By Benjamin Wilkosz
Part 1, 23 December, 2004
- Terminal Velocity, part 2, 16 February, 2005
- Terminal Velocity, part 3, 27 April, 2005
- Terminal Velocity, part 4, 1 March, 2006
- Terminal Velocity, part 5, 28 April, 2006
- Terminal Velocity, part 6, 12 March, 2007
- Terminal Velocity, part 7, 9 October, 2007
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).
As with my last rocket, the Kerberos, the Terminal Velocity functions as a platform to dynamically test the new Avalon007 rocket motor. So, instead of building a rocket and choosing an motor to lift the rocket, the rocket is build around the motor. To maximize the dynamic loads I chose a minimal diameter construction for this rocket.
The fuselage of the rocket is made from 3" phenol tube reinforced with three layers of 160gr/m² glass fibre and the 3mm thick glass fibre fins are reinforced with two layers of 200gr/m² carbon fibre. To minimize the disturbance of the location beacon I use a conventional polymer ogive nose cone.
Because of regulations the Terminal Velocity needs a two stage recovery system. The small drogue chute is ejected at apogee
by a Compact R-DAS flight computer with a Trax-Art timer as a backup. The time for the backup timer is determined by flight
calculations. At 30 seconds into flight a second Trax-Art timer unlocks the main chute compartment. This is an experimental
system, melting a small Dyneema cable to unlock the parachute bay. At 200 metres altitude the R-DAS hopefully will finish the job
by releasing the main chute. All three systems are integrated in one bay, made from glass fibre plates, aluminium flanges and
steel connection materials.
The nose cone contains a small 10mW location beacon, an acoustic beacon and a LED system. The high intensity LED's only blink during the night, functioning as a "last hope" system in cause the rocket isn't found by daylight.
The Avalon007 rocket motor is a 76mm motors, fitting exactly in a 3" tube (ID: 76,2mm). The casing and forward closure are
made from aluminium alloy 6082-T6. The nozzle is made from stainless steel. The motor uses KNO3/dextrose as
Main goals of this motor are high (specific) impulse (approx. 3000Ns), high safety factor and easy to reload. To ensure an easy reload the forward closure and nozzle are fixed with snap rings (DIN472 D70), simultaneously improving mechanical loads on the casing. To boost impulse I strive for an ideal propellant. In order to achieve an almost ideal propellant the KNO3 is dehydrated and grinded. The dextrose is heated, melted and dehydrated at a temperature of 160°C. Next the KNO3 is mixed in using an electronic mixer. After an extended period of mixing the cast pan is closed and the pan is pulled vacuum for 10 minutes. During this vacuum period a small vibrator "lowers the viscosity" of the propellant. The propellant is cast in phenol inliners. These tubes are glued together with resin and two layers of paper/resin and a third layer of aluminium tape function as an extra thermal insulator.
One of the main differences between the Avalon005 (my last motor) and the Avalon007 is the smooth multi-stage nozzle. In order to lower the flow resistance, thereby lowering thermal/mechanical loads on the surface and increasing nozzle efficiency. The nozzle has a multi-stage convergence. Next to it surface roughness is minimized and the ideal average expansion ratio is accurately manufactured.
First test of the Avalon007A was at 't Harde. The test went well but I was aiming for a shorter thrust phase. Therefore I added 10% sucrose to the two first grains. Unexpectedly the Avalon007A (almost explosively) spitted out the 2,2kg of propellant in 1,5 seconds, delivering over 4000N thrust and a damaged casing. The second version, the Avalon007B, used KNO3/dextrose propellant, but was a six grains version with a kn increased 10% to 220. Due to faulty assembly the motor CATO'd. The new Avalon007C is a five grain motor with a kn of 210. As with the first motor the propellant will be KNO3/dextrose. Ignition will be done using a pyrogen and two coated grains. To lower the weight of the motor system, the forward is made from aluminium instead of stainless steel. The stainless steel forward didn't survive the CATO. Also the test bench didn't survive the CATO. A new hydraulic test bench is build for the Avalon007.
New test fires will be undertaken in January 2005. Hopefully the Terminal Velocity rocket will make its first flight in April during NLD21.
Next part: Terminal Velocity, part 2, 16 February, 2005