NAR HPR Aerodynamics & Stability 3

Question 1

During motor burn, propellant mass is consumed from the rear of the rocket. How does this typically affect the stability margin?

Accepted Answer

Stability margin decreases as the CG moves rearward toward the CP

Answer

As propellant burns, the CG migrates aft toward the empty motor casing, reducing the distance between CG and CP and decreasing stability margin.

Question 2

What is 'roll resonance' in high-power rocketry, and why is it dangerous?

Accepted Answer

When induced roll rate matches the rocket's natural pitch/yaw frequency, causing divergent oscillations

Answer

Roll resonance occurs when a spinning rocket's roll rate matches its pitch/yaw natural frequency, causing small disturbances to amplify into catastrophic instability.

Question 3

How does supersonic flight change the location of a rocket's Center of Pressure compared to subsonic flight?

Accepted Answer

The CP moves significantly forward at supersonic speeds

Answer

At supersonic speeds, the CP shifts forward due to changes in the pressure distribution over fins and body, which can dramatically reduce stability margin.

Question 4

What is the recommended minimum static margin for a high-power rocket under NAR guidelines?

Accepted Answer

1 caliber

Answer

NAR and most rocketry authorities recommend a minimum static margin of 1 caliber (one body diameter) for stable flight.

Question 5

Which simulation software is most commonly used by NAR-certified flyers to predict CP location?

Accepted Answer

OpenRocket or RASAero

Answer

OpenRocket and RASAero are the standard free tools used by NAR flyers to model rocket stability, CP, CG, and predicted flight performance.

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

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

NAR HPR Aerodynamics & Stability 3