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Estes Mini Bertha

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Dudley

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I would like to build an Estes Mini Bertha.
Sine I'm a self-admittedly lazy person, first I'll ask... does anyone offer a ready-to-build kit of this rocket?

Ok... I was afraid of that...
I've found plans on-line but am having a hard time locating fin stock.
The last rocket I built was over 50 years ago so I'm not even sure if it's available.
The Estes designator listed in the plan is BFS-20E (75005).
Can anyone please provide some guidance as to where I might find the appropriate pieces?
 

kuririn

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Dudley

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That answered my question.
Thank you very much!
And yes.... those are the same plans I found.
 

BEC

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Hobby Lobby and some Michaels stores (and even some Ace Hardware stores) carry balsa sheets. You just need a bit of 1/16th thick stuff. If you have any old-school aeromodeler friends (those who build or built their planes) they may have pieces big enough to cut those fins from in their scrap boxes.
 

markschnell

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PhlAsh

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I think I used their balsa nosecone for my BT-20 Bertha. I use their vacuformed competition nosecone for the BT-50 Bertha
 

stantonjtroy

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markschnell

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Well THAT is handy. Might have to look at these. When I cloned mine I cut mine from my balsa sheet stash (old School R/C builder) and turned a nosecone from an epoxy/micro bub s
Well, if you have to cut your own fins they don't get much easier than these. I think I bought mine because they were cheap and I was buying other stuff. It was pretty handy, though. I skinned mine with Avery label paper because they were pretty flimsy.
 

CoachSteve

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CoachSteve

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papering fins - i use a mini paint roller
- put white glue on fin,
- spread around with roller until entire fin is evenly coated thinly with glue
- press onto paper
- place fin between 2 flat surfaces (tile, books, whatever stack books on top for weight
- 3 days later, remove fin and trim paper to match fin edges
- do other side
 

neil_w

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Usually I use adhesive label paper, but if I'm doing the glue method then:
1) Put a small dollop of glue on the fin, then spread around with finger. Keep spreading with finger and wiping off excess until the glue layer is *really* thin, barely there.
2) Apply paper, press it out evenly. If you got the glue layer thin enough in step one, it should lay down pretty flat.
3) Do other side
4) Press between books, allow to dry.
5) Sand off excess paper. Apply a dot of glue to any areas where the paper edge is not totally adhered.
6) Seal exposed wood edges with wood glue or CA as preferred.
 

markschnell

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I've been building since 1975 and I can't seem to get the hang of papering fins. They either warp or the paper wrinkles. What adhesive do you use?
I just used the plain white adhesive paper, it's like a plain paper sticker. I've not had any problems with wrinkles in that. I still glue down the edges with CA or white glue, but after primer I've never had any issues with the edges coming up.
 

neil_w

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I just used the plain white adhesive paper, it's like a plain paper sticker. I've not had any problems with wrinkles in that. I still glue down the edges with CA or white glue, but after primer I've never had any issues with the edges coming up.
Same here. Adhesive label is heavy enough that it lays *flat*, and doesn't warp the wood. It introduces some of its own issues, but overall I prefer it. It does not add nearly as much strength to the fins as glued paper, though.
 

stantonjtroy

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This is great but the thread is about the "Mini-Bertha", not the "Baby-Bertha". The "Mini" was one of the Mini Brutes Estes came out with, I think, in the fall of 1971. Been OOP for some time. Flew on 13mm motors. Awesome little rocket.
 

stantonjtroy

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papering fins - i use a mini paint roller
- put white glue on fin,
- spread around with roller until entire fin is evenly coated thinly with glue
- press onto paper
- place fin between 2 flat surfaces (tile, books, whatever stack books on top for weight
- 3 days later, remove fin and trim paper to match fin edges
- do other side
That's basically what I've done. I think I just need to let it cure under compression longer. Much.
 

stantonjtroy

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Thanks for all of the input on papering fins. I'll try it again. We now return you to your regularly scheduled thread. (apologies for the brief hijack).
 

GlenP

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The paper has a grain, just like a balsa sheet, it usually runs along the long edge. Take care to cut the paper for the fins like you are cutting a fin from a balsa sheet, or maybe go perpendicular but in the same direction for the paper that will go on both sides of the balsa. If you have the paper grain in different directions it might warp a thin balsa fin with changes in humidity or when the glue has dried out.
 
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BABAR

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If you go with glue technique, Not a bad idea to put the fins in a fold of waxed paper or parchment paper before sticking it on a book over nite, at least that works for me.

Straight trails!
 

SCooke123

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I'm building a Mini- Bertha now. Used the eRockets fins and nosecone. I papered the fins with the Avery Label paper - they turned out nice.
I have the engine mount, fins, and launch lug installed and drying. Put a first coat of sealer on the nose cone.
I'm thinking of using a streamer on this one - haven't fully decided yet.
Steve
 

GlenP

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I think the mini Bertha is a good candidate for making a mini booster to match, like its full size big sister the Boosted Bertha. Then you would definitely want to use a streamer in the sustainer stage.
 

stantonjtroy

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I'm thinking of using a streamer on this one - haven't fully decided yet.
Steve
This is a good candidate for it. It's a very robust little rocket and on an A10 it'll get some altitude. My original back in the late 70's early 80's (kit) came with a 10" chute. Tight fit in the tube, really need to pack it clean so as not to jam up the tube. When I cloned it I used a chute again (12" cut down to a 10") for nostalgic reasons (DUMB!). My grandson want's his own to drag race mine so I'm definitely going with a streamer on that one.
 

SCooke123

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I think I'll go with a streamer - at least on initial flight.
I thought the same on the tube size = not a lot of room there! Plus with papering the fins they will be a little stronger (hopefully!)
I might try another one using an 18mm mount instead of the 13mm - have to build a regular Bertha first (actually never built one - been doing this since 1967).
Steve
 

Dudley

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What am I not reading correctly from the plans ( http://www.spacemodeling.org/jimz/estes/est0803.pdf ) ?
Isn't a BT-20 body tube for an 18mm diameter rocket?
And isn't the nose cone designation, i.e. BNC-20, supposed to correspond to the BT diameter?
I've just ordered "XXNC-20" nose cones from three vendors and received three different pieces, each for a 13mm tube.
Is it me or did stuff change over 50 years? (Last time I bought rocket parts before this was 1959).
 

Mightymango

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Well the Engine mount tube is a BT5 so a 13mm. The body tube is a bt20.
 

SCooke123

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Dudley - go to eRockets and order the body tube, nose cone and fins. Use the numbers from the plan and you will get the right parts and right length tube. You can order the engine mount too.
 

Dudley

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After doing more research, I think I understand my confusion... the plans I have are for an 18mm (BT-20) "Mini Bertha".
The BT-5 version a lot of guys seem to be building is a "downscale" version.

After doing some Hoosier math...
The BT-20 version body tube length is 220mm.
The "downscale" BT-5 version body tube would be 159mm.

Does anyone have the fin template for the BT-20 / 18mm version?
How about a source for an 18mm "Bertha" style nose cone?
 
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