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.
Vladimir Mikhailovich Myasishchev initially created the M-17 Stratosphera (that’s “Mystic,” to NATO) to shoot down U.S. reconnaissance balloons. By the time of its 1982 first flight—after its designer’s death—it had lost its gun turret and become a spyplane. The design was probably influenced by two earlier projects: the twin-boom Sukhoi Su-12, a 1947 piston-engine recce aircraft that went only as far as prototype, and the Yakovlev Yak-25RV, a high-altitude reconnaissance jet with sailplane-like wings similar to those of the M-17. The Mystic could loiter for four hours at 65,000 feet, but it never achieved the altitude performance of the Lockheed U-2, its U.S. counterpart. Its short fuselage is the single design advantage the M-17 had over the U-2. Says aviation historian Jay Miller, “Jet engines—regardless of whether they are turbojet or turbofan—lose efficiency depending on the length of the exhaust pipe. The U-2’s fuselage and associated lengthy engine exhaust tube have historically been one of its few Achilles’ heels.” A twin-engine descendant, the M-55 Geophysika, flies atmospheric research missions, just as NASA’s ER-2 research craft—civilian versions of the U-2—do in this country.
In aviation’s baby days, twin tail booms were an answer to the question “Where do we put the propeller?” Before Anthony Fokker’s 1915 invention of a mechanism to synchronize the firing of a machine gun with the spinning of propeller blades (the gear first appeared on the Fokker E.1 Eindecker fighter), placing the engine and propeller behind the fuselage cleared the way for a gun in the nose. The U.S. Army banned pusher engines in 1914 after several pilots died in crashes, but many European World War I aircraft used them. The first British airplane designed as a fighter, the Vickers Fighting Biplane 5, also known as the “Gunbus,” had a pusher, as did the Airco D.H.2. Both fighters used a fixed forward gun—and were frequently shot down from the rear.
Former Secretary of the Navy John Lehman became a believer in unmanned aerial vehicles in 1983. After the bombing of a U.S. Marine Corps barracks in Beirut, Lehman viewed a video shot by an Israeli UAV. It showed the Marine commandant inspecting damage. The aircraft had been so inconspicuous that the general had no idea he was on camera, yet Lehman easily recognized the man. The U.S. Navy’s RQ-2A Pioneer UAV was born.
Like the Israeli Scout, from which it evolved, the 450-pound Pioneer has 40 pounds of sensors and cameras up front, balanced by a two-cylinder, 26-hp gasoline engine and pusher propeller behind. Steve Reid, program manager for Pioneer UAV Inc., says the booms, besides supporting the tailplane, have served as a fence around the propeller, preventing injuries in the tight shipboard and battlefield environments where the Pioneer operates.
The U.S. Army Air Forces needed a dedicated military cargo plane so desperately in 1942 that General H.H. “Hap” Arnold ordered development of the Fairchild C-82 Packet after seeing only a rough sketch. Twin tail booms, a high wing, and a low-hung fuselage allowed most wheeled vehicles to drive right into the cargo bay. It had enough room for 44 paratroopers or 2,870 cubic feet of cargo—the size of a standard railroad boxcar, hence its nickname, the Flying Boxcar. Packets, however, played no role in the war. By 1948 the C-82 needed a host of modifications (though not the hatchet job performed by Jimmy Stewart and castmates in the 1965 movie The Flight of the Phoenix). The result, the C-119, now officially the Flying Boxcar, carried more cargo and paratroopers farther and faster. It served in the Korean War, playing a critical role in the Chosin Reservoir breakout in December 1950 by dropping eight bridge sections that created an escape route across a deep gorge (see “Breakout from Chosin,” June/July 2000). In Vietnam, AC-119G Shadow and AC-119K Stinger gunships supported ground combat with flares, infrared sensors, and four Gatling miniguns. The Stinger also had two 20-mm Vulcan cannon. Hawkins and Powers Aviation of Turnbull, Wyoming, still flies a C-82 and two C-119Gs (one was just used in a remake of The Flight of the Phoenix).