Aerofoils for High Speed Flight Flashcards
What are characteristics of slow speed (conventional aerofoils)? What is camber, leading edge diameter, thickness to chord ratio?
- Used in slow speed aircraft such as light planes and gliders
- Highly cambered, large leading edge diameter, large thickness to chord ratio
What are the characteristics of laminar flow aerofoils? Camber? Leading edge radius? Drag compared to conventional aerofoil?
- Designed to maintain laminar flow over aerofoil
- Smaller diameter leading edge
- Moderately cambered
- Lower drag
What are the four main requirements for transonic aerofoils?
1) Increasing Mcrit and reducing Mdet
2) Reducing Cl variations with airspeed
3) Reducing pitching moment variations with airspeed
4) Reducing wave drag
What is the camber of a supercritical aerofoil?
Flattened upper surface - Reduces camber minimizes the flow acceleration over the top surface which delays formation of initial shockwave to higher speeds
What is the rounded leading edge of supercritical aerofoil?
- Rounded leading edge to provide optimization between high and low speed flight
- Reduces flow separation and high angles of attack
What is the purpose of the large section depth reflect camber on lower surface?
- Increases pressure in that part of the aerofoil which recovers the lift lost through the flattening of the upper surface
- Lower shock mirrors upper one and migrates to TE at same time.
What are the 6 advantages of the supercritical aerofoil?
1) Mcrit increased due to delayed formation of initial shockwave
2) Cl variatins reduces due to lower intensity shockwaves and lift recovery
3) Mcdr increased due to delayed onset of shockwaves
4) Wave drag reduced due to lower intensity shockwaves and reduced boundary layer separation drag
5) Increased strength due to greater thickness
6) Sufficient storage space
What are the two disadvantages of supercritical aerofoil?
1) Must be matched with supercritical body design for max effect
2) Not suited to supersonic speeds because of the rounded leading edge
What are the characteristics of supersonic aerofoils and what are the reasons for these? Thickness to chord, camber, max thickness, leading edge
1) Low thickness to chord ratios which reduces shockwave intensity and moves it to trailing edge
2) Little or no camber - as above
3) Max thickness at around 50% chord - as above
4) Sharp leading edge - reduces bow wave intesity and reduces Mdet
5) Shallow Cl vs AoA curve
6) Low Cl max- higher stall speeds
What is the optimum supersonic aerofoil and why is this?
- Flat plate
- Lowest thickness to chord ratio
How is lift created on a flat plate?
Shockwaves and expansion fan.
What are 4 advantages of flat plate?
1) Simple construction
2) Uniform pressure distribution
3) Cp at mid chord for all AoA
4) Most efficient
What are 2 main disadvantages of flat plate?
1) Poor strength/internal capabity
2) Shit slow speed characteristics due to lack of camber
What is the next most optimum supersonic aerofoil?
Symmetrical double wedge with as low a t/c ratio as possible
How is lift is generated on wedge aerofoil?
Expansion fans and shockwaves
