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Aviation History
1909
1909 - 0804.PDF
DECEMBER II, 1909. FABRICS WANTED. To the Editor of FLIGHT. SIR,—I should be much obliged if you would put the following query in your valuable paper : " I should be obliged for the names of firms manufacturing clothing, ' coats, &c.,' out of vulcanized or oiled silk fabrics to communicate with the address below, and send small sample pieces of fabric in the different shades stocked, and also let me know full particulars as to price, &c. This would much oblige one of your constant readers who has difficulty in getting what he requires." Yours truly, 22, Hoole Road, Sheffield. HORACE CECIL LAW. ELASTIC MOTORS. To the Editor of FLIGHT. SIR,—Having noticed the difficulty in obtaining a satisfactory elastic motor for models, I enclose a design which may be of interest to those who wish to make models with as little expense as possible. This sketch will give a good idea of the method of construction. Although it is only a very simple, and quite original idea, I found it to work beyond my expectations. I am thinking of making one with a small gearing arrangement, as in Fig. 2. Wishing your valuable paper every success. Yours faithfully, Askern Spa. C. BELLAMY. FLYERS AND INTER-CLUB COMPETITIONS. To the Editor of FLIGHT. SIR,—Of the many ways in which it is possible for the various' clubs and societies devotfd to aeronautics to encourage the produc- tion and use of first-class British flying machines, let me commend the following :— Each club should concentrate its energies, mechanical, expert and financial, upon the production of a club aeroplane, and make it the club's representative machine in a great inter-club match next season. The machine should be designed by a member or members of the competing club. It should be clear of all published patent claims from abroad. It should be entirely British. Let the clubs foster their own members' ideas, and assist them to patent an€ construct, after submitting plans to a committee of experts appointed by the club. Other members might advise or submit plans, but let it be done through the committee of experts, pledged to secrecy. The committee's choice to be the club's aero- plane, and the property of the club if they pay for it. The patents to be the inventor's. When this scheme was outlined before a certain aero club at their general meeting, it was received enthusiastically, and club secretaries might learn the attitude of their committees and make it known in a report to this paper. Yours faithfully, Fawley. THEO. OSBORN SMITH. VARNISH FOR AIR-PROOFING. To the Editor of FLIGHT. SIR,—We notice in your issue of December 4th that one of your correspondents, Mr. E. Phillips, of Balham, is asking for a varnish to air-proof calico. We would recommend the varnish shown in our price list at Is. per tin, which we are sure would answer his purpose very satisfactorily. This varnish is not heavy, but is very durable and tough when dry. Yours faithfully, THE AUTOMOBILE AND AERIAL SUPPLY CO. Norwich Union Buildings, St. James's Street, W. PROPELLER CALCULATIONS. To the Editor of FLIGHT. SIR,—Your correspondent must have been misinformed when he was told that a 3^ ft. propeller will give 75 lbs. thrust when driven by a 6-h.p. engine. From experiments I have made 1 find that it would be impossible to obtain that result from such a small diameter fan. If your correspondent would state the velocity of the air current given off by the propeller it would be a simple matter to estimate the horse-power in the air-current, but this will not exceed 75 per cent, of the power applied to the shaft. The thrust of a propeller must be caused by the reaction of" setting a given weight or number of cubic feet of air in motion, in the same way that the velocity of a falling body is produced by the- force of gravity. To produce a velocity of 35 miles per hour requires a fall of 40 ft., therefore every lb. of air that passes through the propeller must have 40 ft.-lbs. of energy applied to it. Take the diameter of a fan 3J ft. = 96 sq. ft. area, deduct 33 per cent, for centre, which is not effective, leaves 6-4 sq. ft. 6'4 x 51-3 x -o8 x 40 = 1040 ft.-lbs. air delivered per second. IO4° • - = 20-o lbs. thrust.51 J App. 3-h.p. net. Obviously, 35 miles per hour is not suffiaient to give the desired thrust. But with a fan of J,h ft- diameter, giving 6"4 ft. effective area, we shall require a velocity of 66J miles per hour to produce a thrust of 75 lbs. ^ , -,, , 75 x 66'5 x 1760 x 3 Consequently net h. p. will be 60 x 33,000 = I3'3 h>p- and gives h.p., or power applied to the shaft, at 75 per cent, efficiency = 177 h.p. to produce a 75 lb. thrust. With a similar calculation a 6^ ft. diameter fan, with a delivery of 45 miles per hour, will give a thrust of 107 lbs. and require a gross h.p. of 17*1. I am afraid your correspondent would lead your readers to seriously^ underestimate the power required to drive a flying machine, and I think if your other correspondents will compare these figures with, practical results they will be found to be much nearer the mark. The formulae for calculating these results are :— A = Area sq. ft. covered by propeller in motion. •08 = Weight cu. ft. air lb. V = Velocity ft. per sec. of air delivered by fan. V* Thrust °8 " 64-4 x V x 32 = thrust in lbs. 9000 Bucks. '- = Gross h.p. applied to shaft, assuming. 75 per cent, efficiency. Yours truly, W. LEA WYNN. [The above letter in emphasising the law of action and reaction in its application to aerial propulsion, strikes a true note in aero- dynamic theory, and should be carefully read by all who wish to- study the fascinating problem of propeHer design.—ED.] " SURFACING." To the Editor of FLIGHT. SIR,—As a regular subscriber to your invaluable paper I crave space for the insertion of this letter, in search of information. In model aeroplane making I find it a somewhat difficult task to stretch Japanese silk on the planes, &c. ; the majority of my models, so covered tend to curl when the adhesive is dry. , Perhaps one of your readers could oblige by explaining a method '•«^' <-v>» «'t "o" v>» " laid" satisfactorily. Thanking you inwhereby the silk can be anticipation. Lowestoft. Yours faithfully, L. E. RICHARDS. [The stretching and laying of surface material is one of the most awkward jobs associated with the construction of flyers, whether they be models or full-sized machines. We have even heard of a case where it has taken seven men as long as five weeks to cover a monoplane. R. J. Macfie covered his flyer in a day and a half with four men, by using " formers " or shaped frames on which he stretched the Continental fabric in advance. The frames were so built that they could be applied to the machine in such a manner as enabled the fabric to be fastened down while in its stretched condi- tion. Apart from mere convenience of handling, R. J. Macfie claims for his system that it enables the fabric to be stretched evenly, which is the great secret of success. We hope our readers who have experienced our correspondent's difficulties will offer advice.—ED.] 806
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