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Qrkchrm t1_jduia2f wrote

Reply to comment by pavlik_enemy in Does living in an airplane flight path, near an airport, pose a health risk? What happens to the lead from the jets fuel? by [deleted]

There's an unleaded avgas available that got FAA approval last year. With how slowly aviation moves it may take another 10 years before lead gas gets replaced completely.

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ReadAllAboutIt92 t1_jdujmwq wrote

There is also a promising push within the industry that new build aircraft are fitted with engines that run on alternative fuels. Rotax engines that run on MOGAS (or standard car-grade gasoline/petrol) are becoming more popular. Diamond Aircraft from Austria fit the majority of their aircraft with a modified Mercedes Benz Diesel engine, which has its own issues, but removes the Lead content.

The issue in General Aviation is that these piston aircraft, with the right levels of maintenance, can run for decades, the majority of aircraft that students train in these days are 40-60 years old, still completely safe, and still completely legal, but running on technology that would otherwise be completely obsolete. However these engines keep going because they have the safety record to back them up, and rule number 1 of flying is to reduce risk and maximise safety at every opportunity.

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CluebatOfSmiting t1_jdul5zk wrote

Small electric aircraft already exist. Given the interest in electric aviation by many big name companies including Tesla, the constantly improving battery tech, and the way the companies talking about alt fuels are either still in development or actively dragging their feet in hope that people give up and let them keep making gas cars, we may well end up going all electric before alternate aviation fuels are available...

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dittybopper_05H t1_jdv049g wrote

Electric aircraft do not have the range and likely will never have the range of liquid fueled aircraft. That is, as long as we rely on batteries or some kind of capacitor technology.

That inherently limits their usefulness as a mode of transportation.

Sure, they might be fun to buzz around the field for 45 minutes or an hour, but you're not taking a battery powered Future Cessna to take the family to visit Aunt Edna for Thanksgiving, 500 miles away.

Having said that, if you are talking "electric" in the widest sense, then there might be room for aircraft powered by fuel cells. Those might have enough range, or if not, then a quick stop at an airport midway between to refuel would probably be acceptable, because it wouldn't take long to accomplish.

On the other hand, if you've got an aircraft that comfortably cruises at 88 knots in still air, and has comfortable range of 130 nautical miles, you're going to have to make 3 stops to recharge on the 435 nm trip to Aunt Edna's. Figuring a quick 45 minute recharge and 15 minutes for approach, landing, taxiing to and from the runway, etc., you're adding at a minimum around 2.5 hours to the journey.

So your 5 hour flight is now 7.5 hours long. That works out to about 67 MPH, which puts it in the reach of using a car instead.

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MAS2de t1_jdv9xhs wrote

You're thinking very much in terms of "What can be done with today's electric propulsion and storage technology?" In 30 years will electric planes be more common? Will leaded avgas for small piston planes still be the only common option? Think of where batteries have gone in the last 20 years. Where will they be in 30 years from now? What amazing breakthroughs in lab batteries in the last 10 years are being fleshed out and readied for production in the next 5-10 years? Or even today. Like Amprius doubling the Wh/kg with 1/2 the Wh/L of the previous reigning champs. See how it starts to get difficult to say that electric powered craft will never be viable for your 500 mile trip? Unless engines make some big leap in efficiency that they haven't done in the last century and can suddenly use even half of the 45 kWh/kg available to them and just run away with the range crown, it's possible for ev aircraft to become a viable option in our lifetimes and not just a neat party trick.

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TjW0569 t1_jdvgfs0 wrote

Think of the dangers that batteries pose in aircraft today. Those with a memory may recall the Dreamliner fleet being grounded due to battery fires. Then think of how dangerous they can be with twice the energy in the same volume.
Batteries are like rocket engines, in that they are a chemical reaction that has its oxidizer built into it. Unlike automobiles, there's generally no convenient way to immediately pull over and get out.

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32_Dollar_Burrito t1_jdwdp67 wrote

Think of the dangers that tons of fuel pose in aircraft!

We figured that out, we'll figure out battery safety too

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TjW0569 t1_jdww2yq wrote

The tons of fuel don't have the oxidizer mixed in with it.
So full fuel tanks can't just burst into flame. You need to add oxygen to it. Which is another advantage of fuels: you don't have to lift the oxidizer.

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MAS2de t1_jdvix3r wrote

Car fires happen, so do plane fires. They also have batteries that you can put a bunch of nails through and all that happens is they lose a small amount of capacity. Those batteries are on the market today. Not in mass quantities. But to think that a future battery couldn't hold far more capacity than today's batteries and be safe and have enough other good parameters for aviation is silly.

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[deleted] OP t1_jdvjj9p wrote

[removed]

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[deleted] OP t1_jdvm5u8 wrote

[removed]

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TjW0569 t1_jdvnivx wrote

Lots of gliders have done that in wave. Of course, that's off topic, since they typically have zero emissions.

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dittybopper_05H t1_jdwaczh wrote

This is true, but it's also irrelevant if you live in, say, Topeka, Kansas and Aunt Edna lives in Stevens Point, Wisconsin or Abilene, Texas.

The topography required for that kind of soaring requires both the right topography and the right weather conditions.

I mean, sure, the Perlan 2 sailplane beat the altitude record set by the U-2 spy plane. That doesn't mean the USAF is going to start using sailplanes for photoreconnaissance flights.

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TjW0569 t1_jdwwh65 wrote

You might be surprised where waves can set up. Be that as it may, private ownership of an aircraft able to reach 30,000 feet isn't out of the question.

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dittybopper_05H t1_jdzxwot wrote

You absolutely can own them, many people do. But if you fly between 18,000 feet and 60,000 feet, you must fly under IFR rules, and be in contact with air traffic control.

Above 60,000 feet is uncontrolled airspace, however, so you're free to do what you want if you can reach those altitudes. Good luck getting an aircraft that will fly that high, however.

One of the few aircraft I know of that can operate that high is the Lockheed F-104 Starfighter, and there are 15 privately owned ones in the FAA registry. Most seem to be owned by a couple of corporations, but a handful look like they are either owned individually, or perhaps through an LLC (common for very expensive aircraft).

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MAS2de t1_jdvpflg wrote

This whole thread started because someone brought up the potential future of EV planes. But people keep talking about todays solutions. Electric planes are in their infancy. Many battery technologies and other electrical energy storage technologies are rapidly solving the problems of today's batteries.

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KingZarkon t1_jdwgo9p wrote

>Will leaded avgas for small piston planes still be the only common option?

Leaded avgas will certainly be banned by that point, if not sooner. Older engines designed for leaded gas depend on the lead and other additives (like zinc in the oil) for wear protection but those can be managed by adding a bottle of additives to the gas for planes that still need leaded gas.

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sonicjesus t1_jdysf3s wrote

Has nothing to do with wear. Leaded fuel has a very high autoignition point that prevents knock. Modern fuel uses alcohol, but engines designed for alcohol free fuel are dangerously unreliable.

Modern computer controlled engines mange knock with alcohol added fuel, but when you're ten thousands feet in the air you don't want issues.

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KingZarkon t1_jdzwod4 wrote

>Has nothing to do with wear. Leaded fuel has a very high autoignition point that prevents knock. Modern fuel uses alcohol, but engines designed for alcohol free fuel are dangerously unreliable.

Turns out, it does both, actually.

>Lead allowed the development of higher 'octane number' fuel (the higher the number, the greater the resistance of the fuel to uncontrolled burning in the engine, or 'detonation'), and was also discovered, later, to have the property of protecting valve seats from wear.

Source

As for knock, you could just go all the way. E85, for instance, doesn't detonate, period. You can run the timing all the way to TDC and be fine. Would need bigger fuel tanks, though, so that might cut into payload a bit.

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crispy1989 t1_jdwi9c2 wrote

>Think of where batteries have gone in the last 20 years. Where will they be in 30 years from now?

Is this actually a reliable trend though? We're talking about charge density (energy per unit mass) specifically. Lithium battery tech was invented in the 70's and developed significant charge density refinements up through the 90's. (This is based on a bit of research and my historical recollection; I was unable to find a reliable chart of lithium battery tech charge density over time.) And although there have certainly been further improvements over the last 20 years, my understanding is that they have been incremental improvements and with diminishing returns. Although we may still be able to squeeze out a few small improvements, lithium battery storage tech has already been developed to store close to its maximum theoretical charge density.

Additionally, lithium battery tech is close to the best theoretical electrochemical scenario, so there isn't some new chemical battery tech "waiting in the wings".

At this point, further significant advances in battery charge density will likely require a fundamental breakthrough; and these are uncommon and unpredictable.

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