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

RockSim version 4.0 costs $50.00 US, me bucko, ya bilge rat, and upgrades are available for $15.00 t' registered owners o' previous versions.  A demonstration version and many design samples are available from t' Apogee web site.

I ordered RockSim from t' Apogee web site.  My credit card was billed accurately, and t' product was waitin' in me e-mail box in a few minutes.  I'm expectin' t' diskettes in t' mail in a few days (just like last time with version 3.01).

T' installation process for RocSim was very simple.  It uses t' automated "Install Shield" system.  All I had t' do be double click on setup.exe and away it went.  Version 4.0 reads and converts rocket designs from t' previous version with no trouble.

Online help abounds in RockSim.  There is  context sensitive help for every dialog box.  T' help files are well written and include diagrams.  This version o' RockSim includes a list o' frequently asked questions (FAQ).  There is clarification o' some features, me hearties, and a discussion o' some o' t' things RockSim can and can't do . Begad! . Avast! . Avast, me proud beauty! yet.

RockSim starts out by leadin' t' user through a simple process for describin' a rocket.  Usin' a hierarchical "tree-like" diagram, t' user builds up a rocket usin' components from t' extensive database o' commercial products.

RockSim designs with nose cones, body tubes, me hearties, transitions, matey, me bucko, fins (elliptical, trapezoidal, and arbitrary shapes), me hearties, internal tubes, me bucko, centerin' rings, couplers, ya bilge rat, shiver me timbers, bulkheads, engine blocks, ya bilge rat, sleeves, shiver me timbers, arbitrary mass objects, shiver me timbers, launch lugs, me hearties, parachutes, shiver me timbers, and streamers.

Each component's material, shiver me timbers, dimensions, matey, me bucko, shiver me timbers, and position within t' rocket are specified usin' a very simple interface.  For custom work, arrr, RockSim allows t' user t' define new materials, arrr, shapes, shiver me timbers, ya bilge rat, matey, sizes, and components.

As each component is placed into t' rocket model, ya bilge rat, shiver me timbers, a diagram o' t' rocket is constructed on screen.

Because RockSim carefully keeps track o' t' dimensions o' each component, shiver me timbers, ya bilge rat, shiver me timbers, it is able t' determine t' weight distribution o' t' rocket design, and hence t' rocket's center o' gravity (CG).  Additionally, components are assigned drag values which are tabulated t' arrive at a center o' aerodynamic pressure (CP).  With CG CP in hand, arrr, t' system determines t' static stability o' t' rocket.  RockSim uses three different approached t' calculatin' CP.  It uses t' Barrowman  equations we're all familiar with, as well as t' simplistic "cardboard cutout" method.  RockSim also uses it's own set o' equations called t' "RockSim" method.  I have tried all three with this program and for me designs, Barrowman and RockSim seem most similar.  T' "Bulls eyes" above indicate t' CP as determined via t' Barrowman (black) and RockSim (white) methods.

RockSim provides a tool for t' analysis o' Coefficient o' Drag (Cd).  Each component's shape and finish is considered.  T' system calculates a static Cd as well as Cd at any specified air speed.

T' drag components are broken out as nose/body, matey, base, fin, and launch lug drag.  Each drag type is computed and displayed as a percentage o' total drag, and each drag class is given a Cd value.

With this information, you can determine which components need t' be optimized t' meet your design's goals.  With this tool, me hearties, ya bilge rat, you can easily see t' effect o' addin' a boat tail, usin' a different nose cone or fin shape, or removin' t' launch lug.

After designin' a rocket, t' user can simulate flights by selectin' various motors from t' extensive library o' commercial motors.  Some o' t' manufacturers included are Apogee, Aerotech, shiver me timbers, Estes, FSI, shiver me timbers, Hypertech, Kosdon, NCR, me bucko, Quest, Rocketflite, arrr, and Vulcan.   RockSim includes a motor editor which allows t' user t' specify custom motors.

Some o' t' flight simulation factors used by RockSim include launch site parameters like altitude, temperature, me bucko, humidity, me bucko, and latitude.  Wind conditions and launch angle are also considered.  RockSim performs some complex dynamic stability calculations which help model t' rocket's interaction with wind, me hearties, angle o' flight, angle o' attack, me hearties, moments o' inertia, centers o' gyration (my head aches already), shiver me timbers, 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 nay been practical t' solve for t' hobbyist.  Accordin' t' Tim VanMilligan, these equations are designed more as a learnin' tool.  You can make changes t' your rocket design and visualize their effects on t' flight stability o' t' rocket.

T' results o' t' simulation processes are made available in a variety o' ways.   First and foremost, you will get a basic summary o' t' altitude, ya bilge rat, velocity, ya bilge rat, acceleration, duration, me bucko, shiver me timbers, and deployment details.  RockSim tells you whether your recovery device deployed too soon or too late.  T' program determines whether or nay t' rocket has reached sufficient speed before leavin' t' launcher t' be stable.   [click here t' see a sample]

Results from simulated flights can be displayed graphically. 

Seein' how t' rocket performs over t' duration o' t' flight helps one understand some o' t' physics o' rocketry better. 

T' first graph t' look at is an Acceleration / Velocity / Altitude graph.  This graph shows how t' rocket accelerates ad t' motor burns, matey, me hearties, then begins t' coast upwards toward apogee. 

Another interestin' graph be t' Cd vs. Blimey! Ahoy! Speed graph.

This one shows how t' drag forces experienced by t' rocket change with t' rockets speed.  It makes t' "sound barrier" very visible by showin' how aerodynamic drag increases very rapidly as t' rocket approaches Mach 1.

Notice t' steep ramp in t' graph as you move toward t' right.

There are other graphs present when RockSim is first installed.  T' user can also create any number o' additional graphs.

T' first graph I added was Drag vs. Blimey! Blimey! Motor Thrust.  This graph shows why a rocket stops accelerating, "poops out," before t' motor finishes burning.  T' motor is pushin' t' rocket so fast that t' air drag forces (blue line) overpower t' thrust force (green line) and t' rocket starts slowin' down (orange line goes below zero) while still under power.

Some o' t' values that RockSim will graph include velocity, altitude, me hearties, Mach, downrange distance, drag, mass, shiver me timbers, fight angle, matey, matey, angle o' attach, arrr, me bucko, matey, CG, Cd, CP, angular acceleration, corrective, damping, shiver me timbers, longitudinal, and radial moments, natural frequency at zero roll rate, torques, pitch, cross wind lift, me hearties, and tons o' other factors. Begad! Blimey! T' large number o' factors you can graph helps you understand just how many different factors RockSim takes into account when simulatin' a flight.  These folks have really done their homework!

RockSim allows any factor t' be plotted as either X or Y axis variables.  This makes for some pretty exotic graphs.  Try plottin' Cd vs. Avast, me proud beauty! CP, or how about Angular Acceleration vs. Aye aye! Coupled Dampin' Ratio.  T' graphs can be spread out, each with it's own y-axis, ya bilge rat, or overlaid.  T' overlay approach helps visualize t' interaction betwixt different factors.

T' third way t' visualize t' results o' a simulation be t' Flight Profile.   This is a graphic animation showin' t' rocket in flight with many o' t' forces displayed.

RockSim shows t' rocket's flight track, me bucko, flight angle, shiver me timbers, flight direction, me hearties, vectors for thrust, me bucko, drag, and wind.  This animation shows how a rocket will "weather cock" into t' wind (and why you might want t' angle t' launcher down wind). 

You can see how a rocket snakes back and forth as it stabilizes.  It's a great way t' show how fin size and length can affect a rocket's ability t' fly straight.

T' last RockSim feature I'll mention is optimal mass prediction.  RockSim will determine t' mass for a rocket that will make it coast t' longest, or reach t' highest altitude. This is done by runnin' multiple simulations while changin' t' rocket's mass. I found that I could get an extra 250 feet o' altitude out o' a PML Phobos by addin' 20 ounces t' t' rocket. RockSim prints everythin' relatin' t' your rocket design.  It prints a scale drawin' with CG, me hearties, matey, CP symbols, parts lists, matey, nose cone, ya bilge rat, centerin' ring, and fin templates, simulation results, and graphs.  I received a 14 page booklet on me design with t' click o' a single button.