Is there any reason in particular that you are interested in a belly landing and not a set of gear? Also, what media are you planning on landing on? I am assuming that you are going to shoot for grass but I want to make sure.
Not sure if it'll work, but the first thing I thought of was one of the water-landing planes with pontoons on the wings, so it lands with 3-points down. That way you'd land on the belly with most of the force & have the pontoons to hold you level and protect the antennas, but I'm not sure how well they'd work on surfaces other than water.
After reading your initial post some more I think that I have some some points that you may want to consider. You are going to want to focus on two obvious things; weight and shock absorption. If you want to focus on the drop stall landing method you are going to want to really focus on absorbing that shock. I would not recommend foam because that would create a rather bulky landing system, not as far as weight is concerned but as far as volume is concerned. This will definitely affect your flight characteristics. I would also not recommend a direct belly landing because all of the shock would be directly transmitted to the fuselage...which is not ideal. I would try to create a form of skid system similar to that of a helicopter using reinforced composites. That way you get the best of all worlds. You get the shock absorption that you need, the ground clearance you would need for the antennas, you would reduce the aerodynamic drag of most other systems, and your would still be able to land with both positive forward motion and zero forward motion conditions. Hope that helps.
Yeah, the main reason for doing this is that there are no good landing strips for unmanned testing nearby, so we are forced to use grassy farmer's fields. I am definitely going to try to soften the landing. How that will happen isn't exactly clear. I quite like the design and function of the Puma AE.
So why do you have three antennas underneath the plane? Will they have the capability to fully retract within the fuselage or some form of protection? It looks the Puma uses it's wing as a form of air-brake to make sure that it lands at a low enough speed, but that landing method is fairly complicated...or at least the way in which it seems that AV has it implemented when considering all that needs to be accounted for in a landing like that. Not saying that it can't be done but just stalling the plane and dropping it leaves too much to chance in my opinion. One way that you could more easily perform that same landing would be with a drogue-chute. Just have a servo actuated door that would allow for the deployment of the chute. The chute won't be the main deceleration unit but it would be used to stabilize the decent of the plane.
Hey, so after my share of belly landings I would recommend keeping the CG as close to your skid surface as possible. A pontoon construction works well for a water landing plane, as the sheer force between the water and the pontoon is relatively low, however for gras it might be so high that your plane easily toples over if the pontoons are to high...
I actually had good experience with foam, works well especially if you try a lofty construction. Aerodynamic drag will be rising, but this solution is cheap, easy to construct and robust, thus for a experimental setup well suited.
If you want to have something more elaborated, why dont you try spring loaded skids, which in flight will be retracted in the centerbody. They could be released when approaching landing so that the spring will push out the skids, and also the spring would feather the impact shock. Much more complicated but much more elegant.
These are my thoughts on this...
The old primary gliders from the early days of gliders had skids and a man onboard, so must not have been such a shock or the guy would get ejected on landing. Every plane I've built has been a fiberglass belly lander with the only casualty being paint. Wing loading on my design is medium to light @10 oz/sq ft.