By Benjamin Wilkosz
Part 7, 9 October, 2007

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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).

Terminal Velocity – Post Flight Analysis

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The Terminal Velocity it's before launch.

1st of June – Despite the weather forecast, the weather conditions were ideal for testing the Terminal Velocity. A clear sky with only little wind was necessary to ensure a safe high altitude flight and to ensure the rocket would land within the allowed area. Small adjustments to the drogue chute were made to meet the time requirements of the flight with the expected wind profile.

Because the electronics were double checked and full-scale tests of the parachute system were successful, I did not expect any problems. The preparation of the rocket went smooth, except for one incident. After installing the Avalon 8 motor, the E-Bay and the drogue chute, Erik Dekker and I (Erik was so kind to assist me during the preparations) noticed a strange beep. One of the Trax-Arts started to beep hysterically. In a shock reaction I checked if all the arm switches were deactivated. Since Erik and I could recognize the signal, we deinstalled the E-Bay and contacted the developer of the Trax-Art, Mr. Dekker. After a small discussion we restarted the Trax-Art. This was the quickest option and the only realistic option due to the tight flight schedule that day. I could not risk the whole rocket by deactivating the drogue chute back-up. The second time we installed the E-Bay and the chutes everything went exactly according to plan.

12:30 – The Terminal Velocity stood on the launch pad, ready for its maiden flight. Everything looked just fine. All systems (Trax-Arts, R-DAS, camera and beacon) gave a positive self diagnostic, meaning all the batteries were ok, the igniters were connected correctly and the video signal was transmitted. After a swift evacuation of the launch pad (the effective transmitting time of the video system was approx. 10 minutes, due to the 800mW transmitter) we were forced to cancel the flight for a further 30 minutes. Two F-16 fighter planes crossed the flight pad of the rocket. It was an awesome sight to see the F-16 scratching the horizon, only 200 meters from the launch pad! During the new launch window we reactivated all the systems and the Terminal Velocity was good to go...

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Jan Willem van Susante installs the receiver disk.

Together with Jan Willem van Susante, a good friend of mine, I sat in the grass, approx. 300 meters from the tower. We installed the receiver disk on a small hill and had a beautiful sight on the area. My girlfriend, Jolijn Harmsen, stood at the launch control, ready to push the button.

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The launch.

5..4..3..2..1..Launch! The motor roared to life with no time to waste! The Terminal Velocity left the tower with amazing speed. The Avalon 8 was giving everything to proof itself. After just a second disaster struck. A bang could be heard and a small smoke plume revealed something went terribly wrong. Small parts were separated from the rocket, falling back to earth. My first thought was a motor malfunction but the rocket flew straight on, with an amazing, almost frightening (for me as its designer) acceleration. At that moment, I did not understand what happened, but the rocket kept going on into the blue... To optimize the receiving, we had installed the receiver disk orthogonal to the parabolic path flown by the rocket. It was very impressive to see the rocket flight from this angle!

Once apogee was reached, after approximately 30 seconds, a whistling sound frightened me. A ballistic recovery was imminent, ended by a deep bang.

Disappointed we cut off the power to the camera and receiver before walking back in the direction of the launch tower to get back to the launch control. As we reached the tower, some members of the NAVRO, standing at the tower, started to wave... I should come as quick as possible... something interesting was found. I started to run and as I reached them, I recognized the chutes and the paintwork. They found the whole upper part of the rocket! Except for the booster, everything was laying in the sand, just 20 meters from the tower! After deactivating the systems I discovered an "inconvenient truth". The drogue chute backup charge was ignited... just after the start. The high drag ripped the drogue chute apart and the cable connecting the booster (1000kg static load) with the upper part was ruptured! Despite the huge forces during this violent separation, the smoke trail only showed a small change in flight path during flight. The upper part of the rocket had not parachuted at all, but suffered only minor damage.

Screen captures

After disassembling the E-Bay, the acceleration forces could be seen. All the elements on the Trax-Art and R-DAS were swept to one direction, a sight I can only describe as a small village swept by a shock wave of an atomic detonation. The 9V accumulators were deformed and an arm switch broke under the acceleration force of a 10 gram accumulator! Strange thing happen at high speeds...

The exact cause of the problem needs more investigation. Also the reason why all the other systems did not fire is unclear. Was the launch detected by the other Trax-Art or R-DAS? Was the minimum altitude of 200 meter to activate the R-DAS igniters reached by the upper part? A detailed inspection of video material, flight computers and the suspected Trax-Art will perhaps reveal what went wrong during these hectic seconds.

Despite intensive search efforts the booster section was not found. Unfortunately the Avalon 8 is lost on its first flight. Nevertheless the motor proved its potential to launch large rockets with high accelerations. An analysis of the flight data will follow soon.

A new Avalon 8 motor will be manufactured. This time a few adjustment will be made to ensure the motor has an absolute maximum impulse to volume and impulse to mass ratio (for a KNO3/Sorbital motor). The new Avalon 8+ will deliver 3400Ns at 900N (averaged), with 10% more propellant and a 28% higher Kn as its predecessor, the Avalon 8... pushing it to its limits.

Benjamin Wilkosz

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