Electric Airplanes?

[frfly172]

So I buy an electric airplane, then I have to find charging stations. Can only imagine the charges this FBO will inflict on the aircraft owner.

 

[Flybuddy]

So I buy an electric airplane, then I have to find charging stations. Can only imagine the charges this FBO will inflict on the aircraft owner.

Signature is probably already working on a brochure titled "Charges for your Charges"

Seriously, the Tesla Supercharging stations can do a 75KW pack to 100% in less than an hour. The OP was calculating for 5 hours of flight which is pretty much unattainable with current tech. The 75kw pack weighs over 1000 lbs. That's still pretty heavy even considering losing about half that weight in fuel and engine.
So a fairly heavy 2 seater with an hour + range might be possible along with a 1 hour wait at destination. If your mission is training or flying for breakfast/lunch, it just might work, although we would have to rename the $100 burger.

 

[GeorgeC]

I was in California a couple of weeks back and thought the sun shades they built over parking lots was interesting. I noticed they not only shaded the cars, but produced electricity, too.

I got an Uber driver who was in the solar industry, sounds like if you have land, they have money to put down panels.

Airports have land. I keep wondering about shade hangars with PV on top being a double source of revenue for smaller fields...

Potential taxation benefits aside, my understanding is that utilities would prefer local power rather than having to buy it from a neighboring utility, and solar is a means to that end. Maybe someone else can enlighten us on that aspect.

 

[RyanShort1]

I got an Uber driver who was in the solar industry, sounds like if you have land, they have money to put down panels.

Airports have land. I keep wondering about shade hangars with PV on top being a double source of revenue for smaller fields...

Potential taxation benefits aside, my understanding is that utilities would prefer local power rather than having to buy it from a neighboring utility, and solar is a means to that end. Maybe someone else can enlighten us on that aspect.

That’s true, and the less distance to transport the electricity the better. Reducing the oil dependency is good for national security, so I’m personally for the idea of more people going solar.

 

[tspear]

Signature is probably already working on a brochure titled "Charges for your Charges"

Seriously, the Tesla Supercharging stations can do a 75KW pack to 100% in less than an hour. The OP was calculating for 5 hours of flight which is pretty much unattainable with current tech. The 75kw pack weighs over 1000 lbs. That's still pretty heavy even considering losing about half that weight in fuel and engine.
So a fairly heavy 2 seater with an hour + range might be possible along with a 1 hour wait at destination. If your mission is training or flying for breakfast/lunch, it just might work, although we would have to rename the $100 burger.

The problem with al the math I have basically seen is it assumes a straight conversion of an existing model to electric. Just like cars, they are generally significantly more aerodynamic than gas counter parts. e.g. a lot less cooling drag. Until some samples are built that are optimized for electric, we really have no baseline to compare.

Tim

 

[Stephen Poole]

The problem with al the math I have basically seen is it assumes a straight conversion of an existing model to electric. Just like cars, they are generally significantly more aerodynamic than gas counter parts. e.g. a lot less cooling drag. Until some samples are built that are optimized for electric, we really have no baseline to compare.

There are many experimental electric airplanes that are flying right now, generating good, hard numbers. (Hint: I didn't pull that "100HP" figure out of thin air.) The aerodynamics are also quite well understood. Mooney gained its reputation for speed many decades ago by making the airframe more "slippery." A more recent example, the high-wing Pipistrel Virus LSA, is actually capable of well over 140 knots with 80-100HP, and can be ordered with optional speed brakes to help people land the thing on shorter fields.

As for the other comments here, I enjoyed reading them. I still don't think the numbers work for MASS (<-that's the key) use of solar power to charge a bunch of airplanes. One or two at a time, maybe. Statements like, "My grandaddy's mayonnaise farm runs off o' solar!" don't change the math, or improve the problem. 100 HP, chosen as a number to play with, is about 75KW. If you want to fly for an hour, then even assuming perfect efficiency during the charging process (and no reserve for flying), you'll need 75KW hours of juice to put into the batteries. No way around it.

Assume that the plane can actually cruise with only a fraction of that -- say, 50%, or 37.5KW. Fine. You've increased range to 2 hours of flying with no reserve.

Multiply that by an all-electric fleet, which some people apparently believe is actually possible, and you'll see the problem. We will need a BUNCH of new generating capacity, and only a small percentage can be done with solar or wind.

As Prez Obama said to Romney during the debate, "it's math."

 

[Seanaldinho]

I think they are a cool toy, but a long way from mainstream. Lots of torque could turn a big prop slowly making it efficient.
Of course, infrastructure is a big deal. on a side note, I just got a quote for a solar installation for my house. my total out-of-pocket expense (with incentives) is around $4,000 and it saves me $1900 a year in utilities. In addition, I can charge my electric car for free. That's a pretty good return on investment.
With this kind of incentive and small investment, any FBO would be able to add this to their place. Effectively making charging aircraft free. The airfraft owner would of course be charged, but for the FBO it would be almost an infinite return on investment.
Picture this: pull into the FBO, plug in, grab a courtesy car and go get food, come back in the plane is full.
Who knows, maybe it's not so far off in the future after all.


Sent from my Pixel 2 XL using Tapatalk

What FBOs do you know of with that kind of extra acreage laying around?

 

[Tantalum]

I just got a quote for a solar installation for my house. my total out-of-pocket expense (with incentives) is around $4,000

Damn! You're lucky man. I paid $33,000 for mine back in 2014, it was a 6,000 KW solar system but I typically say between 4K and 5K for output. I got $10K back on my taxes as an incentive but that still means it was a $23K install.. not cheap

I know there are plenty of engineering/techie types here, and I wondered what all y'all thought. I know that some of you will see the latest Gee-Whiz electric aircraft at Oshkosh. That got me thinking.

I've definitely thought about it too. There some legitimate advantages to electric power (CO2 emissions aside) since the motors are much smaller and lighter you can seriously optimize where you place the engine(s) and propellers.. fuel management can be simplified and fuel (er) battery weight can be optimized through the aircraft since those are fixed and will not change and disrupt CG ranges, etc. The machines are quiter, and in theory could not use any energy while on the ground, waiting for a clearance, etc. I also agree that the legacy fleet of C172 and Archers don't make a good litmus for electric viability and those planes were built around ICE

But assume that someone works a miracle and develops a battery that can store gobs and gobs of juice, that will be lightweight, and (biggest miracle of all), reasonably-priced. The way I see it, there's still a BIG problem: physics ... as in, you can't cheat 'im. You have to fill the batteries with energy before you can pull watt #1 from it.

That's the biggest obstacle. We are hard limited by physics. People are hopefully for some kind of miracle break through, but we are pushing the boundaries of what chemistry allows us to do already as it is.. our batteries in the Tesla, Volt, etc., are babysat and still occasionally melt down. The energy storage density of a battery is simply not physically possible. There's more hope that we can find a gravity defying machine (a la Bob Lazar) vs creating batteries with comparable energy density to fossil fuels

Granted, Airbus' flying proof of concept design was pretty cool:

 

[Tantalum]

Can only imagine the charges this FBO will inflict on the aircraft owner

Presumably they'd keep it competitive with whatever they charge for AvGas by some factor..? Granted, you likely will not have the luxury of a 10 minute self service fill up. Now have the top of the wings be solar panels.. and if you don't fly your plane for a few weeks you may end up with a free charge. My dad keeps the 4 marine deep cycle house batteries on his sailboat charged by one solar panel that is attached to the top of the bimini

regeneration on descent

People often say this.. but how often are you actually descending with the engine at idle, and then wishing you had more braking action? And unlike a car where you are constantly decelerating at a rapid rate, a plane doesn't operate like that.. I doubt you could earn back any meaningful juice on descent.. and when IFR anyway you won't have the privelege of big open unrestricted descents. It's likely more efficient to do an idle descent in an electric plane with prop feathered as opposed to using the energy to stay high longer only to regenerate it on the way down in a monster descent. Remember, nothing free in physics..

My opinion is that right now, what I'll call "boost hybrids" make the most sense. Enough combustion power for all normal operations, but an electrical boost system for takeoff, go around, and other situations where you need extra HP for a few minutes.

Theoretically sound, but now you're adding at least 500 lbs to the plane for some boosting power.. you are better off putting a more efficient power plant in there. And most planes cruise near 75% power anyway.. so adding that weight to get up to cruise a little faster just doesn't really seem in practice to make sense. I know some makers are toying with this, but I think until its proven out in practice that's a hard hill to climb

 

[JOhnH]

Doesn’t all of this make a good case for hybrids? The energy density of gas or diesel and existing infrastructure, reduced noise and increased reliability of the main propulsion motor, regeneration on descent, . . .

Somebody do the napkin math on that.

My thought is that a hybrid would create more complexity, more maintenance issues and more expense. The weight of the engine and fuel would probably be better served as extra batteries.

And I really do believe that MUCH better batteries are not too far in the future.

 

[tspear]

There are many experimental electric airplanes that are flying right now, generating good, hard numbers. (Hint: I didn't pull that "100HP" figure out of thin air.) The aerodynamics are also quite well understood. Mooney gained its reputation for speed many decades ago by making the airframe more "slippery." A more recent example, the high-wing Pipistrel Virus LSA, is actually capable of well over 140 knots with 80-100HP, and can be ordered with optional speed brakes to help people land the thing on shorter fields.

That is a conversion. My point was compare to a dedicated electric version; it does not yet exist. ICE design forces many compromises; for example fuel burn affects CG. To help manage needing a wide CG range caused by fuel burn plus crew/passengers/cargo the designed generally increases the down force capability of the tail. Increasing the down force causes additional drag. Look at the nose of the plane, large cooling area, fairly flat or aggressive expansion into the cockpit... The list goes on. Each aspect adds power requirements. This is what I mean by planes not yet designed for electric. It will likely be a decade or more before engineers even know what questions to ask. I am not an engineer and I have managed to ask a couple of companies that are building electric aircraft questions about how/why they did something and they could not answer except that it is how it is always done.

As for the math; yeah it is brutal. The only practical solution like I stated before will be local energy storage; the transmission and distribution lines just do not exist. And the "last mile" will incur massive costs to overcome; much more so than the generating capacity problems.

Tim

 

[tspear]

Theoretically sound, but now you're adding at least 500 lbs to the plane for some boosting power.. you are better off putting a more efficient power plant in there. And most planes cruise near 75% power anyway.. so adding that weight to get up to cruise a little faster just doesn't really seem in practice to make sense. I know some makers are toying with this, but I think until its proven out in practice that's a hard hill to climb

I keep seeing people state 75%. However, only people I know who push that hard are the semi serious cross country haulers. And that is a rather small percentage of the fleet. I know my N/A SR22 we often fly between 55-60% sometimes as low as 50%. This just a simple matter of altitude reducing the available power plus pulling back just a touch on short flights.

Tim

 

[Brad Smith]

All of us reading this thread will die of old age before useful electric aircraft become the norm. Sorry for the negative comment, but it’s the truth.

 

[Bacho]

As far as GA is concerned, an electric charging grid is peanuts compared to electric car charging ambitions. Electric cars will become wide spread first. Charging stations at FBOs will not be an issue IMO. Of course much larger problems remain unsolved.

 

[Old97]

I am not an engineer and I have managed to ask a couple of companies that are building electric aircraft questions about how/why they did something and they could not answer except that it is how it is always done.

Well I can answer that. Because changing things costs money, time, energy, and has risk. Its about 1000 times easier to just says words in the air than it is to put it on paper, make sure its right, and be responsible for the engineering.

Asked another way, how many things do you want to change at once? If something doesn’t work, which change is causing the problem?

 

[JOhnH]

As far as GA is concerned, an electric charging grid is peanuts compared to electric car charging ambitions. Electric cars will become wide spread first. Charging stations at FBOs will not be an issue IMO. Of course much larger problems remain unsolved.

I'm not disputing that, but you have to consider that between airports you might have a hundred gas stations (or ground based charging stations in the future). Each ground based stations would only have to supply a fraction of the power that a few airport based charging stations would.

But until we break ground on some new battery technology, I agree that electric airplanes will be a tiny niche; basically research vehicles.

 

[tspear]

I'm not disputing that, but you have to consider that between airports you might have a hundred gas stations (or ground based charging stations in the future). Each ground based stations would only have to supply a fraction of the power that a few airport based charging stations would.

But until we break ground on some new battery technology, I agree that electric airplanes will be a tiny niche; basically research vehicles.

Actually I think there is a very good chance trainers will switch very soon. The Pipestrel two seat electric trainer is close, Sunflyer seems to hit the numbers for most flight schools. It will only take a couple of years to prove out. At which point the cert factories will make the jump


Tim

Sent from my SM-J737T using Tapatalk

 

[bflynn]

There are many experimental electric airplanes that are flying right now, generating good, hard numbers. (Hint: I didn't pull that "100HP" figure out of thin air.)

The eFlyer (previous Sun Flyer by Bye Aero) uses a 115hp/90kw engine on a 2000 lb frame. The battery has 260w/kg density. They're talking 3 hours duration, with max capabilities 1000 ft/mi climb and 135 kts. Of course, like any electric thing, running it at top speed will drain the battery much, much faster. I suspect the 3 hours duration is at a 65% power setting in cruise, so maybe 2 hours. Still don't know the price, but I have heard or read it reported at > $500,000 (yikes).

 

[sarangan]

Yeah, that's probably what will end up happening. I look at it the opposite from you: I'd use the energy density of petroleum for takeoff power, then cruise with electric.

The way my crazy mind works, one of the first things that impressed me here is how pilots are in tune with the energy usage in flight. "I cruise at 55%, using X gallons per hour." Think that if you could cruise on electric at that 55% or 70%, you're using less.

Ah, my mind is warped, anyway. Always has been.

Even worse, I truly enjoy it. Not really proud of it, though.

I am actually surprised that hybrid cars are as reliable as they are. Most pistons are direct drive, mostly for reliability than for efficiency. Connecting two power plants to the same crank shaft sounds to me like a technology with many weak links.

 

[Tantalum]

I keep seeing people state 75%. However, only people I know who push that hard are the semi serious cross country haulers. And that is a rather small percentage of the fleet. I know my N/A SR22 we often fly between 55-60% sometimes as low as 50%. This just a simple matter of altitude reducing the available power plus pulling back just a touch on short flights.

This is true, but wouldn't one of the appeals of electric power be the ability to maintain rated power up throughout the altitudes, sort of like a turbo? As far as hybrids, I'm not sure I'm understanding how it makes sense in a plane.. are people suggesting a smaller main power plant that will run at basically WOT and then a battery booster pack to get you up to altitude? Feels like we're adding weight to something that is already very weight sensitive and not getting much out of it

 

[flyingbrit]

Now: consider the average FBO. If he/she only has to charge one plane every now and then, meh, maybe it's not a big deal. But if there are several planes on the ramp, each needing a 240V, 40A service to charge in any rational amount of time, that's going to require some very expensive electrical work (and probably a major upgrade to the utility service).

I haven't seen one in person but I'm guessing the typical small airport has a fairly substantial electrical system. For example at my home drone there are about 150 T-hangars each with 120V/20A service. That's a total of 3000A, or 1500A with a 240V split phase system just for the T-hangars. Allowing for 3 larger buildings plus the runway lights then a 240V/2000A service entrance does not seem unreasonable. Given this, providing a few 240V/40A charging stations does not seem like a huge hurdle.

 

[RyanShort1]

My guess is at the rate the aircraft would sell, two charging stations would likely be sufficient... so how much solar would you need for that?

 

[tspear]

This is true, but wouldn't one of the appeals of electric power be the ability to maintain rated power up throughout the altitudes, sort of like a turbo? As far as hybrids, I'm not sure I'm understanding how it makes sense in a plane.. are people suggesting a smaller main power plant that will run at basically WOT and then a battery booster pack to get you up to altitude? Feels like we're adding weight to something that is already very weight sensitive and not getting much out of it

Some of the early stuff I saw on Pipestrel Hybrid Panthera was the generator did not make fast cruise power. Basically the generator was to increase the energy density to the point where you could meet the mission.

Tim

Sent from my SM-J737T using Tapatalk

 

[Tantalum]

Basically the generator was to increase the energy density to the point where you could meet the mission

Thanks.. tantalizing stuff for sure. Still lost on how using batteries (which have a lower energy density than fossil fuels) to increase the net energy density makes sense... unless you can overcome that through the efficiency losses of an ICE.. which are absurdly high, something like 60% to 80% of the energy in fossil fuel is "lost" in an ICE by the time it comes to moving the plane forward

Also makes you appreciated how efficient nature is. A horse eats some dry grass and it's the picture of pure muscle and performance.

 

[tspear]

Easy. The battery allows for the hamburger run, basically 100 miles or 30 minutes of flying if memory serves.
You only enable the generator when going farther.
Go fast mode was limited to something like two hours. About 450 miles...


Tim

Sent from my SM-J737T using Tapatalk

 

[Tantalum]

Easy. The battery allows for the hamburger run, basically 100 miles or 30 minutes of flying if memory serves.
You only enable the generator when going farther.
Go fast mode was limited to something like two hours. About 450 miles...


Tim

Sent from my SM-J737T using Tapatalk

Okay, but how much weight and useful did I sacrifice sacrifice for that free-but-not-really hamburger meal close by

I'm sure there's a use case for it somewhere I'm just not really seeing it yet

 

[flyingbrit]

Also makes you appreciated how efficient nature is. A horse eats some dry grass and it's the picture of pure muscle and performance.

Except the horse weighs about 1000 lbs and only generates one horse power. Not so efficient from that point of view.

 

[schmookeeg]

We're on our second electric car (a BMW i3), and our usage patterns are pretty non-intensive (nee "ideal" for an EV). Neither of us commute, so it's our "grocery getter". We only charge it with a 120V charger, which adds 4 miles per hour of charge. I think it has a max draw of 12 Amps. It has a 120 mile range when full, so it needs 30 hours to go from 0 to hero. Very, very rarely, will we use the onboard generator ("Range Extender"). If this was not enough, I could install a 240V/40A charger in my home.

Mapping this to the plane: I've flown the plane 9 hours this month. That means it has sat idle for about 710 hours.

Let's even go all out and do math on the 600hp. (Play along, I may make an error here )

At 750W per hp, this month I used 9 hours x 600hp x 750W = 4 Million WHr or 4,000 kWh

At 120V/12A, or 1.4kW, I'd need 2,857 hours. Oops.

At 240V/40A ,or 9.6kWh, I'd need 416 hours of charge.

So Barons need "Level 2" Charging.

...

Weight-of-batteries problem aside, if I have a hangar lease, and I have a 120V outlet in my hangar that my landlord pays the electricity for, well, it looks like I could charge about 1,000 kWh of airplane on his dime each month. With a 150hp motor, that's ~8 hours per month of free flying.

That's 100 hours per year of a C172/PA28-class plane.

I think that's typical usage of most plane owners, no?

 

[JOhnH]

We're on our second electric car (a BMW i3), and our usage patterns are pretty non-intensive (nee "ideal" for an EV). Neither of us commute, so it's our "grocery getter". We only charge it with a 120V charger, which adds 4 miles per hour of charge. I think it has a max draw of 12 Amps. It has a 120 mile range when full, so it needs 30 hours to go from 0 to hero. Very, very rarely, will we use the onboard generator ("Range Extender"). If this was not enough, I could install a 240V/40A charger in my home.

Mapping this to the plane: I've flown the plane 9 hours this month. That means it has sat idle for about 710 hours.

Let's even go all out and do math on the 600hp. (Play along, I may make an error here )

At 750W per hp, this month I used 9 hours x 600hp x 750W = 4 Million WHr or 4,000 kWh

At 120V/12A, or 1.4kW, I'd need 2,857 hours. Oops.

At 240V/40A ,or 9.6kWh, I'd need 416 hours of charge.

So Barons need "Level 2" Charging.

...

Weight-of-batteries problem aside, if I have a hangar lease, and I have a 120V outlet in my hangar that my landlord pays the electricity for, well, it looks like I could charge about 1,000 kWh of airplane on his dime each month. With a 150hp motor, that's ~8 hours per month of free flying.

That's 100 hours per year of a C172/PA28-class plane.

I think that's typical usage of most plane owners, no?

That might work for a few people, if they are willing to fly on their batteries charge schedule and not one of their own choosing.

 

[tspear]

That's 100 hours per year of a C172/PA28-class plane.

I think that's typical usage of most plane owners, no?

I believe that is rather high; assuming memory works it is actually around 75 hours a year on the plane is average and 35 hours for the pilots.

Tim

 

[tspear]

Okay, but how much weight and useful did I sacrifice sacrifice for that free-but-not-really hamburger meal close by

I'm sure there's a use case for it somewhere I'm just not really seeing it yet

Pipistrel said the full fuel use fuel load was supposed to be about the same between the gas, hybrid and battery. All were supposed to fly at the same speeds; the delta was the range.
They would never give me hard numbers though. Going through my logbook for the past year, if I had a plane which could fly about 150 miles or less (many around 75), recharge in about five hours and fly home this would cover almost 2/3 of my flights. The problem is the other third; they are 550 to 600 miles; with one exception at 300. So, if the math works, the hybrid is a great stepping solution for someone like me. Where the pure battery does not have quite the range, but the plug-in aspect of the battery does cover a huge percentage of flights.

Tim

 

[Flybuddy]

I have a 2nd gen Chevy Volt...It always shows power usage and is VERY accurate. At 40 mph it uses around 6kw of power. I don't get the 750 watt per hp number. if that's true then I'm only using 8hp to go 40 mph?

 

[jsstevens]

I have a 2nd gen Chevy Volt...It always shows power usage and is VERY accurate. At 40 mph it uses around 6kw of power. I don't get the 750 watt per hp number. if that's true then I'm only using 8hp to go 40 mph?

To sustain 40mph? Probably.

 

[Tantalum]

only generates one horse power

Actually.. the term "horsepower" is dubious at best.. when rigged up with pulleys, etc., a horse actually generates about 15 hoursepower, this has been proven and is a very common misconception.. and a person can product up to 4-6 hoursepower at peak output. Plus the weight of the machine is less important in my analogy. The point was a relatively low caloric intake. One pound of hay is equivalent to 900 calories. One pound of gasoline has 5,200 calories.

 

[jsstevens]

Actually.. the term "horsepower" is dubious at best.. when rigged up with pulleys, etc., a horse actually generates about 15 hoursepower, this has been proven and is a very common misconception.. and a person can product up to 4-6 hoursepower at peak output. Plus the weight of the machine is less important in my analogy. The point was a relatively low caloric intake. One pound of hay is equivalent to 900 calories. One pound of gasoline has 5,200 calories.

No wonder my diet isn't working...

 

[Tantalum]

8hp to go 40 mph

Yes. Some old cars had a PEAK hp of about 20 hp and could cruise at 40 mph no problem. I rigged up my FJ Cruiser with some cool electronics that reads data off the computer real time, showing watts, hp, and torque (not at wheels)... to cruise on the highway in a big boxy aerodynamically dragged ugly car with 33 inch mud tires and a lift requires about 35 hp. That directionally feels correct that your lighter, smaller, FAR more efficient car aerodynamically going slower will only require 8hp, or about a fifth of the power.

 

[Tantalum]

Pipistrel said the full fuel use fuel load was supposed to be about the same between the gas, hybrid and battery. All were supposed to fly at the same speeds; the delta was the range.
They would never give me hard numbers though. Going through my logbook for the past year, if I had a plane which could fly about 150 miles or less (many around 75), recharge in about five hours and fly home this would cover almost 2/3 of my flights. The problem is the other third; they are 550 to 600 miles; with one exception at 300. So, if the math works, the hybrid is a great stepping solution for someone like me. Where the pure battery does not have quite the range, but the plug-in aspect of the battery does cover a huge percentage of flights.

Tim

It's definitely cool stuff. I'm skeptical (as you can tell) but I welcome the advancement

 

[flyingbrit]

Actually.. the term "horsepower" is dubious at best.. when rigged up with pulleys, etc., a horse actually generates about 15 hoursepower, this has been proven and is a very common misconception.. and a person can product up to 4-6 hoursepower at peak output. Plus the weight of the machine is less important in my analogy. The point was a relatively low caloric intake. One pound of hay is equivalent to 900 calories. One pound of gasoline has 5,200 calories.

Perhaps the Kentucky Derby horses generate 15 hp for the race duration of around 2 minutes. However James Watt's horse power unit was based on draft horses working 8 hours per day. If a customer had six horses working at pumping water out of a mine he would sell them a 6 hp engine.

The horses' caloric intake is not that low in reality. It takes about 20 lbs of hay per day to feed a 1000 lb horse, or 18,000 calories. This is equivalent to 3-1/2 gallons of gas, or about 21 lbs. A typical 4 stroke gas engine would produce about 42 hp-hrs of work from this. A James Watt horse would only produce 8 hp-hrs.

Another data point: A stage coach with 4 horses would travel at perhaps 8 mph on a good road. This sounds more like 4 hp than 60, doesn't it?

 

[Tantalum]

Perhaps the Kentucky Derby horses generate 15 hp for the race duration of around 2 minutes. However James Watt's horse power unit was based on draft horses working 8 hours per day. If a customer had six horses working at pumping water out of a mine he would sell them a 6 hp engine.

The horses' caloric intake is not that low in reality. It takes about 20 lbs of hay per day to feed a 1000 lb horse, or 18,000 calories. This is equivalent to 3-1/2 gallons of gas, or about 21 lbs. A typical 4 stroke gas engine would produce about 42 hp-hrs of work from this. A James Watt horse would only produce 8 hp-hrs.

Another data point: A stage coach with 4 horses would travel at perhaps 8 mph on a good road. This sounds more like 4 hp than 60, doesn't it?

And most engines aren't ran flat out either, those 4 horses working all day likely aren't at full sprint either.. realistically 25% - 35% of what they can do compared to a sprint

Take the typical adult for example.. a 2,000 calorie/day diet would likely require more than half a pound of gas (0.08 gallons) if we mechanized our processes with an ICE.. given that 1 gallon of gas (6lb) is >30,000 calories. Nevermind that your body is also keeping internal organs functioning, homeostatic temperature, etc.

A study at USCD showed the efficiency of a human body around 25%, that's not bad considering that we're ultimately just recycling (okay, converting for the pedants) energy that ultimately originated from the sun. If you think about it, our fossil fuel is, ultimately, a form of solar energy since that started with organic matter

More an interesting data observation than a point worth arguing over.

 

[schmookeeg]

That might work for a few people, if they are willing to fly on their batteries charge schedule and not one of their own choosing.

A few? It sounds like it'd work for most of the pilot population?

If the "stolen from my landlord" L1 schedule is no good, an L2 charger would give you 10X the flying, 80 hours per month. That's flight school volume now.

The other side of the equation is the energy cost. I'm in a "cheap electricity" state at 8 or so cents per kWh, but even at 20c/kWh, an hour of "172 class" flying is 125kWh, or $25. Compared with $40 in avgas, and the removal of an entire category of engine maintenance.

It's tantalizing enough that I assume I F'ed up the math somewhere, but not sure where.