PDA

View Full Version : Problems with Round Parachute or Maybe Shroud Lines


brockrwood
05-30-2011, 04:12 PM
Any thoughts on the best

1. Parachute shape?
2. Shroud line material?
3. Shroud line length?
4. Shroud line/shock cord attachment (to nose cone) methods?
5. Parachute material?

I had a rather disappointing day flying an old, trustworthy Estes "Blue Ninja" rocket I had recently repaired. The old 18 inch stock parachute had melted from the heat of several launches (and one time that I forgot to put in recovery wadding)! I replaced the stock Estes parachute with a homemade 19 inch round (circular) parachute made from a black plastic trash bag. The round parachute was attached to the nose with a fishing swivel and six 19 inch lengths of cotton "carpet" string. This is not carpet/button thread but the heavier cotton string you use to make homemade rugs. It is sort of like crochet string but heavier and stronger. I also replaced the broken Estes rubber shock cord with 1/4 inch elastic 2 times the length of the rocket.

When I was making the parachute I noticed that the chute didn't seem to want to open cleanly and easily - the curved "flaps" of the circle between each shroud line attachment point seemed to want to flip over or under rather than fan out and catch the air. I figured a good strong breeze from the descending rocket would fix that.

I also noticed that the heavy cotton string, while it was easy to tie and held a knot great, really tangled easily because of the natural friction created by the cotton. Again, I figured the swivel would take care of that.

Upon launch today the Blue Ninja made a perfect ascent. When the nose blew, however, the shroud lines were hopelessly tangled around the shock cord. The parachute didn't fully open and the heavy, D-powered rocket came down fast on a 1/3 opened chute which was more like a drogue chute or streamer. Luckily it didn't hit too hard (a tree branch slowed it down) and only broke a fin and a launch lug.

At this point, I think I will go back to hexagons for parachute shapes and some slippery nylon kite string for shroud lines.

Any other suggestions or thoughts?

Thanks in advance!

- Brock

Chas Russell
05-30-2011, 04:37 PM
Wow, Brock, a lot of questions. You will get expert answers here, but until then I have a few thoughts...

Shape really doesn't matter until you get into parachutes made from separate sections or gores. It really depends on size and how you cut or purchase them. For some smaller chutes I use circular mirrors purchased from Hobby Lobby or Micheal's (using the 40% off coupons) to cut round ones. Anything more than 12 or 14" I fold silver "rescue blankets" to make octagonal chutes. ASP is one retailer that sells circular parachutes in numerous sizes.

I use carpet thread or very thin kevlar for shroud lines. The rule of thumb is that each line should be at least 1 parachute diameter in length. For competition we use 1.5 diameters (3X attached to two places).

I use adhesive mylar or monocote to attach lines. I did purchase some clear reinforcements like you would use for notebook paper for use on sports chutes. Have only made one that way, but have not flown it yet.

Also consider using talcum powder (not corn starch powder) to lubricate the parachutes prior to packing them. It takes the "stickiness" from the material and also any exposed adhesive on your line attachment. I actually keep my competition chutes in ziplock bags containing talc to condition them.

Hope this helps.

Chas

brockrwood
05-30-2011, 04:41 PM
Thanks, Chas!

Yes, I did use talcum powder, but, as you can see, it didn't help. Octagons, huh? OK, I will make a "stop sign" parachute and see how that works.

Thanks for the ideas!

- Brock


Wow, Brock, a lot of questions. You will get expert answers here, but until then I have a few thoughts...

Shape really doesn't matter until you get into parachutes made from separate sections or gores. It really depends on size and how you cut or purchase them. For some smaller chutes I use circular mirrors purchased from Hobby Lobby or Micheal's (using the 40% off coupons) to cut round ones. Anything more than 12 or 14" I fold silver "rescue blankets" to make octagonal chutes. ASP is one retailer that sells circular parachutes in numerous sizes.

I use carpet thread or very thin kevlar for shroud lines. The rule of thumb is that each line should be at least 1 parachute diameter in length. For competition we use 1.5 diameters (3X attached to two places).

I use adhesive mylar or monocote to attach lines. I did purchase some clear reinforcements like you would use for notebook paper for use on sports chutes. Have only made one that way, but have not flown it yet.

Also consider using talcum powder (not corn starch powder) to lubricate the parachutes prior to packing them. It takes the "stickiness" from the material and also any exposed adhesive on your line attachment. I actually keep my competition chutes in ziplock bags containing talc to condition them.

Hope this helps.

Chas

Chas Russell
05-30-2011, 04:42 PM
I also pack the parachutes by folding them in half and then in quarters. Fold the top down to the bottom, place the shroud lines from bottom to top, fold parachute in half side to side, shroud lines back to bottom, fold again, and again until it fits in tube and wrap the remaining lines around the parachute. The lines pull taut and help to spread the parachute so that it catches air.

C

jharding58
05-30-2011, 06:35 PM
I think the advice from others here will help you; the only offering is that your shroud lines are too thick. There is a lot of mass in line that coarse, and as you observed the line tends to grab. In the recovery system for models it is best if the heaviest element is the chute, the nosecone ejects and drage the shrouds, starts the wrapped canopy spinning to unwrap the remaining shroud and shock cord, then the talcum enables the tnesionon the canopy to start it filling. Properly wrapped, lubricated with talcum, and with smooth lines you should get a clean deploy on any shape canopy; hex and octagonal canopies are simply selected since they are easier to cut and you can loop the shrouds from adjacent "corners".

brockrwood
05-30-2011, 07:00 PM
Understood. What sort of shroud line material do you recommend? I noticed that my daughter's parachute duration "competition" rocket came with really thin but strong thread-like shroud lines. I wonder what they are made of? She got it from the nice folks at ASP Rocketry. I will send them an email...

Thanks again!

- Brock


I think the advice from others here will help you; the only offering is that your shroud lines are too thick. There is a lot of mass in line that coarse, and as you observed the line tends to grab. In the recovery system for models it is best if the heaviest element is the chute, the nosecone ejects and drage the shrouds, starts the wrapped canopy spinning to unwrap the remaining shroud and shock cord, then the talcum enables the tnesionon the canopy to start it filling. Properly wrapped, lubricated with talcum, and with smooth lines you should get a clean deploy on any shape canopy; hex and octagonal canopies are simply selected since they are easier to cut and you can loop the shrouds from adjacent "corners".

Rex R
05-30-2011, 07:03 PM
I've had good results with braided dacron trolling line (15# test) hth
rex

jharding58
05-30-2011, 07:24 PM
Kite string. Unless you want to go with ultralight braided Kevlar. The most important part of any shroud is the attachment to the canopy and to the harness (or in our case I guess the NC) so make sure that the shrouds and canopy are either tied together or encased in really permanent pieces of tape.

BTW, an optimal shroud length is 1.15 times the canopy diameter (115%). In conjunction with a correctly sized spill hole that will reduce topple in the canopy and swing at the harness. A ten inch canopy needs a single shroud length of 11.5 inches. A 19" canopy would use a shroud length of 22 inches.

Solomoriah
05-30-2011, 07:27 PM
I got a roll of braided nylon kite string at the dollar shop a while back, and it makes great shroud lines. It's slick and thin, though not as thin as some types, and it won't unravel like twisted lines will. I've used it mostly for the larger chutes I've built, including my Tyvek chute (which I'm hoping to test soon).

Doug Sams
05-30-2011, 07:30 PM
At this point, I think I will go back to hexagons for parachute shapes and some slippery nylon kite string for shroud lines.

Any other suggestions or thoughts?Yes. Somewhere in the range of 14-18 inches diameter, you want to go up to 8 suspensions lines, as noted herein (ie, octagon).

As for material, I've been using Glide brand, Teflon coated dental floss for the suspension lines. It has worked well for me.

Doug

.

brockrwood
05-31-2011, 02:06 AM
Thanks for all the helpful tips, everyone. The folks in this forum are the best!

- Brock

blackshire
05-31-2011, 02:18 PM
Yes. Somewhere in the range of 14-18 inches diameter, you want to go up to 8 suspensions lines, as noted herein (ie, octagon).

As for material, I've been using Glide brand, Teflon coated dental floss for the suspension lines. It has worked well for me.

Doug

.Indeed--Centuri and FSI (Flight Systems, Inc.) used octagonal parachutes. I never had an FSI kit, but the Centuri 'chutes (particularly the larger ones) tended to open more easily and fill out better than the hexagonal Estes 'chutes.

luke strawwalker
05-31-2011, 05:21 PM
I think a big part of the problem is the shroud line material-- if it's "fuzzy" at all the stuff will tend to grab each other and tangle like velcro... you REALLY need a smooth NON-FUZZY type shroud line... I've used twisted nylon string (trot-line) and heavy carpet thread-- the carpet thread is plenty-- smooth and strong. I've used duct tape squares for shroud line attachment and have had good luck with it-- it's a bit heavy, but the tape is REINFORCED and SO sticky that it's NOT coming loose from the chute without taking the side of the chute out with it! The Trim Monokote is also quite good for this from what I've heard...

The other part is, how you fold the chute. When I pack a parachute for a rocket flight, I pull all the shrouds taut and and point the canopy, then gather all the 'billows' between shroud lines and fold them OUTWARDS lying on top of each other, making an accordioned triangle shape of the chute with the peak at the apex, with the shrouds at one corner and the center of the billows at the other corner. I fold the point over onto the rest of the chute (a little less than halfway so the apex doesn't QUITE come down to the shrouds level) and then start rolling the chute up from the fold. I wrap the shroud lines LOOSELY around the canopy and insert it in the rocket...

I've never had one fail to deploy this way... so long as it comes out of the tube... (had weak ejection charges or one time too much wadding pop the nose loose but not eject the chute-- ouch!)

Later! OL JR :)

mycrofte
05-31-2011, 06:25 PM
I have made my own chutes out of white trash bags and kite string. But, the biggest rocket I have is a Nike-X.

luke strawwalker
05-31-2011, 11:45 PM
I have made my own chutes out of white trash bags and kite string. But, the biggest rocket I have is a Nike-X.

Dr. Zooch swears by 'em...

He even offers a guarantee-- "if your rocket crashes into a smoking crater of twisted paper tubing and shattered balsa bits due to the failure of one of our trash bag parachutes, we'll send you a brand new trash bag parachute absolutely free!" (or to that effect) LOL:)

Seriously I've used trash bag chutes and they work fine...

Later! OL JR :)