Elements of Aeronautics Basic Principles of Flight

Module – 2

BASIC PRINCIPLES OF FLIGHT

Syllabus:
Basic principles of flight – significance of speed of sound; airspeed and groundspeed;
standard atmosphere; Bernoulli’s theorem and its application for generation of lift and
measurement of airspeed; forces over wing section, aerofoil nomenclature, pressure
distribution over a wing section.Lift and drag components – generation of lift and drag;
lift curve, drag curve, types of drag, factors affecting lift and drag; centre ofpressure and
its significance; aerodynamic centre, aspect ratio, Mach number and supersonic flight
effects; simple problems on lift and drag.

1. Write in detail about the aerofoil nomenclature with sketch.

Or
With a neat sketch define nomenclature of asymmetric aerofoil
Airfoil nomenclature

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2. Explain about: Aerodynamic Centre and Centre of Pressure.

Centre of Pressure and its significance

Aerodynamic center

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3. Explain how a pressure distribution over a wing section

occurs.
Pressure distribution over wing section

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4. Discuss: Aspect Ratio, Mach Number and Supersonic Flight

Effects.

Aspect ratio

Mach number

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Supersonic flight effects

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5. Define with equation speed of sound. Explain its significance

in determining airspeed and ground speed.

Speed of Sound

The speed of sound is the distance travelled per unit time by a sound wave as it
propagates through an elastic medium.

The speed of sound in an ideal gas depends only on its temperature and composition.
The speed has a weak dependence on frequency and pressure in ordinary air, deviating
slightly from ideal behavior.
Speed of Sound Equation, 𝑎 = √𝛾𝑅𝑇
Significance of Speed of Sound to Determine Ground Speed and Airspeed

Aerodynamic forces are generated by an object moving through a fluid (liquid or

gas). A fixed object in a static fluid does not generate aerodynamic forces. To generate lift,
an object must move through the air, or air must move past the object. Aerodynamic lift
depends on the square of the velocity between the object and the air. Now things get
confusing because not only can the object be moved through the air, but the air itself can
move.

To properly define the relative velocity, it is necessary to pick a fixed reference

point and measure velocities relative to the fixed point. The reference point is fixed to the
ground, but it could just as easily be fixed to the aircraft itself. It is important to understand
the relationships of wind speed to ground speed and airspeed.

Wind Speed: For a reference point picked on the ground, the air moves relative to
the reference point at the wind speed.

Ground Speed: For a reference point picked on the ground, the aircraft moves
relative to the reference point at the ground speed.

Airspeed: The important quantity in the generation of lift is the relative velocity
between the object and the air, which is called the airspeed. Airspeed cannot be directly
measured from a ground position, but must be computed from the ground speed and the
wind speed.
Mach number, however, is measured with respect to the velocity of the object
through the air, or its airspeed.

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The relationship between ground speed, airspeed, and wind speed can be written in
the following form:

If the wind moves in the same direction as the aircraft, the term Vwind will have a
positive sign. If the wind blows in the opposite direction as the plane's motion, Vwind will
be a negative number.

The airspeed can be sub divided again into four different levels:

• Indicated airspeed: Speed of aircraft as shown on pilot as indicated airspeed.

• Calibrated airspeed: It is the indicated airspeed of an aircraft corrected for both
position and instrument error.
• Equivalent airspeed: It is calibrated airspeed of aircraft correct for adiabatic
compressible flow for particular altitudes.
• True airspeed: Speed of an aircraft relative to undisturbed air is called true
airspeed. It is equivalent airspeed by square root of density ratio.

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Elements of Aeronautics Basic Principles of Flight

6. Derive Bernoulli’s equation and explain its significance in

generation of lift and measuring airspeed.

Bernoulli’s theorem

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Bernoulli’s theorem application for generation of lift

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Bernoulli’s theorem application for measurement of airspeed (Dec/Jan

2017)

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7. Problems

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8. Discuss about the distribution of temperature in the

standard atmosphere.
Temperature related layers:
Troposphere (0 km to 11 km):

• First layer and extend up to 8km near the poles, 11km in mid latitudes and 16km
equator.
• Atmosphere is most dense in this region.
• Temperature decreases from 15ºc sea level to -56ºc and this point is called
tropopause.
• It contains almost all atmospheric water, 90% of air mass.

Stratosphere (11 km to 51 km):

• Starts just above the troposphere and extend up to 51km from earth surface.
• Temperature is constant for 1st 20km (-56ºc)
• It increases at 1ºc /km up to 32km.
• It increases at 2.8ºc /km up to 47km.
• Ozone layer lies in this layer.
• Stratopause separates stratosphere from mesosphere.

Mesosphere (51 km to 85 km):

• It just lies above stratosphere and extend up to 85km high.

• Temperature decreases @ rate of -2.8ºc from 71km to 85km.
• Temperature decreases @-2.8ºc from 51km to 71km.
• Mesopause separates the layers of mesosphere and thermosphere.

Thermosphere (85 km to 600 km):

• Extends up to 600km high.

• Temperature rises rapidly with height up to 300km.
• Due to sun’s energy temperature rises with altitude

Exosphere (500 km to transition with interplanetary space, 10000 km):

• Begins at 500km and extends outward till inter plane space.

• Upper most layer of atmosphere.

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• Merges into space in extremely this exosphere.

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9. Explain about the NACA 2411 airfoil nomenclature with

clear diagram. (Related)

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10. Write a note on: Types drags

Types of Drags

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11. Define Speed of Sound and prove that 𝒂 = √𝜸𝑹𝑻

The speed of sound is the distance travelled per unit time by a sound wave as it propagates
through an elastic medium.

The speed of sound in an ideal gas depends only on its temperature and composition.
The speed has a weak dependence on frequency and pressure in ordinary air, deviating
slightly from ideal behavior.

Derivation of Speed of Sound Equation, 𝒂 = √𝜸𝑹𝑻

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12. Explain with neat sketches factor affecting Lift and Drag.

Factors affecting lift and drag

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13. Problems

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14. Explain Lift Curve and Drag Curve.

Lift curve

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Drag curve

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15. Problems

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16. Problems

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17. Problems

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18. Problems

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