Name ______

AAE 251Intro to Aerospace Design, SpringSemester 2005

Exam #1 (Closed Everything)

Instructions: Read each question completely; show all steps where required; use back of page as needed.

  1. (10 pts)

a)Write down the expression that defines aspect ratio (AR).

b)Sketch and label a relatively high aspect ratio wing and a relatively low aspect ratio wing.

c)What type of aircraft might have a high AR wing? A low AR wing?

  1. (10 pts) Below is the top view of an aircraft. Identify and define the main function for at least 5 items (2 of the 5 you pick must be control surfaces).

  1. (12 pts) List (in proper order) and briefly describe the 3 Phases of Aerospace Vehicle Design.
  1. (10 pts) What are the two sources of the aerodynamic force? What are the two typical components that aerodynamic force is decomposed into? Write down the equation for those two components (hint: in terms of their “coefficients”, the flight condition, and a geometry parameter).
  1. (5 pts) Sketch a depiction of a boundary layer that remains attached, but has transitioned.
  1. (10 pts) Briefly explain what is induced drag and how it arises. Draw a sketch as part of your answer
  1. (10 pts) Sketch an aircraft in steady climbing flight (no rolling). Define the direction of the freestream velocity and draw the forces and angles involved. From this diagram, derive and write down the EOM along the flight path.
  1. (8 pts) Write down the general form of the drag polar equation. Sketch a generic drag polar graph, properly labeling the axes and identifying the two major “types” of drag.
  1. (5 pts) Give the expression for the “Mass Ratio” for a rocket; also, sketch a booster rocket that employs 3 stages in series.
  1. (10 pts)

a)Write down the thrust equation for a generic propulsion device.

b)How does a propeller driven aircraft differ from a jet driven aircraft in how they primarily generate thrust [use insight from answer to part a)]?

c)Write down the equation for efficiency for a generic propulsion device. Which has higher propulsive efficiency: propeller/recip or turbojet propulsion system?

  1. (5 pts) Sketch a plot of CDovs. Mach number up to M=2. Explain behavior in the transonic regime.
  1. (5pts)True or False:

____A Boeing 777 has a lower wingloading (W/S) than a sailplane.

____“Transition” refers to the change from laminar to turbulent boundary layer, while “Separation” refers to detaching of the boundary layer from a surface.

____Flow separation occurs primarily because low energy flow in the boundary layer has insufficient momentum to overcome an adverse pressure gradient.

____Two major consequences of flow separation are increased lift and increased drag.

____A Boeing 777 has a lower lift-to-drag ratio (L/D) than a sailplane.

  1. EXTRA CREDIT (5 pts)-

Using a sketch and a few sentences, describe Lockheed-Martin’s JSF Lift-Fan propulsion concept.

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