Ok,

This is a repost from another forum, but some have asked about my Bertha Build so here it starts.

Our club has a Big Bertha Tri-Athalon contest next month.
Parachute and Streamer Duration plus spot landing.

These are fun by the way, especially if you make it Iron Man rules.

So I took a baby bertha, tossed the little tube and used a 18" bt-60 tube from Red Arrow Hobbies. I built the engine mount with a kevlar shock cord and I am letting it dry.

I put aero-gloss sanding sealer on the fins thick, so I can sand it all back off

I picked the sealer all off my fingers, while feeling a littel dizzy, so I had a beer.

I sized up the body tube and nose cone and sure enough, they fit

Hopefully later I can sand all the sealer off the fins and put it in my BMI-CAD fin jig to make the fins Locked-IN for best performance.

__________________
Art Upton
I am an original AR; pronounce like a pirate says "R"
An AR is an Always Rocketeer, in differance to BAR; although I like to visit BARs now and then.

Ok,

here is the picture of the motor mount.

Notice I used the plastic ring thingy to hold down the kevlar cord I tied a knot in. It is also important to notice I draped the kevlar cord over the glue bottle, to keep the cord from getting glued to the mount at places it should not.

Also I used yellow glue. Not wanting to start a glue thread, but this is the glue I will be using on this rocket, and in very small amounts.

The rocket will need to weigh very little to get good times in duration and saving weight by not using epoxy even though it will build quicker will result in a better performing rocket.

__________________
Art Upton
I am an original AR; pronounce like a pirate says "R"
An AR is an Always Rocketeer, in differance to BAR; although I like to visit BARs now and then.

Remember I said I put on a think coating of Aero-Gloss sanding sealer ?

Well, when it dried I sanded it all off

I then realised I needed my fins sealed to at least look good, even at the slight weight expense, so I put a thin coat on this time.

I didn't have to pick it off my fingers, but I still got dizzy, so I had a beer

__________________
Art Upton
I am an original AR; pronounce like a pirate says "R"
An AR is an Always Rocketeer, in differance to BAR; although I like to visit BARs now and then.

Well,

Since I was dizzy and drinkin' a beer, I figured' I'd do some Cypherin' and got out Aero-Drag.

I worked out a CD of .525 (due to my aero-gloss sealing) and worked out a nice altitude plot below

__________________
Art Upton
I am an original AR; pronounce like a pirate says "R"
An AR is an Always Rocketeer, in differance to BAR; although I like to visit BARs now and then.

CFD Rocket Science

I had to flip the fins and add more Aero-Gloss to them. I got dizzy and so had a beer to feel better. Something about Beer makes me want to play with rocket computer programs.

I little bit ago, I purchased from AeroRocket a program called Visual CFD. It is like having a color wind tunnel in your laptop.

I'm still a 'noob with it, so I put the Bertha into the program to try to learn somemore.

here is one plot I just did

__________________
Art Upton
I am an original AR; pronounce like a pirate says "R"
An AR is an Always Rocketeer, in differance to BAR; although I like to visit BARs now and then.

Another Plot Another Beer

__________________
Art Upton
I am an original AR; pronounce like a pirate says "R"
An AR is an Always Rocketeer, in differance to BAR; although I like to visit BARs now and then.

So for our next tasks, we sanded all that nice and smooth “Glassine” coating on the body tube. You know, that stuff that makes the finish so nice, you have to sand it off

At least we only sanded it off at the part we will glue the fins on, with Yellow Wood Glue.

Next you will see we have the BMI CAD fin jig setup with the 18mm core and the motor mount for the Bertha. The BMI CAD jig can be seen at http://www.bmicad.com/

I got the complete setup with cores from 13mm to 54mm for $129, a Bargain

At NARAM 45 (2003) , my pop-up was next to Trip Barber's during contest week. Trip has been known to have anti-gravity in his altitude competition rockets.

On Wednesday of that week, I got a few mins to talk with him. He told me his secret was using a fin jig to make fins absolutely straight and keep weight down as much as possible. Then make sure you get an absolute straight boost

So , here is what I did today, I also had a beer

Well, we have a problem here, can anyone tell what the problem is?

No, not the blurry picture, what else?

I had a beer to solve this problem.

__________________
Art Upton
I am an original AR; pronounce like a pirate says "R"
An AR is an Always Rocketeer, in differance to BAR; although I like to visit BARs now and then.

Ok, the bertha fin design is not really a good one for a fin jig

So I had to extend the core as much as I could to get a close fit.

Used yellow glue, and held the fins on with masking tape to the jig, and drank the beer sitting on the coaster.

__________________
Art Upton
I am an original AR; pronounce like a pirate says "R"
An AR is an Always Rocketeer, in differance to BAR; although I like to visit BARs now and then.

Here is the part some folks dont like.

The Yellow glue fin fillets. Make fillets like this and support the rocket so no weight is on any of its fins.

You need to do this at 9am and the flip side at 12 noon. Then do another section at 3pm and the flip side of that at 6pm.

So it takes a day to make and dry the fillets for a Four Fin Rocket.

Its the 9am part here so you can see my Green Monster Energy Drink.

Any time after noon you can substitute other favorite beverages to drink between fin fillets.

Hey, isn't it always noon somewhere ?

__________________
Art Upton
I am an original AR; pronounce like a pirate says "R"
An AR is an Always Rocketeer, in differance to BAR; although I like to visit BARs now and then.

Now comes time to Finish and Paint.

I've always wondered why rocket instructions have you put the motor mount in first

Its a good thing I didn't as it makes finishing so much easier.

Contractors paper can be purchased at LOWES for about $8
I use it for lots of things, like masking big rockets.

Roll up some and slip it up the tube.

__________________
Art Upton
I am an original AR; pronounce like a pirate says "R"
An AR is an Always Rocketeer, in differance to BAR; although I like to visit BARs now and then.