macdoc
Philosopher
Given the limited range of EV batteries for planes....using ground power for take off is no stretch and we have millions of vehicles ( trains, trolleys etc ) that derive motive power in motion from stationary source.
Electric Planes
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Given the limited range of EV batteries for planes....using ground power for take off is no stretch and we have millions of vehicles ( trains, trolleys etc ) that derive motive power in motion from stationary source.
Ziggurat
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Yes, they are. You're comparing across different wing designs, each of which may have a different lift to drag ratio, but that's not the relevant comparison. The relevant comparison is different lifts and drags within the same wing design.
Lift isn't a fixed value for a given wing, it depends on multiple factors including both speed and attack angle. As weight changes from burning off fuel, you have to drop lift or you wouldn't stay at the same altitude. How do you do that? Increasing speed or attack angle to increase lift both increases drag, and decreasing either reduces drag. To get more lift out of a given wing, you need to produce more drag. Better wing designs can reduce the drag you get, but they don't change the fact that lift necessarily produces drag. There is no avoiding that with winged flight. Weight decreases efficiency even in level flight. That's never going to change.
macdoc
Philosopher
EV aircraft engines have a very different thrust curve than ICE
lobosrul5
Philosopher
https://en.wikipedia.org/wiki/Thrust_curve
I'm not sure thats relevant to this discussion. At least not how you think it is. The thrust curve of an ICE airplane increases as fuel is burned off. An EV's doesn't.
Ziggurat
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Trolleys use continuous power input, not for just a tiny segment of their journey. The energy required for takeoff is an insignificant fraction of the total energy of the flight. It would be like keeping your electric car plugged in as you pull out of the driveway and only disconnecting as you enter the street. It's not worth doing for the energy saving.
lobosrul5
Philosopher
However, motors more powerful than is needed for cruising, are needed for takeoff. There could be some weight saving by using a JATO system for EV planes... but that seems a bit far-fetched for a small civilian aircraft.
theprestige
Penultimate Amazing
How much catapult would you need, to throw the extra weight of an electric plane into the air?
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I feel like xkcd's economic argument is relevant here.
Obviously staging is a solution to some flight problems. And once you've figured that out, leaving the first stage or main stage on the ground seems like an obvious perfection of the scheme.
And some launch systems do indeed make use of a "ground stage". Artillery, for example. Aircraft carriers. But these are high-acceleration, "short throw" stages. And they have limits. Ground-staged flights to LEO never took off, so to speak. Still haven't taken off.
The challenge seems to be that your ground stage ends up being very long, to provide enough acceleration to get your payload where you want, without jellying and/or dusting the payload. Naval fighters and their pilots are heavily optimized for the sudden shock of a catapult launch. They are also give up efficiency for expedience. Try to catapult-launch a 787 full of regular people and their regular luggage, and you'd need miles and miles of runway.
The commercial airline industry runs on tight margins and maximal efficiency. If catapult runways were the solution, I think they'd have switched over already. And while we woudn't expect ULA to ever innovate for efficiency and lower costs, even SpaceX didn't try to eat ULA's lunch by developing ground-stage to LEO. They saw a much better opportunity in developing a reusable first stage.
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theprestige
Penultimate Amazing
How about a drone with ICE engines and wings optimized for takeoff, that clips on top of an electric airliner optimized for efficient cruising? The drone helps the airliner get off the ground in a reasonable distance at a reasonable acceleration, then detaches and circles back to the airport to pick up its next client.
Or would it be the other way around? Either way, why not that?
Or would it be the other way around? Either way, why not that?
lobosrul5
Philosopher
I think catapults would be cheaper and safer than that myself. The USN has perfected electric catapults if I'm not mistaken. The G-load over a 10,000 foot or longer runway would be acceptable I think.
Now that I think about it though, how would they retrofit existing, busy airports? You gonna take down a runway at SFO for a year?!
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macdoc
Philosopher
"For a single wing design" ......in other words it is not linked - the idea is to decouple drag by improving wing efficiency..... except on takeoff, weight gets less and less a factor as aerodynamic efficiency improves.
macdoc
Philosopher
You are applying ICE limitations conditions to EV limitations.
I some respects those using launch aircraft to get up high enough before using rockets is an intermediate step.
Ziggurat
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You always need engines powerful enough for takeoff. Cruise and land isn't enough. First off, climbing while accelerating after takeoff take just as much power as initial takeoff. Second, you need to be able to abort a landing, and you can't depend on ground power for that.
The only reason anyone ever bothers with assisted takeoff (be it a catapult or JATO) is when their runway is too short. Otherwise there's no point.
Ziggurat
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Where's the head on desk smilie when I need it?
No. You aren't decoupling lift from drag. You're just coupling them at a better coefficient. Just like improvements in engine efficiency don't decouple energy and distance.
macdoc
Philosopher
This field may be progressing faster in the real world than anticipated
https://www.cntraveler.com/story/bookings-open-on-sas-first-commercial-electric-plane
macdoc
Philosopher
You made an absolute statement then added a caveat...."same wing" so no they are not completely linked.
Careful of desk creases.
theprestige
Penultimate Amazing
I'm not exactly sure what you're trying to say, but I'm still in mind of the economic argument.
Greater efficiency is highly desirable to the airline industry, with or without the added weight of EV batteries. If there were significant efficiency gains to be made by a novel wing design, we'd see the airline industry adopting that wing design already. Look at the adoption of winglets, both new builds and retrofits.
So if we're not already seeing a new wing design being adopted, I'm thinking one of two things:
First, maybe it needs a technological breakthrough that we just don't have yet. In which case, it's a non-starter for EV airliners at this time as well.
Second, maybe the efficiency gains are just too marginal and/or come with too many other trade-offs to justify the conversion. In which case, it might be a non-starter for the additional weight of EV airliners anyway. Or, even with the efficiency gains from EV engines, it still doesn't improve the range and performance enough to make EV a viable replacement for ICE over most routes.
theprestige
Penultimate Amazing
How so?
My understanding is that a launch aircraft first stage has been tried, and has been proven to combine the worst aspects of planes and rockets - at least for trips to LEO and beyond.
Obviously a launch aircraft first stage (or second stage, in the case of the Navy) works just fine for launching a missile or a bomb. But that's kind of a niche application. And it apparently doesn't scale to orbit.
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Ziggurat
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No. Drag and lift are coupled. They are ALWAYS coupled. You used an invalid comparison. That's not me putting on caveats, that's you failing to understand the basics of aerodynamics.
Ziggurat
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Yes, this is possible. And it's not necessarily an issue of technology to make it possible as technology to make it cheap enough. We've had composite materials for a long time, but only relatively recently have we been able to manufacture large aircraft components out of composites at a low enough price to be worthwhile.
This is a major consideration.
For example, there are two issues that immediately come to mind for the truss-braced design images that macdoc linked to. One issue is having the wing above the fuselage vs. below. Having it below provides a useful advantage for passenger planes: the wing helps shield the passengers from some of the engine noise. Putting it above, and subjecting passengers to increased noise, is a design compromise. That may or may not be worth increased efficiency.
A second possible compromise for that design is fuel tanks. Those wings look like they take up a lot less volume, which means less capacity in any fuel tanks within the wings. You can increase fuel tank capacity in the fuselage to compensate, but having more fuel in the wings has advantages, so that's another compromise. Maybe worth it, but maybe not, depending on other factors. You still have the issue of how to distribute the weight and volume of your batteries in an electric plane, but that tradeoff might end up different for EV's
For another example of a wing design compromise I know has already been made, look at the 777X. For this version, they wanted to make the wings longer than on previous 777 models, but that made the plane too wide for a lot of airports. So they made the tips of the wings fold up. That adds expense and complexity to the plane. Apparently that tradeoff was worth it for the 777X, but having to add folding wingtips is still a design compromise. Electric planes would have the same limitations on wing length, although since they're entering the market from the small aircraft end, that specific example may not matter for a while.
But regardless, no wing design gets you out of the connection between lift and drag. Which means added weight always comes with a performance penalty.
smartcooky
Penultimate Amazing
Difficult to reconcile this with the fact that the vast majority conventional aircraft known for their STOL capabilities are High-Wing designs... C-130, Pilatus Porter, Short Skyvan and the whole range of DHC STOL aircraft, the Beaver, Otter, Caribou, Buffalo, Twin Otter and Dash 7.
Of course, the primary reasons for this are that high-wing designs are more aerodynamically stable and not affected by crosswinds as much as low wing aircraft. High wing designs also have better landing performance than low wing designs for the same reason as you mention, less ground effect.
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