NASA Contractor Report 178056

FURTHER INVESTIGATION INTO CALIBRATION

TECHNIQUES FOR A MAGNETIC SUSPENSION

AND BALANCE SYSTEM

J. Eskins

THE UNIVERSITY OF SOUTHAMPTON

Southampton, England

Grant NSG-7523

February 1986

NASA-CR-178056

19860010941

NI\S/\

National Aeronautics and

Space Administration

Langley Research center

Hampton, Virginia 23665

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L1GRARY, WIS/\

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MAJS: /*CALIBRATING/*MAGNETIC SUSPENSION/*WIND TUNNEL MODELS

fl" I{\l::;: [)F~AG~/ LIFT./ Fi 11CJ-iIt"M; ,',=V)t'f1E\',.1113/ ~~\JF1EF~f2C}i\i[JtJC.TIhh~ t'i1Al;~\lET:3

Fx - Fz

Ip

K·£

m

x,y,z

x~y~ z'

x'~y",z"

List of Symbols

forces acting on the model

acceleration due to gravity

current in the jth electromagnet

current in the jth electromagnet when mass, mk, is attached to the

model

summed lift current when mass, mk, is attached to the model

drag current, i.e. summation of the currents in the electromagnets

providing drag force

lift current, i.e. summation of the currents in the electromagnets

providing lift force

pitch current, i.e. summation of the currents in the electromagnets

providing pitching moment

current in superconducting solenoid

mean summed lift current for a dynamic oscillation

calibration constant for the ith degree of freedom and jth

electromagnet

calibration constant for the ith degree of freedom (current

providing this force/moment being summed)

z-direction calibration constant per unit solenoid current

inner core/outer can stiffness factor

core to ground stiffness (a magnetic stiffness)

moments acting on the model

mass of the model

mass of outer can (superconducting solenoid model)

mass of inner core (superconducting solenoid model)

mass added to the model to apply a static force or model

time

tunnel axes

translated model axes

translated and rotated model axes

centreline of position trace during a dynamic lift oscillation

yaw, pitch and roll of the model

current phase

position phase

angular frequency

i

..

1 INTRODUCTION

Magnetic Suspension and Balance Systems (MSBS) for wind tunnels offer

many advantages over conventional supports.

The major advantage is :-

a) Elimination of sting interference with no modification of the model

to accommodate the sting

but others include,

b) Ease of model movement allowing dynamic testing

c) Fast, efficient testing at almost any attitude

d) The type of model suspended can be changed without alterations in

the support systems.

To take full advantage of the inherent attributes of MSBS a standard

calibration technique should be developed. For instance, if a model was

changed, but the magnetic core were standard, the whole support system need

not be re-calibrated. However, without mechanical supports between the

model and the tunnel, force/moment calibration of the system is not

straightforward. This report investigates the relationship between the forces

and moments applied to a magnetically suspended model and the currents in

the electromagnet array. The disadvantage of this technique is that the

calibration is performed in the wind tunnel. This wastes tunnel time and for a

large MSBS (LMSBS) would be costly. A method to reduce the calibration time

to a minimum is essential.

Previously most of the calibration of models in SUMSBS was carried out

statically. This is achieved by applying known forces and moments, using

weights and pulleys, and monitoring the currents in the electromagnet array.

For a LMSBS this would be clumsy as well as costly and time-consuming.

An alternative approach to static calibration is dynamic calibration. This

involves oscillating a model in a particular mode (e.g pitch), recording its

motion, in addition to the electromagnet currents, and using the model's

inertia to calibrate the system. Previous work1,2 has shown this to be a

promising calibration method. In principle dynamic calibration can calibrate

all degrees of freedom, for a large range of attitudes, in a very short time.

A major cost of LMSBS is the building and rl,lnning of the electromagnet

array. The physical size of the electromagnets and running costs can be

reduced considerably by using superconducting magnets. A major saving can

be made by increasing the magnetic moment of the model. For conventional

1
cores there is a limit to the magnetic moment per unit volume, but using a

superconducting solenoid1 to provide the magnetic field the magnetic moment

is dependent on the solenoid current. For large models, although there is a

limit to the solenoid current, the magnetic moment per unit volume of model

can be made greater for a superconducting model than the best permanent

magnetic material.

A pilot model was built and flown at Southampton in July 19831 and again

in May 1984. Data from the later tests on this m.odel is included here together

with calibration work on conventional cores.

2 CALIBRATION THEORY

In general the model can be treated as being acted upon by three

orthogonal forces and three moments (see Figure 1). SUMSBS uses ten

electromagnets to produce the required orientation, with some redundancy

therefore in the electromagnet array.

The force/moment balance can be represented as (1).

11

1

2

F 1

3 oX

F

y

Fz K .. (1) lJ

L

M

N

1

9

1

10

The purpose of the calibration is to determine the elements in the array

Kij. There is a further complication in that the matrix Kij is a function of

model position and attitude, (see Figure 1) i.e

Kij = Kij (x, y, z, \P, 8, <1»

Kij is also a function of the magnetic moment of the model. In particular

for the superconducting model, Kij will be a function of solenoid current.

2
This method of calibration involves subjecting a model to one or more

forces and moments (F • N) and monitoring the currents required to hold the x , model at the required orientation. A method of least squares can then be used

to determine elements in Kij.

There are special cases where pure forces or moments are applied or only

certain electromagnets contribute significantly to resisting the applied force

or moment. This is true for calibrations described in this report, where tests

took place with the model central, in position and attitude, in the wind tunnel.

For this case lift force and pitching moment are produced only by the four

electromagnets 1, 3, 7, 5 (Figure 1), and drag force affected only by the two

axially wound coils, 9 and 10. This can be expressed from equation (1) as :-

(2)

with

(3)

with

KS2 =K54 =K56 =K58 =KS9 =Ks,10 =0

(4)

with

In the past equations 2,3, 4 have been further simplified by assuming the

magnitude of the contribution of each coil, to the total force or moment, to

be the same, giving

...

(S)

3
Static calibration involves the application of known forces and torques

Fx - N. A static lift force (Fz)calibration can be represented as

(8)

or

(9)

At least four readings are needed to solve (8), sensibly many more, by a least

squares method. K3 in equation (9) can be found from the gradient of lift

current, h against added weight mkg. Static calibration for pitching moment

and drag force can be analysed in a similar way using (6) and (7).

Dynamic calibrations involve using the model's own inertia to calibrate the

suspension system. For instance, using (5), oscillations in the z-direction,

which could be induced with a view to determining a lift force calibration, can

be represented as

For sinusoidal motion

i(wt +41 )

z(t)=z +ze Z m

fitting a sinusoid to the current

gives

static

dynamic

Taking the real part of the dynamic component

(10)

4
Previous analysis 1,2 did not take account of phase angles, by assuming no

damping and simple harmonic motion with <Pc - <Pz =1800 , giving

2 IL

mw =K - 3 z

(11 )

F (t) = mz + cz + kz

z

For a range of frequencies and amplitudes a graph of !LIz against w2 should

be a straight line with gradient mlK3'

If it is found that phase shifts are present a more general equation for the

motion including damping and stiffness terms could be represented as below

(12)

An analysis similar to above gives

2 I L

mw - k = - K - cos <4> - 4> ) 3 z C z

(13)

- a plot of I . t 2 !:. (,h ,+,. ) agams w - cos 'l' - 'l' Z C z

should be a straight line with gradient mlK3

The same analysis could be applied to all other modes of oscillation to

yield similar results.

For the superconducting model, a lift constant, K3, was found for solenoid

currents of lOA, 15A and 20A. The magnetic moment of the model is directly

proportional to the solenoid current, Is implying

,

F

z = K3 IL Is

The lift constant found by experiment, K3, is given by

(14)

. K3 = K3 I

s

where K3

' will be a constant for this configuration at a central position.

A graph of K3 against solenoid current, Is, should be linear.

5
3 CALIBRATION PROCEDyRE

3.1 Superconducting Solenoid model

The superconducting solenoid model (see Figure 2) is much larger than

conventional models flown in SUMSBS and for this reason in previous

testing1 had been flown 'high', that is with the model suspended well above

the wind tunnel's centreline. This feature had produced some

unsatisfactory results. To suspend the model centrally in the tunnel,the

paths of the four light beams detecting y, z, m, n motions were diverted

using ordinary mirrors mounted to form small periscopes. Restraining

rings were mounted in the tunnel to protect the model and tunnel in the

event of loss of control. The rings also served as a convenient launch pad

during launching.

Several software changes were made to the existing program before the

model was flown. Gains were altered according to calculations, to allow

for the different magnetic moment of the modell, compared to those

normally suspended. Provision for real-time gain selection was included to

optimise the calculated gains. For convenience extra keyboard commands

such as "switch-off current output" and "reverse current polarity" were

included. It was decided to test some devices on the model for providing

roll torque4• Software changes were made so that, using a, keyboard

command, the current in electromagnets 1 - 8 could be incremented

symmetrically to produce pure rolling moment only in addition to their

usual functions. To accommodate these new keyboard commands the

character array size was increased.

Preliminary experiments were performed with the roll current

components commanded and a dummy model flying. These showed no

instability in control. Initial tests with the roll device mechanically

suspended, gave promising roll torque. These devices were tested whilst

mounted to the superconducting model in flight. The results of this work

are detailed in Reference 4.

The majority of testing on the superconducting model was at a solenoid

current of 15A, but some work was carried out at solenoid currents of lOA

and 20A.

3.1.1 Static calibration with the Superconducting Solenoid model

Static calibration was performed by applying known weights to

the model. This was achieved for drag force (Fx), in the negative x6
direction of Figure 1, using a pulley system attached to the rear of

the model. and for lift force and pitching moment (Fz,M) by hanging

these weights at fore and aft stations on the model. Examples of

static lift calibrations at solenoid currents of 15A and lOA are shown

in Figures 3,4. A drag calibration at a solenoid current of 15A is

shown in Figure 5. In the pitching moment calibrations a pure torque

could not easily be applied to the model so a combined force and

moment was applied. This calibration was further complicated by the

fact that the magnetic centre of force and centre of gravity did not

coincide and merely suspending the model produces a pitching

moment about the model's centre of gravity, that needs to be resisted

by electromagnet currents. Further calibration weights added

increase this "suspension moment". These effects were compensated

for and Figures 6,7 show the true pitch calibration at solenoid

currents of 15A and lOA.

Three lift calibration constants were found for solenoid currents

of lOA, 15A and 20A. The variation of lift constant with solenoid

current is shown in Figure 8.

3.1.2 Dynamic calibrations with the Superconducting Solenoid

model

Before these calibrations were performed it was necessary to

calibrate the optical system which is used to monitor the motion of

the model. For this purpose a cylinder, the same diameter as the

model, was moved incrementally with a vernier traverser through the

optical system light beams in the z-direction. All data, including the

signals from the optical system, were logged into the computer

through a 12-bit AID converter. A typical optical system calibration

with fitted curve is shown in Figure 9.

For dynamic oscillations, keyboard commands were used to select

the mode of oscillation, the motion amplitude and frequencies

ranging from 34 rad/s to 101 rad/s. The model was oscillated in lift

(z-direction) for solenoid currents of lOA, l5A and 20A. The data

which were recorded during oscillations included all electromagnet

currents and the model's position signals. Examples of these

oscillations with fitted sine-curves are shown in Figures 10 to 14.

Pitch oscillations at 15A and lOA are shown in Figures 15 and 16.

This work is analysed and compared with static results in Section 4.

7
3.2 Conventional Models

Similar procedures were used in the static and dynamic calibration of

permanent magnet models. Two types of model core were used, the usual

Alnico V core and a samarium cobalt core, which has a larger resistance to

demagnetization. Static lift calibrations were performed using brass rings

fitted around the model. During these calibrations some data were taken

with one of the four lift electromagnets switched off. Using these results

four separate calibrations constants for each lift coil could be extracted.

These are compared with the results obtained from the static lift

calibration plots of Figures 17, 18 in Section 4.

Dynamic lift calibrations were performed on both models over a

frequency range of 18.4 rad/s to 165.7 rad/s. Sample oscillations with

fitted curves are shown in Figures 19 to 22. Analysis of these traces is

included in the next section.

4 DISCUSSION

4.1 Superconducting Model

The superconducting model was successful as a proof of concept

prototype, proving reliable in all its original design functions. Although

the model surpassed all expectations for its performance, it was not ideal

for calibration work in the wind tunnel associated with SUMBS for the

following reasons:-

(i) the model was too large

(ii) the magnetic centre of force and centre of gravity did not coincide

(iii) the core has some freedom of movement within the outer can

4.2 Static Calibrations

Static data taken with the superconducting model seemed to be accurate

and showed the good linearity that had been experienced previously with

permanent magnet models.

The experiments with roll devices proved their feasibility for use with

models without wings4, an example of a calibration curve for the samarium

cobalt roll device is shown in Figure 23.

Previously, the extrapolation back to zero lift current1 of static lift

calibration data for the superconducting model gave an indicated model

mass approximately 700 grams (-40%) less than the true value. This was

thought to be due to the off-centre line suspension (high) producing

8
•

attraction to the upper iron pole-piece. With the model suspended

centrally, ( see Figures 3,4), the extrapolation implies a model mass to

within 196 of the half filled value (liquid helium boil off accounts for 1.496

of the total mass).

Good linearity is also shown for static lift calibrations performed on

Alnico and samarium cobalt cores, Figures 17,18. There is a spread of data

around zero applied mass, these points representing data taken with only

three lift coils used to support the model. Using this data four separate

lift constants were calculated for each model core as follows:-

Alnico core Samarium-Cobalt core

K33 = -0.0809 N/A K33 = -0.0577 N/A

K31 = 0.0707 N/A K31 = 0.0532 N/A

K37 = 0.0759 N/A K37 = 0.0566 N/A

K35 = -0.0669 N/A K35 = -0.0512 N/A

compared with values of K3 =0.0736 N/A for Alnico and K3 =0.055 N/A for

samarium cobalt. Each electromagnet is clearly not contributing the same

lift force per unit current. Although the summed data (yielding K3)are

accurate when all four electromagnets are running, the approach is not as

general as finding four separate constants. Separate calibration constants

for each coil should, it is felt, be used more often.

Analysis of pitching moment calibration data for the superconducting

model was complicated by the fact that pure torque was not applied to the

model. Once this effect was compensated for, the pitching moment

calibration data in Figures 6,7 showed good linearity.

Drag calibrations (e.g Figure 5) carried out on the superconducting

solenoid were satisfactory.

Theory suggests that the lift constant for the superconducting model

should be directly proportional to the solenoid current. The limited data

available plotted on Figure 8 show this to be true.

4.3 Analysis of Dynamic Oscillations

Dynamic lift calibrations performed on the superconducting model1 prior

to this experiment produced some unsatisfactory waveforms. The model's

position followed a sine-curve well but the current needed to produce this

motion was distorted. This was thought at the time to be due to the

attraction to the upper iron pole-pieces mentioned in Section 4.2.

9
The model was suspended centrally for all of the tests covered by this

report, and none of the above distortion is apparent. In this experiment

position data seemed to follow a sine-curve well (the model's motion is

closed-loop controlled) but the current traces contain some noise, less

apparent at the high frequencies, where the actual current signal is larger.

Dynamic oscillation data consisted of scans of data containing ten

electromagnet currents, vertical motion fore and aft, and a reading of

time for each scan.

During the course of analysis various improvements were made to the

technique. For the superconducting model only the middle 15% of the

vernier position calibration was needed because of restrictions on

amplitude imposed by the containment rings. A straight line fit across the

range of the position calibration was not appropriate since the data showed

a slight curve. Therefore a least-squares cubic B-spline fit was used, as

shown in Figure 9. Earlier analysis had relied on a control loop frequency

of 400 Hz giving data points equally spaced 2.5 ms apart and oscillation

frequencies as multiples of keyboard commands. With extra tasks included

in the software the loop rate fell to around 375 Hz. Each data set had an

independent reading of time from the internal clock of the computer and

this was used to time the data points.

It was decided to use a general curve-fitting technique, fitting a curve

of the form

y. =A + Bsin(Ct. + D) I I

where Yi is the motion or current reading and ti is the corresponding time.

This technique fits coefficients A, B, C and D where previously the

practice had been to fit only A and B following the assumption of a known

frequency of oscillation.

Dynamic calibration had been investigated earlier for permanent magnet

models by Goodyer2• These experiments used a small band of frequencies

and obtained results to within 2% of the corresponding static calibration.

The experiments detailed by this report cover a wider range of frequency.

A graph of h/z cos(phase) against frequency squared for the

superconducting model is shown in Figure 24. According to the theory

presented in Section 2 this graph should be a straight line. As can be seen

the data show a shallow curve of the form

Y = a + bx + cx

2

10

(15)
•

where x = w2, the frequency squared.

One attempt to explain the curve uses a representation of a tuned

model5• The construction of the superconducting model allows it to be

treated as an outer can separated from the inner solenoid by a

spring/damper system. Ignoring some stiffness and damping factors5 that

are in the circumstances negligible and simplifying, terms a,b, c in equation

(15) can be related to physical constants

a=h2

ml m2

c=- --

h l Ka

The value of b found from the curve fit implies a dynamic lift constant,

(at a solenoid current of 15A) of 1.27 N/A. The corresponding static value

is 1.30 N/A, a 2.3% discrepancy. For a solenoid current of 20A the lift

constant from dynamic calibration was within 2% of the static calibration

value.

For pitch oscillations of the superconducting model a plot of

lp/cp cos(phase) against frequency squared at a solenoid current of 15A is

shown in Figure 27. The moment of inertia of this model was found by

bifilar suspension and later using a precision torsional pendulum. From the

moment of inertia and the gradient of Figure 27 the pitch calibration

constant was found to be 4% lower than that derived from a static

calibration. The limited data available for Figure 27 show a linear

calibration plot in contrast to the graph shown in Figure 24.

It must be realised the pilot superconducting model is an unconventional

model to fly in the Southampton University MSBS. Apart from points (i),

(ii) and (iii) (discussed in Section 4.1) effects such as

a) liquid helium sloshing

b) induced currents in the model's core

c) aerodynamic damping

11
d) eddy currents in the framework

may be present. These effects have been assumed to be negligibly small or

have been taken into account in the explanation of the curve of Figure 24

for superconducting model data. However some of the effects mentioned

above could also apply to the dynamic calibration of models with

conventional cores. Work prior to this 2 has not investigated dynamic lift

calibration for conventional cores, over such a wide range of frequencies.

For these reasons it was decided to repeat the tests over a broadened

frequency band with Alnico and later samarium-cobalt cores.

The same analysis used previously was applied to the sine-fits for Alnico

and samarium-cobalt data, this is shown in Figures 25, 26. Again according

to simple theory these graphs should be straight lines. Figure 25 for Alnico

data follows a curve similar to that of the superconducting model, but

cannot be explained by the same argu ment of a "tuned model". The

samarium cobalt data of Figure 26 show an S-shaped curve. Neither of

the non-linear curves have yet been explained.

It may be argued that, since the model's position is controlled and

therefore closely follows a sine-curve, more accurate results will be

obtained where the current has a better fit as a result of a higher signal to

noise ratio. This applies at the larger current amplitudes, but, where tests

were repeated at the same frequency for two different amplitudes, one

large and one small, no difference in the results was noticed.

A straight line fit over the low frequency portion of each curve yields

some reasonable results. For Alnico a value of Ka = 0.0725 NtA compared

with 0.0736 NtA found statically. For samarium-cobalt Ka = 0.0549 NtA

compared with 0.0545 NtA in the static calibration.

As for the static calibration technique, the adding of the currents in the

four electromagnets to produce one lift constant is not entirely

satisfactory. Investigation showed that some coils were working harder

than others during the dynamic calibrations. There was also a large phase

difference between current and motion for samarium-cobalt data in the

frequency band 75 rad/s to 125 rad/s of Figure 26. It is possible that there

are other modes of oscillation being excited. For example an 'indicated'

pure lift oscillation may in fact contain some other component of motion

such as pitch or yaw due to faults such as non-linearity or misalignment in

the light beams.

12
..

It is planned to install new position sensors which should be accurate and

invariant and therefore eliminate some sources of error. Further study of

dynamic calibration techniques is planned with an attempt to analyse the

individual contributions of each electromagnet more fUlly. Fourier

analysis on the waveforms may resolve questions on secondary oscillation

modes and noise affecting traces. The new sensors will also enable high

angles of attack to be monitored. With the aid of new software, a move

will be made towards full calibration of the balance in all modes and over a

wide range of attitudes. It is hoped in due course to secure an explanation

the non-linearities highlighted above.

13
REFERENCES

1 Britcher, C.P.

2 Goodyer, M.J.

3 Wu, Y.Y.

4 Goodyer, M.J.

5 Goodyer, M.J.

Performance measurements of a Pilot Superconducting

Solenoid model core for a Wind Tunnel MSBS. NASACR-172243, Nov. 1983.

A preliminary Investigation of the Dynamic Force

calibration of a Magnetic Suspension and Balance

system. NASA-CR-172580, May 1985.

Design of a horizontal liquid helium cryostat for

refrigerating a flying superconducting magnet in a wind

tunnel. NASA-CR-165980, August 1982.

The generation of rolling moments with the

superconducting solenoid model. NASA CR-172520,

Jan. 1985.

The Magnetic Suspension of Wind Tunnel models for

Dynamic Testing. Univ. of Southampton, Dept. of

Aeronautics & Astronautics - Ph.D Thesis, April 1968.

(Available as acquisition number N78-78589 for

chapters 1-8 and N78-78219 for chapters 9-14.)

14

..
y

y'

y"

z'

z

FIGURE 1. SCHEMATIC OF THE 6-COMPONENT MAGNETIC SUSPENSION AND BALANCE

SYSTEM AT THE UNIVERSITY OF SOUTHAMPTON.

15
Fig.2 CROSS SECTION OF THE SOUTHAMPTON UNIVERSITY PILOT SUPERCONDUCTING MODEL

VACUUM VALVE

OUTER CAN

MULTILAYER

SUPERINSULATION

SUPERCONDUCTING

SWITCH

FORMER

ELECTRICAL LEADS

/

SEALED FILL It-JG

TUBE
" ..

<

UJ 30.0

B

tIL.

...J 25.0

20.0

15.0

10.0

5.0

Fig.3 STATIC LIFT CALIBRATION (SOLENOID CURRENT @15A)

GRADIENT a .771 A/N

INTERCEPT ON Y-AXIS =13.818 A

5 10 15 20 25

LIFT FORCE APPLIED, NEWTONS
Fig.4 STATIC LIFT CALIBRATION (SOLENOID CURRENT @10A)

t:

M

...J

35.0

30.0

25.0

20.0

15.0

10.0

5.0

GRADIENT =1.15 A/N

INTERCEPT ON Y-AXIS =20.55 A

1.0 2.0 3.0 4.0 5.0 6.0 7.0 B.O 9.0 10.0 11.0 12.0

LIFT FORCE APPLIED, NEWTONS
J

....

0

u

CD

i!

c

:z:

u

UJ

Z

....

....

z

UJ

""" 8!

(C ::t

U

5.00 l

4.00

3.00

2.00

1.00

•

Fig.5 STATIC DRAG CALIBRATION OF THE SUPERCONDUCTING MODEL AT ASOLENOID CURRENT OF 15A

GRADIENT = .537 A/N

INTERCEPT ON Y-AXIS = 2.79E-02 A

2.0 4.0 6.0 8.0

DRAS FORCE, N

10.0
N

Q

-1.0

10.0

<

g 8.0

Co) 6.0

:t:

Co)

I-

.....

a. 4.0

2.0

-4.0

-6.0

-8.0

-10.0

1.0

APPLIED MOMENT. Nm

GRADIENT =8.72 A/Nm

INTERCEPT ON V-AXIS =8.21E-05 A

Fig.6 PITCH MOMENT CALIBRATION (SOLENOID CURRENT @15A)

'0
..

I

-.4

J

-.2

5.0

<

g 4.0

u 3.0

:I:

U

I-

....

a. 2.0

LO

-2.0

-3.0

-4.0

-5.0

0.2 0.4

APPLIED MOMENT, Nm

GRADIENT a 13.117 A/N m

INTERCEPT ON Y-AXIS • 4.65E-04 A

Fig.7 PITCH MOMENT CALIBRATION (SOLENOID CURRENT @10A)
2.00

i.50

.....

<

... i.OO

N

N Co.)

t:

....

...J

0.50

Fig.B VARIATION OF LIFT CONSTANT WITH SUPER-CONDUCTING SOLENOID CURRENT

GRADIENT· 8.34 E-02

INTERCEPT ON V-AXIS· 3.94 E-02

5.0 10.0 15.0 20.0 25.0 30.0

SOLENOID CURRENT ~)
to

86.00

...... n

U) 84.00 :or:

....

m 82.00

ffi

....

ffi ~.OO

>

78.00

76.00 N

74.00

'n.OD

70.00

*

68.00

Fig.9 VERTICAL LIGHT SENSOR CALIBRATION

*

*

•

12.0 13.0 14.0 15.0

AID READING

16.0
Fig. 10

f6.S

"-

IZ

W 15.5

:J

u

14.5

DYNAMIC LIFT OSCILLATION - SUPERCONDUCTING MODEL (SOLENOID CURRENT=15A,FREGUENCY=34.5 RAD/S

+ :t

77.20 :E

'-

Z

o

H

IH

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9.0913 9.059 9.199 9.159 0.203 9.259 3.390 3.359 9.499 9.4S3 9.599

TIME / SEC

76.79

76.20

7S.7Q r--r--_r__-~-r__---y----r----r--_y__-,--r----,r----.---r-_.-.,.....-_r__-~-r_____r-___, I I I I I I I I I I

0.0130 13.3513 9.1913 9.1513 9.209 9.259 13.3130 9.350 9.490 0 •.450 0.5130

TIME / SEC
0.100 0.150 0.209 0.250 0.300 0.350 9.400 0.450 0.500

DYNAMIC LIFT OSCILLATION - SUPERCONDUCTING MODEL (SOLENOID CURRENT=15A,FREQUENCY=73.5 RAD/S )

0.050

9. 0 -.---.--r---,.--.-----=--.---.--r-----r---r---.----,---..----r----r--~-_r_-..._____,-__r-__,

0.000

Fig. 11

21.9

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u

13.0

TINE /SEC

77.20

76.70

76.20

75.79 r--,---.----,~--r--r---,---.----,r___--r---r---,----r------,r___--r-___._-_r_-__,__-..______r-___. I I I I I I I I I

0.009 0.050 0.100 0.159 0.200 9.250 0.300 0.350 0.409 0.4513 13.500

TINE /SEC

L

L

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o

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9.200 0.225 0.250

TIME /SEC

I

9.176

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0.150

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9.125

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9.199

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9.060

DYNAMIC LIFT OSCILLATION - SUPERCONDUCTING MODEL (SOLENOID CURRENT=15A.FREGUENCY=101.2 RAD/S )

I

9.925

r

9.000

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0.0130 9.025 0.950 9.075 9.103 0.125 0.IS13 0.175 9.2B0 0.225

77.399 TIME /SEC

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Fig. 12

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Fig. 13

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18.8 1-1-,...-----,lr----r-'I--,---rl--r--'I--r--rl--r--'Ir---r--TI--T--"'Tj---T--"?"l-------.1

8.a2a 8.a2S 8.as8 8.075 a.1C3 0.125 0.153 8.1iS a.2£a 8.225 8.2S9

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76.388

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TIME / SEC
Fig. 14

21.8

<

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t-

[5 1-4.8 0:

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7.8

DYNAMIC LIFT OSCILLATION - SUPERCONDUCTING MODEL (SOLENOID CURRENT=20A.FREGUENCY=101.1 RADIS )

8.8 1-1--r---'I~-r--rl--r--"T"I--r--r-I -~-'j--r--rj--r--"T"I--r--""j --r--r-j-~---,

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TIME / SEC

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TIME / SEC

• •
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DYNAMIC PITCH OSCILLATION - SUPERCONDUCTING MODEL (SOLENOID CURRENT=15~FREGUENCY=73.5 RAD/S )

-t8.8 r-.,._---,r-----r-..,.--,.-.---.,...-~--r-__r-__r_-T_____,-__r-.,._ __r____,..-~-_r_~-_, I I I I I I I I I

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Fig. 1S

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DYNAMIC PITCH OSCILLATION - SUPERCONDUCTING MODEL (SOLENOID CURRENT=10A.FREGUENCY=73.6 RAD/S )

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TIME / SEC

(I) -8.£aS

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'.
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so.oo

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3

w

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Fig.17 STATIC LIFT CALIBRATION OF ALNICO MODEL

•

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IHTEOCEPT 00 V-AXIS· 32.99 A

• •

0.5 1.0

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TINE / SEC

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iINE / SEC
Fig.20 DYNAMIC LIFT OSCILLATION - ALNICO MODEL (FREQUENCY=103.0 RAD/S J

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TJ:ME / SEC

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TIME / SEC

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9.489 9.<45e 9.SOO

TIME / SEC

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16.1i r---r---,~--r-.,....--r---,r-----r--r---r---,---r--r---r----.---r--r---r----,r---~--,

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TIME / SEC
DYNAMIC LIFT OSCILLATION - SAMARIUM-COBALT MODEL (FREQUENCY=108.0 RAO/S )

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TIME / SEC

• • ,'.
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10 ROLL !\~"'PS rr~ EACH

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~-:l I

'-""'Ll''D-....

1

10 0 9 m. ern. 2 0 0

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'''~

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•

Fig. 23 CALIBRATION OF THE SAMARIUM-COBALT ROLLING MOMENT ELEMENT

MOUNTED ON THE SUPERCONOUCTING MODEL

37
15000

E........

.::.

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en

:2

aen

0

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:::::I

tt-t

-J

c.;

00 <I

N

........

ffi 5000

u

t:

t-t

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Fig.24 ANALYSIS OF DYNAMIC LIFT CALIBRATION DATA FOR THE SUPERCONDUCTING MODEL

2000 4000 6000 BODO 10000 12000

FREGUENCY SGUARED (RAUlS) **2
80000

Fig. 25 ANALYSIS OF DYNAMIC LIFT CALIBRATION DATA FOR AN ALNICO MODEL

s

......

UJ

en

0

u

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UJ

t-1

<

eo; ,

CQ N

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ffi

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t:

t-1

-I

60000

40000

20000

line calculated from

static calibration

*

*

5000 10000 15000 20000 25000 30000

FREQUENCY SQUARED (RAD/S) **2
Fig.26 ANALYSIS OF DYNAMIC LIFT CALIBRATION FOR ASAMARIUM-COBALT MODEL

120000

.:s

UJ 100000 en

+

+ c..,) BOOOO + *

UJ

c + line calculated from F=.... static calibration

Ill- 60000

0 I +

N

........

ffi 40000

t:

....

..J

20000

5000 10000 15000 20000 25000 30000

•

FREQUENCY SQUARED (RAD/S) **2
II

Fig.27 ANALYSIS OF DYNAMIC PITCH CALIBRATION FOR THE SUPERCONDUCTING MODEL

1500

.......

oS

UJ

U)

iE

U)

0 1000 u

*

UJ

c:6

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ta.

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ffi 500.0

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u

is

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INTERCEPT ON Y-AXIS· 11.038 AI !WJ

1000 2000 3000 4000 5000 6000

FREQUENCY SQUARED (RAOIS) **2
1. Report No.

NASA CR-178056

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

4. Title and Subtitle

Further Investigation Into Calibration Techniques for

a Magnetic Suspension and Balance System

7. Author(s)

J. Eskins

9. Performing Organization Name and Address

University of Southampton

Department of Aeronautics and Astronautics

Southampton S09 5NH

ENGLAND

12. Sponsoring Agency Name and Address

National Aeronautics and Space Administration

Washington, DC 20546

15. Supplementary Notes

Langley Technical Monitor: Richmond P. Boyden

16. Abstract

5. Repon Date

February 1986

6. Perlorming Organization COde

8. Performing Organization Report No.

10. Work Unit No.

11. Contract or Grant No.

NSG-7523

13. Type of Repon and Period COvered

Contractor Rpt. 1/85-9/85

14. Sponsoring Agency Code

505-61-01-02

..

of force on electromagnet

to perform but are proving

There are still some effects

were obtained agreeing to

This report details calibrations performed on three different magnetic cores

for wind tunnel models suspended in the Southampton University Magnetic Suspension

and Balance System (SUMSBS).

The first core investigated was the Southampton University pilot Superconducting

Solenoid model, first flown in July 1983. Static calibrations of lift force, drag

force and pitching moment, together with lift force and pitching moment calibrations

determined by the dynamic method are detailed in this report. Other types of core

investigated in a similar manner were conventional permanent magnets, Alnico and

samarium-cobalt.

All static calibrations gave a linear dependence

current as expected. Dynamic calibrations are faster

to be not as easily analysed as static calibrations.

to be explained but dynamic lift calibration results

within 2 percent of the static calibration value.

17. Key Words (Suggested by Author(s))

Magnetic suspension

Dynamic calibration

Force calibration

18. Distribution Statement

Unclassified - Unlimited

Star Category - 09 •

19. Security Classif. (of this report)

Unclassified

20. Security Classif. (of this page)

Unclassified

21. No. of Pages

43

22, Price

A03

For sale by the National Technicallnformallon Service. Sprtngfleld VlIglnla 22161
,
11