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I promised myself that I would pursue my PPL if I successfully completed my phd. I'm now doing research about the when/how I should do this, and one of the big factors for me is that there's no point in getting a license if I can't afford to fly on the regular. Purchase price is obviously a factor here, but so are fuel costs - and as a climate/energy policy scholar I can't look at fuel without wondering about the future of avgas.

From this perspective, turboprops seem to be in a nice, futureproof spot since biodiesel and synthetic fuels will likely keep anything that can run on diesel-derivatives going regardless of fossil fuels' fortunes. Aside from ethanol, though, gasoline doesn't have any decent alternatives that I'm aware of. But boy howdy do turboprops seem heinously expensive - and basically require one to buy way more aircraft than I think I'll ever have need of (though my long-run dream is to trick out an OV-10 as a bush plane).

Am I overthinking the whole thing here? Is there any anxiety about the future of fuels and what it could mean for piston craft? How does a potential new owner go about selecting for things like powerplant/fuel based on their expected use cases?

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    $\begingroup$ Forget CO2, the huge problem is avgas is the last remaining fuel that contains tetraethyl lead, ongoing replacement efforts have failed to yield a substitute, and the EPA is under pressure to outright ban it. (Plus there's one company that's left making it, and one major lawsuit or plant explosion may very well end supply.) $\endgroup$
    – user71659
    Commented Aug 10, 2021 at 19:01
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    $\begingroup$ My understanding is that many of the newer (i.e. post 1990?) light plane engines -- including classic models made in that time frame -- are rated for mogas, as long as the octane requirement is met. Back when cars were converting, "all" it took was changing valve seat material -- something that could be included in a routine engine overhaul. Meeting 100 octane without ethanol or lead is harder than protecting engine parts that depend on lead. $\endgroup$
    – Zeiss Ikon
    Commented Aug 10, 2021 at 19:10
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    $\begingroup$ @ZeissIkon Not comparable. If you've been following the FAA PAFI, there were multiple concerns about material compatibility, longevity, power, etc. that simply are not (as much) as a safety concern for an automotive environment. You're talking about engines that refuse to use fuel injection and electronic igntion due to safety. For example, when ultra-low sulfur diesel came in, it is well known and documented that it causes fuel system leaks and injector wear. That's not acceptable to the FAA. $\endgroup$
    – user71659
    Commented Aug 11, 2021 at 1:04
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    $\begingroup$ @Harper-ReinstateMonica Not only is TEL itself hard to come by, and probably facing an EPA ban as soon as the FAA certifies an alternative, there’s only one refinery left willing to work with it. Every batch they make requires a complete cleaning of the entire refinery, and lead can’t be transported in pipelines either. It’s expensive for a reason. $\endgroup$
    – StephenS
    Commented Aug 12, 2021 at 1:13
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    $\begingroup$ @alephzero Not everything that annoys you is a conspiracy. Lead in fuels is actually bad, mmkay? $\endgroup$
    – Criticizing Israel not allowed
    Commented Aug 12, 2021 at 8:37

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First off there are piston engines certified for flight and built by Continental that burn Jet-A which I suspect will be in production for the rest of our lifetimes as it powers most of the air fleet out there (i.e. jets and turbo props). Classic designs like the Piper Archer are being built with these engines now which has helped move this into the mainstream by making a super common airframe available with an alternative fuel source. Diamond also makes some higher performance piston aircraft that run on Jet-A like the DA-42 so there are alternatives out there that allow light aircraft to not be reliant on gasoline.

There is also a big difference that sets this whole situation apart from the car gasoline/battery/alternate fuel debate. The FAA; ultimately for something to fly in this country (and I assume you are talking about the US) it must be in some way certified by the FAA (or flown under the experimental category). As such the FAA has largely only approved 100LL and 110LL for use in aviation engines, or better the engines are only certified for use with those fuels. There are some engines that have MoGas conversion options but a big chunk of the fleet ultimately runs on 100LL which creates an interesting supply/demand situation. It's well within the interest of the refineries to continue to make 100LL since there is a very clear market for it, there are no threats of alternatives because there are no certified alternatives. Considering how hard FAA certificates are to come by it would be hard to come up with a new, flight certified, technology fast these days.

Pilots also tend to stick with what they know, and we all know the smell of 100LL...

Makers have been looking for an alternative to 100LL since car fuel stoped using led years ago, and has only managed to certify a single engine to use a new non led fuel as recently as a few weeks ago.

So, sure, one day in the future there may be no more 100LL, there may even be no gasoline, there might be no jet fuel, or even no liquid fuels of any type but that day is likely far off in aviation. Electric aircraft are still a relatively young reality in the useable/production vehicle space and battery energy density is still a real issue to make it competitive.

It ultimately takes two to tango and the FAA (and other governing bodies) will need to certify a non gasoline/Jet-A based power plant that is installed on or STC'ed into a common airframe produced in sufficient numbers to offset the current aviation fleet. On account of the fact that the aircraft that I fly still has ash trays and a working ADF (not that there are any NDB approaches left around me); Im not really worried about things changing too fast...

You can find some of the FAA's updates on the matter here.

Also related

If your really worried, dont buy a plane, join a club

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  • $\begingroup$ Thank you so much for the club link. That possibility had completely escaped my notice. Accept this answer because of the wealth of useful links for me to continue on with. $\endgroup$
    – William Walker III
    Commented Aug 11, 2021 at 13:22
  • $\begingroup$ @WilliamWalkerIII Ive been a member of two clubs at this point (changed due to a move) and rented from various flight schools. Both have been great experiences with great planes that are easy to access and delightful to fly. Dollar for dollar is a way easier path to flying than ownership and I have generally found the planes to be available and well kept. $\endgroup$
    – Dave
    Commented Aug 11, 2021 at 13:26
  • $\begingroup$ are they generally available for longer duration trips. e.g. if I decided to get a chunk of hours in the air by hauling some burner friends to Reno, staying there myself (for ease of access to card rooms more than anything else) and then flying them home some days later be doable under a club? $\endgroup$
    – William Walker III
    Commented Aug 11, 2021 at 13:28
  • $\begingroup$ @WilliamWalkerIII it depends on the club and their rules (each one will have different policies) but generally the planes are available for multi day trips. My club allows multi day trips but I can only have one booked at a time. $\endgroup$
    – Dave
    Commented Aug 11, 2021 at 14:10
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    $\begingroup$ Matter of time before somebody, maybe California, puts their foot down and says "no more leaded avgas. Done." $\endgroup$
    – Harper - Reinstate Monica
    Commented Aug 12, 2021 at 1:01
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Actually, this issue cannot be overthought. The plane that is purchased will have to be lived with or, if not, sold to get something else. Other than the usual host of questions about the mechanical condition of the candidate plane for purchase, and the cost of power-plant/propeller overhaul and inspection certification, will be the cost to bring the plane to FAA compliance. All of this seems to be set on the cost of operation as an ultimate deciding factor. The question always seems to come down to the following; can the plane of choice be bought, maintained, certified, and flown at a reasonable cost.

Within a broad perspective, the overall most important issue in purchasing a plane generally seems to involve the cost of operation. The dilemma that was mentioned should be viewed from the perspective of G100UL aviation fuel, details of which can be viewed here. In July of 2021 the FAA approved Supplemental Type Certificates (STCs) authorizing use of G100UL high-octane unleaded avgas in aircraft piston engines, without modification. At least this is something to consider, in the foreseeable future piston-engine aircraft are not likely to be rendered unserviceable due to the unavailability of leaded avgas, or the need to modify engines to use unleaded G100UL fuel.

Given this view, a perspective of the future of piston aircraft would be that they will not be likely rendered obsolete within a relatively short period of time, but, if they are FAA compliant, will retain their value and remain viable for a rather considerable time. There are no other alternative energy packages that have a similar or greater energy content per unit mass as does avgas in the operation of current-technology piston engines. Consequently, the purchase of a piston powered aircraft will likely remain viable for the intended period of use, at the end of which time the plane will be sold.

Also, keep in mind that retrofitting an aircraft of current design for a new type of power plant, say battery-electric, will be a "big hairy deal" should the power-to-mass ratio of batteries become viable for the required longer operational range of flight that will be demanded of such aircraft. Certifying a piston aircraft for such a conversion is not likely to be easy, or even considered rational, particularly regarding the safety issues, rebalancing, and wing-loading issues that must be overcome to keep the aircraft stable and flyable. In view of this issue alone, piston-powered aircraft in their current state of design and use are likely to be around a very long time, especially when unleaded avgas is available. Or at least, that is the way things seem at the present time.

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    $\begingroup$ "This issue cannot be overthought." Sweeter words, to an academic's ears, do not exist. $\endgroup$
    – William Walker III
    Commented Aug 11, 2021 at 13:22
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Unless you are independently wealthy, you’re going to be flying a piston plane, which means either gasoline (of some sort) or diesel.

There are a few diesel piston engines, which are normally run on jet fuel (aka kerosene), but they’re somewhat rare, and rare means expensive both to buy and to maintain. This is disappointing since these would seem to be the clear path forward, but it’s a classic chicken-and-egg problem.

However, 99% of light aircraft use some sort of gasoline.

Leaded avgas is by far the most common, and also by far the most harmful to the environment. The good news is that most engines under 200hp run just fine on ethanol-free mogas; all you need in most cases is an STC and some placards to make it legal. The key is these engines never needed 100LL (or its predecessor 100/130) in the first place; they ran just fine on 80/87 or maybe 91/96.

Note that finding ethanol-free mogas can be somewhat challenging, but it is far cheaper than leaded avgas. And while the very long term future of mogas isn’t great, it’ll be around for the foreseeable future.

For avgas engines over 200hp, which do typically need 100LL, several companies have been working with the FAA on substitute high-octane unleaded fuels, and there may finally be a light at the end of that tunnel. But as a niche fuel it’ll be expensive, especially if the under-200hp folks all switch to cheap mogas instead. Long term, it would be cheaper to just replace all those engines with diesels.

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  • $\begingroup$ Re "they ran just fine on 80/87", not always the case. A number of engines required the intermediate grade that used to be produced, with octane rating in the low 90s IIRC). So my Cherokee 180 (Lycoming O-360 engine) has an autogas STC (and runs fine on it), but it has to be premium, not regular. $\endgroup$
    – jamesqf
    Commented Aug 11, 2021 at 4:10
  • $\begingroup$ @jamesqf Added reference to 91/96; I assume that’s what you meant. $\endgroup$
    – StephenS
    Commented Aug 12, 2021 at 19:49
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One more take on the subject: for the safety of you and others, I suggest you start your flying hobby with the most cost efficient (read: cheapest safe) setup, and fly, fly & fly. Every dollar you save on the equipment and invest in flight hours, is like money in the bank.

You can seriously start thinking about the deeper concerns of this issue when you have hundreds of hours of flight time. No need to worry about availlability of different fuels and the market scene before that.

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    $\begingroup$ This has been part of my calculus, but thank you for making it explicit. $\endgroup$
    – William Walker III
    Commented Aug 11, 2021 at 13:21
  • $\begingroup$ The wonderful world of aviation is full of temptations, it is very easy to drift from the essentials. God knows I've done it... $\endgroup$
    – Jpe61
    Commented Aug 11, 2021 at 15:09
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Yes, you're overthinking the whole thing. I won't repeat what others have said about diesel and mogas (but I agree).

The airplane you buy now is not necessarily the airplane you'll be flying 5 or 10 years from now. The bottom line - now - is that you're pretty much stuck with 100LL (or if you you make an effort, mogas).

Things will change. But not quickly. Eventually we'll get practical electric GA airplanes, once the batteries get good enough. It'll be years before we see that in experimentals, and more years before the FAA gives its blessing for certified aircraft.

For now, just buy what you can afford (buy less - you'll have money leftover for the unexpected, which you should expect) and go fly.

When things change, you can always sell and buy something else.

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    $\begingroup$ There are electric GA airplanes certified by the FAA (e.g. Pipistrel Alpha) since 2018. They are probably not very practical for longer flights yet, but it's not a certification issue, just battery capacity. $\endgroup$
    – Bianfable
    Commented Aug 11, 2021 at 18:32
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    $\begingroup$ Yeah, I think it's a blunder to think you'll keep airplanes for a long time. Especially if one drives cars til they're totaled. Most Youtubers who are pilots have gone through a series of airplanes. I also think it's a huge mistake to leap straight into a highly technical airplane like a turboprop, there have been high profile accidents where the novice pilot was overwhelmed by workload. $\endgroup$
    – Harper - Reinstate Monica
    Commented Aug 12, 2021 at 1:06

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