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Aviation History
1932
1932 - 0215.PDF
FLIGHT, MARCH 4, 3 932" THE INDUSTRY MODERN AIRSCREWS F OR MANY YEARS past there has been in evidence a ten dency for airscrews to be manufactured from other materials than from wood. Wood has held the field, though not entirely unchallenged, since the earliest days, but it must be admitted that it has certain serious disadvantages. For example, flying through hail or dust storms may easily be disastrous if the airscrew being used is of wood ; furthermore, extremes of temperature and rapid changes of weather often mean that trouble ensues. Both steel and duralumin have been tried with varying degrees of success, as well as moulded material, such as " Micarta." The former are used in a variety of forms, among the most ingenious being ihe hollow steel bladed types made by Metal Propellers, Ltd., Purley Way, Croydon. Hollow Bladed Airscrews These airscrews are made under patents originally taken out by Mr. Leitner and Dr. Watts, and result in an airscrew with detachable blades connected at a hub which allows an iniinite variety of blade setting for pitch. The blades are formed from a series of laminae which, in the first place, are pressed together to form a half-blade. This is done (as shown in our illustration) in a large press, and the firm now have a range of dies providing suitable sized airscrews from those huge ones used for the engines in R.101 down to those for the Hermes or Gipsy engines of light aircraft. After the half-blade has been pressed to its correct sectional form, it is paired with its " opposite number," and 1!ie two halves are tack-welded together. Further operations include welding on the ring by which the blade is secured in the boss, final welding along the join of the two halves, balancing and heat-treating. The balancing is most carefully done, each blade being not only balanced in the ordinary fashion on a horizontal balance, but also on a vertical balance, thus ensuring that the two blades are perfectly matched. For this purpose the tips of the blades are left unwelded until the final balancing, thus allowing an easy means whereby the balance can be achieved. Large numbers of these airscrews are in use by the R.A.F., especially abroad, where they have been found to stand the climate excellently. Stainless-Steel Blades In the past it has been necessary to repaint the blades fairly frequently if the metal had been laid bare due to safety for the same weight or, alter natively, a lighter airscrew for the same factors. Duralumin Blades Steel is, however, not the only material in use at this factory for the manufacture of airscrews, for some of the latest are being turned cut in duralumin. These are made from forgings, and the same type of hub as used for the steel airscrews is being retained. Such a construction allows On the left is the great press at the works of Metal Propellors, Ltd., for forming the halves of the airscrew blades. For small airscrews only two rams are used. On the right is the heat treatment furnace with a canister, in which the blade is slung, ready to be lowered down the shaft of the furnace. (FLIGHT Photos.) flying through rain or dust, as other wise a rusty surface resulted. This has now been overcome through the use of stainless steel. An airscrew with blades made from this material is at present under test, and the re sults so far obtained go to show that great things may be expected from this new departure. The use of rust less material makes it unnecessary to protect the surface in any way, as use will always keep it bright and clean ; moreover, this metal has a higher ten sile strength than has the steel normally used, and it will therefore be possible to obtain higher factors of of the blade root being designed for maximum efficiency, and the section remains almost of the same thickness from the middle of the blade right down to the boss. By this means it is hoped to secure far greater efficiency than has hitherto been found possible, since the root losses are thereby kept down to a minimum, while at the same time the use of the standard hub makes it possible to adjust the pitch of the blades. Other Activities Stainless steel and its application is a subject of the greatest interest, and The airscrews made by Metal Propellors, Ltd., are built up from a series of steel laminae as shown above. A half blade after pressing can be seen on the left. 199
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