Aerospace Lab Midterm 1 (Dr. Paul)

Define Measurement Uncertainty

The estimate of the interval expected to contain the true value

How is Measurement Uncertainty Different than Error

Error difference between measurement and the true value. Uncertainty estimate of max possible magnitude of the error

Why must uncertainty be considered before experiment design?

Uncertainty Analysis determines if the experiment can achieve the required accuracy

What is the FIRST thing Uncertainty Analysis informs

Instrumentation design and resolution

What is the SECOND thing Uncertainty Analysis informs

Define dominate error sources

What is the THIRD thing Uncertainty Analysis informs

Avoid the "hopeless" experiment

How many sources of uncertainty are there

3

Define random uncertainty

Random fluctuations in measurements

What is random uncertainty described by?

Statistical distribution width (Standard Deviation)

Define systematic uncertainty

Bias that shift measurement from a true value

How can you remove systematic uncertainty

Calibration

Define resolution uncertainty

Caused by precision of the instrumentation you are using

What is an example of resolution uncertainty

The smallest readable increment on a scale

Can I just use standard deviation of a measured value for my uncertainty?

No

What is the FIRST reason why you cannot use standard deviation of a measured value for uncertainty?

Standard deviation only accounts for random uncertainty

What is the SECOND reason why you cannot use standard deviation of a measured value for uncertainty?

You may also have systematic and resolution uncertainty

What is the THIRD reason why you cannot use standard deviation of a measured value for uncertainty?

All uncertainties must be combined in quadrature for total standard uncertainty

What does k stand for

Coverage Factor

What is the value of k for 95% confidence with normally distributed data and many sample points

2

What is the combined standard uncertainty also called

Combination of all uncertainties in quadrature

What does U stand for

Expanded Uncertainty

What is the equation for U

U= Coverage Factor * Standard Uncertainty

What does TSM stand for

Taylor Series Method

What is the μR equation name

Taylor Series General Propagation Equation

What does R stand for

Relative Uncertainty

What is the Equation for CD

CD= 2FD/rhov^2s

What is another word for sensitivity coefficients

partial derivatives

What does UMR stand for

Uncertainty Magnification Factor

Define static longitudinal stability

initial tendency to return towards V0 after a perturbation

According to Advisory Circular 23-8C, what is the expected qualitative relationship between stick force and airspeed for a statically stable aircraft?

Negative slope of Stick force vs airspeed

What is the stick force gradient also known as?

The slope of Stick force vs airspeed

What does the sign of the gradient indicate about stability if it is positive?

(+)= statically unstable

If the stick force gradient were near zero, what would that indicate about aircraft handling qualities?

Neutrally statically stable

Define dynamic stability

Characterization of time response of vehicle dynamics once perturbed from trim

What are the two dominant longitudinal dynamic modes in aircraft?

phugoid and short period

Which of these modes typically has: Higher frequency and Strong aerodynamic damping

Short period

What does the decreasing amplitude indicate about the dynamic stability of the aircraft?

(-)= dynamically stable

Explain how the rate of amplitude decay relates to aircraft stability

Faster Decay ->more stable -> poles further into left half plane (LHP)

For short period what is the normal damping range

0.5 to 0.7

Why are small perturbations preferred for stability testing?

Remains near equilibrium point (trim) - Eig(A)

What is the FIRST nonlinear effect that might appear with large disturbances?

Non-linear Aerodynamic Effects

What is the SECOND nonlinear effect that might appear with large disturbances?

Projections of gravity force that fall outside of linearization assumptions