JRP3
Hyperactive Member
Electric planes are being developed. This is a discussion about those. If you wish to have a different discussion you are free to start such a thread.
-
Want to remove ads? Register an account and login to see fewer ads, and become a Supporting Member to remove almost all ads.
Electric planes
- Thread starter doug
- Start date
-
- Tags
- Electric Vehicles
Not sure if anyone has touched on this already, but today's commercial airplane design take great advantage of fuel weight change throughout flight operations. When the wing is fully loaded with fuel, the inertial load from fuel act to relief wing bending loads during heavy take off. At the same time, as the airplane burns fuel, it allows the airplane to climb higher and fly at more efficient altitude. And at the end of the flight, the airplane will be much lighter, so the landing gear do not need to be designed for max takeoff weight.
Also, there is airport landing fee that operators have to pay, so it makes sense to have minimize weight at landing whenever possible.
I do wonder if electric powered airplane would make ETOPS a bit easier given simplistic of electric motor compared to a turbofan/turboprop engine, though the amount of redundancy required to get today's battery technology to ETOPS180 and beyond may make the airplane performance not desirable.
I do believe one way to enable electric propulsion is through the use of fuel cell. It may not be practical for cars, but for a long haul airplane and how airplane naturally want to work, it may continue to leverage the best practice of today's airplane to get necessary performance.
Also, there is airport landing fee that operators have to pay, so it makes sense to have minimize weight at landing whenever possible.
I do wonder if electric powered airplane would make ETOPS a bit easier given simplistic of electric motor compared to a turbofan/turboprop engine, though the amount of redundancy required to get today's battery technology to ETOPS180 and beyond may make the airplane performance not desirable.
I do believe one way to enable electric propulsion is through the use of fuel cell. It may not be practical for cars, but for a long haul airplane and how airplane naturally want to work, it may continue to leverage the best practice of today's airplane to get necessary performance.
Etna
Member
Yes that fuel weight question popped up earlier in this thread.
Basically all-electric and hybrid-electric aircraft will be relegated to regional aviation for the foreseeable future. Regional aircraft burn very little fuel for these short ranges, in terms of % of takeoff weight. So much so, they are designed to land near or at their maximum takeoff weight, unlike long range airliners.
Thus, from structural and landing gear design standpoints, nothing really changes.
Regional aircraft don't burn enough fuel to benefit from step climb during cruise either.
The airport landing fee is an interesting point. My expectation is that landing fees will be structured differently for hybrid and all-electric aircraft (as in - hopefully completely waved) just as part of the same economic incentives provided for cars in many jurisdictions, as a matter of consistency. As a minimum, the extra battery weight should not be a source of landing fee penalty. At least that's what I have in my costs models.
Yes electric propulsion will make ETOPS much easier because of the inherent redundancy of distributed propulsion architecture associated with electric aircraft. Unfortunately long duration all-electric flights are still far in the future to benefit from this.
A lot of companies have been looking at fuel cells (I read an article this week about interest in hydrogen fuel recently being "re-ignited"
) but the challenges of hydrogen storage in airplanes are daunting, technically and financially.
Basically all-electric and hybrid-electric aircraft will be relegated to regional aviation for the foreseeable future. Regional aircraft burn very little fuel for these short ranges, in terms of % of takeoff weight. So much so, they are designed to land near or at their maximum takeoff weight, unlike long range airliners.
Thus, from structural and landing gear design standpoints, nothing really changes.
Regional aircraft don't burn enough fuel to benefit from step climb during cruise either.
The airport landing fee is an interesting point. My expectation is that landing fees will be structured differently for hybrid and all-electric aircraft (as in - hopefully completely waved) just as part of the same economic incentives provided for cars in many jurisdictions, as a matter of consistency. As a minimum, the extra battery weight should not be a source of landing fee penalty. At least that's what I have in my costs models.
Yes electric propulsion will make ETOPS much easier because of the inherent redundancy of distributed propulsion architecture associated with electric aircraft. Unfortunately long duration all-electric flights are still far in the future to benefit from this.
A lot of companies have been looking at fuel cells (I read an article this week about interest in hydrogen fuel recently being "re-ignited"
) but the challenges of hydrogen storage in airplanes are daunting, technically and financially.
Military pilots are generally extremely competent, so I'm sure they'd have no problem getting the extension cord connected from the supply plane to the one being recharged. But this is an area where charging time could be a concern.
I assume you're talking about electric planes, since in-flight refueling of conventional planes is old hat.
SmartElectric
Active Member
Throw away. Why so dismissive? Certainly the integrated cell + structure could be repurposed, or recycled. Given the way battery cells are advancing, the best approach is getting 3 years of life out of the structure and recycling and using newer better battery cells + structure.
The structure could be designed to be rapidly recycled and rapidly reproduced and re-integrated with the plane. First principles man.
At least the electric drive train wouldn't need the constant maintenance like jet/ICE engines do, and this means that cost could be repurposed to the "cell + structure" 3 year "maintenance" (effectively take the structure off the plane, put new on, recycle old).
Yes that fuel weight question popped up earlier in this thread.
Basically all-electric and hybrid-electric aircraft will be relegated to regional aviation for the foreseeable future. Regional aircraft burn very little fuel for these short ranges, in terms of % of takeoff weight. So much so, they are designed to land near or at their maximum takeoff weight, unlike long range airliners.
Thus, from structural and landing gear design standpoints, nothing really changes.
Regional aircraft don't burn enough fuel to benefit from step climb during cruise either.
The airport landing fee is an interesting point. My expectation is that landing fees will be structured differently for hybrid and all-electric aircraft (as in - hopefully completely waved) just as part of the same economic incentives provided for cars in many jurisdictions, as a matter of consistency. As a minimum, the extra battery weight should not be a source of landing fee penalty. At least that's what I have in my costs models.
Yes electric propulsion will make ETOPS much easier because of the inherent redundancy of distributed propulsion architecture associated with electric aircraft. Unfortunately long duration all-electric flights are still far in the future to benefit from this.
A lot of companies have been looking at fuel cells (I read an article this week about interest in hydrogen fuel recently being "re-ignited"
Thanks. Keeping it regional definitely makes sense, and like you said, those small airplane's MTOW and MLW are generally the same.
The landing fee suggestion is interesting. That's a fairly large source of income. It may be okay for a short term to incentivize adaption of electric airplanes, but I am not sure if it's sustainable in the long run from business case perspective.
Here is an interesting question that I just thought of regarding ETOPS. If the batteries are indeed made of thousands of modules like they do in current Tesla cars, then how do you calculate reliability for ETOPS? What happen if individual cells fails? What's the potential chain effect? And what's the suitable redundancy?
In the long run, I do think electric airplanes will need to compete with ETOPS 330 in order to compete against the large twin jets. The ability to do ETOPS 330 enables a more efficient long haul flights.
BTW, I am very curious if Airbus will really go forward with hydrogen propulsion. As you said, storage is an issue, though we have come a long way on that front. And there are also other type of fuels that can be used for fuel cell purpose, though less clean and efficient.
Not sure about small airplane maintenance cost, but major structural changes on a large commercial transport is costly prohibitive. It's one of the reasons for using composite structures in newer airplanes, because composites allows the operators to stretch out the major structural maintenance cycles to minimize cost.
BTW, structural battery may not actually gain performance advantage on an airplane. If we are to put battery on the wing as we do with fuel on today's airplane, then those structural batteries will have to satisfy many of the certification criteria. I don't think it makes sense to put so much complexity into the battery when it can be designed to just be housed inside the wing and let it be as efficient and lightweight as possible.
Etna
Member
ETOPS stands for Extended Twin Operations and there is nothing extended about operating all-electric aircraft.
Having said that, electric propulsion is inherently a lot more redundant for a number of reasons.
It leans itself to distributed propulsion with typically more motors than just one or two. Contrary to combustion engines, having four 250 kW motors rather than one 1000 kW motor is not more expensive to buy, operate and maintain. Additionally there is no loss of efficiency with smaller motors, while smaller turbines are less efficient than larger ones. With four separate motors, you might as well have four separate groups of batteries that may be smartly interconnected. To top it off, the battery packs may consist of a number of strings and in the rare event of cell failure you would only experience partial battery degradation.
Bottom line, instead of losing half your power with a conventional turbine power twin, you'd lose one fourth or probably only one sixteenth and end-up in the same situation of B-52 pilots practicing engine failures.
I would think the redundancy you suggested would still have a range issue in the event of a battery or propulsion failure. A non-working motor will need additional thrust from the other motors to overcome the drags, from the windmilling motor as well as the drag from asymmetric thrust (likely need some rudder inputs throughout the flight as well as flying at lower altitude). Additionally, if a battery cell or a battery bank is lost or suffered reduced power, the airplane would lose range capability and would impact its equivalent ETOPS rating. Unlike JetA, I think battery will be considered as a system that could negatively impact reliability rating and could impacts ETOPS equivalent certification for an electric airplane. The point is that ETOPS allows today's twins to fly more efficient and direct routes instead of routes that stay near diversion airports. A long range electric airplane will need to have that diversion capabilities in order to fly those routes in addition to hitting the reliability requirements needed to flight ETOPS routes.
BTW, ETOPS is not longer just for twin engine jets. It's also for tri and quad jets intended to fly over 180 minutes from diversion airports.
https://www.faa.gov/other_visit/avi...afety/info/all_infos/media/2007/inFO07004.pdf
https://www.faa.gov/other_visit/avi...afety/info/all_infos/media/2007/inFO07004.pdf
SmartElectric
Active Member
"as possible", not quite good enough, as per Tesla, structural battery as part of chassis is a 7% lower cost and weight savings in the overall vehicle according to Tesla battery day slide :
Etna
Member
It won't.
For a twin, you lose 50% of your power and the windmilling/yaw drag of a large high bypass is significant. For a properly designed electric aircraft you lose only 25% or even 12.5% of your power (as is the case on the one I am working on) and in a quad-prop with proper feathering the windmilling drag is negligible (actually there will be no windmilling at all - a just a bit of form drag and on the prop blades). No yaw drag would be present, you simply distribute power to the remaining motors so that there is no residual differential thrust. It sounds easy but it really is.
Similarly, battery packs can be segmented in modules and modules in strings so that any cell failure becomes a non event in terms of energy and power. You can basically have 32 levels of redundancy at no cost.
But this is all a moot point. Most of us (me anyway) will most likely be long dead before all-electric airplanes will have the range capabilities needed to worry about ETOPS.
I sure hope most of us get to see at least regional jets transition to some sort of electric power in our life time.
Thanks for the redundancy ideas. Got to think about that a bit more
JRP3
Hyperactive Member
part 91 ( not carrying passengers for hire)
§ 91.167 Fuel requirements for flight in IFR conditions (Alternate Minimums)
Helicopters must complete the flight to the first airport of intended landing, then fly from that airport to the alternate airport; and then fly after that for 30 minutes at normal cruising speed. Normally, other aircraft are required to have 45 minutes.
JRP3
Hyperactive Member
Etna
Member
From a certification standpoint, glide range cannot be counted in the reserves capacity because it is an emergency condition. Therefore a VTOL plane will be treated just like a helicopter.
SalisburySam
Active Member
That's definitely a big hurdle. I also wonder if lightening protection will be more or less challenging with hydrogen.
SmartElectric
Active Member
Hmm, I think passengers would flock to H2 powered aircraft if the interior was more like this hydrogen based air travel cabin:
Similar threads
