Rocket design in this century :)

[cbwho]

Is there any formulas for wing area vs rocket length?
I what to build a customer rocket.
I know I have to have the center of gravity higher than the center of pressure.
If the fins are too small, not enough pressure (CP too high), weight distribution wrong, then may need to put clay in cone. I'm aware of the balance and string test.

What I plan to built is a faux space plane.
I'm thinking of a design like so:

   !
---O---
 o   o

With the engine "pods" simply being hollow sections of body tubes.

 

[cbwho]

I’m thinking something similar to this: Estes Alien Invader #3003

 

[Ronz Rocketz]

I may have to also...

https://www.spacemodeling.org/jimz/est1281.htm

 

[dhbarr]

Is there any formulas for wing area vs rocket length?
I what to build a customer rocket.
I know I have to have the center of gravity higher than the center of pressure.
If the fins are too small, not enough pressure (CP too high), weight distribution wrong, then may need to put clay in cone. I'm aware of the balance and string test.

What I plan to built is a faux space plane.
I'm thinking of a design like so:

   !
---O---
o   o

With the engine "pods" simply being hollow sections of body tubes.

This should work out pretty well as long as all the fins are toward the rear.

 

[Charles_McG]

Yes, there are formulas, but they aren’t simple. Most people use a simulator, like OpenRocket, to estimate Cp. OpenRocket tweaks one case of solved formulas - it doesn’t do it from scratch. The less like a simple rocket, the less accurate the simulation. It does handle tube fins, so you should be able to get a descent estimate of stability for your design.

 

[GlenP]

https://www.acsupplyco.com/estes/estes_satellite_interceptor.htm

 

[cbwho]

Thanks for the software mention.
That kit looks very cool.

I found this:

For a three fin rocket:

Fin Area in square inches for each fin = 0.17 * [(d+0.5)*L]



d = Body Tube Diameter in Inches
L = Body Tube Length in Inches



For a four fin rocket:

Fin Area in square inches for each fin = 0.13 * [(d+0.5)*L]



A simple rule of thumb for fin width is that it should be at least 1.25 times the body tube diameter.

 

[RoyAtl]

https://www.spacemodeling.org/jimz/manuals/tir-30.pdf
https://www.spacemodeling.org/jimz/manuals/tir-33.pdf
Read the first link. You can use the second link to calculate a "good enough" CP. Those are the basic formulas that both RockSim and OpenRocket use (though both add a little to the basics)

 

[RoyAtl]

What you have to do with an Alien Invader type of design is know how to estimate based on what the effective shape is.. TIR-33 goes into that a little for slightly complex fin shapes. How to boil them down to a more basic shape that is friendlier to the process.

 

[cbwho]

Been reading old forum articles and found mention of the archive:

https://www.oldrocketplans.com/centuri/cen5317/cen5317.htm
F-16 plans. This has a lot of the elements I'm looking for.

 

[GlenP]

I always liked these TV show sci-fi space fighter kits:
https://www.spacemodeling.org/jimz/cen5335.htmhttps://www.spacemodeling.org/jimz/est1310.htm
and the Design Contest X-wing model:
https://www.rocketryforum.com/threads/centuri-design-contest-x-wing-fighter.33071/

 

[modeltrains]

Though likely unable to contribute to this conversation I'll happily follow it and take notes.

 

[cbwho]

I always liked these TV show sci-fi space fighter kits:
https://www.spacemodeling.org/jimz/cen5335.htmhttps://www.spacemodeling.org/jimz/est1310.htm
and the Design Contest X-wing model:
https://www.rocketryforum.com/threads/centuri-design-contest-x-wing-fighter.33071/

Glen, thank you for this post.

Verna rockets mentiond the Viper spaceship.

https://www.vernarockets.com/sitebu...erpictures/.pond/reconviper1.jpg.w560h410.jpg
It seems one could easily dream up something like this by taking a 3 fin rocket and adding tube "fins".

How worrisome is it to grow the fin area of an existing design?



I went to hobby lobby and bought an ESAM, I thinking to modify it to make it more space plane like.

My idea is simple for now...

Take the "top" front fin and slide it all the back in between the top 2 lower tail fins. It's now the rear tail "rudder".

Take the front bottom fin leave it in the same spot but clip it and place the clipped portion at the rear between the lower tail fins.

So now the rear most tail has 6 fins of various sizes and the upper fins are now 3.

I have balsa chunks, so I plan to carve a canopy and glue it on the tube just lower than the nose cone.

I know this moves the CP rearward and increases windcocking potentially but I wonder if it will be a big deal?