RE: Whip Antenna
Shaun, you should have swapped receivers and did the same test again. I would think that the one receiver was off tune in th right direction to work well with the Dean's and/or perhaps the other was off tune for the string. Other possibility is as above: the plane had some source of RF in it that was killing the string, but the base loaded whip was in cleaner space. In that case, a full length whip would have been even better.
One thing is for sure: if the radios worked better with base loaded whips than strings, the manufacturers would sell them that way so they could brag how much better the range was.