Hacker News Reader

Comment by Shivatron | Hacker News Reader

There are two packs, one forward and one aft, each 53 kg (~117 lbs) for a total of 106 kg (~234 lbs).

For comparison, the same weight of avgas (39 gal) will fly a Cessna 172 for just under 4 hours with reserves (assuming 9 gph), compared to the the Alpha’s 60 minutes.

View on HN

These batteries don't get lighter as they fly though do they?

I heard that airliners can't land with a full load of fuel and they have to dump it to land in an emergency. I wonder if that means you can't even replace max fuel weight with the same battery weight because then it'd be permanently too heavy to land.

I wonder if airliners could drop exhausted battery packs by parachute over designated DZs as they fly across the continent or ocean?

>I heard that airliners can't land with a full load of fuel and they have to dump it to land in an emergency

I think the main reason they do that is that way there's less stuff to burn if there's a fire or explosion.

No the main reason is with equal weight it is way harder on the airframe to land than take off.

Electric airplanes are small so it's not as a big of a deal, but it will limit their ability to scale.

Not all airliners can dump fuel. Some have to burn it off to get under maximum landing weight, or just risk land over the prescribed MLW.

These batteries don't get lighter as they fly though do they?

Technically they do - the battery of a Chevy Volt loses half a microgram from full to empty :)

https://physics.stackexchange.com/a/34424/6210

That’s obviously not going to be significant at all and clearly not what I meant.

Hence the "technically" and the smiley :)

hacker news dot com

Jettisonable batteries (or lift magazines of battery + motor) are one design that's been explored. Take-off and initial climb is a major fuel-demand flight phase.

What decade is the 172's engine from? I keep hearing that all GA planes are basically vintage cars.

I'm far from an expert on this but my understanding is similar. I think there are several technical and market reasons for this. First is the simple cost of developing and certifying a new general aviation engine. That cost must be covered by sales in an already cost difficult market. The second part is technical...plane engines are used very differently than car engines. They are not purely steady state but they are typically used in a near steady state way. This makes improvements such as fuel injection less additive beneficial. Ad in that most of the uses of the engines are non-commercial and non-life critical and you have a logic - why would I spend tones more to gain a few points of efficiency on something I use for fun that already costs me an arm and a leg that works. Its the same reason you don't see the most fuel efficient innovations start in sports cars.

example: look at the Lycoming O-360 and the list of planes it is used in.

https://en.wikipedia.org/wiki/Lycoming_O-360

Typically they are equipped with either a Continental O-300 series engine from the 40s, or a more modern Lycoming O-320/360 from the 50s. They hark back to an era of magnetos and manually adjusting the fuel mixture. On the plus side they're so mechanically and electrically simple that there's very little to break. On the downside they're pretty inefficient and carburetor icing is still an issue. Also, they need leaded gas still.

https://en.wikipedia.org/wiki/Continental_O-300

https://en.wikipedia.org/wiki/Lycoming_O-320

https://en.wikipedia.org/wiki/Lycoming_O-360

I'm not kidding about the efficiency either. The Lycosaur O-360 is a 5.9L engine that produces at best 225hp. You can get 245hp out of a 2L Ecoboost in an economy car today. This isn't an apples-to-apples comparison, but it gives you a sense of how far engines have come since the 50s.

A Cessna 172 retrofitted with a modern engine could probably get more than a 50% increase in range, and also cabin heat.

You can get a 172 refitted with a 2L turbo diesel engine which gives about a 38% improvement in range. [1]

[1] https://www.aopa.org/news-and-media/all-news/2015/february/p...

I did a bit of research on this about six months ago, after watching a video of some guys who ferried a Cessna 172 via Nunavut and Greenland to Western Europe.

Google "thielert diesel engine" and you'll find a lot of good info to start from.

https://www.google.com/search?client=ubuntu&channel=fs&q=thi...

They don't use magnetos because they're scared of modern tech, its because magnetos self excite and don't need an external power source to start or keep running. And that modern 2 litre engine isn't going to put out max power like the aero engine will.

The aero engine is also air cooled (so no water pump or radiator) and generally simpler all around. But at the end of the day it has a hilariously large displacement for the horsepower delivered. It's not like the thing is using fancy variable timing or partial charge ignition or cylinder deactivation to save fuel either, it has to fill those cavernous cylinders with a combustible mix on every fourth stroke.

Reply on news.ycombinator.com