce noise output by as much as 50dB. They have also determined the

plane can be controlled with ease at the low speeds segments of flight, such as takeoffs and

landings, showing the plane is stable [10]. This plane may have potential as a passenger aircraft

at some point in the future.

Issues with Flying Wings

Problems have arisen with such an aircraft though. Pressurizing a non-cylindrical

passenger cabin is much more difficult than pressurizing a cylindrical one. NASA and Boeing

have made this one of their top priorities in their experiments with the X-48C. NASA recently

demonstrated a new manufacturing method that would allow the X-48C to overcome the

pressurization issues and be built to full scale [12]. The method uses pressurized flat plates that

have been stitched together with a polymer thread. A segment is shown in Figure 6. Recent

tests have been successful in pressurizing a compartment of the aircraft [10]. A cross section of

this pressurized compartment is shown in Figure 7. A pressurized cabin that would match the

one on the X-48C is to be completed by 2015 [12].There is also the issue of where to place the

emergency exits so that people seated in the very center of the plane may still reach them [11].

Finally, there are a few psychological factors. The general public may oppose such a

drastic change in the shape of passenger

aircraft. Aircraft have been made in the tube

and wing shape for slightly more than a century, and seeing anything else may frighten them.

Secondly, passengers in the heart of the aircraft would have no view of the outside. The fear of

flight is common, and being in the very center of the airplane may not be helpful. Engineers at

Boeing and NASA are hard at work trying to find solutions to these problems, and research is

still being conducted today.

Research is also being conducted by NASA on a bi-directional flying wing, as shown in

Figure 9. This passenger aircraft would basically be two flying wings laid perpendicularly across

each other. The plane would first take off using the subsonic wings, and then would rotate in

mid-air by 90 degrees and use its supersonic wings. This would remove the iconic sonic boom

from occurring when it went supersonic. The project is still in development, but NASA says

flying wings may be in production as soon as 20 years [13].

Figure 8 – A compartment of a full scale X-48C, being tested for pressurization issues with the new manufacturing method.http://d2n4wb9orp1vta.cloudfront.n et/resources/images/cdn/cms/0911hpc_WIP_figure2.jpg

Figure 7 – A portion of a pressured flat plate.http://d2n4wb9orp1vta.cloudfront.net/resources/images/cdn/cms/0911hpc_WIP_figure1.jpg

Figure 9 – A conceptual drawing of the bi-directional flying wing.http://wordlesstech.com/wp-content/uploads/2012/09/Supersonic-Bi-Directional-Flying-Wing-

2.jpg

Conclusion

Flying wings have been around since mankind took to the skies, but issues with stability

and control have kept them grounded. The Germans in World War 2 were able to correct many

of the problems, but it wasn’t until the late 20th century, with the creation of the B-2 Stealth

bomber, that flying wings entered operation status. Through the use of advanced flight control

systems, new materials, and scaled down models, NASA and Boeing are diligently working to

develop an operational flying wing. In the long run, they could be used for the military, cargo,

or civilian use, with their large storage capacity. The potential is there, and now it just has to be

implemented. And in 20 to 30 years, people might find themselves entering a wing instead of a

tube.

References

1) Dezso Gyorgy Falvy. Performance analysis of the “Horten IV”; Flying Wing. Presented at 8 th O.S.T.I.V Congress . [Online]. Available: http://www.acsol.net/~nmasters/H-IV-report.html

2) Loz Blain. (2007, July 29). Blended-Wing Boeing completes first test flight. Magazine [Online]. Available: http://www.gizmag.com/go/7694/

3) E.T. Wooldridge. Early Flying Wings (1870 – 1920). [Online]. Available: http://www.century-of-flight.net/Aviation%20history/flying%20wings/Early%20Flying%20Wings.htm

4) E.T. Wooldridge. German flying wings during World War Two. [Online]. Available: http://www.century-of-flight.net/new%20site/frames/horten%20frame.htm

5) Rebecca Maksel. (2011, August 16). Are any of Northrop’s “flying wings” from the 1940s still around? Magazine [Online]. Available: http://www.airspacemag.com/need-to-know/Need-to-Know-Flying-Wing.html

6) B-2 Spirit Bomber. Northrop Grumman. [Online]. Available: http://www.northropgrumman.com/Capabilities/B2SpiritBomber/Pages/default.aspx

7) Tim Van Milligan. Theory and Practice of Using Flying Wings. Available: http://www.apogeerockets.com/downloads/Newsletter15.pdf

8) Regine Debatty. (2005, Nov 2). The Future of Flying is Batwing. Journal [Online]. Available: http://www.worldchanging.com/archives/003703.html

9) BBC. (2006, Nov 6). ‘Silent Aircraft’: How it works. [Online]. Available: http://news.bbc.co.uk/2/hi/technology/6120132.stm

10) Jeff Sloan. (2011, Sept 1). PRSEUS preform for pressured cabin walls. Journal [Online]. Available: http://www.compositesworld.com/articles/prseus-preform-for-pressurized-cabin-walls

11) Christopher York. (2013, April 4). Blended Wing Body Aircraft, X-48c, Successfully Tested by Boeing and Nasa. [Online]. Available: http://www.huffingtonpost.co.uk/2013/04/15/blended-wing-body-aircraft_n_3083637.html

12) Kevin Bullis. (2013, Jan 24). “Hybrid Wing” Uses Half the Fuel of a Standard Airplane. Magazine [Online]. Available: http://www.technologyreview.com/news/509916/hybrid-wing-uses-half-the-fuel-of-a-standard-airplane/

13) (2013, Aug 30). Supersonic Flying Wing Nabs $100,000 from NASA. [Online]. Available: http://www.technewsdaily.com/6153-supersonic-flying-wing-nasa.html