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#26 2019-11-11 12:30:19

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 19,158

Re: Autonomous Passenger Carrying Electric Aircraft

Rounding up the content that was copied in supercaps..
1 quick charging and possible discharge
2 1/3 the mass of a comparible lithium battery
3 flexible cap arrangement to make variable time of use

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#27 2019-11-11 14:45:34

Calliban
Member
From: Northern England, UK
Registered: 2019-08-18
Posts: 470

Re: Autonomous Passenger Carrying Electric Aircraft

Lithium ion batteries have energy density of 1MJ/kg.  Jet fuel has an energy density of 43MJ/kg.  DC electric motors have a peak efficiency of about 80%.  High bypass turbofans have efficiency of about 33%.  So 1kg of jet fuel yields almost 18x as much work energy as 1kg of batteries.  And a jet fuel powered plane gets lighter as it consumes fuel.

Certainly a poor energy source for a flying machine in which range is proportional to energy per unit weight.  Hydrogen or liquefied natural gas would be far more efficient fuels, at least at the point of use.


Interested in space science, engineering and technology.

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#28 2019-11-11 15:36:33

tahanson43206
Member
Registered: 2018-04-27
Posts: 3,055

Re: Autonomous Passenger Carrying Electric Aircraft

For Calliban re #27

I apologize for bringing into the topic a quote that (apparently) does not use the same units as you have.

However, I'm wondering how supercapacitors compare to lithium ion batteries AND to jet fuel for energy per kg. 

As for the business argument you have introduced .... cost of jet fuel is not the only cost consideration for a transportation company.  Cost of maintenance of complex mechanical systems is a factor, as is the necessity to maintain the infrastructure to supply jet fuel at the airport.

My guess is that a business investor may be interested in looking at destinations where industrial scale power is available, but where jet fuel may not be.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6409971/

Abstract
Present state-of-the-art graphene-based electrodes for supercapacitors remain far from commercial requirements in terms of high energy density. The realization of high energy supercapacitor electrodes remains challenging, because graphene-based electrode materials are synthesized by the chemical modification of graphene. The modified graphene electrodes have lower electrical conductivity than ideal graphene, and limited electrochemically active surface areas due to restacking, which hinders the access of electrolyte ions, resulting in a low energy density. In order to solve the issue of restacking and low electrical conductivity, we introduce thiol-functionalized, nitrogen-doped, reduced graphene oxide scrolls as the electrode materials for an electric double-layer supercapacitor. The fabricated supercapacitor exhibits a very high energy/power density of 206 Wh/kg (59.74 Wh/L)/496 W/kg at a current density of 0.25 A/g, and a high power/energy density of 32 kW/kg (9.8 kW/L)/9.58 Wh/kg at a current density of 50 A/g; it also operates in a voltage range of 0~4 V with excellent cyclic stability of more than 20,000 cycles. By suitably combining the scroll-based electrode and electrolyte material, this study presents a strategy for electrode design for next-generation energy storage devices with high energy density without compromising the power density.

(th)

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#29 2019-11-11 16:00:51

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 19,158

Re: Autonomous Passenger Carrying Electric Aircraft

If flights are often and you charge quickly then you are beating the use of batteries. The batteries do not like the temperatures caused internally within them for fast charging. The motors while they lack the effiecency is not the total picture as its the current draw for rpm that matters for flight. Meaning slower rpm for flight gliding (lower current draw) while higher is for quicker motion to destination ramping up the current needed to make it spin faster.

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#30 2019-11-13 17:05:30

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 19,158

Re: Autonomous Passenger Carrying Electric Aircraft

A very large repost but relates totally for thie topic:

kbd512 wrote:

tahanson43206,

The most advanced super capacitors in commercial production have energy density (specific energy) in line with Lead-acid batteries.  However, these are still pretty expensive and applications remain limited.  Tesla Motors Corp purchased Maxwell for this technology.  Some dev lab 3D super cap technology has reached energy densities as high as 110Wh/kg, or a little less than half of what a commercial Lithium-ion battery can store.  It's an interesting technology for providing bursts of power for very brief periods of acceleration for motor vehicle applications, but not so interesting for powered flight applications which have high constant power requirements.  Trying to power any type of aircraft with Lead-acid batteries isn't very practical.

Super capacitors are capable of dumping stored energy at rates that would destroy Lithium-ion batteries.  A super capacitor bank is a good way to put less wear and tear on a Lithium-ion battery bank from very high discharge rates (for a battery) associated with very brief periods of acceleration measured in seconds.  The battery only has to recharge the capacitor bank and maintain a comparatively minor constant output level to move the vehicle at highway speeds (10hp to 20hp for most passenger vehicles in the 1t to 3t range).  So long as ranges of hundreds of miles are not required, you can make a battery powered motor vehicle lighter and cheaper because you don't need extra battery capacity just to deal with high discharge rates.  The same concept would apply to combustion engine vehicles.  If a vehicle was powered by a combination of super capacitors and a piston engine powering a generator, then a very low displacement engine combined with a super capacitor bank would be sufficient to accelerate the vehicle acceptably well and run it at highway speeds without requiring additional engine power for acceleration.  A free piston engine with a super capacitor bank would be ideal, I would think.

In powered flight applications that use aerodynamic lift to remain airborne, weight is what matters most, followed rather closely and synergistically by aerodynamics.  In short, weight affects power requirements through aerodynamics.  You have to produce sufficient power to propel the wing and everything attached to it through the air fast enough to produce the "up force" required to keep some specific amount of weight airborne at some specific speed.  The power requirement doesn't linearly increase with increasing speed, either.  That's why you design an aircraft to cruise at some optimum speed, with a given load, to a given distance.

The only way to meaningfully improve performance is to increase power, decrease weight, or improve aerodynamics- dependent upon what you're trying to accomplish.  Most aircraft designers do pay attention to the drag generated by their airframe design and try to minimize it for a particular cruising speed.  It's a balancing act to manage the inverse relationship between induced and parasitic drag to minimize total drag for a design cruise speed.  If you want more speed, then you need more power.  That means you need a bigger and heavier engine that consumes more fuel.  You'll need a heavier airframe attached to that bigger engine and bigger gas tanks carrying more gas.  Whether the "gas" is gasoline, kerosene, diesel, methane, hydrogen, or electrons stored in a battery or capacitor is irrelevant to the design goal of "going faster".  You're going to consume more of "it" to go faster.  Period.  If the fuel is electrons wirelessly transmitted via microwave, that's the only practical way I know of to offload the weight of the "gas" and gas tank.  It's going to be a compromise (prioritization) of some kind.

To actually get some specific mass airborne using aerodynamic lift, you must accelerate the wing (and everything attached to it, obviously) fast enough to fly before you run out of available runway, with performance margin to spare.  As a result, you'll briefly need to generate some multiple of the amount of power minimally required to simply remain airborne in level flight.  There's obviously a limit to this, since aircraft can take off vertically when thrust is greater than weight.  Generating that kind of power leads to very heavy engines with very high fuel consumption.  There's no such thing as a helicopter that's more fuel efficient than a fixed wing aircraft carrying equivalent payload to equivalent distance at equivalent speed, for example.

To overcome drag to fly significantly faster without a dramatic increase in power, it's certainly possible to attach tiny wings that only produce sufficient lift to get airborne at high speeds.  However, that typically results in unmanageable takeoff and landing speeds that would impart very high forces into the airframe from all but the most perfect landings.  That would then mandate a very robust design which requires more structural weight to achieve, which then requires more wing to lift it, which then requires more power to push the craft through the air.

Now that we understand why it is that aircraft power plants must be lightweight and consume energy stores with very high energy densities per unit of weight, let's consider the use of an energy store with half of the performance of current Lithium-ion batteries.  In practice, we're going to drastically reduce payload or range or speed, or likely all three, by using a very low energy density storage technology.  Alternatively, we're going to drastically increase the size and weight of any solution competitive with a gas or kerosene engine, and therefore cost.  The energy density issue is an intractable problem, as it pertains to powered flight.  However, if we're willing to trade speed for total delivered tonnage for a given fuel burn, there are certainly practical alternatives to gas turbines and high fuel burns, principally by using a lifting gas to negate part of the power requirement simply to remain aloft.

Modern transport airships are also designed to use aerodynamic lift to remain airborne.  To aid controllability in flight, these airships are slightly heavier than air.  They use speed to vary the amount of lift generated by the inflatable structure to ascend or descend, just like conventional fixed wing aircraft.  The power requirements are lower per unit of mass since less lift is required and lower speeds are involved.  However, moving weight around at highway speeds (60mph to 120mph) and pushing all of that air out of the way still requires a certain amount of power.  The volume of air being displaced by a large cargo transport will closely resemble that associated with an aircraft carrier, so the power requirement is still non-trivial.  Lockheed-Martin designed a cargo airship to use a type of "inflatable suction cup" (reverse hovercraft technology) to glue the blimp to the ground for cargo loading / offloading, negating the need for any sort of specialized ground equipment for cargo transfer.

There are 3 practical applications I see for this technology:

1. Faster commercial cargo transport with less energy consumption than jet aircraft and therefore cost.  An airship will be significantly faster than ocean-going cargo ships while consuming less fuel to achieve the same range with a given payload than a traditional jet airliner.

No dredged shipping channels or docks equipped with gigantic cargo offload cranes are required, so a simple concrete slab with forklifts and CONEX box cranes is all that's required to offload cargo.  The infrastructure and embodied energy cost, since it takes energy and money to mine ore, smelt steel, machine the steel into complex cargo transfer equipment, transport it to the dock site and maintenance costs for all of that stuff are drastically reduced.

Fewer crew are required to man airships, perhaps just 2 to 4 pilots, no different than other commercial aircraft.  To ferry cargo across the Atlantic, from New York to London, the Airlander 10's 90mph cruising speed would equate to a 38 hour flight.  The Airlander 50's projected to have a faster cruising speed of 120mph, so that's a 29 hour flight.  The more economical alternative is a 6 to 12 day journey by cargo ship.  That may not matter for furniture or raw materials, but it matters greatly for food / medicine / aircraft parts.  A Boeing 747 can complete the same journey in 6 hours, but with a 22,000 gallon fuel burn.  The Airliner 50 would burn around a quarter as much fuel to deliver the same tonnage of cargo the same distance.

2. The "Knarr" concept, which uses a solar panel and regenerative fuel cells, wouldn't "burn" any fuel that couldn't be recycled, so the fuel consumption and thus cost drops to near zero.  It's larger than our largest aircraft carriers, but also carries 1,000t of cargo at roughly the same speed as the Airlander 50.  The Knarr only requires 5,600hp to do that.  It's covered with 63,000m^2 worth of thin film solar panels to generate around 12MW of power at noon.  To put this in perspective, our Osprey tilt rotor aircraft are equipped with a pair of 6,150shp Rolls Royce T406 gas turbines.  The Osprey's maximum vertical takeoff weight is 24t.  So, Knarr's cargo capacity is equivalent to 41 Osprey's loaded with gas and cargo to their maximum vertical takeoff weight.  If it's not obvious, helicopters really suck at energy efficiency when compared to fixed wing aircraft or blimps, though they still have their uses.

A single Knarr could deploy a full strength US Armored Company (M1 Abrams MBT's) per flight.  Two squadrons of Knarr's could deploy a full strength US Armored Division (again, our MBT's, not lighter APC's / IFV's) to Europe in approximately 2 days, and we could skip the railhead and pier side RORO operations entirely, so everything would arrive in theater much faster than rail / shipping operations.

3. Airships could act as sky cranes to deliver cargo that would be impractical to deliver by other methods, such as gigantic wind turbine blades and materials for skyscrapers.  Affordable high capacity vertical lift would be an enabling technology for building all sorts of structures.  Cranes would still have their uses.  However, if we were building mile-high skyscrapers, then it'd be a whole lot easier to lower materials to workers waiting below than it would be to hoist them from the ground using cranes with the mass and support structure required to prevent them from toppling over.  There's going to be some kind of practical limit on everything.

So...  Super caps for airships in the immediate future?  Maybe, maybe not.  Perhaps only for take-off power.  Giant airships for cargo transport?  That'd definitely fulfill an actual "need" use case.  Airships are likely more expensive to operate than ocean going cargo ships, but much faster and a lot less expensive to operate than a jet aircraft.  Airships are the only type of aircraft that could make practical use of solar power, since all other forms of powered flight require far more power in a more compact package.  Over time, the use of solar panels and fuel cells to lower fuel costs could lead to justification for "air mailing" nearly everything but raw materials and fuels, especially since the airship can go just about anywhere big enough for it to take off and land without any specialized support infrastructure.  Time is still money in business, so we're unlikely to see airships providing passenger service.  Luxury cruise liners might be an exception to that rule.  The US military would immediately benefit from airships, given the total tonnage of stuff they have to move half way around the world.  Disaster relief would greatly benefit from high capacity vertical lift and no requirement for functional airfields, and perhaps not even a place to land.

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#31 2019-11-16 06:41:02

tahanson43206
Member
Registered: 2018-04-27
Posts: 3,055

Re: Autonomous Passenger Carrying Electric Aircraft

For SpaceNut ...

Here's an update for this topic ... the only mismatch is that (at this point) the aircraft in design/development are NOT autonomous.

However, the company seems worth watching because it is backed by a large corporation (apparently) with deep pockets.

https://www.yahoo.com/finance/news/magn … 40816.html

(th)

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#32 2019-11-17 21:35:57

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 19,158

Re: Autonomous Passenger Carrying Electric Aircraft

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#33 2020-02-21 22:21:03

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 19,158

Re: Autonomous Passenger Carrying Electric Aircraft

Here is a step in the direction of non polluting BAE_successfully_tests_solar_powered_high_altitude_plane

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#34 2020-06-02 20:16:21

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 19,158

Re: Autonomous Passenger Carrying Electric Aircraft

Battery powered plane makes first flight with 750hp electric motor at 100mph and altitude of 2500 ft making a 24 minute loop before landing.

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