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Aviation History
1942
1942 - 0360.PDF
140 FLIGHT FEBRUARY I2TH, 1942 THE JUNKERS JU 88 A-6 A-6 (2 Jumo 211G engines). ^The ralient results emerging from these tests are given in the accompanying tables: — FULL THROTTLE LEVEL SPEEDS Engine r.p.m. 2,400) ; Engine Cowling Gills closed Esternal BOmb Racks Off On On Off Loading Condition Four 250 kg. •MM (external Off Off On Off Petrol Inner wing tanks half full Wing tanks full... Wing tanks full inner wing tanks half full Weight 16. 19,870 22,200 24,350 19,870 Height ft. 16,000 10.0(H) 10,000 5,000 Speeds m.p.h. 281 270 248 261 Super charger gear High High High Low CLIMB3 Loading Condition Ex terna] bom!) racks Off On On On Four 250 kg. bombs (ex ternal) Off Off Off On Petrol Wing tanks fuH. Wing tanks full. Wing tanks full. Wing tanks full. Weight lb. 21,838 •1-J..-2.W 22,200 24,350 Height tt 6,000 16.000 10 00(1 1(1 000 Flying speed T.A.S. m.p.h. 130 1*1 130 ' 140 Rate of climb ft/ mm. 1,370 1,100 1.190* 700' Service ceiling (100 ft. /min.) ft — 26,000 •2I..700* 21,000* Engines " Combat " 1.15 Ata, 2,300 r.p.m. Full throttle 2,300 r.p.m. Full throttle 2,400 r.p.m. Full throttle 2,400 r.p.m. * Estimated values. TAKE-OFF DISTANCE (mean of two take-off runs), Corrected to Zero Wind and Standard Atmospheric Conditions. Loading Four 250 kg. bombs carried externally. Wing tanks full. Weight 24,350lb. ... Distance start io take-off (Mean) Yards 60.1 Distance start to 50ft. Meani Yards 1 028 The programme of tests covered the following points: — (i) Determination of the position error curve. (2) Measurement of full-throttle level speeds (a) with the external bomb racks off; \b) with the external bomb racks on but with no bombs; (c) with four 250 kg. bombs carried externally. Speed measurements were also made at the "combat" rating (boost pressure 1.15 ata, 2,300 engine r.p.m., rich mixture). (3) Partial climbs at 6,000ft. at " combat " rating with the external bomb racks off (superchargers in low gear). (4) Determination or the ceiling by a climb from 16,000ft. at full throttle and 2,300 engine r.p.m. (superchargers in high gear). (5) Measurement of take-off run with the external bombs carried and the wing petrol tanks full. . 'Nursing the Engines In order to conserve the engines, full throttle (1.35 ata boost pressure, 2,400 engine r.p.m., rich mixture) was used as little as possible. Full-throttle running is only allowed for three minutes, and, when the cowling gills are closed, invariably results in overheating of the engines. Again, to avoid overheating, above the full-throttle height with the superchargers in high gear, full throttle and 2,300 engine r.p.m. (not 2,400 r.p.m.) were used. Except for a few points, the measurements at low heights were made at the "combat" rating (1.15 ata boost pressure, 2,300 engine r.p.m., rich mixture). The cruising conditions are 1.10 ata boost pressure, and 2,100 engine r.p.m., weak mixture. The aircraft was timed at various speeds over a 7J miles speed course in order to establish the position error curve. The points are plotted in Fig. iA. These indicate that the position error is independent of speed over the range 160 cttt 2| <rS °i I-a: OO a. 160 ISO 200 220 240 US M.PH BOO Si CD Q 1 400 **** 20 24 BOOST 32 36 INS Hg ABS AC m.p.h. to 220 m.p.h. I.A.S., the mean value being -f m.p.h. The electrically heated pitot static head extends forward from the leading edge of the port wing. The dis tance of the head from the leading edge is 4.22ft. ; the local wing chord is 8.9ft.. and the local wing thickness about 12 per cent. The full-throttle level speeds ob tained under various conditions are shown plotted against height in Fig. 2A. The correspond- ing boost pres sures are given in Fig. 3 A. The engine cowling gills were in the closed position throughout. Speeds w e re corrected on the , density basis above the supercharged height and on the pressure basis below the supercharged height. Boost was corrected on the half-and-half basis above the super charged height and on a pressure basis below these heights. The full-throttle height with the superchargers in high gear is 16,oooft superchargers in low gear is 7,500ft. With the external bomb racks off and the inner wing tanks half full (total weight, 19,870 lb.), the full-throttle maximum level speed is 281 m.p.h. T.A.S. at 16,000ft. with the superchargers in high gear, 2,400 engine r.p.m,, 25,000 Fig. 1A (top) : Position error correction curve. Fig. iB (bottom) : Variation of B.H.P. with boost pressure at constant speed of 2,300 r.p.m. from -f- 3 lb. per sq. in. boost, ground level intake, for Jumo 211 D engines. Fuel, 92 octane, supercharger in low gear. The curve can be applied to Jumo 211 E engines. the estimated full-throttle height with the 20,000 15.000 - 10000 r o UJ T 5.000 5-V V S. 2 1 ; 1 FULL THROTTLIU^ 2400 ENGINE -5W RPM [ESTIMATED] 240 TRUE 260 AIRSPEED 280 M PH 5.000 COMBAT RATING . [BOOST 113 ATA ' Ni ENGINE B.BM. -2.300 " , • SPEED 130 M.PH EAS] Fig. 2A : Full-throttle level speeds (engine cooling gills closed, and boosts as in Fig. 3A). The curves represent: (1), no external bomb racks ; weight 19,870 lb. ; engine r.p.m. 2,400. (2), no externa) bomb racks, weight 19,870 lb.; engine r.p.m. 2,300. (3), external racks, no bombs ; weight 22,200 lb. ; engine r.p.m. 2,300. (4), external bombs j weight 24,350 lb.; engine r.p.m. 2,400. O 500 1000 1.500 RATE OF CLIMB FT/MIN. Fig. 2B : Rates of climb and ceiling. (Boosts in Fig. 3^-) These curves were obtained at a weight of 22,200 lb. with bomb racks on but no bombs. With cooling gills two-thirds open the speed was 130 m.prr? at 16,ooo and 18,oooft. and 125 m.p.h. at 20,000 and 22,000ft. With cooling gi»s one-third open the speed was 120 m.p.h. at 24,000ft.
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