What aircraft type has the greatest weathervaning tendency when taxiing in a direct crosswind?

The aircraft type that has the greatest weathervaning tendency when taxiing in a direct crosswind is the tailwheel-type airplane. This is primarily due to the design and center of gravity positioning of such aircraft.

In tailwheel airplanes, the main wheels are located toward the front of the aircraft while the tailwheel is at the rear. This configuration causes these planes to have a higher moment arm when subjected to side wind forces. As the crosswind pushes against the aircraft, the nose tends to turn into the wind, enhancing the weathervaning effect. This tendency can make it more challenging to maintain control during taxiing in windy conditions.

In contrast, tricycle gear type airplanes have their center of gravity further forward of the main gear, which aids in keeping the nose pointed into the wind and reduces the weathervaning effect. Helicopters and floater-type aircraft (like some seaplanes) have different dynamics, primarily not relying on ground steering in the same manner, and are generally less affected by crosswinds when taxiing on solid ground.

Therefore, the design characteristics of the tailwheel-type airplane make it the most susceptible to weathervaning in a crosswind situation while taxiing.