Hive Ship

[DrewW]

Saw a thread in another place with someone asking about the possibility of a hollow core rocket, basically a flying tube fin. My first reaction wasn't positive, but the next day thoughts (the terrible kind) had taken hold. I've been tweaking in fusion 360 to roughly design this rocket with a somewhat retro sci-fi theme (at least in my mind). neither OR nor RS can currently model so I'm doing lots of hand calculations currently. This project is already giving me plenty of practice in improving my rocketry and 3D printing skills.

I originally went to my terrible rocket names thread for inspiration of core sampler and barely stable...both may turn out to be better names, but I liked the hive idea after designing a custom hex grid fin tail piece to pull the CP further aft.

This will be a dual motor (C5-3 or better) design housed in the innermost tube of the doubled wing pods, each has a novel baffle approach I came up with to push a chute out of the outer tube of each pod. Intended for low flying on very low wind days where folks want to see something different.

 

[rharshberger]

Better hope both motors light simultaneously......

 

[DrewW]

Better hope both motors light simultaneously......

With my clip whip, I suppose they have until the end of the rail otherwise things are going to be really exciting.

 

[rharshberger]

With my clip whip, I suppose they have until the end of the rail otherwise things are going to be really exciting.

Exactly, and if the second one lit is late enough and the rocket doesn't have enough stability to handle the offset thrust...LANDSHARK.!

 

[lakeroadster]

With my clip whip, I suppose they have until the end of the rail otherwise things are going to be really exciting.

FWIW: Even if both motors light simulataneously, it will likely thrust steer due to the wide variance in black powder motor actual thrust output.

Minimizing the lateral distance of the motors from the rockets CG will minimize this problem.​

And canting the motors so their C/L intersects the rockets CG will also help.​

But.. it's a cool design, give it a go. Sometimes the Gods Of Thrust Steer are on Sabbatical.

 

[neil_w]

https://www.rocketryforum.com/threads/heres-a-weird-one.139729/
Your design is quite a bit more radical.

 

[lakeroadster]

My mind sim tells me there is no way to make this design stable? Open Rocket seems to indicate that stability is unobtanium also.

I think this design would work however... but as a tractor motor design... with some ballast to move the CG down. It would virtually look very similar in the static configuration.

 

[DrewW]

My mind sim tells me there is no way to make this design stable? Open Rocket seems to indicate that stability is unobtanium also.

I think this design would work however... but as a tractor motor design... with some ballast to move the CG down. It would virtually look very similar in the static configuration.

Enter the magic that is grid fins!

My math currently has me at ~.6 cal of stability without the judicious use of extra mass.

 

[lakeroadster]

Enter the magic that is grid fins!

My math currently has me at ~.6 cal of stability without the judicious use of extra mass.

So you are thinking the hive acts as a grid fin?

 

[DrewW]

It was designed to be one. See pictures.

 

[lakeroadster]

It was designed to be one. See pictures.

Have you considered that stagnant flow in the tube will hinder it's ability to act as a true grid fin?

And that the length to diameter ratio through the hive will also hinder it's ability to act as a true grid fin?

 

[DrewW]

Have you considered that stagnant flow in the tube will hinder it's ability to act as a true grid fin?

And that the length to diameter ratio through the hive will also hinder it's ability to act as a true grid fin?

Yes I have considered that. The piece I took a picture of is one of many in a family with different grid cell sizes. That one has a min to max spread of aspect ratios of 6-10 others are on the order of 3-7. Given the low velocity expected out of this rocket, I’m expecting choked flow in the range of acceptable. This is based on a conversation I had with an aerodynamicist friend with whom I share all my most terrible rocket ideas.

 

[lakeroadster]

Yes I have considered that. The piece I took a picture of is one of many in a family with different grid cell sizes. That one has a min to max spread of aspect ratios of 6-10 others are on the order of 3-7. Given the low velocity expected out of this rocket, I’m expecting choked flow in the range of acceptable. This is based on a conversation I had with an aerodynamicist friend with whom I share all my most terrible awesome rocket ideas.

Fixed it for you.. ^^^​

 

[neil_w]

Have you considered that stagnant flow in the tube will hinder it's ability to act as a true grid fin?

And that the length to diameter ratio through the hive will also hinder it's ability to act as a true grid fin?

There's stagnant flow inside the grid *and* stagnant flow inside the tube. It'll be interesting to see if this works.

 

[DrewW]

There's stagnant flow inside the grid *and* stagnant flow inside the tube. It'll be interesting to see if this works.

We shall see what becomes of this. Build starts tonight!

 

[tsmith1315]

Very curious, thanks for posting!

 

[jqavins]

(holding my breath with great trepidation) Please make sure your launch controller has a really long wire. Good luck; you'll need it.

 

[DrewW]

Well I started building before taking a photo of the collected components less a few I haven’t made final decisions on yet. So here is a photo of the collected components with the side pods already glued.

 

[DrewW]

First step after deciding on antenna configuration, was gluing the side pods together. Note the nose cone interfaces to both segments. These were designed and 3D printed my me with an open cell internal structure that will act as a baffle and redirect ejection gasses out the outer pod. The nosecone was used to both get squared alignment of the tubes and also a clamp of sorts to help hold the tubes together while the quick and thick dries. Contact area on both tubes was lightly sanded to improve bonding. Nosecone not yet bonded in place while I make final decisions on the overall length of these pods.



also took some time to make an assembly jig to hold alignment while things cure up

 

[Y3kankerous]

Great looking design!
For a while I've been wondering about different configurations for building a Liberator (off of Blakes 7... UK 70s sci fi series) something like this end tube grid fin would be compatible with the look and might be a way to tame thrust steer on a three motor tractor...

Will b very interested to see how it performs!

 

[lakeroadster]

What adhesive(s) are you using to attach the 3D printed parts to the body tubes?

 

[DrewW]

What adhesive(s) are you using to attach the 3D printed parts to the body tubes?

@lakeroadster great straight man for my next step.

When I was thinking about the issue of wing attachment I was originally considering a basswood/balsa built up wing to make sure it was light, strong, and could get good adhesion. While I was modeling I decided to try something a little faster and so my wings got 3D printed. When I printed though I did it with an open “gyroid” structure available in prusaslicer. The wing weight benefits by being approximately 40% the density of the PETG plastic I used, and has a much higher surface area to cross link to the open tube.



on the tube side I’ve decided on a placement and traced around the wing while held in my alignment jig.



First I’m going to take my smallest precision drill bit 0.6mm and make several holes from outside in. Then I’m going to ream and dimple from the inside with a 90 degree pick. I’ll cover the inside with some kapton tape I have to maintain a smooth inner surface and to finally answer your question. I’ll use some 30min epoxy so it can work it’s way through, hopefully forming some Resin rivets.

Work to commence once I finish getting kids tucked into bed.

 

[DrewW]

Alright kids asleep and first wing curing.

 

[BABAR]

https://www.rocketryforum.com/threads/open-body-missile-build-for-my-level-2.24733/
is an open tube design that was beautiful, apparently stable, and had a great upward flight (unfortunately the descent was severely suboptimal.)

it had inboard and outboard motors, but not nearly as outboard as yours.

 

[DrewW]

I guess it was too cold in my garage last night because one of the epoxy bonds was weaker than I would have liked. Took some time to reinforce the joint and fillet to improve the bond. Feeling like it might be strong enough to actually survive a flight now.

 

[Daddyisabar]

Flying two widely spaced D12 motors in pods can be done if one gives into the power of the Dark Side. The Jedi texts clearly state that widely spaced pods are a hallmark of poor rocket design. You will not learn to fly such things from the Jedi. Give in to your feelings and fly the rockets you love. As a youngling I flew an Arado 234 Blitz bomber at the club (the old thread is here on TRF.) As I would tell our Master Jedi Pad Fuhrer; it is just an ignition issue. Nose weight and power are your only friends, especially if you are pushing the envelope on a bit of asymmetric drag. Keep up the scare and push the button.

 

[lakeroadster]

Flying two widely spaced D12 motors in pods can be done if one gives into the power of the Dark Side. The Jedi texts clearly state that widely spaced pods are a hallmark of poor rocket design. You will not learn to fly such things from the Jedi. Give in to your feelings and fly the rockets you love. As a youngling I flew an Arado 234 Blitz bomber at the club (the old thread is here on TRF.) As I would tell our Master Jedi Pad Fuhrer; it is just an ignition issue. Nose weight and power are your only friends, especially if you are pushing the envelope on a bit of asymmetric drag. Keep up the scare and push the button.

"Master Jedi Pad Fuhrer"

 

[Daddyisabar]

Let the mindsim flow. It makes you strong. DO IT!

If you survive the launch we will watch your career with interest.

You must follow all the basic rules, just as any Jedi. Just push the boundaries in your own self interest.

 

[Daddyisabar]

"Master Jedi Pad Fuhrer"

He did his best to protect the Younglings from the influence of the oddroc scum and villainy! We must be cautious.

 

[lakeroadster]

He did his best to protect the Younglings from the influence of the oddroc scum and villainy! We must be cautious.

.
<----- "The Oddroc Scum" now there's a group I'd like to be a member of.. .. Club Jacket, Blood Initiation, etc.