Nehru Institute of Technology Department of Aeronautical Engineering AE3301 Elements of Aeronautical Engineering Anna university Question Bank UNIT II and III PART A 1 What are secondary control surfaces Ans Trimming and balance controls Trim Tabs Trimming Tail Plane and Control Horn are called as secondary control surfaces as these surfaces are small control surfaces and hinged to form a part of main control surfaces 2 Define biplane interference Ans The reason for biplanes are less efficient aerodynamically is less of a factor and can be minimized with proper design but it s still there And it s just basically that the wings interfere with each other Wings don t just affect the air in their immediate vicinity they deflect the air for a decent ways above and below them So if you have wings stacked they ll interfere with each other in that way or Each wing negatively interferes with the aerodynamics of the other For a given wing area the biplane produces more drag and less lift than a monoplane which is called as biplane interference This is the main disadvantages of biplane 3 Define Aerodynamic centre Ans The aerodynamic center is the point at which the pitching moment coefficient for the airfoil does not vary with lift coefficient i e angle of attack so this choice makes analysis simpler where CL is the aircraft lift coefficient Or If the pitching moment at each point is calculated for each values of CL one special point is found for which the CM is constant independent of the lift coefficient This point is called aerodynamic centre At subsonic speed the aerodynamic centre is of the chord from the leading edge 4 Explain the term Empennage Ans The EMPENNAGE sometimes called the tail feathers is the tail assembly consisting of the horizontal stabilizer the elevators the vertical stabilizer and the rudder 5 What is tropopause Ans The tropopause is a transition layer between the troposphere and the stratosphere It is not uniformly thick and it is not continuous from the equator to the poles In each hemisphere the existence of agreed upon one in the subtropical latitudes They overlap each other where they meet The tropopause is characterized by little or no change latitudes one in middle latitudes and one in sub polar tropopauses generally distinct three is in temperature with increasing altitude The composition of gases is about the same as that for the troposphere However water vapour is found only in very minute quantities at the tropopause and above it 6 What is stratopause Ans The stratopause is the top of the stratosphere or is a transition layer between mesosphere and stratosphere It is the zone marking another reversal with increasing altitude temperature begins to decrease with height 7 Define Troposphere and temperature lapse rate Ans The troposphere is the layer of enveloping Earth immediately above Earth s surface It is approximately 5 1 2 miles 29 000 ft or 9 kin thick over the poles about 7 1 2 miles 40 000 ft or 12 5 kin thick in the mid latitudes and about 11 miles 61 000 ft or 19 kin thick over the Equator The figures for thickness are average figures they change somewhat from day to day and from season to season air The temperature of the troposphere generally decreases as altitude increases The rate at which the temperature decreases dT dz is called the Environmental or Lapse Rate ELR Also it is known as temperature lapse rate The ELR is nothing more the difference in temperature between the surface and the tropopause divided by the height The reason for this temperature difference is the absorption of the suns energy occurs at the ground which heats the lower levels of the atmosphere and the radiation of heat occurs at the top of the atmosphere cooling the earth this process maintaining the overall heat balance of the earth 8 Define international standard atmosphere ISA and explain its significance Ans The variation that exists in the conditions e g temperature pressure and density of the atmosphere Since it is true to say that the whole performance of the engine the aeroplane and propeller is dependant on these three factors it will be obvious that the actual performance of an aeroplane does not give a true basis of comparison with other aeroplane and for this reason an International Standard Atmosphere has been adopted If now the actual performance of a certain aeroplane is measured under certain conditions of temperature pressure and density it is possible to deduce what would have been performance under the conditions of standard atmosphere and thus any aeroplane tested any where can be compared after reducing results to the atmospheric conditions This is particularly important where such things are height records are concerned Although there may never be a day when the conditions of the atmosphere all the day up are exactly the same There do serve as a standard of comparing the performance of aircraft 9 What are high lift devices What has prompted their development Ans The high lift devices are Flaps Slats and Slots These devices are used on aircraft where the lift consideration is more than the speed consideration or when the aircraft has to carry more loads E g Transport category aircraft The high lift devices are present in the leading edge and trailing edge of the wing The following are the characteristics of high lift devices High thickness to chord ratio Pronounced camber A well round leading edge Maximum thickness of camber is about 25 30 on the chord line aft of the leading edge NB the following points are given for your understanding purpose Flaps The most common high lift device is the flap a movable portion of the wing that can be lowered into the airflow to produce extra lift Their purpose is to re shape the wing section into one that has more camber Flaps are usually located on the trailing edge of a wing while leading edge flaps are occasionally used as well Some flap designs also increase the wing chord when deployed increasing the wing area to help produce more lift such complex flap arrangements are found on many modern aircraft The first travelling flaps that moved rearward were starting to be used just before World War II and have been followed by increasingly complex systems made up of several parts with gaps in between known as slotted flaps Large modern airliners make use of triple slotted flaps to produce the massive lift required during takeoff Slats and slots Leading edge slats Leading edge slot Another common high lift device is