 FACT: During and at the end of the race between Doug and Notcher,  the Cessna 150/152s flaps are extended. Flaps increase drag and  would be used to slow the aircraft. It is implied that Doug is  flying at maximum speed to try and beat the motorcycle to the finish  line. This couldnt be done with flaps extended. It is an obvious  production necessity to make it appear that the race is close.  Otherwise the Cessna would easily leave the motorcycle behind.