Electric Aircraft - The Thread

I was looking at wind turbine power charts elsewhere and noticed that because of minimum wind speed (before the blades spin), it gets a little jumpstart on the power of cube early in the curve.  The formulas are fairly complex though and I certainly could have overlooked some variables such as:

2 hours ago, nwt said:

Another realization: A good chunk of gravitational potential energy is going out the door on jump run.

Touché.  That's a good observation!

Still, even 5-10% regen return is still free cash.  Resistance on the propeller will cause some weird flight dynamics but nothing an approved ePlane jump pilot couldn't handle since they already do frequent dives and well versed on the dynamics of an open jump door and sudden weight shifts.  Regen ops will be much tamer than those mudane plane-bouncy factors...

Some tests and training might be needed for FAA approval of regen, which might later have rules about regen approvals (like no regen below 1000 feet or such). 

I think you are overthinking it.

First off, a variable pitch propeller would probably do best for regen at low pitch. The relative wind would spin it the fastest there. 
I don't think any exotic stuff would have to be done with the prop to get it to work better for regen. There might be some gains, but the 'cost to gain' would probably be not worth it. The primary function of the prop will still be moving the plane. Regen would be secondary.

The loss of weight (gravitational potential energy) would also not be a huge factor. 
I think the limiting factor would be the size of the prop. It's only going to produce so much drag, and so much energy.

This wouldn't be a big thing no matter what.

You aren't going to regen a significant amount of energy. Not in a 5-10 minute descent. But that's not the point. 

It's far more that some energy can be recovered. That would reduce the charge time on the ground. 

It would take a bit of experimenting to find out how much regen could be achieved and how beneficial it is. 

55 minutes ago, mdrejhon said:

I was looking at wind turbine power charts elsewhere and noticed that because of minimum wind speed (before the blades spin), it gets a little jumpstart on the power of cube early in the curve.  The formulas are fairly complex though and I certainly could have overlooked some variables such as:

Touché.  That's a good observation!

Still, even 5-10% regen return is still free cash.  Resistance on the propeller will cause some weird flight dynamics but nothing an approved ePlane jump pilot couldn't handle since they already do frequent dives and well versed on the dynamics of an open jump door and sudden weight shifts.  Regen ops will be much tamer than those mudane plane-bouncy factors...

Some tests and training might be needed for FAA approval of regen, which might later have rules about regen approvals (like no regen below 1000 feet or such). 

Small propellers will have high drag losses for regen, so actually electric helicopter ops for skydiving will actually be more optimized - electric helicopter climbs to altitude, then does autorotation descent which will (hopefully) recover a significant amount of the energy used to climb (minus the skydivers' gravitational potential energy and drag losses of course).

19 minutes ago, wolfriverjoe said:

This wouldn't be a big thing no matter what.

Well *theoretically*, in an aircraft that climbs to altitude then descends to the same point (no one jumps out), the net gravitational potential energy change is zero, so you should be able to get 100% of the energy of the climb back, minus drag and engine losses. Unfortunately those losses will be pretty high.

17 hours ago, mdrejhon said:

Resistance on the propeller will cause some weird flight dynamics

Nah, pilots are already used to using propellers as speed brakes, so nothing changes much there.

16 hours ago, wolfriverjoe said:

First off, a variable pitch propeller would probably do best for regen at low pitch. The relative wind would spin it the fastest there. 

I think you might be missing the fact that during regeneration, you are going to need significant torque on the prop--it isn't going to be freewheeling. I'd expect the prop settings to be closer to that of a climb than anything else. To put it another way: intuitively, I'd expect the prop settings to be similar when you are trying to transfer the maximum amount of energy between the motor and the air, regardless of the direction of that transfer. Though we do care about efficiency, so maybe a cruise setting would be better... but anyway, this is a minor point as it doesn't affect feasibility--If we ever get to that point, we'll figure it out just fine either way.

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I don't think any exotic stuff would have to be done with the prop to get it to work better for regen. There might be some gains, but the 'cost to gain' would probably be not worth it. The primary function of the prop will still be moving the plane. Regen would be secondary.

Agreed. There should be no changes that affect powered flight in any way and no additional systems apart from the electronics required for harvesting the energy.

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The loss of weight (gravitational potential energy) would also not be a huge factor. 

The energy loss here will be exactly equal to the amount of weight lost in proportion to the total weight--no more, no less. For example, if an otter is fully loaded at max gross weight (12,500 lbs) and drops 23 jumpers at 200 lbs each (4,600 lbs), you've lost 37% of your gravitational potential energy. That's pretty significant, and my gut says jump otters don't operate anywhere near max gross.

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You aren't going to regen a significant amount of energy. Not in a 5-10 minute descent. But that's not the point. 

It's far more that some energy can be recovered. That would reduce the charge time on the ground. 

It would take a bit of experimenting to find out how much regen could be achieved and how beneficial it is. 

I agree wholeheartedly with this sentiment, except for the reference to time. Stop thinking about time and instead think about gravitational potential energy. Time isn't relevant in the way you're thinking, as I've explained previously.

16 hours ago, olofscience said:

Small propellers will have high drag losses for regen, so actually electric helicopter ops for skydiving will actually be more optimized - electric helicopter climbs to altitude, then does autorotation descent which will (hopefully) recover a significant amount of the energy used to climb (minus the skydivers' gravitational potential energy and drag losses of course).

Haha that's a really interesting point, but using a helicopter because it will recover energy better would be like cutting off your nose to spite your face. You are going to spend so much more energy to recover a couple more peanuts!

46 minutes ago, nwt said:

Haha that's a really interesting point, but using a helicopter because it will recover energy better would be like cutting off your nose to spite your face. You are going to spend so much more energy to recover a couple more peanuts!

Yeah, I realised that after I posted

But the maintenance and fuel savings for electric ops will already be massive, so maybe regen is just a tiny bit of icing on the cake.

1 minute ago, olofscience said:

Yeah, I realised that after I posted

But the maintenance and fuel savings for electric ops will already be massive, so maybe regen is just a tiny bit of icing on the cake.

Yes, I think regen would just be a bit of icing. It might end up being useful, but I don't think the success of electric aircraft will depend on it.

4 minutes ago, nwt said:

Yes, I think regen would just be a bit of icing. It might end up being useful, but I don't think the success of electric aircraft will depend on it.

I'm also not quite sure what drives prop sizing on C208s for example, but my guess would be the gearbox loading and max engine power - so I'd imagine with electric, having a direct electric drive and the power advantages you mentioned earlier, you can mount a much bigger prop than before. If you mount the biggest prop that's practical (for ground handling, etc) then you'll get the most benefit out of regen.

Today’s Announcement of a Hummer EV Truck

Today’s release of the 1000 horsepower electric Hummer truck/SUV and its 200 kWh battery going 350 miles and can fast-charge at 0.4 megawatts to refuel 100 miles in just 10 minutes.

Much as we can thank Apple for the ability to buy a terabyte SSD for $100 (Even if the flash is manufactured by someone else), and that we can thank NVIDIA/AMD for kickstarting 3D GPU graphics innovations that now fit in a mobile phone/smartwatch (Even if the GPU is manufactured by someone else) — we have to blame Tesla for turning crazy expensive luxury $500 laptop batteries into viable cheap profitable gigawatt-output electric utility grid batteries (Even if the batteries are manufactured by someone else).

Now about that official Hummer EV...

While the Hummer EV is more expensive than a Model 3 Tesla, since it is using some more proprietary higher power battery than standardized form factors (18650, 2170s, etc)...  the audacity of a Hummer EV out-Hummering a petrol Hummer (longer range than most gas Hummers, more horsepower, better offroading, fastest 0-to-60 in 3 seconds, etc, etc). This continues to portends the unexpected trojan horse of lithium to vehicles formerly never dreamed of going officially electric in our lifetimes. But it’s there, GMC.com website, prototypes already on road, and ready to preorder today!

The audacity that something like that exists today for purchasing..... Hummer? EV? In the same sentence? And drives further than most gasoline Hummers?  Doubletake.

I truly think that people who disbelieves ePlanes are THAT far behind need to look again — even a kick in their behind to really run the numbers again on the fast-moving target — just a little more engineering left to click all the checkboxes for a lightweight ePlane conversion kit with a 10-minute between-loads recharge — I am starting to now think zero passenger jump capacity loss may actually be possible by 2030 for Caravans/Otters, since the electric motor replacing original old turbines are much lighter and may be all the weight savings you need for battery for just 1 load + 30 min level flight reserve capacity with ZERO jumper passenger loss, possibly...

In a recent conversation — too many pilots still disbelieve that ePlanes are hurtling towards real-world practicality for short-range ops and jump-plane ops.  I have to wave a neon checkered flag “yoo-hoo”, to look closer...  Someone needs to write a Parachutist article about this to get the word out since a turbine re-engine is no longer as rubberstampable as IBM in the 1960s and 1970s (“You never got fired for choosing IBM”...until someone did).  

So many planes are approaching re-engine dates in 2025-2030 and many re-engine vendors are ignoring electric (at peril) given the recent surprising performance statistics of this year’s Magnix trials (including the Magnix 750hp having superior go-around rev-up performance than a 900hp Garrett from what I heard — the electric “instant spoolup” factor).  I think vendors need to look at the engine & battery separately; the engine is here now, but the battery is “just about barely” not good enough for jump ops at zero passenger loss (yet), but the rapidity of Tesla means appropriate batteries for jump ops will fit in the necessary profitability no-compromises (except 10-minute between-loads recharge) envelope sooner than later.  

In the trials, the motor apparently is already good enough for skydiving operations; the battery just needs a few more years to catch up.  So approaching the problem at different angles; the motor and the battery(capacity/weight).  And watching Tesla/Hummer/etc — the writing is on the wall...

At first, it might require a more well captialized dropzone (e.g. a Skydive Dubai or a Skydive Perris) to do the headway of being the first (with more expensive lightweight proprietary lithium batteries) and reap the profit/rewards of low-cost jump ops after the high capital cost of being first — gradually chainsaw all the FAA red tape down to get specific conversions kits approved — then the floodgates open as a competitive alternative to normal re-engines, and the cost of ePlane conversion kits really fall (with more commodity Tesla-style batteries).

We’ve been ignoring ePlanes/electric conversions with disbelief for so long, until the Hummer EV / Tesla EV / Magnix wake-up call.  A conversation with disbelieving aviation stakeholder is why I started making a lot of noise in this thread — not because I want to advertise or troll anything — but a big aviation operational cost-savings opportunity red button is flashing.

Texas Turbine should put Magnix on speed dial and get into the electric jump plain conversion business before someone else beats them to the market by 2030...! 

On the note about the pilots I talked to that disbelieve the rapidity of ePlane practicality, think about this:

Suggested Napkin Sketch Timeline
(replace dates with whatever seems more realistic, but you get the idea: start ASAP)

2021: Turbine re-engine vendor partners with ePlane vendor
2022: Somebody proposes FAA draft rules for theoretical ePlane jump ops
2023: Test jump plane conversion, reduced capacity, novelty skydives (like heli or biplane). Possibly, it would be a 50% trainer plane, 50% novelty skydive plane as a partnership between multiple airport stakeholders as a risk-sharing trial;
2025: First official-kit expensive conversion (i.e. Skydive Dubai, Perris)
2025: Full FAA approval as easy or easier than turbine kit.
2030: Capital Cost Parity: ePlane kit as cheap or cheaper than turbine kit, including cost of batteries. Making possible jump tickets cheaper than turbine planes while simultaneously keeping bigger DZO profit.

Planning clearly begins now for 2030.  Anybody who doesn’t begin planning now is already too late to be first.  Push the dominoes.  Lots of dominoes to tip (FAA, mechanics training, test ahead of battery improvements — the outperforming airplane electric motor’s already ready, Test today before too many people re-engine to another turbine, many are going to get buyer’s remorse in 2030)

One more thing.  Actual tests showed $300-$400 avgas replaced by $6 to $30 of electricity.  Magnix tests showed cost-savings scales better in aviation than for cars.  And that’s even ignoring much less maintenance.  Actual number from Magnix electric converted Cessna Caravan.  Any dropzone laughing at electric?  This is the microphone drop below:

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Fuel-free flying may well be the biggest selling point. “This 30-minute flight that we did would cost, in a traditional Grand Caravan, around $300 to $400 in fuel,” Ganzarski said. “Here in Moses Lake and Grant County, 80% of the electricity is renewable. You pay a little over 2 cents per kilowatt-hour. So this 30-minute flight would have cost us around $6 in electricity, compared to $300 to $400 in fuel.”

Apparently, $300-$400 of avgas is what many skydiving dropzones tank up with (approximately) for a sufficiently generous jump altitude.  But it’s in that territory for many common jump planes of the Caravan / Twin Otter variety to non-skimpy altitudes with a full load.

Now, instead of about 2.5c/kWh for locally sourced renewable, and your industrial/commercial rate of your electricity is 12-15c/kWh in other states — then, yes, it’s closer to $30 than $6 per jump lift, and probably cheaper than that since most jump planes fuel less than $300-$400 avgas.  At the most expensive end, 10x savings and literally pennies of fuel per jumper — well under a dollar of fuel per jumper to 13500 feet if you’re getting good rates for your electricity.  And if electricity later goes crazy in your state, just build a solar farm or pay some farmer 10 miles away to build a wind turbine (safely far away from dropzone), and deliver the power to the  dropzone cheaply. Some rural airports have built their own megawatt-scale solar farms as a side business, and that’s unintentionally accidentally convenient for ePlanes.  You’re more 1973-proofed and 2008-proofed than with avgas.  You can’t easily manufacture your own avgas onsite, but you can manufacture your own electricity — The freedom to choose to do so!  

Combined with the far reduced motor-related maintenance, the savings easily pay for the initially high capital cost; a DZ can even keep the tickets the same price initially to payoff capital faster; and drop them later.

Also, due to various reasons (no gears, direct drive motor!!), the 750hp electric may outperform a 900hp diesel for climbs — less horsepower needed for a specific climb rate, because no horsepower is lost in a fully direct-drive propeller.  So there’s an electric dividend that reduces battery size somewhat for a same-time climb to jump altitude.  Or find the sweet-spot climb rate (which might be just only 1 minute slower) — the battery might be downsized slightly more too.  The sweet spot climb rate can be discovered in ePlane experiments.  One might find you need less battery than expected to do 1 jump (in a 25-50% battery discharge) + 30 minute reserve level flight.  The minimum battery weight numbers may almost fits the weight difference of a lightweight Magnix vs original engine already.  With fast 10-to-15 minute between-loads charging increasingly looking potentially feasible, you only need to size battery for 1 jump load with zero passenger loss.  Electric jump plane problem solved in nearer future than expected?

Start planning and thought exercising for the DZ business...Maybe the weight numbers don’t work just quite yet for zero-passenger-loss Caravan but they will very soon.   That’s no reason to avoid planning for electric jump ops now.  With skydiving being too expensive for many, economical electric jump planes will simultaneously raise DZO profits + lower jump ticket prices — we all need it by 2030.

Read again: $300-$400 of avgas in an electric Cessna Caravan only costs $6 to $30 of electricity.  10x to 50x fuel cost savings.  Donkey, meet carrot.  Carrot, meet donkey.

Which DZ wants to be first?

14 hours ago, mdrejhon said:

Read again: $300-$400 of avgas in an electric Cessna Caravan only costs $6 to $30 of electricity.  10x to 50x fuel cost savings.  Donkey, meet carrot.  Carrot, meet donkey.

Which DZ wants to be first?

Everyone already understands that an electric plane could be much cheaper to run. Harping on that does nothing to support the feasibility.

What is the evidence that we will hit the required energy storage densities on your timeline?

You're advocating for DZOs to start planning now. What do you mean by that? What would you have them do, specifically?

Even if the cost of batteries flattens out, petroleum prices will still continue to rise over the long run. Eventually electric airplanes will be less expensive to "fuel."

Also consider how many hangar roofs can be converted to support solar panels. Most hangars have enough spare room for a battery of batteries along the back wall. Municipal airports might even turn a profit!!!!!

Heck! Some of those huge warehouses/logistics hubs in Surrey are bigger than DZs!

Since the average Cessna jump-plane only flies 1/14 of the week, they might break even by selling electricity.

13 hours ago, nwt said:

You're advocating for DZOs to start planning now. What do you mean by that? What would you have them do, specifically?

Year 2020: Advocacy.  Random simple things like the maintenance people subscribing to electric-plane news/sites. Or the DZO emailing a turbine supplier about their future plans of ePlane conversions later in decade. Or participating in aviation (FAA/airport/etc) public information centres where they're asking for comments on new regulations. Or attending a Magnix test or another ePlane vendor's test if they're happening within a few hours drive of you. Ask them questions. Bring a skeptic friend. Write a Parachutist article about your personal experience attending Magnix tests and also corroborate lithium battery industry observations into the same article. Ask for an interview with the point contact of your power company's new battery farm. Even personally test drive a Tesla car (or electric Ford F150, or electric Hummer, when they come out) with one of your skeptic aviation friends. Convince your electric-doubting mechanic coworker. Contact your aviation-nut congressperson. Talk to your friend at FAA. All kinds of random advocacy steps to lower the laughingstock background noise down to a quiet din.

Baby steps. Advocacy. Dispel myths. Learn.

Disbelieving people can inject years of delays in pushing the gearwork (slower advocacy, slower FAA rules, slower convincing, less ePlanes knowledge, etc).  The live-under-rock factor is strong. 

Flap those butterflies so the Chaos Theory so dominoes can fall sooner.

Random Theoretical Examples:
- [2020-Begin] Hypothetically, seven DZOs asks three turbine vendor about future ePlane plans, three turbine vendors contacts Magnix or another ePlane motor/battery supplier, Magnix realizes there's a jumpplane market, Magnix contacts FAA about theoretical jumplane rules, Magnix goes into the jumpplane conversion biz [2030-End]
- [2020-Begin] Hypothetically, somebody's brilliant Parachutist article causes 3 people do a Tesla test drive, 5 people to research Magnix, 2 exhibition jumpers to ask if they can test-jump the magnix eCaravan, 2 DZO accountants to do the math only to suddenly get surprised and speeddial all FAA friends. Then, say, 7 FAA readers, prodded by articles/dropzones to start writing draft documents on time to become final when those good jump-capacity aviation batteries arrive, a dropzone finally buys an ePlane conversion a couple years sooner when they are mature earlier than expected, etc. [2030-End]
- Or whatever, etc. Infinite number of theoretical dominoe paths. Other dominoes to tip. Many dominoes take 5-10 years to finish falling.

Yes, Some advocacy steps are ridiculous and longshots, but a lot of mudane skydiving innovations over the last 70 years sometimes came from surprisingly simple advocacy or manifest watercooler talk or pilot/instructor lounges. And now are instructor/SIM material.  Lots of Chaos Theory Butterflies happened there already...

Also, in another industry (gaming industry, since I operate a research laboratory on high-performance display screens), some of my discussion forum posts incubated an invention that are now in a peer reviewed science journal & my ideas were implemented in certain virtual reality headsets and gaming monitors, with confirmed credit.  Just in September, Samsung Electronics cited me; I now have over 20 research papers that cited either me or my business (Blur Busters / TestUFO), and a few that I am even co-author of (in one paper that included a NIST.gov researcher in a U.S. government-funded peer-reviewed conference paper that I am a co-author of), from something originally incubated in a forum.  From something more casual than this forum thread, that progressiely dominoed all the way there.  So, this is not my first tango at online advocacy (in a different high-skill industry)...  

In a sense, just doing these dropzone.com falls under the "Advocacy" umbrella.  Make a few in the skydiving industry a smidge more aware, recruit people who agree, etc.  I've written a few times for CanPara and Parachutist before (e.g. Canada Big Way, Rainbow Boogie, etc).  Happy to co-write a Parachutist article, I would want help from at least 1 co-author working with me in Google Docs and at least 3-4 proofreaders, maybe even one or two bleeding edge pilots/dropzone accounts/jumpdrivers/DZOs to review, add useful commentary, and fix errors in the article.  So it's a proper electric jump plane wake-up-call article in a national skydiving magazine instead of 1-person speil. 

If you also have writing experience, and movement is desired on a Parachutist article, Google my full name (Mark Rejhon) and reach me through any channel (LinkedIn, email, etc -- I have rarely visited here after the forum upgrade so that's why I still am at 0 rep despite 2766 posts since rep system didn't exist before then).

On 10/22/2020 at 6:31 PM, nwt said:

Everyone already understands that an electric plane could be much cheaper to run. Harping on that does nothing to support the feasibility.

What is the evidence that we will hit the required energy storage densities on your timeline?

You're advocating for DZOs to start planning now. What do you mean by that? What would you have them do, specifically?

The CEO of MagniX is actually a skydiver himself, and he's been interviewed by Pete Allum: https://www.careallfoundation.org/blog-article-9-roei-ganzarski-ceo-magnix

One thing that's also great for electrics is potentially far better safety - carb icing, gearbox failures and most other mechanical failures would become a thing of the past. I'd be far more relaxed between takeoff roll and 1500 feet!

13 hours ago, olofscience said:

One thing that's also great for electrics is potentially far better safety - carb icing, gearbox failures and most other mechanical failures would become a thing of the past. I'd be far more relaxed between takeoff roll and 1500 feet!

Compared to pistons for sure. Turbines seem pretty reliable, though.

5 hours ago, nwt said:

Compared to pistons for sure. Turbines seem pretty reliable, though.

Except for the inability to stop/start them frequently without shortening service life. And their weak point is still the gearbox which electrics can dispense with.

Airbus is actually proposing hybrids which have electric motors powered by a turbine - having a fixed torque generator would get the best out of the turbine while overcoming the range and energy density issues of batteries.

9 hours ago, olofscience said:

Except for the inability to stop/start them frequently without shortening service life. And their weak point is still the gearbox which electrics can dispense with.

Yes, these are clear advantages for electric motors, but we were talking about safety. There's no reason not to feel perfectly safe in a twin otter. How often does a gearbox fail in flight?

9 hours ago, olofscience said:

Airbus is actually proposing hybrids which have electric motors powered by a turbine - having a fixed torque generator would get the best out of the turbine while overcoming the range and energy density issues of batteries.

I saw a presentation from a small company doing electric propulsion, and he said the real killer app for this tech is VTOL aircraft for transport within a large city, where noise is the limiting factor. The flat torque curve allows for large props spinning at lower RPMs, resulting in less noise. That makes a lot of sense regardless of energy storage (batteries vs. hybrid). However, that doesn't do nearly as much for us--most of the advantage for us is in battery storage.

I'm not saying there wouldn't be an advantages at all, but they would probably be relatively small and not very interesting to the jumper's POV, if they made it worth implementing at all.

22 hours ago, nwt said:

There's no reason not to feel perfectly safe in a twin otter. How often does a gearbox fail in flight?

Agreed, I feel much safer in a turbine than a piston but there are still plenty of piston DZs around.

However, gearbox reliability IS a limiting issue - turbine power output is actually constrained by this, which is why Pratt&Whitney took more than 20 years to apply them to civil airliners via the GTF. Plenty of helicopters also have systems monitoring for metal chips in the oil system as gearbox failure there is the main killer (although admittedly, fixed-wing turbine safety record is much better than helicopters).

6 hours ago, olofscience said:

Agreed, I feel much safer in a turbine than a piston but there are still plenty of piston DZs around.

My home DZ is a single C182 operation and I am all too familiar with what that can mean for reliability. But realistically these DZs will be the last to switch to electric.

6 hours ago, olofscience said:

However, gearbox reliability IS a limiting issue - turbine power output is actually constrained by this, which is why Pratt&Whitney took more than 20 years to apply them to civil airliners via the GTF. Plenty of helicopters also have systems monitoring for metal chips in the oil system as gearbox failure there is the main killer (although admittedly, fixed-wing turbine safety record is much better than helicopters).

I'm not sure what you mean to get at here. I'm sure everyone agrees that turbines don't last forever. For the sake of this discussion, does it matter which particular component of a turbine power plant is the weak link?

17 minutes ago, nwt said:

My home DZ is a single C182 operation and I am all too familiar with what that can mean for reliability. But realistically these DZs will be the last to switch to electric.

They would all switch quickly if someone came up with a practical STC'd conversion. An O-470 weighs about 425lbs including accessories and carries about 100 lbs of fuel for 2 loads.

2 hours ago, gowlerk said:

They would all switch quickly if someone came up with a practical STC'd conversion. An O-470 weighs about 425lbs including accessories and carries about 100 lbs of fuel for 2 loads.

So what? It's still only going to carry 4 jumpers.

How much will the electric motor plus batteries weigh, and how much will it cost?

These small dropzones are very capital-limited. If we weren't, we wouldn't be running piston aircraft built 65 years ago. It's not like we don't have better options available if we had more money to spend.

1 hour ago, nwt said:

It's not like we don't have better options available if we had more money to spend.

Because electric motors and batteries will be cheaper than turbines. Not just in operating costs, but in capitol costs. The may very well be cheaper than rebuilding piston engines.

1 hour ago, nwt said:

How much will the electric motor plus batteries weigh, and how much will it cost?

Good question. That's why I said "practical conversion". Why do you think an electric motor pound for pound will be better or cheaper in a large airframe than a smaller one?

5 hours ago, billvon said:

We'll get electric aircraft the same way we got Caravans.  Someone else will buy them in huge numbers then sell them when they get too old to get the performance they want (in our case, range due to aging batteries.)

Given how Teslas have held up (one model S has been driven 1 million km) and how easy it is to change battery packs?

Changing the battery pack will instantly refresh performance to new and will not be anywhere as invasive as changing a turbine or piston engine for example.

No, people will upgrade because there's a newer, better aircraft model available with better performance, probably the clean-sheet electrics. Apple secretly degraded their iPhone performance when the batteries degraded but got caught when some people did battery replacements and found that performance suddenly increased.

9 hours ago, billvon said:

Variable pitch/constant speed props are used because 1) piston engines like to run at a specific speed, 2) you don't want to exceed a certain tip speed at higher speeds (breaking the sound barrier at the tips makes a LOT of noise and drag) and 3) you can't reverse a piston engine to provide beta range braking.  Two of those three aren't a factor for electric motors, and if you want to climb, cruise and descend at similar speeds, there's really not much advantage to a variable pitch prop - and a lot of weight, complexity, cost and risk to reduce.

Good point.

Considering that jump planes are basically climbing and descending as quickly as possible, a fixed pitch prop at low pitch would cover both of those situations. It would make ferry flights really slow, but that's not a super big deal.