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NASA Technical Memorandum 89079 

Potential Benefits of Magnetic 

Suspension and Balance Systems 

(NASA-TM-89079) EOTELIIIAL BEbEEllS OF 

ClAGblE'IIC SUSL'ENS3CN AhC EALALCI: SYSTEHS 

(NASA) u3 p CSCL l4B 

Ni37- 177 16 

Unclas 

G3/0Y 43402 

Pierce L. Lawing, 

David A. Dress and 

Robert A. Kilgore 

February 1987 

National Aeronautics and 

Space Administration 

Langley Research Center 

Hampton, Virginia 23665-5225 
INTRODUCTION 

The concept of using feedback controlled magnetic fields to support models in wind tunnels 

dates back at least to the early 1950’s when work began in France at ONERA. The first 

experimental results from ONERA were reported in 1957, reference 1. An annotated 

bibliography of magnetic suspension and balance systems (MSBSs) is provided in reference 2 and 

serves as a synopsis of existing work in this field. Systems which have been constructed and 

operated for aerodynamic research have been excerpted from reference 2 and are listed in 

chronological order in Table 1. A common feature is their small size, a feature that has, with a 

few exceptions, prevented their use for serious aerodynamic research. 

The development of the magnetic suspension and balance system concept has been supported 

by the Langley Research Center, both through in-house research and through contracts and 

grants, since the late 1950’s with varying degrees of vigor as priorities permitted. In 1971 work 

on MSBS at NASA Langley prompted the suggestion that operating the relatively small wind 

tunnels then fitted with MSBS at cryogenic temperatures would be the best way to increase the 

test Reynolds number, thus overcoming to some extent, the limitations on serious aerodynamic 

research imposed by the small physical size of the facilities. 

The results of theoretical analysis of the cryogenic tunnel concept, and experience in building 

and operating a low-speed cryogenic tunnel, were so promising that all efforts toward MSBS were 

redirected towards the development of transonic cryogenic tunnels as a solution to the problem of 

inadequate Reynolds number capability at transonic speeds. This effort culminated in two new 

wind tunnel facilities at Langley; the 0.3-m Transonic Cryogenic Tunnel, and the U.S. National 

Transonic Facility. The progress in cryogenic tunnels to date is summarized in references 3,4,5 

and 6. 

Following the successful development and demonstration of cryogenic tunnels, research 

activities in MSBS at Langley were resumed in 1977. It soon became obvious that the emergence 

of new technology in superconductivity, large magnet construction, computers, control 

techniques, and innovation in MSBS systems made the application of MSBS to large tunnels, not 

only feasible, but very attractive. References 7, 8, and 9 deal with the system aspects of 

integrating MSBS into large transonic tunnels and reference 10 updates the status of MSBS 

research. The use of MSBS’s to upgrade existing facilities was strongly endorsed at a recent 

testing conference, reference 11. Also, several papers seeking to define the optimum wind tunnel 

for various speeds have called for inclusion of an MSBS, references 12, 13, and 14. 

It is the intent of this paper to outline the potential of a large MSBS to solve existing problems 

related to support interference in wind tunnels as well as to speculate on the potential for unique 

new aeronautical research. An additional section is included on possible spinoff to technologies 

other than wind tunnels. .The overall tone of this paper is intended to be optimistic, predictive, 

speculative, and imaginative. 

IMPROVEMENTS TO CONVENTIONAL WIND TUNNEL TESTING TECHNIQUE 

Static Aerodynamic Coefficients 

The most obvious and straightforward improvement MSBS offers in the determination of static 

aerodynamic coefficients is the complete elimination of support interference error due to flow 

distortion. Figure 1 (taken from reference 15) presents a simple example of this problem where 

the configuration has a large squared-off base area and the primary error due to the model 

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support is in the base pressure coefficient. Even in this simple case there are secondary error 

sources due to distortion of the wake flow. Also, when this configuration is at a high angle of 

attack, thus exposing the support to the flow, the error becomes larger due to increasing tunnel 

blockage. 

Much larger errors can occur in cases where there are large areas of separation with some 

coherent structure. Two examples of such flows are transverse cylinder flow and the flow over 

swept delta wings. The structure in the first case is the coherently oscillating Karman vortex 

street, and, in the second case, the stationary vortex over the wing. Intrusion into either of these 

flow fields by the model support system may cause gross error in the static aerodynamic 

coefficients. 

An example of a cylinder-like flow field occurs when a missile is at high angle of attack, as 

shown in figure 2 (taken from reference 16). The coefficient in this case is shown to differ by as 

much as 40 percent depending on support location. Figure 3 contains a comparison of three 

schemes of supporting a sharp-edged delta wing configuration with differences in rolling moment 

coefficient as a function of sideslip angle as large as 400 percent depending on the support 

scheme (data taken from reference 17). 

An additional source of error due to flow distortion may occur in the transonic flow regime. 

An example of this problem is shown in figure 4, taken from reference 18. Since there is no 

support free data with which to compare, the problem is shown in terms of the difference in 

axial force coefficient for several support configurations. As can be seen, as the Mach number is 

increased through the transonic range, the errors are not only large, but they reverse direction. 

Although magnetic suspension may not offer the same propulsion airflow as available for this 

type of experiment, the use of magnetic suspension has great potential in the evaluation of errors 

due to support interference. Additional information on support interference problems amenable 

to solution by the use of a MSBS is available in reference 19. 

Eliminate Error Due to Geometry Distortion 

Figure 5 serves to illustrate the distortion to the model geometry necessary to allow wind 

tunnel testing of the Shuttle-747 combination using a conventional sting support system. Since 

one of the concerns of this coupling was the effect of the blunt base space vehicle on the vertical 

stabilizer performance of the transport, it would have been desirable not to have altered the 

empennage and reduced the size of the vertical tail. 

Remove Restrictions On Static Testing Due to Supports 

A common restriction of conventional sting support systems occurs in static testing at high 

angle of attack, and the common solution is to use bent or “dogleg” stings. This is usually 

necessary to keep the model away from the test section ceiling. However, even with bent stings, 

large angles of pitch or yaw frequently require the use of an additional, smaller model in order to 

test with reasonable levels of tunnel blockage. With a MSBS the mechanical support mechanism is 

eliminated, and the model can be freely positioned in the center of the test section with no 

blockage or support interference, due to the sting. 

A more complex restriction occurs in testing a configuration in ground effect, either during 

takeoff, landing, or hover. Figure 6 is a photograph taken during tests of the Shuttle Orbiter in a 

landing attitude. To obtain the necessary data it was necessary to construct an artificial ground 

plane in a large tunnel and then use a small model. Note the slot cut through the ground plane 

for the sting. A later phase in the testing required additional slots to be cut in order to obtain 

data for cross-wind conditions+. A MSBS would have required none of these artifices to assist in 

acquiring the data, and the cross-wind testing could have been conducted over a continuous 

sweep of yaw angles rather than at a few discrete angles. 

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Dynamic Stability 

One of the major advantages of MSBS, and the advantage that led directly to the work on 

MSBS at NASA Langley, is the ability of a magnetic suspension and balance system to provide 

more accurate dynamic stability data from wind tunnels. 

Provide Concurrent, Improved, Dynamic Stability Data 

In the typical small-amplitude forced-oscillation method of dynamic stability testing, the 

model must be considerably distorted to allow even the small amplitude (typically 1 or 2 degrees) 

oscillations on the fixed sting support. Further, the typical small amplitude forced oscillation 

mechanism severely limits the location of the center of oscillation, a fact which has in the past 

limited the usefulness of test results on configurations such as the Mercury and Gemini Capsules 

and the Apollo Command Module. 

In contrast, by using a MSBS, there is no distortion of the model to accommodate the support 

system. Further, with a MSBS the oscillation center of the model being tested can be varied at 

will, a very desirable feature for configurations where the center of gravity has not been fixed or 

for a configuration envisioned to have a large shift in center of gravity over its flight envelope. 

Multiaxis Capability 

An additional advantage of MSBS for the classical method of extracting dynamic stability 

information is the ability it provides for simultaneous oscillations of the model, either forced or 

free, about any of the six degrees of freedom of the suspended model. This capability can be 

used, for example, to provide a suitably combined pitching and plunging oscillation in order to 

achieve a pure angle of attack oscillation, thus providing the ability to separate the effects of 

Cm(a1pha) from the effects of Cm(qdot). 

Parameter Identification Techniques 

Although the interest at NASA Langley in MSBS was prompted in large part by the desire to 

find a better way to do small-amplitude forced-oscillation testing in transonic wind tunnels, the 

need for such a capability may have been eliminated by the emergence in recent years of 

parameter identification techniques to determine the dynamic characteristics of physical systems. 

Although not demonstrated, conceptually the use of parameter identification techniques is 

compatible with the requirei-ilent io deteii-iih the dyniidc st&i!ity characteristics ef mode!s ix a 

MSBS. The model would appear to be held rigidly in suspension. However, the dynamic 

characteristics would be extracted from the supporting coil currents as these currents changed in 

response to the demands of the model to be held fixed in space. 

Improve Tunnel Productivity 

Improvement in wind tunnel productivity is an area where MSBS has a particularly strong 

potential. Productivity is considered to be improved if: 

1. the required data is obtained with less tunnel occupancy 

hours, 

2. the data per hour is of higher quality, 

3. fewer models are required, 

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4. less data reduction is required, and 

5. previously unavailable, but desired, data is produced. 

The following paragraphs will discuss a few examples to explain features of an MSBS which 

would provide these productivity improvements. 

The drawings in figure 7 illustrate the 5 model/sting configurations that were necessary to 

obtain dynamic stability data for the crew escape module of an early version of the B-1 bomber. 

The tests were conducted in the Langley 8-ft Transonic Pressure Tunnel. Such relatively large 

tunnels are not only expensive to operate, but their time is valuable in the sense that they have 

more customers than they can serve. To obtain a sufficient data matrix to determine the dynamic 

stability characteristics of the model of the escape module, it was necessary to oscillate the model 

through 5 separate ranges of angle of attack in pitch, 4 ranges of yaw angle, and at 4 roll 

positions; a total of 80 conditions. Since each point in the matrix required the support to be 

changed, the test section had to be opened a total of 80 times. Note that the fifth configuration 

had to have a bulge in the underside to accommodate the balance for the highest pitch angle. 

This attempt to locate the balance oscillation axis on the proposed center of gravity position 

necessitated the construction of an additional model. 

Had this facility been equipped with an MSBS, one less model would have been required, 

there would have been no distortion of model geometry, no supports would have been 

constructed, the data would have been improved due to the lack of support interference, the test 

section would never have had to be opened. The resultant testing time would have been reduced 

from many weeks to perhaps several days. Recourse to reference 20, which documents this test, 

reveals also that this was a sparse amount of data to acquire and that more points would have 

been desirable. Also unavailable are any mixed modes such as Dutch roll. 

Figure 8, taken from reference 21, illustrates one method of evaluating support interference. 

In this example, the evaluation was necessary to allow extrapolation of wind tunnel results to 

flight. Figure 9 indicates the magnitude of the corrections determined and their nonlinearity 

with Mach number. For a typical cruise condition, these corrections are of the order of 10 

percent of the total drag. This is a seizable correction and its application is absolutely necessary 

in configuration synthesis and performance prediction. 

From a productivity point of view, these tests could have been eliminated with a MSBS 

resulting in savings in three areas: First, the family of large, expensive support hardware 

sketched in figure 8 would never have been built. Second, the additional tunnel time to test the 

different support configurations, as well as the test section entries required to make configuration 

changes, would have been unnecessary. Third, the extensive data analysis procedure documented 

in reference 21 would not have been necessary. 

Two- body Aerodynamics 

Figure 10 shows a model wind tunnel model of the Shuttle Orbiter attached to a ferry ship. It 

would be of prime engineering interest in this case to determine the aerodynamic coefficients of 

each vehicle in terms of the Orbiter attitude, axial location, and separation distance. The 

conventional method of obtaining this data is to test several values of each variable, requiring 

many different attachment points. The availability of an MSBS would allow the Orbiter to be 

"flown" to different locations, simultaneously measuring the forces on the carrier ship with a 

mechanical balance and on the Orbiter with the magnetic balance, to determine the sensitivity of 

the aerodynamic coefficients to location and attitude with one test installation. This procedure 

not only reduces tunnel time, test section entries, and extra time for model changes, but also has 

the potential to produce a better answer, thus improving productivity. 

4 
Stores Separation 

One means of studying the problem of separating a store from a carrier aircraft is to 

separately support the model of the aircraft and the model of the store and equip each with a 6- 

component balance allowing simultaneous measurements of the aerodynamic forces. With a 

sophisticated drive for the support of the model of the store, it is possible to simulate the 

positions a store would take during a separation, and to determine the mutual interactions 

between store and aircraft. The practice of this art is summarized in reference 22. Figure 11, 

taken from reference 23, indicates the sophistication and complexity necessary in the drive 

system. In an MSBS equipped facility, only the model of the aircraft would be supported in this 

manner with the support and model being constructed of a non-magnetic material, such as 

stainless steel. The model of the store would contain a magnetic core and would be magnetically 

supported and positioned. The use of magnetic fields as an aid in stores release testing was 

discussed at least as early as 1967, reference 24. 

NEW WIND TUNNEL TESTING TECHNIQUES 

The previous sections of this paper have dealt with at least quasi-conventional applications of 

a near-term technology MSBS. This section assumes the availability of an advanced MSBS 

equipped with the sensors and control systems to allow a model to be freely manipulated in the 

test section, including any angle of pitch, roll, and yaw, and motions such as spin or tumbling. 

Also assumed is the ability to relinquish control of any or all degrees of freedom for intervals of 

time in order that the model can dynamically respond to the forces being imposed. For example, 

releasing the roll control would allow a fighter model at angle of attack to oscillate in roll in 

response to the dynamic forces that induce wing rock. 

General Improvements 

. Computer Controlled Stop Point Trajectories 

Figure 12 serves to simultaneously illustrate the concepts of “computer controlled stop point 

trajectories”, and “designer in the loop”. The example used is a crew escape module being 

ejected from a bomber type aircraft. In this case, the bomber is mounted with a conventional 

blade mount and mechanical balance, and would contain no magnetic materials. The crew 

module would contain a magnetic core, and could be manipulated by an advanced MSBS. The 

envisioned purpose of the test is to determine under what conditions of escape module ejection 

would the crew be able to survive. 

The test might be conducted by first testing with the crew module in place on the aircraft. 

This would provide initial aerodynamic separation forces tending to hold or eject the module; this 

data point would be enhanced by moving the module very slightly and retaking the data in order 

to evaluate tare forces due to friction. A non-aerodynamic initial force and trajectory would be 

assumed consistent with an ejection mechanism, for instance a rocket. This initial trajectory 

would be the one the module would follow in a vacuum. The next point would be obtained by 

moving the module along this prescribed trajectory just enough to allow flow to circulate 

between the module and the cavity as it is leaving in the aircraft. The measured forces and 

moments would then be used to modify the vacuum trajectory and allow the calculation of the 

next point along the modified trajectory. At the next point, forces and moments would again be 

calculated, and so forth. The assumed center of gravity location of the module would be 

constrained to follow the modified trajectory, but the capsule would be rotated as the measured 

aerodynamic moments and calculated moments of inertia would dictate. 

5 
The above process describes the “computer controlled stop point trajectory.” Since this 

trajectory could be programmed to be run many times during a wind tunnel test, it would be 

feasible to make parametric investigations of such effects as the orientation of the bomber, the c. 

g. location in the module, variations of the vacuum trajectory, and settings of the aerodynamic 

control surfaces of the module. If an experienced designer were present in the wind tunnel 

control room, and assuming g loads experienced by the crew were continuously calculated, he 

could identify successful and unsuccessful ejections on line, and in an iterative manner, prescribe 

the perturbation of the conditions for the next trajectory that would define the boundaries of a 

survivable escape. This is the essence of the “designer in the loop” concept, which would reduce 

a process that, accomplished by conventional means, would require months for a partial answer 

compared to a few hours for a complete answer. Obviously other ground rules could be imposed 

such as the module remaining upright, or not spinning, and certainly not impacting the vertical 

tail of the bomber. This information would then be used to decide the safe operational envelope 

of the crew escape system and allow rapid and knowledgeable decisions to be made as to the 

desirability of such system or module design. 

The hypothetical example just described serves to illustrate the manner in which an advanced 

MSBS might be employed to use designer in the loop and/or pilot in the loop to greatly improve 

both accuracy and productivity in system design. 

Safe-Box Concept 

The “safe-box concept,” figure 13, is an example of a magnetically controlled tunnel injection 

system that would have the advantages of conventional ejection systems, e.g. to permit heat 

transfer testing, as well as to provide simulation of a bomb bay or silo launch. Such a device 

might also serve well to determine the aerodynamics of stores in cavities, as well as the dynamics 

of stores release from cavities. 

Fighters 

Testing of fighter mAdels has always offered the wind tunnel experimentalist a challenge; a 

straightforward problem is the high angle of attack required. To maintain force balance 

measurement accuracy as angle of attack is increased, it may be necessary to change balances 

several times since the ratio of beam loads can change by factors of two or greater. Also, it is 

not usually possible to use a single support, and it may be necessary to employ one or more bent 

stings. Finally, at the higher angles and with the attendant massive separated wake, some of the 

aerodynamic coefficients become extremely sensitive to the presence and type of support 

structure, as discussed in reference 16. 

The use of an advanced MSBS eliminates these problems simultaneously with adding new 

capabilities. Once at high angle of attack, a fighter may exhibit the tendency to buffet, wing 

rock, nose slice, or otherwise depart from a stable condition. Since any constraint on model 

motion imposed by the MSBS may be relaxed of abandoned, these tendencies may be explored, or 

artificially induced and allowed to amplify or decay. In addition, high angle of attack 

characteristics may be determined instantaneously. This would allow the determination of, for 

instance, any overshoot in lift coefficient that may occur as a result of the pitch rate employed to 

deliver the fighter to the high lift condition; the next step, and one easily permitted by MSBS, 

would be to examine various pitch rates to establish acceptable values of maximum rate. 

The high angle of attack capabilities discussed above serve as an example of new capabilities 

offered by an advanced MSBS in this one area of fighter testing. Other capabilities offered are 

transient maneuvers including both translations and rotations, pilot-in-the -loop, magnetically 

varied c. g. location, real time computer generated stability augmentation systems, computer 

generated artificial damping, out of flight path pointing, simulated carrier landings, and 

simulated refueling. Further details of fighter testing are beyond the author’s ken, and it is left 

6 

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to the readers imagination to fill in the details of using such a MSBS to solve his particular 

problem. 

Missiles 

The technique of studying two-body or stores separation problems with the aid of an MSBS 

has been discussed in other sections of this paper. The following example is intended to provide 

the philosophy for additional application of advanced MSBS to missile problem solving. 

The safe-box concept, as discussed earlier (figure 13), is an example of a magnetically 

controlled injection system that could provide simulation of a bomb bay or silo launch. If this 

system were available in a trisonic tunnel, a special naval problem of shipboard defense is 

envisioned as an example MSBS application. Since the direction from which a threat might 

approach is not known, it is assumed that the missile launcher would be vertically mounted. The 

most demanding task from such a launcher is interception of a sea level threat. To simulate this 

mission, the missile would first be moved magnetically from a simulated launch tube as shown in 

figure 14. Air blowing from the tube could be used to simulate booster exhaust. This portion of 

the test could be repeated using variations in tunnel speed to simulate different levels of 

crosswind. 

The next phase of this type of launch is a high g turn, requiring the missile to fly at very high 

angle of attack to the oncoming flow. (Since the typical missile of this type has no wings, it turns 

by having some component of thrust normal to the flight path, and the angle of attack is actually 

negative in the aerodynamic sense.) During this maneuver, the Mach number, pitch rate, and 

angle of attack are simultaneously changing. These variables can be studied one at a time or all 

together by the computer controlled stop point trajectory technique discussed earlier. Finally, the 

model will be taken to the supersonic lock-on phase with static stability, dynamic stability, and 

control force requirements having been determined at every point in the trajectory. 

Helicopters 

Figure 15 illustrates an additional capability offered by MSBS in the testing of helicopters. 

The testing underway in the photograph is conducted with the rotor turning from an attachment 

in the tunnel floor. The helicopter body is being tested in the downwash of the rotor but is 

detached from the rotor. The body can be turned through 360 degrees to produce a crosswind 

due to the tunnel flow. This will allow the determination of the static stability of the body in the 

hover mode and under the combined effects of rotor downwash and crosswind. An MSBS is an 

ideal candidate to replace the support used here to turn the body, providing support interference 

free data and greatly increased ease of operation. Also, in this case no particular beam of a 

mechanical balance can be optimized since the maximum load can come from any direction. 

Conceptually, the magnetic balance components can be optimized for the load condition by 

changing the sensitivity constants with each increment of rotation. 

Transports/Bombers 

Figure 16 illustrates an advanced subsonic transport concept typical of the "family concept" of 

more efficient aircraft, reference 25. The use of the twin fuselage scheme presents the wind 

tunnel engineer with the immediate problem of finding a location for a balance. A MSBS can 

ease this problem by locating a magnetic core in each fuselage, creating a virtual core in the 

center of the vehicle. Also removed is the vexing problem of supporting such a configuration, 

both for static and dynamic stability tests. An MSBS also offers a unique capability to determine 

aeroelastic behavior of this type of configuration by supporting one fuselage with a mechanical 

7 
balance while supporting the other fuselage magnetically thus allowing determination of the 

aero/mechanical coupling of the wing and horizontal stabilizer. 

The advanced transport configuration depicted in figure 17 presents a different sort of testing 

problem in that the main lifting surface is so far aft as to preclude any sort of mechanical 

support without severe support interference problems. An MSBS not only erases the support 

problem, but also offers the opportunity to fly this canard dominated design with varying degrees 

of positive or negative static margin, assuming the incorporation of an appropriate active control 

system for the canard. 

Hypersonics 

Most of the advantages of wind tunnel testing with a MSBS at other speeds are also applicable 

in the hypersonic speed range. The problem of alteration of vehicle geometry due to supports 

becomes particularly acute for airbreathing configurations optimized for cruise range. In order to 

reduce both drag and heating, it is necessary to have highly swept, thin wings and stabilizing 

surfaces, as depicted in figure 18. It is obvious that the empennage section of this configuration 

would be grossly distorted by the conventional balance and sting. 

At the present stage in hypersonic research, fundamental studies of wing alone aerodynamics 

are necessary in order to develop optimization methodology. Since the wings are typically as 

shown in figure 19, that is very thin, there is no place for a mechanical balance, and without a 

magnetic balance, quality data is very difficult to obtain. For configurations intended for 

airbreathing cruise, the wings also tend to be very thin, leaving no volume in the model for a 

conventional strain-gage balance. For these configurations, the entire wing would be made of a 

magnetic material in order to be suspended by a MSBS. 

Hypersonics has other special problems that may be well addressed by the use of a MSBS. One 

of the problems of conventional balances which may occur in hypersonic tunnels is high model 

heat transfer rates which induce temperature gradients in the balance. In the hypersonic 

environments necessary for simulation of turbulent boundary layers, these gradients are 

sufficiently large as to require water cooling of the balance, and in a few cases even this is not 

sufficient to reduce balance temperature gradients to acceptable levels. Obviously, a MSBS 

eliminates this difficulty. 

Figure 20 is a photograph of a “parasol wing” configuration. This is essentially a two-body 

configuration since the wing is supported on pylons and there is flow between the body and the 

wing. The performance of the wing is improved in “wave rider” fashion by the compression of 

the flow of the fuselage forebody, and the drag of the fuselage is reduced by the aft body high 

pressures induced by the wing compression. An MSBS would be employed in several ways in this 

case, first to measure the wing alone performance of the very thin wing and then to determine 

the optimum location of the wing, with respect to the body, for maximum wing performance. 

Then a non-magnetic wing would be blade supported and the fuselage magnetically flown to 

determine a similar data set. Finally, the entire optimized configuration would be tested 

magnetically to measure its aerodynamic performance. 

It is possible to obtain this data with a mechanical balance, but the particular advantage of a 

magnetic balance for this type of testing is the ability to mechanically decouple the wing and 

body, support one component mechanically and the other magnetically, and vary the parameters 

of separation distance, fore and aft location, and relative pitch angles. As observed earlier, these 

optimizations can be carried out with one set of models and one set of tests. This procedure not 

only results in increased tunnel productivity and a reduction in models and supports required, but 

also allows the relative positioning of the configuration to be carried to a true optimum during 

the actual testing, thus saving large amounts of data reduction of isolated points, which can only 

approach an optimum. 
Stage Separation 

Another simulation task which may be presented to the wind tunnel engineer is stage 

separation of airbreathing stages. Figure 21 is an artist’s rendition of a follow-on Space Shuttle 

concept. For this concept, two “tugs” with large turbojets are used for take-off and acceleration 

to supersonic speed where they separate and return to the airport. The Shuttle then accelerates on 

a mixed mode scramjet to hypersonic speeds, and finally uses rocket boost for insertion into orbit 

(consult reference 26 for additional information on this concept). The MSBS would assist this test 

by determining the supersonic separation characteristics by magnetically flying away the tug in a 

manner similar to the crew escape scheme discussed earlier. In this case, the MSBS would also be 

used to efficiently optimize the orientation of the tug with respect to the Shuttle; in a trisonic 

tunnel, this could be done across the speed range. 

Aero Systems 

Aero systems is a catch-all term for the systems not considered elsewhere in this paper, but 

for which a MSBS would be advantageous. For instance ground effect machines or hovercraft. 

These craft could be supported in sub-scale with working propulsion plants to determine 

optimum design parameters, crosswind effects, dynamic responses, and, with a moving ground 

plane, effects of roughness or surface obstacles. 

Automobile Testing 

The use of an MSBS also offers unique advantages in the wind tunnel testing of automobiles. 

Figure 22 is a photograph of a racing car under test in the Fiat Research Centre Aerodynamic 

Wind Tunnel. Reference 27 describes this type of testing and its validity for Formula 1 racing 

cars. This reference discusses several testing limitations, and it appears that an MSBS could 

eliminate the support interference problem as well as enhance the testing capability. For 

instance, by supporting the car in axial and !atera1 trans!atic?n on!y, and permitting :he siispeilsion 

and wheels to support the weight in the normal manner, the car would be able to assume its 

natural angle of attack; internal mechanical balances attached to the wheels could then determine 

the remaining forces. While the authors do not purport to understand the intricacies of this type 

of testing, it is fairly obvious that a MSBS would be a powerful tool in automotive testing. 

Towing Tanks and Water Tunnels 

A MSBS could be used with a conventional towing tank by supporting the MSBS on a carriage 

which would roll down the length of the tank as is presently done with mechanical support 

systems. However, the model would “fly” freely either above or in the water as well as 

throughout the air-water interface. The craft could also be allowed to respond dynamically in a 

natural manner; for instance, by turning off the magnetic roll control, the natural roll and roll 

rate cycles could be established. Hydrofoils could be tested in a similar manner and by turning 

off the magnetic lift force, the ship could be allowed to seek its equilibrium depth, and by 

turning off pitch, its natural angle of attack. 

The real forte of the MSBS in water facilities, however, is probably underwater towing, where 

support interference is a more vexing problem. This leads naturally to the application of MSBS 

for water tunnels. Not only is the support interference eliminated but complex model dynamics 

are also easily accomplished. 

9 
POTENTIAL SPINOFF OUTSIDE OF WIND TUNNELS 

Although the development of an advanced magnetic suspension and balance system is justified 

by its potential benefit to aeronautics alone, it is appropriate to consider spinoff applications to 

other technological disciplines. Schemes employing simple magnetic levitation, such as is 

practiced with magnetically levitated trains or magnetic bearings, are well documented and are 

not considered to be a potential MSBS application since there is no active control and usually only 

one degree of freedom. 

MSBS in Medicine 

The use of an MSBS in the field of medicine does not require speculation in this document to 

give it birth since it is already in use and well documented in its own right. Reference 28 

describes its use to "fly" a cylindrical body in the blood stream of an animal test subject in order 

to assess the tendency of blood to clot on materials intended for use in the manufacture of 

artificial organs. The clotting rate could be inferred from the increase in drag of the cylindrical 

body as clots adhered to its surface. Additional uses in medicine are further documented in the 

bibliography. 

Yet another use is imagined as pictured in figure 23, where a magnetic "pipeline pig" is being 

flown through the body circulatory system to the location of a clot. Upon arrival at the clot a 

rotating field will be used to spin the cutter blades to grind away the clot and avoid the trauma of 

conventional surgery. It is also possible that such an application could find use in areas of the 

body that are generally considered to be inoperable, such as deep in the brain. 

MSBS In Robotics 

The capability to handle heavy loads is inherent in magnetic suspension systems for large 

transonic wind tunnels. Based on design studies, these loads will be in the range of 1000 pounds 

for magnetic cores and several tons for superconducting cores. This large load handling 

capability is coupled with a very sensitive position indicator and force and moment measurement. 

The reader is asked to envision such a freely suspended core equipped with arms, clamps, 

grapplers or other appropriate manipulators; a core so equipped could then perform industrial 

tasks. For instance, a suitably programmed MSBS robot could rapidly load heavy pallets from a 

rail siding into a boxcar; or unload munitions from a military transport; or load shells in a naval 

gun tub. Such a robot could also perform hazardous tasks such as cleaning the inside of fuel 

tankers. More intelligently equipped robots could perform inspections and take corrective actions 

in toxic or radioactive environments. 

Orbital Applications 

Space may be an ideal location for application of large MSBSs since the maintenance of the 

low temperatures necessary for the operation of the superconducting magnets is much easier than 

on the Earth's surface. 

Figure 24 illustrates a fanciful ore processing plant in space with several docking ports, which 

have a similarity to protruding wire baskets. Figure 24b is a close-up of one of these docking 

ports illustrating the location of the magnets and the relative size of the ship and docking port. 

The magnetic core aboard the ship is envisioned to consist of a superconducting coil. 

The advantage of such a system might be most obvious for a ship such as a robotic ore 

Such a ship would be programmed to match speed and maneuver within the 

At this point, sensors aboard the station 

carrying vessel. 

sphere of influence of one of the docking systems. 

10 
would determine the relative velocity and location of the ship and the MSBS would align the ship 

and bring it through the docking doors. Once inside the station, magnetic systems would handle 

positioning and unloading of the ship. Departure would be accomplished by the same system 

with a "magnetic push" to launch the ship away from the station. 

Figure 25 is an artist's concept depicting a beam weapon mounted within a spherical MSBS 

system. The "barrel" of the weapon is free to swing through more than a 300 degree arc, with no 

friction and precise pointing. Also there are no electric motors, gears, exhaust jets from vernier 

rockets, or expendables. A similar concept might be employed to aim cameras, antenna, 

telescopes, mirrors, etc. 

EPILOGUE 

In the conservative view, the use of magnetic suspension and balance systems (MSBS) in large 

wind tunnels will eliminate or greatly reduce errors due to supports, restraints due to supports, 

tunnel occupancy time, the number of models required, and data analysis required to evaluate 

support interference. 

In the slightly less conservative view, the use of MSBS will improve data accuracy, highangle-of-attack test capability, dynamic stability test technique, two-body/stores-release testing, 

and provide nearly free flight test conditions in many circumstances. The summation of these 

changes due to MSBS is predicted to be large improvements in wind tunnel productivity. 

In a speculative view, the addition of pilot and designer-in-the-loop concepts may improve 

productivity and at the same time open new vistas in wind tunnel test technique. Although the 

research and development necessary to bring about the fruition of large MSBS's should pay for 

itself in wind tunnel productivity improvement alone, the technology spinoff may be even more 

valuable. 

Some of the new capabilities envisioned in this paper will not evolve due to engineering 

difficulties, and the authors have deliberately allowed their reach to exceed their grasp in many 

areas. However, experience teaches that the unforeseen uses of new technology frequently 

surpass even the most speculative of forecasts. 

11 
REFERENCES 

1. 

2. 

3. 

4. 

5. 

6. 

7. 

8. 

9. 

10. 

11. 

12. 

13. 

14. 

15. 

Tournier, Marcel; and Laurenceau, P.: Suspension Magnetique d'une Marquette en 

Soufflerie. (Magnetic Suspension of a Model in a Wind Tunnel). La Recherche 

Aeronautique, no. 59, July-Aug. 1957, PP. 21-27. 

Tuttle, M. H.; Kilgore, R. A.; and Boyden, R. P.: Magnetic Suspension and Balance 

Systems. A Selected, Annotated Bibliography. NASA TM-84661, July 1983. 

Kilgore, R. A.; and Dress, D. A.: The Application of Cryogenics to High Reynolds 

Number Testing in Wind Tunnels. Part 1: Evolution, Theory, and Advantages. 

Article published in Cryogenics magazine, August 1984. 

Kilgore, R. A.; and Dress, D. A.: The Application of Cryogenics to High Reynolds 

Number Testing in Wind Tunnels. Part 2: Development and Application of the 

Cryogenic Wind Tunnel Concept. Article published in Cryogenics magazine, 

September 1984. 

Lawing, P. L.; and Johnson, C. B.: Summary of Test Techniques Used in the NASALangley 0.3-m Transonic Cryogenic Tunnel. Presented at the AIAA 14th 

Aerodynamic Testing Conference, West Palm Beach, Florida, March 5-7, 1986. 

Kilgore, R. A.; and Dress, D. A.: A Survey of Cryogenic Wind Tunnels. Presented at 

Dipartimento di Ingegneria Aeronautica e Spaziale Politecnico di Torino, Torino, Italy, 

April 14, 1896. 

Bloom, H. L.; et al: Design Concepts and Cost Studies for Magnetic Suspension and 

Balance Systems. NASA CR- 165917, 1982. 

Britcher, C. P.: Progress Towards Large Wind Tunnel Magnetic Suspension and Balance 

Systems. AIAA Paper No. 84-0413, 1984. 

Boom, R. W.; Eyssa, Y. M.; McIntosh, G. E.; and Abdelsalam, M. K.: Magnetic 

Suspension and Balance System Advanced Study. NASA CR-3937, 1985. 

Boyden, Richmond P.; Britcher, Colin P.; and Tcheng, Ping.: Status of Wind Tunnel 

Magnetic Suspension Research. SAE 851898, Oct. 1985. 

AIAA 14th Aerodynamic Testing Conference, West Palm Beach Florida, March 5-7, 1986: 

AIAA CP 861. 

Kilgore, R. A.; Dress, D. A.; and Lawing, P. L.: Some of the Capabilities and Desirable 

Features of an "Ideal" Transonic Wind Tunnel. NASA TM-85484, November 1983. 

Barnwell, R. W.; Edwards, C. L. W.; Kilgore, R. A,; and Dress, D. A.: Optimum 

Transonic Wind Tunnel. AIAA No. 86-0755, March 1986. 

Bushnell, D. M.; and Trimpi, R. L.: Supersonic Wind Tunnel Optimization. AIAA No. 

86-0773, March 1986. 

Boyden, Richmond P.; Brooks, Cuyler W., Jr.; and Davenport, Edwin E.: Transonic Static 

and Dynamic Stability Characteristics of a Finned Projectile Configuration. NASA 

TM-74058, April 1978. 

12 
16. 

17. 

18. 

19. 

20. 

21. 

22. 

23. 

24. 

25. 

26. 

27. 

28. 

Dietz, W. E.; and Alhtatt, M. C.: Experimental Investigation of Support Interference on 

an Ogive-Cylinder at High Incidence. J. Spacecraft and Rockets, Vol. 16, Jan-Feb. 

1979, pp 67-68. See also AIAA Paper 78-165, Jan. 1978. 

Johnson, Joseph L. Jr.; Grafton, Sue B.; and Yip, Long P.: Exploratory Investigation of 

Vortex Bursting on the High-Angle-of-Attack Lateral-Directional Stability 

Characteristics of Highly-Swept Wings. AIAA Paper No. 80-0463, March 1980. 

Price, Earl A. Jr.: An Investigation of F-16 Nozzle-Afterbody Forces at Transonic Mach 

Numbers with Emphasis on Support System Interference. AEDC-TR-79-56, AFAPLTR-2099, December 1979. 

Tuttle, Marie H. and Lawing, Pierce L.: Support Interference of Wind Tunnel Models-A 

Selective Annotated Bibliography. Supplement to NASA TM 81909, May 1984. 

Davenport, E. E.; and Kilgore, R. A.: Dynamic-Stability Tests of an Aircraft Escape 

Module at Mach Numbers From 0.40 to 2.16. NASA TM-X-72680, April 1975. 

MacWilkinson, D. G.; Blackerby, W. T.; and Paterson, J. H.: Correlation of Full-scale 

Drag Predictions With Flight Measurements on the C-141A Aircraft - Phase 11, Wind 

Tunnel Test, Analysis, and Prediction Techniques. Volume I - Drag Predictions, Wind 

Tunnel Data Analysis and Correlation. NASA CR-2333, 1974. 

Arnold, R. J.; and Epstein, C. S.: Store Separation Flight Testing. AGARD-AG-300- 

Vo1.5, April, 1986. 

Billingsley, J. P.; Burt, R. H.; and Best, J. T.: Store Separation Testing Techniques at the 

Arnold Engineering Development Center. AEDC-TR-79- 1, March 1979. 

Covert, Eugene E.: Wind Tunnel Simulation of Stores Jettison With the Aid of an 

Artificial Gravity Generated by Magnetic Fields, AIAA Journal of Aircraft, Volume 4, 

No. 1, 1967. 

Kayten, Gerald G.; Driver, Cornelius; and hlaglieri, J.: The Revolutionary Impact of 

Evolving Aeronautical Technologies. AIAA-84-2445, Nov., 1984. 

Jackson, L. Robert; Martin, James A.; and Small, William J.: A Fully Reusable, 

Horizontal Takeoff Space Transport Concept With Two Small Turbojet Boosters. 

NASA TM-74087, 1977. 

Bonis, Bruno; and Quagliotti, Fulvia V.: A Study of the Validity of Fixed-Ground 

Testing for Formula 1 Racing Cars. SAE 860092, Feb. 1986. 

Lederman, D. M.; Cumming, R. D.; Petschek, H. E.; Chiu, T-H.; Nyilas E.; Salzman 

E.; Collins, R. E. C.; and Coe, N. P.: The Intravascular Magnetic Suspension of a Test 

Device For In Vivo Hernocompatibility Evaluation of Biomaterials. Transactions of the 

American Society for Artificial Internal Organs, Vol. XXII, 1976. 

13 
BIBLIOGRAPHY 

Zapata, R. N.; Parker, H. M.; Moss, F. E.; Hamlet, I. L.; and Kilgore, R. A.: University 

of Virginia Superconducting Wind-Tunnel Balance. Paper presented at the 1970 

Applied Superconductivity Conference, June 15- 17, 1970, in Boulder, Colorado. 

Journal of Applied Physics, Vol. 42, No. 1, pp. 3-5, January 1971. 

1. 

2. 

3. 

4. 

5. 

6. 

7. 

8. 

9. 

Stephens, T.; Covert, E. E.; Vlajinac, M.; and Gilliam, G. D.: Recent Developments in a 

Wind Tunnel Magnetic Balance. AIAA 10th Aerospace Sciences Meeting, Paper No. 

72-164, January 1972. 

Beams, J. W.; Hodgins, M. G.; and Kupke, D. W.: A Magnetic Osmometer. Proceedings 

of the National Academy of Sciences, USA, Vol. 70, No. 12, Part 11, pp. 3785-3787, 

December 1973. 

Tuttle, Marie H.; and Gloss, Blair B.: Support Interference of Wind Tunnel Models - A 

Selective Annotated Bibliography. NASA TM-8 1909, 1981. 

Boom, R. W.; Eyssa, Y. M.; McIntosh, G. E.; and Abdelsalam, M. K.: Magnetic 

Suspension and Balance System Study. NASA CR-3082, 1984. 

Martindale, W. R.; Butler, R. W.; and Starr, R. F.: Study on Needs for a Magnetic 

Suspension System Operating With a Transonic Wind Tunnel. NASA CR 3900, May 

1985. 

Meznarsic, V. F.: The Role of Wind Tunnel Testing in Future Aircraft Development. 

AIAA No. 86-0750, March 1986. 

Ericsson, L. E. and Reding J. P.: Dynamic Support Interference in High Alpha Testing. 

AIAA No. 86-0760, March 1986. 

LaFleur, Sharon S.: MSBS Magnetic Suspension and Balance Systems Newsletter No. 1. 

Published by the Experimental Techniques Branch, NASA Langley Research Center. 

May 1986. 

14 
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41 
1. Report No. 

NASA 'I'M-89079 

NASA Langley Research Center 

Hampton, VA 23665-5225 

2. Government Accasion No. 3. Recipient's Catalog No. 

11. Contract or Grant No. 

4. Title and Subtitle 

Potential Benefits of Magnetic Suspension and 

Balance Systems 

7. Author(sl 

Pierce L. Lawing, David A. Dress and Robert A. Kilgore 

13. Type of Report and Period Covered 

5. Report (kto 

6. Performing Orgrniration codr 

February 1987 

505-61-01-02 

8. Performing Orgrniration Report No. 

12. Sponsoring Agency Name and Address 

National Aeronautics and Space Administration 

Washington, DC 20546 

9. Sscurity Claoif. (of this report) 

Unclassified 

I 

5. Supplementary Notes 

20. Sccurity Classif. (of this pawl 21. No. of Pages 22. Rice 

Unclassified 42 A0 3 

6. Abstract 

The potential of Magnetic Suspension and Balance Systems (MSBS) to improve conventional wind 

tunnel testing techniques is discussed. Topics include: elimination of model geometry distortion 

and support interference to improve the measurement accuracy of aerodynamic coefficients; 

removal of testing restrictions due to supports; improved dynamic stability data; and stores 

separation testing. Substantial increases in wind tunnel productivity are anticipated due to the 

coalescence of these improvements. 

Specific improvements in testing methods for missiles, helicopters, fighter aircraft, twin fuselage 

transports and bombers, stage separation, water tunnels, and automobiles are also forecast. 

In a more speculative vein, new wind tunnel test techniques are envisioned as a result of applying 

MSBS, including "free-flight" computer trajectories in the test section, pilot-in-the-loop and 

designer-in-the-loop testing, shipboard missile launch simulation, and optimization of hybrid 

hypersonic configurations. Also addressed are potential applications of MSBS to such diverse 

technologies as medical research and practice, industrial robotics, space weaponry, and ore 

processing in space. 

7. Key Words (Suggested by Authods)) 

Wind tunnels 

Magnetic suspenson 

Test techniques 

18. Distribution Statement 

Unclassified - Unlimited 

Subject Category - 09 

Y-305 For sale by the National Technical Information Service, Springfield, Virginia 22161