Part 2, 16 April, 2007
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).

Finally a test day! On 4 March we completed the instrumented tests of the booster and upper stage motors of the Quick and Dirty project. These motors are considerably different from our previous motors, since the casing is constructed of glass fibre reinforced plastic. Both motors were tested on our analogue static test bench at the club house of the Scouting club "Van Speijk".

This construction method saves a lot of weight! The burnout weight of the booster motor is almost half of the burnout weight of our previous booster motor of the Spectre IIb and has more than 15% more impulse! The sustainer motor of the upper stage is not optimized and therefore the total impulse and the burnout-weight are in the same order of magnitude as its previous PVC counterpart. This is not a problem because of altitude restrictions.

The booster motor is specially designed to produce a neutral thrust during a relative long duration (±3.5 sec). Also the start up time of this motor is kept extremely short, because half of the grains are painted with rapid ignition primer on their complete burning-surface.

The booster motor was closed with a plastic cap in the nozzle, which keeps the motor free of the moisture of the open air. This cap also provides support for the igniter when the motor is "nozzle down" in the rocket. The thrust-up of this motor was fairly good, as can be seen in the thrust-diagram. The thrust itself behaved as predicted: slightly regressive.

When the motor was silent again, the nozzle was so hot that it melted its way down into the soft thermal-liner. This is a strange sight, since it looks like the motor is equipped with some sort of thrust-vectoring, but it isn't (sadly).

After the burn, the motor produced some unintended smoke because of the melting and burning of the O-rings in the nozzle. This is nothing to worry about, since this happens only after the motor is burned out. But this could become a problem with motors with longer burn time.

The sustainer motor is a 580 Ns motor with tracking smoke, basically a slimmed down version of the upper stage motor of the Spectre IIb. The motor is just for this project and is not intended to be developed further. Probably there will be some development in this diameter, but this will be a motor in a higher impulse class, but this was for this project not feasible due to altitude and time restrictions.

The motors performed as predicted. All results are within 5% of the simulations. Both motor casings had no leakage.

The booster section itself is also almost finished. The coupler and the fins are completed and ready for assembly. The coupler is reinforced with glass fibre. This was applied on the inside of the coupler to ensure stiffness.

The fins are attached with epoxy to the fuselage. A fillet will be applied to ensure stiffness and strength. The fins of the booster are rounded on the leading edge to reduce drag and to delay flow-separation on high angles of attack. Of course high angles of attack are usually not common in rocketry, but since the flight of the Spectre IIb we are prepared for the worst case scenario.

Next part: Quick and Dirty, part 3, 20 August, 2007

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