I'm cert 2 but I want to try to do a more "realistic" looking launch - very slow acceleration.
Is there a way to determine the minimum speed a rocket will be stable? Given light weight, wide CG - CP, big fins etc . can I calculate the minimum G accel - thrust/wt - needed for a given launch rod length?
Thanks
Dan Schwartz

Hi Dan, can you give me some more details on the rocket and motor you plan on using? Usually, going much under a 3 or 4 to 1 thrust to weight ratio leaves something to be desired. I am not saying it would not work, but you could not have much wind. Also, remember that the majority of the slow liftoffs you see on large/commercial type rockets are using active guidance...not something you are likely to see most people doing at a HPR launch.

Mark Koelsch

The rocket is a 7 to 8 foot upscale estes deep space transport (not built yet). If I can build it under 15 pounds, I'd like to use a longer burning motor like J180 or cluster an I154 with 2 small H motors on the sides. I just think it would look good. If it accelerates slowly, does anyone have a 20 ft launch rod?
Dan Schwartz

It will be hard to get a more realistic takeoff. 5 to 1 thrust ratio is what is recommended. Tripoli will let you go down to 3 to 1, but not in all cases. That would be up to the RSO. Size, motor, weight and wind will all have a factor in it. I have done 4 to 1, but it is still not that slow. Rocksim does have data I believe on what point the rocket becomes stable on the rail. This of course depends on the rocket/motor combination. But just because it say?s it will work does not mean it is going to be safe. Your rocket will have bigger fins which is not good in the wind at a slow takeoff. A J180 gives you a ratio of 2.69. I don't think you could get that to past an RSO. To be on the safe side I would stick with the more 5 to 1 ratio. Might not be as real as you want it, but at least you know it will work.
Vern

Mark and Vern
Thanks for your input. I guess I'll put the bigger motor in and just run the video in slow motion
Dan