Boosted Big Bertha

thobin

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I been thinking of picking up the Boosted Bertha but it looks a bit on the heavy side to lift on a C6-0 whats the word on this? I'm sure a mod to a lower 24mm would be easy enough but I like to keep things as stock as I can.
 

BEC

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I have one that is about a dead stock as it could be and yes, on a C6 in the booster it's a calm-weather model only. It's actually a little better with a B6-0 in the booster. There's plenty of stability and it's gap-staged, so modding the first stage to use a C11-0 or D12-0 is certainly doable.
 

thobin

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Some of the videos I have seen the B6-0 is better as it does not have any time to pitch over and fly off to the nether regions. All of the C6-0 videos I have watched, it is almost horizontal before the second stage ignites.
 

Huxter

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The full stack w engines is too much weight for a C11 even. D12 is the smallest engine that I would use in the booster.

I put 2 E engine mounts in mine. I recently hit my all-time high w 2,631 feet at the Salt Flats w the Boosted Bertha!
 

BEC

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Does anyone know offhand, the length of the coupler between the first stage and the sustainer? I used mine for something else and didn't think to measure it. I have another coupler I can cut to size.

thanks!
Ken,

It's 1.5 inches long. About 1/4 inch protrudes into the base of the sustainer.
 

jmasterj

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Converted my son's to a 24mm mount in the booster. I agree with the above that the B6 is a better stock booster than a C6 because of the short burn and lack of low-thrust tail.
 

jmasterj

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Dear Estes,

C5-0 Plz.

Thank you.
I don't think that would be better here. Its tail is even lower thrust than a C6, which could easily let the rocket lean over before staging. A curve like the C11 in 18mm (mostly core burning) would be awesome, but probably has technical problems.

 

BEC

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I don't think that would be better here. Its tail is even lower thrust than a C6, which could easily let the rocket lean over before staging. A curve like the C11 in 18mm (mostly core burning) would be awesome, but probably has technical problems.

I have to agree, having flown some of the new C5-3s, and also having almost two dozen flights on my Boosted Bertha. The new C5-3 is very much like the A10-3T....good kick, then a long, low thrust burn.

I don't quite agree with Wolf's assessment of how it flies, however (though that was an interesting 1 minute+ of video).
 

jmasterj

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My son has had three nice flights on a D12/A8 pairing. Will probably do a D12/B6 pairing at some point, not sure we'll ever want a C in the sustainer.
 

DirkTheDaring

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Whilst we're on the topic, I'd like to replace the cardboard engine mounts on my boosted Big Bertha with plywood. Does anyone know if there's a replacement kit readily available? (I pretty much goofed up the sustainer mount by using too much glue and soaking it, so since I have to replace it anyway, might as well do it right.
 

jmasterj

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I've bought lite ply rings from BMS and eRockets (though now I laser cut my own). I just hand-trimmed the fin tabs on the booster fins, and used some BT-50 I have laying around for the booster motor mount.
 

DirkTheDaring

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I've bought lite ply rings from BMS and eRockets (though now I laser cut my own). I just hand-trimmed the fin tabs on the booster fins, and used some BT-50 I have laying around for the booster motor mount.
I think this is what I'm looking for. BT60 to BT20 plywood. I don't have a laser cutter, alas. Thank you.
 

4regt4

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Converted my son's to a 24mm mount in the booster. I agree with the above that the B6 is a better stock booster than a C6 because of the short burn and lack of low-thrust tail.
Not arguing, just puzzled. I've seen what you are saying first hand, but don't understand it.

The Estes BP motors have that thrust spike initially for (hopefully) good speed off the rod, then a lower thrust burn. The C6 having a much longer "tail". OK. Got that.

But what puzzles me is, assuming you are up to a good stable speed initially, why shouldn't the additional thrust help? I'd think it would build more speed, give more stability.

A bit of a tangent: I've done some sims on single stage rockets using OpenRocket where there is a warning that the rocket is beginning to tumble while on thrust toward the very end of the burn, but still way below apogee. This is with some composite motors that taper off considerably. I don't get this. Why would it be stable during the coast phase, but not while under very low thrust?

And, FWIW, I also have a Boosted Big Bertha on the build pile with the parts needed for 24mm booster.

Hans.
 

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But what puzzles me is, assuming you are up to a good stable speed initially, why shouldn't the additional thrust help? I'd think it would build more speed, give more stability.
One would have to have a C5-0 of current manufacture to find out in this case but....the A10-0T has a big spike and a very weak long tail. I have accelerometer data from flying FlightSketch devices in my Checkmate that show that the thrust tail on some motors is so low that all it seems to do is maintain speed during that part of the burn but doesn't really accelerate. One can actually see that as it boosts as it kicks off, then cruises to staging and then really goes from there (with 1/2A3 or A3 in the sustainer). The model does continue on straight during this wimpy boost, though.

On this recent one you can see in the acceleration data during the thrust tail of the booster burn that it is just barely continuing to accelerate: https://flightsketch.com/flights/3602/

So something like that with the current C5 could happen with the Boosted Bertha.
 

4regt4

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Thanks.

I'll have to find the particular OpenRocket file to reference what I was seeing. For some reason, it showed the rocket as less stable under weak boost than if it were coasting. Puzzling. At least to me.

Hans.
 

jmasterj

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Not arguing, just puzzled. I've seen what you are saying first hand, but don't understand it.

The Estes BP motors have that thrust spike initially for (hopefully) good speed off the rod, then a lower thrust burn. The C6 having a much longer "tail". OK. Got that.

But what puzzles me is, assuming you are up to a good stable speed initially, why shouldn't the additional thrust help? I'd think it would build more speed, give more stability.

The long tail makes it burn longer (obviously) and with the relatively low rod exit speed of a Boosted Bertha on a B6 or C6, any weathercocking will result in more horizontal travel, putting the sustainer farther (horizontally) away from you at staging.
 

4regt4

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Found this out the hard way with the little Mini Comanche 3. It actually works well as a 2 stager, but adding the extra booster causes low launch speed and BAD weathercocking.

I need to find that OpenRocket file. The simulation warning was with a composite that had a triangular shaped thrust curve - sharp initial boost, then a more or less constant taper down to zero with a somewhat long burn time. Had good off-the-rod velocity, the warning said that it was starting to "tumble" at the end of the burn even though that was well before the ultimate apogee.

Hans.
 

Starfire73

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The Boosted Bertha flies like one of those Russian hypersonic anti-ship missiles. No kidding.


Oh my GOSH that is hilarious! I went on the forum looking for some feedback on the BB. I just finished Rocksim'in it out and the weathercocking is unsafe on a C6-0 even in light winds. I was wondering if others found that to be the case in real world flights. Looks like that's the case. I really didn't feel like moding anything this time, but there's no way that C6 will work. I think I'm going to mod the booster to 24mm.

I was afraid if I stayed with 18mm on the booster it would get about 20' up off the pad, turn 90 degrees and ride off into the sunset like your video shows!

That happened to me once before with the Custom Lightnin'. The Lightnin' was a long, kinda' heavy, two stage, 24mm, but a D12 just couldn't lift it fast enough. Even on a calm day, she went up, turned right, and said bye bye! Never saw it again.
 

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Oh my GOSH that is hilarious! I went on the forum looking for some feedback on the BB. I just finished Rocksim'in it out and the weathercocking is unsafe on a C6-0 even in light winds. I was wondering if others found that to be the case in real world flights. Looks like that's the case. I really didn't feel like moding anything this time, but there's no way that C6 will work. I think I'm going to mod the booster to 24mm.

I was afraid if I stayed with 18mm on the booster it would get about 20' up off the pad, turn 90 degrees and ride off into the sunset like your video shows!

That happened to me once before with the Custom Lightnin'. The Lightnin' was a long, kinda' heavy, two stage, 24mm, but a D12 just couldn't lift it fast enough. Even on a calm day, she went up, turned right, and said bye bye! Never saw it again.
As I noted above, I've close to two dozen flights on my Boosted Bertha, which is essentially stock. I have flown it successfully with a C6-0 in the booster more than once without having a land shark, but it does pitch over a bit (this under nearly calm conditions). A B6 in the booster is safer.

If I were to build another (or maybe just another booster stage), I'd definitely consider setting it up for 24x70mm motors. C11 would be better than C6 and D12 would actually likely be good fun indeed. I don't think it would be too hard to do this, even considering that the first stage is vented aft through the centering rings rather than through ports out the body tube.
 

jmasterj

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Why does it have to be vented? That’s the first two stage rocket I’ve seen where it’s vented.
It's gap staged, so it needs vents to allow the sustainer to light instead of just blowing the booster off. BP two stagers often tape the booster and sustainer motors together, but that's not what you get here.
 

heada

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It's gap staged, so it needs vents to allow the sustainer to light instead of just blowing the booster off. BP two stagers often tape the booster and sustainer motors together, but that's not what you get here.
While venting a gapped 2 stage BP rocket is considered best practice it isn't required and there have been many successful gap staged rockets without venting. Vast majority of Estes gapped staged kits aren't vented.
 

jmasterj

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While venting a gapped 2 stage BP rocket is considered best practice it isn't required and there have been many successful gap staged rockets without venting. Vast majority of Estes gapped staged kits aren't vented.
What other gap staged kits does Estes make? Boosted Bertha was the first I've encountered.
 
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