Sleepybhudda,
The engines of the Dash and ATR are not offset, of that you are correct. Both engine are bolted equidistant from the fuselage. Although you could offset an engine such that a critical engine was effectively removed, that would create a spare parts and maintenance nightmare as things like fuel lines, bleed air lines, electrical cables, etc. would suddenly have to have left and right components to account for the differing lengths required.
Now, as I explained earlier, both Bombardier (Boeing and de Havilland before that) and ATR did add design considerations that assists pilots with critical engine loss control and makes it seem as though there is no critical engine. I speak to the Dash as I can converse intelligently about that plane having taught Ground School on all variants for over 10 years now, but the ATR is similar.
The fore rudder, on the classic Dash (100/200/300 and the applicable Q variants) is permitted to travel 16 degrees left and 18 degrees right; the extra two degrees allow for extra rudder input for a failure of the left engine (Note: fore rudder specifically as the trailing rudder is mechanically joined and, thus, not directly controlled by the pilot).
On the Q400 this difference was removed and the rudder is able to travel 18 degrees left and right and this was probably just to save system complexity and a small amount of weight in the Rudder Feel Trim and Summing Unit (about the only device Bombardier did not add an acronym for).
I should also note that this travel is permitted only with flaps extended (5 degrees or more). With flaps retracted (less than 5 degrees), both the Classic Dash and Q400 rudder is permitted to go 12 degrees left and right.
One has to ask what is easier when it comes to aircraft design; is it easier to change the whole mould of the aircraft to counteract an undersireable consequence of physics, or it is better to slap something onto the side of the airplane or make a control go a little bit further to do the same job?
Last edited by +TSRA; 31st Dec 2017 at 19:40.
Reason: Amended for P-Factor clarity. Previous version suggested you could get rid of P-Factor which is clearly false.