It’s common knowledge that most new technologies are overhyped during early development. Technology advisory firm Gartner terms this process the hype cycle and suggests that there are five stages. Sure, it's made up and it's not really a cycle, but we'll go with it:
I would say that we are on the way to the peak of inflated expectations. To my knowledge, no electric aircraft currently hold US type certificates. In Europe, the number can be counted on one hand, and they are mostly motorgliders. Popular publications have begun to feature electric propulsion in breathless terms with beautiful renderings and little critical thought, generally repeating manufacturer claims (e.g. this and this). Industry press has done a better job keeping expectations in check.
The more important question though, is can electric aircraft survive the trough of disillusionment? (In keeping with the topography theme, maybe I'll call it the Disappointment Cleaver)
I recently read two assessments of aircraft electric propulsion; one seemingly too credulous, the other seemingly too skeptical. Let’s dissect them.
European consulting firm Roland Berger released a report (direct PDF link) outlining the electric aircraft trend, intended for business professionals. It opens with all hype: “All indications suggest that we may be on the cusp of a revolution in the aerospace and aviation industries.” After examining the facts, the report ends with an appropriately conservative “watch and wait” recommendation. If you only read the headline and intro, you would get a much more optimistic picture.
Roland Berger analysts have done the hard work of cataloging what they claim are all known electric aviation projects. They count 70, categorized into four types: general aviation, urban air taxi, regional aircraft, and large commercial aircraft. Surprisingly, half of the projects belong to startup firms; industry incumbents are backing just 20%. I was surprised to see that only 31% of the projects use distributed propulsion, and this must include most of the multirotor urban air taxi concepts; this seems low to me. The flaw with this analysis is that it counts by raw number of projects. A better comparison would be percentage of total dollar value being spent, but the data on these projects are very closely held.
The report does review important technical barriers to electrification. I largely agree with their identification of battery and electronics weight and safety as being the largest engineering barriers today. The report claims that 500 Wh/kg is “widely regarded” as the minimum for electric flight; I have seen no evidence of this consensus. The tipping point depends on current economic conditions, and especially the mission. Longer missions require better batteries. To enable real fuel savings in hybrid, commercial fixed-wing applications with useful range, I think the tipping point is probably higher – 750 Wh/kg or more – and this is the assumption used by the NASA-funded SUGAR study. eVTOL concepts can get away with less. I also strongly disagree with their assessment that series hybrid propulsion is not viable. The analysis does not take into account the airplane-level weight and propulsive efficiency benefits illustrated most clearly by the NASA STARC-ABL concept.
Addressing certification barriers, the report correctly notes that changes to 14 CFR 23 will enable GA and ‘commuter’ type electric aircraft to be certified soon. There is
currently no movement to extend these changes to Part 25, which governs
commercial airplanes with 20 or more seats. However, the Part 23 rewrite illustrates that with appropriate analysis methods and enough
lobbying, regulation will most likely not stand in the way of commercial
My favorite part of the report contrasts current optimism about electric propulsion with previous “revolutions” in aerospace, namely supersonic transports (SSTs) and very light jets (VLJs). Both of these innovations failed to break into the mainstream. The comparison of initial hype for these concepts with current hype for electric propulsion is appropriate, but there is an important distinction. SSTs and VLJs were market failures, not technology failures; the technology was intended to open up new market segments, but the market never materialized with costly SST/VLJ operating economics. This is the economic question that urban air mobility concepts must answer: can eVTOL aircraft be built and flown for a price that urban commuters are willing to pay? I suspect the answer is no until autonomous manned aircraft are certifiable, but I am not an expert in the economics of these vehicles.
For fixed wing electric flight, electrification is intended to lower costs on existing missions, not open up previously unobtainable missions, so the SST/VLJ comparison doesn't quite work. However, the authors raise a relevant point for those targeting expansion in the regional airline market. It’s already hard enough to make money in the regional airline business. A competitive electric product will need to really change the operating economics.
Altogether, I think Roland Berger wrote a good report for their intended audience. The quantitative and engineering analysis has a few problems, but by and large the recommendations are reasonable. Read the whole thing.
The second take comes from Paul Bertorelli at AvWeb, writing a snarky response to a recent announcement from Zunum.
“Mark this date on your calendar: 2022. That seems to be when the promised magic of electric airplanes will come together and, we’re assured, you’ll be able to fly to a small airport in an Uber multi-rotor then board an electric hybrid airliner to be whisked off to an airport 500 miles away. Thence to your downtown destination via another Uber air taxi. What a wondrous new world awaits.”
Bertorelli then states the hard facts but begins to temper his position. He correctly notes that current battery specific energy levels are low and that performance claims by startup firms can be hard to believe. He also observes that Airbus has pulled back its own EP development program (Airbus would not agree with that characterization, but I think it is fair). Ultimately, though, the author concludes that electric aviation will arrive, but not yet. He sees that the “slope of enlightenment” will take a long time to climb.
On one hand, I agree with Bertorelli’s complaint about unrealistic promises. Overly optimistic entry-into-service dates are endemic for aerospace companies of all sizes: from the SpaceX Falcon Heavy (originally slated for 2011 – still waiting) to the Terrafugia Transition (in development since 2006; first delivery estimated for 2015 – still waiting) to the granddaddy of all delayed programs, the Lockheed Martin F-35 (development started 1992 – IOC declared in 2015). However, we need to give companies credit for setting aggressive goals. SpaceX routinely fails to meet self-imposed deadlines but only because they're ridiculous to begin with by industry standards. SpaceX still produces impressive capabilities relatively quickly. Elon Musk is an impatient leader but a patient investor. The author acknowledges this at the end: "But what the hell, this is aviation, right? Would-be purveyors of new aircraft always do that and we wouldn’t respect them if they didn’t."
True that, Mr. Bertorelli. We should be grateful that some early adopters are brave enough to try.
So to answer my original question: can electric aircraft survive the trough of disillusionment?
Urban air mobility / eVTOL concepts are technically feasible today and may compete with or replace helicopters to carry wealthy passengers using pilots. If the autonomy certification problem cannot be solved in a timely fashion, I do not believe the operating economics will work for average people. There simply aren't enough skilled helicopter pilots, and if there were, they'd be too expensive. There are also serious air traffic management problems which will take decades to solve.
For fixed wing, the answer completely depends on continued progress in batteries and power electronics. The other technical problems are solvable, and if batteries become good enough the economics will ensure that electric aircraft come to fruition.
What should companies be doing in the interim? Continued learning. Incumbents should be flying as many demonstrators and doing as many bench tests as they can afford in order to build up service experience and design knowledge. When prerequisite technologies reach economic tipping points, the well-prepared firm will already know how to design, build, certify, operate, and maintain electric aircraft with the safety and reliability we've come to expect from conventional aircraft. Modeling and simulation (my research) will help find the happy medium between moving too early and too late.
(Edit: Apparently I wasn't the first to apply the hype cycle to EP. Bjorn Fehrm at Leeham News has a similar take)