"ribbon recovery"?

I'm trying to design a min dia 29mm rocket for the altitude record for our local club, and I was trying to choose a streamer/small chute for recovery (I'm in the design stage). This rocket will have both an altimeter for recording apogee and firing the apogee charge, and a radio tracker transmitter.

For a safe recovery of this size/weight, RockSim calls for an 12-16" dia chute. While I've had success with chute ejection at this size, I've also had chutes that either never ejected, or ejected correctly but didn't open properly (from being compacted in the body tube). I was thinking about a standard streamer, but then I thought about this:

What about an ejection charge that fires at apogee, splits the rocket into two halves that each have about equal weight and drag, connected by very long (maybe 12 ft.) shock cord that is actually a 1" wide ribbon? Now the two parts of my rocket are falling about level horizontally with whatever amount of drag that creates, with 144 sq inches of ribbon connecting them also creating drag. Compare this with 113 sq inches of surface for the 12" chute...

I've done no drogue, dual deployment recovery with my larger rockets (4 inch dia and larger) before, and I've seen these rockets falling fairly slow (for their weight) in this configuration before reaching the main deployment altitude with just regular kevlar shock cord connecting the two halves. This would just be taking this to an extreme in "designing" the shock cord for maximum drag.

I'd have to find a "ribbon" of some kind of material that is strong enough, wide enough, and thin enough for this to work. Anyone done this?

Ric T.

Just a thought... equivalent surface area does not mean equivalent drag.

Use one of the many EMRR tools or others to simulate this and you will probably find that you need the "Mother of all streamers" if you want this to work.

I'm trying to design a min dia 29mm rocket for the altitude record for our local club, and I was trying to choose a streamer/small chute for recovery (I'm in the design stage). This rocket will have both an altimeter for recording apogee and firing the apogee charge, and a radio tracker transmitter.

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I'm designing a line of very small, light altimeters and I wanted to learn more about altitude record attempt rockets. So I looked on line for 29mm body tubes, and I can't find any of them anywhere. When people are talking about 29 mm minimum diameter tubes, are they really referring to BT-55's or BT-60s? Or is there somewhere else to go to get true 29 mm minimum-diameter tubes?

I'd have to find a "ribbon" of some kind of material that is strong enough, wide enough, and thin enough for this to work. Anyone done this?

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I haven't done this, but I have seen some thin, woven-edge, kevlar ribbon at my local composites shop that was about 3" wide. But I think you're on the right track with a narrower, longer version because I can image that it could be easy for the two parts to get twisted up and destroy the surface area.

Never mind about not being able to find 29mm tubes. I guess I wasn't looking very hard before!

i would also worry about the 'ribbon' shock cord twisting around as it falls, reducing the surface area alot. That said, if you build the rocket strong enough it should be able to land from a flat fall well. I had a 38mm min diameter rocket come in flat falling drogueless and the main failed to come out, and got no damage from that. A 29mm rocket with stout fins should be fine landing fast... but a car or spectator might not like the landing if it happened to land near the flight line. a RSO might not like the idea of no parachutes.


Also, if you have trouble finding 29mm coupler tubes (i dont know where to buy them commercially) an old single use motor casing works very well, and, I have seen Tfish use the rocket engine as the coupler, and securely tie the shock cord to the little groove below the knurl of the forward closure, that works well also.

Originally posted by rict
I'm trying to design a min dia 29mm rocket for the altitude record for our local club, and I was trying to choose a streamer/small chute for recovery (I'm in the design stage). This rocket will have both an altimeter for recording apogee and firing the apogee charge, and a radio tracker transmitter.

I'd have to find a "ribbon" of some kind of material that is strong enough, wide enough, and thin enough for this to work. Anyone done this?

Ric T.

Click to expand...

Rick

Why not simply use a 1 or 2 mil mylar streamer. You need ~10 cm2 for each gram of recovery weight. You can get 2 mil mylar streamer kits from https://www.asp-rocketry.com/store/category.cfm?Category=218

The optimum aspect ratio is 10:1 so common sizes are 30"x3" (~60 gm), 40"x4" (~100 gm), 50"x5" (160 gm), 60"x6" (~230 gm), 80"x8" (~400 gm).

Bob

Originally posted by bobkrech
Rick

Why not simply use a 1 or 2 mil mylar streamer. You need ~10 cm2 for each gram of recovery weight. You can get 2 mil mylar streamer kits from https://www.asp-rocketry.com/store/category.cfm?Category=218

The optimum aspect ratio is 10:1 so common sizes are 30"x3" (~60 gm), 40"x4" (~100 gm), 50"x5" (160 gm), 60"x6" (~230 gm), 80"x8" (~400 gm).

Bob

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Yes, I thought about a streamer, and I may still use either a streamer or a small chute. I'm trying to think of something even simpler than either of those.

This rocket should be plenty tough enough to land (once seperated) with the minimum of drag from either a streamer or a chute; just doing some "what if" design stuff.

Ric T.

Okay, this is off topic, so I excuse myself...

Originally posted by Brian Barney

Also, if you have trouble finding 29mm coupler tubes (i dont know where to buy them commercially) an old single use motor casing works very well, and, I have seen Tfish use the rocket engine as the coupler, and securely tie the shock cord to the little groove below the knurl of the forward closure, that works well also.

Click to expand...

I got something that works quite well. (The lack of materials is the source of invention. Or something like that I have had to do this every now and then since my only source of building materials is mail order over the net, not to mention a quarter of the globe! )

If you need a tube coupler but don't have the right dimension... Use a piece of the tube! Cut off two lenghts that are... say 3". Then cut the small 3" tubes open lengt wise. Slide one of them inside the main BT. Using a sharp pencil, mark where the "coupler" overlaps itself and remove it from the BT. Now, cut off the overlap and slide it inside the tube again (you don't need a perfect cut - you can live with cutting off 1/8" too much)
Then take the second short 3", and slide it inside the first "coupler". Mark the second one like you did the first one, remove and cut away the excess. Then simply glue the two short lengts together, using the BT to keep them in place while they dry. Just make sure that the cuts don't overlap, that you push them all the way inside the BT whilst drying, that don't glue them into the tube, and... voila! A tube coupler!

Originally posted by rict
I'm trying to design a min dia 29mm rocket for the altitude record for our local club, and I was trying to choose a streamer/small chute for recovery (I'm in the design stage). This rocket will have both an altimeter for recording apogee and firing the apogee charge, and a radio tracker transmitter.

For a safe recovery of this size/weight, RockSim calls for an 12-16" dia chute. While I've had success with chute ejection at this size, I've also had chutes that either never ejected, or ejected correctly but didn't open properly (from being compacted in the body tube). I was thinking about a standard streamer, but then I thought about this:

What about an ejection charge that fires at apogee, splits the rocket into two halves that each have about equal weight and drag, connected by very long (maybe 12 ft.) shock cord that is actually a 1" wide ribbon? Now the two parts of my rocket are falling about level horizontally with whatever amount of drag that creates, with 144 sq inches of ribbon connecting them also creating drag. Compare this with 113 sq inches of surface for the 12" chute...

I've done no drogue, dual deployment recovery with my larger rockets (4 inch dia and larger) before, and I've seen these rockets falling fairly slow (for their weight) in this configuration before reaching the main deployment altitude with just regular kevlar shock cord connecting the two halves. This would just be taking this to an extreme in "designing" the shock cord for maximum drag.

I'd have to find a "ribbon" of some kind of material that is strong enough, wide enough, and thin enough for this to work. Anyone done this?

Ric T.

Click to expand...

Not sure why you think you have a deployment problem from a 29mm tube?
You should be able to use just about any standard streamer recovery system you want, I'd be sure to add a styrofoam ejection plug, but as long as you choose a size suited to your field conditions you shouldn't have to worry about recovery at all. I'd also suggest a decent amount of tracking powder so you'll see ejection clearly.
29mm is a HUGE amount of space for such a small length streamer, even if you go with a way overweight 2mil thick.
I've had 6 x 96 accordian folded 1mil " in BT-20's without much of a problem at all. and 10" x 100" easily in a BT-50. so your small Streamer will actually be rattling around in there
If your looking at optimum mass, 1mil streamers are a great way to add throw weight without massing up your models balance.
With a simple 4" x 40" 1mil mylar streamer in a BT-20 body, I brought this 6xC cluster Altitude model down from 2185' within 30 yards of the launcher
Hope this helps a Little