Which Formula One car besides the Tyrrell P34 was one of the most radical entries ever to succeed in F1 competition, that used flat panel heat exchangers? 
Tyrrell P34: The Tyrrell P34 (Project 34), commonly known as the "six-wheeler", was a Formula One (F1) race car designed by Derek Gardner, Tyrrell's chief designer. Tyrrell P34:  Along with the Brabham BT46B "fancar" developed in , the six-wheeled Tyrrell was one of the most radical entries ever to succeed in F1 competition, and has been called the most recognizable design in the history of world motorsports. Brabham BT46: The Brabham BT46 is a Formula One racing car designed by Gordon Murray for the Brabham team, owned by Bernie Ecclestone, for the 1978 Formula One season. Brabham BT46:  The car featured several radical design elements, one of which was the use of flat panel heat exchangers on the bodywork of the car to replace conventional water and oil radiators.
The Brabham BT46