My first Recovery setup

[AstroAbaqus]

Dear all here in attachment you will find the recovery system I designed based on OR and information on TFR and other sources. My first scratch build HPR, named Set, will be tall 2.25 meter (88 inch) with a 98 mm (4 inch) diameter with an estimated weight of 3.3 kg (at complete burn out. I am thinking to start immediately with dual deploy but I can change to single deploy relatively fast. I took a nylon shock cord rated 1000 lbf in red, most of the ends are protected by a thick kevlar sleeve and the shock cord is secured to the u-bolt via 6 mm quick links. The shock cord had a total length of 10 meter divided in 7 meter for the drogue and 3 for the parachute. At 3/4 of both the drogue and main shock cords a butterfly knot is done. To this I decided to attach a 1.8 meter of paracord of 6mm rated up to 900 lbf. At the end of the paracord the drogue and the main are attached using a swivel to ensure a free rotation. The drogue is a 24 inch parachute and the main is a 48 inch parachute.

Any advice is more than welcome

 

[rcktnut]

What are your booster and payload lengths? I'd say the shock cord length is pretty short for the main. I would also get rid of the paracord and attach the swivel of the chute to your loop on the shock cord with a quick link. The paracord is unnecessary and is just another item in the recovery chain that could tangle up. Also a 48" chute for a 7.25 lb rocket seems a bit small.

 

[AstroAbaqus]

What are your booster and payload lengths? I'd say the shock cord length is pretty short for the main. I would also get rid of the paracord and attach the swivel of the chute to your loop on the shock cord with a quick link. The paracord is unnecessary and is just another item in the recovery chain that could tangle up. Also a 48" chute for a 7.25 lb rocket seems a bit small.

thank you very much for your advice. So I ordered other 10 meters of high strength bright red shock cordwhich will be given to the drogue and 7 meters to the main. Will remove the paracord, can be useful for other projects. For the 48 inch in reality there is clear chance that for my lvl 1 I will fly my rocket without eBay and in a shorter and lighter version so is for sure ok because I am much lighter. For the full one, my descent rate is around 18ish fps. I know this may be too fast from common experience, and probably I will switch to a 60. However, where I launch is always wet and soft with nearly no roads ( we launch in Scotland) no trees as well so I would prefer a bit faster descent to do end up in a lake.

 

[Handeman]

I agree that the 3 meters is short for the main cord. I would have split them 5 and 5, but that's me. I also agree with removing the paracord.
The 24" drogue seems a little large for that rocket, but you need to watch the decent and adjust based on how the rocket falls. I use a 53" golf umbrella as a main on a 9 lbs. rocket and that works fine on the farm fields of the east coast.

I would also move the swivel from the main chute, to the attachment point of the drogue cord to the fin can. I've never had a main chute twist up because the rocket parts were spinning under it. I have had a fin can spins at 100 RPM on the way down on a DD flight and twist up a drogue cord so bad it twisted the drogue chute right up inside the twisted cord. A swivel on the fin can will do a lot more good then one on a chute.

 

[teepot]

What chutes are you using? Or what companies chutes.

 

[AstroAbaqus]

What chutes are you using? Or what companies chutes.

https://www.blackcatrocketry.co.uk Is a nice small business in Scotland, I already bought some material from them and was top neat. The chutes are really refined not just a large piece of nylon.

This is the main https://www.blackcatrocketry.co.uk/collections/parachutes/products/bcc-pro-series-48
This is the one I choose as drogue https://www.blackcatrocketry.co.uk/products/single-panel-special-edition-chutes?variant=51074730324

Thank you all for your advices, I ordered the 10 meter shock cord, now I don't know if is better to have 7 for the main and 10 for the drogue or just cut the new one in half and keep the others for other projects.

 

[Handeman]

Your rocket is almost exactly the same size as my L2 Cert rocket. I had 4m of shock cord on each end. Had 50 flights and never an issue. Based on that, I would split the 10m into two 5s and save the other for another project.

 

[rcktnut]

+1 to above post. I have a couple the size of your rocket also and have15ft. for both drogue and main, never a problem. I for one don't believe in excessively long shock cords, but you don't want them too short either.

 

[OverTheTop]

If your descent rate is calculated at 18fps with that chute, with those landing conditions, you should be good. I usually aim for 22fps and on not wet ground. It does depend on you fin shape and build quality, of course.