Correct answer is... 4056 kg. It is equal to 8941 lbs. Empty weight of Boeing YB-9 is total weight of the airframe, engine, avionics and all other systems installed by manufacturer. It is higher weight then empty speed of other aircrafts of a similar size. Average is about 2568 kg (5661 lbs).
The biggest civil aircraft has empty weight of 250,000 kg (628,000 lb), so Boeing YB-9 has 2% percent of it's weight. Typical jet airliner has about 39,500 kg (87,100 lb), so in the comparision Boeing YB-9 has 10% of aircrafts like B737 or A320.
Disclaimer: Our articles and data connected to empty weight of Boeing YB-9 are based on public data from various sources. We are very picky to select an reliable data providers, but we cannot guarantee that everything is 100% error-proof. We recommend for any serious purpose - as a rule of thumb - to request offical data about empty weight from manufacturer of Boeing YB-9.