Test 4 Lecture Notes Flashcards
What variables are needed to normalize a yawing moment?
q, S, b
Lect. 33, Slide 7
True or False:
(dC_L / d psi)_vt is the slope of the lift curve of the vertical tail.
False. It’s not the lift curve slope due to the fact that flow over the wing/fuselage combines to generate a sidewash component (but it is close).
Lect. 33, Slide 19
Directional control in yaw is principally determined by ______.
The ability of the rudder to create yawing moments.
Lect. 34, slide
There are seven jobs that the rudder is used for with respect to airplanes. What are they?
- The airplane path on the ground during TO and LNDG
- Spin recovery
- Coordinate the turn
- Induce a sideslip if needed
- Overcome prop effects
- Overcome asymmetric power effects
- Overcome adverse yawing effects
Lect. 34, slide 2
Directional trim changes with speed in straight flight are due almost entirely to ___________. Jet-powered aircraft should have _______ changes.
Singe rotation props.
No trim
Lect. 34, slide 4
Trim changes due to a single-rotation propeller arise from what two effects?
Sidewash effects on the vertical tail
Direct propeller yawing moments from the prop normal force
Lect. 34, slide 4
What are the two effects of the prop sidewash on the vertical tail?
- Increase in relative speed so qt/q is increased
- Increase of the sidewash angle (sigma)
Lect. 34, slide 4
Why is the vertical tail and rudder often offset from the aircraft’s longitudinal centerline?
So that at cruise, no rudder deflection is required. This is especially true when no independent rudder trim is available.
Lect. 34, slide 5
True or False
Having an offset rudder/vertical tail helps to reduce pilot workload.
True.
Lect. 34, slide 5
The greatest cause of directional trim change (for a single prop airplane) with speed is due to _________.
The direct yawing moment created by the propeller.
Lect. 34, slide 6
As the axis of rotation of the prop is included upward wrt the relative wind, the downward moving blade has a ___________ than the upward moving blade.
Higher effective angle of attack.
Lect. 34, slide 6
True or False
Since the prop axis is inclined wrt the horizon, the blades will experience a change in angle of attack throughout their cycle of rotation.
True
Lect. 34, slide 6
If the angle of attack of the aircraft is changed, the prop will produce a _______.
Yawing moment.
Lect. 34, slide 7
If a prop is yawed with respect to the relative wind, a _________.
A pitching moment will result.
Lect. 34, slide 7
True or False
The effects of the side wash and the propeller moment are in the same direction and are additive.
True
Lect. 34, slide 10
When are the effects of side wash and propeller moment greatest?
At low flight speeds and high power levels.
Lect. 34, slide 10
True or False
For a single rotation propeller aircraft, a rudder deflection is required to maintain heading as a change in speed is applied.
True
Lect. 34, slide 11
For a single rotation propeller aircraft as speed is changed the rudder must be deflected in order to maintain heading. This is accompanied by a change in ________.
Sideslip angle.
Lect. 35, slide 11
True or False
Adverse yaw moments are critical at low speeds and the rudder must be sized to overcome these moments, especially near stall.
True
Lect. 35, slide 14
When the rudder is free to float in response to hinge moments, it can have _______________.
An adverse effect on the directional stability.
Lect. 35, slide 20
With respect to rudder free analysis; if the AC sideslips, the restoring moment of the tail _________ and the rudder _________.
decreases
will float with the wind
Lect. 35, slide 20
What is the consequence of having a low pedal force gradient?
It will be difficult for the pilot to hold zero sideslip maneuvers.
Lect. 35, slide 22
What is the consequence of having a high pedal force gradient?
The aircraft will feel sluggish and stiff.
Lect. 35, slide 22
The rolling moment the aircraft experiences in sideslip is primarily due to __________.
The Dihedral Effect.
Lect. 36, slide 2
How is the dihedral effect linked to positive or negative lateral stability?
If the rolling moment generated from the dihedral effect is away from the sideslip, the dihedral effect is positive and the AC is said to have positive static lateral stability.
Lect. 36, slide 2
For a positive dihedral, the wing panel moving into the wind has a _______ delta alpha and thus a ______ incremental lift value, and VV.
positive
positive
Lect. 36, slide 6
What are the sign values for dCl’/dbeta and dCl’/dpsi when positive dihedral is considered?
dCl’/beta is negative
dCl’/dpsi is positive
Lect. 36, slide 9
True or False
A sweepback wing has a negative dihedral effect.
False. A sweepback wing has a positive dihedral effect.
Lect. 36, slide 11
Sweepforward produces a ______ dihedral effect, while sweepback produces a ______ effect.
negative
positive
Lect. 36, slide 13
With respect to the fuselage, if the side force acts above the c.g., what type of rolling moment is produced?
A stable rolling moment.
Lect. 36, slide 14
With respect to the fuselage, if the side force acts below the c.g., what type of rolling moment is generated?
A de-stabilizing rolling moment.
Lect. 36, slide 14
WIth respect to the fuselage, if the sideforce acts above the c.g., what type of dihedral effect is produced by the sideslip?
A positive dihedral effect.
Lect. 36, slide 14
WIth respect to the fuselage, if the side force acts below the c.g., what type of dihedral effect is produced?
A negative dihedral effect.
Lect. 36, slide 14
How do high and low wings affect the dihedral effect?
High wings provide a slightly positive effect
Low wings provide a slight negative effect.
Lect. 36, slide 17
How does the addition of flaps affect lateral stability?
Partial span flaps reduce the effective moment arm thus decreasing the rolling moment. The decrease in lateral stability can be very large.
Lect. 36, slide 18
When combined with sweep, if the wing flap LE is swept aft there is a ___________ dihedral effect that is identical to the general sweep effect.
small positive
Lect. 36, slide 18
How does the prop influence the dihedral effect?
Tractor prop = negative dihedral effect
Pusher prop = positive dihedral effect.
Note: For power on flight, the effect is greatest.
Lect. 36, slide 19
The rolling moment due to rolling velocity is called ________.
Damping in roll.
Lect. 36, slide 22
What are the two reasons why the use of ailerons causes a yawing moment (hint–adverse yaw)?
- Induced drag on the down aileron is increased.
- When the AC starts to roll, the lift vectors on the down-going wing are included backward and those on the up-going wing are inclined forward.
Lect. 36, slide 29
To overcome adverse yaw, one can increase _____.
dCn/dbeta
Lect. 36, slide 34
True or False
At low speeds (or high lift coefficients) a large amount of sideslip will be required with a small angle of bank to achieve a steady sideslip.
True
Lect. 36, slide 38
True or False
Aircraft with large vertical tails in which the centroid of the aerodynamic surface is above the center of gravity will induce a rolling moment.
True
Lect. 36, slide 38
What is spiral divergence? What conditions are necessary to cause it?
Spiral divergence occurs when the static directional stability is very strong in comparison to the dihedral effect. In spiral divergence, when the aircraft is disturbed, it tends to go into an ever-tightening spiral dive.
Lect. 36, slide 41
How is Dutch roll related to spiral divergence?
Dutch roll exists in any airplane in which the ratio of the static directional stability and the dihedral effect falls between the limiting conditions for spiral divergence and directional divergence.
Lect. 36, slide 42
True or False
When directional stability is relatively strong (tending towards spiral divergence) the Dutch Roll oscillation is heavily damped and is not objectionable.
True
Lect. 36, slide 42
True or False
When the dihedral effect becomes very strong, the Dutch Roll motion is weakly damped and the motion is troublesome for the pilot. In some cases it can become dynamically unstable.
True
Lect. 36, slide 42
