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slowslownotbad t1_j5hqh5d wrote

Reply to comment by ObituaryPegasus 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

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.

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deathdragan t1_j5hrehh wrote

I believe this is what u/slowslownotbad was referring to in their previous comment when they spoke on the 30% efficiency decrease

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ALittleSnooInMyPoo t1_j5i9umz wrote

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?

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slowslownotbad t1_j5ipzcr wrote

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.

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MadTrapper84 t1_j5ihm98 wrote

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.

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