# Scale model of the Hail Mary

#### NTP2

##### Well-Known Member
So I have been looking for a winter project and the book project Hail Mary is a fav of mine. so I went and found this rescale of the dimensions in the book(credit to reddit user prefim)that has the author’s approval. I was thinking to put one F in each tank section and 3d print the transition and nose cone at 1/200th or 1/100th scale to give a diameter of standard tubing. thoughts and comments appreciated.

#### Attachments

• 3tubjf5uv7071.png
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TRF Supporter
Clear plastic?

#### NTP2

##### Well-Known Member
Clear plastic?
Yes that’s a problem and that is my thought too but maybe the transition can give enough base drag to make adding nose mass work.

#### NTP2

##### Well-Known Member
All right time for some sims and that is also what brings me to my first problem. How to sim that transition in openrocket I am no expert and I have no idea how to do it, maybe 2 nose cones on each side will approximate it?

#### neil_w

##### OpenRocketeer
TRF Supporter
All right time for some sims and that is also what brings me to my first problem. How to sim that transition in openrocket I am no expert and I have no idea how to do it, maybe 2 nose cones on each side will approximate it?
There is no good way to do it.
Yes that’s a problem and that is my thought too but maybe the transition can give enough base drag to make adding nose mass work.
No, you'll need some fins.

#### NTP2

##### Well-Known Member
There is no good way to do it.

No, you'll need some fins.
Yeah I am going to use fins, but what about a bad way aka use python to calculate the drag and force 2 nose cones to add up to that?

#### neil_w

##### OpenRocketeer
TRF Supporter
Yeah I am going to use fins, but what about a bad way aka use python to calculate the drag and force 2 nose cones to add up to that?
Something like that should be fine, provided that you have a way to really calculate the drag on that transition. Then it's just a matter of careful CD overrides inside OR.

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#### NTP2

##### Well-Known Member
Something like that should be fine, provided that you have a way to really calculate the drag on that transition. Then it's just a careful matter of careful CD overrides inside OR.
Yeah I don’t got the skill but my dad does I’ll have to ask very nicely

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#### NTP2

##### Well-Known Member
No i am too dumb for that I’ll stick to clear fins

#### techrat

##### Well-Known Member
TRF Supporter
Cut slots in the lower ends of the outer tubes that lead to open areas in the bottom of the tubes. They *should* catch some air and help stabilize the rocket once it gets up to speed off the rail/rod....

#### NTP2

##### Well-Known Member
Cut slots in the lower ends of the outer tubes that lead to open areas in the bottom of the tubes. They *should* catch some air and help stabilize the rocket once it gets up to speed off the rail/rod....
Maybe but I want to have a rocket that I can fly without worrying about killing somebody I have seen clear fins and they aren’t as visible as you’d think especially when far away.

#### NTP2

##### Well-Known Member
All right everybody before I get started thanks for all the advice and support I really appreciate all the help. So when I asked my dad for help he said to look at some software called openfoam and it’s exactly what I needed so no reading papers with names like “general formulas and settling velocity of spheres based on theoretical Law” So now to learn the software and make a model.

#### NTP2

##### Well-Known Member
Ok after some research I have a rough idea of what and how to do this first I will get openfoam to give me the CD on a 3d model I can make in CAD then I’ll force 2 nose cones on pods in open rocket to approx the Transition from the crew compartment to the fuel tanks. Does that sound good to everybody?

#### NTP2

##### Well-Known Member
Ok so I have been working on the sim in open rocket, getting all the standard stuff out of the way and it’s very unstable the fins have to be 1m high or more to make it stable I can’t give you a sim file yet (computer problems) maybe tomorrow but if you have a idea help would be appreciated.

#### NTP2

##### Well-Known Member
No ideas until you post the file.
Ok I was hoping this was a standard issue or something I can get it tomorrow after my new parts come in.

Ps that reply was really fast.

#### NTP2

##### Well-Known Member
Ok so no news about a file. but I have settled on 75mm loc tubing and a 29mm motor mount in each tube with the transition and nose cone 3D printed, but I don’t have a 3d printer so I will have send it to a service, can anybody recommend one?

#### Rschub

##### Well-Known Member
Scott at Dragon Rocketry.

Edit: I wonder about the scale, a 1/20 scale would be about 65" high. Is that what you are shooting for? For 3" body tubes you will need about 1/40 or 1/50 scale

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#### NTP2

##### Well-Known Member
Scott at Dragon Rocketry.
Edit ok I found it, it doesn’t look like he offers custom 3d printing which is what I need for that transition it hard to tell, but it’s flat and flush to the 3 tubes sides.

Edit are you sure, 33m tall total 4m diameter it looks like 2 diameters tall so 8000mm tall 8000/100 is 80 mm

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#### DragonRocketry

##### Well-Known Member
Edit ok I found it, it doesn’t look like he offers custom 3d printing which is what I need for that transition it hard to tell, but it’s flat and flush to the 3 tubes sides.
Yes I do 3d printing

#### NTP2

##### Well-Known Member
Edit ok I found it, it doesn’t look like he offers custom 3d printing which is what I need for that transition it hard to tell, but it’s flat and flush to the 3 tubes sides.
Yes I do 3d printing
Ok thanks i guess I will do it through you then.

#### Rschub

##### Well-Known Member
Edit are you sure, 33m tall total 4m diameter it looks like 2 diameters tall so 8000mm tall 8000/100 is 80 mm

Ok.

The way I see your drawing, there are 9 fuel tanks in a 3x3 grid, each 4m dia. The 3 "tubes " are flat stacks of 3 tanks, and 12m in the wide direction. See this image for more views:

#### NTP2

##### Well-Known Member
Ok.

The way I see your drawing, there are 9 fuel tanks in a 3x3 grid, each 4m dia. The 3 "tubes " are flat stacks of 3 tanks, and 12m in the wide direction.
I did not do those drawings a redit user did them

#### NTP2

##### Well-Known Member
Wait, wait wait....
Did I miss a page?
Where? Who? How? When?
I get you that guy is a genius

#### Rschub

##### Well-Known Member
I get you that guy is a genius

#### NTP2

##### Well-Known Member
ok got the open rocket file.

#### Attachments

• hail mary.ork
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##### When in doubt... build hell-for-stout!
Did you use tube sizes that are commercially available?
Select them from the database.
Same goes for the nose cone.
You'll need to add some nose weight, to get the stability around 1.

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