May I suggest you read a bit on the HI forum? We discuss a lot of WHY kukri work there.
In short:
1.) The position of the "sweet spot" on a kukri is, as another pointed out, right where the bit of an axe would be for an equal length tool.
2.) The forward bend works with your body's geometry and with the standard whipping motion used to chop with a kukri. You start with a somewhat loose grip, swing the kukri like you're cracking a whip -- the wrist motion makes it move faster than chopping with a locked wrist. The forward bend then makes sure the kukri makes contact before your wrist locks all the way forward (which would decrease the kukri's speed). This same whipping motion works just as well with machetes, hatchets and tomahawks.
3.) The curved blade, plus the curving motion of your arm swinging means the blade runs as well as pushes. This gives no advantage in splitting (but no disadvantage, either), but when felling, limbing and bucking when you have to go across the fibers, the blade slices the fibers as well as pushing through.
4.) Less surface area making contact means higher PSI ont he contact area, means a deeper cut. The deeper the belly, the more pronounced this will be.
The CPL is right on. If you look at an HI khukri, there is a distal taper towards the end of the grip as well as to the point of the blade. This is in effort to centralize the weight where the blade meets the handle, creating a rotating axis. With a khukri, you aren't doing a full arm chop, the chop is in the rotation of the wrist. You aren't using upper arm strength, but the mass of the blade and the quick short wrist rotation. It's an entirely different deal. Even if you did a full arm swing, the downward stroke of your arm is circular-it's coming inward slightly as well as downward, as it impacts deadfall wood. This is why the inside of the belly comes in handy. Even though the blade may be heavier, it does conserve alot of energy and potential injury due to a missed wild swing versus a short controlled rotating chop. It's not the only way to get the job done, just a very efficient way.
As far as the Cpl's statement on belly goes, you can accomplish this same effect in more 'standard' blade designs by using thinner stock and thinner grinds. This is one reason why a flat ground tramontina is SO effective (of course the downside is an edge prone to denting and rolling)-with thin stock and a thin grind, it doesn't take nearly the same amount of force to bite very deep and controlled. Whereas thick choppers act by decimating material, a thinner, shorter blade bites nice, controlled, precise V notches that Ideally look like this:
V V
.V
as you work your way to the center of the limb. Again this saves energy instead of wildly swinging with a thick, long, decimating convexed chopper. Instead of using brute force to send chunks flying, you are using a short controlled action that's less likely going to bounce off a log and wind up imbedded in your foot or your kneecap. I'm not sure if belly or a flat edge would be more effective for this kind of chopping, I'm pretty sure it's mostly about thin stock and thin grind.
Looking at your design, I think it would be much more efficient if you flipped the handle around-put the handle where the tip of the blade is now, so that the drastic sweep occurs at the end-that's where you want all that forward weight. At that point I'd think it would be a very efficient chopper.
One design that I believe has alot of promise is the 10 inch Paratrooper Martindale. Nice big belly towards the end of the blade. I would love to own one, but they cost 40-50 dollars here in the states and from what I hear the handles are crap. If a maker were to take that design and refine it a bit, I think it would be very successful.
