Chapters on Axes, Wing, Drag Flashcards
Aircraft Axis are?
Longitudinal.
Lateral.
Vertical or Normal.
Taper Ratio is?
Tip Chord divided by Root Chord, and is Always <1.
Aspect Ratio is?
Ratio of the wing span to the average wing chord.
ie.
Aspect Ratio = Span over Average Chord.
Dihedral is?
Wings are angled up slightly.
ie.
Wing tips are higher than the root.
Is Good for stability.
Anhedral is?
Wing tips are angled down below the root.
Wing Tip Vortices are?
Caused by the spa wise flow, which is the pressure differential and inertia of mass flow.
Vortices go down and out.
A large crosswind dissipates it.
Formation of Wing Tip Vortices?
Low speeds are worse for vortices.
High speeds produce relatively small wing tip vortices.
Rectangular wings have larger vortices.
Tapered wings have smaller vortices.
The longer the chord, the greater the driving force for the vortex.
Vortex Intensity is Reduced if?
The Aspect ratio increases.
The Amount of lift produced decreases.
The Aircraft speed increases.
Flaps are deployed as they decrease wing tip vortices since the pressure differential decreases at the tip.
Two Other Effects of Tip Vortices?
Downwash:
Increased downwash = increased induced drag.
Drag increases.
The stronger the tip vortex, the greater the amount of drag and downwash.
Trailing Edge Vortices. Some details…
A change in angle of the airflow over the wings caused by the span wise flow on the upper and lower surfaces, then Mix and cause trailing edge vortices.
Vortices and Downwash.
Vortices suppress upwash,
and increase downwash.
The Effective Airflow - Lift and Induced Drag
Effective airflow is induced by downwash.
Airflow inclined down to the wing which reduces angle of attack, AoA.
The Lift then becomes 90 degrees (ie. perpendicular) to the effective air flow.
Induced drag depends on the lift.
Angle of attack?
Is the angle between the chord line and the relative air flow.
Is the sum of the induced AoA and the effective AoA.
Changes with the Effective angle of attack with Span.
At the Tip:
- Greater induced drag than at the root.
- Greater down wash.
- More vortices.
- Less lift produced.
At the Root:
- Less downwash.
- Less Vortices.
More lift.
The Root will stall first, For a rectangular wing.
Induced Drag is?
A result of down wash generated by tip vortices.
Induced angle of attack is?
A result of downwash due to tip vortices.
High Aspect Ratio pros and cons.
Decrease the induced drag and therefore,
- Decreased Vortices.
- Decreased Downwash.
- Decreased Induced Angle of Attack.
Disadvantages:
- Construction is structurally is hard.
- Risk of Wing strikes on take off and landing.
- High speed flight is hard structurally.
- Aerodynamic Damping so a resistance to roll.
Taper and Sweepback effects?
Reduces tip lift due to wash out and thinner design.
High wing loading Aerofoils have?
A larger pressure difference, with,
increased intense vortices,
increased downwash, and
increased lift induced drag.
Small wing relative to the weight = High wing loading.
What part of an aircraft has the largest effect on induced drag?
The Wing Tip .
Total Drag is?
Parasite Drag plus Induced Drag.
Parasite drag = Form Drag plus Skin Friction Drag plus Interference Drag.
Profile Drag = Form Drag + Skin Friction.
Form Drag is?
Impacted by,
Speed,
Frontal Area,
Shape and streamlining,
Surface (ie. smooth or dimpled).
To decrease form drag:
- Increase the distance aft of the point of max. thickness.
Skin Friction Drag is?
Impacted by;
Speed,
surface area,
boundary layer type, and
surface roughness.
Interference Drag is?
All to do with how smooth the transition from air to flow around the object is.
Think of Fish!
- Fillets and fairings all aimed to reduce interference drag.
Parasite Drag is?
Proportional to:
- Airspeed squared,
- the Surface area of the aircraft,
- the Coefficient of parasite drag.
Coefficient of Parasite Drag is?
Determined by;
- Form drag,
- Skin Friction drag,
- Interference drag.
Induced Drag and Coefficient of drag.
The coefficient of drag is inversely proportional to indicated air speed, I A S, squared .
The coefficient of drag is inversely proportional to aspect ratio.
So as aspect ratio increases, Cdi decreases as there is less downwash and less vortices
Weight makes the induced drag curve move up and to the left . So,
- The heavier you are, the more lift you will need which means more induced drag.
Reducing Tip Stalling Tendency. How?
Vortilon - Creates a vortex barrier to stop span wise flow.
Wing Fence - Physical barrier to stop spanwise flow.
Chine - Engine notch, which at slow speeds, reduces root to tip flow on upper surface of wing.
Notch - Create a vortex barrier to help reduce spanwise flow .
More commonly though:
- Washout at the tip.
- Decreased camber at the tip.
Cross Section effects on Stalling Angle.
Sharpening the leading edge of the wing root will encourage the root to stall first.
Some light aircraft have stall strips (like Toblerone ).
Wing Loading is?
Aircraft Weight divided by Wing Area.
High wing loading;
increases the adverse pressure gradient, the flow energy is lost more quickly which encourages separation and an earlier stall onset.
Aileron Reversal is what?
When approaching the stall, you try to roll one way and in trying to increase the lift on the wing that you are trying to lift, cause it to stall, which means that you actually roll the other way.
The Effect of mass on stalling speed.
Increased mass = increased required lift,
Which means the that the stalling speed is Higher for Heavier aircraft.
Flap Configuration on Stalling Speed.
Flaps and slats will increase the Coefficient of Lift MAX, CLMAX, which means the that flaps and slats decrease the stalling speed.
V S 1 = Stall speed at a clean configuration.
V S 0 = Stall speed in landing configuration.
Landing Gear effects on Stall Speed?
Landing gear will create a pitch down moment which will increase the stall speed.
Propeller Thrust effects on Stalling Speed?
A Power-off Stall has a Higher Stall Speed.
A Power-on Stall has a Lower stall speed as you are gaining ‘free lift’.
Effects of C of G Positions on Stall Speed?
C of G Forward = Higher Stall Speed.
Effects of Swept Wing on Stall Speed?
Reduced CL MAX, compared to a rectangular wing.
Which means a higher stalling angle of attack but a less defined stalling angle of attack.
Effects of Altitude on Stall Speed?
With altitude, the aerofoil loses energy at the leading edge, which gives you less warning to when you are about to stall.
At high altitude,. stalling speed increases due to compressibility.
