Although some are in denial about it, the love affair with batteries for electric airplanes is, for the short term, on hold. To meet minimum performance, designers are increasingly looking at hybrid drives that may incorporate battery systems. In this AVweb VODCAST, Embry-Riddle’s Dr. Pat Anderson explains why this is so. He also explains why the idea of scaling up a DJI drone to carry people doesn’t work.
Home Multimedia AVweb VODCAST: Why Electric Airplane Designers Are Turning To Hybrid Drives
No charging station? No problem.
Why would we change the fuel reserve requirement for a battery powered aircraft? Whether it’s petrol or electrons, the planning requirement is there to ensure the pilot has time in the tank for emergencies or factors that he or she may not be able to control. Headwinds, fuel leaks, leaving the gas cap off, are some factors for a ICE powered airplane. But batteries may have their own issues that may cause excessive consumption beyond unforeseen headwinds. Temperature instability cause variation battery capacity and subsequently in flying range. I’m guessing, but I suppose faulty electrical consumption from the avionics, computer, or lighting systems may reduce range as well.
I think it’s important to design the system to the performance standard, and not change the performance standard to help design the system.
Nice to see an in-depth, intelligent discussion on the status of these vehicles.
To Dr. Andreson,
Do you spend any time thinking about/discussing the underlying costs of electric battery power? For example the cost of mining the components, processing, distributing the materials needed for a battery/aircraft? The cost of remanufacturing components when the batteries are spent?
Another area of inquiry is what exactly is charging up these batteries? In 2019 80% of USA’s electrical power derives from hydrocarbons or coal. I think the reality is inescapable that hydrocarbons as a source of energy in our culture is going to be with us for a long time. (Unless we drop our standard of living and/or accept a significant increase in cost of our energy consumption). Enjoyed the discussion. Thx
The US Energy Information Administration says differently about sources of USA electrical power.
Renewables: 17%, including wind 7.3%, hydro 6.6%, solar 1.8%, biomass 1.4%, geothermal 0.4%
Hydrocarbons: 62% (not 80%), including natural gas 38%, coal 23%, petroleum 1%.
All as of 2019. Source: https://www.eia.gov/energyexplained/electricity/electricity-in-the-us.php
The next question to answer is, what is the _trend_ in sources of US electrical power? EAI says, renewables are doubling by 2050, coal is declining through mid-2020s. For 2050 they forecast:
Renewables: 38%, including solar 17%(!), wind 13%, hydro 5%
Hydrocarbons: 49%, including natural gas 36%, coal 13% (down from 23%).
I read another headline recently that solar electricity is now the cheapest source of electrical power in history, but I can’t cite that source. I read another article about how environmentalists are blocking new coal power plants on economic grounds — the power they are generating is now more expensive than power from renewable alternatives.
The source of power charging these batteries is not an obstacle.
If solar is cheaper than coal, then why are companies trying to build them? They aren’t idiots. Answer: Even if it really is cheaper, solar has a lot of problems that coal doesn’t. Coal can generate power at night and on cold, dark days, for instance…
Jim, buy some solar panels and run your dwelling and your heat and your transportation needs for one year and THEN get back to us on with an opinion (then based on facts). Basing your opinion on government websites and where you have no first hand knowledge holds no weight.
Even though electric motors have reached the high 90% in efficiency, storing the energy you must carry with you is a very difficult problem. A gasoline engine would strain to make 40% conversion efficiency, yet it is very hard to beat a system where 15/16 of the weight (air) required to make power does not have to be lifted and carried, and the exhaust products (also having weight) are dumped overboard.
Here, once again, we see the results of a government trying to pick the winners by subsidizing technologies that are not yet viable. Legislators should be required to tattoo on their foreheads Thomas Sowell’s quote about prices: “It is hard to imagine a more stupid or more dangerous way of making decisions than by putting those decisions in the hands of people who pay no price for being wrong.”
Look it up: Conservative estimates put U.S. direct subsidies to the fossil fuel industry (gas, coal, oil) at roughly $20 billion per year, compared to $2.8 billion for renewables.
Yes the government is picking the winners, but not the ones you think.
These fine folks are opening a can of worms with “down the road expectations” of big bucks. If changing standards for flight operations especially IFR will be OK…color me out. You know the minimum standards for IFR flight were worked out for fuel driven A/C over a long period of time, and we need to feel the fuzzies when the stuff hits the fan. Either that or really long extensions will work.
Good to see a decent reality check from someone who knows whereof he speaks. Also encouraging is knowing Dr. Anderson’s students, as leaders in the field going forward, are receiving a full grounding on where the gotchas lie. We have entirely too many people working in the electric-powered transport field who in their passion to “make it so” willfully or simply unknowingly ignore such things.
I listened to Dr Anderson and Erik Lindberg put on a presentation in Daytona Beach about four years ago. Their Company — Verdego (sp?) — was going to burn up the world with urban air mobility. Well … where did that go? We all know where … the same place Terrafugia went. I just don’t “get” this massive preoccupation with electric powered airplanes. In cars … where the weight of the batteries are less of an impediment … maybe … especially in a hybrid configuration. But in an airplane … you take off and land with the same weight of the batteries and the energy density isn’t there and isn’t likely to be there for a long while. As he says, special missions might demand it but for routine flying … no way.
Interesting juxtaposition of the video. Dr Anderson talking about Buck Rogers machines while PB is sitting in front of a Piper Cub. Me … I’d stick with the Cub. You need one of those single bladed props for the thing. I hear they’re more efficient.
Vertical take off requires a lot more energy than winged horizontal takeoff. If you use electric for vertical takeoff and gas/hybrid for cruise….that is the least efficient way to move things from A to B.
I see hybrid (electric/diesel) propulsion as a great way of minimizing environmental impact. Use electrics to boost climb, use diesel/Jet-A for the cruise. Hovering is never energy-efficient, so STOL aircraft, where half the power comes from electrics and the other half from the reciprocating unit(s).
Supercapacitors are a great alternative to LiPo batteries and do not age the same way!
For smaller planes, a folding prop, and an electric powerplant in the nose, and a pusher unit in the rear, powered by a diesel engine would probably be ideal!
A good presentation. It is nice to listen to someone who takes a realistic engineering approach to a complex problem instead of simply assuming miracle batteries will save it all. Dr. Anderson’s comparison to hybrid and electric land vehicles and how they developed is a good segue to electric aircraft. In the beginning, companies tried to develop pure electric cars, but then moved to hybrid drive designs because the then available batteries were in adequate. It took about 20 years of perfecting hybrid vehicles before battery technology evolved enough to allow pure electric cars. I suspect the same path will be true for battery powered aircraft. He also raises another good point, that using a hybrid design allows engineers to develop the electrical distribution and control systems that will eventually be used on full electric aircraft. In other words, learn how to get most of the needed technology done while waiting for batteries to catch up.
It was good to hear that the E-R engineers learn to be careful in understanding the scaling issues in each link of the engineering chain. We’ve been spoiled by semiconductor logic and memory, with their Moore’s law growth (perhaps now slowing). Batteries don’t get 2X better in energy/weight every two years. It’s more like 5-10 years, and each doubling requires that some major new technology improvement be reduced to manufactured practice..
Hybrid systems open up many possibilities. Form efficiency, weight and balance, to a redundancy for safety. At work I was working on an R&D Project using some large Brushless DC motors. Just for kicks, I connected one motor directly to another and I was amazed at there efficiency. As I turned one motor the other turned at the same rate. While there was some loss of torque transmission the efficiency between the generation of power and the output from the motor was mind blowing. I think for instance the PSR unit on a Rotax engine could be replaced by generator/motor system and would operate more like a constant speed prop with a battery for redundancy with out much weight penalty.
You can get mo/gen efficiency in the 90+% range. In some cases, it would make for a more efficient car: motorize the wheels, have a small battery, and a small engine running at its most efficient regimen. Use the electric reserve for acceleration.
I don’t think it works that way. Airplanes run at full power in takeoff and 75-80% in flight. If you want to compare that to a car then think NASCAR, not Prius as far as use.
Interesting discussion that like insects, quad/octa Copters can’t be scaled up to human size.
Batteries are never going to have the energy density of polluting hydrocarbon fuels. The only energy source I can foresee for green flight is the use of liquid hydrogen, whether via fuel cell or direct combustion.
No need for the extra weight, complexity, and limitations. Fuel is cheap and plentiful and future reserves are in place in Alaska and elsewhere in the US and abroad. Stay with internal combustion and eliminate the regulations that artificially drive up its cost.
What happened to Hydrogen Fuel Cells?