How big is a 1hp scale Harrier?

It would never get off the ground. An LA .46 is about 1hp and can't get out of its own way let alone lift 5+ lbs of airplane straight up.

That's not to say that VTOL models themselves are impractical. Here's a link to a turbine powered one that flies well: The Rig However, he's got about 10kg of turbine thrust to work with.

OS Wankel: heavy & inefficient generator: heavy & inefficient electric ducted fans: heavy & inefficient

A ball-bearing .46 engine will lift ~2Kg straight up, using a large-diameter, low pitch prop. That's using 100% of the useful output of the engine as thrust. You're putting two additional levels of loss into the equation, and will end up without about 25% of the useful power from the engine actually making thrust.

As a side note in 1960 I tested a model of the prototype Harrier, the Hawker P1127 in the NASA 16 foot transonic wind tunnel at Langley Field, VA. We were studying the aerodynamics and static stability at transonic speeds. Our model was machined out of solid aluminum. The fuselage was hollow and we had a hydrogen peroxide hot exhaust simulator blasting out the four nozzles. It was a fun project. I wish I had saved all the calculations I made on the project. Unfortunately all the notes and reports were classified.

The original P1127 had a straight horizontal tail and I redesigned it with a slightly different planform and the -30 degree dihedral to solve a transonic pitch-up stability problem. The Brits didn't like my design but they later adopted it for the remainder of the series.

Thanks All,

Using ducted fans is not the way to go i see now. On the "engine+generator" solution i might note that even if it sounds like a heavy combination, it is only about 2/3'rds the weight of an equivalent battery pack. And it has 5-10 times the endurance.

The hints so far have been : Centrifugal blowers might be the solution. (why?) Letting the engine drive the blowers with a mechanical link. And using throttles in the blowers for fine control.

Thanks again Henrik

Odd. A helium ballon is 0Hp and gets off teh ground quite well.

Its all about tuning the fans for thrust, not speed. Sadly small diamater fans are going to be very far off ideal. A helicopter rotor would do better...you need as much diameter as possible, and a fairly fine pitch. It may not be practicable - not because of the power, but on account of not being able to utilise the power effectively in such fans.

Don't you get technical with me! ;^)