But all these concepts are massively expensive, require safety certification standards for road and air, need dual controls, involve complex folding wings and propellers, and have to be flown from air-strips.

但是所有这些概念都成本高昂，要求路面与空中的安全鉴定标准，需要双重控制，涉及复杂的折叠机翼和推进器，而且必须从飞机跑道起飞。