Aviation & Space

Transforming passenger airline comfort, efficiency, safety & economics — it's in the bag!

Yes, literally, baggage is the weak link in current passenger airline design & systems.  Baggage slows check-in & boarding/loading as well as confusing accountability for safety checks (split between airline, airport & government customs).  On the plane, all baggage constitutes an under-priced waste of space!

Contact me via LinkedIn for a confidential copy of my paper solving the stacking problem in the plane.

For airports, I have to wonder how sub-optimal regulations could be adversely impacting both safety & efficiency, especially given that airlines now allow on-line “check-in” several days before passengers even get to the airport (what then is the point of "check-in"??).  Airport check-in and baggage checks are a source of significant delay in overall flight time, but apart from hand baggage, this is currently outside the control of the airline.

I notice that the French TGV has less stringent and faster baggage checks (but presumably adequate), even though the passenger risk in a major accident could be worse than a medium-sized plane, and I suspect that if major airlines were similarly given full control over all airport baggage processes then they would significantly improve their speed and efficiency, e.g. through initiatives like expedited customs screenings for “pre-approved, low risk” travelers.

Giving airlines control of airport baggage processes would also enable regulators to hold the airline clearly accountable for all airplane safety incidents, so with appropriate oversight they could be given an incentive to minimise risks and maximise safety.  A flexible approach (instead of ridiculous prescriptive measures like plastic forks) could allow airlines to avoid some costly & time-consuming regulatory requirements if they can provide the regulator with persuasive risk analysis indicating that their overall approach achieves a net safety improvement.  For example, the requirement that aircraft must have 4 jet engines to fly some long routes over water seems an incredibly costly and outdated regulation that prevents more efficient, less-polluting & probably safer new aircraft like the A350 or B787/777 flying some routes (including non-stop Sydney to London).  I imagine the money saved from switching to twin-jet planes would probably be much better spent on other safety initiatives.  As the 737-MAX debacle has shown, not only do currently onerous airline safety regulations discourage the innovation of better and potentially safer airplanes, they can actually encourage less safe designs in order to deliberately game the certification process.

Current international aviation laws require all airlines to have insurance, which can pay out compensation in the event of a crash.  However, if there is uncertainty about who’s to blame (as I imagine is often the case) then claimants can find themselves being buck-passed from airlines to aircraft manufacturers, airports & governments etc.  This could be avoided if regulations made airlines clearly accountable whatever the cause – which would be possible if airlines had responsibility for all aspects of operations, including airport baggage checks (it would be up to airlines to sub-contract responsibilities and risks with aircraft suppliers and maintenance facilities etc., but they could not buck-pass a claimant, just as general consumer-rights laws prevent a shopping retail outlet from buck-passing customers to product suppliers).

Perhaps the only risk factor that an airline couldn’t be held accountable for would be a nation’s terrorist risk that results from the government’s public policy. However, the price of this risk that was implicitly included within insurance premiums could potentially be estimated from the range of airline premiums across the industry, and then paid by the government (e.g. through tax relief), or if not, it would be better in any case to have one party responsible, because shared responsibility tends to make no-one responsible and weaken incentives for action.

Meanwhile the US is looking to relax its current ban on overland supersonic flights, as both Spike Aerospace and Lockheed in partnership with NASA are working on designs to eliminate the sonic boom (particularly, the "X-59 Quesst").  Lockheed was also working with Boeing & others on Aerion's Mach-1.4 AS2 business jet and its Mach-4+ AS3 airliner (with the former exploiting "boomless cruise" technology) that could use synthetic, carbon-neutral fuels with modern, efficient turbofan jets by GE – with an aim of first production of the AS2 in 2023, until Aerion announced it had failed to raise funds and would shut down in 2021.  Virgin Galactic & Rolls Royce were also aiming to develop a Mach-3 aircraft to seat 9-19 people.

With commercially viable and affordable supersonic planes set to return (eventually, as there's good reason for scepticism) – which will also create pressure for innovation in standard subsonic services – plus Virgin Galactic already taking people to the edge of space, aviation could be heading for quite a boom!  However, although planes only accounted for just over 2% of all man-made CO2 emissions in 2019 (though twice this impact due to other effects), continued rapid growth in demand could make aviation responsible for a quarter of the world’s “carbon budget” by 2050 (the amount of emissions permitted to keep a global temperature rise within 1.5 degrees Celsius above preindustrial levels), even if fuel efficiency improves by 1% per year.  So given supersonic planes are likely to consume 5-6 times as much fuel per passenger as subsonic jets (although Boom hope to halve that so it's in line with current business-class fuel burn), we need to develop pragmatic aviation emission regulations & incentives now (before industry commits major investments) so as to avoid a huge growth in aviation emissions over coming decades.

Thankfully, a clean aviation industry may be achieved using electric propulsion and/or hydrogen or Sustainable Aviation Fuels (SAF) such as synthetic fuels or biofuels — which could, for example, be made from agricultural waste (potentially powering 90% of Australian domestic flights by 2050), or maybe using solar energy to directly produce fuels such as methanol or hydrogen or "syngas" (a mixture of carbon monoxide & hydrogen ), with "artificial leaves" that could even float on water.  Synthetic kerosene has a major advantage of facilitating a smoother technology transition, as well as needing less land compared to biofuels.

"Green hydrogen" may also be produced through electrolysis from water using, for example, low-cost renewable energy.  e.g. Israeli company H2Pro claims it will get below US$1/kg by 2030, with electrolysers of 95% energy efficiency, which would beat the cost of producing it from fossil fuels.  In the aircraft, hydrogen fuel cells offer the potential for much higher efficiency than conventional engines (or hydrogen-powered turbines, like Airbus is working on), but there are significant efficiency losses throughout the hydrogen energy conversion cycle.  It might also be possible to extract natural hydrogen from underground reserves (though with risks to global warming if tapping it releases methane into the atmosphere).

Hydrogen is usually stored under very high pressure as a gas, or as an ultra-cool liquid (demonstrated with a fuel-cell by "H2Fly"), but "cryo-compressed" hydrogen gas can actually provide a higher energy density than liquid hydrogen, potentially offering 40% longer aviation range, although that advantage is lost in bigger planes as larger liquid-hydrogen tanks have a lower mass/volume ratio (and also as new light-weight liquid-hydrogen tanks are being developed).  Overall, the challenges for hydrogen-powered planes are huge, and perhaps even insurmountable.

Existing short-haul passenger flights currently produce about 25% more emissions per passenger-km than long-haul ones and flights of 1,500km or less make up around a third of aviation emissions, which could be substantially reduced by rapidly-developing electric planes (powered by batteries, SAF, hydrogen or hybrid systems).  Whilst batteries & hydrogen pose many challenges in aircraft, in this paper I conclude that there seems to be no fundamental reason why an electric fan can't produce similar levels of thrust to a turbofan jet, but with greater efficiency due to avoiding the wasted energy in a hot exhaust (or more fundamentally, because of the thermodynamic limits to the efficiency of a "heat engine", including kinetic energy lost as incoming air is slowed & compressed in a jet's combustion chamber).  NB. for interest, that paper of mine also discusses the molecular flows around aerofoils that cause lift (except I don't cover the coanda effect) and over drag-reducing shark skin.

Short-range electric planes are already being pursued by the likes of EasyJet and Airbus (who worked on the E-Fan X hybrid jet with Rolls-Royce), as well as Boeing-backed Zunum (which hoped to be operating by 2022, although that hasn't worked out), as well as many new startups, such as ZeroAvia, which hoped to fly a 76-seat hydrogen-electric  airliner as soon as 2023, with commercial flights of up to 800km soon after (targeting 2025-27 in 2023 – see the video here at 6'45" – whilst it explores cryo-compressed hydrogen gas as an alternative to liquid hydrogen).   Meanwhile Eviation aims to carry 9 passengers in a light-weight, low drag, "lifting body", battery-electric plane called "Alice" (which has half its weight from the batteries) — originally with a target range of some 1,000km or more, to serve regional towns in the US & Australia, with services starting in 2022 (subject to FAA approval), although the revised design that first flew in late 2022 had a substantially lower claimed range of 460km.  Dutch startup Elysian claims it'll be able to produce 90-seat battery-powered commercial airliners by 2033 with a 1,000-km range, which would cover around 50% of all scheduled commercial flights.

The plane designs referenced above are fairly conventional, but a switch from jet engines to electric motors enables more radical designs — contact me via LinkedIn to see a confidential copy of my conceptual design for a 60-80 seat electric plane.

Although pure battery-electric technology seems unlikely to be used on large planes for long flights in the foreseeable future, hybrid systems combining electric motors and traditional engines offer the potential for substantially reduced fuel consumption whilst maintaining range.  For example, Ampaire have demonstrated a 50-70% reduction in fuel consumption (with the potential for a 90% reduction plus maintenance savings of 25-50% and 60% lower noise) on a retrofitted Cessna over a 12-hour, 1,375 mile (2,213km) flight.  Also conventional jets – which are already 80% more efficient than those in the 1960s – still have much potential for improvement, with Rolls Royce's next generation of "Ultrafan" jet engines expected to use 25% less fuel than its existing world-leading "Trent" engines, contributing to its broader goal of reducing CO2 emissions from aviation by 75%, NOx emissions by 90% and noise by 65% or 15dB.

Additionally, new low-drag aircraft designs like the SE200 tri-wing offer the prospect of a similar magnitude of further efficiency improvements.  "Blended wing" designs such as the "Flying-V" may also be able to reduce emissions by over 20%, or potentially even by 50% according to Bombardier, Natilus and JetZero (in partnership with Delta Airlines), which – as shown in the 10th picture here – envisages putting hydrogen tanks alongside  the passenger cabin within a broadened, lift-producing aircraft body.  Along with other design features, blended-wing planes may also reduce aircraft noise by 25dB, making them barely audible outside an airport perimeter (listen to the simulated noise comparison here).

However, although these developments are encouraging, and some airlines are already voluntarily aiming for net zero emissions in coming decades, regulation needs to ensure the industry makes good progress with reducing emissions by encouraging it with incentives to continually do better, rather than applying blunt prescriptive requirements (like mandating the use of "Sustainable Aviation Fuels, which may not be the best approach) or minimum standards (which, because of price competition, generally result in companies doing only the absolute bare minimum).

Innovation in short-range aviation is being spurred by the booming electric vehicle industry, which is delivering highly-efficient, light-weight & high power-density electric motors, including new axial-flux types like those by YASA – who were aiming for over 30kW/kg in 2023 but in 2025 already achieved over 40kW/kg in a record-smashing prototype (and are applying their 28kW/kg Evolito motor to the Flying Whales airship) – or the similarly compact but potentially huge-diameter machines by Magnax, or Donut Lab's similar hollowed-out motors, which may exceed 15kW/kg.  Then there's Koenigsegg's torque-dense "raxial-flux Quark" motor or its "Dark Matter" motor producing 15kW/kg, or Linear Labs' circumferential-flux "HET motor", or the HPDM-250 by H3X or magnet-free motors such as that by "ZF" or Mahle's "perfect motor", or others developed for planes by magniX.

The combination of these significant motor and battery improvements enable radical new aircraft designs, especially for multi-rotor air-taxis with Vertical Take-Off & Landing  (VTOL), such as those by Joby (which completed an 842km flight in mid 2024 using 36kg of liquid hydrogen supplying a fuel cell).  Competitors include the all-very-similar-looking models by Wisk, Beta, Archer & Vertical, or Jaunt’s inherently-safe ROSA "gyrodyne" (developed with Uber Elevate before Uber sold their aviation division to Joby in 2020).

Flying cars are also now a reality: e.g. Klein Vision's "AirCar" prototype is a sporty-looking 2-seater with retractable wings and BMW engine that has done half-hour inter-city flights at 100 knots; prototype 2 will aim for cruise speeds of up to 300km/h (162kt) and a range of 1000km (621mi), with EASA CS-23 aircraft certification and an M1 road permit. Alternatively, you can already buy the compact & sporty "PAL-V" hybrid car-gyrocopter for about Є300k, or perhaps wait for the DeLorean flying car under development!

More unusual e-VTOL designs under development include Lilium (if it survives, which isn't looking promising in early 2025) — which incorporates 36 tiny fan-jets all along the top of its wing surfaces, and could be as efficient as an electric car (making it potentially better than buses or trains) — and Pterodynamics' "Transwing", which has long wings – for highly efficient flight – that fold up compactly like a bird (or pterosaur) during a stable transition through VTOL to/from a small landing zone.

However, because of the overwhelming importance of energy efficiency (for economic as well as environmental reasons), plus safety, the business case for urban air taxis is challenging, and so I think that aside from some specialty VTOL markets (like emergency services), the most viable commercial electric planes over the next decade or two are likely to be longer-ranged, fixed-wing, hybrid-electric aircraft optimised for use on short runways (maybe even under 100m), in order to avoid the weight of extra high-powered rotors and the flight inefficiency penalty of VTOL designs.  For safety reasons, autonomous drones for freight are also likely to become commercial before passenger taxi operations.  It's hard to keep up with the plethora of new (or failing) designs, but the latest assessment of viability for many ventures can be found at the "Advanced Air Mobility Reality Index".

Floating up to space

Electric motors are of course no use for going into space, but we could substantially reduce fuel use for many purposes, including even through use of high-altitude balloons, as I discuss below.

Not surprisingly, Stratolaunch is following a similar approach to Virgin, although with a bigger plane to launch heavier satellite payloads.

But can Virgin's approach be taken further?

Another private "space" company, World View, developed plans to use polyethylene balloons the size of a football stadium to lift a 4-tonne, 8-person (+ bathroom) "Voyager capsule" or up to 9 tonnes (20,000 lb) of cargo to a height of 30km (19 miles) in 1.5 hours (before para-gliding down in just 40 minutes).  So I wondered whether something similar could be used to carry a small spaceship up to an altitude of around 40km, which is over twice the 15km altitude (50,000 feet) that Virgin Galactic's "WhiteKnight2" mothership will release its "SpaceShip2" rocket from (WhiteKnight2 would be limited by its conventional jet engines not having sufficient air to operate any higher, but helium balloons lifted World View's space-suited Alan Eustace to 41.4km in 2014 and also took Felix Baumgartner to 39km in the 1.3 tonne "Red Bull" capsule from which he did the world’s highest skydive in 2012).

Not only would the initial climb by balloon use zero fuel (or a very small amount if it was boosted higher & faster by small rockets), but also I estimate the higher altitude of 40km would reduce the air resistance (drag) for a released spaceship by a factor of over 30 compared to at 15km (the air density, which drag is proportional to, would be reduced by about this factor and also the square of the Mach number – which is a measure of air compressibility – would be reduced by about a third, due to the higher air temperatures and correspondingly higher speed of sound at 40-50km altitude).  So a rocket ignited at 40km would have to fire for even less than the 70 seconds planned by Virgin to reach a peak altitude of 110km at speeds of over Mach 3, which could make it possible to substantially reduce the power and weight of the spaceship rockets & fuel, thus also making it easier to lift through its initial ascent by balloon.

A similar-sized spaceship to Virgin's 9.7 tonne SpaceShip2, but with reduced rocket & fuel weight (partially offset by balloon weight, which was itself 1.7 tonnes even to lift the smaller Red Bull capsule) might require one or two large balloons like World View is planning, or one like this Airlander helium-hybrid airship, which can already lift 10 tonnes for industrial or luxury tourist use (whilst others such as "Flying Whales" plan to lift 60 tonnes or more).

There's just one other problem to solve though, which is avoiding the release of helium after the balloons are detached, because like all other resources, humans are not currently managing this well.  I imagine some kind of light-weight, tension frame/cabling around the balloon with the tension balanced by a spring that is released after the spaceship detaches it, which would then trigger a compression of the balloon so it falls to Earth.  Or maybe a solar powered pump & fan system could slowly re-compress the helium and guide the deflating balloon back to base.  Alternatively, as Space Perspective are now planning, much cheaper hydrogen could be used (e.g. split from water using solar energy), which will lift you higher (because it's lighter than helium) and is not precluded by its over-stated safety issues.

So in the not-so-distant future, time-poor business executives could take off silently by balloon from any tall building right within any global city, ascend to 40km where the balloon would detach and return to base, then rocket into space and 'orbit' half way around the world in an hour (at or close to full orbital speed, which is nearly Mach 23 at 100km altitude) before gliding down to any airport (assisted by advanced rocket guidance systems &/or parachutes).  With possibly only several minutes of rocket fuel burn for a London to Sydney trip, it may even be cheaper and have less environmental impact than current planes!