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Aviation History
1958
1958 - 0560.PDF
576 FLIGHT The Griffith Airliner Explained COMMENTS ON DR. C. T. HEWSON'S R.Ae.S. LECTURE PART I ON April 15, Dr. C. T. Hewson of Rolls-Royce explainedmuch of the basic background-thinking of the now familiarsupersonic VTOL dart scheme of Dr. A. A. Griffith in a Royal Aeronautical Society Section lecture. In the chair wasMr. David Keith-Lucas, director and chief engineer of Short Brothers and Harland. Dr. Hewson presented his case in a logical, step-by-step exposi-tion, repeating a number of familiar arguments, but also filling in a number of gaps. It is clear diat Rolls-Royce believe sincerely inthis scheme as a solution for long-range flight at something like M 2.5 and that, even in these stringent days, a considerable offi-cially-financed programme is in hand. It is, however, essential to appreciate—as Dr. Hewson stated and Mr. Keith-Lucas em-phasized—that despite the imminent VTOL testing of the Short SC-1 the supersonic vehicle is twenty years off. Mr. Keith-Lucas also made the point, and drove it home, thatVTOL as an accomplished fact is with us now, and that it would be tragic if in Great Britain we came to couple it with the far-offdream of the supersonic airliner—wherein VTOL is simply a means to an end. The danger he foresaw was that we mightcouple VTOL with the enormous development costs of the distant supersonic project and thereby fail to apply it to present needs.One recalls that in a recent lecture to the Belfast Branch of the R.Ae.S., the speaker when surveying VTOL commented favour-ably upon ducted-fan lift for a 300 m.p.h. "Heron replacement," tail-sitting jet lift for a zero-take-off interceptor, and a "flat-rising"jet-lift configuration for Naval strike aircraft. Dr. Hewson opened his case with the statement that (althoughtests were incomplete) he believed the very narrow delta, elliptical in section on the centreline, to be the lowest drag or best L/Dshape at high supersonic speeds. Where a conventional thin wing might have a L/D of 6, the narrow delta could achieve 8. How-ever, at reasonable incidence the stalling speed of such an aircraft would be 250/350 m.p.h. [It is of interest to note that at the R.A.E.,Bedford, Open Day last summer a display in the low-speed tunnel suggested very high lift-coefficients at 15/20 deg incidence forsuch narrow deltas on the basis of separated flow which engenders rwo large conical vortices which roll up along and from each ofthe sharply-swept leading edges.] From this it follows that jet lift is the only possible solution—and the resultant thrust must beequally disposed about the e.g. The next stage is that, in order to reduce interference with the airflow over the aircraft, the propul-sion engines must be at the wing-tips, which on a dan means almost the tail and virtually precludes their deflection through90 deg as a lift component. The resulting aircraft, epitomized as a transatlantic project, isthat publicized by the Air League of the British Empire as a M = 2.6 (1,500 kt, 1,730 m.p.h.—or the Atlantic in two hours) aero-plane cruising at 50,000-60,000ft. The passengers would be car- ried in a windowless, pressurized cylinder "since there is littlepoint in looking out at 50,000 to 60,000ft"—a view with which the writer completely disagrees. The crew has its own cylinder, thelift engines are grouped in pairs alongside the cabin and from them air is bled and ducted in a trunk to the three control nozzles, i.e., Conception of a possible VTO long-range transport aircraft. ODttM. VltW OF MRCM AM FROM LJ M£D MTO CO FT ENGMC& MMOM ftrt CONTROL MOZZLES run ftktfiCMGC* coMnutmtftr / .TANKS J -*—-X (IACM j - LIFT tMCMI 1 itoc OF maw** »ULKOM EMGM» OB* COMNUVTMCW!) mOMT WL TANK BY JAMES HAY STEVENS. A.F.R.Ae.S.-f ^ nose, port and starboard. Fuel is carried fore and aft, the tankflow being regulated to maintain a substantially static e.g. Jet-lift thrust is estimated by Rolls-Royce at 10-15 per cent above thegross weight. It is interesting to note that Ing. Zborowski, the Coleoptere protagonist, and other authorities have given 25 percent excess as the minimum to provide adequate acceleration in the crosswind case. On the other hand, the U.S. factor, accordingto Dr. Hewson, is considerably less than 12.5 per cent. The vertically mounted lift-engines (RB.108s, quantity undis-closed, since this could reveal their thrust, but probably a mini- mum of fifty) would have intake shutters in the upper wing surfaceand (Nimonic?) exhaust shutters in the lower surface. Dr. Hew- son made the point that the control jets, even though the bleed-air allowance is appreciable, are additive to the lift thrust, being shared in equilibrium between the three nozzles and maintainedconstant by balanced increase/decrease of control-nozzle area changes so that the total bleed remains constant. These lift engines, the speaker admitted, must be started un-failingly and almost simultaneously because of the high fuel con- sumption (say a thirtieth of the gross weight every minute), bodibefore take-off and prior to landing. In discussion, the speaker admitted that the momentum drag of the lift-jet air would bevery high and is as yet an unsolved factor in the acceleration problem, but he denied that the jet efflux would be a problem inthis respect. On the other hand, questioners established the fact that ground (suction) effect would be sufficiently high to requirea take-off and landing grid some twenty feet above the ground Dr. Hewson said that after hearing the SC-1 fly he felt the RB.108swould require noise suppressors. The lift engines would be mounted in pairs on trunnions andwould be capable of tilting to give an accelerating component which would carry the aircraft beyond its stalling speed—at take-oo and a dFeleratlng thrust before landing. At a tilting rate of 10 deg/sec it had been estimated that the gyroscopic couple wouldbe negligible. The exemplary flight plan presented suggested an initial vertical^!Sb I'SV11* slo ( wlv>" ^y 20ft/sec (l,200ft/min or 14 m.pJi.), to 100ft, followed by tilting of the lift engines to 20 deg and a for-ward-and-upward acceleration to 500ft in a total time of 30 sec At this stage the propulsion engines would be lighted and theaircraft accelerated through the 300 m.p.h. stalling speed, the lift engines being cut at about 350 m.p.h. after one minute's totalrunnuig tune and the aircraft climbing away and accelerating to M —2.5 at 50,000ft. The descent phase was shown diagrammatic-ally, starting at 350 m.p.h., 1,000ft and 5 miles from touchdown Lift engines would then be started, propulsion engines cut andthe lift ones swivelled to give decelerating reverse thrust down to IWttt, from which point vertical thrust would bring the aircraftdown at a mean rate of 20ft/sec—total lift engine running time two minutes. B Dr. Hewson thought that by the 1970s air passengers couldbe conditioned to accepting decelerations of - 0.5 g, thus reducing the lirt-jet running time to one minute—and saving about 3 percent of the gross weight. He admitted that, even though Rolls- Koyce is developmg automatic devices which will give preciselycontrolled rates of descent and the pilot will have an override the approach phase would be "a pretty smart operation." Personally,one would liken it to driving into one's garage at 30 m.p h and putting on the brakes at the threshold to stop precisely at the endwall. Even more involved is the approach phase; although this at first appears preferable to a 5 deg approach at 130 m.p.h., it mustbe realized that only the last 100ft would be vertical-the other yooit (and five miles) would be a decelerating ellipse! A steady rateof vertical descent, which Rolls-Royce appears to have in mind, would entail not only a variable horizontal deceleration, but avariable g effect upon the "bodies" in their windowless container. Dr. Hewson said that the vital necessity of ensuring a supply ofthe fuel and the igniting spark to the lift engines for relighting before the descent would be assured by a ram-air turbine, so thatthese units are independent of the main engines. The actual motoring of the lift jets is still the subject of investigation. Sincethere is suction, not ram pressure above the wing, some form of retractable intake scoop would have to be extended. Probably asmall opening would be used to entrain the airflow at high speed so that a static head could be recovered from the kinetic energyA positive intake efficiency of only 15-20 per cent would give quite a good pressure drop through the compressors at the dynamichead of, say, 500 m.p.h. (To be concluded)
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