Big Bertha / Baby Bertha Weekend Build

[TangoJuliet]

It's another slow weekend at work, so to make good use of idle time I'm going to build the Estes Big Bertha and Baby Bertha kits (1948/1261).


Two weeks ago I procured enough building supplies to do simple builds in my office and completed a Goblin and Mini Fat Boy then, at least to the point of needing paint.


On the Big Bertha I found a slight crimping in the BT about 7" up from the tail end. It's slight and I'm not overly concerned with it. I think once I add primer and paint it'll strengthen it enough for it to last a while, and it won't be noticeable from 10' away.


Motor Mounts are identical in construction and typical Estes.


BTW, I use Titebond II for the majority of my glueing needs. Epoxy and CA get used where absolutely necessary.

BT Fin and Launch Lug markings also get applied in the typical fashion, then drawn out using a door jam in the office.


The Fins are cut free from the balsa sheet (modern laser cutting is so much nicer that the die-crunch days), then match sanded, and the leading edges rounded over per the instructions. Check the fin shape carefully to determine the Root Edge versus the Leading Edge, it's easy to get confused.



About mid-day I'll start to glue Fins to BT's. At the moment, MM's are curing in the BT's.

 

[TangoJuliet]

Fin attachment under way. Alignment is done using a Mk-1A Eyeball... It's good enough for my needs.

 

[Lowpuller]

What do you do for a living? I barely have time to breathe at work.

 

[TangoJuliet]

I used to be a Customer Service Representative (8 years), but for the last 16 months I've been a Ground Control Specialist (similar to Ground Traffic Control, but NOT FAA certified) for Era Helicopters in Houma, LA. When I did CSR work it was 13-15 hours a day non-stop, now I'm strictly 12 hour days with A LOT of idle time on my hands.

 

[TangoJuliet]

The last fin being glued to the Big Bertha, and the first fin being glued to the Baby Bertha.


That's as far as I'll get today. Tomorrow I'll add re-enforcing fillets to all the fins on the larger bird, finish installing the fins on the smaller bird and also add fillets, then glue on launch lugs, and finally, apply a thinned mixture of CWF to all the fins and sand them smooth in anticipation of final primer and paint.

 

[justinwebb]

Now you just need the super big bertha!

 

[TangoJuliet]

A teacher friend of mine uses rocketry in her curriculum and I hope to have several models of various sizes to bring to a launch with the students in the Spring so we can compare them. I'm finishing a Mega Der Red Max at home and still have the standard Der Red Max here at work to build. Is there a Super Big Bertha? MPR is as big as I'm going though.

 

[chrisudy]

Super Big Bertha was a BT-80 based version with a 24mm mount. Estes still sells the plastic nose cone. My fins came from Semroc - eRockets probably has them.

 

[TangoJuliet]

I'll look into it. There's a few other rockets I want to build between now and Spring though. I think I need a few scale models to add to the sport fleet. I've got an old ASP WAC Corporal w/ Tiny Tim that I need to assemble. I bought it almost 18 years ago and never completed it. I recently bought some 1/16" Carbon Rod to replace the now warped dowels that came in the kit.

 

[TangoJuliet]

This morning was spent adding re-enforcing glue fillets and adding the launch lugs.

This afternoon it was time to fill the grain in the balsa fins. While it's NOT Carpenter's Wood Filler specifically, this DAP product is essentially the exact same thing.


Not having any Epoxy brushes with me, I scoop a glob of it into a cut down coffee cup with my finger, add just a touch of water, and mix into a slurry.


Then, again with my finger, I start to paint it onto the fins. It looks horrible, but most of it will get sanded off, kind of like using Primer.


For the N00b's - Because it's water based and I've added additional water, it's important to paint both sides of the fins at the same time. Balsa by its nature will soak up moisture and if only one side is done, that side can swell and cause the wood to warp toward the dry side.

Here's what the untreated grain looks like:


And what it looks like after it's been sanded after drying (these fins are on the Goblin I built two weeks ago):



They could maybe use another coat of filler, but I'll spray a Primer paint before final paint and that should be good enough. After all, these are just low $$ sport models, I don't intend to end up with a mirror smooth finish. But I don't want them looking too amateurish either.

 

[TangoJuliet]

Finished... Minus paint and decals! But this is where I intended to be at this point.

Another note of caution for the n00b's... When sanding the wood filler it will create quite a bit of fine dust. A mask is highly recommended, as well as not having a fan running anywhere nearby! And if you're not wearing a mask, DO NOT breath heavily in the direction of your work, and especially DON'T sneeze!

In this photo of one of the Baby Bertha fins, you can see how well the wood filler smoothed out an area where something had indented the balsa and left and edge with a step. Now it's completely smooth!




Thanks for following along!

 

[Mugs914]

They look great TJ! I have never had a Big Bertha in my life, but looking at yours has me thinking it might be time. Nice job. Oh, and I love that you get to do this at work. Very cool!

I have never tried that type of wood filler either. I usually coat balsa with thin CA glue or go with the traditional dope/filler method. What is the typical drying time for that stuff? Is it pretty easy to sand?

 

[Lowpuller]

More importantly do you ever get to fly in these helicopters you speak of?

 

[TangoJuliet]

Thanks y'all!

I'm very fortunate to be able to do this at work. My office has limited access by a secure pass key, I work alone, Management is rarely here on weekends, and weekends are painfully slow! Even on my busier days there may be hours between the 40 minutes where I'm actually engaged on the radio. Heck, Management even installed a 65" TV on the wall for me to watch!

But believe me, for several years I worked my arse off and suffered from high blood pressure to get to where I am now. I don't want to take too much advantage of it :wink:.

In my current position I don't really have the opportunity to fly anymore, but I have in the past on a few occasions. One year we evacuated our Lake Charles, LA, base due to a hurricane. I was one of the first passengers to fly in our then new EC-225 "Super Puma". Flying doesn't really excite me much anymore though. I get motion sickness too easy. But aviation is in my blood. I've been involved in it all of my adult life in some form or another... Just never as a certificated Pilot.

 

[TangoJuliet]

As far as the wood filler - Drying time is just a few hours really. It sands very easy and creates a very fine, powdery dust. I don't use much CA glue anymore, even in my R/C airplanes. Some people develop an allergy to it. I haven't, but I just don't care for it as much as I did when I was younger. CA is hard to sand and it gets brittle. As a wood hardener, I suppose Thin CA works fine, but I'd rather use something else. That's just me though.