> allowing for a plane which, during descent, could regenerate most of the energy used to make its ascent The Pipistrel aircraft do almost exactly this. They c

> allowing for a plane which, during descent, could regenerate most of the energy used to make its ascent The Pipistrel aircraft do almost exactly this. They claim about 10-15% energy recovery rate for thier regenerative systems. No need for variable pitch either; they simply windmill the main prop.