I used to work in a patent office. Over several months I probably saw several thousand patent applications (usually for about a minute each; my job description was pretty narrow so that's just how it worked out). It's fairly commonplace for some big companies to file for a patent for nearly every single specific, narrow, new idea they get (including new ways of using something that already exists), especially if somebody else can easily copy that idea. Multiply that by a lot of ideas... You oughtta see some of the different schemes out there for getting oil out of the ground!
It looks like they're trying to patent the idea of using six separate and independent engines for improved survivability and wider center-of-gravity range. The language about prop/jet engines is probably fluff to discourage anybody else from laying claim to the idea of a six engined tilt-jet.
Remember, the Wright brothers didn't simply patent the "airplane;" the key to their patent for an airplane was their way of controlling an airplane. They took that approach because they believed that it was the key to their having successfully invented an airplane that actually worked. In particular, they patented wing warping for roll (elevators and rudders were already common knowledge but they were one of the first to figure out roll control). Then Glenn Curtis invented the aileron and they fought about it in court for the next decade...
I can't patent using bolts to hold a wheel on a hub because that's already been invented. I can't patent using 3, 4, 5, or 6 bolts just in case one falls off because everybody already does that too. I could try to patent putting the bolts in backwards, but that might be hard to defend because it's not really much different and besides, there is probably a record of somebody already trying it a long time ago. I could patent drilling the bolt holes on a 45 degree angle as if that will somehow do a better job of holding the wheel on (even if it might actually not) or somehow make a mechanic's job easier to unscrew the bolts. I could also pad my application by saying "and oh, by the way, this includes 30-60 degrees, any number of bolts from 3-6 or more, aluminum bolts, titanium bolts, lemon bolts, bolt kebabs..."
By the way, whether or not an something has technical merit isn't a show stopper per se as to a whether or not it gets successfully approved. Holding up in court in the future is a separate issue too. Either way, it's often cheaper to just file for the patent.
Edit: What Brett said.
