The Volocopter is in fact a Hexacopter where additionally every rotor is triple redundant (eighteen rotors total). Can’t wait to fly in one.
Bringing up coal power is a side issue here, but I want to note that coal-burning power plants are being retired left and right in the US and much of western Europe. And they’re not being replaced by new coal plants. By the time electric planes are ready for prime time (even if it’s just common use for short range regional flights), the coal thing will not be a significant factor.
The trouble with this is that propellers disturb airflow over the wing, reducing its efficiency. And note that a shorter wing tends to be less efficient.
When you ask a component to do two very different things (in this case, store lots of energy and have high tensile strength) it tends to be not especially good at either. You’re likely to do better by assigning the two jobs to two different components, each of which can be specialized. Maybe the two can play well together, like cylindrical battery cells mounted in stiff carbon-fiber tubes.
This feels like a way to take on significant complication and cost (both development and production) for at best small weight savings.
Right - but note that saving weight has much the same benefit for jet aircraft.
Pressurization will be an issue for any high-flying electric plane. Jet engines produce compressed air that can easily be bled off for this purpose; electric planes will need a separate powered system.
And note that at current cruise altitudes (< 40k '), passengers can survive depressurization with drop-down masks and a rapid descent. Much higher, that may not suffice; above 60k, passengers might have to wear oxygen masks.
Engine and battery cooling are also likely to be issues: air at high altitudes is cold, but also “thin”, so dissipating heat is a challenge. (Fighter jets cool their avionics by dumping heat into their fuel.)
For an airline to be financially successful, it must carry passengers at fairly high speeds. One reason is that passengers have come to expect this and will not accept travel plans that involve long times in the air and multi-day trips, as the perceived cost of the delays will be higher than any fare savings.
But the big reason is that the airlines know that money earned by an aircraft is directly related to passenger-miles per day. They want to operate reasonably large, reasonably fast, highly reliable aircraft to maximize this. A very important related factor is that a large and fast aircraft delivers more passenger-miles per crew salary dollar. Pilots are expensive (and currently in short supply) so there a strong motive to maximize passenger-miles per hour.
FWIW Boeing uses electric compressors for cabin pressure on the 787. Bleeding inlet air reduces engine efficiency, kind of like if your car’s engine had a leaky valve seat.
The small propellors along the wing of the X-57 will only run during takeoff and other maneuvers that require greater lift. During cruise, they’ll be shut down and the blades will fold back to reduce drag.
Even folded, they will affect airflow.
Maximum efficiency (as seen in sailplanes, with glide ratios that now reach 70:1) depends on extensive laminar flow *. Which itself depends on extremely smooth airflow over the wing.
I’ll note that this could to some extent be addressed by mounting the multiple motors aft of the wing - “pusher” configuration. But this of course is also where flight controls (ailerons and flaps) want to be.
*The profile drag of a sailplane wing with good laminar flow is roughly equal to that of a 1/8" wire of the same span.
Will these small motors plus a much narrower wing be better than a full-sized wing with no motors? Maybe, maybe not. That’s what NASA is going to test. Whichever one’s the best is what they’ll go with. It doesn’t have to be as good a glider in terms of drag, just be good enough.
At any rate, there is a market for a zero-emission airliner that could fly short to medium routes, even if it’s somewhat slower than jets. There’s people out there who would pay somewhat more for that, just as there were for the earliest EVs.
Got it. You’re hopeful, but can’t offer anything substantial. I admire your optimism, but hope is not a plan.
This is promising for STOL performance, definitely. But that’s not the same thing as cruising efficiency.
You can already do this with turbine engines. As others have mentioned, the 787 uses turbine-generated electricity to pressurize its cabin and for other functions that previously used bleed air. There’s no reason you couldn’t drive distributed props with turbine-generated electricity as well.
And the various winglet/blended tip designs are similarly efficient at reducing wingtip vortices. Again, none of this is unique to electric aircraft.
This has already been done for commercial aircraft—see the 787. And not everything is lighter when made from composites. Anisotropic materials only help when the stresses are anisotropic.
I can see why you might think this is a good idea, but it’s only a good idea if you don’t think about it too hard. You mention many small cylinders, noting that a cylinder is a stiff cross-section in bending. But consider that a rope is made up of many small cylinders, and that’s why a 10mm steel wire rope is so much more flexible than a 10mm steel rod.
No problem, you say? Just use much larger-diameter cells, you say? Well, it’s hard to keep those cells cool, and when you increase the cell diameter, their volume increases faster than their surface area, making them much harder to cool. And since liquid cooling is probably necessary, you’re now carrying more liquid to cool your larger battery (and with a larger heat exchanger, which increases drag).
And since your cells need to be surrounded by coolant, the structural loads will be borne by the cooling jacket, not the cells. (Material at the perimeter of a beam carries the load; I-beams drive all their material to where the load is).
Now you’re just throwing stuff at the wall.
That’s not how materials science works, unfortunately. And the incremental improvements we can expect from future materials will apply to turbine-powered planes as well.
It probably won’t make sense to fly that high. As others have pointed out, you’ll need a heavier fuselage to handle the pressurization. Also, planes at high altitude are generally on the verge of stalling even at their maximum speeds. Electric planes are best suited to short-hop flights, and those don’t get very high.
The tradeoffs involved here are a lot more complicated than you seem to understand. To wit:
Drag goes with the square of velocity, yes, but the term of interest here—the power required—increases with the cube of velocity.
Even so, very few air travelers want to spend more time in the sky; going slower is a non-starter for commercial aviation. And again, flying slower saves energy on any plane regardless of how its powered.
No, there isn’t. There are a handful of new terms with a smaller number of new tradeoffs. And all of the old tradeoffs are still there.
No, they don’t—at least not compared to aircraft in the same role. That the Boeing 737 and the Airbus A320 look a lot alike is a testament to their convergent evolution. The 787’s wingtips are an evolution of those on the 777, etc.
Why is that absurd? You seem to think there’s some ineffable quality to electric planes that makes them “just different” from combustion-powered planes. But they both fly in the same fluid; the most efficient shape is almost completely independent of the power source.
I’ve asked why you think that’s not true, and all you can say is “more research is needed.”
Sure; that’s what Wikipedia says about the X-57, but the thing has yet to fly. And that 5-fold improvement in “efficiency” could mean one of several different things depending on how they’re quantifying the improvement. And I strongly suspect that most of the real-world improvements the X-57 demonstrates will apply to IC and electric aircraft alike.
No, we certainly are not! But though the “factors” may be large, the absolute improvements are fairly small. Electric planes are coming, and they have an important role to play, but the economic and engineering challenges are a lot more complex than your posts suggest.
On competition sailplanes, they tape the canopy gap to prevent even that tiny bit of discontinuity from tripping the laminar flow. Flush riveting will speed up an airplane substantially.
Having a bunch of engines along the leading edge of the wing is not going to make it more efficient. What it MIGHT do is increase STOL capability by keeping the boundary layer attached to the wing at higher angles of attack. But that’s a high drag configuration import for bush planes to get out of tight places, but of limited utility for electric planes.
I took a look at the Eviation ALICE, which seems to be touted as the first commercial, passenger-carrying commuter aircraft.
Hold on to your money. This whole thing feels a bit scammy. For one thing, they are quoting crazy unrealistic times for certification. They haven’t even flown a prototype yet, and they are talking about deliveries to customers in 2022. Not.Going.To.Happen. The thing is a certification nightmare.
First, let me explain why other developers have not put engines out on the tips of the wings:
-
Putting that much mass at the end of the wings will make for some very interesting spin characteristics. They better have a good recovery chute on that thing when they do spin testing.
-
Putting your thrust out on the ends of the wings mean engine failures get extremely exciting. Basically, I suspect that the engine out procedure for either tip engine would be to shut down the other tip engine, and fly on the tail engine alone, which they say the thing can do. But there will have to be extensive testing around all this. The handling characteristics of a plane with two tip mounted engines and one in the tail will be interesting.
-
Tip mounted engines put a lot of stress on the wing roots - both bending stresses and stress from the thrust. You have to make the wing bigger and heavier to compensate, which tends to eliminate the wingtip-vortex gains from tip engines.
Speaking of wings - those are some tiny wings for such a large aircraft. I tried to find the stall speed of the thing, but they’re just saying “under 100 kts”. A King Air, its closest competitor, stalls at 75 in landing configuration.
In early 2019, as they were trying to secure 200 million in funding, they promised the prototype would be finished in a couple of months, and they planned to have FAA permission to fly the thing cross country before the Paris Air Show later that year. That didn’t happen, and now they’re saying that the prototype will flying ‘sometime in 2020’. They are quoting full certification in 24-36 months. This is a crazy timeline, and would represent the fastest certification of a production commercial-use airplane I can think of, let alone a radical one with an entire new power system. As a comparison, the Beech Starship, a similar plane, required six years from flying prototype to certified airplane. And it used completely conventional engines. Its big innovation was the composite fuselage and pusher configuration.
This thing reminds me of the Moller Skycar, the Aurora 500, the SoloTrek, Hyperloop, and other high-tech, ‘disrupting’ designs that appeal to silicon valley investors unfamiliar with aviation but used to disruption from new paradigm-breaking digital products. They seem especially interested in throwing money at impossible things that promise the moon.
Aviation doesn’t work that way. There are no huge gains to be had in efficiency of airframes. Almost every configuration you can think of has been tried. And no, a switch to electric doesn’t open up huge opportunities for massive improvements in aerodynamics. If anything, the need to have such a heavy propulsion system is going to make the aerodynamics worse (higher induced drag for the same payload, along with the need to carry full takeoff weight to landing).
Oh, those guys were also talking about having an aluminum-air battery version flying in 2022. That’s complete horseshit. Aluminum Air batteries are still in the development stage, and aren’t even ready for cars. They aren’t rechargeable, which means they’d have to be removed and swapped for new ones after every flight, requiring a wholly different design for battery storage. The FAA hasn’t even begun to think about how to certify these things for aviation use.
The battery numbers don’t seem to work out. Eviation is quoting a battery pack of 900 kWh weighing 3460 kg. That works out to 260 Wh/kg, which is the quoted rating for a Kokam battery CELL. Battery PACKS do not achieve anywhere near that - more like 160-190 Wh/kg because you need frames to hold the pouches, wiring, cooling and heating hardware, etc. If the cell weight alone is 3460 kg, the weight of the battery system is more likely to be closer to 4500 kg.
So… this thing seems to be over-hyped, with lots of cool CGI renderings, paintings, and mockups, while a prototype has not even flown yet. Now they’re saying the prototype will fly in 2020, and it will be certified shortly thereafter.
Maybe the thing will become real. But the Moller Skycar has been ‘months away’ from untethered flight for about 40 years now. The Solotrek and Aurora 500 vanished when no more suckers could be found to fund them. Hyperloop is at the stage where empty fiberglass shells of futuristic capsules are presented to raise funding, but none of the hard engineering problems have been addressed.
There’s no shortage of fanciful airplane designs that are just on the ragged edge of plausible. One in a hundred will become a real production aircraft, and when it does its specs will be nowhere near what was promised.
Look, I’d love for electric airplanes to be a thing. I’d love to have a flying car. A little electric sport plane to replace my Grumman AA1 would be a hoot. But as someone who has been following aviation development my entire life and even worked as a consultant in the industry, I know what it takes to build real-world airplanes, and now hard it is to eake out even tiny percentage improvements in efficiency. When someone comes along with a product that seems to break all the rules and promises efficiencies no one else has ever managed, I assume it’s never going to happen. And I’m almost always right. We’re still flying 60 year old airplane designs for a reason.
A shorter wing is less efficient for the same area, partly due to wingtip vortex losses. But they fix the vortex losses with wingtip motors. The short wing still doesn’t have an advantage due to wetted area, but the whole point here is to decrease area. That entails an increase in wing loading, which normally would have the side effect of increasing takeoff/landing speeds, but they want to fix that with the extra motors.
Maybe, maybe not. It’s not something you can say definitively before evaluating it. Hence the research.
One of the overarching points I’m trying to make here is that the actual value of the tradeoff is different, and so we should expect a different optimal point.
In any optimization problem, there’s a kind of “exchange rate” between different factors. You can spend $X to save one kilogram. And then you can spend that kilogram to get Y meters of extra range, or speed, or whatever.
All airplanes have the same generic basic qualities, so at a high level the “flow” of this exchange is going to be the same for all types. But the values in play are different. And so the final optimized machine will be different.
Yes, all this stuff will have to be thought through. I wonder if some of the differences can be handled with a change in certification requirements, though: better qualification of the fuselage against rapid depressurization, automated systems to handle the descent, and so on. And then maybe elimination of the masks and oxygen tanks and all that. Rapid depressurization accidents do not seem particularly common and maybe it’s time to reevaluate the requirements here if a new class of aircraft has different demands.
All true, but on the other hand there is a lot of air available at (relatively) high speed (but sub-mach, so nowhere close to what military jets have to deal with).
Yes, but again the current optimal point is set based on the current constraints, and it may not hold true when the constraints change.
A similar example is how container ships have essentially gotten slower over time. Lots of ships are now running at <20 knots instead of >25.
They are subject to all the same basic constraints as airlines: they have a crew which is paid by the day, an enormous capital expense for the ship itself, and customers which want their cargo as soon as possible. So what changed? Well, the teams of people at the shipping company that work to optimize this stuff would have a better idea, but ultimately it’s going to come to some change in the constraints, like the cost of fuel.
I can’t solve this optimization problem right here, but I can confidently say that the final answers are going to be different even when the qualitative factors are the same.
Here’s some literature on improved aerodynamics of electric aircraft:
10.2514/6.2014-2851
10.2514/6.2018-1652
This is research. You’re making unreasonable demands: you can’t make concrete declarations of how things will be before they’re actually developed. Lots of this stuff won’t pan out, but some of it will.
Yes, it is. STOL perf can be exchanged against wing area. And decreased wing area increases cruise efficiency.
Except that turbine craft can’t put engines at the tips, which should have a much more substantial effect than winglets and the like.
Well, I guess a turbine craft could use a driveshaft to move the power elsewhere, but no one seems to be doing that (except for redundancy reasons).
A wire rope isn’t stiff because the individual strands can slide against each other. But that’s the nature of a rope. The cell cylinders could be coupled to each other along their length to prevent their relative motion.
At a high level, it’s a kind of low-density metamaterial. The exact nature of the cross-bracing and the like will depend on the forces it’s subject to, but in general low-density materials have good stiffness, and you can design in exactly the kind of anisotropy you want.
I’m not. NASA is already looking into superconducting motors for aircraft. Others are looking specifically into the combination of superconductors and the cryogenic H2/fuel cell concept. There’s plenty of other research all over the place.
I suppose I’ll have to repeat myself on this point forever, but just because two things have the same qualitative benefits, it does not mean they will converge on the same two optimal solutions. Spending $X to save 1 kg may be worth it on an electric plane but not worth it on a hydrocarbon plane.
Frankly, it seems the exact opposite to me. There’s nigh-infinite dimensional optimization problem here, almost completely uncharted because the basic technology hasn’t been anywhere close to ready until recently. And you’re essentially claiming that basic research is borderline wishful thinking because airplanes aren’t already doing that stuff.
Commercial craft aren’t anywhere close to the most efficient shape, as can already be seen by the numerous other aircraft that are already more efficient. Commercial craft hit a good balance between speed, passengers, efficiency, capital cost, maintenance cost, fuel cost, and a zillion other factors. You can’t simply optimize for one of these factors while ignoring the others, because they’re all interrelated.
No shit. More research is needed.
Let’s suppose that were true (it’s not, because you need an electric drive for the many-prop design they’re going for, but let’s ignore that). Then we have an electric plane that can go perhaps a couple thousand miles and a hydrocarbon plane that can go around the world.
Great; we can then stop using hydrocarbon planes for short-medium routes, because even though they got more efficient, they’re still emitting huge amounts of CO2 while the nuclear/hydro/solar/wing powered electric is not. We can keep using the hydrocarbon planes for intercontinental routes (or use fuel cells, etc.).
The motor doesn’t need air, but the propellor does and so does the wing. At high altitudes, lack of air density requires higher speeds to avoid stalling (stall speed goes up), meanwhile the speed of sound is slower so the usable speed band between too slow and too fast gets narrow (coffin corner). This already happens on jet airliners well below their nominal maximum altitude when heavy.
Induced drag decreases with speed while parasitic drag increases with speed. together they make up total drag and if you plot that on a graph with x = speed and y = drag you will find it is U shaped with minimum total drag at the bottom of the U. This speed is the most fuel efficient (whether the fuel is kerosene or battery charge doesn’t matter) but it is not necessarily the best speed to fly.
Min drag speed is quite slow, and not very stable. If you get slower than min drag, the drag increases which slows you down further. You need more thrust to get back on speed. If you fly faster than min drag then the speed is stable. If the speed increases due to external factors, the drag increases which will tend to return the speed to where it was. If the speed decreases, the drag decreases and the speed will increase again, all without having to change thrust.
The best speed to fly is a trade off between the aircraft’s hourly costs such as hourly maintenance, crew wages, etc and the aircraft’s fuel/charge cost. Having an aircraft that absolutely must fly at the min drag speed in order to be able to stretch the range from the available fuel or battery charge, is not a good thing.
No, but they are very close to the most efficient shape for a commercial aircraft. What makes you think the speed/passenger/efficiency/cost balance will be different if the engines are changed?
As a very simple example, the Harbour Air CEO says this about their Beaver conversion:
If nothing else changed other than this (and assuming similar overhaul costs), then the optimal speed would go down. Because whatever the previous optimal speed was, it was selected as the balance where the (rate of) decrease in running cost equals the increase in passenger income. If you decrease the running cost, then the minimum between the two also necessarily goes down.
Of course that’s not the only parameter that’s changed. “Fuel” cost goes down with electric, and that’s going to apply upward pressure to the speed. If fuel were free, airlines would go as fast as the airframe reasonably allowed (unless there were some non-linear maintenance cost). Fuel isn’t free, so they go slower, and for intermediate values they’d go somewhere in between.
But on the other other hand, going faster decreases the range, which closes off certain routes. Well, you can go fast on the short routes and slow on the longer ones. But there’s the recharge time to consider, which shouldn’t be an impact on the crew (since they can fly a different plane), but is still a cost in that every minute a plane isn’t flying is a minute that the capital cost of the plane isn’t being repaid. More joules for a given length route means a longer recharge time.
These are just a few trivial observations, but even at that it’s clear that you aren’t going to converge on the same optimal speed except by coincidence.
Richard Pearse, I’m curious about something.
It looks like the busiest domestic corridor in Australia would be the Melbourne to Sydney run* - a distance of 713km, according to this site.
What sort of available range would you feel comfortable with, if you were flying that route?
Another thing that comes to mind, while I’m thinking about it: eliminate the vertical stabilizer.
Of course, craft without a tail or rudder already exist, but carry some disadvantages relating to how they achieve stability. Commercial craft haven’t yet gone this route.
Electrics offer another method of achieving stability. Due to the ease of having lots of engines, as well as their fast response time, you can use differential thrust to control yaw.
Because you can have lots of motors, you don’t have to worry about what happens when a handful of motors fail. You can even retain control in case of complete loss of battery power by using the props on one side as generators and routing power to the other side. You can balance torque by balancing thrust/drag between more inboard vs. outboard ones.
Let’s be clear - wingtip vortices do not cause induced drag. Wingtip vortices are the *result of induced drag. The reason they hurt performance is because they prevent the last few feet of wing from being effective lifting surfaces. On a long wing, the area affected by the vortices is lower in proportion to the rest of the wing, which is why shorter wings have a bigger problem with vortices.
In fact, the main reason for winglets is to increase the effective span of the wing without making the wing actually longer. But if you simply extended the wing by the length of the winglets you could achieve the same thing.
It’s not clear to me at all that putting those engines on the end of the wing are going to help efficiency at all. It remains to be seen how propwash will affect the flow over the wing at the tips. It also remains to be seen if the intersection drag of those nacelles negates some of the gain, and whether the reduction in induced drag losses will make up for the increased induced drag required by having a heavier wing structure.
In any event, we’re talking about a few percentage points of efficiency, maybe. Nothing radical. And maybe nothing at all.
The extra motors add weight and complexity. A smaller, highly loaded wing pushes around with high power is not really an efficient way to go. And it means high stall speeds, long takeoff runs, and longer climbs at higher power.
Long thin wings really pay off at very high altitudes. But you pay a price for them at takeoff and landing. As with everything else in Aviation, it’s all a series of tradeoffs. You think you’re gaining efficiency with a high wing loading, then you discover that you need stronger gear for the higher landing speeds and you have to spend more time in climb, and suddenly those theoretical performance gains go away.
We have been optimizing aircraft for a long, long time. There really isn’t any low-hanging fruit left. Performance gains can be had at the margin, or by sacrificing one quality for another. You can make a more efficient passenger jet by getting rid of 1st class, by taking away head and legroom, increasing runway requirements, etc. But all of these bring other tradeoffs. My little Grumman could fly 15kts faster than an equivalent Cessna 150 and much better handling, due to a shorter wing, slightly lower weight, and a higher wing loading. But that gave it worse climb, worse stall characteristics, and the glide capability of a homesick brick. TANSTAAFL applied to aviation: There’s no such thing as free speed or free anything else. Every change you make to improve one factor hurts another.
Take that Eviation plane. Putting the props out on the tips of the wings may help suppress wingtip vortices and improve wing efficiency slightly. But then it requires a third engine in the tail, which again increases weight, complexity and cost. Is that better than having two engines slung underneath the wing in a normal position? I don’t know, but I’ll bet when you add it all up the gains are not all that great, if there are any at all.
Also, putting a prop in the tail means it has to be a small prop which may not be optimally efficient, and it also means you probably need a tailwheel and retract mechanism to prevent smacking the prop on the ground during rotation. Then you have the problem that it’s a real bitch to cool engines mounted in the back of the fuselage, so now you need to add scoops to the airplane, which is another source of drag.
You seem to think that putting engines out on the wingtips just wasn’t possible until we had electric planes, and that huge benefits can be gained from doing it. But the Eviation’s closest competitor, the Beechcraft King Air, uses PT-6 turbines that only weigh about 300 lbs, and put out 500 hp each. The electric motors in the wings of the Eviation Alice are Siemens SP260’s, which make about 350 HP and weigh about 110 lbs. But there are conventional turbine engines in that power range that are not much heavier. The Rolls-Royce RR500 can put out 480 HP for takeoff and run continuously at 400HP. It only weighs 225 lbs.
So you might ask yourself why no one else (other than the VTOL Osprey and the old ‘Flying Flapjack’ test plane), has ever built an airplane with the engines out at the tips of the wings. What you’re gaining in wing efficiency (maybe a few percent) generally isn’t worth the problems with handling, spin recovery, engine failure procedures, and the need for a third engine because you can’t fly with one engine out if the other is at the tip of the wing. Maybe by the time you add all that up together, putting engines at the ends of the wing turns out to be a stupid idea.
Sure. But you should also expect that tradeoff change to make a relatively small difference in the specification you are trying to improve. Moving to electric power doesn’t change any of the fundamental characteristics of an airplane. The batteries actually make it heavier, and weight is a killer of pretty much every other specification in an airplane. Climb performance, cruise performance, landing and takeoff distance, useful load, service ceiling, all get worse when you add weight to the plane. You’re going to have to do some pretty fancy optimization to remove the weight penalty of a 4500 kilo battery.
It’s rarely a question of spending. You can’t just throw money at something and expect improvements. It’s actually about trading off different flying characteristics (worse climb for faster cruise, more range for less useful load, shorter takeoff for less range and payload, etc). Aircraft today are optimized for the mix of characteristics they need. There’s no magic expensive material that can make an airplane substantially better in one metric without hurting others.
Take again the Beech Starship. On paper, it looked super efficient. And the design specs showed it. It was going to be faster, cheaper, and more efficient than the King Air. But by the time it was certified and real-world manufacturing limitations made themselves known, the Starship for all its radicalness wasn’t really any better than the competition. That’s ultimately why it failed in the market. All that money spent on a futuristic, highly optimized design fell apart when the design met the real world and had to be modified. $300 million spent on this ‘futuristic’ plane, and in the end a Piper Cheyenne turboprop was faster, and cost $1 million less.
Finding improvements in aviation is very hard.
More handwaving. You don’t think the major airlines who live under these regulations have thought of that? The regulation has to do with the fact that above 50,000 ft the time of useful consciousness in the case of rapid decompression is less than 5 seconds - not enough time to get an oxygen mask on. That’s why pilots who fly that high are required to wear masks at all times.
These regulations are in place because there have been serious fatal crashes caused by pilot incapacitation due to oxygen loss. A 737 crashed and killed all onboard after the pilots blacked out due to lack of oxygen. Golfer Payne Stewart died when the small jet he was in had a slow oxygen pressurization failure that knocked out everyone inside the plane. The plane cruised on autopilot until it ran out of fuel, then crashed and killed everyone aboard.
So why wouldn’t the airlines do that now? or the bizjet makers? They’d love to save on the cost and weight of a supplementary oxygen system, and it would make their planes more efficient. Apparently, it’s not as easy as you think.
Can you quantify any of that? Which constraints, how will we get rid of them, and what benefits will we gain? If you can’t specifically point to areas of major improvement based on real numbers, then you could use the “we will just change the constraints” argument to justify anything.
Or, they simply lowered the speed to save money, because international shipping has become incredibly competitive and efficient. It could even just be that the increase in cargo sizes in these ships just changed the calculation for optimum speed.
None of this has anything to do with what we’re talking about. Airlines already fly at less than maximum speed to save money. The question is whether we can find a design that will be vastly more efficient without seriously degrading other necessary specifications.
Which qualitative factors?
You’ve *almost *gotten it. Now just apply that same logic to airplanes…
Where have I said it’s easy? Aerospace is, above all, highly conservative, and for good reasons. But the very fact that it’s conservative is evidence that there are yet improvements to be made.
As for this specifically, it’s probably for the same kind of reason why we are only now seeing a serious effort to eliminate side-view mirrors on cars in favor of cameras. ICE cars see an efficiency boost as well, but fractionally it’s not as important. Now, with EVs, it matters more, partly because aero efficiency is more important and partly because each mile of range you add saves at least $50 (since batteries are expensive). Those same tradeoffs weren’t there with ICE cars.
Same kind of thing here (perhaps). Once you change the exchange rate, you can expect previously unimportant things to suddenly become important.