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November 28, 1930 Supplement to FLIGHT

ENGINEERINGSECTIONEdited by C. M.POULSEN

November 28, 1930CONTENTS

P AGETechnical Features of the Air Mail. By Frank Radcliffe, B.Sc,A.M.I.A.E., A.R.Ae.S 81Methodof Stressing Divided Undercarriages. By A. E.Russell, B.Sc.,A.F.R.Ae.S. 84Technical Literature ... ... ... ... ... ... ... ... 88

TECHNICAL FEATURES OF THE IRMAILBy F R A N K R A D C L I F F E , B . S C . , A.M.I.A.E., A.R.Ae.S.

C ontinued fromp.74.)IV.Design for a Mailplane

The purposeof this articleig topointoutsomeof the out-standing features which need investigating and solving ifone wishes to arrive at the ideal mailplane. The problem,atitsbest,is a compromiseand thedesigner mustso arrangethe conflicting featu res th at a true perspective is obtainedanda reasoned choice decided upon. W hat is idealfor onesection of an air route, will not necessarily be quite soefficientforanother. Thusit isnecessarytostateat theoutsetthat thereis no ideal typefor a mailplane, but there mightbein ideal type for a given set of conditions which appertaintoa certain section of air route.Inthelightof theabove,thewriter will endeav ourtos ta tethe co nditionsand then pointout what werethereasonsforarrivingat the design illustratedin Fig. III.The mailplane considered was one suitable for operationon routes with Croydo nas thecentreandlinkingupimpor tantcities 750-1,000 miles di sta nt . Such a service would enablea business man in London to have the whole of WesternEurope within reach of an evening's post, i.e. would makeMadrid, Rome, Vienna, Prague, and Berlin easily as near,fromthepointof viewof t ime,asManchesterorNewcastle.Choice of Design.The projected design as outlined inFig.Il l, is an orthodox, single-engined, high-wing cantilever W-metal mo nop lane pow ered with an Armstrong Siddeley Leopard engineof 813b .h .p .atnormal r .p.m. Thebodyand w ingsaremetal-coveredtoreduce fire risks,and theonlyrefinements applied to the aircraft from an aerodynamicaspent are :()Theavoidance of all sharp cornerson the body cross-section,and theapproach to the best streamline shape;(6)the fitting of a broad Townend ring to serve the dualPurposesof exhaust r ing and of smoothing out the air flowvertheb o d y ; and(c)the fitting of spats over the wheels to reduce thewheel dragand undercarriage interference drag.

Brakesare assumed fitted to the landing wheels to reducethe landingrun, and, if independently operated, would givebette r ground manosuvrability. A tail wheel isindicated inthe side view, and this has been faired into the fuselage aswell aspossible. In order to reduce the dragof the under-carriage still further, internally sprung wheels have beenassum ed. This furthe r simplifies the fittingof the spatsand enables the fittingof air brakes,in theform of rotatingfront track struts ,to besim plified.A high wing monoplane has been chosen in preference toa biplane,or a low wing monoplane,for thefollowing re ason s:

(1) Eliminationofrigginginservice.(2) Stowage of a simple gravity petrol system within thewings.(3) Highest degree of aerodynamic efficiency of this formof body and wing combination.(4)Therelatively bigger chordof the monoplane comparedwith the equivalent biplane should allowof bigger variationsof loadings i.e.,a bigger travel of C.G.)(5)Thepilotisableto sitforwardof theleading edgeof thehigh-wing monoplane and so has a better view forward anddown thanin theother schemes.Choice of Engine.This may give rise to some discussionso tha ta fewnoteson thereasonfor itsselectionmay not beoutofplaceat this juncture. It wasdecided from the outsetto investigateadesign which wouldbepossible with existingengines. This being postula ted, three courses are open forconsideration:(1)A radial air-cooled engine;(2)A water-cooled engine;(3)Aseriesof smaller engines, either air-cooled, or water-cooled.From an aerodynamic s tandpoint the water-cooled enginehas strong claims for consideration. By meansof the la tes tsteam-cooling methodsitwouldbepossibletoreducethebodysize to a minimum whils t the drag from the steam ra diatorwould bealm ost negligible. After weighingup carefully itsmeritsthewriter felt t ha ttheair-cooled engine could certain lyp u tup astronger caseonother counts:a)The easier maintenance of an air-cooled enginedue tothe absence of cooling installation troubles was a factorno t to be lightly disregarded, especially as the fitting of anefficient Townend ring would enablethedragof theair-cooledengine and fuselage to be reduced to a very satisfactoryamount .b)The bigger body behind the air-cooled engine wouldadd to the comfort of the crew and facilitate the use ofapparatusfor pickingup and dropping mail bags.

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