FOR AEROFIAUTICS, NO. 238. The discussion of the relative rneriSs of the several possible wing arrangements in an airplane, of the Fdvsntages to be d-erived by using a single set of wings in a single ulene or %?loo of three superposed sets, has lasted even longer thaii the atrpinent between the partisans of thin and thick wing sections, and the two ques- tions seem equally far from a definite and nll-inclusive solution. There has never been a time, since 1908, when monoplanes and bi- planes were not in direct competition and giving results nearly enough the same so that both types had to be reckoned with, and that the choice between them mas difficult in plar;ni.ng an airplane for any new puryose. In 1909 and 1910 it appeared that the field could be divided between the two types so definitely that there Izould be little overlappingo The monoplane vas to be the airplane for racing ar,d for general use orhere high speed was required, nh-ile the Biplane would receive preference for long flights and for use by cornpara- tively unskilled pilots, Strange to say, one at least of those predictions has found itself directly rwersed by experience, for the most unqualified statement that cai be maae on the subject at the present time is that the biplane is showing itself d-istinctly * From the Christian Science Bonitor9 -2- supertor to the monoplane for racing purposes, the difference in niaximrn speed between the fastest examples of the tao types being close to 20 inriles an hour. The monoplane, on tlic other h3nfi, is T~CW being used for training end for commercial transport, itl.timu~hit has neither of those fields to itself. -.Sumnary of the Choice. In brief sumimry, the most important advmtages cjf the biplane 8318 the possibility of using extern21 bracing more effectively, some- What lower vdng weiglit, the possibility of using higher aspect ratio, 031 ratio of span to chord. of nings, greater coripactness, and %e of- fering of a better and less obstructed field of view in some dims- tions and under some conditions. The monoplane offers as its chief arguments the avoidance of loss of Ring efficj-ency by interference between the several wings, easier assanbly anG maintenance, and a better view in most directions. The factors mhich enter into airplane design can be arranged under the three general headings of aerodynamic efficiency, struc- tura.1 strength and general layout for easy construction and mainte- nance and for the comfort and convenience of pilot and passengers- In making Comparison betmeen the monoplane and biplane under those three headings successively, it should be understood that the differ- ence between tmical airplanes of the two types md of recent design goes deeper than the use of a different number o€ wings. The mono- plane is characteristically an internally braced type, using a iriii?-g SFCtiOn of great thickness, and the external bracing through wires ~Llichused to be employed OE all monoplafizs now appears wit% few exceptions, only on bTplan.3 &.cd triplane e?: frxi'~I~t~?a."be discus- sion of monoplane and biplace must, th&r-efo:l:e, hzve mccii ;n C3r=il;lon with the analysis of the rtualry between thcck and .l;l?.in wings which has already appeared in this column. Aerodynamic Qualities In respect of aerod-mam-ic. qualities, theie is littie t.3 choose between the single set of wiilp;s and the su?exposed sets. The more efficient structural arrangement of the biplane makes it possible, as already noted, to use high aspect ratios and th.3.n wing sections, both of which oGould be favorable to high performance if everythj-ng else were exactly equal, but the ad-vantage thus gained is countes- balanced by the elimina'tion of interference betveen the wings and by the suppression of struts and wires, all of which add to the to- tal resistance encountered in the momplane. Insofar as there is any difference, it is in favor of the thin wing, and so of the bi- plane, at very high speeds, and of the thick ring, most oftsn used in monoplanes, at more moderate velocities, such as are ussd in commerc ial operation. Stability and control, like the factors directly affecting per- Formance, come under the h.ead of aerodynamics, and again there is little difference between the two types. There used to be a comxon 3elief, backed by no very concrete evidence except that of experience -4- with one or two particular designs, that the monoplane was hard to fly, tricky, and unsafe. For about a year prior to the beginnirig of the wax, in fact, the use of all nionoyl?nea cvvned by the SrZtfah Air Service had been discoEtinued and the airplanes plac9cZ in dead storage. This prejudice kied no sound basls for general a-pplicatiou, however, for a properly-designed monoplane is perfectly normal in its behavior and quite a8 easy to fly as asnother sort of airplane- The French Army even uses monoplanes for prixary training, with per- fectly satisfactory results. Structurally, the advan-bage rests entirely witk the biplane. The use of two wings, set parallel to each other and at a consider- able distance apart, makes for an almost ideal simplicity of bracing where wires external to the rings are to be used. A bipland struc- ture can accordingly be made considerably lighter for a given strength than can the monoplane, in vrhich the inemhess supporting the wing mst be entirely self-contained or brought directly from the body, with no intermediate bracing -pointse Something for Both Sides. In comparing the general layout of the two types, there is something to be said on both sides* The biplane starts with a great advantage in being more compact, having smaller over-all dfrnslasions for a given area and therefore requiring less hangar space for stor- age. The monoplane, however, is much easier to assemble and. re- quires no alignment, for a thick wing is built as a unit and cannot get out of shape unless it is actually damaged structurally. Since -5- the wing is all in one piece and- is held in nlace only by a few tolks, it takes fewer minutes to remove or replace it as z mhde than it does hours to perfor:% the same oQeratica on the m.ngs of a biplane. The most important difference of all for certain sorts of se-r- vice is that in field of vie;?r. In most mses the monoplzne wing is placed above the boG.y, approximately on a le-Jel with the pilot's eye. The view vert"sa1l.y downvrard is therefore entirely unobstmct- ed, mhile in the biplane Ybe Iowrer oring Is always in tile 'nay.. This is of decided importance in commercial airplanss, where a clear view of the ground is a great attraction to passengeTs, and in air- planes for military an% r;aval observation, mhese the whole purpose of the d-esign is defeaked if the observer canCot see mhat is happen- ing below him. The thick wing somewhat interferes with the pilotrs vision to the front, to be sure, but this haadicap ca-n be overcome by placing the pilot forward of the :wing, beside the engine, as in the Fokker commercial monoglanes, or by rec?xcing the thickness loc- ally over the body. Balancing all of these qualities against each other, the bi- plane seems likely to continue in favor for rac.ing, for hilgh-speed pursuit airplanes, for seaplanss, and probzbly for bombing airplanes of very large size, with the triplane as a possible rival for the last purpose. It is probable, homever, that the monoplane will grad- ually come to have the fields of commercial passenger trenspost, of sport and touring, and of military observation iTore and rnore to itself = .