pavlik_enemy t1_jdugpas wrote
Reply to comment by jaker1215 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]
Why do we even use avgas with aviation piston engines being what they are today i.e. not particularly advanced? Is it regulations, so engine certified for 100LL couldn't be easily switched to a fuel with less octane number?
But with avgas being just 0.14% of all fuel consumption in US I guess it's not a national issue though people living near small airports could be concerned.
Qrkchrm t1_jduia2f wrote
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.
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.
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...
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.
[deleted] OP t1_jdv8uab wrote
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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.
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.
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
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.
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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TjW0569 t1_jdvnivx wrote
Lots of gliders have done that in wave. Of course, that's off topic, since they typically have zero emissions.
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.
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.
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).
[deleted] OP t1_je0493f wrote
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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.
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.
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.
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.
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.
[deleted] OP t1_jdvm1py wrote
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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.
[deleted] OP t1_jdwo47y wrote
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janoc t1_jdujoxy wrote
It is both regulation (anything aviation takes ages to get certified - both fuel and engines using it must be certified to be legal to use) and also the old engines which simply can't run on unleaded gas.
It is not a question of octane number so much but engine lubrication, fouling and knocking. Older planes with engines not designed for unleaded gas would require additives for this reason - the same as old cars do when fueled with unleaded gas.
Aviation is a slow moving field - not many people still drive cars made in the 60-70s but there are many many planes that are even older than that still in service (esp. with private owners, flight schools, etc.) - and none of them can handle unleaded fuel without additional steps. Either using fuel premixed with an additive (the most common solution) or an expensive engine modification which may not even be available for the old engine types still in use.
Oh and the unleaded avgas is more expensive than regular one too. Given that the price of fuel is one of the largest costs when flying, it is likely not going to help its popularity either.
pavlik_enemy t1_jduog5n wrote
I guess even if the engine is made yesterday it still made with obsolete tech by automotive standards. As far as I understand there was no push for advanced engine tech like fuel injection and ECUs in GA after WW2 neither from customers nor from regulators because whatever was available was good enough and all high-performance applications switched to jets.
slpater t1_jdvb8k5 wrote
So modern piston aircraft have things like fuel injection. ECUs no. It's mainly because there hasn't been a reason to innovate. Piper and cessna (the two largest general aviation manufacturers) haven't had a reason to innovate. The engine suppliers of which there are 2 main ones, haven't had a reason to innovate on anything. Diamond and cirrus are changing this. Diamond is using modified Mercedes diesel engines so they burn JETA (jet fuel is similar in a lot of ways to diesel fuel) their planes also are FADEC controlled. Meaning they do have an ECU that manages the engine. So no controlling fuel flow with a mixture lever, no adjusting the propeller with a lever. The system handles all of that. Add in that it's very expensive to certify a new engine and with little demand for anything new means manufacturers have been able to roll out the same airframe and construction for 50-60 years.
Long story short. Expensive to not on design and engine plus certify it and all its components for flight with little demand for innovation means companies won't bother.
janoc t1_jdvvbcg wrote
That's not really the case. You will find engines that are full of electronics and pretty much comparable to modern car engines.
However! Keep in mind that certifying a new aircraft engine is an order or two of magnitude more complex and expensive process than anything that gets into a car. You want to change the type of spark plugs? Change to an ignition system? Well, tough luck! Needs to be recertified.
There is also the fact that unlike a car engine, where if you get an electronic failure your check engine light comes on and you call a tow truck, in an airplane if something dies, it is a full blown possibly life-or-death emergency.
So you do not want to stuff your plane with a ton of electronic gadgets that could fail. The simpler the better in this case. Or you must provide redundancy, which is very expensive compared to e.g. a pair of magnetos for ignition. The other issue is weight, especially for ultralights but even for bigger aircraft.
The more complex electronics you add to the engine, the more it will cost to have it certified and even more to maintain. Keep in mind that a modern Cessna 182 costs upwards of $600 000 new today, the engine and related avionics being a large part of it.
You can't compare this at all with car engines. It is a completely different regulatory and reliability ball game.
There are plenty of modern electronically controlled (FADEC - that's what you know as ECU from car engines) and fuel injected aviation engines around.
However, typically not in your flight school's 40 years old Cessna 152/172 but in bizjets, larger helicopters and high end GA planes, like Cirrus SR22, DA-62, for example - which has two diesel (!) engines. Lycoming produces multiple engine types that are fully electronically controlled, Continental does as well, Rotax has several fuel injected engines, etc.
Fit_Lawfulness_3147 t1_jduslek wrote
As previously commented upon, lead is an anti knock additive. It increases the octane number. The higher the engine’s compression ratio, the higher the required octane number. The higher the compression ratio the more power the the engine can produce. SO… small aircraft need high octane fuel in order to keep the engine(s) small (light).
troaway1 t1_jdvdkv9 wrote
Small, light AND SIMPLE. No liquid cooling, no knock sensor, no computer controlled fuel injection, no O2 monitoring or exhaust gas recirculation, no transmission. Often the pilot controls the air/fuel mixture manually watching rpm and exhaust temp. Very primitive, but not a lot can go wrong as long as you don't have detonation which tear up an engine pretty quickly.
pavlik_enemy t1_jdv25sr wrote
What I meant by "advanced" was that modern aviation have rather low specific output compared to automotive engines where you could have a 200hp/liter engine in a Toyota so they don't have high compression ratio and/or boost pressure. And these highly efficient engines run on say 98 octane unleaded
quietflyr t1_jdv7kl2 wrote
Airplane engines are designed for torque at low RPM vs horsepower at high RPM, hence the very large bore sizes in aircraft engines.
My Honda Civic has a 1.5L (91 cu in) turbo inline 4, and pulls 174 hp at 6000 rpm, and 162 lb-ft of torque.
A Lycoming O-360 aircraft engine is normally aspirated with a 5.89L displacement, and produces 180 hp at 2700 rpm, but 350 lb-ft of torque.
Pretty massive difference.
Happycracker t1_jdvpj88 wrote
The other thing I frequently see called out about airplane engines is they run these power levels for hours on end. Typical car usage hits peak power for a very limited amount of time before dropping to something minimal.
quietflyr t1_jdvxnop wrote
Yes this is a big one. An aircraft engine will run at 60% power or more for almost the entire flight. A car engine is typically running at far lower power levels than that.
pavlik_enemy t1_jdv9x7j wrote
Interesting. In auto world bore being larger than stroke is usually a sign of high-revving sport-ish engine.
DreamyTomato t1_jdvw9hj wrote
Why so much torque? Cars go up hills, but piston engines are pushing a propellor through air, which at LOW revs doesn't offer much resistance.
Or am I missing a point that cars have gearboxes and maybe planes have no gearboxes? So 2700rpm is the prop speed, same as the crankshaft speed?
(and I believe instead of changing rev speed, prop aircraft change the blade angle. So the engine stays at the same speed, but the load can vary greatly?)
quietflyr t1_jdvx47w wrote
An O-360 is a direct drive engine, the propeller is attached directly to the crankshaft. And that's the case for most light aircraft piston engines. Some (especially more modern ones) have a single speed reduction gearbox.
The only thing an aircraft piston engine does is turn a propeller through the air, and that absorbs nearly 100% of the power produced by the engine. Swinging an 80 inch diameter propeller at 2700 RPM will use a lot of power and required a lot of torque.
You raise variable pitch propellers or constant speed propellers. These are used on some piston engine aircraft (the rest use a simple fixed-pitch propeller) and all turboprop aircraft. They do vary the pitch of the blades to find the most efficient angle both in climb and at higher speeds, due to the mechanics of how a propeller works. But this doesn't really affect the fact that a ton of torque is required to turn the propeller.
motorslug t1_jdvxou6 wrote
That's correct. The bar majority of piston engine aircraft use a direct drive from engine to propellor. More complex aircraft use a constant speed propellor as a form of gearbox, allowing the blade pitch to be altered while maintaining a constant blade rpm.
[deleted] OP t1_jdvw7dc wrote
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seriousnotshirley t1_jdvlmym wrote
Student pilot here, the industry is in the process of moving in that direction. There's a lot of barriers that are slow to get past.
The first thing to understand is that the aviation industry moves slowly and purposely. If a car dies on the highway you coast to the side of the road and usually don't cause an accident. When a plane's engine has a failure that plane is going to need to land somewhere. There's a much higher risk of that causing death and property destruction. Sometimes you're over farmland and get lucky, sometimes you're not. Just google "plane crashes into house" to get a sense of it. There's many many other things that can happen when a plane's engine dies. Because of this the FAA takes slow deliberate steps in changing regulations. One of these is how they certify which engine in which airframes using which gas are permitted. Changes to this need to be certified by someone and for a long time no one had the incentive to do this. I believe getting unleaded fuel certified for most general aviation planes and engines took a change in the way they regulated this, possibly from political pressure.
Next, someone needed to develop an unleaded fuel that can run in existing airplane engines, and there needs to be refinery and distribution capacity. Most planes need 100 octane fuel. While many engines could run 94 octane many need 100 octane. Development on 100 UL didn't start until 2010. FAA certification didn't happen until July 2021 for a single plane (Cessna 172) using a single engine manufacturer. Last September they finally certified it for all planes and engines, though the owner or operator of the plane needs to get a supplemental type certificate for their plane (don't ask me why). Every owner/operator of a piston engine aircraft needs to pony up about $600. Great, except it's not available yet. The developer of the fuel needs to ramp up production capacity and distribution. This is where we are currently at. It's expected to be available in California next year and around the country in 2026.
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The next thing is that airports need to start stocking unleaded fuel. Until there are absolutely no planes that require leaded fuel airports will need to stock leaded fuel. Airports serve a public purpose to the flying community by making fuel available. You don't want to leave a big gap in the us where a pilot flying from point A to point B can't get the fuel they need. Now they need to keep another type of fuel. This requires new tanks and either new pumps or trucks. This will be the next roadblock.
If you want to learn more about general aviation you can do what pilots all do and listen to AVWeb’s Paul Bertorelli.
pavlik_enemy t1_jdw2fza wrote
Thanks, I've watched his two videos on leaded gas and difficulties of developing new aviation engines. My thought was that since modern engines aren't made for extreme performance you could detune them and use lower octane fuels. But since 100LL was probably widely available and there were no concerns about lead there was no reason not to use it otherwise a manufacturer just crippled their engine design.
seriousnotshirley t1_jdwdo3q wrote
Something to remember is that general aviation planes don't typically use modern complicated engine designs. Complicated engine designs are one more way for something to go wrong and planes often fly in very different conditions than cars. Moreover, 40 year old planes are flying 40 year old engines, or at least the designs are that old if the engine has been replaced. It's not legal to just swap a new engine type into an old plane.
GA planes also have tight weight tolerances. They just aren't designed to carry a lot of extra weight and so an engine with lots of extra stuff could easily use up a lot of useful capacity, especially on a four seat plane which is really "two seats and luggage" or "four seats and no luggage".
One of the common questions people have is why planes don't use automobile engines since they are commonly mass produced. The issue becomes that you need a transmission and the extra weight of the transmission makes it difficult to convince anyone to even try getting it certified. I only know of one attempt at it.
Using the Cessna 172 as an example since it's so common, the Continental O-300 engine used for many years is a 6 cyl 300 CI 145 HP engine producing about 230 ft-lbs of torque at 2200 RPM. Note: plane engines can't rotate fast because the tips of the propeller would break the sound barrier and the shockwaves would cause issues (and by issues I mean death and destruction). How many 5 liter/300 CI 6 cyl engines do you know of in cars and how many produce much more torque than HP?
Scooter_McAwesome t1_jdvh1sm wrote
Things move slowly in aviation. Most flight schools will use aircraft built the 60s for training. They all have engins from the 60s as well.
HarryHacker42 t1_jdvl5c5 wrote
Near car freeways, lead in the soil within a 500 feet has higher lead content than soil 1000 feet away. So, cars of the 1920s through 1970s burned leaded gas and left deposits that exist today. I'd bet the same is true of airports with the lead being more concentrated on the areas the planes take off over, as that is when they're burning a lot of fuel.
[deleted] OP t1_jdwsjnw wrote
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sonicjesus t1_jdyqo2j wrote
Man of these planes, much like commercial are over 50 years old. the Ethyl 85 can deteriorate their seals and cause serious midflight catastrophe.
Keep in mind when I was a kid every car around me ran on leaded fuel and burned a gallon of it every ten miles. It's not so much the presence of lead that's dangerous but the fact some people were bombarded with it for decades.
limitless__ t1_jdvaai8 wrote
The honest reason? Who writes the regulations? The same people who have private planes. Banned lead in avgas would basically mean retiring the majority of the private planes in the US. Rich guys don't like that, regulations remain unchanged. If the regulation was pushed through the oil companies would absolutely, 100%, develop an alternative and they'd do it quickly. Right now they have quite literally ZERO motivation to do so.
TjW0569 t1_jdvhaqw wrote
Forty year old Cessnas aren't being flown by the really rich guys that have a shot at controlling regulations.
Endvine t1_jdvoya3 wrote
There’s already a non-leading alternate for 100LL AVGAS. As other people have stated, most really rich people do not fly in piston aircraft; they fly in jets which use a non-leaded diesel like fuel Jet-A. The new fuel has to be widely adopted, reach scale to reduce price, or there has to be a law outlawing leaded fuel in GA aircraft. We have laws banning leaded fuel for cars so creating a new law isn’t that far fetched.
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