YB-9: The first US bomber to use an all-metal airframe, Boeing's YB-9 was an offshoot of the company's Monomail mail plane of 1930. This successfully used stressed-skin construction, and spurred the private venture Model 214 and 215 bomber prototypes, powered by Curtiss G1V and P&W Hornet engines, respectively. Given the military designations YB-9 and Y1B-9, these modern machines proved far superior to existing biplane bombers, being capable of hauling a ton of bombs while outrunning pursuit aircraft. However, despite these capabilities, series production would be limited to five Y1B-9As, as the USAAC opted to buy the Douglas B-18.
Build article on a YB-9 RC foamy
Boeing B-9 for FSX