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Electric Aircraft - The Thread

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48 minutes ago, nwt said:

This is certainly impressive, but the proper comparison would be to the fuel load used for skydiving.

True in that this “seems” more apples vs apples.

On the other hand, a Magnix electric direct drive engine (297lbs) is smaller and weigh less than the original turbine (of apparent lesser performance, despite same or slightly higher horsepower).   And a lot less than piston engines and older turbines (and their respective gearbox/differential that are no longer needed thanks to gearless direct drive).  

This frees up a portion of weight for the minimal 1-skydive fast-10min-charge battery + 30min reserve flight capacity, with potentially zero loss of skydiver passenger capacity.

The battery undoubtedly will weigh more than the fuel load of one skydive, but looks like a one-skydive battery can still now fit within max-takeoff with a full load of skydivers.  

Extra “fuel” weight is vastly far more than compensated by the massive cost savings. ($300 of avgas cut by 90% to 98% in cost to just $6 to $30 depending on your commercial electricity rates)

(DZO accountants.,,. yes..... potentially under $1 “fuel“ per skydiver to 13500 feet!!!!)

With the good instant rev torque that Magnix-trying pilots go wow at — even a near-MTOW load does not feel as dicey as with in a turbine.  

I think the napkin math is starting to look impressive this decade.

Edited by mdrejhon

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1 hour ago, mdrejhon said:

Extra “fuel” weight is vastly far more than compensated by the massive cost savings. ($300 of avgas cut by 90% to 98% in cost to just $6 to $30 depending on your commercial electricity rates)

That might be true, but it might not be. How much more time will it take to get to altitude with that extra weight? How many more planes will a dropzone need to acquire to compensate for this reduced lift capacity? Will jumpers tolerate the longer ride?

e: Also, it becomes apparent that increased flight time will increase the required battery capacity as well.

Edited by nwt

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1 hour ago, nwt said:

e: Also, it becomes apparent that increased flight time will increase the required battery capacity as well.

Actually, probable reduced flight time.

The Magnix can actually climb to altitude faster than the original turbine because you don’t worry about the redline as much — the battery difference between a slow climb and fast climb isn’t too terribly major for the current small envelopes asked of a 1-skydive battery sizing.  

At full 750hp throttle, a >93% efficient Magnix generates only 35 kilowatts of waste heat which is easily cooled by sheer airspeed, and I heard it climbs more vertically than a 900hp for the same weight because of less HP loss (direct shaft drive, no differential).  

But yes, the extra battery weight may cancel this out.   Battery heating is also a factor but the quick climb moots this out; electric car have output more wattage than a Magnix doing a full Nurburgring Loop in Germany.

For practical purposes, I expect no difference between turbine and Magnix electric for a typical jump plane climb.

HP for HP, electrics can outperform avgas, as noticed by R/C hobby airplane pilots. Electric R/C airplanes perform spectacularly.

Sure, the battery capacity is an issue, but you only need to size for a fast climb for 1 skydive load + 30min level flight reserve, which will still weigh less than a full fuel load.  

The kWh per kilogram may need to improve a bit more, but that’s just details from 2020-2030 at this stage — the fast climbing electric jump motor is already here...

Edited by mdrejhon

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2 minutes ago, mdrejhon said:

Reduced flight time. The Magnix can climb to altitude faster; the battery difference between a slow climb and fast climb isn’t too terribly major for the current envelopes asked of a 1-skydive battery sizing.

A heavier airplane will climb slower than a lighter one, everything else being equal. This is a hard fact and you can't hand-wave it away. If you are saying a Magnix-equipped Otter at max gross will get to altitude faster than our current Otters at their current weight... perhaps that might be true but that's a claim that needs to be supported and not just stated a priori.

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13 minutes ago, nwt said:

A heavier airplane will climb slower than a lighter one, everything else being equal. This is a hard fact and you can't hand-wave it away. If you are saying a Magnix-equipped Otter at max gross will get to altitude faster than our current Otters at their current weight... perhaps that might be true but that's a claim that needs to be supported and not just stated a priori.

True, but that may not be a problem — it assumes the lighter motor & other factors don’t fully cancel-out.  

Also — depending on plane — many dropzones don’t always absolute-max throttle their jump ship.  Backing off a bit, especially after takeoff, to a mutually-agreed redline indicator on the dial, for climb performance that makes it easier for the airplane maintenance department & dropzone accountants for avgas consumption.   Some do push it beyond, especially if you’re trying to push loads fast on a busy day, but that can be brutal on the engines of some planes if you’re near the performance envelopes.

In reality, if slower, we are probably nitpicking only tiny percents (e.g. 10% or 20% slower climbs for same plane type) which is within the noise floor of the jump ship variances between dropzones.  And even that assumes we’re using today’s batteries, not tomorrow’s.

Fortunately, from the early tests, it already looks like we’re not going to be seeing 22-minute Cessna 182 style climbs with electric airplanes. 

Edited by mdrejhon

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1 hour ago, mdrejhon said:

True, but that may not be a problem — it assumes the lighter motor & other factors don’t fully cancel-out.  

Also — depending on plane — many dropzones don’t always absolute-max throttle their jump ship.  Backing off a bit, especially after takeoff, to a mutually-agreed redline indicator on the dial, for climb performance that makes it easier for the airplane maintenance department & dropzone accountants for avgas consumption.   Some do push it beyond, especially if you’re trying to push loads fast on a busy day, but that can be brutal on the engines of some planes if you’re near the performance envelopes.

In reality, if slower, we are probably nitpicking only tiny percents (e.g. 10% or 20% slower climbs for same plane type) which is within the noise floor of the jump ship variances between dropzones.  And even that assumes we’re using today’s batteries, not tomorrow’s.

Fortunately, from the early tests, it already looks like we’re not going to be seeing 22-minute Cessna 182 style climbs with electric airplanes. 

Sorry... I mean no offense, but this looks like just more hand-waving and a priori statements. How did you arrive at this 10-20% figure and why is 20% acceptable?

I don't understand your point about noise floor... if my Otter is going to become 20% slower than it is now, why should I care that it's still faster than someone else's? 

e: You're also (I think) assuming that an Otter with a full load of both fuel and jumpers will be within MTOW. That may be true and maybe you've actually done the math, but if it is just an assumption it's not a fair one.

e2: Another thing to consider is that we may need to stay under max landing weight rather than max takeoff weight. If something happens and we are unable to drop jumpers, we can't lighten the load by burning off fuel. Not a huge deal because the difference is only 200 lbs, but something to think about.

Edited by nwt

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(edited)
2 hours ago, nwt said:

Sorry... I mean no offense, but this looks like just more hand-waving and a priori statements. How did you arrive at this 10-20% figure and why is 20% acceptable?

I don't understand your point about noise floor... if my Otter is going to become 20% slower than it is now, why should I care that it's still faster than someone else's? 

(re: noisefloor = I meant “lost in the midpoint of the varying time-to-altitude statistics of all dropzones worldwide”. I should not have tried to summarize that into one word, apologies)

For the specific 10%-20% (yes, wholeheartedly unscientific estimate) is based on previous world experiences in other electrifications — electric cars, radio control airplanes, etc.   They drive similar speed and fly similar speed and climb similarly performant at similar weights. In lots of cases, the electrics outperform in raw performance (witness the electrics beating petrol speed records in some domains).  Also, skydivers will become impatient if the plane climb noticeably slower than other planes in the fleet.  10% slower climb isn’t really noticed by everyone in the load, but a 50-100% slower is definitely noticed by the whole load.

But here’s some scientific observations, that actually brings credence to the point I’m making:

The math is a sudden viability line: Change the battery numbers a bit, and things suddenly go from “Can’t meet MTOW” to “I can fly quickly to full jump altitude”.  Given the small envelope of a single jump lift, the fuzz region is actually much smaller than many people think, since a slow-vs-fast climb isn’t that terribly a large watts-hour delta in the Magnix tests (you consume less power but consume longer ...

It is less variable in “power-consumed-per-foot-gain-of-altitude” with electric than with avgas, simply by virtue of the electric motor being efficient at all RPMs.  (Yes, you have to correctly set your flaps and optimal prop pitch and all, to avoid wasting power in an inefficient climb, but once optimal, it is more  balanced than for avgas.

A slow optimal climb vs fast optimal climb isn’t as much battery watt-hours consumed differences as the fuel-consumed differences because of the efficient-at-all-RPMs behaviors that make it easier to dial the optimal climb.  Putting more of the motor’s energy more efficiently into the climb —

Turbines are most efficient at a specific settings, while electrics are efficient at nearly all settings, giving pilot more flexibility to focus more on adjusting the plane’s surfaces to optmium prop/airframe settings, rather than optimizing the plane to meet the efficiency at the performance settings of a specific turbine motor.   So, the slow-vs-fast climb matters less since it’s a fixed altitude gain, you’re paying energy a more stabilized amount of energy per foot of gain, you’re paying energy a more stable amount of power for a given altitude gain, thanks to the brilliant efficiency of the electric motor in virtually its entire performance range.   There is still a difference (it’s not linear)  but the watt-hours difference is not as big as the fuel difference of a fast-vs-slow climb.

For the first plane, if it climbs too slow, you remove passengers or wait for battery tech to become viable.   The power difference of a fast climb versus slow climb from altitude X to Y (0feet to 13500feet) isn’t going to double the battery size.  

The napkin numbers are touchy: A minor improvement in battery tech suddenly allows the electric airplane to have no disadvantage.  

The “fuzz” between not practical and suddenly fully practical (at no climb performance degradation or jump capacity loss), is actually rather a tight twilight zone that may last only a few years, possibly only a year.   So the moral of the story is when the battery gets good enough, it only needs a little more refining to quickly zero out the remaining performance-related disadvantage. 

But a dropzone will bite the ePlane bait a bit before that, i.e. tolerate a 10-20% climb performance decrease to decrease the size of the battery, to gain the other advantages (like major cost savings).  But yes, replace the “10%-20%” unscientific numbers with your favourite low-percentage threshold where somebody bites the ePlane carrot.  I would bet DZOs also won’t bite at 100% slower climb performance.

That’s what we saw happen in other electrifications.  

Anyway, the point being is that the tech fuzz zone between “Not practical” and a “ePlane climbing at full velocity to jump altitude” is actually shocking small, because of the reasons above described.  Improve the tech just enough and — bam — it’s practical without a compromise.   If we’re going to have compromises, it will only be very short-term like removing 1 or 2 or 3 passengers to meet volume/weight envelopes, but only for as long as battery tech improves even a few percent in a “we-only-need-a-battery-for-1-skydive-plus-reserve” scenario.

Anyway, I just heard back from Magnix CEO he’d be happy to be interviewed for the Parachutist article.  Now to formulate the right questions.

(which may also answer some of these questions too, as well as correct any details in some of my answers, I’ll admit to being wrong sometimes.  But really, there are a lot of details people don’t realize about electric motors, like “high-efficiency-at-all-power-settings” behaviors).

Edited by mdrejhon

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40 minutes ago, mdrejhon said:

(re: noisefloor = I meant “lost in the midpoint of the varying time-to-altitude statistics of all dropzones worldwide”. I should not have tried to summarize that into one word, apologies)

For the specific 10%-20% (yes, wholeheartedly unscientific estimate) is based on previous world experiences in other electrifications — electric cars, radio control airplanes, etc.   They drive similar speed and fly similar speed and climb similarly performant at similar weights. In lots of cases, the electrics outperform in raw performance (witness the electrics beating petrol speed records in some domains).  Also, skydivers will become impatient if the plane climb noticeably slower than other planes in the fleet.  10% slower climb isn’t really noticed by everyone in the load, but a 50-100% slower is definitely noticed by the whole load.

But here’s some scientific observations, that actually brings credence to the point I’m making:

The math is a sudden viability line: Change the battery numbers a bit, and things suddenly go from “Can’t meet MTOW” to “I can fly quickly to full jump altitude”.  Given the small envelope of a single jump lift, the fuzz region is actually much smaller than many people think, since a slow-vs-fast climb isn’t that terribly a large watts-hour delta in the Magnix tests (you consume less power but consume longer ...

It is less variable in “power-consumed-per-foot-gain-of-altitude” with electric than with avgas, simply by virtue of the electric motor being efficient at all RPMs.  (Yes, you have to correctly set your flaps and optimal prop pitch and all, to avoid wasting power in an inefficient climb, but once optimal, it is more  balanced than for avgas.

A slow optimal climb vs fast optimal climb isn’t as much battery watt-hours consumed differences as the fuel-consumed differences because of the efficient-at-all-RPMs behaviors that make it easier to dial the optimal climb.  Putting more of the motor’s energy more efficiently into the climb —

Turbines are most efficient at a specific settings, while electrics are efficient at nearly all settings, giving pilot more flexibility to focus more on adjusting the plane’s surfaces to optmium, rather than optimizing the plane to meet the efficiency at the settings of a specific turbine motor.   So, the slow-vs-fast climb matters less since it’s a fixed altitude gain, you’re paying energy a more stabilized amount of energy per foot of gain, you’re paying energy a more equal amount of power for a given altitude gain, thanks to the brilliant efficiency of the electric motor in virtually its entire performance range.   There is still a difference (it’s not linear as one would like), but not as nonlinear as the fuel difference.

If it climbs too slow, you remove passengers or wait for battery tech to become viable.   The power difference of a fast climb versus slow climb from altitude X to Y (0feet to 13500feet) isn’t going to double the battery size.  

The napkin numbers are touchy: A minor improvement in battery tech suddenly allows the electric airplane to have no disadvantage.  

The “fuzz” between not practical and suddenly fully practical (at no climb performance degradation or jump capacity loss), is actually rather a tight twilight zone that may last only a few years, possibly only a year.   So the moral of the story is when the battery gets good enough, it only needs a little more refining to quickly zero out the remaining performance-related disadvantage. 

But a dropzone will bite the ePlane bait a bit before that, i.e. tolerate a 10-20% climb performance decrease to decrease the size of the battery, to gain the other advantages (like major cost savings).  But yes, replace the “10%-20%” unscientific numbers with your favourite low-percentage threshold where somebody bites the ePlane carrot.  I would bet DZOs also won’t bite at 100% slower climb performance.

That’s what we saw happen in other electrifications.  

Anyway, the point being is that the tech fuzz zone between “Not practical” and a “ePlane climbing at full velocity to jump altitude” is actually shocking small, because of the reasons above described.  Improve the tech just enough and — bam — it’s practical without a compromise.   If we’re going to have compromises, it will only be very short-term like removing 1 or 2 or 3 passengers to meet volume/weight envelopes, but only for as long as battery tech improves even a few percent in a “we-only-need-a-battery-for-1-skydive-plus-reserve” scenario.

Anyway, I just heard back from Magnix CEO he’d be happy to be interviewed for the Parachutist article.  Now to formulate the right questions (which may also answer some of these questions too, as well as correct any details in some of my answers).

A heavier plane doesn't just climb slower, it consumes more energy to climb even if we assume 100% efficiency for the entire system. Not to mention there are also other inefficiencies of flight that would not be improved by a change to electric.

I'm not saying this isn't ever going to work, I'm only meaning to say that I don't think the scenario you posed (batteries for x minutes plus 30 weighs the same as a full load of fuel) is the obvious inflection point I think you were implying.

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Scientific fact:

It’s worth noting — ignoring airplanes — that the energy required to lift a mass X against gravity Y from height A to B — is mathematically a fixed amount of energy in the ideal case regardless of the velocity of lift from altitude A to altitude B. 

Things like friction (air friction, water friction, rolling friction, etc), acceleration/deceleration differences (at beginning/ends of the gravity journey, if acceleration energy is not recaptured), and also motor efficiencies make the gravity-lift math less ideal.

Also, for simplicity, we can effectively ignore gravity gradients (high altitudes have a tiny bit less gravity) or theory of relativity as they are not meaningful error margins at current physical speeds and current altitudes being discussed. 

Now in the case of airplanes — improve the variables (e.g. efficient flexibility of motor at all power settings) so absolute airframe & propeller efficiencies can be better milked.

A plane cannot solve all weak links breaking the ideal (friction is always with us) but it also explains the concept of less battery differential versus fuel differential — getting a tiny bit closer to the ideal formula dictated by laws of physics.

This may not be significant for some airframes but is more for others, but regardless, it’s generally possible to achieve a smaller consumption difference (% difference of slow-vs-fast altitude gain) for an electric for a given altitude gain A to B on the exact same airframe.

Edited by mdrejhon

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...I should also add that the fuel weight lightens as you burn, the battery weight does not.

But the efficiency gains over the short time period of getting to altitude are apparently significant enough to overcome that variable.  It is a big factor for longer flights, rather than the few minutes to altitude where plane lightening is often only essentially a low single-digit percentage of plane total mass, and in many cases under 1% for some fully loaded airplanes.

For the short 8 minutes to 10 minutes to altitude, plane-fueload-lightening is sufficiently small enough (as % of plane mass) that the sheer efficiency of an electric plane motor wins out, by affording pilot more flexibility to milk the airframe/prop settings instead.

A turbine can go much less efficient at certain airframe settings despite being physically airflow efficient, but RPM/torque inefficient for the turbine (burning more fuel).  Thus, the goldilocks airframe/prop settings range is smaller on the same airframe for a turbine than for an electric re-engining on the same airframe.  The electric stays efficient at a wider range of torques & RPMs, so you can work the propulsion efficiencies more physically (pitch, flaps, etc) than worrying about hitting the motor-efficiency sweet spot.

Worry about milking the laws of physics of your airplane, more than worrying about fuel buen.

The efficiency gains of optmium settings far exceeds the 1% airplane mass lightening from fuel load burn over the short timescales we’re talking about.

We lose out over avgas for longer flights, but this becomes a mathematical win-win for jump operations which are just short flights.  The assumption made for longer flights is silly as the sheer shocking short-flight efficiency of an electric flight wins out.

So battery deadweight is far less of an issue for a smaller 1-skydive-designed (+30min reserve) battery than for trying to mimic a fully 100% fueled airplane.

Edited by mdrejhon

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1 hour ago, mdrejhon said:

...I should also add that the fuel weight lightens as you burn, the battery weight does not.

That's true, and it's important, but what you seem to keep glossing over is the fact that the batteries weigh much more than the fuel they will be replacing. You posited that when the amount of batteries required for jump ops weighs the same as a full load of fuel that this would be a clear inflection point. You stated it as if it should be obvious on it's face that it's true and requires no justification because there would be no drawback. I've been refuting this because the plane would clearly be heavier, therefore there is a drawback and you need to show your work for how you've determined the advantages to so clearly outweigh this drawback. That's really all I mean to refute and the rest of the discussion between us has felt circumferential.

1 hour ago, mdrejhon said:

For the short 8 minutes to 10 minutes to altitude, plane-fueload-lightening is sufficiently small enough (as % of plane mass) that the sheer efficiency of an electric plane motor wins out, by affording pilot more flexibility to milk the airframe/prop settings instead.

Again, please show your work. You seem to be in the habit of just spouting out numbers, in this case 1%, without any indication of where these numbers come from. How much fuel does an Otter burn on a typical jump load? How much does an Otter weigh at the start of a typical jump load? This is very straightforward. If you know this information, why don't you tell us and show your work? If you don't know it, why should anyone believe your conclusions?

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After reading a story yesterday about a problem electric car makers have been dealing with another small snag comes to mind. Namely, the fire danger posed by lithium cells. They have been trying to reduce the small, but worrisome number of faulty cells that end up causing fires. I'm sure that quality control measures appropriate to aviation use can solve the problem. But that will definitely increase the cost of the batteries.  Some of the assumptions made in this thread used certain prices of cost per kw/hour for the cells. Like everything else in aviation you can likely count on tripling the price for approved cells with release tags.

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2 hours ago, gowlerk said:

Namely, the fire danger posed by lithium cells. They have been trying to reduce the small, but worrisome number of faulty cells that end up causing fires. I'm sure that quality control measures appropriate to aviation use can solve the problem. But that will definitely increase the cost of the batteries.

For the Boeing 787 they couldn't solve that problem - they had to encase the lithium batteries in a heavy steel container to contain any potential fire.

The NASA X-47 Maxwell uses LFP cells which are considered much less of a fire risk than lithium-ion. Elon Musk is also reported to be planning a change to LFP cells for Tesla cars as they're also a lot cheaper in addition to the increased fire safety, but their main issue is slightly lower energy density.

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1 minute ago, olofscience said:

For the Boeing 787 they couldn't solve that problem - they had to encase the lithium batteries in a heavy steel container to contain any potential fire.

The NASA X-47 Maxwell uses LFP cells which are considered much less of a fire risk than lithium-ion. Elon Musk is also reported to be planning a change to LFP cells for Tesla cars as they're also a lot cheaper in addition to the increased fire safety, but their main issue is slightly lower energy density.

Interesting. Lower energy density by weight, volume, or both?

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On 10/28/2020 at 2:11 AM, olofscience said:

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.

I agree with everything you said, but my point is simpler.

Drop zones have ALWAYS used old, used airplanes.  C182's and C206's, then D18's, then Porters, then Otters, then Caravans.  (The one exception I can think of is Ray's PAC750.)  They do this for one reason only - they are cheaper than new aircraft.

The same will hold for electrics.  And DZ's will use the batteries they came with for as long as they possibly can, until the pilots start refusing to fly loads because they are losing power before the last person exits.  Then there will be much wailing and gnashing of teeth, and the DZO will buy a reconditioned battery - and raise jump prices by $2 a lift.

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17 hours ago, olofscience said:

The NASA X-47 Maxwell uses LFP cells which are considered much less of a fire risk than lithium-ion. Elon Musk is also reported to be planning a change to LFP cells for Tesla cars as they're also a lot cheaper in addition to the increased fire safety, but their main issue is slightly lower energy density.

Significantly lower, actually.  LFP are about 50-70% of the energy-to-weight ratio of good lithium ions.

A second problem is that you can't use a Tesla pack and expect to get the same performance.  A Tesla pack discharges at an average rate of about C/4 - in other words you can drive about 4 hours on a full charge.  If it takes 4 hours to get to altitude no one is going to use electric planes.  People want to get to altitude in 20 minutes, and that means you are discharging at a 3C rate.  Which means you are going to get about 40% less energy out of a given pack.

You can go bigger to change that to a 2C or a 1C rate, but then you are carrying three times the weight.

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1 hour ago, billvon said:

that means you are discharging at a 3C rate

Well, despite the lower energy density, higher discharge rate is something LFP cells do better than lithium ions. In addition to having more cycles.

1 hour ago, billvon said:

You can go bigger to change that to a 2C or a 1C rate, but then you are carrying three times the weight.

For a jump aircraft yes it might take the clean sheets to actually fix this issue - the X-47 is going to test distributed electric propulsion for lowering the weight of the structure, reducing induced drag (wingtip vortices), while adhering to normal takeoff, landing, and stall speed requirements.

 

For reducing weight, I'd even go so far that for a jump aircraft, the pilot doesn't need to be onboard the aircraft. The lift can be flown by AI, with a jump pilot on the ground in a DZ control room ready to take over if the AI needs assistance. Then, they won't need a bailout rig, you'll have room for one more revenue seat, but regulatory wise it could open a can of worms - I might start another topic on this if people are interested.

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5 minutes ago, olofscience said:

For reducing weight, I'd even go so far that for a jump aircraft, the pilot doesn't need to be onboard the aircraft. The lift can be flown by AI, with a jump pilot on the ground in a DZ control room ready to take over if the AI needs assistance. Then, they won't need a bailout rig, you'll have room for one more revenue seat, but regulatory wise it could open a can of worms - I might start another topic on this if people are interested.

Maybe that will happen someday, but it's orthogonal to the electric aircraft question.

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1 minute ago, nwt said:

Maybe that will happen someday, but it's orthogonal to the electric aircraft question.

I think electrification will actually bring this question sooner to aviation - like how electric cars offered advantages in developing self-driving cars. But yes, it is a different question so I'll probably start a different forum post to discuss this.

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1 minute ago, olofscience said:

I think electrification will actually bring this question sooner to aviation - like how electric cars offered advantages in developing self-driving cars. But yes, it is a different question so I'll probably start a different forum post to discuss this.

I'll save my response for the new thread

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Back to the topic of electric aircraft then.

My main problem at the moment is MagniX hasn't released the weight or battery details for the electric caravan that flew earlier this year. If I had those numbers we'd be able to calculate many other  metrics such as climb performance, payload, etc.

Quote

As configured, the Magni500-powered Grand Caravan can carry 4-5 passengers on flights up to 100 miles, taking into account the need for reserve power, says Ganzarski.

I might be able to squeeze the numbers out of this sentence, but it's pretty annoying not having the actual numbers.

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On 11/11/2020 at 3:35 PM, nwt said:

That's true, and it's important, but what you seem to keep glossing over is the fact that the batteries weigh much more than the fuel they will be replacing. You posited that when the amount of batteries required for jump ops weighs the same as a full load of fuel that this would be a clear inflection point.

I never said that -- you remember incorrectly:

Scroll back to the post, and re-read: "That battery, today, already appear to weigh less than a full fuel load, for some aircraft specifications"

So repeating the points:

  • We only need between-load recharging of the batteries between loads;
  • We only need one skydive's worth of batteries, plus 30 minutes reserve;
  • Yes, the partial-batteries will weigh more than the equivalent partially-fueling;
  • However, the partial-batteries will weigh less than a fully fueled airplane.

For more concrete numbers, there are questions I need to ask the electric aircraft makers.  Roei (CEO of Magnix) has agreed to be interviewed for the Parachutist electric jump aircraft article I want to collaborate on -- so before I send them, I have to discuss with co-authors if they're good questions. Don't worry, I won't be publishing anything unsubstantiated in that article.

 (Additional coauthors and proofreaders welcome, contact me)

Edited by mdrejhon

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4 hours ago, billvon said:

A second problem is that you can't use a Tesla pack and expect to get the same performance.  A Tesla pack discharges at an average rate of about C/4

That assumes sustained average (steady highway speed, like level flight)

A Tesla pack can discharge at approximately 5C to 10C in Ludricious acceleration mode, and typically discharges at 2C-3C during brisk acceleration starts by regular drivers.

Yes, you heard me right -- a Tesla 100 kWh battery output more than half a megawatt!   And that's using the laptop batteries they used before the 4680 battery.

It's mainly the battery temperatures you have to worry about but the climb to altitude is short enough, with plenty of cooling opportunity afterwards during the descent.

Teslas are also used at the racetrack now, with the Racetrack Package (on the existing battery pack), which allows sustained high-C operations far longer than a jump lift.

Besides, Magnix already confirms that output is not the weak link for a fast climb to altitude.

The descent also allows enough time for the battery to cool down before being charged, assuming the use of battery cooling mechansims including good heatsinking to the wings.

The Tesla Model 3 Racetrack Package allows a Tesla to do sustained >1C output, typically 2C-3C output with automatic battery heat management -- color coded battery heat is shown on the screen during racetrack use.  That's the same Tesla battery, unmodified.  The Racetrack Mode pushes the battery very hard for much longer than a Magnix will need.

For a faster climb, you will have to size the battery for more frequent sustained 750hp (500kW) to use the full power of the Magnix, but it's quite within the realm of today's batteries. 

A Cessna Caravan accomodates about 2224lbs of fuel.  One Tesla battery pack (capable of 750 kW surge output) is only 1000lbs-1400lbs.  (List of Tesla battery weights, including cooling systems). 

The older P100D (100kWh) battery pack was 1380 pounds using the laptop 18650 batteies capable ot outputting half a megawatt aggregate in Ludricious Mode -- but the 2170 battery based ones were lighter, and now newer Tesla 100kWh batteries using the 4680s are reportedly far closer to 1000 pounds for 100 kilowatt hours including cooling.

Obviously, it is not an apples-vs-apples, but the point being is -- batteries lighter than the fuel load is capable of fully powering a Magnix motor -- including the weight of water cooling.  Now that specific doubt out of the way:

If they design to instead heatsink to the airframe with a bit lighter water cooling, then some weight savings can be had, given the higher airspeeds of colder air at altitude (precisely where the battery begins to heat up -- a while after takeoff and on a fast climb to cold altitude). 

Perhaps it pushes today's batteries hard, but 750kW is definitely within the envelope of "Tesla style" battery architectures -- though one may want to upsize by 2x while including the water cooling that Tesla battery packs use -- to allowed about 5 minutes of sustained 750kW.  But even airplanes don't always sustain maximum horsepower for 100% of the climb, as pilots often taper that of a bit after the takeoff roll, for turbine longevity purposes (so not all 900hp is all in use for the entire duration of climb to altitude).  

But you see, the "C" problem is already actually mostly solved -- however, battery longevity might be down (e.g. like maybe too few flights -- i.e. only 3-5 years of flights) until upsized a bit -- though the improvements made by 4680's longevity and other similar lithium battery technologies by others (competitors propelled by Tesla innovations).

One problem is that Tesla is a bit ahead of competitors in charge management and battery heat management.  It's a bit hard to get large off-the-shelf lithium batteries that can charge/discharge as fast as a Tesla battery (multiple C) without longevity-shortening effects.  

With the great battery management they use to detect and isolate bad cells within packs -- the Tesla battery management systems behaves like many thousands of concurrent battery chargers.  Such technology is now being introduced into other batteries  The cooling tech is part why batteries last longer in many electric cars longer than the batteries in R/C airplanes.

That said, battery technology is improving extremely rapidly. Over the course of 2020-2030 will solve any remaining "C" problem (heating, cooling, supercharging, easier to downsize battery, etc) of a one-skydive-sized battery that doesn't need to be bigger/heavier than it needs to be.   

However, the suitable jump plane electric motor is already here, and it should be tested/experimented by pilots for simulated jump ops.   Tests can be done while the skydiving world awaits jump operations.

See my Advocacy post.

Edited by mdrejhon

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10 minutes ago, mdrejhon said:

I never said that -- you remember incorrectly:

Scroll back to the post, and re-read: "That battery, today, already appear to weigh less than a full fuel load, for some aircraft specifications"

This is an inconsequential semantic difference that doesn't change anything about the discussion we've been having.

Performance of today's Otters at the weights anticipated would be useful information.

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