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The main problem with batteries is, landing weight is the same as take-off weight.

Which means EV planes should weigh close to the weight of an ICE plane with empty tanks. I am not even sure today we are anywhere close to that in terms of gravimetric density for even the highest energy density LiOn battery with Co & Ni.
What are you talking about? All the airplanes I have flown are designed to land with a full tank.

Or look up any regional turboprop specifications, maximum landing weight is generally very close to maximum takeoff weight. As in 95% full tank.
 
What are you talking about? All the airplanes I have flown are designed to land with a full tank.

Or look up any regional turboprop specifications, maximum landing weight is generally very close to maximum takeoff weight. As in 95% full tank.
That is correct, as an Aerospace Engineer that has certified multiple platforms and systems that are directly applicable to this, we always end up certifying max landing weight very close to max TO weight except with special conditions. It's not as efficient really because the lighter an aircraft gets through it's flight plan the lower AOA needed to maintain lift and therefor the CoD reduced make for more efficient flying, but it can be accounted for just fine.
 
I do remember sticking electrolytics in wall sockets as a kid. They do put on quite the show when they blow.
When I was 7-8, I had a homemade electromagnet (wire wrapped around a big nail), connected to a 1.5V #6 dry cell. I used it to collect iron filings at the beach, etc. One day I was in my bedroom and I looked at an extension cord and thought "If this electromagnet works so well on 1.5V, it's going to be awesome on 120V!"

Needless to say, that experiment was not successful.
 
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That is correct, as an Aerospace Engineer that has certified multiple platforms and systems that are directly applicable to this, we always end up certifying max landing weight very close to max TO weight except with special conditions. It's not as efficient really because the lighter an aircraft gets through it's flight plan the lower AOA needed to maintain lift and therefor the CoD reduced make for more efficient flying, but it can be accounted for just fine.
There is a difference between designing and manufacturing something that can handle an edge case (landing with full fuel loaded is an edge case and is not the norm) .vs. making that the default operation. The stresses the landing gear and brakes go through will have a huge wear&tear every time you land with a full weight.
 
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There is a difference between designing and manufacturing something that can handle an edge case (landing with full fuel loaded is an edge case and is not the norm) .vs. making that the default operation. The stresses the landing gear and brakes go through will have a huge wear&tear every time you land with a full weight.
The weight penalty of adjusting gear life cycles to this criteria is below noise levels.

Other design drivers specific to electric propulsion (fuel/battery weight fractions at max payload, etc.) have an impact on takeoff weight that is several orders of magnitude higher than that.
 
I seem to remember there is a guy needing a lot of storage for building cars. He did graduate work on Ultra Caps. He is using batteries for his cars.

I would think if Ultra Caps had an advantage, the guy that knew them reasonably well (and likely still does) would be using them.

That guy would probably be using ultra-caps if they existed. For all the reasons mentioned above, they don't exist. At least not commercial ones safe enough for use in cars or planes.

I agree that [solar synthetic fuels] would make sense if there ever is a large surplus of solar capacity. But that is likely many decades away, unfortunately.

We are either going to built out renewable energy, or we are going to turn the Earth into Venus Mk II by continuing to burn fossil fuels. I fear that governments and industry world-wide are determined to make the latter happen as soon as possible.

Note that next-generation nuclear plants could also be a carbon-free source of electricity for synthetic fuels for air travel, though they present their own sets of problems.
 
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We are either going to built out renewable energy, or we are going to turn the Earth into Venus Mk II by continuing to burn fossil fuels. I fear that governments and industry world-wide are determined to make the latter happen as soon as possible.
It’s more a case of inertia and maintaining existing corporate profits.
Note that next-generation nuclear plants could also be a carbon-free source of electricity for synthetic fuels for air travel, though they present their own sets of problems.
Those advocating a new generation of nuclear power plants (which will take decades to come online, and we don’t have decades) have yet to explain what they are going to do with the radioactive waste they will generate, and the waste we already have sits leaking in surface facilities because no one can agree on what to do with it.

In the US, the Yucca Mountain facility should have been built but it looks like it never will be operational.
 
It’s more a case of inertia and maintaining existing corporate profits.

That's pretty much what I meant. :rolleyes:

Those advocating a new generation of nuclear power plants (which will take decades to come online, and we don’t have decades) have yet to explain what they are going to do with the radioactive waste they will generate, and the waste we already have sits leaking in surface facilities because no one can agree on what to do with it.

In the US, the Yucca Mountain facility should have been built but it looks like it never will be operational.

Advocates claim that next-gen nukes won't produce much waste. They claim (though I disagree) that next-gen nukes could be brought on line faster than sufficient solar and wind can be built. Like I said, they have their own set of problems.
 
Advocates claim that next-gen nukes won't produce much waste. They claim (though I disagree) that next-gen nukes could be brought on line faster than sufficient solar and wind can be built.
Yes, those claims strike me as disingenuous considering that such plants use new technology that has never been employed at scale. Throughout my 68 year lifetime, nuclear power companies have made cost claims that don’t pan out.

We know how to build and scale wind and solar because…it’s already been done. We just need more of it, and we need people to get over their outdated aesthetic objection that wind turbines aren’t attractive and solar roofs look weird.

I have a view of the ocean and I would be happy to see it filled with offshore turbines.
 
^ Totally agree!

When I was young, they promised that electricity from nuclear would be "too cheap to meter." You'd pay a fee to have the wires come to your house, and you'd be able to use all the electricity you wanted, for no additional cost. That sure turned out to be bullfeathers.

I think the real issue is that with solar, you and I can have PV panels on our roofs and make our own electricity. With nuclear (like coal, oil, etc.) people have to buy their electricity from the utility.
 
large, long-distance, heavy-lift aircraft will have to use liquid fuels, either fossil or synthetic, probably forever.
I agree mainly on this, however, the jury still may be out as to whether liquid hydrogen has sufficient volumetric energy density (Wh/kg) to overcome the drag caused by the added volume (including insulation) compared to liquid hydrocarbon fuels (fuels with hydrogen and carbon such as gasoline, diesel, jet-fuel, etc) that are liquid at earth surface temperatures.
Needless to say, that experiment was not successful.
Sounds quite successful - there's a much smarter person in the world for having done that experiment.
 
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The weight penalty of adjusting gear life cycles to this criteria is below noise levels.

Other design drivers specific to electric propulsion (fuel/battery weight fractions at max payload, etc.) have an impact on takeoff weight that is several orders of magnitude higher than that.
I'm currently working on a couple of these projects for companies, can't say who due to NDA, but I will say there are offsets to a portion of these. The fuel load on a traditional propulsion system is not insignificant and you pay that penalty even if you take off and get lighter through the flight plan. Also the engine itself is lighter for electric propulsion compared to traditional. I'm not saying it's a weight positive for electric, but the delta isn't as large as some believe it to be.
 
I agree mainly on this, however, the jury still may be out as to whether liquid hydrogen has sufficient volumetric energy density (Wh/kg) to overcome the drag caused by the added volume (including insulation) compared to liquid hydrocarbon fuels (fuels with hydrogen and carbon such as gasoline, diesel, jet-fuel, etc) that are liquid at earth surface temperatures.

Rockets use hydrogen. If there were an advantage to hydrogen in airplanes somebody would already be doing it. It's certainly possible. Presumably it just costs more. I'm going to guess that the reason rockets use it is the difficulty of getting other fuels to burn fast enough to provide the thrust that a rocket needs.

There are cars that use hydrogen, but they've come up against so many problems that they are not cost-competitive with either gas or batteries. This bodes poorly for hydrogen in airplanes.

Sounds quite successful - there's a much smarter person in the world for having done that experiment.

"I didn't fail a hundred times. I successfully found a hundred ways that don't work." :cool:
 
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The fuel load on a traditional propulsion system is not insignificant and you pay that penalty even if you take off and get lighter through the flight plan. Also the engine itself is lighter for electric propulsion compared to traditional. I'm not saying it's a weight positive for electric, but the delta isn't as large as some believe it to be.
So why would having that weight penalty throughout the flight plan not have a significant impact on the overall efficiency & energy consumption, and design & engineering of the electric aircraft. To me that aspect of EV planes has to be a significant hurdle.
 
So why would having that weight penalty throughout the flight plan not have a significant impact on the overall efficiency & energy consumption, and design & engineering of the electric aircraft. To me that aspect of EV planes has to be a significant hurdle.
Because most of the energy expended is during takeoff. Level flight uses little energy.
 
What are you talking about? All the airplanes I have flown are designed to land with a full tank.

Or look up any regional turboprop specifications, maximum landing weight is generally very close to maximum takeoff weight. As in 95% full tank.
The reason you hear about heavy long haul aircraft dumping fuel before an emergency landing after takeoff is due to weight constraints. Also, they take advantage of weight going down as fuel is burned during the flight to go to a higher altitude part way through the flight which results in less drag from thinner air. Short range, low altitude airplanes have better use case for BEV.
Reality is Boeing and USAF have already qualified jets to use bio fuels but cost more / limited supply so airlines don’t use.
 
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Because most of the energy expended is during takeoff. Level flight uses little energy.
You are mixing up power and energy. Takeoff power is very high but lasts only about one minute. Climb power is high and lasts a few minutes. The electric aircraft I am working on spends 8% of the total kWh on takeoff and acceleration to climb, 42% on climb to cruise altitude, and 42% in cruise for a quick 100 nm mission profile.
 
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So why would having that weight penalty throughout the flight plan not have a significant impact on the overall efficiency & energy consumption, and design & engineering of the electric aircraft. To me that aspect of EV planes has to be a significant hurdle.
It does have an impact but for short range aircraft it is only a negligible range loss between range calculated with weight reducing with fuel burn and range calculated with constant weight.

The reason that the weight penalty does not have a significant impact for short range aircraft flying at normal cruise speed and medium altitudes is that the dominant cruise energy expense is driven by aircraft size (its wetted area) rather than weight (its induced drag). Long range airliners flying at high cruise altitudes are very different and face different challenges.

Practical examples: the flight manual of the King Air B300 shows that fuel burn at 20000 ft, normal cruise speed 300 KTAS between 14000 lb (full tanks) and 11000 lb (tanks at 25% level) is essentially the same (816 lb/hr at 301 KTAS versus 822 lb/hr at 306 KTAS and same 91% torque). Or another example, the ATR 42 has 369 kg/hr/eng at 20000 ft and 296 KTAS at 18 tons (tanks full) versus 371 kg/hr/eng at 20000 ft and 302 KTAS at 15 tons (tanks nearly empty) for high speed cruise, so essentially the same situation as the King Air. You burn a little bit more fuel due to the higher ram recovery at the inlet and your speed is just a few knots higher, so that means a very similar specific range (pounds of fuel or kWh per mile). In short, the difference is barely measurable.

Bottom line is that this significant hurdle does not exist at all. It does matter for long range high altitude airliners but this is an entirely different world.
 
Rockets use hydrogen. If there were an advantage to hydrogen in airplanes somebody would already be doing it. It's certainly possible. Presumably it just costs more. I'm going to guess that the reason rockets use it is the difficulty of getting other fuels to burn fast enough to provide the thrust that a rocket needs.

FWIW hydrogen as rocket propellant its mostly a mass thing. Compared to a hydrocarbon that has that pesky carbon mass that's sort of dead weight, hydrogen is all business. There's a bunch of downsides though, notably that hydrogen requires much more volume (and so larger/heavier tanks), has a different density than O2 (and so requires more complex pumping solutions), and its generally a right PITA to handle.

As a result, 'new' rocket engines these days (Raptor, Archimedes, BE-4, etc) seem to all be going with methane as the fuel of choice.