Tube Launch Boosts Rocket’s Performance

If you want improve a model rocket’s performance, all the common options come with serious trade-offs: you could increase the motor’s size, which raises safety issues, or you could cut …. Tube Launch Boosts Rocket’s Performance. [Con Hathy] was therefore intrigued by the design of the Arcas sounding rockets, which with the aid of a gas-fed launch tube could reach an altitude of 100 km.

Even in models without a gas generator, a launch tube apparently boosted performance, an effect which [Con] was able to replicate in a much smaller model rocket. In theory, as the rocket engine fires, it should pressurize the tube behind the rocket, providing an extra boost out of the tube. To test this, [Con] 3D printed a test rocket, launched it both from a standard rail and from a tube, and compared the results.

During tube launches, a printed sabot fit around the rocket and formed a seal with the launch tube. The results were surprising: the tube-launched rocket actually performed substantially worse than a rail launch. After building a simulation, [Con] found that, as the rocket moves down the tube, the volume of tube it needs to back-fill with gas increases faster than the engine puts out exhaust; it was pulling a slight vacuum behind it, slowing itself down.