First, how do you size the pilot chute to make sure it has enough drag to extracate the bag and chute?
It takes an amazingly small parachute. The mains we used on the Delta III are 28 foot military ejection seat parachutes, and we used man-rated reserve pilot chutes on those, which are about 24" in diameter. On these bags, I believe we used 9" pilots.
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Secondly, are you using shear pins on your nosecones? If so, how to you balance having enough force to make sure they break with having jsut enough oomph in ejecting the bag?
Nope, no shear pins.
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Thirdly, if you are using a dbag in a dual deploy, how much additional altitude would you recommend versus say just a chute with a nomes blanket?
I don't know what you mean by "additional altitude"?
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One other question Kevin. You have what appears to be nylon webbing for the harness below the bag. I assume you are protecting that from deployment charges with something?
I guess I never explained how we load this....
The stack is like this....
Nosecone
Ejection charge
Nomex heat shield
Pilot chute
Deployment bag
So, the ejection charge sits above the heat shield and pilot chute, and is used to simply blow the nosecone off. It's a small charge, as once the nose is off, it has done its job -- everything sits on bulkhead in the coupler that holds the nose cone (the nose has a short piece of tubing attached to it).
That bulkhead is placed such that once the nose comes off, the heat shield and pilot are just a bit above the top of the coupler, so they quite literally fall right out.
The nylon lines are never exposed to the ejection charge.
Kevin, what I meant by additional altitude is as follows. Let's say I have a rocket that falls at about 70 feet a second from apogee after the airframe is split. Using the chutes I do I an eaily blow a charge at 500-600 feet, have it all get out of the rocket, inflate, and have plenty of altitude for it all to happen. With the d-bag, does it add much additional time to the deployment event, and if so how much? In a sense, time and altitude become very linked.
Kevin, what I meant by additional altitude is as follows. Let's say I have a rocket that falls at about 70 feet a second from apogee after the airframe is split. Using the chutes I do I an eaily blow a charge at 500-600 feet, have it all get out of the rocket, inflate, and have plenty of altitude for it all to happen. With the d-bag, does it add much additional time to the deployment event, and if so how much? In a sense, time and altitude become very linked.
Ah, now I understand!
I would expect a neat, orderly deployment to happen as fast, or faster, than a sloppy one. In the case of a sloppy deployment, components may thrash around and get in each other's way, before everything sorts itself out (if it does at all) and they begin to do their job.
How much longer depends on what's happening during deployment.
The altitude required is not only a function of how the system deploys, but also the size of the system -- a 60" parachute will inflate a lot faster than a 28' C9.
Posted: Tue Aug 28, 2007 9:46 pm Post subject: Pattern
fox_racing_guy wrote:
Any word from your friend on a pattern for that deployment
I guess it is time to come out of hiding. I'm the hands in the pictures. I don't actually have a pattern. Most of my stuff is so custom for specific rockets, they are almost all "one of a kind". I will tell you they are very simple for the smaller chutes.
- I draw a circle a quarter inch smaller than the tube and a second circle about a half inch bigger for sewing.
- I determine the depth of the bag by packing the cute into a tube of the correct diameter and measuring how much space it takes up.
- measure and cut fabric leaving the correct extra for sewing
- before I sew it together I edge the bottom and add a piece of nylon tape on top of that in little loops to attach the rubber bands
- I measure and attach the reinforcements you see running down the sides and top... to the top (also forming the loop seen on the top) with a small bit nylon tape one the inside (forming the loop on the inside) leaving the sides free (we will come back)
- sew the cylinder portion together, add the top, sew the reinforcements down on the sides and... PRESTO! It's a bag!
Hi Folks:
Thanks very much for this very informative topic.
When using a deployment bag, how does one *guarantee* that the necessary pilot chute deploys?
I understand about using spring loaded pilot chutes. Is that the only 100% guaranteed way? Or are small pilot chutes so small that they don't have the tangling issues you see in the larger chutes?
And, yes, no system is completely perfect. But this seems to be a heated topic. Can we narrow down to a system of "best practices" for pilot chutes?
Joined: Jul 07, 2007 Posts: 90 Location: One of the birthplaces of model rocketry and Johnny Carson's home town.
Posted: Wed Aug 29, 2007 2:09 pm Post subject:
I think dancerrich will back me up on this but I remember him saying that chutes that use mesh instead of individual shroud lines are the least likely to tangle. Not sure where to find them in small sizes though.
I picked up some small de milaterized chutes for flares and such and they were hard to tangle. I think I got them from Aerocon. _________________ Bill Richardson ENC USNR Ret. TRA 8703 L2 In my opinion stupidity should be painful, very painful. Because if it was there would be alot less of it in the world today.
When using a deployment bag, how does one *guarantee* that the necessary pilot chute deploys?
I understand about using spring loaded pilot chutes. Is that the only 100% guaranteed way? Or are small pilot chutes so small that they don't have the tangling issues you see in the larger chutes?
As you said, nothing is 100% guaranteed. Failures happen, but the goal is to eliminate as many of them as possible.
The biggest failure is in getting the airframe separated -- that doesn't happen and it's game over. So, we'll ignore that.
Relying on an ejection charge to push a parachute out can be problematic, as things can (and do) jam, or charges aren't large enough, or leak, or....
To prevent that, the method we've gone to is an ejection charge that sits on top of a heat shield, on top of the pilot. When the airframe separates, the heat shield and pilot are sitting up high enough that they're exposed to the air, and quite literally fall out of the airframe.
What this typically means is that your coupler is attached to the bottom of the airframe, and the main sits inside in the coupler, high enough that the top of the bagged main sits just a smidge above the top of the coupler. So, when the pilot and heat shield are set on top of that, they're entirely above the coupler lip.
That way, when the upper tube comes off, there's nothing to hold the heat shield or pilot in the airframe -- it literally falls out.
Posted: Wed Aug 29, 2007 11:02 pm Post subject: Also
Additionally, the nose cone is attached to the bottom of the pilot chute with a light kevlar line..... when the nose cone is removed energetcally..... it also helps to start the process which is then taken over by the pilot chute. We put any required weight for stability at the level of the top bulkhead and as a result the nose cones are very light, just a shell really.
As Bill said, a pilot chute with mesh rather than lines is essentially impossible to tangle, so, we use them exclusively. If there are any skydiver riggers in you area you may be able to pick up some from them. They almost always have some that have been condemned for man rated stuff, but are still just fine for our uses. If not, they are not hard to make. I often just sit down and bang one out if I need a special one.
Spring loaded pilot chutes, for us, are used exclusivley for big stuff that we use 24 foot canopies or bigger. Like Delta and Redstone.
Hope this helps,
Kevin
Posted: Wed Aug 29, 2007 11:12 pm Post subject: If you like that one.....
fox_racing_guy, you should see the bags we used for the Delta and are also about to be flown in the Redtone! What a pain to make. But they sure work good. If you check with Troj, I think he has some pictures of them posted somewhere. For those you would have to come to Omaha and sit with me and I could teach you. Have to watch your fingers around my machines though! LOL
Joined: Aug 10, 2007 Posts: 6 Location: Canton, Ohio
Posted: Thu Aug 30, 2007 2:28 pm Post subject:
I'd love to see any more pics Kevin or yourself have to show as I always like experimenting with new things. The down fall of the American textile industry was kinda good for me as I acquired many pro machines over the past 15 years or so such as my Merrow surge machine and many different Reece machines, I really enjoy sewing new and different things like parachutes and deployment bags, I don't show them off as I don't want 1,000 request and I don't really want to start a new business.
For you guys that have never tried this type of thing you might want to pick up a cheapo Singer or Sears machine and try making your own stuff, it's not really that difficult it will just take a little longer with a consumer machine. The hardest thing will be finding Nomex cloth. I don't recommend sewing Kevlar ( or Kevlar thread! ) with a consumer machine as it will destroy needles rather quickly.
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It's a bag!
But this seems to be a heated topic. Can we narrow down to a system of "best practices" for pilot chutes?
