Wednesday, May 15, 2013

The XB-51’s Striking Innovation

After World War II, another threat loomed 
by Wilfred K.

I was employed as a draftsman in Baltimore in 1941. By 1950, I was recognized as a better-than-average electrical engineer, having designed and tested the electric power system for the Martin P4M four-engine bomber. I later designed the electrical circuitry for the Martin-patented Automatic Propeller Feathering Control System for Takeoff Power Failure for the Model 2-0-2 aircraft. In 1951, I was assigned as project electromechanical engineer on the XB-5I bomber. My duties covered electrical, hydraulics and armament. The XB-51 was an excellent medium bomber, and it performed well beyond all specification requirements. It had many unique features including a bicycle landing gear. The forward pair of wheels turned for steering, and its pivoting wing with geared flaps when the pilot moved his flap control for lift during takeoff or landing. The wing leading edge moved up, pivoted over the hinged rear spar and the geared flaps moved down. The aircraft had a rotating bomb door. Before flight, the bombs were loaded on top of the door, which was then hoisted into a cavity in the aircraft belly. For bomb release, the door was rotated 180 degrees exposing bombs to the air stream. Westinghouse air brakes provided maximum braking during landing, along with a small parachute the airplane braked to stop in less than 2,000 feet. Brake control was provided by a brakes-on and -off switch on the panel. The pilot flipped the switch to “on” after touchdown and had maximum braking until the plane stopped.

The XB-51, Martin's Phantom Strike Aircraft
Soon after I reached my office, I had to attend an after-flight meeting with a meeting of the pilot and several engineers. The pilot complained about the high amount of lateral trim. On airplanes with ailerons, lateral trim is achieved by a trim tab on the aileron. Deflection of the trim tab 0 to 5 degrees causes a small opposite deflection of the aileron. Since the XB51 had no ailerons, lateral control was achieved by large flaps to top of the wing, and lateral t rim was provided by a small trim flap on the trailing edge of the wing. Trim was achieved by trim flap motion of zero to 15 degrees. I suggested that we could change the trim indicator to read “0 to 5” instead of “0 to 15.” George Trimble, chief of new design, thought it was a great idea!

During 1950, the XB-51 completed all required flight tests. In 1951 all armament tests were to be done. Early in the year, the airplane was moved into the gun firing revetment. There, Werner Buechal and I observed testing of gun aiming accuracy. Four 20mm cannons were mounted in the nose of the XB-51. During aiming test, each gun was separately loaded with five live rounds, followed by a dummy round. As each gun was fired, its accuracy was checked and adjusted if necessary. At the completion of the alignment of the four guns, we were ready for bomb drops. By specification, we were required to make eight drops of the nine 500 pound bombs at high speed and low altitude. I was asked to take pictures of the bombs as they left the airplane. I asked Herm Meyer, our aerodynamics group engineer, to provide me a plot of the relative location of the bombs and the airplane as the bombs dropped to the ground. After several computer runs, Meyer told me the bombs position during drop was constant 45 degrees aft of vertical

I met with the flight test instrumentation group. We removed the front center bomb and loaded a 45-degree aft-pointing gun camera in its place. The gun camera was connected to the bomb release wiring, so the camera would start running as the bombs were released. A small aerodynamically faired box was mounted on the bottom of the wing carrying a second camera pointed below the airplane to view the bombs as they separated. Captain Willard Horn piloted the plane for each of the eight required bomb drops at 625 mph at 50 feet above the ocean. The results were spectacular! We recorded pictures of each group of eight bombs from release to impact in the ocean. The side camera showed the bombs as they separated. They were completely stable with no tumbling. This was in comparison to problems with B-47 bomb release at 350 mph, with bombs tumbling in the bomb bay after release.

After a flight competition over the Martin airfield between the XB-51 and the British Canberra, Martin was awarded a contract to design and build B-57 bombers based on the British Canberra and the XB 51 contract was terminated. Bob Williams, the XB-51 assistant project engineer was reassigned to head the B-57 project and I was promoted to fill his place. With the XB-51 program terminating, Ralph Draut was reassigned and I became the project engineer.

In January 1952, I signed the contract paperwork with Captain Horn who flew the airplane to Muroc Air Force Flight Test Base in California. He had to stop midway to refuel the airplane, so we sent two mechanics ahead to help with the turnaround. After Horn took off our mechanics flew to Muroc to help the Muroc ground crew to become acquainted with the XB51.

I was summoned to the sales office. I learned that I was assigned to fly to Muroc to talk to Major Lathrop who was to fly the XB-51 while it was at Muroc, and hopefully to speak to General Wolff about the merits of the airplane. I spent some time with Major Lathrop, but learned I would not be able to speak to General Wolff because he was being transferred to Wright Patterson Air Force Base.

After my stay at the base, I drove to the Los Angeles railroad station where I boarded the Santa Fe Super Chief to Chicago. The train stopped in Pasadena and left in the night. The next morning, we awoke to daylight in Winslow. I really enjoyed the trip east viewing the desert, buttes and mountains for the first time as we passed through Flagstaff Gallup, Albuquerque, Santa Fe and Raton Pass. We continued overnight to Chicago, where I changed trains and went to Baltimore on the B&O Capital Limited. When I returned to work, I learned that I was assigned to be XP6M-I assistant project engineer.

In April 1952, we learned that the XB-51 number one crashed during an air show at Muroc. A grandstand was erected beside the runway and was full of Air Force personnel and members of the media along with many cameras including a 35mm motion picture camera handled by a cameraman from Hollywood. Major Lathrop was the pilot. The airplane made two passes, the first at 600+ mph, the second slow with a roll in front of the grand stand. On the slow speed pass, Major Lathrop approached at 250 mph, during the roll the airplane lost altitude and at 270 degrees a wing tip touched the ground. The airplane crashed and tumbled on the runway until it stopped, a pile of aluminum scrap.