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Cora – Kitty Hawk's prototype air taxi [video]

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Re: Cora – Kitty Hawk's prototype air taxi [video]

#221

Post by DennisP »

pc86 wrote: post #172
danielvf wrote: post #124

Earlier quoted context omitted.

We do seem to have different value systems. I believe applying energy to make human lives better is a great thing! Electricity usage in the western world is getting greener fast. Total usage is going down, not up. This isn't going to reverse either of those trends. There's a popular perception that all aircraft burn energy like an oil refinery on fire. The reality is that small piston aircraft are approximately as fu…

> The reality is that small piston aircraft are approximately as fuel efficient as the vehicles around you on the highway This is just objectively wrong. Before taking wind into account, a Cessna 172 travels 120kts on a good day and at altitude and appropriately leaned can get down to 8 gallons an hour. 120 nautical miles in 140 miles (less, but benefit of the doubt and all). That's 17.5 miles per gallon. At cruise a…

He specified "general aviation aircraft not designed in the 1950's." The Cessna 172 was first flown in 1955: https://en.wikipedia.org/wiki/Cessna_172

Also, it may be worth taking into account that airplanes travel in straighter lines.

Re: Cora – Kitty Hawk's prototype air taxi [video]

#223

Post by ozzy6009 »

fastball wrote: post #184
sjs382 wrote: post #140

Earlier quoted context omitted.

The image/graph you're referencing illustrates "United States total primary energy consumption by fuel in 2015". Total, not electric. You were discussing production of electricity, which is shown in the table I linked on that page to be 32%.

Wait, how does that make sense? What kind of energy if not electrical is coal being used to produce?

I looked at the citation, someone put the wrong numbers in the pie chart: https://en.wikipedia.org/w/index.php?title=Energy_in_the_Uni...

Re: Cora – Kitty Hawk's prototype air taxi [video]

#224

Post by sowbug »

patch_collector wrote: post #168
Kequc wrote: post #107

I don't like that they're touting no emissions. Electricity has to be generated and in the US that's mainly coal. Hybrid vehicles are closer to having it right where running the car charges it and you can get by burning significantly less fuel. Strictly electrical has not been shown to be an energy saver or a flag bearer of emissions reduction. In many cases so far it has been a cause of more pollution than modern en…

Is there a good source for electric vehicles causing more pollution than modern engines? I haven't seen anything to that effect. Here's an article that suggests that, in the US, gas cars would need better that 55mpg to have lower emmissions than EVs powered by the grid. In France, because of their different grid generation systems, you'd have to have a car running at 524mpg. https://phys.org/news/2017-11-emissions-wo…

Look up the "long tailpipe" argument. I can never tell whether people using it are genuinely in favor of more effective tactics for reducing carbon emissions, or instead are just trolling EV fans.

Re: Cora – Kitty Hawk's prototype air taxi [video]

#225

Post by adrianmonk »

nickbauman wrote: post #209
danielvf wrote: post #47

Contrary to almost every comment here so far, this is both innovative and energy efficient. Let's talk energy efficiency first. Once it's up in the air, it's has a similar profile to a normal single engine airplane. A Cirrus SR22 can go 1,200 miles on 80 gallons of gas. That's roughly speaking 15 miles per gallon - better than many pickup trucks or large SUVs. And that's while going 180 mph. Slower is more fuel effic…

Maybe remove the rose-colored glasses? 1) 15 minutes? If you flew in a small aircraft regularly, you would know it takes 40-60 minutes to prep a plane from park to airborne in zero traffic. 2) Estimating what the fuel consumption of a small aircraft will be is much, much harder than a surface vehicle. Consider 90% private aviation disasters are a result of pilot error. And 90% of pilot error is in fuel consumption es…

Running out of fuel seems like less of a safety concern with this. Since it can land vertically, there are way more sites where it can make an emergency landing if the range estimate turns out to have been too optimistic.

Also, with a computer flying, you can do something less extreme: actively and continuously manage the compromise between speed and efficiency. If your confidence of reaching your destination drops below the required threshold (say 99.999%), slow to whatever speed is required to achieve that confidence.

Re: Cora – Kitty Hawk's prototype air taxi [video]

#226

Post by pc86 »

sixbrx wrote: post #218
pc86 wrote: post #172

Earlier quoted context omitted.

> The reality is that small piston aircraft are approximately as fuel efficient as the vehicles around you on the highway This is just objectively wrong. Before taking wind into account, a Cessna 172 travels 120kts on a good day and at altitude and appropriately leaned can get down to 8 gallons an hour. 120 nautical miles in 140 miles (less, but benefit of the doubt and all). That's 17.5 miles per gallon. At cruise a…

Well for the autos you need to consider that they may commonly be in rush hour traffic, too, stopped and idling quite a bit.

It's a good thing the EPA has highway fuel economy ratings then so we can compare apples to apples.

Re: Cora – Kitty Hawk's prototype air taxi [video]

#227

Post by pc86 »

DennisP wrote: post #221
pc86 wrote: post #172

Earlier quoted context omitted.

> The reality is that small piston aircraft are approximately as fuel efficient as the vehicles around you on the highway This is just objectively wrong. Before taking wind into account, a Cessna 172 travels 120kts on a good day and at altitude and appropriately leaned can get down to 8 gallons an hour. 120 nautical miles in 140 miles (less, but benefit of the doubt and all). That's 17.5 miles per gallon. At cruise a…

He specified "general aviation aircraft not designed in the 1950's." The Cessna 172 was first flown in 1955: https://en.wikipedia.org/wiki/Cessna_172 Also, it may be worth taking into account that airplanes travel in straighter lines.

I'm talking about overall miles traveled so I'm not sure the straight line thing matters. Yes for the same trip you will travel a shorter distance in a plane. The plane will also be running for 20-30 minutes prior to takeoff and 5-10 minutes after landing.

If you exclude GA aircraft not designed in the mid-20th century, you exclude 90% of GA aircraft and 99% of certified GA aircraft. We can make that distinction if you want but it ignores reality.

Re: Cora – Kitty Hawk's prototype air taxi [video]

#228

Post by ajmurmann »

clon wrote: post #24
Quanttek wrote: post #17

I must say I'm against this development. First of all, even if electric, this is certainly a very inefficient way of transportation that will 'waste' a lot of energy to transport maybe 4 people. The resulting price of this technology will result in the 99% stuck on the ground while the only te 1% can afford the fare. And even if it becomes a regular mode of transportation, do you really want these planes to fly over…

I agree. People talking about flying cars sound a lot like people demanding faster horses. Or flying horses. I do not think the American dream of a private car scales too well to the future, be it with rubber wheels or tiny propellers. Especially given the population growth. Instead, a brief visit to Singapore, for example, will convince anyone what the future of transportation looks like. A public transport system,…

Being a huge advocate for public transportation, I have to admit that it doesn't translate that well to many American cities. Most American cities have too low density.

There is another issue I've noticed with public transit in the US which I haven't experienced elsewhere and have no good explanation for: Too frequent stops. May it be buses in LA or light rail in SF or PDX, they constantly are stopping. It seems like there is a stop on at least every other block making it super slow to go cross town.

Re: Cora – Kitty Hawk's prototype air taxi [video]

#229

Post by jccooper »

assblaster wrote: post #119
syntaxing wrote: post #106

Can anyone chime in how this aircraft is so energy efficient? It seems like the props on the wing will give a ridiculous amount of drag. Also, one of the key requirements for an energy efficient rear prop plane is super laminar air going to through the rear prop for efficient thrust. The wing design seems to remove this advantage. Edit: Also, I thought smaller props for vertical flight is significantly less efficient…

I don't know for sure, but I think that autorotation of the multiple vertical rotors provide substantial lift even if they're not being actively driven, similar to the tree seeds that autorotate as they fall.

From the video the rotors seem to park in fixed wing flight. The extra large hubs may be designed for lift generation, however.

Re: Cora – Kitty Hawk's prototype air taxi [video]

#230

Post by nradov »

ameister14 wrote: post #89
nradov wrote: post #82

Earlier quoted context omitted.

This aircraft can't take off and land any place that a helicopter can't. It's subject to the same laws of physics, and the same safety and noise regulations. But it may find a niche market by being faster, cheaper, and easier to fly than existing light helicopters.

The noise regulations part does make a difference, as this is significantly quieter than a helicopter.

That remains to be heard. The electric motors might be marginally quieter than current helicopter engines but ultimately the rotors still have to move the same amount of air.
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