Naval Architecture in Aeronautics

7/27/2019 Naval Architecture in Aeronautics

1/14

J U LY I, 1920

NAVAL ARCHITECTURE INAERONAUTICS'B y J E R O M E C.H U N S A K E R , E n g . D . , C o m m a n d e r , C o n s tr u c t io n C o r p s , U.S. N a v y

Introductory. As an American, I arn very pleased tohavebeen asked to read theWilbur Wright Lecture forthis year, andfor am o m e n t tostand inthe reflected glory ofmy eminentcount ryman. Wilbur and Orville Wright were the pioneerswho blazed the t rai l , and made the first clearing in the wilder-ness. Weengineers who follow later areonly applyingmodern machinery and met hods of intensive cult ivation intheir original field. Weshould, therefore, keep in mindthe fact that this field isgiven tous int r u s t tokeep fert i le,t h a t its yield ofbenefit tomankind shal l not diminish.I have chosen todiscuss the use ofthe tools ofthe navalarchi tect inaeronaut ics as I consider that the t ime has now

of the very problem of animal t ranspor t by sea that confrontedour naval archi tects in theGreat War. King Hiram ofTyre must have had avery fair naval arch itect who couldfashion ships from cedar ofLebanon wi th a factor of safetyand a range of stabi l i ty adequate to cope with Atlanticstorm waves. Archimedes, however, isgenerally recognisedas thefather of naval archi tecture. Hefirst developedthe laws of displacement and buoyancy and is creditedwi t h the const ruct ion in 264B.C. of the Syracusia of 6,000 tonsa ver i table Dreadnought of an t i qu i t y .The naval arc hi tect pract i ses an art with scientific methods.He appl ies mathemat ics , especial ly geometry inestablishing

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come to uset hem. The naval archi tect is a craf t smanwi th both ar t i s t ic and scientific tradit ions, and the art hepract i ses has a technique perfected by theexperience ofgenerat ions.I t is only afew years since the Wrights gave the aeroplaneto the world, but four of those years were years of astonishingact iv i ty , and the experience of those years isworth moret h a n t h a t offor ty ordinary years . There isal ready a vas t

l ines, displacement and stabi l i ty . Heapplies the met hodsof thecivil engineer inmat t e r s of structural design. Inmat t e r s of resistance andpropulsion he is guided by thetheory of hydro-dynamics. But inall of these appl icat ions,the sure and t rue guide has been exper ience. From tha tremote age when the hollowed-out log canoe replaced thesolid tree trunk down tothe days of sail and steam, thenaval a r ch i t ec t has based his new design upon his l as t .

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CHARTUstore of experience available which thenaval archi tect ' smet hods cananalyse, classify and reduce to useful engineeringt e rms .Whi le aeronaut ics as a useful artand a science is new,naval archi tecture is hoary wi th age. Noah probablyconsidered andevident ly reached a successful solution

* The annual Wilbur Wright Lecture, atthe Central Hall, Westminster,on Tuesday, June 22, 1920.

Fact o r s of safety andcoefficients of allkinds used in apparent lytheoret ical or frankly empirical formulae have been reallyfactors ofexperience.The naval architect 's problem deals with the sea, and wecannot pretend toknow much more of itsmyster ies thant ha t Sy r i an l andsman who marvel led at the way of a shipin the mi ds t of the sea. The forces ofnat u re are st i l l in-calculable, but the design of avessel tobe staunch and safe692


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JULY I , 1920

is not such a dark and dreadful ad ven ture. Confidencecomes from ex perience and the nav al architec t 's most powerfulassistance comes from the scientific analysis of that experienceto reduce its lessons to engineering terms.The naval architect has available a priceless store oflearning accumulated by generations of shipbuilders which,with skill and judgm ent, he can make serve him . He cann otafford to lean too heavily on the past, however, and where anew type of vessel must be produced, imagination andjudg men t of a high order are necessary. There is an ar tisticside to naval architecture, and for many craft the artisticfeeling or "flair" of the designer distinguishes an advancein the art from a routine product.In aeronautics I have yet to see a design representing amarked advance in the ar t made e i ther wi thout this ar t is t icfeeling for form and proportion or made wholly withoutreference to the lessons of the past.General comparisons are impossible, but i t seems to methat in England aircraft designers have followed the navalarchite ct 's methods more tha n in other countries. This is ,

out the faults before his patience or purse is exhausted.For large machines and airships the time and expense requiredare too great for cut-a nd- try me thod s. A large flying-boator an airsh ip is a success or failure on her first flight. Ifbadly overweight, unstable or out of balance there is nochance to rebuild.In our Navy we look with suspicion on the man who ismore concerned with the method of doing things than in theactual doing of them, and to avoid any misunderstanding,I must say here that I wish to make my point as to theut i l i ty of the naval archi tect ' s methods in aeronaut icalengineering by atte mp ting actually to do a few of the thing swhich appear to be needed at this t ime . This work I havethrown into appendices a t tached to this Paper .Abstract of Appendix IWeight E stimation.Both the aeronautical engineer and thenaval archi tect r isk thei r reputat ions wi th weight es t imates .A ship must float on her designed water l ine and an aeroplanemu st fly with th e wing surface provid ed. Serious over-

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CHART HI f ^perhaps, natural in the first maritime power of the world.In England, also, I find a very extensive application of theresults of experimental research, both model and full scale,which really is experience interpreted and analysed byscientific methods.In France I see less influence of experience and perhapsmore originality of invention as shown by occasional radicaldepartures , omit t ing intermediate s teps of development .In Germany there was once a tendency to " professorialdesigns " based too stric tly on theory , resulting in strang eand awkward s t ructures l ike the Taube types . During theWar something happened to reverse this policy, and we sawa series of machines developed step by step, obviously fromexperience.

In Am erica we have suffered from the designs of the in ven torwithout experience and from the practical rule-of-thumbman without theoret ical landmark s to guide him. On thewhole, the successful designs have been produced by menof imaginat ion and judgment applying analysed experiencewith the best theoretical and engineering informationavai lable .For very small machines the inventor type of designerhas been very successful at odd times. He hits on a goodsolution, and by a process of cut and try eventually works

weight in e i ther case ma rks a fa i lure . I t i s only rare ly th atvessels are discovered to be much overweight, but, un-fortunately, overweight has been all too common with aircraft .Naval architects are able to estimate weight with fair precisionfrom unit weights gleaned from past experience and to checkthis es t imate by calculat ion from th e drawings . Duringconstruction, weights are controlled by weighing everythingth at goes aboar d the ship. Fo r aircraft , the practice ofrigid weight control has not been well established eitherin the shop or in the draw ing office. Very often constru ctionis commenced before the drawings are completed, and duringcons truct ion changes and a l tera t ions are incorporated with outreference to their cum ulative effect on the weig ht. A proposedchange may be approved on i ts meri t and not wi th referenceto a definite weight allowance.It is essential tha t before con struction , or even deta ildesign is commenced, a weight estimate should be made inthe nature of a weight allowance which shall be treatedl ike a bank balance and on no account to be overdrawn.Such a weight allowance must be made from the generaldesign drawing s before the d etails are developed and necessarilyis based on past experience with a similar type of construction.Th is is the nav al arch itect 's m etho d, an d to avoid guess-workrequires extens ive records and weight re tu rns from actu al work.

693


3/14

I, 1920

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r The matter of weight estimation for various types of aero-planes is not really such an inaccurate procedure even in thecase of an apparently radical departure from previous typesof construction. I have assembled published weight datafor several hundred different aeroplanes and seaplanesBritish, French, Italian, German and Americanfrom thesmallest to the largest, and while the returns in any individualcase may be unreliable, the general trend is usually quitedefinite. It appears that no designer, whether using solidwood, hollow wood or metal, is getting something for nothing,

or otherwise classed as failures. There may, however,remain some types which ought to be eliminated or for whichthe data is in error. However, the plots give lit tle weightto an individual case and are used to establish the generaltrend of the averages. Mi *I have burdened the Paper with the entire mass of dataas designers may have use for it in some other form, or may

wish to examine more closely the credibility of the evidence.Also, this collection of the weights of present-day machines,in a way, marks the state of the art.

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CHART Y. 6 0 and, in general , the percentage weights for machines ofsimilar type are remarkably al ike.If this conclusion be established, a designer may est imatethe weights of a new design with some degree of confidenceprovided he has d a t a for a somewhat s imi lar type to workfrom. In the tables of Appendix I, I have given weightd a t a for machines which are supposed to represent successfuldesigns of adequate s t rength and power, el iminating all t h a tI know to be weak st ructural ly or grossly underpowered,

The data is summarised on char t s to furnish a guide forus e in prel iminary design. The following general conclusionsappear to be established :(1 ) The weight of wings, struts, wires and tail surfacesamoun t s to a b o u t 20 per cent , of the gross weight for alltypes.(2 ) The weight of body, fuselage, landing gear, boat hull ,etc . , t rends downward from 22 per cent , of gross for one-tonmachines to 15 per cent , of gross for 20- ton m achines.

694


4/14

JULY I 1920

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CHART1.(3) The w eight of power pl ant also trends downw ardfrom 30 per cent, for small to 20 per cent, for large machines.(4) The w eight l ight for machines from the sm allest tothe very ma ximum sizes has to-day a lower lim it at ab out53 per cent .(5) For large flying boats and large aeroplanes the weightl ight i s about the same.(6) The structural weight is\high for low-powered machinesand low for high-powered machines, and in general thebest weight carriers show about 18 lbs. per horse-power.

Examinat ion for Av ia t ion G r ound E n g i n e e r sTH E Air Ministry announces :Arrangements have been made to hold examinations forcandidates desiring to become certified ground engineers(aircraft or engines), under Section 4 of the Air NavigationDirections, 1019, at the following centres during July andAugus t :London , Ju ly 7, August 4, July 21, Augu st 18 ; Bristol,Jul y 27 ; Birmingham, Jul y 28 ; Manchester, July 29 ; Leeds,Aug ust 24 ; Newcastle, August 25 ; Glasgow, August 26.A candidate may apply to be examined as a GroundEngineer to overhaul and inspect al l flying machines and/orengines, or for the examination of any named type or typesof flying machine or engine. The exam inations which maybe partly written, partly oral and partly practical, will bebased on th e syllabi outlined in Air Ministry communiqueNo. 499 issued on Marc h 5. Can didate s desiring to beexamined can obtain application forms from the Secretary,Air Ministry, London, W.C. 2, and should submit theircompleted forms of applications, accompanied by a fee of5s., at least seven days prior to the date on which exam inationis desired. Cand idates should also state at which of th eabove places they wish to be examined.Ae r ia l Mai l Tr anspor t in India , e t c .ADVI C ES just to hand from Calcutta report that the IndianGovernment is prepared to consider contracts of fifteenyears ' dur atio n w ith priv ate firms, for the establish men t ofeffective Aerial Mail Transport Services for India, Burma andCeylon. Aerodromes are to be erected for the purpose, th emain establ ishment connected wi th the Royal Flying Corpsbeing situated at Bangalore. As an initial step in theencouragement of Indian avia t ion, the Bri t i sh Governmenthas recent ly presented to the Indian Administ ra t ion 100aeroplanes of which four are destined for Burm a. A certainnumber are to be placed in the care of the Indian Princes for

yme nt in the)jr ow n territorie s. A nativ e Schoola complete Indian Aerial Servicebe in existence before the end of 1921. At the pr esen t

so owing to i ts geographical position. A Compan yunder the t i t le of H andley Page Indo-Burmese Tra ns-

(7) Similarly, the structural weight is high for low wingloading and vice versa.(8) The wing loading is found to be greater for the largermachines, reaching a maximum of nearly 12 lbs. per sq. ft .for the large flying boats.(9) It appears th at all the evidence from p ast practiceindicates that large flying boats can safely be given a higherwing loading and a higher landing speed than land aeroplanes,and, hence, have a distinct advantage as weight carriers forcommercial purposes. (To be Continued)< ; >

por t, Ltd., for the purpose of undertakin g com parativelyshort passenger and freight services pending the establishmentof perm anen t long distance services to sui t the comm ercialneeds of the cou ntry. An aeroplane works, a school ofinstruction, and an hotel form part of the objects of th eCompany.To O ur Re ade r sAs we continually receive complaints from readers thatthey experience difficulty in obtaining their copy of F L I G H Tpromptly each week, we draw their attention to the sub-scription form which is printe d on page ii i of t he curre ntissue. If this is sent, accompanied by the appropriateremittance, to the publishing offices, 36, Great Queen Street,W.C., i t will ensure F L IG H T being received regularly eachweek upon the day of publ ica t ion.A r t and t h e A i rAN exhibition of aircraft paintings, by Mr. GeoffreyWatson, is to be held at the Brook Street Art Gallery, 14,Brook Street, New Bond Street, for two weeks from July 7.The exhibit ion, which is under the pat ronage of H .R. H .the D uke of York, K.G., and in aid of th e R.A .F. MemorialFund, to which the whole of the proceeds will be given,will be opened informally on the 7th by the Rig ht H on.Lord H ug h Cecil, M.P . (Chairman of the Memorial Fu nd ), at12 noon. The pictures num ber abo ut fifty, and for the m ainpart depict incidents of the air war, but a number of peaceaviation pictures will also be shown. Admission to theGallery will be is. 3d., and the Exhibition will be open dailyfrom 10 a.m. to 6 p.m., and on Saturday from 10 a.m. to1 p.m. , unt i l July 21.Ae r ia l Se r v i c e s in Br az i lNow that the Brazilian Government has definitelysigned a contract wi th the H andley Page Co. , no doubt theservices will soon start . The first stage will be from Rio deJaneiro to San Paulo, the first step to l inking up by airwith Buenos Aires and ultimately with every city of anyimportance in Brazi l , Uruguay and A rgent ina . At Rio,the headquarters wi l l be on the I lha do Gouvernador, wherethere will be a flying school. From San Pau lo, will be ex-tended to Florianopolis, Porto Alegre, Pelotas, Montevideoand so to Buenos Aires. I t i s ant ic ipated t ha t the journeyfrom Rio to Buenos Aires will take 20 hours against the6 to 8 day s now required by steam er. , - - .

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6/14

J U L Y 29, 1920 . " / ' ^

two-dimensional, and can be considered apart from thelateral or asymetric motion. For the longitudinal motion,we areinterested in thepitching oscillations and the criterionthat such oscillations be stable. For aeroplanes of normalJO520

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apparent ly notone-tenth sodifficult. However, theareasand proportions ofcontrol surfaces are theonly thingsnotcovered byspecifications. Wedepend onthe test pilot tostate whether hefinds thecontrol certain andeasy.When animportant fea ture ofdesign is solargely a m a t t e rof judgment andfeeling, we look tonaval archi tec ture for ananalogous problem. Therudders of vessels aremade largeor small, depending on themanoeuvrabili ty desired. Theactual design of such rudders is a mat te r of j udgment andexperience. Foramerchant ship a rudder area from i/75thto 1/iooth thearea of thelongitudinal section oftheship isfound to bequite satisfactory forordinary steering. Forwarships theturning circle is amilitary feature, andtogivequick manoeuvring a rudder relatively twice aslarge isused .The exact size andshape ofrudder touse for any design aredetermined from ananalysis of therudder proport ions ofships of similar type whose turning circles andgeneralbehaviour are known.Such mathematical theory oftheturning ofships asexists' - VARIATION Of VcWITH N U MB ER OPP L A N E S , . -

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Airshipclass ordesignation.

S.S. Zero ..B -(U.S.)E-O-( I t a l i an) . .P T - ,C-(U.S.) ..D -C StarChalais MendonC-M-5Zodiac (U.S.)Ast raNor th SeaM (Italian)R - qR-23R-29R-31L-33L-49R-38*

Volumecubic feet(V).

70,00084,00095,000

127,000176,000182,000186,000210,000320,000328,000340,000360,000440,000889,310997.5OO

1,000,0001,560,0002,013,0002,013,0002,880,000

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FABLE XAreas control surfaces square

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AUGUST 5, 1920

is used in selecting the important variables in the problem,but the analysis results in empirical coefficients.The naval architect's method is applied to obtain empiricalcoefficients for the control surfaces of aircraft of the varioustypes in the third appendix to this paper. I have thereassembled data for a large number of aeroplanes and airships

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FIGURE3which are generally supposed to be successful. The variousmachines are classified by type, and the coefficients for eachtype are averaged in Table I of Appendix III. It is interest-ing to note that the average coefficients for very differenttypes are practically the same. The coefficients for theindividual machines vary more widely and reflect the indivi-duality of the designers. In particular, the average fpr15 German aeroplanes shows an aileron area only eight percent, of the wing area, while the averages for Table I liebetween 11 and 13 per cent. It must be that the Germansdid not desire a powerful lateral control.Table X of Appendix III shows similar coefficients forthe control surfaces of airships. Here we have less uniformity,and it would appear that airship designers had not yet settledupon simple rules. However, experience with airships is stillrelatively limited when we consider the immense numbers ofaeroplanes that have been built.Turning now to the proportioning of the control surfaces ;both experience and wind tunnel experiment teach that thebest control surfaces are narrow trailing portions of fixed

surfaces. This makes for simplicity both structurally andaerodynamically. But a difficulty arises in large machineswhere it is necessary to balance the surfaces to relieve theload on the pilot. I know of nothing more embarrassing thanto have a balanced aileron or elevator flutter violently inflight, unless it be to have the balancing portion twist offentirely.The aeronautical engineer needs some simple rule for thedesign of balanced control surfaces. It is not practicable tomake elaborate wind tunnel experiments for every design andit is not safe to depend too much on judgment. In order touse simple rules, aeroplane designers must adopt forms whichlend themselves to simple computations. Many of the formsof balancing in common use are aerodynamically entirelyindeterminate. For example; consider the types of balancingshown on Fig. 2 of Appendix III. No man can calculate withconfidence the force of the air spilling off a wing tip and strikingan overhanging portion of aileron. There is certainly avortex there of a most uncertain nature. Similarly, in theso-called " dove-tail " method of balancing, where the balanc-ing portion of the control surface works in a recess in thefixed fin, there is a mutual reaction between the two surfaceswhich is highly indeterminate. The Zeppelin rudders haveuntil recently had this form of balance, but I have notedwith satisfaction that the " Bodensee " has changed to apartially overhung type of rudder.TABLE XI

Machine.

A.E.G. BomberA.E.G. BomberA.E.G. BomberT.B.

Control.

AileronsAileronsAileronsAileronsRudderElevator ..AileronsElevators ..Elevators ..RudderElevator ..Elevator ..Aileron

0-830-45-370 -22O-47O -400-650-250-63-550-360 -26O -2O

(wind tunnel testsby Eiffel (Resum6: 1919) show degreeof balancing inorder shown)

Aileron .. 0-50Elevator .. 0-43Rudder .. 0-40Elevator .. 1 -oo (wind tunnel testsshow indication ofinstability)B.E.-20 . . . . Elevator . . 0-64 (wind tunnel testsshow proper degreeof balance)N.C.-4 . . .. Ailerons .. 0-58Breguet 16 BN-2(old)Fokker D-VIIIBreguet 16 BN-2(new)Breguet 17-C-2HS-3FriedrichshafenBomber . .Pfalz Scout..Pfalz Scout..

N.C.Fiat B-R-AFiat B-R-ALe PereVickers VimyThe naval architect has long ago been through similartroubles with ships' rudders in rear of the dead wood aft, andconcluded that he would use a plain trailing rudder hinged

to the stern post with an underhung balancing portion pro-jecting into clean water. The dead wood is cut away forwardof this balancing portion. Spade rudders are used where theycannot influence the dead wood or be blanketed by it.If aeronautical engineers would agree to usesimple overhungbalanced control surfaces, a simple calculation will serve fortheir design. Table XI of Appendix II I summarises acalculation for such control surfaces on a number of machineswhere the centre of pressure of the traihng portion is taken at0.3 chord length and for the overhung portion at 0-2 chordlength. The ratio of balancing to righting moments gives acoefficient which for the normal case free from blanketing orslip stream effects should not exceed 0-65.To sum up, control surfaces of the usual type can bedesigned by use of coefficients taken from similar typemachines of normal behaviour with every assurance that themanoeuvrability of the new design will prove normal.

Balancing Moment.Righting Moment.

Abstract of Appendix IVNormand's Weight Equation (Rigid Airships).There isnothing more profitless than an argument over a proposeddesign between the operating personnel, who are alwaysdemanding enhanced military characteristics, and the con-

structors, who are prone to object to change on the groundsthat their pet design will be spoiled. Most likely both sidesadvance very strong arguments to support a particular viewof the matter. But such a discussion should not rest on a867


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basis of argument alone else it degenerates into somethingresembling that ancient impasse : " Are the mountainsbetter than the seashore ? "As a matter of fact, the effect of any proposed change inmilitary characteristics can be calculated in a sufficientlyapproximate manner to make possible a decision based uponevidence.For rigid airships which closely resemble vessels, I proposethe use of a naval architect's method for analysing suchproblems due originally to that eminent French designer oftorpedo craft, M. Normand, and subsequently extendedandperfected by Prof. Hovgaard. By Normand's method, a"rapid estimate can be made of the cost in displacementinvolved by almost any proposed change in the ship.In the fourth appendix to this paper, I have developedNormand's method to apply to airships by forming the so-called weight equation as the sum of the principal weightgroups each, expressed in terms of the independent and de-pendent variables of the design. This weight equation isthen differentiated to exhibit the effect of a change in any ofthese variables and formulae deduced, analogous to thosewhich apply to vessels, by which a quantitative estimatecan be made for the effect of such change.An airship can be changed in two ways, by preservingsimilitude of form and permitting the volume to vary or byholding constant volumeand changing the ratio of length todiameter. Considering the first case, the factor of propor-tionality N computed in the fourth appendix isabout 4-5 fora shipof L.49type. This means that anaddition of 1,000 lbs.to the weight of any item in the ship calls forsuch increaseinother items, tokeep theperformance the same, that the totallift must beincreased 4,500 lbs. For battleships N is of theorder ofonly 2-5, indicatingamuch more favourable situation.The principal reason airships appear to be at a disadvantagecomes from the longitudinal members of the hull structurewhose weight increases as the fourth power of the lengthof the ship.Consider, now, the effect of holding volume constantandchanging thefineness of theship. The longitudinal membersof the hull vary in weight as the third power of the lengthand the first power of the diameter, while the weight of thetransverse frames varies as the fourth power of the diameter.If theship befattened up,weight issaved on the longitudinalsand lost on the transverses. But if the ship be too longoriginally there will result an important nett saving inweight.Finally, I have applied the method to a rigid airship ofthe Zeppelin type (L.49) in an example to show howpracticalanswers may be obtained. The displacement of L.49 isassumed to be 1,940,000 cu. ft., or 129,800 lbs. If it beproposed tomake a newdesign which shall besimilar to L.49,except to have 2,000 lbs. more bombs, a 25 per cent, heavierouter cover, a 15 per cent, more speed, the newship must begiven 13,890 lbs. more displacement, or a total volume of2,145,000 cu. ft. The net price paid in displacement is,therefore, about six tons.On the other hand, if the ratio of length to diameter be

AUGUST 5, 1920

reduced from 8 to 7, the ship can be built lighter, and thecalculations show that a saving in the newdesign of nearlyfive tons is due to this change of form alone. Asafinal resulta newship resembling L.49 mightbebuilt havingtheproposedchanges incorporated, and only be slightly larger than L.49 ;i.e., 1,990,000 cu. ft. The principal dimensions compareas follows : ' ;.Length L.49, 634 ft., newship 584 ft. *Diameter L.49, 78:7 ft., new ship 83-5 ft.It would appear that a decrease in the length diameterratio is of great advantage, andwere it not for the necessityto consider theheight of existing hangar door, airships mightwell be made fatter than the German models.

Normand's MethodNormand's weight equationW +W= W W B W c e tc . = 2W ZA typical member of the weight equation isW AL^D^07" tor where ratio L/Discons tan tW ALetc .

and W =. kU >AW AL .. After differentiating (4), ^v~= 3 T~iW AL Aa

After differentiating (3), -^- =*"+ *""+ e t c-After subs ti tuting (5)in (6)AW = 2AW Z = N2W Z ( z*+ e tc . ) ,

(1)(2)

(3)(4)(5)(6)(7)

Where N = ^W~=4"&7 f o rL-493wIf weight variables andvolume are constant and L/Donlychanges AW AL . 2AD o (8)

(9)w= ALD2and

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14.770^ for L-49.I

Ft.Original : L. 643Plus additional 2,000 lb.bombs L. 657And 25 per cent, heavier coverfabric - . . L. 665And 15 percent, saved onlongi-tudinals andmain transvers s L. 650And 5 percent, more speed . . L. 665And length/diameter reducedfrom 8 to 7 L. 584(T o be Concluded)

Ft.0.78-7D. 80-5Cu. ft.

1,940,0002,080,000

D. 81-5 2,145,000D. 79-6D . 81 -5 2,008,0002,145,000D. 83-5 1,990,000

COMMERCIAL AVIATION IN NORWAYIN the report on the Commerce and Industry of Norwaydown to the end of theyear 1919, Mr. C. L.Paus, commercialsecretary to H.M. Legation, Christiania, states that therewas on December 31, 1919, only one company in Norwaywhose object it is to carry on air traffic on acommercial basis.The name of this company is DetNorske Luftfartrederi A./S.,Christiania."No air service has as yet actually been commenced, andthe date of its commencement depends upon theattitude ofthe Norwegian Government towards an application made bythe company for financial assistance. The NorwegianMinistry of Commerce have been petitioned to make a grantof Kr.1,200,000 to be applied to the initiation and operation

between May 1, 1920, andJune 30,1921,of an air service fromChristiania via Kristianssand S. to Stavanger, and fromChristiania via Goteborg to Copenhagen. It appears, how-ever, that theMinistry areunwilling to recommend the grantof a larger sumthan 60,000 kroner for theperiod inquestion,and if this decision is maintained it is, therefore, improbablethat air traffic will be opened during 1920. In anycase, it isunlikely that operations will pass beyond the experimentalstage during the coming year. It is understood that thecompany have not yet purchased any aeroplanes, and thatthey are not altogether unwilling to postpone their opera-tions on the ground that commercial aviation is still in itsinfancy."

R.A.F. Marriage Allowances : , . - " - ; :BY the Air Ministry Weekly Orders, dated July 19,the separation allowance, dependant's allowance, and specialparents' allowance to the families of married airmen of theRoyal AirForce arediscontinued. In substitution for themmarriage allowances are to be issued. In the case of airmenwho extended their service in the Royal AirForce under theterms of the Order of January 3, 1919, or re-enlisted in theRoyal Air Force under the terms of the Order of May 10,1919, the new Regulations shall not apply to such of themas retained during their present engagement a reserved rightto thecontinuation of Army separation allowance, allotmentsof pay, and family allowance.

With effect from September 30, the rates of marriageallowance will be as follows :(a) For a wife, gs. 6d. perweek ; wife and one child, 19s. ; wife and two children,26s. bd.; wife and three children, 325. ; for each additionalchild, 3s. (b)For children where no allowance is admissiblefor a wifeFirst child, 95.6d.; second child, 7s. bd.; thirdchild, 5s.6d.; each additional child, 3s. Therates ofmarriageallowance will vary annually according to the index figurefor the cost of living aspublished by theMinistry of Labour.Marriage allowance is normally issuable for the wives andlegitimate children or step-children of(a) airmen whohaveattained the age of 26 years; or who are over 26, now-serving andalready married.86 8


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M3CUW1 S S S

A f T t R B O W f :. >.; "i .3-- / W f l > BO O T

F i g . 1: Seap lane float. Mo del N o. 2103-B88 8

A U G U S T 12, 1920

NAVAL ARCHITECTURE IN AERONAUTICSN By JEROME C. HUNSAKER, Eng.D., Commander, Construction Corps, U.S. Navy

( C o n c l u d e d f r o m p a g e 8 6 8 ) ' . . . ' - . W , ' - L "- 1 -.'' ; ' > ; Abstract of Appendix V

The Model Basin,-Naval architects first came into aero-nautics in connection with seaplanes. The aeroplane was . :"developed before the seaplane, and at first the great problem ' . ,:.was to design the boat or float so that the seaplane could v- :;actually leave the water. The early attempts were, rarelysuccessful, and it was not until a satisfactory form of planing - .bottom had been developed by model experiments in the .. -towing basin that any consistent success was had. Thecontribution of the model basin to aeronautics is too wellknown to be gone into here. Existing methods and apparatuswhich had been developed for the study of the resistance ofships were immediately available so soon as it could bedemonstrated that Froude's law of corresponding speedsapplied to the planing action of. flying boats. Such a veri-fication was soon demonstrated by the successful performance ^of seaplanes designed from the results of model tank experi-ments.It is now possible to test in the tank, at small expense andno risk, any proposed form of planing hull, and to determine . whether or not such a hull is worth constructing full scale. It 'is , therefore, possible to eliminate a great many types which 'would prove to be disappointments, and it is also possible toexperiment with a great variety of minor modifications inform to determine the effect upon general behaviour of thesemodifications. As a result of the last four years' work at the -experimental model basin at the Washington Navy Yard bymy colleagues, Commander Richardson and CommanderMcEntee, two forms have been developed which for generalpurposes we have found superior to the others. One is apontoon which has been used on single and twin float seaplanesand the other is a form of hull which was used for the N.C.flying boats. These forms may not be the best known, as " _regards resistance or any other single feature, but have provedof all-round utility. With the permission of the Chief Con-structor, I am giving the lines and resistance curves for thesemodels in the fifth appendix as they are a very fair representa-tion of the present state of the art. \It will be noted that these forms are both what is called" vee bottom," and although this form of bottom behaveswell in rough water and reduces the shock of landing, it is objectionable on account of the spray thrown out from thechine. For a twin float installation, this is often a serious "matter, as the spray gets in the propeller and causes trouble.A recent scheme to protect the propeller from spray has beensuggested by Mr. Grover C. Loening. For twin float machineshe proposes floats with a bottom sloping outboard from theinner chine. This appears to eliminate all spray between thepontoons throwing it outboard.The experiments in the towing tank record all those thingswhich can be measured, but do not record the spray and waveformation. We have recently undertaken the study of the

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wave formation which accompanies a planing boat by theuse of an ultra-rapid morion picture camera, which takespictures at eight t imes the ra te of the commercial machine.^Vhen projected on a screen at ordinary speed (16persecond),this gives a view of the whole wave system to a microscopictime scale. Th is work istoo new to warran t anyconclusions from it, but Imention it asbeing a sug-gestive mean s of s tudyinga very complex state ofaffairs.An extension of theusual work of the modelbasin has led to the in-vestigation ofthe s t rengthof flying boat hulls toresist theshock of landing.For this purpose, accelero-meters aremounted in thehull. Attempts touse theR.A.F. accelerometer weredisappointing. This in-strument had been usedin the air for acrobaticflying with ver y satisfac-tory results, but it ap-pears that the force atlanding is too suddenlyapplied to be easilymeasured by this type ofapparatus. Ano ther typ eof accelerometer, devel-oped by Dr. A. F. Zahm,lias been used with veryconsistent resu lts. Thisinstrument depends onlyon the deflection of aseries of l ight verticalsprings by a series ofmasses,and gives a definitemaximum.

With this in s t rum entlandings have been madein smooth water, and itappears that jthe verticalcomponent is seven timesgravity and the hori-

zontal component 2-5 t imes gravity. An R.A.F. ins t ru-ment mounted alongside the Zahm ins t rument ga\-e at thesame time three times gravity and 1 7 t imes gravity, 'respectively. The large vertical components are noteworthy,-and appear consistent with our experience where engine

fOR'D BOtWBODY PL AN.F i g . 3: Seaplane Boa t. M odel No.2081 C

889


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A U G U ST 12 , 1920

foundations on flying boats and pontoon struts have failed,although they were designed for a load factor of eight.Conclusion,In this paper I have discussed in rapid suc-cession five applications of naval architecture which couldonly be developed in detail in the appendices. ConsequentlyI cannot expect to have dem onstra ted more than the existenceof these methods of attack and to have advertised their utility.It will be noted that two principal methods only have beenused.The first is analysis of experience by means of a comparisonof percentage weights, percentage of control areas, etc., fora large num ber of successful aircraft. Similarly an analysis ofexperience is attempted in the comparison of metacentricheights. Normand's method of differentiating a weightequation is also based upon experience, and the method willnot a t ta in i ts maximum value unt i l weight s ta tements for agreat many more airships are available.I cannot urge too strongly the general advantage to theart which would result from the full and frank publication oftechnical information regarding not only successful designsbu t failures as well. The failures in par ticu lar are priceless,but perhap"s it is too much to expect of human nature that apost mortem on a bad design will see the light of day.The second peculiarly naval architectural method used inaeronautics is model experimentation. A theory of similitude,geometrical, mechanical or dynamical, is used to applymodel basin tests of boat hulls, wind tunnel experiments

on aerofoils, and model propeller tests. ' Such a generaluse of similitude in design is unique in engineering practice,and forms the closest bond between the naval architect andthe aeronautical engineer.The analysis of experience is really a statistical method forwhich trust wo rthy data in qua ntity are necessary. Giventhe necessary information, the naval architects ' methods notonly reveal the pa st and presen t state of the art as representedby engineering coefficients and averages, but also show thetren d of the more successful designs. In tha t way, futuredevelopment can be predicted and the most promising direc-tions for improvement.To avoid leaving the impression that the naval architect islooking backward exclusively, I should like to tak e the oppor-tunity to recall the astonishing success of the little airshipbuilt by Dup uy de Lome in 1872. This emin ent nava l archi-tect attained by his professional skill the maximum successwhich the s ta te of the mechanical art a t th at t ime permit ted.His little hand-propelled " Aerial Ship " exhibited all of theprincipal features of our modern non-rigids in their funda-men tal forms. Control and stability were correctly under-stood and provided for. An air-speed meter was also provided.The requirem ents of our modern theory of suspending acar below a non-rigid gas bag were met by his suspensionsystem. A ballonet and blower were used in accordancewith good practice. More remark able still , Dup uy de Lomemade the envelope of two-ply rubberised fabric and doped itwith a very fair gelatine, glycerine, acetic acid varnish tomake i t t ight .I quote from a contem porary account :* . -" The stability was something marvellous ; several personsmoving about in the car at the same time did not produceany oscillation. A descen t was inte ntio nall y made from 1,020metre s to 600 metres with out making use of the ballonet.The folds on the balloon then became very marked, and itwas interesting to observe the tension of the various ropes

as they m aintained th e major axis of the balloon in a horizontalposition." The complete agreement of the results of the trial withthose foretold by the inventor will be obvious to everyone.Such an agreement, usually so rare, is the m ore e xtraord inary,as in this case all the bases of calculation had to be discovered." Henceforth aerial navigation may be said to possess atheo ry of stability and propulsion. The true history ofballooning will date from the 2nd February, 1872, a new eramark ed by the invention of the navigable balloon, and ren-dered illustrious by the n ame of Du puy d e Lome, so wellknown in connection with scientific progress and invention."The name of Dupuy de Lome deserves to be rememberednot only as the leading na val archi tect of his day, but alsothe first naval architect to apply his art to aeronautics. UIn closing, I should like to express my appreciation of thisopportunity to present before this society some of the laterknowledge of the Navy Department in an effort to make atleast a small retu rn for the very valuab le work which theRoyal Aeronautical Society has done in publishing and dis-tributing for the benefit of the art the best knowledge ofBritish aeronautical engineers. My Chief, Admiral D. W.Taylor, Chief Constructor of the Navy, especially welcomed^


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M T VAUGUST 12, 1920

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this continuation and extension of the cordial relationsestablished during the War, and authorised me to discloseanything oreverything ofvalue in thepossession of theBureauof Construction and Repair.The Secretary of the Navy is much pleased tha t an officerof the United States Navy hasbeen invited this year to read

memorial to my coun tryma n. This early recognition of theWrights by this society has ample justification, for this veryhall might notstill exist to-night had not Wilbur and OrvilleWright's invention been overhead to protect it.In honouring Wilbur W right, wemeet on a common ground.Friendly relations between our countries will be furthered

Photograph of a full-size flying boat, show ing spray Photograph of model of Loening twin floats under testthe Wilbur Wriglit Lecture, and desires me to express hisgratification. The foundation of the Wilbur Wright Lectureis an'institution very much to the credit of the Royal Aero-nautical Society, which is not only the oldest aeronauticbody in the world, but also the first to found a permanent

by Trans-Atlantic flying, and it seems very appropriate thatthe most intimate contact should be maintained by thosetechnical and scientific workers who are striving for the sameend : the improvement and application of the gift of nightleft us by Wilbur Wright. .. ,v . _Training the Young Idea - -FOR some time now the 3rd Hampton (Middlesex)Troop of Boy Scouts have had an Air Section, and now,through the generosity of the Aircraft Disposal Co., it hasachieved a cherished ambition and become the possessor ofa real aeroplane. This machinea De H. 6is completewith 90 h.p. R.A.F. engine and propeller, and the boys,Hnder theguidance of their airinstructorMr. Jo s6 Roberts

are striving harrf to learn- all they can of the principles offlight and the construction and assembling of aeroplanes,being spurred on by the promise that those who becomeproficient will be taken to one of the aerodromes and given,a flight on an up-to-date machine.The Scoutmaster, Mr. E. R. Home Gall, and every memberof the 3rdHampton Troop aredeeply grateful to the AircraftDisposal Co., Ltd ., for their generous and public-spirited gift.89I

Documents

Naval Architecture in Aeronautics