Correct answer is... 4.1 m/s It is equal to 800 ft/min. It is lower then climb speed of other aircrafts with similar size. Average is about 23.5 m/s or 4618 ft/min.
Climb speed is counted in km/h or mph units. It would not be handy for pilot to convert it from hours to lower values. So climb speed is often described as vertical distance per seconds or minutes. To give an example, Douglas DF with it's climb speed of 4.1 m/s that takes off from airfield of elevation 100 metres (300 feets) will reach flight level 100 (10,000 feets or 3 km above mean sea level) after about 12 minutes.
Disclaimer: Our articles and data connected to climb speed of Douglas DF 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 climb speed from manufacturer of Douglas DF.