JNTU B.Tech IV Year FLIGHT VEHICLE DESIGN Previous Question Paper (October/November - 2020 - R16)

Aircraft design is an iterative process divided into three primary phases: Conceptual Design, Preliminary Design, and Detail Design. The process begins with mission requirements and evolves through increasing levels of fidelity.

The flow of the design process is as follows: Mission Requirements → Conceptual Design → Preliminary Design → Detail Design → Manufacturing & Testing.

1. Conceptual Design: This is the initial phase where the basic configuration, size, and weight of the aircraft are determined. Key activities include trade studies, weight estimation, airfoil selection, and establishing the general arrangement. The goal is to verify if the aircraft can meet the mission requirements within a reasonable cost and weight.
2. Preliminary Design: Once the configuration is frozen, this phase focuses on refining the design. Wind tunnel testing and high-fidelity computational fluid dynamics (CFD) are used to finalize aerodynamic characteristics. Structural layouts, control system integration, and systems architecture are developed in detail. The design is optimized for performance and stability.
3. Detail Design: This is the final phase before production, involving the creation of comprehensive engineering drawings, material specifications, and manufacturing processes. Every individual component, fastener, and system interface is defined. This phase results in the "frozen" design ready for the production line.

These phases are highly iterative; if a design fails to meet performance targets during testing, the process loops back to earlier stages to adjust parameters such as wing loading, thrust-to-weight ratio, or structural materials.

To determine the ratio of take-off fuel weight to take-off total weight, we use the Breguet Range Equation for jet aircraft:

Given data:
Range (R) = 7,900 km = 7,900,000 m
Velocity (V) = 760 kmph = 760 / 3.6 = 211.11 m/s
SFC = 0.018 g/(N·s) = 0.000018 kg/(N·s)
L/D = 16

Substituting these values into the range equation:

Solving for the weight ratio:

The fuel weight (W_f) is the difference between take-off weight and landing weight (W₀ - W₁). The ratio of fuel weight to take-off weight is:

Thus, the ratio of take-off fuel weight to take-off total weight is approximately 0.0412 or 4.12%.