The Rise of the Black Hawk
Dave Jenney '53 helped create a helicopter that changed the face of American combat
If David Jenney didn't exist, he would be fun to invent: A brilliant mechanical engineer who admittedly isn't much good under the hood of a car; a distinguished gentleman who knows the sweat and pain of long-distance running.
He can discourse on the dissymmetry of local flow velocity across helicopter rotor blades, yet his most recent engineering feat is a squirrel baffle for the birdfeeder. His invention looks uncannily like a one-gallon milk jug with the handle cut off. You can see it from the breakfast nook in the warm and tidy home that Jenney and his wife, Janet, share in his hometown of Mattapoisett, Mass.
He is a champion sailor who enjoys the sun and bracing salt air while considering the mathematics of variable forces at work on the vertical planes of sail and keel. It's not that he can't relax; it's just that he can't stop himself from seeing the possibilities in the world around him--and most of all, the possibilities in himself.
In 1970, when the U.S. Army called for a new transport helicopter with a third engine to be built on an existing two-engine platform, Jenney's team of engineers at Sikorsky answered with the Black Hawk. It featured new airfoils and blade shapes, vibration absorbers, and most revolutionary of all, a canted tail rotor that kept the aircraft in balance while allowing room for a third engine. Today the UH-60A Black Hawk is the Army's primary utility/assault helicopter, used for air cavalry, electronic warfare and medical evacuation. In assault operations, it can move a squad of 11 combat troops and equipment, or carry the 105-mm M102 howitzer, 30 rounds of ammo and a six-man crew. Since 1973, Sikorsky has built more than 2,000 UH-60s for government use.
Imagining the future of rotary flight
In the 100 years since the Wright brothers flew at Kitty Hawk, the men and women who build aircraft have tried to go faster. Engineers and test pilots continue to push the envelope of airframe and engine design, along with the limits of human endurance.
In designing helicopters, engineers face a unique speed barrier: whereas a fixed-wing aircraft will stall when it goes too slow for its wings to provide lift, a helicopter will stall when it goes too fast, but for the same reason--its rotary wings can't provide sufficient lift. In a dry bit of understatement typical of his personality, Jenney puts it this way: "Blade stall is to be avoided--not analyzed."
The weight and performance capabilities of early helicopters were modest "to say the least," says Jenney, who spent 40 years in the business. "They were slow and vibrated so as to shake your fillings loose." Still, helicopters were doing things that no other machines could do, and Jenney found himself at the forefront of dramatic advances in helicopter design.
To put his lengthy career in perspective, consider this sentence from Jenney's 1996 lecture to the American Helicopter Society, speaking of the early days of helicopter design: "A favored text [proposed] a numerical solution of the equations of motion of an offset flapping blade, but it required a computer to solve those equations." But it required a computer.
The Slide Rule Age
When Dave Jenney and his team of engineers began crafting the evolution of the helicopter in the early 1950s, the sole computer at United Aircraft Research Labs (forerunner of Sikorsky) was a brand new IBM-701. It filled a large air-conditioned room.
While waiting for technology to catch up, Jenney and his fellow engineers wielded slide rules with the speed and single-minded devotion of samurais. There were no high-speed workstations on every desk, no CAD/CAM, no virtual modeling.
The mechanics of helicopter flight are so complex, the variables so great, that the details required to adequately model the wake and the blades remain a challenge even for today's fastest computers. "Prediction of loads, vibrations and noise still requires some degree of empiricism," says Jenney.
The advent of early computers, as large and sluggish as they were, together with routine testing in the 100-mph wind tunnel at the research labs, helped designs advance quickly. While computer-aided design was just emerging, the usefulness of the helicopter was being demonstrated in dramatic fashion over the battlefields of Korea. It was, says Jenney, "a great time for an engineer to enter the helicopter field."
Over the course of his career, Jenney consistently delivered innovative concepts for rotary-wing aircraft, including new airfoils, blade shapes and vibration absorbers. He also bridged the gap between theory and practice by developing analytical methods and demonstrating steady improvement through experimentation.
Among the significant achievements of the Jenney-led design teams at Sikorsky are early vertical takeoff and landing aircraft and the Rotor Systems Research Aircraft, described by Jenney as a "complex flying rotor laboratory," created for NASA.
"He was an engineer's engineer," says Art Linden, a longtime colleague. "He always stayed close to the technical arguments, and if he wasn't winning his point, he would draw back, put his argument together, and come back at it again." (Linden retired in 2000 as vice president of Sikorsky's program.)
Dave Jenney keeps a model of the Comanche in his study. Beginning this year, more than 1,000 of them will be built for the U.S. Army.
The design concept that Jenney is most known for is the canted tail rotor. Now it's a familiar sight on the world's most advanced helicopters, including the famous Black Hawk. The tilted tail was an innovative solution to a practical problem; the U.S. Marine Corps wanted to increase the lift capacity of the Sikorsky model CH-53, but couldn't afford a new aircraft design program. Adding a third engine meant using larger main and tail rotors, but moving the tail rotor 6 feet aft threw the aircraft out of balance.
Jenney's solution (he credits his design team, though everyone else credits Jenney) was to cant, or tilt, the tail rotor 20 degrees off vertical, producing enough lift to balance the aircraft--now with a third engine--without having to extend the nose. Pilots frowned at the idea and salesmen resisted something that looked so odd, but there simply was no denying the results it delivered.
Twenty years later, the U.S. Army Black Hawk that Dave Jenney helped create is a reliable veteran. In various configurations (U.S. Air Force Pave Hawk, U.S. Navy Sea Hawk, U.S. Coast Guard Jay Hawk) it is used for air assault, air cavalry, electronic warfare, search and rescue, medical evacuations, disaster relief--even executive transportation. With ballis- tically hardened flight controls, redundant electrical and hydraulic systems, a self-sealing crash resistant fuel system, and energy-absorbing landing gear and crew seats, the Hawk has proven to be reliable, durable and survivable in the toughest condition.
At the time he retired, Jenney was still breaking boundaries as engineering director of the Comanche program, a joint venture of Sikorsky and Boeing. With stealth techno-logy, fly-by-wire controls and a composite fuselage, the Comanche helicopter will carry rotary aircraft design--and Dave Jenney's legacy--well into the 21st century.
Jenney's other love is sailing; he is restoring his boat, the JANCAP.
Jenney's mild demeanor belies his undeniable grit. He presents himself like a cerebral academic: quiet, gracious, refined and unfailingly polite. It is counterintuitive to learn that he has completed 19 marathons.
Most people would consider completing even one marathon to be a lofty goal and noteworthy achievement. Jenney has pushed and punished his wiry frame through 19, including six Boston Marathons, with a personal best of two hours and 53 minutes.
"I wanted to know if I could do it," he says, matter-of-factly. "I wanted to know if I could overcome the mental as well as the physical barriers, when every step hurts, but you've got to persuade yourself to keep going." Regardless of the obstacles, Jenney has a blend of tunnel vision and tenacity that allows him to reach his goals, to take disappointment and setbacks in stride, to just keep going. At 72, he still logs 25 miles a week in his running shoes. "I'm not speedy," he says, "but I'm persistent."
Persistent indeed. In 1953, fresh out of WPI (where he studied on full scholarship), Jenney joined the newly formed helicopter research group at United Aircraft Research Labs, which would become United Technologies Corporation, parent company to Sikorsky Aircraft. He attended the University of Connecticut nights to collect his MSME. Then, still working full time, he started out in pursuit of his doctorate in mechanical engineering--a pursuit that would become an academic marathon. Jenney sat for his qualifying exam the day after he started work at Sikorsky, and he was sent back to the drawing board, his thesis being deemed incomplete.
For sheer outrageousness it is hard to beat Jenney's doctoral thesis. He proposed a rotor with blades thin enough to roll up like window shades. The rotor of Jenney's "convertiplane" could be put away at high speed when a wing would assume the work of lift.
True to form (call it persistent, tenacious, focused--crazy also comes to mind), Jenney stayed in the race, working the problems in his thesis at night and on weekends, while leading the way in helicopter research and design by day. He succeeded in building a working model. "The high point of my thesis defense--to me, at least," says Jenney, "was starting up that model and watching it rise from the conference table."
Dave Jenney completed his Ph.D. in 1968, about the time his design team was creating the S-67, a concept machine that would set the helicopter speed record of 221 mph. It took him 10 years to complete his doctorate. It took his design team one year to go from concept to speed record. The S-67 never sold. No matter, says Jenney. "We're always learning things along the way."
Ever the aerodynamicist, even in retirement, Jenney says the most productive direction that the helicopter industry can take is to dramatically reduce cost and improve affordability. Reduced costs won't result from innovations in accounting, he counsels, but in improving aerodynamic efficiency and fabrication methods. In the WPI tradition, engineers need to look on this next step as an integral part of their job. Dave Jenney likes to imagine the market potential of the helicopter industry if costs were reduced by 50 percent. "That would be a man-on-the-moon type accomplishment," he says, as he laces up his running shoes.
- United Technologies Corporation
- Black Hawk helicopter
- Journal of the American Helicopter Society
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Last modified: Sep 02, 2004, 11:32 EDT