Ok. Getting ready to launch tomorrow for L1. I've got everything worked out now and tested except for one detail which is chute selection. I'm launching a Binder Design Excel Plus 54 dual deploy.
The stock chutes in the kit are nice and durable looking with substantial shroud lines that look like the can stop a truck - good stuff. However, when putting in the specs on Open Rocket, I get the following:
Rocket weight (empty): 2.7 kg
Drogue: 9"
Drogue Drag Coefficient: 1.4 (I estimated here)
Drogue Descent Rate: 30 m/s
Main: 36"
Main Drag Coefficient: 1.4 (again, estimate)
Main Descent Rate: 7 m/s
Isn't the drogue descent rate too fast here? I thought drogue descent was optimally under 60 fps. This is falling at 100 fps. I suppose that's OK since the main is built like a tank and can take the deceleration when the main pops. If I up the Cd to 1.7 (seen that estimate in places as well), the drogue descent goes down to 26.8 m/s (88 fps). Still high, but closer to the 40-60 I've seen.
On to the main, the stock chute will put the rocket on the ground at 7 m/s (15.6 mph). I had read that under 6 m/s is best. This is based on my assumption of a Cd of 1.4. OR defaults to 0.8 which is way too low. Is a 7 m/s impact ok? I do have a larger chute on hand that is 60" and packs down to a similar size. However, the shroud lines aren't as substantial. It would put the rocket down at 5.6 m/s using the manufacturer's statement that their Cd is 0.8. I like that speed better, and popping the main at 1000' won't make it drift too far; especially since winds are predicted to be 2-4 mph. I'm just worried it can't take the hit of deploying at 88-100 fps.
The 60" chute I have is from Sunward:
https://www.sunward1.com/para.htm
Says a 7 lb rocket will fall at mid-range speed.
I seem to be overthinking everything a day before L1.
The stock chutes in the kit are nice and durable looking with substantial shroud lines that look like the can stop a truck - good stuff. However, when putting in the specs on Open Rocket, I get the following:
Rocket weight (empty): 2.7 kg
Drogue: 9"
Drogue Drag Coefficient: 1.4 (I estimated here)
Drogue Descent Rate: 30 m/s
Main: 36"
Main Drag Coefficient: 1.4 (again, estimate)
Main Descent Rate: 7 m/s
Isn't the drogue descent rate too fast here? I thought drogue descent was optimally under 60 fps. This is falling at 100 fps. I suppose that's OK since the main is built like a tank and can take the deceleration when the main pops. If I up the Cd to 1.7 (seen that estimate in places as well), the drogue descent goes down to 26.8 m/s (88 fps). Still high, but closer to the 40-60 I've seen.
On to the main, the stock chute will put the rocket on the ground at 7 m/s (15.6 mph). I had read that under 6 m/s is best. This is based on my assumption of a Cd of 1.4. OR defaults to 0.8 which is way too low. Is a 7 m/s impact ok? I do have a larger chute on hand that is 60" and packs down to a similar size. However, the shroud lines aren't as substantial. It would put the rocket down at 5.6 m/s using the manufacturer's statement that their Cd is 0.8. I like that speed better, and popping the main at 1000' won't make it drift too far; especially since winds are predicted to be 2-4 mph. I'm just worried it can't take the hit of deploying at 88-100 fps.
The 60" chute I have is from Sunward:
https://www.sunward1.com/para.htm
Says a 7 lb rocket will fall at mid-range speed.
I seem to be overthinking everything a day before L1.