Lesson 6 Stall and Spin Awareness

Stall- loss of lift and increase in drag that occurs when an aircraft is flown at an angle of attack greater than the stall angle of attack
Angle of attack- angle between relative wind and chord
Critical angle of attack- angle at which stall occurs, never changes
Airspeed- aka dynamic pressure. Difference between ram and static

Va- maneuvering speed, speed at which the plane can be stalled at max gross weight without exceeding structural load limits
Load factor- ratio of lifting force of the wings to actual aircraft weight or L/W
Higher LF drives stall speed up at the square root of the LF
Vso- stall speed in the landing configuration
Vs1- stall speed in a specific configuration

Altitude and Temperature
Altitude- has no real effect on stall speed indicated airspeed is self correcting
Temperature- same as altitude no real effect on IAS

CG- has a significant effect on stall speed
an aft cg will make entry easier and recovery difficult
The reverse is true for a forward cg
As cg shifts aft, tail down force decreases
This causes less induced drag
This requires a lesser angle of attack for the same speed
This in turn lowers stall speed
The reverse is true for a forward cg
Flaps and Gear- can affect stall speed
Flaps lower stall speed
Gear down causes more drag which in turn requires more power which lowers stall speed

Weight – an increase in weight increases stall speed
Higher alpha is needed to support heavier weights
Less reserve alpha

Stall Facts
Stalls only happen when the critical angle of attack is exceeded
This may occur at any airspeed or pitch

Stall Facts
In order to make this happen, washout is built into the wing
As alpha is increased, airflow separation occurs at the aft edge of the root
It moves forward and outward

Stall Facts
Snow, ice, or frost on the wings- even small amounts can significantly increase the stall speed
Frost disrupts boundary layer flow,
Ice changes the shape of the wings and adds weight

Stall Facts
Turbulence- causes higher stall speed
Gust causes changes in relative wind thereby increasing angle of attack
Usually measured in feet per second (fps)

Stall Facts
Distractions- improper airspeed control while looking for something
Usually happens when something out of the ordinary takes place
Like and engine failure
Stall spin die

Stall Recognition
By definition a stall is any uncommanded pitch change when in the stall configuration
Stall horn goes off
Mushy feeling in the flight controls
Loss of RPM on fixed pitch prop
Reduction of sound of airflow around canopy

Stall Recognition
Buffeting, uncontrollable pitching or vibrations
Kinesthesia is the sensing of change in direction or speed of motion
Instructor yelling at the top of his or her lungs
Followed by ” you fail” or “you suck”

Types Of Stalls
Power on stall – takeoff and climb-out
Loosing partial power after takeoff in the climb
Power off stall – simulates approach situation
Trying to stretch the glide
Improper airspeed management anywhere in pattern
Total power failure after takeoff
Elevator trim stalls – on the go around or premature flap retraction
Cross control stalls – aileron opposite rudder input, commonly happens on base to final turn

Types Of Stalls
Accelerated stalls- abrupt or excessive control movements
abrupt change in alpha causes airflow separation from leading edge first
Steep turns
Pull ups
They occur at higher than normal airspeeds

Types Of Stalls
Secondary stalls- usually occur when recovery is too abrupt
Instant fail on any checkride except CFI where they are required

Stall Recovery
Key factor is remaining in positive control by reducing angle of attack
Maintain rudder control to keep unwanted yaw to a minimum
Negative g’s can hinder recovery
Apply maximum allowable power

What 2 things have to be present aerodynamically to enter a spin?
1. Stalled wing and
2. Some kind of yawing force

To intentionally enter a spin the elevator is held full back and the pilot kicks in full rudder in the direction desired for rotation and holds them there until ready for recovery
The spin will always happen in the direction of the rudder deflection
Ailerons may exacerbate the spin – neutralize them
Depending on the aircraft they may increase or decrease rotation rate

Are You Coordinated?
Right turn, ball out to the right = slipping turn (too much left rudder)
Right turn, ball out to the left = skidding turn (too much right rudder)
Terry Haws memorial slide

Categories / Spin Requirements
Normal category airplanes are required to pass a 1 turn spin or a 3 second spin whichever is longer.
However they are placarded against spins.
As with all other categories it must be impossible to obtain uncontrollable spins with any use of the controls.

Categories / Spin Requirements
Acrobatic category the plane must recover after 6 spins or 3 seconds whichever is longer
Must be able to recover from any point in the spin

Categories / Spin Requirements
Utility category airplanes can be certified in the normal or acrobatic categories with appropriate placards and markings identifying which is which

Spin Testing
The only way to be fully sure of an aircraft’s tendencies in a spin is to test them in a spin
Test pilots have the luxury of a spin chute or an ejection seat
You have niether

Spin Potpourri
A cross controlled airplane will generally rotate in the direction of the rudder
A deflection of aileron at slow airspeeds may cause the upward moving wing to stall because the aileron has demanded an increased angle of attack

Spin Potpourri
In a spin deflection of the ailerons may increase or decrease the rotation rate
An airplane may be able to spin in the utility category but when loaded in the normal category it may not recover

Spin Potpourri
Steep spiral is when the wings are not stalled but one wing is producing more lift than the other
Airspeed builds rapidly as the airplane is flying toward the ground
In a true spin, both wings are stalled but one wing is less stalled than the other
Airspeed is generally slow, even though the plane’s pitch may be nearly vertical nose down

Types Of Spins
Incipient spin- from when the airplane stalls and rotation starts until the spin becomes fully developed
Fully developed spin- Angular rotation rates airspeed and vertical speed have stabilized

Types Of Spins
Flat spin- near level pitch with the spin axis near the cg of the plane
Usually unrecoverable

Spin Recovery
1. Close the throttle
2. Neutralize the ailerons
3. Determine direction of turn
4. Apply full opposite rudder
5. When rotation slows apply forward elevator briskly
6. Neutralize rudder
7. Gradually apply up elevator to return to level flight
8.Throw the mother-in -law up on the dash
Use the PARE acronym

Aerodynamic Traps
Back side of the power curve
Region of reverse command
a pitch up results in a higher descent rate
Just backwards from normal

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