AEROLAB MODULE NO. 3

Question 1

In aeronautical applications, the
measurement of ____________ in a wind
tunnel, forces and momentums, is a very
difficult task due to the required accuracy.
The wind tunnel balances, comprised by
several hardware and software components,
provides directly the pursued measurements,
with high accuracy and reliability

Answer 1

aerodynamic loads

Question 2

In aeronautical applications, the
measurement of aerodynamic loads in a wind
tunnel, forces and momentums, is a very
difficult task due to the required accuracy.
The _______________, comprised by
several hardware and software components,
provides directly the pursued measurements,
with high accuracy and reliability

Answer 2

wind tunnel balances

Question 3

In aeronautical applications, the
measurement of aerodynamic loads in a wind
tunnel, forces and momentums, is a very
difficult task due to the required accuracy.
The wind tunnel balances, comprised by
_________________________,
provides directly the pursued measurements,
with high accuracy and reliability

Answer 3

several hardware and software components

Question 4

What comprises of a Six-Component Balance?

Answer 4

Drag, Lift, Side Force, (Pitching, Yawing, Rolling) Moment

Question 5

What comprises a three component balance?

Answer 5

Lift, Drag, Pitching

Question 6

What comprises a two component balance?

Answer 6

Lift and Drag only

Question 7

A wind tunnel balance is an incredibly
complicated device and its design and
construction are much better left to _______________________.

Answer 7

left to engineers of balancing than to engineers
of tunnels.

Question 8

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 8

External Balance

Question 9

They are placed inside the
model; thus, no or little 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 9

Internal Balance

Question 10

Types of Model Mounts

Answer 10

External: Two strut, Three strut
Internal: Single Strut, Sting

Question 11

Any wind tunnel balance is of necessity a
compromise between the ____________________ and the
____________________.

Answer 11

required maximum load capability of all components;
accuracy required for minimum loads

Question 12

For an internal balance, the solution to this
problem is much easier, as many balances can be
planned and installed for various load ranges, and
one chosen for the desired loads.

A danger with an inner balance is that the loads of the model can ___________________.

This can lead to a ____________.

Answer 12

unintentionally exceed the ability of the balance;
faulty balance

Question 13

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

Answer 13

thorough analysis

Question 14

The estimated loads a balance has to bear are
primarily a feature of the ________________________.

Answer 14

size and speed of the tunnel test section

Question 15

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

Answer 15

fourfold

Question 16

In general usage _____ types of external
balances were used. These balances are
named for their main load-carrying members _________________.

Answer 16

four ; wire, frame, yokes and pyramid

Question 17

Four External Balances

Answer 17

Wire type, Platform, Yoke, Pyramid Balance

Question 18

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 18

Wire Balance

Question 19

Wire Balances

There’s a strong ______ on the wires that was
hard to accurately determine. The wires appeared to
split, which would result in the ______.

Answer 19

tare drag ; model losing

Question 20

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

Answer 20

less stable and flexible

Question 21

Wire Balances

The space occupied is very __________

Answer 21

large

Question 22

Platform, Yoke, and Pyramid Balances

These balances provide
mechanisms for changing the
_______________ and
transmit the _________ down
into a system of linkages
that separate them into force
and moment components.

Answer 22

angle of attack and yaw ; model loads

Question 23

Platform, Yoke, and Pyramid Balances

For Linkage type, the strut being
rigid, minimizes ___________.

Answer 23

deflection

Question 24

Platform, Yoke, and Pyramid Balances

By choosing __________,
interaction loads can be reduced to
a small value.

Answer 24

proper linkages

Question 25

Platform, Yoke, and Pyramid Balances __________ can be encounter in high speed flows.

Answer 25

Deflections

Question 26

Platform, Yoke, and Pyramid Balances Is it suitable for large test section tunnels? Yes, No or Maybe?

Answer 26

It is not

Question 27

Platform, Yoke, and Pyramid Balances _________ drag is more when three point strut support is exhibited.

Answer 27

Interference

Question 28

External Balances The linkage system by which the force and moment components are separated have gradually worked into three different fundamental types what are those?

Answer 28

Platform, Yoke, Pyramidal

Question 29

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

Answer 29

lack of rigidity

Question 30

____________ 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 30

Deflections

Question 31

Deflections must be _________ to where they are negligible or they must be evaluated and accounted for in the data reduction process.

Answer 31

kept down

Question 32

What is the greatest source of deflection?

Answer 32

The mounting mechanism

Question 33

Deflections must be long in reaching out of the test section and thin to prevent _____________.

Answer 33

overinterference

Question 34

The only way that the wind tunnel engineer can solve deflection is to use ___________ materials for the strut. By having a deep and stable structure, deflections in the balance frame can be reduced

Answer 34

high-modulus elasticity

Question 35

Balance linkages and Pivots A large number of levers are the main components of an external balance and are built to have minimal ________ under high load. That increases their ________ and also increases their ________.

Answer 35

deflection ; weight ; height

Question 36

Balance linkages and Pivots Usually, the joints between the levers are ________ with very limited _______

Answer 36

Pivots ; angular motion

Question 37

Early pivots were _______ in wind tunnel balances. Because the edges of this can be damaged by shock loads and can bear loads only in a compressive direction, they have been replaced by flexure pivot.

Answer 37

knife edges

Question 38

The benefits of ________ include: 1. They may be designed to withstand loads between the coupled members in either direction with no loss of motion. 2. They are practically frictionless and thus reduce the symptoms of hysteresis. 3. They can survive treatment which is relatively harsh. 4. They are practically wearproof; therefore they remain constant for an infinite period of time.

Answer 38

flexures

Question 39

For external balance calibration, calibration takes at least ________ for a professional crew to calibrate the new balance.

Answer 39

3 months

Question 40

__________ 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 40

Calibration

Question 41

Transducer of Internal Balance

Answer 41

Strain Gauges, Piezoelectric devices

Question 42

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

Answer 42

Internal Balance

Question 43

The _____________ is compounded by several items that allow the conversion of physical forces into digital values that can be managed by a computer. Several components comprise this and the selection of their properties will have an important impact on the system behavior.

Answer 43

data acquisition system (DAQ)

Question 44

Of these two, strain gages far ________ piezoelectric devices. The reason for this is that although piezoelectric devices are extremely stiff and have outstanding frequency response, they do not measure steady loads well.

Answer 44

outnumber

Question 45

disadvantage of piezoelectric devices

Answer 45

extremely stiff, have high outstanding frequency response and does not measure steady loads well.

Question 46

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

Answer 46

Synonimous

Question 47

The calibration method serves various purposes including:

Answer 47

1. Loading the balance to show 2. Determining the coefficients of equilibrium 3. Defining deflections as load feature 4. To check the repeatability over short periods of time 5. Tests reliability for longer periods of time 6. Defines sensitivity or minimum response load 7. To detect hysteresis

Question 48

The calibrations require a rather elaborate __________. The system provides capability for the balance to be rotated through 360deg and pitched in the vertical plane.

Answer 48

calibration rig

Question 49

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 49

pitching motion

Question 50

This means the model attachment portion is kept horizontal for all loading conditions since this system uses weights and gravity to apply the loads. It also allows the _______________ to be measured.

Answer 50

balance and sting deflection

Question 51

__________ are used to apply the loads. These are indexed so that various values of moments can be applied while holding the normal or side force constant.

Answer 51

Calibration bars

Question 52

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 ____________ rather than by some adjustment device, so that the precision of reproducibility is close to the limits of the machine tool.

Answer 52

pins, buttons, or splines

Question 53

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

Answer 53

zero load

Question 54

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

Answer 54

balance coefficients