dual deploy chute question

for an approx 4lb rocket, do I need anything more than say a pair of appropriatly sized top flight nylon chutes? (current guess is 1.6Kg, 18" & 30") or will I need to find some super dooper chutes. thanks
rex

The drogue should be smaller than that or else you won't gain terribly much from dual deploy.

You could probably just use a streamer if you have one handy. As for the main it depends on the brand. Check their web site for a chart.

I know the sizes are off*. I was asking if I needed the Super Heavy Duty chutes or would regular nylon work.
rex
*can't nail down size untill I get a built weight for my scratch build DD bird.

For a 4 pound rocket you'll be fine with a regular nylon chute, at least if deployment goes right.

Have someone who flies a lot of DD look over your setup before you fly. I got good advice from Brent that made my first DD flight go well, and from someone else that made the difference to my L2 cert flight. There's a lot of little things to look at. If it's all set up correctly, you'll have a successful flight, and the standard Top Flight chute will do the job.

I was hoping that would the case, thanks. ayup deffinatly gonna have it looked at .
rex

You will be A-OK with Top Flight's "Standard" line for your project. You'll definitely want to consider a smaller drogue, if you use one at all. On my little DD's, I go drogue-less, on the bigger ones I use only a ten or twelve inch. I used a twelve in my Darkstar at MWP, it was twenty-two pounds on the pad.

gee, I thought the idea was to limit descent speed to 50 - 64 fps...was I mistaken? looks like I may have to get a bigger main though a 12 -15" drogue and a 36" main will bring it in at over 20fps...and I don't have a) a wildman rocket(wood/cardboard) or b) lots of space for a main.
rex

I don't do much sim'n, so I can't say what the rate was under drogue. Flying my Minni-Magg dual deploy I used a ten inch drogue, was just enough to keep the payload above the rest. It spit out the 72" Top flight standard main @ 700' and all was well. That one is about 14 lbs. flight ready.

one calculator has your mmagg dropping under drogue at 150 fps.... I'll grant you that it shouldn't drift very far at that speed, but I'll bet that it is a bit of a jolt when the main opens.
rex

For what it's worth, I plan on using Top Flight chutes on my 3-4 lb dual deploy. I may have to rethink my drogue size though.

Keep in mind that the weight hits the main gradually. The whole works is essentially falling from apogee in a horizontal line, then cascades (?) down to vertical when the main is deployed. Watching it in real time doesn't reveal a great deal of shock, to the naked eye at least.

Top flight chute are fine RexR. I would get rid of the drogue though.

On the DD flights I've seen, the main opened slowly, almost majestically.

Rex R said:

gee, I thought the idea was to limit descent speed to 50 - 64 fps...was I mistaken? looks like I may have to get a bigger main though a 12 -15" drogue and a 36" main will bring it in at over 20fps...and I don't have a) a wildman rocket(wood/cardboard) or b) lots of space for a main.
rex

Click to expand...

The drogue is mainly to keep the parachute bay away from the fin can, and ideally a little above it. Normally your fin can is the draggier and often lighter part of the rocket, and will want to hang up above the part with the chute in it. If it's directly above when the chute comes out, you've got trouble.

That being said, a fairly small drogue will do the job. I use 12" drogues on 8 pound rockets without any problem. The drogue gets attached directly to the ubolt on the electronics bay (and of course wrapped up carefully in a nomex pad).

A lot of different things can happen with DD.

With no drogue, you can get the upper section going nosecone down, pulling the fin can with it and actually falling ballistic. Long shock cords can be fatal in that situation because the main opens and then the upper falls to the end of it's cord, and the fin can fall past both and hits the end of its cord with a lot of force.
With no drogue, you can get the fin can falling almost flat, just slightly fin down, and it will actually fly that way, pulling the upper section with it. If you're lucky it will be flying into the wind, if your unlucky, it flies with the wind. Either way it can add a lot of horizontal distance to where the rocket lands.

With a drogue, you want the upper section to stay at or above the fin can. I prefer to have the upper section well above the fin can so the can stays pointing down and you don't get any of the flying effect.
The size of the drogue you need can be a trail and error type of thing. I tend to start larger and work down until I get it falling the way I want.

I also make my own drogue chutes that are about 3/4 as tall as the diameter (almost cone shaped), and have relatively large spill holes. This seems to work quite well as the drogue stays stable while falling fast. Drogues without spill holes seem to spin and shake side to side very quickly when falling fast.

As for needing heavy duty chutes, not really. Most of my main chutes are made from old umbrellas. They are not rip-stop and were made in China. All I've done is sew the shroud lines on. I have a golf umbrella, 53", I use as a main for a 10 lb rocket and it's never had an issue. I also always use a drogue and keep the upper section above the fin can so the cord is stretched out well by the time the main opens. It never has a large shock load on it.