I don't understand? "When towing Aerocarts, planes instantly double or triple their payload capacity. This is because their capacity is limited by the takeoff / landing weight – not what they can safely pull through the air." But later, on "How it works" section it is apparent that the main plane still has to tow the cart behind it when taking off. What's the trick that makes this work? Extra set of wings?
Yes, the wings of the glider provide lift that otherwise would not be present. The engines still need to produce more thrust to pull the glider but that's expected, the extra cargo doesn't come free.
That... kind of makes sense. But (the way I* see it) modern large aircraft aren't very overpowered (otherwise they would be less efficient), so their engine power is just a little bit above what's needed to get them into the air with a "usual" runway size in ~ the worst possible conditions ("hot & high"). Which means that they would need ~ double the runway length to take off with a glider in tow? So this works with the small aircraft they're currently testing with (they just have to use a longer runway), but if they want to extend it to larger cargo jets, they would risk exceeding the limitations of existing airport runways?
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* - someone who has an interest in aviation, but no professional background or training therein