Incidently, Alan Bond the chap behind HOTOL and Skylon has admitted in the past that he was inspired by the XL5.
Come on Alan, you know no one is going to biuld you a very long runway when we all know Gerry Anderson was right with the railway launch solution nad XL5 is a better name than Skyon.
OK maybe the 'kicker' at the end of the XL5 launch rail isn't exactly practical but it will allow the craft's undercarriage to be a lot lighter (landing mass only to support).