Lecture 3 - Airplane Stability via Horizontal and Vertical Tail Design Flashcards
(17 cards)
3 main function of HT and VT
Control + Trim + Stability
What 2 things must the tail be powerful enough for?
Each phase of flight and single-engine ops
What percentage of aircraft have a conventional tail
80%
2 pros of conventional tail
Roots of both HT and VT convieniantly attached to fuselage
Large effectiveness of VT because interferance with fuselage and HT increases effective aspect ratio
3 pros of t-tail
HT away from engine exhaust; less aero. interference.
Stylish
Leaves rudder un-blanketed at post-stall AoA; can be smaller than conventional tails; rudder remains in relatively clean airflow.
3 cons of t-tail
Increased weight
Forces can generate asymmetric lift in yaw
Can be in the wing wake of main wings in stall or post-stall; leads to deep stall due to control ineffectiveness
2 ways to prevent deep stall
Add elevator down spring; produces mechanical load on elevator that moves in to nose-down position
Dorsal fin
3 pros v-tail
Combines functions of HT and VT with “ruddervators”
Out of wake
Less interference drag due to fewer tail surfaces
2 cons v-tail
Increased load
Control system mixer needed due to possible interaction of elevator / rudder control forces
3 pros h-tail
Reduced height
Added redundancy
VT surface stalls at very high yaw AoA
2 cons h-tail
Increased weight
Control complexity
What effect does a dorsal fin have
Increases permittable yawing moment before VT stall
Effect of ventral fin (2 things)
Improves stall characteristics and dutch roll characteristics
Control surface area equation
Chord (c) * Span (b)
Surface area of frustum
Derivation of lHT
Start with Swet formula
Sub-in equation for SHT
Differentiate WRT Swet
Solve for lHT
Assumption made when optimising HT and VT simaltaneously
lHT = lVT
