design and construction of wind tunnel models

REPORT 20 o -

h-a: O o_

ADVISORY GROUP FOR AERONAUTICAL

RESEARCH AND DEVELOPMENT

REPORT 20

DESIGN A N D CONSTRUCTION OF

W I N D TUNNEL MODELS

by

JOSEPH J. MUNCEY

and

DAVID M. POTE

FEBRUARY 1956

NORTH ATLANTIC TREATY ORGANIZATION

PALAIS DE CHAILLOT, PARIS 16

REPORT 2 0

NORTH ATLANTIC TREATY ORGANIZATION

ADVISORY GROUP FOR AERONAUTICAL RESEARCH AND DEVELOPMENT

DESIGN AND CONSTRUCTION OF WIND TUNNEL MODELS

by

Joseph J. Muncey

and

David M. Pote

This Report was presented at the Eighth Meeting of the Wind Tunnel and Model Testing Panel, held from February 20th to 25th. 1956 in Rome, Italy.

SUMMARY

The Cornell Aeronautical Laboratory major wind tunnel is prescheduled to operate on an around-the-clock schedule. The achievement of accurate results under pressure of such a schedule has posed many problems in the design and construction of wind tunnel models. This paper discusses some methods and techniques which have been evolved.

SOMMAIRE

La souf f le r ie pr inc ipa le du Cornell Aeronautical Laboratory es t prevue pour un fonctionnement ininterrompu de 24 heures par jour . L 'obtent ion de r e s u l t a t s p r e c i s en presence d'un programme auss i charge a pose de nombreux problemes r e l a t i f s a la conception e t a la cons t ruc t ion des maquettes pour sou f f l e r i e s . Quelques unes des methodes e t des techniques elaborees en consequence sont i c i examinees.

533.6.071.3

3b8g

i i

CONTENTS

Page

SUMMARY ii

LIST OF FIGURES iv

1. INTRODUCTION 1

2. TYPES OF MODELS 2

3. MODEL DESIGN 3

4. METHODS OF CONSTRUCTION 5

5. RELATED MODEL AND WIND-TUNNEL EQUIPMENT 7

6. MACHINERY AND TOOLS 8

7. THE MODEL MAKER

8. QUALITY CONTROL

9. CONCLUSIONS

FIGURES 10

DISTRIBUTION

i i i

L I S T OF FIGURES

Fig.17

Fig.18

Typical subsonic model

Typical high-speed model

Reflection-plane model

Propeller nacelle assembly

Example of model making practice

Strain-gage hinge-moment installation

Example of model making practice

Supersonic model components

Internal pressure rake

Propeller duplicating machine

Propeller blade inspection

Molded plastic fiberglass fuselage shell

Method of Installing pressure tubes in thin airfoil sections

Tolerance for high-speed wind-tunnel models

Tolerance for high-speed wind-tunnel models. (Proposed)

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iv


Joseph J. Muncey and David M. Pote*

1. INTRODUCTION

The Wind Tunnel Department of the Cornell Aeronautical Laboratory offers a testing service to the aircraft industry and, because of heavy demand, operates its variable-density &k ft x 12 ft tunnel (2.6 m x 3.6 m. After modernization it will be 8 ft x 8 ft transonic.) on a 24 hours per day schedule. During the past year over 4000 hours of tunnel occupancy have been logged.

The airplane designer is naturally anxious to obtain test data as soon as possible. This desire is reflected in a demand that wind tunnel occupancy follow design specification by a minimum of time. As a result, a great deal of pressure is placed upon the model designers and upon the model makers to accomplish their tasks rapidly. At the same time, rather high standards of dimensional similitude between model and prototype airplane are required.

In our substantially unique position of designing, building and testing models for many different airplane companies, we have developed a number of special design features and methods of construction. We hope that the ones we can present in this paper will be of Interest to you.

2. TYPES OF MODELS

The models most frequently tested in the C.A.L. tunnel include the following types:-

(i) Subsonic model, usually about 60 in. span. (150 cm) (11) Transonic model of 18 to 48 in. span. (45 to 125 cm) (iii) Reflection-plane model of approximately 48 in. half span. (125 cm) (iv) Flutter models, approximately 18 in. chord x 36 in. span. (45 cm x 125 cm) (v) Propeller models of 4, 5, and 6 ft diameter. (125, 150, and 180 cm)

(i) Subsonic model The subsonic type of model is a complete model (Fig.l). It is sting mounted, houses

a six-component balance and all movable surfaces are equipped for hinge-moment measurements. An extensive-pressure survey system and duct rakes are also installed. This model is of composite construction, reinforced wood fuselage with metal wing and tall surfaces. A few of these models are powered by high cycle variable frequency motors equipped with propellers of exact scale. These models have movable control surfaces.

(ii) Transonic model The usual transonic model (Fig.2), also sting mounted, now of approximately 18 in.

span will be increased to 48 in. span after tunnel modernization. It is subjected to

'Respectively Superintendent of the Model Shop and Ass i s tan t Head of the Wind Tunnel Department, Cornell Aeronautical Laboratory, Buffalo 11, New York.

high loads which demand hardened steel for structural members. This type is complete in detail and fully instrumented. Within the fuselage and bolted directly to the wing it houses a balance capable of measuring three moments and three external forces. This model can be tested with or without canopy, tail, dropped leading edges or nacelles.

(iii) Ref lect ion-plane model A subsonic reflection-plane model (Pig.3) usually has a half span of approximately

48 inches. It is mounted on a balance system located beneath the tunnel floor. The plane of symmetry of this half span model is located approximately 1& in. above the floor. A non-metric marginal-sealed plateau fills the 1,4 in. gap. A grounding strip is attached to register interference. The horizontal tail is isolated on a separate balance. This is a fully instrumented model.

(iv) F l u t t e r models The airfoil flutter model is constructed of flexible materials molded, bonded and

assembled in such fashion that specific bending and torsional stiffnesses can be achieved. Models are suspended from an oscillator attached to the tunnel ceiling. Subsonic, transonic and supersonic types are instrumented to measure frequency and amplitude of flutter.

(v) P rope l le r models Cornell operates a 2000 h.p. propeller dynamometer within a removable tunnel test

section. The assembled propeller models measure 4, 5, or 6 ft in diameter (See Fig.4). They are mounted on co-axial shafts projecting from a pedestal type nacelle. Thrust, torque and blade bending are measured during single rotation to 7800 r.p.m. in an airstream approaching Mach 0.9. The propeller hubs, both manually adjusted and controllable, are machined from two steel blocks joined at the blade center line. The average hub is about 10 in. diameter x 9 in. long (25 cm x 23 cm). The blade retention sockets are precisely machined and the shaft hole is broached to match the dynamometer shaft. The blades are machined and hand finished from hardened alloy steel forgings.

To round out this paper, we mention here some examples of special model design.

(vl) Helicopter rotor blade assemblies for whirl tests to determine blade characteristics. Assemblies up to 84 in. (214 cm) in diameter are rotated by an instrumented hub. Motion and attitude records are transmitted through slip rings.

(vii) Engine nacelle models are fitted over and extend forward of the propeller dynamometer nacelle. Propeller effectiveness pressures and flow recovery are measured. Remotely operated valves regulate flow.

(viii) The dynamic stability model Is a balanced light weight three-dimensional model of extreme rigidity. Forces, moments and oscillation data are recorded simultaneously. Maximum frequency is 15 oscillations per second. Model weight cannot exceed 15 pounds (6.8 kg). This type of model is usually suspended at the forward end of a spring-type sting which permits the model to oscillate about a point located at the airplane center of gravity or any point forward to infinity. An internal flexture type balance is located between model frame and sting for the measurement of pitching moment and normal force.

3. MODEL DESIGN

We believe the theoretical ultimate in model design would be a hollow model made from one piece of steel. This configuration would offer rigidity, strength, and smoothness beyond anything obtained by joining together numerous separate parts. It is obvious that this ultimate is not practical. Need for housing the balance, and provisions for moving the control surfaces and for external configuration change prohibit such simple design. Therefore, rigid fit of mating parts is essential. Any relative movement or deflection will contribute to erroneous data. All sound models have been the accomplishment of successful co-ordination among the Aerodynamics, Design, and Shop groups. It is imperative that the design group be given detail specifications as to the requirements of the aerodynamic or engineering group before starting the detail design of a model. Specific items of information furnished either by the customer or the Cornell Aerodynamics Department are as follows:

(1) All basic model dimensions or a complete set of templates reduced to model scale.

(2) The required test configurations which determine the extent of complete removal components.

(3) The maximum angle range of tests in pitch, yaw and roll, and the approximate maximum applied loads on the model, including normal force, pitching moment and side force.

(4) Movable surfaces, if any, and desired angle settings, along with the approximate maximum hinge moment expected during the tests.

(5) Which hinge moments to be measured.

(6) The number of load and moment components that are to be measured, along with their approximate maximum values, will assist in the selection of the proper balance to be used or indicate the need of the design of a new balance.

(7) The desired number, size and locations of all pressure orifices.

(8) Any other special instrumentation that is required. Examples are provision for measuring forces on external stores, or for total vertical or horizontal tail loads.

(9) The type and extent of inspection required.

While meeting these aerodynamic specifications, the design must also fulfil other basic requirements that have been found necessary for the satisfactory performance of any model. These requirements include the following:-

(i) Strength and rigidity. Adequate rigidity has been obtained by designing all structural members and attachments to have a safety factor of at least five on any critical item, based on the ultimate failure stress of the materials used. (See Item (6) for loads).

(ii) Simplification of design for ease of fabrication, assembly and model changes is of utmost importance. Detail parts are usually designed to facilitate the use of our own shop techniques.

(iii) Certain general rules of good practice which we have found essential to reduce down-time, for example:-

(a) Movable-surface hinge-moment measurements always present a difficult problem, especially on small models such as the 18 in. span transonic models. On larger models hinge pins supported by small anti-friction bearings and a moment resistive tab can be used, and care must be exercised in locating the position of the hinges in order that the supporting surface deflection will not cause binding in the bearings. Only two bearings or two points of support should be used on any surface of this design. Three supports will always cause trouble due to binding of the bearings due to surface deflections. Figure 5 is a typical example of the design. The small model hinge moment measurement presents many more problems. In the first place, the surface thickness is not adequate to enclose or hold a bearing; therefore, flexure type hinges must be used. By incorporating a strain gage beam as an integral part of this flexure and using detachable angle blocks for angle adjustment, hinge moments can be measured with a considerable degree of accuracy. See Figures 6 and 7.

(b) See Figure 8. The vertical surface includes an integral square beam at the base, the aft end of which is bolted to the fuselage. A slot is cut forward approximately three-quarters along the way from the aft end between the airfoil shape and the top edge of the beam. This allows the beam to twist under side load of the vertical surface. Strain gages attached to the beam provide measurement of normal force.

(c) See Figure 9. When horizontal tail surfaces are located high on the vertical surface, attachment is accomplished by a disk that is machined at the center of rotation at the inboard end of the horizontal plane. This disk is recessed into the vertical surface. By bolting through the disks and vertical surface, adjustment and locking are obtained.

(d) See Figure 10. When the horizontal tailplane extends from the sides of the fuselage, it is common to machine a shaft of suitable diameter and length at the center of rotation at the inboard end of each tailplane. The shaft is fitted to the aft end of a cantilever beam which is housed within the fuselage. Angular 'V blocks clamp the shaft to the beam aft end, thus providing a range of angle settings. The Individual beams provide for moment and normal force measurement.

(e) By standard measurement technology used in the C.A.L. tunnel, the balance system, as well as pressure leads and hinge moment gage leads, of a sting model must be confined inside the model and sting. Clearance between parts, sting and model is very critical because the internal cavity housing these items is restricted in size by internal air flow through the model. Therefore, interference between metric and non-metric parts must be indetectable throughout the test. When possible, it is more profitable to Insulate the

entire model from the balance and sting. This is accomplished at the mounting point of the model at the forward end of the balance. When it is impossible to insulate the model at the balance attachment, insulated grounding circuits should be mounted on the balance and/or on the sting, where interferences are most likely to occur.

(f) It is also desirable to design loading points into the model. Such points are used when it is necessary to check the main balance calibration without disassembling or removing the model from the wind tunnel. Loading rigs, used as aids in the calibrating or check-calibrating of movable-surface hinge-moment balances, should also be provided.

(g) For fast and accurate installation of models in the wind tunnel, it is important that a leveling plate be provided along with each model. The leveling plate, when attached to the model, gives a ready reference plane with respect to some known reference line through the model. Therefore, any desired pitch, roller yaw angle can be readily set when installing the model for test.

4. METHODS OF CONSTRUCTION

As just described, the design of a model is largely dictated by requirements of the data desired. At the same time, allowance must be made for practical methods of construction. Ingenious methods of construction can often permit the design to be simplified and, in some instances, ingenuity is needed even to make the design possible of accomplishment. From our contact with other model makers throughout the United States, we have observed that basic methods of construction do not differ substantially from one company to another. Details of construction vary more, however, depending upon the ingenuity of the model designers, supplemented by the skills of the model makers. (See Figures 11 and 12)

As a result of the large number of occupancy hours of the C.A.L. tunnel, our Model Shop constructs an average of about 15 models each year. This has made it practical for us to assign a particular group of craftsmen in a well-equipped shop exclusively to making models. Thus, we have been able to rely heavily on the experience of those people. Although our shop is well equipped with power tools, we have found that a relatively large amount of hand work is desirable to produce a given model in the shortest elapsed time. For example, several shapes of wing leading edge may be tested with the basic center section. In such cases the interchangeable parts must be carefully blended to the basic part. If the original part is steel and the interchangeable parts aluminum, the machining and blending will be less difficult, and a mechanic skilled in the use of a file can achieve the desired results accurately and relatively quickly.

One rather important situation in which we have found it highly worthwhile to use powered duplicating equipment is the manufacture of model propeller blades (Pigs.13 and 14). Of any given design, we usually make five Identical blades. We have achieved the best compromise between total elapsed time and cost by making the first blade essentially by hand methods, after which it is used as a master on a hydraulic shaper-type planer equipped with a duplicator tracer follower to control the shaping of the additional blades. Lest we give an erroneous impression as to the amount of hand work,

we shall briefly describe making the first blade. We start with a forging somewhat oversize. The hub retention end and plan shape is lathe-turned between centers. After template location and twist layout are established, excess metal is removed on a ram type shaper machine, followed by hand grinding and filing to finished dimensions. Later blades require only the lathe work before the planer operation. We have found that the shaper will remove material to within +0.005 in. of the desired dimensions (0.13 mm), after which the blades are hand ground and filed to final size.

Model construction is started by the preparation of layout plates and templates. The templates are cut from plates photographically reproduced to model scale from full scale loft layouts, or the templates are cut from a layout on a metal plate. Upper and lower airfoil section templates should be notched and locked at the leading edge to avoid shifting. The edges should be parallel to the chord line joint. The outside edge of fuselage section templates should be square and parallel to provide a working reference.

Composite construction, reinforced wood or fiberglass is common for large models where all metal would be too heavy and costly (Pig.15). The fuselage shape is built over a steel skeleton consisting of a box or tube beam to which a tapered wing beam is attached. The fuselage beam houses the balance and provides a means for tall attachment. Aileron and flap hinge brackets are secured to the wing beam. Wood blocks with spanwise grain are resin-bonded and machine-screwed to the edges of the wing beam. Wood blocks of chordwise grain are then bonded to top and bottom of the wing beam and edge blocks. Wood blocks are also fitted and attached to the fuselage beam and, by the use of templates, this assembly of wood blocks and beams can be reduced to a smooth model of desired shape. Bonded fiberglass is being used increasingly for parts such as fuselage, nacelle, external store and duct, particularly where contours are complex, and loads are not high.

Metal wings are machined either from heat-treated alloy steel plate or from a forging hammered to an oversize shape. If strength requirements allow aluminum to be used, it should be a heat-treated plate or forging. The machining methods are practically the same for either metal, except that with aluminum, cutting speeds can be increased to a degree where an aluminum wing will cost approximately 75% as much as a steel wing. The rough stock is first shaped to maximum thickness. Next, the plan shape is cut to a layout on the piece. The blank is then mounted on a plane table and with height gage and scriber the dihedral, twist and contour template locations are established. At several span locations, grooves are cut to form the contoured surface. The blank is then placed in" a shaper machine which removes the excess metal between grooves. The wing is held by a ball-and-socket swivel clamp that permits alignment under the cutting tool, which follows along percentage lines from root to tip. After machining, the final accurate finish is obtained by disk grinding and hand filing. Caution must be exerted to maintain straight lines between templates. Gage blocks are used to control exact temperature fit. Polishing time can be reduced if abrasive powder is added to the oil-coated abrasive cloth. A spanwise motion is prefered when polishing tapered wings. A satin smooth finish of approximately RMS 5 is usually obtained.

Interchangeable parts, such as a series of tall cones, are fitted to milled flats and jig-drilled for pins and screws. A line of tangency must blend or fair with each of the changed parts. If the original unchanged part is steel and the changed parts aluminum, the matching and blending will be less difficult. Standard 'go, no-go' plug

and r ing gages w i l l help c l o s e - f i t t i n g r e l a t e d balance p a r t s . I t i s p r a c t i c a l t o shape nace l les and a i r scoops from separa te blocks tha t a re f i t t e d to the adjacent surface. The in t e rna l template f i t t i n g should be completed before shaping the outer surface.

The method of i n s t a l l i ng pressure o r i f i ces and tubes to the outer model surface is determined by model s ize and sect ion thickness. A prac t i ca l solut ion for th in sect ions is to locate and d r i l l the s e r i e s of o r i f i ces c l ea r through the sect ion (Pig.16). The d r i l l diameter should equal the inside diameter of the lead-away tube. On the opposite surface, s l o t s are milled for the lead-away tubes, equal to the tube outside diameter. The tube ends are sealed with hard solder and the tubes soft soldered smooth with the surface. F ina l ly , using the d r i l l e d hole as a guide p i l o t , the d r i l l is passed through one wall of the tube. For heavy a i r f o i l or body sec t ions , the tubes can be soldered d i r ec t ly to s t e e l . In wood and aluminum, brass bushings are used. The tubes are led away embedded in a p l a s t i c f i l l e r or solder f i l l ed channel or s l o t s cut in the opposite sur face . Pressure tubes i n s t a l l e d in movable sur faces should terminate in a small covered recess junct ion box milled under the sur face . Matirtg-plck-up tubes are led through s l o t s in the wing or f in t o a s imi la r covered r e c e s s . These corresponding tubes are connected by a f l e x i b l e p l a s t i c tube which allows angular s e t t i n g of the control surface. The se lec t ion of tube depends on the app l i ca t ion . Soft corros ion-r e s i s t a n t s t e e l or pure nickel a re used for surface p re s su re s . For exposed rakes , hard-drawn tube should be used. The tube gage diameter depends on the allowable s l o t s i ze and the choking ef fec t in duc t s . 0.032 in. outs ide diameter x 0.010 in. wall (0 .8 x 0.25 mm) to 0.062 in. ou ts ide diameter x 0.015 in. wall (1.6 x 0.4 mm) w i l l permit s a t i s f ac to ry manometer response. The diameter of s t a t i c holes should never be less than No.80 d r i l l (0.0135 in. or 0.343 mm).

5 . RELATED MODEL AND WIND-TUNNEL EQUIPMENT

Guided miss i le and bomb models are s t i ng mounted. They house a six-component ba l ance. Miniature miss i les are pylon supported. Others are posi t ioned unattached in the presence of the model. Cornell b u i l t a unique posi t ioning device tha t clamps to the s t ing . Stores can be moved in three d i rec t ions and pitched +10°. This adjustable s t ing support cons i s t s of a double doveta i l p l a t e 6 in. x 12 in. (15 cm x 30 cm) a t tached to the forward end of an aux i l i a ry s t i n g . Two v e r t i c a l doveta i l s l o t s are cut on one face and two c i r c u l a r dove ta i l s l o t s of 25 in. (63 cm) cen te r rad ius on the opposite face. This locates the s t o r e cen te r of r o t a t i o n 25 in. (63 cm) forward of the p l a t e . The s to re is held a t the end of a small s t i ng , the a f t end being f i t t e d to the c i r c u l a r s l o t s . Ver t ica l and c i r c u l a r motion i s obtained by individual motor driven worms meshing with worm gear s e c t o r s . Motors, gears , bearings and pos i t i on indicators are encased within a streamline pod.

Transducers are i n s t a l l ed under the surface of dynamic and f l u t t e r models. They e l e c t r i c a l l y t ransmit pressure values to a recording device. Transducers are a l s o used in s e r i e s with manometer lead-in tubes to record pressures automatically. Cornell has in use a pressure-scanning switchvalve which s e l e c t s eight individual pressures and d i rec t s them to a s ingle manometer tube or recording device. The valve is operated by remote con t ro l .

Posi t ion i n d i c a t o r s conserve tunnel time when used with remote cont ro l devices . Potentiometers and cam-or linkage-operated s t ra in-gage beams are used to indicate the position of movable surfaces.

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Remote con t ro l d e f i n i t e l y reduces tunnel shut-down time. Cer ta in Cornell models are equipped for remote operation of control surfaces , duct valves, posi t ioning external s t o r e s and r o t a t i n g guided miss i l e f in assembl ies . Small geared motors are coupled d i r e c t l y to torque sha f t s or jack screw are operated by chain-dr iven sprocket nu t s . When model s i z e w i l l allow, the Lear ac tua tor i s i n s t a l l e d . These ac tua to r s include l imit switch and posi t ion indica tor .

In te rna l model balance types are so numerous t ha t we can mention only a few basic requirements. Until recent ly Cornell has used SAE-4340 s t e e l exclusively for balances and r e l a t e d p a r t s , but now we are having good r e s u l t s with Armco No.17-4 cor ros ion-r e s i s t a n t , hea t - t r e a t ab l e s t e e l . Machining to close symmetrical tolerance i s e s s e n t i a l , e spec ia l ly on small f l exures . We suggest Sheff ie ld or Raytheon Ult rasonic machining as a method of cu t t ing small narrow s l o t s in drag member d e t a i l s . When furnace brazing i s requi red , sample t r i a l u n i t s of s i m i l a r dimension should be brazed to determine movement and the inducement of s t r e s s . Considera t ion should be given t o space for s t r a i n - g a g e clamps. For balance t o s t i n g connect ion, we recommend male and female tapers with key and draw nut.

Box type c a l i b r a t i o n durmy model can be weldment of four ground p l a t e s . Ins ide accuracy can be held by Inser t ing three removable ground square blocks a t each end and center before welding. All loading holes should be j i g - d r i l l e d to ensure symmetrical accuracy.

6 . MACHINERY AND TOOLS

Universal mil l ing machines lead the l i s t of useful machines for the model shop. The adjustable head for v e r t i c a l mil l ing and boring affords a means of removing metal t o a given template or reference surface. Shapers and planers offer speed in removing excess metal . They are the most e f f i c i e n t for facing common p l a t e s or block in preparat ion for layout. These machines a re , or can be, equipped with automatic t r ace r dupl ica tors . Lathes, both l a rge and smal l , a re used ex tens ive ly t o machine c i r c u l a r work of a l l desc r ip t ions . Certain new la thes incorporate rapid t raverse for fas t , accurate operat ion . S tee l or aluminum bodies of i r r egu la r and e l l i p t i c a l cross sec t ion can be dupl i c a t e d by a t r a c e r at tachment geared to r o t a t e a wood or p l a s t e r model behind the hydraul ic -cont ro l led tool ca r r i age . Worthy of spec ia l mention are the small s ens i t i ve d r i l l presses , with which the mechanic can ac tua l ly feel and apply pressure feed when d r i l l i n g small holes.

7 . THE MODEL MAKER

The e f f i c iency of a shop depends l a rge ly on the s k i l l of the men who a c t u a l l y do the work and t h e i r wil l ingness to follow ins t ruc t ions . Selec t ing a man for the job he does we l l should a t t imes be n e g l e c t e d , in order to t r a i n more men for a l a r g e r v a r i e t y of j o b s . We have found t h a t experienced p a t t e r n makers and too l makers are anxious to loca te in a well organized model shop where they can advance t h e i r s k i l l . When there are severa l good ways to do a c e r t a i n job, we allow the shop man to do i t h is way. This promotes i n i t i a t i v e and s a t i s f a c t i o n .

An honest, f r i end ly , mutual understanding between the shop supervisor and h i s men wi l l r e s u l t in team work necessary to expedite the making of a qua l i ty product. Uniform

distribution of work, with care not to overload a certain group, will prove the value of carefully planned schedules.

8. QUALITY CONTROL

Quality control and the inspection of models including a reliable record or report, is a necessary function of any engineering-shop combination. Here at Cornell, the inspector is an unbiased individual, reporting to a superior who is not a member of the engineering-shop group. Legible drawings, specifications and a standard tolerance chart should be the basis of acceptance or rejection. Tolerance charts of allowable error should vary with model scale (Figs.17 and 18). We recommend the practice of checking the job in the machine, on the bench, or whenever a set-up or layout could be in error. Final assembly inspection is made on a granite plate. Reference and construction lines established during fabrication are used by the inspector. An adjustable model sting mount fixed to the inspection room wall over the plane table permits a set-up comparable to the wind-tunnel support. Inspection equipment includes a vacuum pump for checking pressure systems, Magnaflux, and propeller-balancing ways. A ready reference for the engineer or customer is a three-view drawing, showing such actual dimensions and angles which are of special significance.

9. CONCLUSIONS

The achievement of accurate models in minimum time and a t low cost i s the goal of the Model Designer-Maker team. Best r e s u l t s can be accomplished by a mutual understanding of ava i l ab le methods of cons t ruc t ion and the advantages and l i m i t a t i o n s of each; by continuous, c lear communications during the en t i r e period of model construction; and by continuous a t t en t ion to myriads of d e t a i l s .

We an t i c ipa t e the future trend w i l l favor a i r c r a f t of r ad ica l design, as judged by present s t anda rds . The models w i l l be complicated and subjec ted t o higher loads . Development of improved engine a i r ducts , refinement of nace l le shape, 'coke b o t t l e ' fuselage l ines and airborne weapons are but a few of the d e t a i l s tha t are l ikely to be found on new a i r c r a f t . These w i l l chal lenge the s k i l l s of the model des igner and builder as have the designs of the past .

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F ig . l Typical subsonic model

Pig.2 Typical high-speed model

11

r

Fig.3 Reflection-plane model

Fig.4 Propeller nacelle assembly

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A-A F i g . 5

INCHES 1 2

. 1 , 1 , 1 . 1 . I , I . 1 \ 1 2 3 4

CM 5 6 7

F i g . 6

13

Fig.7 Strain-gage hinge-moment i n s t a l l a t i on

STRAIN CAGES Pig. 8

14

ANCLE ADJUSTMENT

SCREW

INCHES I 2

1 1 • [ . | i i . ! • [ • 1 1 • • | • | . | i J

• ' • ' • ' • ' • •

1 1 ' [' i y

• i • n I 2 9 4 5 6 7

CM

F i g . 9

INCHES I 2

• i • | ' i ' 1' i ' i 1 1 ' I ' i• |M Y

i i i i i l i i . i i i i l \ 2 3 4 8 6 7

CM

STRAIN GAGES

Fig.10

15

Fig.11 Supersonic model components'

Fig.12 Internal pressure rake

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Pig.13 Propeller duplicating machine

Fig.14 Propeller blade inspection

• M H m M ^

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Fig.15 Molded plastic fiberglass fuselage shell

STEP ( I ) DRILL ORIFICE

STEP (E) MILL LEAD

TUBE SLOTS

B—EL—S STEP ( 3 ) SOLDER TUBES

IN SLOTS

M t i STEP (4-) PASS DRILL

THRU TUBE WALL

Fig.16 Method of Installing pressure tubes in thin airfoil sections

19

LOCATION OF M A X I M U M THICKNESS OF AIRFOIL OR BODY

.008

.006

.004

.002

ooe

U 004 X o

- .006

Ul o z < tr ui

.008

.010

.012

.014

.016

PLUS

2 0 4 0 6 0

1

i I

8 0

% OF A I R F O I L OR BODY L E N G T H

MINUS

^

TEMPLATES

AIRFOILS

BODIES r

/ F

^

/ '

W \

^

- -

^

KT]

- i 1 '•

L

1 0 0

h

-

-

• —

-

—

.20 MM

10 MU

-.10 MM

2 0 MM

3 0 MM

N O T E !

I n f l e c t i o n po in t to be l o c a t e d a t s t a t i o n of m a x i m u m ,

t h i c k n e s s but a l w a y s at same v a l u e of t o l e r a n c e .

T o l e r a n c e at n o s e , s t a t i o n of m a x i m u m t h i c k n e s s ,

a n d at t r a i l i n g edge are f i x e d at va lues s h o w n .

A N G L E TOLERANCE t 1 /4° OVERALL ASSEMBLY TOLERANCE 1 . 0 2 5 J.J.M.

Pig.17 Tolerance for high-speed wind-tunnel models

20

PLUS AND MINUS

TOLERANCE

.60 MM

.50 MM

- .40 MM

. 3 0 MM

.20 MM

JO MM

Q t t l - r r

10 IS 20 ES JO SS 40 43 SO MODEL SCALE IN PERCENTAGE

Fig.18 Tolerance for high-speed wind-tunnel models. (Proposed)

DISTRIBUTION

Copies of AGARD publications may be obtained in the

various countries at the addresses given below.

On peut se procurer des exemplaires des publications

de 1'AGARD aux adresses suivantes.

BEI4GIUM

BELGIQUE

Centre National d'Etudes et de

Recherches Aeronautiques

11, rue d' Egmont

Bruxelles.

CANADA Director of Scientific Information

Services, Defence Research Board

Department of National Defence

•V Building

Ottawa, Ontario.

DENMARK DANEMARK

Military Research Board Defence Staff Kastellet Copenhagen 0.

FRANCE

GERMANY ALLEMAGNE

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ICELAND ISLANDS

ITALY ITALIE

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Greek Nat. Def. Gen. Staff 3. MEO Athens.

Iceland Delegation to NATO Palais de Chaillot Paris 16.

Centro Consultivo Studi e Ricerche Ministero Difesa - Aeronautica Via Salaria 336 Rome.

LUXEMBURG

LUXEMBOURG

Luxemburg Delegation to NATO

Palais de Chaillot

Paris 16.

NETHERLANDS PAYS BAS

Netherlands Delegation to AGARD 10 Kanaalstraat Delft, Holland.

NORWAY

NORVEGE

Chief Engineering Division

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Deputy Chief of Staff/Material

Myntgaten 2

Oslo.

Attn: Major S. Heglund

PORTUGAL Subsecretariado da Estado da

Aeronautica

Av. da Liberdade 252

Lisbon.

Attn: Lt. Col. Jose Pereira do

Nascimento

TURKEY

TURQUIE

M. M. Vekaleti

Erkaniharbiyei Umumiye Riyaseti

Ilmi Istisare Kurulu MiidurlUgu

Ankara.

Attn: Colonel Fuat Ulug

UNITED KINGDOM

ROYAUME UNI Ministry of Supply TIL, Room 009A First Avenue House High Hoiborn London,W.C.I.

UNITED STATES

ETATS UNIS

National Advisory Committee for

Aeronautics

1512 H Street, N.W.

Washington 25, D.C.

$ Printed by Technical Editing and Reproduction Ltd

95 Great Portland S t . London, U. l .

AGARD Report 20

North Atlantic Treaty Organization, Advisory Group

for Aeronautical Research and Development


Muncey, J.J., Pote, D.M.

1956 20 pages, incl. 18 figs.

The Cornell Aeronautical Laboratory major wind

tunnel is prescheduled to operate on an around-

the-clock schedule. The achievement of accurate

results under pressure of such a schedule has posed

many problems in the design and construction of

wind tunnel models. This paper discusses some

methods and techniques which have been evolved.

Presented at the Eighth Meeting of the Wind Tunnel

and Model Testing Panel, held from February 20th

to 25th, 1956, in Rome, Italy.

AGARD Report 20



DESIGN AND CONSTRUCTION OP WIND TUNNEL MODELS

Muncey, J. J., Pote, D.M.












533.6.071.3

3b8g

533.6.071.3

3b8g

AGARD Report 20



DESIGN AND CONSTRUCTION OP WIND TUNNEL MODEI4S


1956 20 pages, Incl. 18 figs.




results under pressure of such a schedule has posod






to 25th. 1956, in Rome, Italy.

AGARD Report 20





1956

20 pages, incl. 18 figs.











533.6.071.3

3b8g

533.6.071.3

3b8g

AGARD Report 20




Muncey. J.J., Pote, D.M.











to 25th. 1956, in Rome, Italy.

AGARD Report 20




Muncey, J. J., Pote, D. M.



tunnel Is prescheduled to operate on an around-



many problems In the design and construction of






533.6.071.3

3b8g

533.6.071.3

3b8g

AGARD Report 20





1956

20 pages, incl. 18 figs.




results under pressure of such a schedule has posod

many problems In the design and construction of





to 25th, 1956. In Rome, Italy.

AGARD Report 20




Muncey. J.J., Pote, D.M.












533.6.071.3

3b8g

533.6.071.3

3b8g

design and construction of wind tunnel models

Documents