This set of Aircraft Design Multiple Choice Questions & Answers (MCQs) focuses on “Configuration Layout – Conic Fuselage Development”.
1. The purpose of the longitudinal control lines is __________
a) to connect end points, shoulder points and tangent point of different conic curves
b) to connect tangent points at half distance only of same conic curve
c) only to produce control of lifting lines of same curve
d) to change lifting line slope
Explanation: Longitudinal control lines are used to develop smoothly – lofted fuselage. Longitudinal control lines will connect end points of different conic curves. It is also used to connect different shoulder points and tangent points to respective shoulder points and tangent points of different conic curves.
2. What do you mean by longitudinal control lines?
a) Smooth lines which controls overall shape of the conic cross-section
b) Lines which expands to vertical direction only
c) Lines which go in horizontal direction only
d) Line which can be expanded only in lateral direction
Explanation: Longitudinal control lines are smooth lines through which conic curves are connected. Since, it connects all different conics, it will control the overall shape of the body itself during lofting.
3. Define control station.
a) Original cross-section used for longitudinal control lines
b) Auxiliary lines
c) Conic shape with circle only
d) Elliptic contour only
Explanation: Control stations are original cross section which are used to develop longitudinal lines. Control stations are also known as control cross- section. Control stations can be any type of conic curve. It can be circular, elliptic or any c/s as per our requirement.
4. As a designer we need to design a single engine fighter A/C having circular nozzle exhaust. Most appropriate control station for nozzle exhaust is ____________
a) circle with nozzle exhaust diameter
b) square of circle diameter
d) elliptic shape
Explanation: Control station are the original cross-section which are required to complete the lofting process. Here, our main body is nozzle which has circular cross-section. Hence, original shape required to loft this nozzle will be circular also. Hence, control station should be circle with similar diameter as the nozzle.
5. Following diagram represents _______________
a) cross-section development via longitudinal control lines
b) vertical plane
c) arbitrary body with circle profile only
d) body with elliptic profile only
Explanation: Above diagram is representing the development of a typical cross-section via longitudinal control lines. Lines which are connecting various cross-section is nothing but the longitudinal control line. This diagram is showing either typical plan or side view.
6. Typically, a fuselage is lofted by using 5-10 control station based on requirements of fuselage.
Explanation: Control station or control cross section are used to develop the longitudinal control lines. These control stations are drawn to enclose the different internal components.
7. If distance between shoulder point and tangent point is much higher then, it will produce ____________
a) flat C/S shape
b) circle shape only
c) circle with diameter as distance
d) circle of radius as distance between points
Explanation: Selection of the shoulder point plays vital role in conic curve. If shoulder point is too far from tangent point it will result in flat c/s shape. Similarly, if it is too close it will generate non-flat curve.
Explanation: Above diagram is showing typical conic development. As shown shoulder point s is much near to the tangent point C. Now as a result of this it will generate square or rectangle cross section depending upon distance AC and BC. Hence, correct option will be square.
9. As a designer our task is to generate fuselage through conic lofting method. If an intermediate C/S shape is elliptic then, what should be the appropriate value of conic shape parameter?
Explanation: Given, intermediate cross section = elliptic.
Conic shape parameter CSP = DS / DC, where D = midpoint of line drawn from end point A to end point B, C = tangent point, S = shoulder point.
When CSP = 0.4142 and AC = BC then it will generate circular shape.
Now, when CSP = 0.5 it will produce parabola. Hence, to generate elliptic cross section value of CSP should be between 0.4142 and 0.5 based on our requirement.
Explanation: Given, a parabolic contour.
A parabolic shape has conic shape parameter of 0.5.
Conic shape parameter CSP = |DS|/|DC|
From Pythagorean Theorem, |DC| = 6.24.
Hence, |DS| = CSP*|DC| = 0.5*6.24 = 3.12.
11. Which of the following is correct?
a) Flat wrap technique is cost effective
b) Flat wrap is very costly
c) Flat wrap is not lofting method
d) Flat wrap is very much lift producing
Explanation: Flat wrap method is used for flat surfaces. Complex curvature are required more money to fabricate. If a surface is flat-wrapped then we can directly wrap a flat sheet around its cross section. By doing so we can reduce the cost and hence, it is cost effective.
12. Let’s consider we want to loft fuselage by using flat wrap method then, __________
a) longitudinal control lines must be straight
b) longitudinal control lines must be curved
c) longitudinal lines must be avoided
d) always use cross shape parameter
Explanation: Typically, to use flat wrap method following 2 conditions are required. 1. Longitudinal control lines needs to be straight and 2. Tangent angles of conic should remain constant longitudinally.
Explanation: Above diagram is showing a typical problem during lofting namely, ‘circle to square adapter’. In such cases, designer is required to loft body with different cross-section. For e.g. A nozzle of typical jet is square at inlet but at front face it is circular. Hence, such problems are required to be solved through various techniques of circle to square adapter.
14. What is meant by ’butt-plane 40’?
a) Buttock plane is at a distance of 40 unit from fuselage centerline
b) Buttock plane is at a distance of 20 unit from fuselage centerline
c) Buttock plane is at a distance of 80 from fuselage centerline
d) Buttock plane is at the 40° from fuselage centerline
Explanation: Butt-planes or buttock planes are defined as vertically oriented cuts which are used for fuselage lofting verification. It cuts from the horizontal intersection of the A/C with vertical planes. These planes are defined by their distance from centerline. Hence, butt-plane 40 can be interpreted as butt plane is at distance of 40 unit from aircraft centerline.
15. Buttock-planes are used to __________
a) evaluate the smoothness of A/C fuselage
b) evaluate Lift
c) find lift curve
d) find lift curve slope
Explanation: Buttock planes or butt planes are vertically oriented cuts which can be used to find smoothness of the A/C fuselage. Lift curve slope is found by using lift and AOA. Lift can be estimated by measuring pressure difference between upper and lower surface.
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