Cluster Model in Rocksim ?
 

How does one create a 2 engine cluster model using Rocksim? I don't see any options in the centering rings. Do you use a Pod to do this? Also is it possible to can't the engine tube a couple degrees. If not I'd still like to model a cluster model. I plan on test flying the model tomorrow but I would still like to modify it so I can use two of the correct engines.




John Boren

Years ago I built a TLP Exocet MM-40, which flys on 2 24mm motors. I thought that I created a rocksim file, but perhaps not. I did find this on rocketreviews. While the graphic doesn't appear to list a two-motor cluster, the BOM does.

When you have your body tube, add an "inner tube" and select motor mount [1]. Then in the design tree, select "Cluster"[2], then next. I picked the two engine option, then you can rotate the tubes horizontal (default) or other orientation. I don't see an option to cant the motors (a la Titan?) but you can change the radial position of each motor tube to space them farther apart.

OH...I fully understand your question now...how to create the centering ring for said cluster DOH! Hmm...I'm not sure. I used CAD to make my GTII centering rings, letting the tubes at 3.5 degrees cut the ring for me.

EDIT: Well now, I selected the body tube, inserted a Centering Ring. The default put it at the front of the tube. When I drug the location back, the "Drilled Holes" window magically popped up! Here is the template RS created..

So what your saying is I am Freaking Blind. I've been using that software for six years now and I've [U]NEVER[/U] seen that Cluster button.

Thank you very much.


John Boren

It took me a while to figure it out...I've only done 2 clusters with it, several years ago, and I didn't remember the CR trick until tonight :)

Here is a modified K-21 GTII I modeled back in 2013. I just learned tonight how to move the tubes out so they don't touch, so they are 0.49 from the center. That makes the bottom ring correct for the K-21 but the upper ring would need to be .407 to obtain the 3.5 degree cant each motor has on the actual model.

John,

As is the case with any other piece of software, the hard part is knowing where to look. :confused: (heavy sigh)

To simulate the effect of canted motors on a model rockets flight visit Apogees Peak of Flight Newsletter #226 "The Effect on Altitude from Canted Rocket Engines" by Tim Van Milligan https://www.apogeerockets.com/educa...wsletter226.pdf . A cant angle of only 2 or 3 degrees in the motor mount tubes will not make much difference in the flight chracteristics and it is probably not worth going through the trouble of creating the custom engines for the flight simulation.

To get the templates for the centering rings for canted motor mounts you will need 2 simulations; one with the motor tubes placed at the distance they will be at the top of the canted cluster where the forward centering is to be located and a 2nd simulation with the motor tubes placed at the distance apart in the mount where the aft centering ring is located. Then just print the forward and aft centering ring templates from the appropriate simulation.

By the way, you don't have to fly the same motors in each tube of the cluster. I have flown my FlisKits Deuces Wild with Estes C6-5 and B6-6 motor combination many times, all I did was match the sustained thrust and the total motor duration (thrust phase plus delay time). This should also work for the D12-5, E9-4 and the D12-7, E9-6 motor combinations, but I haven't tried these yet. http://www2.estesrockets.com/pdf/Es...rust_Curves.pdf