Reefing a parachute

[HighFlight]

Anyone here have much experience with parachute reefing methods? I have a 36" Iris chute from fruitychutes that I intend to use in an upcoming build, but due to the necessary drop tests of this particular project, the parachute could potentially be deployed at terminal velocity, in this case, about 160 mph.

I'd like to experiment with a simple ring slid onto the shroud lines to choke off the canopy while packing it. Theoretically, it should choke the chute during deployment, not letting it open fully, until the rocket slows down somewhat, then the ring slides down the lines and the parachute fully opens. I figure this should work, at least somewhat, so long as the ring isn't so large that it can slide UP the lines and get stuck on the canopy itself. Since the iris type chutes are toroid shaped, I really can't use any sort of reefing slider that contains anything internal to the shroud lines.

"Real" reefed parachutes are able to control when the ring slides down, or cut the ring in place. But I think for this scale, that is a bit impractical.

Before I proceed though, I wanted to ask around here to see if there is anything else I should be aware of?

 

[Fdog]

I have personally jumped several reefed round parachutes. Only one of them (the AT-3) was a pulled down apex design like the Iris. It used a 6-point spider slider. This worked great at high speed (120 mph) but was eminently choppable - meaning I cut the frickin thing away alot - at slow speed (60 mph) because the slider held the skirt closed, and canopy expansion forces were very low.

I suspect the same fate would be in store if you try to cobble together a ring system to hold the lines closed with the Iris. Also, to be honest, all the design did was take away the initial high-g transient, overall g loading was still quite high.

I very much enjoyed the jumps with the HX400, which use the Sombrero slider. The openings were very smooth and reliable, no matter what the airspeed. If I was going to deliberately reef a parachute, this would be the design I'd find some way to use, although the mesh exterior of the sombrero would be space consuming.

Butler has the patent, you can research it I think, to get an idea.


All the best, James


PS: Linky to sombrero

 

[CarVac]

I have personally jumped several reefed round parachutes. Only one of them (the AT-3) was a pulled down apex design like the Iris. It used a 6-point spider slider. This worked great at high speed (120 mph) but was eminently choppable - meaning I cut the frickin thing away alot - at slow speed (60 mph) because the slider held the skirt closed, and canopy expansion forces were very low.

I suspect the same fate would be in store if you try to cobble together a ring system to hold the lines closed with the Iris. Also, to be honest, all the design did was take away the initial high-g transient, overall g loading was still quite high.

I very much enjoyed the jumps with the HX400, which use the Sombrero slider. The openings were very smooth and reliable, no matter what the airspeed. If I was going to deliberately reef a parachute, this would be the design I'd find some way to use, although the mesh exterior of the sombrero would be space consuming.

Butler has the patent, you can research it I think, to get an idea.


All the best, James


PS: Linky to sombrero

How would the GLR sliders compare? For most dual deploy purposes, since they are at speed during main deployment, it doesn't need the "force open the bottom" that is effected by the hemispherical shape of the Sombrero. I am considering getting one for my 96" Spherachute to prevent inversion.

edit: https://giantleaprocketry.com/products/components_recovery.aspx#Slider

I think it would have a better effect on a round canopy than on the triangular canopy they show in the video.

 

[HighFlight]

I guess maybe I should back up a little. Deploying a 36" chute on a 2-ish pound rocket at 150 mph... is that doable without any sort of reefing / staging?

 

[CarVac]

I guess maybe I should back up a little. Deploying a 36" chute on a 2-ish pound rocket at 150 mph... is that doable without any sort of reefing / staging?

Why?

150 is awfully fast for a descending rocket, especially one of that size, even if drogueless. If you are doing this without separating at apogee then I would suggest staging the deployment by at least breaking it apart on the way down a thousand feet before opening the main.

Speaking of which, why has nobody tried that?

Also, that is a much larger parachute than is necessary.

 

[Fdog]

How would the GLR sliders compare? For most dual deploy purposes, since they are at speed during main deployment, it doesn't need the "force open the bottom" that is effected by the hemispherical shape of the Sombrero. I am considering getting one for my 96" Spherachute to prevent inversion.

edit: https://giantleaprocketry.com/products/components_recovery.aspx#Slider

I think it would have a better effect on a round canopy than on the triangular canopy they show in the video.

Weeeelll...we did try a few jumps with a 26' LoPo using a regular old ram-air (rectangular) slider. It "sorta" worked but would occasionally end up skewed sideways and hang up about 6' down the lines, distorting the canopy and resulting in a chop; also we ended up with popped stitching on the skirt panel that was inbetween the line bundles.

<shrugs> Using the Giant Leap slider might work though, in your proposed use it's (proportionally) much larger than what we used. Only one way to find out, throw it out the back of a pickup at 100 fps.

As an aside, 100 fps is quite low speed in the parachute opening world. I wouldn't expect to see a significant reduction in opening forces as seen by the airframe overall. I'd have to balance that against opening reliability.

Knowing you, I expect to see a complete testing series with an analysis of opening forces....


All the best, James

 

[Ravenex]

I guess maybe I should back up a little. Deploying a 36" chute on a 2-ish pound rocket at 150 mph... is that doable without any sort of reefing / staging?

I'm currently building a rocket that with engine casing will be around 6lb and Gene at fruity chutes recommended his 30" Iris for a 22 fps decent rate.

 

[Lowpuller]

Google, parachute diaper. This would be my suggestion.


Sent from my iPad using Rocketry Forum

 

[HighFlight]

Thanks all for the info. Looks like I have some reading to do, and possibly some design changes.

CarVac that's a good idea, I was just trying to avoid a dual deployment if I could. No real reason though. Just thought it would be simpler this way, not having 2 ejection charges. I know 36" is larger than I need. Its just what I had already. It was intended for something else originally.

In the mean time, I did some sub-speed testing.
[video=youtube_share;WpkD7fpkQ2k]https://youtu.be/WpkD7fpkQ2k[/video]

 

[Fdog]

Nicely done on the video! There's good data to be had there.

As a helpful FYI, snatch force is defined as the impact generated by the bag (or parachute) hitting the end of the lines, not the deceleration generated by the parachute opening.


All the best, James

 

[CarVac]

Weeeelll...we did try a few jumps with a 26' LoPo using a regular old ram-air (rectangular) slider. It "sorta" worked but would occasionally end up skewed sideways and hang up about 6' down the lines, distorting the canopy and resulting in a chop; also we ended up with popped stitching on the skirt panel that was inbetween the line bundles.

<shrugs> Using the Giant Leap slider might work though, in your proposed use it's (proportionally) much larger than what we used. Only one way to find out, throw it out the back of a pickup at 100 fps.

As an aside, 100 fps is quite low speed in the parachute opening world. I wouldn't expect to see a significant reduction in opening forces as seen by the airframe overall. I'd have to balance that against opening reliability.

Knowing you, I expect to see a complete testing series with an analysis of opening forces....


All the best, James

I wouldn't be against making a custom slider myself if the GLR isn't suitable, but I'm not sure exactly what would work best.

Testing is probably key, but testing at full speed would be tough... I don't have a pickup, and there are no nearby deserted roads on which to go 70 mph and throw a parachute out the back. (It's probably not a very good idea on the NJ Turnpike)

 

[HighFlight]

thanks Fdog, didn't realize I was not using the right terminology.
The reefing ring did not keep the canopy choked for nearly as long as I hoped, but it definitely helped.

 

[Bat-mite]

Any reason you can't use an altimeter/timer and a cable-cutter?

 

[HighFlight]

bat-mite, I'll be perfectly honest here: part of my problem here is that I don't know some of the techniques used in mid and high power rocketry, and more specifically, where to get components like a cable cutter for a reasonable price. But after reading the previous statement, please don't think I'm some joe-schmoe that has absolutely no idea what I'm doing. What I DO know about, quite extensively, is radio control and FPV. Normally you'd find me under a different username on the FPVlab forum. I'm one of the more prominent members over there. You can probably figure it out based on some of my other youtube videos. Also, I have a degree in aerospace engineering, and I'm a mechanical & test engineer on the Orion program.

I was intentionally holding back the intended application that spurred my original post, because I've seen elsewhere that some folks tend to get upset when it has been attempted before. Let's just say that the current (horizontal) speed record for an FPV RC aircraft is "only" 209 mph ;-)
https://fpvlab.com/forums/showthrea...LEARDERBOARDS)&p=334820&viewfull=1#post334820

What I have in mind is more "rocket" and less "aircraft" though, so without some speed, it will be more like falling with style, but hopefully controllable. The first drop tests will be from a friend's FPV aircraft at several thousand feet, just to see how controllable it is.

I don't have an L1 cert yet, so that necessitates keeping things on the light side, and the FPV gear adds a significant amount of weight already. Just trying to save weight where I can.

If you have suggestions for specific products, like a cable cutter, I'd love to hear them.

 

[Bat-mite]

Not sure if this would work for you or not, but maybe worth a look. https://lkal32.blogspot.com/p/cable-cutter.html

 

[HighFlight]

Neat little device. Any examples for how to implement this as a reefing line cutter without having wires routed all the way up the shroud lines? Routing them to the confluence point is better I think.

 

[Bat-mite]

No, the wires are definitely a drawback. Interesting thread.

 

[GregGleason]

Here is a thread on reef-line cutting:

https://www.rocketryforum.com/showthread.php?17067-Chute-Reef-Line-Cutter

Greg

 

[jcato]

Neat little device. Any examples for how to implement this as a reefing line cutter without having wires routed all the way up the shroud lines? Routing them to the confluence point is better I think.

It's called 'Control Line Reefing' (Google will show you a lot re: sailing - but not recovery methods - have to check out Knacke for a discussion on this). At any rate, you route your reefing line around the canopy skirt and exit (i.e. draw down the reefing line between 2 adjacent reefing rings) at several points (I would recommend 4) and come down to the confluence point - mounting your cutter there. (I would gather the (4) control lines (which is actually just the extended portion of the reefing line) with a short, single loop of line thru the cutter - that way, all (4) are released simultaneously (and you only waste that 'gathering loop' per flight - and not have to replace the entire reefing line)).

Note that, as implemented, this is just one, long reefing line that happens to come down to the confluence point at 4 (equi-distant) points around the canopy skirt. I, additionally, sewed a small 'D-ring' in the skirt between 2 adjacent reefing rings as my exit point (4 places). The reefing rings themselves were simply 3/8" 'cabone' rings found in the Crafts section at Wal-Mart (but, you could also use (even smaller) beads (1/4" or so - kind of 'ball' shaped) available there in the Crafts section - what I'm doing in my ringsail).

On the scale of canopies in the hobby, the canopy will not respond like a full scale canopy (i.e. somewhat squidded) in the reefed state - rather, the canopy will form a ball shape (almost like a ballute) - but that still acts as a retarder and will lessen the inflation forces. This is the reason I would recommend 4 control lines (instead of 2), as that makes the canopy symmetrical enough to not start rotating (a possibility with only 2 control lines - as you risk a 'figure 8' reefed shape and if it's not perfectly symmetrical, it could start rotating).

But, it works, though.

-- john.

ADDENDUM: Now *this* looks interesting:

https://nsrdec.natick.army.mil/LIBRARY/00-09/R09-18.pdf

--jhc.

 

[jcato]

<snip>
ADDENDUM: Now *this* looks interesting:

https://nsrdec.natick.army.mil/LIBRARY/00-09/R09-18.pdf

--jhc.

I'm wondering why something like this couldn't also be used to thread a tubular shock cord through -- pull out a little bit of slack (i.e. loop) and let the shock load stretch it back out. Would just about have to work. These 'Kellem grips' are sold at every electrical supplier to support vertical runs of electrical wiring in buildings - in many sizes.

 

[HighFlight]

hmm... my parachute has no rings where the shroud lines attach to the skirt.

 

[Winston]

Anyone here have much experience with parachute reefing methods? I have a 36" Iris chute from fruitychutes that I intend to use in an upcoming build, but due to the necessary drop tests of this particular project, the parachute could potentially be deployed at terminal velocity, in this case, about 160 mph.

I'd like to experiment with a simple ring slid onto the shroud lines to choke off the canopy while packing it. Theoretically, it should choke the chute during deployment, not letting it open fully, until the rocket slows down somewhat, then the ring slides down the lines and the parachute fully opens. I figure this should work, at least somewhat, so long as the ring isn't so large that it can slide UP the lines and get stuck on the canopy itself. Since the iris type chutes are toroid shaped, I really can't use any sort of reefing slider that contains anything internal to the shroud lines.

"Real" reefed parachutes are able to control when the ring slides down, or cut the ring in place. But I think for this scale, that is a bit impractical.

Before I proceed though, I wanted to ask around here to see if there is anything else I should be aware of?

Glad to see someone experimenting with this. Previous short thread on reefing rings if you missed it:

https://www.rocketryforum.com/showthread.php?56344-Plastic-reefing-rings-for-HPR&highlight=reefing

 

[Winston]

This guy experimented with a reefing ring on a large water rocket 'chute:

[video=youtube;P_XEJ6swY0w]https://www.youtube.com/watch?v=P_XEJ6swY0w[/video]

 

[jcato]

hmm... my parachute has no rings where the shroud lines attach to the skirt.

That's not surprising - I know of none (in the hobby) that does (mainly, I would conclude, because reefing is just not that widespread or accepted). You'll just have to put them in yourself (not that hard -- see below)...

The first is the 3/8" 'cabone' rings (the tape that anchors the ring to the skirt is a 3/8" ribbon weave nylon):


Here is the small 'bead' type (1/4" dia +-) (the green line is the reefing line). This was sewn into the radial seam with about 3 or 4 'rounds' of kevlar thread and then the thread was wound around the base of the bead 3 or 4 times (like they do with buttons sometimes, to make them stand out from the base fabric):


This the 'D-ring' mentioned in my previous post (the skirt exit point for the 'Control Line Reefing' method) - with the control line threaded through it (I ran the 3/8" tape up to the two adjacent radials to help spread the load back to the radial seams):

 

[Winston]

I'd like to experiment with a simple ring slid onto the shroud lines to choke off the canopy while packing it.

Definitely keep us updated on your progress. Something even easier to make than a "slider" would be nice to have to reduce incidents of zippering from inaccurate or incorrectly chosen motor delays.

 

[HighFlight]

for my project I decided to go with the simple ring that I tested in the video, with a break-in-half body tube design and a foam plug on the kevlar line at the lip of the tube to further reduce the chance of zippering. I may do some more tests with a tube instead of a ring, but I won't be doing an "active" reefing line cutter for this one. I've yet to test it for real though. Waiting on my e-matches and a few other things to arrive.

I will definitely keep some of these concepts in mind though.

 

[G_T]

With an iris chute there is another possibility.

Have the chute made with the center set of lines separately gathered from the main outer set of lines. Have the outer set drawn a few inches closer than standard deployment, on a separate line gathered by a ring to parallel the first at the location the shroud lines normally are collected. Release those couple inches via cable cutter. Now what one is doing is converting an IRIS chute to a conventional hemispherical chute for the higher speed portion. This greatly reduces the Cd.

I hope the description is clear enough, though it probably isn't.

Gerald

 

[CarVac]

With an iris chute there is another possibility.

Have the chute made with the center set of lines separately gathered from the main outer set of lines. Have the outer set drawn a few inches closer than standard deployment, on a separate line gathered by a ring to parallel the first at the location the shroud lines normally are collected. Release those couple inches via cable cutter. Now what one is doing is converting an IRIS chute to a conventional hemispherical chute for the higher speed portion. This greatly reduces the Cd.

I hope the description is clear enough, though it probably isn't.

Gerald

I found that the inner attachment points on the Iris Ultra I have worked with weren't very robust when not pulling parallel to the fabric properly. I am not sure that would be a great idea.

 

[G_T]

??? I probably didn't explain it very well.

Upon toroidal chute manufacture, the inner shrouds are collected to a single point and the outer shrouds are collected to another point. In the case of the IRIS Ultra, these are both connected at the chute attachment point. Disconnect them. Put a small metal ring on one set of shrouds at the gathering point. Route a line to the other set of shrouds through the ring.

There is no change to how the shrouds connect to the fabric.

Now, with appropriate line control, one can alter the chute's inflated profile from hemispherical or elliptical, to toroidal, with a large change in Cd.

Gerald

 

[CarVac]

??? I probably didn't explain it very well.

Upon toroidal chute manufacture, the inner shrouds are collected to a single point and the outer shrouds are collected to another point. In the case of the IRIS Ultra, these are both connected at the chute attachment point. Disconnect them. Put a small metal ring on one set of shrouds at the gathering point. Route a line to the other set of shrouds through the ring.

There is no change to how the shrouds connect to the fabric.

Now, with appropriate line control, one can alter the chute's inflated profile from hemispherical or elliptical, to toroidal, with a large change in Cd.

Gerald

The act of pulling the center down from a pseudo elliptical configuration will strain the connection, because it will start out pulling perpendicular to the fabric. On the Iris we used for Bare Necessities, a few of the center shroud lines came partially undone when I picked it up by the pilot strap and the wind inflated the canopy. It still worked fine but I would reinforce them if i were to try that.