Correct answer is... 21 m. It is equal to 67 ft. Larger aircraft length is often connected to higher passangers or cargo capacity of an aircraft. The longest civil aircraft is 84 m (275 ft) long, so Dornier Do 31 has 24% percent of it's length. Typical jet airliners has about 35m, so in the comparision Dornier Do 31 has 24% of aircrafts like B737 or A320.
Disclaimer: Our articles and data connected to length of Dornier Do 31 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 length from manufacturer of Dornier Do 31.