This much I know: Sun ‘n Fun is my first big airshow of the season and every year manages to put a new spring into my aeronautical step. Like many pilots, I emerge from the doldrums of winter ready to see lines of new airplanes, scads of new products and shiny faces everywhere. Where Oshkosh is about the crushing crowd, overpriced bratwurst, Lineys at night and big airframe announcements, it’s become more likely to find more — and, to me, more interesting — news on the engine front at Lakeland.Let’s dig in. Two actual engines and one engine program captured my attention for most of the show, but first this: For fans of the Franklin engine, there’s good news. I was contacted by one of the principals of a new company that has bought the rights to produce the venerated engines. I’m told that the equipment has been moved to a new location and that production of certain critical parts — cylinders and cases — will resume this summer. The goal is to crank out enough parts for 100 engines in the first go, with an eye toward resuming production of whole engines later.Along the same lines, I also heard a rumor — utterly unsubstantiated in the best internet-columnist fashion — that a certain well-known American company in the business of making aircraft engine parts was interested in helping the new owners of Franklin establish a beachhead here. This discussion was more in the realm of “it could happen” rather than “it will happen,” but it’s tantalizing to think that a company with the skills to build a lot of diverse parts could build a business case for putting more Franklin components into the hands of U.S. pilots. There’s life in this one yet.
New Engines, Big and Small
From a revitalized Superior, whose president Tim Archer was positively glowing with good news stemming from the company’s purchase by Thielert, comes a big, new engine called the XP-400. It’s clearly a direct response to Lycoming’s IO-390 four-cylinder engine for the Experimental market. I have to wonder how many guys with RV-7s and 8s are clamoring for the extra power, but that’s for Superior and others to reconcile. I’ve also heard the argument that a very high power four-cylinder could stand in for lower-power versions of the O-540 that are so much in demand for the Van’s RV-10. But the -10 guys are turning out to be quite conservative, so I can just imagine the internal argument for a low-revving, low-stressed six winning over a highly stressed (comparatively) big four. But I’ve been wrong more than once …Superior’s engine takes two paths to more displacement: more bore and stroke. Before we get into the numbers, it’s important to understand that the engine, like the IO-390, is based on the larger, angle-valve cylinder heads that are used on the 200-horsepower (and up) four-cylinder Lycomings and, in sets of six, on the high-power 540s. There has always been a bit of confusion here because Lycoming brilliantly left the displacement the same between the angle-valve engines and the smaller, lighter, power-limited, parallel-valve engines. An IO-360-A and an IO-360-M are completely different engines; they share not cylinders, cases, pistons, crankshafts, weight, horsepower or size. My favorite use of this misappreciation came from Mooney, whose salesmen used to call the TLS Bravo’s TIO-540 engine essentially the same as the Navajo’s turbo six, thereby implying that its 270 hp was positively loafing for an engine capable of 350 hp. Ah, yes; the two were as similar as an ant and an anteater. But I digress.Superior’s new engine starts from good stock, then, using the more massive heads, which are inherently capable of producing more power primarily because they can reject more heat. I’ve also heard that the angle-valve combustion chamber is slightly more efficient, though I’ve heard from one prominent builder that the parallel-valve engine is actually better because it can be made to have an efficiency-improving squish band. If the connection between Superior and Thielert bears the best fruit, Thielert’s experience coaxing finicky diesels into aero use will inform this design as well, though maybe not right away. (Can you imagine how good we could have it if our existing engines had truly modern combustion-chamber shapes?)The tactic with the XP-400 was to provide competitive power — it’s rated for 210 hp at 2700 rpm now — without resorting to a high compression ratio or extreme ignition timing. Displacement makes “easy” power possible, and to that end, Superior took the angle-valve 360’s bore dimension from 5.125 inches to 5.25, and extended the stroke from 4.375 to 4.625 inches. Seems like a lot, but the cylinder bores only need grow a sixteenth inch from the centerline, meaning that existing head castings can be used. The barrels are new, of course, but the expensive pieces can be retained. (Lycoming boosted the IO-390’s bore alone from 5.125 to 5.319.)By using the 5.25-inch bore, Superior was able to use rings meant for Continental big-bore engines fitted to brand-new pistons that result in a modest 8.5:1 compression ratio. For reference, the standard, angle-valve IO-360’s is 8.7:1. While everyone was told the IO-390 would have the same compression, it turns out to have an 8.9:1 ratio.More displacement comes from additional stroke; for the XP-400 that’s a mere quarter-inch more than the IO-360/390 engines. Superior was able to machine this extra stroke — the big end is just an eighth-inch further from the main-bearing line — from O-360 blanks. Like the IO-390, the 400 will use a counterweighted crankshaft. Crescent-shaped weights are pinned to the crankshaft at the back end to absorb high-order harmonics. In exchange for increased engine weight and rotational mass, the counterweighted crankshaft can make the engine smoother and will assuredly make life easier on the propeller. (These high-order vibrations can wreak havoc on a metal prop, and they’re the primary influence that prop manufacturers check when approving a certain engine/prop combination.)This engine packs a few clever touches, including a new Ryton (composite) sump with a choice of front- or rear-facing servo locations. The current IO-390 spec comes with a front-facing inlet only. Superior’s roller lifters and specially ground camshaft carry over from the XP-360. Thanks in part to new case castings and the weight savings of the sump, the engine is expected to come in from 294 to 305 pounds … which is 3 to 14 pounds less than is claimed for the IO-390.Superior says the new engine is, for now, aimed at Experimentals, but will also be certified for production aircraft. While certifying an engine to Part 33 standards is no walk around the block, at least Superior has been there, with its Vantage engine. When dealing with certification issues, having a history with the regulating body is a definite plus. Moreover, the XP-400’s comparatively mild state of tune will help. The 8.5:1 compression ratio will make it compatible with 91-octane auto fuel (as well as 100LL) and should keep the cylinder stresses and temperatures down.As this is written, Superior has neither flown the engine nor set a price. Expect it to come in around $30,000, maybe a little bit more. It will be part of Superior’s customers-build-their-engines program at its Dallas-area headquarters.The XP-400 is currently in dyno testing, with deliveries expected to start this summer for Experimentals. Frankly, I see that as extremely aggressive. It’ll be called either gutsy or foolhardy, depending upon the field experience of those first few engines.
If the XP-400 aims to play at the top-end of the four-cylinder market, then ECI’s new IOX-340 hopes to raise the reputation of the lowly (but well regarded) O-320. I had a long visit with Jimmy Tubbs, ECI’s VP of Engineering, on the way to Lakeland this year, and we spent a lot of time talking about the 340. “We looked at stroking a 360,” he says, “but we were worried about torsionals” — that would be those torsional harmonics acting on the crankshaft. Increase the stroke or the potency of the combustion event, and you increase the level of torsional stresses. Do both, and you’d better seriously beef up the crank.Tubbs and ECI see a market emerging below the bellwether O-360 — the engine that is found in, oh, about 75% of all homebuilts — for a relatively inexpensive engine that’s powerful and light. To that end, they started with an O-320 and stretched the stroke from 3.875 to 4.125 inches. (Yes, that’s exactly the dimension Lycoming gave its 340 in 1954, creating either a long-stroke 320 or a short-stroke 360, depending upon how you care to view it.) The 320, 340 and 360 share a 5.125-inch bore in parallel-valve cylinders, so there’s tremendous savings there in pulling parts for one engine from another engine’s bin.Lycoming was never very successful with the 340, probably because it was so close to the 320 in power — 160 to 170 hp at 2700, from contemporary materials, only 10 up on the 320 — and externally identical to the more powerful 360 that arrived in 1955.Which brings us back around to: Why? Because some modern thinking has brought the 340 up to and, according to ECI, slightly beyond the performance achieved by a typical O-360. OK, so: How?ECI has thrown a bunch of tricks at the 340 in the quest for more power without extra weight. The engine will come with the company’s new, mechanical, fuel-injection system, which promises to be simple and light compared to more traditional choices — and cheaper, too. It has a magnesium sump and induction divider standard, while the machined throttle body is so small as to be missed on the walkaround. The 340 also gets flow-matched cylinders with 9.0:1 compression pistons — a-ha, there’s some of the newfound power, as the “high-compression” 320s and 360s are saddled with an 8.5:1 ratio. Venturi valve seats, which flow better at partial valve openings, also help improve power.”Frankly, we were surprised,” says Tubbs. “We didn’t think it would be quite this strong. Not that we’re complaining …” How strong? Would you believe 185 hp? Pretty good, I’d say, for an engine to be 3% more powerful than a 6% larger engine.Moreover, ECI is justifiably proud of getting weight out of the engine, which for some builders is just as important as more power. (Actually, it should be for all builders, but we’re not quite that enlightened.) Tapered cylinder barrels account for nearly a pound per cylinder. While most Lycoming cylinders have a constant-diameter finned cylinder barrel, these have a smaller OD near the crankcase. Makes sense: Most of the heat is rejected through the head itself and the oil system. Progressively less heat comes down the barrel, so the benefits of large fins all the way to the crankcase are largely for manufacturing. (Continental has used tapered cylinder fins on the GTSIO cylinders for years.) To help builders, the IOX-340 engine will come with special inter-cylinder baffles that match the tapered barrels.Like the XP-400, this engine is not yet flying, but will be very soon. ECI expects the engine to be available through various field shops later this year. Unlike Superior, ECI doesn’t want to build whole engines, but prefers to provide the bulk of the components for outside entities to build.
Finally, A Thunderbolt From The Blue
A year into an ambitious program by Lycoming to provide certain engine shops access to a host of factory parts so that they could build entire engines from kits, Lycoming announced a program of its own at Sun ‘n Fun. Called Thunderbolt engines, they are factory-built “custom” engines for the Experimental market. Not only will buyers have access to a variety of configurations — the aforementioned IO-390 sump issue is one example — that are currently hard to find, but the program will extend into different engine families. Moreover, the consumer will deal directly with Lycoming on sales.Again, Lycoming is showing an aggressive side, going after market share in even the smallest of corners. (It must have hurt to see Mooney become an all-Continental company with the introduction of the turbo-normalized Acclaim and the ditching of the Bravo to a subtle spattering of crocodile tears.)But I have to wonder about the long-term repercussions. Taking a revenue stream away from engine builders and kit manufacturers isn’t the best way to ensure after-sale support from the field. A company principal of one of the designated kit-engine builders had a two-word response to the news and, after calming down, admitted that it was a fairly cutthroat maneuver in a notoriously small community. (I can imagine owners of these shops getting on the phone with ECI and Superior, or even visiting their tents during Sun ‘n Fun, working up an alternate plan.) Lycoming’s current management, headed by Ian Walsh, is clearly out to shake it up. Let’s hope they know what they’re doing.
Got motors on your mind? Check out the rest of Marc’s columns.