Friction-fit Booster: CATO or failed separation?

[smstachwick]

When the booster on my two-stage Luna Bug came back in pieces, I had assumed that it CATOed. Looking back at my flight prep, however, I’m thinking that something else happened entirely.



Since the rocket is featherweight recovery, I didn’t bother to friction-fit the sustainer’s motor. I only taped the motors together. However, I think my decision to not friction-fit the booster motor was a fatal error.

My hypothesis as to the cause of the booster’s disintegration: When staging occurred, either the burn-through of the booster or the firing of the sustainer motor ejected the unsecured booster motor from the booster, with the actual booster stage still attached to the casing of the upper-stage motor that acted as a coupler.

Then, either the burning particles from the booster motor or the flame from the sustainer motor scorched the booster, eventually leading to complete breakup and separation of the booster stage. This is supported by the survival of the upper portion of the booster and the burn marks on the pieces of paper tubing that remained attached to the recovered fins.

Has anyone experienced this or seen anything to indicate that this is plausible?

 

[rharshberger]

It wasn't a CATO, as you stated the booster failed to separate after sustainer ignition cooking the still attached booster. I have lost a couple of Commanche-3 boosters this way over the last 30 years.

 

[kuririn]

Yeah, I think that's probably what happened.
Happened twice to my little circle in the past two months.
Instead of friction fit some kits have a motor block glued behind the booster motor. When the booster motor stages and kicks away from the sustainer motor it pulls the booster section with it.
Some kits have engine hooks for both motors and a small gap between them. Does not appear to affect the reliability of staging.
Heck, I tried an experiment a couple of months ago. Launched three two stagers but didn't tape the booster and sustainer motors together as called for in the instructions. All three staged perfectly.
YMMV

 

[Sandy H.]

I had a motor kick out of my Fliskits Corona (with booster option) once and the failure was practically identical (i.e. build a new booster. . . ). I 'feel like' my solution was to glue a motor block to the bottom of the booster stage so that even if the ring fin that held the 2 stages together was tight, the motor wouldn't be able to exit without the booster section. Regretfully, it crashed the next flight, so maybe I was completely wrong with that thought!

In all fairness, I was still fairly new to staging and my return to rocketry from childhood, so I likely had multiple problems that people wouldn't have after gaining more experience.

Rebuild and re-fly. I like the design!

Sandy.

 

[DigBaddy]

That's a bummer your booster got cooked like that. As others have mentioned, the rear engine block in the booster may be the way to do it here. The Estes Twin Factor has that (and a block in the front of the sustainer too). Slap in a pair of motors, mate the two stages and light 'em. Super easy!

One thing I have noticed is that the rear block can make igniter and plug insertion a challenge, especially when it's well below freezing outside. Use as short of a block as you can, and that will make life easier.

Staged 13mm is fun. I've been meaning to use more of my cheap Viking bulk pack to make a simple two-stage Viking that uses 13mm motors. Maybe I'll move that up the build queue.

 

[smstachwick]

Thanks for the input!

As originally built, the booster was too short to accommodate a rear motor block. Even making use of its full length would leave the motor flush with the end, without any room to glue one in. I ended up cutting it for better stability margins. A motor block would require a longer sustainer, which I’m not really prepared to do.

 

[kuririn]

Thanks for the input!

As originally built, the booster was too short to accommodate a rear motor block. Even making use of its full length would leave the motor flush with the end, without any room to glue one in. I ended up cutting it for better stability margins. A motor block would require a longer sustainer, which I’m not really prepared to do.

Friction fit will work fine.
Just make it a little snugger on the booster for the next launch.
Happy flying!

 

[Scott_650]

I had a motor kick out of my Fliskits Corona (with booster option) once and the failure was practically identical (i.e. build a new booster. . . ). I 'feel like' my solution was to glue a motor block to the bottom of the booster stage so that even if the ring fin that held the 2 stages together was tight, the motor wouldn't be able to exit without the booster section. Regretfully, it crashed the next flight, so maybe I was completely wrong with that thought!

In all fairness, I was still fairly new to staging and my return to rocketry from childhood, so I likely had multiple problems that people wouldn't have after gaining more experience.

Rebuild and re-fly. I like the design!

Sandy.

My Corona cooked it’s booster too - I haven’t rebuilt the booster yet, I’m wary of redesigning something Jim Flis did, I know he’s better at this than I’ll ever be, so I’m leaning toward doing per the instructions - though your idea is more what I’m accustomed to for a two-stager.

 

[smstachwick]

New booster! I just have to glue on a launch lug.

Look for a flight report, I’m hoping to fly on Sunday if DART doesn’t get blown out that morning. If they do, scheduling issues mean that it’s entirely possible that I might not be able to get it into the air this season.

 

[BABAR]

Rear booster block can be done easily, cheaply, with almost no weight penalty and minimal recessing.

using the same tubing as the motor mount (or the body tube, for minimum diameter) I cut out a 1/8” long ring. I snip out a segment so it juuuuuust rolls up inside the end of the booster (you need to account for this length in your booster section, so add 1/8“ to your plan. Glue it just inside the tail end of the booster, white glue is fine.

incidentally, I use the same technique for standard FORWARD engine blocks on sustainers or single stage rockets, but I go with 1/4” length. mark your used (or not) motor casing for the depth you want for placement, and do a few glueless practice runs to make sure you can smoothly push it into place without it uncoiling. Then use WHITE glue, smoothly advance it into place to the marker on your casing and immediately pull out the casing. White glue is much less likely to “lock” the casing, you do NOT want a fast tack.

for NON GAP staging (taped or otherwise) usually I will put the end block in the booster first, I tape two motor casings (whether I plan to use tape or not in flight, this is just for placement of the sustainer block), load the two into the booster, and then use the booster and motors to place the motor block for the sustainer so it goes in just the right depth.

using this rear motor block, no need to friction fit the BOOSTER, and the recess depth is minimal so you avoid Krushnic effect and igniter placement shouldn’t be that difficult.

hope you get two straight trails and two short walks!

 

[dpower]

I fly a lot of LPR 2 stagers, and have had this happen a few times, if the booster motor wasn't secured in the booster stage, and the stage stays attached and gets cooked. Doesn't happen very often now that I've improved my techniques. I do prefer booster designs with an aft motor block, but in some designs this is problematic, so just get a tight friction fit with masking tape. Enough flying and you'll get a feel for how tight it needs to be.

 

[smstachwick]

I fly a lot of LPR 2 stagers, and have had this happen a few times, if the booster motor wasn't secured in the booster stage, and the stage stays attached and gets cooked. Doesn't happen very often now that I've improved my techniques. I do prefer booster designs with an aft motor block, but in some designs this is problematic, so just get a tight friction fit with masking tape. Enough flying and you'll get a feel for how tight it needs to be.

For the most part I’ve been flying 13mm LPR as multistagers. My Super Goblin goes too high for my local field with a booster and I don’t have anything else converted for it.

So most of my two-stagers that I’ve been flying have just been friction fitted butt staging. The exceptions are my Super Goblin and my Super Gnome.

https://www.rocketryforum.com/threads/super-gnome-estes-gnome-two-stage-conversion.168905/