Flowfield characteristics that make high alpha aerodynamics difficult to predict
Separated Flows --> nonlinear aerodynamics, unsteady flow, heavy dependence on WT data
GA: prevention/recovery from spins, tail damping power factor
Fighters: resistance to departure from controlled flight
Transports: control/prevention of pitch and deep
Nominal pitching moment variation with alpha. What to look for
minimum value of nose-down pitching moment is critical
Describe nominal directional stability characteristics with alpha
Vertical tail provides stability, but is in the wake from the wing at high AoA
Describe normal variation of Cl beta with alpha
SEE PIC
How does control effectiveness change with alpha
less effective at high alpha and low speed
especially true for yawing moment
Reasons for AoA limiter
to prevent planes from going above certain AoA and unable to recover from stall (nose down)
Departure
occurs when planes depart controlled flight; may develop into a spin
How do modern fighters differ from GA airplanes in terms of characteristics that influence spins?
Fighters: elevators down first, then rudder against spin
GA: rudders against spin first, then elevators down
Arrange tail surfaces to aid spin recovery
#NAME?
Interrupted leading edges
discontinuous LE improves stall characteristics (i.e. wing cuffs)
Kinematic and Inertia coupling
kinematic roll: at 90 deg alpha becomes beta
inertia: rolling forces nose up
Modifications to the F-100
Vertical tail size increased
span increase
Cnb,dyn
may not be a good predictor, only approximate
LCDP
Lateral control departure parameter (a good predictor)
LCDP = Cnb - Clb (Cnda / Clda ) > 0
Negative value imply roll reversal
Closed loop parameter
Problems preventing routine supersonic passenger travel
never have enough thrust to reach [L/D]max
At cruise, Cd0 dominates
What is unique about the XB-70? How is this related to a key consideration in supersonic aerodynamics?
Folding wingtips to increase directional stability and minimize the AC shift
Ways to reduce volumetric wave drag
follow the area rule
increase fineness ratio l/d
What's not intuitive about the shape of a minimum wave drag axisymmetric body?
- blunt noses. The slope at the nose is 90 degrees and the LE radius is 0.
-Better to have pressure at the nose where dS is small rather than further aft
-shapes are geometrically bunt while being aerodynamically sharp
Harris Wave Drag Code find the wave drag
#NAME?
Why would anyone ever want to consider an oblique wing plane?
- Improves volumetric area distribution for low zero-lift wave drag
- spreads lift longitudinally and laterally to reduce drag due to lift (induced drag)
- AD-1 built by RT Jones
At supersonic speed, what is meant by the term subsonic edge and supersonic edge?
Subsonic edge: Mn < 1
Supersonic edge: Mn > 1
Why would you care? for subsonic edge, top/bottom surfaces can communicate
Subsonic edges CAN generate leading edge suction
Supersonic edges CANNOT produce leading edge suction
What is conical supersonic flow? Can you use that theory for a flat delta wing?
Conical flow means that span wise pressure distributions look the same at every longitudinal station
How does your expected value of leading edge suction affect the choice of planform?
...
What is meant by the terms arrow wing and modified arrow wing?
#NAME?
What is conical camber?
Special type of camber applied to delta wing supersonic aircraft to reduce drag due to lift
why do supersonic planes use fuel transfer?
to control c.g. location to maintain a relation between the c.g. and the a.c. that allows control of the plane with minimal control surface deflection to reduce trim drag
ways to cope with ac shift from subsonic to supersonic speed
#NAME?
ways to reduce strength of sonic boom
#NAME?
what mach number would be the start of hypersonic flow regime? why?
- mach numbed at which supersonic linear theory fails
- when gamma is no longer constant
- from mach 3-5
why is aerodynamic heating an issue? identify an issue
- normal surface temperature reaching around 1350 on X-15
- skin buckling, window cracking, parts literally melting
Are noses and leading edges of hypersonic vehicles rounded or blunt? why?
blunt. forces a detached shock and most of the heat dissipates into the flow field rather than on the vehicle
what do you need to know to make a simple estimate of surface pressures at hypersonic speeds?
only the geometry
what is meant by a "shadow region" on a body?
portion of the body not facing the flow; Cp = 0
where is lift generated on a hypersonic body?
the portion of the body facing the flow
Why did the X-15 have a wedge shape for the vertical tail
to ensure enough directional stability
what are surface considerations for control surfaces at hypersonic speeds?
#NAME?
What is a scramjet engine
similar to ramjet, but flow through combustion chamber is supersonic
how do you integrate a scramjet into a vehicle
all important forces are on lower surface of hypersonic vehicle. must be placed underneath
What do you remember the most about the SR-71 paper?
Pitchup limits? Chine increases directional stability and reduces the aeroelastic effects due to pitching moment
Heating? Ejector flap temp reach 1100?F