PEOPLU who are not conversant with aircraft manufacture and all that it entails sometimes express surprise at the high cost of machines. They point to an aeroplane, which they may describe as” a lot of wood., a lot of fabric, sundry metal bits and, an engine,” and, then turn to the popular, comprehensively

equipped car, and, demand to know why there is so much divergence in the respective prices. That the former probably represents a month’s total output of a factory while the latter is produced on a colossal scale may be accepted as a partial explanation, but one needs to go further into the sub

ject before the inquirer becomes satisfied that the modern light aeroplane is something more than a winged, packing case, priced at an exorbitant figure. No one can deny that the modern cheap car is astonishingly well-made and re

liable, but the workmanship and material put into it cannot possibly compare with that fotuid in aircraft production. Quality of raw material, care in its selection, and extreme accuracy in manu facture are the basic rules in British air craft building ; only by adherence to these can reliability and safety be ob tained, and no better way could be found, of showing the uninitiated to what pains the manufacturer goes in securing these vital qualities than a visit to a works ; the British Salm.son works, for instance. Of French origin, Salm.son engines were first made many years ago, and a charac teristic is that they have always been of the radial type. In modern times, the most famous unit turned out by this con

cern is the A.D.9—the little 40-50 li.p. nine-cylindered engine which is fitted to the Klemm monoplane, the Mon,ospar

experimental maculae, Hinkler’s ” Ibis,” and a number of French light ‘planes. This engine is now being built in this country by the British Salnason. Aero Engines, Ltd., at their very modern factory at New Malden, Surrey, on the Merton by-pass road. The English version of the A.D.9, besides being British-built throughout,

has sundry modifications embodied in its design, such as dual ignition, and from start to finish its manufacture is unusually interesting. The cylinders emerge from the “rough stores in the form of forgings, to go through a series of operations which result in their reaching a stage when they are

machined. all over with cooling fins, and valve openings in the domed head in the finished state.

During the whole of the machining of all parts, compressed air is used, to dispel the swarf in order that the very fine limits with which the operations a r e carried through may not be varied in the slightest degree. Thereafter, the cylinders pass to another section of the works when the in,auction, and exhaust passages and rocker-arm posts are welded on to the heads. The passages are made of sheet steel, and therefore have perfectly smooth internal surfaces. The next step is the tinning of the head, prior to casting the aluminium fins on it. This is an interesting and intricate operation; the cylinder is placed in a mould, after being heated up to a prescribed temperature and the aluminium is poured in. The mould used is made of a special sand compound, and is so hard, after being baked, that it will even withstand

being dropped on a concrete floor.

The crankshaft (which has a singlethrow), like the cylinders, is received at the works as a rough forging, and each one has a “test piece” cut from it which is checked and examined. in the works inspection department. The shaft when completed. is hollow, and has an oilway drilled diagonally through the rear web. The connecting rod assembly consists of

one master rod and eight auxiliaries ; the latter are attached to the solid big end of the master rod by the usual wrist pins. The valve gear of the A.D.9 comprises a cam ring which carries ten cams in two rows ; it is driven at I /10ths engine speed through a train of epicyclic gears. The cutting of the internally toothed rings in, this assembly is a wonderful piece of work, and. the meshing is so fine that there is no semblance of back lash whatsoever.

In the crankcase one finds a further example of the high standard of workmanship which characterises the whole of the British SaLmson,. Formed in, two sections, it is made from an aluminium alloy, with internal and external webs for stiffening purposes. In order to obtain perfect oil-tight joints the cylinders are first of all lapped onto their respective flanges, before the holding-down studs are put in place. The front half of the crankcase carries the valve gear and to the rear half are attached the oil pumps, magnetos and induction ring. The oil pumps which, like all the other parts of the A.D.9, are made in the New Malden works, are of the gear type, and they are driven from the tail shaft of the engine. The pump assembly undergoes a separate test before being attached to the power unit. If the visitor to the Salmson works is impressed, with what he sees in the num facture of the A.D.9, he will undoubtedly be further so on learning of the Air Ministry “type tests” which the engine had to pass before acceptance. Attached to the works lit a test shop, and here the engine was installed on a dyanamometer to undergo its trials, the intensely searching nature of which is revealed in the following list : After a preliminary power curve run—

Two periods of 10 hours each on 9/10ths full throttle with a final run of 5 minutes at full throttle.

Two periods with calibrated air screw at 2,100 r.p.m. (the A.D.9’s maximum r.p.m. is 2,200) of 10 hours duration each.

Two periods—one of 9 hours at full throttle and 1,955 r.p.m.—the other, of 1 hour at full throttle and 2,100 r.p.m.

A slow-running test of 10 minutes at 460 r.p.m., an acceleration test, and a high speed test at 2,430 r.p.m. for 1 hour.

The unit which was submitted for these tests behaved perfectly throughout and required no adjustments or replacements of any sort ; which entitles the British Sa1mson to take its place in the circle of really good aero motors.