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Aviation History
1949
1949 - 2034.PDF
8oo FLIGHT, 22 "December 1949 U.S.A.F. Trainer Aircraft . . . accessibility of engine ami acci ssories, but on the face of itthis seems a bit harder to justify. Admittedly, a six-man maintenance crew had been timed to remove and install anengine in slightly over 20 minutes; however, we suspect that a six-man engine crew for a two-seater trainer would be lookedat askance by commercial school-operators. A possible answer might be found in designing the rear half of the fuselage withdetachable joints aft of the engine bay, following jet-fighter construction again. Judging from the view of the mock-up, the XT-30 wouldhave been a clean, square-cut,' straightforward low-wing job with a span of 36ft 4m, length of 36ft ioin and overall heightof 13ft 7m. The submerged engine was an 800 h.p. Wright R-i $00 radial, similar to that installed in the T-28, hence themaximum fuselage-width must have been at least 4ft 6in in the region of the rear cockpit. Cooling, we believe, was arrangedthrough an air scoop on the underside of the nose cowling. Incidentally, looking at the long fuselage nose and bubblecanopy forward of the e.g., one cannot help feeling that the vertical tail geometry is shy on dorsal finning. Estimated performance was a top speed of 286 m.p.h. atro,oooft, a cruise speed of 190 m.p.h. for 6J hours, and a service ceiling of 29,600ft. A picturesque gross weight of5,999 lb was also quoted, a figure which may be taken as an impressive token of the weight guestimator's art, seeing thatthe power plant alone (not to mention the rest of the equip- ment supplied from outside sources) could vary as much asplus or minus 10 lb. Furthermore, since the T-28 is now quoted at 6,759 lb, it is tolerably certain that the XT-30, with itsremote airscrew drive, would have scaled something over the 7,000 lb mark—which, no doubt, is impressive hindsight onour part! Because the airframe designer must perforce make the bestof existing power plants within the desired power range, it is no reflection on either the T-28 winner or the XT-30 runner-upto say that they both suffer from the handicap of trying to mate an overgrown seven-cylinder radial engine of 50m diameterwith a two-seater tandem cockpit layout, resulting in a body width at least 50 per cent greater than is really necessary ordesirable for aerodynamic and vision requirements. Perhaps this sort of excess elbow-room may be more pardonable at thehigh-powered advanced stage of training, but it strikes us as a bit awe-inspiring for the raw recruit. Indeed, it rather re-minds us of the first time we were persuaded to straddle a horse —we were amazed at the enormous expanse of the beast in planview! Doubtless it is better to have the chrysanthemum behind,rather than in front of qne's face, but nevertheless the sub- merged-rear-engine scheme is a belated attempt to make thebest of the existing engine situation at the expense of engineer- ing complexity, weight and cost. A dozen or so years ago theBell fighter layout appealed to us very strongly as an out- standing design concept but, to-day, in view of the rapidadvance of the turbine art, the logical answer for the pre-jet trainer is obviously the small-diameter turboprop engine onthe lines of the A.S. Mamba or the R.R: Dart. We suggest, though, that the power required might be trimmed back to 500or 600 s.h.p. for a tandem two-seater layout. FAIRCHILD T-31 As mentioned earlier, the T-31 started out as the NavyXNQ-i, being the winner of a design competition for a primary- basic trainer sponsored by the Bureau of Aeronautics. Invita-tions to bid were also extended to Beech, Boeing, Bell, Convair, Curtiss-Wright, McDonnell, and North American. As a matterof record, the Navy XNQ-i prototype was first flown as far back as October, 1946, flight evaluation tests being conductedby the Navy throughout the following year. Although no pro- duction contract resulted on the naval side, the Air Force be-came interested in it as a primary trainer and further flight tests were continued at Wright Field last year. Early thisyear Fairchild received an $8,000,000 U.S.A.F. contract for 100 aircraft plus spares, and primary flight training on T-31Swill commence early next year. A study of the T-31 shows a conventional, square-cut, low-wing tandem two-seater in the 300 h.p. class, with a tailwheel landing gear configuration, large one-piece bubble canopy, ex-ternally hinged slotted trailing-edge flaps, and stressed-skin construction throughout—except for the control surfaces, whichare fabric-covered. Illogically, perhaps, from the standpoint of lateral control effectiveness, the ailerons are not slotted,although they appear to have a modest degree of nose balance. Only the main wheels, are retractable, folding inboard intohousings forward of the front spar at the junction of the wing with the fuselage, the retraction mechanism being electricallyoperated. The engine is a Lycoming R-680-13 nine-cylinder radial witha normal rating of 280 h.p. and 295 h.p. for take-off. Engine cooling air and exhaust gas are taken out through lauvred grillesaround the sides and bottom of the cowling, leaving the top cowl panel flush and the windshield unobstructed by oilsmudge. The Hamilton-Standard constant-speed airscrew has the blade roots neatly faired off with a fair-sized hub spinner.This latter refinement is conspicuously absent from the T-28, where its effect on blade efficiency might have been consideredeven more beneficial. Undoubtedly the most advanced design feature of the T-31is the functional layout of the cockpits, wherein the character- istic shape of the aircraft part or unit (e.g., wing flaps, landinggear, etc.) is reflected in the shape of the corresponding control- handle in the cockpit; thus, the flap lever handle is shapedlike an aerofoil element, the landing gear retraction levei knob is patterned after a wheel and tyre, and so on. Engine con-trols are grouped on the left side and all the electrical switches are neatly ranked on a console on the right. The radio equip-ment is also neatly tucked away on the right side. Instruments are illuminated by indirect red lighting for night flying, withthe flight instruments arranged in the centre of the panel, enclosed by a white boundary-line, and the other instrumentsgrouped around them. FAIRCHILD T-31 Power Plant.—Engine : Lycoming R-680-13 nine-cylinder radial ; normal rating (s.l.) 280 h.p. at 2,200 r.p.m. ; take-off power (s.l.), 295 h.p. at 2.300 r.p.m. Airscrew : Hamilton-Standard, constant-speed, two-bladed, 8ft 3in diameter. Tankage : fuel, 80 U.S. gal (wing tanks) ; oil, 6 U.S. gal. Dimensions.—Spin 41ft 5in ; length 27ft 11 in ; height 8ft 9in ; landing gear track 9ft I in ; wing area 236 sq ft ; aspect ratio 7.25. Weights and Loadings.—Gross weight 3,750 Ib ; weight empty 2,817 Ib : useful load 933 Ib (instructor and pupil, 400 Ib, fuel 480 Ib, oil 53 Ib); wing loading 15.9 Ib/sq ft ; power loading 12.7 Ib/h.p. Performance.—Stalling speed (3,500 Ib) 56 m.p.h. ; cruising speed (65 per cent normal power) 142 m.p.h. ; maximum speed (s.l.) 166 m.p.h. ; initial climb l,070ft/min ; service ceiling 19,500ft ; take-off run (over 50ft obstacle) 1,190ft; maximum range 900 miles at 110 m.p.h. ; endurance 4.7 hours at 142 m.p.h. BEECH T-34 and TEMCO T-35 Two other '' private venture '' primary trainers were builtand flown during the past year or so in competition with the T-31, namely the Beech T-34 Mentor and the Temco T-35. Arecent report—which must be taken with a large dash of salt— says that the Air Force may cancel the T-31 contract andre-examine the T-34 and T-35, tmt such a change of design policy at this late date seems hardly likely, despite the savingin cost to the taxpayer by reason of the lower .power bracket of the two private venturers. Bearing in mind, however, thealmost feminine changes of front and face of the Air Force over the past twelve months, it might be as well to completethe numerical record with a passing note on these low-cost trainers. The Beech T-34 xs a stressed-skin, tandem-seated, low-winglayout, powered (like the same firm's Bonanza iour-seater per- sonal aircraft) with a Continental E-185-1 fiat-six enginedelivering a maximum of 185 h.p. at 2,300 r.p.m. (It seems more likely that production aircraft would be fitted with theE-185-3 engine rated at 205 h.p. at 2,600 r.p.m. for take-off, since this later type engine is now installed in the 1949 RyanNavion four-seater.) The airscrew is Beech's own design with an electrically controllable variable pitch and efficient-lookinghub spinner. Claims have been made that many of the airfrarue partsare interchangeable with those of the Bonanza, and so the T-34 could be offered to the Air Force in quantities for around$20,000 as against $50,000 for the T-3r. In view of the fact that even a primary military trainer would have to bedesigned for aerobatic load factors, it is a bit difficult to see how much of the structure could be interchangeable betweenthe two types, other than detail fittings and assemblies, per- haps. Certainly the slimmer fuselage and orthodox cruciformtail of the T-34 bear little structural resemblance to the wide, automobile-type body and butterfly vee-tail of the Bonanza. All the same, the Beech contender has a number of excellentfeatures in its favour. In spite of the modest power rating., the all-round performance is nearly as good as that of theT-31, although the latter has more range and endurance—albeit costing double the fuel consumption to get it. A good reasonfor the performance equality lies in the smaller wetted surface area of the T-34, which balances the slightly better wing-power loading parameter of the T-31. Two further points in favour of the Beech design are the fully retractable nosewheei-type landing gear and the better view over the low nose- cowling of the flat-type engine. In passing, it might be said in this connection that if theprancing pistons must remain with us in the low-power cate- gory for some years yet, the best all-round engine partner is
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