The rotor blade of a helicopter experiences unsteady flow even when the helicopter is flying straight and level at a steady velocity. True or false? Why?
Consider the same problem when the helicopter is hovering out of ground effect on a calm windless day.
In hover, is it O.K. to neglect the influence of the rotor wake in computing rotor loads? Why?
Air is made up of discrete molecules, yet we analyze aerodynamics assuming that air is a "continuum". Why? Give examples of conditions where this is not a good assumption.
The pressure of air at a given location at a given instant is 210,000 N/m2 and the density is 1.2 kg/m3. Find the temperature.
Why do disturbances propagate at "the speed of sound"? What does this speed depend on? Why?
What is Prandtl's Lifting Line Theory?
Nitrogen has a molecular weight of 28. How many molecules of nitrogen are present in 1 cubic meter of nitrogen at standard conditions?
What is "flutter speed" of an aircraft? How can we increase it?
What is the Glauert Solution procedure for the steady lift and induced drag of a finite wing?
The lift-curve slope of a modern airfoil is very close to the ideal value. Its zero-lift angle of attack is -3 deg.
Estimate its lift coefficient at 10 degrees angle of attack.
An aircraft has wings with a "dihedral of 5 degrees". Are the wing tips higher or lower than the wing root?
What does fatigue life prediction have to do with unsteady aerodynamics?
When an airplane is in straight and level flight, is the effective angle of attack of the wings, at any given section, greater or less than the geometric angle of attack? Why?
How is the stress-strain relation for solids different from that for fluids? What is a non-Newtonian Fluid?
Derive the relation connecting the lift coefficient and angle of attack of a thin airfoil in steady incompressible potential flow
Find an example of a stress-strain relation for a non-Newtonian fluid.
You and another bird were flying abreast (noses would hit a wall at the same instant) at the same altitude on parallel courses, at the same speed and altitude. At 11:22:03 am on Friday, a Boeing 747 zipped by about 200 feet overhead, going the same way. As it happened, you were directly under the mid-semispan of the left wing, and the bird was under a point 10 feet outboard of the left wing tip. At 11:22:23 am, you started feeling the induced velocity of the vortex system left behind by the 747. If you were flying along the positive x-direction, plot (qualitatively) the trajectories of yourself and the bird in the y-z plane starting at 11:22:23 and going on for the 5 seconds until your control system compensated for the disturbance.
Write down, without looking in any book, the law of conservation of mass as applied to flow through a control volume.
Now do the same for Newton's 2nd Law of Motion.
What are Newton's First and Third Laws of Motion?
In a closed circuit wind tunnel (such as the John J. Harper Wiind Tunnel in tthe Guuggenheim Building), air goes round and round through a big tunnel, getting whacked by a big fan, then going through an expanding passage, then through a set of straightening vanes, honeycomb and screens, through a narrowing passage, zipping by an ugly-looking model in the test section, past a clutter of tubes, wires, camera lenses, laser beams and several grinning faces, then back through an expanding passagge, turning a corner and getting whacked by the fan again and so on.
Sketch this situation. Then plot the following quantities as a function of distance along the tunnel axis.
a) Stagnation Enthalpy per unit mass of the air. Identify where heat is put in/taken out, and where work is put in/taken out.
b) Momentum of the air per unit mass.
c) Static pressure.
d) Static enthalpy
e) velocity
What is pressure?
Write down the unsteady term in the Momentum equation.
What are the unknowns that we try to solve in fluid dynamics?
What are the basic facts that we use to generate enough equations to solve for these?
Why are unsteady-aerodynamics problems more critical in the transonic regime than in other regimes?
Why don't all planes have nice triangular wings like the Mirage 2000 or F-16XL?
Is the lift on a wing equal to the airfoil lift-per-unit-span times the span? If not, is it greater or less? Why?
What is a streamline? Write down equations describing a streamline.
You drop a ball from an airplane. How will you calculate its velocity when it hits the ground?
What are "body forces"? Write a body force term in the momentum equation.
Why does the pressure term on the rhs of the momentum equation (and the energy equation) have a negative sign in front of it?
Define work ( as viewed by the fluid, not by someone struggling through 26 silly questions on a Friday night). As Georgia Tech's star Goal Line Defensive Tackler, you exert 200 Newtons along the direction of the vector 2i + 0j +3k, on an FSU Running Back weighing 300lbs. The FSURB moves 5 feet along -2i +0j -10k. Calculate the work done by you.
Define circulation. A wing is placed at negative angle of attack in a flow which goes from right to left. Is the circulation around a section of the wing positive or negative?
Consider a rectangular box, which experiences pure shear strain along all edges. Sketch the shape of the box at a subsequent time.
Write down a vector expression in terms of velocity for dilatation.
What is a "Substantial derivative"?
What is the "Kutta condition"?
What is Kelvin's theorem?
Where is the aerodynamic center of a thin symmetric airfoil?
What is the difference between the "aerodynamic center" and the "center of pressure"?
What happens to the a.c. and the c.p when angle of attack is increased?
How is the Navier-Stokes equation different from the Euler equation?
Derive the Bernoulli equation for incompressible steady flow.
A long circular cylinder is placed perpendicular to the freestream in steady incompressible flow. The freestream static pressure is 100,000 N/m2 and velocity is 50 m/s. What is the pressure at the 120-degree azimuth location on the cylinder surface?
The sliding sunroof of your car is above the front seats, ahead of the section of maximum cross-sectional area of the car. At 65 mph, if you open the sunroof, will the mosquito that is buzzing around your ear feel an upward or downward draft? why?
Sitting in traffic on a cold morning, you see clouds of condensation drifting around the cars in front of you, and watch what happens when the cars coming in the other direction move through these clouds. The clouds don't get carried away. Instead they are pushed first towards your lane, then away towards the other car, then again towards your lane and then back to their original position. Explain this.
What is a velocity potential? Does it have direction? What is irrotational flow?
How can you get away with a potential flow analysis when you have vortices and circulation to deal with?
What are the types of fluid motion that can generate net force in an inviscid flow?
In compressible flow, there can be lift even if there is no circulation. Can this be true? Explain?
Derive the velocity jump across a vortex sheet, using line integrals of velocity.
Derive the differential form of the momentum equation from the integral form.
Can you model the flow around an airfoil at angle of attack using only sources and sinks? Why?
Two fighter planes zip by in formation, one flying exactly above the other. Plot the subsequent trajectory of the right wing tip vortices of the two planes after the planes have gone.
A right-handed QuarterBack throws a long "bomb" with 15 seconds to go, exactly as practiced in Play # 93, putting a lot of spin (clockwise as viewed by the thrower) on the ball, with the spin axis exactly coinciding with the major axis of the ball and its trajectory. The stadium lights reflecting off the rain drops make it hard to see the ball until it is almost there, but the reciever has faith in the QB: the ball is aimed to land exactly on the receiver's chest where he stands free at the 10-yard line, according to Play #93. Unfortunately, a cross-wind gust comes up from the QB's left after the ball has left his hand. The receiver feels it and starts moving to his left to compensate. Just in time, he remembers the stuff his coach told him after she had taken AE6030. Should he also move forward or back? Why?
Do the center of pressure and aerodynamic center coincide for a cambered airfoil? Why?