ZeroAvia announced yesterday its SuperStack Flex fuel cell architecture has achieved greater than 1 kilowatt per kilogram (1.0kW/kg) net power at full system level. The configuration includes a thermal management system and “has been successfully demonstrated in a 150kW net power configuration for a major customer.” ZeroAvia credits its use of additive manufacturing (aka 3D printing) for its test results. The technology is designed to expand unmanned aerial vehicle (UAV) and vertical takeoff and land (VTOL) aircraft capabilities “as well as opening new applications in aerospace and other sectors,” according to ZeroAvia.
I must say that I can barely understand the green techno speak being used to announce/advertise this step in the chase for carbon neutral propulsion. It sounds just wonderful but my wallet is home to more moths than money. Is money sprouting on trees and bushes now? If it can pay for itself I’ll be around to collect the dividend once this is at the finish line.
But, here, these guys are bragging that they have developed some equipment, and for each kilogram of it they can light ten 100 W light bulbs. Uhhh… woo-hoo I guess. It’s almost a good start.
I just looked up the weight and power of the PTA-67B powering the Pilatus PC-12. This engine produces 890kW with 236kg of weight. So this fuel cell would be about four times heavier to produce the same power (if it can be built this big). This does not count the actual electric engine or engines needed to propel the aircraft, plus electric wires and any buffer storage battery which I assume is part of the concept. Still, compared to pure electric designs based on lithium batteries alone this doesn’t sound too bad. The 890kW power is certainly not needed for most phases of flight. Batteries can supply additional power during takeoff so the fuel cell can be smaller. It only needs to be big enough to support cruise power. Of course there is the hydrogen storage but that’s a separate topic.
I can’t in any way condone the foolishness of electric aviation, but I am afraid I must point out that power density comparisons are only valid if you include time of delivery of said power system including fuel and fuel storage/handling systems. The first set of numbers would be the optimum duration of a real world case of battery, fuel cell or thermal engine at the max VFR range at safe power levels of the least capable system. The next set should be the IFR range of each and finally the real flight profile of BEV, fuel cell and thermal engines first in max range VFR and finally max range IFR flight profile at range/duration of the most capable system. As soon as you display those numbers the actual utility of systems can come into focus. Of course in similar airframe with same, full payload.
Need I point out that the most crude and obsolete system in aviation - normally aspirated, spark ignition, leaded avgas burning in a “homebuilt” airframe built on a shoestring budget mostly with volunteer labour has demonstrated nonstop global circumnavigation carrying a crew of 2. Get back to us when your greenwash investment ripoff projects can do that.
Fuel cells are very clean, and the increased “watt density” here is great. But what is always forgotten is fuel, particularly the storage part. To gain any kind of range requires a bulky (heavy) array of very high pressure tanks, each containing the most flammable gas known. And cryogenic storage is out of the question due to the extremely low temps of liquid hydrogen. Until this can be resolved the practicality is low.
Fuel cells can be clean in OPERATION, but the production, transportation and storage of Hydrogen seldom meets that standard (most stripped from natural gas). What we short-sightedly see and hear about as “zero emissions” is almost always displaced emissions - completely ignoring the whole cycle.
My concern is most of what we see in “green” transportation is simply more expensive ways of continuing to squander resources to do more of what got us into trouble in the first place.
I was involved with wind tunnel model testing using sintered metal parts about 10 years ago. They needed a lot of hand work to make them smooth enough for model testing and they tended to be brittle. Whatever this manufacturer is using the sintered metal for probably doesn’t need to be that smooth, but I hope they have improved the strength in the last 10 years.
Try releasing some in a closed fuselage and let me know how that works for you. I’ve worked with both methane and propane for many years. If allowed to escape, they will dissipate and be reasonably harmless (yes, even LP, although it is more dense than air). Contain them and they have explosive effect. Perhaps the H2 storage is force-vented?
No, I wouldn’t care to release H2 into an aircraft cabin - but I wouldn’t care to vent jet fuel tanks there, either.
But if I was a passenger on a plane where they told us to brace for impact, I’d rather be riding with H2 than with liquid-at-room-temperature hydrocarbons.