Flyers are REQUIRED to know the expected altitude their rockets will fly with the motor(s) installed. Under no circumstances can rockets fly higher than our FAA Waiver allows, 4500′ AGL. For EX motors, flights must be under 90% of the waiver (4050′) per Tripoli rules.
NOTE: The RSO will have final say whether the rocket can fly with the installed motors! If you select a motor that will give an unsafe flight profile (too little thrust for rocket weight), or is judged to be in danger of exceeding our waiver, you will NOT be allowed to fly. If you have questions, please consult the METRA Prefect or President.
Expected altitudes should be determined by the flyer at home prior to coming to the launch as part of their planning. At the launch, the RSO or Prefect can help with this determination – there are Motor/Weight/Rocket diameter/Altitude charts at the RSO table. Expected altitudes can be determined in many ways:
1. Rocket Design / simulation programs. Some examples follow:
- OpenRocket is a free, open-source, and fully featured model rocket simulator that allows you to design and simulate your rockets before actually building and flying them. Unlike most free programs, OpenRocket is a full design tool, allowing the user to fully configure a rocket, including all internal components, with the ability to make 3D views of the finished rocket, and print fin and ring templates. OpenRocket is written in Java, and will run on any platform with a Java runtime engine installed: Windows, Macs, Linux, Android smart phones & tablets, etc..
- RASAero is a free, combined aerodynamic analysis and flight simulation software package for model rockets and high power rockets, amateur rockets, and sounding rockets. RASAero is likely the most accurate simulation program, with the ability to accurately calculate aerodynamic coefficients as a function of speed. Algorithms are tuned with wind-tunnel and actual flight data by the authors.
- WinRoc is a free, older, but but simple and fast to use suite of Windows programs for flight simulation, and determination of optimal ejection delay.
- wRASP is another older and free Windows program that simulates the flight of a rocket in one dimension (one degree-of-freedom), allowing determination of how high a rocket might fly with a particular motor and what the best ejection delay time might be. wRASP is derived from older programs going back to an original BASIC program written by Harry Stine in 1979.
- RockSim is a commercial program from Apogee Components that costs $125 and runs on Windows and Macs. It is a full-featured rocket design (all internal and external components) and flight simulation program.
- SpaceCad is a commercial program that costs $80 and runs on Windows. It is a full-featured rocket design (all internal and external components) and flight simulation program.
3. Dr. Andreas Mueller made Performance Nomograms for rockets with Aerotech motors. These are charts where you can look up altitude and time to apogee based on the selected Aerotech motor, rocket diameter, drag coefficient, air density, and rocket mass. They can be a little difficult to use, but very detailed, with 221 pages of tables.
4. Much simpler charts (only 5 pages!) based on motor total thrust ranges were prepared by Dean Roth and distributed by Tripoli Wisconsin as part of a larger packet of RSO information. They require knowledge of total motor thrust, and assume medium Cd, air density, a neutral thrust curve, an average burn rate. They only cover a common range of rocket diameter and weight.