SS&C-3-5

Question 1

Wing downwash defines the strength of what two other properties?

Answer 1

The strength of the bound vortex

The strength of the trailing vortices at the tips

Question 2

All bodies of revolution are _______.

Answer 2

De-stabilizing.

Question 3

Ahead of the wing, there is an _____ that adds to the flow making (d beta)/(d alpha) _____ unity.

Answer 3

induced upwash

greater than

Question 4

Aft of the wing, there is a _____ that subtracts flow from the freestream making (d beta)/(d alpha) _____ unity.

Answer 4

Downwash

Less than

Question 5

In the region between the wing LE and TE, at the intersection (d beta)/(d alpha) = _____.

Answer 5

Zero

Question 6

All bodies of revolution are ______.

Answer 6

De-stabilizing.

Question 7

True or False

Munk’s method makes use of the fineness ratio.

Answer 7

True

Question 8

What is the angle beta in Multhopp’s method?

Answer 8

The sum of the freestream and induced angles of attack.

Question 9

The movement of the c.g. has a large effect on the _____ contribution to static stability.

Answer 9

Wing’s

Question 10

dCM_cg/dCL is equal to the difference in what two terms?

Answer 10

The x_cg minus x_ac

Question 11

What is the neutral point and how is it defined?

Answer 11

The neutral point is where the c.g. would have to be placed in order for the aircraft to exhibit neutral static stability.

It is found at the point where dCM/dCL = 0.

Question 12

Describe the neutral point in terms of aircraft instability.

Answer 12

The neutral point is the aft limit of where the c.g. can be placed before the aircraft exhibits unstable static stability.

Question 13

True or False

The stick-fixed neutral point is only a function of the aircraft geometry.

Answer 13

True

Question 14

What is the primary factor in determining an aircraft’s longitudinal static stability?

Answer 14

The location of the c.g. along the aircraft’s longitudinal axis measured in percent of the mean geometric chord.

Question 15

A thrust line of action above the c.g. produces a ______ moment.

Answer 15

Nose down pitching

Question 16

A high thrust line is ____

A low thrust line is ____.

Answer 16

Stabilizing

De-stabilizing

Question 17

A propeller ahead of the c.g. produces a ____ moment.

Answer 17

nose-up pitching

Question 18

A propeller behind the c.g. produces a _____ moment.

Answer 18

Nose-down pitching

Question 19

A prop ahead of the c.g. is ______.

Answer 19

De-stabilizing

Question 20

A prop behind the c.g. is ______.

Answer 20

Stabilizing

Question 21

The propeller slipstream affects what four aspects of the aircraft’s longitudinal static stability?

Answer 21

The slipstream affects the:

1. Wing-fuselage moments
2. Wing lift coefficient
3. Downwash at the HT
4. Dynamic pressure on the HT

Question 22

The velocity of the slipstream (vs) is a function of ______.

Answer 22

The thrust coefficient.

Question 23

What two properties of the propeller affect the downwash at the HT?

Answer 23

The thrust and normal force coefficients.

Note: Both are created entirely by the prop.

Question 24

The slipstream effect on the HT moment varies primarily with ____.

Answer 24

The aircraft lift coefficient.

Question 25

If the tail carries an ____ it is stabilizing.

Answer 25

Upload

Question 26

If the tail carries a ____ it is de-stabilizing.

Answer 26

Download.

Question 27

What is the primary consideration when placing the exhaust gases from a jet engine and the horizontal tail?

Answer 27

Keeping enough distance between the two that downwash effects from the exhaust do not affect the tail’s angle of attack (slipstream interactions are minimized).

Question 28

What are the three primary contributions of a jet to the equilibrium and static stability of the aircraft?

Answer 28

1. The direct thrust
2. The direct normal force
3. The indirect effect of the induced flow at the tail due to exhaust.

Question 29

How does the line of action of the jet thrust force affect static stability?

Answer 29

> If the thrust line is above the c.g.—> Stabilizing.

> If the thrust line is below the c.g.–> De-stabilizing

Question 30

What creates the normal force on a jet inlet?

Answer 30

The change in momentum of the airflow.

Question 31

The local flow at the inlet is a combination of what two factors?

Answer 31

1. Free stream flow

2. Upwash of the wing

Question 32

The slope of xa/c is _____.

Answer 32

Positive

Question 33

The slope of (dCM/dCL) fuselage is ____.

Answer 33

Positive

Question 34

The slope of the tail contribution to static stability is ____.

Answer 34

Negative

Question 35

What are the two main requirements for aircraft longitudinal static stability?

Answer 35

1. dCM/dCL <0

2. CM_0 >0

Question 36

From left to right, give the contributions of the neutral points (both power off and on) to the c.g. limits of the aircraft.

Answer 36

N0 Power on
N0 Prop windmilling
N0 Geometric