SS&C-3-5 Flashcards
Wing downwash defines the strength of what two other properties?
The strength of the bound vortex
The strength of the trailing vortices at the tips
All bodies of revolution are _______.
De-stabilizing.
Ahead of the wing, there is an _____ that adds to the flow making (d beta)/(d alpha) _____ unity.
induced upwash
greater than
Aft of the wing, there is a _____ that subtracts flow from the freestream making (d beta)/(d alpha) _____ unity.
Downwash
Less than
In the region between the wing LE and TE, at the intersection (d beta)/(d alpha) = _____.
Zero
All bodies of revolution are ______.
De-stabilizing.
True or False
Munk’s method makes use of the fineness ratio.
True
What is the angle beta in Multhopp’s method?
The sum of the freestream and induced angles of attack.
The movement of the c.g. has a large effect on the _____ contribution to static stability.
Wing’s
dCM_cg/dCL is equal to the difference in what two terms?
The x_cg minus x_ac
What is the neutral point and how is it defined?
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.
Describe the neutral point in terms of aircraft instability.
The neutral point is the aft limit of where the c.g. can be placed before the aircraft exhibits unstable static stability.
True or False
The stick-fixed neutral point is only a function of the aircraft geometry.
True
What is the primary factor in determining an aircraft’s longitudinal static stability?
The location of the c.g. along the aircraft’s longitudinal axis measured in percent of the mean geometric chord.
A thrust line of action above the c.g. produces a ______ moment.
Nose down pitching
A high thrust line is ____
A low thrust line is ____.
Stabilizing
De-stabilizing
A propeller ahead of the c.g. produces a ____ moment.
nose-up pitching
A propeller behind the c.g. produces a _____ moment.
Nose-down pitching
A prop ahead of the c.g. is ______.
De-stabilizing
A prop behind the c.g. is ______.
Stabilizing
The propeller slipstream affects what four aspects of the aircraft’s longitudinal static stability?
The slipstream affects the:
- Wing-fuselage moments
- Wing lift coefficient
- Downwash at the HT
- Dynamic pressure on the HT
The velocity of the slipstream (vs) is a function of ______.
The thrust coefficient.
What two properties of the propeller affect the downwash at the HT?
The thrust and normal force coefficients.
Note: Both are created entirely by the prop.
The slipstream effect on the HT moment varies primarily with ____.
The aircraft lift coefficient.
If the tail carries an ____ it is stabilizing.
Upload
If the tail carries a ____ it is de-stabilizing.
Download.
What is the primary consideration when placing the exhaust gases from a jet engine and the horizontal tail?
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).
What are the three primary contributions of a jet to the equilibrium and static stability of the aircraft?
- The direct thrust
- The direct normal force
- The indirect effect of the induced flow at the tail due to exhaust.
How does the line of action of the jet thrust force affect static stability?
> If the thrust line is above the c.g.—> Stabilizing.
> If the thrust line is below the c.g.–> De-stabilizing
What creates the normal force on a jet inlet?
The change in momentum of the airflow.
The local flow at the inlet is a combination of what two factors?
- Free stream flow
2. Upwash of the wing
The slope of xa/c is _____.
Positive
The slope of (dCM/dCL) fuselage is ____.
Positive
The slope of the tail contribution to static stability is ____.
Negative
What are the two main requirements for aircraft longitudinal static stability?
- dCM/dCL <0
2. CM_0 >0
From left to right, give the contributions of the neutral points (both power off and on) to the c.g. limits of the aircraft.
N0 Power on
N0 Prop windmilling
N0 Geometric
