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Aviation History
1925
1925 - 0456.PDF
JULY 16, 1925 of the Royal Aeronautical Society, by Sir Henry WhiteSmith, who proposed that for any future light 'plane com- petitions entrants of machines should be required to statethe price at which they were prepared to sell their machines in batches of 25 or 50. All we claim to have done is to takethis suggestion and to incorporate it in the scheme outlined in the following notes. Briefly, then, the scheme is asfollows :— 1. Limit the engine power by placing a limit of 325 lbs. on the weight of the engine itself plus the fuel andoil jit consumes in four hours at full power. 2. Awarding marks for whatever performances are thought to be desirable.3. Divide the number of marks so awarded to competitors by a figure representing, either directly or otherwise,the price at which entrants are prepared to supply their machines in batches of 25. It is, of course, realised that such limitations would necessi-tate the very closest co-operation between engine designers and aircraft designers, since no aircraft manufacturer wouldbe able to estimate figures of cost unless he knew definitely the price at which he could obtain the particular engine hewas using. This, however, would by no means be an evil, and in the past there has, we are afraid, been too little co-operation between the engine designer and the aeroplane designer. It is, of course, evident that there would be diffi-culties in committing oneself to such a figure of cost, and in any case this figure would very largely depend upon the attitudeof the Air Ministry. To a great extent it rests with the Air Ministry itself to bring the price of machines down by leavingaircraft constructors a free hand in the choice of materials and in the particular use made of the materials. Certainmethods of construction are now banned by the Air Ministry which are giving excellent results elsewhere. A case in pointis the Fokker system of welded steel tube fuselage construc- tion. We mention this particular case not because we neces-sarily regard this form of construction as being particularly suitable for light 'planes, but as an instance of how theAir Ministry, by vetoing a cheap form of construction, is preventing cost from being reduced. Another stumblingblock to cheap construction is the insistence by the Air Minis- try of inspection of every part that goes into an aeroplane.Until all these stupid restrictions are removed there is little hope of getting the cost of light 'planes down to reasonablefigures. If the Air Ministry is really serious in its desire to popularise aviation, then it could do so in no better or surerway than by withdrawing all interference with the manu- facturers. As we have repeatedly pointed out in FLIGHT,British aircraft firms can be depended upon not to turn out unsafe machines. The reputation of a firm is something whichno sane man would jeopardise for the sake of being able to save a few pounds, but, if left to themselves, we are quite sure thatBritish aircraft designers and constructors would be able to produce light 'planes of ample strength in every way, simplyby devising methods of construction different from those at present in use. All that is required is that they should not behampered by official interference. •% Doubtless, the costing departments of the firms wouldhave rather a hectic time, and it would obviously not be possible for firms to state their price when first entering themachine, nor should there be any need for them to do so, although the statement of cost should, of course, be madebefore the actual start of the competition. To remove any uncertainty, it would obviously be necessary, or ratherdesirable, that the Air Ministry should commit itself to order- ing a batch of the machines gaining the highest award, andto encourage the cheap machine to some small extent, it might be advisable to put in a clause to the effect that wheremore than one machine obtained the same number of marks, the prize should go to the machine selling at the lowest price.It is, of course, somewhat difficult to forecast accurately how such a scheme would work, but, in order to obtain someidea, and so as to get a basis for discussion, we might assume that the competition itself would be of the same nature asthat held at Lympne last year, i.e., marks awarded for greatest speed range, quickest take-off, and shortest pull-up. Notthat we necessarily consider that this is the best possible method of comparing performances, but for the time being itwill serve as a basis. The speed range in last year's competi- tion was, it may be remembered, based upon the formula V max. — Vmin. n-S3 V min.in which V max. is the top speed and V min. the low speed. It was stipulated that the low speed must not exceed 40 m.p.h.and no marks were awarded for a speed range of less than 33 per cent. For each m.p.h. speed range, expressed as a per-centage, eight marks were awarded. In the take-off competi- tions machines had to clear an obstacle 20 ft. high in theshortest possible run, and one mark was awarded for each yard by which the distance required was less than 450 yds.In the pull-up competition, machines had to come in over an imaginary hedge 6 ft. high, and pull up in the shortest possibledistance beyond the hedge, one mark being awarded for each yard by which the distance required to pull up was less than150 yds. For the purpose of our argument, let us suppose that thesame kind of competition under the same rules is being held next year, and then let us examine how our suggested scheme.might be expected to operate. If we take as an average light 'plane (in the more modernsense of the term, as indicated by the limit of 325 lbs.), one having an engine of 60 b.h.p. To be within the 325 lbs.this engine could have a weight of 3 lbs. per h.p. (180 lbs.) and a consumption of 0-61 lbs./h.p./hr. It seems reason-able to suppose that with this horse-power and, without going into ultra-refined design, a top speed of 80 m.p.h.could be obtained. If we assume that the low speed of this machine was 38 m.p.h., the speed range would be 42m.p.h., and the number of marks awarded would be 620. If we further assume that this machine could clear theobstacle with a run of 250 yards it would gain a further 200 marks. By pulling-up in 70 yards the machine would gain80 marks, or a total of 900 marks. If it is further assumed that such a machine could be sold in batches of 25 at £750,the " figure of merit," which we may term the number of marks gained divided by the price, would be ^—- =1-2. / oOAt the upper end of the scale we should have a machine designed as efficiently as possible, with an expensive efficientengine. It may be supposed that by careful design such a machine, if fitted with an engine of 75 h.p., weighing 2-25lbs. per h.p. (169 lbs.), and having a consumption of 0-515 lbs./h.p./hr., could obtain a top speed of 95 m.p.h., and ifwe assume that the low speed was the same as before, i.e., 38 m.p.h., the speed range would be 57 m.p.h., and thenumber of marks would be 930. If such a machine could clear the obstacle in 200 yards it would obtain 250 marksfor take-off, and by pulling-up in 70 yards it would gain 80 marks, or a total of 1,260 marks. In order to obtain thesame " figure of merit " as our " average " machine, the price of the refined machine must not exceed £1,050, and itseems rather doubtful whether such a high-quality machine could be built for less. At the other end of the scale let us examine the cheapmachine, in which a good " figure of merit " is aimed at by a low price, rather than high performance. An engine of 50h.p., weighing 3-75 lbs./h.p. (187-5 lbs), could have a con- sumption of 0-685 lbs./h.p./hr. The top speed might be70 m.p.h. only, and the low speed 40 m.p.h., giving a speed range of 30 m.p.h., and an award of marks for a speed rangeof 340. As such a machine would probably have a con- siderably higher power-loading it seems reasonable to supposethat its take-oS would require 300 yards, so that the marks gained under this head would only be 150. There is noreason to suppose that the pull-up would be any worse, and, therefore, we may take that to be 70 yards, giving 80 marks.Thus for the cheap machine, with the performance outlined above, we should obtain only 570 marks. To give the same" figure of merit " as the " average " and the " refined " machines, the cheap machine would have to sell at £475. Assuming these figures to be roughly representative of the" refined," " average," and " cheap " types of machine, designers would be free to decide for themselves which typewas the more likely to attain the higher "figure of merit," and of the three it would seem that if a two-seater capableof doing 70 m.p.h. for four hours could be produced for £475, it would meet the requirements of light 'plane clubsand of most private owners. On the other hand, there is no reason why the probably smaller number of clients whowould prefer a more " sporting " machine, and who would be prepared to pay £1,050 for a machine that would givethem a top speed of 95 m.p.h., should not be catered for, so that any firm deciding to build this type of machine forthis class of customer would be at liberty to do so if it was considered that, with the power of 75 h.p., the assumedperformances were attainable, and that the machine could be built for a little over £1,000. It thus seems to us that thescheme, or some such scheme, would definitely tend to limit the power and the cost of light 'planes, and thus it is, wethink, worthy of some consideration by those who will be responsible for the future of light 'plane development inGreat Britain. We do not by any means mean to suggest that this schemeis perfect, and, personally, we regard it merely as a basis 456
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