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Aviation History
1919
1919 - 0373.PDF
MARCH 20, 1919 It is futile to express resistance of any kind according to a iaw involving fractional indices such as— Resistance = KV" where n = a fraction between 1 and 2. as this value of n is gradually and continually changing as VI increases. The ultimate drag coefficients, i.e., those obtained when resistance is varying as V4, are now known faiily accurately for most forms of bodies, and the coefficient for any new form of body can be estimated by a consideration of these. A similar method of plotting is applied to wing research, although there is much more research work waiting L to be done OB wings than there is on body resistances. Plotting Out Laboratory Results on Airscrews. The older methods of plotting were to plot thrust and torque coefficients on a slip base. This has almost entirely V been replaced by plotting them on a base — when V = tians4ational speed of airscrew through the air, n the revolu" tions per second, and D the diameter of airscrew. V When the value of -= is fixed the angle of incidence of the relative wind to any section of the blade is also fixed, and so the thrust and torque coefficients will likewise be fixed, subject to variations due to viscosity, which, on account of the relatively high speed of the blades through the air as compared to other objects, may be neglected for all practical purposes. At first sight it appears immaterial whether the coefficients V nD be plotted on a base -= or —- . The list of coefficients m- wD V dicate that there are three different types of coefficients, each for thrust torque and power, and it is here intended to indicate the best base on which to plot them. Taking for example thrust coefficient (b) T/ = —^U-. pn XJ Suppose n and D be fixed while V is varied, then T/ will V be proportional to thrust, — will be proportional to V. V Therefore if TS be plotted against ^= the curve will show how thrust varies with velocity, other things remaining the same. Now take Tc = vsn« • if V and D ^e kePt t^e same while » be varied, then the true connection between thrust and revolutions, other things being unaltered, will be represented mm nD V by a curve T, plotted on a base of -r=- and not -=- as has been y done frequently. The plotting of T, on a -=- base and T, ' wD nD . on -y- is meaningless. Similarly T/'= thr^4t/w! should be plotted on ?P base, as it then shows variation of thrust with diameter when the speed ratio is constant. The same reasoning applies of course to the torque and power coefficients. Sometimes it is found convenient in performance calculations V V to plot airscrew results on —- base instead of -^, where * = r np nD r V experimental mean pitch of the airscrew, i.e., p = —, when the airscrew has no thrust and is merely '* floating." As regards methods of plotting the coefficients, what has been V V said with regard to -= corresponds also with —. The nU * np coefficients, however, are still referred to D not p. It niay be noted that most airscrews have their maximum efficic-ncv V at — = -75 approximate. Summary of Recommendations. 1. Universal use of absolute coefficients. 2. Adoption of standard body axes in accordance with N.P.L. practice. 3. Adoption of ~L.C lettering in preference to ¥Lt. 4. Adoption of thick type L for Lift in printing and double stroke L for typing. 5. T for Thrust, Q for torque, D for dia. and p for pitch of an airscrew. P for pressure. H for power, n for revs, per sec, XYZ forces along body axes, LMN moments round corresponding body axes. T0 Tc', T/' notation for the three kinds of airscrew coefficients. 6. That fractional indices as n in V" be abolished for all work even in so-called^skin friction experiments. 7. In airscrew workifce/plot:— •mDi • To Q>, H„ n H, on .^r'base. ; T/, Q>', H/, if He' on ^ base". , " nD " ' ' T,",Q>",H", 7, H/' on ~ base. $> <s> <•> <$> A Sop with Entry for " Daily Mail " Prize THERE is now another British competitor for the Daily Mail trans-Atlantic prize, a Sopwith machine having been entered by Mr. R. O. Cary, managing director of the Sopwith Aviation Co., Ltd., on Tuesday. The biplane, which will be piloted by Mr. H. G. Hawker, accompanied by Lieut.- Gomdr. Mackenzie Grieve, R.N., as navigator, is of 46 ft. 6 in. span, and is fitted with a 375 h.p. Rolls-Royce " Eagle" engine. The special features include a 400-gallon petrol tank, which it is estimated will hold enough for a 25-hours' flight, and the arrangement of the top of the fuselage to form a lifeboat, when detached. Mr. Hawker, with Commander Grieve", in a trial recently covered 900 miles in 9 hrs. 5 min. Mr. Hawker, Commander Grieve and the machine left Liverpool on March 18 for Newfoundland. They propose to leave St. John's at 4 p.m. (American time) one afternoon and hope to land, at Brooklands at 4 p.m. (Englisk time) the next afternoon, a flying time of 19J hours. > The R.A.F. Paris-London Mail IT is authoritatively stated that the R.A.F. Paris-London mail and passenger service has been very successful. Though confined to the carrying of urgent official mails, and passengers on business in connection with the Peace Conference, it*has also served as a medium'"f6r obtaining data and experience, which will prove of great value in the near future, for es tablishing regular mail and passenger services for civilian purposes. The R.A.F. detachment carrying out this work, officially known as No. 2 Communication Flight, is situated a few miles outside Paris. The machines used are Handler Pages arid D.H.4's. Each morning a weather report is telephoned from England, as well as from the meteorological station in France, and as a result of this the orderly pilot telephones to the Headquarters of the British Peace Commission and states whether flying is feasible and whether it is desirable to dispatch mails or passengers. If the report is favourable the mails and any passengers are at once sent out to the aerodrome by car, the machines usually setting off about 9 a.m. If the weather is unfit for flying no time is lost by this arrangement, and the mails are dispatched by the morning boat train. The departure of each machine is telephoned to London, and when the plane arrives at Hendon a King's messenger is waiting to take the mail bag direct to Whitehall. The average time taken for the trip is 2J hours, while the " re cord "is 1 hour 50 min. This was set up by a pilot who made the two-way journey in 3 hours £0 min. Some Distinguished Passengers -,fr . As showing the saving of time effected it may be noted that on March 16, Mr. Bonar Law was in conference with the Prime Minister in Paris at 10.30 a.m. An "hour later he left Paris on a D.H. 4, landed at Hendon at 1.55 p.m., and at 2.15 p.m. was in his£*tfdy in Downing Street. Gen.: Seeley On Saturday), iftew from Folkestone^ tq.Paris in the fast time,of 1 h. 14 rhln.'for the 172 miles. v> ' - On Wednesday lastMr. J. H. Thomas, M.P., availed him self of a Handley-Page machine to go to Paris in order to discuss the industrial trouble with the Prime Minister, while Mr. H. B. G. Larkin, of the Commonwealth Government line of steamers, went by the air way to Paris to confer with Mr. W. M. Hughes, the Australian Prime Minister. 373
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