By Benjamin & Rafaël Wilkosz
The Kerberos is being built to provide us with a flying test platform for the Avalon 005 motor system and Thiemo's new PaDS. Initially we aimed to break the sound barrier with this rocket, but during construction it turned out to be a little heavier than expected, so reaching Mach 1 is out of the question... That isn't a bad thing if you remember that NAVRO restrictions do not allow us to fly over 2 kilometres!
Avalon 005 Motor System
After a long period of development, with many ups and downs, Benjamin managed to build a proper functioning motor, called Avalon 005. All motors made were fuelled with potassium nitrate/dextrose/sucrose grains. Prototype 001, 002, and 003 were never intended to be used in rockets, just to gain experience in how to build motor systems, casting solid rocket fuels and to study erosive effects. Then Avalon 004 was built. This motor should have powered a rocket but it exploded during the first test run. The nozzle and forward closure however did survive the explosion and were used to construct the Avalon 004 B. Its new motor casing was much shorter. This caused the motor weight to impulse ratio to be less efficient, but this motor worked properly. Therefore Benjamin decided to construct a more efficient motor system; the Avalon 005. This motor already had three successful test runs and the fourth is being scheduled for 8 August, 2003 to measure the exact specifications of this motor. Finally it will run for the last time on 5 September during the flight of Kerberos!
Construction of the fuselage
The body tube consists of a 3-inch phenol tube (this is the smallest available diameter to fit in the Avalon 005 motor system). It is reinforced by laminating multiple layers of carbon cloth over it. The fins are attached to the fuselage by our so-called "fin-block" (see left). The fin-block is produced as follows. A simple cardboard tube is chosen that fits around the motor and inside the 3 inch body tube. The fins are glued to this cardboard tube using CA and epoxy resin. Then cloths of carbon/aramide and glass fibre are being laminated over one side of the fin, the cardboard and one side of another fin. An aluminium ring was inserted into the cardboard tube to prevent it from deforming due to the weight of the moulds and the many clamps used to force the laminate upon the fins. After the epoxy resin has cured, the access material is cut off to regain the original shape of the fins. The glass fibre cloth is laminated over the carbon/kevlar cloth not only for stiffness reasons but also for the fact that aramide fibres are very difficult to cut. Finally sleeves were milled into the body tube and this "fin-block" was glued into the body tube. The nose cone was bought at Caveman Rocketry and is made of glass fibre. Also the parachute bay is a phenol tube laminated with glass fibre. The decision to use glass fibre for the upper parts of the rocket is for the following reason: carbon can shield electromagnetic fields and because our rocket will carry a transmitter on board to gain the rocket back after landing, we thought it would be wise to use another material than carbon. The aluminium ring mentioned above was not only made to prevent deformation of the cardboard tube, but will also be used as the lower centre ring for the Avalon 005 motor.
To minimize weight and size we decided to equip the rocket with a single stage parachute system, for which we were granted permission by Gerben-Jan Ligthart. Normally rockets that fly over one kilometre must have a double staged parachute system. The next problem we encountered, caused by the decision to use a single staged parachute system, was the requirement for the rocket to land within 90 seconds. If one uses a double staged parachute system first a streamer or very small chute will be deployed so it loses altitude very rapidly. The final metres the rocket will be slowed down by a large chute, thus it lands safely. Kerberos will weight about 5,8 kilograms (fully loaded) and the total impulse of the Avalon 005 is about 1400Ns, so it is expected to reach a maximum speed of 830km/h and an altitude of 1500 metres. A simple calculation will teach us the rate of descent must be about 17m/s or 60km/h. To meet this requirement a small (60 centimetre) Roy Brown parachute is chosen to return the rocket "safely" to earth.
During the earlier stages of the Kerberos, we were looking for a flight computer for the Kerberos. We contacted Thiemo van Engelen. Knowing he was developing a new deployment system, and we have seen this systems operating with success, I thought this would be the right flight computer for the Kerberos. But when I informed no PaDS's (Parachute Deployment System) were in stock, but luckily Thiemo offered to fly his upgraded experimental PaDS. This way I had a computer and Thiemo will acquire test results with the new PaDS. The PaDS is a barometric deployment system. Till now, the PaDS didn't measure acceleration. In order to expand the possibilities of the PaDS, Thiemo added this feature. Except for a small acoustic beacon all the electronics are stored in the top of the rocket, the glass fibre nose cone. For the parachute system we use two computers, the PaDS (main) and the Trax-Art. Initially we planned to fly with the PaDS only, but after some consideration we decided to use a Trax-Art to backup the PaDS, since this computer is going to use a experimental new acceleration system. To locate the rocket, we use three systems. Primarily we will search the rocket with a 300mW location beacon, positioned in the top of the nose cone. Once we are near the rocket, an acoustic beacon will guide us to the exact location. In case we don't find the rocket, we installed a "last hope" system, a blinking High Intensity LED system. When darkness covers the landscape, maybe some military personal from the shooting range will "check out the strange lights".
Motor test 8-8-2003
Another successful run of the Avalon 005! (A reliable motor at last!) See for the test results the graph below.