Electric planes

[MontyFloyd]

I think this first flight is a great achievement for all those involved.

Nonetheless, the design is still fatally flawed since they completely miscalculated realistic empty weight and battery weight fractions required to maximize range as much as possible, considering the limitations of pure battery powered propulsion.

Note that this week Eviation quietly updated their web site with a takeoff weight increasing from 16500 to 18400 lb and range slashed from 440 nm to 250 nm. That gets them closer to reality but still not quite there yet. Notably, the 30 minutes VFR reserves is of no use in a commercial environment.

They acknowledge this since their new CEO said this week that "the aircraft will enter into service when battery technology evolution will get us the energy densities to make a product that is commercially viable".

This could be a long wait.

It is a good effort into that direction, and I am proponent of BEA, but also hate to see hype bullshat that borders on or is outright fraud.
I commend you for laying down those numbers!

Yep. Batteries will continue to improve, and our electric cars will lose a little weight or gain a little range from year to year. But the tipping point to commercially viable electric planes is a very long way off and may never happen. And a nine-passenger plane is too small for any but the tiniest markets. The float planes I took to and from San Juan Island, and to and from Katmai, AK, were around that size, but the single-engine planes I took to and from safari lodges in Kenya were a bit bigger, IIRC. Teeny tiny markets.

Hawaii, Alaska, Maldives, other places need those, the numbers are there, but the big money is not.
Flip side, the Cessna 208 could probably be easily converted to BEA for a fraction of a completely new build.

 

[daniel]

Hawaii, Alaska, Maldives, other places need those, the numbers are there, but the big money is not.
Flip side, the Cessna 208 could probably be easily converted to BEA for a fraction of a completely new build.

Still just a minuscule segment of the aviation market. I'm all for them, and I would pay double to fly on an all-electric plane if I was going to fly somewhere. Electric cars have the potential to displace 90% or more of today's gasoline cars. Electric planes have the potential to displace about 0.0001% of the aviation market.

 

[MontyFloyd]

In a hybrid system it is the other way around. Turbines are best used for energy intensive parts of the flight while batteries are used for power intensive parts. So you use batteries for takeoff and climb, and smaller turbines to extend range in cruise.

You just changed my mind, it fits!
At higher alt fuel consumption is much less, and the turbine will be more efficient at providing cabin air.
Thus a lower power turbine will be needed with the motor making up the climb performance gap.
The prop could be used as an air break to generate the battery on decent.

A pressurized electric aircraft requires up to 5% of battery energy for the Environmental Control System, not negligible but not a difficult issue either.

I assume that requires an all electric air pack, which adds weight when tapping bleed air avoids this need.

Seems we agree a fully BEA is not feasible, but a balanced hybrid will greatly improve economy.

Found and article but not read a paper on performance

https://pdfs.semanticscholar.org/6d30/baa77e3f2a8efe8f7a345d299ad115cce14f.pdf

 

[MontyFloyd]

In a hybrid system it is the other way around. Turbines are best used for energy intensive parts of the flight while batteries are used for power intensive parts. So you use batteries for takeoff and climb, and smaller turbines to extend range in cruise.

Visual to your explanation in 1 image.

 

[RSpanner]

Maybe someday.

 

[JRP3]

Hmm, what about a longer aircraft carrier type catapult system?

 

[Etna]

The prop could be used as an air break to generate the battery on decent.

Not going to work. If you regen it adds torque to the prop, which adds drag, which steepens the descent slope, which reduces range. Turns out you will need more energy to cover the lost range than you gained in regen, it is always a net loss except for badly planned late descents.

 

[Electroman]

The prop could be used as an air break to generate the battery on decent.

Very interesting. Using regen to slow down a plane during descent and on the runway after landing.
The down side of course is the added weight, space and cost for an hybrid design which often cancels the savings on fuel costs. Unless of course you could have a smaller turbine engine for just coasting.

 

[MontyFloyd]

Not going to work. If you regen it adds torque to the prop, which adds drag, which steepens the descent slope, which reduces range. Turns out you will need more energy to cover the lost range than you gained in regen, it is always a net loss except for badly planned late descents.

Even a correct landing path will make use of propeller as an airbrake right at touchdown.
Piston aircraft have far more propeller airbrake effect than turbine, so it would be advantageous for a turbine to have regen-airbrake.

Plus the regen motor will also be the electrical source for flight systems.

Then consider there are many locations that require steep approaches, so regen will pay for itself.

 

[MontyFloyd]

Very interesting. Using regen to slow down a plane during descent and on the runway after landing.
The down side of course is the added weight, space and cost for an hybrid design which often cancels the savings on fuel costs. Unless of course you could have a smaller turbine engine for just coasting.

NO added weight, as the motor is motor/generator.
Jets already use that, the generator is also the engine starter motor.

 

[daniel]

Hmm, what about a longer aircraft carrier type catapult system?

I think gliders sometimes use that. I think I've seen videos of a glider being launched by a winch system. And I've watched R/C gliders launched that way. I wonder how much energy you'd actually save launching a passenger plane that way. A glider is a very different sort of beast.

 

[ThomasD]

How large of a catapult/winch system would you need to launch an Airbus A380-800?

 

[MontyFloyd]

I think gliders sometimes use that. I think I've seen videos of a glider being launched by a winch system. And I've watched R/C gliders launched that way. I wonder how much energy you'd actually save launching a passenger plane that way. A glider is a very different sort of beast.

Yes, there is Winch and Tow, tow can be by another aircraft, or if runway/road long enough even a car can tow launch.
(I have done winch and air tow)

Catapults are realm of naval aviation, to do so with airliner will require MASSIVE reinforcement of nose gear. Alternative is a harness hooked to hard points (was a very common system)

It would be very expensive item that is use for about 10 to 20 seconds in a flight.

 

[Electroman]

.. and how big should be the rubber band ?

 

[ThomasD]

We are going to need a larger sling shot

 

[daniel]

How large of a catapult/winch system would you need to launch an Airbus A380-800?

A VERY big one.

 

[daniel]

BTW, a glider only has to get high enough on launch that it can start to catch thermals, and nobody uses a glider when they have to get to a specific destination. A commercial airliner is going to go up to 30-ish thousand feet and thermals won't be much help. Even a short-hop commuter or puddle-jumper plane won't really benefit from a winch-launch. A winch or catapult might provide, what? maybe half a percent of the energy needed to get you to cruising altitude. An aircraft carrier has to get planes above stalling speed in the length of the ship. It's not about saving fuel. It's about not dropping off the end of the runway into the sea. Bottom line: For a glider a winch is great; for a passenger plane, it's pretty much useless.

 

[JRP3]

We are going to need a larger sling shot

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[ThomasD]

Have they actually launched anything into outerspace?

 

[JRP3]

I don't think so as of yet. 25K feet so far NASA Tests Gigantic Slingshot for Hurling Objects Into Space