FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1923
1923 - 0310.PDF
15 ft. in diameter, and weighs 83 tons. It is mounted on a concrete foundation, and is partially surrounded by a working platform. An observer on this makes settings and readings by looking into the tank through small glass windows. The density of the air in the tank is controlled by two compressors driven by electric motors. Continuous stages may be secured from one-tenth of an atmosphere to twenty atmospheres. Cir- culation of air is effected by a two-blade propeller of special design, 7 ft. in diameter and driven at 900 r.p.m. by a 250 h.p. synchronous motor mounted on a separate foundation outside the tank. The drive shaft is made tight against air leakage where it passes through the head of the tank by a loosely packed gland, through which oil is circulated. The concept of such a tunnel was originated by Dr. Max M. Munk, and this particular one was designed by him ; and the mechanical equipment was designed and installed by Mr. D. L. Bacon, both members of the Staff of the Committee. The latter is in charge of the operation of this tunnel as well as of other tunnels in the Committee's laboratory. It may be of interest to note that when the tunnel is operate ing at its greatest density, it is equivalent in scale to a tunnel 100 ft. in diameter running at 60 miles per hour. It takes about an hour and a half to " inflate " the tank fully. Another method for obtaining a large Reynolds number, which is used by the Committee, involves the accurate measurements of the motion of an actual aeroplane in flight. To this end the Staff of the Committee have perfected a large number of recording instruments. Among these may be mentioned a single-component accelerometer; a three- component accelerorneter; a three-component angular velocity recorder ; a control-position recorder ; a control- force recorder ; an air-speed meter ; an angle of attack recorder, and an electric chronometer. The Committee owes the design of these instruments to the exceptional ability of two of its staff, Mr. F. H. Norton and Mr. H. J. E. Reid. The latest instrument developed, and one used in work about which I shall speak later, is a form of kymograph. It consists of a streamlined body, shaped like a bomb, from the front end of which projects an N.P.L. pitot tube, and which has a tail appendage to render the whole directionally stable. There is a transverse shaft through the centre of mass, to the two ends of which are attached suspension wires leading to winches in the cockpit of the aeroplane, so that when the latter is in flight, the kymograph may be lowered to a distance of 25 ft. so as to be in undisturbed air. In the upper forward surface of the " bomb " there is an opening closed with a cylindrical lens, outside of which is a small vertical mirror, so that the rays of light from the sun may be reflected through the lens and then through two crossed slits on to a photographic film. The pitot tube is connected to a capsule manometer, whose motions are recorded on the same film. This is wound on a drum, inside of which is a constant speed electric motor driven by a current led in through the suspension wires. When the aeroplane is flown in a direction away from the sun, the kymograph takes a position along the direction of the relative wind, and a continuous record will be made of the angular position of the sun with reference to this direction. An observer on the ground observes simultaneously the altitude of the sun ; and so one obtains a record of the angle between the flight path with reference to the air and a horizontal line. The air-speed is measured at the same time, as is also the angle of attack of the aeroplane itself. There- JUNE 7, 1923 fore, if gliding flights are taken, values of the ratio of lift to drag may be measured at various angles of attack at known air-speeds. This method is obviously independent of vertical air currents. As an illustration of its accuracy, a chart is shown giving the values of angle of glide with reference to air- speed at different values of V/ND, in which V is the air-speed, N is the number of revolutions per second of the propeller, and D its diameter. B5' a preliminary model investigation it was found that the value of V/ND was 1 -02 for the condition of zero torque. These, and alt other " free flight " tests under the direction of the Committee, have been carried out by Mr. F. H. Norton and Mr. W. G. Brown with the aid of the Com- mittee's most skilful test pilot, Mr. Thomas Carroll. Unfortunately for the purposes of this paper, the com- pressed air tunnel was actually put into daily operation for observation purposes only about the first week in April, and so I can report the results of only two series of tests. For this reason, although I have no cause to question their accuracy, they should, I think, be regarded as provisional. The first scale effect measurements undertaken were on spheres. There is nothing novel in this problem, but some of the results are interesting. Spheres of various sizes were studied in the two tunnels, with their supporting spindles in the direction of the airstream and at various angles to it ; other spheres were towed suspended at a considerable distance below an aeroplane in flight ; and finally certain spheres were taken aloft by an aeroplane on particularly quiet days and allowed to drop, their motion being determined by theodolite observa- tions from the ground. This test was undertaken both to obtain large Reynolds numbers and to investigate the condition of turbulence in the new wind tunnel. If time were available, I would call attention to several interesting features of these curves. The second test on the subject of scale effect was made with reference to a type of aeroplane itsing thick wings and having small parasite resistance. A Fokker D-7 was selected for this purpose. An aeroplane was equipped with suitable apparatus, and a model of one-fifteenth scale was made which was fitted with its proper propeller. Series of measurements on models and in full flight have been made, the aerodynamic characteristics of lift and drag being measured. If the use of these scale effect methods justifies our present hopes, we shall be able in a comparatively short time to place at the disposal of the designer of aircraft a wealth of informa- tion which should increase markedly the accuracy of his work. Sir Richard Glazebrook said that many years ago, more than he cared to think of, he and Dr. Ames had been fellow students, at any rate as regards the subjects they studied, which were very different from that of aerodynamics. Our thanks, he thought, were due to Dr. Ames for having suc- ceeded in impressing upon the proper authorities the very great importance of research work. He believed work of the kind indicated in the lecture was of vital -importance, and expressed regret that this country had not been able to carry on, notably with airship experiments. He recalled the first occasion on which a lecturer before the Royal Aeronautical Society had shown slides of pressure plotting over the surface of a wing. That was some ten or twelve years ago, and the lecturer was Professor Petavel. It was sad to realise that we had not been able to continue the work, and unless we set to work at once on similar lines to those indicated by Dr. Ames we should get left behind. THE INTERNATIONAL AIR CONFERENCE. THE preliminary programme of the International Air Congress, which is to take place in London from June 25 to 30, is as follows :—• Monday, June 25 (morning).—;Opening Ceremony at the Institution of Civil Engineers, Great George Street, West- minster. Inaugural address by His Grace the Duke of Sutherland. Afternoon.—Simultaneous Sessions of Groups A, B, C and D, for reading and discussion of papers at the Institution of Civil Engineers Tuesday and Thursday, June 26 and 28.—Visits by members to various places of aeronautical interest. Wednesday, June 27 (morning and afternoon).—Simultaneous Sessions of Groups A, B, C and D for reading and discussion of papers at the Institution of Civil Engineers. Friday, June 29 (morning and afternoon).—Simultaneous. Sessions of Groups A, B, C and D for reading and discussion of papers at the Institution of Civil Engineers. Saturday, June 30 (morning).—Concluding meeting of members in General Assembly, under the chairmanship of the Secretary of State for Air (Lieut.-Col. the Right Hon. Sir S. J. G. Hoare, Bart., C.M.G., M.P.), at the Institution of Civil Engineers, Great George Street, Westminster. The programme of evening entertainments for the members of the International Air Congress is now, we understand, complete. In addition to the items shown on the official programme, which we are able to publish below, a number of private dinners are being arranged. Any reader wishing to attend any of the official functions should communicate with the General Secretary, International Air Congress, 7, Albemarle Street, London, W. 1. Monday, June 25, 9.0 p.m.—Reception by the President (His Royal Highness the Duke of York, K.G., K.T.), in the King Edward VII Rooms, Hotel Victoria, Northumberland' Avenue, S.W. 1. " Wednesday, June 27, 9.0 p.m.—Reception by the Lord Mayor at the Mansion House. Thursday, June 28, 10.0 p.m.— Reception by His Grace the Duke of Sutherland (Chairman of the Congress Main Com- mittee) at Hampden House. . . .: Friday, June 29, 9.0-11.0 p.m.—Visit to the Science Museum, Exhibition Road, South Kensington. Saturday, June 30, 8.15 p.m.—Banquet in the King Edward VII Rooms, Hotel Victoria, Northumberland Avenue. 310
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
