Page 26 - Volume 11 Number 12

The Model 60 Duke was aimed at the owner-flown segment of the business aircraft market. Introduced for the 1968 model year, the Duke represented the best Beech Aircraft Corporation could offer in an airplane having a distinctive design, possessing ultra-high performance
and cabin comfort rivaling that of the highly successful Model 90 King Air. For its time, the Duke was the ultimate lightweight twin-engine, piston-powered business airplane available. (WICHITA STATE UNIVERSITY LIBRARIES, SPECIAL COLLECTIONS AND UNIVERSITY ARCHIVES)
The Duke also would answer a fresh challenge from competitor Cessna Aircraft Company with its Model 421 that featured a pressurized cabin that seated up to six occupants. A prototype first flew in October 1965. The pressurization system (4.2 psi maximum differential) allowed a cabin altitude of 8,000 feet at an airplane altitude of 20,000 feet. The Model 421 proved to be a great success for Cessna Aircraft, with 200 built in 1968, the first year of production. Powered by two Continental (T)urbosupercharged, (G)eared, (S) upercharged, (I)njected, (O)pposed six-cylinder piston engines (TGSIO-520-D) each rated at 375 horsepower, the new Cessna had a maximum speed of 286 mph at an altitude of 16,000 feet and a service ceiling of 26,000 feet. In terms of overall performance and cabin comfort, the Model 421 would prove to be a worthy competitor to Beech Aircraft’s powerful Duke.
By early 1966 construction of a pre-production prototype of the Model 60 (designated constructor number P-1) was well underway, and the airplane flew for the first time on December 29, 1966, with engineering test pilot Bob Hagan at the controls. As mentioned previously, the Duke would borrow heavily from the 56TC/A56TC’s fuel system, cowling and engine installations, all of which had be developed and proven on the Turbo Barons. The Duke’s engines were the same Lycoming turbocharged TIO-541-E1A4 units installed on those aircraft and turned Hartzell three-blade, constant- speed, full-feathering propellers that featured a diameter of 6.2 feet. Performance calculations indicated that the Model 60 would have a maximum cruising speed of 278 mph at an altitude of 25,000 feet, and a service ceiling of 30,800 feet (very similar to the Turbo Barons).
Although the Duke shared many of the basic airframe systems with the Model 56TC/A56TC, there were some differences. Whereas the 56TC used an NACA 23017-5 airfoil at the wing root, the Duke’s wings employed a NACA 23016-5 airfoil at the root, changing to the same
24 • KING AIR MAGAZINE
23010-5 airfoil used on the Model D55 Baron at the wing tip. The all-metal, cantilever wings spanned 39 feet 4 inches and featured a total area of 213 square feet. Wing chord was 9 feet 2 inches, dihedral 6 degrees, with incidence set at 4 degrees at the root and 1 degree at the tip. Wing loading was 31.6 pounds per square foot while power loading was 8.8 pounds per horsepower. Flaps were operated electrically, as was the tricycle landing gear.
One major advantage of the Duke over the 56TC/ A56TC was its pressurized cabin that was only beginning to appear in an aircraft of the Duke’s class. Bleed air from the turbosuperchargers was routed into the cabin where valves automatically regulated cabin altitude in response to the pilot’s input to a controller in the cockpit. The system was capable of maintaining a maximum differential (difference between atmospheric pressure outside of the airplane compared to air pressure inside the cabin) of 4.6 pounds per square inch (psid). The differential provided sea level conditions in the cabin up to an airplane altitude of 10,000 feet, and a cabin altitude of 10,000 feet at an airplane altitude of 24,800 feet.
As for the cabin, a center aisle flanked on each side by two seats were standard, but six seats were optional (although when fitted with six seats the cabin was snug). Many customers opted for six seats based on mission requirements. Entry into and exit from the cabin was through a hinged door located on the left,
DECEMBER 2017