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Aviation History
1942
1942 - 1438.PDF
a FLIGHT Fifth in the New Recognition Series AIRCRAFT TYPES AND Boston III and Hudson V Bombers INCORPORATING a number of modifications recom mended by the British Purchasing Commission as the results of experience gained with earlier editions, the Boston III, or DB-7B, is basically similar to the Havoc II, or DB-7A, which is the Boston in night-fighter form. Both the 7A and 7B differ from the original DB-7 in having Wright 14-cyl. Double-row Cyclone air-cooled radial engines in place of the Pratt and Whitney Twin- Wasp units fitted to the earlier Bostons. These Cyclones are the GR-2600 type, giving 1,275 nP- a* 2,300 r.p.m. at 12,oooft., with'1,600 h.p. at 2,400 r.p.m. for take-off. The chief structural difference between the Boston III and its predecessors is a longer nose section (which no doubt accommodates increased armament), an increased fin and rudder area demanded by the increase of power, and nacelles which extend still further behind the trailing- edge of the wings. Incidentally, the increased area of the vertical tail surfaces is accompanied by a change in their contour, that of the Boston III (and Havoc II) having a steeper slope to the leading-edge of the fin and an appre ciably broader apex. Another important feature of its tail group is the pronounced dihedral angle given to the tail- plane, which is greater than that of the wings. A tricycle undercarriage is another distinctive feature of the DB-7 range of Douglas aircraft. Performance figures for the Boston III and Havoc II as in service with the R.A.F. have not yet been released for publication, but the DB-7B is identical with the U.S. Army Air Services' A-20 attack-bomber, except for certain items of service equipment peculiar to each air force, and American reports quote a top speed of 350 m.p.h. at 12,oooft. for their A-20 aircraft. Its armament consists of four fixed machine guns in the nose (two on each side), two flexible guns in the rear cockpit, and a single flexible gun firing down from the parachute hatch. American figures also give a maximum bomb-load of 2,000 lb. All-metal construction, with flush-riveted stressed skin covering is employed throughout. EXTENDED NACELLES iCHT Span .. Length Height Wing Area DIMENSIONS 61ft. 4in. 47ft. 4in. /8ft. lin. 464.8 sq. ft.
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