Whirlaway, XHJD-1

By the end of World War II, James McDonnell, founder of McDonnell Aircraft Corporation, realized before most of his competitors that the helicopter was not merely a fad. He saw on the horizon large military helicopter contracts and invested heavily in the emerging rotorcraft industry in order to win some of this lucrative business. Unfortunately, McDonnell pursued a technological dead end. The result of his efforts, the McDonnell XHJD-1 "Whirlaway," represents the last attempt by a major American aircraft manufacturer to field a conventional helicopter with laterally spaced, main rotors.

McDonnell started his company in 1939 when the impending war seemed to promise a plethora of lucrative government contracts to aircraft manufacturers. Three years later, McDonnell was still a subcontractor nowhere close to selling his own designs. To leapfrog companies that had already soaked up the best contracts, he tried to anticipate the next wave of military aircraft by developing new technologies such as jet propulsion and helicopters. McDonnell invested in the Platt-LePage Aircraft Company. In return, the firm gave McDonnell's engineers access to data on helicopter design. Platt-LePage had recently flown the first U. S. Army helicopter of World War II, the XR-1 (see NASM collection). This design employed twin lateral rotors, a layout based on one of the world's first practical helicopters, the Focke Wulf Fw 61. By 1944, McDonnell owned a controlling share of the company and his own team of engineers was hard at work on helicopter rotor designs.

McDonnell was determined to win a new Navy contract for a large rescue helicopter announced in 1944. He set about constructing an improved and scaled-up version of the XR-1 using engineering data obtained from Platt-LePage. On March 23, 1945, McDonnell received a Navy contract to build a flying prototype designated the XHJD-1 and officially nicknamed the "Whirlaway." Navy leaders were quite satisfied with the development of Frank Piasecki's XHRP-X (see NASM collection) tandem rotor helicopter but they wanted a backup design in case the Piasecki project faltered. The Navy was most interested in McDonnell's assurance that the "Whirlaway" test program would be unprecedented in scope for a rotary-wing aircraft. McDonnell intended to make up for the general lack of formal engineering studies into large helicopters by thoroughly documenting each test flight. The Army was well ahead of the Navy in developing military rotorcraft and naval planners lacked the confidence to invest heavily in unproven technology. McDonnell intended to exhaustively research and document the performance and potential of his lateral-rotor design and convince the Navy to procure it in quantity.

The most novel aspect of the "Whirlaway" design was to use one engine for each main rotor. McDonnell engineers had to develop a complex transmission system that enabled one power plant to power both rotors if one engine failed. Otherwise, an engine failure would result in a catastrophic loss of control. Like the Platt-LePage XR-1, the "Whirlaway" fuselage was made of steel-tube covered with fabric. A vertical stabilizer and rudder were required to make sure yaw control was adequate in forward flight. Experience with the Fw 61 showed that helicopters with lateral main rotors could be difficult to precisely control in yaw, particularly during turns at low speed. Designers configured the XHJD-1 to carry as many as eight passengers but the helicopter flew only with the equivalent weight in test instrumentation.

The rotors turned at the ends of stub wings that provided more than 10% of total lift in forward flight, and up to 30% total lift during autorotation. Engineers had to build the wings very strong to support the weight of the rotors, engines, mounts, transmissions, and interconnecting drive shafts. The "Whirlaway" weighed considerably more than the Piasecki XHRP-X designed with the tandem main rotors and single engine mounted in the fuselage.

The "Whirlaway" carried 817 kg (1,800 lb) of test instrumentation. McDonnell intended to give Navy engineers voluminous quantities of data to help them better understand the engineering principles and aerodynamic phenomenon associated with twin, lateral-rotor helicopters. McDonnell sold the Navy on flying the XHJD-1 as a test prototype but he ultimately wanted a production contract. However, his preference for the Platt-LePage approach to designing large helicopters doomed the project. The "Whirlaway" fell victim to many of the same problems that failed the XR-1 several years before. McDonnell engineers were hard at work on the design for a full year before they won the XHJD-1 contract but another year passed before the helicopter was ready to fly. This lengthy development period contrasted sharply with McDonnell's competitors who turned out new designs in half that time. When the "Whirlaway" finally flew on April 27, 1946, with test pilot Charles R. Wood at the controls, the company was far behind Piasecki and Sikorsky in developing large helicopters.

Once test flying began, the ghost of the XR-1 continued to haunt the XHJD-1. Significant vibration and control problems plagued the McDonnell helicopter, just as they had dogged the Platt-LePage aircraft. Adding a horizontal stabilizer and elevators improved yaw control and mounting the rotors on shock absorbing mounts helped combat ground resonance problems. The aircraft eventually began to fly and perform reasonably well but by then, the "Whirlaway" was fast becoming obsolescent. Pilots flying the helicopter still managed some impressive feats such as flying out of ground effect at the considerable gross weight of 5,806 kg (12,800 lb) and on another flight, the climbed the aircraft to 3,648 m (12,000 ft).

McDonnell's "Whirlaway" succumbed to the darling of the Navy helicopter procurement officers, the Piasecki X-HRPX. This impressive aircraft flew more than a year before the XHJD-1 and the Navy quickly lost interest McDonnell's helicopter. The U.S. Air Force expressed mild interest in the project after technicians mounted a rescue hoist on the helicopter but they too chose the superior Piasecki design as that service's arctic rescue helicopter (designated the H-21). Since the McDonnell experiment, aircraft designers have abandoned the twin, lateral rotor helicopter layout but Bell Helicopter Textron has used a variation of it successfully in tilt-rotor aircraft such as the Bell-Boeing V-22 Osprey. Bell and Boeing have had to rely on fly-by-wire systems to overcome the flight control difficulties inherent in the configuration. This technology was not available to McDonnell's engineers.

James McDonnell kept the XHJD-1 flying until June 1951. With just 250 flight hours logged, he retired the "Whirlaway" and donated the aircraft to the Smithsonian Institution.

Rotor Diameter: 15.2 m (50 ft)

Length: 9.8 m (32 ft 2 in)

Height: 4.1 m (13 ft 6 in)

Weights: Empty, 3,629 kg (8,000 lb)

Gross, 4,990 kg (11,000 lb)

Engines: (2) Pratt and Whitney R-985-AN-14B, air-cooled radial,

450 horsepower

References and Further Reading:

Francillon, Rene J. "McDonnell Douglas Aircraft since 1920: Volume II." Annapolis, Md.: Naval Institute Press, 1990.

Labermont, Paul. "Helicopters and Autogyros of the World." Cranbury, N.J.: A.S. Barnes

and Company, Inc., 1970.

Spencer, Jay P. "Whirlybirds: A History of the U.S. Helicopter Pioneers." Seattle: University of Washington Press, 1998.

Roger Connor, Russell Lee, 9-21-01