Electric Airspeed Record.

[Flying Phil]

Max Torque - I totally agree with you that an electric powered 747 is a non flyer......but a multiple passenger carrying electric powered aircraft would not have to be 747 size or shape, or speed. passengers will accept all sorts of compromises to get cheaply on their holidays or visits. We have accepted the slow down from Concorde days, we accept the slower total time travelling due to transport/security delays, we will accept the need for environmentally more friendly (possibly electric) flight systems.
I am not decrying the Laws of Physics - I respect them - but hope that we use them to push the boundaries of what can be achieved.

......Go IN51GHT.....

[Equus]

Max_Torque said:

The long, and frankly, fairly lethal history of large airships is littered with hull losses due to the wrong kind of weather at the wrong moment.....

To be fair, the history of large (rigid) airships wasn't all that long, and ended in the days when the strongest lightweight material available to us was duralumin, covered with doped cotton.

[911newbie]

The stuff about using PV on planes is I'm afraid not going to work. I keep seeing people bring this one up, often immediately following the idea to windmill one or two engines whilst in cruise to regen power..... sigh.

I've been mulling over the whole electric aircraft concept for a while and I'm struggling to see what the advantage is. All the major Aeroengine makers are have been talking about this for some time.

What I think they are aiming at is - a sinlge gas turbine, sitting out of the external airflow, providing power to electric motors and props on/in the wing (or elsewhere). This turbine can spin at one speed all the time and gain some efficiency vs current operation. This requires some batteries somewhere in-line to provide additional power at take off and to be on hand available at landing.
But the weight of the batteries is the killer here. Is the extra efficiency worth the additional weight of the batteries ?

I just cannot see as case for hybrid electric planes. It's probably a case of either full electric or gas turbine.

Longer term what I think we're waiting for is for the next battery chemistry to come along, and one with power denisty approaching that of current fuels. What I'm hearing is that could be ten years away, with only a few % of gains left in Li-ion in the intervening time.
The real leap forward will come when/if batteries become sufficiently power-dense to do a full flight without an additional power source on board.

Perhaps with that in mind, it would be worth getting a test vehicle together so you can start learning all about the realities of electric flight well in advance of new battery tech arriving.

There are a few interesting companies around working on metal - air batteries, which are as far as I understand things only rechargable back at the factory. Rather limiting their use unfortunately. Fuji Pigment announced a rechargable metal-air battery but I don't know if that worked in the end ?

Anyone in the know want to tell us about battery tech ?

Edited by 911newbie on Sunday 6th January 13:30

[911newbie]

Equus said:

Max_Torque said:

The long, and frankly, fairly lethal history of large airships is littered with hull losses due to the wrong kind of weather at the wrong moment.....

To be fair, the history of large (rigid) airships wasn't all that long, and ended in the days when the strongest lightweight material available to us was duralumin, covered with doped cotton.

Low weight and high strength isn't the problem with airships, lack of ability to control which direction you're heading is, plus terrible speed.

There might be a business case for cargo in airships, as per the Airlander company. I don't know how well that is working out though.

[Equus]

911newbie said:

Low weight and high strength isn't the problem with airships, lack of ability to control which direction you're heading is....

If you have adequate strength in the airframe, ability to control direction is merely a matter or applying sufficient thrust.

[anonymous-user]

Equus said:

911newbie said:

Low weight and high strength isn't the problem with airships, lack of ability to control which direction you're heading is....

If you have adequate strength in the airframe, ability to control direction is merely a matter or applying sufficient thrust.

Which is where the fundamental concept of "wing loading" comes back in. Low, or "Ultra low" wing loads are a real 'mare. Lets face it, that airlander ship proved it again recently when a minor loss of control (actually a miss timing of ballasting) mean't they flew straight into the ground....

(watch the footage, it's ridiculous and they were, imo, extremely lucky not to have killed the flight crew, which would have probably sunk the project)

[anonymous-user]

911newbie said:

What I think they are aiming at is - a single gas turbine, sitting out of the external airflow, providing power to electric motors and props on/in the wing (or elsewhere). This turbine can spin at one speed all the time and gain some efficiency vs current operation.

er, passenger jets already pretty much operate at a single state! They are not very dynamic, they don't suddenly have to stop at traffic lights or to let an old lady and a dog cross in front of them. No, they take off, and within say 10min, are established at best cruise, where they sit, sometimes for as much as 15 hours, till they throttle back to flight idle, in order to land.

"Load leveling" is therefore a non starter.


The only way to reduce energy consumption is:

1) better L/D


You'll see those two letters a lot in discussions like this, because they really are the crux of what matters!

Now i could be wrong here, but as far as i know, there are no "magic bullets" left when it comes to improving L/D in the near term (lets say the next 25 years). Take a look at a the normalised drag curves for an aircraft:



It's clear that a lower total drag comes from either

a) flying slowly and improving lift but not increasing lift induced drag (Probably the best route for low speed propeller driven electric aircraft)

b) flying fast and reducing parasitic drag (the current approach with jet airliners, see propulsive efficiency graph below)


In all cases, the critical question is "how good can we practically make L/D" and still have a viable aircraft? The "practically" bit is important. Plenty of techniques to reduce drag have been tried that although achieving significant reductions, bring massive side effects (such as more mass, nasty stall characteristics, susceptibility to icing etc etc).

A modern wide body jet perhaps today sits at an L/D of between 14 and 20 (depending on trim) and a modern, ultra efficient, single seat unpowered glider at upwards of 50. For me, that suggests that a sensible upper limit, within current technology (see note at bottom) would be having practical high speed wide body jets at an L/D approaching 30. The glider gets to >50 because it really has no fuselage, carries one person (in discomfort!) and has no mass penalties for "annoyances" such as engines, radar, undercarriage/brakes etc etc. A "Low speed" aircraft, ie one that has low drag from the airframe parts that don't create lift, could perhaps be even higher than 30, but i just can't see how it's going to get much better than that



2) better propulsive efficiency.

Compare propulsive efficiency for various power architectures:




It should be clear why current jet aircraft fly at the speed they do (and why supercritical wings optimised for a good L/D at those speeds has been the current optmisation point)

Today, electric planes means electric motors and props, although that is not necessarily a requirement (Heating a working fluid can be done as well). And that naturally means a reduction in the speed optmisation point. Prop technology has come a long way, with ducting, and blade design widening the operating window significantly (High bypass turbofans are effectively "propeller" driven....../argument)

Not for nothing is this new electric speed record targeting 400mph, as that is about the most efficient speed for a prop!

So the question is, (within current tech)can propulsive efficiency be significantly increased? Again the answer is a qualified "yes". People will tell you that an electric motor is very efficient, and indeed it is, but a jet engine is also actually very efficient too (because "waste heat" adds to thrust, unlike for an ICE or electric motor, where waste heat must be dumped overboard uselessly). Modern ducted fans owe a low of there efficiency to the fan on turbofan engines. These have been getting bigger and bigger, and slower and slower (leading to 2 or even 3 shaft jet engines with gearboxes to drive the fan). If there was an 'easy win' then surely the likes of RR or GE would have found it by now? Incremental gains, and optimisation gains are there to be had, but these are quantitatively only in the few percentage points magnitudes.



In summary, i could see 10% improvements being possible (but expensive and difficult) in both L/D and PrpEff. In effect, those would reduce energy consumption by 19%. That is not to be sniffed out, and total, even with fossil fuelled Jet aircraft would be worth millions to the operators, but it doesn't help us (not even close) with out requirement to power airliners with batteries!




NOTE: "within current technology"

There could be a radical breakthrough in our understanding in some area of physics that allows us to achieve a huge step change in what would be considered "typical" performance. However, increasingly, thanks to our ever increasing knowledge, these events are becoming less likely. In conjunction, projects are now limited by other parameters, such as politics and costs, rather than by purely technical ones. In order to make a realistic estimate of the feasibility of battery powered mass air transport, we have to, for now, ignore these technology singularities, and concentrate on achievable, incremental improvements in order to estimate future capabilities.

[anonymous-user]

911newbie said:

Longer term what I think we're waiting for is for the next battery chemistry to come along, and one with power denisty approaching that of current fuels. What I'm hearing is that could be ten years away, with only a few % of gains left in Li-ion in the intervening time.
The real leap forward will come when/if batteries become sufficiently power-dense to do a full flight without an additional power source on board.

What people tend to miss is that there is, obviously if you think about it, a fundamental limit to the maximum energy density of a battery! Batteries use electro-chemistry to generate a potential difference and a flow of electrons when the circuit is completed. However the very physics of our universe limit the maximum energy available. For a battery, at a fundamental level two things matter when considering specific energy:

1) the mass (density) of the materials used in that battery

2) the Electro-Potential (electromotive force) of the active elements used in that battery


So, clearly, the "best" battery has the lightest elements combined in such a fashion as to provide the highest Electro-Potential. Simple eh!


The problem, is that numerous other factors come into play, ranging from things like, availability/cost, toxicity, life, electron mobility and internal resistance, stability etc etc. Todays "Lithium" cells are actually really not that bad, with lithium being the 3rd lightest element, and 5th highest EP. Of course, there exact capability depends on their elemental make up, and unfortunately iron, used for it's stability is a heavy element.

Practically, current best (bare) energy density is around 250 W.h/kg. Various research projects using current (but state of the art) tech suggests practical "best case" lithium batteries could be built with roughly 4 or 5 times that density. No one has yet demonstrated viable volume production of these cells.

For comparison, kerosene has a bare energy density of around 12,000 W.h/kg. That is 48 times the capability of currently available mass produced cells, and still roughly 10 times that of the virtual "best case" lithium cells


What we can do however is to assemble a theoretical battery, with the highest possible energy density, and in fact, we can "cheat" a bit by making one of the compounds used air, and take that from the operating environment (as do most internal combustion engines). if we do that, the theoretical (bare) energy density could be as high as 11,000 W.h/kg, eg matching the energy density of kerosene! Those batteries however are firmly in the "next level technology" category, and as far as i am aware have only been proven on a very small scale lab test, ie with compounds on a slide and not a real cell of any kind. (if they have to carry their own oxygen, then the figures fall to around 5,000 W.h/kg) one other advantage of a cell that does not carry all of it's elements is safety. Having no oxygen in the cell means thermal run-away is significantly reduced)

[Flying Phil]

Max Torque
"In summary, i could see 10% improvements being possible (but expensive and difficult) in both L/D and PrpEff. In effect, those would reduce energy consumption by 19%. That is not to be sniffed out, and total, even with fossil fuelled Jet aircraft would be worth millions to the operators, but it doesn't help us (not even close) with out requirement to power airliners with batteries!"

But I thought we were suggesting using P-V for the main energy source (sufficient for cruise), supplementing with a relatively small battery pack for take -off and climb electrical needs. If the p-v could also be structural as in a "smart" p-v skin......Then part of the recharge comes during descent and part "on ground" recharge.

[Tony1963]

The airports and routes are gonna be very busy during daylight hours!

[pingu393]

Max_Torque said:

I can't believe you're not a millionaire dude! I mean, what with being able to make that zero drag plane!

(hint, getting the mass to altitude is IRRELEVANT (because the PE is recovered when you descend...) what MATTERS is drag!.

If you read my assumptions, I stated that the power calculation was ONLY to lift the aircraft, not to make it move horizontally - and there was barely enough power to do that.

Wouldn't I need the energy before the ascent, otherwise I couldn't descend ?

I was a millionaire once, then the Italians joined the Eurozone .


I think that I basically showed that a 100% PV aircraft would not be able to power a 747-sized object to FL330, as 71% of the available power is needed just to gain height.

Drag and engine efficiencies would only need to be considered if the PV idea was feasible - which it isn't.


Using solar cells as a supplementary power source is worthy of consideration, especially if they can form part of the structure, rather than being bolt-on parts. The same could be used on car roofs and bonnets, perhaps.

[Storer]

I suspect RR are aware of the issues listed above. They have been involved in aircraft for a while now!

I would imagine that they are looking at elements of an electric aircraft. In this case it is probably the electric motors and propellers. After all, they do currently make the engines!!!!

Their next step will possibly be using fuel cells to turn hydrogen into electricity. Hydrogen is energy dense and can be produced using green energy (on the ground, obviously) and turning it into electricity would allow for very quiet aircraft. That gives the operators planes they can fly 24 hours a day.

Refuelling would take a similar time as current avgas, but the fuel tanks would weigh more to maintain the pressure to keep the fuel liquid.

The aircraft will be slower but we have seen the peak of cheap, rapid air travel. Unless we are able to teleport around the globe we will be travelling less and slower in the future.

[anonymous-user]

Storer said:

I suspect RR are aware of the issues listed above. They have been involved in aircraft for a while now!

I would imagine that they are looking at elements of an electric aircraft. In this case it is probably the electric motors and propellers. After all, they do currently make the engines!!!!

And yet this project is using off-the-shelf motors supplied by Yasa, and as far as i know, a conventional propeller, and i'm going to guess is using Williams Battery modules. Precisely non of that moves "electric aircraft" forwards by any practical amount. In fact, this entire project can be done in virtual simulation by an undergraduate (which i suspect has already been done to show it's predicted Vmax...)

Storer said:

Their next step will possibly be using fuel cells to turn hydrogen into electricity. Hydrogen is energy dense and can be produced using green energy (on the ground, obviously) and turning it into electricity would allow for very quiet aircraft. That gives the operators planes they can fly 24 hours a day.

This is a better idea, but better yet, just burn the hydrogen in the jet engine we already have! (worth noting that most of the "noise" from a modern plan is NOT from combustion, but from air-rush noise, which is why higher bypass turbofans are quieter)
Even better, just use bio-kerosene. No changes to the plane required at all that way!

[Storer]

Max

Bio fuels are far from green. I used to grow some and they involve the use of inputs produced from fossil fuels. A long way from zero CO2

The biggest issue is actually the lack of productive land available to produce non food crops.

With population growth we will struggle to feed the population from the available land and fresh water available.
Do not rely on bacteria or algae to produce the volume of fuel we will need to utilise current propulsion technology.

[smig12345]

poing said:

ash73 said:

Batteries are heavy, so let's put them in an aeroplane. Stupid idea.

That's killed it, I doubt a single person on that project ever thought about that. Unless an electric parrot is heading this way.

I think this is a great project and there are so many commercial advantages to electric aircraft. As I understand it EasyJet are investing a fair amount into the concept. Something they pointed out, that I hadn't considered, is the idea of having more late night flights because they are currently restricted due to noise issues.

So far they are only looking at short distances but the kind that are perfect for the UK. Sounds similar to the motoring world where they talk a lot about the final mile but with the big distance stuff using a different technology.

I know these kind of projects will have their doubters but there were people saying an aircraft would never cross the Atlantic not too many years ago.

Exactly! It wasn't too long ago people were saying it was impossible to get to the Moon, it was impossible to travel faster than the speed of sound, if you travelled over 60 mph on a train the air would be sucked out of your lungs, etc, etc.

Like it or not the future is electric. I think it's great British companies like Rolls Royce, Yasa, Electroflight, etc are doing something like this, it shows British engineering in a positive light around the World. I think we as a country should invest heavily in this so that when it is common place in years to come we will be leaders in the World market. It is going to come on in leaps and bounds in the future. We don't have many industries left in the UK, we should invest heavily in this high tech industry of the future.

[GliderRider]

Max_Torque said:

And yet this project is using off-the-shelf motors supplied by Yasa, and as far as i know, a conventional propeller, and i'm going to guess is using Williams Battery modules. Precisely non of that moves "electric aircraft" forwards by any practical amount. In fact, this entire project can be done in virtual simulation by an undergraduate (which i suspect has already been done to show it's predicted Vmax...)

There is a very big difference between modelling something on a computer and actually making it work for real ( The old saying is 'Garbage in, Garbage out'). There are so many variables which only come become apparent when one actually functionally tests a system, that it keeps test houses, test tracks and test pilots in work. If it were that easy we would go straight from design office to manufacture to delivery to end user with no protoypes, no development and no testing.

What Rolls-Royce are doing is giving their engineers a chance to experience the real world problems that come about when shoehorning off-the-shelf components into an existing airframe and then pushing the limits of the performance envelope. My guess is they will learn one heck of a lot.

There is alread one route for which an electric 'airliner' is being given serious consideration: Electric Islander

[anonymous-user]

smig12345 said:

poing said:

ash73 said:

Batteries are heavy, so let's put them in an aeroplane. Stupid idea.

That's killed it, I doubt a single person on that project ever thought about that. Unless an electric parrot is heading this way.

I think this is a great project and there are so many commercial advantages to electric aircraft. As I understand it EasyJet are investing a fair amount into the concept. Something they pointed out, that I hadn't considered, is the idea of having more late night flights because they are currently restricted due to noise issues.

So far they are only looking at short distances but the kind that are perfect for the UK. Sounds similar to the motoring world where they talk a lot about the final mile but with the big distance stuff using a different technology.

I know these kind of projects will have their doubters but there were people saying an aircraft would never cross the Atlantic not too many years ago.

Exactly! It wasn't too long ago people were saying it was impossible to get to the Moon, it was impossible to travel faster than the speed of sound, if you travelled over 60 mph on a train the air would be sucked out of your lungs, etc, etc.

Like it or not the future is electric. I think it's great British companies like Rolls Royce, Yasa, Electroflight, etc are doing something like this, it shows British engineering in a positive light around the World. I think we as a country should invest heavily in this so that when it is common place in years to come we will be leaders in the World market. It is going to come on in leaps and bounds in the future. We don't have many industries left in the UK, we should invest heavily in this high tech industry of the future.

well that's all super isn't it, Thanks god, that's it all fixed and sorted. Lets just get on with making 'lecy airlines now then eh.

Oh, wait, we can't because the laws of physics prevent it. And that's the rub, loads of people who don't understand engineering and physics can shout all they like but as Scotty so rightly said on many an occasion "you canne change the laws of physics captain".....

All those things you mention, crossing the atlantic, breaking the sound barrier, getting to the moon or even going faster than 60 mph on a train, what do they have in common? Have a think? Well, i'll tell you, despite none of them breaking the laws of physics, none of them were achieved until certain key technologies were mature enough to support than endeavour. Be that external combustion engines with sufficient thermal efficiency to drive a heavy, draggy stream engine and carriages to over 60 mph, internal combustion engines reliable and powerful enough to fly across the atlantic, the development of electronic control systems, ultra high performance turbopumps, cryogenic fuels storage, handling and combustion systems to provide sufficient thrust to get juust enough mass to the moon and back to support a manned operation, or the understanding or transonic compression effects on control surfaces and the impact of aerothermal heating to allow an aircraft to punch through the sound "Barrier". In each case, there was no fundamental physical barrier to the successful achievement of those tasks, just an incremental, stepwise maturing of critical tech.

Today, battery electric airliners are not feasible. Sorry, that's just the way it is. In maybe 25 or 50 years we may have a technology singularity that provides a "shortcut" to a viable,workable solution, or we may not. That could of course happen tomorrow. And there's the rub, we just don't know.

As i have explained in my previous post on this thread, the challenges are well understood (max L/D max PrpEff, max EnergyDensity). Nothing is that new, that novel, or mis-understood, we are simple too far away from a viable solution with current technology.

[fatbutt]

https://jalopnik.com/rolls-royce-hired-formula-e-e...

The info graphic is interesting. Why use cells when packs from companies like XALT are a better packaged solution?

Edited by fatbutt on Sunday 6th January 22:54

[anonymous-user]

GliderRider said:

There is a very big difference between modelling something on a computer and actually making it work for real

Interestingly, these days, there actually isn't. Modern computer aided design, simulation and modelling means like never before we can understand the critical design tradeoffs and make complex, multi-dimensional optimisations before any real hardware is made. Take the 777, designed way back in the early 1990s (so a dinosaur compared to todays "virtual" design resources) and yet the prototype airframe was actual sold and put into fleet service after it's development program!

These days, thanks to VR suites and simulators, i can actually "sit" in the cars i help develop, do laps of the Nurburgring, carry out extensive lifecycle analysis years before we make any actual physical cars.


Sure, there is always the nitty gritty of getting down and making it all work, although increasingly this is a game of systems integration, ie getting all the bits to talk to each other electrically, rather than complex, iterative or even "trial and error" type work.

Take this new speed record plane. I'd sure RR already have a simulation of the aerodynamics, of the propeller, and of the motors and batteries. All those things already exist. They will have checked and optimised numerous factors, run lots of simulation to establish critical design points for the airframe. Things like airframe mass, wing truss bending, control system gains, the drag co-efficient vs AOA, all those things and many more can be worked out before building the thing these days.


In fact, the biggest single design compromise for this new aircraft will be the decision on total energy vs mass. That directly influences max speed because of the L/D ratio. There will be a minimum battery mass to support the peak power requirement (which is a trade off on cell life vs discharge rate) but from that point onwards, every extra mile of range will cost them and reduce the max speed. But all that can be, and i'm sure is already modelled and decided.........

[anonymous-user]

fatbutt said:

https://jalopnik.com/rolls-royce-hired-formula-e-e...

The info graphic is interesting. Why use cells when packs from companies like XALT are a better packaged solution?

Edited by fatbutt on Sunday 6th January 22:54

i'd suggest 4 letters

C O S T


To make this project fly, it's looking like everything is as "off the shelf" as possible, hence the existing airframe, yasa motors, and pre-existing battery modules.

On problem becomes immediately apparent when you look at the data sheet for the yasa 750r motor

750R_datasheet

And that is the large derate, even at relatively low coolant temps for the motor. From around 200kW peak (at 750V) to just 70kW continuous. Datasheet shows between 90 and 92% efficiency at the propellers design point (2400rpm), so that's between 5.6 and 20 kW heat rejection per motor (@70kW 92% and 200kW 90% respectively), which is pretty trivial, which suggests to me that the cooling of that motor is pretty poor.

Ok, they ought to do a lot better than 60 degC inlet coolant temp (trade off with cooling drag obvs) so i'd imagine they'll squeeze a bit more than 70kW continuous out of it, but the motor is nothing to write home about really......