Chapters on Stalling, Spinning, Ground effect Flashcards
Low Speed Stall.
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.
Rectangular Wing Stalling Characteristics.
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.
Elliptical Wing Stall Characteristics.
Decreased wing tip vortices.
Trailing edge vortices are consistent.
Whole wing will stall together.
Potential violent wing drop.
Moderately Tapered Straight Edge wing stall characteristics.
The Wing is efficient!
Stalls in the middle of the wing first.
Can be violent.
Swept Wing and highly tapered wing stall characteristics.
Tips work harder than root.
No stall warning.
Bad wing drop.
Unstable aircraft.
Deep Stall, or a Locked in Stall.
Horizontal stabiliser will no longer produce downwash to pitch the nose down.
Key Things to enter the spin.
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.
Autorotation.
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.
Fully Developed Spin occurs when…
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.
Effect of C of G position on spin.
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.
Mass Distribution effects on a Spin.
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.
Recognising and Avoiding the Spin.
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.
Spin Phases and Generic Recovery.
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!
Spin Avoidance.
By not stalling!
If the aircraft shows any signs of stalling, un-stall the wings.
A Spiral Dive…
… 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.
2 types of stall warner.
Natural or buffet.
Artificial such as flapper switch, audio warning system.
Recognising the stall.
Relatively low airspeed.
Sluggish slow responses.
Unresponsive.
High nose attitude.
But An accelerated stall may show no signs!
Rectangular wing stall Symptoms.
Increased buffet.
Possible wing drop.
Abrupt nose down pitch.
Loss of altitude.
Swept wing stall warning.
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.
Forward swept wings stalls.
Good stalling characteristics, likened to a rectangular wing.
But these are hard to manufacture the structural stiffness required.
Canard Design in regards to stalling.
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.
Artificial Stall Warning Systems.
Audio buzzer or alarm.
Lights.
Stick shakers.
Stick pushers.
Stick Shaker.
Quite violent and will start either 5 degrees or 5 knots above stalling speed.
Stick Pusher.
Cannot be overridden by human!
Operates at 2 knots or 2 degrees over stalling speed, which ever is larger.
Stall recovery.
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.
What to do when stick pusher activates.
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.
Recovery at the stall.
Smoothly pitch nose down, slowly apply thrust.
Once airspeed has increased to a safe margin above stall speed, pitch up to regain lost height.
Stall Warnings Requirements.
Stall margin is the greater of 5kts or 5% and is V.s.w.
When does ground effect impact the aircraft?
1 wingspan off the floor.
The Closer to the surface has the greater effect.
Can become a problem within half a wingspan.
Cause of Ground Effect?
Down wash sheet reduced.
Effective Angle of attack increases.
Entering ground effect, you get…
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.
Leaving Ground effect.
Induced drag increases.
Total drag increases.
Lift decreases.
Stalling Angle of attack increases.
Nose pitches up!
A.S.I. returns to the correct value.
