I've been looking and looking for 2way Airborne radio in WWI... All I can find is a "spark transmitter" for morse, which was 1way only, Air>Ground, short ranged and line of sight.. Ground to air comms was by colored panels layed out on the ground.. Arty spotting was usually done by balloonists with a hardwired field phone, connected directly to the batteries...
I'll keep looking tho..
RC