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Flight Perf. & SS > Chapter 8 > Flashcards

Chapter 8 Flashcards

1
Q

True or False
The airplane’s angle of attack determines the lift coefficient and very closely its speed of flight, whereas the sideslip on the whole is quite useless.

A

True

Perkins and Hage Ch 8, Pg 315

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2
Q

What are some practical uses for sideslip?

A

It increases the aircraft drag which helps to

1) Create a steeper approach angle on landing
2) Acrobatic flight
3) Flight with an asymmetric power condition

Perkins and Hage Ch 8, Pg 315

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3
Q

What are the three degrees of freedom for directional stability and control?

A

Translation along the y axis (v)
Rotation about the x and z axes (phi and psi)

Perkins and Hage Ch 8, Pg 316

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4
Q

Describe the angle of yaw.

A

The angle of yaw (psi) is the angular displacement of the centerline of the airplane from some azimuth direction.

Note: In general, psi does not equal beta.

Perkins and Hage Ch 8, Pg 316

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5
Q

For sideslip during which a straight path is maintained, the angle of yaw (psi) is ________________ to beta.

A

Equal but opposite in sign

Notes: beta = -psi. See Fig. 8.1

Perkins and Hage Ch 8, Pg 316

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6
Q

WIth regards to aircraft testing and design, where are yaw and sideslip most often used respectively?

A

Yaw is normally used in wind tunnel testing
Sideslip is normally used in flight testing

Perkins and Hage Ch 8, Pg 317

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7
Q

Define static directional stability.

A

The tendency of the airplane to develop restoring moments when disturbed from its equilibrium angle of sideslip.

Note: Sideslip is usually assumed to be zero for most analysis methods.

Perkins and Hage Ch 8, Pg 317

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8
Q

How is directional static stability determined for a given airplane?

A

By summing up the stability contributions for each component of the airplane.

Perkins and Hage Ch 8, Pg 317

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9
Q

For static directional stability, the curve of Cn vs. psi must be ________.

A

Negative

Perkins and Hage Ch 8, Pg 317

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10
Q

True or False

The contribution of the wing to static stability is small compared to other aircraft components.

A

True.

Extra Notes: The contribution is small and the factor that affects it the most is the angle of wing sweep.

Perkins and Hage Ch 8, Pg 318

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11
Q

With regard to the directional stability & the contribution from the wing, what factor will influence the main wing’s contribution?

A

The sweep angle (Lambda)
(to a lesser extent) wing dihedral

Perkins and Hage Ch 8, Pg 318
Lect. 34, Slide 15

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12
Q

Swept-back wings contribute a slight __________.

A

increase to directional stability.

Perkins and Hage Ch 8, Pg 318

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13
Q

Swept-forward wings have slight ______________.

A

Directional instability.

Perkins and Hage Ch 8, Pg 318

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14
Q

True or False

The contribution of wings with no sweep is a major contributor to directional static stability.

A

False, the contribution from straight wings is practically negligible compared to other components on the airplane.

Perkins and Hage Ch 8, Pg 318

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15
Q

True or False
In the directional sense, the center of gravity’s movement due to loading changes has a large effect on directional stability.

A

False, the position of the c.g. has a negligible effect on the directional stability for most aircraft configurations.

Perkins and Hage Ch 8, Pg 318

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16
Q

The contribution of the fuselage and nacelles to the directional stability of the airplane is usually _______ and one of the _______ factors.

A

Unstable
Major

Perkins and Hage Ch 8, Pg 318 & 319

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17
Q

True or False
The yawing moment of the fuselage at an angle of yaw is a great deal easier to estimate than the pitching moment due a given angle of attack.

A

True.

Notes: The reason is that longitudinally the fuselage operates in a very complicated flow regime including upwash ahead of the wing and downwash behind the wing.

Perkins and Hage Ch 8, Pg 319

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18
Q

True or False
The directional stability of the combination of the wing plus the fuselage is usually slightly different from the sum of the two components obtained separately.

A

True.

Notes: This is due to the interference flow created at the wing-fuselage juncture.

Perkins and Hage Ch 8, Pg 320

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19
Q

Why is the directional stability of the combination of the wing plus the fuselage slightly different from the sum of the two components obtained separately?

A

Because when you calculate them separately you don’t take into account the interference flow created at the wing-fuselage juncture.

Perkins and Hage Ch 8, Pg 320

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20
Q

The wing fuselage interference effect is normally slightly _________ but its magnitude is usually never larger than _________.

A

Stabilizing
Cn_psi ~~-0.0002

Perkins and Hage Ch 8, Pg 320

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21
Q

With regard to the position of the wing on the fuselage, how does a high, medium, and low wing affect the fuselage/wing interference effect magnitude?

A

High is slightly stabilizing (Cn_psi ~-0.0002)
Medium is slightly stabilizing but less so than high (Cn_psi ~-0.0001)
Low has no effect or is de-stabilizing (~0)

Perkins and Hage Ch 8, Pg 320

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22
Q

How does the prop position affect the directional stability?

A

Tractor Prop = Destabilizing
Pusher Prop = Stabilizing

Perkins and Hage Ch 8, Pg 321

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23
Q

The propeller contribution to directional stability arises from the ___________.

A

The side force component at the prop disc created because of a given angle of yaw.

Note: This is the same effect that creates the prop normal force as discussed in Long. Stability.

Perkins and Hage Ch 8, Pg 321

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24
Q

The derivative dC_Y_p / dpsi is the same as ____.

A

dC_N / dalpha_p

Perkins and Hage Ch 8, Pg 321

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25
Q

The directional stability contribution of the prop with fullpower is roughly _________.

A

1.5 times that of the windmilling prop.

(Cn_psi) _FP ~= 1.5(Cn_psi)_windmill

Perkins and Hage Ch 8, Pg 322

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26
Q

A pure flying wing type airplane with swept-back wings, pusher props, and no fuselage will have ________.

A

Slight directional stability.

Perkins and Hage Ch 8, Pg 322

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27
Q

For most configurations, the summation of the wing orientation, fuselage, wing-fuselage interference, and prop contribution will be _______.

A

De-stabilizing.

Perkins and Hage Ch 8, Pg 322

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28
Q

The vertical tail should be placed _______.

A

As far aft of the c.g. as practical.

Perkins and Hage Ch 8, Pg 322

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29
Q

How does the sidewash due to the fuselage come about?

A

From the crosswind force created on the fuselage at some angle of yaw.

Perkins and Hage Ch 8, Pg 323

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30
Q

How does the sidewash due to the wing form?

A

The vortex sheet attached to the wing causes an inborad motion of air above the vortex sheet and an outboard motion of the air below the vortex sheet.

Perkins and Hage Ch 8, Pg 323

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31
Q

The sidwash from the fuselage gives a ________flow in the airstream beside the fuselage.

A

Destabalizing.

Perkins and Hage Ch 8, Pg 323

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32
Q

The sidewash from the fuselage gives a _____ flow to the air above the fuselage wake.

A

Stabalizing.

Perkins and Hage Ch 8, Pg 323

33
Q

The sidewash from the fuselage gives _________to the flow below the wing-fuselage intersection.

A

practically no sidewash

Perkins and Hage Ch 8, Pg 323

34
Q

True or False

Almost all the sidewash comes from the wing vortex sheet.

A

False. Almost all sidewash comes from the fuselage.

Perkins and Hage Ch 8, Pg 323

35
Q

For a low wing aircraft, the sidewash causes a _______.

A

Small stabilizing effect.

Perkins and Hage Ch 8, Pg 323

36
Q

True or False

A high wing design should have a very large sidewash influence.

A

False.
A high wing design should have a very low sidewash influence.

Perkins and Hage Ch 8, Pg 323

37
Q

The effective angle of attack for the vertical tail is the ________.

A

Difference between the yaw angle and the sidewash angle.

(alpha_vt)_eff = psi - sigma

Perkins and Hage Ch 8, Pg 323

38
Q

True or False

Too much static directional stability can be dangerous.

A

False. It’s not dangerous but it can create problems with coupling.

Perkins and Hage Ch 8, Pg 326
Lect. 33, Slide 23

39
Q

What creates adverse yaw?

A

When the airplane is rolled into a turn, the deflection of the ailerons creates more drag on the high wing, creating a yaw in the opposite direction of the turn.

Perkins and Hage Ch 8, Pg 327

40
Q

The use of the rudder to maintain zero sideslip in turns is called _________.

A

Coordinating the turn.

Perkins and Hage Ch 8, Pg 328

41
Q

What is the critical condition for adverse yaw?

A

High lift coefficient with full aileron deflection.

Perkins and Hage Ch 8, Pg 328

42
Q

What is slipstream rotation?

A

The slipstream behind the prop has a rotational component which changes the angle of attack of the vertical tail and creates sideslip.

Perkins and Hage Ch 8, Pg 328

43
Q

What is the critical condition for slipstream rotation?

A

High power at low speed.

Perkins and Hage Ch 8, Pg 328

44
Q

In most cases of high-performance airplanes, the rudder is the ________ tool to recover from a spin.

A

Primary/major

Perkins and Hage Ch 8, Pg 328

45
Q

For a single-engine airplane having high directional stability, if tricycle gear is used, the crosswind takeoff and landing requirement on the rudder can be ____.

A

Neglected.

Perkins and Hage Ch 8, Pg 328

46
Q

How can the slipstream rotation be completely mitigated?

A

By using counter-rotating props.

Perkins and Hage Ch 8, Pg 328

47
Q

For high-performance airplanes with a single-engine, single prop, what are the major considerations taken into account when designing the rudder?

A

The rudder power must be sufficient to aid in:

  1. Slipstream Rotation
  2. Spin recovery

Perkins and Hage Ch 8, Pg 329

48
Q

For an airplane equipped with counter-rotating props, what is the major consideration for rudder design?

A

Spin recovery

Perkins and Hage Ch 8, Pg 329

49
Q

For multi-engine airplanes, what is the main consideration for the design of the rudder?

A

Asymmetric Power Situations (Engine Out)

Perkins and Hage Ch 8, Pg 329

50
Q

Maximum rudder deflection are normally around ______.

A

+/- 30 degrees.

Perkins and Hage Ch 8, Pg 329

51
Q

True or False
The effectiveness of the rudder stays constant when speed is varied at full power, even if the vertical tail is in the slipstream.

A

False.
The effectiveness of the rudder varies considerably for these conditions. This is due to the effect of the slipstream velocity, which at low speed gives a high ratio of eta_vt.

Note: eta_vt = qt/q

Perkins and Hage Ch 8, Pg 329

52
Q

Rudders located in the prop wash will be ______ at low speeds and high power, and ________ as the speed of the airplane is increased.

A

highly effective
will lose effectiveness

Perkins and Hage Ch 8, Pg 329

53
Q

True or False
The rudder power required to overcome the adverse yaw during rolling maneuvers is usually not very high and seldom is considered for the design of the rudder.

A

True

Perkins and Hage Ch 8, Pg 330

54
Q

Adverse yaw moments are _____ at low speeds.

A

Critical

Perkins and Hage Ch 8, Pg 330

55
Q

The tendency for most rudders to float rapidly at high angles of sideslip leads to _________.

A

Rudder Lock

Perkins and Hage Ch 8, Pg 336

56
Q

The pedal force required of the pilot is a function of the difference between _________ and _______.

A

The required rudder angle
The floating angle

Notes: See Fig. 8-18 P&H

Perkins and Hage Ch 8, Pg 336

57
Q

True or False

One way out of rudder lock is to cut down the rudder effectiveness.

A

True

Perkins and Hage Ch 8, Pg 336

58
Q

True or False

A dorsal fin will help mitigate rudder lock.

A

True

Perkins and Hage Ch 8, Pg 337

59
Q

What are the two major effects of a dorsal fin?

A
  1. Increase the fuselage stability at high angles of sideslip.
  2. Reduce the tendency of the VT to stall at a given alpha_vt.

Perkins and Hage Ch 8, Pg 337

60
Q

What are the two central problems that directional stability and control is focused on solving?

A
  1. To insure that the airplane will tend to remain in equilibrium at zero sideslip
  2. To provide a control to maintain zero sideslip during maneuvers that induce moments that create sideslip.

Perkins and Hage, Ch 8, Pg 315

61
Q

What variables are needed to normalize a yawing moment?

A

q, S, b

Lect. 33, Slide 7

62
Q

True or False:

(dC_L / d psi)_vt is the slope of the lift curve of the vertical tail.

A

False. It’s not the lift curve slope due to the fact that flow over the wing/fuselage combines to generate a sidewash component.

Lect. 33, Slide 19

63
Q

For positive static directional stability, C_n_beta must be ________.

A

Positive.

Lect. 33, Slide 28

64
Q

What two factors determine the stability of the fuselage?

A
  1. Side projected area
  2. Location of the c.g. wrt to the fuselage.

Lect. 34, Slide 3

65
Q

True or False

For streamlined fuselage shapes, the value of Cn_beta will be large at the quarter-length point.

A

False. It will be nearly zero at this location.

Lect. 34, Slide 3

66
Q

With respect to directional stability and control, the fuselage contribution can be stable if the c.g. is _______ of the quarter length point and unstable if the c.g. is ______ of the quarter length point.

A

forward
aft

Lect. 34, Slide 3

67
Q

True or False

A positive value of beta produces a positive tail yawing moment.

A

True

Lect. 34, Slide 7

68
Q

True or False

A negative value of beta produces a negative tail yawing moment.

A

False. It produces a positive value.

Lect. 34, Slide 7

69
Q

True or False

A sideslip angle from either the left or right will create a stable yawing moment.

A

True

Lect. 34, Slide 7

70
Q

For power-off conditions, the angle of attack of the tail is equal to ___________.

A

Beta.

Lect. 34, Slide 8

71
Q

What is the benefit of a cruciform tail?

A

The sideslip effect would cancel out.

Lect. 34, slide 13

72
Q

If the wing is offset by beta, the leading wing will have a _______ drag magnitude than the trailing.

A

greater

Lect. 34, slide 16

73
Q

How is the net moment of the advancing and trailing wing calculated?

A

By subtracting the moment of the leading wing from the trailing wing.

Lect. 34, slide 17

74
Q

If the aircraft is disturbed from equilibrium about the z-axis it will begin to oscillate in yaw. The damping for these oscillations primarily comes from ______.

A

The vertical tail.

Note: However, some small contributions come from the wing.

Lect. 34, slide 17

75
Q

True or False
The same factors that contribute to the contribution of the vertical tail to the directional static stability also contribute to the damping in yaw (except for the tail length which is to the second power in the damping equation).

A

True

Lect. 34, slide 22

76
Q

The tail damping term varies directly with the _____ and inversly with the ___________.

A

Yawing velocity
forward flight velocity

Lect. 34, slide 22

77
Q

True or False

The velocity at the wingtip of a wing experiencing a yawing velocity will be the same as the flight velocity.

A

False. The upwind wing experiences a +dV while the downwind wing experiences a -dV.

Lect. 34, slide 24

78
Q

Drag forces act through the _____ of the panel’s area.

A

centriod

Lect. 34, slide 25

79
Q

How does the fuselage damping stack up against the tail or the wing’s contribution to damping in yaw?

A

The fuselage contributes a small amount to the damping in yaw.

Lect. 34, slide 26

Flight Perf. & SS (26 decks)

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