Seeking comment and opinion on my recovery system design

I'm designing the recovery system for my Gizmo XL DD. It is an 8" diameter all fiberglass stubby rocket. It will weigh somewhere close to 40lb when complete.

I am leaning towards the Fruity Chutes Iris Ultra 96" as my main chute. It will be packed in a deployment bag, with a 24" pilot chute, and a slider ring around the shroud lines to make for a nice controlled chute deployment.

I built the av-bay with dual U bolts spaced 180 deg apart. I plan to use 1/2" kevlar Y harnesses coming off the av-bay then switch to 11/16" nylon shock cord, quick links where appropriate. By the time the main chute inflates, everything should be nearly perfectly lined up straight.

All this, plus the fact that the payload bay body tube is nice thick fiberglass, leads me to believe I'll have a fairly zipper resistant system.

What I am stuck on deciding, is what descent speed to size my apogee drogue for.

Descent rates from Open Rocket simulations:

81 ft/sec with a 24" drogue
108 ft/sec with a 18" drogue
163 ft/sec with a 12" drogue

I'm trying to make the tradeoff between risk of damage from too fast of a descent rate for safe main deployment vs too slow of a descent rate and wind drift.

I think I'm leaning towards the 12" drogue. Your thoughts?

I think the 160'/second is a bit fast. I think 80-100 is better.


Mark Koelsch
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Ditto what Mark says, 160'/sec is pretty darn quick. You want either the 18 or 24 inch drogue.

I have nearly the exact same setup on my Ultimate Darkstar and it works great. Don't have the slider ring, though. Good luck!

Yep yep yep; agree with Mark and Carl!

Not saying it's right, but our Gizmo XL DD (that just flew last weekend at LDRS) is setup with a 36" Ultra X drogue and two 96" standard chutes: all Top Flight manufactured. There is a bit of noseweight in the thing to offset a 98-4G in the rear end.

Enjoy!

-Eric-

I also favor bringing them down quick. If you were to bring it down at 163ft/s (I get slightly faster speeds) then I would make sure that the main chute can handle the forces of deployment at that speed. IMO the fruity chutes Iris Ultra can handle it, but you would want to test that. If it were I, I would bring it down on the 18" drogue chute. Assuming that you are using a drogue chute with a Cd of 1.5 then the 18" would bring the 40lb. rocket (does this include empty motor casing weight?) down at ~115.2ft/s which I think is fine… assuming the main opens. The 24" chute with a Cd of 1.5 will bring it down at ~86.4ft/s, just fyi.

I always look for somewhere around 90 fps on a drogue......
The 18" chute seems perfect.......

Teddy

When you did your descent calculations, did you include the cross-sectional area of the rocket? I'm not sure if you did a drogueless apogee deployment that you would obtain a 160 fps descent rate as the cross-sectional area of the split rocket exceeds that of a 12" drogue.....

Bob

bobkrech said:

When you did your descent calculations, did you include the cross-sectional area of the rocket? I'm not sure if you did a drogueless apogee deployment that you would obtain a 160 fps descent rate as the cross-sectional area of the split rocket exceeds that of a 12" drogue.....

Bob

Click to expand...

What a great point.....
I was wondering why the drogueless decent rate seemed to fast.....
I don't think it's going to fall at 160 fps even drogueless.......

Teddy