A simple dipole will do what you want. That is a lot of power in the
airborne TX. 400 mw is still over kill and 40 mw will probably do the
job. At some point you will need to regain control with conventional
RC equipment and getting a signal into the airplane with that much
radiated power may not be easy.

If you are short on the RC airplane experience I suggest you consider
a Telemaster from Hobby Lobby. Smaller versions are available for
experience and the Senior (8 foot span) with carry many pounds of pay
load.

What you are considering is called an RPV and is a hot item in
military use now days.
John Ferrell W8CCW

On Sat, 03 Dec 2005 01:06:53 -0600, Chris W wrote:

Does anyone know of a good design for a reasonably high gain
bidirectional antenna for a 440mhz video TX? I am putting a 4 watt A/V
TX in an RC plane that will fly on auto pilot directly away from the RX,
make a 180 degree turn and fly directly back. So to get the best range
I was thinking some kind of bidirectional yagi. Depending on element
spacing and how big of a plane I get, I can probably only have 3
elements maybe 5.
John Ferrell W8CCW