Lycoming's View: Airworthiness by Design, Not Luck

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For decades, general aviation has been operating and designed around a single fuel – 100LL. Now environmental and economic pressures are driving the search for an unleaded alternative. Lycoming firmly believes that an equivalent performance unleaded aviation grade replacement for 100LL is the best total solution for our industry overall. We also know that using automotive blends in aviation is possible for certain engine models if you put the correct controls in place on the fuel. Lycoming's consistent objective is to give our customers as many fuel choices as possible while still maintaining airworthiness.

In the following three guest blogs, Lycoming specifically addresses the topic of automotive fuels for aviation, including our approval to operate certain Lycoming O- and IO-360 engines using an automotive specification fuel. Lycoming strongly recommends a thorough review of the latest revision to Lycoming Service Instruction 1070, "Specified Fuels."

Lycoming is well aware that other aviation equipment manufacturers have allowed "pump gas," in some cases with ethanol. In the details they provide warnings and cautions addressing some of the issues we raise in these articles, leaving it to the operator to assess risk in using a fuel where they do not know the core properties other than octane. We do not agree with that approach.

Two terms are used repeatedly throughout this series: "pump gas" and "mogas." "Pump gas" refers specifically to fuel that conforms to the ASTM D4814 or Euronorm 228 specifications for automotive fuel and is available for retail purchase at automobile filling stations. "Mogas" refers specifically to fuel that also conforms to the ASTM D4814 or Euronorm 228 specifications, but controlled and labeled differently such that it is "fit-for-purpose" for aviation.

Part 3

Lycoming tests every engine that rolls off our assembly line. We take them into one of our test cells, attach a propeller and appropriate sensors, and then operate them through a range of tests. These tests can last from an hour up to four hours. We also use our test cells to evaluate components and new products. Every year we do this for about 3000 to 4000 engines. Lycoming purchases and consumes a lot of avgas.

So Lycoming has something in common with every owner and operator out there. We all experience pain at the pump. The price of fuel is going up for everyone, regardless of your mode of transportation. According to, the average price of 100LL between May 19 and July 13, 2011, was $5.79 (U.S.) per gallon in the United States, a 128 percent increase over the 2001 price of approximately $2.54 per gallon. In 2011 automotive pump gas is currently averaging $3.64 per gallon in the United States, a 254 percent increase over the 2001 low average of $1.04 per gallon. But wait, those pump gas prices are not at the aviation FBO.

According to, the average price for mogas at U.S. FBOs currently stands at $4.44 per gallon, a whopping 327 percent higher than the 2001 automotive pump gas price. Admittedly, these are averages and not representative of prices everywhere. Leave it to economists to figure out the comparison of 2001 U.S. dollars to 2011 U.S. Dollars, but the point is still valid. Fuel prices rose dramatically in the last decade and have made General Aviation more expensive. Coupled with the desire to move piston aviation to unleaded fuel and avgas distribution availability outside the Americas and Europe, the cost issue has created significant pressure to find ways to tap into the economies of scale that come from using higher volume lower-cost fuels like pump gas.

Lycoming's automotive gasoline approval, however, did not allow pump gas. We simply can't approve pump gas for our existing products if the first objective is airworthiness. What we did approve is a fuel from the pump gas production sources that is controlled well enough to provide predictable behavior on the engine. Airframers would need to do the same. Lycoming believes companies advocating the distribution and use of automotive gasoline in aircraft ought to consider the same controls. This is airworthiness by design.

The Lycoming mogas is an option for the fleet that could use low- octane fuel. It might be less expensive than 100LL – but we all know that retail price and production costs are two different things. We also know that the "free" services provided by our FBOs need to be covered somehow. In the end the Lycoming mogas is a low-grade aviation fuel from automotive blend stocks. The same angle was previously attempted more than a decade ago with the ASTM 82UL avgas effort. You might have noticed that no FBO offers 82UL. That's an indicator that even when presented with an option, demand has not been sufficient to support a two-grade aviation gasoline fuel system.

Environmental challenges, price pressures and availability are all considerations for every owner and operator. It's the reason why Lycoming approved mogas, but it's not pump gas. It's an unleaded option that could be considered for aviation, but we fear the applicability is too low to be a universal solution and you will pay a premium over pump gas. It's the reason why we've publicly called for – and actively support the efforts towards – an unleaded replacement fuel for 100LL.

In our plant, we evaluate our performance as a business using five metrics. Four of those metrics are ranked and in order they are Safety, Quality, Delivery and Cost. The fifth is Leadership and Teamwork. Safety comes first and Cost comes last in the ranked items. We applied that same philosophy to our mogas approval where we designated the specification of pump gas such that we arrived at Lycoming's mogas. That is how we achieve Airworthiness by Design, rather than by luck. We did it and did not publicize it because our fifth metric, Leadership and Teamwork, demands that we consider all the angles, and we did not conclude that industry and owners would be best served by a distractive argument on mogas because in the end, it's a low-grade aviation gasoline with what we feel is limited broad application.

Concluding and as stated in our previous articles, Lycoming's goal as an engine manufacturer is to provide as much fuels flexibility for our customers as possible without compromising airworthiness. A mogas option could be possible for the existing fleet, but it's not pump gas. In the end, we all agree that Airworthiness by Design is the objective.

The ongoing dialog regarding the distribution and use of unleaded automotive fuels in aviation needs to be solidly based upon this consideration and the subjects raised in this three-part series. You'll find many of the same considerations in the FAA's Unleaded Avgas Transition ARC charter. These considerations are why Lycoming continues to believe that piston aviation is best served by pursuing an unleaded aviation specification fuel to replace 100LL.

Comments (96)

To be honest, I'm not sure that I agree that "airworthiness by design" is the objective. Airworthiness lends itself to discussions of certification, traceability, and such. I believe our thrust needs to be safety and economy in operation, and I do believe this could possibly be achieved by pump gas. The thousands and thousands of aircraft operated over the last 20 years on pump gas with no ill effects whatsoever would seem to refute the claim that we must have a "FAA certificated aviation spec "special" mogas" I see two issues affecting general aviation - fuel cost and fuel availability. It is foolhardy to address one without the other.

Posted by: Josh Johnson | August 10, 2011 7:03 PM    Report this comment

"The thousands and thousands of aircraft operated over the last 20 years on pump gas with no ill effects whatsoever"

Mr. Johnson, could you please provide a reference source for the claim you have just made?

Posted by: DAVID COLEMAN | August 10, 2011 7:10 PM    Report this comment


No one is keeping you from pouring mogas into your airplane. Or pump gas for that matter, when is the last time the FAA checked your tanks? Go ahead and play armchair engineer. Pump gas is widely available and cheaper than 100LL.

Just try not to ruin my passion and investment by cheering on the loss of 100LL. My IO550 needs every octane point it can get. I must say its nice to climb with the VSI firmly pegged at over 2K FPM. Or cruise at 200Kts.

Posted by: Brad Vaught | August 10, 2011 8:21 PM    Report this comment

"The thousands and thousands of aircraft operated over the last 20 years on pump gas with no ill effects whatsoever would seem to refute the claim that we must have a "FAA certificated aviation spec "special" mogas"

The problem with this statement is that there's no good data to prove or disprove it. You'll see what you want to see in whatever data is available and what is available is largely anecdotal from both sides of the argument.

I review many accidents reports each month and don't see a consistent pattern of accidents involving mogas. Then again, only 100 or so airports have it, so market penetration is minimal.

In that context, the chief problem for mogas is lack of confidence. If buyers were more confident and as price sensitive as we imagine, there would be a groundswell of demand for it.

I don't see this. The claims for mogas interest and demand seem somewhat overstated to me. My sense of it from surveys and e-mail we get and from my own research is that there's a serviceable trickle of demand for mogas. It may or may not turn into a torrent. If demand is going to increase, mogas acolytes will need sell against natural market prejudice. That may be possible. Or not.

For me personally, that would require a posted spec on the pump. Where did this gas come from? When was it tested? When was it delivered? Who's standing behind it?

Posted by: Paul Bertorelli | August 11, 2011 5:57 AM    Report this comment

If the pump says Shell or Chevron or Exxon, I have reasonable assurance that regardless of who refined the gas--it could come from anybody's refinery for relabeling--someone is paying close enough attention to it to slap their name on it.

I don't get that feeling from a plain-Jane white gas pump with no labeling on it. The U-fuel SportFuel idea helps this, but needs to get the specs and supply chain stuff upfront as almost the primary selling consideration, with price secondary.

One thing I find troublesome here is that major oil companies won't go on the record supporting auto gas for airplane because of NSIU--not suitable for intended use. This is largely for legal reasons, but they have technical basis, too, related to delivery and storage issues.

It's not that Shell or Exxon gas is somehow better, but that when you have major suppliers in the market saying do not use this fuel for airplanes--regardless of the reason--you further erode confidence.

This is not the stuff of a realistic, stable market.

Posted by: Paul Bertorelli | August 11, 2011 6:04 AM    Report this comment

This has been an interesting series, thank you Michael and Paul for doing it. We'll provide a few comments at GAfuels shortly. One glaring aspect has not been addressed however. Other than the concerns of Lycoming's legal department, how much of the company's continued reluctance in endorsing autogas is the result of market pressure? After all, Lycoming really missed the boat on powerplants for the fast-growing LSA sector, where nearly all engines from Rotax, Jabiru, ULPower and others run best on 91+ AKI autogas. I see too that Superior again offers its superb XP-320 and XP-360 engines for experimentals, and they too are approved for 91+ AKI ethanol free autogas. Lycoming makes great products, and it is good to see them joining their peers in supporting autogas, albeit slowly.

Posted by: Kent Misegades | August 11, 2011 6:36 AM    Report this comment

By calling for an unavailable 93 Octane Fuel, Lycoming has avoided dealing with the issue. Most Premium fuel is 91 Octane. Neither Petersen nor EAA STC's found a neccesity for 93 octane. Engines originally approved for 80/87, or 91/96 fuel are generally perfectly happy on 91 Octane Mogas. Every example I know of where Mogas is used, results in fewer maintenance problems, and longer cylinder life. Lycoming by calling for a currently unavailable fuel is giving the appearance, but not the substance of dealing with this issue. The current STC's were not a matter of "Luck". A lot of this issue is being driven by Lawyers, not Engineering.

Posted by: BRIAN HOPE | August 11, 2011 7:47 AM    Report this comment

I don't know if anyone noticed, but the fuel issue illuminates the class divide in aviation.
You have the business flyers and the folks with the high-powered cruisers that need the 100LL, contrasting with the "just barely able to afford to fly" people. The folks that are trying to remain in aviation need the $1/gal cheaper fuel for their C-150, Cub, Tripacers, and various VW/Jabiru/O-200 powered small creekhoppers. Even the RV-4/6/7/8/9 people could use the cheaper fuel when using the modestly powered version of the aircraft that Van envisioned.
I know that if I had a convenient, known source of ethanol-free 91/93 AKI fuel at my airport (GMU) I'd use it if I had a STC.
No, this won't help the Bonanza, Comanche, and Baron owners, but I don't think they need the help, honestly.
One thing is for certain; the constant bickering, name-calling, derision of smaller light aircraft, and put-downs of recreational flyers will NOT help grow aviation and keep it viable. Why do we do this to each other? I see it at another local (nearly empty) airport with the Jets vs. gliders bickering and whining.
Can;t we all just get along and support aviaiton in all it's forms, even if we need to be more flexible (have more fuels)?

Posted by: Scott Thomason | August 11, 2011 8:23 AM    Report this comment


I think you hit the nail on the head. No one here is telling anyone they can't go out and purchase pump gas at the local gas station and put in into there plane.

My issue is the diversion of industry resources (especially struggling FBO's and small cash strapped airports) into a non-aviation spec. product. Putting in the infrastructure and assuming the liability for a fuel of unknown quality and insignificant profit potential is bad policy and bad business.

Paul is right as well. You need a fuel that everyone can be confident in, or else you will not have a stable and realistic market.

While some of you have years of experience and make aviation your 24/7 passion, we should not expect the new guy off the street who is interested in learning to fly to feel the same way as you.

Posted by: DAVID COLEMAN | August 11, 2011 8:32 AM    Report this comment

I thought Lycoming's argument was well-thought out and supplied great data to support it. I interpreted Lycoming to say that "yes, the fuel can work", but that there are some things that throw uncertainty to "pump" gas that cannot be controlled by the user, and thus at some point you might be a test pilot. Thus, there is a risk with using gas from the "pump" that would not be there, or at least be highly reduced, if we had a regulated version.

Take the info, use it as you wish. I give Lycoming credit for thought and leadership on this subject.

Posted by: STEPHEN EGOLF | August 11, 2011 8:42 AM    Report this comment

Scott - 14 models of the Bonanza are covered by FAA-granted, Petersen autogas STCs, as are many other light planes, warbirds, radial-engines, etc. For users of autogas, debate for/against it ended decades ago.

Let free markets decide what fuel mix is best. At some airports, it is autogas + avgas. At others it is avgas + Jet-A. If 94UL or 100UL can be produced at a price people will pay, add them too. Reducing choices always results in higher costs for everyone. Drive more away from the lower end by forcing a high-priced fuel on them, and you can kiss all but Jet-A GA goodbye. We all lose.

Posted by: Kent Misegades | August 11, 2011 10:48 AM    Report this comment

Brad, respectfully, I believe my qualifications rank me a bit above an armchair engineer.

I also would not argue Mr Kraft's qualifications, however I think it is important to keep his comments in context - manufacturer acceptance of pump gas would mean accepting a large amount of liability for Lycoming. I understand this, but also believe there is a balance between economy and safety. Perhaps some tort reform is part of the fuel solution.

As for the thousands of aircraft running mogas, I'd say the lack of incidents would prove my point - if we indeed had aircraft dropping from the sky due to mogas believe me there would be an AD rescinding all mogas STC's. I'm guessing the true number is tens of thousands of mogas users over the years, but I concede that argument is hard to prove due to the fact that most mogas users have historically used pump gas.

I have no problem with a person needing 100LL, and as I have mentioned in prior posts, I have customers with 100LL only aircraft who do need it. Just don't leave us low compression guys who can't afford an IO-550 powered aircraft paying $2 more per gallon so you can have your fun. And before we settle on an alternate fuel - look at all the costs. If you're flying a Bonanza or Cirrus 100LL only aircraft, it might be more prudent to accept some mods to the aircraft so you can operate on lower octane fuel. It's amazing how fast $2 a gallon or whatever the number is will count towards an upgrade at 25 gal/hr

Posted by: Josh Johnson | August 12, 2011 9:35 PM    Report this comment

FWIW, I think Kent Misegades has it about right. Start offering some alternatives and see what the market will support. Perhaps if we start moving more aircraft to unleaded fuel, the EPA will get off the backs of the leaded fuel users at least until such a time as they can transition their aircraft to an unleaded fuel (perhaps at overhaul time) One thing for certain, leaded fuel will go away sooner or later - better for it to go away because no one needs it anymore.

On a slightly different note, with the 100LL scare going on right now, whatever would ail some of the manufacturers to not be producing new aircraft compatible with unleaded fuel is beyond me.

Posted by: Josh Johnson | August 12, 2011 9:44 PM    Report this comment

"...some of the manufacturers to not be producing new aircraft compatible with unleaded fuel is beyond me."

If you look an inch beyond the surface at the market forces involved here, you'd say instead...oh, I see. Buyers are essentially uninformed about what drives this market and many think that what's true for me, must be true for everyone else, too. Part of the problem is that the aviation press--mea culpa--has done a crappy job of reporting on this issue and these guest blogs from Lycoming are an attempt at filling in the missing bits of the puzzle.

You know, of course, that manufacturers have attempted to build engines capable of burning lower octane fuels. That was the driving motivation behind Continental's PowerLink system introduced more than a decade ago to utter market disinterest.

All of the OEMs tried PowerLink in some form. There were solvable technical issues with it, but none felt the investment would pay back because customers weren't asking for it. The uncertainty over fuel supplies was just that and that uncertainty hasn't really changed much.

Right now, Cirrus claims that its TSIO-550-powered SR22 with low compression pistons will operate on 94UL--a fuel that currently doesn't exist in the U.S. and may never exist given the market reality that we are not going to have a two-fuel system. We will have a single fuel, with a mogas niche of some kind. It's unclear if Cirrus is getting any market traction with this claim.

Posted by: Paul Bertorelli | August 13, 2011 5:20 AM    Report this comment

With its IE2, Lycoming has a major investment in technology that still won't allow a high-output engine to operate safely on even 94UL fuel, although lower power variants might work. Again, that runs into the two-fuel dead end.

Consider how the legacy fleet drives the fuel equation. If the market returns to relative robustness, Lycoming will sell a few hundred of those IE2 engines a year, against thousands of engines already in the fleet that require 100LL and that represent the lion's share of aviation piston fuel demand.

Ask yourself if, at this point, you'd consider an expensive conversion to an IE2 or PowerLink-type solution now rather than waiting until the 100LL uncertainty is resolved. Now imagine trying to sell into that kind of market.

Last, the world market and heavy fuels. World growth in piston GA is thought to tilt toward Jet-A-burning piston engines. Continental has made the bet on that, Lycoming hasn't. Diesels are making inroads, but we haven't seen any hair-on-fire sales numbers here.

Posted by: Paul Bertorelli | August 13, 2011 5:39 AM    Report this comment

Consider that these are small companies with tight margins in an industry with just stupidly high capital costs for new products. Make a mistake on one, and you lose a lot of money. Case in point is PowerLink. Whether because of market timing, technical shortcomings or just bad luck, it was an expensive flop. It may yet redeem itself.

In GA, buyers have always been fickle and hard to come by. They say they want things--high tech engines, airframes and so forth--then they don't buy these things when they're made available, avionics being the exception.

Taken as a whole, the factors aren't beyond anyone's grasp. You may call them lack of vision or foresight, timidness or just bad management, but they are still real considerations for companies trying to survive selling airplanes.

Posted by: Paul Bertorelli | August 13, 2011 5:40 AM    Report this comment

With a TIO-540 (300HP) heading toward TBO I'm one of those folks anxiously waiting for a better solution. I'd be willing to spend a bit more to get an engine solution that is based on a widely available fuel and I think the RR500 small turbine would be a much better solution for the 100LL crowd. Why? Because most of us use our aircraft for longer, higher flights anyway and would be in turbines if we could afford them. If Rolls Royce or another provider could work with the FAA to create a more streamlined approval process thousands of existing aircraft could go turbine. More customers would create incentives for lower pricing and better support as well.

The big stumbling block (to my naive mind) is certification. If there was a way to simplify or at least establish some standard CG, HP, and installation standards, use data from the large installed base of P210, Bonanza, and Malibu conversions and then convince the FAA to allow a cost-effective STC process we could eventually move to Jet-A and 94UL. Lyc and Continental could OEM or license the RR engine technology and develop a (hopefully) thriving service business for the GA market.

Posted by: neil cormia | August 13, 2011 9:49 AM    Report this comment


Thanks for presenting the views of Lycoming towards the avgas issues. And thanks for including many of your viewpoints regarding the other participants in the industry. This is the best coverage I've seen regarding the avgas issue.

GA is a curious industry. I'm less grey than you are, but I've been around longer. There is always someone generating some buzz, lot's of passion, but 98% of it never happens.

Neil is talking about a turbine retrofit for the GA. Not gonna happen. Simplifying certification, not gonna happen. We're ossified.

When Thielert was talking about 300Hp diesel, I had enough curiosity to contact them when they wanted a 340 for STC purposes. Thankfully, my conservatism pulled me back from that.

So, I still need 100 either LL or UL. Much simpler than hoping for magic solutions.

Posted by: Edd Weninger | August 13, 2011 1:40 PM    Report this comment

I'm not sure why all the talk about impossible certification of aircraft engines, massive capital infusions, electronic gizmos and such to make aircraft compatible with lower octane fuels. Many of the aircraft and engines out there once offered a combination of power plant and airframe that accepted 80 octane fuel. I would surmise that the reason we see 100 octane aircraft is simply that it is the fuel available today. IMHO, the reason FADEC and such failed is that it offered no clear benefit to the consumer. Same thing with 80 octane compatibility in the past. Since aircraft sales are down already, it's hard to tell how much the fuel availability issue plays into whether new purchasers are reluctant to buy, but it has to be a factor.

If we're really looking for an available fuel worldwide, I believe we need to be looking at making aircraft compatible with ethanol laced pump gas. Probably looking at in tank boost pumps, and I know the phase separation thing is an issue, but I'm sure there is an answer to it. I'm not convinced the diesels will really be viable - seems like they vibrate themselves to pieces, but it will be interesting to watch.

For those who believe the EPA would never really ban 100LL, take a hard look at what they've done with refrigerants. Owners of old equipment are basically screwed, and these guys compose a much larger market segment than we do.

Posted by: Josh Johnson | August 13, 2011 9:31 PM    Report this comment

Well, Edd, if we all believe its "not gonna happen" then it surely won't. However, in some small segments turbine retrofits have already happened so I know it's possible but at a market limiting price point. The key is to provide an incentive(usually $$$) for agencies and companies to do it.

I agree that incenting the FAA is a long shot. But RR certainly has an incentive in the form of a larger market. Wouldn't you want 2 RR500s on your 340?

I'm sure a lot of people said the Cirrus folk and Van(Vans Aircraft) could not build a viable business too. Of course, fire would never have happened if the FAA had been around in caveman times...

Posted by: neil cormia | August 14, 2011 9:28 AM    Report this comment

"I'm not sure why all the talk about impossible certification of aircraft engines, massive capital infusions, electronic gizmos and such to make aircraft compatible with lower octane fuels."

Did you read past the part about the legacy fleet? That's why. Unless you understand and acknowledge those numbers, you'll continue to believe in unrealistic market expectations.

"If we're really looking for an available fuel worldwide, I believe we need to be looking at making aircraft compatible with ethanol laced pump gas."

That's already been done by Rotax. Tecnam and Remos are, to name two, who approve their airplanes for up to E10. Many owners resonate with this and buy for that reason alone. Rotax may have been headed that way with the V6 engines but that project failed.

Why? See above.

Posted by: Paul Bertorelli | August 14, 2011 4:43 PM    Report this comment

I was refering to new aircraft in regard to 80 octane fuel. A huge number of aircraft that are now 100 octane high compression aircraft at one point were made compatible with 80 octane. The legacy fleet has a big problem with no good answers. The more common aircraft should be well supported no matter what the fuel of the future is - i'd be real nervous if I were flying a high compression somewhat obscure normally aspirated twin.

Posted by: Josh Johnson | August 15, 2011 6:37 AM    Report this comment

What's obvious is that nothing is done, year after year after year. Now we hear "gee, Lycoming can run on gasoline" like it's big news. At this rate Aviation will die out just before the first drop of new approved gas ever gets made. That's a realistic market expectation at this point.

Posted by: Mark Fraser | August 15, 2011 8:31 AM    Report this comment

" The legacy fleet has a big problem with no good answers. "

This is the problem that exists in plain sight without many people seeing it. The legacy fleet *is* aviation. On the typical airport, if you strip away all the airplanes that aren't legacy--say less than 10 years old--you don't have many left. (Even most of them require 100-octane.)

Without those owners, you don't have a viable hangar community, you probably can't support much of an FBO or maintenance facility and thousands of vendors from Aircraft Spruce to Garmin won't have customers to sell to.

You can argue that 80 percent of the legacy fleet doesn't need 100-octane all you want, but unless and until that market declares itself willing to support and adapt to mogas or some two-fuel system in a significant way, the airplanes aren't supported well enough to sustain.

If people keep saying "they" (whoever that is) need to do something, what is that something that's going to effect a turn around? There is no one thing, but a lot of little things.

Posted by: Paul Bertorelli | August 15, 2011 9:14 AM    Report this comment

"what is that something that's going to effect a turn around?"

The only thing that will kill the 100LL stranglehold on GA is for the EPA to kill 100LL without consulting the FAA. 80% of GA (and all new LSA's) don't need the stuff anyway. That's how you turn it around. That's the "one big thing" that has a chance.

Everything else has failed.

Posted by: Mark Fraser | August 15, 2011 9:53 AM    Report this comment

I suspect the biggest issue is volume of fuel sold. Avgas is a boutique fuel already. The largest consumers of this fuel, volume and dollar wise, are the high-compression, high power singles and twins that turn in the most hours a year flying cross country for business, pleasure, or both, burning at least 20gal/hr/engine. Avgas is a hard enough fuel to get refined and delivered at a reasonable price, not that almost $6/gal is what I'd call reasonable, because of its low volume compared to automotive gasolines and the dedicated delivery infrastructure thanks to TEL. Split that market in two, or really more like 2/3-100MOL required against 1/3 90-ish MOL required, and you'll see refiners quit making avgas of any flavor due to a lack of volume and profitability. Then we're all screwed. I think there are some great reasons, beyond the environmental, to ditch the TEL, if we can do it without causing problems for the airplanes that do the most flying and burn the most fuel. But from a pure economic perspective, I think we're going to have to do it as a 1-fuel system. By all of the articles, blogs, and websites I've read, lots of really smart chemists seem to be close to having this licked if we can just give them a little more time and a little more money to develop a solution. Then our main problem will be cleaning up all the lead in 100LL tanks around the country - and that's no small feat.

Posted by: Charles Seitz | August 15, 2011 10:31 AM    Report this comment

The "dedicated delivery infrastructure" exists not so much because of the TEL contaminating other fuels, but because of other fuels contaminating Avgas (Pump Gas is not Mogas).

Gut Check: If your reason for supporting Mogas as an Aviation fuel is driven primarily by price, you're in for a major disappointment. When and if automobile-base stock-derived Mogas is made available legitimately, it will be at least as expensive as 100LL.

Mogas will be even more of a "boutique fuel" than 100LL and will still need a dedicated delivery infrastructure to assure quality.

Posted by: KRIS LARSON | August 15, 2011 11:59 AM    Report this comment

If you stop 100LL, "the market" shifts dramatically as people WILL migrate. There is no need clean up 100LL in storage tanks any more than you'd need clean out 100LL from aircraft tanks. 100LL will automatically be flushed as the replacement fuel is used. There is no determent at all to not flushing out storage tanks before refilling them with a "pump gasoline".

Posted by: Mark Fraser | August 15, 2011 12:10 PM    Report this comment

"The only thing that will kill the 100LL stranglehold on GA is for the EPA to kill 100LL without consulting the FAA'

EPA action without FAA consultation isn’t going to happen! The FAA has the statutory power to veto EPA in this regard if it (FAA) deems such action by EPA will have an adverse impact on safety. From the AOPA website:

“The Clean Air Act requires that EPA consult with FAA when issuing proposed emission standards for aircraft, and EPA is prohibited [emphasis added] from issuing those regulations if that consultation reveals an adverse impact on safety or noise...”

The safely threat that would be imposed on a large portion of the (legacy) fleet by the elimination 100LL before a workable alternative is approved and available is clearly not something the FAA can permit. Nothing is going to happen until the currently-underway process by the UAT ARC runs its course.

Posted by: William McClain | August 15, 2011 12:36 PM    Report this comment

A One-Fuel (plus modification) solution can work. But the One-Fuel is not 100MON unleaded and it’s most definitely not Mogas. It’s an unleaded Avgas that can be easily modified to 100MON.

In Europe 91/96UL has already proven itself as capable of replacing ALL piston aviation fuel except for a small number of legacy aircraft like warbirds. It can be produced cheaper than 100LL and can be easily modified by adding a small amount of TEL to 100MON. That would make modified 91/96UL (100VeryLL) the "boutique fuel" with all others running on 91/96UL.

The only thing an unleaded 100MON Avgas does is allow Lycoming and Continental to continue to sell 50 year old technology for premium prices. Paul pointed out that the technology exists but no-one will buy an IE2 or Powlink engine until the economics support it. Make the operators who need 100MOM pay for it and stop making the majority of operators who don’t need it pay for it. Only that way will operators have a real choice. Pay more for 100MOM or pay to modify your engine. Your choice.

Today, your only choice is 100LL (even if you don’t need 100MON) or, for the few aircraft that have the STC, questionable quality “Pump Gas”. For me, that’s no-choice.

Posted by: KRIS LARSON | August 15, 2011 12:36 PM    Report this comment

I really want to know why the FADEC systems aren't selling. It seems like such a no-brainer. Easier to non-existent engine management, lower fuel burns, easy starts, and you can run lower octane fuel safely. Seems like at current prices, it would pay for itself pretty quickly.

Posted by: Charles Seitz | August 15, 2011 3:03 PM    Report this comment

Note to self: Get Cherokee 235, and love pump gas!
Oh, already doing that!

Sorry, Guys!

Fun to read all this stuff, though!

Posted by: Ron Brown | August 15, 2011 3:20 PM    Report this comment

Note to Self:

(These piston drivers are never going to stop in-fighting and get their collective acts together to prevent getting steamrolled into $8.00+ 100UL)

DONE! - Picking it up Wed.

Sorry Guys, That's about 15,000 gallons a year of Avgas demand that just evaporated. Or to put it another way, you would need 20 LSA flying 150hrs a year each to make up for the lost demand from just one operator like me.

How many LSAs do you have at your airport? We had 2 (until I sold mine), now there’s one. But I hear the Cessna Flight Center will be getting a Skycatcher (they’ve been saying that for 3 years now).

Posted by: KRIS LARSON | August 15, 2011 5:45 PM    Report this comment

Kris, your suggestion of $8 a gallon 100UL is my exact fear. I've been hearing people say it will be the same price as 100LL - in my humble opinion, they've been sniffing the stuff a little too much!
Personally, I think Todd Petersen's water injection looks very interesting to me for either a mogas or 94UL future for the high compression engines. Yes it's expensive, but quite possibly less than running 100UL for a few hundred hours. 94UL at least stands a chance at costing the same as 100LL does now, probably won't be any cheaper though.

Posted by: Josh Johnson | August 15, 2011 9:06 PM    Report this comment

What about installing pumps that dispense easily refined 93UL mogas, the same feedstock for 100LL. Then if you desire 100LL add it by pressing a button on the pump to have the pump mix it as it is dispensed.

As a safety feature put a dye in the lead admixture and only use the fuel if the admixture comes out a certain color.

Then everybody wins!

Posted by: Brad Vaught | August 16, 2011 8:30 AM    Report this comment

Interesting that no one has mentioned how harmful lead is to the human body. From Wikipedia:

"Lead interferes with a variety of body processes and is toxic to many organs and tissues including the heart, bones, intestines, kidneys, and reproductive and nervous systems. It interferes with the development of the nervous system and is therefore particularly toxic to children, causing potentially permanent learning and behavior disorders."

Lots of doctors and researchers now are finding links between criminality and lead exposure in children.

Personally I am much more concerned about what's good for my body than what's good for that lump of metal made by Lycoming.

Posted by: Gordon Arnaut | August 16, 2011 9:18 AM    Report this comment

Neil Cormia's idea is the only one that makes sense. The light aircraft industry should be transitioning to turbine power for the so-called high-performance segment, while the low performance segment should transition to autogas.

Small turbines with recuperative cycle can be as fuel efficient, or better, than piston engines. An example of recuperative cycle is the Chrysler turbine car and many Darpa projects involving turbine manufacturers.

An SFC of 0.5 is easily achievable with a simple low-pressure ratio turbine engine with recuperation that can be produced as cheaply as a piston.

Posted by: Gordon Arnaut | August 16, 2011 9:25 AM    Report this comment

Gordon, Methanol in fuel does the same thing. What's your point?

Posted by: Mark Fraser | August 16, 2011 9:32 AM    Report this comment

Gordon - show me a turbine manufacturer who wants to take a chance on building such a turbine. Anyone else remember Innodyn of several years back? They were planning to certify a small turbine that could easily replace a piston engine at a fraction of the weight and the same cost as the big cast iron behemoth. They had a twin-turbine model too where they would tie two of the smaller units together into one gearbox to replace the big bore engines. However, they had a real problem with fuel burn being way higher than the piston engines they aimed to replace.

Unless GE, RR, Pratt, or Honeywell can and will produce such an engine as you describe, at a price point and with conversions that make financial sense, with fuel burns at or below their equivalent piston engines, I don't see it becoming reality.

Posted by: Charles Seitz | August 16, 2011 9:43 AM    Report this comment

Not to mention the STC mountain.

Posted by: Edd Weninger | August 16, 2011 9:48 AM    Report this comment

Charles, the current turbine manufacturers are not interested in light aircraft because it is peanuts. I work in the Part 25 industry and it is a huge business.

Lightplane sales are something like 2 percent of turbine GA sales, which itself is dwarfed by the commercial transport segment. Not to mention military.

So no you are not going to see GE or Pratt or even Garrett (Honeywell) making this engine because they are not interested in this segment.

Innodyn is a ridiculous concept. Anyone who knows anything about thermodynamics knows that you can't make a low compression engine fuel efficient.

The high compression turbines used in big turbofans are more fuel efficient than the best diesel engines. Alternately, small turbines used in stationary applications are nearly as efficient using low compression and a heat exchanger (recuperative cycle).

Posted by: Gordon Arnaut | August 16, 2011 10:19 AM    Report this comment

Well it looks like RR is interested in this segment after all. They've got the RR300 in the Robinson R66 that is apparently applicable to fixed wing uses as well and the RR500 planned for certification next year that could replace a big bore piston for about half the weight. Fuel burns are higher, but so are the speeds, so it all probably averages out in the end. So maybe there's a turbine in my future after all.

Posted by: Charles Seitz | August 16, 2011 10:27 AM    Report this comment

This is the way to go for light aircraft, but there are some technical hurdles, such as heat exchanger (HX) technology that is compact, light and inexpensive. That is not the case with current HX technology, which works very well for stationary and marine turbines, but not for aero propulsion.

I am working on a patent-pending HX technology that delivers on that. The technology demonstrator engine will have 200 shp and SFC under 0.5.

Yes the legacy piston fleet can and will be converted to cheap and efficient turbine power. STCs are a necessary process but that is not as big a mountain as original type certification.

Posted by: Gordon Arnaut | August 16, 2011 10:30 AM    Report this comment


Brad has a winner!

If you substitute 91/96UL (which is already certified and needs less lead to make it 100MON), this could be implemented TODAY.

Posted by: KRIS LARSON | August 16, 2011 10:37 AM    Report this comment

The RR300 is not a bad simple cycle engine. Compression is about 9 or so, so it can deliver SFC of about 0.6 to 0.7, depending on power level.

The higher the power, the more efficient the engine. So at lower power you will burn more fuel per hp produced.

Also turbine efficiency improves with cold temps, so that is why you have better efficiency at altitude.

Speed also comes into the formula, so a 300 mph airplane burning 50 percent more gas than a 200 mph plane is not a bad deal.

Posted by: Gordon Arnaut | August 16, 2011 10:37 AM    Report this comment

Mark, my point is that I have no interest in flying in an airplane where I am breathing lead. I think anyone flying such a fuel should think carefully and seriously about this issue.

Methanol is toxic too, but not like lead. Also let's not confuse methanol with ethanol, which is simply alcohol like the kind you drink (which is not exactly good either).

Posted by: Gordon Arnaut | August 16, 2011 10:45 AM    Report this comment

Gordon, So does salt. My point being is that people are NOT DYING from 100LL, they are not getting sick, their kids are fine too.

It's completely irrational to believe 100LL is a health problem. look around. Reality trumps Wikipedia every time.

Posted by: Mark Fraser | August 16, 2011 10:52 AM    Report this comment

Mark, if you think 100LL is fine then I must disagree.

I certainly hope and pray that people are not getting sick and their kids are fine too. But talk to people in the medical field and see what they say. Lead is a health problem and that is beyond dispute by now, with more knowledge coming on stream all the time...

Posted by: Gordon Arnaut | August 16, 2011 11:08 AM    Report this comment

I am working on a patent-pending HX technology that delivers on that. The technology demonstrator engine will have 200 shp and SFC under 0.5.

That's still a loser, unless it is well under .5. Continental's best engines run at .39. The difference between .39 and say, .48 will make up for a lot of price escalation in gasoline. Not to mention purchase cost of the engine itself.

RR's engine is supposed to deliver in the mid-5s. That's pretty good, but it's still high 20s to 30 GPH. In a small airframe, there's no place to put enough fuel and it's not going fast enough to produce good range.

So the airframe will have to be the right size. I'd never say never, but it will take some doing to make the economics work well enough to build the engines and airframes in sufficient volume to be affordable.

Posted by: Paul Bertorelli | August 16, 2011 12:28 PM    Report this comment

When Pratt launched the 600 series engines, the design brief wasn't efficiency. The customers wanted low-purchase price and maintainability, which Pratt achieved with a simplified build up and lower parts count.

They can probably add efficiency to the list, but it won't be cheap. Still, it will happen. It has to. The economics will find the natural water level with regard to price and volume. So the little turbine GA airplane you imagine--it will happen--will cost $900,000 to $1.5 million, a little less than a new Meridian.

But it will be evolutionary, not revolutionary technology, just at Pratt's 600s are.

Posted by: Paul Bertorelli | August 16, 2011 12:34 PM    Report this comment

And just to prove the issues with ethanol in fuel, I just got word from my local Stihl dealer that the reason my weedeater won't start is because the fuel was water contaminated. They see lots of this as the ethanol in automotive fuel causes water that previously would have just flowed through and ended as a wee bit of steam to instead separate out and get all up in the engine. Let's hear it for stupid government bureaucrats and their corn based ethanol subsidies!

Posted by: Charles Seitz | August 16, 2011 12:40 PM    Report this comment

"Lead is a health problem and that is beyond dispute"

Gordon, it's not a health "problem" because there are no patients. On the other hand, there are thousands of health problems(patients) every day from just exposure to sunlight!

What you meant to say is that it's a health risk. What is the risk? It's LOWER than either natural sunlight or solar radiation. Basically stay inside at that point if you're risk assessment elevated 100LL to a threat.

Posted by: Mark Fraser | August 16, 2011 12:58 PM    Report this comment

Let's hear it for stupid government bureaucrats and their corn based ethanol subsidies!

No, not bureaucrats, Charles. Elected representatives from the corn states, Bob Dole being one of the original authors. But I doubt if even he believed it would metastasize into the racket it has become.

Posted by: Paul Bertorelli | August 16, 2011 1:08 PM    Report this comment

Paul, I think a lot of piston owners will take a turboprop with SFC of 0.5.

Especially if the purchase cost of the engine is the same or less than a piston.

At even an altitude of 10,000 that turbine engine with 0.5 SFC at sea level will be on a par with any Conti I guarantee you.

The price of a turbine engine varies directly with its complexity. The Pratt Canada 600 is a fairly simple engine with a centrifugal compressor like you will find in a big turbocharger. Simple and keeps costs down.

The combustion temperature is kept modest so the hot section does not use bleed air cooling of the turbine blades, which adds complexity and therefore cost.

The downside is that fuel efficiency in turbines is a function of compression ratio and temperature. So you pay in efficiency.

That's for a simple cycle engine. A recuperated engine is much simpler because it prefers low compression.

The high efficiency microturbines that are getting diesel like numbers today use have one moving part, the compressor and turbine wheel on a common shaft, exactly like you will see in a turbocharger.

How much does a turbocharger cost? That's the engine right there.

Posted by: Gordon Arnaut | August 16, 2011 2:11 PM    Report this comment

The RR engine is just a modernized Allison 250. What they have done is eliminated the axial compressor that used to be on the Allison (4 to 6 stage) and redesigned the centrifugal compressor to give a fairly high pressure ratio by itself, somewhere around 9.

So they have simplified by eliminating the axial blower and reduced costs. Modern aerodynamics makes this possible.

I don't know where you are getting the 0.55 SFC number but that is pure marketing. Go to RR website and download the RR500 spec sheet.

Takeoff SFC at 475 hp is 0.62.

Maxmum continuous, 400 hp SFC is 0.65

Normal cruise, 350 hp SFC is 0.68.

Still decent numbers for a simple cycle engine but a recuperated engine is a whole new ballgame. SFC of 0.5 represents a fuel burn reduction of nearly a third.

Posted by: Gordon Arnaut | August 16, 2011 2:25 PM    Report this comment

So that is where evolution has got us, new small turbines like the RR and the Pratt are much better than small turbines of a few decades ago. Just like the large turbofans are light years ahead of the old turbojets.

But the recuperative cycle is a revolution. It has already revolutionized the power generation industry where every turbine engine is recuperated and getting efficiency that no other engine cycle can match.

The aero engine industry is very much trying to make recuperated cycle work, because it means engines can be a lot simpler and cheaper...and the small engines can really increase efficiency too.

But like I said there are technical hurdles and progress is being made. Biggest issue is the size of the heat exchangers has to shrink, plus the flow path has to be straight through instead of a lot of twists and turns. There are solutions...

Posted by: Gordon Arnaut | August 16, 2011 2:35 PM    Report this comment

Gordon, if you're so concerned about the lead in aviation fuel, do something about it. Call/write/email your Congressmen and Obama. Don't just sit there and complain.

Unleaded Avgas already exists (91/96UL) and is certified to run in 70%-90% of aircraft piston engines. The only thing preventing its use in the US is the bureaucratic gridlock perpetuated by those who stand to profit from the status-quo.

It would be one thing if no alternative existed, but 91/96UL exists and is already certified. It won't work for 100% of the aircraft but how many thousands (millions?) of tons of lead have been pumped needlessly into the environment during the 20+ years that 91/96UL has been available?

Nobody likes lead. But 100% of piston aircraft have been using leaded gas for almost 30 years when only 10%-30% need it. That’s just stupid.

Posted by: KRIS LARSON | August 16, 2011 2:44 PM    Report this comment

And just one final point. Let's take the 200 hp turboprop engine I am working on and let's say it gets only 0.5 SFC even at cruise altitude of 10,000.

At 3/4 power, 150 hp it will be burning 75 lb of fuel. At a JetA weight of 6.7 lb/gal on average, that is 11.2 gals.

Even if we say that a 200 hp Lyc cruising at 150 hp is delivering an SFC of 0.4 (which would be outstanding) that is 60 lb/hr, or 10 gph. So the difference is 1 gph.

Now just to make things interesting, we can make that recuperated turbine engine achieve SFC of below 0.4, simply by increasing its HX effectiveness. I have the numbers to back that up.

Posted by: Gordon Arnaut | August 16, 2011 2:45 PM    Report this comment

I'm curious about the 200 Hp choice. I would think you would want to replace the 520s and 550s.

They are the people that might consider the expense of changing worthwhile. They don't want a 150 kt cruise.

Posted by: Edd Weninger | August 16, 2011 3:01 PM    Report this comment

Edd, the 200 hp choice is for a demonstrator to prove the HX technology.

You are correct that a piston replacement engine would be in the 300 to 500 hp range (thermodynamic hp, then flat rated to below that figure).

My choice of engine size is dictated by the fact that I am using off the shelf parts, compressor wheel, turbine, wheel etc. The idea is to build the engine and prove the concept.

Btw, the parts I am using are readily available from Garrett and cost peanuts. The super compact, straight-through flow HX is the real technology breakthrough...

Posted by: Gordon Arnaut | August 16, 2011 3:23 PM    Report this comment

OK, get on the stick. I'll need new 300 Hp engines in 2022.

Posted by: Edd Weninger | August 16, 2011 3:28 PM    Report this comment

That RR300 engine was mentioned and is in the new R66 helo.

Have a look at the SFC numbers.

Takeoff power 300 hp gives SFC of 0.7.

Max continuous 240 hp is SFC of 0.73

Normal cruise of 220 hp gives SFC of 0.79

Economy cruise of 180 hp SFC is 0.86.

Now that is gulping a lot more gas than the Lyc 540 it is replacing. Still it will almost certainly outsell the piston helo.

Posted by: Gordon Arnaut | August 16, 2011 3:43 PM    Report this comment

I love the idea of a fuel efficient small turbine but I'm not naive enough to think it will ever be cost effective. It's a $200,000 solution to a $10,000 problem.

We already have very fuel efficient 350hp turbocharged engines capable of running on unleaded gas. We just don't have unleaded Avgas. Tell me again why we need small turbines?

The inherent inefficiency of turbine operated down here in the troposphere (large “carbon-footprint”) will doom them too as C02 has been demonized just as much as lead.

Posted by: KRIS LARSON | August 16, 2011 4:02 PM    Report this comment

"Tell me again why we need small turbines?"

'Cause there's nothing like the smell of burning Jet-A and the whine of a turbine. :)

Posted by: Charles Seitz | August 16, 2011 4:05 PM    Report this comment

Tell that to the people around the Santa Monica airport...

Posted by: KRIS LARSON | August 16, 2011 4:18 PM    Report this comment

Kris You are wrong on a couple of counts.

Turbine engines are some of the most fuel efficient engines yet devised and carbon emissions decrease with less fuel burned.

Here is a numerical example. The Airbus A320 is a narrowbody airliner powered by a pair of CFM turbofans putting out 27,000 lb thrust each.

At cruise of M0.8 and FL350, each engine puts out 5000 lb of thrust at a SFC of 0.545 lb fuel per each lb of thrust, per hour. So each engine is burning 5000 x 0.545 = 2725 lb of fuel/hr, which is about 407 gph of JetA an hour.

Now how much would a piston engine burn, even assuming an exceptional SFC of 0.4 lb of fuel per hp per hour?

We can easily figure that out by relating thrust to power. Basic phsyics tells us that power = thrust x velocity.

Mach 0.8 at FL350 is 461 knots true, which is 778 feet per second. So the power each engine is making is 5000 lb thrust x 778 fps = ~3.9 million ft-lb/s.

One hp = 550 ft-lb/s so we divide that through by 550 and get 7,072 hp.

Now that is thrust hp (THP) coming OUT of the prop, so engine power will have to be more because the prop is not 100 percent efficient. Assuming a very good prop efficiency of 85 percent, we divide THP of 7072 by 0.85 and get 8320 engine hp.

Now assuming we could even make a piston engine capable of putting out that much power at the thin air of 35,000 ft, it would burn 8032 hp x 0.4 SFC = 3328 lb of fuel.

That is 22 percent more fuel than the turbofan is burning.

Posted by: Gordon Arnaut | August 16, 2011 4:32 PM    Report this comment

So that's the efficiency side of it. Aviators still think we are in the 1950s when turbojet aero engines burned a lot more fuel.

Now the cost side of things. The small turbine that Robinson is putting in his helo costs more than the Lyc it is replacing. We don't know for sure, but probably double is a good guess.

Now that is an engine that if you take it apart you will find it has four turbine wheels, two stages on the high pressure side that drives the compressor wheel. Plus another two stages on a free shaft that drive the power takeoff through a gearbox.

As I mentioned earlier RR did simplify things by applying modern fluid dynamics to the compressor and eliminating the several stages that used to be there.

But that is still a lot more expensive parts than a recuperated cycle engine which is basically a turbocharger, with one compressor wheel and one turbine wheel.

The heat exchanger makes possible the great efficiency, PLUS the simplicity.

So there is nothing naive about thinking an aero turbine engine can be very cost effective. The technology pieces are there now...

Posted by: Gordon Arnaut | August 16, 2011 4:41 PM    Report this comment

Btw, the specs on civil turbofan engines can be found here:

And turboprop turboshaft here:

Posted by: Gordon Arnaut | August 16, 2011 4:49 PM    Report this comment

A friend of mine has purchased an R66 to replace his R44. He's expecting a higher fuel burn for his missions as a trade off for hot and high operations.

So we'll see in a few months.

Posted by: Edd Weninger | August 16, 2011 4:50 PM    Report this comment

Paul mentioned the Pratt 600 series and this is representative of a good small turbofan.

Here we find that efficiency is not nearly as good as the big engines. Small engines as a rule can never be as efficient as big engines because they have more surface area per volume and this is where friction losses occur. (Volume increases by cube while surface increase by square).

The Pratt 617 makes ~1700 lb of static thrust in the Embraer Phenom 100. Flight tests confirm that this airplane will cruise at 360 knot at FL330, which is M0.6.

Fuel burn is 337 kg/hr (741 lb/hr, ) at this speed and altitude.

Pratt does not give cruise thrust numbers but the similar Williams FJ44 has a cruise SFC of 0.75, which is about typical for small turbofans. (Quite a bit higher than the large engines).

So cruise thrust works out to fuel flow of 741 / 0.75 SFC = 988 lb total or 494 per side.

To find power we multiple thrust times speed and get 494 x 360 knots x 1.15 (to convert to mph) x 88/60 to convert to fps and get ~300,000 ft-lb/s.

Divide by 550 ft-lb/s we get 546 THP. Divide again by prop efficiency of 0.85 and we get 642 engine hp per side.

Assuming piston engine SFC of 0.45 (a lot of turbocharged piston flyers would be thrilled with this) we get fuel burn of 289 lb/hr, which is 48 gph per side, so just under 100 gph total.

The Pratts are burning 110 gallons of Jet A total or 55 per side.

Posted by: Gordon Arnaut | August 16, 2011 5:08 PM    Report this comment

continued from above...

So the piston engine is better here assuming you could even make a piston engine that can put out 650 hp continous at above 30,000 ft. (How much would it weigh?)

That's a pretty tall order, and all while burning under 0.5 SFC.

Yes we could build piston airplanes that can go 360 kt because we did that in WW2. But I think a Phenom 100 with a pair of turbofans sounds a lot better, no?

Posted by: Gordon Arnaut | August 16, 2011 5:11 PM    Report this comment

Umm.... Gordon....

Did you not notice I said:
"The inherent inefficiency of turbines operated down here in the TROPOSPHERE"

If you're not sure where the troposphere is, Google it. But it ain't above 30,000 feet (that would be the stratosphere).

Now you need a $2,000,000 solution to the $10,000 problem because the only way you're getting to FL300+ is with a pressurized airplane...

Why do people keep insisting we need a quantum leap in technology for a problem that has a 1990's solution? i.e.: electronic engine controls. All we really need is a reliable source of unleaded aviation-grade fuel.

Posted by: KRIS LARSON | August 16, 2011 5:44 PM    Report this comment

Btw, if we did the same number crunching for a small turboprop we would find much better fuel efficiency. that's because of the propulsive efficiency of a prop over a small fan.

Physics tells us that the most efficient way to make thrust is to move as big a mass of air as possible by as small a speed increment as possible.

So if we took that same engine core that's in the Pratt 617 and put a gearbox and prop on it it would get much better efficiency than that small fan which is only 18 inches in diameter.

If you crunch the numbers any of the small turboprops like the King Air, Pilatus, TBM etc are not taking a back seat to pistons in fuel efficiency.

Take the Socata TBM 850 turboprop. This airplane's torque gauge will show 109 percent at FL280 at cruise of 315 kt.

That's 763 hp (1.09 x 700 hp flat rated). Fuel flow here is 230 liters per hour, which is just over 60 gph.

That works out to 407 lb/hr, which gives an SFC of 400 / 763 = 0.53.

Not too shabby.

compare to the Columbia 400 turbo, which POH says 25 gph at high speed cruise of 235 kt at FL250. That's 85 percent engine power of the 310 hp TSIO550 engine, so 263.5 hp on 150 lb of fuel, which gives SFC of 0.57.

Posted by: Gordon Arnaut | August 16, 2011 5:59 PM    Report this comment

Kris, the troposphere goes as high as 65,000 ft in the mid latitudes, in summer. Quite a bit less at the polar regions, but still to 25,000 ft at the lowest.

Anyway the point of the examples is to show that turbines are in fact more efficient than people think.

The Brayton cycle on which turbine engines run is inherently more efficient than the Otto cycle on which pistons run.

Turbine engines are well suited to airplanes due to their extremely high power density, robustness, smoothness, etc. Not to mention fuel...

Small turbines with recuperation can be as fuel efficient as the biggest turbofans, which no small piston engine can approach, even diesels.

They can also be extremely simple machines and quite inexpensive.

Posted by: Gordon Arnaut | August 16, 2011 8:19 PM    Report this comment

"They can also be extremely simple machines and quite inexpensive."

They can be, but yet they are not. It's time for a reality check. If things were simple and cheap then they'd already be done.

Which is simpler and easier? A 100/96 AvGas replacement OR designing a small turboprop, then adapting it to an airframe, and then getting it certified? Basically a retrofit is nuts.

Posted by: Mark Fraser | August 16, 2011 8:59 PM    Report this comment

"If things were simple and cheap then they'd already be done."

And if the Wright brothers had lived by those words we would still be flying kites.

Posted by: Gordon Arnaut | August 16, 2011 9:12 PM    Report this comment

I happened to be perusing my archives and found the first coverage we did on diesels and the emerging small turbofans under the GAP project. The year? 1997.

Gordon, I could take your numbers and plug them right into that coverage because the claims were similar. The fuel efficiencies were proposed to be a third better--they aren't--and the costs of these new engines were targeted to be one-tenth of the then conventional powerplants.

Yet the two GAP flagships--the diesel and what became the Williams EJ22--failed. There are various technical reasons for this, but the larger one is a failure of vision in marketing and economics.

The GAP believers plugged some numbers into spreadsheets, thought they saw enough data to confirm these and just accepted them going forward. I would submit that in even thinking about a 200-HP turbine to compete with gasoline engines, you are making the same fundamental mistake that others have: Assuming this is a mass market if volume can be achieved with low enough prices. It's Eclipse all over again.

Posted by: Paul Bertorelli | August 17, 2011 5:03 AM    Report this comment

This kind of thinking continues to be the lost Holy Grail of aircraft and engine designers who have never tried to sell anything in a market that doesn't behave the way they think it should.

There is no historical evidence to suggest a magic price point that makes what's now a $180,000 turbine engine an $18,000 turbine engine. You can pencil out the numbers on the manufacturing side and these are probably realistic. The unrealistic part is how buyers respond, which is to say the assumed volume is not there and won't be there.

What will be there are markets like the Meridian, the TBM and likely the resurrected Eclipse. Healthy enough numbers to support a robust, but not large-volume business. I believe the small turbine airplane will happen, but it won't be 200 HP because no one would bother buying that. It will be closer to 400 HP because for all that money, buyers will want to go high and fast, just as they always have.

Posted by: Paul Bertorelli | August 17, 2011 5:14 AM    Report this comment

"And if the Wright brothers had lived by those words we would still be flying kites."

Hardly. The Wright brothers were in a race to the inevitable. They also were perusing a patent. So even in the beginning of Aviation the focus (at least with the Wright brothers) was on selling and collecting royalties. They were 19th century capitalist and "inventing" was the way to an end.

Today is no different. Business is still business. You don't invest millions into something that will sell in low volume for mere thousands. Likewise, owners of older $100k airframes won't invest in $400k engines because financially, it's nuts.

GA WON'T get a return on investment by leaving a 0.57 piston and buying a 0.50 turboprop. Technically it's better, but practically it's dumb.

Posted by: Mark Fraser | August 17, 2011 7:23 AM    Report this comment

Wow - wake up this morning and all kinds of new comments! Wheee!!

SO, what I read is that while, TECHNICALLY, there COULD be a turbine under every future cowling, PRACTICALLY, it ain't gonna' happen, because of our amazing free market capitalist system that won't bear the costs associated with such. Excellent. So back to the original point - at some point we're going to have to "get the lead out". There's an alternative in 91/96UL. It will work for somewhere between 70-90% of the fleet, but that portion of the fleet doesn't consume 70-90% of the fuel, more like 50%. The big piston drivers need a solution. What is it? Do we go tell them to mod their engines? Do we try and sell everyone on retrofitting digital electronic controls to their engines to keep the things from detonating, run smoother, easier, and better? I for one don't really like the engine management chores associated with flying piston engines, so I'd love to swap in a computer to do the annoying work for me.

And why, oh why, haven't the OEM's gotten aboard the Powerlink/IE2 bandwagon? I'd have thought that Cirrus especially would have tossed the mechanical linkage system they run for an all electronic system a long time ago. As I recall, the single lever control with mechanical linkages was supposed to be a short term solution until the engine guys got their act together on electronic systems.

Posted by: Charles Seitz | August 17, 2011 8:42 AM    Report this comment

My guess is you'll see movement soon on the FADEC front in new airplanes. Probably later this year or next sometime. Cirrus and Beech on the PowerLink, Cessna with IE2.

The market timing just hasn't been right until now.

Posted by: Paul Bertorelli | August 17, 2011 9:13 AM    Report this comment

Paul, here is the final report from Williams on the GAP program. //

Just put "http:" in front of that.

And here is an earlier report from Williams: //

The stated purpose of the GAP program was to develop a "revolutionary" low-cost turbofan engine that would "revive" light (defined as under 5,000 lb) GA.

Fair enough. You don't need to be a Nasa rocket scientist to realize that is what we need.

ON page there is a graph showing light GA sales by year. In 1978 17,000 new airplanes rolled off assembly lines. This was when you could reasonably expect to go and buy yourself a brand new airplane.

today we have total light airplane production of about 700 a year.

But look at Nasa's projections on that graph. 10,000 airplanes a year by 2007 and 20,000 a year by 2017.

Obviously it hasn't happened. And the failure of the GAP program to deliver that magic bullet engine was one of the reasons. Not the only one, but a big one...

Posted by: Gordon Arnaut | August 17, 2011 9:46 AM    Report this comment

At issue is suitable fuel availability and cost. Clearly, and I say again clearly and unarguably the direction is toward a heavy fuel, diesel, JP4 etc. Lycoming and Continental have been sitting on their hands for years/decades unable or unwilling, who knows why, to take the initiative to adapt to where the rest of the world/market is going expecting the world/market to adapt to them; a loosing position in a capitalistic system. Piston diesels are coming and indeed are here and their numbers, due to high demand, will grow. The only place in the world that will use avgas is the US. How backward is that? You guys with the high performance pistons are going to have to settle for a lower grade fuel and throttle back a bit giving up some performance, mix your own, pay a sky high price with limited availability for the fuel you desire, or fly the airlines and guess what they are burning! That is unless the not-so-forward-looking engine manufacturers decide to adapt to the market. The turboprops and diesels are here and more on the way. Keep your gassers till they wear out or avgas isn’t available and by then the heavy fuel burners will be here dragging a screaming and kicking Lycoming and Continental behind.

Posted by: Dan Andrew | August 17, 2011 9:52 AM    Report this comment

Now let's start with the stated objective of the program, to deliver a turbine engine for one tenth the cost.

Now Sam Williams is no dummy, neither are the Nasa guys. If they didn't think it could be done they would not have signed on to such a lofty goal.

So what happened? Well the reasons why they did not deliver on that turbine engine at 1/10'the cost is purely technical.

Look at the details on that Williams engine. That is a 3-spool engine for crying out loud, like the biggest RR turbofans. Not even Pratt or GE make 3-spoolers.

The thing is incredibly complex. Read the report, they had to make their own machine tools in order to get the fineness of finish needed on those tiny compressor blades.

I could go on and on. That little compressor is a thing of beauty no doubt, but how much does it cost to make that thing?

Now look at a simple one-piece centrifugal compressor wheel in a turbocharger or in that RR300 and 500, or even in that Pratt 600.

Which one is the way to go for cheap cost?

Posted by: Gordon Arnaut | August 17, 2011 9:53 AM    Report this comment

Frankly this choice of architecture is absolutely bizarre.

it was the wrong choice of engine architecture. That is why GAP failed, and I'm not the only one saying that. Ask Gerry Merrill.

There is only one way that the affordable turbine can be made and that is to use the recuperative cycle. That means a heat exchanger in the exhaust stream that transfers heat to the stream comign off the compressor and going into the burner.

This recycling of "lost" heat energy means you can cut your fuel burn in half, or more. It also means a dirt simple engine architecture with ONE compressor wheel, ONE turbine wheel and a burner can.

That's it.

This how the microturbines are made and they are getting efficiency equal to large turbofans.

The FJX engine was a miniature large turbofan (a RR 3-spooler to be precise). It did achieve fairly good efficiency, but the cost and complexity was out of this world.

Posted by: Gordon Arnaut | August 17, 2011 9:58 AM    Report this comment

Now the question is why, if recuperation is so great that no one is doing it?

Well there is a technical reason for that and that is the size and weight of conventional heat exchangers. A new technology is needed.

As I mentioned I am patenting a new technology that addresses these issues and will make the recuperated cycle a reality for propulsion engines.

This new technology utilizes both materials and process inovations and results in an extremely compact, light and rugged HX that is very resistant to fouling from the exhaust gas.

It is also a straight-through flow path unlike any gas turbine HX to date. This is a breakthrough.

lastly it is also quite inexpensive to manufacture.

I am planning to have a running 200 hp engine at Oshkosh 2012. I also have plans for a 500 lb thrust turbofan using the same engine core.

As I mentioned I am using strictly off the shelf turbomachinery, the compressor and turbine wheels are ready made pieces that cost peanuts and have been proven in millions of hours of use.

that is how you make a turbine engine for 1/10'th the cost.

Posted by: Gordon Arnaut | August 17, 2011 10:05 AM    Report this comment

And finally a note on fuel. Yes heavy fuel is the only alternative going forward, so let's be realistic and accept that.

A boutique gasoline fuel is ridiculous and will not help aviation. Nasa knew that 15 years ago and that is why they excluded gasoline from their engine program.

Airplanes run on heavy fuel and small planes need to get with that program.

In fact there is no reason not to have a 100 hp turboprop and I have one of those in the works too.

Basically a turbocharger with a burner can and an HX. Will cost less than a Rotax.

Posted by: Gordon Arnaut | August 17, 2011 10:10 AM    Report this comment

Gordon, you have all the answers. Why don't you design and build such power plants and save GA from our collective ignorance?

Posted by: Mark Fraser | August 17, 2011 11:22 AM    Report this comment

How about this? Laser-thorium cars and trucks and ground units, no longer require fueling of any sort! Therefore Big Oil doesn't even know what to do with all that liquid hydrocarbon gasoline and kerosene! It's cheaper than water!

Turbines, therefore, again become the aviator's dream.

Lycoming is bought, not by Moguls with no concern about small customers, but by a true altruistic individual who helps small customers power their legacy and experimental aircraft with reliable power, instead of lawyers and the FAA condemning their engines and parts over big-business entanglements.

No thanks to Avweb for eliminating my post about how Lycoming actually treats their customers!

Posted by: Ron Brown | August 17, 2011 1:20 PM    Report this comment


C.A.R.B is giving out free grants to CA diesel truck owners to throw away their existing engines and replace them with cleaner $50k-$60k new engines.

If EPA would provide grants to owners to replace
their engines with fully certified new "no-lead" engines - we could all stop arguing and get along.

Posted by: MARC SALVISBERG | August 17, 2011 1:39 PM    Report this comment

"Now Sam Williams is no dummy, neither are the Nasa guys. If they didn't think it could be done they would not have signed on to such a lofty goal."

Please. They signed on to get a lot of no-strings government developmental money that could be plowed back into the commercial business. They were working with 50 cent dollars.

If you have a running 200 HP turbine at OSH 2012, I will happily come and cover it. I still believe it is a dead-end marketwise, unless it can be as cheap as an IO-360, fuel costs and availability notwithstanding.

Larger horsepower turbines, well, that's different. Although I have covered many more failures than successes and have had more smoke blown my way than the average person should have to endure, I remain stupidly open minded.

Posted by: Paul Bertorelli | August 17, 2011 2:41 PM    Report this comment

"...I remain stupidly open minded."

And this is why we love you, Paul.

Posted by: Charles Seitz | August 17, 2011 2:57 PM    Report this comment

There might actually be something to the grant idea - either to install no-lead engines or perhaps more likely to install ethanol-free unleaded at airports. The deal might require a sunset date perhaps 10 years or so in the future on the installation and overhaul of existing engines which require leaded fuel except for historical aircraft.

Posted by: Josh Johnson | August 21, 2011 4:02 PM    Report this comment

Thanks for a new, word, Cristina!

Posted by: Ron Brown | August 29, 2011 4:54 AM    Report this comment

"Portraiture" in English, by the way.
All of we lecherous "flysticks" are wondering about your "portrait", I'm certain, human nature being what it is!
There should be a really good song about German girls, if only in our hearts!

Posted by: Ron Brown | August 29, 2011 5:06 AM    Report this comment

So, a little late on the blog but here is my 2 cents...
I fly a 150. I use ethanol free 90 octane gas that runs on my plane just fine and costs me $3.83 per gallon purchased (2013 prices). 100LL at my airport costs $6.55. Before I purchased the 150 I use this ethanol free fuel for several years in my car and every other engine with no issues. I test each load for ethanol and have never seen any. Now folks out there are saying that confidence or cost is not enough to warrant this kind of fuel... I guess I'm much more poor than the average aircraft owner and see that if I fly 1,000, that's over $16,000 of savings! Enough for an overhaul. Would I love the convenience of filling at my FBO? Sure! Do I feel I need to pay for 100LL so that I "pay" for the free services the FBO offers? Nope. I already pay my tie-down fees. I just cant justify spending that much more. And, I get lower lead content in my engine to boot. I welcome feedback to hear why I should not use this fuel...

Posted by: Lamberto Roscioli | April 11, 2013 9:56 AM    Report this comment

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