Lecture 4 - Aircraft Longitudinal Stability 1 Flashcards
(19 cards)
What is the static margin?
The difference between neutral point and CG.
What happens as CG moves forward (5 things)
Heavy nose
More stable
More force needed on controls
Stalls at higher speed
Less manoeuvrable than rearwards CG
What is static margin expressed with respect to?
Datum or MAC
What is static margin of stability?
Distance CG can travel rearwards before reaching NP.
What values of static margin make an aircraft stable/unstable?
SM > 0; stable
SM < 0; unstable
What moment is needed for correcting a perturbation that increases AoA?
Negative
What is a characteristic of stick-fixed pitching moments? What is an assumption made here?
Controls held fixed
Elevator deflection assumed 0
What is the pitching moment coefficient in trimmed S+L flight?
0
Geometric AoA vs Absolute AoA?
Geometric AoA: angle between freestream velocity and chord line.
Absolute AoA: angle between freestream and zero-lift line.
Where should the CG be in relation to aero. centre?
Ahead
What is the pitching moment coefficient at the neutral point?
0
Three steps to remember when making initial sizing of HT
Minimise Swet
Determine lHT
Determine SHT
What does a rear CG promote? What does a forward CG promote?
Stability; favourable (less) force needed to control
4 symbols for pitching moment coefficient
Main parts of stick-fixed Cm/alpha graph
2 main stability conditions for pitching moment coefficient
dCm/da < 0
Which requires
Cm,0 > 0 (otherwise a/c can’t be trimmed)
Stability criteria for wing’s contribution to pitching moment
The 3 conditions for lomgitudinal static stability
