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X-48B Blended Wing Body Research Aircraft Makes First Flight; Potential for Fuel Savings

9 August 2007

061027a_lg
The blended wing X-48B on the ground.

A prototype blended wing body (BWB) research aircraft—the X-48B—developed by Boeing, NASA’s Fundamental Aeronautics Program, and the Air Force Research Laboratory at Wright Patterson Air Force Base, recently made its first flight.

The Boeing BWB design resembles a flying wing, but differs in that the wing blends smoothly into a wide, flat, tailless fuselage. This fuselage blending helps to get additional lift with less drag compared to a circular fuselage.

This translates to reduced fuel use at cruise conditions. A study by Boeing (Liebeck, 2004) concluded that an 800-passenger BWB aircraft sized for a 7000-n mile range could deliver a 27% reduction in fuel burn per seat mile compared to a conventional design with comparable specs.

Also, because the engines mount high on the back of the aircraft, there is less noise inside and on the ground when it is in flight.

070726c_lg
The X-48B in the air.

Three 50lb each thrust JetCat P200 turbojet engines enable the composite-skinned, 8.5% scale research vehicle to fly up to 10,000 feet and 120 knots in its low-speed configuration. Modifications would need to be made to the vehicle to enable it to fly at higher speeds.

The unmanned aircraft is remotely piloted from a ground control station in which the pilot uses conventional aircraft controls and instrumentation while looking at a monitor fed by a forward-looking camera on the aircraft.

The 21-foot wingspan, 500-pound, remotely piloted X-48B test vehicle took off for the first time on 20 July and climbed to an altitude of 7,500 feet before landing 31 minutes later.

The X-48B flight test vehicle was developed by Boeing Phantom Works in cooperation with NASA and the US Air Force Research Laboratory to gather detailed information about the stability and flight-control characteristics of the BWB design, especially during takeoffs and landings. The two X-48B research vehicles were built by Cranfield Aerospace Ltd., in the United Kingdom, in accordance with Boeing requirements.

Up to 25 flights are planned to gather data in these low-speed flight regimes. Following completion of low-speed flight testing, the X-48B likely will be used to test the BWB’s low-noise characteristics, as well as BWB handling characteristics at transonic speeds.

Two X-48B research vehicles have been built. The vehicle that flew on 20 July is Ship 2, which also was used for ground and taxi testing. Ship 1, a duplicate of Ship 2, completed extensive wind tunnel testing in 2006 at the Old Dominion University NASA Langley Full-Scale Tunnel in Virginia. Ship 1 will be available for use as a backup during the flight test program.

NASA’s Subsonic Fixed Wing Project team under the Fundamental Aeronautics Program has long supported the development of the blended wing body concept. It has participated in numerous collaborations with Boeing, as well as several wind tunnel tests for different speed regimes. The team is focused on researching the low-speed characteristics of the design and expanding its flight envelope beyond the limits of current capabilities.

NASA is interested in the potential benefits of the aircraft: increased volume for carrying capacity, efficient aerodynamics for reduced fuel burn, and, possibly, significant reductions in noise due to propulsion integration options. In these initial flights, the principal focus is to validate prior research on the aerodynamic performance and controllability of the shape, including comparisons of the flight data with the extensive wind-tunnel database.

Contingent upon further testing and program funding, a military cargo version of the BWB could be operational in the 2015-2020 timeframe, according to Boeing.

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August 9, 2007 in Aviation, Fuel Efficiency | Permalink | Comments (20) | TrackBack (0)

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Comments

B-2?

B-2B

The BWB doesn't look all that stealth to me and any B2 follow on will probably be a stealth design. A BWB craft is thicker in the middle than a flying wing design such as the B2.

I guess there's no such thing as a window seat. They could put some external cameras in and put the feed through to the TVs I suppose.

Tim,

You said:

"The BWB doesn't look all that stealth to me and any B2 follow on will probably be a stealth design. A BWB craft is thicker in the middle than a flying wing design such as the B2."

Maybe so, but take a look at a top view or plan-form view of the B2, the F117A, and the BWB's, they all seem to have an aft facing center point in the center-body region. On the B2 they call it a beaver-tail if my memory is correct. They all may be relying on what the Horten 229 had, that which the Horten Brothers seemed to stumble upon, also called a cuspidate tale. The question is and I have seen it posted, and that is this cuspidate, may change some flying wing characteristics for the better.

Now if Boeing will only add "C-Wings" to their BWB for even greater(?) efficiencies....

The B-2 designers came up with a truly quiet aircraft, and apparently without even trying, by putting the engines on the top of the plane where both intakes and thrust were above the long-chord wing where the noise of the engines would be reflected up towards the sky where it doesn't bother anybody. On this plane, they didn't quite do that. This narrowly-missed opportunity is an injustice to all the long-suffering airport neighbors of the world. The only reason planemakers don't work far harder on this is that the reduced land values are not reflected in the airlines' costs.

Possible fixes are (1) move the engines further forward, (2) extend the wing further back around the engines, so that there is a tongue below them, or (3) make a telescoping reflective tongue that is used only on take-off. The tongue could be hinge-connected like a flap but airstream-supported so it doesn't add much structure. Active antinoise systems could help further, both with radiated and cabin noise. Advanced sound insulation could compensate inside the plane for forward-shifting the engines, such as maybe aerogel and multiwalled structure.

Put a noise tax on airplanes to balance those reduced land values and Boeing will suddenly consider these solutions dead obvious.

They should do it quickly though; this plane would mean much less pollutants and contrails in the upper atmosphere, longer ranges, easier sale of the switch to alternative fuels and other benefits. Would make laminar flow control more achievable. Could be designed more bomb-robust. All things that we need right now.

@P Schager -

in addition to the NASA/Boeing project, there are at least two other BWB airliner designs in less advanced stages of development.

One is the AC20.30 project at Hamburg University of Applied Sciences.

http://www.ac2030.de/

The other is the silent aircraft initiative, a collaboration between MIT and the University of Cambridge (UK).

http://silentaircraft.org/design

Note in particular the location, cowling and exhaust designs for the engines. Commercial passenger jets are currently expected to jettison an engine in the event of an uncontrollable fire. That is why they are mounted underneath the wings of current-generation airliners, using 2-3 large bolts filled with explosive charges. It's not clear if/how BWB designs with engine mounts inside or above the body will offer this safety feature.

On the other hand, commercial airliners do not need to avoid radar, quite the contrary. Therefore, high bypass turbofans can be used, delivering both increased efficiency and reduced noise. A significant portion of the noise currently generated during landing actually stems from the flaps and landing gear rather than the engines, so there are many pieces to the noise puzzle.

It more fuel efficient and quieter, but does it sacrifice speed?

You wrote:
"Note in particular the location, cowling and exhaust designs for the engines. Commercial passenger jets are currently expected to jettison an engine in the event of an uncontrollable fire. That is why they are mounted underneath the wings of current-generation airliners, using 2-3 large bolts filled with explosive charges. It's not clear if/how BWB designs with engine mounts inside or above the body will offer this safety feature."
-----
This is not true. No major commercial aircraft has this feature. There are no explosive bolts. Engines cannot be jettisoned on any Boeing 7x7 series or any Airbus A3x0 series . Engines have fallen off but that is quite rare.

"Commercial passenger jets are currently expected to jettison an engine in the event of an uncontrollable fire. That is why they are mounted underneath the wings of current-generation airliners, using 2-3 large bolts filled with explosive charges."

That's pure bull-oney.

There are mounting pins designed to fail if the engine vibrates too much, so the engine will depart the airplane before it tears a wing up, but no explosive bolts holding the engines.

Quote: "The Boeing BWB design resembles a flying wing, but differs in that the wing blends smoothly into a wide, flat, tailless fuselage. This fuselage blending helps to get additional lift with less drag compared to a circular fuselage."

Comment: Additional lift is definitely NOT NEEDED when cruising in turbulent air, since it will put stress on the airframe and discomfort on the passenger, forcing every single internal structures, bolts and nuts to be beefier and heavier.

Current airliners have small wings that is sized for comfortable, low-stress cruise at high speed. When more lift is needed during slow-speed takeoff and landing, the wing's front and rear flaps will be deployed that will triple the lift coefficient of the wing as a whole, as if the wing is 3x larger. But, at these slow speed, turbulence will not be felt as much as at high speed. Lift or turbulence disturbance increase at the square of the airspeed. Double the airspeed and you will quadruple the stress toward the airframe when penetrating turbulence.
The BWB cannot use flaps, nor any is needed, due to the huge lifting surface, but that is a huge disadvantage, since the effective lifting surface area cannot be further reduced at fast cruise speed to ensure low reaction to turbulence. The use of flaps increases noise and power requirement significantly, but, at low speed, you would want to rev up 'em turbines anyway, just in case you need quick power for a quick climb above a huge downdraft or downburst, but em' turbofans take a long long time to spool up.

For very big airliners, in the 800-passerger range, the BWB may be worth a look again, since increase aircraft dimension will cause a weight gain proportional to the cube of the dimension increase, but the surface area will only increase as the square, meaning that large aircraft will need proportionally larger surface area than a smaller aircraft. Or, the large aircraft can fly faster, but, at high altitude, we run into the sonic barrier as the economical speed limit.


Quote: "This translates to reduced fuel use at cruise conditions. A study by Boeing (Liebeck, 2004) concluded that an 800-passenger BWB aircraft sized for a 7000-n mile range could deliver a 27% reduction in fuel burn per seat mile compared to a conventional design with comparable specs."

Comment: Is this 27% increase in fuel efficiency as compared to a B-777 or to the "Dreamliner B-787", with about as much an increase in cruise efficiency without having to resort to the BWB configuration with the above mentioned disadvantage, with further disadvantage being poorer longitudinal stability in turbulent air penetration phase.

@ paul, R Michael -

I stand corrected on the explosives, my apologies.

However, the bolts are apparently designed to fail in the event of excessive vibration, e.g. after a vane failure, allowing gravity to separate the damaged engine from the stricken plane. Granted, that's a rare enough event but if you mount the engines on top of or inside the aircraft, this passive protection would no longer be available.

Actually, burying the engines are NOT a good idea because of potential fan blade separation hazards. Besides, putting the engine pods on the back center of the BWB already reduces noise because the plane's body shields much of the noise from the engines to start with. And don't forget today's engine nacelle designs already reduce noise to start with by dissipating the hot exhaust gases that generation much engine noise.

Sorry to italicize subsequent postings. I hope this will correct it. :)

Oops, that din't quite undo the italization. I hope this will do it. The following is a correction to my previous posting:

Comment: Is this 27% increase in fuel efficiency as compared to a B-777 or to the "Dreamliner B-787", the latter having about as much an increase in cruise efficiency over the formerwithout having to resort to the BWB configuration with the above mentioned disadvantage, with further disadvantage being poorer longitudinal stability in turbulent air penetration phase.



That should fix it.

This design seems exciting to me. Looks a little like the "sonic cruiser" that was pushed aside in favor of the 787. These fat wings could hold lift fans, like the F35 JSF, and therefore sort of drop into a airport rather than fly low over folks and bother them with noise. Time will tell, but this looks like a nice replacement idea for the C-17. Faster, more fuel efficient, quieter, and with lift fans, able to bring the goods to short runway locations. And like the 787, this could solve the turblence issue by simply flying above 40,000 feet.

Check this out. Google Images, GB-888A. Compared to the tubes, this 1964 Burnelli design would be built in 1/2 the time, cost 1/2 or less, use 1/2 or less the runway (takeoff/land @ 110 mph), carry more than twice the load using the same amount of fuel and easily cut your fares by 30 to 50%, and, above all save the lives of thousands of future flyers in survivable accidents.

Sure, the BWB could do most of this too except for the airfare. With the astronomical price tag and long production your airfare will only increase.

Also see, www.meridian-Int-res.com/Aeronautics/Burnelli_AIAA.pdf
and aircrash.org

Think Safe, Think Simple, Think Green!

I'm workin' on it.

What role in the development of the BWB did the earlier Boeing studies of Burnelli's concept have? The work was suspended when Burnelli Corp stated that it would sue Boeing for copyright infringement. The Boeing designation was the 767!

what other changes that can be done to the BWB aircraft to improve it ?

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