FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1956
1956 - 0655.PDF
Three aspects of the recently re-opened Southern California Co-operative Wind Tunnel: the main control room (above); the fans (right) and the model carts (below), showing the supersonic, transonic and subsonic carts from left to right. Pasadena Expansion IN Flight of May 4 there was a detailed description of the newAircraft Research Association wind tunnel near Bedford. Inthe leading article to that issue we commented on the fact that, although this is the first large, high-speed tunnel to be builtin Britain on a co-operative basis, such a facility has been avail- able to the aircraft companies of California since World War 2.The Southern California Co-operative wind tunnel was con- ceived in 1940; it was originally financed in the ratio of Douglasand Convair one-third each, Lockheed and North American one- sixth each. In 1948 half of Convair's share was purchased byMcDonnell. The original tunnel was a 12,000 h.p. subsonic installation and it has been operated for eleven years, on a non-profit-making basis, by Caltech. The original cost was $2.5m, which in those days was worth about £600,000. In 1951 the owner-companies authorized an elaborate modifi-cation programme to give the tunnel transonic and supersonic capability. There are now two 20,000 h.p. electric motors eachdriving two fan stages, and the upper Mach-number limit has been raised to 1.8. The tunnel can be operated at pressures from0.1 to 4 atmospheres and models can be mounted in subsonic, transonic or supersonic carts each of which forms a completeworking section. The working section has a width of lift 3in and a height of 8ft 6in (the transonic throat is slightly smaller),and models of up to 8ft span can be accommodated. The rebuilt tunnel was dedicated on April 25 of this year and iscertainly one of the most valuable tunnels available to any private manufacturers. Cost of the modification was $8m, and the re-placement cost of the complete tunnel—at today's prices—is put at $14m, or £5m. THE TUBE WIND TUNNEL—A PROPOSAL OTHER things being equal, the power required to drive awind tunnel varies directly with the Mach number andwith the square of the Reynolds number. In recent years both these factors have been rising rapidly, so that today theprovision of a transonic or supersonic tunnel capable of accom- modating a fair-sized model is a major undertaking. There are, of course, several quite different types of tunnel.The closed-circuit, fan-driven tunnel is probably the most efficient and the cheapest to run but it is also the most costly; inour issue dated May 4, for example, we reported on a new tunnel at Bedford costing between £1.3m and £1.5m contributed by 14of the biggest companies in the British aircraft industry. Possibly the cheapest type of continuous tunnel is the injection tunnelenergized by turbojets. Particularly if the engines are already available, the capital cost of such an installation may be no morethan perhaps £150,000 (or less, according to size of the working section), but the operating cost is exceedingly high. Althoughsuch tunnels leave much to be desired, they have been constructed by several British companies owing to their low capital cost.Other comparatively cheap alternatives are the intermittent tunnels, in which the working section is part of an open-endedtube attached at the appropriate end either to a pressure vessel or to a vacuum chamber. In either case the tunnel can run only dur-ing the time taken for the pressure accumulator to discharge to a particular minimum pressure (well above atmospheric) or for thevacuum flask to reach a maximum internal pressure which is still substantially less than that of the surrounding atmosphere. In his paper Prof. Ludwieg compares the constructional cost AERODYNAMICISTS have doubtless dreamed of meeting an Orientalpedlar who could say: "Look, mister, I got nice tunnel, very cheap, big Reynolds number, big Mach number, self-governing, you buy, yes?"The pedlar now seems to have materialized as Herr. H. Ludwieg, a professor in the applied mechanics department at Gottingen specializingin laminar flow. At first sight his "tube tunnel" seems to be the most economical method yet devised for obtaining fair measuring times athigh Mach and Reynolds numbers. of a pressure accumulator and a vacuum vessel. His conclusionsare—naturally enough—that the vacuum vessel is the more expensive, but his ratios of cost are much higher than previousestimates; for a 10:1 pressure ratio he quotes 630:1. The assump- tions made in determining the costings are not published but,irrespective of the figures themselves, there is no denying that the trend they reveal is generally admitted. Unfortunately, in a pres-sure-accumulator tunnel, it is exceedingly difficult to maintain constant still pressure and temperature upstream of the workingsection; in contrast, the vacuum tunnel can draw air from the atmosphere, so that this requirement is met automatically. It ischiefly for this reason that vacuum tunnels are found much more frequently than are pressure tunnels. Yet another alternative to the more conventional types of tunnelis the shock tube, which basically consists of a long tube sealed at the ends, divided into two portions by a thin diaphragm so thatthe gas pressure in one portion of the tube can be raised well above atmospheric while the other portion of the tube isevacuated. When the diaphragm is ruptured a compression shock-wave travels down the previously evacuated portion of the
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
