Never having owned an iPad, please take these comments with a big grain of salt!
You can probably download anything small enough to an iPad, but SCARM is a Windows only program. To have it work on an iPad, you would have to find a piece of Apple software that allows you to open and work with Windows software which would be a very convoluted process. SCARM is a very small program, so most any old second-hand Windows-based laptop with internet connectivity, 2GB of memory and a small hard drive would allow you to use it.
Alternatively, there is a completely free, but more complex, track planning software called XtrackCAD which works on Windows, Linux and MacOS. Since it creates its own file extensions, you can even create a plan in Windows and share it with someone using a different operating system. The time, money and frustration you save with planning now will be well worth it in the end.
Be warned, though, that I don't know if any of this will work well, or at all, on an iPad only.
Chuck
