Evolution and limit of battery energy density

[Tommy Cookers]

Multirotor drones are entertaining. What's less reliable and efficient than spinning a big propeller slowly, spinning 8 of them quickly!

the multi so-called rotor is inherently less efficient
because it accelerates downwards a relatively small amount of air by moving it fast
relative to an equivalent 'proper size' helicopter rotor - this made for acting on a larger amount of air so moving it slower
the lift here comes from momentum (velocity) change not kinetic energy (velocity squared) change
KE is wasted energy

this is the reason why ....
rotary wings are less efficient than fixed wings
rotary wings in hover are less efficient than rotary wings in translational flight (eg moving forward)
rotary wings in hover-out-of-ground-effect HOGE are less efficient than in HIGE

similarly
greater efficiency ie minimum KE cost for a given 'thrust' occurs when accelerating fluid that is moving forward
ie the propulsor working on boundary layer fluid - remember a body moving in fluid drags along the adjacent fluid layer
ships with such internal 'jet propulsors' use higher rpm lower torque engine types as ....
BL allows less fluid but more acceleration (for a given efficiency ie momentum vs KE outcome)

in aircraft the (liquid-cooled) electric motor is better suited than the ICE to positioning for BL
and BL propulsion can reduce airframe drag

[nzjrs]

Multirotor drones are entertaining. What's less reliable and efficient than spinning a big propeller slowly, spinning 8 of them quickly!

the multi so-called rotor is inherently less efficient
because it accelerates downwards a relatively small amount of air by moving it fast
relative to an equivalent 'proper size' helicopter rotor - this made for acting on a larger amount of air so moving it slower
the lift here comes from momentum (velocity) change not kinetic energy (velocity squared) change
KE is wasted energy

this is the reason why ....
rotary wings are less efficient than fixed wings
rotary wings in hover are less efficient than rotary wings in translational flight (eg moving forward)
rotary wings in hover-out-of-ground-effect HOGE are less efficient than in HIGE

similarly
greater efficiency ie minimum KE cost for a given 'thrust' occurs when accelerating fluid that is moving forward
ie the propulsor working on boundary layer fluid - remember a body moving in fluid drags along the adjacent fluid layer
ships with such internal 'jet propulsors' use higher rpm lower torque engine types as ....
BL allows less fluid but more acceleration (for a given efficiency ie momentum vs KE outcome)

in aircraft the (liquid-cooled) electric motor is better suited than the ICE to positioning for BL
and BL propulsion can reduce airframe drag

I agree with you, sorry if my sarcasm wasn't clear! (I should have also written '8 smaller ones' to be doubly clear )

[Andres125sx]

much higher than any current plane or helicopter

My point was more from first principles; 4-8x as many rotors/motors vs removal of the rotor-head and the rotor-shaft assemblies in a conventional helicopter. I think the reliability long-term of both approaches, in actual commercial passenger use, very much remains to be seen (remember: the like for like comparison, if we get to speculate about future vehicles and say a 30 minute ride is enough, is electric helicopter vs electric multi-rotor)

Actually I was unconsciosly comparing electric helicopters vs electric multi-rotors as that´s my experience, if you take into the ecuation an ICE then difference is even higher.

But no, a multicopter rotor is just an electric motor with a prop, no more moving parts than the bell of the motor and the prop, only the bearings suffer some wear so maintenance is sporadic, that´s thinking about drone to carry people, with RC drones maintenance simply do not exist, spin the motor by hand from time to time to check it moves free and smooth and it´s done.


OTOH an helicopter rotor is an extremelly complicated mechanism with moving parts all around wich require huge and frequent maintenance to keep them all adjusted and without excessive wear



They´re day and night, simply can´t be compared

[theblackangus]

OTOH an helicopter rotor is an extremelly complicated mechanism with moving parts all around wich require huge and frequent maintenance to keep them all adjusted and without excessive wear
https://media.mscsoftware.com/cdn/farfu ... k=cR4BjuEY

They´re day and night, simply can´t be compared

Your being a bit unfair here, your picture above is a very old and more complex heli head =)
New helis have a less complex head with no need for the additional fly bar, but a bit more electronics.

You are also glossing over the fact that multi-rotors need more complex electronics and sensors to keep themselves in the air, so more room for software problems than a classic heli.

There is a trade here for mechanical complexity vs electronic complexity. (Multi rotor fly away syndrome anyone?)

I have "nearly no" maintenance with my heli either, as long as I don't crash it.
If I crash either my multi-rotor or my heli its usually alot of rebuild on either =)
Just because there are fewer "moving parts" doesn't mean there are less things to fix, non-moving parts break as well.
And frankly it seems like my multi-rotor motors are more prone to fail than any of the parts in my heli, never had a single heli motor fail even in a crash.

I don't know what you are doing to your heli that you need to re-adjust stuff all the time. Im good unless I crash it, and I fly helis small to big. All in all my feeling is that they are about the same maintenance, with planes being slightly less.

Sadly both suffer very limited flight times with batteries, vs gas (Heli/Planes).
The flight time ratio per pound for standard batteries is close to 1:1 more batteries = very limited extra flight time.

Hopefully that will change in the future, as I do like using a battery vs gas for my flying craft =)

[Andres125sx]

OTOH an helicopter rotor is an extremelly complicated mechanism with moving parts all around wich require huge and frequent maintenance to keep them all adjusted and without excessive wear
https://media.mscsoftware.com/cdn/farfu ... k=cR4BjuEY

They´re day and night, simply can´t be compared

Your being a bit unfair here, your picture above is a very old and more complex heli head =)
New helis have a less complex head with no need for the additional fly bar, but a bit more electronics.

It was first picture I found, didn´t spend too much time searching

You are also glossing over the fact that multi-rotors need more complex electronics and sensors to keep themselves in the air, so more room for software problems than a classic heli.

There is a trade here for mechanical complexity vs electronic complexity. (Multi rotor fly away syndrome anyone?)

That suppossed electronic complexity is actually quite easy to achieve. Anyone can purchase today a flight controller and gps to build an autonomous drone for around $100, this one is including long range tx/rx wich is only needed for rc aircrafts

https://www.banggood.com/Holybro-PIX32- ... rehouse=CN

So no, no complexity at all, it´s quite simple

And yes, I´ve seen my 10k$ drone fly away, but that was at first stages of drone development (around 10 years ago) and with hobby material, not certified aeronautic one. Different worlds

If I crash either my multi-rotor or my heli its usually alot of rebuild on either =)

Who´s being unfair now mate?

Any heli crash, even if it´s not a huge crash, suppose a complete rotor rebuild, while most multi crashes suppose a prop change and keep flying, if it was a tough one unscrew an arm and its motor and substitude it with a new one. Can be done even in the flying field

Just because there are fewer "moving parts" doesn't mean there are less things to fix, non-moving parts break as well.

Of course, but moving parts need some adjustment for smooth and play-free movement and are a lot more easy to break than a solid one

And frankly it seems like my multi-rotor motors are more prone to fail than any of the parts in my heli,

Try a different brand, only my first motors 15 years ago failed, and they were 5$ motors. From then 15-50$ motors have never failed, and I´ve used some dozens different brands

Sadly both suffer very limited flight times with batteries, vs gas (Heli/Planes).
The flight time ratio per pound for standard batteries is close to 1:1 more batteries = very limited extra flight time.

Hopefully that will change in the future, as I do like using a battery vs gas for my flying craft =)

I´ve always agreed that´s the limiting factor for multirotors. But since today there are passenger drones with 30 minutes range they´re already viable for short trips, so any new battery improving current energy density will make them even more viable

[mzso]

Batteries with some level of improvement certainly won't make them viable. They weren't viable with fuels readily available that have greater energy density than even the most advanced future batteries hope to have.

I think when comparing energy densities it is necessary to take into account conversion efficiency. A kilogram of petrol may well contain 45 MJ but only 10 to 20 is recovered as work in the ICE. Big range because ICE efficiency is very variable. Electric motors are more efficient.

Even so batteries are a long way off, maybe an order of magnitude so there’s a long way to go.

Perhaps. But you also shouldn't forget, that with hybridization more of that energy can be used with ICE engines.
In F1 they claim that they gone past 50% efficiency with the power units. It sacrifices some of the weight advantage, but is brings a lot more than putting more batteries in an EV.

And the weight of the power unit and it’s ancillaries, cooling etc. Need to be factored in.

But we know from cars that EVs are much heavier even when everything is included. And still bring less range.

[mzso]

The technology for all that is already here, even the automatization.

Which technology brings the breaking of laws of physics that makes it viable energy cost wise?

Problem is how to regulate, but they can be fully autonomous today, an autonomous drone is several orders of magnitude easier than an autonomous car.

This baseless and frankly wrong. Aircraft can fly in 3d and when you add other aircraft in there it becomes really complicated.

And collisions and other accidents will be far more often fatal.

[mzso]

I think the obsession with energy densities in comparison with liquid fuel is overrated. Energy density nor weight has never really been a factor in car development so why should it be a breaking issue for electric vehicles. If you could pump gas in every parking spot we wouldn’t be driving around with 60 liter fuel tanks anyway.

Since we were talking about aircraft it's of cardinal importance.

Besides it also matters a lot in cars. More weight makes it less efficient and poorly handling. And more dangerous in an accident.

[mzso]

Multirotor drones are entertaining. What's less reliable and efficient than spinning a big propeller slowly, spinning 8 of them quickly!

the multi so-called rotor is inherently less efficient
because it accelerates downwards a relatively small amount of air by moving it fast
relative to an equivalent 'proper size' helicopter rotor - this made for acting on a larger amount of air so moving it slower

It also makes them even noisier.

[theblackangus]

<Other stuff removed for sake of staying on topic, as I was mostly just giving you a hard time about your comparison - Which I would love to actually continue just not here =-)>

I´ve always agreed that´s the limiting factor for multirotors. But since today there are passenger drones with 30 minutes range they´re already viable for short trips, so any new battery improving current energy density will make them even more viable

The problem here, as always with batteries, is with weight to flight time advancement and re-charge time. 30 minutes surely is great for a personal flying vehicle (Not discussing the real challenges with flying vehicles and safety), but if I have to spend longer than 30 minutes to recharge then the usefulness erodes with charge time.

Is that 30 minutes in point to point flight, or is it 30 minutes in hover? (honest question as we both know they result in significantly different flight times).
Was the 30 minutes with an actual occupant, if so what was the occupants weight?
What is the decrease in flight time per occupant kg?
What is the flight time with 2 occupants, as many of my short trips are always with the wife?

Energy density to weight of system is king in flight use cases.

What about all the insulation needed to keep out the multi-rotor buzz and make it mercedes quiet? (sarcasm)

[theblackangus]

I think the obsession with energy densities in comparison with liquid fuel is overrated. Energy density nor weight has never really been a factor in car development so why should it be a breaking issue for electric vehicles. If you could pump gas in every parking spot we wouldn’t be driving around with 60 liter fuel tanks anyway.

Since we were talking about aircraft it's of cardinal importance.

Besides it also matters a lot in cars. More weight makes it less efficient and poorly handling. And more dangerous in an accident.

+1

[theblackangus]

Problem is how to regulate, but they can be fully autonomous today, an autonomous drone is several orders of magnitude easier than an autonomous car.

This baseless and frankly wrong. Aircraft can fly in 3d and when you add other aircraft in there it becomes really complicated.

And collisions and other accidents will be far more often fatal.

You both have points there.
Autonomy in the air is much easier from the point of view that there are very few distractions from anything other than vehicles. No random road crossings, clutter, etc,. Also avoidance is generally easier (at low volume aircraft) as there is alot of immediate room to avoid into. Also the navigation part is much easier.

Mzso is correct in that accidents are likely to be fatal more often, and the consequences of a malfunction mean the collateral damage over a habited area is much much greater.

This last point means the "no maintenance" part goes out the window. You will need to do a lot of pre-flight checks and rely on complicated software with LOTS of sensors (redundancy, agreement management, etc) and each time before flight there will need to be a strict checking to ensure those are really functioning as needed. Fixing problems will be complex as any flying aircraft, not just replacing an arm. The consumer and prosumer grade electronics are not nearly redundant enough for transportation level flight and risk management IMHO.

[Andres125sx]

The technology for all that is already here, even the automatization.

Which technology brings the breaking of laws of physics that makes it viable energy cost wise?

Not sure what you mean with viable energy cost wise, energy used is electricity, wich can be 100% renewable, and even if not they will need a lot less energy than any ICE aircraft as efficiency is much much better on electric motors

Problem is how to regulate, but they can be fully autonomous today, an autonomous drone is several orders of magnitude easier than an autonomous car.

This baseless and frankly wrong. Aircraft can fly in 3d and when you add other aircraft in there it becomes really complicated.

Maybe the baseless statement is yours sir. Most difficult part of an autonomous car is how to detect/prevent/dodge any unexpected problem, from cars turning when they shouldn´t to pedestrians invading the road. Many people claim human intuition can´t be replaced to prevent these situations, but intuition is only needed when you can´t know what any other vehicle or person will do, if the only objects around are aircrafts with transponders telling anyone their route autonomous control becomes quite simple as nothing unexpected will happen contrary to what happens daily at any road.

As I stated earlier I´m assuming L5 autonomous crafts with no posibility for manual flying as I think that´s the only chance for these crafts to be viable for anyone

[Andres125sx]

Besides it also matters a lot in cars. More weight makes it less efficient and poorly handling. And more dangerous in an accident.

Tell that to the thousands SUV owners who will never go off road

[Andres125sx]

The problem here, as always with batteries, is with weight to flight time advancement and re-charge time. 30 minutes surely is great for a personal flying vehicle (Not discussing the real challenges with flying vehicles and safety), but if I have to spend longer than 30 minutes to recharge then the usefulness erodes with charge time.

Agree. But we all know manufacturers are improving this dramatically, some even claim under 10 minutes charge times, so this will be a problem for very little time, if it still is

Is that 30 minutes in point to point flight, or is it 30 minutes in hover? (honest question as we both know they result in significantly different flight times).
Was the 30 minutes with an actual occupant, if so what was the occupants weight?
What is the decrease in flight time per occupant kg?
What is the flight time with 2 occupants, as many of my short trips are always with the wife?

I asked myself all that too, but sincerely didn´t waste any time searching. I´d bet it´s with one passenger and no luggage

What about all the insulation needed to keep out the multi-rotor buzz and make it mercedes quiet? (sarcasm)

Wrong, mercedes equivalent machines are far from quiet