Build Thread: Zeerust Alpha

[Jeff Lassahn]

While playing around with stability calculations, I've been looking at a lot of streamlined shapes and tail tapers. It's all made me want to build something with that retro, ultra streamlined look. I was thinking it was going to be too hard to get all the curves right, until I realized you can use cut down ogive nose cones for things other than noses (I know I'm not the first one to figure this out, but it still makes me happy!)

So here's my design, the Zeerust Alpha, perfect for that little family picnic trip to the Canals of Mars.

It's all stock parts, with the tail made from a hacked up version of the nose cone (Would this be a 3F8N?)
Now I just wait for the ordered parts to arrive...

 

[BABAR]

3F4NC4TC (tail cones)

 

[Ronz Rocketz]

Epoxy the pods cause they’ll take a beating in the air. At least that’s what I’ve observed unless you just use the tube sans NC.

 

[Mugs914]

Love the look! Following...

 

[Jeff Lassahn]

Parts have arrived.

Some things I found out cutting down the tail piece:
It's good to mark the fin locations before cutting the tip off the cone because the end point makes a good reference for keeping the lines straight.
You can use masking tape to lay out a geodesic on the curved piece so the fin lines are straight.
An engine mount centering ring has an inside diameter that's the right size to use to mark the cut point.
It takes a lot of cleanup to get the inside of the cut to a reasonable geometry, first trimming the edge with a blade then sanding smooth.

Here's the parts:

 

[Jeff Lassahn]

Making the fins today.

I'm trying out for the first time laminating the balsa with paper. It works great, there's a nice smooth surface and the fins are quite strong.
I tried using onion skin tracing paper first, which doesn't work at all -- it bunches up and won't lay flat on the balsa. Normal typing paper is definitely the way to go.

I drew the fin cutting templates on the paper, used basic white glue to laminate it to both sides of a balsa sheet, then cut the fins.

I finished the unpapered leading and trailing edges with a couple of passes of sanding to round and coating with Elmer's Wood Filler.

The combination of paper and wood filler reinforce the pointed tips so they survive cutting and sanding -- with just balsa they would have snapped off for sure.

On the whole it's been a big success.

 

[SCooke123]

Looks good so far. I like the design - has the 1950's "B" Sci-Fi Movie vibe to it.

 

[Jeff Lassahn]

Since I'm going to have a tube joint at the tail anyway, I'm planning to do rear ejection (or maybe mid-rear ejection) The design goes something like this:

 

[Jeff Lassahn]

Awesome but useless fin pods! I dunno, maybe it where we keep the Cavorite...

If I were doing it over again, I'd choose balsa nose and tailcones for these instead of plastic. I ended up having to do a bunch of sanding and filling to clean up the seams, and balsa might have made that all easier. Still think plastic is the way to go for the main body, though.

 

[Jeff Lassahn]

Gluing up fins to the tail. I'm using Gorilla glue for the wood to plastic joints. I'm not accurate enough to get a really exact fit on the curved fin root edges so having a glue that does a little gap filling makes things work better. There's a bit of bubbling around the edges, but I'm adding fin fillets now that hopefully will hide all that.

 

[Jeff Lassahn]

Where's the Center of Pressure of this thing?

I've got two opinions. With OpenRocket, I hacked in a set of tube fins to try to model the pods, they're probably not very accurate. CP at 28.8cm (without the pods it give 27.9cm)

With the CFD program I'm working on, I get the CP at 30cm

So the answer is probably somewhere between 10mm and 30mm behind the body to tail seam. Which means I'll want the CG to be maybe 20mm in front of the seam.

 

[GlenP]

I would still swing test it before adding too much nose weight to shift the cg that far forward unnecessarily. The pods give additional drag stability that I am not sure if open rocket predicts very well. The CFD sim is probably getting it a little better. I think you are on the right track.

 

[neil_w]

Where's the Center of Pressure of this thing?

I've got two opinions. With OpenRocket, I hacked in a set of tube fins to try to model the pods, they're probably not very accurate. CP at 28.8cm (without the pods it give 27.9cm)
View attachment 425877

If you post the ORK file and give me the pod specs (position, diameter, nose and tail cones) I'll chuck it into the alpha OR and see what it says.

 

[Jeff Lassahn]

Here's the ORK file.
The pods are 40mm BT-5 bodies with a 30mm elliptical nose and 38mm ogive tail.

 

[neil_w]

Here it is in the new OR, with CP measurement:

I can't make any claims for its accuracy at this point, but that's what it says. Never mind the CG, I don't have any of the interior stuff in there (long story ).

 

[Jeff Lassahn]

Cool. So not only does it have pod support, it can also do non-straight fin roots!

 

[neil_w]

Yep, fins can attach to nose cones and transitions.

 

[Jeff Lassahn]

Everything's glued up and ready for paint.
Here's the tail section with parachute compartment:


And here's the full stack:


I've got some "Blue Galaxy" blue-purple colorshift paint that I'm going to finish it with.

 

[Jeff Lassahn]

It's done!
Local cat suspects alien invasion.

 

[SCooke123]

Nice looking.