The trend is to a natural taste ... so, this Christmas, give a cigarette that offers the true, natural taste offine tobacco. Give Capstan. CAJ»STAN' renects the trend to a natural taste l~Vbt1LVJll C.C.IIJA 426
I The Arm-Chair Pilot 11. Portable Polars N the last article - ON THE BEST SPEEO TO FLY - 1 considered some simple extensions to the standard theory of cross-countries, but none of these lessened the need for a compact, .accurate, universal calculator. Ideal'ly, a cockpit calculator should be able to give quick answers to problems that could be solved with the aid of the glider's polar curve and a set of drawing instruments. In general it is Fequired to relate the following variabies: height, distance, wind strength, lift or sink, thermal strength, air speed, and crQss-country speed, which are interdependent by virtue of the glider's polar. Some of these are dealt with by the best's~ed·to-f1y ring, and what is really needed is a supplementary calculator to d'eal with the glide path. Various designs are in current use*, but I hope thal some of the ideas in this article will encourage a fresh look at the problem of calculator design. I want to suggest that it may be fruitful to use linkages rather than the slide-rule principle, a linkage being a collection of hinged and linked rods subtly arranged so that attached pointers indicate the values of the related variables. One way of inventing such linkages would be to take a course in nomography, but since I have not done this I have been forced to think along different lines. The basic ingredient of a linkage ,calculator must be the polar itself, so the first thing to do is to conjure up a simple linkage which will trace the polar, transformed if necessary. For all practical purposes we may regard the equation *1 must apologize for the lack ~f references to other people's calCUlators, particularly to those described in earlie.t numbers of Si\lLPLANE AND GLIDING. This is due to the lamentable lack of back numbers on the boat on which I am travelling_ The mid-Atlantic environment must also be blamed for any errors and omissions in the ensuing argument. by ANTHONY EDWARDS 427 s = Av" + 131 v, where '\' is the sinking speed and 'v the forward velocity, as a satisfaetoTy approximation to the polar, but I know of no linkage which will reproduce this curve. We tberefore have to think of 'a "linkable" curve which fits this equation well enough. A. parabola with its axis vertical is a natural first choice, but it turns out to be a poor fit. An ellipse with one axis vertical is much better, and - in retrospect - is the perfect curve for our purposes because we only have to stretch the forward-velocity scale by the appropriate factor in order to achieve a circle, which is the simplest of all "linkable" curves. The required stretch may be found as follows. Consider tbe transformation v =:0 ku of s = Av 3 +Blv, and choose that value of k which makes drI du (the rate of change of the radius of curvature of the new polar (s, u) witb u) zero at the value of v for which the most accurate approximation is required. In this region the new polar will thus be approximated by a circle, and hence tbe old polar (.I', v) by an ellipse. It is easily found that the radius of the ci rcle, r, is given by (I + (3Ak 3 u 2 - Blkuz J2'),112 6Ak 3 u + 2Blkll 3 and that k 2 is V"(Av" - B) (Av· + B) (3Av· - B) (<strong>15</strong>A1'" + B) where II is vI k and v is the chosen velocity. _ For iIIustratiop, let us take A to be 3.7 X 10'· and B to be 82, which gives a best gliding angle of nearly I in 29 at about 40 knots, and a minimum sink of 2.1 f.p.s. at 33 knots. We would like the approximation to be particularly good in the region 35 to 75 knots, so we choose v equal to 90 fp.s., or just over 53 knElts, whence k 2 is 13.5 and r is 37.7 fp.s. on the scale of the sinking speed. The co-{)rdinates of the centre of the circle are easily found to be 39.8 f.p.s. sink and 51.1 Lp.s. forward velocity. The excellence of this approximation is shown in tbe table.
- Page 1 and 2: SAILP A & G 101 G December 1964 - J
- Page 3 and 4: SAILPLANE AND GLIDING OFFICIAL ORGA
- Page 5 and 6: 1964 -1965 T. has been a staggering
- Page 7: T Entries for World Championships H
- Page 11 and 12: TAIL WIND FIG.Z: MARKn PORTABLE POL
- Page 13 and 14: TATE GALLEllY 1740 W THE KRONFELD E
- Page 15 and 16: frustrating or even impossible, For
- Page 17 and 18: Pilot A B C D E FG Table I Distance
- Page 19 and 20: Memories of the Stone Age of Glidin
- Page 21 and 22: The Shaw Slingsby Trust HERE is sad
- Page 23 and 24: Monday, 6th July Task: a 212t-mile
- Page 25 and 26: liE pulley launch is based' ,on the
- Page 27 and 28: Our tow-car is a V-8 Fordomatic sal
- Page 29 and 30: cable drop. The puIley is left unat
- Page 31 and 32: small enough to be installed inside
- Page 33 and 34: with the transmitter, which necessi
- Page 35 and 36: 1956. at about mid-day, a big heap
- Page 37 and 38: Northamptonshire Northumbria Ouse P
- Page 39: on a piece of paper and had dropped
- Page 42 and 43: Camphill takes the Beer Tray by PET
- Page 44 and 45: ·WRIGHT Ft.NE QUALITY BUILDINGS --
- Page 46 and 47: CORRES·PON DENCE REVIVE THE WINCH!
- Page 48 and 49: "We have been to two such weeks, bo
- Page 50 and 51: It's almost like 80ating on air Tow
- Page 52 and 53: Adv~r'ist!menu, with remittance. sh
- Page 54 and 55: CLUB NEWS 'jb OUR Editor paid a mos
- Page 56 and 57: the Kite 1 77 km. to Plymouth to co
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mers have now all gone home express
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the site, together with the prospec
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flies Graham Smith completed his ba
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Grunau 2B 01 the Cheviots Club flie
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Peter Coldney sends this photograpl
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distance Ic:gs on his last flight w
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CANADA UEBEC Soaring Club reports:
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HOLLAND A FTER our Nationals five p
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August 11th, frontal air mass Free
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ous cockpit make it as comfortablt:
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I Bristol Gliding Club NYMPSFlELD,
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From the makers of Senior Service a
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