The Inside Story
The Tigershark radar was initially defined, under Carter administration policy, as one that had to be inferior to the APG-66 on the F-16A. By the time the radar subcontractor was selected, Carter was out of power, and the Tigershark was in competition with the F-16A for export orders. So the initial configuration defined was one that was superior to the F-16A in all aspects, except radar range. By 1983 the F-20A was now being considered in competition with the F-16C which had an entirely new-technology APG-68 radar equivalent to the F-20A. So the Extended Range Radar was defined, with additional features and increased range that leapfrogged the APG-68. At each step of this process the F-20's radar was believed to be superior technologically, with lower weight and cost, and higher reliability, than the F-16 equivalent.
F-20 Radar Selection
The F-5E used a modest Emerson radar that was little-more than a gunsight and fire-control aid for the advanced versions of the AIM-9 Sidewinder. Taiwan's fighter requirement was for capability to launch the AIM-7 Sparrow radar-guided missile. This would require a much more capable radar. Candidates considered in various configurations of an advanced, re-engined F-5X aircraft in the period 1977 to 1979 assumed a stand-alone radar supplemented existing F-5E avionics. Likely candidates in these studies were a version of the F-16 radar with a smaller antenna to fit in the F-5 nose, or a new design proposed by Emerson Electric. In May 1979 it was decided to revert to the 'Engine Change Only' F-5G-1 with F-5E avionics for marketing and ITAR clearance purposes. However the specification for a much more ambitious and advanced avionics suite was being refined for eventual development under an 'F-5G Phased Improvement Program'.
In August 1980 definition of the F-5G-2 configuration was completed. Specifications were released in the fall, and competitive bidding held in the first quarter of 1981. The new radar was would be part of an completely new-technology avionics suite, connected together using a MIL-STD-1553 data bus. The radar would take full advantage of the digital revolution, offering 16 radar modes for a variety of air-to-air, air-to-ground, and air-to-sea missions. At the same time bidders were asked to quote options for additional modes, which would take the radar to a capability beyond that of the APG-66 in the F-16A. This was prohibited under Carter's PD-13, but Northrop had an eye on future development potential for the radar, and a possible change in the administration at the White House in the November 1980 presidential elections. Radar bids were received from:
So despite the expense, General Electric was selected for the radar. The General Electric radar was selected, and a Master Agreement for design, development, and options for 512 production aircraft was signed on 5 June 1981. The baseline development program had a cost of $64 million; however from the beginning Northrop authorized $7.5 million worth of engineering options which took the radar beyond the capability limits set by the defunct Carter administration's PD-13. Average cost per radar for the 500 shipset master agreement to the beyond-PD-13 configuration was $628,912 in 1986$.
In October 1982, with the Taiwan sale blocked and no immediate launch orders in view, Northrop decided to reduce the effort it was funding to the minimum necessary to fly the GI1001 avionics test and demonstration aircraft while still keeping the program in a position to still deliver aircraft within 24 months of an order. For the equipment subcontractors this meant completing qualification test on their equipment so it would fly on GI1001; but deferring the multiple-lifetime reliability test that was to ensure that the equipment would be of the highest quality in production aircraft.
This gruelling test consisted of taking two production-representative radars, subjecting them to thousands of hours of simultaneous pressurization / depresurrization and thermal cycles equivalent to what they would see in service. At the same time they would be shook, rattled, and rolled at forces far higher than they would ever seen in service. Every time this torture resulted in a failure, the reason would have to be found; the cause corrected in the design; and then the test restarted, until two aircraft-lifetimes without a failure attributable to design were achieved.
Deferring this test meant stopping work on two preproduction systems. But at the same time the engineering team working on the radar would have to be kept together, to complete qualification for GI1001 flight test, and then to support flight test of the aircraft. Since each avionics vendor was responsible for the software in their system, this would also mean software support to modify the programs in each system if problems detected in flight test had to be rectified. This, inevitably, meant that the cost of Northrop and it co-investing subcontractor's programs would now start growing beyond that originally planned.
GI1001 began flight test in August 1983. Discussions with the Koreans produced enough confidence to begin development of the improved equipment the Koreans required to exceed the F-16C in all performance parameters. Development of this advanced F-20 aircraft was started in November 1983. In the case of the radar, the cost of the one-year delay was $ 18.87 million. During this period Northrop had also switched to a dual-redundant MIL-STD-1553 bus to ensure the 'digital aircraft' would remain operating even in the event of major battle damage. This change cost another $200,000 in aircraft development and increased the cost of the 500 shipsets of radars to $840,985.
Upgrading the radar to match the range of the new AN/APG-68 on the F-16C meant a large number of changes. The range was mainly achieved through more sensitive signal detectors and processing, and by increasing the size of the radar antenna. The larger radar antenna was accommodated without changing the aircraft mold line and aerodynamics by mounting it farther aft within the radome. This however meant design changes to the aircraft structure to rearrange the equipment bays in the aircraft nose. This in turn was made possible by the decision to develop a new-technology single gun to replace the obsolete twin-M39 guns inherited from the F-5E. It was also decided to incorporate into the baseline and demonstrate the aircraft's AIM-7 Sparrow radar-guided missile capability.
Construction of a single prototype (system 7) of the new larger-array antenna was authorized. All of the changes (17 in all) to upgrade the radar to the new long-range, AIM-7-capable configuration amounted to an extra $2.6 million. Supporting continued fight test and debugging of the radar was another $3.4 million through the third quarter of 1986. To complete development, qualification, and reliability test of the new radar after a production go-ahead would cost another $33.9 million. The recurring cost of the radar rose again to $ 888,460 for 500 shipsets in 1986$.
A final radar version for the 1986 USAF Air Defence Fighter mission required the addition of new Electronic Counter-Counter-Measure modes to defeat the efforts of incoming Soviet bombers to jam or deceive the F-20 radar. These additional modes would have cost another $43 million in nonrecurring costs and brought the radar unit price over $ 1 million.
To summarize then:
* radar originally proposed by General Electric for the Taiwan Indigenous Fighter. They later selected the GE APG-67 instead.
After the F-20
The APG-67 ended up being used in its intended applications after all - it was selected over Westinghouse equivalents for the Taiwan Indigenous Fighter (later called the Ching Kuo); a Taiwan F-5 upgrade called the F-5-2000; and the Korean A-50 light fighter/trainer. However it never received a major order, and true to his word, Neutron Jack sold the GE radar business to Lockheed Martin in the defence consolidation of the 1990's. In an ironic twist, Northrop-Grumman bought the Westinghouse radar business in the same period, so that today Northrop builds the F-16 radar, and its competitor Lockheed-Martin the radar that would have gone into the F-20.
The F-20A avionics system incorporated the highly reliable General Electric AN/APG-67(V) radar, designed for a 200 hour MTBF. It was an X - band, pulse - doppler, digital, multimode radar, using low pulse repetition frequency (PRF) in the look up mode, medium PRF in the look down mode, and high PRF for velocity search.
The detection range of the AN/APG-67(V) permitted the F-20A to detect most adversary aircraft before the F-20A, with its low radar cross section, was detected by the adversary.
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© Mark Wade, 1997 - 2006 except where otherwise noted.
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