2. Stage

[dongfang]

Hi,

OK so I tried the Gardena interstage of mine again, the last couple of days. As you might have seen in the pictures above, it worked fine with my small, full-throat nozzle booster (4-5 flights all had perfect separation).

I now tried with:

- A 3 * 2 l booster with a 17 mm ID "carburetor tube" (a tube that mixes air and water, similar to when using foam. It improved performance in a separate test I made). Result: Failed to separate, 2 of 2 flights.

- The same booster, with the "carburetor tube" cut off. There remained a 17 mm ID tube as the nozzle, now just extending a couple of mm into the bottle. That should increase thrust, at the cost of burn time. Result: Again failed to separate, in 1 flight.

From the results of the flights, I get it that the sleeve of the Gardena failed to fall. The acceleration never overcame the pressure from the sustainer (pressing the male and the female Gardenas together and letting the sleeve fall).

It seems that this staging mechanism, in its current form, needs the thrust of a full throat booster. Nothing wrong with that really, but I like the 17 mm nozzles better, because the launcher I have for those is better, and the stresses on the rocket will be smaller.

I have a redesign idea; it will come after evaluating it. It basically consists of omitting the check valve, and have a plug with a pinhole through it protruding from the female Gardena insterstage into the nozzle of the sustainer, and sealing against the inside of it. That should reduce the area on which the sustainer pressure works to pull booster and sustainer apart - from about pi * (16 mm / 2)^2 mm = 64 * pi mm^2, to (9 mm / 2)^2 mm = 20.25 * pi mm^2; 3 times less. (16 mm is the OD of the male Gardena, where the seal is now, and 9 mm is the ID where the seal will be moved to).

Regards
Soren

[Tim Chen]

Hi Soren,

I like your idea for solving the problem. I think it should work that way. If it doesn't work I would be very surprised!

[dongfang]

Hi,

As I might have written somewhere, I did not get the Gardena staging mechanism to work with a larger, heavier, smaller acceleration booster. The problem was that it was triggered (sleeve falls down) by the booster's push on the sustainer overcoming the sustainer's pressure in the Gardena (pushing the 2 parts together and releasing the sleeve).

I have solved it by reducing the porting area in the Gardena: Instead of sealing it on the outside as normal, I seal it on the inside.


I found a 6 mm to 10 mm (as far as I remember) hose connector, and stuffed that into the female Gardena from the hose end. I put a suitable O-ring on it, supported by 2 pieces of 6 mm hose. The 6 mm end with the O-ring seals against the inside of the male Gardena. See my previous post. No machining was needed, just ghetto construction.

I also added some PVC plumbing on the sleeve, to add a little weight. A couple of hose clamps could also have done it. That worked! Now the stages separate, at the right time.

Here are a few pictures. I will post some launch pics in the photos section now.

Regards
Soren

[dongfang]

Hi,

Ooops no, I put that hose coupler in the Gardena from the front side I can see

Regards
Soren

[water rock1]

Could some two stage systems can be used on FTC

[Spaceman Spiff]

Could some two stage systems can be used on FTC

Yes they can. There was an old world record setting water rockert called "millennium" that used a FTC upper stage. If I remember right, it used a crushing sleeve system.

[josh333]

thats so simple... Does it work well

[dongfang]

Hi,

Sure it does! I have documented a flight here - the only flight with it so far, becuase I found that my field is too small for 2 stage rockets.

You can also find a flight of the unmodified version (without the nylon hose coupler in the Gardena) on YouTube; search for my user name skuula. That was with a booster with a lot more thrust, that was able to get the unmodified version to separate. The booster was expended already at ~2 meters, but going up fast. There is also one of a failed-separation flight, which is what made me think of the modification.

Kind regards
Soren

[r0bster]

what keeps the ring from not comin off....????

[r0bster]

can u show a graph showing everything put together and labeled........

thankz

[Erik V.]

Dongfang/Soren,

Could you please post a more detailed digram of the 2 stage mechanism with the gardena valve and the way the male and female parts attatch to the bottle? I'm not getting it at all.

Thanks

[dongfang]

Hi Erik (Danish??)

Well ... the best answer I can come up with is really: Understand how it works, and then reinvent solutions for the details.

For the understanding part, buy a male and a female Gardena, and remove the spring as described. Try playing a little with them: Attach them together, observe how the sleeve just falls down by itself, except when you pull at the 2 couplers - that will make the sleeve stay.

Attaching the male to a bottle: I got a 3/4 inch male (the most common one anyway) and ground away some of the threads inside it. I filed off some of the threads on a bottle too, and they would fit together pretty well. I sealed it with thick 24 hour epoxy.

Attaching the female to a bottle: I used a female for a thick 19 mm hose, and put a piece of thin PVC aquarium hose on it. With that, I could just squeeze it into a bottle, using soap to grease it. I filed the hole in the screw-on ring a little bigger so it would fit over a bottle. The photos should explain it I think.

The Version 2, that works with low-thrust boosters: I was just lucky to find something that would fit inside the female and also extend into the male when assembled. If you desparately need one of those hose connectors and the O-rings, maybe I could send a set to you.

But OK I will try to make a proper manual some time (I will fly it again soon). But my main point is still: Just understand how it is supposed to work, and then come up with your own ideas for the details. Your junk boxes and your parts availability situation are different from mine anyway

Regards
Soren

[Erik V.]

Hi Erik (Danish??)

Well ... the best answer I can come up with is really: Understand how it works, and then reinvent solutions for the details.

For the understanding part, buy a male and a female Gardena, and remove the spring as described. Try playing a little with them: Attach them together, observe how the sleeve just falls down by itself, except when you pull at the 2 couplers - that will make the sleeve stay.

Attaching the male to a bottle: I got a 3/4 inch male (the most common one anyway) and ground away some of the threads inside it. I filed off some of the threads on a bottle too, and they would fit together pretty well. I sealed it with thick 24 hour epoxy.

Attaching the female to a bottle: I used a female for a thick 19 mm hose, and put a piece of thin PVC aquarium hose on it. With that, I could just squeeze it into a bottle, using soap to grease it. I filed the hole in the screw-on ring a little bigger so it would fit over a bottle. The photos should explain it I think.

The Version 2, that works with low-thrust boosters: I was just lucky to find something that would fit inside the female and also extend into the male when assembled. If you desparately need one of those hose connectors and the O-rings, maybe I could send a set to you.

But OK I will try to make a proper manual some time (I will fly it again soon). But my main point is still: Just understand how it is supposed to work, and then come up with your own ideas for the details. Your junk boxes and your parts availability situation are different from mine anyway

Regards
Soren

Ok, I understand it now. I was just confused before because when you were talking about the male and female gardenas, I thought you were talking about male and female threads. Thanks for the help.

Oh, and I'm from the US.

[Andrewlee]

batkiter,
could you possibly post a video showing how the mechanism works I think I have a pretty good idea...but it would be cool to see it in motion

[Batkiter]

batkiter,
could you possibly post a video showing how the mechanism works I think I have a pretty good idea...but it would be cool to see it in motion

Hallo Andrew!

I cannot make a video available, which is rocket sold. The description of function of the mechanism is however rather exact. Me would nevertheless interest, which you introduce yourself for improvement.

Batkiter