Electric Airspeed Record.
Discussion
pingu393 said:
Flying Phil said:
Max Torque makes some very good points but seems to assume a direct substitution of solar electric for gas turbine. I would have thought an electric powered passenger plane would be optimised slightly differently ie slightly lower speed, lighter weight, larger proportional wing area, small but useful on board batteries for max power, charged up when on the ground or when descending.......obviously we are in the early days of a revolution but CO2 emissions from Aircraft could well be the next environmental target. IN5IGHT is getting in on the ground floor!
You beat me to it. I was going to post similar comments.MT is assuming that 400 people will be crossing the Atlantic at 600 knots in these aircraft.
I see it very differently. I can see it being used for cargo. 100 tons crossing the Atlantic at 250 knots.
The point about night flying is a very valid one, but it will soon be the case that if you can see, you can generate
.All that really matters for an aircraft is the L/D ratio and the engines propulsive efficiency. The jet engine is already actually very good in this respect, because the exhaust heat add to it's thrust (unlike say an car engine, where the waste heat is dumped overboard without being able to provide useful work). Propulsive efficiency for a high bypass ratio turbofan is also pretty decent too. And of course, all planes already "regen" in that they effectively glide back down to land (usually at a minimum thrust level commensurate with providing a safe and comfortable decent profile).
So we are left with the L/D and the energy density. If you can build a plane with a significantly better L/D (and we are talking about requiring something like a 5x improvement to even start to make a battery plane work in the real world) then why wait for batteries, as that tech would be worth billions today. You could walk into Airbus or Boeing and they'd give you a blank cheque for your knowledge!
It would be far more useful to work on the synthesis of artificial liquid fuel created from ground based renewable energy that to try to make batteries in planes work., imo...... (And those projects are indeed also ongoing, but they get less column inches that "we're going to make a really fast plane" type ones.)
poing said:
As I understand it EasyJet are investing a fair amount into the concept.
er, no they are not. They grabbed a few "column inches" and some free publicity by jumping on the green bandwagon by announcing a completely impossible dream to run electric aircraft by 2027 on some of it's routes. They have sensible left a lot of wiggle room as to what that actually quantifies as, because there is no way you're going to have a passenger certified electric aircraft by 2027.... (Hint, the completely conventional 777 took 5 years to get from prototype to service, the necessary 'lecy tech needs to be ready in 3 years)The final issue, never mentioned is that a modern airline literally lives or dies on the utilisation of it's aircraft. Critical to that is the turn-around time. So your aircraft arrives at the terminal with a flat battery, you need to recharge it. Problem is, the battery is tens of MWhrs. So unless you have a nuclear powerstation (or an even more massive battery and necessary power conversion equipment) for each terminal gate, there's going to be a problem there.....
Edited by anonymous-user on Saturday 5th January 18:39
Flying Phil said:
I would have thought an electric powered passenger plane would be optimised slightly differently
Agreed, but unfiortunately, you can't beat the laws of physics yeteg:
slightly lower speed.
Ok, fair enough, even if we ignore the issues with air traffic control from having slow planes (and as the fleet changes over these are not trivial) and the issues with lets say doubling current flight times in terms of passenger comfort and acceptance, then the problem remains that cruise speed is already the critical design point for a modern airliner, and whilst faster does equal more drag, it's not actually that simple, especially when you add propulsive efficiency into the equation. Modern super critical wings are optimised to fly fast, and slow speed flight (lets say 50% of the current cruising speed) requires a very different wing, especially given that the plane now has to LAND at GTOW! (Today, you actually cannot land a widebody jet with a full fuel load without damaging it!) So we need a wing that provides much more lift (to support a heavier aircraft) but supply that lift at a lower speed. That, i'm afraid means drag, lots, and lots of it. Now i'm sure that with sufficient investment and work, we can re-optimise our wings to work at slower speeds and regain some of the losses, but that's going to take a lot of time.
lighter weight.
How? In case you haven't noticed a modern passenger jet isn't exactly an old cart horse. They are increasingly composite (carbon fibre) and have airframes highly optimised for high strength and low mass. A boggo 777 already has about 8 tonnes of carbon fibre structure, and the rest is lightweight high strength alloy. I simply can't see where you can save significant weight, sorry (if it were easy, it would have been done, as aircraft mass is the single biggest driver of economy (mass x L/D = consumption)
larger proportional wing area.
Ok, great, what does this get you? Other than more drag and an aircraft that is horribly sensitive to wind sheer / turbulence?
small but useful on board batteries for max power,
An airliner cruises at around 85% of max power. "small" batteries are pointless. There mass will reduce overall consumption.
charged up when on the ground or when descending
On the ground, fine (other than the issue of the charger power required) but charging batteries whilst descending is REALLY silly! (Think about it.....)
Flying Phil said:
.......obviously we are in the early days of a revolution but CO2 emissions from Aircraft could well be the next environmental target. IN5IGHT is getting in on the ground floor!
Aircraft CO2 is undoubtedly a major problem over the next 5 to 20 years. However, today, batteries are not the answer to help our existing high volume passenger services reduce their impact. I'm not knocking this flag waving project by RR, it'll be a lot of fun, but that's really all it is.Thanks Max Torque and again you make a lot of very good points - but I am puzzled by your comment about not being able to recharge when descending. An aircraft at cruising altitude and speed has a lot of Potential and Kinetic Energy. This is currently dissipated by heating the atmosphere by increasing the drag in flight and in the brakes when on the runway. In an electric aeroplane the propellors would use that energy and turn the motors into generators changing some of the PE and KE into Electrical energy stored in batteries (or super capacitors?) - as do many vehicles now.
Flying Phil said:
Thanks Max Torque and again you make a lot of very good points - but I am puzzled by your comment about not being able to recharge when descending. An aircraft at cruising altitude and speed has a lot of Potential and Kinetic Energy. This is currently dissipated by heating the atmosphere by increasing the drag in flight and in the brakes when on the runway. In an electric aeroplane the propellors would use that energy and turn the motors into generators changing some of the PE and KE into Electrical energy stored in batteries (or super capacitors?) - as do many vehicles now.
An aircraft at height has Potential Energy, stored in it's mass. As it descends, that energy can be 100% recovered, simply by descending and used to propel the aircraft against drag. To get the furthest distance from any given height, the aircraft should be configured to have the best glide slope, (effectively the highest L/D ratio) possible for what ever the mass and hence wing loading of the aircraft. Modern passenger aircraft do not deploy speed brakes or other "Lossy" devices unless absolutely necessary (required to maintain horizontal separation for air traffic control reasons, or to more quickly lose height, again, as directed by ATC). This way, all of the aircraft's PE is recovered. All aircraft already "regen" in this fashion (a negative vertical g, means lower total wing loading, which means a reduction in the wings effective AOA, which means less drag, which means either an increase in speed or a decrease in propulsive force). The additional losses incurred for the necessary requirement to re-configure the wing into a high lift at low speed profile for landing (spoilers, slats etc) are un-avoidable, and will of course be significantly higher for a plane that has to land at it's Take Off Weight (one that doesn't burn a liquid fuel as it flies and hence gets (significantly) lighter) because the wing will have to provide a commensurately larger amount of lift.
Any "system" that aims to recover that PE indirectly, ie through a turbine and generator for example, cannot ever be 100% efficient in terms of power transfer, nor avoid extra parasitic drag from the act of that recovery, and hence is LESS EFFECTIVE at recovering PE, as compared to simply descending at max L/D (min drag profile)
Regarding Kinetic Energy (KE)
Aircraft actually fly within a relatively narrow and typically fairly constant speed range for the majority of their flight regimes, with only final approach really being any significantly slower (and this portion is just a few miles, compared to the hundreds or even thousands flown during the cruise period). As the minimum safe flying speed of the aircraft is set by it's mass and the L/D ratio, recovering KE in flight is not a sensible goal, as an aircraft can only fly so slowly and remain, er flying! After touch down, yes, a system could be envisaged that slows the aircraft on the runway that can recover the KE, rather than using friction brakes that simply convert the energy to waste heat. However, as the total energy recoverable is a small percentage of the total energy used to overcome drag for the rest of the flight, today that is not viable to implement. For a heavier plane, landing at it's GTOW, then yes, it becomes more advantageous, especially for short haul where the cruising portion of the flight is shorter
Thanks again Max Torque - but are you not assuming that the flight parameters are the same for an electric plane as a conventional plane - where it is trying to get the maximum range with the minimum fuel, so effectively "coasts" for the last 30 mins of the flight swapping PE for KE against drag? The speed change is still from what 500mph to 200mph on final approach? An electric plane, which might want to recharge, could have a differing descent profile - whilst still flying...
I am learning a lot from this thread and your contribution Max.
I can see that replacing existing jet aircraft (that I believe produce 17% of all CO2 emissions) will not be simple. I suspect it will require a combination of technologies to solve the issue as well as a drastic reduction in the amount of air travel/transport.
However, electric cars were around over 100 years ago, and the Toyota Prius only resurrected the use of an electrical hybrid by a mainstream manufacturer a few years ago. The Prius now seems crude as things have moved on a lot.
To say a project like the RR Electric plane is a waste of time is unfair and incorrect. RR would not be spending money on it if they didn’t think they would learn a lot from it. Positive PR may be an additional benefit for the company, but they will need to start exploring alternatives or can get quickly left behind. Look at Ford for an example of that!
Just because YOU don’t believe a project has any value, it does not mean that others think the same. In life there are often may ways of doing things that achieve the same or a similar result. I know you can’t change physics, but we need to explore all the alternatives.
Doing nothing is not an option for RR
I can see that replacing existing jet aircraft (that I believe produce 17% of all CO2 emissions) will not be simple. I suspect it will require a combination of technologies to solve the issue as well as a drastic reduction in the amount of air travel/transport.
However, electric cars were around over 100 years ago, and the Toyota Prius only resurrected the use of an electrical hybrid by a mainstream manufacturer a few years ago. The Prius now seems crude as things have moved on a lot.
To say a project like the RR Electric plane is a waste of time is unfair and incorrect. RR would not be spending money on it if they didn’t think they would learn a lot from it. Positive PR may be an additional benefit for the company, but they will need to start exploring alternatives or can get quickly left behind. Look at Ford for an example of that!
Just because YOU don’t believe a project has any value, it does not mean that others think the same. In life there are often may ways of doing things that achieve the same or a similar result. I know you can’t change physics, but we need to explore all the alternatives.
Doing nothing is not an option for RR
Max_Torque said:
Ok, that's a big number, but each RR RB211 on the 747 develops a maximum of 258kN of thrust at an massflow of 728kg/s, which is a power of just about 45MW, and there's 4 of them fitted to that plane.
If we consider cruising at about 85% of peak thrust (fairly typical for a wide body jet), the engines would therefore be making 153MW, so the additional power from the solar panels could, at absolute best (assuming they have no effect on drag or mass) add an additional 1.3% range.....
I assume you mean peak thrust at altitude. Cos there’s no way you have anything like peak available take off thrust is at cruising altitude due to air density, nor do you need it to maintain flight. If we consider cruising at about 85% of peak thrust (fairly typical for a wide body jet), the engines would therefore be making 153MW, so the additional power from the solar panels could, at absolute best (assuming they have no effect on drag or mass) add an additional 1.3% range.....
Aircraft rarely take off at full thrust to reduce engine fatigue. Something an electric engine also might allow optimisation. I know I’m in danger of comparing passenger jet to a small prop aircraft doing that though.
Interesting project none the less! Even if for small island hopping or reconnaissance type exercises or stunt planes.
Probably engine up for UAV to take over wankel!?
Edited by JonnyVTEC on Saturday 5th January 23:23
Max_Torque said:
If we consider cruising at about 85% of peak thrust (fairly typical for a wide body jet), the engines would therefore be making 153MW, so the additional power from the solar panels could, at absolute best (assuming they have no effect on drag or mass) add an additional 1.3% range.....
A 400tonne 747 cruise at a TAS of 930km/h at an L/D of 15 (probably a bit optimistic) is about 67.5MW. I doubt it'd crack 100MW in reality but nevertheless Max's point stands. PVs for the wings is a waste of time and they probably wouldn't even pay for their own weight. AER said:
PVs for the wings is a waste of time and they probably wouldn't even pay for their own weight.
That's using current technology.I don't know the answer, but how many MWs of light energy are there available? There must be a light power density value that can be used - similar to the chemical power density value of fuel.
That is where the answer to feasibility lies. You are assuming that the very low efficiency PVs that we have at present won't do the job. I am assuming that PV efficiency will be MUCH better in the future. If there isn't enough light energy it's a "no-go", otherwise it's a "possible".
The solar constant for earth is 1.36kW/m2 so even assuming 100% efficient PV with maximal insolation a 747 wing is only 680kW or so.
Very expensive PVs are north of 40% so even if they become widely available we're still only looking at 272kW. At the same flight conditions the whole PV shooting match has to weight much less than the break-even point of 1.6tonnes or about 3kg/m2. A complete non-starter IMO
Very expensive PVs are north of 40% so even if they become widely available we're still only looking at 272kW. At the same flight conditions the whole PV shooting match has to weight much less than the break-even point of 1.6tonnes or about 3kg/m2. A complete non-starter IMO
AER said:
The solar constant for earth is 1.36kW/m2 so even assuming 100% efficient PV with maximal insulation a 747 wing is only 680kW or so.
Very expensive PVs are north of 40% so even if they become widely available we're still only looking at 272kW. At the same flight conditions the whole PV shooting match has to weight much less than the break-even point of 1.6tonnes or about 3kg/m2. A complete non-starter IMO
I agree that it is a non-starter, but not because of weight. Weight is only valid using today's technology. It is a non-starter because there is insufficient energy density. Even if the airframe were weightless, the cargo would be at least 100 tons.Very expensive PVs are north of 40% so even if they become widely available we're still only looking at 272kW. At the same flight conditions the whole PV shooting match has to weight much less than the break-even point of 1.6tonnes or about 3kg/m2. A complete non-starter IMO
mgh = 100000kg x 10 x 10000m = 10 GJ required to raise 100 tons by 10 km
Power to raise 100 tons by 10km in 1000 seconds = 10MW
Power density = 1400W/m^2
Area = 1000m^2 (including wings, fuselage and tailplane)
Possible power = 14MW
My man-maths is probably wrong, but it shows that a Boeing 747 sized aircraft (weighing just 100 tons) made of 100% efficient PV cells could get to 30000 feet in 20 minutes, but...
It assumes...
100% efficiency.
All the energy is used to gain height and none is used to gain distance.
100 tons is just not enough weight to include air-frame and cargo.
This is why it wouldn't work. Not because PVs are inefficient.
The aircraft would need to carry its own fuel. Perhaps, PVs could be used to supplement onboard fuel. Downside to batteries is that they have to be carried for the whole flight. As mentioned earlier, this will require a stronger air-frame and landing gear.
As an aside, I fly model aircraft and they have moved towards electric and away from liquid fuel. Lots of electric models do not take-off from the ground, but are hand launched. Perhaps, a catapult launch could help reduce the on-board energy store. It's a practical solution for small aircraft, but probably not for a 747
.The issue is weight as much as it is power density of the insolation. The PV is just the beginning of the process. You then need to wire it all back to where you want to use it even before you add the controller/inverter/converter needed to manage system voltage. As I calculated before, it's most unlikely to pay its way in cruise even with unrealistic PV efficiency assumptions.
It really does go in the stupid ideas file for now and evermore!
It really does go in the stupid ideas file for now and evermore!
Edited by AER on Sunday 6th January 09:44
AER said:
PS. Why can't the greenie dreamers do the maths themselves? It's not so hard
Probably because there are many Many examples of maths being used to prove what cannot be done......and then it is done, because the assumptions are shown to be invalid.......I'm sure we will see some very clever and innovative uses of PV technology in aircraft in the future.Flying Phil said:
AER said:
PS. Why can't the greenie dreamers do the maths themselves? It's not so hard
Probably because there are many Many examples of maths being used to prove what cannot be done......and then it is done, because the assumptions are shown to be invalid.......I'm sure we will see some very clever and innovative uses of PV technology in aircraft in the future.robinessex said:
Flying Phil said:
AER said:
PS. Why can't the greenie dreamers do the maths themselves? It's not so hard
Probably because there are many Many examples of maths being used to prove what cannot be done......and then it is done, because the assumptions are shown to be invalid.......I'm sure we will see some very clever and innovative uses of PV technology in aircraft in the future.All inputs into equations should be either universally standard constants (to an acceptable number of significant figures), results based on experimentation, or specifications. If any of the inputs are missing, guesses have to be made.
e.g PE = mgh
m was "guessed" at 100 tons. The actual value may be closer to 95 tons.
g was an approximation (10 <> 9.81.....)
h was a guess. The ceiling height may actually be decided to be 9500 metres
1500 seconds may be decided to be quick enough to get to 9500 metres
This gives a power requirement of 5.9MW - a bit different to 10MW in the original.
pingu393 said:
robinessex said:
Flying Phil said:
AER said:
PS. Why can't the greenie dreamers do the maths themselves? It's not so hard
Probably because there are many Many examples of maths being used to prove what cannot be done......and then it is done, because the assumptions are shown to be invalid.......I'm sure we will see some very clever and innovative uses of PV technology in aircraft in the future.All inputs into equations should be either universally standard constants (to an acceptable number of significant figures), results based on experimentation, or specifications. If any of the inputs are missing, guesses have to be made.
e.g PE = mgh
m was "guessed" at 100 tons. The actual value may be closer to 95 tons.
g was an approximation (10 <> 9.81.....)
h was a guess. The ceiling height may actually be decided to be 9500 metres
1500 seconds may be decided to be quick enough to get to 9500 metres
This gives a power requirement of 5.9MW - a bit different to 10MW in the original.
(hint, getting the mass to altitude is IRRELEVANT (because the PE is recovered when you descend...) what MATTERS is drag!.
I did the calc's in my first post, showed that a 747 sized aeroplane has a massive power requirement, and using 100% efficient panels (no where near the real world) and the absolute best case solar irradiance (4x that at ground level at 40,000 feet), the panels can only contibute a few % to the energy consumption of the plane, and that's with the best case assumption that those panels and power electronics add no additional mass or drag.....
And there's the problem. The average man in the street thinks "how hard can in be" when they see headlines like "Easyjet to fly electric airliners in 2027" and without being able to fully understand the physics, jump on the band wagon!
But Physics doesn't lie. You can wrap it up any way you want, but the raw figures tell us that solar assistance for large body passenger aircraft is a non starter. end of. Having been told that, then you get the "yeah, but the technology will improve", and of course, yes it will, but it WON'T CHANGE THE LAWS OF PHYSICS.
Our assumptions for the solar assistance were already hugely optimistic:
1) Panels capture all of the total solar energy at altitude, all the time, in all flight regiems, and convert 100% of that to electricity
2) panels and power electronics weigh nothing and add no drag to the aircraft
And even with those, frankly ridiculous boundary conditions, we are talking about as little as a 2% contribution. If as any kind of engineer you look at that and say "but yeah, we can make that work" then frankly you need to get another job........
Storer said:
To say a project like the RR Electric plane is a waste of time is unfair and incorrect.
I have never said that, and i never will. The project will be a lot of fun, it will keep some clever engineers in a job, provide and interesting topic for learning for everyone, provide RR with many column inches and excellent PR. It may even inspire some young kids to become engineers.All if that is very worthwhile!
BUT.
What it won't do is in any way change the viability (non viability) of battery electric passenger jets. That sort of greenwash doesn't help, as all it does is to set un-realistic expectations in the publics mind.
ash73 said:
Storer said:
I can see that replacing existing jet aircraft (that I believe produce 17% of all CO2 emissions) will not be simple.
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