The MD-11 being stretched relative to the DC-10, it not only had a longer moment arm for the horizontal stabilizer, the MD-11 had a fuel tank in the horizontal stabilizer which the DC-10 did not have. The tail tank enabled fine tuning the CG inflight. This had two effects: it enabled reducing trim drag caused by the tail to increase range. It also meant there was a narrower CG range to deal with, so the stabilizer could be made smaller.
Last edited by KenV; 10th Nov 2014 at 14:30.