world's first airline with electric-only aircraft

kbd512 · 2019-04-02 10:53:49

tahanson43206,

I can edit the posts, if you wish. However, all of this information is freely available for anyone who wishes to use it.

Designing Your Homebuilt by John Roncz

John Roncz gives a presentation at EAA AirVenture detailing his work on Voyager, Global Flyer, Beechcraft Starship, and other projects (he's done the aerodynamics work on 52 different aircraft):

John Roncz: Inside story about Rutan designs. Airventure 2011, Oshkosh.

How the Rutan homebuilt designs are made:

Building the Rutan Composites - by Ferde Grofe, presented by Burt Rutan and Mike Melvill - full DVD

Here's a company with some interesting stories (for those of us who can't afford Invar and Kovar molds):

Why It Goes So Fast - The Arnold Company

How It's Made - The Arnold Company

Moldless, Low Drag Wheelpant - The Arnold Company

Making A Molded Fuselage - The Arnold Company

Making Fiberglass Molds - The Arnold Company

A website dedicated to Rutan / Scaled Composites designs:

AviaDesigns: Stargazer

Note that aerodynamics doesn't just apply to aircraft and spacecraft. Sailing vessels, high speed landing craft, motor vehicles, and wind turbines all benefit greatly from improved aerodynamics.

If you join the EAA, you can download and use DSS SolidWorks for free:

EAA - SOLIDWORKS Resource Center

There are a slew of other free CFD tools, but here's another one:

USU Aero Labs - MachUp

Here's a good general info resource:

CFD Online

NASA has a program used to study aerodynamics that's free of charge:

Can't recall the name of the silly program. It's stated in one of the X-57 papers. I'll add it later when I find it.

Edit (found it): OpenVSP

X-57 "Maxwell", a real electric aircraft that's been design-optimized as an electric aircraft by NASA:

X-57 Technical Papers

Notice how fuel cells help make the X-57 a more practical aircraft:

Integration Concept for a Hybrid-Electric Solid-Oxide Fuel Cell Power System into the X-57 "Maxwell"

NASA Administrator on the X-57 and future space exploration efforts:

NASA Administrator Jim Bridenstine talks about the X-57 and aerospace at Scaled Composites

Last edited by kbd512 (2019-04-02 11:37:43)

louis · 2019-04-02 14:39:27

Has Musk's approach to this problem been discussed?

https://www.inverse.com/article/53026-t … -plane-fly

kbd512 · 2019-04-02 16:32:33

Louis,

Elon Musk's approach is to remove unimportant little things like the horizontal and vertical stabilizers and rely upon thrust from motors on gimbals to provide directional control authority. He's hardly the first to have that idea. In the past, others have experimented with that idea and determined that relying upon vectoring thrust to provide control authority is generally not a good idea. I'm sure it can be done, given sufficient computer and control mechanism redundancy, if cost isn't an issue.

Q: Can we produce practical electric aircraft using today's technology?
A: Yes, but not using today's battery technology.

LSA = "Light Sport Aircraft" - A FAA-recognized category of experimental amateur built (E-LSA) or special factory-built aircraft (S-LSA) with certain design (fixed pitch propeller, fixed landing gear except for gliders, single non-turbine engine) / speed (Vs - 45kts, VH - 120kts, Vne - 135kts for gliders only) / weight (1,320lbs for single engine land; 1,430lbs for single engine amphibious / seaplanes) / passenger carrying restrictions (1 passenger allowed).

Bye Aerospace - Projects - Sun Flyer

SunFlyer 2's battery packs actually store 260Wh/kg for the complete pack, not just the cells themselves. Its entire pack weighs 353.8kg / 820lbs. SunFlyer 2 weighs 1,460lbs (empty) with a 115hp Siemens electric motor installed. The SunFlyer 2 is being sold for $349,000.

Arion Aircraft - Lightning LS-1

Arion Lightning LS-1, the airframe used by SunFlyer 2, weighs 850lbs (empty) with the 120hp Jabiru 3300 piston engine installed. That means the battery ALONE used by the electric version of the same aircraft is within 30lbs of the empty weight of the gas powered airframe. The Arion Lightning LS-1 (S-LSA, meaning factory-built) is being sold for #119,000 (doesn't include paint and interior, but does include avionics and everything else; you don't get to choose avionics on S-LSA's, there are a set of certified factory avionics packages, but you can if you build it yourself). You only get the repairman certificate from FAA for aircraft you build yourself, too.

FAA - Repairman Certificate for Amateur-Built Aircraft

You really should do the homework problem from Post #21. It was intended for you to do your own calculations so that you would know for yourself what kind of energy density these new batteries would have to have in order to produce an aircraft with similar weight / range / speed to any existing gas powered airframe, ignoring the fact that the battery powered aircraft won't get any lighter as it flies. Please do your own calculations and let the rest of us know what you came up with.

louis · 2019-04-02 17:21:37

I trust Musk's calculations more than my own! They need to get to 400 Whs per Kg minimum and preferably 500 Whs per Kg. That's why Musk has hooked up with a company focussed on achieving those figures.

kbd512 wrote:

Louis,
Elon Musk's approach is to remove unimportant little things like the horizontal and vertical stabilizers and rely upon thrust from motors on gimbals to provide directional control authority. He's hardly the first to have that idea. In the past, others have experimented with that idea and determined that relying upon vectoring thrust to provide control authority is generally not a good idea. I'm sure it can be done, given sufficient computer and control mechanism redundancy, if cost isn't an issue.
Q: Can we produce practical electric aircraft using today's technology?
A: Yes, but not using today's battery technology.
LSA = "Light Sport Aircraft" - A FAA-recognized category of experimental amateur built (E-LSA) or special factory-built aircraft (S-LSA) with certain design (fixed pitch propeller, fixed landing gear except for gliders, single non-turbine engine) / speed (Vs - 45kts, VH - 120kts, Vne - 135kts for gliders only) / weight (1,320lbs for single engine land; 1,430lbs for single engine amphibious / seaplanes) / passenger carrying restrictions (1 passenger allowed).
Bye Aerospace - Projects - Sun Flyer
SunFlyer 2's battery packs actually store 260Wh/kg for the complete pack, not just the cells themselves. Its entire pack weighs 353.8kg / 820lbs. SunFlyer 2 weighs 1,460lbs (empty) with a 115hp Siemens electric motor installed. The SunFlyer 2 is being sold for $349,000.
Arion Aircraft - Lightning LS-1
Arion Lightning LS-1, the airframe used by SunFlyer 2, weighs 850lbs (empty) with the 120hp Jabiru 3300 piston engine installed. That means the battery ALONE used by the electric version of the same aircraft is within 30lbs of the empty weight of the gas powered airframe. The Arion Lightning LS-1 (S-LSA, meaning factory-built) is being sold for #119,000 (doesn't include paint and interior, but does include avionics and everything else; you don't get to choose avionics on S-LSA's, there are a set of certified factory avionics packages, but you can if you build it yourself). You only get the repairman certificate from FAA for aircraft you build yourself, too.
FAA - Repairman Certificate for Amateur-Built Aircraft
You really should do the homework problem from Post #21. It was intended for you to do your own calculations so that you would know for yourself what kind of energy density these new batteries would have to have in order to produce an aircraft with similar weight / range / speed to any existing gas powered airframe, ignoring the fact that the battery powered aircraft won't get any lighter as it flies. Please do your own calculations and let the rest of us know what you came up with.

SpaceNut · 2019-04-02 17:59:43

Of what the passenger or the vehicle mass plus people, bagages ect... Make them pedal for the flight....

https://www.popularmechanics.com/flight … -16441824/

https://en.wikipedia.org/wiki/Human-powered_flight

kbd512 · 2019-04-02 18:22:16

Louis,

I trust that you can do basic math. I believe in you, even if you don't believe in yourself. I like your creativity and interesting ideas, certainly lots of stuff I've never seen or heard of. I just wish you would put some numbers to your ideas to determine how well they'll work in the world of math and engineering. I know that imagining the future can be more fun and interesting at times, but technological and economic reality is still in effect at all times.

Follow me here:

Arion Lightning LS-1's 120hp Jabiru 3300 weighs 178lbs (in a roughly flyable configuration). This motor consumes 5.5 gallons of 100LL at cruise power. AVGAS is 6lbs per gallon, so fuel consumption is 33lbs per hour.

Siemens 115hp / 89kW SP70D electric motor weighs 57lbs and consumes 66.75kWh at cruise power setting (75%).

Intelligent Energy's 100kW PEM fuel cell weighs 73.5lbs in an a ready-to-use configuration.

H2's HHV is 39.39kWh/kg, but we only get 70% of that using Intelligent Energy's PEM fuel cell, so 27.573kWh/kg.

LNH3 is 2.58kg / gallon at -33 and 17.755% H2 by weight, so 0.458kg of H2 per gallon of LNH3.

66.75 / 27.573 = 2.42kg of H2 per hour at cruise.

2.42 / 0.458 = 5.28 gallons of LNH3 at cruise.

5.28 * 5.69 = 30.05 pounds per hour at cruise.

We save just over 21.45lbs of weight on gas by using LNH3. Our fuel cell and electric motor, even with an inverter, would be no heavier than the gas powered motor they replaced. The 21lbs of weight we saved on gas would be consumed by our new fuel tanks to hold the LNH3. However, we end up with an aircraft that doesn't burn anything, doesn't have any emissions except N2 and H2O, and retains the same performance as the gas powered airframe. Normally we'd stop there and call it a day, but let's see what would be required for the batteries to produce equivalent performance.

Let's assume the motor and inverter weigh about 100lbs. That gives us 318lbs or 144kg (78lbs left over from the gas powered motor plus 240lbs left from the AVGAS) to play with.

The gas powered aircraft can cruise for 7.27 hours (40 gallons total capacity / 5.5 gallons per hour = 7.27 hours of endurance).

66.75kW (cruise power) * 7.27 hours = 485kWh

485kWh / 144kg = 3.368kWh/kg

All we need is a battery that can store 3,368Wh/kg. No sweat, right?

Except that we don't seem to have batteries that store 368Wh/kg, much less 3,368Wh/kg.

Can better aerodynamics and lighter materials overcome the need to provide that much continuous power?

To a point. The SunFlyer 2 (or "eFlyer 2"?) version of the Arion LS-1 seems to have a better L/D and glide ratio, but both birds are already constructed with carbon fiber and even CNT has strength and stiffness limitations. When we have 3kW/kg batteries, presuming they're not priced like Unobtanium, those of us who fly will be dancing a jig. We have a long, long way to go on that. The fuel cell technology is already available.

How long do you want to wait for 3kWh/kg batteries to get back to where we are now with gasoline, in terms of performance?

Edit:

* a 100kW fuel cell still has plenty of excess capacity to produce extra power at take off (turning our 89kW motor into a 98kW motor)

* running avionics, electrics, and air conditioning (for those times when that giant fan out front isn't keeping our pilot cool)

* electric trim servos

* electrical variable pitch propeller

* electrical retractable landing gear

Note:
You can't have retracts or variable pitch / constant speed props on LSA's, but Experimental Amateur-Builts (EAB's) can have both. So long as you have the appropriate endorsement for complex aircraft in your logbook, you're good to go.

Last edited by kbd512 (2019-04-02 20:00:53)

kbd512 · 2019-04-03 13:35:52

Louis,

Here's a YouTube video I found wherein the presenter uses "back-of-the-envelope" (it's not exact since there are various ways that clever aerodynamicists can reduce the energy requirements, but it's very much in the right ballpark and coincides quite well with what we know of actual electric aircraft and electrification proposals) calculations for determine flight range on batteries:

Are Electric Planes Possible? - Real Engineering

Please note that the 737 example he used has a flight time of about 15 minutes using batteries that have the same weight as the jet fuel. Alternatively, the batteries alone would weigh roughly 3.25 times the max takeoff weight of the aircraft to provide equivalent range.

He came to the same conclusion I did- we might see electric airplanes in the near future, but not using Lithium-ion batteries. Oddly enough, he also believes that fuel cells are the way forward for this specific application. He, like so many others, has fixated on using gaseous or liquid H2, as if those were the only stores of H2 available for use. Pure LH2 is indeed very light, but devilishly difficult to store near absolute zero temperatures and it occupies tremendous volume. GH2 is even worse, on that account, due to the extreme pressure it must be stored at to obtain a significant quantity of LH2. LNH3 happens to be storable at room temperature at relatively low pressures typical of those used by automotive fuel pumps. LH2 and LCH4 both require cryogenic temperatures for storage or absurdly high pressures that are impractical for static or stationary use with current technology and wildly impractical for an aircraft.

It turns out that the Hydrogen economy of the Haber-Bosch process is already quite good, but a new process on the horizon has already exceeded 90% conversion efficiency, with respect to efficient Hydrogen utilization. At present, LNH3 is around one quarter the cost of jet fuel at retail prices. At wholesale prices and with fuel savings considered, it's more than an order of magnitude cheaper. All industrialized countries already use LNH3 in agriculture as the fertilizer of choice and they use lots of it.

Interestingly, this new process uses Lithium to efficiently produce NH3:

Jens Nørskov: Generation of Ammonia Using Solar Energy | GCEP Symposium – October 18, 2017 - Stanford Precourt Institute for Energy

From past posts, it can clearly be seen that small turboprops / gas turbine engines are relatively inefficient and burn more gallons of Jet A when compared to a gallon of LNH3 energy equivalent that would first be split by a plasma cracker and then injected into and reacted with O2 inside a fuel cell. Recall from the video posted above how critical weight is to the entire energy efficiency equation, as I have stated like a broken record. As the mass of fuel increases, the mass differential becomes more profound. Basically, you start carrying more fuel to carry the weight of the extra fuel you'll need to burn. Note that that's the exact problem that rocket designers face. It's a vicious cycle. It applies to aircraft, too, just not quite as extreme of a problem as it is in rockets. All airline services operate large and heavy jets with a voracious appetite for Jet A, thus the mass savings becomes more profound as this system scales up. For the "heavies"- the 747's / 787's / A350's / A380's of the world, the mass savings is proportionately more dramatic. Any mass inefficiencies on the part of heavier electric motors and fuel cells and fuel storage containers is immediately offset by the fuel mass savings.

Assuming proper design (always a major assumption), gas turbine engines increase in efficiency with size up to the thermodynamic or Carnot efficiency limit of a simple cycle. The GE90 turbofans achieve a 36% thermodynamic efficiency, for example. Unfortunately, truly massive engines are required to achieve good fuel economy. The outsized GE90 and new GE9x are good examples, in that regard, as are very large turboprops. Even then, that only happens at significant altitude where the air is thinner and the power requirements to achieve a given speed are significantly less than at low altitude where the air the plane is moving through is significantly thicker.

If we don't try to achieve six impossible things before breakfast, then electrification of flight is possible using current technology. If people are insistent on waiting until battery energy density increases significantly, then they'll be waiting for decades for an aircraft that matches the performance of existing aircraft. If we start at 250Wh/kg and battery capacity increases by 3%, year over year, every year, as it has for all recent history, then we'll need to wait about 88 years for batteries to match the energy density of gasoline. If you live for another 47 years, then you'll see large scale commercialization of 1kWh/kg batteries, which would be the point at which we can replace small turboprops with batteries. Could we achieve a breakthrough before then? I certainly hope so, but decades of concerted research around the world with tens of billions of dollars backing it has yet to yield such a breakthrough.

louis · 2019-04-03 18:31:07

Kbd,

That first vid is based on a "state of the art" 278 Wh per Kg. I've already made clear what is required (based on what Musk says - no personal knowledge) is 400 Wh per Kg and 500 Wh per Kg preferably.

Musk is not known for chasing impossible technologies. The vast majority of his technological forays have had a good, not a bad, outcome.

Electric jets appear to be v. possible at 500 Whs per Kg battery storage - that's all that really matters.

kbd512 wrote:

Louis,
Here's a YouTube video I found wherein the presenter uses "back-of-the-envelope" (it's not exact since there are various ways that clever aerodynamicists can reduce the energy requirements, but it's very much in the right ballpark and coincides quite well with what we know of actual electric aircraft and electrification proposals) calculations for determine flight range on batteries:
Are Electric Planes Possible? - Real Engineering
Please note that the 737 example he used has a flight time of about 15 minutes using batteries that have the same weight as the jet fuel. Alternatively, the batteries alone would weigh roughly 3.25 times the max takeoff weight of the aircraft to provide equivalent range.
He came to the same conclusion I did- we might see electric airplanes in the near future, but not using Lithium-ion batteries. Oddly enough, he also believes that fuel cells are the way forward for this specific application. He, like so many others, has fixated on using gaseous or liquid H2, as if those were the only stores of H2 available for use. Pure LH2 is indeed very light, but devilishly difficult to store near absolute zero temperatures and it occupies tremendous volume. GH2 is even worse, on that account, due to the extreme pressure it must be stored at to obtain a significant quantity of LH2. LNH3 happens to be storable at room temperature at relatively low pressures typical of those used by automotive fuel pumps. LH2 and LCH4 both require cryogenic temperatures for storage or absurdly high pressures that are impractical for static or stationary use with current technology and wildly impractical for an aircraft.
It turns out that the Hydrogen economy of the Haber-Bosch process is already quite good, but a new process on the horizon has already exceeded 90% conversion efficiency, with respect to efficient Hydrogen utilization. At present, LNH3 is around one quarter the cost of jet fuel at retail prices. At wholesale prices and with fuel savings considered, it's more than an order of magnitude cheaper. All industrialized countries already use LNH3 in agriculture as the fertilizer of choice and they use lots of it.
Interestingly, this new process uses Lithium to efficiently produce NH3:
Jens Nørskov: Generation of Ammonia Using Solar Energy | GCEP Symposium – October 18, 2017 - Stanford Precourt Institute for Energy
From past posts, it can clearly be seen that small turboprops / gas turbine engines are relatively inefficient and burn more gallons of Jet A when compared to a gallon of LNH3 energy equivalent that would first be split by a plasma cracker and then injected into and reacted with O2 inside a fuel cell. Recall from the video posted above how critical weight is to the entire energy efficiency equation, as I have stated like a broken record. As the mass of fuel increases, the mass differential becomes more profound. Basically, you start carrying more fuel to carry the weight of the extra fuel you'll need to burn. Note that that's the exact problem that rocket designers face. It's a vicious cycle. It applies to aircraft, too, just not quite as extreme of a problem as it is in rockets. All airline services operate large and heavy jets with a voracious appetite for Jet A, thus the mass savings becomes more profound as this system scales up. For the "heavies"- the 747's / 787's / A350's / A380's of the world, the mass savings is proportionately more dramatic. Any mass inefficiencies on the part of heavier electric motors and fuel cells and fuel storage containers is immediately offset by the fuel mass savings.
Assuming proper design (always a major assumption), gas turbine engines increase in efficiency with size up to the thermodynamic or Carnot efficiency limit of a simple cycle. The GE90 turbofans achieve a 36% thermodynamic efficiency, for example. Unfortunately, truly massive engines are required to achieve good fuel economy. The outsized GE90 and new GE9x are good examples, in that regard, as are very large turboprops. Even then, that only happens at significant altitude where the air is thinner and the power requirements to achieve a given speed are significantly less than at low altitude where the air the plane is moving through is significantly thicker.
If we don't try to achieve six impossible things before breakfast, then electrification of flight is possible using current technology. If people are insistent on waiting until battery energy density increases significantly, then they'll be waiting for decades for an aircraft that matches the performance of existing aircraft. If we start at 250Wh/kg and battery capacity increases by 3%, year over year, every year, as it has for all recent history, then we'll need to wait about 88 years for batteries to match the energy density of gasoline. If you live for another 47 years, then you'll see large scale commercialization of 1kWh/kg batteries, which would be the point at which we can replace small turboprops with batteries. Could we achieve a breakthrough before then? I certainly hope so, but decades of concerted research around the world with tens of billions of dollars backing it has yet to yield such a breakthrough.

kbd512 · 2019-04-03 20:02:33

Louis,

You didn't watch the video, did you?

That advertisement for SkillShare at the end of the video was directed at people who think magic will happen with 500Wh/kg batteries. Elon Musk can't repeal the laws of physics. Those laws are governed by basic math. That may not be what you want to here, but it's still reality. No appeals to the authority of a man who has never built an aircraft in his entire life will ever change that.

There is no magic in the 500Wh/kg number that Elon Musk spouted off. The Airbus A320 example from the video uses 72.28MWh of energy to go from Heathrow to JFK. If the battery capacity is 278Wh/kg, then the weight of the batteries, as stated in the video, is 260,000kg. If the batteries store 500Wh/kg, the weight of the batteries is 144,560kg. The max takeoff weight of the A320 is 78,000kg. The batteries would weigh 1.85 times the max takeoff weight of the A320. If the weight of the fuel is double the maximum takeoff weight of the entire aircraft, then the aircraft isn't going anywhere. Making the plane bigger or stronger won't help. It takes energy to move weight through the air. That is the not-so-magical physics problem that 500Wh/kg batteries can't solve with a result nearly as good as the A320.

The maximum fuel load of the A320 is 22,177kg, so an equivalent weight of 500Wh/kg batteries would provide 11,088,500Wh or 11MWh, or 15.3% of the capacity that would provide equivalent range to the A320. That provides just over 64 minutes of flight time, as compared to the 7+ hour flight times that the turbofan powered A320 achieves. To achieve the same result with the same "fuel" load, the 500Wh/kg battery must transform into a 3,259Wh/kg (72,280,000Wh / 22,177kg) battery. Will you live to see anything like that? Wonders never cease, but don't hold your breath waiting. Chopping the tail off an aircraft like the A320 won't make up for 6/7th of the energy loss from using 500Wh/kg batteries. Most of the drag comes from the wing (generating enough "up force" to keep that bird in the air). Unless the bird gets a lot lighter, which batteries won't help accomplish, quite the opposite in fact, then using batteries is compounding an already severe problem.

Would you buy an aircraft that has 1/7th or less of the range or flight time of its contemporaries?

Maybe you would, but no airline service that wants to stay in business will.

There's an appropriate energy technology for every application and batteries are not appropriate for aircraft at current or future 500Wh/kg energy density levels. Unless Elon Musk has an anti-gravity device, then he has no ability whatsoever to overcome the effect of gravity on an aircraft in flight. If he does have an anti-gravity device, then he doesn't need anything that has wings on it.

kbd512 · 2019-04-03 20:52:55

Let's go through another exercise where we compute the energy required using Hydrogen fuel cells. Maybe enough repetition will cause the basic concepts to sink in. If not, it's still an easy thing to do.

Our A320 needs 72,820,000Wh of energy to fly for 7 hours.

So...

72,820,000Wh / 27,573Wh/kg = 2,621kg of H2

2,621kg / 0.458kg of H2 per gallon of LNH3 = 5,723.6 gallons of LNH3

5,723.6 gallons * 5.69lbs/gallon = 32,567lbs

The A320's maximum fuel load is 7,190 gallons of Jet A

7,190 gallons * 6.8lbs/gallon of Jet A = 48,892lbs

The A320's pair of CFM-56 engines provide a combined 16MW of power at takeoff, or thereabouts, so our fuel cell weighs 5,333kg or 11,757lbs, at 3kW/kg. That just gobbled up most of our weight savings over our kero-burners. The fuel tanks and electric motors will gobble up the rest. The Magnax motors, at 15kW/kg, would weigh 1,066kg or 2,352lbs. That's a dramatic improvement over the CFM56. We have 2,216lbs of weight remaining to play with to construct the LN3 fuel tanks. Something tells me that we'll be a bit over on our weight allocation.

What does all of this prove? Well... We really need 5kW/kg fuel cells, for starters. That reduces our power pack weight to 3,200kg. We could really use 30kW/kg electric motors (just for 60 seconds worth of takeoff power). We could use expanding N2 in an open cycle to dump the heat through a gas heat exchanger. If we have those things, then we're sitting pretty. We'll have bested the kerosene burning A320 on range or endurance while operate at the same speeds. Nothing emitted from our brand new E320's "tailpipe" isn't already in the air.

Our LNH3 is 1.5 times as energy efficient in this particular application. Notice how the efficiency of the gas turbine engine improves as the size of the engine increases? It's almost like there's a pattern developing here. Anyone here want to bet that our LNH3 energy equivalent is even closer to 1 for an even more fuel efficient aircraft like the GE90-powered 787?

louis · 2019-04-04 04:35:42

I did take a quick look at the video. It seemed to be using 278 Whs per kg as the best you can hope for from a battery.

Musk's proposal is for a VTOL aircraft. Does that make a difference to the peak power requirement? Intuitively I'm thinking it possibly does but I've no idea.

One thing I wonder about - delta planes were seriously considered as an alternative to the winged tubes we eventually opted for. Many designers think the delta shape is far superior.

What if you had a huge VTOL delta plane 100 x 100 x 100 metres wedge shape cover in PV array , to carry the equivalent of a 747. You would have enormous surface area (4300 sq. metres) that could generate significant amounts of electricity from PV. Obviously no good for night flights but...

kbd512 wrote:

Let's go through another exercise where we compute the energy required using Hydrogen fuel cells. Maybe enough repetition will cause the basic concepts to sink in. If not, it's still an easy thing to do.
Our A320 needs 72,820,000Wh of energy to fly for 7 hours.
So...
72,820,000Wh / 27,573Wh/kg = 2,621kg of H2
2,621kg / 0.458kg of H2 per gallon of LNH3 = 5,723.6 gallons of LNH3
5,723.6 gallons * 5.69lbs/gallon = 32,567lbs
The A320's maximum fuel load is 7,190 gallons of Jet A
7,190 gallons * 6.8lbs/gallon of Jet A = 48,892lbs
The A320's pair of CFM-56 engines provide a combined 16MW of power at takeoff, or thereabouts, so our fuel cell weighs 5,333kg or 11,757lbs, at 3kW/kg. That just gobbled up most of our weight savings over our kero-burners. The fuel tanks and electric motors will gobble up the rest. The Magnax motors, at 15kW/kg, would weigh 1,066kg or 2,352lbs. That's a dramatic improvement over the CFM56. We have 2,216lbs of weight remaining to play with to construct the LN3 fuel tanks. Something tells me that we'll be a bit over on our weight allocation.
What does all of this prove? Well... We really need 5kW/kg fuel cells, for starters. That reduces our power pack weight to 3,200kg. We could really use 30kW/kg electric motors (just for 60 seconds worth of takeoff power). We could use expanding N2 in an open cycle to dump the heat through a gas heat exchanger. If we have those things, then we're sitting pretty. We'll have bested the kerosene burning A320 on range or endurance while operate at the same speeds. Nothing emitted from our brand new E320's "tailpipe" isn't already in the air.
Our LNH3 is 1.5 times as energy efficient in this particular application. Notice how the efficiency of the gas turbine engine improves as the size of the engine increases? It's almost like there's a pattern developing here. Anyone here want to bet that our LNH3 energy equivalent is even closer to 1 for an even more fuel efficient aircraft like the GE90-powered 787?

kbd512 · 2019-04-04 11:53:57

Louis,

Post #34 in this thread has the calculations in it for the magical 500Wh/kg batteries.

Let's break this down one more time.

The video posted a figure for 278Wh/kg because that's real current battery technology that an airplane manufacturer can actually purchase.

The video computed the energy usage of the Airbus A320 flying crossing the Atlantic Ocean as 72.28 MegaWatt-hours / 72,280,000 Watt-hours.

That works out to 10,325,714.3 Watt-hours per hour, for 7 hours.

10,325,714.3 (average output required, in Watts) / 16,000,000 (maximum static thrust of the A320’s pair of CFM-56 turbofans at sea level, in Watts) = 64.5% (average equivalent throttle setting for the entire flight from Heathrow to JFK)

The A320's maximum fuel load is 27,200L of Jet A. Jet A weighs 0.82kg/L. Jet A1 is .804kg/L. The difference is relatively minor. Jet A1 (used in Europe) is better quality fuel than Jet A (used in the US).

0.82kg/L * 27,200L = 22,304kg of Jet A

I used 6.8lbs per gallon of Jet A (the calculation we use in the US), thus 48,892lbs / 22,177kg. It really doesn’t matter. Either way, the A320 has 22,000kg (22t) of fuel onboard by the time it takes off.

In terms of battery power, ignoring the fact that a battery powered airplane is never getting any lighter without dropping batteries in flight:

278Wh/kg * 260,000kg (260t) = 72,280,000 Watt-hours

556Wh/kg * 130,000kg (130t) = 72,280,000 Watt-hours

The A320’s maximum take off weight (MTOW) is 78,000kg (78t).

130t (weight of a 72.28MWh Lithium-ion battery at 556Wh/kg) / 78t (A320 MTOW) = 1.66

At 556Wh/kg, the batteries alone are 1.66 TIMES the A320’s MTOW. No Airbus A320 with a 130t battery will ever leave the ground.

The most important equation turns out to be rather simple and requires very little math:

Battery Weight > Max Takeoff Weight = No Bueno

What is a battery-equivalent energy density to replace jet fuel?

72,280,000Wh (total energy requirement) / 22,000kg (weight of the A320’s full jet fuel load) = 3,285Wh/kg (minimum battery energy density required to replace jet fuel, ignoring constant battery weight)

It’s shocking how much energy an airliner requires to move at the speed of a bullet, isn’t it?

Chopping the tail off the aircraft won’t make up for the fact that a 556Wh/kg battery is a paltry 16.93% (556 / 3,285) of the energy density of jet fuel. There’s a simple reason for that. The major energy expenditures come from lift-induced drag and parasitic drag.

What two problems only get worse with heavier airplanes?

Lift-Induced Drag (heavier planes need more lift and more lift creates more induced drag)
Parasitic Drag (even at the same speed, because the plane has more wing surface area to carry more weight)

You’re going to have to give up range, speed, payload capacity, or, in all probability, all three.

Elon Musk’s Imaginary Electric Supersonic VTOL Airplane

All VTOL aircraft are absurdly inefficient and guzzle fuel in a hover because their engines have to support the entire weight of the airplane with thrust and still have power margin left to maneuver and accelerate or transition to horizontal flight. If you lose an engine, you’re going down. The fact that no F-35B ever crashed during the test program is a testament to the capabilities of Lockheed-Martin’s / Rolls-Royce’s / Pratt & Whitney’s engineers and the military test pilots who flew the test articles. That said, the only F-35 to ever crash was a F-35B model (the VTOL variant). It was supposedly the result of fuel starvation, but the accident is still under investigation. At least the pilot walked away, but he was also strapped to an advanced Martin-Baker ejection seat. The Harriers were crashed by the dozens, even after the test program was complete. The accident record for VTOL aircraft has clearly improved with the F-35, but I think we’re still another generation away from a VTOL system that’s utterly reliable. I trust in the greater reliability of electric motors over the mind-blowingly complex after-burning turbofans like the F-135 that powers the F-35, but failures typically happen when stress on the motor and battery are maximized, as it would be in a hover.

There has never been an airliner with a thrust-to-weight ratio (TWR) greater than 1 in the entire history of flight. Concorde had a 0.37 TWR. Going supersonic is about aerodynamics first and thrust second. The F-111 and B-1 are the only real examples of aircraft that are designed to fly at supersonic speeds at low altitude for any significant distance. The B-1A was designed to fly slightly faster than Concorde at high altitude, then the modified B-1B was designed to fly just over Mach at low altitude and has no hope of catching up to a Concorde at high altitude. F-111 was slightly faster than Concorde at high altitude. Again, aerodynamics. F-111’s TWR is 0.61 (significantly higher than Concorde) and B-1’s TWR is 0.28 (significantly lower than Concorde). If you tried to fly Concorde supersonic at treetop level, it’d probably induce stress failure in the skin and spars that would rip the wings off the plane.

Why haven’t we ever built a VTOL airliner, never mind a supersonic VTOL airliner or an electric supersonic VTOL airliner?

The design requirements are wildly divergent. Concorde proved that you don’t need a TWR greater than 1, or anything close to it, to sustain supersonic flight. In point of fact, any such design would necessitate carrying extra heavy motors just for VTOL flight or absurdly powerful motors and complex control mechanisms to control the direction of thrust. It’s a comically senseless idea, even if you can do it.

Solar Powered Airplanes

With 50% efficient solar panels that we don’t have (reality vs magical thinking again), 4,300m^2 would provide an absolute maximum of 2,257,500We (4,300m^2 * 525W/m^2) at high noon, assuming no other inefficiencies or losses. That sounds like a lot, until you realize that an A320, which is not large by airliner standards, is using 10MW of power, on average, to move a much smaller wing through the air. If the solar panels were 100% efficient, you still get 4,515,000We (4,300m^2 * 1050W/m^2). The Antonov An-225’s wing area is 905m^2. 4,300m^2 is 4.75 TIMES the wing area of the AN-225. Again, no airliner will buy something 4.75 times the size of the AN-225 that can’t fly as fast as a regular jet and has a passenger capacity similar to the A320 or 737.

Fuel Cell Powered Airplanes

The only technology we currently have that has any hope of matching the speed and range of a turbofan powered airliner is a very efficient PEM fuel cell and NH3, which would be liquid at 1 ATM of pressure in the stratosphere. I didn’t pull that out of my rear end. I looked at current technology and figured out what we have that could realistically replace gas turbines. This is the only other technology that provides the energy density and power density required to propel a prototypical airliner through the air at the same speed and to the same distance for equivalent weight.

Electric Aircraft with Today's Technology

Do you want real and useful electric aircraft that you can fly aboard using today's technology, in another 5 years or so, or do you want to dream about solar and battery powered electric aircraft that might be practical in another half century or so?

SpaceNut · 2019-04-04 16:50:27

EV Battery 600 Miles

kbd512 · 2019-04-04 18:04:31

SpaceNut,

Google "Alevo". These are the same people who promised revolutionary batteries before, never delivered, and went bankrupt. Prior to that, they were "Fortu Holdings", never delivered, and went bankrupt. Is this time different than the previous two times? Time will tell. Deliver the batteries first. All claims from Innolith are highly suspect based upon their past two abject failures.

Edit:

In case the point isn't clear, I'm talking about the management team at Innolith, not the researchers or other employees. That said management practices can make or break a company.

Eviation Alice - Tesla Battery Pack
MTOW: 13,999lbs (6,350kg)
No Battery + Pax Weight: 6,369lbs (2,889kg)
Battery Capacity: 900kWh (260Wh/kg)
Battery Weight: 7,630lbs (3,460kg)
Range: 650 miles (1,046km) with IFR reserves

Eviation Alice - Innolith Energy Battery Pack
MTOW: 13,999lbs (6,350kg)
No Battery + Pax Weight: 6,369lbs (2,889kg)
Battery Capacity: 3.46MWh (1,000Wh/kg)
Battery Weight: 7,630lbs (3,460kg)
Range: 2,498 miles (4,021km) with IFR reserves

That’s 1.18 times the range of the Pilatus PC-12NG. It’s 3,549lbs heavier, though, and appears to have a higher stall speed. Maybe we could simply match the range and lose some of the battery weight to keep the landing speeds out of the light jet range. The propellers in the wingtips thing is kinda stupid and likely to result in deaths from loss of control if you lose an engine on takeoff. If those motors were all moved to the tail to make it a single propeller, multi-motor vehicle, then this thing might have a future if it actually comes in at that $2.9M price. That’s about half of a nicely appointed PC-12NG.

Last edited by kbd512 (2019-04-04 19:07:16)

SpaceNut · 2019-04-04 19:44:20

Googled/Bing same thing for inorganic electrolyte instead in which the first link was about that company.
https://www.greentechmedia.com/articles … #gs.4dawxu

Current lithium-ion batteries use liquid electrolytes, which pose significant safety challenges due to the presence of reactive and highly volatile organic solvents. Solid electrolytes, particularly those made of inorganic compounds like sulfides, offer a promising alternative for safe, reliable, stable, and long life cycle electrochemical cells. One challenge for adoption of solid-state sulfide electrolytes is high resistance present at the electrode/electrolyte interface and a narrower electrochemical stability window when compared to oxide materials.

https://www.mdpi.com/1996-1073/6/9/4448/pdf
A Liquid Inorganic Electrolyte Showing an Unusually High Lithium Ion Transference Number: A Concentrated Solution of LiAlCl4 in Sulfur Dioxide

https://www.sandia.gov/ess-ssl/docs/pr_ … Poster.pdf

https://link.springer.com/content/pdf/b … -0%2F1.pdf

louis · 2019-04-04 19:54:49

I'm don't think I contribute much to this except to say Musk isn't normally out by a factor of 7.

I am interested in electric aircraft taking their place in the world of flight. I think that will begin with passenger carrying drones. We are just about there with those for short urban flights. I think recharging of such drones will eventually allow them to fly considerable distances.

I don't get the same feeling about small aeroplanes, but we shall see.

kbd512 wrote:

Louis,
Post #34 in this thread has the calculations in it for the magical 500Wh/kg batteries.
Let's break this down one more time.
The video posted a figure for 278Wh/kg because that's real current battery technology that an airplane manufacturer can actually purchase.
The video computed the energy usage of the Airbus A320 flying crossing the Atlantic Ocean as 72.28 MegaWatt-hours / 72,280,000 Watt-hours.
That works out to 10,325,714.3 Watt-hours per hour, for 7 hours.
10,325,714.3 (average output required, in Watts) / 16,000,000 (maximum static thrust of the A320’s pair of CFM-56 turbofans at sea level, in Watts) = 64.5% (average equivalent throttle setting for the entire flight from Heathrow to JFK)
The A320's maximum fuel load is 27,200L of Jet A. Jet A weighs 0.82kg/L. Jet A1 is .804kg/L. The difference is relatively minor. Jet A1 (used in Europe) is better quality fuel than Jet A (used in the US).
0.82kg/L * 27,200L = 22,304kg of Jet A
I used 6.8lbs per gallon of Jet A (the calculation we use in the US), thus 48,892lbs / 22,177kg. It really doesn’t matter. Either way, the A320 has 22,000kg (22t) of fuel onboard by the time it takes off.
In terms of battery power, ignoring the fact that a battery powered airplane is never getting any lighter without dropping batteries in flight:
278Wh/kg * 260,000kg (260t) = 72,280,000 Watt-hours
556Wh/kg * 130,000kg (130t) = 72,280,000 Watt-hours
The A320’s maximum take off weight (MTOW) is 78,000kg (78t).
130t (weight of a 72.28MWh Lithium-ion battery at 556Wh/kg) / 78t (A320 MTOW) = 1.66
At 556Wh/kg, the batteries alone are 1.66 TIMES the A320’s MTOW. No Airbus A320 with a 130t battery will ever leave the ground.
The most important equation turns out to be rather simple and requires very little math:
Battery Weight > Max Takeoff Weight = No Bueno
What is a battery-equivalent energy density to replace jet fuel?
72,280,000Wh (total energy requirement) / 22,000kg (weight of the A320’s full jet fuel load) = 3,285Wh/kg (minimum battery energy density required to replace jet fuel, ignoring constant battery weight)
It’s shocking how much energy an airliner requires to move at the speed of a bullet, isn’t it?
Chopping the tail off the aircraft won’t make up for the fact that a 556Wh/kg battery is a paltry 16.93% (556 / 3,285) of the energy density of jet fuel. There’s a simple reason for that. The major energy expenditures come from lift-induced drag and parasitic drag.
What two problems only get worse with heavier airplanes?
Lift-Induced Drag (heavier planes need more lift and more lift creates more induced drag)
Parasitic Drag (even at the same speed, because the plane has more wing surface area to carry more weight)
You’re going to have to give up range, speed, payload capacity, or, in all probability, all three.
Elon Musk’s Imaginary Electric Supersonic VTOL Airplane
All VTOL aircraft are absurdly inefficient and guzzle fuel in a hover because their engines have to support the entire weight of the airplane with thrust and still have power margin left to maneuver and accelerate or transition to horizontal flight. If you lose an engine, you’re going down. The fact that no F-35B ever crashed during the test program is a testament to the capabilities of Lockheed-Martin’s / Rolls-Royce’s / Pratt & Whitney’s engineers and the military test pilots who flew the test articles. That said, the only F-35 to ever crash was a F-35B model (the VTOL variant). It was supposedly the result of fuel starvation, but the accident is still under investigation. At least the pilot walked away, but he was also strapped to an advanced Martin-Baker ejection seat. The Harriers were crashed by the dozens, even after the test program was complete. The accident record for VTOL aircraft has clearly improved with the F-35, but I think we’re still another generation away from a VTOL system that’s utterly reliable. I trust in the greater reliability of electric motors over the mind-blowingly complex after-burning turbofans like the F-135 that powers the F-35, but failures typically happen when stress on the motor and battery are maximized, as it would be in a hover.
There has never been an airliner with a thrust-to-weight ratio (TWR) greater than 1 in the entire history of flight. Concorde had a 0.37 TWR. Going supersonic is about aerodynamics first and thrust second. The F-111 and B-1 are the only real examples of aircraft that are designed to fly at supersonic speeds at low altitude for any significant distance. The B-1A was designed to fly slightly faster than Concorde at high altitude, then the modified B-1B was designed to fly just over Mach at low altitude and has no hope of catching up to a Concorde at high altitude. F-111 was slightly faster than Concorde at high altitude. Again, aerodynamics. F-111’s TWR is 0.61 (significantly higher than Concorde) and B-1’s TWR is 0.28 (significantly lower than Concorde). If you tried to fly Concorde supersonic at treetop level, it’d probably induce stress failure in the skin and spars that would rip the wings off the plane.
Why haven’t we ever built a VTOL airliner, never mind a supersonic VTOL airliner or an electric supersonic VTOL airliner?
The design requirements are wildly divergent. Concorde proved that you don’t need a TWR greater than 1, or anything close to it, to sustain supersonic flight. In point of fact, any such design would necessitate carrying extra heavy motors just for VTOL flight or absurdly powerful motors and complex control mechanisms to control the direction of thrust. It’s a comically senseless idea, even if you can do it.
Solar Powered Airplanes
With 50% efficient solar panels that we don’t have (reality vs magical thinking again), 4,300m^2 would provide an absolute maximum of 2,257,500We (4,300m^2 * 525W/m^2) at high noon, assuming no other inefficiencies or losses. That sounds like a lot, until you realize that an A320, which is not large by airliner standards, is using 10MW of power, on average, to move a much smaller wing through the air. If the solar panels were 100% efficient, you still get 4,515,000We (4,300m^2 * 1050W/m^2). The Antonov An-225’s wing area is 905m^2. 4,300m^2 is 4.75 TIMES the wing area of the AN-225. Again, no airliner will buy something 4.75 times the size of the AN-225 that can’t fly as fast as a regular jet and has a passenger capacity similar to the A320 or 737.
Fuel Cell Powered Airplanes
The only technology we currently have that has any hope of matching the speed and range of a turbofan powered airliner is a very efficient PEM fuel cell and NH3, which would be liquid at 1 ATM of pressure in the stratosphere. I didn’t pull that out of my rear end. I looked at current technology and figured out what we have that could realistically replace gas turbines. This is the only other technology that provides the energy density and power density required to propel a prototypical airliner through the air at the same speed and to the same distance for equivalent weight.
Electric Aircraft with Today's Technology
Do you want real and useful electric aircraft that you can fly aboard using today's technology, in another 5 years or so, or do you want to dream about solar and battery powered electric aircraft that might be practical in another half century or so?

kbd512 · 2019-04-04 20:40:11

Louis,

You get a certain number of Watt-hours per kilogram of fuel from burning various liquid hydrocarbons fuels. Those figures are fairly substantial, even though the thermodynamic efficiency of the engines using them is nothing to write home about. You can either match that with a battery or fuel cell and electric motor combination that provides equivalent energy output, or you can't. If you can't, then you have to give up speed, range, payload, or a little bit of all three. It's that simple. You can easily make or break an aircraft design with aerodynamics, but there are no clever tricks to deal with gravity. Less weight is always better, provided that the aircraft stays in one piece.

A 1,000Wh/kg battery provides less than 1/3 of the energy content equivalent of a kilogram of jet fuel when that fuel is burned in a large high bypass turbofan engine in the stratosphere. You can reduce your speed, reduce your range, and/or reduce your payload. Those are the trade-offs to consider. So far as I know, not even Elon Musk can repeal gravity. When we can manage that, we no longer need aircraft to fly.

louis · 2019-04-05 05:18:58

I appreciate all you say but I just find it difficult to believe that Musk can't do that simple comparison on a calculator...so there must be more to this.

kbd512 wrote:

Louis,
You get a certain number of Watt-hours per kilogram of fuel from burning various liquid hydrocarbons fuels. Those figures are fairly substantial, even though the thermodynamic efficiency of the engines using them is nothing to write home about. You can either match that with a battery or fuel cell and electric motor combination that provides equivalent energy output, or you can't. If you can't, then you have to give up speed, range, payload, or a little bit of all three. It's that simple. You can easily make or break an aircraft design with aerodynamics, but there are no clever tricks to deal with gravity. Less weight is always better, provided that the aircraft stays in one piece.
A 1,000Wh/kg battery provides less than 1/3 of the energy content equivalent of a kilogram of jet fuel when that fuel is burned in a large high bypass turbofan engine in the stratosphere. You can reduce your speed, reduce your range, and/or reduce your payload. Those are the trade-offs to consider. So far as I know, not even Elon Musk can repeal gravity. When we can manage that, we no longer need aircraft to fly.

kbd512 · 2019-04-05 11:25:50

Louis,

Perhaps what we actually can do can be more authoritatively explained by George Bye, of Bye Aerospace and SunFlyer / eFlyer fame, since his company has actually built an electric drone and two electric aircraft, one of which is currently being certified by the FAA. I trust their explanations about what we can and can't do more than someone who has never built an aircraft, even if that someone is Elon Musk. I understand the hero worship associated Mr. Musk, and there's no doubt in my mind that he's an extraordinary high-performing individual, but rocketry is an entirely different game. Some of the basic concepts are shared between design of rockets and aircraft, but rockets don't generate lift to fly- they use pure thrust. Inert mass fraction, thrust, and specific impulse are the key metrics that determine rocket performance. Total mass and lift-to-drag ratio are the key metrics for powered flight, as that is what drives energy consumption to remain airborne without resorting to using pure thrust. Sufficient thrust is still required to achieve a given speed. However, that number can also be exceptionally low as compared to a rocket and still producing a high performance aircraft.

This article comes from the Institute of Electrical and Electronics Engineers (IEEE):

Cheaper, Lighter, Quieter: The Electrification of Flight Is at Hand - by George Bye

This Aviation Stack Exchange article provides a more detailed breakdown of the energy requirements and how aerodynamics and weight affect them (not intended for those who don't like math, but it does provide a more complete explanation):

What energy density is required for the batteries in order to make an all-electric analogue of the Cessna 150 or similar plane?

The Stack Exchange article explains how important the Lift-to-Drag (L/D) ratio is to performance, as well as weight and energy density. We're really talking about the specific energy (Watt-hours per kilogram) of the batteries, but that term has become synonymous with energy density in common usage and that is why I use "energy density" when I talk about batteries.

The only magic to be had is in the aerodynamics of the design and also in the potential energy recovery capabilities of an aircraft using a windmilling propeller to recharge the batteries during descents. The SunFlyer (eFlyer?) and Pipistrel Alpha Electro (Alpha Trainer) are intended as pattern trainers. That means staying in the landing pattern and practicing take offs and landings- the two most critical phases of flight where a lot is going on. It's incredibly important to hone these skills and electric aircraft can only help immeasurably by lowering fuel costs, but we're not going to be doing any cross-country flights with a 3 hour flight time at 70mph. The SunFlyer generates a bit more thrust from its propeller thanks to a better cowling design, has less drag from air inlets used for motor cooling, and it uses novel weight distribution that battery form factor enables. All of these factors add up to a 15% reduction in drag, as compared to a Lycoming-powered Cessna like the kind that I fly.

The Lycoming air-cooled boxer engines (most are four-bangers, by numbers in the fleet, but there are 4 / 6 / 8 cylinder versions) are not terribly efficient, as they are 1930's technology, and require lots of cooling air flow, which generates substantial drag. Compared to an electric motor, it's not efficient at all on energy use, though still significantly more fuel efficient than a gas turbine that generates equivalent power, if substantially heavier than a gas turbine.

Lycoming - IO-360
Power Output: 200hp
Fuel Burn: 11gph (with everything set up correctly, never a given; 12 or 72lbs/hr is what we normally burn down low; can be appreciably less than that with electronic ignition and timing but we use carbs)
Weight: 325lbs or so without accessories, but some installations and engine options are nearer to 400lbs, so 350 is a better average number
Fuel: 100LL / AVGAS (6lbs/gallon)
Note: weight varies so much because of different pistons / exhaust / alternators / starters / fuel air servos / oil capacity / etc

Turbine Aeronautics - TA200TP
Power Output: 200hp
Fuel Burn: 14.6gph / 99lbs/hr
Weight: 150lbs (all-up weight with all required accessories)
Fuel: Jet A / Jet A1 (6.8lbs/gallon)
Note: There's a 200 pound weight differential between these engines, so if weight was more important than fuel burn (weight drives fuel burn, since it drives power required), then you could fly for about 6 hours in an aircraft of equivalent weight (engine + fuel) and with equivalent performance, as compared to one powered by our trusty IO-360, before the fuel economy savings of the IO-360 begin to overtake the turboprop.

How?:
350lbs (piston engine) + 396lbs (fuel- 11gph * 6lbs/gallon * 6hrs) = 746lbs
150lbs (turboprop engine) + 596lbs (fuel - 14.6gph * 6.8lbs/gallon * 6hrs) = 746lbs

There's a reason you don't see turboprops under about 400hp in light aircraft. The 8 cylinder Lycoming IO-720 is around 400hp, for comparison purposes. The turboprops are more expensive to buy, more delicate in operation, and more expensive to maintain. The TBO's are typically longer for turboprops than piston engines, which reduces operating costs if you fly a lot. That's why commercial services generally use turboprops. The maintenance costs can add significantly to total cost with maintenance-intensive engines.

A jump school would use a lightweight turboprop aircraft to swiftly climb for altitude, drop off their parachutists, beat the parachutists to the ground, and already be in the process of picking up the next load of parachutists by the time the first load of parachutists hit the ground. Having that Lycosaurus hanging off the nose of your bird is like having an extra person sitting on the nose at all times. The flight times are only around 15 minutes or so, thus the turboprop is pretty much always lighter with a given fuel load.

Edit: Added power output figures for both engines (doh!)

Last edited by kbd512 (2019-04-05 11:28:03)

kbd512 · 2019-04-05 12:20:20

I thought that this may better explain the energy economics of fuel cell operation:

Just another Fuel Cell Formulary by Dr. Alexander Kabza

Edit:

Here's another great quote taken from this little gem:

Fuel Volumetric and Gravimetric Energy Density compared - Or neglected Real-world physics
Let's see.. Maybe gasoline is the fuel of choice ... because of it's volumetric energy density? And liquid hydrogen makes good rocket fuel because of its gravimetric energy density?
Reality: a gallon of Gasoline has more hydrogen than a gallon of liquid hydrogen - in other words gasoline is a great way to store hydrogen fuel. The only economic source of hydrogen at this time is oil anyway. You could write your congressman to change the laws of physics. Often, reality doesn't fit our emotional wants and desires, but reality can be a stubborn thing to deal with - it doesn't go away when you quit believing in it.
The numbers compiled here varied a bit - the definitions of gasoline and diesel are not precise; Gasoline and diesel fuel are a mixture of about 100 different molecules who's ratios vary from batch to batch. Diesel fuel should be very similar to gasoline. Diesel is preferred for trucks due to torque/rpm curves. A turbine should have about the best hydrocarbon economy - BUT it must be run in a very narrow range to achieve that and has a very slow ramp up making it uneconomical for cars and trucks.
Battery calculation that gets ignored
(We call this arm waving of venture vultures 1 -- note that venture vultures can't really fly no mater how hard they flap their arms)
On rechargeable batteries there is a cycle life time - often 100 - 400 (some claims of 1000 - but with hugely derated use). If you take the capacity of the battery times the number of cycles you get a total energy out over the life time of the battery. This then can be used to calculate a Wh/cost so it can be compared to primary fuels - such as gasoline. Even ignoring the cost of the energy required to recharge these batteries, the costs are not in the ball park for vehicular use.
Besides The best of lithium batteries are 36 TIMES larger than gasoline. Standard lead acid batteries are 200 times larger AND heavier.
1 Venture vultures are those folks that make a living off of the venture capital investment of folks that didn't study math or physics.

These quotes are over 10 years old now. They're still as accurate today, with respect to the fundamental problem, as when they were originally written. Considerable time and effort has gradually closed the gasoline-equivalent energy density gap between gasoline and batteries, but we still have a long way to go. Is there a real breakthrough just over the horizon? Well... There's at least one new claim every week for as long as I can remember. I've yet to see any materialize as commercial products.

Last edited by kbd512 (2019-04-05 13:21:05)

louis · 2019-04-05 13:58:22

Why not have battery changers for passenger carrying drones (PCDs)? PCDs have no problem hovering. You could have battery changer stations at high level located every 10, 20, 50 miles or so (according to how advanced the battery technology is). The drone sweeps in and, controlled by the sort of technology used to park cars automatically, aligns perfectly over the battery changer. Main battery is released (smaller supplementary batteries keep it in flight) and then replaced. Total replacement time 90 secs. The PCD continues its flight.

Last edited by louis (2019-04-05 16:08:43)

kbd512 · 2019-04-05 16:58:30

Louis,

Byzantine complexity to contend with the fact that the technology isn't ready won't help. Helicopters require a lot of extra power to take off and land. That makes the power provisioning problem worse, not better. The overwhelming majority of people don't travel by helicopter because helicopters aren't practical for providing economic transportation. If they were, do you think the moderately wealthy people living in LA would ever get on the 405 and sit in traffic for two hours every day?

Gas powered cars are half the price of battery powered cars, but every city in the world that provides economic transportation for its citizens uses buses and trains rather than cars. The same economic forces are hard at work when it comes to mass air travel. If you want to pay considerably more, then you can pay for private transportation. It's almost as if universal economic forces are at work there. Substituting more expensive battery powered aircraft for far less expensive battery powered cars only makes the economics problem far worse.

Someone also has to purchase and operate the aircraft, even if it doesn't require a pilot. There's no such thing as a zero-maintenance aircraft and all rotary wing aircraft, irrespective of power plant, have maintenance requirements that greatly exceed that of fixed wing aircraft. Ask a helicopter owner how much they pay their mechanic and how much they pay for spare parts. Personal aircraft are very expensive, relative to the amount of revenue they could possibly generate. That's why you don't see any cheaper gas powered PCD's today.

Computers could handle the increase in air traffic, until they stop working- reason unimportant, and then you need humans to make decisions that computers still can't make. You also have to convince people to fly in aircraft without pilots on board. Good luck with that. You might do it, but I wouldn't. Most people I know wouldn't do it, either. Airbus and Boeing have had a number of crashes caused by the very computerized systems that were specifically created to prevent crashes.

louis · 2019-04-05 19:28:46

Helicopters are unsafe and quite large. PCDs are small and safe (because of multiple simple rotors).

A battery changer is not complex at all. You could basically have batteries on an elevator/lift - charged batteries come up to the platform over which the PCD hovers guided by parking technology. The PCD automatically releases the battery pack when it is over the appropriate location - that pack is taken down by conveyor to be recharged. The PCD moves forward and is fitted with the new battery pack.

If you want "byzantine complexity" think about a gas/petrol filling station...that's way more complex!

This battery changing would all be computer controlled. There would be little complexity to the process. It might be require major capital investment, I accept, to build the charging stations.

This is an interesting video about the problems with battery changers for land EVs.

Seems to me that most of the problems referred to there wouldn't apply to PCDs. The likelihood is that, as with aeroplanes, only a few models would dominate the market - Airbus v Boeing. This isn't like the car market. Also, whoever got the best model in the air could dominate the market - this is more like Betamax v VHS. A battery changer station for PCDs does not required any underground facilities. Everything can be above ground, which helps on costs.

I really do think PCDs will replace car taxis for a lot of business users. In London a lot of the main rail stations are a few miles (= often a good 40 minutes in traffic) from the financial centre. The airports are positioned well away from the centre, so you are looking at 2-3 hour journeys). There will be a lot of demand for PCDs I think. Small aeroplanes can't fit the bill because of landing space. Helicopters are extremely noisy.

Most aircraft crashes are caused by human error, not computer error. The recent Boeing crashes appear to be something of an exception owing to poor initial design.

An aircraft with all its control systems is an inherently way more complex system than a drone. I think a 747 has over a million parts - with hundreds of thousands being flight-critical. I think a drone would be much more on a par with a car (probably a lot less complex than an ICE automobile). Modern automobiles are extremely reliable - again it is human error that causes most accidents. Drone maintenance I think will be way simpler than helicopter or aircraft maintenance. I think it will be more a replacement maintenance - usually just simply throw away things like rotors after x amount of travel because they are simple machines and it will be simple to do that, discard and replace.

A drone will have few of the hazards encountered on the road - pedestrians, cyclists, mud or oil on the road, water on the road, poor visibility, over-signage etc. So I think computer controlled flight will present even fewer dangers than we see with self-drive cars on land.

I think people will warm to the PCD v. quickly and feel safe using them.

kbd512 wrote:

Louis,
Byzantine complexity to contend with the fact that the technology isn't ready won't help. Helicopters require a lot of extra power to take off and land. That makes the power provisioning problem worse, not better. The overwhelming majority of people don't travel by helicopter because helicopters aren't practical for providing economic transportation. If they were, do you think the moderately wealthy people living in LA would ever get on the 405 and sit in traffic for two hours every day?
Gas powered cars are half the price of battery powered cars, but every city in the world that provides economic transportation for its citizens uses buses and trains rather than cars. The same economic forces are hard at work when it comes to mass air travel. If you want to pay considerably more, then you can pay for private transportation. It's almost as if universal economic forces are at work there. Substituting more expensive battery powered aircraft for far less expensive battery powered cars only makes the economics problem far worse.
Someone also has to purchase and operate the aircraft, even if it doesn't require a pilot. There's no such thing as a zero-maintenance aircraft and all rotary wing aircraft, irrespective of power plant, have maintenance requirements that greatly exceed that of fixed wing aircraft. Ask a helicopter owner how much they pay their mechanic and how much they pay for spare parts. Personal aircraft are very expensive, relative to the amount of revenue they could possibly generate. That's why you don't see any cheaper gas powered PCD's today.
Computers could handle the increase in air traffic, until they stop working- reason unimportant, and then you need humans to make decisions that computers still can't make. You also have to convince people to fly in aircraft without pilots on board. Good luck with that. You might do it, but I wouldn't. Most people I know wouldn't do it, either. Airbus and Boeing have had a number of crashes caused by the very computerized systems that were specifically created to prevent crashes.

kbd512 · 2019-04-06 00:46:19

Louis,

This topic was supposed to be about the practicality of airline services using electric aircraft and I'm trying to remain focused on the topic. I recognize that you're quite enamored with this idea of passenger carrying drones, so I've created a new topic entitled "Autonomous Passenger Carrying Electric Aircraft" to further discuss your ideas there.

louis · 2019-04-06 03:58:33

Fair enough.

kbd512 wrote:

Louis,
This topic was supposed to be about the practicality of airline services using electric aircraft and I'm trying to remain focused on the topic. I recognize that you're quite enamored with this idea of passenger carrying drones, so I've created a new topic entitled "Autonomous Passenger Carrying Electric Aircraft" to further discuss your ideas there.

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