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Aviation History
1963
1963 - 0588.PDF
566 McNAMARA ON TFX . . . of engine thrust-reversers for in-flight deceleration, as well as for reducing ground roll after landing touchdown. To date, engine thrust-reversers have never been used in flight on operational fighter aircraft, nor have they ever been employed on supersonic aircraft. The only operational experience has been on subsonic commercial jet transports and cargo-type aircraft in which the engines are mounted on outboard pylons underneath the wings.* The Boeing design uses two engines nestled in the fuselage with their nozzles exhausting hot gases directly alongside the horizontal and vertical control surfaces. The full effect of this hot-gas efflux is unknown. Assurance that longitudinal and directional stability was not impaired could not be obtained without extensive flight tests, in addition to considerable developmental wind tunnel testing. Since flight testing cannot occur until late in the development phase, the Boeing design would impose an added degree of risk in terms of meeting an early operational date for the TFX . . . "The second area in which Boeing's approach seemed likely to produce more complicated development problems was its proposed powerplant installation with top-mounted inlets. The fourth evaluation report commented that Boeing's location of the inlets on top of the fuselage, in combination with the Boeing subsonic diffuser design, results in significant distortion of the air flow at the engine face under most conditions, and prohibitive distortion during high-angle-of-attack operation. The report noted that the effect of this distortion on engine operation is virtually impossible to predict accurately, and it can only be determined by actual testing of the engine in flight under the distortion conditions delivered by the induction system. In contrast, General Dynamics chose a conventional "straight through" installation and inlet design which the evaluation group considered to be a good selection for the TFX aircraft—one which should give the best trade-off in terms of performance, complexity and operational problems . . . "The third area in which the Boeing approach involved greater development risks was its extensive use of titanium in its wing carry- through structure. We have had some experience in the use of titanium in other Department of Defense weapons systems but mainly in heat-resistant applications and where high stress levels in thick plates are not involved. The fourth evaluation report observed that data concerning the fatigue design properties of titanium, in the thickness Boeing proposed to use in the wing carry-through structure, is very limited, and that this raises the question of the advisability of using such thickness. "The report further commented that the effect of temperature on structural details, especially in the aluminium-to-titanium splice, can be expected to be quite pronounced in producing metal fatigue, and the report concluded the Boeing fatigue test programme showed lack of realism. In fact, Col Gayle, the TFX system project officer, sent a letter to the competing companies pointing out that, in the judgment of the Aeronautical Systems Division, it was not advisable to use titanium in fittings which are subject to heavy load, * And on Comets, Caravelles, Tridents, VClOs and a Hunter—Ed, "Flight International." An early test Pratt & Whitney JTF-IO, the winning F-l 11 engine FLIGHT International, 18 April 196 ! nor in heavy-section areas because of a lack of data relating to sue;, use. If Boeing's proposed use of titanium did not work out an . heavier steel had to be used to replace the lighter metal, I realize; that not only would the operational capabilities of the Boeing plan suffer, but additional costs would be incurred. "In contrast, the General Dynamics design solved the problem c wing loading by the ingenious but simple expedient of providing a bolt-on extra wing extension for the Navy version of the aircraft instead of employing relatively unusual applications of an exotic metal. . . "I discovered additional evidence of unrealistic cost estimates in the Boeing proposal. In the judgment of the evaluation group, Boeing was overly optimistic in its estimate of production tooling and was dangerously low in estimating the manufacturing hours for both the development and production phases. It appeared to me that Boeing simply did not appreciate the complexities of developing the TFX. This is understandable because Boeing's past experience in aircraft development and production has been with bombers and transport aircraft—experience which is largely inapplicable to the TFX estimating. "In a development contract for a complex new weapon system like the TFX, there inevitably will be engineering change orders. The cost of change orders is borne by the government. Consequently, when two proposals both meet military requirements as did Boeings and General Dynamics', the proposal which seems likely to involve less change, with consequent delays and increased costs, is to be preferred. "Aside from the matter of cost over-runs induced by multiplicity of change orders, there are other reasons why credibility of costs must be carefully evaluated in a fixed-price incentive contract. "It is true that any costs over the contract ceiling are at the expense of the contractor and not the government. Nonetheless, if after several years of effort it appeared that a contractor's costs were going to be far in excess of the ceiling, say, by several hundred million dollars, the contractor would be in very serious financial difficulty. He would then be motivated to take every possible cost saving alternative. These alternatives could have a serious adverse impact on the continuity and quality of the development. "In short, while incentive contracts are generally important to force efficient management and obtain good estimating, where the dollar expenditure is exceedingly large, as in the case of the TFX, it is imperative that we make our own judgment of cost estimates. This is the only way we can insure that a contractor, through optimism or misunderstanding, has not imposed a ceiling on himself that could lead to serious degradation of the development. This result would hurt the Department of Defense as well as the contractor." Comparison of Operational Factors During the hearings in Washington before the Senate Permanent Investigations Subcommittee last month, the figures tabulated below were inserted to give members of the committee an idea of the quantitative operational performance relationship between the two rival aircraft—or, some would say, three rival aircraft, because the civilan experts in the Department of Defense have stressed that, in their opinion, Boeing proposed two distinct aeroplanes for the two user Services. The figures are based on a programme of 1,700 aircraft. Contractor's programme cost ($ x 10') Air Force programme estimate ($ x 10*) Adjusted AF programme estimate ($ x 10*) Ferry range, external tanks (n.m.) Ferry range, internal tanks (n.m.) Reaction time at —65°F Landing distance over 50ft (ft) Weight of F-l 1 IB (lb) F-l 1 IB close-in defence loiter (mm) F-l 1 IB distant defence loiter Carrier accommodation (F-l 1 IB number) Area intercept radius (n.m.) Total weight of ordnance, wings in Total weight of ordnance, wings out Nuclear bamb load Air-to-ground missiles Demolition bombs Land mines Cluster dispensers Rocket launchers Fire bombs Air-to-air missiles GD/Grumman 5,455.5 7,083.2 5,803 X X 2X X + 590 X + 2,208 X X X + 5 X X X X X X X X X X Boeing 5,364.2 6,983.0 5,387.5 X + 1,100 X +450 X X X X + 30 5iX X X+ 177 X+ 11% X + 69% X + 50% X + 50% X + 105% X + 70% X + 180% X + 44% X + 250% X + 100%
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