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

made to show airspeed differential, and itwould probably be fairly easy to differentiatebetween the differential related tocircling flight and that arising from a suddengust or lull. The above rules would bedifficult to memorise at-first, but with theaid of a ready reckoner and some practice,would soon become fairly instinctive. That"kick in the pants" may be held to be amOre convincing indication, and so may thetilt of a winglip, but they only indicate afail accompli. Gust indication ought togive an appreciably earlier and longerdistance indication of the presence anddirection of a thermal centre.It looks as though there should beappreciable variatiol15 in pressure around athermal as a result of local changes in thespeed of passage of surrounding air, aconcentration of streamlines on either flankdecreasing pressure while a high-pressureregion builds up on the downwind side.Does tbis help to account for the earplopping experienced in strong thermalconditions? And could that lead to falsetransient readings of the variometer?HitheJ'to I had always associated suddengusts and lulls with the sudden vectorialaddition or subtraction arising from thechange in vertical velocity Qf the sailplane'senvironment. No doubt this does contributetowards the phenomenon, but wereit the only factor, we could expect anincrease in airspeed 011 entering a thermalirrespective of direction of flight in relationto wind direction-which is n01 whatactually happens.Quick reaction to thermal indication is animportant thing, especially when flying fastbetween thermals, lest we overshoot them.Is sudden change in airspeed iD the sense Ihave suggested a reliable pointer? If so, isit the first pointer of the several differentones? ]f it is, it may be the best to go by.The famous and reliable PE RAV rA barograph. Models for sailplanes(left) and for aeroplanes (right). - For details write to:PERAVIA LTD. BERNE/SWITZERLAND-154-