NAR HPR Rocket Design & Aerodynamics 2

Question 1

What is the primary purpose of a boat-tail transition on a high-power rocket?

Accepted Answer

To reduce base drag by smoothing airflow at the aft end

Answer

A boat-tail transition tapers the aft body diameter inward, which reduces turbulent wake and lowers base drag.

Question 2

A rocket's center of pressure (CP) is determined primarily by:

Accepted Answer

The geometry of the rocket's external surfaces exposed to airflow

Answer

CP is a function of the rocket's external aerodynamic geometry — fin area, nose cone shape, and body diameter — not internal mass.

Question 3

Which nose cone profile generally produces the lowest drag at supersonic speeds?

Accepted Answer

Von Kármán (Haack series)

Answer

The Von Kármán (LD-Haack) nose cone is mathematically optimized to minimize wave drag at supersonic velocities.

Question 4

If you increase fin span while keeping fin area constant, what is the expected effect on stability margin?

Accepted Answer

Stability margin decreases because CP moves forward

Answer

Longer, narrower fins move the CP forward relative to short wide fins of equal area, reducing stability margin.

Question 5

What phenomenon causes fin flutter, and at what flight regime is it most dangerous?

Accepted Answer

Aerodynamic resonance where airflow oscillations match fin natural frequency, worst near transonic speeds

Answer

Fin flutter occurs when aerodynamic forcing frequency matches the fin's structural resonant frequency, typically most severe in the transonic regime.

(NAR HPR) NAR High-Power Rocketry Certification Practice Test