I am looking for Mark Sullivan's altitude predictor on the internet. My old website address does not work. Is anyone familiar with this old website and how it might be found?
What is special about the Sullivan predictor? Web-based simulators usually use simplified forms of the differential equations governing flight trajectory, like using constant thrust, constant air density, constant Cd. Thrustcurve is similar and will get you in the ball park for altitude and delay time. RockSim, OpenRocket, RASAero, and wRASP use numerical integration with fewer assumptions and are far superior tools.
especially once the CD of a particular airframe was dialed in.
Yes, of course. Cd is critical to any type of simulation. Adjusting a constant Cd to match your altimeter's barometric altitude is somewhat helpful, but not robust. It becomes a catch-all for everything wrong in your flight. Wind tunnel, ballistic measurement, or CFD is the best way to get Cd vs. speed.
If Markworld (never heard of it) and Sullivan do what I think they do, then it is mathematically impossible for them to be "more accurate" than RockSim, OpenRocket, RASAero, and wRASP. The latter softwares capture the physics more precisely, assuming they are coded correctly, of course.
Ask yourself how "accurate" a simulation can be, and how do you confirm it with any statistical significance? Motor thrust and wind variation at the time of the actual flight are impossible to predict. If your electronics and simulations repeatedly correlate within 10%, then consider yourself lucky, call it good, and move on. Once dialed in, as you say, then RockSim, OpenRocket, RASAero, and wRASP should give you better odds than simplified equations.
The motor guide in Thrustcurve.org probably does what you are wanting, and gives you many motor results at the same time. Very handy. Perhaps a good compromise for you is wRASP, where you only need mass, diameter, and Cd, but the calculations are more precise. RockSim, OpenRocket, RASAero all require you to input the complete geometry of the rocket before you start simulating, and that is time consuming.
Quick, fast and dirty what-if calculations.In a word: simplicity. Essentially, enter body dia, motor, and CD and it spit out a fairly accurate flight prediction. True, there are way more advanced and involved methods, but that's not the intent. I really miss the Markworld program, if I was looking for ballpark estimates in speedy fashion, that was the program. As for accuracy, it depended upon the flight envelope; for most non-extreme mid-high power flights, I found it to be much more accurate RockSim, especially once the CD of a particular airframe was dialed in.
Give me three minutes with a rocket and the Markworld program, and I'll give you a more accurate speed and altitude prediction than the "superior" RockSim.
-Eric-
Enter your email address to join: