That has always seemed like a kludged design to me.
Why not have a lightweight aerodynamic shell with wings that the car pulls into from behind like going up the rear ramp of a cargo plane ? Closed up it would be fully aero unlike the clamp-on wing-prop assembly in this photo.
The rear wheels of the car could ride on a roller system to transfer the power of the car’s drive train to props on the wings, while pads under the front wheels transfer steering impetus to the rudders. Then you just need to control elevation and you’re all set.
Of course, running most car engines continuously at the power level required for flight would be beyond most cars.