October 24, 2024, ©. Leeham News: We do a Corner series about the state of developments to replace or improve hydrocarbon propulsion concepts for Air Transport. We will find that development has been very slow.
We don’t have, and will not have, a certified and produced aircraft that can transport passengers using anything but classical propulsion concepts this side of 2028 and probably 2030 if we put the bar above five passengers.
This is 14 years after the flight of the Airbus E-Fan in 2014, which started a multitude of studies and projects to explore new, more environmentally friendly ways to propel aircraft.
Figure 1. The Airbus E-fan flying at the 2014 Farnborough Air Show. Source: Wikipedia.
Why is the progress so slow? Normal aircraft development takes seven to a maximum of nine years?
What is the status?
To better understand the progress made by the alternative propulsion projects to date, we start by reviewing the present status of the most well-known projects.
We start this week with the battery electric and hybrid aircraft projects that have flown a certified aircraft, a prototype, or a functional model. If we hadn’t put this restriction, we would have to listed over 200 projects that are still to fly anything other than scale models:
- The only certified electric aircraft is still the Pipistrel Velis Electro, a very light two-seat basic trainer. I have sat in one, and it’s very crude and basic (you sit on the floor in a lightweight plastic seat pan). The endurance is about one hour, which is OK for basic flight training as the pupil is often finished in the head before the endurance is up.
The Pipistrel Velis Electro. Source: Pipistrel.
- The project that is probably the closest to the final form and, therefore, certification after the Velis is the Beta technologies Alia CX300, which started as a VTOL project named Alia A250, where Beta first developed the forward flight function and then started the problematic vertical flight part. The forward flight part went so well (it has flown multi-hop long-distance flights over half of the US. The prototypes have now flown 40,000nm) that the market asked for a version for normal flight, now called Alia CX300 CTOL. It has flown a maximum flight of 336nm and will take a pilot and five passengers. FAA Part 23 certification of the CX300 started in March 2023. Certification and delivery are targeted for next year.
Alia CX300 prototype. Source: Beta Technologies.
Alia CX300 cabin. Source: Beta Technologies.
- A project that has flown is Eviation Alice. It did one eight-minute flight, and then the aircraft was mothballed as it no longer represented what could and should be certified for nine-passenger transport. Presently, the project is waiting for improved batteries, with certification and delivery at the end of the decade. The final form aircraft is a classical tube-and-wing aircraft.
Alice first and only flight 9 September 2022. Source: Eviation.
Alice final form, with a classical tube fuselage. Source: Eviation.
- Voltaero has flown a development aircraft, a converted two-motor Cessna 337. The front piston engine has been replaced with two electric motors on the pontons. The final configuration is quite different: a pusher design with a clever parallel hybrid configuration of a Kawasaki piston engine and electric motors driving a pusher propeller.
The Voltaero Cessna 337 test aircraft for electric propeller engines. Source: VoltAero.
The final prototype for certification is a quite different pusher design with a small battery hybrid. Source: VoltAero.
- Ampaire has flown two functional models or test aircraft, depending on what has been tested. One is a Cessna 337, where one engine has been replaced with a diesel piston engine in a hybrid with an electric motor, and the other is a conversion of a Cessna Caravan, where the turbine engine has been replaced by a diesel piston engine in a hybrid with an electrical motor. Exactly where these projects stand today is unclear.
The Ampaire Cessna 337 with one engine replaced by a diesel engine and electric motor. Source: Ampaire.
The Ampaire Cessna Caravan, with the gas turbine engine replaced by a diesel engine and electric motor. Source: Ampaire.
It’s noteworthy that the largest aircraft that has flown to date in this category is the nine-seat Alice non-conforming prototype, and the only battery-electric aircraft with a demonstrated range that makes it operationally interesting is the VTOL derivative Alia CX300.
Next week, we will discuss the background to the very limited progress in this segment.
Related
One key is longer life of the batteries as they cost to replace. The other is glide ratio to maximize range. Fuel cells and LH2 and mass efficient but cost reduction/certification rules are still in the works. If you are +19 pax the twin pilot cost is a major drag, maybe there is an opening for EASA/FAA pilotless aircrafts if Honeywell/Thales/Garmin/RTX can do and integrate everything inside the shell fuselage. That way the UAM’s just design the shell and paintjob while the big companies above do the rest.
Glide ratio is irrelevant as you cant glide to the destination full stop.
Dukeofurl wrote
Glide ratio is irrelevant as you cant glide to the destination…..
No…. L/D is a measure of aerodynamic efficency and the higher the L/D, the less fuel you burn to get the mission flown at any given weight. It matters a lot and is the entire reason the 777x wingtips are duch a big deal
777X extra wing span has nothing to do with glide ratio. Its literally for gliders only.
The longer wings improving range is from lower induced drag. But the A330 had almost the same wingspan as the 747-400 for similar reasons
The time airline pilots consider glide ratio is total engine failure and thats when the designers come up with the details for the pilots instructions
The rest of the world knows aerodynamic efficiency from Lift/Drag ratio
Check the Breguet range equation where CL/CD is a factor.
https://web.mit.edu/16.unified/www/FALL/thermodynamics/notes/node98.html
Your link has the proviso
“Range and endurance have been mentioned in the preceding sections – and we have introduced that for maximum range the pilot should fly at
Vmr, whilst to fly for maximum endurance the pilot should fly at
Vmr
However – the above speeds are valid only for unpowered flight. So these speeds are suitable for a glider, but *once an engine is introduced* to an aircraft, these speeds no longer give the maximum range or the maximum endurance.”
Which is my point , gliders arent passenger planes ( the pilot can only go there with total loss of thrust)
Ask Captain Sullenburger
No, it is valid for both, SFC is also in the equation as is amount of fuel at start and landing. One way to reduce power consumption is to reduce time at T-O power and there are different ways, one is external power thru a power chord that release at transition to horizonal flight, another is elevated AAM vertiports allowing for a dive off the edge like a bird to pick up speed and transition to horizonal flight, a third is jettison electrical boosters for T-O.
Here is another project:
https://harbourair.com/earth-day-eplane-update/
It seems to me for electric aircraft, energy capacity of batteries when scaling up just isn’t there. Not even close. Promises of game changing batteries are as present as they where 10-15 years ago.
It is the root cause of e.g. EVTOL companies going south. Like Lilium ($1.4B).
Amazing how developers, environmentalists, politicians and investors fooled themselves on sticking with it, despite all the free evidence provided to them by people that know better, like e.g. Bjorn. Not only amazing, scary..
https://leehamnews.com/2022/09/02/bjorns-corner-sustainable-air-transport-part-35-lilium-battery-cells/
For me the EVTOL has always been a classical solution looking for a problem.
Ignoring real world constrains using irrelevant reference technologies, developments.
I think there are some niche short routes to/from islands where the technology can make sense – particularly if modular battery packs can be quickly exchanged… enough to build out proof of concepts but that’s not enough to build an industry.
Examples can include BOS-ACK, YVR-YYJ, MIA-FPO, DAR-ZNZ, Athens to nearby Greek islands…
That’s IMHO why airlines like Cape Air, Harbour Air and Air Canada are looking to partner with developers.
Miami-Bahamas is 100nm as the crow flies.
Thats exactly the sort of route thats out of reach and no electric plane with 30-50 seats even on the horizon
The flights are only from Ft Lauderdale and the current tech gives 30 min by regional jet or 55 min by ATR
The closest US airport to Freetown is at Palm Beach and thats 75 nm but Google flights doesnt show any scheduled
Probably more worrying is the changeover to less energy dense chemistries by the auto industry in favour of safer/more reliable ones. I don’t see energy density improving & the tech seems to have plateaued
Thank you Björn for another excellent article. Totally agree that we are decades away from heart of the market 100-200 seaters being electric but there are two niches that might be worth a brief comment. One being observation we have many electric small drones with cameras these days finding many applications. For example inspecting my roof is perhaps best done with a small drone. Another is self powered gliders. If I were a glider pilot which I’m not, it sounds kinda cool to be able to self launch without having to find a tow plane (https://youtu.be/VcHd9Nglijc?si=Qq0fCePJWRXiBHC6)
My baseline for the Pipistrel Trainer is the C-150/152.
My typical logged training time was 1.5 hours. That was from a large Airport and there was 15 minutes flight time to and from a non populated training area.
Two 200 lb people would overload the Pipistrel. Ok, not all people are 200 lbs, but, 180 lbs with footgear as well as some flying equipment (computer, maps, case). Pushing the limit severely.
Now 1 hour flight time, you better be at an Airport that is 5 minutes from a flight area (you are going to have to be away from the airport and 10 minutes is probably more realists).
Oh, and a recharge as soon as you return before you can fly again.
Compare that with the C150/52 that could fly two x 1.5 hour training flights a day on one tank (some variation in tank sizes but schools order the large tanks). 4.5 hours in econo cruise.
So all in all, the Electric is severely limited. Sure batteries will improve, but I don’t see any of it having realistic ops.
So how does the Alia CX300 get 336 miles with 5 pax? Maybe 100-120 miles with today’s battery levels.
Dukeofurl wrote
The time airline pilots consider glide ratio is total engine failure………
No….. L/D which is the expressiion of glide ratio is used every flight when the pilot back calculates his idle decent initiation point. He knows the speed to fly and altitude to convert to optimise fuel burn coming down……. L/D is the reason the folding wingtips are on a 777x. The wing span they chose raised the aspect ratio, higher aspect ratio wings are almost always the better choice as their L/Ds are higher. The 777x is span limited by gate code, so to fly their optimal wing, they needed to fold it. Lots going on besides the simple no power glide calcs which for the record are usually flown at minimum sink speed, not max L/D to allow the greatest time to resolve the problem unless a landing is planed such as it was at Gimli. Wben tbe 747s that went 4 engines out and were working on restarts in the volcano plume, they flew min sink speed……
So L/D is the measure used in for flying airliners …which is what I said !
Glide ratio only comes into it when NO power but as planes descending always have thrust whatever a theoretical glide point would be never has any bearing
777X wing span has no relation to the lift or drag equations
L=Cl*(ρ*V2*A/2) shows this .
the variable A is wing AREA
Drag equation has similar form but Cd
What you are thinking of is induced drag, where AR is aspect ratio ( or square of SPAN/Wing Area
Cdi = (Cl^2) / (pi * AR * e)
For lower fuel consumption in cruise long wing span is preferred, but its extra weight too so favours long range flights
‘Glide ratio’ as a term never comes into any of these standard aerodynamic equations as thrust is a consideration.
Maybe true but trust me, Glide Ratio was always on a pilots mind.
If the longer wing did not give less drag, then there would be no benefit to it.
Gliders had long wings for a reason. Harder to mfg in an airliner as the weight issue needed to keep them from breaking before the 150% test limit.
Of course I am looking at it from a simplistic standpoint.
Glide for a LCA is not a concern, until it is. A320 into the Hudson would be another one.
I would hazard a guess that best glide is also best speed to try to re-start engines per the two 747s that experienced that (or was it one?) Anchorage KLM was one and out Indonesia way was another but forget if they lost all engines on that one.
I would think it is a number on the list for any pilots, multi engine loss while not common certainly has occurred.
As I recall a DC-10 or L1011 out of Miami lost two. Something about oil level plugs stuck back in wrong. The only reason it was not all 3 was they could not reach the tail engine sans a lift and for whatever reason, you have to check two but the third no. Hmmm.
There also was a 747 into Japan that lost the last engine on touchdown. So they were down to one which is not much better than none (well a lot better as they eeeked out to the field).
Fuel mis management I believe.
https://en.wikipedia.org/wiki/Eastern_Air_Lines_Flight_855
It was magnetic oil chip detectors not installed properly.
All 3 engines failed for one part of the descent – so without power-but got one restarted for landing
The flight crew, deservedly got awards
Great topic. One aspect I would like to see addressed is the protection of these aircraft programs against icing as part of their certification basis and their choice of propulsion system. Electric de-icing ( ATR type ) or pneumatic anti-icing ( most airliners exposed mainly in climb or descent because flying at high FL)?
I’ll cover it.
Bjorn
Easy to forget ATA 30, but you have plenty of de-icing power on ground while charging and in theory you could have an isolated heated container with de-ice fluid installed in the aircraft to use in flight. Once you have fuel cells as part of the power supply the heat is “free”.
No its not. Fuel Cell has to perform worst case scenario which means it has to be sized for that.
I don’t think fuel cells are any more going to work than batteries.
Fuel cells will first be used as APUs. Then you can use heat besides electrical power
What fuel?
And then how do you get the heat where needed and or more electrical which makes it bigger and heavier.
What works in space out of necessity is not a good answer where economics rule.
You fundamentally need to reassess your precepts. Net Zero and the ideology behind it has nothing whatsoever to do with the technicalities of achieving a “zero emission” airliner and everything to do with a political ideology to control and restrict the freedom of movement of individuals.
If an airliner could fly on pixie dust and fairy farts some other rational motive would be found to restrict their use.
Not only do you not have the answer, you don’t understand the question.
Agree with you observation there is a lot of politics, greenwashing and non-sense driving developments
But we have to be strong enough to not deny we have an environmental problem for our short term selfish objectives.
To tackle it, to avoid being tackled in a thousand ways not so far ahead.
Oh no ….someone who has ‘done their homework’…LOL