Module 00: The Basics - Parts of a Model Rocket

How model rocketry works from NC rocketry site

What is the function of a nose cone in a rocket?

It splits the oncoming air so the rocket is not shoving a flat disc through the atmosphere. Its shape sets a big share of your total drag, and on most low-power rockets it is also the part that pops off at ejection to let the parachute out.

Where do you add ballast in a rocket?

In the nose cone to pull the center of gravity (CG) forward.

What can happen if the nose cone is too light?

The center of gravity (CG) sits too far aft, causing the rocket to become unstable.

What can happen if the nose cone is fitted too tightly?

It may not separate, preventing the parachute from deploying and resulting in a ballistic descent.

What is the function of a payload bay in a rocket?

It is the compartment carrying whatever the rocket exists to carry. (For us that is a raw egg in foam). Payload mass sitting forward of the CG actually helps stability — but it is still mass, so it costs altitude.

What can happen if there is loose padding for the egg?

The egg cracks from the deployment jolt, not the landing. That jolt is far more violent than touchdown.

What is the function of the parachute in a rocket?

It's the folded canopy, with flame-proof wadding packed underneath it. The chute is sized so the rocket lands slowly enough to survive but not so slowly that it drifts away.

What is the function of wadding in a rocket?

The wadding is the only thing between hot ejection gas and thin plastic.

What can happen if the parachute is packed too tight?

It never inflates.

What can happen if there's no wadding?

You get a canopy with a melted hole in it, which is nearly the same as no canopy.

What is the function of the shock cord in a rocket?

It's the tether holding the nose cone, body and parachute together after separation. It has to absorb the shock of deployment, so it wants to be long — roughly three times the rocket's length — and either elastic or heat-resistant nylon.

What can happen if the shock cord is too short?

It snaps taut instantly, either breaking or slicing a zipper down the body tube.

What can happen if there's a weak paper mount?

The nose cone simply leaves.

What is the function of the body tube in a rocket?

It's the air frame. It carries every load in the rocket: thrust pushing from the back, drag pushing from the front, and bending loads any time the rocket flies at an angle.

What are the material scales for the power of the body tube?

Kraft paper for low power, fiberglass and carbon for high.

What can happen if the body tube is undersized?

Buckles under thrust or zippers at deployment.

What's wrong if the spiral seams are left unfilled?

They are a small problem but real drag penalty.

What is the function of a launch lug in a rocket?

It's a short tube glued to the side that slides over the launch rod. It holds the rocket's attitude through the first meter of flight, while it is still too slow for the fins to do anything.

What do bigger rockets use instead of a launch lug?

They use rail buttons on an aluminium rail instead.

What can happen if the launch lug is glued on crooked?

The rocket leaves the pad already turning.

What can happen if the launch lug is sized too tight?

It binds on the rod, eating the exit speed you need.

What is the function of centering rings on a rocket?

They are discs of plywood or card that hold the motor tube exactly on the center line inside the body tube, and transfer the motor's thrust out into the air frame.

What can happen if the rings are not square?

It cants the motor. Thrust then does not point down the rocket's axis, and it flies a long lazy banana.

What is the function of the motor mount on a rocket?

It is the internal assembly that holds, aligns, and secures the rocket engine inside the larger body tube. It is made by the motor tube, its centering rings, & some way of stopping the motor moving — a spring-steel engine hook on small rockets, a screw-on retainer on big ones.

What can happen if there's no retention on the motor mount?

The ejection charge fires the motor out the back instead of pushing the nose cone off the front. The chute stays packed.

What is the function of the motor in a rocket?

It's the propellant, delay grain and ejection charge in one sealed package, exhausting through a nozzle at the back. The code on the side tells you total impulse class, average thrust, and the ejection delay in seconds.

What can happen if the motor delay is too short?

The chute comes out at speed.

What can happen if the motor delay is too long?

The rocket is already falling nose-first.

What is the function of the fins in a rocket?

It's the entire stability system. Fins generate a sideways force whenever the rocket is at an angle to the airflow, and because they sit at the very back, that force pulls the center of pressure behind the center of gravity. (Everything in Module 01 is really about fins.)

What can happen if the fins are misaligned?

The rocket rolls hard, bleeding altitude.

What can happen if the fins are too thin or too flexible at high speed?

They flutter and tear off.

What is the function of the igniter in a rocket?

It's a thin bridge-wire coated in pyrogen, pushed up into the motor's nozzle and held there with a plug. The launch controller passes current through it, it flashes, and the propellant lights.

What can happen if the igniter is not pushed all the way to the propellant?

It fires without lighting the motor, which is a misfire.

What should you do if a misfire happens?

Wait a full minute before approaching to make sure there's no delayed ignition hangfire. Then, replace it.