52049er is more or less right. The stabilizer area was reduced by one 3rd compared to the DC-10. It was assumed by the MDC engineers that the longer arm of the longer fuselage would compensate the stability loss. Unfortunately, once more the engineers got it wrong. Flight tests revealed an unstable aircraft in pitch. No problem, just put a bunch of computers and everything will be sorted out
On the MD-11 they are called LSAS, longitudinal stability augmentation system.
Just a few tech infos, the MD-11 now carries fuel in the stab for C.G. adjustment. Also the elevators have slots in front of them that open when the elevators are activated.
Now, is the MD-11 less stable? YES
Afraid? Well, no