Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Australia's first electric aircraft has begun test flights

abc.net.au

Post reply on HN
Print view View original

71–79 of 79 posts

Re: Australia's first electric aircraft has begun test flights

#71

Post by chrismorgan »

chrismorgan wrote: post #38
scoggs wrote: post #19

Earlier quoted context omitted.

Very cool, right? I had a brain fart when I read the title on the front page thinking it was a self-driving electric plane, for some odd reason, and my heart skipped a beat. >It costs about $3 an hour to run the plane's engine, one-tenth the cost of a fuel engine. This sounds really great and at only €65,000 ($78196.30USD) it sounds like a steal that will scale nicely once it can carry the 5+ passengers it intends to…

Where’s the €65,000 number coming from? I found http://www.flypipistrel.com/price-lists/PIPISTREL-ALPHA-ELEC... which suggests €159,000. That datasheet also says 700 cycles to 75% battery capacity, rather than the “about 1,000” of this article. The $3/hour figure doesn’t seem to me to match the other numbers, either: 60kW for takeoff and 20kW for cruising; let’s ignore takeoff (it’s rounding error) and just call it 2…

Further to the running costs: if replacing battery cells worn out by 700 one-hour-flight cycles costs €12,000 (again citing http://www.flypipistrel.com/price-lists/PIPISTREL-ALPHA-ELEC...), that’s €17.14/hour, which is over AU$26.

So if you consider that to be a “fuel cost” (seems reasonable to me), then your “$3 an hour to run the plane's engine” has multiplied by ten—so much for “one-tenth the cost of a fuel engine”! (Yes, to make the comparison fair we need to factor engine maintenance costs into it, which can reasonably be expected to fall in the electric motor’s favour, but I don’t care to speculate how it may balance out this matter of the battery cost.)

Re: Australia's first electric aircraft has begun test flights

#72

Post by totalZero »

chrismorgan wrote: post #70
totalZero wrote: post #55

I look forward to the day when solar panels are efficient enough that an aircraft can appreciably recharge its batteries while gliding.

I looked for a figure and found this suggestion for sunny days: 800W/m². If the plane uses 20kW while flying, this would mean you’d need 25m² of 100% efficiency solar panels to fly without draining the battery. 10.5m wing span, depth uncertain but looks to be under a metre, and we’re not even halfway there. The fuselage isn’t suitable for a solar array. The tail, maybe a bit. Verdict: ignoring solar panel mass and fr…

Some numbers from the conventional-engine version: http://pipistrel-usa.com/models/alpha-trainer-tech.html

The wing area for this aircraft is 9.29m^2, and the glide ratio is 17:1 at 74mph. Let's say you fly for an hour and then glide through a descent of 12,000 feet (ceiling is 18,000 at max weight). That gives you about 90 minutes of solar absorption time.

Assume we only fly at noon on clear sunny days to get 1kW/m^2 of solar energy (nice round number). That's 13.9kWh of incident energy on the wings. If we can capture that at 25% efficiency -- today's best commercial cells are around here, although about twice the efficiency has been achieved by researchers -- it's 10.5 minutes of additional powered flight, or about 3 minutes of climb. (I think that 3 minutes of climb yields an added 3660 ft of altitude or 11 minutes of glide.)

4kW from propeller generation during the glide phase yields another 6 minutes of powered flight.

I agree with your conclusion for this particular aircraft's geometry; it's not enough to sustain flight indefinitely. Still, other solar aircraft have demonstrated that sustained solar flight of manned aircraft is possible, and one such aircraft, Solar Impulse 2, has even circumnavigated the globe (albeit interrupted by a few stops along the way).

Re: Australia's first electric aircraft has begun test flights

#73

Post by chrismorgan »

totalZero wrote: post #72
chrismorgan wrote: post #70

Earlier quoted context omitted.

I looked for a figure and found this suggestion for sunny days: 800W/m². If the plane uses 20kW while flying, this would mean you’d need 25m² of 100% efficiency solar panels to fly without draining the battery. 10.5m wing span, depth uncertain but looks to be under a metre, and we’re not even halfway there. The fuselage isn’t suitable for a solar array. The tail, maybe a bit. Verdict: ignoring solar panel mass and fr…

Some numbers from the conventional-engine version: http://pipistrel-usa.com/models/alpha-trainer-tech.html The wing area for this aircraft is 9.29m^2, and the glide ratio is 17:1 at 74mph. Let's say you fly for an hour and then glide through a descent of 12,000 feet (ceiling is 18,000 at max weight). That gives you about 90 minutes of solar absorption time. Assume we only fly at noon on clear sunny days to get 1kW/m^…

That all sounds about right, except for the generation part (see below) which is but a minor factor anyway.

Indefinite solar-powered flight is understandably not a goal of Pipistrel for this craft; it will be interesting once it gets to the point where it’s a more commercially feasible design goal.

I love how you rounded up to 1kW/m² to get a nice round number, then multiplied by 13.9!

It’s worth noting on the propeller generation point that it’s going to be more efficient not to use it if you’re trying to maximise range: it will diminish your glide ratio; it’s mostly for when you actively want to go down, and might as well retrieve and store most of the lost kinetic energy. If the Trainer gets 17:1, I’d expect the Electro would get roughly that 17:1 if merely idling, but lower if regenerating; I don’t care to speculate on the numbers—I’m not a pilot or an electric car expert and it’ll take me too long to calculate the actual energy rates involved. But physics more or less decrees that it can’t regenerate more power than it will take to regain the additional lost altitude. (I say only “more or less” because of things like gravity assist manoeuvres, which are fascinating but not applicable to craft like this.)

I was rather sloppy in the way I brought the regeneration up in my earlier comment. It was true, but not relevant because of this last paragraph. I didn’t think it through when I mentioned it at first.

Re: Australia's first electric aircraft has begun test flights

#74

Post by dogma1138 »

bobsil1 wrote: post #68
dogma1138 wrote: post #65

Earlier quoted context omitted.

It doesn’t work like that there are more “denser” batteries than what Tesla uses, their density isn’t that impressive while they benefit from it its not something they are driving. P.S. Drones use LiPo batteries.

They're driving down mass-market LiIon specific energy cost ($ per Wh/kg) via Gigafactory. No?

They are reducing the cost of Wh/Kg maybe but they are not necessarily increasing the Wh/Kg ratio Tesla isn’t pushing for super high density.

The cost isn’t the issue here it’s the weight a Tesla battery pack is heavy as fuck and Tesla really hasn’t worked that much on reducing its actual weight because there are easier paths to make a car lighter.

Drones use LiPos because at these scales LiIon isn’t viable.

Re: Australia's first electric aircraft has begun test flights

#75

Post by pkolaczk »

wallace_f wrote: post #42
pkolaczk wrote: post #21

Earlier quoted context omitted.

Typical coal power plants have practical electric efficiency 40% but total energy efficiency is 60-70%, because they produce electricity and useful heat . Also 40% is a theoretical (lab) value for a non turbocharged diesel engine - in practice most engines are operated out of their optimal range, they are turbocharged (a turbo increases power output at the cost of decreasing compression ratio and thermal efficiency),…

Are you sure about your statement on turbos reducing efficiency? Some of the most economical consumer engines are turbocharged--in fact auto makers commonly cite mpgs as a reason to use turbos; so I am confused.

Yes. Turbocharging increases mpg not by increasing thermal efficiency, but by allowing to use a smaller and lighter engine. A lighter engine means less mass to accelerate, therefore less energy to spend. A smaller engine means less internal friction so less energy lost. However this theory works well if you actually don't use the full power that turbo gives you, or you use it only occasionally. These engines have great advantage in lab mpg tests, but in real dynamic driving the advantage diminishes. The main problem is that by adding a turbo, you need to decrease the compression ratio of the engine, which decreases thermal efficiency. Another thing is that turbo needs some energy to be powered, and also has some of its own energy losses. This is not free.

Re: Australia's first electric aircraft has begun test flights

#76

Post by totalZero »

chrismorgan wrote: post #73
totalZero wrote: post #72

Earlier quoted context omitted.

Some numbers from the conventional-engine version: http://pipistrel-usa.com/models/alpha-trainer-tech.html The wing area for this aircraft is 9.29m^2, and the glide ratio is 17:1 at 74mph. Let's say you fly for an hour and then glide through a descent of 12,000 feet (ceiling is 18,000 at max weight). That gives you about 90 minutes of solar absorption time. Assume we only fly at noon on clear sunny days to get 1kW/m^…

That all sounds about right, except for the generation part (see below) which is but a minor factor anyway. Indefinite solar-powered flight is understandably not a goal of Pipistrel for this craft; it will be interesting once it gets to the point where it’s a more commercially feasible design goal. I love how you rounded up to 1kW/m² to get a nice round number, then multiplied by 13.9! It’s worth noting on the propel…

Agreed. It is probably too generous to assume the ideal glide ratio and simultaneously assume generation via the prop.

Depends on a lot of stuff though. It's not a question of energy creation -- the energy of the system includes energy in the air. Generally freewheeling generates more drag than a stationary propeller (google "ESC brake vs freewheel" to see what R/C hobbyists have to say about this). However, you may have an unusual situation where maintaining the ideal glide velocity requires braking, and in such a case it is presumably more efficient to brake via the propeller.

Suffice it to say that even in the ideal case, this particular aircraft would have trouble maintaining flight via solar power, but other aircraft are proving that this is a viable possibility.

Re: Australia's first electric aircraft has begun test flights

#77

Post by totalZero »

mac01021 wrote: post #62
totalZero wrote: post #55

I look forward to the day when solar panels are efficient enough that an aircraft can appreciably recharge its batteries while gliding.

Could they do that if solar panels were 100% efficient?

On this aircraft, no. On other aircraft, it has been done without 100% efficiency.

https://en.wikipedia.org/wiki/Solar_Impulse#2015–16_circumna...

^ About 118 hours of manned flight between Japan and Hawaii.

Re: Australia's first electric aircraft has begun test flights

#78

Post by wallace_f »

pkolaczk wrote: post #75
wallace_f wrote: post #42

Earlier quoted context omitted.

Are you sure about your statement on turbos reducing efficiency? Some of the most economical consumer engines are turbocharged--in fact auto makers commonly cite mpgs as a reason to use turbos; so I am confused.

Yes. Turbocharging increases mpg not by increasing thermal efficiency, but by allowing to use a smaller and lighter engine. A lighter engine means less mass to accelerate, therefore less energy to spend. A smaller engine means less internal friction so less energy lost. However this theory works well if you actually don't use the full power that turbo gives you, or you use it only occasionally. These engines have gre…

The new Honda Civic comes in a 1.5 turbo and a 2.0 NA, the turbo being the heavier package--but which still delivers higher mpgs. And if the turbo has more efficiency due to less internal friction, that still creates more useful energy out of the same amount of fuel, no?

Re: Australia's first electric aircraft has begun test flights

#79

Post by pkolaczk »

wallace_f wrote: post #78
pkolaczk wrote: post #75

Earlier quoted context omitted.

Yes. Turbocharging increases mpg not by increasing thermal efficiency, but by allowing to use a smaller and lighter engine. A lighter engine means less mass to accelerate, therefore less energy to spend. A smaller engine means less internal friction so less energy lost. However this theory works well if you actually don't use the full power that turbo gives you, or you use it only occasionally. These engines have gre…

The new Honda Civic comes in a 1.5 turbo and a 2.0 NA, the turbo being the heavier package--but which still delivers higher mpgs. And if the turbo has more efficiency due to less internal friction, that still creates more useful energy out of the same amount of fuel, no?

You are right, but now we are not discussing thermal efficiency, but total mpg which is related, but not the same thing. Efficiency being equal, you'll get more mileage from an electric car, because it can get back some energy from regenerative breaking, and it definitely has less internal friction.
Post reply on HN