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Aviation History
1929
1929 - 0213.PDF
JANUARY 31, 1929 THE AIRCRAFT ENGINEER SUPPLEMENT TOFLIGHT cent., is sold in Germany to-day under tlie trade name of " Motalin," for use in high compression engines. Unfortu- nately iron carbonyl as an antidetonant has several disadvan- tages which, up to date, have not been overcome, the major one is that the sparking plugs are affected by an accumulation of iron oxide on the insulators which results in shorting. In the case of tetraethyl lead the halogen bearer results in the production of a volatile lead compound which is readily expelled from the cylinder through the exhaust ports, no such equivalent has yet been discovered for iron carbonyl, and thermo-dynamic investigation suggests that there is little chance of so doing. Nickel carbonyl is another efficient antiknock of the metallic compound group. However, here again there are serious disadvantages in its use which have so far not been overcome. Firstly, the cost is high and %\ times as much nickel carbonyl by volume is required as is of lead tetraethyl to achieve similar results. Secondly, the resulting deposits in an engine using a nickel-treated petrol are deleterious, thej being of a hard gritty nature which, of course, would cause excessive wear and tear in the engine. No chemical reagent has as yet been found to alleviate this trouble in use. Also nickel carbonyl is extremely unstable. It is a curious fact that all very effective antiknocks are poisonous, nickel carbonyl, iron carbonyl and tetraethyl lead being of the same order in this respect. In fact, someone has defined an antiknock as a substance which is " expensive to make and poisonous."' One other antiknock compound not mentioned is thalhum ; a British patent has been granted to the Asiatic Petroleum Co. Ltd., and Mr. A. C. Egerton for this invention. Several methods are suggested in this patent to utilise thallium or a compound thereof to prevent detonation, one of them being to introduce by some means a vapour of thallium into the cylinder. From a practical point of view it is rather doubtful whether any great measure of success is likely to be met with by the use of thallium as an antiknock, the difficulties of the method of application being far from easy to overcome. The Dupont Chemical Corporation, at Wilmington, Del., are manufacturing tetraethyl lead under very strict super- vision and with entirely adequate equipment. Medical examination of the personnel is insisted on and closely adhered to. The plant is of the most up-to-date type and ventilation is as nearly perfect as possible. At the present moment this product is turned out in considerable quantities with abso- lutely no risk or trouble. In 1925 the daily output was 1,000 gallons of tetraethyl lead per day, and 1 gallon is sufficient to treat 1,500 gallons of petrol. During the last two and a half years no poisoning has occurred among employees in the tetraethyl lead plant. The manufacture of tetraethyl lead is as follows : Lead and sodium are smelted together to form a lead sodium alloy which is pigged and crushed to a coarse powder. The pow- dered alloy is then put into autoclaves with heat control, and gaseous ethyl chloride passed over it, the resultant products are crude tetraethyl lead (PbEt4) and sodium chloride. The liquid tetraethyl lead is drained off and steam distilled, the vapour being caught and condensed. The distilled tetraethyl lead is then passed through to storage tanks. The filtered tetraethyl lead is then blended with ethylene-di- bromide and halowax oil which has the distinctive red analine dye dissolved in it. The blended fluid is then filled into drums, the rilling being conducted in draught chambers to prevent escape of vapours and the hose lines all carry canvas bag filters. The concentrated ethyl fluid is now made in one mixture, consisting of 54-5 per cent, tetraethyl lead, 36-4 ethylene dibromide and 9 per cent, halowax oil. The specific gravity is 1-79 at 20° C. It is entirely soluble in petrol and does not settle out. The fluid is poured into 50-gallon steel drums, very carefully sealed and shipped from the factory at Wilmington to the refineries of the various oil concerns. At each of these refineries is erected a bulk blending mixer, which device automatically mixes the fluid with the petrol in proper proportion, delivering straight into a large storage tank without allowing the concentrated fluid ever to come in contact with the air. The United States Airships " Shenandoah " and " Los Angeles" with Packard and Maybaeh aero engines res- pectively, used a mixture of aviation petrol with 8 cc. and 11 cc. of ethyl fluid per gallon. For any long distance flights, such as the Honolulu flight on PN9 machines, ethyl fluid was carried in small steel containers so that the fuel picked up en route could be properly treated to give it the necessary antiknock value. Capt. Mackintosh and Mr. Hinkler, during their recent non-stop flight attempt to India, adopted this latter method in case of forced landing where suitable fuel would not be procurable. The United States Naval Air Service think very highly of this fuel, and it is used to a large extent in their standard aircraft. It is by now quite well known that the British entries for the 1927 Schneider Cup air race were using concentrations as high as 10 cc. of ethyl fluid per gallon of aviation and benzol. The British Air Ministry and the Bristol Aeroplane Com- pany, have done now a considerable amount of experi- mental work; however, the results obtained are not as yet procurable for publication, although it has been intimated that they are of a satisfactory nature. At one time it was believed that there was a limit to the quantity of fluid which could be added to a gallon of petrol without giving trouble, but later experiments seem some- what to refute this opinion, it now being possible with careful manipulation of various spirits and various concentrations of this fluid, to achieve excellent results in very high com- pression engines, ratios as high as 9-5 to 10:1 having been used successfully. However, these higher concentrations are not advisable or necessary for the average automobile engine. 3 cub. cm. of tetraethyl lead per gallon of motor spirit is considered ample for ordinary purposes. Com- pression ratios as high as 6-5 to 1 can be used quite satis- factorily on this blend. These latter remarks are of necessity subject to considerable latitude, especially as ordinary petrol varies very considerably in its antidetonating qualities. IN THE DRAWING OFFICE. DETAIL STRESSING. By H. PAEKIKSON, A.R.Ae.S.I. Since the innovation of all-metal construction, designers have been, and still are, faced with an increasing number of " aristocratic " metals which necessarily have varying stress figures and therefore require individual consideration. In the D.O. where the major portion of detail stress work is carried out, the draughtsman, in personal experience, prefers to do his figure juggling through the medium of tables arranged on a labour- and time-saving basis. The following table is computed for an hypothetical mate- rial having stress values of: fb = 10 tons • ins., ; ft = 10 tons, n ins.; fs = 10 tons, • ins.; and is arranged such that for any given material the fb, fs and ft values, within the limits enumerated, may be obtained by a simple proportion of required and hypothetical stress-values. Example 1. Required : shear and tensile strength of ^-in. diameter M.S. bolt, For M.S.: fs = (say) 25 tons, • ins. : ft = (say) 30 tons• ins. From table, fs or ft = 4,398 lbs.25 fs J-in. diameter M.S. bolt =^X 4,398 = 10,995 lbs. 30 ft fin. diameter M.S. bolt = ^ X 398 = 13,194 lbs.
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