Razorback - From the TV Series "The Expanse"

[lakeroadster]

We headed to Walmart today and I looked at foamboard... also looked at some 3/16" corrugated cardboard....

Ugh.

Way too flimsy.

<---- See here for details

I got home and had an epiphany: By the time I reinforce foamboard or cardboard... I might as well just make the body from plywood. I've got the wood working tools, so why not?

I re-ran the simulation using 1/4" plywood (I have some in the woodshed). It doesn't change stability, and since I'm using G motors they have enough thrust to still have a decent apogee.

My new mantra, per NAR: "Rocket weighs no more than 3.3 lbs (52.8 oz) (1.5 kg) all up."

Might have to use balsa or cardstock for the visually cool Epstein drive pieces parts.

 

[lakeroadster]

Revised the drawing set to Rev 05: Fuselage is now made from 1/4" plywood.

See posts 23 and 24.

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[lakeroadster]

Fuselage Templates

Whipped out my vintage T-Square and made some cardboard (cereal box) templates for the fuselage. This allows me to easily transfer these to plywood by just placing them on the plywood and tracing around it with a pencil.

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[Daddyisabar]

Nothing beats good ole Baltic Birtch!

Not like the old black and white movie days, now you can just put in a bigger motor!

 

[Tobor]

Fuselage Templates

Whipped out my vintage T-Square and made some cardboard (cereal box) templates for the fuselage. This allows me to easily transfer these to plywood by just placing them on the plywood and tracing around it with a pencil.

View attachment 580087View attachment 580088View attachment 580089​

I love the old T-Square. Had one just like it during my high school mechanical/architectural drafting days.

 

[lakeroadster]

Fuselage Plywood Panels

Cut the plywood for the fuselage. I started using my 1940's era DeWalt radial arm saw... and it died. Some kind of an electrical issue. Finished up using my Scroll Saw.

Also made an assembly fixture that should help in getting everything square and true before gluing everything together.

I used shipping tape to mock-up the sub-assembly, just for a visual of upcoming attractions.

The components weigh 19.5 ounces.

It's looking a lot like a teepee at this point...

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[lakeroadster]

Weight Reduction, Fuselage Assembly & Gluing Fixture

Weight Reduction​

I used a 1" diameter Forstener bit to drill 54 holes 1/8" deep into the back of the fuselage body. Component weight went from 19.5 ounces to 18.1 ounces... a 1.4 ounce decrease. Yeah, that's not much, but it was easy to do so why not.​

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Fixture​

I built a fixture to hold all the components together, yet allow positioning the fuselage so the glue joints could be filled in the ideal flat position.​

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It consists of a flat base plate and a 1-1/8" dowel center mast. The flat base plate has nails driven into it to hold the bottom of the fuselage pieces in place. At the top of the mast is a bolted plate that holds the top of the fuselage pieces in place​

Now the tedious task of filling all the glue joints begins... I'm gluing 3/16" dia. poplar dowels on the inside of the glue joint for each seam. This helps prevent the glue from running through the outside joint, and will make the joint stronger when I run fillets on both sides of the dowels.

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[Pappy]

love your work, dude. true mojo.

was the razorback the ship the tweaking kid flew into the weird blue sphere, resulting in his slow mo disassembly, to the tune of a reworked cover of deep purple's 'highway star?' (best.scene.ever.) love that series. imo best true scifi show ever (suspending the physics of the blue s*).

next up, the Rocinante... ??

 

[neil_w]

was the razorback the ship the tweaking kid flew into the weird blue sphere, resulting in his slow mo disassembly, to the tune of a reworked cover of deep purple's 'highway star?' (best.scene.ever.) love that series. imo best true scifi show ever (suspending the physics of the blue s*).

No, it was Julie Mao's racing craft. https://expanse.fandom.com/wiki/Razorback

 

[lakeroadster]

love your work, dude. true mojo.

was the razorback the ship the tweaking kid flew into the weird blue sphere, resulting in his slow mo disassembly, to the tune of a reworked cover of deep purple's 'highway star?' (best.scene.ever.) love that series. imo best true scifi show ever (suspending the physics of the blue s*).

next up, the Rocinante... ??

I'm partial to this...

 

[lakeroadster]

Glue Fillets Day 03

I've applied 2 layers of Gorilla Wood Glue. The plywood really sucks up the glue.

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Now I'm using Titebond Quick and Thick. The goal is to fill the gap such that a uniform radius can be sanded at the corners. I could just use CWF, but it has very little strength and will likely chip off easily. Trying to avoid that.

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[KenECoyote]

FANTASTIC build and super idea Lakeroadster!

I'm in love with the craft and I think it makes a very cool rocket!

 

[Tobor]

Glue Fillets Day 03

I've applied 2 layers of Gorilla Wood Glue. The plywood really sucks up the glue.

View attachment 580781View attachment 580782​

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Now I'm using Titebond Quick and Thick. The goal is to fill the gap such that a uniform radius can be sanded at the corners. I could just use CWF, but it has very little strength and will likely chip off easily. Trying to avoid that.

View attachment 580783​

Have you considered using miniature lumber for the corners?

Etsy has a lot of dollhouse lumber. Here is an Etsy list of Dollhouse Quater Rounds (Link)

Google search result for Dollhouse Scale lumber (Link)

 

[lakeroadster]

Have you considered using miniature lumber for the corners?

Etsy has a lot of dollhouse lumber. Here is an Etsy list of Dollhouse Quater Rounds (Link)

Google search result for Dollhouse Scale lumber (Link)

Interesting, it's truly amazing what is available nowadays.

I can make pretty much whatever I need in regard to cutting lumber down to size, and I have a wood shed full of lumber, left over from years of projects around our property.

I think the the process of gluing the joint, followed by sanding, should work just fine. We'll see.

Thanks for the suggestion.

 

[neil_w]

In my estimation it will take a *LOT* of Q&T to get the effect you're looking for. I have had trouble with that sort of thing in the past, and I wasn't trying to fill nearly so large of a gap. My suggestion would be to get some reasonable amount of glue fill in there for strength, and then top it off with CWF and sand to shape. Finish with an application of thin CA to harden up the CWF layer and you're good to go.

 

[KenECoyote]

Glue Fillets Day 03

I've applied 2 layers of Gorilla Wood Glue. The plywood really sucks up the glue.

View attachment 580781View attachment 580782​

_________________________________________________________________________________________________________________________________________________________________

Now I'm using Titebond Quick and Thick. The goal is to fill the gap such that a uniform radius can be sanded at the corners. I could just use CWF, but it has very little strength and will likely chip off easily. Trying to avoid that.

View attachment 580783​

Try ~1/4" square wood strips glued in and then sanded round. You can choose softer wood to make it easier. There may even be quarter round stock available.

 

[lakeroadster]

@neil_w - @Tobor - @KenECoyote thanks. No worries... I just laid in the last Q&T glue joint.

The problem with adding "lumber" is the gap wasn't consistent. It varied from nearly nada to 1/4", and it's not 90 degrees, it's 60 degrees... ish.

Originally I had planned on using 1/8" round poplar dowels, but they also didn't work due to the inconsistent gap.

Might get to do some sanding tomorrow... looking forward to getting that yellow latex paint off my Razorback, and removing the fuselage from the fixture.

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[lakeroadster]

Ramblings of a maniacle mind....

I had what I thought was an epiphany today, or maybe I was just channeling @Daddyisabar... see post #7. What if I were to move the motor as far forward as possible for powered flight, but still build the awesome looking Epstein Drive for display purposes.

So I made a duplicate of the OR simulation, modified it and to my initial surprise it didn't make much of an impact at all on stability.

I guess that makes sense since the fuselage is by far the heaviest piece of the rocket and moving the motor doesn't really change the CD much.

But then I got to thinking, on a rocket like this where more than half of the conical body is removed, what is the real diameter used to calculate caliber of stability?

I'm hoping I'll learn a lot about the stability of this fuselage once I get it glued together, sanded down, and I can then do a swing test.

Another thought... will stability be helped by air being pulled in through the side openings, kind of like GDS? Or are the openings too far away from the motor? Reminds me of the discussions @BigMacDaddy was having regarding his finless Bullet Bobby.

 

[Cape Byron]

But then I got to thinking, on a rocket like this where more than half of the conical body is removed, what is the real diameter used to calculate caliber of stability?

Damned good point. These are the things that keep my old mind a'tickin'.

 

[Charles_McG]

But then I got to thinking, on a rocket like this where more than half of the conical body is removed, what is the real diameter used to calculate caliber of stability?

Definitely a case for the % of length version of stability.

 

[lakeroadster]

Definitely a case for the % of length version of stability.

I recall reading something about that? Is that something I can glean from Open Rocket?

 

[Charles_McG]

I recall reading something about that? Is that something I can glean from Open Rocket?

OR doesn't calculate it that I'm aware of. But it's just (Cg-Cp)/Length expressed as a percent. I think the rule of thumb is 10-15%. I -believe- it's usually preferred by people who like LONG rockets, thinking that stability in calibers overstates reality. But it's been a while since I've read one of the detailed discussions.

 

[neil_w]

I recall reading something about that? Is that something I can glean from Open Rocket?

 

[Charles_McG]

View attachment 580979

Thank you for the correction, @neil_w . I can always count on you to keep me honest.

 

[Charles_McG]

I recall reading something about that? Is that something I can glean from Open Rocket?

I don't mean to be a pessimist, but I think the swing test is going to be more informative than OR. For the % calc, I think you'd have to back out the base-drag adjuster. That leaves you at 63%, which is really high.

I couldn't tell from the screen shot the diameter that you ate using for the base drag correction. My thought is that it should be based on the drive nozzle.

I sure hope it flies. It looks great!

 

[KenECoyote]

Ramblings of a maniacle mind....

I had what I thought was an epiphany today, or maybe I was just channeling @Daddyisabar... see post #7. What if I were to move the motor as far forward as possible for powered flight, but still build the awesome looking Epstein Drive for display purposes.

So I made a duplicate of the OR simulation, modified it and to my initial surprise it didn't make much of an impact at all on stability.

I guess that makes sense since the fuselage is by far the heaviest piece of the rocket and moving the motor doesn't really change the CD much.

But then I got to thinking, on a rocket like this where more than half of the conical body is removed, what is the real diameter used to calculate caliber of stability?

I'm hoping I'll learn a lot about the stability of this fuselage once I get it glued together, sanded down, and I can then do a swing test.

Another thought... will stability be helped by air being pulled in through the side openings, kind of like GDS? Or are the openings too far away from the motor? Reminds me of the discussions @BigMacDaddy was having regarding his finless Bullet Bobby.

View attachment 580959

It may behave like a badminton birdie or shuttlecock, which has holes in the body like netting.

 

[neil_w]

Thank you for the correction, @neil_w . I can always count on you to keep me honest.

Being the author of the release notes gives me something of an advantage in knowing about all the new features, however obscure (the % display is new to 22.02).

 

[Daddyisabar]

Ramblings of a maniacle mind....

I had what I thought was an epiphany today, or maybe I was just channeling @Daddyisabar... see post #7. What if I were to move the motor as far forward as possible for powered flight, but still build the awesome looking Epstein Drive for display purposes.

So I made a duplicate of the OR simulation, modified it and to my initial surprise it didn't make much of an impact at all on stability.

I guess that makes sense since the fuselage is by far the heaviest piece of the rocket and moving the motor doesn't really change the CD much.

But then I got to thinking, on a rocket like this where more than half of the conical body is removed, what is the real diameter used to calculate caliber of stability?

I'm hoping I'll learn a lot about the stability of this fuselage once I get it glued together, sanded down, and I can then do a swing test.

Another thought... will stability be helped by air being pulled in through the side openings, kind of like GDS? Or are the openings too far away from the motor? Reminds me of the discussions @BigMacDaddy was having regarding his finless Bullet Bobby.

View attachment 580959

I've been told that channeling Daddyisabar is very dangerous; leading to mindsims, possible necromancy, dark arts oddrocs and overall unnatural design.

Put that motor forward and still make it look good!

All will be made safe and sound through computer simulation and swing testing!

 

[Cape Byron]

All will be made safe and sound through computer simulation and swing testing!

All will be made safe and sound through computer simulation and swing testing!

Fixed it for you.

 

[lakeroadster]

I don't mean to be a pessimist, but I think the swing test is going to be more informative than OR. For the % calc, I think you'd have to back out the base-drag adjuster. That leaves you at 63%, which is really high.

I couldn't tell from the screen shot the diameter that you ate using for the base drag correction. My thought is that it should be based on the drive nozzle.

Agreed, on all counts.​

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I had initially discussed, see post #1, installing Lexan panels in the fuselage openings, thus making the full diameter of the rear of the fuselage the correct diameter for the base drag hack cone.​

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But it don't mean a thing, if it ain't got that swing.​

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I sure hope it flies. It looks great!

Me too, and thanks.​

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Various versions of The Razorback have been built and flown successfully, so we know it's possible (ref. @SecondRow 's post #2).​

Trying to replicate this rockets "wonky" (it's a technical term) fuselage in Open Rocket, in a manner that accurately represents the aerodynamics of the as built fuselage for simulation purposes, seems to be beyond the scope of the program. At least at this point.​

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And that's fine... it's what makes this an interesting scratch build.​

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As we all learned from Harry Callahan "A man's got to know his limitations." Some folks however tend to prefer the "boldly go where no man has gone before" mindset.​