acceptable velocity for chute deployment.

If you google this usenet group with "John Cato Tom Binford chutes", you'll find alot of good chute discussions from a couple years ago. The gist is in controlling controlling the deployment...

50" chute for a 4 pound rocket? Got a big field?

Andy

I just got my level 1 yesterday so I can't offer much experience but here's my thinking:

I'd like to know how you are going to fire the ejection, I haven't seen a speed sensitive ejection gizmo (maybe some acceleromiters do something like it). Therefore your options are to use a timer, altimeter or magnetic device. The timer could be the motor delay grain of course.

Safe deployment speed seems a funny idea anyway. The answer has to be the slowest you can get, but once the airframe is split the drag multiplies and the rocket will slow down quickly. What you want to do then is to try and delay the parachute opening after it has been ejected. This is what folk are doing with drougless 2 stage recovery. You can do this in a number of ways:

1. Arrange the chute so it is not itself ejected by the charge - so the charge sends the nose of which pulls out the chute.
2. Use a deployment bag

1. Use long shock cord (my RSO thought the shock cord had broken because the chute took so long to deploy- I had over 30' on a 5' rocket)

2. Roll the shrouds and some shock cord round the folded chute.

I'm sure there must be more options.

Thinking about why you want slow deployment: to minimize stress and chances of failure of the recover chain or zippering of the airframe. ROL suggests every part of the recover chain should be built for 50 times the weight of the rocket so for a 4lb rocket you want everything to be able to take your weight and more. I find the hardest thing to test with my weight is the attachment of the recovery gear to the airframe - has anyone any advice about this?

Of course now I'm level 1 I have so much wisdom I need a motto so here it is:

Test everything - including advice - especially mine.

Good luck and have fun,

Halam

Halam I agree that the deployment speed should be the slowest you can get it but sometimes s*#t happens. You rocket can weather c*ck so it can be going significantly faster at deployment no matter what method you use. Plus early or late ejection can cause higher deployment speeds. I also agree you should build the deployment system to withstand significantly higher stress than you hope for. Where I disagree is with your chute packing style. A member of our club is a certified parachute rigger and he says never wrap your shroud lines around or inside the chute. He says a lot of the rocket chutes he repairs have holes in them from the shroud lines moving across the nylon so fast they generate enough heat to melt the material. He recommends Z folding the chute then Z folding the shrouds and tying them together with rubber bands or tape. The tape should be able to break easily. This will soften the opening of the chute. On my grandsons rocket we built it Zipperless so the chute is in the forward tube and has to be pulled out. When the ejection charge fires the whole forward part of the rocket moves forward. There is a five foot long piece of tubular Kevlar between the motor section and the nomex chute protector. When the chute protector is pulled from the forward body tube there is a 10" drogue attached at this point. The drogue starts to slow the motor section and pull the recovery harness from the forward body tube. The recovery harness is also Z folded and tied together with rubber bands. The recovery harness starts to pull the shroudlines out then the chute By this time the motor sections is slowing before the chute starts to open. He highly recommends deployment bags. He also recommends having the chute so it is pulled out of the body tube or deployment bag by the shroud lines. First in Last out. Just a suggestion as you stated test everything including advice.

Sometimes s*#t does happen, so I am trying to determine my margin of error.

Halem, it's not such an unusual of "funny" idea to ask what is the maximum stress that any system can / should tolerate while trying to determine you margin of safety. I am using rocksim and neither the 6sec or 10sec delay is ideal. (delpoying at apogee) I want to know if my velocities are acceptable.

Let me ask the question again in another way. What kinds of speeds are you guys getting at successful deployment? One other thing; my shock cord is about 10 feet of 1/4" diameter Kevlar Bungie Cord.

Andy, I calulate a 50 inch round shoot to decend at about 18 ft per second for a 4 pound rocket. How fast do you like your rockets to hit the ground?

Anywhere from 5 fps (during duration contest) to don't care so long as it's aerodynamic garbage (falling safe) and on the (grassy) fairway. i.e. ejects the nosecone & shockcord but with no chute/streamer. Folks living in rocky desert may balk...

Finished your reading yet? Binford was a resident Jedi Knight here once...

Plan on the worse your recovery system will see (full deployment at maximum terminal velocity...) Anything less is gravy...

At terminal velocity or less...

Kevlar bungie?!?!

Your *really* need to read Cato & Binford on this.

Best, Andy

Until I started using electronic deployment in my EZI-65, I used to fly it on either an AT H123W-S or H112J-S. Both worked fine. The best flights were on an I211W-M. As near as we could tell, chute deployment was almost right at apogee.

I used the 35" chute that came with the kit but I thought the rocket came down a little too fast so I got a 45" one. That worked fine and the only time I had problems with long distance recovery was when I flew it on a J350W for my L2 cert.

I know we want to do everything "right" especially the first time, but t think sometimes we have a tendency in rocketry to overanalyze. For Level 1 HPR rockets built from kits do what we did before RockSim, etc. Build it, put a motor in it, attach the parachute, and have fun flying! Save the extensive analysis for the more complex rockets you'll fly later (my $.02) The EZI-65 is a good, basic, sturdy HPR rocket, and mine has been very forgiving of operator error. Larry Lobdell Jr.

Thanks Larry, I like to analyze in order to learn and since I glassed the rocket it is no longer the same weight. The weight of the rocket unpainted is

3.5 pounds. Larry Lobdell Jr. wrote: Also, this isn't the first time. I have been flying G clusters for several years, but haven't bothered to get certification until now. I just wanted to approach this a little more scientifically instead of lighting a fuse and running, hoping for the best outcome. (Yes I really am that old, I remember lighting Visco fuse to light Estes rockets)

"lizardqueen" wrote

I agree entirely, I have simulated dozens of rockets and though its synthetic it helps develop a feel for rocket performance that would take so much more time and expense to develop.

I have two horrors I try and avoid: heavy stuff falling on anyone's head and the RSO turning my rocket away and not being able to fly because of some failure on my part in thinking the whole flight through. Simulating as many scinarios as I can helps with both.

To answer the question that started this all off, (remember I'm fairly new to this) I expect to deploy below 50mph and would be very stressed if I anticipated 100mph deployment - but more worried about zippering than recovery chain failure.

I like low cost rockets so I would not choose Kevlar bungie. I used 3 feet of Kevlar cord and a great heap of nylon. Nylon is strong and stretchey with some damping. Bungie may spring back and clang your nose into the airframe.

Good luck, when do you plan to fly?

H

I remember doing that too!! A friend and I started a rocket club in high school back in 1965. Light the fuse, run, and turn around just in time to see the rocket take off. Those were the days....

I like the idea of clustered G's. How many have you clustered at once? Since I got back into rocketry in 1990 I fly mostly staged or staged and clutered 38 & 54 mm stuff. I find it satisfying to have a successful flight when there are multiple possibilities for failure, or error. But I don't fly too often because it's expensive, so mostly I watch and learn from others. However now that our kids are out of the house maybe I can afford 2 J570's & an airstarted K700 staged to a K185 for one really awesome flight :). And a Ham license, ATV transmitter, rocket camera, and .... You've done rockets for a while too so you know how it goes. Larry Lobdell Jr. I'm still curious how you came up with lizardqueen

Nah, he will just get distracted then drop the hobby in disgust.

Toss the bungee and get some 1/2" tubular nylon, 25 ft. should be sufficient. Bungee sux. Others will argue this point. I don't care. Bungee sux.

If you are really worried about ballistic deployments go to a deployment bag with drogue chute.

If you have to choose between delays, go with the short rather than the long (assuming the difference is split, as in either 2 sec short or 2 sec long).

Halam Rose, I hope to make it to the California October Skies on October 13, 14, or

1. I wasn't going to use all Kevlar bungee; just a segment to absorb shock. Most of the shock chain will be tubular nylon.

Larry, Yes those were the days. I can't believe I'm old enough to say that, but we didn't know how lucky we were in our little unregulated, unmicromanaged world. Now if you did the things that we did then, your parents would be sent to jail. For God's Sake We Rode Bicycles without Helmets! Oh the humanity! Anyway, mostly I flew clusters because I was too lazy to jump threw the regulatory hoops, and I wanted the higher power motors. Now I'm doing it along with my niece and nephews and I'm trying to be legit. The most I ever clustered at one time was 4 G motors. That is quite a spectacle, but a little scary, and way too expensive. I decided that a level 1 cert would help. Plus it's getting harder to find places to fly, even in Illinois where I go to fly with family on summer trips. I might try a winter flight this year. Should be fun in the snow.

We didn't know what we had back then. We'll never see that simple world again, will we? :(

I can't count the miles I rode my bicycle without a helmet. I traded the bike in on a small motorcycle (Honda Super 90). But I must confess I started to wear a helmet (voluntarily) after my first good wipe out.

No more merry-go-rounds, and sledding down BIG hills on pieces of scrap cardboard either. Waaaaay too dangerous. Sigh. IMNSHO, I think the lawyers ruined it for everyone.

Fortunately there aren't to many hoops for Level 1, unless the ATFE has its way.

Let's see, a 480ns Level 1 reload is about 1/2 the cost of 4 SU G motors. So I guess it's less expensive, at least until you go ahead and start flying Level 2.

Fun flying in the snow? I used to live in MI & flew with Tripoli Michiana. I just moved to Phoenix so I traded bitterly cold winter launches for heat stroke. But I hear IL has a little better weather than MI. Good launch sites are hard to find there, but at least for now there are more open spaces here in the SW.

BTW, is that Kevlar bungee like the one from Giant Leap Rocketry? If so you should be fine. My wife made me a bungee for my EZI-65 by sewing together 2 lengths of 1" wide plain old sewing elastic!! It worked fine until I found RMR on the web and learned that such things don't work (that's what I meant earlier by overanalyzing, although I have learned a lot of good stuff here too). When I graduated to altimeter deployment I diid replace it with 1/2" tubular nylon. Larry Lobdell Jr.

Yep, Kevlar bungee exactly like Giant Leap. I saw it while looking a fiberglass and it looked like a great idea. Intuitively, it seems that a little elasticity is a good thing to avoid the sudden jolt at the end of deployment. It seems there is a lot of binary thinking in rocketry culture. It's either no fiberglass or a ton of fiberglass, no elasticity or total elasticity. I guess I'll listen to both sides of the arguments and then pick the middle or wherever my intuition tells me to go. I'm not quite serious enough to collect real data and there doesn't seem to be a lot of facts out there; only dogmatic hardcore opinions. Anyway bottom line-it's all just for fun and if things are learned in the process that's all the better.

I don't know if it's the lawyers, or whiny people that see deep pockets, but the world does seem over-regulated. Maybe it's inevitable when you have too many people on the planet? Maybe politicians searching for a cause de jour? Who knows? But it is a pity. Orwell had it right-just off by a few decades.

good wipe out. See the process works. A few bumps and the helmet goes on VOLUNTARILY! It's good to protect the kids, but I don't regret for a minute learning the hard way.

I was kidd> Resp> >

Andy, you were spot on with your answer. Google Cato and Binford.

I think the idea is that if there's a jolt at the end of deployment, your cord isn't long enough. It should be long enough that drag slows down the separating parts and there's no jolt.

-- Roger

If Cato and Binford fans have something to say-just say it or provide a