DD/Balistic spreader questions

[prowlerguy]

My first question is:

Is there an accepted min alititude at which you should deploy your main chute? I have seen 600', 500', and 300' mentioned. I know that sink rate and parachute deployment times are variables here, but I didn't know if there was some sort of rule-of-thumb or safety minimum published.

On a related subject, has any attempted or seen the use of a balistic spreader- type device on a main parachute?

 

[Ryan S.]

I would go with 500 as the least for bigger rockets higher. it also depends on shockcord length. If you have a real long shock cord you want your main coming out higher

 

[daveyfire]

I've done 300' ... once. With a PML Phobos and an R3C. Opened up nice and quick.

I usually go with 800 or 1000, because big chutes can take a while to open. I'd stick above 500 feet if possible, mostly because I've seen several rockets not have their chutes unfold, and they would've if they had had more time. The failure of "The Beast" at LDRS 22 comes to mind -- from the videos it looks like the chute came out but just didn't have time to unfurl. So I'd say stick with above 500 if you're deploying anything bigger than about 5 feet. If you're under that size, I'd imagine you could go with 300... heck, the old ALTS2 would blow the main at 250... but the altitude always looks lower than it is when your big investment is falling that fast!

 

[prowlerguy]

Thanks for the reply. I'm curious though. Why so high, when on an ejection seat you can get a full sized canopy opened in less than 200'? That's why I asked about the use of devices like ballistic spreaders to force the chute open sooner. Also, it would seem that PD competitors would be looking for ways to get air in their chutes as soon as possible.

Also, does anyone use parafoils with R/C control to steer their rocket back to the launch site? I saw an R/C man that would be dropped from an R/C plane, and it occured to me that a similar system should be workable for a recovery device in a rocket. If you employ an R/C failsafe deployment system, you already are lifting a receiver.

 

[powderburner]

I sure would like to see the details of using a device like a spreader, at least for rocketry applications.

For NAR modroc competition purposes, we just folded our chutes verrrrryyyyy carefully (and we all had our 'secret' patterns for folding). Any device to assist the deploy would have to be quite small, light, and reliable to be able to make much improvement over plain chute-stuffing.

Maybe for high-power it would make more of a difference? Still, it's one more level of complexity (and potential failure/disaster) that is unnecessary, as long as you can just deploy 100 or 200 feet higher?

 

[jetra2]

Giant Leap Rocketry sells this thing that slides over your parachute that they call a "Slider", I believe. I don't know if it lets your chute open quicker, but it DOES make it open gentler.

IMHO, I would have the parachute open at 500'. That's kinda pointless when the rocket only goes 650', ain't it?

Jason

 

[prowlerguy]

You're probably right. The difference in a PD bird would be rather small. Still, at the highest level of any competition, people tend to look for any advantage, however small (look at the different wheels used by bicyclists depend on the race).

But on a big rocket, I would think the drift difference between 800' or 500' and 200' might mean the difference between getting your rocket back or not. In any case, HPR is very far away from what I am doing now, so I will let it rest. However, I do have an idea for an LPR device. I'll need to prototype it and test it first, but I'll eventually do an update.

 

[powderburner]

Prowlerguy,
Please keep us advised of your development efforts. You now have me interested. I wanna see what you are working on, especially if it works with low/mid-power.