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Aviation History
1960
1960 - 0216.PDF
216 FLIGHT, 12 February \%K Supersonic Transports at the IAS . . . should suffer no great discomfort." A typical climb-out to cruisealtitude would encompass the following three steps: (1) climb at a constant equivalent airspeed of 312kt to 37,500ft; (2) a constantaltitude acceleration at 37,500ft to an equivalent airspeed of 55Okt; and (3) a constant equivalent airspeed climb at 55Okt to M3 cruisealtitude (70,000ft). Descent would be initiated some 350 n.m. from destination at a constant equivalent airspeed of 312kt. Cabinfloor angles would vary between plus and minus 7 per cent. / A 250,0001b steel M3 transport might cost upwards of $160mto develop, while a 500,0001b supersonic aeroplane could run as high as $210m. The former figure, according to the speakers, wasone-third greater than the development cost of today's 300,0001b subsonic turbojets. These data were based on assumed sales of100 supersonic and 200 subsonic aircraft. The initial cost of a M3 250,0001b faster-than-sound transport would hence be approxi-mately $llm, while the 500,0001b supersonic aircraft might each cost roughly $20m. Despite these apparently large sums, Lockheedstudies had shown that "the small supersonic transport's superior work capability will provide a profit potential greater than that ofthe subsonic jet." As the speaker put it, "The supersonic transport is technically feasible as well as financially sound." Fig 4. Estimated first cost per aircraft for 100 units Points from the Lockheed representatives' summary included: "In the supersonic transport, the United States has an opportunityto demonstrate to the world its technological leadership over the Soviet Union. In our opinion, the government would be justified in supportingthe development of a supersonic transport simply for national prestige, not to mention all the other reasons. Such a programme would not bewithout precedent. We have only to look at the shipbuilding industry, where substantial funding by the government is represented in our fleetof privately operated flag bearing vessels. A recent example would be the world's first nuclear merchant ship, Savannah. "When military applications of the supersonic transport are considered,it should be noted that a properly 'sized' aircraft can fulfil the 'multi- mission' concept as defined by Gen Thomas D. White, US Air ForceChief of Staff. Studies indicate that it can accomplish at least the fol- lowing military missions : (1) supersonic tanker; (2) recoverable booster;(3) reconnaissance; (4) MATS cargo-passenger; (5) special air mission. "While the value of the supersonic transport to the nation warrantsserious consideration in terms of substantial Government support, we in industry must recognize our responsibility. When we consider thechallenge and all its implications, it is obvious that our system of free enterprise and individual initiative is being put to the test. We, of theair industry, are being challenged—and the outcome will have far- reaching effects. It may very well represent a turning-point in our history."To meet this challenge, new and unique approaches could be utilized to finance development of a supersonic transport. Seriousness of theproblem demands some fresh thinking, new approaches and fast action. We could already be behind—and not know it. We cannot afford to losemuch time arguing and waiting between sessions of government bodies. "A supersonic transport could move into production if the airlines ofAmerica would pool their resources. One basic aircraft could serve all airlines. And, anyway, it is doubtful if more than one design wouldprove practical economically. . . . Rounding out the session were two papers by members of twonon-profit-making—but no less enthusiastic—organizations. Speak- ing on Noise Aspects with Emphasis on Sonic Boom were MessrsLina, Maglieri and Hubbard of the Langley Research Center. The noise problem was not unknown to the airline industry, buta new source of noise—the shock wave pressures produced by sonic booms—would cause some aggravation to an already serious prob-lem. Two strong shock waves, one at the bow and one at the tail, were created by supersonic aircraft. NASA had recently madeavailable the results of wind-tunnel and flight test measurements of the shock-wave pressures at large distances from the source ofthe disturbance. Amongst the actual flight data were results of a •series of M2 test nights at altitudes up to 60,000ft. One of thequantities measured during these tests was the rise in ground pressure, and, if subsequent projections for the data for M3supersonic transports (at 70,000ft) were valid, "there is a good chance That several million people would hear the booms producedby a supersonic flight from coast to coast in this country." Clean aerodynamic design was deemed compatible with therequirements for minimizing shock-wave noise, and apparently no special aerodynamic tricks (other than low drag design) woulceffectively reduce the sonic boom. Mach number was considered the "least significant" of the parameters influencing noise, one;-the speed range at which the booms were first produced wa, exceeded. For example, the authors contended that increasingthe speed from M1.5 to 3.0 theoretically increased the intensity of the sonic boom by only about 26 per cent. The most significantoperational variable, in their opinion, was the distance of the observer normal to a supersonic aircraft's flight path (in bothlateral and vertical directions). During tests conducted with super- sonic fighter and bomber aeroplanes, the noise intensity producedby flight at 60,000ft was only about one-third of the noise recorded for flights at 30,000ft. The presence of heavy overcasts seemed tohave little effect on the pressure rise created by the sonic boom. Even cloud layers 30,000ft thick produced no substantial noiseattenuation, according to the speakers. Analytical theory had shown that sonic booms existed at Machnumbers slightly greater than unity; however, actual flight prac- tice had proved that atmospheric refraction caused shock waves tobe curved sufficiently to miss the ground completely at certain "cutoff" Mach numbers. The exact speed at which such cutoffoccurred varied with temperature and gradients, altitude and flight path angle. Consequently, aeroplanes having good climb perform-ance might operate at relatively high Mach numbers without pro- ducing severe noise problems. But, conversely, descents had to bemade at reduced velocities to prevent sonic booms. During one test run cited by the Langley representatives, the boom producedby supersonic flight at a climb angle of 10° developed less than one-eighth the ground-pressure rise incurred by level flight atthe same altitude. "In summary of what has been learned of the sonic boom problem, it appears that once a good aerodynamicdesign has been developed for a given size aircraft, only small reductions in sonic boom intensities could be expected fromfurther changes in external shape. The real hope for solution to the problem lies in the manner in which the aircraft is operated." Engine noise was also of great concern. It was obvious to theengineers from Langley Field that aircraft noise varied widely, depending upon the choice of powerplant. And if proper con-sideration were not given to the community annoyance problem, an engine might be employed which had unacceptable noisecharacteristics. On the other hand, "the possibility exists of choosing a powerplant that would be as good as, or possibly betterthan, those currently in use." The final paper dealt with the Potential VTOL Capabilities ojSupersonic Transports. Presented by R. H. Miller of Massa- chusetts Institute of Technology, it stated that an obvious meansof improving safety during the final approach and landing of supersonic types was to increase the time available to the pilotto correct accumulated approach errors. In the author's view, the ability to approach at "low to zero speeds" (depending uponvisibility) and inspect, select and reject (if advisable) a landing area would unquestionably increase the probability of safe opera-tion. A VTOL capability could accomplish this function. The term VTOL, in so far as airline operation was concerned, impliedmuch more than simply the ability to perform a zero roll landing or take-off under emergency power. If routine VTOL operationswere to be achieved, four criteria must be met: (1) complete omni-directional flight capability at all times, regardless of windconditions, this requirement "obviously meaning the ability to fly backwards and sideways as well as forwards, at speeds inexcess of anticipated winds"; (2) complete and adequate control at all times about all axes, a necessity which implied the use ofreaction-type rather than aerodynamic controls; (3) positive posi- tion stability at all times about all axes; and (4) a vertical flightcapability even in the event of engine failure. Mr Miller further opined that the concept of a STOL aircraft with limited VTOLcapabilities (at "off-loaded" gross weights), while attractive in certain military operations, "had no place in the scheduled com-mercial transport field, since the advantages of VTOL operation will lead to traffic control and approach techniques, airport sitingand landing areas which would preclude the use of a STOL. According to the MIT spokesman, if the engine-out conditionwere considered realistically as an emergency condition and not a training requirement at full gross weight, it might be permissibleto allow the remaining engines to operate (for short periods) out- side their normal regimes. Over-speeding and excessive tempera-tures might be thereby incurred, but the time required to free the aircraft from a hazardous height/velocity situation might be insuf-ficient for the engines to reach well-above-normal equilibrium temperatures. In any event, incidents of engine failure with jetengines to date had been so few "as to warrant consideration of the overspeeding and discarding of engines in the event of failureas an economically feasible procedure." Concluding his remarks, Mr Miller suggested that, because thelanding gear of conventional transports accounted for about 5 per cent of the gross weight, the provision of a VTOL capability in aM2 transport "is just possible without loss in payload." In the case of a M3 vehicle, "a net balance of 2 per cent (in weight)in favour of the VTOL transport remains."
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