# 12. CONSTRUCTING A “THRUSTOMETER”

from Come Fly With Me – Exploring Science through aviation and aerospace concepts.

SUBJECT: Science
GROUP SIZE: Small or Large
TIME: 2-60 minute periods
TYPE OF ACTIVITY: Student Investigation or Teacher Demo.
TEACHING STRATEGY: Expository Guided Discovery
CONCEPTS: Thrust, Power Curve, Action/Reaction
SKILLS: Measurement Interpreting Data Experimentation
Objective: To help students understand the difference in thrust power by constructing a device to measure thrust.

Materials: three 2 x 4’s (for base and swinging arm); one piece of pressed board or plywood for upright; small piece of wood for stopper; 4 brackets; small piece of wood to block front of engine; bolt; 4 washers; 2 nuts; wire; drill; graph paper; bricks; various size model rocket engines.

thrust demonstration setup

detail of rocket

pen trace path

Procedure:

In order to answer questions about how much thrust a particular rocket engine has, the students can construct a device that will measure various engines for model rockets. The first diagram shows what a homemade “thrustometer” looks like. and the second diagram shows how to make one:

Note that the 2 x 4 is free swinging on a bolt fastened securely to the plywood back.
The rocket holder must also be firmly constructed and attached. Look at these sketches and be sure you understand the need for each part of this rocket holder.

Attach a sheet of graph paper and a marker pen to the thrustometer and move the swinging 2 x 4 to see if the pen moved smoothly and if the graph paper is properly placed. When all is ready, attach a small engine securely in the rocket holder and get students a safe distance away. Then field test the thrustometer.
If the 2 x 4 arm doesn’t move, the wood is too heavy for the engines. If it quickly swings to the stopper, then there isn’t enough weight on the arm. What is needed for the arm is an optimum weight so that a small engine will move it a little and a big engine wi11 move it close to the top.

Once you have found the proper weight for the arm, set off several model rocket engines and calibrate the amount of thrust as shown on your graph paper.

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