w w w . 5 s t a r n o t e s . c o m Skin friction drag and pressure drag. 1. Skin Friction • Due to shear stresses produced in boundary layer. • Significantly more for turbulent than laminar types of boundary layers. 2. Pressure Drag • Due to static pressure distribution around body - component resolved in direction of motion. • Sometimes considered separately asforebody and rear (base) drag components. 3. What is ISA? Since the physical properties of the air are dependent upon temperature, and the performance of the aircraft is dependent upon the air density, pressure and temperature, correlation of performance data is dependent upon some assumed standard lapse rate. For convenience, an International Standard Atmosphere has been adopted based on an average linear lapse rate at 40 degree north latitude which has been empirically chosen after a study of average lapse rates observed throughout the world. 4. What are the conditions required for minimum drag and minimum power? Also there must be a single value for the angle of attack which gives: –Maximum L/D, minimum TR and minimum D. –Thrust Required TR must be proportional to 1/(L/D) or 1/(CL/CD) –I.e. speed for minimum drag or minimum thrust required must correspond with speed for maximum lift/drag ratio. www.5starnotes.comwww.5starnotes.com
• Due to shear stresses produced in boundary layer .• Significantly more for turbulent than laminar types of boundary layers.
2. Pressure Drag
• Due to static pressure distribution around body - component resolved in direction ofmotion.• Sometimes considered separately as forebody and rear ( base ) drag components.
3. What is ISA?
Since the physical properties of the air are dependent upon temperature, andthe performance of the aircraft is dependent upon the air density, pressure andtemperature, correlation of performance data is dependent upon some assumedstandard lapse rate. For convenience, an International Standard Atmosphere has beenadopted based on an average linear lapse rate at 40 degree north latitude which hasbeen empirically chosen after a study of average lapse rates observed throughout theworld.
4. What are the conditions required for minimum drag and minimum power?Also there must be a single value for the angle of attack which gives:
– Maximum L/D, minimum TR and minimum D. – Thrust Required TR must be proportional to 1/(L/D) or 1/(CL/CD) – I.e. speed for minimum drag or minimum thrust required must correspond withspeed for maximum lift/drag ratio.
. c o 5. What is meant by the degree of freedom and how much required for airplane?
The aircraft has six degrees of freedom, namely three translational and threerotational. The longitudinal axis is denoted by x-axis towards the forward nose sectionof the fuselage. The y-axis points towards the starboard position and the z-axisvertically downward. The degrees of freedom signify the various modes the aircraftcentre of gravity can translate and rotate freely in all directions.
6. What is meant by dihedral effect?
The phenomenon of rolling moment due to sideslip is termed dihedral effect andis not a static stability in the true sense of the word. An airplane is said to have stabledihedral effect if a negative rolling moment (left wing down) is created as a result ofpositive sideslip. The dihedral stability is the ability of the aircraft to recover from aroll without pilot’s intervention. If the wing is tilted upwards from root to tip, it has adihedral. Dihedral is good for Lateral stability.
7. What is meant by dihedral angle?
The dihedral angle is defined as the angle between the plane of each wing andthe horizontal. When the aircraft is unbanked and level. And is positive when wing liesabove horizontal plane. Negative dihedral is used in some aircraft and is known asanhedral. The tilting of the lift vector on each wing, associated with wing dihedral, isresponsible for a minor destabilizing contribution towards the yawing moment due to
yaw. However the contribution is insignificant compared with the effect of wingsweepback.
8. What causes induced drag?
The drag resulting from lift is called induced drag. From the potential theory, itcan be shown that with no circulation about an aerodynamic body the lift is equal tozero. With a finite value of circulation a lift forces results, which in turn produces aninduced drag force. From the classical theory it was impossible to explain theformation of this circulation without the assumption of a viscous fluid in the boundarylayer setting up the circulation.
9. Why does an airplane require a vertical tail or fin? The main contributor to the static directional stability is the vertical tail or fin.
Both the size and arm of the fin determine the directional stability of the aircraft. Thefurther the vertical fin is behind the C.G the more static directional stability theaircraft will have. (This is often called the weather vaning effect, because it works thesame way as a weather vane.).
10. Distinguish between troposphere and stratosphere.
The atmosphere is categorized into different levels or strata , defined inaccordance with the temperature profile and separated by narrow transition zones.We are only interested in the lower two strata, i.e. the troposphere & stratosphere .
. c o 1. What is operating principle of jet engine?
Air is collected and accelerated rearwards to a high velocity and the reaction dueto this is transmitted to the aircraft as a forward thrust
2. What is the difference between propeller propulsion and jet propulsion?
Both are forms of reaction propulsion but jet engine produces its thrust byaccelerating small amount of air at high velocity & the propeller moves large mass ofair at low velocity
3. The important parts of an airplane
• Wings• Fuselage• Empennage• Landing Gears• Control Surface• Engines
• Weather conditions vary around the globe, from day to day.• Taking all these variations into design is impractical.• A standard atmosphere is therefore defined, that relates fight tests, wind tunnel
tests and general airplane design to a common reference. This common reference is called a “standard” atmosphere
21. Two forms of Powered Controls
• Servo-assisted – Hydraulic pressure transmitted to servo actuator which assists
mechanical linkage to move surface. – Linkage still available if power is lost but system then very heavy to
operate.• Fully power-operated
– Control signals transmitted hydraulically, electrically (fly-by-wire) oroptically (fly-by-light).
22. AIRCRAFT INSTRUMENTS
Flight instruments Engine instruments Navigation and communication instruments
