3D Balance Calibration

Question 1

Six-Component Balance

Answer 1

• lift
• drag
• side force
• rolling moment
• yawing moment
• pitching moment

Question 2

A wind tunnel balance is an incredibly complicated device and its design and construction are much better left to engineers of _________ than to engineers of _________.

Answer 2

balancing, tunnels

Question 3

In an ___________, they are placed outside the model, inside or outside the wind tunnel chamber test section, but they always introduce some interference in the wind flow.

Answer 3

external force balance

Question 4

In an ________________, they are placed inside the model; thus, no interferences are introduced in the wind flow by the balance components, but a mechanical support for the model is always needed to maintain it in the test chamber and change the model orientation if desired.

Answer 4

internal force balance

Question 5

placed outside the model, inside or outside the wind tunnel chamber test section

Answer 5

external force balance

Question 6

they always introduce some interference in the wind flow

Answer 6

external force balance

Question 7

they are placed inside the model

Answer 7

internal force balance

Question 8

no interferences are introduced in the wind flow by the balance components

Answer 8

internal force balance

Question 9

a mechanical support for the model is always needed to maintain it in the test chamber and change the model orientation if desired

Answer 9

internal force balance

Question 10

model mounts for external balance

Answer 10

two strut, three strut, single strut, sting mount

Question 11

model mounts for internal balance

Answer 11

single strut, sting mount

Question 12

Any wind tunnel balance is of necessity a compromise between the ___________________ of all components and the _________________.

Answer 12

required maximum load capability, accuracy required for minimum loads

Question 13

For an _________, the solution to the problem of compromise between required maximum load capability of all components and the accuracy required for minimum loads is much easier, as many balances can be planned and installed for various load ranges, and one chosen for the desired loads.

Answer 13

internal balance

Question 14

A danger with an internal balance is that the loads of the model can ____________ the ability of the balance.

Answer 14

unintentionally exceed

Question 15

A danger with an internal balance is that the loads of the model can unintentionally exceed the ability of the balance which can lead to a _________.

Answer 15

faulty balance

Question 16

For an ______________, it is important to use a thorough analysis to try to account for and form of model and test for which the balance will be used over a number of years.

Answer 16

external balance

Question 17

The estimated loads a balance has to bear are primarily a feature of the _________ of the tunnel test section.

Answer 17

size and speed

Question 18

If a tunnel size is _____, the size of the platform and the loads are increased fourfold for a set vehicle-to-tunnel-size ratio, platform attitude and tunnel speed.

Answer 18

doubled

Question 19

In general usage, four types of external balances were used. These balances are named for their main load-carrying members which are:

Answer 19

• wire
• frame
• yokes
• pyramid

Question 20

The model was usually mounted inverted so that the aerodynamic lift applied to the weight to prevent the wires from being removed, as the resulting stress can never be reduced to zero.

Answer 20

Wire Balances

Question 21

In wire balances, the model was usually mounted inverted so that the aerodynamic lift applied to the weight to prevent the wires from being removed, as the resulting stress can never be ___________.

Answer 21

reduced to zero

Question 22

In using wire balances, there’s a strong tare drag on the wires that was hard to accurately determine. The wires appeared to spilt, which would result in the model ______.

Answer 22

losing

Question 23

Why use wire instead of string?

Answer 23

because of deflection

Question 24

Wire balances turned out to be much _______________ than the alternatives and since the are very early days of aeronautics have not been used extensively.

Answer 24

less stable and flexible

Question 25

In using wire balances, the space occupied is _________.

Answer 25

very large

Question 26

These balances provide mechanisms for changing the angle of attack and yaw and transmit the model loads down into a system of linkages that separate them into force and moment components.

Answer 26

platform, yoke, and pyramid balances

Question 27

Platform, yoke, and pyramid balances provide mechanisms for changing the angle of attack and yaw and transmit the model loads down into a ______________ that separate them into force and moment components.

Answer 27

system of linkages

Question 28

For linkage type, the strut being rigid, minimizes ________.

Answer 28

deflection

Question 29

For linkage type, the strut being ______, minimizes deflection.

Answer 29

rigid

Question 30

By choosing proper linkages, interaction loads can be reduced to a _________.

Answer 30

small value

Question 31

___________ can be encountered in high speed flows.

Answer 31

deflections

Question 32

These balances are not suitable for large test section tunnels.

Answer 32

platform, yoke, and pyramid balances

Question 33

Interference drag is more when ____________ is exhibited.

Answer 33

three point strut support

Question 34

The linkage system by which the force and moment components are separated have gradually worked into three different fundamental types which are:

Answer 34

platform, yoke, pyramidal

Question 35

One of the most troublesome problems of wind tunnel balances is this; the lack of rigidity.

Answer 35

deflections

Question 36

One of the most troublesome problems of wind tunnel balances is the __________.

Answer 36

lack of rigidity; deflections

Question 37

__________ in the balance may move the model from the resolving center and invalidate the moment data or nullify the balance alignment so that part of the lift appears as drag or side force.

Answer 37

deflections

Question 38

Deflections in the balance may move the model from the resolving center and invalidate the moment data or nullify the balance alignment so that part of the lift appears as ___________.

Answer 38

drag or side force

Question 39

Deflections must be kept down to where they are _______ or they must be evaluated and accounted for in the _________.

Answer 39

negligible, data reduction process

Question 40

What is the greatest source of deflection?

Answer 40

mounting mechanism

Question 41

The mounting mechanism must be long in reaching out of the test section and thin in order to prevent ________________.

Answer 41

overinterference

Question 42

The only way that the wind tunnel engineer can solve the issue of overinterference in deflections is to use ___________________ for the strut.

Answer 42

high-modulus elasticity materials

Question 43

By having a _________, deflections in the balance frame can be reduced.

Answer 43

deep and stable structure

Question 44

By having a deep and stable structure, deflections in the ______ can be reduced.

Answer 44

balance frame

Question 45

A large number of ______ are the main components of an external balance and are built to have minimal deflection under high load.

Answer 45

levers

Question 46

The large number of levers as main components of an external balance increases their ______ and ________.

Answer 46

weight, height

Question 47

Usually, the joints between the levers are ______ with very limited angular motion.

Answer 47

pivots

Question 48

Usually, the joints between the levers are pivots with very limited __________.

Answer 48

angular motion

Question 49

Early pivots were _______ in wind tunnel balances.

Answer 49

knife edges

Question 50

Because the edges of the knife can be damaged by shock loads and can bear loads only in a _______, they have been replaced by flexure point.

Answer 50

compressive direction

Question 51

Because the edges of the knife can be damaged by shock loads and can bear loads only in a compressive direction, they have been replaced by __________.

Answer 51

flexure pivot

Question 52

The benefits of flexures include:

Answer 52

- may be designed to withstand loads between the coupled members in either direction with no loss of motion - practically frictionless - can survive treatment - practically wearproof

Question 53

One of the benefits of flexure is that they may be designed to withstand loads between the coupled members in either direction with ________________.

Answer 53

no loss of motion

Question 54

One of the benefits of flexures is that they are practically frictionless and thus reduce the symptoms of ___________.

Answer 54

hysteresis

Question 55

One of the benefits of flexures is that they are practically _________ and thus reduce the symptoms of hysteresis.

Answer 55

frictionless

Question 56

One of the benefits of flexures is that they are practically _________; therefore they remain constant for an infinite period of time.

Answer 56

wearproof

Question 57

________ takes at least three months for a professional crew to calibrate the new balance.

Answer 57

calibration

Question 58

Calibration takes at least _________ for a professional crew to calibrate a new balance.

Answer 58

three months

Question 59

The at least three month time frame for calibration presupposes that sufficient shop facilities are required for all kinds of improvements, and acknowledges that several modifications would almost certainly require the first "_________."

Answer 59

calibration

Question 60

It involves loading the balance components to see if they read what they should, testing the system deflection, calculating the natural frequency of the balance in order to prevent resonance, and applying fluctuating load.

Answer 60

calibration

Question 61

Calibration involves:

Answer 61

- loading the balance components to see if they read what they should - testing the system deflection - calculating the natural frequency of the balance in order to prevent resonance - applying fluctuating load

Question 62

These balances are normally supplied to the customer already calibrated and with the acquisition system.

Answer 62

internal balance

Question 63

In an internal balance, the number of measured components can also vary between __ and ___.

Answer 63

1, 6

Question 64

What does DAQ stand for?

Answer 64

data acquisition system

Question 65

It is compounded by several items that allow the conversion of physical forces into digital values that can be managed by a computer.

Answer 65

data acquisition system (DAQ)

Question 66

Several components comprise the DAQ and the selection of their properties will have an important impact on the _________.

Answer 66

system behavior

Question 67

Give at least five DAQ

Answer 67

- mechanics - sensors or transducers - weight balanced sensors - pneumatic and hydraulic sensors - electromagnetic sensors - spring sensors - strain-gauge sensors - electronic amplifiers - wires - analog to digital converter (ADC) - software

Question 68

types of transducer for internal balances

Answer 68

stain gauge, piezoelectric

Question 69

Of the two transducer for internal balances, _______ far outnumber _________ devices.

Answer 69

strain gages, piezoelectric

Question 70

Although piezoelectric devices are extremely stiff and have outstanding frequency response, they _______________.

Answer 70

do not measure steady loads well

Question 71

In practice, the terms internal balance and internal strain gage balance are effectively ____________.

Answer 71

synonymous

Question 72

Give at least three purposes of calibration method

Answer 72

- loading the balance to show - determining the coefficients of equilibrium - defining deflections as load feature - to check the repeatability over short periods of time - tests reliability for longer periods of time - defines sensitivity or minimum response load - detect hysteresis

Question 73

The calibrations require a rather elaborate ________.

Answer 73

calibration rig

Question 74

The system provides capability for the balance to be rotated through ________ and pitched in the ________ plane.

Answer 74

360 deg, vertical

Question 75

The ____________ is used to keep the applied load system aligned to the model attachment portion of the balance, just as the model will be when the system is loaded in the tunnel.

Answer 75

pitching motion

Question 76

The pitching motion is used to keep the applied load system aligned to the __________ of the balance, just as the model will be when the system is loaded in the tunnel.

Answer 76

model attachment portion

Question 77

The model attachment portion is kept ________ for all loading conditions since this system uses weights and gravity to apply the loads. It also allows the _______ and ______ to be measured.

Answer 77

horizontal, balance, sting deflection

Question 78

_____________ are used to apply the loads.

Answer 78

calibration bars

Question 79

Calibration bars are indexed so that various values of moments can be applied while holding the ______________.

Answer 79

normal or side force constant

Question 80

When the model is attached to the balance, the orientation of the loads applied to the balance has to be positively and precisely associated with the __________.

Answer 80

model orientation

Question 81

When the model is attached to the balance, the orientation of the loads applied to the balance has to be positively and precisely associated with the model orientation. This alignment is typically done by ____, ____, or _____ rather than by some adjustment device, so that the precision of reproducibility is close to the limits of the machine tool.

Answer 81

pins, buttons, splines

Question 82

The calibration bar is leveled to _____. As loads are applied to each loading station, the bar is again leveled and the sting and calibration bar deflection is reported along with the ________. The measures are of _______. Used during test to correct the indicated angles of attack.

Answer 82

zero load, outputs of the balance, deflection

Question 83

In order to get the balance coefficients and estimate their reliability, a ____________ are needed. The time required to do a full calibration of the six-component balance with manually applied loads runs into ______, involving many people.

Answer 83

large number of load combinations, weeks