Aircraft with their engines "underslung " have the advantage, normally, of more power tends to give a climb ( which may be compensated by the A/P). Looking at the traces of AF447, when power was reduced to Flight Idle briefly, the nose came down by a few degrees. (A/P was OFF) The aircraft may have been in an unrecognised stall at that time.
Even simple gliders tended to be wiinch launched from under the Pilot's seat . Or aerotowed from the nose. In each case this was to get the better performance.
Perhaps something like the 4 knots mentioned may apply to other aircraft with underslung engines, depending on where the engines are located in relation to the " Vertical C of G". (Usually one only considers the Fore and Aft C of G.)
LT
Last edited by Linktrained; 31st Aug 2015 at 18:24.