To answer a few of Ross's questions: The testing done on my RV9 in 2010 was an actual side by side test against Van's factory RV9A with CS prop. It was conducted by a professional (Ken Krueger, Vans Chief Engineer, who I suppose would know a thing or two about testing aircraft). He does not mention in the article whether or not the factory 9A was running LOP in the "economy" test. However, as we were readying to do the test, he said: "this test is for best fuel economy. You use every trick you know to get the best economy out of your plane. I am going to do the same". My guess is, he would have done exactly as he directed, and would have run LOP. Of course, I could employ no "tricks" to improve my economy. For me, it was simply setting climb power for climb, cruise power for cruise, and landing when we were done. We both flew side by side, same day, same route. APPLES to APPLES. I achieved 33.2 Statute MPG and He achieved 23.9 Statute MPG. The trip was 166 Statute miles, covered at an average ground speed of 149 Statute miles per hour. And this was done with a diesel that is not as efficient as the Conti CD155. Were conditions "just right" for me and not for him? I have no idea.
Here again, this was not: "so-and-so reported getting XX fuel burn at XX altitude one day". I've come to believe that we pilots are somewhat like fishermen when we share our speed and fuel burn figures. How often in these very forums do we read "flying along at XX altitude, I've seen XX speed and XX fuel burn"?. What "I've seen" is really not a clear picture of what that particular aircraft or power plant actually does on a regular or average basis. I hope you get my drift here. I think most of you will.
If you read the article about the more recent test Ken did, you'll find that most of your questions are answered. The test was between a very light, well built Sportsman and my Sportsman (not so light, and not as well-built
). The gas Sportsman had a Superior O-360 with one Lightspeed electronic ignition and one mag, turning a two blade Hartzell CS prop. In Ken's words: "This aircraft turned out to the ideal choice for the gas-to-diesel comparison because the airframe is completely standard and is likely the lightest Sportsman around". In this test, both aircraft were tested for economy and speed at different altitudes as follows, and I will only include the LOP figures because that's all you seem to be interested in.
Gas: Full Throttle and 2500 rpm cruise:
135 KTAS @ 5600' DA LOP 9.6 GPH, 14.1 NMPG
130 KTAS @ 9500' DA LOP 8.8 GPH, 14.8 NMPG
129 KTAS @ 11,800 DA LOP 8.2 GPH, 15.8 NMPG
Diesel 75% power cruise:
123 KTAS @ 5000' DA 6.0 GPH, 20.5 NMPG
126 KTAS @ 9500' DA 6.0 GPH, 21.0 NMPG
130KTAS @ 11,500 DA 6.1 GPH, 21.4 NMPG
I know that the next thing you're going to say is that the gas plane was not equipped with the latest electronics, and that with the finest technology, it would have bested the diesel. I have still seen no proof of that, and I think that most would agree that the this plane represents a fairly high percentage of traditional engine-equipped planes out there.
To address your Toyota Hybrid scenario: yes, Hybrids are inching ever closer to diesel economy, but it takes the assistance of batteries to do it. And look at all the extra cost, not to mention environmental waste, weight, and complexity associated with Hybrid solutions. I know there are those pursuing hybrid technology for aircraft, but that's another subject for another day...
If there are gas aircraft out there with better average economy than a diesel, I have not heard of them. It might be that there simply aren't enough FADEC gas aircraft out there and no one has actually tested them against comparable diesel aircraft. BUT - if we go to the automotive world, there certainly has been. Take the Ford F150 Ecoboost against the Dodge 1500 Ecodiesel. I happen to own several of the Fords (for my work) and one of the Dodges (my personal transportation). Unofficially we have compared the two in same-way conditions on the freeway between here (NV) and our Utah office. At freeway speeds, not babying either truck for fuel economy (just setting cruise at 77mph), we struggle to average 20 mpg with the smaller 2.7 Ecoboost. Even worse with the larger 3.5 engine. The Ecodiesel averages 27 mpg. But don't take my word for it. A quick look at Fuelly.com shows that, averaged over millions of miles, hundreds of owners, and all types of driving, the F150 Ecoboost averages 16.6 mpg. The Dodge Ecodiesel averages 22.7. Can we agree that both Ford and Dodge are employing the very latest in electronic engine management, maybe even more advanced that what we see in the EAB aircraft world??? Of course, the Ford has it's 700-lb-ligher aluminum body, which should give it leg up. If gas engines are do darned efficient, I wonder why Ford has announced a 3.0 diesel F150 for 2018??? Silly truck manufacturers
I wonder why Cessna, Piper, Diamond, and Robin all currently offer diesel models, and Cirrus, Mooney, and others are developing diesel models? Could it be that they see a market for these products? Maybe they don't know what you know....
I understand that initial cost plays a huge part in overall cost to own and operate an aircraft. However, I won't share my initial cost; I don't know it! And because it does not even remotely represent what's available today. Because i was a first adopter, a developer of the CD155 FWF for the Sportsman, I had a LOT of costs that would not need to be spent today by someone installing a CD155. For example, we (Glasair and I) ordered an entire Cessna 172 conversion kit, figuring we would be able to use most, if not all of it in the Sportsman. We ended up using very little of the kit and now i have many thousands of $$$ in parts in my hangar that are of no use to me. This, along with all of the money spent to develop new parts. I also purchased tools and diagnostic equipment unique to the CD engine so that I can service it myself. Best as I can tell, and this is pure speculation, the premium for the CD155 should be no more than $15-20K over and above a Lycoming o-360/CS FWF package. The delta should be even less when comparing to a certified Lycoming engine/prop, which would be an apples-to-apples comparison. Of course, as the market matures and gets more comfortable with the diesel, that cost should go down. Hopefully it will.
As far as cost of ownership goes, this engine so far, at 420 plus hours, has cost me nothing, other than 100 hour oil changes (an oil changes runs about $200 in costs, with filters, oil, etc.), and fuel. Over the lifetime of the engine, there will be one gearbox inspection, (i'm not sure of the cost, but I think around $2500-3000), and a fuel pump, I think around $1200. As has been mentioned, as EAB, I'm under no obligation to follow these guidelines. When I was at the factory seminar, our instructor told us of operators who had received permission from their government (New Zealand IIRC) to run far beyond the mandated limits, with no issues. According to Ken's article, based on cruise alone, not factoring in taxi and climb, and all else being equal, it is $22.95/hr cheaper to fly the diesel Sportsman. Over the life of the engine, assuming current fuel price delta, that equals a $48,195.00 savings. Yes, some of that will be spent on maintenance, and you've spent maybe half of it on initial cost. But, considering the fact that the Lycoming will also most likely require maintenance, I think it's safe to say that you can still save money owning a diesel. Even if it's a wash, you've flown in a safer plane, and you've enjoyed its simplicity of operation. I do understand that there are many ways to "do the math", and frankly, I don't care. I enjoy developing and flying diesels and I know they're more efficient. Do the math the way you want...
There have been two service bulletins in the 3 1/2 years I have owned this engine: the first was to add a plug-in starter circuit mod in the starter loop and install engine software update. No cost. The second was to install a pin to alleviate a wear issue that some were experiencing on the turbo wastegate shaft. Mine had no such wear, but I installed the pin anyway. The factory provided the parts and a fixture. The fix was simple; took about 45 min.
I am hoping to replace the WAM in my RV9 with a CD155 in the near future. I think it will make it a good performer compared to a "standard" RV9, high-tech or otherwise. It will be interesting to find out if I'm right...
Kurt
RV9 WAM 120 diesel 560 hours
Sportsman CD155 420 hours.