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Aviation History
1950
1950 - 0859.PDF
Tail umbrella: Boeing are investigating several methods of decelerating the landing run of their jet types, and the experiments have included the use of the tall parachute, here seen in action on the XB-47 bomber. Reverse-rocket motors may also be tried AMERICAN NOTEBOOK " Pennellizing" the Civil Jet : Some Trial-kite Flying by Boeing By Stanley H. Evans, F.R.AcS., A.F.l.Ae.s. FOLLOWING our recent discussion on jet-transportdesign desiderata (February 23rd) comes anothersparkling volley from a top-ranking player in the Boeing design team. - In the March issue of the Boeing Magazine, under the title of "jet Airliner Design Prob- lems," Mr. Maynard Pennell, Boeing's chief of Preliminary Design, outlines the principal design characteristics which a superior jet transport should possess—as seen through the Boeing looking-glass. Naturally enough, since a bird in the air is worth two on the board, the reflection has all the military airmarks of the B-47 Stratojet bomber. Basically, says Mr. Pennell, the most important of several reasons for progressing from piston-engine to turbojet in commercial aircraft is speed. To Boeing en- gineers, however, the speed potential of the jet airliner is not just another reduction in travel time, but rather the opportunity to advance, in one big leap, to speeds that cannot be surpassed for a long time to come; in other words, it offers the ability to push right up to the foothills of the Mach mountain or transonic divide—which in the case of the standard 35-deg sweepback means in the region of M = o.9o or practically 600 m.p.h. above the 35,000ft level. Whether, however, this objective is the maximum or the cruising speed is not categorically defined. The distinction, as we see it, is important. Mr. Pennell is cautious enough to point out that for commercial operation supersonic speeds remain consider- ably farther than just around the corner, since the problems associated therewith are beyond the power of currently available jet units—at least within reasonable economic limits; thus, for other than military or special purposes, it will probably be necessary to await the development of new sources of power or other unforeseen technical innova- tions. But in the meantime, says Pennell, Boeing are satisfied that they have opened the doorway to the upper limit in subsonic speeds by writing their civil jet pre- scription around the B-47 military formula—meaning, more specifically, the thin wing of high aspect-ratio and emphatic sweep. The evidence for this diagnosis is based upon the proved performance of the XB-47 during the past couple of years. Thig jet-bomber experience—tempered with knowledge gained from designing conventional transports—has put on American drawing-boards to-day the most advanced turbojet transport designs in the world, says Pennell! Which is a bold (but wistful) claim, if we dare say so, for it amounts to the wishful thought that a bird on a blueprint whistles louder to the customer than the bird already " whittling " in the blue. This sales philosophy may have had some factual basis at the time the Stratocruiser was projected from its military antecedents (the B-29 and C-97), when world competition was less keen, but to-day the com- mercial situation is entirely different. Furthermore, the military attributes of an aircraft are no automatic recom- mendation for its fitness in the commercial sphere ; in fact, post-war experience has proved quite the contrary. Most of the design characteristics enumerated by Mr. Pennell in defence of the Boeing civil-jet proposals have already been discussed in these pages, so we need not go back over the same ground. The underlying motif—or perhaps one might more truly say the outstanding theme— is, of course, the thin, flexible, high-aspect-ratio wing and the peduncular poddery concomitant therewith. The ex- ternal pod theme, according to Boeing thinking, is con- sidered virtually a must for the jet transport as well as the military bomber, which seems to us rather a specious argument in view of the conjoint nature of the two features. The "must" in this postulate is that, like Siamese twins, they must stand or fall, live or die, together. One difference freely acknowledged by Boeing engineers is that the wing loading of the jet transport wDl have to be lower than that permitted in the B-47. Just now much lower is not yet divulged, although further data are promised in a second article by Pennell. Currently, we believe the B-47 ^ taking off at around no lb/sq ft, a loading which is likely to climb still higher as take-off and landing techniques are perfected with a view to poshing up the range performance. On the evidence of the Strato- crniser's wing loading of a shade over 80, it seems a fair guess that that of the Boeing civil jet will not fall much below, say, 90. Comparing this with the modest 52 of the Comet shows how deeply the military-missile influence has penetrated into American commercial planning. And nothing shows more penetratingly how wide is the gulf that separates the design philosophies of Boeing and de Havil- land. (On stalling speed, for instance, the difference amounts to roughly 30 m.p.h. in favour of the Comet—and the passengers' health!) Under present C.A.A. regulations, commercial aircraft must demonstrate their ability to land over a 50ft obstacle
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