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The Blended Wing takes flight
May 15, 2006, by Bill Cawthon
In my Promotex column for November 1, 2002, I wrote about some of the projects being developed at the Phantom Works, which sounds like a super-secret "black" operation but is really Boeing's advanced technology research and development business unit. There is a lot of classified work going on, but much of what is learned in those advanced-technology projects is used to make better aircraft for civilian use, as well.
One of the projects I was able to discuss in that column is moving closer to reality. In April, Boeing, NASA and the U.S. Air Force Research Laboratory began wind tunnel tests on large-scale models of the X-48B, a very futuristic-looking aircraft that could change the way high-capacity airplanes are designed in the years to come. Later this year, the models will travel to NASA's Dryden Flight Research Center at Edwards, California, where they will begin flight testing.
The two models have a 21-foot wingspan and were built in Great Britain by Cranfield Aerospace Ltd., which also built the remote control system for the aircraft. Like the B2, the test models are built mostly of lightweight composite materials. In fact, the models weigh just 400 pounds each. Each model is powered by three turbojet engines capable of carrying the plane to 10,000 feet and at a top speed of about 120 knots. Those numbers many not sound very impressive but they will be enough to test a number of concepts.
The X-48B is what is known these days as a blended wing body. Years ago, everybody called them flying wings for the simple reason that's what they looked like. However, this modern interpretation of an old idea is really a hybrid, drawing from both flying wings and conventional aircraft. Unlike planes such as the Northrop YB-49, which first flew in October 1948, a true BWB has an airfoil-shaped body and high-lift wings. Instead of the tail found on most airplanes, the blended wing body uses special moveable surfaces on the trailing edges of the wings to provide stability and control. This design allows the entire plane to generate lift. It also reduces the drag caused by a conventional fuselage and tail, increasing fuel economy. To make the deal even sweeter, the shape of the body allows for more payload or passenger space, further increasing overall efficiency.
Aerospace engineers already know the BWB concept is valid. In fact, a smaller blended wing body aircraft first flew in 1989 and has been in active service with the U.S. Air Force for nearly ten years. The B-2 Spirit stealth bomber is a BWB and the experience and knowledge the Air Force has gained through the B-2 program is being used to further the state of the art in BWB technology.
Work on a large blended wing body aircraft like the X-48B began in 1991 at McDonnell-Douglas. Working with NASA and teams from Stanford University, UCLA, Clark Atlanta University in Georgia and the University of Florida at Gainesville, McDonnell-Douglas developed a design that forecast the shape of the X-48B. In July 1997 representatives from government and industry watched a propeller-driven scale model lift off at El Mirage Dry Lake, California. The model had a 17-foot wingspan and was designed as a 1/16 scale representation of a giant blended wing body aircraft capable of carrying 800 passengers or more than a quarter-million pounds of cargo. The model was built by Stanford graduate students working under Dr. Ben Tigner, who later went on to become an engineer with Boeing's Phantom Works.
While the blended wing body aircraft looks as modern as tomorrow's news, the elegant simplicity of a flying wing has fascinated aircraft designers and engineers since the dawn of aviation. German aircraft pioneer Hugo Junkers patented a design for a tailless glider in 1910 and began working on an airliner capable of carrying passengers in its wings in 1919. Unfortunately, the Allies ordered the plane destroyed in 1921 because it exceeded the size limitations imposed on Germany following World War I. Junkers had visions of flying wings carrying a thousand people across the ocean, though the only airplane he ever built along the lines of his dreams, the G38 of 1931, could carry only 34. By the way, that 34-passenger capacity, which included some people seated in the wings, made the G38 the largest airliner of its day.
Flying wings got a lot of attention in the golden age of aviation. Airlines, eager to compete with ocean liners, were looking for a new airplane that could carry enough fuel to cross the Atlantic while being able to carry enough passengers to make the trip. The flying wing's low drag and large internal capacity made it a natural candidate for the role but problems with stability and control kept it on the sidelines.
In Germany, Walter and Reimar Horten were experimenting with radical glider designs. The Horten's tailless sailplanes used a large, albatross-style wing and had a small fuselage in which the pilot lay prone. The Horten's gliders fascinated Jack Northrop, one of the founders of Lockheed.
In 1939, after stints at Lockheed and Douglas, Northrop had formed his own aircraft company in Hawthorne, California. As the hostilities in Europe and Asia grew, he focused on flying wings for military applications. He believed a flying wing could carry a larger bomb load, fly faster and have a longer range than the conventional aircraft of the time.
In April 1941, the U.S. Army Air Corps requested new designs for a bomber that could carry 10,000 pounds of bombs and have a range of 10,000 miles. The intent of the government request was to have a bomber that could reach Germany in the event that Great Britain fell to the Nazis. The Army wanted the new plane to have a cruising speed of 275 mph and a top speed of 450 mph. Specifications called for a service ceiling of 45,000 feet.
The Army originally went to Boeing and Consolidated Aircraft but expanded the contract in May to include Northrop. The Army ordered a single flying wing, designated the XB-35, in November of 1941. Because of the amount of groundbreaking engineering involved, the Army's contract with Northrop also called for a one-third scale version of the XB-35. This plane was called the Northrop N-9M.
Serious work on Northrop's flying wing began in 1942. Since the plane would have no tail or rudder, split flaps on the trailing edges of the wings were used for steering. The original contract called for a single prototype but it was expanded to three in 1943 and a fourth was added shortly thereafter.
To keep the weight down, the N-9M was built partly from wood. The first plane was powered by a pair of 290-horsepower Menasco C65-1 engines. The first flight of the N-9M was two days after Christmas in 1942 but mechanical problems dogged the plane. It crashed in May 1943, killing the pilot.
Since the Menasco engines had been particularly troublesome, they were replaced by 400-horsepower Franklin engines in later aircraft.
Early testing showed the Northrop flying wing had a lot of bugs. In addition to mechanical problems, flight data indicated the full-size plane would probably not meet the original specifications for range and speed.
Despite the setbacks with the N-9M, work continued on the XB-35. The Army ordered a second plane in January 1942 and expanded the order to include thirteen pre-production YB-35s in 1943. But the war would end before the Northrop's full-scale flying wing ever took to the skies.
In June 1946, the first XB-35 took off from Hawthorne for a 45-minute maiden flight. As with the N-9M, there were problems and after a total of just 27 test flights, both planes were grounded. There were serious problems with the XB-35's contra-rotating propellers and signs of metal fatigue were already showing up in the exhaust system. The biggest problem of all was the fact the plane was insufficiently stable to serve as a bomber.
Despite the problems with the XB-35, the military still had enough interest in the flying wing to proceed to the pre-production YB-35. Flight testing of the revised YB-35 began in 1948, but by then it was already obvious the future lay with jet propulsion. The new U.S. Air Force was loath to completely write off the investments in the flying wing, so Northrop converted two of the YB-35s to jet power and the new plane was designated the YB-49.
The eight-engined YB-49 made its first flight in October 1947 and the first flights were very promising. The new plane set an unofficial endurance record by flying above 40,000 feet for six hours and set a transcontinental speed record with a four hour, twenty minute flight from Muroc AFB in California to Andrews AFB in Washington, D.C.
But as had been true of the N-9M and XB-35 before it, the YB-49 still had serious flaws. A structural failure is blamed for a crash that killed famed test pilots Glen Edwards (Muroc AFB was renamed in his honor) and Daniel Forbes on June 5, 1948.
Ultimately, the flying wing program was scrapped. There were too many unresolved design issues and even with eight jets, the YB-49 couldn't carry a load of nuclear weapons comparable to that handled by the Convair B-36 and the new jet bombers being developed by Boeing. But the dream never died and aviation technology finally caught up with the flying wing concept in the B-2 Spirit. With the research on blended wing bodies being conducted today, it is still possible that we will see something like the thousand-passenger airliners envisioned by Hugo Junkers. A BWB aircraft capable of carrying as many people as an Airbus A380 would have a wingspan only slightly wider than a 747 and would use less fuel.
Right now, the blended wing body is still in the earliest stages of testing and development. But it might not be too many years before we start to see a whole new type of airplane wearing the colors of airlines around the world.
Who knows? Maybe we'll even get a Herpa Wings model.
See you next time!
- Bill Cawthon
Bill Cawthon is a modeler and collector. His primary hobby interests are vehicle models in 1:87 and 1:160 scales and model railroading. He is one of the creators of the award-winning "Grimy Gulch" model railroad layout.
In real life, Bill is a marketing and public relations consultant working with the information technology and hobby industries. He is an associate editor for Model Railroad News and writes a monthly column on the U.S. light vehicle industry. He is a member of the 1/87 Vehicle Club and the Texas Auto Writers Association.
He lives in Houston, Texas with his wife, Marge, and their children.
Bill's columns appear twice monthly on Promotex Online. To learn more about him, click here.
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