., The Aircraft Growth Factor B!J GROUP CAPTAll\1 II. FOOTTIT "An ai.rplane isn't really built; it is a process of evolution." -Ediuarcl F. B11 don Chief En_qi11eer, Dou,q/{1s Aircraft Co. IT COULD only happen in pre-war England. The time was 1934 and t11e .drawing office of The Bristol Aeroplane Company were working hard on a new rnvin-engined airliner, the Model I 43. At the same time Lord Rothermere was shopping around for :i super~fa~t person:il rp. d i( ' . I ll p l. 111< ;.!JO\\' tl1 , : il l \ \'t: llt o·n. As Newey points out. ··i t is inter esting to note t'hat the Anson V, \\'ith some mudifica l'ions in fus:::-lage equip me nt. is still in vperat ion in \'arious parts of Canada. mostly as a bush ,;rans port. but in one or two casn on sched ui!cd airlint service ." This. rhcn. is the record of one air craft's growl'h . A growth th:it in clLHkd structural changes. and ran the gamut from ci\' il a·irliner. to a recon naissance plane. ,then ·:i tr:ii ner, and fin ally hack -to its origin:d occupation. And who knows- ~he Anson ·s growth may not he O\·e r yet. 11hc re is no doubt that a design team, struggling with the detail de sign of a new airplane. could never \·isualize and allow for such growth as fi nally blossomed in the Anson. St ill there a re se\'eral sign JlO!;tS along the design h ighway that point the way fur general growth putenria•l in the basic s-tru·ctu re. room to grow I 1'' THE FIRST place there is the use of design ingenuity 111 the struct ural layout. Since the cxpensi\'l: tooling is usual ly t ieJ ·in with the ,fuselage.:. w ing, ·tail and landing gear structure. any growth changes. · which must be economical, should have the .minimum effect on the stressed parts of rhese componen ts. This does not mean that the basic structu re wun'-t change o ver the life cycle of the air ·plane. But it does m ean that each major step shou ld he a relatively small one as fa r as the stn1cture is concerned. An example of th.is design ingenu :1\ i , rh,· s1r;i:gh: ,cctioncd 111,chgc of 11 1. 111~· ll H 1\k111 r :.! 11 -..11p r h . f :\" kn:p:n~ the fuselage cross section u1,llurm oYer m uch of i ts length, there is not onh· an excellent passenger cahin. hut, more important from •the growth \'iewpoin,. it is possible to adJ in ;1dd itional fuse lage bays, wirh m inimum s,ruclllra l ch:inge. :is the design g rows. Some p-res,:ent day airliners ha\'e had two or more of tihese sect ions added as the fusdage has been lengthened throu).rh several model changes. T here may he an :ierodyna1nic foss with a constant cross section:il fusehge. But it is bet ter to accept th is and keep the d oor <}pen fur a ,lung. profitable productio n run. l'here is also the possihility or de signing the structure for a hig-her gross weight than initiall y cuntcmJ>latnl. 1 n this way many m odifications can Ix: addtd. as the airpla ne grows hca \'in, withou t changing t he basic a irframe. But this is a two eJ\!nl sword. Any des ig ner 1h:n takes it !itc r:ill v can t:tsi l;· end up wirh a he:1\' )' a i;pL111e tha·t carries little pa yload. Competitive F actor: Ahout ,the onh cr.itt-rion ror judging. in general term;, such a growth allol\'ancc scheme for commercial a irplancs. is to assess th r allowance against a ·•competi ti\'e fac tor." I n other words, wha,tever the airplane has to compe te with, will limi,t the growth allowance in t,he b lue print stage (Figure 1 ) . For a -la rge t ranspor,r ai•rplanc, heing designed fo r t he.: hlue rihbon airlines on t,he t rans Atlantic or trans-Continental ru n, there is 1prnb:ibly very li ttle initial g rowth allowance possible . The route is too rompctitive. On die othe r h and. thtrc arc Ford T~ri-rnotor , . of the !.,:,· AIRCIUFT t '· tion of a new runway at RobcrYal Municipal Airpont. Mr. Marler noted that the DoT operated more than 100 of these and assisted financially "or otherwise" at ;1 grc:1t many others. CESSNA 172 ( Co111i1111cd from page -I J ) threatening to do all day. Reluctantly we slid into the circuit behind our Twin Bonanza friend. The circuit speed which feels comfortable is 80 mph with a progressive drop off to 65 on finals. The wind on the long runway at the Island Airport was 30 degrees cross and gusty to boot, so an "over the hedge'' speed of 60 mph was maintained. Recom mended runway threshold speed is 50 mph. There is very little round-out required on this airplane, and we "landed" rather carelessly about three feet above the ground! The under carriage withstood this treatment handsomely. After lowering rhe nose· wheel to the runway, the 172 stopped in prac.tically its own length. This is not as unbelie\'able as it would at first seem. Powerful Elevators: The nosewheel can be held off -the ground down to VOKES .. ~~~- ~~ ..... ~ .. - ,..i;.-tt .. :,.,- 1·ery low forwa rd speeds due to good elevator efTectiveness. Bob \Vong de monstrated tbs most YiYidly while proceeding -oYer the grass ,to the r.amp. At fast walking-pace taxi with :half elevator up, ,the nosewheel rose off the ground. 1N e covered a few hundred ya rds in this uniqne attitude before reaching the ramp. The most interesting feature of the 172 is, of course, the tricyclf'. gear, and undoubtedly Cessna's have dom a good job with it. As usual, the fly ing public knows what it wants. and in -this case has got it-with a tricycle undercarriage! The docile ground handling of this aircraft will, I am sure, commend it to all pilots. Cessna 's predict -that the 172 will 1101 oust the 170 from the market that is a\'ailable for this type of aircraft. But on only 30 minutes acquaintance wirh the 172, my money is on its being first past the post when -the reckoning is made. GROWTH FACTOR ( Cu111 i1111ed from p,1gc 20 / 1910 era, still operati;ig in South America. The only competition on scme routes there are ox-:arts or a few PIONEERS OF SCIENTIFIC FILTRATION ,,· automobi-les. An airliner or cargo plane designed to -operate over this count-ry may have a reasonably hrgc growth allowance righ t from the first dr:1wing. For military airplanes the growth allowance ·on the design gross weight still \'aries wi~h the commercial "com petitive factor'',

The Aircraft Growth Factor

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