So far, none of his verticaltake-off and landing prototypes has risen much more than a few feet.
目前为止，他的任何一款垂直起降的原型机还没有离地超过几英尺。
2
However at current rates, it would take 4, 000 years before the tower is as slanted as the Leaning tower of Pisa which leans by four degrees and is around 12ft off the vertical.