Rocksim, rail buttons, and exposed "inside" tubes...

[Rick Lindsey]

Hi guys! Has anyone simulated a rail button (as opposed to a launch lug) in rocksim? I suppose I could just add a launch lug to add some drag, but I have no idea how the drag of a lug compares to that of a button.

Also, I know older versions of rocksim didn't account for inside tubes in drag calculations, is that still the case? Do they count for cp calculations? I've got exposed motor tubes that are marked as "inside". They overlap the body tube by about 6", and have about 9" exposed. I'm afraid if I tweak the file to declare them as "outside" tubes then the overlap will confuse things. I suppose I could remove the inside portion, and replace them with actual inside tubes *ponder*.

I've attached the rocksim file (made with the rocksim 8 demo) in case there are any questions about the design in question. The "fin reference" is just a smaller diameter tube of nearly zero length that I used to pull the root of the fins in between the motor tubes (as opposed to hanging out in space).

thanks!

-Rick

View attachment SevenUp_ED.rkt

 

[Sailorbill]

Rick just make a single fin that is the same width and height as a rail button and say it is rounded. Should work for drag. Not sure about the tubes.

 

[teflonrocketry1]

Visit this thread for my RockSim files of both sizes of rail buttons:
https://www.rocketryforum.com/showthread.php?t=25366

These files are also available at:

https://www.rocketreviews.com/rocksim/railbuttons_dot_com_series1000eailbuttonv8.rkt

https://www.rocketreviews.com/rocksim/railbuttons_dot_com_series1500railbuttonv8.rkt

The EMRR links might not work since I can not read the site directly, my ISP considers EMRR to be a "bad" site and automatically blocks it. So I have to translate the site back into English from Babel Fish Translation.

Bruce S. Levison, NAR #69055

 

[teflonrocketry1]

I checked over the RockSim file everything looks good; I made some minor corrections and set up delays for the motors. You might need a level 1 certification to fly this design on anything larger than C11's due to the combined propellant weight and the final weight of the completed rocket.

Bruce S. Levison, NAR #69055

View attachment SevenUp_ED_mod.rkt

 

[Rick Lindsey]

Thanks, Bruce. So I know what to different next time, what were the errors you corrected? I purposefully left delays off the motors since I'm planning to use plugged motors and electronic dual deployment.

Are the "inside" motor tubes already being handled appropriately, or can I just neglect them for the purposes of this sim?

thanks!

-Rick

 

[teflonrocketry1]

Rick,

Here is the fully detailed design with all the external tubes created as they should be to include their wetted surfaces in the drag calculations. This was all done outside the RockSim program with a word processor and calculator.

For details on how the outside tubes were clustered visit:

https://www.apogeerockets.com/education/downloads/newsletter119.pdf

The wetted surface area of the outside tubes was calculated manually and programmed into the RockSim file with a word processor.

Bruce S. Levison, NAR #69055

View attachment SevenUp_ED_mod2.rkt