Gary Larsen's Farside Rocket - A BT-80H Scratch Build

[Daddyisabar]

By hook or by crook, it will fly!

 

[grapetang]

I'd say it'll fly. With enough nose weight, it'll fly straight. With less, it may wobble a bit as it corrects itself (or tilt the rod/rail).
Go Team Thag!!!

 

[lakeroadster]

Thag Simmons finished the CAD drawings... *** Updated 2024-03-04 to Rev 01 ***

I went ahead and made the Nose Cone Shoulder a separate piece and tenon fit the Nose Cone onto it. That'll give me options... in the event an "anomaly" happens during flight and I need to make adjustments.

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[5x7]

The fin leading edges are not straight, they have a slight arc if you are going for accuracy.

 

[lakeroadster]

And the CAD Model... (see Post 55)

 

[sr205347d]

And the CAD Model...

View attachment 633733

Just curious, does the CAD model tell where the GG is wrt the engine centerline? Because, irrespective of the external aerodynamics, an offset GC will induce a pitch/yaw moment during thrusting.

Even if so, after construction, it could be useful to mount a shaft into the motor mount to check balance.

 

[lakeroadster]

Just curious, does the CAD model tell where the GG is wrt the engine centerline? Because, irrespective of the external aerodynamics, an offset GC will induce a pitch/yaw moment during thrusting.

Even if so, after construction, it could be useful to mount a shaft into the motor mount to check balance.

I'll check it tomorrow.​

 

[Rob Campbell]

Thag Simmons finished the CAD drawings...

I went ahead and made the Nose Cone Shoulder a separate piece and tenon fit the Nose Cone onto it. That'll give me options... in the event an "anomaly" happens during flight and I need to make adjustments.

So sad what happened to Thag Simmons.

 

[Azamiryou]

So sad what happened to Thag Simmons.View attachment 633758

What I love most about this is that when this comic came out, paleontologists didn't have a name for that part. So now the actual name for it in scientific literature is "thagomizer".

 

[cvanc]

...And this is why I freakin' love science

 

[lakeroadster]

Just curious, does the CAD model tell where the GG is wrt the engine centerline? Because, irrespective of the external aerodynamics, an offset GC will induce a pitch/yaw moment during thrusting.

Even if so, after construction, it could be useful to mount a shaft into the motor mount to check balance.

It's pretty close to the rockets C/L​

 

[sr205347d]

Given the, um, uncertain nature of the aerodynamics, I would get that lined up so that you don't induce any un-necessary moments. If you add nose weight, put it on the green side.

 

[lakeroadster]

Given the, um, uncertain nature of the aerodynamics, I would get that lined up so that you don't induce any un-necessary moments. If you add nose weight, put it on the green side.

Looking at the rocket, from an aero standpoint the nose wants to push right. Looking at the rocket from a cg standpoint the nose wants to push left.​

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I'll leave it as is, fly it, and go from there.​

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[Dotini]

Would a swing test be inappropriate?

 

[lakeroadster]

Would a swing test be inappropriate?

I'm big on swing tests. Every one of my rockets gets one and this one won't be an exception.​

 

[sr205347d]

Consider that off the rod, the thrust is high and the speed is low, so the moment due to thrust will dominate. (A long rod will minimize this.) Then at burnout, the speed is high, and the thrust is zero, so any aerodynamic moment will will be all there is.

 

[Daddyisabar]

That big bottomed cone has plenty of room for active stabilization gear...

 

[jqavins]

Some rockets call for a heads up launch. This will call for heads up, fingers crossed, and butts clenched.

If it were me, I would shift the MMT laterally to align with the CG and apply a slight of fin cant to try to approximately counter the nose cone angle. Canted fins don't seem to be ruled out by the cartoon as drawn, and are certainly in line with the cartoon as conceived.

But then, if it were me, I wouldn't build it; I'd sit back and let some lunatic do it.

 

[jqavins]

Also, for structure sake, I'd add an off-centering ring in section 2.

 

[Dotini]

Some rockets call for a heads up launch. This will call for heads up, fingers crossed, and butts clenched.

If it were me, I would shift the MMT laterally to align with the CG and apply a slight of fin cant to try to approximately counter the nose cone angle. Canted fins don't seem to be ruled out by the cartoon as drawn, and are certainly in line with the cartoon as conceived.

But then, if it were me, I wouldn't build it; I'd sit back and let some lunatic do it.

If it were me, I'd add 18" to the length, and put "invisible" clear plastic fins on - enough to quadruple the fin area. Belt and suspenders FTW.

 

[lakeroadster]

If it were me, I'd add 18" to the length, and put "invisible" clear plastic fins on - enough to quadruple the fin area. Belt and suspenders FTW.

With all due respect: You've missed the entire "mission" of this rocket: "To build the rocket exactly as drawn by Gary Larsen."​

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And in regard to Lexan fins... ​

 

[lakeroadster]

Also, for structure sake, I'd add an off-centering ring in section 2.
View attachment 633883

Virtually zero loading on these pieces due to the 1" dowel.​

 

[Dotini]

With all due respect: You've missed the entire "mission" of this rocket: "To build the rocket exactly as drawn by Gary Larsen."​

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And in regard to Lexan fins... ​

In Seattle, I've grown up with Gary Larsen as my native and most beloved cartoonist. His intoxicatingly proportioned cartoons will lead you down the garden path of enjoyment all day long. I know you, and know you will succeed in this project - but maybe just not right away.

 

[jqavins]

Virtually zero loading on these pieces due to the 1" dowel.​

Perhaps "for structure sake" was not the way to say it. I'm thinking of the mitered joints, and the possibility that even simple handling could knock as unsupported edge-to-edge joint apart. So it's not for overall strength, but just to keep that piece still.

 

[lakeroadster]

The fin leading edges are not straight, they have a slight arc if you are going for accuracy.

They are indeed... good catch!​

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I updated the CAD model to have the arc on the fin tops, and added the CG dimensions to the drawings. Updated Post 33.​

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[ReynoldsSlumber]

the entire "mission" of this rocket: "To build the rocket exactly as drawn by Gary Larsen."​

With that in mind, if it flew straight and true... that wouldn't exactly be "scale," would it?

 

[jqavins]

I don't know about that. Larson's people never launched theirs within our view (if at all). Maybe they got lucky?

 

[BABAR]

Rockets with various offset nose cone designs seem to fly just fine. Admittedly this one is a little more off-kilter than most, but I tend to think that as long as the fins are straight and the motor is close to center of mass and/or drag, then it's likely fly pretty straight.... or if not perfectly straight, then not too far off line. I mean, there are lots of airplane-style designs with large wings that tend to arc over somewhat, and no one has a problem with them.

Canting the fins to compensate without really knowing in advance how the rocket is going to behave seems like a bad idea to me.

You could also try to contact @jflis and see if he has any good wisdom to impart from his time developing the Spitfire.

Concur. My MIRV sustainers based on the Estes rocket of same name had extremely offset nose cones and never had any stability issues.

https://www.rocketryforum.com/threads/success-mirv5-sustainer-stable-and-actually-decorated.155169/

 

[lakeroadster]

Let The Build Begin.... Rings and Tubes

Cut the various rings, as well as the body tubes and coupler. Cut my left index finger on a 1" Forstener bit... so pardon the blood on the fins.​

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[Blast it Tom!]

Dear glory, you move fast! You go from question to conception to design to building in what, a week or so? You do more rocket-wise in a week than I think I do in several months! And you have R2D2 and that other one going as well...