When the Wright brothers first took to the air, the fuel they used was a straight run gasoline with only about a 37-octane rating.
Straight run is basically a light fuel that boils just below the kerosene fraction and has no additional processing done to it. Due to the poor cooling of the Wright engine, it usually started detonating or pre-igniting shortly after takeoff.
Since straight run gasoline was one of the limiting factors for aviation, especially for the military, a huge research effort was launch by the oil companies, the military, plus numerous other research agencies in the early 1900s for a better solution.
When I started working for Shell, one of my projects was working on lead scavengers. This led to a lot of looking through old research reports on the subject. I was really surprised at the scope and amount of basic research done on the subject.
The first work was refinery process changes that would reduce the knocking tendency of fuels. It was quickly determined that they could improve the fuel some, but they needed an additive to help them meet the requirement of many newly developed aircraft engines.
Then they figured out that most liquefied metal compounds worked to reduce knocking in test engines, however all of the metals tested had some negative side effects. For example, iron compounds greatly increased engine wear, the manganese additive cause red whiskers on the plugs, the lead additives would short out the spark plugs, and on and on.
But work continued, concentrating on finding scavenger compounds that would negate the bad side effects of the metallic additives. They eventually found that a lead compound used with a combination of bromine and chlorine scavenger agents (plus a phosphorus supplemental additive) could be used in high compression engines. This worked especially well with a new alkylation refinery processed fuels. This resulted in 100/130 avgas, which had no lead limit, but usually contained about 3 grams of lead per gallon.
The fuel for lower compression engines had a 0.5 grams of lead per gallon limit or 80/87 fuel. This worked well with the lower spark plug core temperature for these engines.
The 100/130 avgas was just what the high-powered military aircraft used in World War II needed. These fuels allowed the Allied aircraft engine manufacturers to greatly increase the compression ratios and performance of their engines and gave the Allied forces a significant advantage over the German and Japanese forces.
After the war, the aviation community settled on the two fuels and they remained unchanged until the early 1970s.
At that time the commercial aviation world had converted over to almost all Jet-A engines and the volume of avgas had gone down to an almost insignificant percentage of the world fuel market. That meant the total volume was too low to support two separate grades.
The oil industry reached a compromise and converted over to just one grade, 100/130 low lead. In this compromise the level of lead in 100/130 was limited to 2 grams per gallon and the 80/87 fuel was eliminated.
Unfortunately, this compromise did not work well for either sector of general aviation. The increase from 0.5 to 2 grams lead per gallon caused spark plug fouling and increased engine deposits on many aircraft.
And even though the lean rating of 100LL was greater than the old high leaded fuels, the decrease in the rich rating for the 100LL fuels resulted in a significant increase in knocking complaints.
The lead story on the automotive gasoline side was similar. The demand for increased performance caused an octane race. In the 1960s compression ratios kept increasing. By the late 1960s, there were numerous high-performance vehicles with 11 to 1 compression ratio or even higher.
Then in 1971, most of the auto manufacturers reduced the compression ratios into the 8 to 9 to 1 ratio to allow for the use of unleaded auto gas. They have now switched to electronic fuel injection and timing controls, plus many other systems, to return back to the 1960s performance levels using lower octane fuels.
The piston aviation community is now facing the switch to unleaded fuel with lower anti-knock performance in the real world than 100LL and probable exhaust valve recession in many engines. And the industry and government want to do it with no changes to the engines.
I feel this is an impractical goal without a research effort similar to that done before World War II that included thousands of very talented research scientists.
And the more important question: Who is willing to pay for it?
“It is in fact an option that is available right now and it is totally practical if you want to keep flying – especially if you are somewhere in the world where only Jet A or Diesel fuel is available.”
Look up the last Air Venture Cup race where a twin Comanche handily outran a diesel Twin Diamond Star. Interesting too that the Diamond Star just had an engine upgrade that cost more that the Twin Comanche is worth!
And the souped up twin Comanche AvGas burning engines had to be rebuilt right after the race – plus – they used over twice as much fuel – but the Diamond was loaded up and flown back with nothing more than a fuel top off.
Audi has Diesel powered closed wheel Grand Prix race cars – they’re just as fast as the other cars and yet they only have to make a pit stop for fuel about 30% less as the others – so give it some time for the aviation version of Diesel – (Heavy Fuel Engines) – to be fully developed and they will ultimately run off and hide from the 70 plus year old technology that are still turning props in the Comanche.
When EPS and SMA finish certifying their 350 and 400 plus HP heavy fuel engines – the 100LL engines will start fading away – along with 100LL.
Whenever you modify a gas engine for more power you shorten it’s life dramatically – but do that with a Diesel and it just smiles at you – during WW2 certain P51’s – P38’s – and F4U’s had their engines modified to produce more power for special missions – and those AvGas engines barely lasted for just that one mission – just like any other AvGas engine that is highly modified.
And GOD forbid that someone would have to belly in a plane with 100LL in it’s tanks – the least little spark would cause an ignition and will result in a virtual explosion with no time to escape – but let’s take the same scenario with a plane with Jet A in it’s tanks – which plane would you stand a better chance of escaping an explosion in a fire?
And before you try to say that a turbine powered aircraft ignites a fire right away – just think about an engine that is literally breathing fire out of it with such a ferocity that it can flip cars over – that sucker will ignite asbestos – but not so with a Diesel engine – even with a catastrophic explosion of a Diesel engine like maybe throwing a rod – it still does not ignite a fuel fire.
You can literally throw a lit match in a puddle of Diesel fuel and the Diesel simply snuffs out the lit match – now try that with a – (very small) – puddle of 100LL or maybe some 94UL – and get ready to run – – – but since Diesel or any heavy fuel is so hard to catch fire – it will give you a safety buffer to get away from the plane before the fire could really get going – that is – if there even is a fire.
So again I ask – with greatly reduced maintenance and far greater reliability and safety margins – especially when you’re in the soup – (full IFR) – what fuel and what engine do you want to have in your plane?
Are we not supposed to be striving to improve civil aviation?
I think you are under the same wrong understanding that I had. I was disabused of that.
We are having cold weather, and there was a semi-pulling a trailer with JETA in it. Well, apparently the driver side-swiped a guardrail here in Indy on 20FEB20 (I465 & I70)? Closed a ramp for a day. So was it the JETA in the tank trailer or was it the saddle tanks on the tractor that started this fire? And which of them detonated? Because someone got it on video and apparently there were two detonations.
Under the right conditions, Jet or Diesel will flash. Get it vaporized, and it will go.
I no longer think of the stuff being that much safer than gasoline.
The tanker that caught fire and exploded is an excellent example – (see below).
What I previously wrote is that Diesel or Jet A requires considerably more to ignite it than 100LL and requires quite a bit of heat to get it to flash or ignite – it’s why you can throw a lit match into a small puddle of ambient temperature Diesel and it will snuff out the match – but do not try that with 100LL or 94UL.
The overpass tanker rig that wrecked in Indy and caught fire had some sort of ignition source that became red hot and came into contact with the heavy fuel – like a shorted battery terminal and those rigs have some serious battery power with at least 2 or more group 31 batteries – (you can actually weld with just one group 31 battery) – and because of their location – they almost always short out in a crash or in an impact.
The denser fuel – (#2 Diesel) – has the most BTU’s and therefore is the heaviest per gallon – Jet A has a little less density and is therefore a little lighter and not as many BTU’s.
The OAT has an affect but not specifically that much unless it starts causing the fuel to gel and that’s when the pilot will add Prist or some other anti gelling agent.
Getting back to the Indy tanker rig – there are more than 2 tank compartments in those fuel haulers and once enough of the fuel burns or in this case – a hole in one or more fuel compartments pours out till there is a perfect mixture of air and fuel – (stoichiometry – 14.7) – in each tank – then it will explode and the denser the fuel is – i.e., – (Diesel or Jet A) – the bigger the explosion will be.
But having said that – the point is – heavy fuel is much safer than 100LL or 94UL because it takes a lot more to ignite it and it burns slower – so imagine having to belly in your aircraft because your gear has failed and that that aircraft along with almost every modern aircraft usually has the battery located far away from the fuel tanks with a master solenoid cut off switch – hopefully you remember to turn the battery master switch off – but for added safety – with a Diesel heavy fuel engine in the nose – you have a much better chance of not having the fuel ignite if any should splash on it and it will give you precious more the time that you need to run away from the plane after bellying it in – or in the case of the Indy rig – time to get out and run away before it reaches stoichiometry and explodes.
The thing you might be overlooking with the Indy tanker rig is that some good Samaritans – (including a woman who had just given birth) – had the time to help rescue the driver and even though the driver was seriously burned – they all had enough time to get away without getting killed or turned into crispy critters – do you think that would have happened if that truck had been hauling 100LL ?
A hot Diesel engine does not have enough exterior heat to ignite liquid Jet A – or #2 Diesel – (maybe if you sprayed a fine mist on the exhaust manifold when the engine is under a heavy load).
Therefore – if you want to be as safe as you can be – what fuel and what engine would you want in your plane?
The Indy semi tanker crash is an excellent example of the safety of Jet A and Diesel over 100LL AvGas – and when the investigation is finished – you’ll find that the group 31 batteries shorted out and started sparking which is what actually ignited the fuel – (you can weld steel with just one of those things) – but you can squirt raw Diesel on a hot Diesel engine and all it does is produce a white smoke – and that is only if the engine is hot.
What you’re missing is the fact that the driver was able to have enough time to escape before the separate compartments in the tank reached stoichiometry and exploded – albeit he was burned – yet he did survive and was even helped by good Samaritans including a woman who had given birth a few days earlier.
Now imagine if that tanker was hauling 100LL – the fuel would have burned at a much faster rate – “much” – faster – and upon reaching stoichiometry – (which is around 14.7) – it too would explode – and all that would have happened within a very short time compared to Diesel or Jet A.
People would have actually been killed.
So I ask the question – what fuel would you want in your tanks if you had to do a gear up landing – or if you were in a wreck that ruptured your fuel tanks and you needed every second you can get to run away?
Every second counts – right?
I know about the batteries, I have driven semis, and still have my CDL-A.
And I am also familiar with the white smoke. Starting old diesel trucks — they will blow white smoke until you put a load on the engine, and about a half mile or so, they will finally be warm enough to burn it all.
So, which would I rather have? Diesel/Jet over gasoline.
Gees, I burn Swift Fuel’s 94 octane in my Cessna 150 without any mods or problems. Since there is no lead in the fuel, there’s no plug fouling and the engine stays cleaner inside. Meets all proper ASTM criteria and costs me $4.25 a gallon. Best stuff around, a superior fuel. Swift’s higher 104 octane fuel has been tied up in the FAA’s FAPA approval program that was recently and abruptly halted, once again delaying a replacement fuel for 100LL. I think Swift is pursuing a simplified STC route to allow the use of this fuel in most all piston powered airplanes.
Classic car owners use adaptations to the engine and fuel additives to keep them running:
https://www.classiccars4sale.net/classic-car-how-to-guides/restoration/a-guide-to-unleaded-additives
Maybe this community has some insight about the similar situation airplanes are having now.
You’re linking an article about additives that are supposed to keep a classic car with soft valve seats running without Tetraethyl lead.
The FAA will not allow any additives that have not been fully vetted and approved – and it is up to the maker of the additive to prove their claims to the FAA.
Most of those additives are just hype to sell you a product – if they really wanted to prove that their product does what they say then they should seek FAA approval – after all – you can’t just pull over to the side of the road and park your airplane if the engine quits from using some additive – so whatever the FAA approves must do exactly what it promises and at the very least it must do no harm.
Lead does 2 things – it helps raise the octane by slowing the burn of the fuel so that detonation is delayed in higher horse power engines and it acts as a lubricant for the exhaust valve seat.
You have to understand that direct drive – (non geared) – aviation engines are slow turning engines that are turning a propeller that cannot be turned much above 2800 RPM – so slowing the fuel burn with a higher octane fuel is imperative for them to function and still achieve their rated horse power.
I don’t know if it’s possible in airplanes given the low RPM, temperature and torque requirements, but car engines can be adapted to use methane, propane, methanol, ethanol, butanol, natural gas, hydrogen (very dangerous) and other fuels with high octane rating.
The original parameters of the engine aren’t preserved (HP, consumption, …) but it works.
Not possible – the weight and shape of the fuel tanks that would be required to hold enough of the pressurized gaseous fuel would make it prohibitive to carry in an aircraft – pressure vessels require a heavy gage steel or aluminum round shape – like the fuselage of a pressurized aircraft.
You mentioned ethanol which is not gaseous but is not practical either – it has the octane but not the BTU value – a gallon of ethanol is equal to about 80,000 BTU’s and a gallon of unleaded 87 octane gasoline is about 119,000 BTU’s which interestingly is about what 100LL is.
BTU’s tell you how much power a fuel can produce and the octane tells you at what rate the fuel burns – there’s a lot more to it than that – but that is the basics.
People think that a higher octane increases the BTU’s but it only slows the burn rate which allows the timing to be advanced which produces more power.
You would have to burn considerably more ethanol to achieve the same horse power thereby considerably reducing range – further – ethanol is corrosive and you would need to install heavier stainless steel fuel lines – fuel tanks – etc. – plus – you would need to flush it regularly as ethanol is hygroscopic and any humidity or moisture would be readily absorbed and start to immediately corrode the entire fuel system.
Not sure why anyone would ever want to put an ethanol laced fuel in any vehicle – Alaska has quietly outlawed it because of the severity of damage it can cause a vehicle thereby requiring state agencies to go rescue someone stuck in a vehicle out in the wilderness – any fuel using it will degrade in a matter of days and will become almost unusable in a month or two.
Airplanes using 100LL can sit for several months between uses and 100LL will last an amazingly long time – hot rodders store their vehicles with 100LL in the tanks for years without any degradation of the fuel system.
I personally helped recover an aircraft stored in a hangar that had been sitting for over 20 years – the fuel was as fresh as the day that it was pumped in and the tanks were completely pristine with no degradation whatsoever.
Jet-A – (basically refined kerosene) – will also store for very long periods and has a BTU rating of over 128,000 so it will produce even more power per gallon when you burn it in a Diesel – and therein lies the answer – Diesel powered aircraft engines.
Even butanol? It seems to match the octane rating and energy density closely.
If an engine replacement becomes necessary to adequate existing airplanes then many types of reduction gears, engines and fuels can be adopted (including diesel engines, of course).
The technology advanced a lot since the classical engines were designed in the 60’s.
Any fuel you are going to use in an airplane needs to also be looked at from the temperature ranges that aircraft operate.
From 110F to -40C (or colder) the fuel must be able to be “piped”, injected/carburetted and then burned. If it forms ice or just becomes sludge, you can’t use it.
Even JetA needs a bit of heat at altitude because it tends to “jelly” if it get too cold.
You’re correct in that butanol is a much closer match to mogas and it blends with both Diesel and mogas better than ethanol – but alas – it too is a corrosive and it’s also hygroscopic – therefore – the FAA or any knowledgeable pilot will not allow butanol to be put in the fuel tanks of their piston pounding aircraft.
Having said that – I would take butanol blended into my mogas any day of the week over ethanol
I wonder if the corrosion is significant inside the piston (after mixing with air). If it isn’t, maybe certain coatings could protect the pipes, fuel tanks and other intermediate components.
Many cars where I live run on ethanol and last for years without any issues related to the fuel.
That’s because an automobile can carry the extra weight of stainless steel without any problem – and if you have a small percentage of ethanol – (E10) – mixed with mogas and your vehicle has the heavier stainless steel and or plastic tanks and fuel lines then you should be just fine – however – this will not be allowed in an aircraft and the FAA will not approve any fuel or additive or modification that in the least way can cause a problem – and ethanol is a huge problem in an aircraft – you just can’t pull over and park and wait for AAA to come help.
FAA will do everything that can be done to make an aircraft as safe as possible – (and they need to be thanked for that) – some things that they do might be a little archaic and they are slow to approve and/or help with some things that could be very beneficial – (like Diesel engines) – but their heart is in the right place and they will do everything that is humanly possible to keep the flying public as safe as they possibly can.
As for ethanol – it is very hygroscopic and corrosive – (thus the need for stainless steel components and plastics) – and when mixed with gasoline will make your fuel degrade within days because it will not store for more than approximately 30 days – (especially in humid climates) – (Alaska has outlawed it) – and unless you add a costly sum of additives to make it store for a few months – it simply will not last – butanol would be a superior additive over ethanol.
On the other hand 100LL avgas will store for years without degradation – so if you fly only when the weather is nice – (like most of us) – what fuel would you want in your tanks?
Why not do what the auto mfg. co. do, use low obtain fuel in your aircraft just alter the timing and it will burn just fine. How many people have a newer auto or pick up truck, I have a ford f-150 with a v-8 engine, it is rated at 310 h.p. it does this on 87 octane fuel, but how? it’s a high compression engine putting out 310 h.p. I called the factory, what they said was,” its all done with timing” that’s all it is, in other words, the h.p. is not that important as to the octane needed to burn and produce high h.p. it has to do with the timing at the time of combustion. Point being, use electronic ignition on your aircraft (which is available) quite cheaply I might add and you don’t need to use 100 octane in your aircraft. Call Ford motor co. and get it right from the people that do this on a daily bases, it’s great, achieve the same results using low octane fuel that you get with 100 octane. How cool is that???
Yes – it’s amazing what they are doing with engines – but ask the ford engineers at what RPM does that kind of horse power – (HP) – occur?
I think you will find out that it only happens at a very high RPM – (usually around 5000 or higher) – and yes – at those RPM ranges they can do marvelous things with combustion dynamics to make them run on low octane fuel using: – timing – direct injection – head and piston design – and so on – but are you going to be driving your pick up around at that RPM all day?
Since you can’t spin a propeller much above 2700 RPM – (very bad things will happen) – and your ford engine simply will not develop anywhere near its rated horse power at those lower RPM’s – so now you’re stuck with a couple of choices –
You could make a gearbox that reduces the final output shaft to less than 2700 RPM – but now you’ve just added more weight to your aircraft and the fuel consumption at 5k RPM for the engine is considerably more than what an equally rated HP direct drive aviation engine uses.
The other question is – if you run an engine at 5k RPM all day long just so you can burn 87 octane Mogas and develop the rated HP – how long do you think it will last?
And if you try to make an automotive engine run at a lower RPM so it will last longer and not destroy itself and yet still develop the HP that’s required for the particular aircraft it’s mounted to – then you’ll need to make it much larger in displacement and increase the compression ratio – but now the low octane fuel is too volatile and pre-ignites.
So you have 2 choices – reduce the timing – (which lowers the HP) – or increase the octane so that the fuel burns slower.
If you make the proper HP while turning the prop at less than 2700 RPM and also keep the engine RPM low enough to make it last then you will have an aircraft engine.
Then there is the the major issue about 87 octane Mogas – it will only last about 30 days or less in the tank before it starts to degrade – and even less if it has any ethanol in it – whereas aircraft and high performance race cars with 100LL in their tanks have been found sitting for over 20 years without any degradation of the fuel.
Diesel engines are a much better choice – they make their rated HP at low RPM’s and will run on a multitude of fuels – (peanut oil – vegetable oil – Diesel fuel – Jet-A) – and so on – and the FAA knows that it will be faster and safer to certify a Diesel than to try and come up with a replacement for 100LL – or at least a replacement that is equal to what 100LL now costs.
If the FAA outlaws 100LL – the price of the replacement will become astronomical and the Diesel engine manufacturers will rejoice – kind of like a mandated ADS-B that has taken place.
There are currently enough Diesel manufacturers with certified engines that can and will supply the market and the higher HP versions are needed are near certification.
Yes – there will be a replacement fuel – (or fuels) – available to those who can’t afford the Diesel upgrade – and for some it will just not make financial sense to upgrade their bird to a Diesel – but this is America and we do have choices – hope this all helps – but for the absolute real and correct answers – look for and read any and all articles written by Ben Visser – he’s the guy that really has the answers for all things fuel and oil and more.
I just wanted to point out that what you described (high RPM horsepower, combustion dynamics, running on low octane fuel, gearbox) describes a Rotax 912/914. They actually last LONGER than a legacy LyCon running all day at rated power……and do it on less fuel. I just wish I had a Rotax 912 on my C150 instead of Continental 0-200.
That is not to disparage what you say, because diesel engines are superior in every way. And electrics are superior to diesel….so here we go, around and around.
Sorry if I didn’t clarify – we were discussing engines in the 300 HP range that ran on 87 octane mogas – however – the physics and rules are still the same.
The Rotax engine you are talking about is a good engine and a good example because it’s a small and very light engine of around 82 cid and only weights around 140 lbs – therefore the moving mass of the pistons – rods – crank – etc. – is dramatically lighter than that of a larger displacement 300 HP automotive engine in the same RPM range and therefore can be safely spun up to 5800 RPM to produce its rated 100 HP – but then you’re still looking at the poor qualities of 87 mogas – and the potential of it degrading quickly in your entire fuel system – if you don’t fly for a couple of months – then you’re looking at a potential entire fuel system flush.
Yes – an electric motor would be the best to swing a prop – but we’re a very long way from the battery density technology to give them an equal range and currently the recharge time is several hours in exchange for an hour of flight time.
Practically speaking – a Diesel is the best choice for the foreseeable future right now – they’re available in the smaller HP class and development and FAA approval is nearing the end for the larger HP versions – and they are far superior to most of the 100LL engines.
Getting the lead out is not a technologically difficult problem. Doing so at a reasonable price, is. Doing so within the present aviation culture, entrenched old-line manufacturers and an FAA that codified ancient technology has become close to impossible. Ideas are cheap, implementation, expensive. Take Continental’s diesels, for example. $100,000+ conversion for a C-172 and, IIRC, hard expiration at “TBO”, which is a misnomer because the engines cannot be overhauled.
Traditional GA is in deep trouble.
Evolving GA engine technology from AvGas to fuel-efficient, globally available jet fuel is a necessity that can only be done effectively with an entirely new engine design. That’s why we’ve been diligently working with the FAA as we develop the DeltaHawk engine. DeltaHawk’s two-stroke design means every piston fires at every revolution, supplying power similar to a four-stroke, in a much smaller package. DeltaHawk engines burn jet fuel and are both supercharged and turbocharged. The engines are 40% more efficient than AvGas engines – providing improved range, higher non-fuel payload and lower cost of ownership. And, contrary to some other posts, we have found the FAA to be extraordinarily helpful and straightforward to deal with.
I salute you DeltaHawk and am looking forward to seeing your engine become certified and I think that the 2 stroke design should prove out to be the most reliable and trouble free available.
Everything in our fleet is Diesel – including our cars – but I do miss our old Detroit 2 strokes that just never would quit – (the EPA mandates forced us to retire them) – but I can safely tell the readers of this that it pays to spend the extra money up front for a Diesel as it saves tremendously over time in comparison to anything with a gas engine – most of all – the peace of mind it gives you because it’s by far more reliable than any avgas engine in the same class.
I wish you had a 350HP version as I will be having our Malibu STC’d with a 350HP Diesel as soon as one becomes certified – and I think it’s a smart move by the FAA to help certify the Diesels as soon as possible as having Diesel replacements for avgas engines should take the pressure off of them for having to come up with what I think will be a very pricey 100LL alternative – (sorry Swift).
As for a 350 plus HP engine – it’s looking like maybe EPS or SMA will get there first – I hope you’re working on that large of a HP version and that you get there soon.
There is no doubt that there are many Malibu owners that are ready to make that switch – I did the math based on what our Diesel fleet produces and depending on what bird it’s going in – it does balance out to convert to a Diesel and by the end of TBO – it becomes all gravy.
What’s not to like? – no mixture worries or worries about detonation – no lack of available lower cost Jet-A world wide – no fouled spark plugs – greatly reduced fuel consumption with lower emissions and lower maintenance costs – and an engine that will actually reach TBO or TBR without having the need for a top end.
The problem I find is, you contact the people (FAA) in your area for starting the certification process for an engine and they just stop responding. I was part of a small group looking at certifying a rotary engine (think Mazda 13B — Wankel). So I asked them for information I would need to do a business plan.
When the FAA will not tell you what the requirements are, you can’t do a biz plan with reasonable numbers to know how much capital one has to raise to get the job done. Or to know what hurdles you have to jump to get the TC for that engine (we haven’t even gotten to STCs for use of said engine).
This particular Rotary design was used in a 2 rotor configuration to develop 600+ HP to go after the time to climb record (and a Harmon Rocket was the plane it was mounted on).
I mention all of this because this engine doesn’t care about what gasoline is used. It can handle MOGAS with NO alcohol or 100LL. The engine, PSRU, water & oil, as I recall weighed less than an IO360. And used a special alloy for the apex seals that withstood a turbine runaway (got to 80# of boost before being shutdown).
The point here is, the FAA taxes to get an engine certificated is difficult to find out when the FAA will not respond to requests. We need to know how many engines the FAA will require us to give them (hence the “FAA Tax”). You don’t get those engines back.
There was another engine I had been looking at. It is an opposed piston engine, and in one configuration it burns diesel, Kerosene, or JET-A. In another configuration it is burning gasoline and it doesn’t care if it has TEL in it or not. I know that the diesel is in production but I can’t tell you who is using it — classified the last I was told. Draw your own conclusions.
Folks, from where I sit, the FAA is the problem.
And so, go Experimental and use the engine(s) you need. Fuel costs are much lower if you can burn other than 100LL or 100UL. And the planes are cheaper for what you can get, if you are willing to build your own. Just say’n’.
If you’re serious about getting a new engine certified you have to do your homework and find out which FSDO has the personal that specializes in certifying new engine types – and you don’t do that by calling them.
In other words – you cannot go to just any FSDO or any FAA office and expect the same results – even though they are all supposed to give you the same level of help – they don’t – just ask Martha Lunken at Flying Magazine – a still recovering former FAA employee.
Now go get that engine certified – we need it.
I did my homework and that led to me being told to contact the Chicago ACO. They were supposed to connect me with the right people because at that point the FAA was “restructuring” for the new part 23 certification. And then they stopped responding to emails unless their auto-reply was working.
The time for me to work on this has come and gone.
Anyone serious about getting an engine certified would have actually done the work. Shooting emails to the government is useless.
The homework here was not done
How serious do you have to be?
Is this serious enough:
An engine was built. It was used with a Harmon Rocket to set the Time to Climb Record. This was done to prove to detractors that the Wankel was quite capable.
That engine, based on a 2 rotor 13B Mazda, was put on a dyno, and was producing something over 600HP, using a GT60 (?) turbo-charger.
Meanwhile, understand, this was a “crowd” working at getting to the point of a common design.
So, there were multiple engines that had been built around the 2 rotor 13B engine, with different turbo-chargers, and different custom built PSRUs and put in different experimental aircraft in different countries.
Discussions were had about what the FAA required, etc. for certification and then the new Part 23 rules came about… So that is when I decided to ask the FAA what was needed to allow us to come up with a biz plan. I was sent a snail mail letter (from the ACO) with the email address of who I was to contact. And I was pointed at several FAA documents, which were already marked as obsolete or were about to be because of the changes in Part 23. But I read them.
Then the FAA shutdown.
So, a month or so after the FAA was back, I started trying to get this started again. And the only time we got response was when the guy who was to be our contact, had an auto reply set up.
And now, because of various situational changes, we have lost the engineer, and others. And my circumstances have changed. So this project has died.
But what do you think is serious?
How many machinists do you need? How much capital do you have to have? How many airplanes do you need to put this engine in to prove it works?
An abundance of misconceptions in both the article and comments so far.
1) Lead is bad for humans. Hopefully there are none who would disagree with that.
2) EPA defines as Hazardous Waste and requires special handling for liquids containing more than 5 mg/liter of lead. 100LL has up to 560 mg/liter, 100 times that what is considered hazardous.
3) While aviation fuel as a whole is a small segment of the fossil fuel industry, it’s responsible for HALF of the airborne lead pollution from ALL sources in the USA.
4) Top-line US military aircraft did not run on 100/130 octane, they used 115/145 octane as did most all of the piston airliners of the 1950’s. While they can run it, allowed manifold pressures are considerably reduced, limiting horsepower.
5) While it’s true that conventional aircraft engine controls are mired in the 1930’s, modern ones won’t solve a fundamental problem: conventional A/C cylinders are too big. With size, the fuel burn starting near the spark plug has plenty of time to ignite, via infrared heat from that flame, fuel ahead of the flame front. This is detonation. (This is why “full rich” is required. Boiling, rather than burning, the extra fuel delays the process).
6) Optimal cylinder size in this regard is around 400 cc, assuming normal bore/stroke dimensions. This is why compression ratios of 10:1 or more on regular mogas has become the norm for ground transportation but remain unheard of for LyCons.
7) A lead-free economical replacement for 100LL is not coming. As the author states, the “additive” angle has been explored now for close to 100 years. The test fuels examined in the last couple of decades by several different companies has found that any replacement will no longer be petroleum-based, but an entirely synthetic cocktail. Even something as common as house paint is $20/gallon.
8) Legacy solution: reduce compression. IIRC for example, Lycoming used to list an 80 Octane version of the O-360 rated for 172 hp vs 180 hp; a minor sacrifice to keep flying. I believe that they simply replaced the connecting rods with a slightly shorter version. Now, of course, they’d rather sell you a brand-new engine. Thus, I doubt if they would do in this direction without a lot of push.
9) Real solution: small displacement, geared engines. Rotax is kicking butt and has proven beyond any doubt that with modern software tools, resonance and other problems associated with 1950’s engineering are no longer an issue.
Great article! Could someone explain the two numbers like 100/130? Are these both octane numbers? WE seem to just refer to 100 octane.
Yes Sir – 100LL is called that to make it a quick reference when talking about Avgas.
The 130 octane component is referring to what the maximum octane is under a full rich condition – (which occurs at a full power and full rich condition that happens at take off) – once you start leaning the engine when you reach cruising altitude the octane is reduced to 100.
To put it another way – 100/130 is the minimum and maximum the fuel will produce.
If you contact or read any articles written by Ben Visser – he explains it in a far better technical way than anyone else you will encounter.
Which engine produces more emissions, the diesel engine or the gasoline engine? This is the question gentlemen, we are talking about emissions that come out of the tail pipe in all airplanes. If all airplanes used jet -A and diesel fuel, the emissions would be horrible right ?? So I guess what we need to concentrate on is, how to cut down on emissions not to reinvent a new type of fuel. As far as the price of aircraft fuel goes it will never go down no matter what, so if we can come up with a type of exhaust that will douse the emissions similar to the one on vehicles it might work or at least have something to work off of in order to make a comparable fuel that will be except able in aircraft and satisfy the industry. Maybe, just maybe…
It depends on what fuel you use – and that’s the beauty of a Diesel engine – you can burn a multitude of fuel/s that will not produce toxic emissions – some of them can make you hungry – but it’s all about cost – peanut oil or vegetable oil is lot more moola than Jet-A.
If you stand behind a turboprop you get a considerably large amount of Jet-A emissions – and yet – I know of no one that has become sick or dropped dead as a result of working around said Jet-A engines – even after 30 plus years – good right? – sure it’s not the best air to breathe and the turbine produces a huge amount of exhaust versus a Diesel – but still not the instant killer that one might imagine.
As for the Diesel engine itself – they use Diesel engines in the mines like the Hutchinson salt mine in Kansas – (largest one in the USA) – and they use a compilation of different fuels like peanut oil and other types – those guys are doing quite well and they all live out their lifespans – as I stated – yes those special fuels are quite costly – but they will not harm you – and when burning Jet-A a Diesel produces a fraction of the emissions of what a turbine kerosene burner produces – and it also produces a fraction of harmful emissions compared to a big Lyc or Continental burning 100LL.
If you do the math – a Diesel pays for itself in fuel cost and a greatly reduced fuel burn and maintenance – for some with the right airframe – the cost of STC’ing a Diesel into it will come back to the owner with those reduced operating cost’s – – – over time of course – but it will come back.
Gone are the days of the black sooty smoke seen in the old Diesels.
Diesels have made great strides and we have only touched just the tip of the iceberg.
By 2040 or so, gasoline powered aircraft will probably be found only in museums and barns.
The problem was stated very well, the cost of overhaul of a piston engine can exceed the value of the airframe, and diesel conversions are even more expensive and less practical. Add the difficulties and expense of increasingly scarce and expensive boutique fuels, and legacy aircraft become less and less appealing.
We are not doomed, however. Probably within the next decade, the energy density of batteries will increase to the point where it approaches that of gasoline, and the charge times will decrease significantly as well. We’ve already seen huge drops in the price of batteries. GA will be electric, no (local) pollution, no noise, no vibration. During the transition, new airframes will be “cleaner” to maximize efficiency, no protruding rivet heads, more lightweight composites like carbon fiber.
A lot of what we’re flying today is 50 year old technology or older. Yes, it works, but the writing is on the wall, we need to move to newer stuff. It will cost money, but when was the last time anyone promised us that aviation was going to be cheap? Electric airplanes will actually be less expensive than gasoline airplanes because they are much simpler. TBO on electric motors is measured in decades, you change two ball bearings and you’re good for another 20 years. Instead of “SMOH” being quoted in aircraft ads, we’ll see “TSBX”, or Time Since Battery Exchange.
Time and progress march on, march with it or get left behind.
I hope you are correct. Electric engines would be a huge boon for GA, for a lot of reasons.
But the math isn’t on your side. To get the equivalent useful energy (taking into account the far greater energy efficiency of electric motors) of 50 gallons of 100LL, you would need over 5,800 pounds of batteries. This assumes you are using some of the best batteries available right now.
Obviously no aircraft design is going to be able to cope with that. Batteries will have to get almost 20x more energy dense than they currently are to compete with gas, and that isn’t something that can be done with the tiny incremental improvements we are currently seeing.
Someone is going to have to come up with a revolutionary new way of storing electrical energy to make it viable in aircraft. That may very well be possible, but I haven’t seen anything to make me think it’s likely to happen soon.
To say that Heavy Fuel – (Diesel) – engines are “less practical” is completely wrong.
It is in fact an option that is available right now and it is totally practical if you want to keep flying – especially if you are somewhere in the world where only Jet A or Diesel fuel is available.
Yes – right now it is going to cost considerably more to purchase and have a Diesel installed in an aircraft that has been STC’d for your aircraft – (and there are currently not a lot of STC’s out there) – but that is slowly changing and provided your aircraft is a worthy candidate you are virtually guaranteed to make your initial investment back in the considerably less operating costs.
The TBR and TBO numbers are also increasing and a Diesel will almost always make it to TBO or TBR and even exceed it – (barring any incidents like a prop strike) – and – you can burn a multitude of fuels – plus – a Diesel emits a fraction of the pollutants versus a 100LL Avgas engine.
If you have the means – you can purchase a new Pipe Archer DX – or any number of Diamond aircraft – and several others are quietly working on Diesel – (Heavy Fuel) – powered aircraft.
Sorry – but to say that they are impractical – (or as you stated) – “less practical” – (is again) – completely wrong.
With the millions of $$ spend so far to replace 0.7% of the gasoline used in the US.
see https://www.eia.gov/dnav/pet/pet_pnp_refp2_dc_nus_mbbl_a.htm ;
my big concern is that there is only one source of TEL in the world, in England.
https://en.wikipedia.org/wiki/Innospec
If the supply of TEL stops, all of our piston aircraft are grounded, except for those with the mogas stc, AND can get autogas without ethanol.
I was buying tons of that great red 80/87 avgas back in the late 80s, up until about 1990. That is contrary to Ben’s statement that we went to 100/130 in the early 70s. Am I mis-reading something here?
I got a kick out of the writer above stating he can get avgas for $4.50 per gallon and premium alcohol free auto gas for $2.90. WOW. Add $1.25 to those numbers here in the NW.
Of course the issue here is the very low production of gasoline powered GA aircraft and the high cost of upgrading an aircraft to either electronically controlled fuel injection or diesel engines. It is impractical to spend $40 – $80,000 to replace an otherwise perfectly good engine on a $30 -$60,000 aircraft. So the vast majority of us are stuck in the past as we can afford neither a New Aircraft or a New Engine design. For the 10 – 20 years I have left to fly, I don’t anticipate retiring my carburated Lycoming and Continental engines, which are currently running on a mixture of 15% 100LL mixed with premium Mogas. If 100LL dries up, as far as I’m concerned, it will make little impact on my operations. My concern has more to do with the high cost of 100LL (Now averaging around $4.50/gal) while autofuel costs continue to decline (Premium alcohol free Mogas is roughly $2.90/gal in our area). The one thing I think we can count on is that whatever boutique fuel replaces 100LL, it will be even more expensive and help to continue in the decline of general aviation.
We need more General Aviation, not less. Every human activity uses valuable resources. We have already dealt with the main polluters. Wasting time and energy chasing after every tiny bit of pollution must be already causing more than any possible gains in an uncertain future. Finding a practical alternative fuel, is already looking like a giant, giant boondoggle, with no practical substitute to 100LL likely to be found. General Aviation is already burdened with more than enough challenges. Taxpayer money would be better spent by expanding opportunities for youth to learn about aviation and to get involved, as well as for us seasoned pilots to stay involved, so we can expand the teaching of technology to even more young people, demonstrating the joys of flying. We need to further the economic benefit to society afforded by a growing rather than a shrinking segment of aviation.
I have witnessed the enormous waste of money the government spending on the ”NEW” Aviation program. A well known aviation facility on the east coast of Florida was given the book and funds on how to do these tests.
Competitors supplied their fuel mix. The requirements were ridiculous. The first go around (yes there are more) ran out of funds with little or no results. Typical GOVERNMENT PROGRAM. BTW the facility is on its second set of the Government new aviation fuel program. Millions more to be wasted…
So why not plan on using Diesels? If EPS can overcome the FAA hurdles I would think that they would be able to provide us with the engines we need – what say you?
At the very least – one would think that someone like Continental or Lycoming would jump in and buy EPS and finish the certification.
Thanks Pat
Why not? Because, as great as that solution might be in the long run, it would cost a fortune (at best) and would probably (finish) killing general aviation (at worst), at least in the United States.
First, there are only a small handful of these engines currently on the market. So, while the ones available have (probably) been very carefully crafted to cover the widest cross-section of the piston engine market possible, they simply will not cover the entire legacy fleet. That means, without developing and certifying more engines (at enormous expense), some number of legacy aircraft will be grounded, probably forever. Think of the radial crowd, for one instance. It’s also worth considering that these engines are inherently heavier and often liquid cooled, which adds even more weight; many light aircraft with tricky weight and balance envelopes won’t be able to cope. Fewer aircraft means (even) higher aircraft prices. It also means even less demand for aviation related services and equipment which, again, means (even) higher prices, at least until the companies fold.
Then, there is the problem of certifying these engines to be installed in more than the tiny handful currently possible. Someone has to pay for that and jump through all the FAA hoops to get it done. Then, the end result has to be affordable enough that aircraft owners can actually have them installed. (Keep in mind that simply overhauling the existing engines already regularly costs more than the airframes are worth!) That is a tall order, even in the most ambitious of business plans.
In short, the hurdles faced in supporting the legacy fleet are huge, while only the wealthy can practically consider new aircraft (even today). So, without some major change in the regulations for certifying aircraft, it is unlikely that what you ask would ever work economically.
Very good article Ben,
Unfortunately switching to the most sophisticated fuel injection and ignition yields only a 3-4 point reduction in Octane Requirement. Not enough for most engines to take all the lead out. The reason we can’t achieve the low octane requirement with EI/EFI (compared to car engines) is that we are using air-cooled engines which have unusually dirty combustion chambers due to their high oil consumption. Air-cooled engines have high oil consumption because of higher engine temps requiring greater tolerances. Porsche eventually realized that and stopped making their iconic air-cooled boxers.
Direct injection can provide another drop of 3-5 points in octane requirement. The combination would be enough to use mogas in anything we fly but the development costs of a Direct Injected engine is far too great for the aviation industry.
You’re not wrong – but there is always a way and there are always those that can figure it out.
Continental already has a couple of certified Diesel engines – and SMA is producing diesels and developing a new 6 cylinder version – and then there are a few new aircraft powered with Austro Engines – along with a few others currently in development.
Piper offers a Diesel powered DX Archer – along with Diamond and it is happening – albeit – at about the pace of molasses flowing in winter – but spring time is upon us and the weather is beginning to warm – it is happening and the flow rate is increasing.
People are noticing that 100LL might disappear in the near future – and engine manufacturers like Lycoming have chosen the route to make a modern ECM controlled engines that will run on mogas – perhaps that will be a way to overcome.
I think we can all agree that when fuel refiners no longer are making a decent enough profit on 100LL then it will disappear – 100LL has almost disappeared entirely through different parts of the world in Europe and Africa.
Just like everything in aviation – it all takes time – and it all is expensive – but it is all worth it for those with the Flying Habit – we need our fix and I believe that Diesel – (Jet-A) – is going to be the choice.