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Aviation History
1935
1935 - 0283.PDF
FEBRUARY 7, 1935- FLIGHT. 139 The addition of the " conservatory " roof above and a bomber's position below somewhat mars the clean lines. (Flight photograph.) load range of 1,500 miles at an average cruising speed of 165 m.p.h., but there seems to be little reason to doubt that the claim is substantially correct. Driving a Hamilton Standard two-bladed controllable- pitch airscrew, the nine-cylinder Wright "Cyclone" en gine is rated at 715 b.h.p. at 7,000ft. and 1,950 r.p.m. As the machine weighs* fully loaded, 7,5001b., a maximum speed of 226 m.p.h. must be regarded as remarkably good, and bears out the impression of "clean" aerodynamic design which one forms on inspecting the machine. Structurally, also, the Northrop 2E must be admitted to be well above the average in efficiency, the ratio of gross weight to tare weight being 1.948. There are many ways of judging efficiency, and no simple ratio such as that quoted can be expected to tell the whole story. So many things have to be taken into account, such as stiffness, strength, durability, and ability to stand manhandling. But assuming a given aircraft to be satisfactory in ser vice, the percentage of its own weight which it will carry as disposable load does give an indication of the skill with which the designer has solved his many conflicting problems. In the case of the Northrop 2E the machine carries just under 95 per cent, of its own weight. Until quite recently an average figure for a very wide range of types has been 65 per cent, of the tare weight, so that it must be conceded that the designers have shown skill. In spite of the fact that the machine is a cantilever mono plane, the wing weight is under 2.4 lb./sq. ft. This figure includes machine-gun mountings, leading-edge landing lights, navigation lights, and aileron mass balances. An inspection of the structural methods employed does not reveal any very great refinements. For example, the wing covering is of one gauge throughout, and no attempt has been made to save weight by having a heavier gauge near the wing roots and a lighter gauge at the tips. The wing structure itself is of what might be termed the multicellular type. That is to say, the box-section spar to which we have become accustomed in this country is not used. Instead, the designers employ a number of plain channel members, to the flanges of which the wing cover ing is riveted. In between these channel-section members or spars the Alclad wing covering is stiffened by stringers of " Omega " section. The wing ribs are generally similar to the '' spars'' in that they are light channels with flanged circular lightening holes. They are, of couise, riveted to spars and covering. An interesting feature of the wing design is the manner of attaching the outer wing portions to the centre-section. and Ih Umt: Note the trimming "tabs " on the elevators, a the mass balance which disappears into the tailplane. in o HUpper mernD«" of the cruciform stern piece is twisted er to reduce yawning due to the rotating slipstream. (Flight photographs.)
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