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

The largest electric aircraft just flew [video]

youtube.com

Post reply on HN
Print view View original

351–360 of 389 posts

Re: The largest electric aircraft just flew [video]

#351

Post by class3shock »

horsawlarway wrote: post #333
class3shock wrote: post #155

Doing some math. Regional jets get somewhere around 45.9 seat miles per gallon (1). So 30 seats, going 125 miles would take around 80 gallons of jet fuel. This is likely low because all the jets listed are bigger and likely flying longer flights that are more efficient but just go with it. Jet fuel has a specific energy of 12 kwh/kg and a density of 6.7 lb/gal (2). So 80 gallons of jet fuel is 536 lb, or 243 kg, and…

They discuss quite a bit of this in the video. I actually thought it was a decent walk through of why they're targeting the space they're targeting, and how they're thinking about exactly these problems. Some items to consider from the video 1. short flights spend an large amount of energy simply having the engines running during taxi to/from the runway. 2. Take-off also consumes much more fuel than cruising. 3. 1 &…

1-3. Agreed

4. Remember my predicted number is on the low side of how much juice they would need. Of course they get much better efficiency than a conventional jet on taxi and takeoff, so maybe it ends up being closer to what you are saying. I wish they had some more hard data.

5. Yep, commented on this in another post but even just removing takeoff wear and tear on a conventional engine would be big.

6. I would take that with a big dose of salt. United has a deal with Boom (a complete fraud of a company in my view) to purchase planes. So maybe not the best metric.

7. I haven't done the math but the $5 takeoff doesn't pass the smell test for me. $5 doesn't buy much juice (50 kWh? So like a gallon of jet fuel?) and getting a 30k+ lb plane to cruising altitude is not trivial.

"Personally - I don't know if they'll make it work, but it's definitely an interesting play, with more real thought put into it than most attempts I've seen."

Totally agree, which I never thought I would say about an aerospace startup.

Re: The largest electric aircraft just flew [video]

#352

Post by [deleted] »

nradov wrote: post #336
seanmcdirmid wrote: post #319

Earlier quoted context omitted.

I remember reading about making ground effects electric planes for this reason. You need a reserve, but if your plane could double as a boat and was flying over water, that would satisfy the requirement.

As long as water conditions allow for a safe landing. In much of the world that severely limits when you can operate due to storms or ice. In practice routine use of ground effect vehicles will be mostly limited to lakes and inland seas with fairly benign weather. Like I don't think we're going to have regular passenger service from San Francisco to Los Angeles or Detroit to Cleveland.

[deleted]

Re: The largest electric aircraft just flew [video]

#353

Post by labcomputer »

tonyarkles wrote: post #216
dmitrygr wrote: post #200

Earlier quoted context omitted.

Current aircraft have * MULTIPLE HOURS* of fuel tanks. Compared to dozens of minutes of battery that this thing has.

Typical reserve requirement is 30 min for a turbine aircraft (45 for piston). Given the 125 mile battery-only range and the probability that it flies at at least 200 kts (230 mph), it’s pretty unlikely to hit even a 30 min reserve on only batteries. I like the design, I think they get the problem and have a decent solution for it

> Typical reserve requirement is 30 min for a turbine aircraft (45 for piston).

For private, yes. For airlines, the requirement boils down to basically enough fuel to "fly to the intended destination as scheduled, then loiter for XX minutes, then fly at normal speeds to a pre-designated alternate, land".

For short flights, that means the fuel loaded at departure can be more than twice what is actually needed to get from A to B...

Which is why the hybrid approach is fairly clever: You can use it for ~125 mile flights, and remain 100% electric on ~95% of flights. Whereas, without the reserve turbine the practical limit would be ~60 miles. On the ~5% of flights requiring more range, you're still mostly operating on electricity.

Re: The largest electric aircraft just flew [video]

#354

Post by labcomputer »

tonyarkles wrote: post #313
dmitrygr wrote: post #269

Earlier quoted context omitted.

> and have a decent solution for it Unless we ignore the additional maintenance cost of having to completely different proportion systems to maintain (and it is worse than a twin engine plane, because the propulsion systems are different, so you have to stock up on more different kinds of parts and possibly have different kinds of mechanics on staff to understand them)

Something that wasn’t super clear to me was whether the turbines are actually used for propulsion or if they’re used solely as generators to recharge the batteries/power the electric motors. I could honestly see it going either way. Having the turbine, electric motor, gearbox, and potentially clutches to isolate the turbine or electric motor from the transmission seems pretty viable though. This would waste a little…

Yea, that wasn't super clear to me, either.

But... given that turbine APUs already exist for ground power and are already engineered to be as light as practical, my naive guess would be that it's easier, simpler and faster to just use a COTS APU as a series hybrid rather than trying directly couple a turbine to the propeller.

On inspections and overhauls: I'd expect that not needing to start the turbine at all on a given flight massively helps the economics of the airplane. Turbines often have parts that must be replaced after a given number of (startup) cycles, and that's going to be especially important for a turbine that is only expected to run for a short time (if at all) at the end of a flight.

If you only start the turbine on, say, 5% of flights, that means you get 20x as many flights before overhaul/inspection. I could see that being incredibly attractive to airlines.

Re: The largest electric aircraft just flew [video]

#355

Post by labcomputer »

tonyarkles wrote: post #218
Toutouxc wrote: post #179

Earlier quoted context omitted.

> Aircraft fly with a buffer of fuel though to avoid such situations, so why can't an electric aircraft fly with a similar buffer on it's range? Because the required buffer is HUGE and we’re at a point where electric planes barely have enough energy for the actual route. So they’re doing the sensible thing here, flying the actual route electrically and falling back to combustion if the plane needs to divert.

To that point, the battery capacity they’ve got, rough envelope math, is maybe 10 minutes beyond reserve. They’d likely need at least double, probably triple battery capacity to fly useful routes all-electric with enough reserve stored in batteries. The turbines are a great move.

> They’d likely need at least double, probably triple battery capacity to fly useful routes all-electric with enough reserve stored in batteries.

Yup. And to bring this point home:

"Only" doubling the battery capacity likely eats well over half of the payload capacity, in terms of mass. So your 38 seat plane is now a 19 seat (or fewer) plane.

Re: The largest electric aircraft just flew [video]

#356

Post by tempestn »

chermi wrote: post #344
golem14 wrote: post #238

Earlier quoted context omitted.

The real benefit really seems to be that the electric motors have a much smaller failure rates than mechanical ones running near their top rpm. The hybrid motor can run at a much optimized RPM, so the idea is that this will improve the overall safety margin of the overall design. I could be wrong, but that's what the video said.

So basically like diesal-electric trains? My understanding that's almost certainly outdated was that the issue with electric planes was weight due to batteries, so added mass from a generator sounds bad.

Having the generator as backup means you need a lot less battery though, so it saves weight overall.

Re: The largest electric aircraft just flew [video]

#357

Post by panick21_ »

AmVess wrote: post #125
Scrimptech wrote: post #3

Hope it's accurate. Sounds good to be true.

It's true. Good? Nope. This thing will burn giant piles of cash in repairs, and that's not even considering battery replacement, which completely obviates the entire point of this thing.

Electric engines well known for requiring repair, unlikely jet engines who are known for being easy to maintain.

Re: The largest electric aircraft just flew [video]

#358

Post by panick21_ »

mandeepj wrote: post #129

Hybrid! That's what happens when you build new devices around old infra. Steve Jobs didn't design the iPhone around Carriers; it was the other way around.

Controversial opinion I know but we should design things that can kill potentially 100s of people in the same way as consumers electronics.

Re: The largest electric aircraft just flew [video]

#360

Post by labcomputer »

jmward01 wrote: post #154
werdnapk wrote: post #134

Earlier quoted context omitted.

So what do regular aircraft do when they run out of fuel? They require a forced landing. Aircraft fly with a buffer of fuel though to avoid such situations, so why can't an electric aircraft fly with a similar buffer on it's range? ie. Always fly less than the current charged range of the aircraft.

Lots of down votes on this but it is a legitimate question. The goal is likely to have the majority of flight off of batteries. That being said, the total weight of the emergency fuel plus generators is likely far less than the weight of the extra batteries they would haul around for the safety margin they need. So they end up lighter and more capable AND don't need to burn fuel. That being said, I wouldn't be surpri…

> That being said, I wouldn't be surprised if they didn't start the generators during critical phases so they may end up using some fuel for a flight, but not much.

I would guess the opposite. Many parts in a turbine engine are "lifetime limited" by number of engine starts. That is, you are required to tear down the engine and replace certain parts after a certain number of engine cycles.

That makes the economics of the turbine hybrid radically different if you need to start it every time you land vs. only the rare cases where you need to dip into fuel reserves.

For example, the PT6A (a common 500-1000hp turboprop) requires the turbine and compressor disks to be replaced every 16,000 cycles. That's about 5 years of commercial service at 4x round trips per day. But if you only start the engine once in every 10 flights, now those components (theoretically) last for 50 years of flying.

Post reply on HN