Algodoo

Does not use scripting or density changes, just newton's third law. accelerates upwards increasing from one to three g's over about thirty seconds, reaching incredible heights.

The Unique and Powerful engine design allows an arbitrary sized fuel store which I have used to the max. If it runs slowly, delete some of the fuel. It will still fly well.

Use the arrow keys to stabilize.
The next step is thrust vectoring and staging!