The Shiv

[geof]

The Shiv is a 55" futuristic longneck two-stage parallel cluster scratch design capable of flights over 2000 feet with its maximal motor configuration. The booster section of this rocket is particularly unusual for several reasons. First, it has a ring fin which separates to leave the sustainer ringless. Second, it carries an assymetrically mounted parallel 13-mm motor whose sole purpose is to rear-eject a 15-foot streamer for booster ring recovery. Third, the interior of the booster section includes a baffling system for rear ejection gasses and a venting system for forward gap staging. I'll be flying this tomorrow and writing up the details for EMRR. In the meantime, here are some photos.

Geof

 

[geof]

This first photo is the most interesting because it shows all the guts. You can see the 24mm booster tube, 13mm ejection motor tube, 18mm rear ejection streamer tube. Those weird walls are the baffle system. The forward part of the assembly is constructed for gap staging to the sustainer, and will be covered by the transition shroud laying behind. That BT70 tube goes over the whole assembly, too.

 

[geof]

Gluing on some fins.

 

[geof]

Here is a dryfit of most parts except the ring fin. This is over 4.5 feet tall.

 

[geof]

Next some photos of the finished rocket. First is an overall shot on the grass.

 

[geof]

Here is a shot of the booster area. Notice the venting holes in the transition shroud. These holes are to promote successful gap staging. Sustainer separation occurs right at the forward edge of the black ring.

 

[geof]

Here is the business end of the booster. The 13mm ejection motor tube sends ejections gasses through the baffle system and out the oval-shaped 24mm ejection tube, forcing out a 15-foot streamer to soften booster recovery.

Of course, the 1/2A3T-2 motor will give an exciting 2-second delay before deployment. By my calculations, that still leaves a couple hundred feet for the streamer (I hope!). This part of the design is highly experimental.

 

[geof]

Finally, here is a photo of the two stages separated.

Wish me luck tomorrow...this was a complex project with a lot of time invested in design and construction. I'm starting with D12-0 + 1/2A3T-2 staging to D12-7, which should go about 1200+ feet. If I put a E9-8 in the sustainer (which I probably won't attempt tomorrow!) it should go 2050ft!

Geof

 

[TWRackers]

Will you be stuffing anything into the rear-eject streamer tube to keep the streamer from coming out early under acceleration? Maybe a ball of recovery wadding?

 

[geof]

Yes. A small piece of wadding above the streamer to ensure that the ejection gasses *push* the streamer out (and just in case the baffle doesn't entirely work), plus a small ball of wadding below the streamer to prevent it from falling out early.

 

[DaveCombs]

INCREDIBLE work, geof. That's one of the coolest scratch builds I've ever seen. Good luck with your flight!

 

[uncle_vanya]

Originally posted by geof
The Shiv is a 55" futuristic longneck two-stage parallel cluster scratch design capable of flights over 2000 feet with its maximal motor configuration. The booster section of this rocket is particularly unusual for several reasons. First, it has a ring fin which separates to leave the sustainer ringless. Second, it carries an assymetrically mounted parallel 13-mm motor whose sole purpose is to rear-eject a 15-foot streamer for booster ring recovery. Third, the interior of the booster section includes a baffling system for rear ejection gasses and a venting system for forward gap staging. I'll be flying this tomorrow and writing up the details for EMRR. In the meantime, here are some photos.

Geof

Do you have a RockSIM file? Exact dimensions? This would be a heck of neat rocket to upscale as well. This is sweet. Tell us how it flies!

 

[geof]

Thanks. I do have a Rocksim file with exact measurements, which I will post later and submit to EMRR.

If you are thinking about upscaling to APCP motors, this would be a very challenging project and I would absolutely *love* to see it done successfully. The good part is that you would eliminate the need for gap staging and its venting issues. Also good: the booster streamer ejection via 13mm motor could be switched to electronic ejection and a chute.

The hard part is that you now have a 2-stage composite motor design with (possibly two) electronics assemblies (staging and booster ejection). There is plenty of excess stability margin so you've got some flexibility for adapting the upscale. It sounds even trickier than the original, but lots of fun!

Geof

 

[PunkRocketScience]

Originally posted by geof
Here is the business end of the booster. The 13mm ejection motor tube sends ejections gasses through the baffle system and out the oval-shaped 24mm ejection tube, forcing out a 15-foot streamer to soften booster recovery.

Of course, the 1/2A3T-2 motor will give an exciting 2-second delay before deployment. By my calculations, that still leaves a couple hundred feet for the streamer (I hope!). This part of the design is highly experimental.

I like the design Geof!

I added two A10-3T's to my Estes Renegade Booster to pop 'chutes out of the side pods as I kept breaking fins off. With a central 24mm, your 2 second delay should be fins. The 3 second one on the Renegade pops the 'chutes in plenty of time for them to open.

 

[powderburner]

Originally posted by geof
... it shows all the guts...

I like your creativity on solving the problem of getting a recovery system deployed on a booster. That's a tough design challenge and it looks like you have a good solution. I thought the built-in baffle was clever too.

One little idea for possible improvement: if you could tie off a thread somewhere, pass it across the width of the streamer tube below the streamer and around a few corners and across the space in front of either motor, the thread would positively retain the streamer during peak thrust and the ejection charge (or booster burn-through) would sever the thread and allow the streamer to deploy. Might be too late to incorporate now, might want to play with that on the Mk II version?

 

[tonypv]

That's one cool design! Very sharp!
Nice job!
If that was a kit I'd buy it a heart beat.

 

[geof]

I got a launch pic just a hair too early; I'll post it later if I have time.

The maiden flight was D12-0 + 1/2A3T-2 staging to D12-7. It was a very windy day on the prairie with steady winds at least 15mph and stronger gusts. The rocket was actually blown over on the pad once (breaking a plastic part of my pad).

Both motors ignited. The Shiv leaped of the pad and angled 45-degrees downwind. This was clearly rod whip or wind-related somehow because she flew true and straight after that. Staging was flawless, and the booster tumbled well until the streamer ejection charge fired. The full streamer ejected and the booster was recovered without damage.

The D12-7 in the sustainer absolutely tore through the sky on its oblique angle. We lost sight of the sustainer downrange, and took off with binoculars and walkie-talkies to find it. We found it nearly a mile downrange, and the story was obvious from inspection.

Due to its flight angle, ejection occurred at an extreme speed. The thin mylar chute was completely ripped away...only dangling shroud lines remained. The sustainer came in ballistic, and the nose portion lawndarted one inch into the prairie dirt. The thin neck on this portion broke right at the upper balsa transition. The rear portion of the sustainer somehow landed unblemished.

So, I need to make a clean cut on the neck and grind away a shoulder on the transition, then glue it back together. The neck will be about .75in shorter. Aside from making a new chute, she'll be ready to launch again, but on a less windy day.

The design is clearly stable and both the gap staging and rear ejection worked flawlessly. Despite the damage, I consider it a successful first flight and she'll fly again this season for sure.

Geof

 

[rosko_racer]

Creativity and imagination at its best. GEOF, that is e x c e l l e n t work!!! Love the design and your unique aproach of deploying a recovery system for a stage section. Will keep looking at EMRR for your review and the sim file.

 

[rokitflite]

Uhhhg Sorry about the crash, that is one beautiful model! I hope the repairs go smoothly.

 

[cjl]

Too bad about the crash - it is a BEAUTIFUL model. Will this be flying at MHM?

 

[geof]

It looks like I may be on a plane to Anchorage and miss Mile High Mayhem. That would be a real pity. We'll see.