Chapters on Stalling, Spinning, Ground effect

Question 1

Low Speed Stall.

Answer 1

Caused by excessive Angle of Attack.

Boundary layer separates earlier as it no longer has the energy to stay on as the adverse pressure gradient is high.

Lift can no longer keep up with demand, so results in Lift collapse.

Question 2

Rectangular Wing Stalling Characteristics.

Answer 2

Elliptical Lift distribution.
Increased vortices at the tips.
Coefficient of Lift, CL, is highest at the root.
Root stall first as reach the critical AoA first.
No violent wing drop.

Question 3

Elliptical Wing Stall Characteristics.

Answer 3

Decreased wing tip vortices.
Trailing edge vortices are consistent.

Whole wing will stall together.
Potential violent wing drop.

Question 4

Moderately Tapered Straight Edge wing stall characteristics.

Answer 4

The Wing is efficient!
Stalls in the middle of the wing first.
Can be violent.

Question 5

Swept Wing and highly tapered wing stall characteristics.

Answer 5

Tips work harder than root.
No stall warning.
Bad wing drop.
Unstable aircraft.

Question 6

Deep Stall, or a Locked in Stall.

Answer 6

Horizontal stabiliser will no longer produce downwash to pitch the nose down.

Question 7

Key Things to enter the spin.

Answer 7

Aircraft must already be stalling to induce a spin.
1 wing more than the other.

Leads to autorotation.
A Pitch, roll, yaw combination.

The lower wing has stalled more than the higher wing.

Question 8

Autorotation.

Answer 8

When both wings are stalled.
The Centre of Gravity is way behind the Centre of Pressure.

The Lower wing produces more drag, which leads to a yaw, roll, pitch sequence.

Airspeed will be low.

Question 9

Fully Developed Spin occurs when…

Answer 9

the aircraft maintains being in a pitch, roll, yaw cycle at a stable, low speed and will continue to do so with out any input from the pilot.

Question 10

Effect of C of G position on spin.

Answer 10

Forward C of G = produces a Nose down spin, which is easier to recover from.

An Aft. C of G = produces a Flatter spin which is harder to recover from.

Question 11

Mass Distribution effects on a Spin.

Answer 11

An Aft Distribution = produces a Flatter spin

A Forward Distribution = produces a Steeper spin, which is easier to recover from.

The Lateral distribution is the dominant factor impacting how you spin.

Question 12

Recognising and Avoiding the Spin.

Answer 12

You will have to be stalled before you start to spin, so reduce the A o A when you are stalled and that should avoid the spin.

Question 13

Spin Phases and Generic Recovery.

Answer 13

Incipient Stage:
Starts when beginning to autorotate.

Fully Developed Stage:
Steady pitch, roll, yaw.

Recovery Stage:
Reduce power, Oppose yaw with full opposite rudder, install wings with the control column locked and central until buffet stops and then slowly recover

Don’t put control column too far forward as you may invert!

Question 14

Spin Avoidance.

Answer 14

By not stalling!

If the aircraft shows any signs of stalling, un-stall the wings.

Question 15

A Spiral Dive…

Answer 15

… is when you are not stalled and the airspeed and g will increase rapidly.

To recover from a spiral dive,
close power,
level wings gently,
and ease of the dive.

Question 16

2 types of stall warner.

Answer 16

Natural or buffet.
Artificial such as flapper switch, audio warning system.

Question 17

Recognising the stall.

Answer 17

Relatively low airspeed.
Sluggish slow responses.
Unresponsive.
High nose attitude.

But An accelerated stall may show no signs!

Question 18

Rectangular wing stall Symptoms.

Answer 18

Increased buffet.
Possible wing drop.
Abrupt nose down pitch.
Loss of altitude.

Question 19

Swept wing stall warning.

Answer 19

Artificial stall warners e.g audio, visual.
Stall prevention systems.

Tips stall first with rapid roll rates.
Movement of C o P fwd which leads to a pitch up, combined with tailplane downforce.
This produces a very unstable stall.

Question 20

Forward swept wings stalls.

Answer 20

Good stalling characteristics, likened to a rectangular wing.

But these are hard to manufacture the structural stiffness required.

Question 21

Canard Design in regards to stalling.

Answer 21

These are much more efficient aerodynamically.

The canard will stall first, which will then send dirty air over the main wing which decreases the efficiency of the main wing and flaps.

Question 22

Artificial Stall Warning Systems.

Answer 22

Audio buzzer or alarm.
Lights.
Stick shakers.
Stick pushers.

Question 23

Stick Shaker.

Answer 23

Quite violent and will start either 5 degrees or 5 knots above stalling speed.

Question 24

Stick Pusher.

Answer 24

Cannot be overridden by human!

Operates at 2 knots or 2 degrees over stalling speed, which ever is larger.

Question 25

Stall recovery.

Answer 25

First indication:
Reduce angle of attack.
Increase power to a safe speed.
Use small and gentle aileron and rudder inputs to put into safe attitude.

Disconnect autopilot if engaged.

And be careful increasing thrust with underslung engines as it will create a pitch up moment.

Question 26

What to do when stick pusher activates.

Answer 26

Apply thrust.
Disconnect autopilot.
Trim.
Allow for airspeed to increase and avoid rudder inputs.
Once stick shaker deactivates, pitch up smoothly to regain lost altitude.

Question 27

Recovery at the stall.

Answer 27

Smoothly pitch nose down, slowly apply thrust.

Once airspeed has increased to a safe margin above stall speed, pitch up to regain lost height.

Question 28

Stall Warnings Requirements.

Answer 28

Stall margin is the greater of 5kts or 5% and is V.s.w.

Question 29

When does ground effect impact the aircraft?

Answer 29

1 wingspan off the floor.
The Closer to the surface has the greater effect.

Can become a problem within half a wingspan.

Question 30

Cause of Ground Effect?

Answer 30

Down wash sheet reduced.
Effective Angle of attack increases.

Question 31

Entering ground effect, you get…

Answer 31

Induced angle decreases.
Effective angle increases.
Induced drag decreases .
Lift increases .
Stalling A o A decreases.
A.S.I. under reads.

You then float and balloon.
Nose pitches down as force on tail plane reduces.

Question 32

Leaving Ground effect.

Answer 32

Induced drag increases.
Total drag increases.
Lift decreases.
Stalling Angle of attack increases.
Nose pitches up!
A.S.I. returns to the correct value.