Wednesday, December 02, 2015

Yes. Yes there is an ekranoplan Rocksim model

Well, my inability to get Rocksim to cooperate ate at me until I decided to give it another try. The trick is that I couldn't copy pod-on-pod structures or their constituent parts. For instance, there is a pod on the main body to mount the forward motor mount. There's a fin on that, then more pods and then the motor tubes. Since you can only add pods to single fins, I had to build one side and then the other. It would have been nice to use the copy feature but, once I realized my problem, it wasn't too bad.  I ended up rebuilding things from scratch and it seemed to work. The model isn't pristine but the major parts are pretty close. I added a mass element to fudge the actual mass and slid it around until the CG also matches reality.

Here is a side view. Check out where the CP is! If I believe that, the CP-CG shouldn't be an issue. But, should I believe it?

ekranoplan1

The next image is a rear view with a stability graph overlay. It's not as clear as on my screen but it appears to be stable in both axes. But, is it?

ekranoplan2

I still plan to swing test it but my guess is I'm Ok with no nose weight. I ran a sim and got:
  • Max. altitude = 372 ft...I guess I can believe that.
  • Max. velocity = 337 ft/s...still OK.
  • Max. acceleration = 17724 ft/s/s...say WHAT?
  • Time to apogee = 2.5 s....OK.
  • Velocity at deployment = 336 ft/s...that's not good.
  • Optimal delay = 0.65 s...ugh.
  • Velocity off a 48" rod = 58 ft/s...that's good.
These don't all add up when viewing the flight profile and graphs. Oh well, GIGO.

But the 3D render is nice:
ekranoplan