Lecture 5 - Aircraft Static Longitudinal Stability 2 Flashcards
(20 cards)
Components of overall pitching moment coefficient
Wing, tail, fuselage
Graph of Cm,cg / abs. AoA for fuselage, wing, complete airplane, tail.
Which is the main contributor to longitudinal static stability?
Tail alone biggest contributor (very -ve slope)
CG/ACw/ACt diagram for conventionally-winged a/c
CG/ACw/ACt diagram for canard a/c
2 pros of canard
Front wing airflow unaffected by rear wing wake and propulsion system.
Improved aero. perf. at high AoA / near stall.
What does Cm,cg,t mean?
Pitching moment coefficient of the tail, about the CG.
Downside of conventional tail?
Can be affected by front wing’s downwash.
What is downwash?
Downwards deflection of air by a/c wing or heli. rotor blade.
Downwash angle symbol
ε
Tail pitching moment about CG equation. What 6 approximations are made?
-ltLt
Lt»Dt
lt»zt
Mac,t=0
-Steady, straight, unaccelerated flight
-Constant power setting
-Small angles
Diagram of forces and moments on tail, with respect to CG
3 more complex roles of HT
Provides longitudinal stabilty
Provides longitudinal equilibrium
Trims a/c
What is downwash angle?
Angle between freestream velocity and velocity of airflow at tail, changed due to downwash.
CLW general equation
CL,0 + CL,alpha,omega * alpha
What is η and typical values for conventional tail and t-tail
Tail efficiency coefficient
Conventional: 0.9ish
T-tail: 1
What is Vh?
Horizontal tail volume ratio
Equation at NP
dCm,cg/dalpha = 0
Stick-free SM position vs Stick-fixed?
Free ahead
Alternative static stability criterion
dCm/dCl < 0 (from graph)
therefore Cmalpha < 0
Mnemonic for types of speed
ICET
PCD
IAS +- position error = CAS
CAS +- compressibility = EAS
EAS +- density = TAS
