FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1950
1950 - 0040.PDF
2t>- THOTJft FLIGHT, 5 January 1950 DESIGN of TURBOPROP TRANSPORTS Mr. >4. F. Russell's Lecture to the I.Ae.S. in Washington PART II: Gust Alleviation, Weight Analysis, Conclusion IN has Wright Brothers Lectare, given before the I.Ae.S. i»WasiBBJgtafi, Mr_ A. .E. Rnssell, BJSC, A.FJt.Ae-S., t&krftksigDCr trf the Bristol Aerofilane Company's aircraft divjsiosB, first discussed: the esseaiials of airframe desiga dictated by the use ol tttrbopsops. A digest of this part erf the kcttnre appeared in Fkgkt last week. 1m the second part, summarized here, Mr. RnsseE went on tp^disestss gust allevia- tion:,, weight analysis, Barfexcairiage desiga xwi ©Sher aspects of tilt subject. Tbe deteetioB of gffists at Jong-range by nwiaaf, lie said;, depended om dead formatioa: font experience had sfaowra that severe efetaifoaaees eaold ©ceiir in. dear air. They had,, there- fore, to assume- that aircraft ccmld- not avoid" gusts. In certain circumstances, it might be desirable to find means whereby the applet! leads on the wiags in gusts could be reduced, and: there were two methods erf aebievrrtg this. One was by so arranging t&e response of the aircraft that alleviation toot place automatically; the other was. by detecting and measuring some quantity associated with the gust (e.g., gust velocity) and using it to operate a servo mechanism which supplied the alleviation. An example of the first type of alleviation was to cause the wing to twist nose-down, as the load due to an up-gust built up, thus reducing incidence at the tip. This entailed either a forward distribution of the flextrral and inertia axes, or a skew binge at the root. The flutter and structural problems of these solutions for straight wings led one, suggested the lecturer, to seek more feasible alternatives. For the second type of alleviation, a symmetrical ap-gssfc— which, was usually ;-.•.-•_: the most severe case—m i g h t be alleviated by nose- down pitching of the whole aircraft. Analysis, however, had shown that the angular accel- erations were greater than normal elevator power could pro- vide. While this approach might be made to work and produce some favourable effect on the structure, it would, no doubt, be balanced by eqoal but opposite reactions of ike oz oo TIME (sec) O-5 Fig. 5. Curves showing distribution of lags in gust alleviation for the Brabazoo \ with power-operased The lecturer sag- - gested that by far the most attractive solwtion made use of symmetric motion of the ailerons, either by direct mechanical conpiiag or by a servo mechanism. This system, while poten- tially capabfe of reducing the bending mameafc at the wing root by 50 per cent, ami of almost completely eliminating the bending on the outer wing, did not involve ranacceptabfy large pitching or vertical nrotion of the aircraft. A device ahead of the wing which measured directly a change of incidence due to a gust was, in the lecturer's opinion, probably the most promising method of gost detection,, operation, of the ailerons being by some power oar servo system. Thie essential need was to keep the time lag for tbe set ol opesatkais within the small margins permissible, so that the- aIteviatK» was synchronized with the arrival oi the gust. Ira a forge- araciaft, by virtue of a long body extending forward of the wings, sosoe advance warning was possible. The efficiency o>£ aDJeviafekva fell ofl rapidly with increasing lags. In Fig-. 5 was shown the distribtrtion of lags in the response to the British variety erf gust for the Brabazon I, the total lag being Jrast aeceptabfc. Oa the subject of flatter, Mr. RBSSCH thewgbt that it was by no m«arjs confined to large aircraft, although, at oate tinae it was considered that flutter of such aircraft -wDald insvolve considerably more detailed analysis than that foe smaller types. It now appeared, however, that it was not so nmefa ol the aircraft which. mattered, bat the type of O9 OS ASPECT RATIO - 100 -4 65 Vfc- 18 -290m.()ih.E.A.S. ISO 4O SO 6O 7O 8O WING LOADING (lb/4q ft) Fig. 6. Curves of wfng weight/gross weight ratio for gust and manoeuvring cases, showing, variation with span and wing loading. structure em- ployed and, in fact, any new aircraft designed to- modern strength theosies would, require a complete flutter analysis. The next sub- ject dealt with by Mr. Russell was weight analysis. In older (he stated) to de- termine the lay- out of a wing • that would satisfy airworthi- ness require- ments and permit the higfcest pos- sible efficiency in operation, it was necessary to select a wing 1 o a d i n g a n d , " "" aspect ratio involviag a balance between the weight of the structure to satisfy the demands of 'strength and stiffness, and the weight <si the fttel' appropriate to the particular performance- charaatiesistics. For this pea-pose, setae rusBe had to be established waerefcy ifie effect of these variables e» ptuT© weight coaM be assessed. The isflBjeaiGe ol size had be incltided. Methods of weight analysis feS into faor separate categories saceessively approaching an. increased aider of accuracy: p) a general survey for the purpose o£ suggesting probable trends and comparing the relative mieiits of different forms of laywwt and types of power plant; (ii) a particular design study of an aircraft whose form and type of power plant had already been decided as a result of a general survey; (iii) in the detail design stage when weight estimates could be made from production drawings; (iv) in the manufactured state, when actual weighings could be made of details, components and the complete aircraft. With a basis for estimating the weight of the structure for different sizes of wings, subjected to specified applied loads, and taking into, account the dynamic effects, it was possible to draw a general picture from which the weight of a particular wing could be assessed. As an example, the wing structure weigfcts sfeowB im Fig. 6 had been produced. Of the two sets of carves shown, one was for an ultimate strength factor of 3.75, aod the other for the appropriate gust factor at a true speed o£ 375 m.p..h. at 16,oooft with a representative over- swing factor oi 1.2 and a factor of safety of 1.5. The difference between these two sets of curves indicated the effective saving made possible by efficient gmt alleviation. TABLE R Yfmt loading 45 55 65 75 45 55 65 75 55 55 55 Aspect ratio ,9 I© IO m\ m f» m IB- 3 10 Fuef far SJMTO mifes range &333W SJrtB S.3S3 0.333 &3tt 0J2*(JJ88 03® 0J09 Wing structure Wight f».i32W JO. 123no. 117 : 10.112 i rD.I60 .j 0.140 H .0.125 to. iisfO.lll a f 0.123 t0.135 Fwel -(- wing weight 0.465 W 0.47 r 0.479 0.488 0.493 0.433 0.487 0.49t 0.499 0.471 0.4« From Fig. 6 and other data, it was possible to> formulate an ofjpiaikHi o€ the imffaesce oi wm-g leading" and aspect ratio OB operating economy, the results being listed in Tafote- II. From, tins, the fefibwimg conclosions could be drawn:— (E> \V"rth mf gmt alfevisttosi and with an aspect ratio* cf 10,
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
