I am a high school teacher. In my high school Aerospace Engineering class, I have the kids design and build an A engine powered streamer rocket optimized for maximum flight time. We are having issues with OpenRocket simulations. Attached is an example OpenRocket file.

This design uses an Estes A3-4T or A10-3T engine, a BT20 Airframe and a 6" wide folded tracing paper streamer. The expectation is that the kids will use OR to select the streamer length that will maximize flight time. Too short and it goes high but comes down fast. Too long and it comes down slow but does not go very high. There should be an optimal length. When we use the Rocket Optimization tool in OR, the results are very erratic and don't make sense. Some streamer lengths have zero flight time. When we do multiple simulations where we manually change the length of the streamer from 40" to 220" in 10" increments, the results are better but still have some peculiarities. See the attached “streamer size evaluation” pdf file. It is a pdf of an Excel file where we have graphed flight time as a function of streamer length using multiple manual simulations.

One observation is that if you look at the velocity and acceleration data for any given simulation, there is a significant “saw tooth” on the velocity and acceleration during the descent. To me this indicates that somewhere in the simulation numbers are being truncated to too few digits. This is a small rocket so the values involved are small. I am not software smart enough to dig into how OR does the calculations. I suspect that somewhere in there something is not using floating point variables and it is getting truncated. Would any of your software people be willing to look into the implementation of the numerical integration equations? The Runga-Kutta algorithm should be very precise even with small values if implemented well.

One last note. We have tried setting the time step to as small as 0.00001 s and it does affect the results but it does not fix them.

Thank you to everyone who has contributed to OpenRocket! :smile: It is a great program overall. I use it in my Aerospace Engineering class and my after school Rocket Club uses it too. All together that’s about 100 high school kids a year. We could never afford to buy RockSim. - Andy Buchanan

View attachment 2016 Bludger II T20 6.ork

View attachment Streamer Size Evaluations A.pdf

This design uses an Estes A3-4T or A10-3T engine, a BT20 Airframe and a 6" wide folded tracing paper streamer. The expectation is that the kids will use OR to select the streamer length that will maximize flight time. Too short and it goes high but comes down fast. Too long and it comes down slow but does not go very high. There should be an optimal length. When we use the Rocket Optimization tool in OR, the results are very erratic and don't make sense. Some streamer lengths have zero flight time. When we do multiple simulations where we manually change the length of the streamer from 40" to 220" in 10" increments, the results are better but still have some peculiarities. See the attached “streamer size evaluation” pdf file. It is a pdf of an Excel file where we have graphed flight time as a function of streamer length using multiple manual simulations.

One observation is that if you look at the velocity and acceleration data for any given simulation, there is a significant “saw tooth” on the velocity and acceleration during the descent. To me this indicates that somewhere in the simulation numbers are being truncated to too few digits. This is a small rocket so the values involved are small. I am not software smart enough to dig into how OR does the calculations. I suspect that somewhere in there something is not using floating point variables and it is getting truncated. Would any of your software people be willing to look into the implementation of the numerical integration equations? The Runga-Kutta algorithm should be very precise even with small values if implemented well.

One last note. We have tried setting the time step to as small as 0.00001 s and it does affect the results but it does not fix them.

Thank you to everyone who has contributed to OpenRocket! :smile: It is a great program overall. I use it in my Aerospace Engineering class and my after school Rocket Club uses it too. All together that’s about 100 high school kids a year. We could never afford to buy RockSim. - Andy Buchanan

View attachment 2016 Bludger II T20 6.ork

View attachment Streamer Size Evaluations A.pdf

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