Fork-tailed Devils and Flying Shoes
What does the Northrop P-61 have in common with Burt Rutan's SpaceShipOne?
- By Mark Gatlin
- Air & Space magazine, January 2005
NASM (SI Neg. #00010700)
(Page 3 of 4)
With a wingspan of 73 feet, Caproni’s Ca.3 biplane bomber was one of the largest aircraft fielded in World War I, almost 20 feet wider in span than the war’s other twin-boom biplane bomber, France’s Caudron G.4. (It was a big-airplane war: Handley Page built a four-engine giant with a 120-foot wingspan.)
Like so many of its contemporaries, the Caproni bomber used a combination of pusher and tractor propellers; Caproni placed the pusher at the rear of a short, bathtub-like fuselage, the only ungraceful feature of a beautifully proportioned airplane. Its most famous missions were low-level night raids, flown in 1917 across the Adriatic Sea, to surprise the Austro-Hungarian fleet while it was at anchor in Pola (today Pula), Croatia.
The year before, a second gunner’s position was added above the rear engine. “It must have been a ferociously difficult position,” says Morrow, the author of The Great War in the Air (Smithsonian Institution Press, 1993). “It was located up and in the slipstream and the weather. Many of those crews won Italy’s highest honor for bravery in combat. I marvel at what men did in World War I.”
A MACHINE FOR SEEING
What must the view have been like from the Abrams Explorer? The two-place crew nacelle, pushed so far forward that not even the wings encroached on the scenery, was glazed top and sides with plexiglass, like the nose of a World War II bomber. Flying by November 1937, the Explorer was one of the first U.S. aircraft with a twin-boom configuration, used so that the radial pusher engine could be mounted aft, where it wouldn’t block the view. It is one of only a few aircraft of any configuration designed solely for surveying and mapping. Early on, the Army was interested in Talbert Abrams’ camera platform, but decided instead to convert fighters for combat photo reconnaissance. Civilian markets didn’t materialize. Undaunted, the former Marine pilot went on to start the ABC Airline (“Always Be Careful”) and was famous throughout hometown Lansing, Michigan, for his airplane-shaped house. Today, his Explorer is awaiting further restoration at the National Air and Space Museum.
At virtually the same moment Abrams was creating the Explorer, across the Atlantic another twin-boom aircraft was being designed and built for maximum visibility, but the client had no interest in surveying. Conceived in February 1937 and flying by July 1938, the Luftwaffe’s Focke-Wulf 189 Uhu (Owl), known as Das Fliegende Auge (the Flying Eye), had small, air-cooled engines and retractable gear in the booms and a generously glazed central nacelle on top of the wing. Though armed with six machine guns, two cannon, and, at times, spray canisters of mustard gas, most 189s flew short-range reconnaissance missions on the Eastern Front. One was a personal transport for Albert Kesselring, a supreme commander of German air and ground forces.
To make the first nonstop, unrefueled flight around the world, Burt Rutan designed a flying fuel tank. “The Voyager booms hold a large percentage of the fuel,” Rutan says, “and [the fuel] had to be mounted along the span to keep the wing spar from being too heavy.” Two tanks in each boom, four in each aft wing, one in each canard, and three in the fuselage held 7,000 pounds of fuel, or 72 percent of the craft’s gross takeoff weight.
The long, thin wing was not stiff enough to support the booms. Rutan’s solution was to stiffen the structure by connecting the forward tips of the booms to a canard wing to hold them in position and keep them from twisting the main wing. To conserve fuel, the aircraft was to be powered most of the trip by one engine (the pusher), so Rutan mounted both engines on the centerline. After its nine-day flight in December 1986, Voyager landed with just 106 pounds of fuel, or about 16 gallons—enough for a little over three hours’ flying.
Twin booms are becoming almost as much a hallmark of Rutan’s designs as the ever-present canards. He also uses the configuration on the Global Flyer, in which record holder Steve Fossett intends to attempt another solo around-the-world flight before April 2005.