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Aviation History
1956
1956 - 0440.PDF
440 FLIGHT, 20 April 1956 STARFIGHTER Lockheed's Mach^2 Fighter for the U.S.A.F. By THE TECHNICAL EDITOR FOR more than two years aeronautical enthusiasts have beeneagerly swopping meagre "unconfirmed details" of the Lock-heed F-104 supersonic fighter. In conformity with a possibly unrealistic Pentagon decision, its characteristics, likethose of other recent U.S.A.F. prototypes, have been a closely guarded secret. Now, however, "the wraps" are off. A Pressunveiling was being held in California on Tuesday of this week and there are grounds for believing that at this function anattempt was to be made on the world speed record. A Flight representative was present and his despatch will appear in a futureissue. This account has been prepared in advance, so that readers can become familiar with the remarkable F-104 at theearliest possible moment. Fast aeroplanes have always been a forte of the Lockheed Air-craft Corporation. America's first real jet fighter was the Lock- heed Model 80 (later XP-80 Shooting Star), which was enabledto fly 100 days from the start of design by the generosity of the de Hayilland Engine Company, who shipped to Lockheed theonly flight-cleared Goblin they had to hand. The Shooting Star went into major production shortly after World War 2 and over7,000 derivatives have since been built (many powered by turbo- jets similar to the Rolls-Royce Nene, which, incidentally, was firstair-tested in a Shooting Star airframe). During 1947 a large twin- engined fighter was developed to meet the U.S.A.F. requirementsfor a long-range "penetration" fighter. Designated L.153, or XF-90, two prototypes were flown extensively. It is not generallyknown that the type was dived beyond the speed of sound, but no production order was placed. The opportunity for Lockheed to enter the true supersoniclists came in 1951, when the Air Force worked out its specifica- tion for an "air-superiority fighter." This concept has changedsomewhat in recent years, but can be considered principally as a fighter which can destroy enemy fighters. All-weather capability,long range and ability to operate from forward bases were not requirements of the specification, which was biased in favour ofextreme all-round performance and cheap and reliable operation. Behind the specification lay long, and often heated, discussionswith pilots back from Korea. The encounters between Sabres and Migs had served to emphasize the importance of maintaininga high standard of serviceability and reliability throughout all combat operations. A classic example of the Air Force's failure todo so is provided by the A-1CM radar gunsight, which gave so much trouble that Col. Francis Gabreski, a Korean "ace," wenton record as saying that he would rather sight his guns with the aid of a piece of chewing-gum stuck on the windscreen. This state of affairs gradually gave rise to pressure for asmaller, lighter and more reliable fighter which could not only be kept in fighting trim but would also provide a marked increasein all-round performance. American pilots had become heartily sick of looking up at the undersides of Migs, and the lightweightfighter was frequently looked upon as the panacea which would put its owners literally on top. Some relief was provided by new equipment such as the A-4gunsight, the "black box" components of which could be removed and replaced in a matter of minutes. The shortcomings in per-formance were more fundamental and gave rise to the air-superi- ority concept. Several firms submitted projects, but it was earlydecided that responsibility for this development would be placed with Lockheed's California division at Burbank, with the AirForce designation F-104. A powerful design team was quickly assembled around Clarence L. ("Kelly") Johnson, the chief engi-neer. Johnson has never quite subscribed to the idea of a light fighter and certainly not to the concept of a stripped-down air-craft. His opinion, which seems to be common-sense, is that one might get a few top-notch men capable of doing well with suchequipment, but that in practice one must design for the run-of- the-mill pilot for whom a "gum-sight" is strictly out. Initial weight estimates, therefore, came out somewhere nearthat of a Sabre, but in most other respects the Lockheed design was startling. At the end of 1951 Lockheed knew they would beusing a single turbojet with afterburner and it has stayed that way through a large number of projected airframe configurations. Thebasic design work was immeasurably assisted by the Air Force/ N.A.C.A. research with supersonic aircraft, which had obtainedaerodynamic data at Reynolds numbers appropriate to the F-104 at up to 90,000ft and Mach 2. Lockheed also ran several thousandhours in their own tunnels and in the Southern California Co- operative Tunnel, in which they have a one-sixth share. In the F-90 the company made some use of ballistic modelsdropped from high altitude, but the terminal velocity thus attained was insufficient for the new fighter. Free-flight work entailedthe use of vehicles fitted with F-104 aerodynamic surfaces and launched from ramps in the desert under the thrust of 5in rocketmotors. Data were also obtained from existing aircraft embody- ing components expected to be designed into the future fighter.Assistance was given by the N.A.C.A. and Cornell with variable- stability aircraft capable of simulating the behaviour of the F-104. One of the first design choices was the type of wing to use.After looking extensively at other wings, the company settled upon a true supersonic aerofoil with very low aspect-ratio, nosweep-back and the unprecedented thickness/chord ratio of 3.4 per cent. No other aircraft, then or since, has had so thin a wing,and Lockheed's firm determination to employ such an aerofoil can only be regarded as courageous. In passing, we rememberthat Johnson was once introduced as a member of the fraternity "No Delta Wing." As in most missiles, virtually everything had to be put insidethe fuselage, which, at the same time, had to be of minimum frontal area with a profile suitable for high supersonic speeds.Lockheed were well aware of the N.A.C.A. area rule, but transonic interference drag was never a problem with the 104. Area ruleis less applicable to "wholly supersonic" aircraft, and in any case the Lockheed fighter's wing volume is exceedingly small. Fuselage design was complicated by the overriding importanceof obtaining optimum flow into, and out of, the turbojet—particu- larly when, as in mis case, the engine was to develop half itsmaximum-speed thrust as a ramjet. Supersonic-intake design is an exceedingly complex subject which Lockheed and theN.A.OA. had to explore thoroughly. With a modern axial engine most of the trouble is likely to occur at the top end of the speedrange. It is essential to get rid of the boundary layer and singular importance also attaches to the manner in which this is accom-plished. Boundary-layer growth is usually a function of fuselage length ahead of the intake, and so it is remarkable that Lockheedbelieve they have attained a better inlet-air distribution than in any other aircraft now flying.
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