Volume 16 No 1 Feb 1965.pdf - Lakes Gliding Club

GUDING-SAIlING Q' >,)~WATER SKI-tNG' ~,~COfIlIbine 3 exc,j'ing sports in T ' ~_"me.." holidoy in 'hO~glorious surroundings of0..011', lObAY. utoJl equip·~"' all Pfoyided i"c1udes two...... _. _SiNt", gliders, Sailing dinghies,.. ~-----==--Sp••dbailts & Skis .nd ~---~Berm."don S!oop !tc•• Quolified"'::il'e:'.....~::i:?::; '-;...-:;;ii1~Ii!IIii.1r,... InShycho", Llce",ed 2 ".' _ ......hotel, Minicoach transport. hperlJilnd b.~in.n.rsweJcome.From 25 gn. (FULLY ,INCLUSIVE)Brochur. hom:AIR WESTWARD17,. Victoria Str••t, '~9nton, DevonA paragraph headed "Conclusions" inthis section begins:"For most operations. a nominalsafety height margin of 2,000 ft. may bejudged sufficient to ensure safety offlight. If, however. there are reasons toexpect strong mountain wave effects, e.g.from the available forecasts or in-flightreports, from the appearance o'f cloudsor from the pilot's previous experienceof the route, the best insurance againstencountering severe rotor zone turbulenceor sustained down-draughts is anadequate height margin above any highground on the route."ApPENDIX.-A ten-page Appendix followsthe four pages of general information.This goes into details and givesmuch of the information to be foundin Mr. C. E. Wallington's "Meteorologyfor Glider Pilots", so there is no needto repeat it here. The disastrous galewhich damaged more than half Sheffield'shouses on 16th February, 1962, isattributed to the fact that, below thelevel of maximum wave amplitude, thehorizontal winds are strongest in thewave troughs and weakest in the crests.How best to escape from a sustaineddowncurrent is again discussed: "Thechoice between seeking an upcurrent afew miles towards, or away from. thehigh ground upwind depends upon thecircumstances. If the aircraft is alreadyso near to the high ground that thedowncurrent is obviously descending thelee slope itself-as distinct from a leewave further downstream-no rising airis likely tl) be found unless the ridge iscrossed. In such circumstances it is normallywiser to look for rising air furtherdownstream, subject to there being asufficient height margin available in thatdirection." Also, "where no attempt is26made to counteract height changes, the~ircraft's height variations when flyingInto wind are out of phase with anyairstream waves, so that the aircraft isliable to be at its lowest height whenactually over the highest ground."The points. already made about autopilots,rotors, wind deviations, icing, andaltimeter errors af>e further elaborated,and then we come to the pamphlet'smost novel feature-a method of calculatingsafety heights for a v'ariety ofterrains and of flying tracks in relationto the terrain.First, to get the safety height over anisolated hill, you take the height of thecrest above the foot of the slope (h),multiply by the wind speed at flight level(V) and divide by the aircraft's groundspeed (G). The result, h x V IG, is theamount of height you could lose (orgain) when flying directly up or downwind over the hill. (The foot of the ridgeis the lowest ground within 5 miles inBritain or within 10 miles in Alpine-typeregions.)To allow for flying along a continuousdowncurrent parallel to a ridge. youmultiply by a factor K, which is theratio of the length of the ridge to thehorizontal distance between its crest andfoot. This makes the formula Kh xV IG. (It is applied if your course iswithin 30° of the line of the ridge andthe wind direction is within 30· of theperpendicular to the ridge.)Then, jf there is wave motion as well,the upward or downward flow may beeven steeper than the hill slope, so youadd another 50 per cent, giving finally:1.5 x Kh x 'V IGTo save time in applying this formula,you can prepare your maps beforehandby drawing lines (isopleths) of equal Kh,using K = I for isolated peaks. But youare recommended to draw your isopleths10 miles further out, to allow for winddeviations upsetting your navigation.It is emphasised that all these safetyheights are not merely to be measuredfrom the tops of the hills or mountains;they are to be adde