FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1937
1937 - 1514.PDF
57' FLIGHT. JUNE IO, 1937. The force at any instant, in the machine's original direction, is ( —wv'/gr) sine, where 0 is the angle turned through at that instant. This is obviously a maximum when 6 = 90°, i.e., when the machine is half round the turn ; at this point the aeroplane has no velocity in its original direction (relative to the air), and has a maximum acceleration of — v2/r in its original direction. The only function of the engine is to keep the machine travelling at the uniform velocity v, and it has to supply no extra power for this purpose. 1 should also like to point out to Mr. Robertson that if the day had been calm and his machine had been doing 60 m.p.h. and had turned through 180° to do 60 m.p.h. in the opposite direction, the total change in velocity relative to the ground would still be 120 m.p.h., i.e., 60 m.p.h. —( — 60 m.p.h.), and exactly the same accelerating force would have to be applied by the air (if the aircraft made a turn of the same radius) as in the case when the wind was blowing at 60 m.p.h. Thus, it should be obvious that, as " Indicator " pars it, "no movements of an aircraft in a constantly moving mass of air can have any possible effects other than those which are made by the controls." IAN L. MCLAREN. Angus. Y OUR letters on down-wind turns are very interesting be cause of some extraordinary explanations. Perscnally, I think Mr. YV. E. Gray and Mr. Crcssley seem to hit the nail en the head fairly well, although Mr. Robertson should find that with his heavily loaded machine plenty of extra spied would be equally necessary for a turn into wind. As Mr. Gray points out, the fact that wind speed is greater at 100ft. helps a machine landing down-wind, but it also hinders it in climbing down-wind—on the other hand, it helps a climbing machine into wind, but when descending into wind it stalls quicker, because the stream of air moving towards the machine is slowing up as it approaches the ground. In other words, flying into wind near the ground helps a climb and quickens a fall, while flying with the wind near the ground is all wrong, anyhow. There is just another point of view I haven't heard men tioned—I should imagine that a gust of wind travelling across country would have a tendency to roll slightly near the ground on account of ground friction—in other words, it would have a depressing movement in front and a slight uplift at the back. Thus, a machine travelling down wind might con ceivably experience a long and steady fall with a sharp rise on striking the slower air in front. All the same, they should cancel each other out more or less, and in any case no two gusts are the same—one may be rising while the next may be falling towards the ground. A heavy machine would -be uncomfortable, anyhow, and it would be pretty terrifying turning down wind near the ground on a bumpy day, as Mr. Robertson suggests, simply because he would be facing the wrong way if he met a strong down- draught. P. PRIEST. Huddersfield. ALTHOUGH I do not remember having seen it in print before, the subject of down-wind turns is an old one which has in its time given rise to many heated discussions and not a few displays of the results of confused thinking. Mr. Robertson's argument (p. 553 last week) concerning momentum is best answered, perhaps, by asking him to imagine himself to be in a boat on a river flowing at five miles an hour and rowing upstream at such a speed that he is travel ling towards the source at five miles an hour; that is to say, his speed relative to the bank is five miles an hour. Now, if he wishes to travel downstream at five miles an hour will he turn round and row like—well, row hard? Or will he just stop rowing? It is not the momentum of the machine that matters, it is the change in momentum. If m is the mass of the machine, V its speed relative to the wind, and v the speed of the wind, the momentum before making the turn is m(V — v), and after making the turn the momentum is m( — V — v). Consequently the change in momentum is 2mV, which is independent of the speed of the wind. Of course, as " Indicator " says, this is true only if the speed of the wind remains constant. Since acceleration is a rate of exchange of velocity, the adjective "instantaneous" is employed correctly only when it is used to define a particular value of a variable rate at a given instant. I imagine, however, that when Mr. Maufe (p. 553) says that it is impossible for an aircraft to accelerate instantaneously he intends to convey the fact that a definite period of time must be occupied in the process of increasing or decreasing spsed by a given amount. This is correct, and it follows that his illustration of an aircraft turning suddenly into wind must be incorrect, since the act of turning involves angular acceleration Even were such a thing possible, there ssems to be some flaw in Mr. Maufe's argument. His glider is flying down wind at speed V relative to the wind, the speed cf the wind being v, his ground speed, therefore, being V + v. He now suddenly turns into wind, retaining, as he says, his original ground speed. He is, therefore, moving as before but facing in the opposite direction, or, in other words, he is flying backwards at a wind speed V, which seems to me to be a condition of flight so unusual that it borders on the in credible. J. D. BLYTH (Lt. Col.). Cheltenham. MR. BROOK AND RECORD BREAKERS I SEE, according to last week's Flight, that Mr. H. L. Boook has written to you regarding his '' hanging over the bar of the Royal Aero Club " statement. He falls back on the old defence of being misunderstood. I challenge him to plead that he was misreported. The facts are that he made that statement not only to me but to about a dozen other Pressmen when he arrived at Heston. Later, when we talked to him at Grosvenor House, I recalled what he had said. He then repeated the statement that he was convinced that unless one hung over the bar of the Royal Aero Club one did not get any bouquets, and elaborated upon it from notes which he had written on the back of his map in the machine. The state ment was definite and positive. If Mr Brook now regrets it he should not have said it. RONALD WALKER. London, E.C.4. IN BRIEF Mr. J. Myles Bickerton writes to warn other private owners of the activities of an individual who broke into his hangar at Denham and stripped his aeroplane, the booty including a Sperry horizon [£Cm), Husun compass (^25), Sestrel compass £10), Sidcot suit, flying boots and maps, and a bag of tools. "My instrument board was destroyed," writes Mr. Bickerton. " Whilst it is difficult to be grateful to the thief for not doing further damage by scratching paint or injuring the aeroplane in any other way, I am quite thankful he was air-minded! . As my groundsman already sleeps within 60 yards of the hangar it is going to be difficult to prevent such an ' accident' happening again " Forthcoming Events June 11-14. Hungarian Aero Club : International Conference. June 12. Bristol and Wessex Aeroplane Club : Garden Party, Whitchurch. June 15-20. Magyar Pilota Picnic, Hungary. ,'une 20. R.Ae.C. or Belgium: Gordon Bennett Balloon Race, Brussels. June 21-28. Federation Aeronautique Internationale : London Conference. June 26. Royal Air Force Display, Hendon. June 28 and 29. S.B.A.C. Display, Hatfield. July 1. Aero Golfing Society : Flight Trophy. July 3. Newcastle-on-Tyne Aero Club : Newcastle Trophy Race. July 3. Ramsgate Airport, Official Opening. July 4-18. Aero Club of Germany : Wasserkuppe Gliding Meeting. July 10. Cardiff Aeroplane Club: London-Cardiff Race. July 11. Herts and Essex Aeroplane Club: Air Display, Broxbourne. July 11. Italian Aero Club : Circuit of Rome. July 15. Aero Golfing Society : Jubilee Cup. July 17. Portsmouth Aero Club : Garden Party. July 17-18. Deauvllle Rally. July 23-August 1. Swiss International Meeting. July 24. Devon Air Dav and Race : Plymouth and Exeter. July 30-August 15. "Avia" Aero Exhibition, the Hague. July 31. Cinque Ports Flying Club : Folkestone Aero Trophy Race. July 31 -August 2. Yorkshire Gliding Club : Opening Meeting Sutton Bank. August 1-14. Yorkshire Gliding Club: Instructional Camp, Sutton Bank. August 3-September 7. Public Schools Aviation Camp. Norwich. August 6-7. Austrian Aero Club : International Rally, Lake Worth. August 14. Eastbourne Flying Club: At Home. August 14-22. Yorkshire Gliding Club : Open Contest, Sutton Bank. August 21. Thanet Aero Club: Aviation Meeting and Race. August 21. Midland Aero Club : " At Home." August 28 and 29. Cinque Ports Flying Club : Lympne Inter national Rallv and Wakefield Trophy Race. August 28-September 25. B.G.A. National Soaring Com petition, Great Hucklow. September 10-11. R.Ae.C. : King's Cup Race.
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
