P4 Supersonic Flight

Question 1

What is the speed range for supersonic flight?

Answer 1

Mfs > Mdet

Question 2

What are the characteristics of supersonic aircraft in regards to the formation of lift?

Answer 2

There is NO UPWASH/DOWNWASH
LIFT is produced by the PATTERN of SHOCKWAVES and EXPANSION waves: PRESSURE DISTRIBUTION (can be that of the whole aircraft)
There is nearly NO LIMIT to the SHAPES of supersonic aerofoil

Question 3

What are the general summary of supersonic wing characteristics?

Answer 3

CL/CD is RELATIVELY LOW;
NO STALL AoA;
Location of MAXIMUM THICKNESS to CHORD RATIO does NOT affect LIFT or DRAG very much and does NOT affect LOCATION of CoP for a SYMMETRICAL AEROFOIL;
Location of MAXIMUM THICKNESS to CHORD RATIO affects DISTRIBUTION of Cp and CoP

Question 4

What is the pressure coefficient equation?

What does each factor represent?

Answer 4

For thin sharp-edged wings of small camber at low incidence in 2-D shock-free supersonic flow,

Cp = 2e/√M^2 - 1

e: ANGLE between AIRFLOW and SURFACE

Question 5

What are the cross sectional and planform types of supersonic wings?

Answer 5

CROSS SECTIONAL:
DOUBLE WEDGE;
BI-CONVEX;
HEXAGONAL;
THIN PLATE;

PLANFORM:
SWEPT WING;
UNSWEPT WING;
DELTA WING;
VARIABLE SWEEP WING

Question 5

Describe the characteristics of a thin plate aerofoil?

Answer 5

NOT very RIGID

Question 6

Describe the characteristics of a bi-convex aerofoil?

Answer 6

SAME MAX DRAG as that of DOUBLE WEDGE wing;
NO significant REDUCTION in LIFT was found with HIGH AoA ( No stall a < 30o );
Agree with theory well;
LOCATION of MAX T/C is at 25% to 75% of chord

Question 7

Describe the characteristics of a double wedge aerofoil?

Answer 7

Popular shape for supersonic flight;
The LOCATION of MAX T/C NO EFFECT on LIFT and CP, and a LITTLE on DRAG
LOCATION at 40 – 60% of chord;
HIGH WAVE DRAG;
BEST T/C RATIO depends on the MACH NUMBER of the supersonic flight

Question 8

What are the characteristics of an ideal body shape?

Are there any characteristics that have significant disadvantages?

Answer 8

Follows AREA RULE;
SLENDER shape;
SHARP LE/TE making BOW SHOCK ATTACHED but SOURCE of KINE HEATING;
BODY produces LIFT at SMALL AoA

Question 9

Explain the characteristics of swept wings?

Answer 9

Better lift at low M
Relatively low drag at high M;
Tip effects – reduce lift

Question 9

Explain the characteristics of unswept wings?

Answer 9

Better L/D ratio;
Experience twist and bending stress;
Large sweep angle – wing works effectively Tip stall with a small sweep angle;
Can produce subsonic L.E.

Question 10

Explain the characteristics of delta wings?

Answer 10

Simple, long cord, low t/c ratio;
Rigid structure;
Large area for given wing span – low wing load; Higher skin friction;
Popular for supersonic flight

Question 12

Explain the characteristics of variable geometry wings?

Answer 12

Best L/D RATIO throughout whole flight
Low speed: straight;
High speed: swept

Question 13

What is a common feature of planform wings?

Answer 13

the angle of the sweptback leading edge is smaller than the Mach angle (within the Mach cone) – subsonic leading edge

Question 14

What is the equation for drag in supersonic flight?

Answer 14

D = Dfriction + Dwave + Dvortex + Dlift

Question 15

Explain the types of drag in supersonic flight?

Answer 15

Dfriction: Due to FRICTION because of VISCOUS AIRFLOW mainly SKIN DRAG NOT as DOMINANT but source for KINETIC HEATING;
Dwave: Due to FORMATION of SHOCKWAVE around whole BODY;
Dvortex + Dlift: Associated with LIFT including drag caused by VORTEX (INDUCED DRAG) and drag derived from PRESSURE DISTRIBUTION around plane which PRODUCES LIFT

Question 16

What are the characteristics of the boundary layer in supersonic flight?

Answer 16

Boundary layer of supersonic flow is very thin
• Flow profile is relatively simple – linear
• Boundary layer (turbulent wake) separation is not an issue in term of lift. It is part of formation of supersonic waves, increases drag.
• Viscous force (friction) is relatively small, but
• Skin friction contributes to kinetic heating significantly

BOUNDARY LAYER forms due to VISCOSITY of AIR;
VERY THIN;
SPEED of PARTICLES on SURFACE is 0 and INCREASE quickly to reach FREE STREAM SPEED;
AIRSPEED INCREASES LINEARLY in direction PERPENDICULAR to SURFACE

Question 17

What are the characteristics of boundary layer separation in supersonic flight?

Answer 17

Occurs particularly as TURBULENT WAKE

Question 18

What design features are used to protect against kinetic heating?

Answer 18

MATERIALS;
INSULATION;
SURFACE RADIATION;
SURFACE COOLING

Question 19

What design features are useful for supersonic control?

Answer 19

ALL MOVING SLAB control surfaces CONTROLLED INDIVIDUALLY;
Fully POWERED-OPERATED CONTROL SURFACES;
SYNTHETIC STABILITY and AUTOMATIC CONTROL to ensure STABILITY and ACCURACY

Question 20

What is kinetic heating?

Explain the sources of kinetic heating?

Answer 20

HEATING of a SOLID BODY produced by HIGH SPEED travel through air where KINETIC ENERGY is CONVERTED to HEAT/THERMAL ENERGY;
FRICTION in BOUNDARY LAYER: KINETIC energy is consumed to OVERCOME FRICTION to keep flow forward. WORK done AGAINST FRICTION will CHANGE to THERMAL ENERGY. The surface FRICTION is EXERTED on will be HEATED and TEMPERATURE INCREASED. TURBULENT produces HIGHER TEMPERATURE;
STAGNATION POINT: ENERGY equation shows when V = 0 TEMPERATURE INCREASES;
SHOCKWAVE formation: Requires ENERGY and air TEMPERATURE INCREASES sharply BEHIND shockwave. The GREATER the MACH, the HIGHER the TEMPERATURE