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Aviation History
1955
1955 - 0251.PDF
FLIGHT, 25 February 1955 251 TWO SUPERSONIC FIGHTERS ; ; —in the News: F-100 and F4D DEVELOPMENT problems, already acute in anymodern military aircraft, become truly formidable inaircraft designed to achieve sustained supersonic speed while fully equipped as a line-of-battle fighter. The first machine in this category was North American's F-100 Super Sabre—the first of the "sonic centenarians" of the U.S.A.F. fighter lineage. As briefly discussed last week, the F-100 ran into its firstreal trouble as late as last autumn, by which time the Los Angeles plant was filled with airframes in various stages of completion andmany aircraft were ready for issue to U.S.A.F. squadrons. Three Super Sabres were destroyed in quick succession, and eachaccident seemed to be the result of some fault in the aircraft. The most significant accident occurred on October 12th, 1954.On that day George Welch, North American's chief engineering test pilot, was booked to perform the most severe structural testthen applied to the type; his flight-test card called for a super- sonic dive with a symmetrical pull-up at the medium altitude of23,700ft. Taking off in a heavily instrumented research F-100, Welch called up at 11 a.m. to report that he was ready to start todive at his aiming point of Rosamond Dry Lake, Mojave Desert. What ensued was reported by a pair of B-47 pilots on their wayback to Castle A.F.B. from practice bombing over the Salton Sea. The Stratojet was at 25,000ft over Palmdale when its crewspotted the contrails of the F-100 at a height estimated at 45,000ft. As tiiey watched, Welch rolled-off to the right andbegan his dive between three and a half and five miles ahead of die bomber. The F-100 passed their altitude diving at 70 to80 deg, and moving so fast that they had to turn their heads rapidly to follow it. Then, without any previous sign of instability,it broke up in what appeared to be an explosion. North American engineers flew to the scene and started aninvestigation with personnel from die U.S.A.F. Flight Safety Directorate at Norton A.F.B. A complete plot was made of theexact position of every piece of wreckage, and the parts were then taken back to the company's main plant at Inglewood. Here,the real investigation got under way. One line of the search was based upon the exposed film found in a camera which hadbeen mounted in the fin of the F-100 to record the behaviour of the port slab-tailplane. Although the electric power to thiscamera had been cut during the break-up, the camera had taken a few more frames under its own momentum. When the film was developed and projected, an erratic shadowwas seen to race across the surface of the tailplane; it was cast by the fin and rudder, and indicated that the aircraft had experi-enced a violent and unusual type of manoeuvre. By employing a model illuminated by a light placed exactly at the bearing andazimuth of the sun at the time of the accident, this manoeuvre was reproduced fairly accurately. Later, oscillograph records were recovered which gave actualcontrol forces and positions; and these provided what the com- pany's chief engineer, Raymond Rice, termed "the first andmost reliable real clue as to the probable primary cause." The records showed that the F-100 had suddenly taken aviolent yaw to starboard—no quantitative data have been re- leased, but the yaw was termed "considerable"—resulting inrapid loading beyond the design limits, and hence disintegration. The yaw resulted from the coupling of the principal moments ofinertia; this largely took the form of a rapid transfer of energy from the roll axis to either the pitch or yaw axes, and back again.This behaviour had never before been met, and is only serious in aircraft with large, long fuselages and short-span wings.Secondary terms in the design equations, formerly ignored, now have to be calculated. Uncontrolled gyrations of the type which proved fatal to theF-100 can be met by fast low-aspect-ratio aircraft with any type of wing-plan. They can be encountered at critical angles ofattack or at critical load factors; in the case of the F-100, they were met at from 1 g to 3 g. Supersonic velocity was not, ofitself, a contributing factor. Normally, any violent, or unco- ordinated, rolling manoeuvre results in pitch and yaw which isdamped by the tail; in the F-100, however, the moments ex- ceeded the capacity of the tail to restrain them, and it was atthat point that the aircraft went violently out of control. The unusual final assembly line at Torrance, with Douglas F4Ds ("Fastest Naval Aircraft," below) lying in a trough in the floor. The one-piece method of making the fuselage and wing is stated to ease production considerably. Modifications were soon put in hand, and three modifiedproduction F-lOOAs have since been intensively flown. In par- ticular, violent rolling manoeuvres have been done at all conditionsof speed and loading, without trouble. The modifications include: one foot added to each wing-tip (span now 38ft) so producingand aft-shift of e.g.; 27 per cent more area to the vertical tail, thus returning it virtually to the form of the tail on the YF-100prototype; and minor changes to improve control "feel." Earlier this month, the 100-plus F-lOOAs now built were "ungrounded." Fastest Naval Aircraft. The other level-sonic fighter in thenews is the bat-like Douglas F4D Skyray. Powered, like the Super Sabre, by an afterburning Pratt and Whitney J57, theF4D is the fastest (and the fastest-climbing) aircraft in any Navy. The basic design of this carrier-based intercepter was settledin 1948. The requirement of catapulting (zero to 80 knots in the length of the accelerator) inevitably added weight; but, althoughthe F4D has rather less range than day fighters, the weight- limit of 20,000 lb (two-thirds that of contemporary fighters) isregarded as remarkable. Robert Rahn, chief test pilot of the Douglas El Segundo factory,established the present world 100-km circuit record in an F4D. Another record—the world speed record—was set in the sameaircraft by Jim Verdin, who also became an El Segundo pilot and was tragically killed in a prototype A4D Skyhawk onJanuary 13th. Verdin has described his first solo introduction to the Skyray as follows: "Like most pilots I had to find outsomething for myself. Through my own error I put the airplane into a spin. I spun all right—six times. I got out of that one,and I went on to fly the airplane with a lot of success that day. In spite of that introduction, I've grown to have more confidencein the F4D's performance than in any other airplane." Not only has the F4D ample flight performance, but it is alsoproving to be something much more valuable—a good fighting aircraft. In addition to four of the new 20mm U.S.N. cannon,the Skyray can carry six packages each housing seven 2.75in rockets, four packages of 19 rockets, two 300-U.S. gal tanks ortwo 2,000 lb bombs, under its wing racks. The aircraft at present in production at Torrance are of the F4D-2N type, fitted withfull all-weather radar "locked-on" to the autopilot. FORTHCOMING EVENTS Feb. 26. Northern Heights Model Flying Club: Annual dinner and dance. 26. S.L.A.E. (South-eastern Area): "Fire Protection and Prevention Equipment in Aircraft," bv A. Cdre. Sir Vernon Brown, C.B., O.B.E., M.A., F.R.Ae.S. Hon., M.S.I.A.E. 1. R.Ae.S. Section lecture: "The Scientific Approach and Research in Aircraft Production," by Prof. J. V Connolly, B.Eng., F.R.Ae.S. 3. British Institution of Radio Engineers (North-western section): "Computing Circuits in Flight Simulators," by A. E. Cutler, B.Sc., Ph.D. S. British Interplanetary Society: "Radio Exploration of Space," by R. C. Jennison, B.Sc. 5. British Interplanetary Society (Midlands branch): "The Path to Space Travel," by K. W. Gotland. 5. The Cranfield Society: Annual dinner and annual general meeting. 9. R.Ae.S. Graduates and Students Section: Annual general meeting and film show ("The Society Overseas," by A. M. Ballontyne, T.D., Ph.D., A.F.R.Ae.S.). Sept. 5-11. S.B.A.C. Show, Farnborough. R.Ae.S. Branch Fixtures (to March 15th) Mar. 1, Boscombe Down, "Developments in Gliding," by A. H. Votes. Mar, 2, Brough, "Pilots' Limitations in Aircraft Design," by W/C. H. P. Ruffell Smith; Luton, "Aerial Photography." Mar. 3. Isle of Wight. "Aircraft Engineering in the Arctic," by Maj. James H. Webb, U.S.A.F. Mar. 8, Bristol, Second Barnwell Memorial Lecture, by Walter Tye. Mar. 15, Manchester, "Helicopters," by C. S. Hislop; Belfast, "Aerial Photography," by Charles Brown. Feb. Mar. Mar. Mar. Mar. Mar. Mar.
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