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Aviation History
1955
1955 - 1718.PDF
2 December 1955 837 MORE THOUGHTS ON THE P.I —with Reference to True Supersonic Efficiency PARTICULAR significance attaches to the recent Ministryof Supply announcement that, since its early flights in thesummer of last year, the English Electric P.I has frequently sustained supersonic speed in climbing flight—this, it may besupposed, without the use of reheat or rocket boost. It is well known that the use of rockets or afterburning entails a relativelyhigh fuel consumption, sufficient to make the employment ol such devices severely limited on a time basis. Since the spaceavailable for fuel in a high-speed fighter is restricted, this implies that a fighter which relies upon such devices for the attainmentof the necessary performance must be limited to interceptions fairly close to its base, up to the maximum safe proximity to theguided-weapon zones. For example, it seems obvious that the Saunders-Roe SR.53 turbojet/rocket intercepter will be employedin such a manner, and will accordingly have a limited range but an altogether exceptional performance in the vertical plane. Conversely, although it seems logical that the P.I should alsobe provided with afterburners, the performance already demon- strated suggests that the employment of reheat could be on amodest scale—perhaps only during the final manoeuvres required to intercept a high-flying target. The aircraft has also shownthat it has all the manoeuvrability required, and its aerodynamic characteristics should be such as to avoid the transonic troubles(at one time described officially as "the thunderclap hazard"). which would ruin the chances of most fighters against a bomberflying at a steady speed in excess of M = 0.9. The P.l's "very heavy armament?>, recently referred to by the Minister ofSupply, would explain why the aircraft is larger than present subsonic-climbing fighters; and the fact that it has two engineswill be welcomed by pilots who appreciate that complete power failure in a supersonic fighter not only results in a highrate of descent but may also lead to failure of the flight controls and other systems. A fighter capable of destroying any poten-tial enemy aircraft at the greatest possible range and with thehighest possible order of relia- bility would seem to be a keyfactor in the defence of the West. As outlined in the articles re-ferred to above, the drag rise at transonic Mach numbers isgoverned by what is generally known as the area rule. Applica-tion of this rule to the P.I is possible with fair accuracy fromthe published three-view draw- ing. It results in the type ofarea distribution shown in one of the accompanying diagrams.The final result seems to give an almost perfect curve for mini-mum drag and, in fact, the Ministry of Supply stated re-cently Flight, November 25th, page 808) that the aircraft wasdesigned in full knowledge of the area rule. We cannot say towhat extent the English Electric Co. were able to obtain truepictures of transonic flow over the P.I during tunnel testing but These diagrams emphasize the fact that, although it may appear "un- streamlined" to eyes brought up on subsonic shapes, the P. 1 (far right) has a much better distribution of cross-sectional area than aircraft of more conventional appearance. DURING the past few weeks we have published several references to the problems of high-speed flight, from which it is possible to synthesize this further note bearing specifically upon the supersonic fighter. The previous references are: "A Note on the P.I" (September 16th), "The Area Rule" (September 30th), "A British Approach to Area Rule" (November 18th) and "Transonic Design—M.o.S. Statement" (Novem- ber 25th). It is also pertinent to refer back to the three-part article by J. W. Fozard entitled "The Supersonic Fighter," which appeared in three successive issues dated 10th, 17th and 24th December, 1954. it is appropriate to recall that the company have had a transonictunnel at work for over three years—far longer than anyone else outside the N.A.C.A. In any case, flight testing of the actualprototypes must, by now, leave very few gaps in the company's knowledge of what they are doing. The neat way in which the complete design has been inte-grated to give the optimum result is clearly shown by the manner in which the drawing has been prepared. The highly swept wingrequired to avoid transonic handling troubles is seen to spread its volume over the entire length of centre fuselage, the latterhaving a constant cross-section in consequence. Admittedly, we recently described the P.I as having "all the shapeliness of asuitcase" yet the area distribution, with all taper confined to the regions fore and aft of the wing, is seen to be completely in con-formity with the area rule. The fall-off in cross-section at the rear is slightly reduced by the tail surfaces but this appears tobring the shape nearer to the optimum illustrated by the N.A.C.A. In contrast, the other diagram shows how a fighter of moreconventional appearance can prove to have a very bad area dis- tribution. Although the hypothetical fighter illustrated wouldhave slightly lower fuselage drag than the P.I (if both fuselages were tested separately and in isolation in a high-speed tunnel), (concluded on page 840) FIN AND RUOOE TAILPLAt FIN AND RUDDER TAILPLANE NOZZLE MNTAKE NOZZLES'
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