Wright Weport August 2017
Welcome to the Wright Weport for August 2017. Note: long weport ahead for Labor-Day-beach-reading purposes!
- Why Wright: Lower emissions, lower costs
- Technical: Building a test stand
- Batteries: Latest learnings
- Business: Seeking China/India airline contacts
- In the news: Aviation’s business model, New startups, Shifting to electric transportation
- Past weports: here
In late spring, we began systematically evaluating and monitoring advanced battery and electric motor technologies. We developed a clear understanding of the energy storage technology and electric motor design features that would be the best fit for a large airplane. We are continuously monitoring developments at battery and motor suppliers, and we have a short list of favorites.
In early summer, we challenged our engineers to design a propulsion system that will help our airplane travel faster and farther than its rivals. With input from our senior aerospace advisers, our mechanical engineering team generated several high efficiency fan concepts to be put to the test. The design files for our favorite concept are complete, and we will begin constructing it soon.
How will we test our propulsion systems?
Propulsion Part One, Thrust and EnduranceOur electric fans will be mounted onto a steel structure called a test stand. They will be connected to the same motor controllers and batteries that we will use later on during flight tests. This assembly can tell us how much thrust our fans generate, how efficient they are, and how reliable they are. By running long term experiments on our test stand, and by simulating failures, we will be able to root out any reliability problems that emerge from our mechanical design or our power electronics.Propulsion Part Two, Just Add AirframeOur ground test assembly will eventually evolve into an everything but the airframe system, allowing us to run full dress rehearsals of a test flight without leaving the ground.
What happens after the ground tests?
Micro Wright One Test FlightWe plan on constructing several subscale aircraft that very closely mirror their full scale counterparts. Like a doll house, each subscale aircraft will have most of the detail of a real airliner but at a fraction of the size.
Written by Joe Adiletta of 24M, with help from Alex Girau of Advano.
Wright has taken a close look at the economics of rechargeable batteries for use in large airliners.
We asked ourselves this question, “If we want to build an electrically powered airliner that offers cost savings over a conventional airliner, how long must the batteries last?”
The answer is a sliding scale, depending on the cost of electricity and jet fuel. But the answer sits squarely in the multiple thousands of cycles.
Here is a bit more on our thinking about battery cycle and calendar life:
Less Depth of Discharge, More Cycle Life
With all lithium ion chemistries currently on the market, smaller charge-discharge cycles (narrower SOC band) are non-linearly accretive to battery life. In other words, if you get 1,000 cycles out of a battery at 100% depth-of-discharge (DOD) cycling, you will get more than twice as many equivalent cycles by doing 50% DOD cycling, many more than 4x at 25% DOD, etc. The takeaways from this: Charge a little bit at a time, opportunistically. Oversize your battery so that each mission does not fully drain the battery.
Temperature Affects Calendar Life
Degradation of lithium ion batteries occurs via two primary routes, typically called cycle life and calendar life. Cycle life refers to the number of charge-discharge cycles that the battery sees, while calendar life degradation happens via time, just sitting around. Calendar degradation mechanisms are exacerbated by temperature. In this case, higher temperatures are worse for capacity fade over time. Thermal cycling may also cause capacity to fade. The effect of flight conditions on battery cycle life must be studied carefully.
Higher Voltage More Problems
Similar to higher temperatures mentioned above, calendar degradation is also exacerbated by higher voltages. Electrolyte improvement may improve cycle life in high voltage applications. There could be additives that improve discharge capacity because they reduces SEI formation and thus free captured lithium, but a non degrading electrolyte is key to cyclability. Keep an eye on that as new battery chemistries emerge.
Slower Charging and Discharging is Better
As mentioned above, degradation of lithium ion batteries tends to come from cycling and calendar effects. On the cycling side of the ledger, the slower the battery is charged/discharged, the longer the lifetime, typically. Rapid recharging between missions may harm the battery’s cycle life leading to unfavorable economics. If you swap battery packs instead of rapidly recharging them, you may be in a better place economically.
Forget about the Memory Effect
In the early days of portable electronics, when Ni-Cd and NiMh batteries were commonplace, the “memory effect” of these cells was well known. In short, if you consistently charged and discharged these cells within a narrow range of state of charge (SOC), they seemed to “remember” this method of operation and lost significant capacity. Lithium Ion does not suffer from this behavior.
We’re interested in learning about the Chinese and Indian aviation markets. The US still leads the world with 719 million passenger flights annually, but China’s #2 at 436 million, and India’s #3 at 100 million.
And each country has numerous short routes, for example Bangalore-Chennai in India.
We’re already working with airlines in Europe and the Americas, and now we’d like to speak with folks from the aviation communities in China and India. Does anyone know folks at airlines such as SpiceJet, Jet Airways, or China Eastern Airlines?
Thank you in advance!
In the News
Thanks to Meghan, Jess, Jared, Rayyan, Jess, Ralph, Jenn, Eli, Doug, Dean, Doug, Brian, Jen, Raja, Judd, Thomas, Nabil, Jude, Eli, Mark, Stonly, Bink, Marsha, Rhett, Shaun, Tuto, Michael, Steve, AJ, John, Jeff, David, Darold, Chip, Randy, Doug, Noam, Joe, Ben, Andy, Mike, Jason, Blake, Alex, David, Bennett, Bill, Paul, Bernard, Vijay, Ian, Adam, Scott, and everyone else who helped out and/or sent over words of encouragement.
Happy Labor Day!
Jeff and Aaron
PS: We really hope you’re enjoying these updates. But if at any time you’d like to stop receiving them, please just do so here. No hard feelings — we all understand inbox overload!
PPS: Wright song of the month: Paris Combo – Fibre De Verre