Part 8, 15 April, 2006
By Mark Uitendaal and Leon Krancher

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Disclaimer: all liability waved! The contents of this page is presented for informational purposes only. Do not try to recreate any experiments presented in this page. The NAVRO and the author of this article cannot assume responsibility for any use readers make of this information. In The Netherlands it is forbidden by law to own this type of propellant if you do not have an exemption of the "Wet Explosieven Civiel Gebruik" (WECG).

Motor test in Dordrecht

Finally, a thrust curve! On 19 February we tested in Dordrecht with other members of NAVRO. The test site is a field that is used by a Scouting group. Ironically the Scouting group is called "Van Speyk", after a Dutch naval hero, who rather blew up himself and his ship than surrender himself to the enemy. Luckily these are more peaceful times!

After a very relaxed set up of our experiments we inserted the booster motor in the booster fairing. The reason that the motor was tested this way is that we can also test the thrust disk, interstage connector and thermal aspects of the whole motor and fairing combination. The booster was attached to the test bench and the igniters where connected to our launch box.

After some other preparations the bench was ready for the test, and everything was ready for the test.

After the ignition signal the distinctive plop sound was heard and after one second the motor roared to life. The motor kept emitting smoke for over 5 seconds although the last second it wasn't under pressure. After a quick check it we concluded that the motor was still structurally sound and everything was OK! No leakage and the booster fairing is still ready for flight.

Then it was time for the next test. This test was conducted by the Alblasserdam team of NAVRO. The motor hesitated a bit and then came to full pressure. The sound was really overwhelming and probably much louder than our own booster motor! I guessed that the motor burned for 6 or 7 seconds before tailing of.

After this test it was time for our J420-SG. This motor is a derivative of our reliable J420-SB motor but with a different grain configuration. The motor is extended with a smoke grain to reduce the air resistance when the Spectre IIb is coasting upwards. The sound of this motor was dwarfed by his two big predecessors.

After the test we went home for data analysing. The data was recorded by a digital DV camera. After picking 30 data points and put them into our spreadsheet the following to figure occurred:

To calculate the total impulse of the two motor I used the Rhiemansum method to calculate the total integral. The total impulse of the booster motor turned out to be 1956Ns. This is somewhat lower than the anticipated 2000Ns. Also our J420-SG motor performed lower than expected: 640Ns against 670Ns in the previous test. Probably it has something to do with the crappy weather when we casted the grains. Actually, it was snowing when we casted this batch.

Now for the big question: Is this motor suited to fly? After several simulations with this thrust curve with RockSim we calculated the tower exit velocity will be 20.5m/s. Just enough to be certified by NAVRO. We hope that the weather will be good and the winds calm at the 28 April.

Next stop: The launch!

The end of a project

The Spectre II was launched at NLD23, but not very successful. Read more about the conclusions of the Spectre II project and it's follow-on project: the Quick and Dirty.

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