Discussion in 'High Power Rocketry (HPR)' started by Ben Martin, Mar 4, 2019.
Ah, my work here is done.
I tested the ejection charges today. I went with 2g for the drogue and 1g for the main. More testing will be done in two week, probably will increase the main charge.
Looked kind of underpowered for the main, but I don't have that mich knowledge.
I've heard that the main is just supposed to get the nosecone off since the nosecone will pull the parachute out of the payload bay. I'll probably increase it to 1.5g and see the results, but I think 1g would work great for flight.
I think that is a dangerous generalization. Is it possible for the nose to pull out the rest of the laundry, maybe, depends on how tight its packed and how much other volume you have in the chamber in question.
IMO, retest at 2 grams for the main.
I pulled on the nosecone with maybe a few pounds of force and the parachute slid right out after the test. What stopped it from coming out was the nosecone hitting the grass. I'm confident that it would have smoothly deployed. But I am going to test again with 1.5g as 2g is way overkill for the very small payload bay volume. The backup charge will be 150% of the final main amount I decide on, likely 1.5 or 2g.
I know the general rule of thumb is that it's better to push a parachute out than to pull it. Maybe that rule or this situation carries subtleties that I'm not aware of.
It seems like the gas just went around the parachute and popped the nosecone off. I'll test with 1.5g next weekend and see if it has similar results, but I'm nearly 100% confident that it would have deployed reliably with only 1g. In addition, I have a backup charge to ensure the safe deployment of the main in case the flight does not go as tested.
The calculator gives 1g as a bit over 10psi with 3 shear pins which is good. 2g would be over 20psi, which is dangerous in itself. 1.5 produces the upper end of the PSI range with 15psi, I'll have to test it to see if it's too much.
The payload bay is only 4in x 15in with the parachute taking up 80% of the space. It has 3 shear pins for the nosecone.
I use 1.4g in my 4" MC SDX3 with 2 2-56 nylon pins. I looked at my L2 flight data and the main was set for 500' and drogue decent rate was 45f/s. Main fired right on time but the air frame fell another 100' in about 2 seconds to get everything in line and slowed down to a slow 11f/s. Yes its good the nose cone came off, there is a chance the main would rattle out but that takes time, then it needs to inflate and slow the air frame down.
My main is set at 900 with backup at 700 for the first flight. Depending on the results the main might be lowered to 700 and the backup at 500. This gives it time to fully open and settle. I'll test with 1.5g but will probably reduce the main charge to around 1.2-1.3g with the backup at 2g.
Launched Starship for the first time today.
Main: 1.2g, 1.5g backup (900ft for main, 700ft for backup)
Drogue: 2g, 2.2g backup (1 second delay for backup)
Parachutes: 9ft main, 2ft drogue
All charges were set off by the dual Stratologger CFs set with full redundancy. Everything went flawlessly besides a tangled booster which will be easily fixed by moving the swivel.
Video of launch:
Pictures: Shown below.
Looks like it was a great day. I’m sorry I missed the launch. Hoping the weather is as nice in December.
It was a beautiful day. Perfect day to launch as the weather was great and best of all, no wind! You were attending something a "bit" more important. Hope to see you next month if the weather is nice!
More pictures from first launch.
Video from our prospective:
Launch pad camera:
Impressive project. Based on some of the decisions you discussed in this thread (not launching in poor wind, and ground testing deploy charges), I think you have a bright future in rocketry and whatever career path you choose.
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