TRA Advanced Study Guide - Technical Questions part 1

Which of Newton’s Laws best describes the behavior of a rocket motor?

• Newton’s First Law: A body continues in its state of rest or of uniform motion in a straight line unless it is compelled to change that state by forces impressed upon it

• Newton’s Second Law: The rate of change of momentum is proportional to the force impressed and is in the same direction as that force

• Newton’s Third Law: To every action there is always an equal and opposite reaction

How does Newton’s Third Law “To every action there is always an equal and opposite reaction” relate to rocketry?

• That the blast deflector must be strong enough to push the rocket off the launch pad at ignition.

• That a rocket flies because the rocket motor “pushes” the rocket in a direction opposite of the exhaust jet.

• That the thrust of a rocket motor is proportional to the air density at the launch site

What are the three forces acting upon a rocket during flight?

• Thrust, rocket diameter and finish

• Nose cone shape, thrust and drag

• Gravity, thrust and aerodynamic drag

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What are the three major factors that determine the maximum altitude of a high-power rocket in vertical flight?

• Lift-off weight, propellant weight and motor thrust

• Fin size, propellant weight and motor thrust

• Motor thrust, rocket weight, and aerodynamic drag

For an inherently stable rocket, which statement about the center of gravity (CG) and the center of pressure (CP) is true?

• The CG must be behind the CP relative to the desired direction of flight

• The CG must be forward of the CP relative to the desired direction of flight

• The CG must move forward (in the desired direction of flight) during the motor burn

A 4" diameter rocket with its motor is determined to have the center of gravity (CG) four inches behind the center of pressure (CP). Is this a rocket likely to be stable?

• No, the CG should be at least two body diameters behind the CP

• No, the CP must be behind the CG for the rocket to be stable

• Yes, the CP is one body diameter in front of the CG

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The center of pressure (CP) of a rocket is generally defined as:

• The balance point of the rocket without the motor

• The total area of the fins, airframe and nose cone divided by two

• The point at which aerodynamic lift on a rocket is centered

What is the “rule-of-thumb” for a stable rocket?

• That the center of gravity should be at least one body diameter in front of the center of pressure

• That the center of gravity should be very nearly at the same point as the center of pressure

• The rocket should balance near or at the center of gravity

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You are at the launch site and decide to fly your rocket on a heavier motor than you simulated it on. Which statement regarding CG is true?

• One can install the motor, recovery system and payload and determine the balance point of the rocket as it is ready for flight

• One can balance the rocket with the motor hardware alone because that is the condition of the rocket after motor burnout

• It is not necessary to test for the center of gravity when using a heavier motor because it has more thrust

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What ordinarily happens to the center of gravity (CG) of a rocket during a solid rocket motor’s thrusting phase?

• The CG stays the same

• The CG shifts forward

• The CG shifts aft

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