Instructor: Prof. Dr. Serkan ÖZGEN Date: 11.01.2012 1. a) (8 pts) In what aspects an instantaneous turn performance is different from sustained turn? b) (8 pts) A low wing loading will always increase aircraft weight and cost. Explain why. c) (8 pts) What is a cruise climb? Explain. d) (8 pts) Explain how and why T/W and W/S affects the takeoff distance? 2. Consider a jet trainer aircraft with two turbojet engines. a) (4 pts) Considering a simple cruise mission without loitering, sketch the mission profile. b) (24 pts) Calculate the fuel weight fraction for this mission if M cruise=0.9, range=1200 nm, cruise altitude=36000 ft. Assume that C=0.9/h, (L/D) max=11. c) (16 pts) Calculate the gross weight of this aircraft taking W e/w o=1.59w o -0.10. Take student and instructor pilot weights as 90 kg each. Assume payload weight = 0. 3. (24 pts) Select a T/W and W/S for the same airplane as in Q.2 for the following requirements (take payload weight = 0): i. Stall speed < 160 ft/s @ sea level (assume C L,max=1.5), ii. Instantaneous turn > 16 o /s at 280 knots at h=36 000 ft. ρ/ρ SL=0.533 at 36000 ft, ρ SL =0.002377 slug/ft 3. a SL, speed of sound at sea level = 1116.4 ft/s a, speed of sound at 36000 ft = 968.7 ft/s 1 kg = 2.2046 lb 1 knot = 1.689 ft/s 1 nm = 6076 ft Write neatly. Show all steps of your work including iterations. Good luck!
Instructor: Prof. Dr. Serkan ÖZGEN Date: 11.01.2012 1. a) (8 pts) What is the importance of specific excess power for an airplane? Why is this particularly important for a fighter? b) (8 pts) What are the design approaches that can be employed in order to reduce the wave drag of an airplane? Explain briefly. c) (8 pts) What is the most important difference in the way trailing edge and leading edge devices increase lift? Explain. d) (8 pts) Name three design approaches for reducing the radar cross section of an airplane. 2. Consider an airplane with the following characteristics: W/S = 70 lb/ft 2, Drag polar: C D = 0.02 + 0.15C L2, T/W) SL = 0.9 If the airplane runs out of fuel at an altitude of 36 000 ft, a) (12 pts) what is the furthest distance it can glide (neglect density variation)? b) (12 pts) what is the maximum duration that it can stay in the air (neglect density variation)? 3. Assume that the same airplane defined in question 2 is flying at an altitude of 36 000 ft and M=0.8. (neglect variations in the drag polar and weight) a) (12 pts) What is the maximum rate of climb for this airplane at the specified condition? b) (8 pts) What is the maximum acceleration for this airplane at the specified condition? c) (12 pts) What is the maximum load factor that can be achieved in a sustained turn for the specified condition? 4. (12 pts) What must be the maximum lift coefficient for the same airplane above so that it can perform a 18 o /s instantaneous turn at an altitude of 36 000 ft and a speed of 350 knots? ρ/ρ SL=0.533 at 36000 ft, ρ SL =0.002377 slug/ft 3. a SL, speed of sound at sea level = 1116.4 ft/s a, speed of sound at 36000 ft = 968.7 ft/s 1 kg = 2.2046 lb 1 knot = 1.689 ft/s 1 nm = 6076 ft Write neatly. Show all steps of your work including iterations. Good luck!
Midterm Examination 1 Prof. Dr. Serkan ÖZGEN 22.11.2012 1. a) Explain why high speed airplanes are aerodynamically more smooth compared to low speed airplanes. b) Explain why the airfoil stall characteristics are directly related to wing stall characteristics only for high aspect ratio wings. c) Explain why required thrust increases during a sustained turn. d) What is the condition for an airplane to climb with a given climb gradient. Explain. 2. Consider a single engine jet trainer with the following characteristics: T/W = 0.45, CD = 0.016 + 0.15CL 2, CL,max = 1.4 (with maneuvering flaps), CL,max = 1.5 (with trailing edge and maneuvering flaps). Select a wing loading for this airplane if the takeoff distance (ground roll only) is to be less than 2000 ft, the stall speed less than 150 ft/s and the maximum instantaneous load factor to be greater than 7 at 350 knots, all at sea level. 3. For the same airplane above, calculate the maximum climb gradient at sea level. Good Luck! Note: In the explanations try to use your own words. Show all steps of your work and write neatly. 1
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Instructor: Prof. Dr. Serkan ÖZGEN Date: 11.01.2013 1. a) (8 pts) What is the energy height of an airplane? Why is this concept particularly important for a fighter airplane? b) (8 pts) What is the supersonic area rule? Why is it important? c) (8 pts) What is the most important difference in the way trailing edge and leading edge devices increase lift? Explain. d) (8 pts) Which two wing planforms will minimize the RCS of an airplane? Explain briefly how. 2. Consider a wing with the following characteristics: AR = 2.5, Λ LE =50 o, λ=0.25. a) Calculate the lift curve slope of this wing at M=1.4. b) What is the induced drag factor for the same wing at the same Mach number? 3. Consider an airplane with the following characteristics: W/S=60lb/ft 2, T/W) M=0.9, 30000ft=0.5, C D) M=0.9, 30000ft=0.017+0.2C L2. a) Determine whether this airplane will be able to perform a sustained turn at M=0.9 corresponding to n=4 at an altitude of 30 000ft. b) What is the climb rate that can be achieved by this airplane at M=0.9 and h=30 000ft. c) What must be the limit load factor n limit so that the airplane is capable of achieving an instantaneous turn rate of 22 o /s if C L,max=1.3 at h=30000 ft? ρ/ρ SL=0.375 at 30000 ft, ρ SL =0.002377 slug/ft 3 a SL, speed of sound at sea level = 1116.4 ft/s a, speed of sound at 30000 ft = 994.8 ft/s 1 kg = 2.2046 lb 1 knot = 1.689 ft/s 1 nm = 6076.1 ft Write neatly. Show all steps of your work including iterations. Good luck!
I Midterm Examination Instructor: Prof. Dr. Serkan ÖZGEN Date: 27.11.2014 1. a) (8) Give two examples to the cases where aerodynamical and structural considerations suggest contradicting design characteristics. b) (8) What is a spoiler? Explain why it is used and its advantages. c) (12) Consider a tailless (flying wing) airplane. Give two advantages and two disadvantages of such a design. d) (8) Explain how the empty weight of an airplane varies with airfoil thickness and wing loading. Explain. 2. Consider a jet trainer with a wing leading edge sweep angle of ΛLE = 45 o and a maximum takeoff gross weight of 12 000 lb. a) (8) Estimate the design Mach number of this airplane. b) (24) Assuming that the airplane is a typical jet trainer estimate the empty weight fraction of this airplane. 3. The wing reference area of a general aviation aircraft is 14.5 m 2 and wing mean aerodynamic chord is 1.8 m. The longitudinal stability requirements dictate the tail volume coefficient to be 0.9. If the maximum fuselage diameter is 1.6 m, estimate: a) (24) the tail moment arm, b) (8) the horizontal tail area. Hint: there is no single correct answer for this question. You will need to make justifiable assumptions. In the explanations try to use your own words. Show all steps of your work and write neatly.
I Instructor: Prof. Dr. Serkan ÖZGEN Date: 12.01.2015 1. a) (8) Explain how leading edge and trailing edge devices increase the lift of a wing in different ways. b) (8) Explain the reasons why the tricycle is the most common landing gear configuration. c) (8) Explain the reasons why the longitudinal and vertical positions of the CG of an airplane are important. d) (10) What is the major inlet type that a chin inlet usually belongs to? Explain the reasons why a chin inlet may be advantageous for an airplane. 2. Consider a single engine general aviation airplane with the following characteristics: Wing loading: 17 lb/ft 2, Power-to-weight ratio: 0.07 hp/lb, Aspect ratio: 8, Vmax: 160 knots, Vcruise: 100 knots, Maximum takeoff gross weight: 2200 lb, CDo = 0.02. a) (10) What is the empty weight fraction of this airplane? b) (24) Assume that the airplane is redesigned and the aspect ratio of the wing is increased to 10. How much will the weight of the airplane change if the wing loading, taper ratio, parasite drag coefficient, fuel weight fraction, power-to-weight ratio and the maximum speed of the airplane is not changed? The airplane carries two crew members and no payload. 3. (32) How much will the L/D of the same airplane change during cruise? Assume that the cruise speed does not change. Take ambient density as 0.002157 slug/ft 3. 1 knot = 1.688 ft/s. In the explanations try to use your own words. Show all steps of your work and write neatly.