Kit Bashed Oddroc Gap stage help

[JAL3]

In a moment of depravity, I decided that I wanted to kitbash a combination of a Sunward Flat Foot and a Squirrel Works High 5. I am planning on using the larger diameter, but shorter BT55 from the High 5 for the Booster but use the 4 foot fins from the Flat Foot on that stage.

The Booster will use the BT50 from the Flat Foot and the fins from the High 5. I am going to look for some kind of doll head to substitute for a nose cone.

I have only built 2 staged models thus far. An Applewhite 3 Stage Cluster Cone has staged perfectly each time. It inserted a C6-0 into a D12-0 and an A10-P into the C6-0. The other attempt was an Estes CC Express wiich failed to ignite the sustainer motor from the C11-0 Booster. It was also in direct contact for all practical purposes.

As I think about this, I realize that the gap is a long one and that I have the additional complication of staging at the change of BT size. Does anyone have any suggestions as to the best way to do this?

[Intruder]

Put some vent holes in the booster centering rings. For the interstage section, I would make something similar to the Laser-X nose cone assembly.

If you are going to use 18mm power, center a BT-50 coupler into a BT-55 coupler. Make the BT-50 coupler long enough to reach from the aft end of the BT-55 coupler to about a 3/4 to a whole inch inside of the BT-50 upper stage plus some extra length for a transition section. Have the interstage section permanently attached to the booster stage.

If you are going to use 24mm power, just make the motor mount tube long enough to reach from the aft end of the booster past the top end to incorporate a transition. Cut some vent holes in the stuffer tube and the centering rings. Then just put a BT-50 coupler into the top of the stuffer tupe.

[Eagle3]

Strongly agree with everything Intruder said. The only time you don't put the vent holes in the centering rings is when you're going minimum diameter. Run a stuffer tube up the sustainer and put vent holes in it near the top.

In gap-staging, think of the pressure your trying to relieve as water. You want it to flow out of the booster while leaving a straight shot for the burning particles from the motor to the sustainer. The pressure doesn't matter if it leaves out the back through the centering rings or the straight out the sides of the booster. However, one is a much cleaner look. ;)

[JAL3]

Thanks for both the answers. They bring up more questions though... :rolleyes:

My original intent was to stick with 18mm like in the original kits but now am wondering if I should upsize to 24mm because of the weight and drag involved. I'm leaning that way, in any event.

I'm unfamiliar with the Laser X except as an image on a facecard. I do understand that you are recommending the transition/interstage be an integral part of the booster.

I am familiar with the idea of venting. I need a pair of holes in the top of the stuffer tube. I am less clear about putting them in the centering rings. Would there even be enough room for a BT55 to BT20 let alone a BT55 to BT50? I guess I'm asking the diameter of the holes.

Something else I thought of this afternoon is that the booster will be aerodynamic. In order to avoid a core sample, I need to rig a streamer or something. Stuffing it into the stuffer tube would block sustainer ignition. It I put it in the booster BT but outside of the stuffer tube, it would not eject. I thought about stuffing it into the sustainer but am faced with not having any place to put it. Any ideas?

[Eagle3]

I've cut notches in 2050 rings before as vents. It doesn't need to be much, but I've never developed a formula on size vs volume.

Here is a link to my R&D report regarding recovery ideas.
http://www-personal.umich.edu/~buzznau/Gap-StageR&D.pdf

[barone]

........Something else I thought of this afternoon is that the booster will be aerodynamic. In order to avoid a core sample, I need to rig a streamer or something. Stuffing it into the stuffer tube would block sustainer ignition. It I put it in the booster BT but outside of the stuffer tube, it would not eject. I thought about stuffing it into the sustainer but am faced with not having any place to put it. Any ideas?
Well, here's a complicated approach......

The vent holes you put in the centering rings are venting the pressure to the rear of the rocket while the flaming hot material is going to the sustainer motor. You need that pressure to deploy a recovery device. I'd opt for a parachute instead of streamer.

When you assemble your stuffer tube, use a tube coupler to slip fit the motor mount portion to the section going to the sustainer. The portion going to the sustainer needs to be glued in place. If you use two centering rings for it, just make sure the ejection gases can get from your vent holes and back afte beyound the aft centering ring. The motor mount will not be glued in the rocket but slip fitted into the stuffer tube. Shock cord anchored to the aft centering ring of the stuffer tube and attached to the motor mount. The parachute attached to the motor mount between the motor mount centering rings. Parachute folded and placed between the motor mount centering rings and installed into rocket. When the pressure from the motor blows through to ignitew the sustainer, the pressure blows the motor mount and recovery system out the aft of the boost.

Wha cha thing? :rolleyes:

[Solomoriah]

Tricky. Sounds like an R&D project for sure.

[Intruder]

Well, here's a complicated approach......

The vent holes you put in the centering rings are venting the pressure to the rear of the rocket while the flaming hot material is going to the sustainer motor. You need that pressure to deploy a recovery device. I'd opt for a parachute instead of streamer.

When you assemble your stuffer tube, use a tube coupler to slip fit the motor mount portion to the section going to the sustainer. The portion going to the sustainer needs to be glued in place. If you use two centering rings for it, just make sure the ejection gases can get from your vent holes and back afte beyound the aft centering ring. The motor mount will not be glued in the rocket but slip fitted into the stuffer tube. Shock cord anchored to the aft centering ring of the stuffer tube and attached to the motor mount. The parachute attached to the motor mount between the motor mount centering rings. Parachute folded and placed between the motor mount centering rings and installed into rocket. When the pressure from the motor blows through to ignitew the sustainer, the pressure blows the motor mount and recovery system out the aft of the boost.

Wha cha thing? :rolleyes:

So your basically saying to make the booster rear ejecting. GENIUS!

If you are going to use 18mm power. I would use the same interstage method as the 24mm. However, have a 2050 centering ring in the aft end of the stuffer tube. That way the motor mount tube will fit in the stuffer tube. Also, the stuffer tube will contain most of the burning particles, which would reduce the chance of damage to the recovery system.

[JAL3]

I've cut notches in 2050 rings before as vents. It doesn't need to be much, but I've never developed a formula on size vs volume.

Here is a link to my R&D report regarding recovery ideas.
http://www-personal.umich.edu/~buzznau/Gap-StageR&D.pdf

Thanks for the link. I downloaded a copy to peruse at leisure (when my secretery isn't looking). I appreciate it.

[JAL3]

Well, here's a complicated approach......

The vent holes you put in the centering rings are venting the pressure to the rear of the rocket while the flaming hot material is going to the sustainer motor. You need that pressure to deploy a recovery device. I'd opt for a parachute instead of streamer.

When you assemble your stuffer tube, use a tube coupler to slip fit the motor mount portion to the section going to the sustainer. The portion going to the sustainer needs to be glued in place. If you use two centering rings for it, just make sure the ejection gases can get from your vent holes and back afte beyound the aft centering ring. The motor mount will not be glued in the rocket but slip fitted into the stuffer tube. Shock cord anchored to the aft centering ring of the stuffer tube and attached to the motor mount. The parachute attached to the motor mount between the motor mount centering rings. Parachute folded and placed between the motor mount centering rings and installed into rocket. When the pressure from the motor blows through to ignitew the sustainer, the pressure blows the motor mount and recovery system out the aft of the boost.

Wha cha thing? :rolleyes:

I think it sounds intriguing. It also sound like something I am sure to mess up. That makes it more intriguing. I think I follow what you're saying but do you have any sketches?

Thanks for the input.

[JAL3]

Tricky. Sounds like an R&D project for sure.

Like my T shirt says, "If I knew what was going to happen, it wouldn't be research."

[barone]

I think it sounds intriguing. It also sound like something I am sure to mess up. That makes it more intriguing. I think I follow what you're saying but do you have any sketches?

Thanks for the input.
I'm not good at sketches but let me see if I can re-phrase it differently.......

Select the length of tube you need for the stuffer and motor mount built together.......for the sake of this example, let's use a 12" length of 18mm BT (BT20). Now, the stuffer is going to be used inside a BT50. So, you need four centering rings to center the BT20 into the BT50. One centering ring is glued at the forward end of the stuffer tube. A second ring glued to the stuffer tube at 6" (in the middle). A third is glued onto the stuffer tube at 2" (from the rear) and the last is glued on at a 1/2" from the rear of the stuffer tube.

So now you have four centering rings glued on the stuffer tube at 1/2", 2", 6" and 12". Now, between the 6" and 12" centering rings, punch vent holes into the stuffer tube. I'd imagine 3 1/4" holes at equal ditance around the stuffer tube would be sufficent. Now punch vent holes in the 6" centering ring. The vent holes in the 6" ring will allow the pressure to pass to the aft end of the rocket.

Now, cut the stuffer tube apart 3" from the rear of the stuffer tube. Glue an 18mm coupler in the short section of stuffer tube so that it extends into the forward end of the short stuffer tube 1/2". Now, the coupler will act as the engine block as well as the tube coupler for the stuffer tube. Attach a 12" length of Kevlar to the long stuffer tube between the 6" and 12" centering rings and thread thru a vent hole in the centering ring so it hangs to the aft.

Glue the long section of stuffer tube into the BT50 so that the 6" centering ring, the one with the vent holes, is 6" from the aft end of the BT50. Attach a parachute to the short stuffer tube (call it a motor mount now) between the 1/2" and 2" centering rings. Attach an elastic shock cord to the forward end of the 2" centering ring. Tie the other end to the Kevlar thats attached to the long stuffer tube. When the glue sets, the motor mount should be able to slide into the aft end of the BT50 and the coupler mate the stuffer tube. Just fold the parachute up and install it between the 1/2" and 2" centering rings while installing the motor mount.

Now, in theory, you've just built a rear ejection booster. The gases will vent into the area between the 6" and 12" centering rings, pass through the 6" centering ring to pressurize the area between the 6" and 2" centering rings. The gas has no place to go so it pushes against the 2" centering ring, blowing the motor mount with the attached parachute out the aft end of the booster. With the motor mount attached to the booster with the Kevlar and elastic, the parachute should safely lower both.

Does those words draw an adequate picture?

[JAL3]

Does those words draw an adequate picture?

They do. I'm going to tinker with this and see what I can come up with.

Thanks,

[Intruder]

Story Cut

Not to be Private Picky or anything, but I assume when you say "center the BT-20 into the BT-50" you mean "center the BT-20 into the BT-55".

To JAL3: Make sure that the motor mount fits VERY loose. Otherwise the blow-through pressure will separate the stages instead of of ejecting the recovery.

[barone]

Not to be Private Picky or anything, but I assume when you say "center the BT-20 into the BT-50" you mean "center the BT-20 into the BT-55".

To JAL3: Make sure that the motor mount fits VERY loose. Otherwise the blow-through pressure will separate the stages instead of of ejecting the recovery.
I'm not familiar with what he's using for bashing. BT 50 was just an example. Could just as easily been "center the BT-50 into the BT-60".... ;)

[JAL3]

Not to be Private Picky or anything, but I assume when you say "center the BT-20 into the BT-50" you mean "center the BT-20 into the BT-55".

To JAL3: Make sure that the motor mount fits VERY loose. Otherwise the blow-through pressure will separate the stages instead of of ejecting the recovery.

I Picked up on that but got the general idea. I'd also figured out that the motor mount needs to be loose. What I don't know is what define's loose. That looks like one of those empirical question that will be hard on the fins until it is answered.

[barone]

I Picked up on that but got the general idea. I'd also figured out that the motor mount needs to be loose. What I don't know is what define's loose. That looks like one of those empirical question that will be hard on the fins until it is answered.
You want it tight enough that it doesn't fall out when held in launch position but loose enough that it falls out when shaken (not stirred ;) ). Ideally, the coupler acts as the device holding the motor mount in the rocket. The motor mount centering rings just keep the motor mount from rattling around. Using rear ejection like this, you definitely don't want to paint inside the aft end of the body tube. If you can pull the motor mount out without the CRs binding, you should be ok.

[JAL3]

You want it tight enough that it doesn't fall out when held in launch position but loose enough that it falls out when shaken (not stirred ;) ). Ideally, the coupler acts as the device holding the motor mount in the rocket. The motor mount centering rings just keep the motor mount from rattling around. Using rear ejection like this, you definitely don't want to paint inside the aft end of the body tube. If you can pull the motor mount out without the CRs binding, you should be ok.

I hope you're proud of yourself. This is going to take much more time that I had originally thought and thereby deprive all those other worthies in my build pile of my attention. Well, its for a good cause.

THanks for the advice. My club is launching tomorrow and then I will be finishing one project that just needs sanding and paint. After that, it looks like a rear ejection project.