24mm Big Bertha? Mini-Bertha?

[wscarvie]

Hi all,

Has anyone tried to put a 24mm motor mount in either an Estes Big Bertha or Baby Bertha? Just wondering what you did, if anything, to make the rocket a bit stronger, and whether you needed to add any nose weight.

Assume Estes D and E engines, please.

Thanks much.

 

[powderburner]

I built one, just for fun. I used the fins that came with the kit, glued on with white glue. I normally use only small fillets, and did those out of white glue too. I balanced it with a bit of nose weight to get the c.g. back up to where it was on the original version. I did not use rocksim (or anything else) to predict the altitude.

On the first launch, the rocket basically went out of sight. It may have left the county for all I know. Never saw it again. But it was fun!

 

[pdooley]

I built one from a Walmart baby bertha. I used a full 18" body tube in place of the baby tube, so technically it is a Big Bertha. Built the engine tube just long enough to hold an E engine. Got some 50-60 centering rings from BMS.
I used a mylar streamer in place of any kind of parachute.
I didn't use any nose weight. The BB is inherently overstable due to the fin design and length.

The first flight was on an E9-8. Very impressive, high flight. Even on a streamer it drifted pretty far.
Second flight was pretty much the same. I musta misaligned the fins or motor mount because it got a lot of spin.
This time she got hung up in a tree. I left her there.

I have another BB with an 18mm mount, I peeled that out and up'd it to 24mm. Can't wait to launch it next meet

BTW, I didn't do anything different. Used yellow glue, etc.
The E9 is not really a high thrust motor, just long burn.

 

[vjp]

I put an "E" mount in my Baby Bertha, although I've only flown it once, on a D12-7. Fantastic flight.

I didn't add any nose weight to mine, although I did reinforce the fins with epoxy/fiberglass cloth, and replaced the chute with a streamer. (I fiberglassed because I want to be able to fly it with E30's, if I get the chance).

Extending the MMT for an Estes "E" motor leaves very little room in the BT for wadding and recovery system. Also, the close proximity of the shock cord mount to the ejection charge nearly burned my shock cord in two - I will be replacing it with braided kevlar before I fly it again.

 

[wscarvie]

Thanks, everyone.

It sounds like this is a fun and easy project. I got the idea when looking at the plans for an Estes Maxi-Streak on JimZ's site. Basically it's a Baby Bertha with different fin geometry. It looks like a very well fed Mosquito.

I'm going to try this one. It's fast to build and sounds like fun to fly. I'll certainly be going with streamer, and probably only in low wind. Long drifts on the island where we fly tend to put rockets in the Bay.

Thanks again.

 

[Fore Check]

If you have any extra parts laying around to clone a Goblin, you can put together another rocket that will go incredibly high on an E9-8. The Meteor (#2025) is essentially a Goblin with different fin geometry.

I put one together on RockSim with an E engine mount. RSim predicts over 2300' on an E9-8. I've noticed that RSim altitude predictions seem a bit conservative. Closer to 1/2 mile on this one would not suprise me in the least.

The plans can be found here: https://plans.rocketshoppe.com/estes/est2025/est2025.htm

 

[wscarvie]

Thanks Fore Check,

Seems to be a whole family of these little D and E powered birds out there. I get the feeling that, if I cloned a Mini-Streak (for example) and changed the nose cone from the Big Bertha style rounded cone to a long Ogive, I'd suddenly have cloned an entirely different rocket

Thanks again.

 

[MetMan]

Will,

Jumping in a bit late here, but I've got a Baby Bertha modified for a 24mm D (or C11). I changed out the round nose cone for a 3:1 ogive cone--it gives it a cool 50s sci fi look.

The only strengthening I did was to add bond paper CA'd to the fins. This was to prepare for harder landings with a streamer for recovery--it sims to ~1800ft!

MetMan

 

[wscarvie]

Thanks MetMan.

Good idea on the paper reinforcement. I've been wanting to try that anyway, and this would be a perfectly appropriate bird.

How did you spread CA onto enough paper to cover such large fins and still get the paper on before it dried? Any special trick to getting it onto the fin without wrinkling it?

Thanks!

 

[pdooley]

It sounds like this is a fun and easy project. I got the idea when looking at the plans for an Estes Maxi-Streak on JimZ's site. Basically it's a Baby Bertha with different fin geometry. It looks like a very well fed Mosquito.

Here's a pic of my Maxi Streak. It books on D-12's.

 

[pdooley]

And one of the 24mm BB:

 

[MetMan]

Originally posted by wscarvie
How did you spread CA onto enough paper to cover such large fins and still get the paper on before it dried?

Will,

I used a Rocksim file to print out fin templates on the paper and cut them so they basically fit over the balsa fin. Then lay the paper fin overlays on top of the balsa fins so they are lined up well and spread out thin CA on top of the paper. The thin CA soaked right in. If you get too much on there, use a tissue to soak up the excess. Do it outside or near a window though--the fumes are murder!

You might want to use latex gloves--I stuck my fingers together pretty good!

MetMan

 

[wscarvie]

Originally posted by MetMan
I used a Rocksim file to print out fin templates on the paper and cut them so they basically fit over the balsa fin. Then lay the paper fin overlays on top of the balsa fins so they are lined up well and spread out thin CA on top of the paper. The thin CA soaked right in. If you get too much on there, use a tissue to soak up the excess. Do it outside or near a window though--the fumes are murder!

Well now, that's just brilliant. I was trying to figure out how I'd pick up a floppy piece of paper soaked in glue that sticks anything together and get it positioned over the wood

Thanks much!

 

[wscarvie]

Sweet pics, pdooley. I especially like the paint job on the Maxi-Streak.

Thanks for sharing.

 

[powderburner]

When I add paper or cardstock covering to balsa fins, I usually work with thinned white glue. You get a lot more working time with that stuff, and you don't gas yourself in the process.

I have used CA a few times, but my technique is a little different than MetMan's. I make no attempt to pre-cut the paper to the exact size of the fin, but instead use oversized paper. I lay down a piece of waxed paper, put the first paper sheet on that. I drip out plenty of thin CA on one side of the fin and spread the CA with a q-tip to try to get the whole side of the fin wet. Working quickly, I drop the fin onto the paper and press, then drip more CA onto the opposite side of the fin. Spread some more (remember which end of the q-tip to grab) and slap on the second layer of paper. Cover with more waxed paper. Pile on the old magazines, and let the fin sit for two beers. Uncover, peel off the waxed paper, trim the excess paper with an X-acto and a straight-edge. CA the edges all around and let cure thoroughly before sanding smooth.

But this is really, really stinky, messy, and kind of dangerous. I recommend the white glue. Thin it 1:1 with water and it works great. It is cheaper, easier, much less hectic, and much easier on your nasal tissues. Try it once on some scrap or a spare fin and I'll bet you never go back to CA.