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Aviation History
1919
1919 - 1341.PDF
PREDICTION OF AEROPLANE PERFORMANCE* By I. M. LADDON, Aeronautical Engineer, U.S. Air Service THE following method of estimating aeroplane per formance was outlined to the author by Lieut. Alkan of the French Aviation Mission. It consists in com paring the aeroplane whose performance is to be found with the actual performance of an aeroplane of similar type on a power and a surface loading basis. The actual performances of three different types of aeroplanes are given on the chart on p. 1342. These aeroplanes are all good, clean designs ; therefore, when comparing an aeroplane that is poor aerodynamically with any one of the above, an allowance should be made in the high speed obtained. In extreme cases this allowance may run as high as 10 m.p.h., but for all ordinary designs no allowance need be made. The ceiling is not correspondingly affected. Curves of actual performance shown include the three common types : (a) Single-place scout, (b) Two- place fighter or reconnaissance aeroplane, (c) Three or four-place, twin-engined bomber. By selecting the proper type for comparison one can make an accurate prediction. It has been the author's experience that the results obtained through this simple method are much more reliable than those given by the old laborious method of computing the parasite resistance, horsepower required, available, etc. It should prove quite useful to the designer, since it affords a rapid and accurate means of estimating how changes in weight, surface * From Aviation, U.S.A. <$> <s> Searchlights for Aerodromes THE Air Ministry announces that as a temporary and emergency measure to assist belated aircraft to locate their aerodromes after dusk, the Air Ministry has arranged for vertical searchlight beams to be projected from the following aero dromes about dusk till all overdue machines have arrived :— Hounslow .. 1 vertical beam. Kenley .. 2 vertical beams. Lympne .. 3 beams, arranged in a triangle. or horsepower affect the performance of the plane in question. Example—Twin-engined aeroplane : weight, 7,200 lb. ; horse-power, 800 ; surface, 900 sq. ft. The obvious plane to use for comparison is the twin- engined bomber. 1. Find the intersection on reference line B of a straight line through the propeller efficiency and horse-power. 2. Join this point to the surface and note the inter section on line V. 3. Find the intersection on reference line C of a straight line through weight and surface. 4. Join point on reference line C to point on refer ence line B, and note intersection on line A. The linear difference between the points found on lines A and V and the corresponding points given for the plane which it is being compared with are the measures of the relative ceiling and speed. 5. Construct a curve similar to curve C, using ordinates increased (or decreased) by the difference in altitude (C-K) and abscissa? increased (or decreased) by the difference in speed (C-K). 6. From the point of absolute ceiling (E) draw curve parallel to curve D. This curve gives the minimum speed for horizontal flight at given altitudes, while the curve first con structed gives the high speed. The enclosed area is the speed range. <•> <•> U.S. Warships to Carry Seaplanes ANNOUNCEMENT was made by the U.S. Navy Department on September 13 that every American warship of the second class is to have a seaplane included in its equipment. It is stated that the U.S. naval authorities are convinced that the time has passed when a direct attack on sea coast cities may be made by a battleship fleet however powerful; the attack will be by seaplanes launched from a moving base of dread noughts at sea. The Pfalz trip lane, fitted with rotary engine. 1343
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