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

[lakeroadster]

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The A.C.M.E. Spitfire uses a similar design but it doesn't match the actual comic. So I used the actual Farside comic and set about to draw a scale model of the iconic rocket.

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Armed with these dimensions I picked a body tube size, BT-80H, and then scaled all the dimensions based on that body tube. I fired up the CAD station and created a Model.​

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I then built an OpenRocket simulation using a straight line version but with the actual diameter and lengths from the CAD model. I wanted to know what size motor might be needed.​

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Looks like a flyer. So I knocked out a CAD drawing showing the configuration of the fuselage.​

It's a rear eject spool design with a 29mm motor mount. None of that is shown in the CAD model / drawings.​

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So here's my question... What would you anticipate the flight of this rocket to look like?

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Will the nose cone direct it into an arc that will produce a lawn dart?​

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Will it crab in flight, flying crooked?​

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Thanks for reviewing this data... and for your comments.​

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Fliskits A.C.M.E. Spitfire ---------- My "True To The Comic" Version​

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[ljwilley]

The acme spitfire usually flies straight, but even though this is similar I don't know if it would have the same effect. It may produce and arc-like flight, but I don't think it would be as extreme as a lawn dart. Just my 2 cents.

 

[ljwilley]

I do like the build idea!

 

[Azamiryou]

I would expect the nose cone to create a pretty significant instability. The Spitfire nose cone is basically pointed forward and centered.

Now the shroud at the bottom may counteract it — it looks like it sticks out in the correct direction to do so. But is it enough?

The fins could be angled also to counteract it.

 

[Daddyisabar]

A REPORT FROM WITHIN THE GUILD 0-0-0. Send a Certified Level Three Navigator to High Country Good View. Dangerous and Abominable mindsimming detected.

"I see plans within plans... I see true comic book crookedness, a big nose cone and tiny offset fins, I see much aerodynamic sin. I see many tiny base drag hacks behind the nose cone, pushing the limits of doing the math. I see the CP creeping forward with every subtle atmospheric change, very difficult to navigate. I see much thrust and nose weight to compensate. I see long thick rods and clear mountain air. The perchlorate must flow!

I was not here, I did not say this."

 

[K'Tesh]

You might want to reach out to Jim Flis... He's still in the hobby, and I remember him saying that he went though a number of iterations before he got the Spitfire to work.

 

[Daddyisabar]

The high degree of crookedness exposes the treachery and villainy behind this endeavor. Shrouded in the Dark Side it is. We must be cautious. Reach out with your feelings to find the safest path.

 

[SolarYellow]

I'd build smaller, lighter, cheaper ones first to get the design dialed in to something that flies. Like BT-55 or BT-60.

 

[Rob Campbell]

Following. This is going to be epic.

 

[Daddyisabar]

The model rocket tribe will give you new name: RUNNING FROM CROOKED ARROW.

 

[Daddyisabar]

View attachment 633550​

The A.C.M.E. Spitfire uses a similar design but it doesn't match the actual comic. So I used the actual Farside comic and set about to draw a scale model of the iconic rocket.

​

View attachment 633544​

Armed with these dimensions I picked a body tube size, BT-80H, and then scaled all the dimensions based on that body tube. I fired up the CAD station and created a Model.​

​

View attachment 633545​

I then built an OpenRocket simulation using a straight line version but with the actual diameter and lengths from the CAD model. I wanted to know what size motor might be needed.​

​

​

View attachment 633546View attachment 633547​

Looks like a flyer. So I knocked out a CAD drawing showing the configuration of the fuselage.​

It's a rear eject spool design with a 29mm motor mount. None of that is shown in the CAD model / drawings.​

​

​

View attachment 633548View attachment 633549​

So here's my question... What would you anticipate the flight of this rocket to look like?

​

Will the nose cone direct it into an arc that will produce a lawn dart?​

​

Will it crab in flight, flying crooked?​

​

Thanks for reviewing this data... and for your comments.​

​

​

Fliskits A.C.M.E. Spitfire ---------- My "True To The Comic" Version​

​

View attachment 633563 View attachment 633565 View attachment 633550​

The Jedi and Sith are identical in many ways. Only subtle differences.

Can the straight and narrow thrust line and nose weight overcome the aerodynamic crookedness of the nose cone? Which one will the scales of the Force tip towards? This is not a Hollywood fantasy. I am not a crook.

 

[Daddyisabar]

I would use a Flis style asymmetric nose cone to offset most of the sin up front. Keep as much crookedness as possible hid under that safety hat. Still would look good when compared to comic strip version.

 

[OverTheTop]

That cone at the rear is your friend for stability. Looks like there might be enough of it to compensate for other wonkiness. Maybe cant a fin so it will cone rather than arc, maybe?

I would start with a small, short-burn motor. And double the regular safety distance (complex rocket).

Looking good

 

[BABAR]

If you ain’t cheatin’ you ain’t tryin’

One trick that stays faithful to the cartoon (since motor isn’t seen) would be to recess the motor forward a bit, since you have that big reverse tail cone in the back.

My understanding is that Uncle Krushnic grants you about 1/2 body width recession before he starts stealing your thrust.

Sooooo…. @Daddyisabar , could moving the motor forward count as a Jedi voodoo maneuver? Seems like it’s kind of like adding nose weight, without actually increasing the mass of the rocket.

 

[BABAR]

Oh yeah, one other trick. @KenECoyote used this successfully in his Candy Cane rocket. Brilliant idea.

Can you cant the motor to match the canted nose cone?

 

[BABAR]

Yeah I know, I need to get a life. I think @neil_w used a trick of canting the fins to match the desired trajectory.

I got this to work.

 

[Daddyisabar]

Despirate measures for Despirate oddrocs. Such builders must use all available tricks to assure some confidence the envelope has not been pushed too far. Those nefarious techniques are just crutches to cover up extremely poor rocket design. That's what our old RSO Jedi would tell me and his Jedi mind tricks worked!

Just make it look marvelous!

 

[Daddyisabar]

Oh yeah, one other trick. @KenECoyote used this successfully in his Candy Cane rocket. Brilliant idea.

Can you cant the motor to match the canted nose cone?

Multiple canted tractor motors up front will ALWAYS solve your oddroc problems, but could they be hidden in a big witches hat nose cone with ducted rear ejection? No, that would just be crazy. Who has ever done a thing like that? Say with a sports scale MR capsule.

 

[5x7]

I suggest putting another bigger fin in back, as if it’s hidden in the picture. I built one of these and that is what I did, the fin is in the same style of the other fins. I put in a lot of nose weight and it flew OK.

 

[lakeroadster]

I suggest putting another bigger fin in back, as if it’s hidden in the picture. I built one of these and that is what I did, the fin is in the same style of the other fins. I put in a lot of nose weight and it flew OK.

It has three equally spaced fins... the one is merely hidden in the static view.​

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[lakeroadster]

Can you cant the motor to match the canted nose cone?

Sure... but I wonder if that's really needed? Let me ponder that idea.​

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The fins could be angled also to counteract it.

That would make the rocket spin around its longitudinal axis? I'm "cautiously optimistic" that the fins need to be straight.​

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[Capt. Eric]

I would be very cautious about copying a design exactly the way a comic strip artist drew it. There's probably a reason Gary didn't work for NASA. (Apologies to Mr. Larson).

 

[lakeroadster]

I would be very cautious about copying a design exactly the way a comic strip artist drew it. There's probably a reason Gary didn't work for NASA. (Apologies to Mr. Larson).

That's the fun of it.... making it exactly like the cartoon.​

And for the record... there are lot's of great rocket scientists that didn't work for NASA​

 

[Azamiryou]

That would make the rocket spin around its longitudinal axis?
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I mean pointing (a little) in the same direction as the nose cone, so they create lift opposite that caused by the nose cone and they cancel each other out. It shouldn't take much, since fins generate a lot more lift than nose cones.

You could be right, even straight fins might provide enough correction.

(Spinning it would probably help keep it pointed up, but that would be cheating.)​

 

[MarsLander]

I think the fin in front is canted incorrectly vs. Larsen. If you place re:Larsen, may help counteract your nose cone...

 

[neil_w]

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.

 

[Dotini]

Larsen has a great sense of proportion, so you have half the battle won. I'd guess it'll be unstable due to averaged length/width ratio and disproportionate drag from the front end. But then, I wear both a belt and suspenders.

 

[Azamiryou]

If you place re:Larsen, may help counteract your nose cone...

Turns out Larsen is a rocket scientist, after all!

 

[jflis]

Cool project! I have my doubts though…. LOL

But with regard to the ACME Spitfire, there is another difference that must be taken into account…. The design being presented here is a scratch build from someone with some real skills and experience.

The ACME was designed to be a mass produced KIT that could be successfully built by modelers of many different levels of skill and experience.
It will be interesting to watch this thread. My guess is that the model will somersault coming off the pad…

 

[lakeroadster]

Cool project! I have my doubts though…. LOL

But with regard to the ACME Spitfire, there is another difference that must be taken into account…. The design being presented here is a scratch build from someone with some real skills and experience.

The ACME was designed to be a mass produced KIT that could be successfully built by modelers of many different levels of skill and experience.
It will be interesting to watch this thread. My guess is that the model will somersault coming off the pad…

Well... I'll give it a try, as Larsen drew it, and we'll see. Thanks for your thoughts.​