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Aviation History
1949
1949 - 0955.PDF
6i8 F LI G HX MAY 26TH, it)-]9 NORTH-AMERICAN SUPERSONICS Vacuum-type Tunnel Designed to give Velocity of Mach 5.25 IT is, of course, widely realized that, bothin manpower and fiscal strength, ourAmerican friends have some very con- siderable advantage over us. Some measureof what this difference in resources can mean is offered by the fact that, at the Los Angelesbase of North American Aviation Incor- porated, has been built a supersonic windtunnel which in size and capacity far out strips anything possessed in this country, notonly by our aircraft manufacturers, but by government establishments as well. Certainly,North American's supersonic tunnel is the largest of its kind operated by an aircraftcompany in the United States, but that a private company should have a piece ofresearch equipment beyond the resources of jur whole country, impoverished though wenay be is, to say the least of it, a sorry state jf affairs. We have supersonic tunnels over here, ofcourse—in point of fact, we have quite a number of them. But they are all quite smalland of quite low supersonic-speed capacity. Model of guided missile being mounted in tunnel working section. Nozzle blocks of varying profiles permit air speeds of a range equivalent of from 930 to over 4,000 Vn.p.h. at sea level. In this connection, it.should, nevertheless, in all iprness bepointed out that we are feeling our way, aid/the experience gained with our present small supersonic tu^ should serve as useful foundation data upon which to Besign and Plan layout of the wind-tunnel show- ing the disposition of the four major elements. «0'2" PUMP BLDC. larger tunnels of greatly increased capacity. Just how far off these larger tunnels are, however, cannot as yet be stated. Based on tbe German Kochel design, the North American tunne] has a working section i6in square and is capable of producing an airflow velocity of Mach 5.25, i.e., 4,000 m.p.h. As an entity, the tunnel consists of four major units: a dry- air storage tank with a capacity of 22,500 cu ft; a 36,000 cu ft vacuum chamber; the tunnel working section connecting the storage and vacuum tanks; and the vacuum pumps. The vacuum chamber is of approximately prolate spheroid form tinuous: a test run averages about 15 sec in duration, andre-exhaustion, for example, takes about 6.3 min for a Mach number of 4.38.The specimen-balance is of the "sting" type, in which upper and lower quadrants are rigidlyjoined at the centre by a sting, or arm, which projects forward r':.into the air-stream. The quad-' - rants operate in ball bearings '''carried in fully adjustable sup- . ports. The specimen-mountitself is motor-operated, and . the specimen can be set to any ' 'angle of attack between zero and +12 deg; angular changescan be made at rates up to 3! deg/sec. Forces imposed on 'the sting are measured by ' strain-gauges at various points.For observation, an adapta- tion of the well-known .schlieren optical system is em- - plcyed. A beam of light isdirected across the working sec- tion, and the compression andexpansion of the air flowing past the model refracts the light in varying degrees, so that,through a series of mirrors, the shadow-patterns can be viewed, ' or filmed to provide photographs of the airflow characteristics. ' .. A detailed description of the tunnel appears in the current(May) issue of Aircraft Production. HERMES V PROGRESS T^HAT the Hermes V, with its Bristol Theseus turboprops, is expected to be ready in time to make its public debut1 and can, it is said, be evacuated to a 99.8 per cent complete at the S.B.A.C. Display in September was announced in the ,,D^,,,,^ chairman's statement circulated for the annual general meeting of Handley Page, Ltd., held last Thursday at Cricklewood.vacuum.Operation of the tunnel is essentially simple. Whilst the vacuum chamber is being evacuated, the storage tank—which That the newest Hermes will have thermal de-icing was also ••-•; has a balloon-like inner container—is being filled with dry air mentioned, though whether it will operate by "bleeding" ;; ,—.-_..;_ » —J =--- * J- - •-" -r .. from the power units or by Self.contained heaters was not _ ' i specified. ••'-'- In general, the statement reviewed Handley Page achieve- (moist air would condense into fog under the influence of the very low temperature in the test section, interfering with observation and, by reason of "condensation shock," causing _ _ erratic forces to act upon the specimen). The one tank having ment from the early days—appropriately, for tins was thebeen emptied and the other filled, a gate valve in the tunnel duct is opened and differential pressure between the tanksforces the dry air violently through the tunnel working section into the vacuum chamber. Operation, naturally, is not con- company's fortieth year of existence-—to the present time,when the Hermes IV, 25 of which have been ordered by B.O.A.C., are in full production. On the military side, theHastings is proving its worth in service on the Berlin Air Lift.
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