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Module 1: Models for Constraint Analysis

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They key points from this module are:
Constraint Analysis: The key task to be done in conceptual design is to identify the requirements that drive the design; Constraint Analysis is used to achieve this.

Typical constraint - Transport Aircraft:
Customer requirements such as Design and Maximum Cruise Mach number.
Climb rate while operating at specified altitudes.
Stalling speed at takeoff and landing
Balanced field length
Service ceiling

Raymer's Big Six Parameters
(1) Wing related parameters:
• Thickness ratio or Thickness to chord ratio (t/c)
• Taper ratio (λ)
• Sweep (ᴧ)
• Aspect ratio (AR)
• Wing loading (W/S)
• Thrust or Power loading (T/W)

The two possible approaches to Constraint Analysis:
Approach one
Estimate W/S from the constraints on Stalling speed, Landing distance, Service ceiling, etc.
Then estimate T/W that you need to meet the other constraints.

Approach two
Estimate W/S from the constraints on Stalling speed, Landing distance, Service ceiling, etc.
Then estimate T/W that you need to meet the other constraints.

Constraint Analysis - Transport Aircraft :

Steps in Lift-to-Drag Ratio (L/D) Calculation in Second Stage Climb
(1) Calculate the Atmospheric parameters during Second Stage Climb (SSC).
(2) Calculate the Mach number in SSC.
(3) Calculate Oswald Efficiency in SSC.
(4) Calculate the induced drag coefficient in SSC.
(5) Calculate the Lift/Drag ratio in SSC.

Steps in Calculating Lift-to-Drag Ratio (L/D) in Missed Approach:
1) Calculate atmospheric parameters during Missed Approach.
(2) Calculate the Mach number of the Aircraft in Missed Approach.
(3) Calculate Oswald Efficiency in Missed Approach.
(4) Calculate the induced drag coefficient in Missed Approach.
(5) Calculate the Lift/Drag ratio in Missed Approach.

Typical Constraints in Military Aircraft - They are classified as Constraint in the Customer and Airworthiness requirements.
(1) Customer requirements:
• Sustained Turn Rate at specified Mach number (M) and Altitude (H).
• Instantaneous Turn Rate at specified W (weight) and Altitude (H).
• Maximum Mach number at specified Altitude (H).
• Specific Excess Power at specified Mach number (M) and Altitude (H).
• Climb Rate while operating at specified Altitude.
• Stalling Speed at specified Weight (W) and Altitude (H).
• Takeoff and Landing Ground Roll.
• Absolute and Combat Ceilings under International Standard Atmosphere (ISA) + X conditions.

(2) Airworthiness requirements:
This refers to the requirements specified by the regulating agencies.
For Military Aircraft, it is easier to use the Master Equation for Constraint Analysis. The Master equation will be used to present the relationship between the Wing Loading (W/S) and Power Loading (T/W) parameters.

The Steps in Refined Sizing:
(1) Finalize the design mission profile.
(2) Assume parameters like Aspect Ratio of the Wing (ARwing), SFCs, Crew Weight (Wcrew) and Payload (Wpay).
(3) Carry out the Initial Sizing of estimates.
(4) Estimate Aerodynamic Efficiency.
(5) Carry out Constraint Analysis.
(6) Carry out Refined Sizing.