To me only two kinds of rockets are worthed to be build:

  • The crowd-pleasers
    • Rockets with long burning motors, very well visible two-stage parachuting, clustered motors, boosters.
    • Nice fantasy models like the TinTin rocket, the flying coke bottle, UFO's, etc.
  • Rockets which perform very well
    • Those that set altitude records.
    • Or those that go very fast.

Mach 1.3

In the last kind I have searched to see if it is possible to do that with a normal Aerotech. After some simulation with RockSim it seemed quite feasible, even with a small motor, like an H238T or an H220T. And a 29mm motor is the minimum diameter which fits an R-DAS, because after all a flight computer is compulsory to measure how fast the rocket flew.

As airframe I have used PML 29mm tube and to keep it light I haven't laminated the tube and chose to parachute by separating the nosecone. Not laminating would later prove a fatal error of judgment. A massive conical polyurethane nosecone and "through the wall" G10 fins and a few coats of fluorescent orange complemented the tube.

The first opportunity to launch came unexpected, it was an invitation from the Czech rocket club from the Plzen area, near the place I work on my current project. A complication was that the ceiling was 600 meter, but no worries there, as the R-DAS was programmed to deploy the parachute after 2 seconds of flight, after all it was about speed, not altitude. Some damage to the rocket was to be expected, but I thought I had a good chance the motor casing and the R-DAS would survive.

The Flight

After a safety inspection I could place the rocket (which I have named "de Wortel" (carrot) after its color) in the Blacksky rail. After the countdown the rocket left the launch platform very rapid, only to disintegrate completely on an altitude of 150 meter (roughly 500 feet). The airframe was shattered in pieces and even the solid polyurethane nosecone was broken in two. Fortunately the safety on the launch day was very good, so there never was any danger to the spectators. Another piece of luck was that both the motor casing and the R-DAS were recovered undamaged.

Back to the drawing board

It is always a good idea to check the internet if something unexpected happens to find out what happened. I have known a long time (and it is often visible in the rockets smoke trial) the air does not move homogeneous. It is very well posible that two adjacent layers of air move in totally different directions. This off course induce tremendous powers on the airframe. Something I discovered is that in the (real) rocket community the design specifications assume accelerations of + and - 20 G in each dimension. Taking in account the rocket only weighed 400 grams, could you stress a 29mm PML tube with 8 kilos without destroying it? Or was it the minute margin which all nosecones have? Two design changes for the next attempt: Deploying the parachute from the rear side (the airframe has no detachable parts, the motor is blown out of the rear side and takes out the parachute as well) and an airframe which is glass fibre/epoxy laminated.

To be continued!

Bert Koerts

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