3D Balance Calibration Flashcards
Six-Component Balance
- lift
- drag
- side force
- rolling moment
- yawing moment
- pitching moment
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 _________.
balancing, tunnels
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.
external force balance
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.
internal force balance
placed outside the model, inside or outside the wind tunnel chamber test section
external force balance
they always introduce some interference in the wind flow
external force balance
they are placed inside the model
internal force balance
no interferences are introduced in the wind flow by the balance components
internal force balance
a mechanical support for the model is always needed to maintain it in the test chamber and change the model orientation if desired
internal force balance
model mounts for external balance
two strut, three strut, single strut, sting mount
model mounts for internal balance
single strut, sting mount
Any wind tunnel balance is of necessity a compromise between the ___________________ of all components and the _________________.
required maximum load capability, accuracy required for minimum loads
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.
internal balance
A danger with an internal balance is that the loads of the model can ____________ the ability of the balance.
unintentionally exceed
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 _________.
faulty balance
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.
external balance
The estimated loads a balance has to bear are primarily a feature of the _________ of the tunnel test section.
size and speed
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.
doubled
In general usage, four types of external balances were used. These balances are named for their main load-carrying members which are:
- wire
- frame
- yokes
- pyramid
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.
Wire Balances
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 ___________.
reduced to zero
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 ______.
losing
Why use wire instead of string?
because of deflection
Wire balances turned out to be much _______________ than the alternatives and since the are very early days of aeronautics have not been used extensively.
less stable and flexible
In using wire balances, the space occupied is _________.
very large
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.
platform, yoke, and pyramid balances
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.
system of linkages
For linkage type, the strut being rigid, minimizes ________.
deflection
For linkage type, the strut being ______, minimizes deflection.
rigid
By choosing proper linkages, interaction loads can be reduced to a _________.
small value
___________ can be encountered in high speed flows.
deflections
These balances are not suitable for large test section tunnels.
platform, yoke, and pyramid balances
Interference drag is more when ____________ is exhibited.
three point strut support
The linkage system by which the force and moment components are separated have gradually worked into three different fundamental types which are:
platform, yoke, pyramidal
One of the most troublesome problems of wind tunnel balances is this; the lack of rigidity.
deflections
One of the most troublesome problems of wind tunnel balances is the __________.
lack of rigidity; 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 drag or side force.
deflections
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 ___________.
drag or side force
Deflections must be kept down to where they are _______ or they must be evaluated and accounted for in the _________.
negligible, data reduction process
What is the greatest source of deflection?
mounting mechanism
The mounting mechanism must be long in reaching out of the test section and thin in order to prevent ________________.
overinterference
The only way that the wind tunnel engineer can solve the issue of overinterference in deflections is to use ___________________ for the strut.
high-modulus elasticity materials
By having a _________, deflections in the balance frame can be reduced.
deep and stable structure
By having a deep and stable structure, deflections in the ______ can be reduced.
balance frame
A large number of ______ are the main components of an external balance and are built to have minimal deflection under high load.
levers
The large number of levers as main components of an external balance increases their ______ and ________.
weight, height
Usually, the joints between the levers are ______ with very limited angular motion.
pivots
Usually, the joints between the levers are pivots with very limited __________.
angular motion
Early pivots were _______ in wind tunnel balances.
knife edges
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.
compressive direction
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 __________.
flexure pivot
The benefits of flexures include:
- 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
One of the benefits of flexure is that they may be designed to withstand loads between the coupled members in either direction with ________________.
no loss of motion
One of the benefits of flexures is that they are practically frictionless and thus reduce the symptoms of ___________.
hysteresis
One of the benefits of flexures is that they are practically _________ and thus reduce the symptoms of hysteresis.
frictionless
One of the benefits of flexures is that they are practically _________; therefore they remain constant for an infinite period of time.
wearproof
________ takes at least three months for a professional crew to calibrate the new balance.
calibration
Calibration takes at least _________ for a professional crew to calibrate a new balance.
three months
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 “_________.”
calibration
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.
calibration
Calibration 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
- applying fluctuating load
These balances are normally supplied to the customer already calibrated and with the acquisition system.
internal balance
In an internal balance, the number of measured components can also vary between __ and ___.
1, 6
What does DAQ stand for?
data acquisition system
It is compounded by several items that allow the conversion of physical forces into digital values that can be managed by a computer.
data acquisition system (DAQ)
Several components comprise the DAQ and the selection of their properties will have an important impact on the _________.
system behavior
Give at least five DAQ
- 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
types of transducer for internal balances
stain gauge, piezoelectric
Of the two transducer for internal balances, _______ far outnumber _________ devices.
strain gages, piezoelectric
Although piezoelectric devices are extremely stiff and have outstanding frequency response, they _______________.
do not measure steady loads well
In practice, the terms internal balance and internal strain gage balance are effectively ____________.
synonymous
Give at least three purposes of calibration method
- 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
The calibrations require a rather elaborate ________.
calibration rig
The system provides capability for the balance to be rotated through ________ and pitched in the ________ plane.
360 deg, vertical
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.
pitching motion
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.
model attachment portion
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.
horizontal, balance, sting deflection
_____________ are used to apply the loads.
calibration bars
Calibration bars are indexed so that various values of moments can be applied while holding the ______________.
normal or side force constant
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
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.
pins, buttons, splines
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.
zero load, outputs of the balance, deflection
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.
large number of load combinations, weeks
