PTT, Dave Un­win

Pilot - - CONTENTS - Dave­un­win

What's the best de­sign for the job? Lat­est is not al­ways best

There is often a temp­ta­tion for afi­ciona­dos of Western aero­nau­tics to sneer in a su­pe­rior and con­de­scend­ing fash­ion at the var­i­ous air­craft pro­duced by the de­sign bu­reaux of Antonov, MIG, Tupolev and Yak. While writ­ing up my re­port on the SZD-45 Ogar (see p.24), it oc­curred to me how a coun­try’s cul­tural, philo­soph­i­cal and even po­lit­i­cal ide­olo­gies can be re­flected in an air­craft’s de­sign.

I re­mem­ber chat­ting to a US Navy pi­lot who opined that “if it’s ugly it’s Bri­tish, if it’s weird it’s French, and if it’s ugly and weird it’s Rus­sian”. He also stead­fastly main­tained that the So­vi­ets “copied ev­ery­thing”. Blink­ered by big­otry, this in­di­vid­ual didn’t pos­sess the in­tel­lec­tual ca­pac­ity to un­der­stand that, with any wellde­signed ma­chine, form must fol­low func­tion. Sim­i­lar to the Ogar, another air­craft that I’ve flown which is a prod­uct of the Cold War and well il­lus­trates the clar­ity of think­ing often dis­played by the Soviet de­sign bu­reaux, is the Antonov AN-2. In­deed, the AN-2 is a par­tic­u­larly good ex­am­ple of prag­matic de­sign.

In 1947, when Western aero­nau­ti­cal en­gi­neers were glee­fully con­tem­plat­ing the myr­iad ap­pli­ca­tions they could find for the new jet and tur­bo­prop engines which were be­com­ing avail­able, they must have been both amused and be­mused by Antonov’s lat­est but anachro­nis­tic de­sign, which was a big bi­plane pow­ered by an air-cooled ra­dial en­gine! Yet, for the kind of mis­sions for which the air­craft was in­tended, it re­mains an em­i­nently prac­ti­cal so­lu­tion and prob­a­bly ex­plains why so many were built over such a long pe­riod of time.

Firstly, why a bi­plane? Well, the orig­i­nal re­quire­ment is­sued by the USSR’S Min­istry of Agri­cul­ture and Forestry spec­i­fied a ma­chine that, while not overly fast, could op­er­ate from small, un­pre­pared strips on short sec­tors. It is a sim­ple fact that good STOL per­for­mance is in­ex­tri­ca­bly linked to a low wing load­ing, which in turn re­quires a large wing area. That means ei­ther two very big wings, or four, stacked two on top of each other and sep­a­rated by I-type in­ter­plane struts−i.e. a bi­plane! To in­crease its Stol-abil­ity still fur­ther, it has lead­ing-edge slats on the up­per wings and flaps on all four wings. The ailerons on the up­per wing also droop when the flaps are ex­tended.

Antonov knew that as state air­line Aeroflot op­er­ated in four of the world’s five ma­jor cli­matic zones, its air­craft had to be ca­pa­ble of func­tion­ing in widely dis­parate con­di­tions, rang­ing from the sav­age sub-zero tem­per­a­tures of a Siberian win­ter to the sear­ing sum­mer heat of the Gobi Desert. This is one of the rea­sons the Soviet de­sign­ers tended to pre­fer air-cooled engines, and pneu­matic sys­tems over hy­draulic. One clever fea­ture is that the two large bat­ter­ies slide in and out on racks that fea­ture built-in con­nec­tors. Ex­treme cold can suck the life out of even the best bat­tery very quickly, so this ar­range­ment al­lowed crews eas­ily to take the bat­ter­ies out and store them some­where warm overnight.

Another ex­cel­lent facet is that the on-board en­ginedriven com­pres­sor, which recharges the eight-litre air tank, can also be used to in­flate the tyres and oleop­neu­matic shock ab­sorbers. And how would you know if the oleos were a bit de­flated? Sim­ply open a small door on the main leg fair­ing and see if the mark for the air­craft’s cur­rent weight is aligned with the in­dex mark on the strut.

Per­haps my favourite fea­ture though is that the fuel sys­tem has a built-in pump for up­lift­ing fuel. When re­fu­elling from a 200-litre drum in the mid­dle of the steppes, open a hatch in the belly, con­nect the hose and away you go! To say that the AN-2 is an in­cred­i­bly ver­sa­tile ma­chine would be a huge un­der­state­ment. A con­sid­er­able num­ber of vari­ants were built, in­clud­ing ded­i­cated crop-sprayer, am­bu­lance, float­plane, wa­ter­bomber and para­trooper ver­sions. AN-2S were ex­ported to all the old War­saw pact states, as well as many other coun­tries.

Antonov pro­duced at least 5,000, while PZL’S Mi­elec fac­tory in Poland and China’s Nan­chang Air­craft Man­u­fac­tur­ing Com­pany built many more un­der li­cence. The grand to­tal man­u­fac­tured is pos­si­bly as many as 20,000, with pro­duc­tion only ceas­ing in 1995. Not bad for a ma­chine that most Western ob­servers con­sid­ered ob­so­lete be­fore it even en­tered pro­duc­tion! Just like that other icon of Soviet en­gi­neer­ing, the Kalash­nikov as­sault ri­fle (which also made its de­but in 1947, whence its name, Av­tomat Kalash­nikova 47) the AN-2 isn’t the most so­phis­ti­cated ma­chine, but it gets the job done.

As for the al­le­ga­tion of copy­ing... well, it is true that Rus­sia’s Arka­dia Shvetsov bureau de­vel­oped the ninecylin­der air-cooled Ash-62 from the Wright Cy­clone R-1820, but as the Cy­clone was one of the most re­li­able aero-engines in the world at this time, this ap­proach seems em­i­nently log­i­cal. Sim­i­larly, there is noth­ing revo­lu­tion­ary about the AK-47, it is sim­ply a com­bi­na­tion of the best fea­tures of the Garand M-1 used by the Amer­i­can army and the Ger­man STG44 for, as Mikhail Kalash­nikov him­self ob­served, “each de­signer seems to have his own paths, his own suc­cesses and fail­ures. But one thing is clear: be­fore at­tempt­ing to cre­ate some­thing new, it is vi­tal to have a good ap­pre­ci­a­tion of ev­ery­thing that al­ready ex­ists in this field”.

This re­ally is ex­cel­lent ad­vice−and ad­vice that some mod­ern air­craft de­sign­ers would do well to heed!

The AN-2 is a good ex­am­ple of prag­matic de­sign

Pi­lot’s Flight Test Edi­tor op­er­ates a Jodel D.9 from a farm strip and has logged stick-time on ev­ery­thing from ul­tra­lights to fast jets

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