CH5: Takeoff Weight Estimation

Question 1

Define the “fixed weight” of the aircraft.

Answer 1

The fixed weight is the payload (crew, expendable weapons, cargo, etc.)

Fundamentals of Aircraft and Airship Design, Nicolai, Pg. 124

Question 2

Define the aircraft’s “empty weight.”

Answer 2

The weight of the aircraft’s structure, propulsion, subsystems, avionics, instruments, etc.

Fundamentals of Aircraft and Airship Design, Nicolai, Pg. 124

Question 3

What is the weakest part of the conceptual design analysis?

Answer 3

Estimation of the aircraft’s empty weight.

Fundamentals of Aircraft and Airship Design, Nicolai, Pg. 125

Question 4

For a particular mission, how is the fuel fraction calculated?

Answer 4

Calculate the weight fraction for each phase of the mission, then multiply them all together.

Fundamentals of Aircraft and Airship Design, Nicolai, Pg. 126

Question 5

True or False
For a low-performance aircraft (cruise is less than Mach 0.4), the weight of the fuel burned during climb out can usually be ignored when conducting a first-order analysis.

Answer 5

True.

Fundamentals of Aircraft and Airship Design, Nicolai, Pg. 127

Question 6

What is the aircraft growth factor?

Answer 6

The ratio of the change in takeoff gross weight to the change in payload weight.

Fundamentals of Aircraft and Airship Design, Nicolai, Pg. 139

Question 7

As takeoff weight increases (the aircraft gets larger), the empty weight fraction ________.

Answer 7

Decreases

Extra Notes: See Fig. 5.4

Fundamentals of Aircraft and Airship Design, Nicolai, Pg. 139

Question 8

Explain why the empty weight fraction decreases as takeoff weight increases (as the aircraft becomes larger).

Answer 8

1. The structural efficiency of larger vehicles is better.
2. Many aircraft components, such as avionics, hydraulics, etc., do not scale with weight.

Fundamentals of Aircraft and Airship Design, Nicolai, Pg. 140 & 141