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Aviation History
1923
1923 - 0308.PDF
HT are the forces to which the fixed and moVa'ble surfaces and the envelope of an airship are subjected when it is making manoeuvres ? The first of these led to an extensive investigation in the standard wind tunnel. One series of tests was on four model aerofoils without ailerons, having square elliptical and positively and negatively raked tips ; the second series was on wings having raked tips with ailerons adjusted to different settings. The models had a chord of 6 ins. and a mean semi-span of 18 ins., and the method of images, recommended in one of the British R. and M. reports, was adopted in the investigation. A large number of series of openings were made in the surfaces of the aerofoil, and each was connected to a liquid manometer. The results give a great deal of what U5O 6O BO 90 100 inXnM dr «FM* *• m.r.k. QMt UH-tl fokkir D-fU. no 120 GLIDE TEST OF FOKKER D.7 : The curves are plotted v . . . on base of airspeed in m.p.h. is apparently new information concerning the air flow near thetip of a wing. They will soon be published both in tabular and in graphical form, so that designers can calculate withease the distribution of lift between the ends of the wing spars, the shears and bending moments, and the aileronefficiency. Further, with the knowledge obtained, proper distribution of load in sand testing is facilitated. The mostimportant general conclusions are that tips with a positive rake give an erratic distribution of lift near the tip of theaileron, and that this may be avoided by the use of a negative rake. Considerable new light is also thrown upon the questionof aileron balance. In order to study the air-flow about a high-speed pursuitaeroplane, a Thomas-Morse MB-3 machine was rebuilt and suitably prepared for experimentation. This has a maximumair-speed of 145 m.p.h. A large number of holes were made in the two surfaces of both the upper and lower wings ; thesewere connected by rubber tubes to recording multiple mano- meters mounted in the fuselage ; so in this way sixty recordscould be made simultaneously. The manometer, which has been described in published reports of the Committee, consists of a series of metal capsules, across the middle of each of which is stretched a metal diaphragm. In most of the tests the two holes facing each other on opposite sides of the wing were connected to the opposite sides of the capsule ; but in some cases only one hole was so connected, the other side of the capsule being joined to a reservoir in the cockpit communicating with a static tube whose opening was in the interior of the wing. Special attention was paid to the distribution of pressure in the slipstream and near the leading and trailing edges. Since there is such a great variation in pressure over a wing, each capsule was adjusted separately so as to have the proper sensibility corresponding to the opening with which it was connected. At the leading edge pressures as high as 200 lbs./sq. ft. had to be measured, while further back the pressure often did not exceed 30 lbs./sq. ft. An accelerometer, a recording air-speed meter, a control position recorder, and an electric chronometer were also installed in the aeroplane. The information specially desired was the distribution of lift over the portions of wings in the slipstream during steady flight and that over the entire wings during violent manoeuvres. Measurements were made at air-speeds of 70, 115 and 145 JUNE 7, 1923 miles per hour at closed, medium and full throttle under conditions of steady flight, and also during three manoeuvres, a roll, a flattening out of a dive and a vertical bank at 150 m.p.h. The result can be understood most easily by the use of graphical methods. Contour lines of pressure may be drawn on a model of the wings ; or, what is far more striking, three- dimensional models may be constructed. The numbers adjacent to any contour line indicate the total pressure upward in lbs. per square foot, i.e., the combination of the effects on the two sides of the wing. The relief maps also give the combined effects. Some of the most striking facts observed are :— -V-;"-l•"'.. 1. The lift in the slipstream during steady flight is far from uniform on this aeroplane ; at high air-speed and high engine- speed a lift of 100 lbs./sq. ft. was observed on the leading edge of the upper wing, while on the leading edge of the lower right wing there was an area of down pressure of 60 lbs./sq. ft. 2. At lew air-speed and high engine-speed, that is while climbing, there was at the trailing edge of the lower left wing, near the fuselage, a down pressure of 70 lbs./sq. ft. 3. When the suction on the upper surface of a wing was measured with reference to the air inside the wing, it was found to amount to as much as 76 lbs./sq. ft. in steady flight, whereas in one isolated point an inward pressure of as much as 24 lbs./sq. ft. was observed. 4. In flattening out of a dive the wings support only 80 per cent, of the total load on the aeroplane, whereas in a vertically banked turn at 150 m.p.h., where the acceleration rose to 4 • 2 g. the wings carried 90 per cent, of the load, the remainder being borne by the fuselage and tail surfaces. 5. In steady flight at 145 m.p.h. the lift per sq. ft. of the upper wing is twice that of the lower, the total lift of both wings being about 400 lbs. greater than the weight of the aeroplane, balancing the down load on the fuselage and tail. This fact is, no doubt, due to the rigging of this particular aeroplane, i.e., to the angular difference between the wings, and to the lower wing being almost at zero lift. It is important to add that this MB-3 machine is a single- seater, so that the pilot has to control the machine and press the button which starts all the automatic recording devices. This investigation of the MB-3 proved so interesting and offered so many suggestions that further studies of pursuit aeroplanes have been called for ; the plans are now perfected for similar investigations of the latest types of military fighting too >r/qn> —Ma/ Tunnel without honeycomb ,No.l. TuTnei'with fine honeycomb e 3 A .5.6 8 I B 3 4 S 6 B IO C.™» ot'mw nti*U*a of « tphm at &$in*i R«<fi.oMi Kuab, 308 30 30 405Q< Curves giving resistance of a sphere at different Reynolds numbers. The curves are plotted on a logarithmic base (Reynolds numbers 10-5). aeroplanes. One problem in this connection is to comparethe inherent advantages and disadvantages of monoplane and biplane machines. As is well known, the United States is interested in the construction of airships. The Navy has practically finished a large rigid, and the Army has well under way a semi-rigid. As is equally well known, the actual scientific knowledge of the aerodynamics of airships is not extensive. At the request first of the Navy and later of the Army, our National Advisory Committee undertook to study and report upon the airship designs made by these two services. In connection with this work one of the technical staff of the Committee, Dr. Munk, elaborated a certain theory of the airship which was distinctly novel, but led to results at variance with accepted practice.
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