NAR HPR Rocket Design & Construction 2 — Questions and Answers
Question 1: What is the primary function of a boat-tail transition on a high-power rocket?
- Increase payload volume
- Reduce base drag by tapering the aft end (Correct answer)
- Provide a mounting point for fins
- Increase stability margin
Correct answer: Reduce base drag by tapering the aft end
A boat-tail reduces base drag by smoothly tapering the rocket's diameter at the aft end, reducing the turbulent wake behind the airframe.
Question 2: When bonding fiberglass airframe sections, which surface preparation step is most critical for joint strength?
- Painting the surface with primer
- Sanding the bonding surfaces and wiping with acetone (Correct answer)
- Heating the fiberglass before bonding
- Applying wax to prevent epoxy from spreading
Correct answer: Sanding the bonding surfaces and wiping with acetone
Sanding creates mechanical tooth for adhesion and wiping with acetone removes oils and contaminants that would prevent a strong epoxy bond.
Question 3: What does a positive pitching moment coefficient (Cm > 0) indicate about a rocket's aerodynamic stability?
- The rocket is statically stable
- The rocket will self-correct after a disturbance
- The rocket is statically unstable (Correct answer)
- The rocket has neutral stability
Correct answer: The rocket is statically unstable
A positive Cm means the aerodynamic moment tends to increase the angle of attack rather than restore it, indicating static instability.
Question 4: What material property is most important when selecting epoxy for a high-power rocket motor mount subject to thermal cycling?
- Low viscosity for easy application
- High glass transition temperature (Tg) (Correct answer)
- Rapid cure time
- Translucent color for inspection
Correct answer: High glass transition temperature (Tg)
High Tg epoxy retains strength at elevated temperatures, which is critical near the motor mount where heat from motor operation is significant.
Question 5: In high-power rocketry, what is the purpose of a thrust plate (or thrust ring) in the motor mount assembly?
- To center the motor in the tube
- To transfer motor thrust directly to the airframe structure (Correct answer)
- To retain the motor during coast phase
- To protect the aft closure from heat
Correct answer: To transfer motor thrust directly to the airframe structure
The thrust plate transfers the compressive thrust load from the motor casing directly to the airframe, preventing the motor tube from bearing all the thrust force alone.
Question 6: Which fin planform shape provides the highest efficiency (lift-to-drag ratio) for supersonic high-power rockets?
- Delta (triangular) fin (Correct answer)
- Elliptical fin
- Clipped delta fin
- Constant chord (rectangular) fin
Correct answer: Delta (triangular) fin
Delta fins have low aspect ratio and sharp leading edges that perform well at supersonic speeds by minimizing wave drag.
Question 7: When designing a dual-deployment recovery system, what is the role of a drogue parachute?
- Deploy at apogee to slow descent to landing speed
- Deploy at apogee to stabilize descent and slow the rocket slightly before main deployment (Correct answer)
- Replace the main parachute if it fails
- Separate the payload from the booster section
Correct answer: Deploy at apogee to stabilize descent and slow the rocket slightly before main deployment
The drogue deploys at apogee to stabilize descent and reduce speed to a safe level for main parachute deployment at lower altitude.
NAR HPR Rocket Design & Construction 2
What is the primary function of a boat-tail transition on a high-power rocket?