OT leaded aviation fuel

[J Tiers]

.................

It would also be a great opportunity to drag aircraft engine designs into the 21st century; fuel injection, electronic fuel ignition, 4 valves per cylinder, liquid cooling etc. One ignition per spark plug, no more HT leads. Higher specific outputs (in a world where 150BHP from a 5 liter engine is seen as "normal"). Even, shock, horror, only 1 spark plug per cylinder

Ian

It is not that simple.

Aircraft are driven by safety rules. Safety DOES "rule". If you "dragged aircraft engine designs into the 21st century", there would not be another one produced for years.... It takes a very long time to get an engine "certified", and it is expensive. The total market for aircraft engines is tiny, compared to autos, and even auto companies do not enter into that sort of design project lightly.

By demanding that engines be "new, clean designs" you would shut down piston engine usage. First the requirements would have to be established. Then designs to those requirements would have to be done. Then they would have to be certified. Finally, every individual aircraft design would have to be certified for installation of the updated new engine appropriate for it.

Not all engine types would have an updated design. For just one example, here are still aircraft flying with a Continental A-40, a rather low power 4 cylinder engine designed somewhere in the 1930s. I believe there were around 2700 ever built. It is unlikely that a new version of that power level would be attempted, and those aircraft may not be able to be certified for a heavier, newer, higher power engine. They would then be grounded permanently, and lose all value overnight. There are other examples as well. Now you get into the "takings" debate.

It is a low volume usage, overall, and we already have the 100LL fuel. If the oil companies can get a no-lead fuel certified, then that is the approach to take. It would be a "single target" approach, and would not subject every piston engine aircraft owner to a $40,000 expense to replace the engine.

Even "just" a tear-down to replace valve seats may cost several thousand $ per cylinder. Everything in or on an aircraft is a lot more expensive, because it must be "certified for flight", and specially qualified people have to do the work. And even those people screw up, the engine failure rate soon after overhaul is fairly high compared to after a few hundred hours.

If you say "OK we will rely on incremental replacement, as engines get replaced normally", then you will have to explain exactly how that is different and better than what exists now. Because it is effectively not any better.

If you suppose that you will EVER get one plug per cylinder, I think you are dreaming.

Remember that thing about "safety rules"? Having just ONE of anything complicated (like an ignition system) that is critical to flight in an aircraft that may fly over mountains, or Lake Michigan, etc, is just not going to happen. Nor should it.

[A.K. Boomer]

For sure actually kinda a loaded question as depends how you look at it --- last pump standing or what I remember witnessing as far as vast majority...

So true with power per weight gains they could be making, but little turbo charged direct injection gassers would be having a few more failures im afraid,,, those big lumbering low output engines do have a pretty good track record for dependability... plus the fact that the engines displacements match the prop speed, they would have to gear down the little buggers so they could be in their range - more complications... and there goes some of the weight bennies...

[Cheap Jon]

Thanks to the EAA for doing the test, many aircraft have a FAA auto gas certification.

Jon
SW Mi

[sid pileski]

I’ll say this, I use 100ll in my model engines. Way less crap in it and it smells better than today’s petro.
Also, a gallon will not go bad in a year or whatever it takes for me to use it up.

Sid

[ironmonger]

As regards the installed base of old engines, has there been research done regarding the use of 100LL in modern fuel injected electronic ignition engines that are derived from motorcycles or cars? These are primarily used in experimental aircraft, so the old school logic would not apply to them. If I owned one I would want to know. Or is automotive fuel available on the flight line for the new boys...

[mickeyf]

Years ago, when I was working in GIS, one of the projects was for mapping a third world country's phone system. Ultimately, they Leapfrogged over fixing their deteriorating, unreliable copper phone lines to building cell towers. Recently someone mentioned here about how we might have skipped CFBs and gone directly to LEDs. This already old article may suggest the aircraft analogue to those situations:

https://www.theguardian.com/world/20...ight-in-canada

[tom_d]

Not totally true as there has been magneto ignition systems for advance and retard for the last 125 years or so.

Almost all (?) spark ignition aircraft engines retard the ignition during cranking.

Aircraft engines have two separate magnetos, and two spark plugs per cylinder. There is a model of Bendix mag that has an auxiliary coil in the starting circuit that's activated during engine start. This coil simultaneously grounds the engine's other mag, rendering it inoperative, and produces what's called a "shower of sparks" that occur at a retarded timing as compared to normal engine operation. This is to aid in engine startup. Once the starter circuit is released both engine mags operate normally, with fixed timing.

[tom_d]

Tom_d,

I know what you mean about "Any replacement fuel would have to be compatible with every single piston engine aircraft flying today", but how did the car world do it? They must have also used the same argument against eliminating lead (and the fact that the Ethyl Corporation would lose millions had a lot to do with it I guess).

One option would be to have more than one grade of fuel, as is done for cars (I can pick from E15 (95 octane +15% ethanol) or E5 (98 octane + 5% ethanol) (and diesel of course, sometimes LPG. occasionally 102 octane, but rare). Costs would go up a bit probably.

Another way may be to add a lead replacement: https://www.holtsauto.com/redex/prod...ent-multidose/ but this would no doubt involve type approval etc.

I know that older car engines can have their valve seats replaced with harder metal, after which they can use unleaded fuel. Also an option maybe?

If the aviation industry don't respond, they may be the next target of the Eco's, possibly flight bans over cities etc. Far fetched? Try entering many German cities with a pre-2009 diesel: https://www.reuters.com/article/us-g...-idUSKCN1NK28L Millions of cars & vans are affected by this, not just a relatively few light aircraft.

Ian

Many reasons for the difference. The auto industry was able to respond by shear volume of engines produced. There's more to spread the research dollars around. The auto industry, both manufacturers and end users, have substantially more latitude when it comes to experimenting than does the aviation industry. Any change you want to make to an FAA certificated aircraft comes with a resounding NO from the FAA. First you must ask; "mother may I?" and then they will have strict rules, polices, and procedures to follow for even the most minor of changes. This all takes time and, more importantly, money.

At one point there were several choices available for aviation fuel. Not that long ago 130 octane fuel was an (expensive) option. Today we must settle for 100LL only. I'm going to suggest the biggest reason for the consolidation was the military's moving away from piston engines into an all jet fuel powered fleet. With the loss of that market it's economically impossible to offer a variety of fuels to the refinery's remaining customers. As it stands now there are only a few refineries making 100LL, and it's only done a few times a year. Because of the lead content there are procedures that must be followed to avoid contamination of the system.

There are other options for fuel available. Many of the engines in use today will operate on high octane "pump gas" that is run in automobiles. There are limitations, though. Auto fuel will not run in higher compression aviation engines. And it's limited to carburetors only. Auto gas in an aviation fuel injection system vapor locks with incredible speed. The most important concern when contemplating the use of an automobile fuel in any aircraft is that there must be NO ethanol in the fuel. None. In addition to the damage ethanol would cause to gasket materials, like many have experienced with our old yard equipment, ethanol holds water. That's all well and good on the ground, but when you're at altitude and the temperature is well below zero degrees Fahrenheit the slightest amount of water is going to make for a bad experience.

[tom_d]

I’ll say this, I use 100ll in my model engines. Way less crap in it and it smells better than today’s petro.
Also, a gallon will not go bad in a year or whatever it takes for me to use it up.

Sid

Works well in model aircraft engines. Works well in 2 stoke engines in weed trimmers and chain saws. Gotta be careful though, to label the containers. 100LL has a blue tint to it, so it already looks like some gas does when mixed with oil. As to shelf life, I've had some that was a decade old that looked and smelled just as if it was newly refined. Biggest problem with long term storage is to keep the container tight! The fuel will not go bad, but it is quick to evaporate if left in an open, or vented container.

As regards the installed base of old engines, has there been research done regarding the use of 100LL in modern fuel injected electronic ignition engines that are derived from motorcycles or cars? These are primarily used in experimental aircraft, so the old school logic would not apply to them. If I owned one I would want to know. Or is automotive fuel available on the flight line for the new boys...

Don't know about any formal research, but aviation fuel works well in electronic fuel injection systems. Where it does NOT work is with emission systems that rely on a converter. The lead will wipe out a catalytic converter in short order. Major concern with automotive fuel on the flight line is that it must not contain ethanol. No matter what the engine, when using aviation fuel it's important to monitor the spark plugs. Lead deposits can accumulate around the insulator and cause fowling if not cleaned on a regular basis. How often to check the plugs all depends on the way the engine is being operated. Altitude, speed, mixture control, and heat range of the plug are among the variables.

[tom_d]

For sure actually kinda a loaded question as depends how you look at it --- last pump standing or what I remember witnessing as far as vast majority...

So true with power per weight gains they could be making, but little turbo charged direct injection gassers would be having a few more failures im afraid,,, those big lumbering low output engines do have a pretty good track record for dependability... plus the fact that the engines displacements match the prop speed, they would have to gear down the little buggers so they could be in their range - more complications... and there goes some of the weight bennies...

Yep. Off hand I can't think of any non aircraft designed engine used in aviation that doesn't have some sort of belt and pulley or gear driven reduction drive. Weight, maintenance, reliability. All come in to play. It's frustrating, as there are so many proven reliable engines out there. It's just not a simple thing to bolt a propeller on the front and go aviating.

[Optics Curmudgeon]

There are many homebuilts using converted Volkswagen engines, all direct drive.

[Optics Curmudgeon]

Just to clear some things up, tetraethyl lead is used in 100LL fuel to increase octane rating, made necessary by the large (25 degree, typically) spark advance used to get reasonable power from low compression engines. Valve lubrication has nothing to do with the presence of lead in the fuel, in fact lead is a major cause of valve problems in air cooled aircraft engines. 100LL has, in addition to tetraethy lead, ethylene dibromide, used as a scavenger to try and get lead compounds out the exhaust rather than have them deposit on engine components or in the oil. It's only partly effective, and a common place for remaining lead compounds to deposit is on valve stems. Lycoming engines are more susceptible to this than Continentals, the deposits eventually cause valve sticking, at first when the engine is cold. The early result is rough running at first start, referred to as morning sickness. Eventually a fully stuck valve results, leading to generalized excitement. Lead may help with valves in water cooled auto engines, but it's trouble for air cooled aircraft engines, which operate with higher cylinder and head temperatures.
Swift Fuels has developed a 94 octane unleaded fuel (UL94) that's FAA approved, via an STC (supplemental type certificate) for use in about 75% of the GA fleet, basically those engines with compression ratios of 7.5 or below. It's available at a number of airports around the US now, and its use is expanding. Swift also has a 100 octane version that is the full equivalent of 100LL, but the FAA hasn't approved that one yet. Aircraft engine manufacturers are already increasing the time between overhaul times for engines running on unleaded aviation fuel.
As for new (post 1930's) engine designs, consider the Rotax 912 and 914, both certified and in use in numerous certified aircraft, the 914 powers the Predator drone. Rotax engines have water cooled heads and air cooled cylinder barrels. On the non certified side there are a number, including the D Motor, a water cooled, fuel injected flathead aircraft engine with FADEC engine controls. It's actually a viable alternative for homebuilts.
I, for one, am looking forward to unleaded aviation fuel to show up at my local airport, it will cost more but will also solve a couple of vexing problems with aero engines.

[barracudajoe]

FYI - Lead was first added to gasoline in 1921 and was the result of auto industry research, before that gas was unleaded and WWI planes all ran on it. The quest for more power led to higher compression engines and the need for anti-knock additives.

https://www.eesi.org/papers/view/fac...engine%20knock.

[J Tiers]

Apparently those Rotax engines are not all trouble free..... I saw some info on problems specific to them, which I need to find again. Just an example (perhaps) of another reason why engines for aircraft do not have radical new designs very often, too many new variables and unknowns.

You really do not want a lot of variables and unknowns when you are flying over territory which you do not want to have to try to land on (and get it right first try).

The 737 MAX was "certified" in its old form with the questionable MCAS behavior..... Something to remember with regard to "certified", even though "certification" is a necessary requirement. In that case, the "certified" version may not have had the exact same behavior of the shipped version with "minor and inconsequential" changes. It's those things that "won't screw up anything" which often bite you.

Not everyone agrees on the problems, and there is some evidence that they are not all really "Rotax" problems... for instance the following:

https://midwestflyer.com/?p=3412

[Optics Curmudgeon]

Not everyone agrees on the problems, and there is some evidence that they are not all really "Rotax" problems... for instance the following:

https://midwestflyer.com/?p=3412

From ten years ago.....