Double or triple parachutes?

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brockrwood

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I recently flew a scratch built cluster rocket at a local park launch with friends. The model rocket had a sustainer engine in the main body tube and two “strap on” booster tubes glued onto each side of the sustainer tube. Each booster tube had its own engine and its own shock cord and parachute.

Upon deployment, one booster tube parachute was lost when the shock cord broke in half. The other booster tube parachute deployed as did the sustainer parachute. The rocket landed safely on both parachutes.

This made me think: I have seen a lot of rockets crash or have hard landings because of a parachute coming out as a “para-wad” and not opening up. Maybe it makes sense to pack TWO, slightly smaller, parachutes into the body tube? If one paracute ends up being a “para-wad” upon ejection, maybe the other one still opens up and the rocket is saved?

Anything we can do to improve the chances of getting a rocket back in one piece is worth doing, it seems to me. This is especially true for any rocket we have diligently spent days building and painting and making look really nice.

This might not work on BT-20 or BT-50 sized rockets, because of space limitations in the tube. It should work on BT-55 and up sized rockets.

Using thin dry cleaner bags for the parachutes will help fit two of them into the body tube, I would think. Two dry cleaner bag parachutes ought to fit into a tube as small as a BT-50, if you use button thread for the shroud lines.

Any thoughts?
 
I've thought about this possibility, but only to slow a rocket's descent without having to use a larger parachute which may not fit in the rocket's main body tube.

I think using a "backup parachute" can have its place, but if the problem it's trying to solve is the failure of the primary parachute to fully deploy, then a more effective strategy is finding out why the primary parachute didn't fully deploy.

Adding a second parachute to serve as a backup will add weight, launch prep time and increase the chances of tangled lines. But it doesn't address the reason you're installing a second parachute to begin with.
 
I've thought about this possibility, but only to slow a rocket's descent without having to use a larger parachute which may not fit in the rocket's main body tube.

I think using a "backup parachute" can have its place, but if the problem it's trying to solve is the failure of the primary parachute to fully deploy, then a more effective strategy is finding out why the primary parachute didn't fully deploy.

Adding a second parachute to serve as a backup will add weight, launch prep time and increase the chances of tangled lines. But it doesn't address the reason you're installing a second parachute to begin with.
My assumption, perhaps not a valid one, is that no matter how carefully prepared the parachute is, it may not deploy fully. That means that the chance of the parachute not fully deploying is always nonzero. Therefore, out of an abundance of caution, one should include a second parachute in the rocket. Then you have two parachutes, and the chance of both of them not deploying should be lower than the chance of just one of them not deploying. This is the same as the idea of redundant systems in an airplane, no?
 
This is the same as the idea of redundant systems in an airplane, no?
Yes, but my understanding is that the primary system has reached a level of reliability that can't be reasonably improved. In other words, it's reached a point of diminishing returns. But with model rockets, perhaps it's better to install a nylon parachute* instead of a plastic one to improve reliability.

*I'm not 100% sure nylon 'chutes are more reliable than plastic ones, but it's my assumption that they are, especially in colder weather.
 
Woven Fabric Parachutes! Yes, I now use nothing but woven parachutes since I often fly in cold weather. I have also used 2, 24" nylon sheet plastic parachutes in my Estes V-2 for the original reason posted: One of them always opens and often enough in cold weather one parachute did not. I have not yet had a tangle problem but each chute has it's own "extension line". However, I have since replaced the 2 sheet plastic parachutes of the V-2 with a single Woven Nylon parachute.

Also, I modify all my chutes by at least adding a circular central vent-hole and sometimes add stitches to where the shroud lines attach to the fabric.

At this point all my parachutes and streamers are detachable, have fishing swivels and split-rings for attachment, stored hanging in a closet and installed before I head out to launch and interchangeable for wind conditions or thermals, yes, I have had a rocket visibly hang in the air and go back up in a "Hat Sucker" thermal (term borrowed from RC Gliders and Freeflight).
 
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Sizing question.... would you size it for safe recovery speed on only 1 chute. If so, then with both chutes, you would have a VERY long walk to recover, or in a thermal watch it drift away. If sized for safe recovery on both chutes, then 1 may prevent catastrophic damage, but likely some damage from "hard" landing.

I like multiple chutes, but it's the visual show I am after. The redundancy / added complexity is just side effects. One helps, one hurts, so it's a wash as far as I am concerned....
 
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Less is more. Use one good quality parachute (ripstop nylon or better).

Part of the issue is if both chutes don't "blossom" at the same time (which is just about impossible) then one blossoms and slows the decent rate to the point that the second chute won't blossom.

I've had this happen with my F-79 twice, it's designed to have (2) rear-eject parachutes. I vowed to never again design a rocket that has to have dual parachutes, nor a recovery bay so small that I have to use thin mil plastic chutes.

007 Lawn Dart.JPG
 
"SLIDERS" (more complexity) they go over the shroud lines and start up at the parachute end. They slow the opening of the chute as they slide down to the end of the shroud line. This helps both (or more) chutes all "blossom".

BUT

If the slider is too small, not smooth, or can shift "up" to far; it will hang up, holding the chute closed.
 
If your parachute isn't opening, then you are not likely packing it correctly, or are wrapping the shroud lines around the chute. If it's coming out as a wad, try folding it neatly, and then looping the shroud lines within the folded chute, NOT wrapping it around the chute. If you're still having problems, try some talcum powder on the chute, maybe it's just sticky.
 
Just my personal opinion, but I would focus my efforts on practicing proper parachute packing technique to maximize it successfully opening, and leave the multi-chutes for novelty purposes on LPR models.
 
What type / manufacturer parachutes are those?
I made those. 36" ellipsoid, 1.1 oz nylon. I wrote them up in Peak of Flight a while back. I've evolved my methods a bit since but the basics are there.

PoF article

I make chutes as Front Range Rocket Recovery. These would be in the $250-270 each range due to the extra gores and sewing (I flat fell all seams so it takes longer than just serging).
 

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Sizing question.... would you size it for safe recovery speed on only 1 chute. If so, then with both chutes, you would have a VERY long walk to recover, or in a thermal watch it drift away. If sized for safe recovery on both chutes, then 1 may prevent catastrophic damage, but likely some damage from "hard" landing.

I like multiple chutes, but it's the visual show I am after. The redundancy / added complexity is just side effects. One helps, one hurts, so it's a wash as far as I am concerned....
This particular rocket needs a chute at least 16 inches in diameter. But it is a weird rocket made of three BT-20 tubes. It is hard to fit even a small parachute into a BT-20 so there is no way a 16 incher will fit.

I am trying to shoehorn two 11.75 inch parachutes into the tube. I am using thin plastic and button thread for the shroud lines. Still a tight fit.
 
If your parachute isn't opening, then you are not likely packing it correctly, or are wrapping the shroud lines around the chute. If it's coming out as a wad, try folding it neatly, and then looping the shroud lines within the folded chute, NOT wrapping it around the chute. If you're still having problems, try some talcum powder on the chute, maybe it's just sticky.
Wrapping the lines around the chute should not affect whether or not it opens. I have been packing mine like that for over 40 years. It slows the opening and reduces opening shock.
 
So when using 3 chutes I have seen it recommended to use risers for each chute so that there is a single line from each chute going to the connection point on the recovery harness/rocket, that way as the chutes open they have room to spread out (think about how multi chute pictures the chutes are all pulling away from each other) by adding a 18" or 24" riser (or whatever is recommended by the newsletter mentioned below) to each chute the canopies have that much extra room to open without hitting each other as they do so. Somewhere there is a document on how to rig 3 chutes to a single shock cord mounting point and getting fairly reliable opening on all three.

Edit: source for clustering parachutes was Apogee Newsletter #187
 
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This particular rocket needs a chute at least 16 inches in diameter. But it is a weird rocket made of three BT-20 tubes. It is hard to fit even a small parachute into a BT-20 so there is no way a 16 incher will fit.

I am trying to shoehorn two 11.75 inch parachutes into the tube. I am using thin plastic and button thread for the shroud lines. Still a tight fit.

Bummer. I'm assuming it's a scratch build?

You have arrived at that point of time where form does not fit function. It's a painful lesson.

Post up a photo of the rocket. Maybe seeing it will help us to come up with an alternative.
 
I don't do it any longer simply because I'm too lazy to chase down multiple pieces but there was a time when I would use multiple parachutes but I also had the rockets separate into two completely different pieces. My old Customer Rockets Equinox would split in the center and the top half would come down with a 15in chute where the lower would come down with an 18in chute.

I tried multiple chutes in a rocket that came back in one piece a few times and they tend to tangle up more than anything else. Then there is the fun of chasing it down when both do open and you now have twice as much chute is needed :)

I don't typically have parachute failures. In fact I don't see any in my log from the past year.
 
I tried putting a bunch of powder in a chute to make a small cloud at ejection for visibility. It just made a lump of powder in the chute that did not unfurl and deploy. Use only a little bit of powder on the chute so it does not stick to itself, not a large wad of powder in the chute. Unpack and repack right before launch, don’t leave the chute packed overnight or for a long time before flight.
 
I recently flew a scratch built cluster rocket at a local park launch with friends. The model rocket had a sustainer engine in the main body tube and two “strap on” booster tubes glued onto each side of the sustainer tube. Each booster tube had its own engine and its own shock cord and parachute.

Upon deployment, one booster tube parachute was lost when the shock cord broke in half. The other booster tube parachute deployed as did the sustainer parachute. The rocket landed safely on both parachutes.

This made me think: I have seen a lot of rockets crash or have hard landings because of a parachute coming out as a “para-wad” and not opening up. Maybe it makes sense to pack TWO, slightly smaller, parachutes into the body tube? If one paracute ends up being a “para-wad” upon ejection, maybe the other one still opens up and the rocket is saved?

Anything we can do to improve the chances of getting a rocket back in one piece is worth doing, it seems to me. This is especially true for any rocket we have diligently spent days building and painting and making look really nice.

This might not work on BT-20 or BT-50 sized rockets, because of space limitations in the tube. It should work on BT-55 and up sized rockets.

Using thin dry cleaner bags for the parachutes will help fit two of them into the body tube, I would think. Two dry cleaner bag parachutes ought to fit into a tube as small as a BT-50, if you use button thread for the shroud lines.

Any thoughts?
Also a good rule of thumb is to figure a 10% loss of efficiency due to multiple chutes when you are calculating surface area. But multiple chutes are also more stable--you get less oscillation than with a single parachute.
 
Kind of confused, does this entire rocket stay attached and recover as one unit, or are there three separate parts that recover independently?
 
Kind of confused, does this entire rocket stay attached and recover as one unit, or are there three separate parts that recover independently?
The two pods have their nose cones glued shut. I use booster engines (zero delay) in the pods. There are vent holes.

Yes the whole thing with spent engines stays together. The nose pops off just below the payload bay. It is a three engine cluster. That makes it tail heavy. I have big fins on the back and clay in the nose.

Recovered weight with spent engines is 130 grams (about 4.6 ounces). That is pretty heavy for one 12 inch parachute, no?
 
The two pods have their nose cones glued shut. I use booster engines (zero delay) in the pods. There are vent holes.

Yes the whole thing with spent engines stays together. The nose pops off just below the payload bay. It is a three engine cluster. That makes it tail heavy. I have big fins on the back and clay in the nose.

Recovered weight with spent engines is 130 grams (about 4.6 ounces). That is pretty heavy for one 12 inch parachute, no?

Have the booster motors self eject... then just use a streamer for sustainer recovery. :dontknow:
 
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