SUPPLEMENT TOPLIGHT

THE AIRCRAFT ENGINEERAUGUST 30, 1928

cQ

Z

o

350

300

200

150

100

;

"z

\

'- /

"1 1 1 1 1 1 1 1 1 1 ! ; 1 1 1 I 1 ! l : l i 1 1 1 1 M 1 I I J 1 1 1 .1 J 1 i 1

1 i ' 1 , ! 1 1 1

FIG. 5.

'1''

/

1111

7]

:;

i,iitii i r

900?

1200 1800 2400 3000 3600 4200 4800 5400 6000 6600TOTAL VOLUME OF ONE FLOAT- EXPRESSED IN LBS.

7200 10 20 30 40SPEED IN KNOTS.

A perusal of recent technical publications also indicatesthat a considerable amount of experimental work has beendone in America, in "" springing " the floats from the stepfor alighting on ice.

It is more than probable that the desire to produce floatseconomically will tend to the simplification of acceptedpresent-day design of lines. One means of doing so is tomaintain a constant radius for the deck aft of the step, theskin above chine being wall-sided. This eliminates a con-siderable amount of panel-beating.

In the event of such a system becoming generally recog-nised the coefficient values given in this article would, ofcourse, have to be revised as data accumulated to conformwith the new ' ; lines." The method of drafting out theapproximate shape could then be applied in similar fashionto that described.

It seems unlikely that the present-day shape for planing-bottom will be drastically modified. I t is at least safe toassert that any appreciable advance in hydrodynamic per-formance can only be looked for as the result of thoroughand exhaustive tank-tests.

Several firms interested in seaplane development abroadhave already installed test-tanks for this purpose.

Although to some extent the lines design and structuralrequirements are co-ordinated, the constructional features andmethods of assembly have not been discussed at length here,as they do not strictly come within the scope of this particulararticle.

On Fig. 5 the weights of floats for some twenty seaplanesare plotted against total buoyancy, giving a useful approxi-mation to the weight which may be expected in dural floatconstruction.

Fig. 6 shows the total water resistance of a comparativelvclean float on a base of speed, for a seaplane of 4.000 lb.all-up weight.

TECHNICAL LITERATURE.SUMMARIES OF AERONAUTICAL RESEARCH

COMMITTEE REPORTS.

These Reports are pubhshed by His Majesty's StationeryOffice, London, and may be purchased directly from H.M.Stationery Office at the following addresses : Adastral House,Kingsway, W.C. 2 ; 28, Abingdon Street, London, S.W.I;York Street, Manchester ; 1, St. Andrew's Crescent, Cardiff ;or 120, George Street, Edinburgh; or through any book-seller.

CHARTS FOR THE CALCULATION OF AIRSCREW THRUSTAND TORQUE COEFFICIENTS. By J. D. Coales. Communi-cated by the Director of Scientific Research, Air Ministry.R. & M". NO. 1114 (Ae. 287). (7 pages and 12 diagrams.)September, 1927. Price M. net.

About eight years ago, charts were produced for the purpose of simplifyingthe calculations of the thrust and torque coefficients of airscrews. At thattime, the theory of airscrews was not so well established a? it is now, and thecharts were not published because of the discrepancies that were found tooccur between the calculated and full-scale values of torque coefficients. Thecharts are based on the same equations that occur in the modern VortexTheory of airscrews, as given in "Aerofoils and Airscrew Theory," by H.Glauert, and are equally valid whether the Vortex theory or the older inflowtheory is followed.

Besides generally reducing the amount of computation in the completeestimation of an airscrew performance, the curves enable the thrust andtorque coefficient of an airscrew at a particular value of V/nD, to be obtainedwith a minimum of trouble.

A SURVEY OF LONGITUDINAL STABILITY BELOW THE STALL,WITH AN ABSTRACT FOR DESIGNERS' USE.—By S. B. GATES,M.A. Presented by the Director of Scientific Research, AirMinistry. R. & M. No. 1118 (Ae. 291). (27 pages and 22diagrams.) July, 1927. Price Is. 3d. net.

A new system of units, in which the resistance derivatives are expressed asnon-dimensional quantities has been suggested by Mr. Glauert in reportK. & M. 1093.* This allows a much more compact analysis of longitudinalstability below stalling than has hitherto been given. In this work, thetheory has been thrown into such a form as may bring it within the scope ofdesigners.

A description of longitudinal stability is attempted in terms of the twoquantities practically at the disposal of designers :—Position of centre ofgravity and size of tail. With these co-ordinates, and certain other para-meters, the region of longitudinal stability is defined on a series of planediagrams ; and in typical cases the plane lias been covered by curves fromwhich the damping and period of the phugoid motion may be estimated.

An abstract of instruction? for using the diagrams is added.

* R. & M. 1093. A non-dimemional form of the stability equations of anaeroplane.—R. Glauert.

MODEL EXPERIMENTS WITH REAR SLOTS AND FLAPS ONAEROFOILS R.A.F. 31 and R.A.F. 26. By H. B. Irving,B.Sc, A. S. Batson, B.Sc, and A. L. Maidens. R. & M,No. 1119 (Ae. 292). (8 pages and 8 diagrams.) November,1927. Price M. net.

This is a continuation of general research on the slotting of aerofoils.Aerofoils of sections R.A.F. 31 (with front slot) and R.A.F. 26 (without front

slot) were fitted with rear slots formed by the gap between flap and mainportion and the best position of flap when at 20° to main wing found. In thecase of R.A.F. 31 experiments were limited to one shape of slot, while onR.A.F. 26, three variations were tried.

The rear slot on R.A.F. 31 gave a maximum lift coefficient with flap at 20and front slot open of nearly 1 -2, being over double that of the originalaerofoil. The rear slot itself gave an increase in lift coefficient of 0 15 withfront slot open and flap at 20°. With flap at 0" and front slot closed the rearslot increased the minimum drag by about 10 per cent., but there was noappreciable alteration in maximum lift/drag ratio. Maximum lift with flapat 20° and front slot open occurred at 18 • 3°, compared with 23 • 8° incidence onthe aerofoil with front slot, but without flap, and 12 • 3° on the original unslottedaerofoil.

On aerofoil R.A.F. 26, the highest lift coefficient obtained was 0-753 or55 per cent, more than on the original aerofoil (0-485). The increase inminimum drag was only about 2 per cent.

In all cases, maximum lift is much more sensitive to changes in flap positionwhich alter the width of slot than to changes in a direction parallel to the

748/