Apogee Components RockSim Design Software (2.x-4.x)

Apogee Components - RockSim Design Software (2.x-4.x) {Software}

Contributed by Larry Rubanka

Manufacturer: Apogee Components

This program is an ideal design and analysis tool for the  rocketry hobbyist.

RockSim version 4.0 costs $50.00 US, and upgrades are available for $15.00 to registered owners of previous versions.  A demonstration version and many design samples are available from the Apogee web site.

I ordered RockSim from the Apogee web site.  My credit card was billed accurately, and the product was waiting in my e-mail box in a few minutes.  I'm expecting the diskettes in the mail in a few days (just like last time with version 3.01).

The installation process for RocSim was very simple.  It uses the automated "Install Shield" system.  All I had to do was double click on setup.exe and away it went.  Version 4.0 reads and converts rocket designs from the previous version with no trouble.

Online help abounds in RockSim.  There is  context sensitive help for every dialog box.  The help files are well written and include diagrams.  This version of RockSim includes a list of frequently asked questions (FAQ).  There is clarification of some features, and a discussion of some of the things RockSim can and can't do . . . yet.

Building a rocket model one component at a time (click for full view)

RockSim starts out by leading the user through a simple process for describing a rocket.  Using a hierarchical "tree-like" diagram, the user builds up a rocket using components from the extensive database of commercial products.

RockSim designs with nose cones, body tubes, transitions, fins (elliptical, trapezoidal, and arbitrary shapes), internal tubes, centering rings, couplers, bulkheads, engine blocks, sleeves, arbitrary mass objects, launch lugs, parachutes, and streamers.

Diagram of complete model (click for full view)

Each component's material, dimensions, and position within the rocket are specified using a very simple interface.  For custom work, RockSim allows the user to define new materials, shapes, sizes, and components.

As each component is placed into the rocket model, a diagram of the rocket is constructed on screen.

Because RockSim carefully keeps track of the dimensions of each component, it is able to determine the weight distribution of the rocket design, and hence the rocket's center of gravity (CG).  Additionally, components are assigned drag values which are tabulated to arrive at a center of aerodynamic pressure (CP).  With CG CP in hand, the system determines the static stability of the rocket.  RockSim uses three different approached to calculating CP.  It uses the Barrowman  equations we're all familiar with, as well as the simplistic "cardboard cutout" method.  RockSim also uses it's own set of equations called the "RockSim" method.  I have tried all three with this program and for my designs, Barrowman and RockSim seem most similar.  The "Bulls eyes" above indicate the CP as determined via the Barrowman (black) and RockSim (white) methods.

Drag coefficient analysis

RockSim provides a tool for the analysis of Coefficient of Drag (Cd).  Each component's shape and finish is considered.  The system calculates a static Cd as well as Cd at any specified air speed.

The drag components are broken out as nose/body, base, fin, and launch lug drag.  Each drag type is computed and displayed as a percentage of total drag, and each drag class is given a Cd value.

With this information, you can determine which components need to be optimized to meet your design's goals.  With this tool, you can easily see the effect of adding a boat tail, using a different nose cone or fin shape, or removing the launch lug.

After designing a rocket, the user can simulate flights by selecting various motors from the extensive library of commercial motors.  Some of the manufacturers included are Apogee, Aerotech, Estes, FSI, Hypertech, Kosdon, NCR, Quest, Rocketflite, and Vulcan.   RockSim includes a motor editor which allows the user to specify custom motors.

Some of the flight simulation factors used by RockSim include launch site parameters like altitude, temperature, humidity, and latitude.  Wind conditions and launch angle are also considered.  RockSim performs some complex dynamic stability calculations which help model the rocket's interaction with wind, angle of flight, angle of attack, moments of inertia, centers of gyration (my head aches already), and a whole lot more factors than we can go into in this article (and a whole lot more than I understand).

In other words, this analysis will tell you if your rock will wiggle around as it flies.  These are very complicated (and large) calculations that have not been practical to solve for the hobbyist.  According to Tim VanMilligan, these equations are designed more as a learning tool.  You can make changes to your rocket design and visualize their effects on the flight stability of the rocket.

The results of the simulation processes are made available in a variety of ways.   First and foremost, you will get a basic summary of the altitude, velocity, acceleration, duration, and deployment details.  RockSim tells you whether your recovery device deployed too soon or too late.  The program determines whether or not the rocket has reached sufficient speed before leaving the launcher to be stable.   [click here to see a sample]

Altitude, Velocity, Acceleration graph (click for full view)

Results from simulated flights can be displayed graphically. 

Seeing how the rocket performs over the duration of the flight helps one understand some of the physics of rocketry better. 

The first graph to look at is an Acceleration / Velocity / Altitude graph.  This graph shows how the rocket accelerates ad the motor burns, then begins to coast upwards toward apogee. 

CD vs. Mach number graph (click for full view)

Another interesting graph is the Cd vs. Speed graph.

This one shows how the drag forces experienced by the rocket change with the rockets speed.  It makes the "sound barrier" very visible by showing how aerodynamic drag increases very rapidly as the rocket approaches Mach 1.

Notice the steep ramp in the graph as you move toward the right.

Drag vs. Thrust graph (click for full view)

There are other graphs present when RockSim is first installed.  The user can also create any number of additional graphs.

The first graph I added was Drag vs. Motor Thrust.  This graph shows why a rocket stops accelerating, "poops out," before the motor finishes burning.  The motor is pushing the rocket so fast that the air drag forces (blue line) overpower the thrust force (green line) and the rocket starts slowing down (orange line goes below zero) while still under power.

Flight profile details

Some of the values that RockSim will graph include velocity, altitude, Mach, downrange distance, drag, mass, fight angle, angle of attach, CG, Cd, CP, angular acceleration, corrective, damping, longitudinal, and radial moments, natural frequency at zero roll rate, torques, pitch, cross wind lift, and tons of other factors. The large number of factors you can graph helps you understand just how many different factors RockSim takes into account when simulating a flight.  These folks have really done their homework!

RockSim allows any factor to be plotted as either X or Y axis variables.  This makes for some pretty exotic graphs.  Try plotting Cd vs. CP, or how about Angular Acceleration vs. Coupled Damping Ratio.  The graphs can be spread out, each with it's own y-axis, or overlaid.  The overlay approach helps visualize the interaction between different factors.

The third way to visualize the results of a simulation is the Flight Profile.   This is a graphic animation showing the rocket in flight with many of the forces displayed.

RockSim shows the rocket's flight track, flight angle, flight direction, vectors for thrust, drag, and wind.  This animation shows how a rocket will "weather cock" into the wind (and why you might want to angle the launcher down wind). 

You can see how a rocket snakes back and forth as it stabilizes.  It's a great way to show how fin size and length can affect a rocket's ability to fly straight.

Optimum Mass graphs (click for full view)

The last RockSim feature I'll mention is optimal mass prediction. 

RockSim will determine the mass for a rocket that will make it coast the longest, or reach the highest altitude.

This is done by running multiple simulations while changing the rocket's mass.

I found that I could get an extra 250 feet of altitude out of a PML Phobos by adding 20 ounces to the rocket.

RockSim prints everything relating to your rocket design.  It prints a scale drawing with CG, CP symbols, parts lists, nose cone, centering ring, and fin templates, simulation results, and graphs.  I received a 14 page booklet on my design with the click of a single button.

Other Reviews
  • Apogee Components RockSim Design Software (2.x-4.x) By Moira Jean Whitlock

    This is computer software whose purpose is to aid model rocket designers in choosing materials, motors, and parts for a stable rocket flight. There is a data base of known manufacturers and parts and you can create custom parts yourself. You can simulate flights with chosen engines and get a predicted altitude and speed. You can also see if your chosen delay allows ejection at apogee or ...

Comments:

avatar
K.B. (January 1, 2001)
For about 2 weeks I've been playing with RockSim 3.0 trying some new designs. I previously had WRASP, VCP . . . and all the freebie download stuff of which many are must haves. So when I sent my $30 to Apogee I wondered if it was worth the bucks? The answer ... yes. It is for the person designing a new rocket and not just predicting altitude for standard models (for which WRASP does fine). The program is not without a few limitations (as no program is) but it is a fine addition to your software collection if you like creating new rocket designs. I have no business connection with Apogee, in fact this was my first order, I just think folks like to know about good products (I yell just as loud about bad products).

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