NAR HPR Rocket Design & Aerodynamics 3

Question 1

What is the 'transonic dip' effect on a rocket's stability margin?

Accepted Answer

CP shifts forward near Mach 1 due to changing aerodynamic coefficients, temporarily reducing stability

Answer

Near Mach 1, the normal force coefficients of fins change, causing CP to migrate forward and temporarily reducing the stability margin.

Question 2

What is the purpose of a drogue parachute in a dual-deployment recovery system?

Accepted Answer

To stabilize the rocket in a nose-down attitude and slow descent from apogee to low altitude before main deployment

Answer

The drogue deploys at apogee to slow the rocket and keep it stable during high-altitude descent before the main parachute opens at lower altitude.

Question 3

Which factor most directly affects the 'weathercocking' tendency of a rocket in a crosswind?

Accepted Answer

Stability margin — higher margin increases weathercocking tendency

Answer

A more stable (higher margin) rocket has a stronger tendency to turn into the wind (weathercock) because its CP is farther aft of CG.

Question 4

When computing stability with Rocksim or OpenRocket, why does the software show two CG positions?

Accepted Answer

One for the loaded (full propellant) configuration and one for the burnout (empty) configuration

Answer

As propellant burns, CG shifts; software shows both full-load CG (launch) and burnout CG to ensure stability throughout the flight.

Question 5

What is 'roll coupling' and why is it a concern for high-power rockets?

Accepted Answer

The tendency for a rolling rocket to develop pitch and yaw oscillations due to gyroscopic effects

Answer

Roll coupling occurs when a spinning rocket's gyroscopic forces couple with pitch/yaw modes, potentially causing violent coning or divergence.

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