Ask advice from an expert: improving fiberglass manufacturing

Two events were scheduled for today. The first was a static test of the N-2 rocket motor. In the previous test, the nozzle could not withstand the pressure increase and popped out, so two improvements were made to the test: the groove depth was increased and the snap ring was doubled.

Members keeping their distance from the test apparatus.

As it turns out, today’s test was not conducted. The reason was that there was a problem with the igniter. Since we had not prepared a spare igniter, we had to conduct two tests including this motor in the next test.

In the afternoon, we invited a fiberglass expert to JKUAT to teach us how to fabricate fiberglass airframes. He had originally worked for vehicle industry, where he learned fiberglass manufacturing.

When we showed them the tools we were using, he gave us the following advice immediately.

  1. Use a Fiber cloth (for the outer layer) or Tissue mat (for the inner layer) instead of a Glass mat
  2. Use a 2-inch paintbrush instead of a roller
  3. Use epoxy resin instead of polyester resin
  4. Use mirror graze polish (looks like vaseline) when removing from the mold
  5. Use aluminum for body tube molds, not PVC resin
  6. Use gelcoat for the final layer

The students, who had been engaged in fiberglass production by trial and error, listened to the opinions of the professional.

Students receiving manufacturing instruction. A bucket of water is always prepared for emergencies.
First, apply the releasing agent to the mold
The hardener mixture should be varied depending on the layer. The inner layer should have less hardener (takes longer to cure), and as it gets closer to the final layer, more hardener (cures faster). Specifically, for the inner layer, use 1/4 capful of hardener to 350 ml of resin. In the final layer, use 1 capful per 350 ml of resin.
Remove air bubbles by pressing down with a brush. Work quickly.
Glass mat is made of two layers, like tissue paper, and can be separated into individual sheets. In the production of this body tube, the first layer was for one sheet, the second layer was for two sheets (full), and the third and final layer was for two sheets (full).

Today was also a day of progress for all teams, as the boards ordered from JLCPCB arrived.

Flight control team’s board
Avionics team’s board

11. November 2022
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Communication test between flight computer and ground station

Today, the avionics team was conducting a communication test of the ground station at JKUAT’s farm.

During setup
Flight computer mounted in avionics bay
The two in the foreground are quite good at programming
Dashboard. Real-time sensor information and video are displayed.
Verify that dashboard values have been updated
Transport flight computer farther on foot
Sensor data could be received at a distance of about 920 m. Video images were limited to a distance of about 500 m.
Dashboard screenshot

09. November 2022
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N-2 rocket body fabrication

Today the airframe team was building the fiberglass rocket body.

First, a sheet of polyethylene is wrapped around the PVC tubes (one 56 mm and two 75 mm) that will serve as the mold. This was done to make it easier to pull the cured fiberglass out of the mold. The students initially used polyethylene sheets, but the wrinkles in the polyethylene sheets adversely affected the dimensions of the final product, so they explored other methods (such as using a cling film). In the end, none of the methods worked, and they came back to the first method.

The black part is polyethylene sheet
Resins to be used
Curing is accelerated when the catalyst is mixed with the resin. The color changes from blue to light blue.
Homemade platform
Wrap the glass mat around the PVC tube mold 3 times, apply resin and let it cure
Bubbles are present. Room for improvement.

07. November 2022
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Improvement of solid motors and testing of recovery mechanisms

I have previously blogged about the N-2 rocket’s improved solid motors.

Since the aluminum combustion chamber melted in the recent test, the static test had to be conducted with the combustion chamber changed to mild steel. I was just in Japan on a business trip, but under the supervision of my colleague, the students were able to successfully conduct the test.

In the video above, the test stand is plodding along, and this was caused by the bulkhead coming loose from the rocket motor. The bulkhead came off because the groove in the combustion chamber that stops the snap ring to secure the bulkhead was too shallow. The following test was conducted to improve on this point.

The thrust curve is shown below, with a peak thrust of 514 N recorded. This time, the nozzle, not the bulkhead, was ejected, resulting in a rapid pressure drop. Next, the nozzle side was also tested with a deeper groove in the snap ring.

Thrust curve
Ejected nozzle
It was a wonderful growth that everyone was wearing safety goggles properly

Now, in addition to the improvement of the solid motor, another important thing is the recovery mechanism, i.e., the recovery of the rocket by parachute. Unfortunately, the recovery by parachute has not been successful so far, and it is a long-cherished goal to achieve it in the next launch of the N-2 rocket. The ejection of the nosecone uses pyrotechnics, specifically an explosive called crimson powder.

Preparation for nose cone separation experiment
Nose cone separation test (failure)
Nose cone separation test (success)

In addition, to test the control program (state machine) implemented in the flight controller, the team built a water rocket for the experiment.

Attach circuit to water rocket
Appearance of water rocket
Water rocket launch (failure)

Water rocket launch (success)

Water rocket launch (success)

02. November 2022
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Visiting Japan with JKUAT Students

I visited Japan with 10 JKUAT students and 5 JKUAT faculty members. The students were invited by the Tokyo City University as part of an exchange program called Sakura Science, which is implemented by the Japan Science and Technology Agency (JST). The students stayed in a laboratory working on robot and drone control, and conducted experiments in a research environment that they could not experience in Kenya.

JKUAT students working on drone experiments
Visit to JAXA ISAS with JKUAT faculty members
Eagerly searching for electronic parts at Akizuki Denshi at Akihabara
Students being briefed at SUSUBOX Akihabara office
At Suitengu

31. October 2022
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