JNTU
JNTU B.Tech III Year AIRCRAFT PERFORMANCE AND STABILITY Previous Question Paper (August - 2022 - R18)
Answer any five questions. All questions carry equal marks.
Main
Deduce a relationship between geometric and geopotential altitudes.
Answer
The gravitational acceleration g varies with altitude h according to Newton's law of universal gravitation. The weight of a unit mass at altitude h is equal to the force of gravity at that height, defined as:
where g₀ is the acceleration due to gravity at sea level and R is the radius of the Earth. The geopotential altitude H is defined such that the work done against gravity to reach height H is the same as the work done to reach geometric altitude h in a constant gravity field g₀. Integrating the force over the distance dh:
Substituting the expression for g(h):
Integrating from 0 to h yields the relationship:
Explain in brief about the importance of stability of atmosphere. Draw with a neat diagram.
Answer
Atmospheric stability describes the tendency of an air parcel to return to its original position after being displaced vertically. It is determined by comparing the Environmental Lapse Rate (ELR) with the Adiabatic Lapse Rate (ALR).
1. Stable Atmosphere: Occurs when the ELR is less than the adiabatic lapse rate. A displaced parcel becomes cooler and denser than the surrounding air, creating a restoring force that pushes it back to its equilibrium position.
2. Unstable Atmosphere: Occurs when the ELR is greater than the adiabatic lapse rate. A displaced parcel remains warmer and less dense than the surrounding air, causing it to continue rising (buoyancy), which leads to turbulence and vertical cloud development.
3. Neutral Atmosphere: Occurs when the ELR equals the adiabatic lapse rate; the parcel remains at its new position.
Stability is critical in aviation as it dictates the presence of turbulence, vertical wind shear, and convective activity, directly affecting aircraft control and passenger comfort.
Diagram description: A vertical axis representing altitude and a horizontal axis representing temperature. A line representing the ELR is plotted alongside a steeper line representing the ALR. In the stable case, the ALR line is to the right of the ELR line at higher altitudes, indicating the parcel is cooler than the environment.
Mention various types of air breathing and non-air breathing engines. Explain any two air breathing engines and draw schematic diagram of it.
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Calculate the pressure, temperature and density at 15,000 m in the I.S.A. The pressure at sea-level is 101325 N/m2, the sea-level temperature is 288 K and the lapse rate is 0.0065 K/m.
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What are the different methods of drag reduction? Explain each with suitable diagrams.
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Discuss aircraft force system needed for formulating the performance equations of motion.
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Derive an expression of thrust produced by the jet engine aircraft.
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An aircraft is cruising at true air speed of 100 m/s under ISA condition at an altitude at which the density of free stream is 0.526 kg/m3. Calculate the equivalent air speed.
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An aeroplane has a wing loading of 2400 N/m2, and its drag equation is CD = 0.016 + 0.055 CL2, calculate its maximum lift/drag ratio, the minimum drag speed and the lift/drag ratio at a speed of 100 m/s, E.A.S.
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Derive an expression for minimum power condition in steady level flight.
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An aeroplane is flying at some multiple ‘m’ of the minimum drag speed in a steady level flight, then Prove that: (D/W) = (1/2) * (m2+1)/m.
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Prove that equivalent airspeed for min power is 0.76 times the equivalent speed for minimum drag.
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Deduce a relationship of minimum load factor in context of the steady level flight and turning flight.
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With the help of mathematical expression, explain in brief about the Pull down maneuver.
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Explain the process of take-off with the help of a diagram and discuss how take-off distance is estimated.
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Explain the cruising method of constant angle of attack and constant Mach number with neat sketches.
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