# CEV modeling

1. Nov 22, 2005

### schemp98

Hello,

I need to model a generic CEV re-entry, and was wondering if anyone could guide me towards a resource for mass properties (drag coefficients, mass, inertias, initial velocity, etc). Thank You

Shaun

2. Nov 23, 2005

### enigma

Staff Emeritus
Ugh. I hate to say it, but that is not a trivial thing to do.

I was doing a design project my senior year, and we 'broke' two different FEM programs trying to model it (fluent and femlab). Neither were designed to handle hypersonic flows. We ended up waving our hands and saying "we're going to assume that it works" based on the expertise of our advisor and shapes of the Apollo and Gemini reentry vehicles.

It was a long time ago, so I'm going from memory with this info:

You start getting significant atmospheric drag around 50km. We were told that you'd want to have a reentry angle of between 2 and 4 degrees from circular. One of the guys in my team did the orbital dynamics to determine what sort of burn we needed using a one sided hohmann transfer and calculated our entry velocity at that point. We pulled atmospheric densities off of a NASA site and curvefitted it. We were originally going to try to do an ODE simulation using MATLAB before we gave up to focus on other sections of the design (only so much you can do for a one semester course with a 8-person team).

3. Nov 23, 2005

### Clausius2

I would say it is pretty impossible to obtain accurate data if you want to compute it numerically. Ok, maybe you are able to simplify the reentry and watch your CEV as a point falling on earth if the only thing in which you are interested is on the large scale kinematics of the vehicle. A numeric flow simulation is out of scope if you are not using a supercomputer. Take into account that the Reynolds# as such altitudes may be of the order of 10 millions. Personally, I made a numerical simulation of the reentry flow of a CEV sometime ago (Enigma knows about my simulation), with M=4.52 and Re=1250, which is pretty unrealistic.

4. Nov 28, 2005

### schemp98

Thanks for your replies, I think I should have elaborated on my situation...

Right now, I just need to create a simple model of a CEV falling straight down (with some neglible horizontal velocity)

I already have a 'skeleton' of a model up and running. Basically, I just need to find physical characteristics such as weight, surface area w/ and w/o parachutes open, and forces of the thruster (approximations are fine).

Any ideas on where I could easily find this stuff? Thanks

Shaun