We have been hard at work designing the motor and the specific nozzle dimensions, and the rocket that the motor will power.
The nozzle shape we went for, called the de Laval nozzle, is a very versatile shape used on the Soyuz rocket, the Saturn rockets and many others, not least for its efficiency, simple design and low cost.
It uses a convergent-divergent shape, which means it gets narrower then gets wider, converting the high pressure and temperature gases into low pressure and high speed gases very efficiently, as shown in the diagram below.
Using BurnSim, a rocket motor simulation program, we have found the ideal throat diameter and exit diameter. The results of the simulation are below.
We then converted the data from BurnSim into something the rocket design software ‘OpenRocket’ could use, and designed a rocket that the motor would work with.
Rather counter-intuitively, we had to add 400 grams of dead weight to the rocket in order for it to fly higher. This is because without the dead weight, the rocket would experience more drag because it would be travelling faster, so would reach a lower altitude. As shown in the graph below by the red line, the drag increases when its speed approaches the speed of sound, or Mach 1.
The graph for the altitude, speed and acceleration is below.
With the 400g of payload, the rocket reaches an altitude of 1030m. Just for comparison, the entire rocket with motor weighs ~650g, of which the motor takes up 180g. Inside the 400g of payload, we may put:
- GPS which will provide latitude, longitude and altitude data.
- Altimeter just in case the GPS fails
- Antenna to transmit the GPS data
- Electronic parachute deployment system, reliant on altitude data (hence the altimeter)
- Small camera for good footage
- Arduino to control all of the above equipment, and to record the data should the antenna fail.
In terms of looks, we have two potential designs:
We also haven’t decided on a name, but will decide on a colour scheme and name for the rocket before completion.
With this 60cm rocket we hope to achieve the following goals:
- Find an optimum nozzle for our motors
- Create a telemetry system
- Achieve 1000m altitude