Longitudinal Control (SS&C 7) Flashcards
What three items in the stability equation could be used to create a trim moment to balance a change in lift coefficient?
- Wing moment about the a.c.
- c.g. position (xa/c)
- Angle of attack of the horizontal tail (HT)
For an aircraft that has a horizontal tail, the effectiveness of what parameter is limited in its ability to create a trimming moment in response to a change in equilibrium lift coefficient?
The moment about the aerodynamic center.
CMac
The magnitude of Cm_ac is dependent on what three items?
- Geometric Twist
- Aerodynamic twist
- The trailing edge flap (if installed)
On a flying wing, what is the major trim control device?
The flaps
As c.g. moves forward, equilibrium CL is _____.
Reduced
As c.g. moves aft, equilibrium CL ____.
Increases
What are the two basic types of horizontal control?
- All moving surfaces (stabilators)
2. Combination of a horizontal stabilizer and an elevator flap.
Deflecting the elevator increases the ____ of the horizontal tail as a whole.
Chamber
A upward elevator deflection is considered _____. (Sign conventions)
Negative
A downward elevator deflection is considered _____. (Sign conventions)
Positive
What is the elevator control power?
The magnitude of the change in pitching moment coefficient per degree of elevator deflection.
What is the definition of the elevator effectiveness parameter? (Def, not Eq. )
The rate of change of the tail angle of attack with respect to elevator deflection.
True or False
A downward deflection of the elevator changes the angle of attack at zero lift by shifting it left.
True
True or False
A downward deflection of the elevator changes the CL_stall value by shifting it down.
False. It shits upward.
How does elevator deflection change the pitching moment curve?
It only shifts it up and down along the Cm axis. The slope does not change.
The elevator angle required to trim to the desired CL is proportional to _____, and inversely proportional to ____.
dCM/dCL
CM_delta_e
de = de0 + ((dCM/dCL) / Cm_de)*CL
The slope of the elevator deflection vs CL_trim is dependent on _____.
The c.g. location with respect to the N0
Printed Handout: Pg. 21
When the c.g. is at the neutral point, the slope of the deltea_e vs CL_trim will be _____.
Zero
The most forward c.g. location in free flight is determined by ____
The elevators’ ability to trim that aircraft at all lift coefficients up to CL_max.
If the c.g. moves forward, ____ elevator is required for trim.
More
If the c.g. moves backward, _____ elevator is required for trim.
Less
The extent of the aircrafts c.g. range depends almost entirely on the _____.
Elevator power derivative
The magnitude of the elevator power depends on what four terms?
- Slope of the tail lift curve (a_t)
- Tail Area (S_t)
- Tail length from the c.g. (l_t)
- Elevator effectiveness (tau)
Printed Handout: Pg 25
Being in ground effect ____ the tail angle of attack. This requires more _____ to keep the aircraft in trim.
reduces Negative (up) elevator deflection
