Chapter 22 - Longitudinal Stability Flashcards
Longitudinal Stability is a disturbance in
Pitch
A horizontal stabilse is which kind of aerofoil
symmetrical or slightly negatively cambered
An up gust does what to the THS
Creates a higher AOA so the a/c wants to return to equilibrium
What x2 factors of the tail plane create greater stability and is called tail …..?
area
distance from CofG
=tail volume
In terms of pitching moment which 3 factors create a more stable a/c
speed
area
Chord
With area and chord being mostly a contact what can have greatest effect on pitch moment
Speed or dynamic pressure
Static stability is shown using a graph with what on the Axis
Absolute AOA and pitching moment coefficient
In a positive stable aircraft a pitch up requires what coefficient response
negative
Variable static stability is common with swept back what does act like
Very stable until it reaches stalling AOA and then becomes negatively unstable and will pitch up more
Wings give more stability why
Because of the CP is usually behind the CG
Fuselage is more unstable why
Because the fuselage CP is really far in front of the CG causing pitching up
Engines are more unstable why
because of their angle to the RAF and the suction
The neutral point is?
The most aft point for the CofG before it becomes statically unstable
In isolation are flaps more stable
yes because it moves the CofP back
In reality are flaps more stable
no because they effect the elevators and tailplane with the dirty air
In reality are flaps more stable
no because they effect the elevators and tailplane with the dirty air
Stick position stability
Means the stick must be moved in the same direction as it is to trim the a/c
Stick force stability requires that a change in speed = different force req
increase speed = push down and hold
decrease speed = pull back and hold
Aft CofG position the tailplane is trimmed
LE up - a/c nose down
Fwd CofG position the tailplane is trimmed
LE down - a/c nose up
What is added to either the control surface or column to provide manoeuvre stability
bob weight
Commercial jet liner requires which stick force
high
EASA require an aircraft to have positive longitudinal stability - how is that measure?
The amount of time it takes to get to half amplitude
Aerodynamic damping happens in pitch, what causes it
When the pitch of the aircraft decreases the down force on the tail plane as a result of the effective airflow being changed.
At higher altitudes what happens to aerodynamic damping
becomes less
Longitudinal dynamic stability has x2 types?
Short
Long (Phugoid)
Details of short period oscillation
1-2 seconds
Large variation in AOA + LF
Pilot induced oscillation (PIO) make it worse
happens to an aircraft with strong stability
Details of long period oscillation
1-2 minutes
little change in AOA
Airspeed will rise and fall with the oscillation
happens to a/c with a weak stability
Static and dynamic stability do what with altitude
decrease
