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Comment by eptcyka | Hacker News Reader

Small planes will be able to ride off the EV battery tech for about 50 miles max.

Small electric aeroplanes already exist and are in serial production. See https://www.tu.no/artikler/i-dag-skal-avinor-sjefen-og-samfe..., https://www.pipistrel.si/plane/taurus-electro/overview.

I stand corrected - last I checked, a production all-electric aircraft could do 15 minutes of flight time. It's nice to see a 4x improvement in the Pipistrel case. However, a 60 minute flight time is still 3 times smaller than the petrol counterpart.

We could make aircraft carbon-neutral by using carbon capture and producing synthetic fuel from water, like what the US Navy is working on: https://phys.org/news/2017-10-nrl-patent-carbon-capture-devi...

As a backup for engine failure that could be a substantially safer and cheaper alternative to a second engine.

A "small" 737 will do about 50 miles, yeah. But by small I meant like small small: https://www.eviation.co/alice/

Yeah but you can use the potential energy of the plane to produce power, just like car going down hill. Probably not gone work for small planes but it does have interesting advantages and new ways of thinking about planes.

For an airplane, there's no particular reason to turn potential energy into chemical energy for storage. Use the potential energy more directly to glide down to your approach point.

Airplanes are typically "driven" (using positive power) all throughout the flight regime, including descent and approach.

> Airplanes are typically "driven" (using positive power) all throughout the flight regime, including descent and approach.

No, not really. Descent in most aircraft is typically done at idle. In jet powered aircraft, final approach will be done with the engines at some speed above idle, but that is to minimize spool-up time during a go-around, rather than because the aircraft needs the thrust.

The airplanes where electrics could possibly compete are piston powered and flown with power in the descent. Electrics don’t even compete well there yet (and may never as they are just as heavy on landing as takeoff). For airplanes with higher fuel burn (long haul jets), they benefit significantly from being lighter at the end of the flight. Even my piston airplane picks up about 5 knots in cruise at 1/4 tanks vs full.

In jet descents, we rarely get what we prefer which is a slam dunk approach (much more fuel efficient to stay up high). Many times we’re down at 10K feet for 20+ miles because of sequencing. It’s only in the less busy airports where jets can regularly get slam dunk flight idle approaches.

Even there, you probably want to use potential->kinetic rather than potential->chemical->(later) kinetic transfers because of unavoidable losses at each conversion. On the runway, using regen instead of thrust reversers or beta/reverse would be helpful, but that's a vanishingly small part of the overall flight regime.

> Descent in most aircraft is typically done at idle.

Went on my first flight in decades last year. The moment we started out descent really stands out to me, I remember the eerie-ness of hearing the engines slow down a ton all of a sudden and no one looking disturbed by it at all.

Idle turbo-fan engines produce enough thrust to taxi around an airport

Even so, the aircraft still needs to make a comfortable gradual descent. It must maintain lift as it descends, otherwise it will stall (aerodynamically) and fall out of the sky. The controlled descent takes most of the energy that you might think could be recovered by e.g. windmilling the electric fan motors as generators.

I'm not sure what you're talking about with "must maintain lift as descends otherwise it will stall and fall out of the sky"...

Wings stall when they exceed their critical angle of attack. A descent is inherently a low AoA maneuver. Heck, in pretty much all aircraft of decent performance, they have devices on the wings to help "spoil" the lift of the wings to help the plane descend more quickly. They're sometimes called speed brakes, sometimes called spoilers.

Right, but you need a certain amount of forward speed relative to descent to maintain that AoA (assuming you want to maintain a fairly gradual, level descent; most passengers would find a steep nose-down descent alarming).

If you scrub off all your forward speed by turning your propeller/fan into a generator to charge the batteries, you have to push the nose down to maintain AoA.

Here is a quote from Pipistrel <https://www.pipistrel.si/plane/alpha-electro/overview>

Alpha Electro, the new 2-seat electric trainer: the greenest way of learning to fly!

Performance of the Alpha Electro 2-seat electric trainer is tailored to the needs of flight schools. Short take-off distance, powerful 1000+ fpm climb, and endurance of one hour plus reserve. The Alpha Electro is optimized for traffic-pattern operations, where 13% of energy is recuperated on every approach, increasing endurance and at the same time enabling short-field landings.

Using propeller in the "beta" range for improved short-field operations and power recovery is a definite benefit to the Pipistrel. It's also an airplane that can't legally fly 95 miles/150 km and achieves those power recovery numbers only in pattern operations. I don't see that as representative or substitutive for even piston airplanes use cases.

I want this plane! why learn and deal with all the issues of an old school engine if you have this plane...

Well, you might want to fly more than 100 miles...

Of course you don't turn it into chemical energy, I'm talking about batteries. And it defiantly makes sense.

> Of course you don't turn it into chemical energy, I'm talking about batteries.

How do you think batteries store energy, if not chemically?

By windmilling the propeller? This massively increases drag.

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