27" as no relation to 27Mhz at all, manufacturers tend to make their antenna as short as possible for ease of installation,specially for car use and making the antenna longer don't make it better
in any way since there is others factors in effect:
http://www.rc-cam.com/ant_exp.htm
Range at ground level is always less than while flying so you can't expect to have the same range as a plane on any frequency band. The antenna position is also very important (Tx and Rx)because
of the signal pattern. The Rx antenna works best when vertical and the Tx antenna should not be pointed at the model since the signal strength is minimal in that direction.