Would you fly on an electric plane? And what technology is needed to make this unholy powertrain work? The challenges will lead to extraordinary designs...
This is the electric aviation thread!
In this thread we'll cover:
-Different electric & hybrid aircraft power systems.
-The challenge of full electric: Closing the energy gulf.
-Enabling tech: Batteries, motors, aerodynamics.
-Will it work?
Expect incredible concepts & links to specialist aerodynamics threads!
Cycle 1: Turbo-electric power.
A gas turbine engine with generator, DC buses & convertor drives electric motors, no battery storage: This could eat 10% efficiency, but buys the ability for integrated airframe concepts such as boundary layer ingestion & distributed propulsion.
Hybrid-electric.
Like a car engine, an aircraft engine is most efficient at it's design cruise condition. By using rechargeable batteries & electric motors, hybrid cycles try to smooth out engine demand so it spends more time at it's most efficient point.
Cycle 2: Series hybrid.
A turbo electric layout plus a battery bank, the propulsor is electrically driven. Heavier even than the turbo electric cycle, it does however allow the engine to stay at optimal running condition, a net benefit for short haul & regional aircraft.
Cycle 3: Parallel hybrid.
A transmission box allows either engine or electric motor to power the prop. More complex but lighter than series hybrid with fewer conversion losses, but leads to the engine running off-design more often. Considered less efficient than series hybrid.
The trouble with hybrids is that, just as a hybrid car is best at town & city driving, a hybrid plane is best at short haul & general aviation: Long haul aircraft spend too long at their design condition for hybrid power systems to be of much use.
What about pure electric?
Cycle 4: Battery electric.
Conceptually the simplest setup, it's simultaneously the most "green", as a zero emissions aircraft, and the most difficult, which we'll get into.
Pictured: The RR 'Spirit Of Innovation' demonstrator. At 345mph, the fastest electric plane.
If we do it, it won't be for convenience: The specific energy of kerosene is 48 times higher than lithium ion batteries: An unbridgeable gulf?
Electric motors are 90%+ efficient while the thermodynamic efficiency of gas turbines are ~55%, making the ratio 'only' 1:29
Enablers 1: Batteries.
Li-ion batteries, the gold standard, max at ~250Wh/kg.
Li-sulphur, on the Airbus Zephyr have shown 500Wh/kg but so far only 1350 cycles.
Solid state: Fast-charging and 500-1000Wh/kg. Under development.
Li-Air: Potentially 1700Wh/kg, but a long way off.
Enablers 2: Motors.
Conventional motors have a specific power of 1-5kW/kg, less than gas turbines.
-In 2021 H3X & Wright Electric tested 250kW & 2MW motors with 13 & 10kW/kg.
The EU sponsored ASuMED project is developing high temperature superconductor motors for 20kW/kg.
Batteries of 800Wh/kg are probably a minimum for electric aviation: If we assume that 1000 is achievable then that brings the usable specific energy ratio with kerosene down to 1:7.
This means that aerodynamics must do some heavy lifting to get it down to low single figures...
Enablers 3: Distributed propulsion.
Electric powertrains allow this: Extremely high bypass low pressure ratio propulsors with blown wing effects maximizing efficiency.
The hybrid electric EcoPulse aircraft shown is halfway through flight testing proving this concept.
A thread on distributed propulsion is linked below, featuring the ONERA Dragon concept: A medium range airliner showing a 7%-12% efficiency benefit from distributed propulsion alone. Hybrid power storage could increase this further.
This wake energy management technique reduces flow field energy loss and can improve the efficiency of propulsors by embedding them in the aircraft boundary layer. A structurally robust well-sited prop is needed.
Definitely the biggest ask of airframers & airports, and not strictly necessary, it remains a potentially optimal platform from an efficiency standpoint, and works well with distributed propulsion & BLI.
The NASA N3-X concept uses all three aero enablers in a long range turbo-electric flying wing with cryocoolers enabling superconducting motors and higher turbine inlet temperature.
60% more fuel efficient than current state of the art, it's an idealised design but instructive.
Another rich opportunity for hybrid power is helicopter aviation, where it would be worth 10% in efficiency all on it's own without other improvements. Airbus recently tested this as part of an emergency back up power system for the FlightLab helicopter.
Novel hybrid electric/ turbo-electric power architectures, with a gas turbine engine at the core, have huge potential from short to long range, and we should move that way, but the aerospace industry might not leap without a push.
What about pure electric aircraft..?
Frankly, pure electric is a lost cause everywhere except short range and city transport niches: The specific energy gulf is just too large.
But it's still important: Electric aviation's huge energy challenge forces it to deal with unconventional design, and this is it's value.
The city eVTOL niche is tiny, almost a joke, but it's the only electric aviation sector plausible right now, making it a technology incubator.
Inconsistent regulation could kill it dead, and it's important we don't do that: Technology grows from seeds, which we should water.
So let's hear it for the challenge of electric aviation, because it might, just maybe, be a catalyst that will move us beyond the tube, wing & twin configuration.
So the future might actually look like the future.
Papers used are shown, I hope you enjoyed this!
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Is it an island of fog breathing has-beens, or a nascent industrial juggernaut? What, in fact, does Britain do well?
Here's a thread of a few surprising things…
Motorsport!
Almost all of the world's Formula 1 teams are based in this tiny region in Oxfordshire & Northamptonshire, which also supports 3,500 companies and 40,000 people in motorsport.
This is known as 'Motorsport Valley’ (not actually a valley).
The jet engine!
The world's 2nd largest widebody jet engine maker, Rolls-Royce, is a UK company, and also manufactures engines for helicopters, fighter aircraft and the F35B vertical lift system.
The thread below covers a small slice of their wizardry.
The world's thinnest & strongest material, a one-molecule thick film of it could build a hammock that could hold up a cat, invisibly.
It was isolated 20 years ago, but what has happened with this super-material since then? And how do you mass produce it?
Read on...
Graphene, a hexagonal one atom thick graphite crystal film, was theorised for decades but never characterised.
In 2004, Andre Geim & Konstantin Novoselov isolated & characterised a layer of Graphene in the University of Manchester using scotch tape (!)
And it's incredible.
With a tensile strength over 100 times greater than steel, thermal conductivity 5 times better than diamond, electrical conductivity comparable to copper and complete impermeability across its atom-thick membrane, graphene has revolutionary potential.
Not every scientific study involves drugged rodents or non-binary fish. Here's a selection of really massive, or just impressive, scientific projects for your viewing enjoyment.
Let's start…
Fusion!
The National Ignition Facility was originally built to simulate nuclear bomb detonation, but has since fronted inertial fusion power research. In 2023 it first achieved controlled fusion ignition, producing more power from deuterium/ Tritium fusion than was applied.
Inertial fusion relies on lasers focusing vast power on a target, just for an instant. It also produces some impressive set-pieces: Do you recognize this movie that featured the National Ignition Facility?
The question you always wanted answered: How does a combine harvester work?
In this thread we take a dive into these awesome machines!
The combine is among the greatest feats of automation in history, with one of the biggest effects on society. It freed entire towns & villages from the backbreaking toil of harvest and, with other innovations, took America from 90% of it's population in agriculture to 2% today.
What does a combine need to do? We'll use wheat as the example.
-Cut the stalks.
-Threshing: Separating useful grain from the stalks.
-Winnowing: Separating grain from the chaff (seed husks).
-Storing & moving the grain.
-Neatly depositing the stalks.
The purpose of education is to tell the truth, right?
Not always. Sometimes it's to tell you a simplified fib, a not-quite-truth that almost explains things and prepares you for the truth as an adult.
This is a Lie-To-Children. Let's list a few, and you can add your own…
We'll start small: Subtraction.
Young children are often taught, in math, to subtract the smaller number from the bigger number. This familiarises them with the concept, but makes negative numbers impossible.
Later on, we learn a more complex reality.
Another lie:
Sticks and stones will break my bones, but words will never hurt me.
As some of you may know, a few days ago Reaction Engines went under. This was a company that for 30 years had been slowly developing a revolutionary hypersonic hybrid powerplant.
SABRE: What is it and why is it important?
I'll do a proper deep-dive thread soon, but this is a taster:
SABRE is an engine designed to go from zero to orbital injection speeds while staying fuel efficient, unlike a rocket.
It's a turbo-compressed air breathing hybrid rocket.
But why…?
Here's a graph showing fuel efficiency and airspeed for different aircraft powerplants. Currently only one, rockets, spans the entire speed range.
But rockets are inefficient, partly because they have to carry all their oxygen with them.