Tried searching but came up empty handed. Trying to figure out if there is a method to the madness for choosing the altitude for the JL to release the chute? Or just start at something conservative and go from there?
What altitude for JLCR?
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It partially depends on your landing site. Is it flat or hilly? If hilly you want to set it for a higher altitude since you can't predict if it will be over a hill or valley when it releases.
Also, there is a delay from when it releases to when the chute fully opens and slonws down your rocket. That delay is dependent on the size of the chute and your packing technique. So the longer the chute tales to open, the higher you want the release.
Conversely, the higher it is set for, the more drift you will have. How big is your site? How many trees are nearby that will snag the rocket? If your site is small or has a lot of tress nearby, then you want it to open lower.
I'm not certain there is some super-duper equation that you can just plug in this type of info and get a correct answer...
So yes - start conservation and work from there may be the best bet...
Also, there is a delay from when it releases to when the chute fully opens and slonws down your rocket. That delay is dependent on the size of the chute and your packing technique. So the longer the chute tales to open, the higher you want the release.
Conversely, the higher it is set for, the more drift you will have. How big is your site? How many trees are nearby that will snag the rocket? If your site is small or has a lot of tress nearby, then you want it to open lower.
I'm not certain there is some super-duper equation that you can just plug in this type of info and get a correct answer...
So yes - start conservation and work from there may be the best bet...
So far (20-30 flights, maybe?) I've only used the chute release in rockets of 1 kg or less with chutes of 36" or less that open quickly. I typically set it at 300'. For the first flight of a rocket in this class, or if the wind is low and I don't have to worry about drift, I set it at 400'. Once when the wind was pretty high, I had the idea of setting it to 200'. It worked, but it was heart-in-mouth watching it come down.
If I ever decide to use it in bigger rockets, or near hills, etc., I'll certainly go higher.
If I ever decide to use it in bigger rockets, or near hills, etc., I'll certainly go higher.
-Slick-Ice
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It also depends on how you pack the parachute. If you roll that thing up tight with the lines inside of it then you might take 200 feet to open. The IRIS-3 I usually set at 300 if there is any wind since it is so light.
The IRIS-4 500 is the lowest I would set it for. It doesn't drift much because it weighs like 10 lbs.
The IRIS-4 500 is the lowest I would set it for. It doesn't drift much because it weighs like 10 lbs.
Rschub
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It kind of depends on what kind of reaction you want to get from the crowd, and your underwear budget.
There is a 100 ft setting for a reason, am I right?
There is a 100 ft setting for a reason, am I right?
Yup. I gotta stop at Walmart on the way home.
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My experience:
100' Crash
200' may result in a crash
300' is interesting and a little exciting
400' Normally where I set my 4" stuff on a small field
500' pretty typical
If you have a 4" fiberglass rocket, I'd give it 200'-300' or more for the parachute to open.
100' Crash
200' may result in a crash
300' is interesting and a little exciting
400' Normally where I set my 4" stuff on a small field
500' pretty typical
If you have a 4" fiberglass rocket, I'd give it 200'-300' or more for the parachute to open.
JimByrne
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Give it an extra 100' for opening time
It depends on the launch area and weight of the rocket, complexity of your chute/shock cord. If it takes a little for it to open you want it higher. I tested mine out on my Big Daddy, and have added extra safety tethers/steamer. And use hair bands, but I've not had an issue with the bands they give you yet.
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I’ve also heard they have a +/- 100ft accuracy. I wouldn’t want to temp fate. I typically use 400’ for our site. 300’ on a windy day and a light rocket. I’d be nervous going lower.
Most of my rockets are DD and I've only been using my JLCR on two different rockets. They both come down fin first with the bundled chute trailing and acting as a drogue and open very quickly when released. The 4" one I always use 200 ft. on. The 2.2" one, I usually use 200 ft. on, unless I think the LCO needs some excitement, then I'll set it for 100 ft. Never had a crash yet. Haven't had an LCO crash yet either, but I did get a little worried about Neil at LDRS36. 
I do think "start at something conservative and go from there" is a very good approach.
I do think "start at something conservative and go from there" is a very good approach.
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This was a really good answer, and it's the advice I would give.
As an aside, it's important to keep in mind that the release altitude you choose has nothing to do with how hard your rocket will land. A rocket that releases at 1000' will land at the same speed as the same rocket releasing at 200'. It will just be in the air longer and land in a different place.
You can verify this by recording your launch with a recording altimeter. On the altitude plot, straight lines are constant speeds. Notice how quickly the curved lines straighten out after the rocket ejects (while tumbling) and after the main deploys. The rocket is not speeding up the whole time it is descending, it speeds up for only a second or two before it reaches terminal velocity and then the speed stays pretty constant.
I only mention this because I have a theory that this is what leads many people to worry about releasing too close to the ground.
Very true. My own concern with releasing too close to the ground is largely simple nervousness, but also inconsistency in speed of the chute itself opening when I use a bunch of different chutes in different rockets. 300' gives me plenty of altitude to overcome any problems there. Maybe I'll try 200' again though for some of my rockets/chutes that I've gotten to know better.
Tried 200' again today, and it worked fine. I couldn't be nervous about it because I lost it against the sky and didn't see it land.
A friend saw it open successfully at low altitude as planned.Similar threads
