Volume 8 No 3 Jun 1957.pdf - Lakes Gliding Club

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*Chosen alikefor theGLIDERTRAINERFIGHTERBOMBERAIRLINER• • •because of theirRELIABILITYLONG LIFEACCURACYECONOMY[ PULLINI ELECTRICALI1 TURN AND SLIP INDICATORSR. B. PULLIN& CO. LTD.PI-IOENIX WORKS, GREAT WEST ROAD, BRENTFO RD, MIDDLESEXT.I.ohoo~., EAUo; OQI1/3 & 366113 G.-m., PULlINCO. W••ohooe, Loodoo-152-
Detection and Location of Thermalsby Air Commodore L. P. Moore, C.B.E.I <strong>No</strong>ne's limited experience of thermalflying, the first symptom almost invariablynoticed on ~tering or lea:ving athermal has been a qUIck: change ofaIrspeed.But only recently has otle found that thenature of this change is related to directionof fl.ight in relation to wind direction, asfollows:-(4) Entering thermal into wind or"falling out" downwind-suddendecrease in airspeed.(b) Entering downwind or falling outupwind-sudden increase in airspeed.(c) Falling out crosswind on downwindside of thermal-rapid airspeedchanges up and down and burble.The significant thing about these gusts isthat they are usually the first indication ofentering or leaving a th~rmal; the sequencebeiIli a sudden gust or lull followed by asense of acceleration up or down followedby a variorneter reading; the lag betweenthem being the result _of the sailplane'sinertia. It seems therefore that gusts andlulls may be a good-if not the bestindicationof the presence and location ofthetmals.It occurs to me that the above experiencemay well be explained by the accompanyingdiagram if we agree the theory now widelyaccepted, that thermals drift downwind at alesser speed than that of the Wind; treatingthe thermal as an obstruction in the path ofthe airstream.By reducing t he ground speed of thethermal to zero andconsidering a hori~ontalcross-section ofit and ofits environment onthe plane in which the sailplane is circling,we have the air around the thermal streamingdownwind past it, producing eddies inthe wake and a local increase of windspeedon the flanks. The diagram depicts andel\plains, I hope, adequately how I believethe phenomenon is caused.If this explanation is right, a device thatwould measure airspeed differential betweenwingtips ought to go much further in providinga means for detecting and locatingthermals, as follows ( opposite sides of a diaphragm could beDIAGRAM r.AI!t$1JLl..P />IUC1..E.NTTA(. :lltNJluN. A .TH"ItAfIt~01
Page 2 and 3: new altitude to glidingOu R new lig
Page 4: Lasham to Land's Endby A. J. Deane-
Page 7: tremely heavy whenever encountered,
Page 10 and 11: House,-.lames's,I.ondon,-120-
Page 12: -EASY HANDLING should combine witht
Page 15 and 16: particularly good flying Qualities
Page 17 and 18: Finally, how often should you lubri
Page 19 and 20: Locking wire \~I \(a)At least 3 ful
Page 21 and 22: 1t..,'LL~ ,. ~ 'you\~. ''I?sFor and
Page 23 and 24: TOM DAVIDSON,C.FJ. - SCOTTISH GLIDI
Page 25 and 26: B.G.A. NEWSNatianal Oampioasbips 19
Page 27 and 28: During this high-speed trial, a spe
Page 29 and 30: the adjoining hill. At a lecture to
Page 31 and 32: keep GOOD MEN DOWNandrs ofl.NES....
Page 33 and 34: By th.is time I was down to 5,000 f
Page 35 and 36: The1956-57 Australian Championships
Page 37 and 38: counting themselves a no contest da
Page 39 and 40: Na_P. WildburJ. J. ConnollyJ. F, We
Page 41: hampering, though it was clearer so
Page 45 and 46: THIS GLIDINGWHAT has happened to th
Page 47 and 48: CluL~Ass~m1onNavs•ENTRIESare comi
Page 49 and 50: CROWN AGENTSOUR A.G.M. was held on
Page 51 and 52: · . . '. '""\OUTSTANDING ·1-26 fl
Page 53 and 54: eaching 1,800 and 2,000 ft. on 2O-m
Page 55 and 56: in his Kite 11, and this was the be
Page 57 and 58: A.S.l. ,out of action" but Alan tol
Page 59 and 60: BRISTOL GLIDING CLUBInitial T,ainil

Volume 8 No 3 Jun 1957.pdf - Lakes Gliding Club

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