EMEC 368 Introduction to Aerospace – Midterm Test November 1, 2012
Name _____________________________________________
Multiple Choice, 1 pt. each
1. What causes an airplane to turn?
A. Rudder pressure or force around the vertical axis.
B. Horizontal lift component.
C. Vertical lift component.
2. During a constant bank level turn, what effect would an increase in airspeed have on the rate
and radius of turn?
A. Rate of turn would decrease and radius of turn would increase.
B. Rate of turn would decrease, and radius of turn would decrease
C. Rate of turn would increase, and radius of turn would increase
3. Rate of turn can be increased and radius of turn decreased by
A. decreasing airspeed and increasing bank.
B. decreasing airspeed and shallowing the bank.
C. increasing airspeed and increasing the bank.
4. Conditions that determine the pitch attitude required to maintain level flight are
A. airspeed, air density, wing design, and angle of attack.
B. flightpath, wind velocity, and angle of attack.
C. relative wind, pressure altitude, and vertical lift component
5. If both the ram air input and drain hole of the pitot system are blocked, what airspeed indication
can be expected?
A. Constant indicated airspeed in a descent.
B. Decrease of indicated airspeed in a climb.
C. No variation of indicated airspeed in level flight, even if large power variations are made.
6. Under which condition will pressure altitude be equal to true altitude?
A. When the atmospheric pressure is 29.92 inches Hg.
B. When standard atmospheric conditions exist.
C. When indicated altitude is equal to the pressure altitude.
7. During a skidding turn to the right, what is the relationship between the component of lift,
“centrifugal” force, and load factor? (The mechanics of a “skid” are the same in an airplane as in
a land vehicle.)
A. Centrifugal force and horizontal lift are equal and the load factor is decreased.
B. Centrifugal force is less than horizontal lift and the load factor is increased.
C. Centrifugal force is greater than horizontal lift and the load factor is increased.
Name _____________________________________________
Problem 1. (20 pts) We can re-write dynamic pressure in terms of pressure and Mach number with
some simple algebra:
q = ½ ρ V2 = ½ p/RT V2 = ½ p/RT V2 γ/γ = 1/2 γ p (V/a)2 = ½ γ p (M)2
After completing its mission in orbit around the earth, the Space Shuttle entered the earth’s atmosphere
at a very high Mach number and, under the influence of aerodynamic drag, slows as it penetrates more
deeply into the atmosphere.
During its atmospheric entry, assume that the shuttle flew at Mach numbers corresponding to the
altitude, h (assume standard atmosphere conditions exist). Use the table below to report your
calculations:
h, km
M
p
q∞
60
17
50
9.5
40
5.5
30
3
20
1
a) Calculate the corresponding values of the free stream dynamic pressure at each one of these
flight path points (15 pts.)
b) Examine and comment on the variation of q∞ as the shuttle entered into the atmosphere (5 pts.)
Name _____________________________________________
Problem 2. (18 pts) The mass flow of air through a supersonic nozzle is 1.5 lbm/s. The exit velocity is
1,500 ft/s and the reservoir temperature are pressure are 1000 0R and 7 atm (14,812 lb/ft2),
respectively. For air, use cp = 6,000 (ft . lb)/( slug 0R).
a) Using the energy equation, calculate the temperature of the exit Te (8 pts).
b) Assuming ideal gas and isentropic processes, calculate the reservoir and exit
densities ρ0 and ρe. (4 pts)
c) Calculate the area of the nozzle exit Ae.(Note: Be careful of your units on this
calculation.) (6 pts)
Name _____________________________________________
Problem 3 (25 points) The NACA 2412 Airfoil has been our model airfoil for high wing, single engine
Cessna aircraft. It is a relatively thin and efficient wing cross-section.
a) What do each of the numbers in the 2412 designation represent? (5 pts)
Consider the NACA 2412 airfoil at an angle of attack of 60, and a Re = 8.9 x 106 . (Assume a fully
turbulent boundary layer).
b) Calculate the percentage of drag from pressure drag due to flow separation (form drag)
by comparing your calculations to the data provided in Appendix D (10 pts).
c) Compare this to the results of your Homework Problem 5.34, and comment on the
magnitude of cd as the angle of attack of the airfoil is increased (10 pts).
Name _____________________________________________
Problem 4. (30 pts) The General Atomics Predator UAV (Figure 6.63 in Anderson) has the
following characteristics:
a)
b)
c)
d)
e)
f)
g)
h)
i)
Wing Area = 11.45 m2
Wingspan = 14.85 m
Oswald efficiency factor = 0.7
Max Weight = 1020 kgf
Fuel Weight = 295 kgf
Power Plant – Rotax 85 hp (Note: 1 hp=746 watts)
Two blade variable pitch prop, efficiency = 0.9
Specific fuel consumption = 0.2 kgf/(hp . hr)
Zero-lift drag coefficient = 0.03
Assume that the aircraft if flying at its maximum velocity of 62.6 m/s
A. Calculate specific fuel consumption in consistent SI units for the use in Range
and Endurance calculations. (5 pts)
B. (13 pts) Calculate the Range of the Predator at sea level.
C. (12 pts) Calculate the Endurance of the Predator at sea level.
Note: This is not a difficult problem, but please pay attention with consistent units.
Solution
If severe turbulence is encountered during a flight, the airplane should be slowed to the design
maneuvering speed because the
A. airplane will stall at a lower angle of attack, giving increased margin of safety.
B. maneuverability of the airplane will be increased.
C. amount of excess load imposed on the wing will be decreased.
Note: A “coordinated turn” is one in which you feel no lateral forces. It is the source of the term “flying
by the seat of your pants” wherein if you feel a lateral load on your buttocks, the turn is not
coordinated. Use these descriptions and your understanding of the forces on a flight vehicle to answer
the following question.
8. The primary reason the angle of attack must be increased, to maintain a constant altitude during
a coordinated turn is because the
A. use of ailerons has increased the drag
B. thrust is acting in a different direction, causing a reduction in airspeed and loss of lift.
C. vertical component of lift has decreased as the result of bank.
What is the relationship between centrifugal force and the horizontal lift component in a coordinated
turn?
A. Centrifugal force exceeds horizontal lift.
B. Horizontal lift exceeds centrifugal force.
C. Horizontal lift and centrifugal force are equal.
9. If both the ram air input and drain hole of the pitot system are blocked, what airspeed indication
can be expected?
D. Constant indicated airspeed in a descent.
E. Decrease of indicated airspeed in a climb.
F. No variation of indicated airspeed in level flight, even if large power variations are made.
10. Under which condition will pressure altitude be equal to true altitude?
D. When the atmospheric pressure is 29.92 inches Hg.
E. When standard atmospheric conditions exist.
F. When indicated altitude is equal to the pressure altitude.
11. What altitude is indicated when the altimeter is set to 29.92 inches Hg?
A. Density
B. Standard
C. Pressure
12. If the air temperature is +8 0C, at an elevation of 1,350 feet and a standard (average) lapse rate
in the Troposphere exists, what will be the approximate freezing level?
A. 9,350 feet MSL
B. 3,350 feet MSL
C. 5,350 feet MSL
During a skidding turn to the right, what is the relationship between the component of lift, “centrifugal”
force, and load factor? (The mechanics of a “skid” are the same in an airplane as in a land vehicle.)
D. Centrifugal force and horizontal lift are equal and the load factor is decreased.
E. Centrifugal force is less than horizontal lift and the load factor is increased.
F. Centrifugal force is greater than horizontal lift and the load factor is increased.
The rate of turn at any airspeed is dependent upon
A. the horizontal lift component.
B. centrifugal force.
C. the vertical lift component.
When airspeed is decreased in a turn, what must be done to maintain level flight?
A. Decrease the angle of bank and/or increase the angle of attack.
B. Increase the angle of attack.
C. Increase the angle of bank and/or decrease the angle of attack.
When airspeed is increased in a turn, what must be done to maintain a constant altitude?
A. Decrease the angle of attack.
B. Decrease the angle of bank.
C. Increase the angle of bank and/or decrease the angle of attack.
Problem 1 is similar to Problem 4.29 With results from 4.28
Problem 2 is similar to Problem 4.11
Problem 3 is similar to Problem 5.35
Problem 4 is similar to Problem 6.25-6.27