Due to the extensive engineering required for the new aircraft, the initial order comprised two prototypes of the XB-35, with an additional plan by Northrop to construct two smaller all-wood models known as the Northrop N-9M (M for model). These scaled models served to evaluate performance and stability, essential for the Flying Wing design. Notably, Jack Northrop enlisted the expertise of Theodore von Kármán, a prominent aeronautical designer of the time, on a part-time basis. Von Kármán endorsed Northrop's initial design and spearheaded the tooling for prototype construction, as elaborated in "Goodbye Beautiful Wing" by Terrence O'Neill (citation needed). The N-9Ms doubled as flight trainers, crucial for familiarizing pilots with the unconventional all-wing configuration.
In early 1942, intensive design efforts commenced on the XB-35. Diverging from traditional aircraft, which rely on rudders for lateral control, the Flying Wing design necessitated an innovative solution. Consequently, clamshell-like split flaps, termed "flaperons" (a fusion of flap and aileron), were integrated into the wingtips. Operating in unison with aileron control, these flaperons were manipulated to adjust the aircraft's roll. Additionally, for yaw control, one side's flaperons would open both upward and downward, inducing drag and steering the aircraft. Manipulating both rudder pedals would activate both sets of flaperons simultaneously, allowing for precise adjustment of airspeed or glide angle.
I saw one of the N-9Ms fly at an air show at Point Mugu. I believe that it was from the Chino Air Museum.
Northrop N-9M - Wikipedia
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