Surly the extra "weight" is classed a ballast and is par for the course?
When I used to fly full size, I mostly had 3 passengers, so had to do the weight/balance calculations and then decide who could sit in the front with me and how much fuel I had to drain from the tanks in order to fly!
As far as I could tell, with very rough calculations, my craft seemed to work better with me in the front and 2x20L full Jerry cans just behind me, otherwise I got spray coming up over the front, not a lot, but there anyway.
This was at Lock Fyne which is where I wanted to test this out properly, but the bearings decided to go south so ended my fun!
The ideal would be moveable fuel tank(s)
There's two sides to the trim equation...
The first is the obvioius one - wieght distribution, and everyone is familiar with moving kit around to obtain better trim. This is the way that all single-cushion compartment craft are trimmed.
The second is cushion pressure distribution. When a partition skirt is used, the cushion pressure may be varied fore & aft, as a means to control the trim. With a little ingenuity, this pressure can be varied automatically.
The Sev has a skirt partition, which is designed to reduce the cushion pressure in the front partition in response to craft trim - if weight moves back and the craft nose goes up, the front compartment pressure drops, acting to re-trim the cushion for the new wieght distribution. This works because the front compartment is fed from the aft compartment via the partition air-gap. If the nose rises, more air as able to escape from the front curtain but cannot be replenished from the rear due to the partition, so the pressure falls and trim is restored.
A very similar principle is used for Bryan's skirt divider, although the air is supplied by the plenum rather than the rear compartment.
The Sev system relies on trimming the two curtain skirts correctly, and on the fact that the front curtain is larger than the divider (it is this that makes the pressure fall when the nose rises).
The Sev system has a given range of adjustment that can be accomplished. It is designed to cope with the "normal" variation in payload. It has to be set up initially by trimming the relative lengths of the divider and fron curtain - and this usually takes a while to get right for the first timer. Get it wrong and the skirt can drag, reducing top speed, or the whole craft can go unstable and repeatedly bob up & down (called 'porpoising'). Ironically, my first skirt was right at first cut, whilst it took me several trims (and a little assistance from John) to get the second right.
When properly trimmed, an empty Sev will trim with the front curtain airgap about 6" or more (nose well up). When you grab the bow and force it down, initially it is easy to do so, but when the curtain gets about 1" from the floor, it suddenly goes very stiff - it feels like it just went solid. This point should be very distinct, and tells you the automatic trim system is working well. Adding the pilot to the craft should bring the craft down to the "stiff" point, and it should be pretty insensitive to quite large changes of trim. My craft flies just the same whether its me or Nathan at the helm.
Ian