#### MClark

##### Well-Known Member

Does Open Rocket or other program have the ability to give the volume of the airframe?

M

M

- Thread starter MClark
- Start date

Does Open Rocket or other program have the ability to give the volume of the airframe?

M

M

If you google "volume of cylinder", a calculator will be the first search result.

Cones and cylinders I can do.

M

You said airframe in the OP. That's what you got!

I call the nose cone, tube and tail cone the airframe

M

M

- Joined
- Mar 18, 2012

- Messages
- 9,281

- Reaction score
- 40

Let's look at the equation for an elliptical nose cone.

y=R*sqrt(1-[x^2/L^2])

Where

R=Radius

x=distance from tip of cone

L=Total length of cone

Plug in lengths and values for what you know. Let's do a 1" wide nose cone 3" long.

y=0.5*sqrt(1-[x^2/3^2])

y=0.5*sqrt(1-x^2/9)

This is the X/Y coordinates of any point on the side of the nose cone. To figure out the volume, we use calculus.

The equation for the volume of a solid revolved around the x axis is the integral from 0 to L of the equation squared times pi.

This math will be as follows:

Integral from 0 to 3:

0.0833333*Sqrt[9-3^2] + 0.75 ArcSin[0.333333*3]-0.0833333 * Sqrt[9-0^2] + 0.75 ArcSin[0.333333 0]

This equals approximately 0.927.

pi*integral from 0-3 squared:

3.14*(0.927^2)=2.69 cubic inches.

View attachment Fletcher Cd Optimization.pdf

M

- Joined
- Mar 18, 2009

- Messages
- 4,364

- Reaction score
- 148

- Joined
- Aug 9, 2013

- Messages
- 9,955

- Reaction score
- 83

I'm developing a system for molding things, and knowing the volume of rocket shaped things might be helpful. but I'm going to make the first mold blocks regardless as I already see them in my head, and that's good enough for me.

- Joined
- Jan 11, 2013

- Messages
- 6,059

- Reaction score
- 364

You are a very bright young man indeed...

You've got the potential for some incredible future....

Be very careful making choices in life ....

Teddy

- Joined
- Aug 9, 2013

- Messages
- 9,955

- Reaction score
- 83

If I ever win the Megabucks and start my own Rocket Factory, I hope you are in need of a job.So, to do a volume calculation will require a bit of calculus. Attached is a copy of a paper I wrote for a class I was in. On the second or third page, there's a list of the nose cone shapes and the equations for the cross section. Essentially what you have to do is calculate the value of the equation of the nose cone revolved around the axis. This is done with some calculus.

Let's look at the equation for an elliptical nose cone.

y=R*sqrt(1-[x^2/L^2])

Where

R=Radius

x=distance from tip of cone

L=Total length of cone

Plug in lengths and values for what you know. Let's do a 1" wide nose cone 3" long.

y=0.5*sqrt(1-[x^2/3^2])

y=0.5*sqrt(1-x^2/9)

This is the X/Y coordinates of any point on the side of the nose cone. To figure out the volume, we use calculus.

The equation for the volume of a solid revolved around the x axis is the integral from 0 to L of the equation squared times pi.

This math will be as follows:

Integral from 0 to 3:

0.0833333*Sqrt[9-3^2] + 0.75 ArcSin[0.333333*3]-0.0833333 * Sqrt[9-0^2] + 0.75 ArcSin[0.333333 0]

This equals approximately 0.927.

pi*integral from 0-3 squared:

3.14*(0.927^2)=2.69 cubic inches.

Math hurts my head.

I do appreciate and respect those that can master it though.

Reinhard

- Joined
- Jul 9, 2015

- Messages
- 296

- Reaction score
- 0

This assumes you know the cross-sectional area of the nose cone volume, and can plot or sketch it on some cardboard. First, take your area and half it, to get the swept area. Then take your cardboard cutout and cut it in half too, along the center axis. Find it's balance point (centroid) and measure the distance to the center axis. Then apply the following formula:

V=2*pi*D*A

Where:

A = Cross-sectional area of the revolved solid. (area of the cutout)

D = Distance from the centroid to the axis.

That's it. Works easily for simple geometry and great even on more complex stuff. I recently used it to estimate the fluid volume change for a replacement reactor vessel head I'm designing for a nuclear power plant. Came out to within 1% of the Solidworks estimate.

- Joined
- Aug 9, 2013

- Messages
- 9,955

- Reaction score
- 83

That method is too realistic for most folks here, but exactly what I resort to, as I learned it in 6th grade.If you have the parts, then you can use the water volume displacement method.

Folks want virtual garbage or over-complicated innuendo to fulfill there lack of common sense skill sets nowadays.

It's probably a bad idea if your rocket is made of conventional materials, but with CA and Epoxy Saturated composite, you can dunk them all day long with no distortion.

Last edited:

But it requires you to have a physical model. It's useless for virtual simulations which is a valid method for optimizing designs. Each has its place.That method is too realistic for most folks here, but exactly what I resort to, as I learned it in 6th grade.

Folks want virtual garbage or over-complicated innuendo to fulfill there lack of common sense skill sets nowadays.

It's probably a bad idea if your rocket is made of conventional materials, but with CA and Epoxy Saturated composite, you can dunk them all day long with no distortion.

- Joined
- Aug 9, 2013

- Messages
- 9,955

- Reaction score
- 83

I have plenty of physical models.But it requires you to have a physical model. It's useless for virtual simulations which is a valid method for optimizing designs. Each has its place.

Why would you not have a mock-up physical model to use for test purposes???

I even have a few "Physical Models" in my trash bin.

It would be great to create everything in virtual limbo word, but jeez! Can't anyone create real life anymore?

I rarely even discuss Mindsim anymore, because not many understand that it is real, but my launch videos speak for themselves so $%^& anyone who does not think I can make an airfram and wings/fins fly in a stable fashion.

I'm working on something new and crazy right now, and it will not be discussed here nor will there be a "Build Thread" for just that reason.

Saran Wrap and 3M "Scotch" Permanent Double Sided Tape will let you make your volume observable.

If you are even worried about things like this, you can certainly afford $3.50 worth of materials and the second order to BMS if you get your precious one off build wet.

[emoji1010] Steve Shannon [emoji1010]

The reason I was looking for a way to calculate the volume is for a contest I have been working on. Water (Or beads etc.) displacement could work but there is a potential for the airframes to be very large, size is tied to impulse and burn time.

People will say the volumes should be calculated before the rocket gets to the field but reality is it doesn't happen, I have run other contests.

The rocsim solid I will have to get the program and try it.

M