The spring powered parachute system has been fraught with problems, ranging from spring power issues to a nonfunctional release mechanism.
A month ago, we had to decide if we wanted to continue with a spring powered system or switch to a new power method. We decided that sticking with the spring system was the best option. A few weeks later, after more revisions and testing, we found our self facing the same question. This time, we chose to try something new. Our next test was to be powered by CO2.
The type of CO2 we used, comes in small canisters that are commonly used in applications that need a small quantity of pressurized gas such as beer brewing. These canisters are made of aluminum and are sealed by a thin layer of metal that is punctured to release the gas.
The purpose of this test was to determine if CO2 was a valid source of power, and to evaluate the difficulty of switching to a CO2 system. In the interest of saving time and money, we reused the shell of the Gen 3 parachute system as a base for our test.
While test 7-1 did not go as expected, the fix was quick and relatively simple. We fabricated a diffuser to split the flow of the gas. We also added a small plate to keep the gas contained until the parachute was clear of the tube. We performed two more tests, 7-2 with the diffuser and plate and 7-3 with just the diffuser. 7-3 was the most successful.
For these tests, we released the gas by puncturing the canister manually. This approach works if the test is ground based, but this is not feasible during a flight test. We came up with two possible solutions. We could either use a system that punctures the canister remotely, or a system that punctures the canister early and stores the gas in an reservoir until the system is triggered.
We chose there reservoir option due to it’s customizability and simpler design. It also can vent gas if needed, which is required for high altitude use (due to the lower relative air pressure at high attitudes). The CO2 system will be made up of 3 different parts:
- A reservoir
- A main valve, that releases the gas from the reservoir to activate the system
- A pressure release valve, used to vent the gas from the reservoir if the pressure becomes too high.
This is where the high pressure of the CO2 becomes a problem. When stored in a canister, CO2 is partially liquid and at a PSI (Pounds per Square Inch) of ~850. When the canister is opened, the liquid will quickly flash to gas. This process also causes the CO2 to become extremely cold. This means that any parts we want to use have to be rated for 850+ PSI and be resistant to cold temperatures. The only parts we could find that fit these specs are both large and extremely expensive.