What will power our vehicles in the future?

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#2944432 20-Jul-2022 19:58

mkissin:
Technofreak:

An interesting article on the future of electric aviation.

Even the lead item for the article is talking about electric engines power from a turbine. Not sure why you'd bother.

https://www.bbc.com/news/business-62120130

Same reason you might design a series hybrid car. Efficiency.

The way in which a hybrid car can gain efficiency is quite different to what might be achieved with an aircraft. I'm not sure burning fuel in a turbine to convert to electricity gains anything in the way of efficiency.

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#2944433 20-Jul-2022 20:06

Technofreak:

An interesting article on the future of electric aviation.

Even the lead item for the article is talking about electric engines power from a turbine. Not sure why you'd bother.

https://www.bbc.com/news/business-62120130

Reading between the lines of what is going on here (as an engineer, but with no aviation experience):

- The choice of a tri plane, allows more lift at lower speeds, vs a single winged aircraft with the same wing length. But still the choice of a tri plane is odd, modern materials, mean longer single wings are the more efficient choice (like a glider). One would only go with a triplane layout if they need the plane narrower for storage or the likes.

- Pritty much, the slower your plane is, the more efficient it is.

- Hence it seems probable that this aircraft is set up to fly a slow cruiser for lower power requirement's, hence greater efficiency.

- They are hyping short take off / landing. A traditional 19 seater, like the beachcraft 1900 that air NZ used to run need's an about 1.15km runway. If they want to run off feilds like great barrier (930m), Waiheke (655m), more power for takeoff would be helpful.

- Above two point's means a greater differential in power needed for takeoff vs cruise, hence making a hybrid power-train, where the batteries can do say 3 mins of help for take off is more viable than a traditional plane.

I question the economic's. They are talking about GBP25 tickets for a 330km flight, and the question posed is "Why do we not use aeroplanes like we would a bus?".

Issue is that with a 19 seat capacity aircraft is a hard size to make work economically (Air NZ no longer runs the beach-craft for economic reasons), this will need to be a two pilot plane due to size, and if it is slow, that means more time for the same trip vs a conventional plane. Obviously one can't treat a 50 passenger bus (with a single, fairly cheap to train driver), in the same way as a 19 seat plane, with two well paid Pilots.

mkissin

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#2944434 20-Jul-2022 20:06

I’m an electrical engineer, not aerospace, so you may be right.
However, in general, being able to run an engine/turbine at its most efficient point and use the electricity generated is significantly more efficient than just having to run a normal motor at whatever torque/speed is required. I don’t see why that would be different for an aeroplane when the engines are probably optimised for cruise operation, rather than takeoff (which actually uses most of the fuel, relatively speaking) for example

Technofreak

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#2944435 20-Jul-2022 20:07

empacher48:
Technofreak:

An interesting article on the future of electric aviation.

Even the lead item for the article is talking about electric engines power from a turbine. Not sure why you'd bother.

https://www.bbc.com/news/business-62120130

For example:

The A320 APU without modification can produce 90kVA of power while burning 126kg/hr of Jet A as well as providing bleed air for pressurisation up to FL220. Admittedly the power provided is AC.

If you can use that power to run two electric engines it would be better than running two turbofans/props.

It is a simple step forwards to reduce emissions until all the other issues are solved with other options, especially if you’re using SAF.

It’s not an end product, but a step in the right direction that could be implemented in the next 5 years, rather than 10 to 20 years for almost everything else in the drawing board.

Granted one turbine will be more efficient than two but the picture of the aircraft in the lead item shows a single ducted fan. It very much looks one turbine powering one electric motor. I'm not sure there's much gain if any there.

Rolls Royce are betting a fair bit of money on turbines being the way for the foreseeable future. https://www.avweb.com/ownership/engines/rolls-royce-ultrafan-reaches-final-build-phase/

I think GE are doing something similar.

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#2944443 20-Jul-2022 20:49

empacher48:

For example:

The A320 APU without modification can produce 90kVA of power while burning 126kg/hr of Jet A as well as providing bleed air for pressurisation up to FL220. Admittedly the power provided is AC.

If you can use that power to run two electric engines it would be better than running two turbofans/props.

It is a simple step forwards to reduce emissions until all the other issues are solved with other options, especially if you’re using SAF.

It’s not an end product, but a step in the right direction that could be implemented in the next 5 years, rather than 10 to 20 years for almost everything else in the drawing board.

The engines on a A320 are somewhat in excess of 20,000kW each (hard to do an exact conversion as only the thrust value is advertised). The 90kW of electrical power off the apu has no hope of flying that plane.

Turbine engines are pretty efficient at cruise speed (cira 40%), so running them directly coupled with fan's / props is generally a pretty good call. Downside is they are horribly inefficient at idle. Big efficiency gains could be made in aviation, by only starting them up the minimum warm up time before take off, and shutting them down on landing. (would need to deal with the taxi via other means, perhaps a robotic tug?). Could gain even more if the engines could be shut down in the decent, but would need some means to do a go around if required.

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#2944444 20-Jul-2022 20:50

mkissin:

Same reason you might design a series hybrid car. Efficiency.

Pure series hybrid cars are very rare, for the reason of efficiency. Only ones I can think of are the BMW i3 REX & Nissan note e-power.

Stuff like the Outlander PHEV will mechanically couple the engine with the directly with the driving at cursing speeds with the engine running, as it is more efficient to than converting rotation to electricity and back again.

Also, Planes and boats as a general rule cruise at a relatively high percentage of peak power (well north of 50%), with relatively little variation of power setting. Mean's drivetrains can be tuned for efficiency at cruising speeds with relative ease.

Car's only need cira 20 - 25kW to cruise on the open road, but consumers demand often north of 100kW for rapid acceleration, hill climbing etc. The vast variability in power requirements means more opportunities to gain efficiency via a hybrid power-train.

Technofreak

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#2944445 20-Jul-2022 20:52

Scott3:

Technofreak:

An interesting article on the future of electric aviation.

Even the lead item for the article is talking about electric engines power from a turbine. Not sure why you'd bother.

https://www.bbc.com/news/business-62120130

Reading between the lines of what is going on here (as an engineer, but with no aviation experience):

- The choice of a tri plane, allows more lift at lower speeds, vs a single winged aircraft with the same wing length. But still the choice of a tri plane is odd, modern materials, mean longer single wings are the more efficient choice (like a glider). One would only go with a triplane layout if they need the plane narrower for storage or the likes.

- Pritty much, the slower your plane is, the more efficient it is.

- Hence it seems probable that this aircraft is set up to fly a slow cruiser for lower power requirement's, hence greater efficiency.

- They are hyping short take off / landing. A traditional 19 seater, like the beachcraft 1900 that air NZ used to run need's an about 1.15km runway. If they want to run off feilds like great barrier (930m), Waiheke (655m), more power for takeoff would be helpful.

- Above two point's means a greater differential in power needed for takeoff vs cruise, hence making a hybrid power-train, where the batteries can do say 3 mins of help for take off is more viable than a traditional plane.

I question the economic's. They are talking about GBP25 tickets for a 330km flight, and the question posed is "Why do we not use aeroplanes like we would a bus?".

Issue is that with a 19 seat capacity aircraft is a hard size to make work economically (Air NZ no longer runs the beach-craft for economic reasons), this will need to be a two pilot plane due to size, and if it is slow, that means more time for the same trip vs a conventional plane. Obviously one can't treat a 50 passenger bus (with a single, fairly cheap to train driver), in the same way as a 19 seat plane, with two well paid Pilots.

Trouble is a triplane doesn't provide more lift at lower speeds or any speeds, being up to 25% less efficient than a monoplane. Don't take your facts from the guy promoting that aircraft.

Slower is not necessarily more efficient. There is a sweet spot for all aircraft on the drag curve but it's not slower is better, there's a point where slower is very much worse than being just a little bit faster than the optimum speed. It also has to be remembered it costs energy to carry fuel, so the longer you're airborne the more fuel you'll need to carry the fuel to cover the extra time. That's a very simplistic explanation as there are multiple factors affecting fuel efficiency of an aircraft.

The STOL performance can be easily achieved with a monoplane.

I can see how batteries for takeoff might work in some situations but generally the weight of the batteries will negate any gains.

A nineteen seat aircraft can and does still work in New Zealand. Air New Zealand cited economic reasons but there was much more to it than that. You can make figures add up to the answer you want/need. Funnily enough there's an operator quite successfully running 19 seat aircraft on some of the old Air NZ routes.

I should disabuse you about one thing. Regional airline pilots especially those flying 19 seat size aircraft are not all that well paid, and even more so considering their qualifications. The Captain might be considered to be on reasonable money but the Co-pilot will be struggling.

You're right to question the economic's. When I start to see ticket prices like that I see a person without a proper grasp on what it costs to operate an aircraft and the associated airport and airways charges. When I see someone telling the world his triplane aircraft is more efficient I see someone who hasn't got a grasp on the basic aerodynamics involved.

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Scott3

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#2944499 20-Jul-2022 21:14

Technofreak:

Granted one turbine will be more efficient than two but the picture of the aircraft in the lead item shows a single ducted fan. It very much looks one turbine powering one electric motor. I'm not sure there's much gain if any there.

Rolls Royce are betting a fair bit of money on turbines being the way for the foreseeable future. https://www.avweb.com/ownership/engines/rolls-royce-ultrafan-reaches-final-build-phase/

I think GE are doing something similar.

I think betting on high efficiency turbofans is fairly safe money. And the most common way to boost efficiency is to increase the bypass ratio, making the engine physically bigger, I don't think we have hit the limit with that yet.

For Medium & Long haul flights, Some kind of liquid fuel to burn is the only viable option with current or foreseeable tech. Turbine engines are currently the most efficient way to do this for a plane, so having the most efficiency turbofan on the market will be good for any brand. (gut feeling fuel cells might be a bit heavy for planes)

Should note that turbines can be run on pretty much anything that burns, so if we have a breakthrough with third generation biofuels, or decide to run planes on hydrogen etc, it will just be a small tweak for the manufactures to change the fueling system to suit.

Electric planes have some potential on short routes, but higher energy densities than currently available are quite desirable. Also, we will either need to drop payload a lot on similar size planes, or build much bigger, heavier planes (and matching runways etc.) to carry the same payload). I don't think we will see 100+ Pax electric aircraft operating in NZ in the next 15 years, so still lots of opportunity to sell turbine engines even to short haul operators.

empacher48

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#2944503 20-Jul-2022 21:19

Scott3:
The engines on a A320 are somewhat in excess of 20,000kW each (hard to do an exact conversion as only the thrust value is advertised). The 90kW of electrical power off the apu has no hope of flying that plane.

Turbine engines are pretty efficient at cruise speed (cira 40%), so running them directly coupled with fan's / props is generally a pretty good call. Downside is they are horribly inefficient at idle. Big efficiency gains could be made in aviation, by only starting them up the minimum warm up time before take off, and shutting them down on landing. (would need to deal with the taxi via other means, perhaps a robotic tug?). Could gain even more if the engines could be shut down in the decent, but would need some means to do a go around if required.

The engines on the A320 are rated higher than what we actually use. Most take offs are significantly de-rated. Even TOGA isn’t anywhere near 100% available thrust from the V2500’s. We don’t usually get to the max available thrust figures until we are over FL270. Also 80% of the thrust from the V2500 comes from the fan at the front and 20% is from the hot section.

They also need a 5 minute warm up at the start of the flight and a 3 minute cool down at the end of the flight. Most days here in NZ and Australia (with the exception of 34R in Sydney) we have to hold at the holding point for a minute or two to complete the warm up before we depart, and sometimes up to a minute holding on the gate at the end of the flight. Some busier airports worldwide may benefit from robotic tugs.

But the joys are with a new propulsion technology the aircraft can fly at its optimum altitude. It doesn’t have to operate above FL300 to get the best fuel burn vs TAS as a jet does. So you can operate the smaller turbine at its optimum level to get the most power out of it.

Scott3

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#2944525 20-Jul-2022 21:44

Technofreak:

Trouble is a triplane doesn't provide more lift at lower speeds or any speeds, being up to 25% less efficient than a monoplane. Don't take your facts from the guy promoting that aircraft.

Slower is not necessarily more efficient. There is a sweet spot for all aircraft on the drag curve but it's not slower is better, there's a point where slower is very much worse than being just a little bit faster than the optimum speed. It also has to be remembered it costs energy to carry fuel, so the longer you're airborne the more fuel you'll need to carry the fuel to cover the extra time. That's a very simplistic explanation as there are multiple factors affecting fuel efficiency of an aircraft.

The STOL performance can be easily achieved with a monoplane.

I can see how batteries for takeoff might work in some situations but generally the weight of the batteries will negate any gains.

A nineteen seat aircraft can and does still work in New Zealand. Air New Zealand cited economic reasons but there was much more to it than that. You can make figures add up to the answer you want/need. Funnily enough there's an operator quite successfully running 19 seat aircraft on some of the old Air NZ routes.

I should disabuse you about one thing. Regional airline pilots especially those flying 19 seat size aircraft are not all that well paid, and even more so considering their qualifications. The Captain might be considered to be on reasonable money but the Co-pilot will be struggling.

You're right to question the economic's. When I start to see ticket prices like that I see a person without a proper grasp on what it costs to operate an aircraft and the associated airport and airways charges. When I see someone telling the world his triplane aircraft is more efficient I see someone who hasn't got a grasp on the basic aerodynamics involved.

Good response.

Mentioned the efficiency hit from a tri-plane (vs longer single wings) in my comment. Does seem an odd choice for an efficiency critical aircraft.

My comments on slower, being more efficient, was with regards to a clean sheet design like this one, vs typical speed in the 19 seater class. I'm pritty confident one could come up with a more efficehnt design if they were targeting a say 160 knot cruise speed, vs say a 280 knot one (the cruise speed of a Beachcraft 1900).

Good point on the likes of Originair, which are operating fine with this size of aircraft.

I meant well paid air crew relative to a bus driver, perhaps I am wrong about this? Had assumed that any pilots flying multi pilot engines good payed alright given their expensive qualifications. (I know pilots doing single pilot sightseeing flights will work for cheap as a means to accrue hours).

On economics, I looked up some Originair prices at a random date. Wellington to Nelson, cheapest of the week was $150, so well more then the GBP 25 of the much longer UK route mentioned in the article.

Technofreak

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#2944526 20-Jul-2022 21:44

Scott3:

Electric planes have some potential on short routes, but higher energy densities than currently available are quite desirable. Also, we will either need to drop payload a lot on similar size planes, or build much bigger, heavier planes (and matching runways etc.) to carry the same payload). I don't think we will see 100+ Pax electric aircraft operating in NZ in the next 15 years, so still lots of opportunity to sell turbine engines even to short haul operators.

There in lies the problem with current battery technology. It's nowhere near energy dense enough by a factor of greater than 30. Higher energy densities are not just desirable they are absolutely necessary.

From an economic perspective reducing payload wont work.

Bigger heavier aircraft require more powerful engines requiring more fuel both for take off and cruise. It becomes a bit of the tail chasing the dog scenario

Also most regional airports are around the 1300 metre mark in length. There's a lot of money to be spent making them longer for heavier aircraft plus in some cases their PCN (Pavement Classification Number) may not support heavier aircraft. There's more to it than just making a bigger aircraft.

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#2944528 20-Jul-2022 21:47

When I first started working with airports it became rapidly clear that concrete is a big deal. Some of the technology involved is really interesting, particularly rapid replacement concrete which means that they can replace sections of runway/taxiway in a few hours.

Technofreak

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#2944549 20-Jul-2022 22:02

Scott3:

Good response.

Mentioned the efficiency hit from a tri-plane (vs longer single wings) in my comment. Does seem an odd choice for an efficiency critical aircraft.

My comments on slower, being more efficient, was with regards to a clean sheet design like this one, vs typical speed in the 19 seater class. I'm pritty confident one could come up with a more efficehnt design if they were targeting a say 160 knot cruise speed, vs say a 280 knot one (the cruise speed of a Beachcraft 1900).

Good point on the likes of Originair, which are operating fine with this size of aircraft.

I meant well paid air crew relative to a bus driver, perhaps I am wrong about this? Had assumed that any pilots flying multi pilot engines good payed alright given their expensive qualifications. (I know pilots doing single pilot sightseeing flights will work for cheap as a means to accrue hours).

On economics, I looked up some Originair prices at a random date. Wellington to Nelson, cheapest of the week was $150, so well more then the GBP 25 of the much longer UK route mentioned in the article.

One of the main reasons for biplane and triplanes was for structural strength. You can make a biplane or triplane wing very strong, but it's not aerodynamically efficient, whereas a monoplane takes much better engineering to get its strength. As an engineer you will know this anyway.

Regarding cruise speeds, I think you might be getting two measures of airspeed mixed up, Indicated Airspeed (IAS) and True Airspeed (TAS). The 280 knots you mention is very likely a TAS figure which at 25,000 feet equates to an IAS of 190 knots. 160 IAS equals just over 235 TAS at 25,000 feet. A TAS 160 at 25,000 is giving an IAS of just below 110 knots which is getting pretty slow for an aircraft like this.

Regards to a clean sheet design. When it comes to aerodynamics, in level flight weight equals lift. Drag is a penalty of lift. Increase the weight you increase the drag. There's been a significant amount of research around reducing this drag. Any new design is only going to give small incremental gains. Same goes for form or shape drag. I don't think there's big gains to be had certainly not to offset the weight penalties of current battery technology.

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Tinkerisk

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#2944580 20-Jul-2022 23:39

Scott3:

Reading between the lines of what is going on here (as an engineer, but with no aviation experience):

- One would only go with a triplane layout if they need the plane narrower for storage or the likes.

>> Nope, one would go with folding wings.

- Pritty much, the slower your plane is, the more efficient it is.

>> Nope, the slower it is, it has more time to burn energy to reach the destination.

- Hence it seems probable that this aircraft is set up to fly a slow cruiser for lower power requirement's, hence greater efficiency.

>>> Nope, see above.

- I question the economic's. They are talking about GBP25 tickets for a 330km flight, and the question posed is "Why do we not use aeroplanes like we would a bus?".

From month to month, another pig is herded through the village (glossy studies are a dime a dozen, very few are ever realised).

- with two well paid Pilots.

>> These times are also more or less over and single pilot cockpit is not a taboo either.

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#2944617 21-Jul-2022 07:57

Tinkerisk:

>> Nope, one would go with folding wings.

Wing fold mechanisms add structural complexity and weight. And therefore increase fuel burn. In some circumstances, like naval aviation, the gain in weight is outweighed by the reduction in physical dimensions on the hangar deck.

>> Nope, the slower it is, it has more time to burn energy to reach the destination.

This is ignoring thermodynamic law.

>>> Nope, see above.

See above.

>> These times are also more or less over and single pilot cockpit is not a taboo either.

In your dreams maybe. While humans are fallible there will be a requirement for more than one at the controls. Likewise, while the automatics are good, the environment is too dynamic for full automation.

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