For the longest time I've been trying to come up with a plausable way to make a Harrier supersonic. I've read all about the various methods that were design to accomplish this, from a PCB Pegasus modified Harrier, through the HS P.1154 to the BAe P.1214/1216 projects. I've read somewhere that RR even proposed a much more powerful Pegasus with thrust output upped to between 30,000 and 35,000 lbs. This invovled many refinements to the existing Pegasus and also an increase in the fan diameter of around 3-4 inches more than the standard Pegasus and keeping with the cold/hot nozzles idea. It wasn't proceded with because the whole engine would have had to be bigger and the GR.5/AV-8B was already well underway at the time, and there just wasn't any room for this engine to fit in the fuselage.
Most of my thoughts had revolved around how to convert a Harrier to have ramp style air intakes but the biggest stumbling block was how to intergrate the swivelling nozzles. One of my thoughts was to have two smaller engines with swivelling hot exhaust similar to the P.1216 and a rear fuselage like a Jaguar or Phantom but placing the cold nozzles always proved to be a problem. That was until the F-35 came along which is an aircraft I really like (one of the few I think), the cold air louver system seemed to me a really clever way of duplicating what the swivelling nozzles do, the only thing that I don't like about the F-35 system is the horizontal fan, gearbox and driveshaft, too much dead weight being dragged around for 90% of any mission and all the space that could be used for other equipment. Still I like the approach the F-35 has gone in but don't get me wrong, I still love the Harrier.
I'm not sure when I started to rethink how to make a supersonic Harrier but I began to realize it would have to be a totally different design. And it would have to revolve around the engine which would have ramp style intakes (my favorite system). An idea started to form in mind while I was working on another project where I'm planning on making an Avro Atlantic powered by turbofan engines with fan diameter about the same as a Harrier's and installing them into a Vulcan wing. This involved some new ducts and engine bays with the bypass air exiting above and below the wing. It dawned on me that a regular type of turbofan would be a way for my new Harrier and then after studying a number of videos of turbofans on airliners I suddenly thought of a way to use the bypass air for the cold air lifting source. I had been watching how certain turbofan engines actuate their thrust reversers, one type has the whole rear end of the nacelle move backwards to expose a gap where the bypass air is redirected through. I thought if the mechanism was used to direct air down some ducting instead of just blasting out the sides I could have a pretty good VSTOL engine. I also decided almost right away the bypass air would go out two ducts and the hot exhaust would have just one nozzle. The two cold air ducts would have gimballed louvers on the bottom of my new fuselage and that these same ducts could also control pitch, roll and yaw through the louvers and through a variable area control inside the ducts. With that figured out it was on to deciding what to use for my model.