Originally Posted by
Takwis
Boeing has already done that trick, back in 1984. When replacing the underslung JT-8Ds with the new CFM-56s, they had to push them out front (canard style), and then, yes, had to put a hefty strake on the side of the engine, to direct airflow where it needed to go. The engines got bigger at the NG stage, and the strake got a little bigger, too. I suspect there is a limit to how much you can do with that same solution...and the MAX (aptly named, for a number of reasons) reached, or passed, that limit. Hence the MCAS. I rather like PEI_3721's, solution, in that, at least it would be better than MCAS!
I still believe that one can still build a 707 type airplane, with cables, and pulleys, and servo tabs and balance bays...clean it up with more modern aerodynamics, new engines (only two of them, alas), stick 'em under the wings for nostalgia's sake (sorry PEI), and have it behave more predictably, more safely, more comfortably, more intuitively than an electric jet. But then, I'm getting close to retirement, and so are my ideas.
Tak, that's NOT why the strake is there, The reason for the strake is engine out approach - basically if the engine is not running, at higher angles of attack all that airflow spilling out of the inlet can cause flow separation on the wing - the strake acts as a big vortex generator to re-energize the flow and keep it attached over the wing. That's why you'll see strakes on the inboard side of the nacelles of most wing mounted big turbofan engines. Not to say they may not help in the way you're suggesting, but that's not why we put them there.
As for the engines being hung below the wings instead of out front - there are two main reasons for that unrelated to ground clearance (granted, the MAX is a pretty extreme case due to ground clearance). One is rotorburst - sticking the engine out front limits the amount of wing (and associated systems) that are exposed to damage due to a rotorburst. The other is that it's aerodynamically better - if the engine is too close to the wing, at cruise speeds and power settings you get interference drag due to the interaction of the fan flow with the free stream airflow. The drag penalty can be substantial - as much as 2% fuel burn. On the 747-8, they couldn't mount the engines as far forward as they wanted due to flutter issues and had to pay a not insignificant drag penalty as a result.