BE/B Eng Bachelor of Engineering Bachelor of Aerospace Engineering 3 — Questions and Answers
Question 1: In a supersonic nozzle, what determines the exit Mach number?
- Chamber pressure alone
- The ratio of exit area to throat area (Correct answer)
- The propellant mass flow rate
- The nozzle divergence half-angle
Correct answer: The ratio of exit area to throat area
For supersonic flow, the exit Mach number is uniquely determined by the area ratio (Ae/At) through the isentropic area-Mach relation.
Question 2: What is the primary advantage of a delta wing configuration for supersonic aircraft?
- Higher lift-to-drag ratio at subsonic speeds
- Reduced wave drag and improved supersonic stability (Correct answer)
- Better low-speed handling characteristics
- Lower structural weight per unit area
Correct answer: Reduced wave drag and improved supersonic stability
The highly swept delta wing generates leading-edge vortices and has a thinner effective cross-section relative to freestream flow, reducing wave drag at supersonic speeds.
Question 3: Which parameter is conserved along a streamline in inviscid, adiabatic flow according to Bernoulli's equation for compressible flow?
- Static pressure
- Dynamic pressure
- Total (stagnation) enthalpy (Correct answer)
- Mach number
Correct answer: Total (stagnation) enthalpy
For inviscid adiabatic flow, total enthalpy h0 = h + V²/2 is constant along a streamline, which generalizes Bernoulli's equation to compressible flows.
Question 4: What is the function of a reaction control system (RCS) on a spacecraft?
- To provide main propulsive thrust for orbit insertion
- To control attitude and perform small translational maneuvers in space (Correct answer)
- To deploy solar panels and antennas
- To regulate thermal gradients across the spacecraft body
Correct answer: To control attitude and perform small translational maneuvers in space
The RCS uses small thrusters (often hypergolic) to control spacecraft orientation and make fine translational adjustments where aerodynamic surfaces are ineffective.
Question 5: In fatigue analysis of aerospace structures, what does the stress ratio R represent?
- Ratio of maximum stress to ultimate tensile strength
- Ratio of minimum stress to maximum stress in a cycle (Correct answer)
- Ratio of cyclic amplitude to mean stress
- Ratio of fatigue limit to yield stress
Correct answer: Ratio of minimum stress to maximum stress in a cycle
R = σ_min/σ_max defines the loading character: R = -1 is fully reversed, R = 0 is pulsating tension, and R = 1 is static.
Question 6: Which effect causes an aircraft to experience a nose-up pitching moment when flaps are deployed?
- Increase in lift acts behind the center of gravity
- Shift of the aerodynamic center forward of the center of pressure
- Increased camber moves the center of pressure aft relative to the center of gravity (Correct answer)
- Increased drag acts above the thrust line
Correct answer: Increased camber moves the center of pressure aft relative to the center of gravity
Flap deployment increases camber and shifts the additional lift aft, moving the overall center of pressure behind the CG and creating a nose-down pitching moment (not nose-up); if this is reversed, it indicates CG is aft of the new lift center.
Question 7: What is the primary function of a phase-locked loop (PLL) in spacecraft communication systems?
- To amplify the received signal before demodulation
- To synchronize a local oscillator to the incoming carrier frequency (Correct answer)
- To filter thermal noise from the receiver antenna
- To encode telemetry data for error correction
Correct answer: To synchronize a local oscillator to the incoming carrier frequency
A PLL tracks and locks onto the incoming carrier's phase and frequency, enabling coherent demodulation of the signal even with Doppler shifts.
BE/B Eng Bachelor of Engineering Bachelor of Aerospace Engineering 3
In a supersonic nozzle, what determines the exit Mach number?