Chapter 6

Question 1

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.

Answer 1

True

Perkins and Hage, Pg 267

Question 2

True or False

The airplane is less stable with the elevator free than with the elevator locked.

Answer 2

True

Perkins and Hage, Pg 267

Question 3

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.

Answer 3

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

Question 4

What creates the hinge moments on the elevator?

Answer 4

The integrated pressure distribution over the surface of the elevator.

Perkins and Hage, Pg 268

Question 5

True or False

The boundary layer has little to no effect on the magnitude of hinge moments.

Answer 5

False.
The boundary layer has a large effect. For this reason, potential theory cannot fully describe hinge moment magnitudes.

Perkins and Hage, Pg 268

Question 6

What are the two major variables that govern the pressure distribution over the tail, and therefore the flap?

Answer 6

1. The angle of attack
2. The flap (or elevator) deflection angle

Perkins and Hage, Pg 268

Question 7

An increase in the angle of attack tends to cause the flap to float ____.

Answer 7

Upward.

Perkins and Hage, Pg 269

Question 8

The slope of the hinge moments with changing flap deflection is normally ______.

Answer 8

Negative

Perkins and Hage, Pg 271

Question 9

The floating tendency is caused by which hinge moment derivative?

Answer 9

C_h_alpha

Perkins and Hage, Pg. 272

Question 10

As soon as the control surface starts to float up, a new pressure distribution due to the parameter _____ is created which tends to _______.

Answer 10

C_h_delta
prevent the elevator from floating up (creates a restorative moment)

Perkins and Hage, Pg. 272

Question 11

The equilibrium floating angle varies with _____.

Answer 11

Angle of attack

Perkins and Hage, Pg. 272

Question 12

On control surfaces, it is important to ____ the floating tendency as close all possible to ______. This means C_h_alpha should have a _______ slope.

Answer 12

Reduce
Zero
Negative

Perkins and Hage, Pg. 273

Question 13

In order for the pilot to move the controls, the slope of C_h_delta must be ______.

Answer 13

Negative

Perkins and Hage, Pg. 273

Question 14

What is the most common method used for aerodynamic balancing?

Answer 14

The set-back hinge method.

Perkins and Hage, Pg. 273

Question 15

How does the set-back hinge method work?

Answer 15

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

Question 16

When the hinge line is moved too far aft, the control is said to be ______.

Answer 16

Overbalanced.

Perkins and Hage, Pg. 274

Question 17

The hinge moment parameters C_h_delta, and C_h_alpha are very sensitive to ________. They increase positively in magnitude when ______.

Answer 17

Hinge line position
The hinge line is moved aft

Perkins and Hage, Pg. 274

Question 18

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.

Answer 18

True

Perkins and Hage, Pg. 275

Question 19

What are three common methods to increase aerodynamic balance on the tail?

Answer 19

1. The horn balance
2. The internal seal
3. Beveled trailing edge

Perkins and Hage, Pg. 277

Question 20

A trim tab can be used for what three purposes?

Answer 20

1. A trimming device
2. A balancing device
3. A primary control

Perkins and Hage, Pg. 279

Question 21

What is the primary benefit of a trim tab?

Answer 21

It can create large balancing moments about a control hinge line. The helps stabilize the elevator.

Perkins and Hage, Pg. 279

Question 22

The slope of a control hinge moment vs deflection will be ______.

Answer 22

Negative

Perkins and Hage, Pg. 280

Question 23

The two-dimensional c_h_delta_tab derivative depends on what three factors?

Answer 23

1. Airfoil section
2. the flap chord to airfoil chord ratio (cf/c)
3. The tab chord to airfoil chord ratio (c_tab/c)

Perkins and Hage, Pg. 280

Question 24

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 ______.

Answer 24

Neutrally stable stick-free.

Perkins and Hage, Pg. 282

Question 25

The pilot’s force at the top of the stick is determined by the __________.

Answer 25

Hinge moment at the elevator and the geometry of the controls.

Perkins and Hage, Pg. 285

Question 26

True or False

The stick force variation with speed is independent of stability level.

Answer 26

True

Perkins and Hage, Pg. 288

Question 27

If an airplane possesses stick-free stability, a ____ tab setting is required to trim out the stick force.

Answer 27

Nose up

Perkins and Hage, Pg. 289

Question 28

A large stick force gradient will have what effects on the pilot’s ability to control airspeed?

Answer 28

The airplane will resist changes in airspeed for a given control setting, and make trimming the aircraft easy.

Perkins and Hage, Pg. 290

Question 29

What are the two most common pull methods to equalize stick forces?

Answer 29

1. The downspring
2. A bobweight

Perkins and Hage, Pg. 292

Question 30

What is the stick-free neutral point?

Answer 30

The center of gravity location where (dCM/dCL)_free = 0

Perkins and Hage, Pg. 294

Question 31

The stick-free neutral point is _____ to the starting point of the mgc than then Power-off the stick-fixed neutral point.

Answer 31

Closer.

Perkins and Hage, Pg. 294