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Discussion in 'Flight Following' started by brien23, Dec 8, 2020.
I still think we’re such small potatoes that nobody in gov cares either way.
I have a IO-360 lycoming with the Surefly variable timing. 8.7 compression. I am guessing that I could run on the 94UL, without a problem. I think that it is the turbo engines that really need the 100LL.
This issue has been a concern ever since I bought an airplane. This going to be swell maybe I should sell now, while I can. Get a Starduster II with a O-360 for fun and run mogas.
I wouldn't bet on that. We are the last leaded fuel on the planet. I think that "Finally doing away with the last of the leaded fuels would be perceived as a feather in their cap. All they know is 'lead bad, must get rid of'. The unintended consequences are rarely a thought. Way back, I remember a push to 'get ride of chlorine'. Chlorine is a toxic gas after all. It took somebody pointing out that cholera and other water born diseases would kill way more than the occasional industrial poisoning. Their ignorance is matched only by their zeal for quick solutions.
It's been decades since I first heard the trope that 20% of the sales base burn 80% of the 100LL. I just wonder if there's been a more recent snapshot at this supposed truism. Is the canyon between running a turbine vs flogging turbo pistons like a scalded ape really the difference between making black and financial insolvency?
The loss of HP may be sufficient to reduce the climb performance for many singles, or single-engine performance in many twins, to unacceptable and unsafe levels. That is in addition to reducing the utility of the aircraft to perhaps impractical levels. It would be analogous to the local authorities telling you that you needed to reduce the square footage of your home to meet newly adopted non-grandfathered building code requirements. I mean, who would object to that?
Turbo normalize engines excluded.
I think it was found to be relatively easy to get to 93 or 94UL without using lead or exotic avgas formulations and still meet the other requirements of av fuel (vapor pressure, solvent compatibility, etc.) And that will serve SOME higher compression engines. But getting to 100 octane is apparently more difficult while meeting all the other fuel requirements for aviation fuel, AND doing it at an affordable cost. It is not a simple chemistry problem.
I looked at some stats, it looks like the typical continental and Lycoming is 8.5:1 compression with turbocharged versions at 7:1
is that actually "high" compression? I was under the impression high compression is closer to 12 or 14.. per the EPA in 1975 the average car was 8.2:1 .. most cars today in which most people are putting 87 octane gas is around 10:1
My understanding was that the lead was added for knock and to assist with the valves.. seems like competent fadec could take care of the knock issue
Today’s vehicles can get by with higher compression due to better controls over ignition timing, fuel and variable valve timing. I think just having computer control over our ignition and fuel would let us run a lower octane fuel without losing hp. Shouldn’t be hard to develop a system for our engines
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"Shouldn't" is a big word.
And yet here we are. 30 years later... I could understand the lack of an stc for older planes. But the new stuff coming out has done nothing. Unless you count the heavier and lower horsepower diesels.
The volume is low and the regulatory barrier to entry is high. the Diesels do have slightly less horsepower however all of the ones I know of are turbo, at cruise altitude the diesels end up being far more efficient
The diamond 62 will carry 7 adults on 12-14 gallons per hour combined at over 150 ktas.. and with an almost 2000 hour TBO I bet these engines last longer than most big Continentals..
i guess you didn’t walk very far from “another engine thread”
My understanding is that that 7:1 is what you have when the the turbo isn't ... turboing. The whole point of turbo is to boost more air and fuel into the cylinders - so you have actually higher compression when the turbo is working - thus turbo charged engines need high octane fuel.
Then why do they have it if they cant sell it?
In general, the turbocharged engines and anything with a compression ratio of >8.5:1 need 100LL. But the rest of the fleet would be OK with 93 octane or better (again, generalizing).
Once upon a time, it was claimed that the "working" recips were the ones which needed 100LL and they also consumed the majority (70%, IIRC) of avgas. I bet nobody dares to do that study today. That study is 20-30 years old and in those days, there were still a fair number of "working" Beech 18's, WWII vintage fire bombers, and DC-X recips in the low budget freighter role, most of which needed 100LL. Times have changed and I bet that whatever "working" piston aircraft remain, they consume a relatively small fraction of today's 100LL.
Regardless, there are *some* aircraft which do require it. It would be awful if by the stroke of a pen, all of those aircraft were substantially devalued.
The latest update (8/20/2020) just says, "The FAA, fuel suppliers, and aerospace manufacturers continue to develop high octane, unleaded fuel formulations. The goal of these efforts is to identify fuel formulations that provide operationally safe alternatives to 100LL. The PAFI program continues to support the efforts of fuel producers as they bring forth alternative, unleaded fuels for testing and evaluation." ----Kind of a kick-the-can-down-the-road update from the FAA.
Having just bought a new vehicle with all that fancy electronic engine controls, I'm not sure it's ready for aviation. Read reviews and message boards about a lot of new vehicles from all brands, and you'll find lots of problems, service bulletins, recalls, etc. I'd wager at least 10% of new vehicles have some form of issue from minor to total failure. My dealer even went over lemon law as required and admitted they have only had to do that twice.
How many new GA engines are sold a year? Maybe 5,000? And that includes everything from O-200's to Rotaxes to IO-580's. Let's say you target the O-320/O-360 market and create a new, higher tech engine. Maybe you sell 2,000 engines a year. 1/3 for new aircraft and the balance for upgrades/replacements. Given that it costs millions (and not 2 million, lots more) to design, build, certify, and set-up for manufacturing a new engine, how can anyone make a successful business out of developing a new aircraft engine?
Most of the time anything under 9.5:1 is a normal compression ratio suitable for lower octane fuels. Once you get above 10:1 you start needing to use 91/93 octane to combat detonation at high load. Of course that's simplified, and I'm speaking in generalities without discussion of static vs dynamic compression and other attributes that can affect detonation (like aluminum vs iron heads, variable timing/compression, etc).
Turbocharged engines start with a below normal static compression ratio in order to provide for the additional air/fuel being injected by the turbo. Turbo engines generally start with 7.0-7.5:1 compression, but add 10psi of boost it effectively runs closer to 11:1. Getting past 12:1 is pretty difficult to do with any pump gas.
Eh. Mazda makes 13:1 static compression NA engines that run on 87. VVT of course with some other tricks.
Right, and Infiniti has a variable compression turbo engine that can get up to 14:1 on 91 octane. However, in both of those cases there is quite a bit of tech/complexity involved in achieving that. Direct injection being a big part of that, as well as some very efficient combustion chamber mechanisms. Most of that isn't too useful for marine/Aviation applications since wide power adjustments aren't really common for most aircraft.
Notice the cylinder volume and RPM generated by those high compression engines (often motorcycle engines). The cylinder volumes are small, and when the engine is making "real" power, the RPM are way up there. In comparison, our engines make full power at relatively low RPM and have huge cylinder volumes.
Why does this matter? Detonation. Cylinders with large volumes are far more prone to detonation than engines at the other end of the spectrum. I'm not a hard core engine guy, but the "why" goes something like this:
In small cylinders, the flame front burns through the small cylinder volume fast enough that the fuel burns before the pressure and temperature at the "corners" of the combustion chamber self-ignite the unburnt mixture. In larger cylinder volumes (where the flame front has to travel several times as far), the fuel in the corners (the farthest points from the spark plugs) gets heated and compressed a lot (that's a technical term) before the flame front arrives and you need high octane to make sure the fuel in the corners burns before it detonates.
Here's a 1962 paper on the effects of cylinder size on detonation and octane requirements if you don't mind registering:
I keep hearing this as well, how a small minority of the recip planes out there burn the majority of the 100LL. 20% of the airplanes burn 80% of the total supply of 100LL, or similar. Poked around the web briefly, but couldn't find a good source.
Have to think it can't possibly be true anymore, right? Likely for the reasons kyleb points out above?
Who is burning 100LL in big commercial operations now a days? Call it any operation with more than 50 aircraft, flying ~750 or more hours/year? Cape Air with their Cessna 402s I guess? Who else?
Definitely not for Aviation.
Even the Ag guys have moved from Stearman and Ag-Cats to turbine powered hardware. There just aren't a lot of working recips any longer, unless you count training, pipeline patrol, and banner towing.
The thermal efficiency of the engine is directly related to its compression ratio. You get a higher conversion of heat to mechanical energy the higher the compression ratio. That means a lower mass flow of fuel/air for a given output compared to a lower compression ratio Otto cycle engine.
Lowering the compression ratio is "going the wrong way" for aircraft applications.
At some point, the topic of leaded aviation gas will become a political football. Because there is no solid plan for it, it will happen overnight.
The EAA saw this coming years ago, and they pushed for a partial solution that (if it had been successful) could have kept most environmental lobbies off of GA's back.
They started with 2 very simple steps: Mogas STCs for small planes and offering Mogas on airfields.
But cheap Mogas STCs have not really caught on, and some buyers consider it a negative if a plane has it installed.
In addition, the few airfields that brought Mogas on seem to be phasing it out.
The old AOPA flight planner had an option to suggest routes with Mogas, but that went away with the change to iFlightPlanner. I don't know of any other flight planning software that has that option.
The fact that this failed is going to cost airports and piston aircraft owners (especially those of us running legacy engines) a lot of money, because when leaded gas is phased out, instead of a 2 decade sunset period that the EAA was prepping us for, it will be a 2-5 year sunset period. When evaluating the environmental impact of leaded gasoline, the conclusion will be that pilots, airplane owners and the FAA cannot be trusted to phase out lead, so it will have to be banned, and it will be banned quickly. Best case scenario may be that a single company like Swift will set the price for AvGas for all of the US. Worst case could be that there is no fuel with a higher octane rating the 91, and the modifications required to function with that restriction will result in a large chunk of the piston twin fleet being declared a total loss. Conservatives will not care because for someone to make enough money to matter to conservatives, that someone is already flying a jet. Liberals won't care because they cannot differentiate a Lear owner from a Sonex owner.
And pilots will be angry, but none of them will be able to admit that our lack of willingness to fly Mogas (when safe and available) will be partially to blame.
One solution would be-- =gasp=-- offering two grades of fuel at airports. Now where have I heard of that before?
Or ship one grade of UL fuel, and very small amounts of octane booster (lead or other) and mix it at the pump. Or add it to the aircraft's tank afterwards, like us little guys do with TCP now (or MMO! ), or the jet guys do with Prist. Used to be, you could buy real lead additive at auto parts stores, we had a '69 Bonneville convertible with a high compression 428 that needed it or it would ping like a 1975 Ford going uphill on a hot day.
The A-65 in my T-Craft required 73 octane minimum. Ran great on leaded car gas when that was still available.
Problem with mogas is getting it without ethanol. Some states, it simply isn't available. The EPA requires mogas to be oygenated; you can do it with MTBE which is undesirable for several reasons and outlawed in many states, or you can add ethanol since it's cheaper and heavily subsidized, politicians don't care about the undesirable effect on your engine, if they even know where the engine is in a car. We'll probably have ethanol as long as we have politicians in corn states, making mogas not an option for aircraft.
It doesn't really have to be mogas. It can be an unleaded fuel with 93 octane and the appropriate additives and vapor pressure. That would still be a less expensive product than 100LL, because of the issues lead brings to the table.
As far as blending at the pump or by hand, tetraethyl lead is nasty stuff. I wouldn't want Joe 6 pack messing with the stuff in a concentrated form. So I'm not sure how you get around the issue of the aircraft which need the high octane stuff.
Most engines have been rebuilt at least once, and should have hardened valve seats by now.
Continental says that they believe their engines can make rated power on any of the proposed 100LL replacement even at slightly lower octane.
The problem is production at this point.
Been 50 years. They were talking about this when I started flying two decades ago. I'm not going to hold my breath.
Years ago Lycoming built an O-360 engine that was rated at 168 hp for 80/87 fuel. The same parallel valve engine delivers 180 hp today on 100LL. That difference is comparatively minor. What might the O-360 deliver on MoGas which exists with an equivalent octane greater than 80/87? Fuel injection and angle valves raised the O-360 engine to 200 hp on 100LL just by these two items. (I don't think compression was raised between the 180 hp O-360 and the 200 hp IO-360.
I realize there is a slight difference in octane measuring methods between the two numbers, but how many engines are running in test cells to establish that difference between MoGas and 100LL. I bet there are none. Maybe there never have been any controlled tests beyond the present STCed engines?????
Most of the working grade piston aircraft run high compression engines that require 100 octane fuel. Most of the piston aircraft will do OK on 94 octane. But the big bore engines use about 80% of the aviation fuel used, since they use more fuel and are flown many more hours per year. So I guess that we will se 100 around for a long time.
With a username of Petersen, shouldn't you know?
As discussed earlier in the thread, that statistic is obsolete and probably goes back to the tail end of the radial era where the WWII and immediate post war radial types were still in use commercially.
I expect the existing, elaborate distribution system for aviation gasoline (mostly because it contains TEL) is almost certainly going to remain in place for any unleaded fuel substitution. Even the distribution road tankers are likely to continue to be segregated from carrying any other gasoline blend product. The volume of avgas consumed continues to decline (this COVID year didn't help) and even if the refiners use some sort of automotive spec base for their avgas blend they won't want it to be mixed in any way with the mogas supply system. Among other things, the liability issues are magnificent. Remember, right now they sample and test every single run of avgas to ensure it meets the specifications before anything gets loaded in a truck.
You missed the point. Set aside your obsession with horsepower.
Where is the lead mixed into the avgas in the distribution chain? I imagine it isn't at the refinery, its at the distributor. And I doubt they have a truck or two that are specialized to only delivers avgas.