Lots of down votes on this but it is a legitimate question. The goal is likely to have the majority of flight off of batteries. That being said, the total weight of the emergency fuel plus generators is likely far less than the weight of the extra batteries they would haul around for the safety margin they need. So they end up lighter and more capable AND don't need to burn fuel. That being said, I wouldn't be surprised if they didn't start the generators during critical phases so they may end up using some fuel for a flight, but not much. Total guess on that though.
> That being said, I wouldn't be surprised if they didn't start the generators during critical phases
I somewhat doubt that. Part of the advantage of the design is that the generators don't need to be sized as big enough to power take off, climb and a potential go-around on landing. They only need to be sized as big enough for cruising.
So powering them up during critical phases wouldn't help with safety. If anything, normal operating procedures might actually require shutting them down during critical phases.
What this does mean is that the batteries need to be reasonably full when it comes into land, possibly as high as 50%. And most go arounds will require immediately powering up the generators, so it probably needs to be fuelled for all but the shortest flights.
> That being said, I wouldn't be surprised if they didn't start the generators during critical phases so they may end up using some fuel for a flight, but not much.
I would guess the opposite. Many parts in a turbine engine are "lifetime limited" by number of engine starts. That is, you are required to tear down the engine and replace certain parts after a certain number of engine cycles.
That makes the economics of the turbine hybrid radically different if you need to start it every time you land vs. only the rare cases where you need to dip into fuel reserves.
For example, the PT6A (a common 500-1000hp turboprop) requires the turbine and compressor disks to be replaced every 16,000 cycles. That's about 5 years of commercial service at 4x round trips per day. But if you only start the engine once in every 10 flights, now those components (theoretically) last for 50 years of flying.
> vs. only the rare cases where you need to dip into fuel reserves.
There aren't that many existing flight routes that will fit into the 125 mile range (though the existence of this plane might change that), so I suspect we will see most of these planes go into service on slightly longer routes. So they will probably still need one cycle per flight.
Though... The video isn't quite clear if the 125 miles is what they can fly without starting the turbines or if it's what they can fly without needing the turbines ready to act as an emergency reserve. I actually suspect it's the later and this aircraft can make it to 200+ miles without starting the turbines.
Where I live, there aren't that many 125 mile flights, but there are a lot of 200 mile fights.
I also suspect the turbines are sized so that only need to start one of the two turbines on most flights, which would extend lifetime a lot. Ideally the turbines would be sized so that one is enough for cruising, and with two you can actually charge the batteries after a go-around (enough to enable a second and third go-around)
