Simple Interstage Idea

[dongfang]

Hi,

Just asking your comments on this simple staging gadget I have come up with.

There's a booster (1st stage) and a sustainer (2nd stage) stacked the usual way. The sustainer has a male Gardena coupler as its nozzle, and it fits into a tube on top of the booster. It is also pressurized through the booster.

When under pressure on the pad, 3 (or 2 or 4...) bolts will keep the sustainer down in the tube. The bolts have springs to extract them; on the pad, the bolts hold the sustainer down, and the shear force from that keeps the bolts in.

At launch, the booster must accelerate so much that the sustainer is forced down in the booster's tube (ie. acceleration * sustainer mass > (area of tube * sustainer pressure) + friction forces). Shouldn't be a problem. There is now no more shear forces to hold in the bolts, and they will be shot away by their springs (and get lost, but hey, every respectable rocket leaves some junk behind ).

Later, the booster will lose some acceleration, and acceleration * sustainer mass < (area of tube * sustainer pressure) + friction forces. At this time, the sustainer's Gardena coupler will pop out of the booster, and continue on its own.

What do you think; will it work? Is it too inefficient to have no coasting phase between booster burn-out and sustainer "ignition"?

Regards
Soren

[dwrrule]

The only problem i see is replacing parts, besides springs an bolts flying every were!!! Why not use a crushing sleeve?

[dongfang]

Hi,

What's a crushing sleeve? Can you explain the idea?

I guess if I use little leaf springs instead of helixes, I could make it so the bolts stayed attached.

Regards
Soren

[sporter2k5]

The only problem i see is replacing parts, besides springs an bolts flying every were!!! Why not use a crushing sleeve?

I like the simplicity of crushing sleeve. I think people sometimes just want to invent new ways of doing stuff. I think that's a great attitude. Soren's idea looks like it may be workable. I think it may be more able to stand higher pressures than other systems.

I also think Soren could tie some strong fishing line through the springs and bolts and that would keep them from getting lost if he ties it to the rocket. I'm not a big fan of all the metal parts on the pressurized parts of the rocket but it's clear if it matters to anyone they can replace them with nylon bolts and plastic springs.

[dwrrule]

Heres a really good idea of how its made an how it works.

http://ourworld.compuserve.com/homepage ... taging.htm

[dongfang]

Hi,

Aah I found out what a crushing sleeve is. I would have preferred to simply use the female Gardena counterpart on the booster... but there must be something to slide the sleeve. All I could think of was to tie a weight around it. The acceleration should then force the weight down. Maybe some other mechanism (leaf spring, whatever) engages into the gap and holds it open.

But weights on a rocket?? Hmm.

Does anyone know a way to open those Gardena females, and remove the spring? I also need a sensible way to attach one to the throat of a bottle. Maybe one of those for a larger host could be plugged right in.

Thanks for the other suggestions, I will look at them...

Regards
Soren

[dwrrule]

or you can look at the pics on my site. "washington-water-rockets.tripod.com" this is the crushing sleeve i made an use and you can also see the video of it working.

[dongfang]

Hi,

As far as I can see, the http://ourworld.compuserve.com/homepage ... taging.htm is pressure controlled; mine is acceleration controlled. That's more or less the same in a water rocket

Regards
Soren

[Tim Chen]

Hi,

Aah I found out what a crushing sleeve is. I would have preferred to simply use the female Gardena counterpart on the booster... but there must be something to slide the sleeve. All I could think of was to tie a weight around it. The acceleration should then force the weight down. Maybe some other mechanism (leaf spring, whatever) engages into the gap and holds it open.

But weights on a rocket?? Hmm.

Does anyone know a way to open those Gardena females, and remove the spring? I also need a sensible way to attach one to the throat of a bottle. Maybe one of those for a larger host could be plugged right in.

Thanks for the other suggestions, I will look at them...

Regards
Soren

I think that gardena couplers are held together by a bunch of tabs that let the inside portion slide in and snap into place, but they have a barb on the tab that only allows it to snap in one direction. You have to pry them apart with a small blade or something.

[dongfang]

Hi,

I just got a female Gardena, for 16-19 mm hoses (in other words, a larger hose than that of the most common Gardenas). If removing that screw-on crushing ring, it fits just fine over the throat of a bottle! The barb in it must be sealed against the bottle with a piece of PVC hose, a piece of garden hose, 2 pieces of pipe + epoxy and an O-ring in between, or whatever...

I think I will try to use that. I will have to get the spring out, and add a small weight of some sort around the release sleeve thingy.

Regards
Soren

[dongfang]

Hi,

Heey this is starting to look real good.

I managed to remove the spring from the Gardena. That crushing sleeve on it will simply fall down, unless you are pulling quite hard on the attached male. But the chamber pressure will do just that when the rocket is on the pad, and the acceleration when the booster goes off will cause the sustainer to push well into the booster, and sleeve to fall.

I begin to believe that the Gardena pair is a relly easy and reliable staging mechanism... to be continued... as soon as I get out of office, and get some sleep! It´s 23:22 in the night now, and I hate database migration operations.

Regards
Soren

[dongfang]

Hi,

Just an update: I have tried it out today. It works great! In fact, it's the most reliable part of my whole set-up: The parachute flap hinge fell off (note to self: Throw away CA glue), the launcher wouldn't seal, the booster splice had a leak ... but the stage separation worked beautifully on every launch.

I had to hold up the orange ring on the Gardena with a piece of plastic foam, so it wouldn't fall down by itself on the pad. As soon as there is more than a couple of bar in the rocket, it will stay up by itself, and the foam could be removed.

At launch, the booster (1.5 l + 2 l PET bottles spliced bottom to bottom) took the SOAR sustainer (Same Old Air Rocket, 4 * 0.5 l PET) up without any tendencies to jackknife or zigzag. Within very very short time (maybe too short), the sustainer separates, continues straight up, and blasts the booster with so much water that it comes (tumbling; no fins and no recovery system are needed on the booster) down again very soon. The sustainer makes a funny kind of rain shower (spread out pretty much on the ground).

This is definitely a very simple way to make a reliable 2-stager.

I will be back later with a complete description of how to construct it - but for now: Just take a Gardena female for a 16-19 mm hose, remove the spring, put a plug with a tiny hole in it, and fit it on top of the booster (use PVC hose to seal). Epoxy the throat of the sustainer into a male Gardena. Make it all nice and straight. The booster must have a larger nozzle (in the lower end) than a Gardena. That's all there really is to it.

Regards
Soren

[iskess]

Can someone point me to a tutorial on how to build a crushing sleeve? All websites seem to be taken off line, I can't find anything with google.

[rockets-in-brighton]

Can someone point me to a tutorial on how to build a crushing sleeve? All websites seem to be taken off line, I can't find anything with google.

Yes, I have a cache I can dig out. You can still fond the pages using the Wayback Machine.

[U.S. Water Rockets1]

Can someone point me to a tutorial on how to build a crushing sleeve? All websites seem to be taken off line, I can't find anything with google.

Yes, I have a cache I can dig out. You can still fond the pages using the Wayback Machine.

Someone needs to do a modern refresh of the crushing sleeve. That would be something a lot of people could make use of.