Several months of acrimonious arguments between Autonetics and Norden followed, Norden claiming that the IDS's original specification was beyond the state of the art.ĭevelopment problems with the F-111D's advanced avionics caused so many delays that the Air Force decided to acquire the simpler F-111E as an interim version. By mid-1970, the problems with the Norden integrated display set were still not resolved. By late 1969, the Mark II system was still not ready. The radar problems required that the radar doppler unit be redesigned, which in turn caused interface problems with the Norden integrated display set. The Autonetics attack radar needed several improvements in its initial design, and the Norden integrated display set required extensive changes. There were difficulties in integrating the various complex electronic components with each other. The F-111D went through a rather protracted development cycle before it was deemed fit for service. It was delivered to the Air Force on June 30, 1970, only one day after the lifting of the F-111 delivery hold order imposed after the F-111A crash of December 11, 1969. It was equipped with the new P-9 engines but did not have a complete Mark II system. The main forward-looking attack radar of the F-111D was the APQ-130, with MTI, Doppler beam sharpening, and illumination for radar-guided AAMs. The Mark II system included 7 major components-an inertial navigation set and attack radar built by the Autonetics Division of North American Rockwell, an IBM computer system, converter and panels by the Kearfott Division of Singer-General Precision, Inc., an AN/AVA-9 integrated display set by the Norden Division of United Aircraft Corporation, a Doppler radar by the Canadian Marconi Company, a horizontal situation display by the Astronautics Corporation of America, and a stores management set by the Fairchild Hiller Corporation. They are normally sealed closed by spring-loaded doors which are pushed open by air pressure when additional air flow is needed. These blow-in doors were a set of auxiliary inlets which enabled extra airflow to reach the inlet duct during takeoff or when the engine is at full power but the aircraft is moving slowly. The Triple Plow 2 intakes were mounted four inches farther from the airframe in order to improve the boundary layer "plow", and the translating cowl was replaced by a series of blow-in doors. In addition, the F-111D was provided with Triple Plow 2 air intakes, which were intended to correct the F-111's seemingly chronic problems with compressor stall. This system was a first generation version of what later came to be known as a "glass" cockpit. The aircraft were equipped with Mark II microprocessor avionics with improved air-to-air capability. It was powered by a pair of Pratt & Whitney TF30-P-9 engines, each rated at 12,000 lb.s.t. F-111D was the designation given to a more advanced version of the F-111.
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