Optimal length of parachute shroud lines?

[BABAR]

Figured we'd gotten the shock cord question answered. Any opinions on optimal length of shroud lines? I have been using twice diameter of chute. (actually, since I cut 4 lines for my 8 hole chute, each line goes to two holes, so it is really 4X diameter of chute, but counting each line individually (chute to snap swivel) it is 2X diameter.

Also any preferences of 6 sided versus 8 sided chutes (I'm talking low power here)? I just use 8 cuz it is easier to fold and cut (fold in half, fold in half, fold in half, and cut.)

Most of my chutes are cut out of shopping bags (Hobby Lobby, Gander Mountain, Target. Walmart bags are too flimsy and ugly colored.)

Tom

 

[Micromeister]

Tom:
Really depends on what your doing with your models. That is competition PD or Sport chutes.
Sport flying generally 1-1/2 to 2X diameter is fine while baring in mind you will not get a completely open canopy with that length. 2.5 to 3x is my usual shrould length for full Parasheet & Hemi-Chute opening.

Snap or Barrel Swivels are a Great addition to any chute to save on Shrould line tangles.
using a parallel cross-canopy line attachment rather then corner to corner (estes instructions) all but eliminates Shroud line twist.
As far as the number of Shroud lines that again depends on how much of a cupped canopy your really interested in. Plastic or mylar (non-porus) Parasheet canopy materials spill air from under the rim from the least resistant side. This Air spilling process then proceeds to the next segment then the next and so on creating the rotational oscillation we see so often as the model decends. This process also creates some pretty distructive impact force on the model with contact with the ground. To greatly lessen this process two thing will help. A: install a spill hole in the top of the canopy & B: lengthen the shrouds by 1 to 2 diameters.

As an aside, many competition flyers using 1/4mil mylar competition chutes do not use a spill hole but increase the length and number of shrouds for 6 to as many as 12 or 16 to help the mylar form a "better" cupped canopy. After a flight or two these very thin mylar ParaSheets take on an semi-Hemi shape with the lightest (gram) models.
Hope this helps some

View attachment 6-Shroud line (12 attachment points)-b1c_12-03-09.pdf

 

[UrbanKnight]

Considering the small fields my students fly on, and the unnecessarily large chutes many of the BT50 rockets come with, the shorter the better for them. I sometimes have them cut huge spill holes and/or tape the shroud lines 1/4 of the way up just to avoid having them drift away.

 

[darthgriffin]

I prefer 5 shroud lines. After buying a bunch of Estes chutes, I found the plastic too thick and don't pop open well if you leaved them packed for a long time (I'm lazy).

My favorite chute is to pick up some of those colorful star shaped mylar balloons from the dollar store. When laid flat on the table you can easilly cut off the edges to make a pentagon. Tying 5 individual shroud lines sucks, but they make for great chutes.

 

[BABAR]

All answers appreciated. THANX!

 

[Sooner Boomer]

I prefer 5 shroud lines. After buying a bunch of Estes chutes, I found the plastic too thick and don't pop open well if you leaved them packed for a long time (I'm lazy).

Applying cornstarch or baby powder to the chutes will make them very slippery and easier to open, even if they're packed for a long time. The way the shroud lines and shock cord are wrapped around the chute can greatly affect how quickly the chute opens, too.

 

[GregGleason]

Applying cornstarch or baby powder to the chutes will make them very slippery and easier to open, even if they're packed for a long time. The way the shroud lines and shock cord are wrapped around the chute can greatly affect how quickly the chute opens, too.

Talc (or baby powder, which is mostly talc) is better than cornstarch. Cornstarch, when it is dispersed into a mist, is flammable or explosive (as in what you find with grain elevator fires or explosions).

Greg

 

[Micromeister]

Absolutely Correct Greg!
Never Ever use Cornstarch or cornstarch baby powders to powder chutes. Can cause considerable explosion & fire damage to both Rocket and surrounding area. I made that mistake once on a 2.6" model with 2- 24" estes style chute. Blew all to tiny pieces.. got back a very short charred fin can.

Talc baby powder is the way to go. I use it on nylon chutes as well just for the ejection cloud to help with spotting.

 

[Sooner Boomer]

Well, I hope you two have that out of your systems now! You make it sound as though cornstarch is more dangerous than the black powder in the engines. It is NOT!. If you are properly rigging the recovery system using wadding, the cornstarch will NEVER see the heat or flame of the ejection charge. If it does, your parachute will melt, and this was because YOU did something wrong! You're what's dangerous, not the powder.

 

[jpummil]

Well, I hope you two have that out of your systems now! You make it sound as though cornstarch is more dangerous than the black powder in the engines. It is NOT!. If you are properly rigging the recovery system using wadding, the cornstarch will NEVER see the heat or flame of the ejection charge. If it does, your parachute will melt, and this was because YOU did something wrong! You're what's dangerous, not the powder.

Case of "The Monday's"?

 

[mdoering]

Case of "The Monday's"?

Maybe he was one of the angry people in the TRA snowmobile conversation... :rofl:

 

[AfterBurners]

I used to make chutes out of the Hefty brand trash bags. The black flex type bag. I made they 8 sided with spill holes and my line were 1.5x the chutes diameter. Some of my best chutes were hand made...anyway I guess as long as the lines are secured you should be fine with whatever shape you go with.

 

[Sooner Boomer]

I used to make chutes out of the Hefty brand trash bags. The black flex type bag. I made they 8 sided with spill holes and my line were 1.5x the chutes diameter. Some of my best chutes were hand made...anyway I guess as long as the lines are secured you should be fine with whatever shape you go with.

How did you attach the shroud lines to the plastic bag?

 

[luke strawwalker]

I prefer 5 shroud lines. After buying a bunch of Estes chutes, I found the plastic too thick and don't pop open well if you leaved them packed for a long time (I'm lazy).

My favorite chute is to pick up some of those colorful star shaped mylar balloons from the dollar store. When laid flat on the table you can easilly cut off the edges to make a pentagon. Tying 5 individual shroud lines sucks, but they make for great chutes.

I made one of those from a star shaped balloon that drifted down onto the place... found it tangled in the fenceline. What I did was make 5 shroud lines that go across from one point of the star to the corresponding "crotch" between stars on the other side... they all cross in the middle. SO, technically speaking, it's got ten shroud lines... the point ones are necessarily longer than the ones going to the crotches between points...

Later! OL JR

 

[luke strawwalker]

Talc (or baby powder, which is mostly talc) is better than cornstarch. Cornstarch, when it is dispersed into a mist, is flammable or explosive (as in what you find with grain elevator fires or explosions).

Greg

Not to pick nits too much, but it's not a mist... it's an aerosolized particulates...

Greg is exactly right, but the odds are VERY LOW you'd get an actual ignition. While I don't recommend it, I've used regular flour for "tracking powder" when I was younger, and even put a handful of flour under the rocket motor to create a large "billowing cloud" at liftoff... never had an ignition of the aerosolized flour particles... BUT, our science teacher DID create a "dust explosion" in class one time... took a cookie tin and punched a hole in the bottom, ran surgical tubing out the hole and stuffed a small funnel in the end still inside the tin, then put a tea candle inside the tin and a spoonful of flour into the funnel, and slapped the lid on, then blew a sharp puff of air through the surgical hose to aerosolize the flour particles inside the tin... the candle then lit them off and POOF! blew the lid right off the tin and produced a good size fireball...

Look up "cremora fireballs" for more information...

Later! OL JR

 

[AfterBurners]

How did you attach the shroud lines to the plastic bag?

I used plastic reinforcement like most plastic chutes have and used a hole punch to make the holes. I just double knotted them. I tied a knot around a pencil and that provided enough gap as to not tear the chute when it opened. I was told you never want to cinch your knot against a plastic chute. The ESTES chutes are tied the same way.

I also attached my lines across from each other, not corner to corner. When you attach them corner to corner you always get a line that tangles.

 

[gpoehlein]

I used plastic reinforcement like most plastic chutes have and used a hole punch to make the holes. I just double knotted them. I tied a knot around a pencil and that provided enough gap as to not tear the chute when it opened. I was told you never want to cinch your knot against a plastic chute. The ESTES chutes are tied the same way.

I've done it that way, but most of the time, I just put a small square of 1/2" Mylar tape (I found it at Blick's), on each attachment point. I then punch a small hole in the center with a small hole punch (I found a set of scrap booking round hole punches of differing sizes - the 1/8th inch hole is perfect for this. If you draw a small dot in the center of the tape with a Sharpie, you can find it in the hole punch easier. For extra strength on large chutes, I have put a small piece of tape on both sides of the chute before punching the hole.

For really bit chutes (36") on egg models I will usually run the shroud lines over the top of the chute, with a couple of small pieces of Mylar tape to hold it in place. Tape at center after all the shrouds are in place with an "X" of tape. Gather all the ends of the shrouds and tie them together with one simple knot.