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. 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.
i don't know