Submitted by lughnasadh t3_10iq1ok in Futurology
Reply to comment by slowslownotbad in Seattle-based Jetoptera is developing a vertical takeoff aircraft that can travel at almost 1,000 km/h with a radically simplified new type of engine. With almost no moving parts, it uses super-compressed air to create vortexes for thrust. by lughnasadh
Most aircraft don't have the space for more fuel tanks to carry 30% more fuel so there's a big issue with that right off the bat. Also that increases the weight of the aircraft, not just from the fuel itself as the airframe will have to be strengthened to carry the extra weight. Weight is by far the most important limiting factor when it comes to range so if youre looking to fly very far at all. Carrying 30% more fuel is a huge issue for most types of aircraft and is not gonna cut it.
Have you done ATPL flight planning? Most commercial jets operate economically on routes that are much shorter than their max range.
Plenty of 787s are doing NY-LAX.
I believe this is what u/slowslownotbad was referring to in their previous comment when they spoke on the 30% efficiency decrease
Isn't that also because the pilots have to have surplus fuel for their alternate landings as well as possible holding patterns due to emergencies or priority changes?
Yeah, alternate fuel stuff seems complicated but it's basically a scenario-based planning exercise. Like, I'm gonna do a long overwater flight to a remote destination, so I need gas for depressurization or single engine failure or weather holding/divert. I'm legally required to carry gas for certain things at certain times, and I can add extra if I want to. But I need to plan to arrive at a low enough fuel state that I can land below maximum landing weight.
That last point is gonna be most limiting for ammonia fuel in certain missions; because NH3 is less energy dense, it will require pilots to routinely land with a greater fuel load of unburned contingency gas. This will cut into usable payload.
So it's not a perfect solution, but it's got tonnes of promise.
Not a pilot, but yes they do take extra fuel. I believe it's like 5% of the trip total as extra for taxiing and weather reroutes, plus enough to get to an alternate airport if your destination is not viable. Plus aircraft carry an emergency reserve of 30 minutes worth of flight time. If you break into that last bit, you're likely declaring an emergency and ATC will give you priority sequencing to land.
You want to have enough for safety and wiggle room, but not just full to the brim as that's a lot of extra weight to carry around, which means you burn through fuel faster.
You're assuming that aircraft are already filled up to max, and thus would need extra tanks and being reinforced to hold them, etc.
That's just a wrong assumption though.
Take most any flight within Europe, or even coast to coast US like JFK to LAX as u/slowslownotbad mentioned. These flights run a couple hours, 5 tops, right?
Now let's look at an aircraft like the 737-800. It burns ~5,000 lb of fuel per hour, with a max capacity of 46,000+ lb. A 5hr flight would burn 25,000 lb of fuel. You take enough fuel onboard to get to the destination, plus an extra amount in reserve (startup, taxiing, weather diversions, holding pattern at destination), and then enough beyond that to get to an alternate airport if you can't make the planned destination.
For the sake of argument, let's say that added up to 30,000 lb. That still leaves 16,000 lb empty on the longest continental flight. That right there is beyond the 30% increase we are talking, so it's not crazy to think that airlines could switch over to a greener fuel on flights under certain distances. They'd have the capacity.
I'm not arguing the rationale that there are plenty of routes where this is possible. What I'm saying is that there is a huge penalty in the max range of the aircraft, and that makes them much less versatile, limits their route options, and are much less attractive to airlines. You're much more likely to see alternative fuels such as compressed hydrogen used (Rolls-Royce has already run an engine on hydrogen) than you are to see something used that would result in such a huge range penalty.
But even if airlines were to transition over just their short haul flights, that would make a huge difference in terms of fuel/emission savings. It doesn't have to be all or nothing.
When I worked in ATC I learned that airlines (here in Canada, at least) drafted up 3 flight plan proposals for each flight. One was the shortest time, one was the most fuel efficient routing, and one was the cheapest (considering fuel and ATC charges for how many sectors you cross, etc).
I'm sure it wouldn't be hard to factor in alternative fuels when making those calculations.
To add to my previous comment, taking the 787 Dreamliner that someone else had mentioned, you're talking a max capacity of 223,000 lb, and maybe 10,000 lb an hour. Flying JFK to LAX is a joke with that capacity. Definitely room for a less dense fuel in those tanks.
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