Correct answer is... 998 kg. It is equal to 2200 lbs. Empty weight of Stewart S-51D Mustang 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 286 kg (631 lbs).
The biggest civil aircraft has empty weight of 250,000 kg (628,000 lb), so Stewart S-51D Mustang has 0% percent of it's weight. Typical jet airliner has about 39,500 kg (87,100 lb), so in the comparision Stewart S-51D Mustang has 3% of aircrafts like B737 or A320.
Disclaimer: Our articles and data connected to empty weight of Stewart S-51D Mustang 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 Stewart S-51D Mustang.