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WE complete in this issue the publication of the scries of articles by MR. JAMES E. THOMPSON of VULTEE AIRCRAFT on “Designing for Machinability”; for permission to republish which from the pages of AERO DIGEST we are greatly indebted to the Author and Editor, MR. GEORGE F. MCLAUGHLIN. We have never read anything so informative and instructive on this subject, the importance of which for rapid production it is impossible to overestimate, and our admiration for it has increased with each re‐perusal of it necessitated by the repeated re‐readings called for in the various stages of proof correcting prior to final publication. We should like to see MR. THOMPSON'S introductory paragraphs, which appeared on page 289 of our October 1941 issue, posted up in large letters in every detail‐design office and we feel that the best service we can do is to reprint them verbatim here.

AFTER viewing the Messerschmitt Me. 110, one is impressed by the fact that here is an aeroplane provided with terrific striking power, but with practically no defensive armament or armour. The four machine‐guns and two cannon, tightly packed into the nose of the fuselage, provide heavy lire power, and contrast sharply with the single flexible machine gun supported on a primitive mount in the aft cockpit. A quickly detachable, external bomb rack designed to carry two bombs, apparently of the 500 lb. class, is provided for use on missions where attack of ground objectives, such as troop concentrations, would be the principal purpose.

DRILLING, REAMING, COUNTERBORING, THREADBORING, ETC. THROUGHOUT the design of every machined part the designer should follow the practice of visualizing the machining involved, and make a genuine effort to design for “machinability” by avoiding all difficult operations. This factor cannot be over‐emphasized, as it is only too easy to complicate the machining of a part unnecessarily by lack of forethought during the design.

Machine may bo defined as a machine tool which removes metal by causing the work, securely held in a vice or fixture, to be fed against a revolving cutting tool, called the milling cutter, having one or more cutting edges—usually several.

Grinding consists of generating an extremely accurate surface by applying a rapidly revolving abrasive wheel to the surface to be finished. Although it is generally thought of as a finish‐machining process, grinding often is employed as a complete machining process, in that the work is ground down from the raw stock condition to the finished dimensions without rough turning or other machining.

ANDREW Carnegie stands apart from all other library benefactors. No other man has given so much, or given so widely, in the cause of library progress. Although the United Kingdom was not the main recipient of his bounty, it received from him, personally, about £12 million, and considerable sums, in addition, from the Trust which he founded. It might well be expected, therefore, that his name would always be in our minds and that we would remember him more kindly than any other library benefactor. But it is not so.

13. In a vertical air speed responsive instrument, the combination of a chamber enclosing a substantial volume of air; a constricted passage connecting said chamber with the atmosphere; a differential pressure responsive member connected to respond to a difference in pressure inside said chamber and the atmosphere, respectively; a movable member connected to be actuated by said pressure responsive member; and an element responsive both to variations in pressure and temperature of the air inside said chamber and connected to increase and decrease the resistance of said passage to a flow of air therethrough upon a rise in pressure and drop in temperature, and a drop in pressure and rise in temperature, respectively, whereby said member will be moved in true response to a vertical air speed, irrespective of changes in altitude and viscosity of the air.

A hollow metal blade for a controllable‐pitch propeller having an integral base end flange formed to provide an annular thrust bearing race on one side thereof and a closely adjacent blade turning gear sector, on the opposite side thereof, and a closure member for the base end of said blade carried by said blade and formed to provide a thrust bearing surface opposed to the thrust bearing surface on said flange.

In a fastener for securing a plurality of supporting members together one of which employs a rotary pin provided with radial arms; a fastener element for co‐operation with said pin comprising a keeper on another of said supporting members and formed with an axial bore to receive the end of said pin and radial elongations connected to said bore to admit the passage of the radial arms, the opposite marginal edges of said bore and elongations within said keeper being inclined upwardly in opposite directions providing cam surfaces for engagement by said radial arms and a spring‐tensioned actuator associated , with said cams, means normally latching said actuator thereto under spring tension, and means for unlocking said actuator from said cam upon insertion of the pin axially in said keeper.

An aircraft retractable undercarriage comprising a landing wheel strut having pivotally articulated upper and lower sections, a landing wheel carried at the lower end of said lower section, said upper section being ipivotally mounted at its upper end upon said aircraft, a worm wheel sector fixed to said lower section concentrically with the pivot axis of said articulated connection, a worm meshing with said sector, a bearing rotatably mounting said worm upon said upper section to be positionally fixed thereto and to have its thrust axis directed generally upwardly toward the upper pivoted end of said upper strut section with the strut in extended position, a prime mover mounted upon said upper section adjacent the position of said worm and operatively connected' to the latter, and strut brace means pivotally connected to said strut and extending laterally therefrom into pivotal connection with said aircraft at a position spaced from said pivotal connection of said upper strut section.