Originally Posted by
Volume
It is relatively simple maths, if you want to have the required thrust the engine will have such a large diameter, that the real challange will be designing the landing gear.
Actually, the main problem is the design of the low pressure turbine, as it needs to spin at the same rotational speed as the fan (which will be very low with such a large diameter). We have geared turbofans now, but not for those diameters and thrust levels (about 825 kN /185 klbf per engine, assuming a thrust to weight ratio of 0.3, which is higher than the current 0.25 with 4 engines due to the single engine inoperative climb requirements).