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Rakovnické minimakety 2024


Pohár Jiřího Merty 2024

Rapier L1 - measuring the thrust

Some time ago one could read on internet web forums that “rapiers are not what they used to be”. I’m new in the category, but as I’m distorted by my scientific professions, I was thinking of measuring the thrust of the motors.

First, unsuccesful, attempt to measure motor thrust with amateur equipment

First attempt

Stand with attached motor

Stand with L1

Unfiltered record of single motor thrust measurement

Unfiltered record of
single L1

The first idea was clear. Put the motor into ply test bed, put the test bed into the scales, fire the motor and see what thrust we got. As I have a pharmacy in the house I live in, I asked them for precise scales and made an experiment. Photo of it is unclear, but gives the idea. The test was successful only by firing the motor. The thrust seemed to be so irregular that I could not really read any reasonable value. Therefore I decided to get the complete record of the thrust course.

I asked my colleagues, the measuring gods, and we got measuring stand together. Force sensor HBM DFS2 together with Multi-Channel Electronic PC Measurement Unit Spider 8 (also by HBM) and ordinary notebook. I would like to thank guess who ? HBM company for the equipment. Sampling frequency was set to 100Hz. We put the stand into the smoking area, opened the window and made the first attempts. But the slow-match burned out and the motor did not ignite. I used other motors, but the result was the same, finally one light up and we got the first measurement. The next day I brought another box of Rapier L1 and we repeated the experiment. This time we got 4 motors running, results are in the graph below.

First graph shows the raw data - thrust of the first motor (first box). You can see that the thrust is irregular and is of an interesting shape. The deflection below zero is given by the loss of weight of burned motor.

Second graph shows all the thrust courses together. All data are filtered by the floating average filter. You can see that the motor from the first box does have different course shape compared to the others, which are not regular, but somewhat similar.

Results of thrust measurement for five Rapier L1 motors

Results of thrust measurement for five Rapier L1 motors

Average thrust and time of burning roughly corresponds to the manufacturer data. The thrust is irregular, all we can do is to measure it, but hey, what else can we do.

Author: Ruja