CH4: Aircraft Operating Envelopes

Question 1

What is the cause of “buffet” on an aircraft?

Answer 1

Turbulent airflow separation interacting with the fuselage and control surfaces.

Fundamentals of Aircraft and Airship Design, Nicolai, Pg. 103

Question 2

True or False
Buffet proceeds stall and is more noticeable at higher speeds.

Answer 2

True

Fundamentals of Aircraft and Airship Design, Nicolai, Pg. 103

Question 3

The aircraft’s maximum thrust occurs when what two quantities are equal?

Answer 3

Thrust available and thrust required.

Fundamentals of Aircraft and Airship Design, Nicolai, Pg. 104

Question 4

True or False
The maximum dynamic pressure limit for an aircraft is an aerodynamic limitation.

Answer 4

False. It is calculated using aerodynamic theory, however, it is a structural limitation.

Fundamentals of Aircraft and Airship Design, Nicolai, Pg. 104

Question 5

Explain why large dynamic pressures result in structural problems.

Answer 5

Large dynamic pressures result in flow instabilities which can cause flow separation. The turbulent separated flow interacts with the fuselage and control surfaces creating a resonant feedback loop that builds in amplitude. If the loop is not broken, structural failure can occur.

Fundamentals of Aircraft and Airship Design, Nicolai, Pg. 104

Wikapedia-Aeroelasticity

Question 6

What are some advantages to designing an aircraft that can operate at large dynamic pressures?

Answer 6

The aircraft can fly faster at lower altitudes. This is an important design point for military aircraft.

Fundamentals of Aircraft and Airship Design, Nicolai, Pg. 104

Question 7

What are the drawbacks of designing an aircraft to accommodate large dynamic pressures?

Answer 7

Designing an aircraft to withstand high dynamic pressures results in heavier fuselage structures. This significantly increases the total weight of the aircraft.

Fundamentals of Aircraft and Airship Design, Nicolai, Pg. 104

Question 8

In terms of aerothermal heating, what two locations on the aircraft are of primary concern?

Answer 8

The stagnation points and the lower surface.

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Question 9

What section of the FARs is concerned with aircraft noise?

Answer 9

FAR 36

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Question 10

What are the two primary characteristics when choosing an aircraft engine?

Answer 10

Thrust per engine weight and specific fuel consumption.

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