Stick-Free Neutral Point (SS&C 9)

Question 1

True or False

(ddelta_e/dCL) provides criteria for stick-fixed longitudinal stability.

Answer 1

True

Question 2

True or False
If the float angle for each lift coefficient was the same as the angle required for equilibrium, the pilot would not have to put in any input. In this case, the aircraft would be deemed neutrally stable stick free.

Answer 2

True

Question 3

Describe the relationship between elevator float and lift coefficient if the aircraft is to be considered stick-free stable.

Answer 3

For a new and increasing lift coefficient, the elevator floats upward but less than the angle necessary for equilibrium. The pilot must apply an aft force on the stick to obtain the proper equilibrium deflection.

Question 4

Describe stick-free instability.

Answer 4

For increasing lift coefficient the elevator floats upward to an angle greater than what is necessary for equilibrium. The pilot must push the stick forward to obtain the equilibrium deflection.

Question 5

The free elevator moment with respect to lift coefficient derivative is considered _____.

Answer 5

De-stabalizing

Question 6

If Ch_alpha / Ch_delta is large and positive, what effects take place.

Answer 6

The stability contribution of the horizontal tail is significantly reduced.

Question 7

At the trim speed, the stick force is equal to _____.

Answer 7

Zero

Question 8

For speeds below trim the pilot will be required to apply _____ on the stick.

Answer 8

Pull forces

Question 9

For speeds above trim, the pilot will be required to apply _____ on the stick.

Answer 9

Push forces

Question 10

How are the gearing relationships between the stick and the elevator obtained?

Answer 10

The work done at the top of the stick is equal to the work done at the elevator.

Question 11

True or False

variation of the stick force is independent of stability level.

Answer 11

True

Question 12

An aircraft possessing stick-free stability will require a_____ trim tab setting to trim the aircraft.

Answer 12

Nose up

Question 13

If the aircraft is unstable, to trim the aircraft at a given speed, the trim tab must be orientated _____.

Answer 13

Nose down

Question 14

How does the stick force gradient change when the CG is moved?

Answer 14

The gradient becomes more stable as the CG moves forward, and more unstable as the CG is moved aft.

Question 15

What could friction within the controls cause?

Answer 15

The transition from static to kinetic friction could cause hysteresis on the required stick motion.

Question 16

What are the three most common ways to artificially improve the stick force gradient?

Answer 16

The bobweight, down-spring, and spring tab.