It's annoying how antiquated the engines used on these single engine planes. Continental is selling engines designed in the 60s that are just so inefficient.
Continental sells a range of general aviation engines based on modern Mercedes Benz diesel car engines, initially developed by Thielert as the Centurion. They run on regular Jet-A fuel, and are extremely efficient.
I think these, combined with biofuel based Jet-A are a good solution to this problem, as electric tech is a long ways from having the range needed.
Maybe someone who knows more could chime in why these haven't already completely replaced the ancient air cooled leaded gas motors? My guess is that they're very expensive...
I think this is the $100000 conversion alluded to in the article. Not sure what makes it cost that much. Maybe the same thing that seems to have caused GA to stagnate, very small volumes combined with high certification costs.
(There's also a company called Austro engines that makes aero diesel engines, AFAIU even based on the same MB car engines Continental/Thielert uses. I think Austro is a subsidiary or spinoff of Diamond, so that's where you see these engines used.)
I would guess that whatever makes it cost so much would equally apply to this solution once it is certified and not experimental. The gas V8 will be much less fuel efficient than a small turbo diesel, especially at altitude where the turbo offers huge advantages.
Those Mercedes engines are found in small cars and delivery vans around the world, and are widely available and pretty cheap. For example, the Centurion 3.0 uses a Mercedes-Benz OM642 which is found in Freightliner/Sprinter vans, Jeeps, and tons of other very common cars. You can buy these engines straight from Mercedes for like $8k.
In this case, the author mentions using an aluminum marine GMC V8, but not which one exactly. This is most likely based on the LS V8s, which are fairly expensive motors, and a pretty ancient design (e.g. pushrods).
> I would guess that whatever makes it cost so much would equally apply to this solution once it is certified and not experimental.
Bingo! Yeah, I was wondering the same while reading the article.
> a pretty ancient design (e.g. pushrods)
Does it matter? The engine is significantly derated vs. the original car engine, so max rpm is going to be much lower, thus no problem with valve float.
Modern direct injection diesels still use OHC, even though they run at really low RPM, so valve float can't be the only reason virtually all modern engines use it. I think this is because it allows for larger and better positioned valves, or even more valves (e.g. DOHC/4 valves per cylinder), making the engine breath better. I imagine the advantages of that would be even greater at altitude.
I'm not saying OHC aren't better, they certainly are (in most respects). Just saying that I wouldn't consider pushrods a showstopper either.
(As an aside, when aviation engines started going with 4V designs in the 30'ies, it wasn't only about breathing, but better cooling of the valves was an equally big motivation.)
You need to get the whole airframe certified to change the engine. If the airplane hasn't been in production for 40 years+ who will pay for that? Does the engineering data needed to start that process even exist anymore?
Interestingly, I found that the airplane in question here, the Cessna 172 was actually sold with the Thielert / Continental diesel, but ended up cancelling it because they were so much more expensive than the gasoline models that nobody bought them:
The market for small planes is basically entirely gone; the entire amount is so small that they can't really get through the cost of certification for the amount they sell.
It's not "gone" as if evaporated; it has been murdered by the certification requirements.
The odds of a random stranger dying from a light aircraft falling on them are trivial, several orders of magnitude less than the odds of their being hit by a car or being killed by inactivity; the pilot is free to refuse to take off, so risk appraisal really is on them; it's time to dump safety bureaucrats into your nearest woodchipper and CHANGE. THE. LAW. if you want ANY interesting activities or skills to survive.
FAA is incentivized to do nothing and sit on its hands. It's a mess. A good quarter of the country is medically barred from ever flying, even solo. The chances of this changing are 0 and it'll get worse.
Insert the "who could have done this" meme with the FAA shooting interest in flying and # of pilots.
The medical system is really messed up. I would love to eventually get my PPL, but I also highly suspect that I have undiagnosed ADHD, and I don't want to essentially sign away my right to ever get treatment. Fortunately Microsoft Flight Simulator and VATSIM scratch the itch to fly for now, but it still sucks that I'll probably never get to actually do it in real life.
Disclaimer: this is not legal advice, it's just to give you some ideas. AOPA and EAA have resources that can professional advise you.
Note that 'undiagnosed ADHD' holds as much weight as me saying you have bad energies. There are many conditions that masquerade as ADHD to a layperson, including some purely psychological ones (they are no less real, but are very different from a neurodivergent brain and require very different treatment).
If you are otherwise a high functioning adult (can function in society, operate vehicles safely, etc), get your third class medical, which should be no problem. You have to disclose diagnosed conditions. Do a discovery flight and ask for an opinion from the flight instructor. If he thinks you are fit, go start your training and enjoy.
If, one day, you do get diagnosed (with ADHD or some other disqualifying condition) AND require medication, then it's a problem. If you don't need medication (because most if not all ADHD medications are prohibited), don't try to renew your third class medical (because, if you get denied, it's a big problem) and get advice about BasicMed. It has far less requirements; my understanding is, unless there's something strictly prohibited, if a doctor signs you up you are good to go.
You won't be able to fly commercial or faster than 250knots but I suspect you don't care.
Failing all the above, there's light sports aircraft and gliders(no medical requirements, you just need judge yourself to be capable and unlikely to be incapacitated) – although I am not sure you can operate them while taking meds; some professional advice required here.
Disclaimer 2: Obviously the above assumes that whatever you have does not impair you. This is just to get around FAA's antiquated view on mental health while complying with the law. The most important thing is to be safe. If you really can't due to health issues, then don't, even if a doctor says you are fine.
Just about everyone who has ever undergone psychiatric care cannot ever get a medical. There is technically a process but it is extremely difficult and expensive.
Some conditions are uniformly disqualifying, for good reasons. But it results in a perverse situation where a regular person can choose to either get mental health care or fly, but not both.
Pilots don't suffer from depression, smoke pot, take many types of medication as a child, or have many other issues because if you did - the FAA might pull your medical and you can't fly after that. It can cost tens of thousands to try to get the FAA to let you fly again if a medical gets botched. And that is still an if...
I didn't see that as a black-label warning on the drug information sheet for fluoxetine, or even as being a minor side effect. My shrink didn't mention anything about auto-failing a PPL medical either, but I suspect that was because he was a Freudian.
Getting treated for cancer, for example, effectively bars you from flying. There are lots of medical things like this.
If these things are that bad, those same people shoudn't be driving either. And this is probably true. However, if you applied these same restrictions to driving, people would absolutely go nuts on you.
No, that is not true. I got treated for cancer two years ago (surgery and radiation), it was contained (not metastatic), I have twice since passed a Class 2 Medical. I talked to my Aeromedical Examiner, I talked with my treating doctors, they talked to each other, it worked out -- so far.
It's not the certification: flying is an expensive hobby, with a huge time commitment. People have moved on to other hobbies and fads.
We see the same with dinghy sailing. It used to be a big scene with hundreds of ordinary people showing up for regattas. It was killed by windsurfing (at least here in Europe) and just people moving on to other things ,not regulation of any sort.
> It's not the certification: flying is an expensive hobby, with a huge time commitment.
People have plenty of expensive and time consuming hobbies. All hobbies are at least time-consuming, that's what a hobby is.
All certifications add to the expenses. It's the reason why one can't buy a headset off amazon and have to pay 1k for a used headset. Sure, safety requires certifications but I guess we went overboard. It's also the reason why GA aircraft are expensive to this day, even those build 40 years ago. It's pretty expensive to keep maintaining old tech at low volumes. I'm rooting for Diamond and their car-derived engines (as well as the Experimental aircraft scene).
Note that boats are also notoriously expensive.
There's a very good parallel to your example: gliders. You want to fly cheap (just to fly, not to go places)? Go soaring. Problem is, it's even more location-dependent.
That's a circular argument. Recreational flying is an expensive hobby because of the certification barrier. Most of the price is in fuel inefficiencies and expensive maintenance of ancient engine designs. Airframe parts are expensive because they're obscure and certification requirements prevent modern equivalents from being used instead. And so forth.
I dunno. I'm pretty sure the lack of barriers to entry, inconvenient and costly certification, and safety nannying helped windsurfing get ahead there too. That and dinghy clubs inevitably devolve into race clubs that revolve inexorably around the race safety boat, and if you just want to noodle about or explore you're out of luck unless you are geographically lucky or you can afford a yacht. (which is great. But it's an uncommon privilege)
Right, but that's the problem: with no market, things can't get cheaper because there's no capital to innovate with. That's why General Aviation is in a death spiral (ironically, since "death spiral" is a GA term): fewer people buying planes, companies exit the market and remaining companies have to charge more per-plane to cover fixed costs, GA becomes more expensive, fewer people buy planes, etc.
Why is nobody willing to take a risk to revive this market? If the only thing preventing a revival is cheap planes, couldn't someone get some investor to pay for all the certifications of their modern, fancy, efficient, cost effective plane, and then sell a million of them?
That is essentially how any new industry works. EV's were too bad/impractical/expensive until Tesla decided to take the risk and put down the capital to make them mainstream. Why can't/doesn't someone do the same for GA?
...which incidentally has a very nasty problem brewing with Continental engines, grounding of all of the manufacturer's fleet running Continental engines that were made in the past few years.
It's actually an aviation crises in the making with 1000's of SR-22s.
Part of the problem is that this V8 engine is a 2x improvement. It's definitely an improvement, but a sub 10x improvement isn't enough to bring on a revolution. The article alludes to investors' lack of appetite for the risk, I suspect a larger improvement would convince them.
If he actually got this V8 certified and Cessna switched to then it might be dirt cheap to run but the 172 with it preinstalled might be $1M because they will sell so few and have so much engineering & certification cost to amortize.
That's how silly it all is, and why it will stay stuck in Experimental.
VLJ's are cute, yes. I'm slightly hopeful about small scale turboprops too. Yes, generally turbines don't scale down very well (well, applies to VLJ's to an extent as well), but if they only could make the capital costs of a turbine decent enough, the reliability, power/weight, and cheap and available Jet A-1 would still make such a thing attractive, I think.
There's a couple of companies working in this space:
There's a secondary issue that in a lot of places the sky is a lot more crowded and the airports are very crowded.
I wanted to be a pilot. I took lessons in the 1990s at a small field, relatively uncrowded, relatively low cost. I stopped due to weather/money.
When I tried again after I finished college where I lived things were more expensive and the airspace was so crowded you would run up costs waiting in line to take off, and the whole thing was much more stressful.
It has to be fun, in a busy enough environment it becomes stressful enough fewer people want to fly.
I learned to fly in Southern California literally under the bravo umbrella - wait time was never significantly bad (maybe $20 of “time”) and I has substantial radio/tower/airspace experience by the time I got my PPL.
The efficiency difference isn't as much as you might think.
Car engines today are much more efficient than they were 50-70 years ago, but that's because the difference between maximum power and cruise power for a car ranges from about 5x to 20x. Much of the efficiency gains come from devising ways to deliver short bursts of power from a small engine, such as variable valve lift and turbocharging.
General aviation aircraft cruise at about 75% power. There's much less to be gained by optimizing the engine to run efficiently at 10%, and running a small engine at high RPM and high boost continuously is a recipe for frequent service intervals.
That's ignoring improvements to transmissions, tires, and aerodynamics in cars that aren't relevant to planes. There's certainly room for improvement, but not to the dramatic degree we've seen with cars.
> The efficiency difference isn't as much as you might think.
True, the BSFC numbers of these old school aero engines aren't that bad, actually.
> General aviation aircraft cruise at about 75% power. There's much less to be gained by optimizing the engine to run efficiently at 10%
I think the real advantage isn't a small efficiency gain in optimal conditions, but rather that with a modern FADEC there's less pilot workload, with a single lever for selecting the thrust the pilot wants, and the electronics takes care of selecting the optimal parameters (throttle position, amount of fuel, ignition timing etc.) for that thrust setting, taking into account input from a number of sensors (temperatures, pressure, etc.). And all those sensors provide data that can be logged and help with planning maintenance before something goes pear-shaped up in the air.
> running a small engine at high RPM and high boost continuously is a recipe for frequent service intervals.
The Rotax aero engines rev to a max of almost 6000 rpm, cruise is ~5000 rpm, and they have a normal(?) TBO of 2000 hours, including the turbocharged 914. (The turbocharged 915iS has a TBO of 1200 hours, but I suspect it's due to the engine being relatively new, probably the interval will be extended when more experience has been gained?). Of course, these engines are designed for that from the ground up, not saying you could take a random car engine off the street and run it at 5000 rpm for 2000 hours.
I think if you want to see 'modern' gasoline powered piston aviation engines, you have to look elsewhere than Lycoming or Continental. ULpower and Rotax make fuel injected aero engines with FADEC. I think Rotax has even certified some of their models.
If I recall correctly, Cessna was found infinitely liable for every plane manufactured, meaning that each new plane off the assembly line increased their potential overall liability without liability over decades-old planes expiring and decreasing it.
> If I recall correctly, Cessna was found infinitely liable for every plane manufactured, meaning that each new plane off the assembly line increased their potential overall liability without liability over decades-old planes expiring and decreasing it.
I think that is one of the reasons why the upcoming electric small planes are such a huge thing - getting rid of not only combustion engines, but very old and inefficient combustion engines. Could be a real game changer.
They are probably not going to take off (pun intended) any time soon. Just fuel reserve requirements alone are about the full range they have.
I suspect hybrids will be developed first. Basically an APU sending power to the main motor + a relatively small battery. The 'APU' can be relatively compact and deliver a lot of power, with less engineering requirements (can place it anywhere, doesn't need to interface with a prop). If it fails you have some emergency battery power. Electric motors are incredibly strong and have very few moving parts, so reliability is higher. They are also light.
Net net, there's some complexity and the combined equipment may be heavier (may! existing powerplants are some heavy beasts) but there's probably advantages.
Yeah BEV / Teslamania obscures the fact that what automotive REALLY should have done was hybrids from year 2005+ for virtually every vehicle as the first step. Instead, they are doing the great leap to full electric.
In my vision a compact rotary (that inside-out rotary patent a few years ago looked even more promising) would recharge the battery subsystem. Or maybe a fuel cell.
The same would probably work for GA. Really, hybrids will work regardless of the battery tech for the next couple decades.
Yes, considering the first hybrid with the Prius was available as early as 1998, the car industry should have switched to hybrids in the early 2000s. But unfortunately they didn't. Just keeping selling pure combustion engined cars was far too profitable. I think Tesla did indeed play a huge role in pushing full electric cars. Which today is of course the correct technology for most applications as it skips the combustion engine completely.
Hybrid planes would be quite attractive, but of course the certification bareer which might be too large
I thought going directly to BEV was a good plan, but then someone on this site pointed out that if civilization needs to go to BEVs, and there is X supply of battery materials, should we use those in 100kwhr packs for full BEVs, or in 20 kwhr battery packs for PHEVs that will deliver 80-90% of trips electrified?
So you effectively electrify 5x the number of cars...
But, that opportunity has passed, at least we are moving towards electrification.
I'd literally fly a bicycle with wings for fifteen minutes at a time if that made [fixed-wing] aviation more affordable. I live in one of the better-off eastern-bloc countries and I make significantly more than most people I know, but getting a PPL would almost certainly ruin me financially at this moment.
I know that paragliding and hang gliding exist, but those are a bit out of my comfort (and safety) zone.
Technically it is a microlight but top speed and handling are much closer to a regular GA craft. I absolutely loved it and if my eyesight was better I'd definitely go for a license.
