NASA TECHNICALMEMORANDUM

x

I -

z

FULL-SCALE SUBSONIC WIND TUNNEL REQUIREMENTS

AND DESIGN STUDIES

Mark W. Kelly, Kenneth W. Mort, and David H. Hickey

Ames Research CenterMoffett Field, Calif. 94035

(NASA-TM-X-62184) FULL SCALE SUBSONIC WINDTUNNEL REQUIREMENTS AND DESIGN STUDIESM,.W. Kelly, et al (NASA) Sep. 1972 50 p

CSCL 1 4B

September 1972

NASA TM X-62,184

G3/11

FULL-SCALE SUBSONIC WIND TUNNEL REQUIREMENTS

AND DESIGN STUDIES

Mark W. Kelly, Kenneth W. Mort, and David H. Hickey

Ames Research Center

SUMMARY

This paper summarizes the justification and requirementsfor a large subsonic wind tunnel capable of testing full-scaleaircraft, rotor systems, and advanced V/STOL aircraft propul-sion systems. The design considerations and constraints forsuch a facility are reviewed, and the trades between facilitytest capability and costs are discussed. The design studiesshowed that the structural cost of this facility is the mostimportant cost factor. For this reason (and other consider-ations such as requirements for engine exhaust gas purging)an open-return wind tunnel having two test sections wasselected. The major technical problem in the design of anopen-return wind tunnel is maintaining good test section flowquality in the presence of external winds. This problem hasbeen studied extensively, and inlet and exhaust systems whichprovide satisfactory attenuation of the effects of externalwinds on test section flow quality were developed.

Cetaiis S ;u alosbe inthis ouStudied nms be betiris~uied oe ~iuoi$h~

INTRODUCTION

The studies reported here were initiated in 1967 whenthe Aeronautics and Astronautics Coordinating Board (AACB)requested a general study to determine the need for newnational aeronautics facilities. The Aeronautics Panel ofthe AACB organized three working groups to consider facilityrequirements for three types of aircraft: (a) subsonic andV/STOL; (b) transonic and supersonic; and (c) hypersonic.

In 1968 the Subsonic and V/STOL Working Group identi-fied the need for a large subsonic wind tunnel capable oftesting full-scale rotor systems and high performance V/STOLaircraft. Over the next two years the Aeronautics Panelreviewed the justification and technology requirements forthe facilities proposed by the Working Groups and, in October1970, recommended to the AACB that a large engine test facil-ity and the large subsonic wind tunnel described herein beconstructed. In December 1970, NASA organized an Inter-Center Working Group (comprised of personnel from NASAHeadquarters and the Ames, Langley, and Lewis Research Centers)to conduct further design studies of the Full-Scale SubsonicWind Tunnel. In February 1972, this Group selected a two-test section, open-return wind tunnel concept for thisfacility. Further design optimization studies are presentlyin progress.

One of the prime factors which motivated the AACB toinitiate the study to determine the need for new aeronauticalfacilities was the recognition that improvements in effec-tiveness and economy of aeronautical systems have only beenachieved by the extensive use of ground-based facilities.Another important factor was the recognition by the AACB thatthe United States had not initiated any new major aeronau-tical facilities since the Unitary Wind Tunnel program in1950.

In their original instructions to the Subsonic andV/STOL Working Group the Aeronautics Panel of the AACBdirected the Working Group to consider planned future air-craft programs and the facilities required for the developmentof these aircraft. To support this effort the advanced plan-ning groups of the various military services and NASAsubmitted requirements for various military and commercialmissions. Several points became clear. First, it was obvious

2

that the facility could not be built soon enough to con-tribute to the development of specifically planned aircraft;so the Working Group interpreted the more generalized long-range mission requirements in terms of aircraft for themore distant future. Second, this exercise showed that thebasic aircraft development trends and technical problemswhich justify the facility are more fundamental and morecertain than specific aircraft development programs. And,third, there was no single absolute requirement in terms ofeither aircraft or problem solution which would justify thefacility, but there were numerous technical problems forwhich the proposed facility would provide solutions in suchan effective and efficient manner that it could be expectedto pay for itself many times over. This situation makes thepresentation and substantiation of the justification a pro-tracted process. In brief, however, the points which willbe made are as follows:

1. There is a rapidly growing demand for improvedand increased transportation caused by thegrowing economy and population of the nation.Meeting this demand will far overtax ourpresent transportation systems, and is criti-cal for improvement of the quality of life inthis country. Traffic congestion and aircraftnoise are a key retardants to the developmentof adequate transportation.

2. The use of STOL, VTOL, and other high lifttechnology aircraft will provide solutions fora significant part of the transportation re-quirement. These same technologies arerequired for a number of military missions.

3. The key problem in the development of theseaircraft is the reduction of the technical andfinancial risk of the aircraft developmentprogram. This program risk can be reduced bytesting the critical components of the air-craft (e.g. V/STOL propulsion systems androtors) at an early stage in the developmenteffort, so that expensive and possiblycatastrophic failures are avoided later inflight.

3

FUTURE AIR TRANSPORTATION REQUIREMENTS

Civil Requirements

A number of studies have documented the growing prob-lems in providing the transportation facilities required tocontend with the estimated growth in population and economyof the United States. For example, the domestic airlinesalone expect the number of passenger miles flown in 1980 tobe more than double that flown in 1970 (see reference 1).An even greater increase is expected in air cargo operations.When viewed in the context of the current congestion atlarge airports, it is clear that a major technical challengemust be met if the forecasted transportation capability isto be realized.

Figure 1 shows the major problem areas for civil airtransportation as identified by the Joint DOT-NASA CivilAviation Research and Development Policy Study (reference 1)along with the associated technological disciplines. Withthe exception of avionics, all of these disciplines wouldbenefit from the type of facility proposed in this report.

The economic impact of aircraft noise and congestion iswell documented. For example, figure 2 (taken from reference2) shows that congestion around our major airports cost theairlines nearly 160 million dollars in 1969. It is esti-mated in reference 2 that the accompanying cost to passengersdue to terminal area delays was an additional 100 milliondollars. It is further estimated in reference 2 that theselosses will grow to 600 million dollars for the airlines and400 million dollars for passengers by 1980 unless correctiveaction is taken. The economic and environmental impact ofthe aircraft noise problem has been the subject of a numberof reports and will not be further discussed herein. Sufficeit to say that the problems of aircraft noise and air trafficcongestion are exacting significant economic and environ-mental penalties at the present time. Further, if theseproblems are not adequately dealt with they will seriouslylimit the transportation capability of the nation and thegrowth of the air transportation industry.

4

Application of high-lift and V/STOL aircraft technologyto civil aviation requirements.- References 3 through 10show that the use of reduced takeoff and landing (RTOL) air-craft and V/STOL aircraft can be expected to provide signif-icant relief of the aircraft congestion and noise problems.As shown in figure 3, this will be accomplished by shiftingmost of the short-haul traffic away from the major airportsto small V/STOL ports. This should have a major impact oncongestion since over 50 percent of the air traffic ispresently funneled into only 14 major airports. Moreover,the major transportation demand for all scheduled carriers(both air and surface) is for trips between 50 and 500 miles.In addition to relieving the air traffic congestion and noiseproblem the high-performance RTOL or V/STOL transport alsowill produce large savings in total time required for tripsof this stage length. These savings accrue from two factors.First, the takeoff and landing facilities can be. closer tothe passenger's destination with resulting savings in thetime and cost of ground transportation to and from the air-port. Second, the improved low-speed flight capability ofthe aircraft makes it possible to reduce the time lost in airand ground maneuvers in the terminal area and thereby to re-duce the required airport- to-airport time.

Figure 4 (taken from reference 11) shows the noiseimpact of various forms of transportation systems, both airand ground. This figure shows that the use of V/STOL air-craft significantly reduces the land area exposed to highnoise levels compared to that for conventional aircraft(CTOL). Moreover, for trip lengths more than 50 miles theair systems expose less land to excessive noise than theground transportation systems. This is due to the factthat the aircraft is far removed from any potential listenerthrough the major portion of its trip. Also shown in

figure 4 is the amount of land which must be acquired forthe use of the transportation systems. The air systems havean obvious advantage here since no extensive rights-of-wayare required, and the use of V/STOL aircraft, maximizes thisadvantage, since it minimizes the amount of land which mustbe acquired for airports.

The basic economic and environmental factors just dis-

cussed are not new. As a matter of fact, these areessentially the same factors which have historically driventhe development of high-lift systems on aircraft and whichhave produced the improvements in maximum lift coefficient

5

shown on figure 5. Present short and medium range jettransport aircraft are equipped with very sophisticatedmechanical high lift devices. Further reductions in take-off and landing distances and the associated benefits ofimproved low-speed flight capability can only be achievedthrough the use of the powered-lift technology of V/STOLaircraft. Thus, the present interest in V/STOL transportaircraft is a logical extension of the high-lift technol-ogy trends for conventional aircraft.

Other civil applications of V/STOL aircraft.- Thepreceding discussion has been directed at the applicationof V/STOL aircraft to scheduled commercial transportoperations. It should be noted, however, that there aremany other uses for V/STOL aircraft. For example, theheavy-lift helicopter has already shown its value in manymissions, both commercial and military. The helicopter isbeing used as a utility transport in a variety of commer-cial applications in spite of its deficiencies. This initself is a testimony to the economic value of the utilityprovided by vertical flight capability. For example, theuse of helicopters for carrying personnel and equipment toand from the off-shore oil rigs along the Gulf coast alonehas accounted for more than 1 million flight hours.

Summary of civil aircraft requirements.- It is clearthat basic factors such as the growth of the population andeconomy of this country will create a rapidly growing demandfor transportation; and it is equally clear that the qualityof life in the United States will be determined in a largepart by how well these transportation requirements are dealtwith. While there is room for debate about the level ofgrowth in the transportation requirement, there can be nodoubt that transportation capabilities will be taxed to theutmost. This is already evident in terms of the air andground congestion in and around metropolitan areas. Thepotential of aircraft utilizing V/STOL technology to providesolutions for a significant part of this transportationrequirement has been documented in a number of studies. Thesolution of the technical problems associated with the devel-opment of such aircraft constitutes a large part of therequirement for the proposed full-scale wind tunnel, as willbe shown in a subsequent discussion of V/STOL aircrafttechnology.

6

Military Requirements

Conventional aircraft.- Many of the aircraft missionrequirements dictated by military operations impose stringentrequirements on landing and takeoff performance, low-speedflight characteristics, stall and spin characteristics, etc.For. example, the achievement of satisfactory landing andtakeoff characteristics for carrier-based aircraft withoutpenalizing high speed performance requires a careful com-promise between high-lift aerodynamics, high-speed aerodynamics,structural weight, and complexity. A similar situation existsfor most tactical aircraft since they are required to usesmall unprepared fields which place a premium on landing andtakeoff characteristics. Even large, long range militarytransports have generally quite stringent takeoff and landingspecifications compared to their commercial counterparts.For example, the C5-A military transport is required tooperate out of 4000-ft. fields with a 100,000 lb. payload.

V/STOL aircraft.- The value of V/STOL aircraft in alimited war situation has been proven by the widespread useof the helicopter in Vietnam for such missions as transpor-tation, air-rescue operations, reconnaissance, tacticalsupport of ground forces, and recovery of downed aircraftand other equipment from hostile territory. In a less con-strained military situation where the enemy may be able toattack large air bases with either conventional or nuclearweapons, dispersal of aircraft to a number of small siteswill be mandatory for survival. The vulnerability of largeair bases (and aircraft that need long runways) has beendemonstrated on a number of occasions, one of the mostrecent being the destruction of the Egyptian Air Force onthe ground by the Israeli Air Force at the outset of the1967 conflict.

As mentioned previously, the AACB requested the militaryservices to review their long-range requirements for aero-nautical weapons systems to help determine the ground-basedfacilities required to develop these systems. The require-ments included a heavy-lift helicopter, a variety of V/STOLtransports, anti-submarine warfare aircraft, rescue aircraft,and V/STOL fighters and tactical aircraft. The aircraftperformance-requirements for many of these missions dictateV/STOL aircraft with considerably higher speed capabilitythan is available from conventional helicopters.

7

BASIC TECHNOLOGY PROBLEMS

Conventional Aircraft

As previously discussed in connection with figure 5,the problems of air traffic congestion, noise, and airporteconomics have forced a long-term trend towards highermaximum lift coefficients. A fundamental problem encounteredin the design of high lift systems is the prediction of thefull-scale flight characteristics near maximum lift from dataobtained from wind tunnel tests of small scale models. Thereare two aspects to this problem. First, the model tests areconducted at considerably lower Reynolds numbers than thosefor full-scale flight conditions. Second, there may existsubtle, but important, differences between the model and thefull-scale aircraft. Typical of these differences are leak-age through the structure, deformation of flaps and slatsunder load, exhausting cooling air in regions of marginalflow stability, surface discontinuities, roughness, brackets,etc., all of which are details of the full-scale structurewhich cannot be duplicated at model scale. When discrepanciesoccur between predicted and actual flight characteristics, itis usually impossible to tell whether the cause is due to thedifference in Reynolds number or to detailed differencesbetween the model and the actual aircraft. The full-scalewind tunnel is a valuable tool in developing satisfactoryhigh-lift systems and in defining discrepancies between pre-dicted and actual performance, so that design procedures canbe improved.

Low-Disk Loading V/STOL Aircraft

The main technical problem areas for low-disk loadingV/STOL aircraft are rotor control, dynamic stability, dynamicloads, and performance at high flight speeds. These charac-teristics are highly dependent on the unsteady aerodynamicforce inputs to the rotor and the dynamic characteristics ofthe rotor and its control system (including such real-worldfactors as backlash, break-out forces, and nonlineareffects). The unsteady aerodynamic forces on the rotor sys-tem are critically dependent on Mach number, Reynolds number,and advance ratio. Therefore, wind tunnel tests must beconducted at flight values of these parameters if they areto be meaningful.

8

Figure 6 (from reference 12) provides a graphicillustration of the complexity of the aerodynamic phenomenaencountered by a rotor blade. On the advancing blade (wherethe rotor rotational velocity and the aircraft flight ve-

locity add) there are compressibility and shock wave effects.The local Mach number, angle of attack, skew angle, Reynolds

number, and dynamic pressure vary both with time (i.e., bladeazimuth) and with radial location. On the retreating bladehigh angles of attack and dynamic stall are encountered.In some flight regimes the blade may encounter the vortexsystem shed by the preceding blade with accompanying impul-sive loadings which produce both vibration and noise. In

each revolution the blade encounters most of the aerodynamicproblems faced on a fixed wing aircraft, and these problemsare compounded by the dynamic environment of the rotor.

The dynamics problem of rotary wing aircraft is

graphically illustrated on figure 7 (also taken from refer-ence 12). The rotor itself is a flexible system derivingmuch of its stiffness from centrifugal force effects. Ithas many elastic modes, with significant coupling effectsthrough inertia, structural, and aerodynamic effects, and

these are often subtle and easily overlooked or inadequatelyaccounted for. The rotor itself is flexibly mounted to theairframe, and significant coupling may exist between the

rotor modes and airframe modes. The rotor control system

represents another dynamic system which may couple with

either rotor or airframe vibratory modes. Finally, thepilot may interact through the control system to create

pilot-induced oscillations. This complicated dynamic system

is continuously excited by complicated aerodynamic and

inertial forces (represented by the hammer).

Because of the complexity-of the aerodynamic and

dynamic phenomena encountered by a rotor system it is es-

sential that test conditions accurately represent those to

be encountered by the flight vehicle. As explained more

completely in reference 13 it is generally not possible to

faithfully duplicate on rotor models all of the aerodynamic,

dynamic, and mechanical characteristics (i.e., backlash,

friction, etc.) of concern. Furthermore, the consequences

of an inadequate allowance for any one of these phenomena

may result in catastrophic failure of the rotor system.

Therefore, full-scale wind tunnel tests of advanced rotor

systems prior to flight test at high speed are an essential

9

step in the development of high-performance rotary-wingaircraft. However, the performance levels of some existingand many forecasted advanced rotary-wing aircraft are beyondthe capabilities of the 40- by 80-foot wind tunnel, which isthe only facility available for this work at present.

High-Disk Loading V/STOL Aircraft

One of the critical problems for fan or jet V/STOLpropulsion systems is distorted inlet flow. Effects ofdistortion are shown schematically in figure 8. Modestamounts of distortion cause modest though important degra-dations in engine thrust and efficiency. Some criticallevel of distortion causes engine stall with resultinglarge losses in thrust, unsteady flows through the engine,blade vibrations with attendant high blade stresses,excessive turbine temperatures, and attendant risk ofdamage to the engine.

The thrust loss due to engine stall can be catastrophic.For the VTOL airplane the entire airplane weight is supportedby the propulsion system at takeoff and landing. The STOLairplane also derives a large measure of its lift from thepropulsion system at low speeds. Therefore, it is mandatoryto avoid engine stall, and it is desirable to minimize theperformance losses associated with lower levels of flowdistortion.

The circumstances that lead to flow distortion for liftengines and fans are shown on figure 9, which illustrates atypical lift fan for a VTOL airplane. After the VTOL air-plane leaves the ground, the airplane accelerates forward toachieve wing supported flight. During this transition thelift fans must operate in highly distorted flow caused bythe air turning approximately ninety degrees to enter thefan. This large turning may induce flow separation at theinlet lip and fan hub which causes further distortions.This highly distorted flow may stall the fan.

Stall in a fan or compressor is associated with thestall of the individual rotor blades and is analogous tothe stall of helicopter blades previously discussed.However, the performance of many blades in rows and stages

10

as they occur in a compressor significantly complicates theprediction of compressor stall, and it has been found thateach engine design exhibits its own unique characteristics.Thus, the testing of full-scale engines is the only satis-factory way known of determining its stall characteristics.

Another undesirable consequence of engine inlet flowdistortion is the generation of noise. While the engine fanand compressor stages generate noise even in a uniform flow,the noise generated by these rotating aerodynamic surfacesis significantly increased in the presence of flow distortion.The noise constraints to be imposed on commercial V/STOL air-planes are very stringent. The precise determination ofengine noise and the design of efficient noise suppressionsystems will depend on tests of full-scale engines in thedistorted flow induced by the full-scale airplane.

The economics of full-scale engine testing warrants somecomments. It is generally accepted that the building andtesting of small-scale, external aerodynamic airplane modelsis far less expensive than the testing of a full-size model.This however, is not the case with engines. Once a commit-ment has been made to design and build an engine for anaircraft application, it is usually less expensive to buydemonstrator versions of that engine for research and devel-opment purposes than it is to build a half- or quarter-scalemodel of the engine. This is because changing the scale ofthe engine by factors of two or four requires an extensiveredesign and redevelopment effort to insure satisfactoryoperation. These factors account for a major portion of anengine model cost and usually exceed the cost of a fullscale engine for which the cost of design and development isspread over many engines. Thus, the use of full-scale enginetests in contrast to tests of model engines is the moreeconomical approach, and, in fact, is the only cost-effectiveway to study problems such as engine stall which were describedin the preceding paragraphs.

FULL-SCALE TESTING TO REDUCE PROGRAM RISKS AND COST

The preceding sections of this paper have discussed thepotential for application of advanced high-lift and V/STOLaircraft in meeting the transportation needs of the nation,and have reviewed some of the technology problems associatedwith these aircraft. A related problem is that of convincingthe public that the proposed aeronautical systems are, infact, economically and environmentally viable solutions.

The ability of the aerospace community to present acredible case for advanced aeronautical systems has beenseriously eroded by a number of extremely expensive failuresof advanced aircraft. These failures have been widely pub-licized and have prompted considerable criticism. It isclear that this situation must be remedied and public con-fidence restored in the aerospace community's ability todeliver on its promises.

A number of studies have been conducted to find meansof reducing the risk in advanced aircraft programs. One ofthese (reference 14) examines the role of test facilities inthe aircraft development process. According to this studythere is a consensus among experienced technical personnelthat more use of test facilities would significantly reducethe risk of advanced aircraft programs. This study alsoconcluded that increased use of facilities would improve theperformance of the end product. These are the prime justi-fications for the proposed full-scale subsonic wind tunnel.The use of such a facility to determine the characteristicsof critical components of advanced aircraft (e.g., rotors,engines, etc.) before committing large funding to the air-craft program would significantly reduce the program risk.Moreover, this testing could be done prior to selection ofthe contractor for aircraft fabrication, so that competi-tion could be maintained beyond the paper study phase, andadditional data would be available to guide the final selection.

The points made in the preceding paragraph are summarizedin figure 10. In brief, it is believed that the full-scalesubsonic wind tunnel is required to reduce the risk and costof advanced aircraft programs. The program risk is reduced

12

by providing tests of critical components early in the pro-

gram and by maintaining competitive options through this

phase. The program cost is reduced by minimizing failuresduring the subsequent high cost phases of the program, byminimizing expensive flight testing, and by improving theperformance of the end product.

An example of how this philosophy is being applied by

the NASA and the U.S. Army in the procurement of a tilt-rotor research aircraft is illustrated in figure 11. Thisfigure presents the program cost as a function of time. Thecost curve follows the "S" curve typical of most advanceddevelopment programs. In the first phase, which involvesless than 5 percent of the total cost, full-scale tests oftwo competitive rotor systems are being conducted to determine

their dynamic and performance characteristics. At the con-clusion of this phase a single contractor will be selected tobuild the aircraft. The aircraft itself will be tested in

the 40- by 80-foot wind tunnel before the first flight tominimize the possibility of unexpected problems being en-

countered during flight tests. Figure 12 shows a photographof one of the rotors for this aircraft installed in the 40-

by 80-foot wind tunnel for dynamics testing, and a sketch of

the complete aircraft installed in the wind tunnel. As dis-cussed in a later section of this report a similar test

program has been followed in the development of a number of

experimental aircraft. In many cases the full-scale windtunnel tests proved to be essential in that deficiencieswere found that could have been catastrophic if encountered

in flight.

ALTERNATIVES TO A NEW FULL-SCALE WIND TUNNEL

In view of the high cost of a new full-scale wind tunnel

a number of alternatives have been considered. A summary of

these is provided on figure 13 along with their relative

advantages and disadvantages.

The small-scale pressure wind tunnel is a valuable

research facility in that it provides the means to independently

13

determine Mach number and Reynolds number effects. How-ever, it is not possible to achieve full-dynamic similarityon models in a pressure wind tunnel, and it can not be usedfor testing engines. Therefore, it does not meet thetesting needs for the full-scale wind tunnel, and was notconsidered further.

The high-speed track was studied to determine the fea-sibility of utilizing such a facility to conduct the testingenvisioned for the full-scale wind tunnel. However, the highspeed track has a number of disadvantages. A prime disad-vantage is the high acceleration the test article must besubjected to during starting and stopping. Another disad-vantage is the short test time available which is inadequatefor careful dynamics testing. Because of these and otherdeficiencies listed on figure 13 the high speed track wasdropped from further consideration.

Another alternative considered was to conduct the pro-posed full-scale testing in flight, either with prototypeaircraft, or with components (e.g., rotors or engines)mounted on existing test aircraft. However, flight testingis expensive in terms of the cost per data point. Further,it is usually not possible to control the test conditions inflight as well as they can be controlled in a wind tunnel.Finally, the consequences of a failure of the test hardwarein flight are much more hazardous than the consequences ofa failure in the wind tunnel. For these reasons flighttesting was not considered to eliminate the need for thefull-scale wind tunnel. In fact, a prime objective of thefull-scale wind tunnel is to reduce the cost and risk of theflight testing required.

The feasibility of uprating the test capability of theexisting 40- by 80-foot wind tunnel has been proposed as analternative to the proposed new full-scale wind tunnel.However, it does not appear that any feasible modificationsto the 40- by 80-foot wind tunnel would provide all of thetest capability desired in the new facility. Modificationsto the 40- by 80-foot wind tunnel could significantly enhancethe full-scale testing capability of this wind tunnel, andmay well be justified on their own merit. Therefore, designstudies are currently in progress to determine the cost anddown-time required to up-grade the test capability of the

14

40- by 80-foot wind tunnel. The modifications being con-sidered are repowering the wind tunnel to provide a testspeed of 300 knots in the existing 40- by 80-foot testsection, and the addition of a new 80- by 120-foot low-speed test section.

FULL-SCALE WIND TUNNEL DESIGN STUDIES

Aircraft Size and Speed Trends Relatingto Facility Requirements

Conventional aircraft.- Over the years the increasingdemands of mission requirements and economics have dictateda long term trend toward larger aircraft. A result of thisis that the existing full-scale wind tunnels are no longercapable of testing most operational aircraft. As shown byfigure 14, even modern fighter aircraft tax the capabilityof these facilities. As a result of this, current researchand development tests for the F-14 and F-15 fighter aircraftare being performed with 3/4-scale models rather than full-scale test vehicles; and the use of such models will not getat the important interface between structures, propulsion,and aerodynamics.

Rotorcraft.- Figure 15 shows the variation of rotordiameter or aircraft span with gross weight and payload forsingle rotor compound helicopters and tilt rotor aircraft.These variations result from fairly well-defined limits onrotor disk loading and rotor weight. Therefore, the trendsshown on figure 15 can be expected to be valid into theforeseeable future. The largest diameter rotor which can betested in the 40- by 80-foot wind tunnel is about 60 ft.,and, for this size rotor, the tests are limited by windtunnel wall constraint of the flow to low wake angle con-ditions (i.e., high speeds and low lift coefficients).Figure 15 shows that, with this limitation on aircraft span,the 40- by 80-foot wind tunnel is far too small to test full-scale transport rotorcraft, and is capable of testing onlythe smaller utility and tactical aircraft.

15

Figure 16 shows the increase in the rotorcraft speedrecords with time, and demonstrates the feasibility of op-erating advanced rotorcraft up to speeds of the order of300 knots. However, it should be recognized that the morerecent high speed records have been achieved only with smallexperimental rotorcraft having extremely limited flightenvelopes. There is as yet no operational rotary wing air-craft capable of flight speeds over 200 knots. In contrast,the maximum speed of the 40- by 80-foot wind tunnel is only200 knots. This deficiency in facility speed capability isanalogous to that which existed for transonic facilities inthe forties which prompted the construction of the X seriesof high-speed research aircraft.

The economics of transport missions dictates higherflight speeds than are available from current helicopters.Even for relatively modest stage lengths, speeds of 250 to350 knots are required for economic operation. As discussedpreviously the most serious technical risks for high-speedrotorcraft are rotor dynamic stability and vibratory loadsin high speed flight. The magnitude of these problems canbe expected to increase at least with the flight velocitysquared. Therefore, the increase in rotorcraft speeds fromthe current 200-knot level to the 300-knot level can be ex-pected to more than double the rotor dynamic stability andvibration problem.

In summary, the long-term trends in size and speedrequirements for advanced rotorcraft indicate a need forvehicles having rotor diameters or spans of up to 100 ft.,and capable of flight speeds of 300 to 350 knots. A full-scale wind tunnel capable of testing these rotor systemswould require a test section size of at least 60- by 120-feet and a speed of at least 300 knots.

High-disk loading V/STOL aircraft.- Figure 17 (fromreference 13) shows the typical variation of aircraft spanwith gross weight and payload for a variety of high-diskloading V/STOL and STOL transport aircraft concepts. Ingeneral, STOL aircraft concepts for which the wing carriesa major share of the weight (such as the externally blownflap and the augmentor wing) are near the upper bound ofthe shaded area on figure 17, while concepts for which thepropulsion system carries the major share of the weight (such

16

as lift fan aircraft) are near the lower bound of the shadedarea. While the size trends shown on figure 17 for high diskloading V/STOL aircraft are not as well defined as thoseshown on figure 15 for rotorcraft, they nevertheless indicatethat aircraft having wing spans from 60 to 100 ft. will berequired to perform the transport missions envisioned forthese aircraft.

The primary technical problems for these aircraft are inthe low-speed flight range (up to about 150 knots) where thereis strong interference between the flow through the propulsionsystem and that over the airframe. Under these conditions theaircraft wake is deflected through a large angle and the flowconstraint effects of the wind tunnel walls become the limit-ing factor in determining the wind tunnel size requirements.On the other hand, in high speed flight these aircraft aremore or less conventional in their operation, and require nospecial test requirements other than those used for cruiseflight of conventional aircraft. Therefore, the test require-ments for most high-disk loading V/STOL aircraft can be metin a wind tunnel with a maximum speed capability of 150 knots.However, the effects of the constraint of the flow becomeincreasingly serious as the speed is reduced (and the wakeangle is correspondingly increased). Therefore, these air-craft dictate the size requirements of the proposed facility.

Facility Size and Speed Requirements

The aircraft size and speed trends discussed in the pre-ceding paragraphs are summarized on figure 18 along with theapproximate test section widths required to accommodate testsof these aircraft. At the lower speeds, corresponding to thetransition flight regime of V/STOL aircraft, the size of thetest section increases rapidly as the flight speed decreases.This increase in size is required to alleviate the growth ofwind-tunnel wall constraint effects with increasing wake angleas the speed is reduced. These test-section width require-ments are shown as approximate areas rather than definitivelines since they are dependent on a number of factors. How-ever to conduct tests of large V/STOL aircraft having wingspans of 100 ft. at speeds of 50 knots and less, a test

17

section width of 200 feet is indicated. On the other hand,at the high speeds and low lifts corresponding to the regimeof prime interest for advanced rotorcraft, a test-sectionwidth of at least 120 ft. would be required.

Wind Tunnel Configuration Studies

A number of wind tunnel configurations have been studiedto determine the best compromise between the conflicting speedand size requirements discussed in the preceding section.Some of these designs are shown on figure 19. Broadly speak-ing, they included a simple closed-return design similar tothe 40- by 80-foot wind tunnel but scaled up to a test sectionsize of 75- by 150-foot and a speed of 300 knots, an open-return wind tunnel having the same size and speed character-istics, and a number of two test-section designs. Thesestudies showed that the cost of the structure in a windtunnel of this size was the most important element of thecost, and this fact focused attention on the open-return windtunnel designs which minimize the amount of structure.

The main disadvantage of an open-return wind tunnel isthat the flow in the test section is not isolated from theeffects of external winds. Thus, the flow quality in thetest section may vary from day to day unless special atten-tion is paid to the design of the inlet and exhaust sectionsof the wind tunnel. A number of experimental investigationshave been conducted to develop inlet and exhaust sectionswhich will ensure satisfactory flow quality in an open returnwind tunnel. The investigations conducted at the Ames ResearchCenter are reported in reference 15, wherein it is concludedthat satisfactory flow quality can be achieved in the testsection of an open return wind tunnel under nearly all weatherconditions prevailing in a moderate environment such asexists at the Ames Research Center.

The main advantages of the open-return-wind tunnel are:(1) it provides the minimum structural cost, and (2) it doesnot require a purging system to eliminate engine exhaustgases from the wind tunnel air flow. This latter point isparticularly important for the full-scale wind tunnel since

18

it is intended to operate V/STOL aircraft propulsion systemsin it. The power required for an open-return wind tunnel isabout the same as that of a closed return wind tunnel, sincethe kinetic energy lost at the exit of the open-return windtunnel is about equivalent to the energy lost in the cornersof a closed return wind tunnel.

In summary, the cost of an open-return wind tunnel willbe less than that of a closed return wind tunnel providedthat the cost of the inlet and exit treatment required forsatisfactory flow quality in the open-return design is lessthan the cost of the return circuit, the heat exchanger, andthe exhaust gas purging system in the closed-return windtunnel. The design studies and wind tunnel experiments con-ducted to date show that satisfactory flow quality can beachieved in an open-return wind tunnel with relativelyeconomical treatment of the inlet and exit sections of thefacility.

The concept selected for the proposed full-scale sub-sonic wind tunnel is shown on figure 20. This is an open-return wind tunnel having two test sections driven by acommon power section. The particular combinations of testsection size and speed were selected to give the bestcompromise between the conflicting test requirements forhigh-disk loading and low-disk loading V/STOL aircraftdiscussed in the preceding section of this paper. Thisdesign provides the maximum test capability for the minimumcost. It also provides for high utilization of the facilitysince tests can be conducted in one test section while theother test section is being prepared. Finally, it providesan advantage in budgeting for the facility in that the con-struction can be phased if necessary, with one test sectionbrought into operation initially and the second test sectionadded at some later date.

19

ECONOMIC CONSIDERATIONS

The overall judgement that must be made in consideringthe proposed facility is whether the research and develop-ment value of the work performed in this facility willjustify its cost. Since this facility should have an oper-ational life of at least 25 years, it is obviously impossibleto make a detailed and specific cost-benefit analysis. How-ever, it is possible to arrive at a reasonable perspectiveon the value of the proposed facility by considering twofactors: (a) the estimated cost of future aircraft programsand the possible contributions of the full-scale wind tunnelin reducing these costs; and (b) the experience of theexisting full-scale wind tunnels.

Costs of Typical Aircraft Programs

The prime justification for the proposed facility isthat the cost of the facility ismreasonable in terms of thecost of the aircraft programs which it would support, andin terms of the savings that can be realized for theseprograms over the costs that would be incurred in the ab-sence of the facility. This assessment is difficult tomake. However, some perspective on this can be realizedby considering the costs of typical aircraft programs suchas are described in reference 16.

Figure 21 compares the funding schedule for a typicalproduction aircraft program (from reference 16) with thecost of the proposed facility. Figure 21 shows that thefirst major input from tests in the facility occurs prior toflight test when both the level of funding and the rate ofincrease of funding are low. These tests typically wouldinvolve full-scale demonstrator hardware of the high-riskitems (e.g. rotors, fans, engines) installed in inexpensive"boiler plate" airframe mockups. Data obtained at thisearly stage of the program has extremely high leverage onprogram costs, since the funds committed are still low.The second period of major influence of the facility shownon figure 21 corresponds to the early flight test stage.

20

If unanticipated problems are encountered in flight, theaircraft can be returned to the full-scale wind tunnel forrapid and safe exploration of these problems. The alter-native to this is continued flight tests with the accompany-ing risks to the aircraft and pilot. By the time flighttests can resolve major discrepancies the cost of the pro-gram exceeds that of the facility. In addition, by thattime commitments have been made such that the cost incurredby changing the design may be as much as the funds expended.Thus, the cost of the proposed facility should be viewed asan insurance premium which reduces the risk of potentiallosses in advance technology programs to acceptable levels.It is quite likely that, without the assurance provided byearly tests of critical components in the proposed facility,many advanced aircraft programs (e.g., high-speed rotorcraftand V/STOL aircraft) will not be initiated due to excessivetechnical and financial risk.

Experience with Existing Full-Scale Wind Tunnels

NASA has operated full-scale wind tunnels since the late1920's, and there is considerable historical evidence of thevalue of this type of facility. The first NASA full-scalewind tunnel (the 20-foot Propeller Research Wind Tunnel)showed the absolute necessity of using cowls for radialengines and variable pitch propellers for high performanceaircraft. The incorporation of these features provided thefirst high performance transports which launched the era ofpractical commercial air transportation. Similarly, theapplication of this research to fighter aircraft culminatedin the high-performance radial engine fighters of World WarII fame.

While the prime justification for both the 30- by 60-and the 40- by 80-foot wind tunnels was for drag reductionstudies of military aircraft, the major contributions ofthese facilities have been in technological areas which werenot anticipated at the time the facilities were planned.The contributions of these facilities to the research anddevelopment of V/STOL aircraft is an example of this. The

21

40- by 80-foot wind tunnel has more than paid for itself bypreventing failures of experimental V/STOL aircraft inflight. These aircraft encountered failures during testsin the 40- by 80-foot wind tunnel which could have beencatastrophic in flight. All of these failures involved thecomplicated interface between aerodynamics, dynamics, andstructures. Therefore, tests of the full-scale hardwarewere the only way that these problems could have been dis-covered. For example, the XV-1 compound helicopter encoun-tered a rotor speed instability during the wind tunnel testswhich required changes to the rotor control system. Testsof the XV-3 in the 40- by 80-foot wind tunnel were requestedafter a catastrophic rotor-pylon whirl instability was en-countered in flight, resulting in loss of the aircraft andserious injury to the pilot. After two tests in the 40- by80-foot wind tunnel, separated by a one-year analysis effort,this stability problem was alleviated so that a highlysuccessful flight research program could be completed. Asa result, the tilt rotor aircraft is considered today to beone of the more promising high performance rotary wing air-craft concepts. The first wind tunnel test of the XH-51rigid-rotor helicopter ended in a break-up of the rotor dueto a bonding failure. The rotor'blade was redesigned, asuccessful wind tunnel test was completed, and the XH-51went on to a highly successful flight research program whichculminated in a rotorcraft speed record. During wind tunneltests of the XV-5A lift-fan airplane, structural failure ofthe fan inlet guide vanes was encountered. If these hadfailed in flight and entered the fan rotor the aircraftwould have been lost. Also, excessive deflection of the fanexit louver control mechanism was encountered during thesewind tunnel tests. This would have severely limited the fan-supported flight envelope of the XV-5A. Both of theseproblems were remedied following the wind tunnel tests, andthe XV-5A airplane has completed a series of successfulflight research programs. The lift-fan propulsion system iscurrently considered to be one of the most promising con-cepts for a high performance V/STOL airplane.

The total cost of the aircraft programs which have beensaved by tests of the full-scale aircraft in the 40- by80-foot wind tunnel has more than offset the total cost ofconstruction and operation of this facility for 25 years.To these savings could be added the savings due to the

22

cancellation of flight test programs of aircraft which had

been shown by full-scale wind tunnel tests to have fundamen-

tal deficiencies. A partial list of such aircraft is the

Kaman K-16 tilt wing, the Avrocar, and the Vanguard low-

disk loading fan-in-wing airplane.

Actually, the most important contributions of the full-

scale wind tunnels have been in research areas where it isnearly impossible to put a firm dollar magnitude on the value

of the contribution. The contributions of the full-scale

wind tunnels to the development of the externally-blown flap

and the augmentor wing turbofan STOL aircraft are almost

solely responsible for the fact that these concepts are today

considered to be the most promising types for application to

large commercial and military STOL transport aircraft. Theuse of the full-scale wind tunnels was also instrumental in

establishing the feasibility of conventional landings of

lifting body spacecraft. This included tests of all of the

full-scale flight vehicles in the 40- by 80-foot wind tunnel

plus studies of free-flight models in the 30- by 60-foot

wind tunnel. These studies added immeasurably to the confi-

dence level required before flight tests could be initiatedwith these radically new and different aircraft. This is

perhaps the best example of an application of the full-scale

wind tunnels to fill a need which could not have been

anticipated when the facilities were justified.

Since the cost of the proposed full-scale wind tunnel

has already been compared with the typical cost of current

aircraft programs, it is of interest to compare the cost of

the existing full-scale wind tunnels with representative air-

craft current at the time these facilities were justified.

This comparison is presented on figure 22 which shows the

variation in airplane cost and wind tunnel cost with time.

This figure shows that the cost of the proposed full-scale

wind tunnel relative to the cost of current aircraft is, if

anything, less than the cost of the 30- by 60- and 40- by

80-foot wind tunnels relative to aircraft costs at the time

these facilities were built. In addition, the need and the

potential for-both military and civil air transportation is

much more apparent now than it was at the time the existing

full-scale facilities were justified. In retrospect our

predecessors showed a high degree of foresight and couragein building these facilities during the great depression

23

(the 30- by 60-foot wind tunnel) and at the outset of WorldWar II (the 40- by 80-foot wind tunnel).

CONCLUSIONS

The following conclusions were drawn from the studiesdiscussed in this paper:

1. Basic factors such as growth of the populationand economy will create a growing demand fortransportation in the United States, and themajor portion of this transportation demandwill be for trips between 50 and 500 miles.

2. The problems of aircraft noise and air trafficcongestion must be alleviated if this demandfor air transportation is to be met. The useof V/STOL aircraft will provide significantreductions in air traffic congestion by shiftingmost of the short-haul traffic away from themajor airports to small V/STOL ports. Inaddition, the use of V/STOL aircraft will subjectless land area to high noise levels than willsurface transportation systems.

3. There are a number of military missions whichrequire the development of high-performanceV/STOL aircraft.

4. The major problem associated with the developmentof advanced V/STOL aircraft is the technical andfinancial risk of the aircraft development pro-gram. This risk can be significantly reduced byconducting full-scale tests of the criticalcomponents of the aircraft (e.g., V/STOL propul-sion systems and rotors) prior to the go-aheadfor the complete aircraft system. To conductthese tests, a subsonic wind tunnel capable of

24

testing vehicles with spans up to 100 feet andat speeds of about 300 knots is required.

5. While the primary justification for the newfull-scale wind tunnel is for the developmentof V/STOL aircraft, experience with theexisting full-scale wind tunnels shows thatthis facility will be very useful in thedevelopment of conventional aircraft as well.

6. A two-test section, open-return wind tunnelprovides the maximum test.capability for theminimum cost.

25

REFERENCES

1. Anon.: Report of the Joint DOT-NASA Civil AviationDevelopment Policy Study, Vol. II, NASA SP-266,1971.

2. Galbreath, A.; and Warfield, R. M.: Terminal AreaAirline Delay Data, 1964-1969, Federal AviationAdministration, Washington, D. C., September 1970.

3. Wimpress, J. K.: Aerodynamic Technology Applied toTakeoff and Landing. Annals of the New YorkAcademy of Sciences, Vol. 154, Art. 2, Pages 962to 981, November 1968.

4. Deckert, W. H.; and Hickey, D. H.: Summary andAnalysis of Feasibility-Study Designs of V/STOLTransport Aircraft, J. Aircraft, Vol. 7, No. 1,January-February, 1970.

5. The Boeing Company: Study of Aircraft in Short-HaulTransportation Systems, NASA CR-986, 1967.

6. Fry, B. L.; and Zabinsky, J. M.: Feasibility of V/STOLConcepts for Short-Haul Transport Aircraft, NASACR-743, 1967.

7. Marsh, K. R.: Study of the Feasibility of V/STOLConcepts for Short-Haul Transport Aircraft,NASA CR-670, 1967.

8. The Lockheed-California Company: Study on theFeasibility of V/STOL Concepts for Short-HaulTransport Aircraft, NASA CR-902, 1967.

9. Anon.: Technical and Economic Evaluation of Aircraftfor Intercity Short-Haul Transportation, FederalAviation Agency-Air Defense System-74, Vols. I, IIand III, April 1966.

10. Kuhn, R. E.; Kelly, M. W.; and Holzhauser, C. A.:Bringing V/STOL's Downtown, Astro. Aero., September1965.

26

11. Simpson, R. W.: Summary and Recommendations for theNASA/MIT Workshop on Short Haul Air Transport,Flight Transportation Laboratory Report 71-4,October 1971.

12. Tapscott, R. J.: Rotorcraft Applications and Tech-nology, Paper No. 20 in Vehicle Technology forCivil Aviation, The Seventies and Beyond.NASA SP-292, November 1971.

13. Kelly, M. W.; McKinney, M. 0.; and Luidens, R. W.:The Requirements and Justification for a New Full-Scale Subsonic Wind Tunnel, NASA TM X-62,106,February 1972.

14. Mitchel, James G.: The Test Facilities Role in theEffective Development of Aerospace Systems,AFSC-TR-71-01, September 1971.

15. Mort, K. W.; Eckert, W. T.; and Kelly, M. W.: TheSteady-State Flow Quality in a Model of a Non-Return Wind Tunnel, NASA TM X-62,170, September1972.

16. Harris, N. D.: Forecasting Military Aircraft,Space/Aeronautics, 1968.

27

U)

onL1U)

Z

JO

<

0I

ZO

U)

*00

>-

0-J0Z00CU)O

3

(f)z>.

owzLJH IE3I

zo 0

D

SU) -

0oo

0 0

Q9

00zI *

C3

0

LL

_

J Z

m o <

C0 0

bJ0

CDIa-

C,)

U)

0czI-C>)-Jozzz0r-'-0

crm0Cr

0-

¢)

.r,

* a)

\ -J

0U 0N

-

LLJ U-j_] Z/ 0C

N-D

8 \

X

cz

.

0 0

0

U.

_j I

Q

~~

~~

~~

~~

O

o~~~~~~(16

d~) I

U)O

O

~~~~~~o %

~~

~~

~~

~~

~~

~~

~

-J L

~~~~i L

L~

9Bz

s~~~~~~~~~~~~~~~~~~~~~ zQ

~~

~~

~~

~~

~~

~~

~z

<0

w

-(/-

1

I

IH

- I

C.

<

U,

(O

La. I

-j

<

o.

o o

"- -

L~~~~~~~~~~~~~c

(dr) I.-~~~~~~~~orA

0H

0 L

I C

(C)

,PH

0 NdFCf)

rr ~

I v~r

NJr

a

H!w

C)0

o°~~~~~~~

<

0*~·· 0~~~~~

<

V

~~~~~~~~~~~~~~~~~~~~c-I<

U

-J

06

0,

~~

~~

~~

~~

Z

0

Icl.I '8

Z) I--

rr-~~~~~~~~~~~~~~~~~~~~z~~ti

L3

~~

~

": ~~~J-

"r~/(J/I f~

·f' '':5~~ :'"i~":i::i:"~

"''"" ~:"'"'·.

~ .

· ....

:::...::~.:.:.:.:....:.:.:.:.:,:.:~

~ ......ssssa

·I~

~~

~~

I~17~

~~

~~

~~

~~

~~

~~

~~

~~

~~

~~

~~

~~

~~

~~

~~

~~

~~

~~

~~

~~

~~

~~

~~

''''''''': m

3~

Q O ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~8~~~~~~~~~~~~~~~~~~

·~~~~~~~~~~~~~~~~~~~~~~~~~~~, I~~~~~~~~~~~~~~ii::.-....".

-I~

~~

.1

....

47 :;f~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~I.--.

---r. ~ ...---

~··--.·.·2...~:

3I~

~~

~~

~I

-- ooo

n,-~

~~

~~

Oo

Z

n

_J V

LbJLIJ

3 I

o C

l0

<0>

6

I -1 -

HU

J O

d

Uf) c

Oz

Zz-_ 07

(D

zz,0

oIE4

o4z .0o-I

O3

U-

O

,UO3

Iw0

) U

-

zLL

LLLL

0I-

Cz llE~

ZdbJ-

,-

w00

ztLem -J0LIa_(33

Lfi-

blr a)

.1Pr4

L-

0Wd

o

CN

00

· 0--

XE0

00I

II

I

0 C

QLj

O

XI-co

do.,,

LL

I

n)Oz0Zzw- z0 Ir

1oa0z-

LL

JL

LJ .

0 0

~o o

u m

m

h e

goL

z

F-xIii

-JCo

0

.E

asA{60

.r-

LIll

0 w0-

o U)

I w

<E

S

z)Z

L

O

z L

w

Y

wr w

z3 ,

J D

m

z

w

w

Oz

0-

o I

Iz <

0a: LL

V)

C-J

H

L

L

I, wz

o z

LL <

LL w

0o c-~~-~-

-i

H

0 w

z

L~J to

Z

: LL

w0

a-

0zZILJ

zzLLH-

0\a-

.HCL

·rH

0zL0

0

II Z

ZD (>

O

-F-

a

o

I Z

00~

-0

=)L

Zb

J

-UJ

c

, 0

rw

-J,

LL 0

o ao0

a. Gr

.H

_

m: p

N

>m

0nS

I-3ZO

z o

nz

Oo

!l -

>3 ID

-

i- L

z(.

(3

U)

LU

LLJ-JI-JlJIn-

0LULU

zLU

It--

UzZar-0LL.

or -L

a.

0v I-rIzoLU-J 0_1J-I

3~O

(0

0cr

LLJ

z0LJ

o--

-a -

3 F-

o

0W

LU

.

o 0

lo

rX4

rz

.lM'

1.1

1.1

1.!

O/V 3131dWO0

SlS31T'IA 31VOS llAJ

aS

n-

LLJ

LL_ o

s

LL

~J a '''N::::::

LL.) 00

IL

--O

~O

~

C3~

F

iiil I

1.I

un-

La.J -J

.

0 0

0':D

Jua a

1'-s- V

__ _i

LLJ O

O

O

O

O

O

C/)

~ ~

~ IU

~os

0.S

O

~VI00

l 1n-"

1 IIO

U1

I

ROLE OF 40X80 ft WIND TUNNEL IN TILT ROTOR AIRCRAFT DEVELOPMENT

SINGLE ROTOR COMPLETE RESEARCH AIRCRAFT

F i g u r e 12

NAIIONAl AMONAUTICS AND SfACi AOMWBUATKW AMfS lESEAKCH CINTH, MOFFIT7 WIO, CAI»0«NIA

= rl I-- r-I

C,,

C")

I"-- f- rm

-E m .-- rl I'-

I -C x X Co

-, --4

-r r- G'

--4

--4 r'r

---4

--a rI

-4

"'

crl,

r-r'

l Z

rrnI~

-·

-I

-o

-6I-r1

m

'

ql

o 2

'rl

am

-)

cn

cn

Cl

am -4 cn -4.

--<

-C

-C

C,,

~cn

cn

_

_ C

n

C/'

C--

' 'r

l =

l rI

Z

r

C-,

-G~

C

C

C

r0

C_

ME

~

~ ~

7

ME

~ ~ ~

~ ~

~ ~

~~

~2

I'

'r'

I''1

r'l

I r'l

~,G~

0 C

nC

~0

~~

1

---I

CA

)r'

- -~

rqin

rr

r -

_iq

i

I-I

' r'

=

rrl

O~

~~

~~

~rr

C-1

m1

m,

a,

I ~

I 0

m~

~

m

m

-(

- a--

rn

ITJ.

c OD

H' w

z-

() O -1

C r r I p~ rH Cm r

RO

TOR

Or

o ro

-O

IO , O

o O

o F0 On

: ol

0 Z

> G

)

o N)

0oa) O (0

4 0n(0 x

o ) O 0 0 o

DIA

ME

TER

,

0o

o

OR

WIN

GO

)0

SPAN

, ft

o0 a , I-

(C0w

rr;

C)

>- r

O--0

m

_r1 "l ;

0

.~r-

(

:0 0;u

0 0 O TI

-1 (I) r(I Z 0 C/)

II

II

I

oo

80sS

4oUl

,XV

MA

I

U)

00w E~

0w0 U)

illbJL

LQ

-

U-

crC)

00

o0l)_Dtokc0)'A

_

Cr

was0)M

4·rlw

r

00 N)

LD

z -LL

Tt-i

z O-J

LLJ

OLL

NcoU-

b:

0C:

_J

CO

ZH

Iz --

0CN

I-Uf)

O0>LI

0W-

>L

00

OO0 00-)0

0-0

O

C3(U)

00

0

0

(Dci

IZ

I

cn >

CL a:0 i

O

C\J

(0-

0 aO

0O

zan O0

-.4Q)

w:3bo

*,.R-

II

00

LLi

iQ:~

U)

[r'0 ,z

0U

0z

~~Lu 0

<

.F

--zz

o 0

(1 ',

-o

z -

-J-

o (9

L0

<

z 0

a.:3 L

-·

W0 11ouJ~~b

':

(r '~~~~LJ

U-

00- ,,

z -

I .

. .: :

....

z I

z~O

Q

O

O

~~

~~

0 0

0 0

0 0

IC) 0

LO) 0

LO)

LL

J~~

~~

~~

~~

~~

.

C~~~~~~ .

CM -

Z

r -

4

Z

I, NI

.I I

~0

0U

0

00

~t 'HI~~~~(]I 3N

£~

3cS

II~E

I

O0

cic/)

zF- Lud

WU)

-0rl(

(ON3

X X

O 0

O

O0

O

0ro

(D

O

O0

10

0-ro

00X

XO

O

< O

Ea 6< EZ

4

oz

4 < z

ztz I

0rt-'

(9LL.z0L

LzC)llJ

:zL3

LLJc>L

J

LJ

(/3

00I')gg3

001,00xI'--L-NI-

C0o-,4

·rH

C U'

4-

oo

c0)yr

bo

W o

>

00_ O0

z00 :DLL-z0C

)I

LI_ 0-jz __l z~ZZz2

4-O.-

O o

00xom

-

zo Z

Z

L l

C

Z

(D)

ZI

-J

0Q

HJ 00

oO J

LL

...I

<.Q

Z

Z

w~

~

Kw

tiI

H

--

LLJ >

0

O

J

nOW

C)

tL

U

<~

~~

~-J

ZWi:

LL ~~~~Z

Z~

LLJ

5C

:: fn'-

z

o>

W

LL LL

i L

00

0 -

o0

0 ,

0

U)0

0

0 0

d 0 U

0 0 4-

LL

Z

a. m

8el

a(o 'J

w

-'

LL

I--

'-

ZO O~~z

a- L

')

o o~- -

~ --

~ -- -

--

-- t-- -

-

:D

FL

Z

(r

Z

a_

-- 0:

000

I1 0~

.O C

9 ::~

I0lO

0.L

O

O-

L

rQ

Q_

r

'

sio

llop

Jo S

UO

!I0 ILZ

'SIS

OO

VYVHO

td 3A

IivlVyn

lH

I

o o

O

SJ J lop

0(o00)o_on

jo suo!ll!w

'IS0

3

13NN

nl CiNIM0oC

D

00It.

%imLII0

00

.SOO3 jIVO813

V.S

O3 13N

Nnl

(NIM

00-

SJDIIO

P JO SU

O!II!W

'I.lSO0

.L-VOIIV

NA

SA--A

RC

- C

omL

, Calif.

0

00HU

)

LL

Cr

Cl

wt

00)

b>JLL

zU.I IzLLJ

ii30a> a)0)

crw

0IOa

0)

00

0

LI

I!

I