At our launch tests on 22nd of March, we used our 2rocket vehicles, H1 and H2. Both of them were designed and built by our team members from scratch.
The rocket’s wet mass is 2472g. Its center of gravity (CG) is located at a distance of 74,4cm from the nose tip and its center of pressure (CP) lays 27,6cm aft of the CG, at 102cm, with stability margin of 2,72 cal.
There are several types of nosecones, our team chose to use the ogive cone for thismodel, however, the H2 has a different approach to that.
According to simulations, the H1 rocket with our 122-G85 Solid Rocket Motor (more details here: https://asat.gr/2019/03/29/rocketry-propulsion-sub-team/) can have an apogee of 90,3m with maximum acceleration of 49,4 m/s2 (~5g) and maximum speed of 37,5m/s (Mach 0,11)
|Center of gravity (CG)||74,4cm|
|Center of pressure (CP)||102cm|
|Stability margin||2,72 cal|
|with 122-G85 Solid Rocket Motor|
|Max acceleration||49,4 m/s^2 ( ~5g)|
|Max velocity||37,5m/s (Mach 0,11)|
The H2 rocket is the second optimized rocket. The fins of the rocket were designed and manufactured implementing a Supercritical Airfoil, specifically NACA 0011.
Its length is 75cm, it has a max diameter of 6,4cm and a wet mass of 1078g. As it is obvious, the H2 is much smaller and lighter than H1. Its center of gravity (CG) is located at a distance of 47,6cm from the nose tip and its center of pressure lays at 58,3cm, with a stability margin of 1,68 cal.
Instead of ogive cone, like in H1, the team decided to use an ellipsoid type cone for this model in order to reduce the drag coefficient. This geometry was selected through simulations.
Due to its small size and its light weight, H2 (also implementing our 122-G85 Solid Rocket Motor) can reach an apogee of 447m with a max velocity of 102m/s (Mach 0,30) and max acceleration 128m/s^2.
|Center of gravity (CG)||47,6cm|
|Center of pressure (CP)||58,3cm|
|Stability margin||1,68 cal|
|with 122-G85 Solid Rocket Motor|
|Max acceleration||128m/s^2 ( ~13g)|
|Max velocity||102m/s (Mach 0,30)|
In both rockets, we use a 91cm diameter parachute and a pyrotechnic mechanism for its deployment. You can read for our pyrotechnic mechanism here: asat.gr/2019/04/01/rocketry-pyrotechnic-mechanism. The rocket’s tube is made from fiberglass – the material was selected due to its high strength to weight ratio – and the fins and nosecone are 3dprinted with PLA for ease of manufacture.
As it was mentioned, last month we launched our H1, H2 rocket vehicles. Here is a brief description of how the launches went:
- The H1 rocket followed a straight flight path, despite the small thrust to weight ratio, which is due to its high mass. Unfortunately, the deployment of the parachute failed due to issues with the altimeter, which were resolved after the recovery of the rocket and the rocket had a hard impact with the ground. Luckily, the damages were minimum, 2/3 fins were detached from the rocket airframe, however the fiberglass tube and the nosecone were intact with minimum scratches. There was no damage to any other parts of the rocket including the electronics, the pyrotechnic mechanism, the recovery system and the skeleton structure of the vehicle.
- The H2 rocket had an excellent launch! There was also no diversion from the flight path and when it reached apogee, the altimeter gave the signal and the pyrotechnic mechanism was activated in order toignite the black powder and provide enough pressure to the piston to deploy the parachute. The rocket had a normal descendexperiencing no damage during the flight or the landing.
- The rocket motors worked perfectly in both rockets, providing the expected thrust and burn time since there was no gas leakage orover pressurization of the casing than expected. The ignition system performed nominally.