Lab 06: Rocket Thrust Measurement

Lab Overview

Course: AE 417 – Aerospace Structures and Instrumentation Laboratory (David Sypeck / Reshma Kubsad) | December 3, 2025
Objective: Build and calibrate a strain-gage cantilever beam load cell, then use it to measure thrust-time profiles for five Estes solid rocket motors and compare extracted propulsion parameters against manufacturer specifications.
Motors tested: A8-3, B4-4, C6-5, C11-0, E16-4 (Estes black-powder solid rocket motors)
Instrumentation: Aluminum cantilever beam with half-bridge strain-gage load cell, digital strain indicator, TracerDAQ data acquisition software, calibration masses (1, 2, 3 kg), hose clamp motor mount, STP oil damping fluid
Test location: Outdoors; data acquisition under a canopy tent with the motor nozzle pointed downward into a fire-safe deflector container

Outdoor test setup — equipment cart (Fig. 6)

Cantilever beam and calibration masses (Fig. 3)

Estes solid rocket motors A-through-E class (Fig. 5)

Calibration & Methodology

Before live fire testing, the beam was statically calibrated by hanging known masses (1 kg, 2 kg, 3 kg) from the motor clamp end and recording the stable voltage plateau at each load. A linear fit to the four voltage-force pairs (including zero) produced the calibration equation:

F = 32.931 × V − 40.732

This equation was applied to all subsequent voltage-time recordings to convert them to thrust-time curves. Each motor was mounted with the nozzle pointing downward, an igniter inserted and secured with the correct color-coded plug, and the launch controller armed. Data acquisition was started ≈3 seconds before ignition to capture the baseline. Total impulse was computed by trapezoidal integration of the thrust-time curve; average thrust followed as I_t / t_b.

Voltage vs Time — calibration (Fig. 8)

Force vs Time — calibration (Fig. 13)

Rocket igniters and color-coded plugs (Fig. 4)

Results & Analysis

All five motors produced thrust-time profiles consistent with black-powder solid rocket behavior: an initial ignition surge, a sustained thrust plateau, and a sharp burnout. The C6-5 motor was selected for detailed analysis and comparison against Estes published specifications.

Parameter	Measured	Estes Spec	% Difference
Peak thrust (N)	13.55	15.3	12.1%
Burn time (s)	2.1	1.6	27.0%
Total impulse (N·s)	8.53	10.0	15.9%
Delay time (s)	4.8	5.0	4.1%
Average thrust (N)	4.6	—	—

The 27% burn time deviation is the largest discrepancy and is attributed to ignition delays, beam damping, and hobby-grade motor manufacturing tolerances. The higher impulse class motors (C11-0, E16-4) produced peak thrusts of ≈30 N and ≈30 N respectively, with distinctive sharp ignition spikes visible in their voltage-time profiles.

Thrust vs Time — C6-5 (Fig. 17)

Thrust vs Time — E16-4 (Fig. 15)

Thrust vs Time — B4-4 (Fig. 14)

Data Processing

TracerDAQ acquired voltage-time CSV files at a fixed sample rate. The calibration equation converted all voltage readings to force; the pre-ignition baseline was subtracted to zero the thrust axis. Total impulse was computed by numerical integration (trapezoidal rule) and average thrust by dividing by burn time. Below is a representative processing outline; full TracerDAQ data files to be embedded here.

% Calibration: voltage to force linear fit
% Known masses: 0, 1, 2, 3 kg → forces: 0, -9.81, -19.62, -29.43 N
% Measured voltages: 1.243, 0.940, 0.640, 0.352 V
F = 32.931 * V - 40.732;   % calibration equation

% Subtract pre-ignition baseline, zero thrust axis
baseline = mean(F(1:pre_ignition_samples));
Thrust = F - baseline;

% Total impulse via trapezoidal integration
It = trapz(time(burn_start:burn_end), Thrust(burn_start:burn_end));

% Average thrust
t_b  = time(burn_end) - time(burn_start);   % burn duration
F_avg = It / t_b;

TracerDAQ CSV data — all five motors

Calibration curve — voltage to force

C6-5 thrust parameters vs Estes spec