Stalling Flashcards
Does the wing stall at the stalling (critical) angle of attack?
NO
It is the angle at which the wing produces maximum lift before stalling
How does aspect ratio affect the effective angle of attack
Low aspect ratio = High effective AOA
high aspect ratio = low effective AOA
On a rectangular wing, what part stalls first and why
The root
Because there is a greater downwash at the tip causing a smaller effective angle of attack
Less downwash at the root causing s greater effective angle of attack
Why is it more favourable to have a stall start at the wing root
Turbulent air hits the tailplane causing natural buffer = stall warning
Ailerons remain in un-stalled flow for longer = some lateral control
Wing drop is less pronounced
How does effective angle affect the aircraft stalling angle
Greater effective angle
Less the stalling angle
How does downwash affect the stalling angle
Bigger the downwash the bigger the stall angle of attack
What part of an elliptical wing stalls first
The training edge
Why does an elliptical wing have undesirable stall characteristics
Stall is sudden
Little / no buffer on tailplane
Ailerons ineffective
Large roll rates if wing drops
Where does a moderately tapered wing stall first
The middle
What are the stall characteristics of a moderately tapered wing
No stall warning (buffer)
Ailerons quickly become ineffective
Where does a highly tapered - swept wing stall first
Wingtip
Highly tapered / swept wing stall characteristics
Wing tip stalls first
Can have big roll rate (if one wing stalls first)
Ailerons don’t work well
No buffet (warning)
Centre of pressure moves forwards = pitch up
Increased downwash at wing root increases tailplane downforce = increasing AOA
What type of aircraft if most likely to be involved in a deep stall
Low tapered wing, sweepback and high elevator
What causes a deep stall
The cp moving forward on the wing causing the aircraft to pitch back, this puts the elevator into the turbulent wake of the stalled wing losing its effectiveness
What does a wing fence do
reduced spanwise flow on a sweptwing aircraft by creating a physical boundary to help try and prevent the wing tip stalling first
What does a vortilon do
Attached to leading edge
During High angles of attack it protrudes into upper wing spanwise flow
Causes tight High energy turbulent “barrier” to try prevent spanwise flow
To try and stop wing tip stalling first
How does washout and reduced camber stop wingtip stall
Washout out means the tip is at a lower angle of attack than the wing root
Meaning that it won’t reach its critical angle as soon
What thickness-chord ratio has the highest stalling AOA
A high thickness to chord ratio
(Big leading edge radius) increases the AOA
What can be added to the wing root to try and make the wing root stall first
A stall strip on the leading edge
Makes a sharper leading edge
What thickness - chord ratio has the most progressive stall
High thickness - chord ratio
What thickness - chord ratio has the least progressive stall
Low thickness- chord ratio
What is wing loading
The aircrafts weight divided by the wing area
What affect does wing loading have on stalling angle of attack
Harder you make the wing work the lower the stalling angle of attack
What affect does trailing edge flaps have on the stalling angle
Reduce the stalling angle
How can ailerons affect the stall
A wing which is close to the stall if aileron is used (aileron down) this has the same affect as a trailing edge flaps and reduces the stall angle (therefor putting the wing into a stall)
How does weight affect stalling speed
More weight = more wing loading required = faster sleep when Cl = max
How does landing gear affect the stall speed
Landing gear creates drag Infront of cg = downward moment = greater downforce required from tailplane = created lift required from wings
How does thrust from a propeller affect stalling speed
The air behind the propeller (slipstream) creates high energy, fast air over the wing meaning it can create more lift for a slower airspeed
How does a jet engine affect stall speed
At high angles of attack there is a vertical component to the thrust which acts with the lift reducing the lift required therefor reducing the speed required
How does cg affect stalling speed
Forward cg = more downforce from tailplane required = more lift from main wing required to counteract = higher stall speed
How does a sweepback wing affect stall speed
Because sweepback isn’t perpendicular to airflow = Clmax is less therefor faster speed is required
How does high altitude affect stall speed
Below 300kt TAS Air has plenty of time to move round wing
Above 300kt TAS air has less time to move round wing
More energy required = higher stall speed
How does contamination affect stall speed
More weight = higher stall speed
Turns airflow into turbulent airflow = more energy used = separation earlier = stall speed higher
What is load factor
The ratio of lift to weight
What increases load factor
Turning, pulling out of a dive
When additional lift over that required to balance the weight is needed
What is the equation for load factors in a turn
1/cosangle
What is the equation for load factor
Lift / weight
What will the load factor be if lift = weight
1
What will the load factor be if lift is less than weight
<1
What will the load factor be if lift is greater than weight
> 1
What is autorotation
Occurs after the stall but before the spin is fully established (first 360°)
What causes autorotation
During stall when one wing stalls more than the other = more drag on that wing = yaw = spin
Outer wing travels faster = more lift = roll
What is the first stage of a spin
Incident spin (first 360°)
What is the 2nd stage of a spin
Fully developed spin
What is the 3rd stage of a spin
Recovery
How does cg affect the spin
Further forward the cg the more nose down moment = the steeper the spin
How does the lateral distribution of weight affect a stall
Weight at wing tip = when wing stalls greater moment = steeper roll
What is an incipient spin
The autorotation before the first full turn
What is a fully developed spin
When the aircraft has completed the first 360° and is yawing rolling and pitching
How to recover from a fully developed spin
Close power
Oppose yaw with opposite rudder
Install by pushing column forward (neutral)
What is the difference between a spin and a dive?
A dive is NOT a stalled condition
What are classic aerodynamic indications of a stall
Increase buffet intensity
Possible wing drop
An abrupt nose down pitch
Loss of altitude
How to tell you are stalling in a swept wing aircraft
Artificial stall warning systems and stall prevention systems are critical to the safe operation of swept wing aircraft
Are artificial stall warning systems required in every aircraft
Required for all aircraft
Essential for aircraft with limited aerodynamic stall warning
What are the different artificial stall warnings
Audio warning
Warning lights
Indicators on primary flight display
Stick shakers
Stick pushers
How does the flapper stall switch work
Activated when stagnation point is “behind” / underneath flapper switch
Not a true AOA indication
How does a AOA vane work
Aligns itself to the relative airflow
Where do forward sweep aircraft stall first
The root
How does a fixed AOA probe work
2 pressure channels
When air doesn’t hit channels straight on one of them has higher pressure than the other one
Computer works out the difference to determine the AOA
How does a rotating AOA probe work
There are 2 channels
When AOA changes the pressure is unequal in the channels
Motor rotates probe until channels are of equal pressure
Computer calculates the angle
What do the pitch limit indicators show you (eyebrows)
Maximum safe pitch up angle
In what aircraft are stick shakers and pushers found
Conventional flying control systems eg Boeing
What to do to recover from a stick pusher
Apply thrust
Disconnect the autopilot
Trim
Allow the airspeed to build
Once stick pusher deactivates pitch up smoothly into climb attitude
What is the EASA regulations in cs 23 for Vs1
Must be 1.2 x Vs1 at 50ft
What is the EASA regulations for Vs0 for cs23
Must be 1.3 x Vs0 at 50 foot
How are Vs1 and Vs0 calculated
With engines idol, power off , cg max forwards, max mass
What is Vsr
Reference stall speed
Is a CAS airspeed defined by manufacturer which may not be less than 1G stall speed
What is the cs25 regulations for Vsr1
At 35 feet must be 1.13 x Vsr1
What is the cs25 regulations for Vsr0
At 50 foot must be 1.23 x Vsr0
What is another name for Vsr
Vs1g
What is the v speed for when lift collapses
Vs
Vs = 0.94 x Vs1g
What are the stall warmer required safety margins
Greatest out of 5kts or 5% of Vs or Vsr
What is the stick pusher safety margins
Greatest out of 2kts it 2%
