Big Bertha on a 24

[ActingLikeAKid]

I just got a Big Bertha and was going to build it to spec and then I said "wait a minute.... I bet this would scream on a D...." No reason not to, right? And I can always adapt down to an 18 if I want to keep it close...

 

[013Rocketry]

I have a Bertha that I regularly fly on E9s. Flies great!

 

[BEC]

Yes. I have built a Big Bertha with a mount that will take E9s/E12s. A BB on a D12-5 is actually quite a nice flight. On Es (or Aerotech F44s) it's Chute Release time (at least at my nearby flying sites).

 

[ksaves2]

I have a Bertha that I regularly fly on E9s. Flies great!

You better ditch those paper centering rings and build accordingly. (Try plywood) I flew a beat up BB on an APCP D and it was it's last flight. Shockcord broke but the rocket still would have been "toast". The paper centering rings gave way and motor
shoved itself inside the tube. Duct taped a keychain camera on it so have the video stashed away somewhere. It actually flew not so high and I have another kit lying around to be built but I will use appropriate centering rings. I strongly suggest you
do that or laminate the paper rings with fiberglass cloth. (which is too much work) Kurt

 

[dhbarr]

You better ditch those paper centering rings and build accordingly. (Try plywood) I flew a beat up BB on an APCP D and it was it's last flight. Shockcord broke but the rocket still would have been "toast". The paper centering rings gave way and motor
shoved itself inside the tube. Duct taped a keychain camera on it so have the video stashed away somewhere. It actually flew not so high and I have another kit lying around to be built but I will use appropriate centering rings. I strongly suggest you
do that or laminate the paper rings with fiberglass cloth. (which is too much work) Kurt

A middle ground is to just use the paper CRs as a pattern to make matching balsa CRs, woodglue together. Plenty tough unless you're planning some 6g CTI stuff.

 

[snrkl]

I wouldn’t worry about the cardstock CRs with D12 motors.

I’ve got PLENTY of BT60 rockets with card stock CRs that fly D12s...

If you want to keep it to 18mm but fly Ds, remember Aerotech has d motors in 18mm...


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[ksaves2]

I wouldn’t worry about the cardstock CRs with D12 motors.

I’ve got PLENTY of BT60 rockets with card stock CRs that fly D12s...

If you want to keep it to 18mm but fly Ds, remember Aerotech has d motors in 18mm...


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That's what ripped through my BB an 18mm D. I still wouldn't trust paper cardstock with anything more than a C if one is looking for longevity. That said, I fiberglass cloth laminated paper cardstock rings in another project, doubling the number of rings
and it handled H's and I's fine. Too much work so I just go with plywood now. Kurt

 

[dhbarr]

That's what ripped through my BB an 18mm D. I still wouldn't trust paper cardstock with anything more than a C if one is looking for longevity. That said, I fiberglass cloth laminated paper cardstock rings in another project, doubling the number of rings
and it handled H's and I's fine. Too much work so I just go with plywood now. Kurt

Well, yeah. A c6 maxes at 14N, a d10 at 25, and a d21 at 32.

The composite motors get there almost instantaneously, where the Estes d12 ( highest peak thrust BP IIRC) takes a quarter second to get up to 30N, with 4mm less CR diameter to flex.

It's not about C vs D, it's about how quickly that motor attempts to jam a nosecone-shaped hole through the sky.

 

[snrkl]

Well, yeah. A c6 maxes at 14N, a d10 at 25, and a d21 at 32.

The composite motors get there almost instantaneously, where the Estes d12 ( highest peak thrust BP IIRC) takes a quarter second to get up to 30N, with 4mm less CR diameter to flex.

It's not about C vs D, it's about how quickly that motor attempts to jam a nosecone-shaped hole through the sky.

Good call on BP vs AP - haven’t looked at the 18mm AP thrust curves. I yield to those that actually engaged their brains before they posted (unlike me! ;^p )

I have launched many Estes d12 BPs on cardstock CRs though. I’ve found Apogee’s cardstock BT60 to 24mm CR rings work great for that.

 

[Steve Shannon]

I threw away the centering rings and MMT in my Big Bertha and wrapped the BT in fiberglass. For a motor mount I peeled the outside layer off a Giant Leap 38 mm MMT and found that it slid right in. I trimmed the MMT short so the stock nosecone would still seat. Then I did a poor job of glassing the balsa fins. Disgusted at myself I set it aside. I’ve moved it back and forth on the workbench for the last 11 or 13 years. Someday I’ll finish it.


Steve Shannon

 

[snrkl]

I threw away the centering rings and MMT in my Big Bertha and wrapped the BT in fiberglass. For a motor mount I peeled the outside layer off a Giant Leap 38 mm MMT and found that it slid right in. I trimmed the MMT short so the stock nosecone would still seat. Then I did a poor job of glassing the balsa fins. Disgusted at myself I set it aside. I’ve moved it back and forth on the workbench for the last 11 or 13 years. Someday I’ll finish it.


Steve Shannon

Lol - an almost MD Big Bertha - you’ve got to finish it and post the flight video now...

 

[Steve Shannon]

Lol - an almost MD Big Bertha - you’ve got to finish it and post the flight video now...

Yeah, I suppose I’ve stepped in it now. [emoji91]


Steve Shannon

 

[BEC]

I've not had any issues with the paper CRs and D12s, E12s or even the F44 in my 24mm mount equipped Big Bertha. I have had one such Big Bertha blown apart by a CATO (I don't recall if it was E9 or E12) but never had the motor mount fail.

That said, an 18mm mount (more unsupported span of paper rings) on a D21 might be something that wouldn't hold up to too many such launches, especially the thin rings that come in a standard Big Bertha kit. I do have a much flown Semroc Vega (Semroc's "Big Bertha" equivalent) which has done a bunch of D10 flights with no issues. But I don't think I've ever flown it on a D21.

 

[Rex R]

given the fact that the Bertha was derived from the Ranger, it is not surprising that a Bertha does very nicely on C11s and D12s . lol I have built an md bertha using loc 38mm motor tube, flown once on a G67 OR said 2500'. I used semroc centering rings on my payload version, a 3.5oz. payload is my standard load for a D12 .
Rex

 

[Sabrina]

Big Bertha does just fine on 24mm power. Like this 24mm F32 I flew in mine. :dark:

 

[Bill Gibson]

I've got a 24 mm Big Bertha that flys just right on a D12-5.....a very nice combination!
Just wanted to mention that anytime I beef up 18mm rockets for 24mm power, I make doublers made out of lightweight porous balsa or foam and glue them to the paper spacers. The width of the doublers range from 1/8" to 3/38" which increases the glue surface area to the body tube without increasing the weight a lot. Works GREAT!!

 

[sl98]

I upgraded my BB to 24mm. I used a Priority Mail box and hand cut CR's. They have held up just fine to 18/20 D's, D12's and 24/40 E-11's. I have Priority Mail box CR's in a 29mm Super BB that have held up to G's.

Don't forget the 24mm C11''s. A favorite motor of mine in my BB is the C11-5.

 

[RainierWolfcastle]

If worried about the CR strength an easy fix is to make 3 or 4 rectangles from balsa or ply that fit the space from top CR to lower CR and outside diameter of MMT to the inside diameter of the body, those ribs provide a great deal of surface area for adhesion as well as preventing the CR from flexing under load. You could even cut or drill material from the centre of the rectangle to reduce weight if required without sacrificing much strength.

 

[ActingLikeAKid]

If worried about the CR strength an easy fix is to make 3 or 4 rectangles from balsa or ply that fit the space from top CR to lower CR and outside diameter of MMT to the inside diameter of the body, those ribs provide a great deal of surface area for adhesion as well as preventing the CR from flexing under load. You could even cut or drill material from the centre of the rectangle to reduce weight if required without sacrificing much strength.

I really like that idea - extra strength, not a ton of weight, and way easier than cutting custom CRs!

 

[MikeyDSlagle]

If worried about the CR strength an easy fix is to make 3 or 4 rectangles from balsa or ply that fit the space from top CR to lower CR and outside diameter of MMT to the inside diameter of the body, those ribs provide a great deal of surface area for adhesion as well as preventing the CR from flexing under load. You could even cut or drill material from the centre of the rectangle to reduce weight if required without sacrificing much strength.

I did something similar to my Super Neon XL going from 24 to 29mm. Then squirted some 2 part foam in the voids between the ribs. Still not finished the thing though so don't how strong it is.

 

[Forever_Metal]

You need to be careful with the AT d21's.

We cato'd 3 in a row from 3 different packages (1 each package) bought at different times by 2 separate individuals. Blew the motor mount apart in my 'Bertha. The only reason the other guy didn't have any damage to his birds was that he placed the d21 inside a cleaned out 24mm spent case.

If you can wait Estes is releasing a Super size edition soon (check the coming soon on the website).

I had just started an upscale myself...

fm

 

[paulm]

24mm motor mount with scew on retention, through the wall basswood fins, flys great on any 24mm motor!

 

[dmgrime]

Flew my scratch BT60 bertha clone with 24mm mount and TTW basswood fins on an old Aerotech F21W single use a club member had.

Chuffed for what seemed like forever and the took off like a scalded cat. Out of sight but recovered with a slight zipper only... repaired and still flying.

Fun stuff.

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[hcmbanjo]

If worried about the CR strength an easy fix is to make 3 or 4 rectangles from balsa or ply that fit the space from top CR to lower CR and outside diameter of MMT to the inside diameter of the body, those ribs provide a great deal of surface area for adhesion as well as preventing the CR from flexing under load. You could even cut or drill material from the centre of the rectangle to reduce weight if required without sacrificing much strength.

That's the ticket!
Here's a link with pictures from my build blog:

https://modelrocketbuilding.blogspot.com/2016/04/estes-hi-flier-xl-3226-build-part-3.html

 

[MoeB]

Big Bertha does just fine on 24mm power. Like this 24mm F32 I flew in mine. :dark:

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Very cool way to "soup" up the Bertha...I like it!

 

[snrkl]

Very cool way to "soup" up the Bertha...I like it!

Ok - now I want to build a bigger bigbertha and paint it so it looks like a stack of soup cans...

 

[tHoagland]

So, I have to add a short story about my Daughter's Big Bertha to this thread....

She was 11 years old and I was trying to get her to build and fly more as a way to spend time together. I'd made some progress, she'd designed and built a couple of small rockets and seemed to be having fun. So when she asked to pick out a new rocket from Performance Hobbies (on-site vendor at the launch), I of course said sure and she picked out a Big Bertha.

When we got home I started looking at it and said " Hey Emma, you know what? Instead of building this stock you could change out the motor mount and use bigger motors "

Emma (with a lot of excitement): "I could?!?"

Me (excited that she's excited): "You could, you could fly with an E or F motor"

Emma (still excited): "Really?"

Me: "You know what that is?"

Emma: " Yes.......Sarcasm".

I was dumbfounded and realized I may be in real trouble as she she gets older.

 

[DaveW6DPS]

I have a Big Bertha with the stock 18mm mount. Flies great on 18/20 D24 reloads.
I am looking forward to trying the new D16 Q-Line motors.

Of course this thread has me thinking of a new build with 24mm motor mount.

 

[BABAR]

Ok - now I want to build a bigger bigbertha and paint it so it looks like a stack of soup cans...

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Sounds like would work great with a wrap around decal