Chapter 6 Flashcards
True or False
The magnitude of the control force, or stick force, required of the pilot to change the speed from any given trim condition cannot be related directly to the stability criterion with fixed elevator analysis.
True
Perkins and Hage, Pg 267
True or False
The airplane is less stable with the elevator free than with the elevator locked.
True
Perkins and Hage, Pg 267
True or False
If the elevator is balanced so that it will float down with an increase in the airplane’s lift coefficient, it will obtain a lower restoring moment than was obtained with the elevator fixed, and will consequently be less stable.
False.
If the elevator is balanced such that it floats down with greater CL, the restoring moment is greater, thereby increasing static stability.
Perkins and Hage, Pg 267
What creates the hinge moments on the elevator?
The integrated pressure distribution over the surface of the elevator.
Perkins and Hage, Pg 268
True or False
The boundary layer has little to no effect on the magnitude of hinge moments.
False.
The boundary layer has a large effect. For this reason, potential theory cannot fully describe hinge moment magnitudes.
Perkins and Hage, Pg 268
What are the two major variables that govern the pressure distribution over the tail, and therefore the flap?
- The angle of attack
- The flap (or elevator) deflection angle
Perkins and Hage, Pg 268
An increase in the angle of attack tends to cause the flap to float ____.
Upward.
Perkins and Hage, Pg 269
The slope of the hinge moments with changing flap deflection is normally ______.
Negative
Perkins and Hage, Pg 271
The floating tendency is caused by which hinge moment derivative?
C_h_alpha
Perkins and Hage, Pg. 272
As soon as the control surface starts to float up, a new pressure distribution due to the parameter _____ is created which tends to _______.
C_h_delta
prevent the elevator from floating up (creates a restorative moment)
Perkins and Hage, Pg. 272
The equilibrium floating angle varies with _____.
Angle of attack
Perkins and Hage, Pg. 272
On control surfaces, it is important to ____ the floating tendency as close all possible to ______. This means C_h_alpha should have a _______ slope.
Reduce
Zero
Negative
Perkins and Hage, Pg. 273
In order for the pilot to move the controls, the slope of C_h_delta must be ______.
Negative
Perkins and Hage, Pg. 273
What is the most common method used for aerodynamic balancing?
The set-back hinge method.
Perkins and Hage, Pg. 273
How does the set-back hinge method work?
By moving the hinge point aft of the nose of the flap, the magnitude of the hinge moment is reduced (the moment arm goes down).
Perkins and Hage, Pg. 273
When the hinge line is moved too far aft, the control is said to be ______.
Overbalanced.
Perkins and Hage, Pg. 274
The hinge moment parameters C_h_delta, and C_h_alpha are very sensitive to ________. They increase positively in magnitude when ______.
Hinge line position
The hinge line is moved aft
Perkins and Hage, Pg. 274
True or False
The sharper the nose shape of the control surface, the farther aft the hinge axis will have to be moved in order to reduce the hinge moments to zero.
True
Perkins and Hage, Pg. 275
What are three common methods to increase aerodynamic balance on the tail?
- The horn balance
- The internal seal
- Beveled trailing edge
Perkins and Hage, Pg. 277
A trim tab can be used for what three purposes?
- A trimming device
- A balancing device
- A primary control
Perkins and Hage, Pg. 279
What is the primary benefit of a trim tab?
It can create large balancing moments about a control hinge line. The helps stabilize the elevator.
Perkins and Hage, Pg. 279
The slope of a control hinge moment vs deflection will be ______.
Negative
Perkins and Hage, Pg. 280
The two-dimensional c_h_delta_tab derivative depends on what three factors?
- Airfoil section
- the flap chord to airfoil chord ratio (cf/c)
- The tab chord to airfoil chord ratio (c_tab/c)
Perkins and Hage, Pg. 280
If the elevator floating angle at each lift coefficient happened to be the same as the elevator angle required for equilibrium, the airplane would be termed ______.
Neutrally stable stick-free.
Perkins and Hage, Pg. 282
The pilot’s force at the top of the stick is determined by the __________.
Hinge moment at the elevator and the geometry of the controls.
Perkins and Hage, Pg. 285
True or False
The stick force variation with speed is independent of stability level.
True
Perkins and Hage, Pg. 288
If an airplane possesses stick-free stability, a ____ tab setting is required to trim out the stick force.
Nose up
Perkins and Hage, Pg. 289
A large stick force gradient will have what effects on the pilot’s ability to control airspeed?
The airplane will resist changes in airspeed for a given control setting, and make trimming the aircraft easy.
Perkins and Hage, Pg. 290
What are the two most common pull methods to equalize stick forces?
- The downspring
- A bobweight
Perkins and Hage, Pg. 292
What is the stick-free neutral point?
The center of gravity location where (dCM/dCL)_free = 0
Perkins and Hage, Pg. 294
The stick-free neutral point is _____ to the starting point of the mgc than then Power-off the stick-fixed neutral point.
Closer.
Perkins and Hage, Pg. 294
