Supercharging: The Turbo Alternative

Bill Beaton chose a centrifugal supercharger for racing and cruising.

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Built for speed, not beauty, Bill’s Vortech-supercharged parallel-valve IO-540 projects a purposeful, engineering-centric personality. That it can thump out far over 400 hp to the propeller backs up the posture. Sky Dynamics one-piece valve covers add a bit of cylinder stability; the large, downward-facing passage forward of the exhaust is the supercharger inlet.

It’s a bit of a shock to recall U.S. government research identified turbo-supercharging as the golden path to altitude compensation way back in 1918—and ever since the flying community has held turbocharging close. If you’ve flown a plane that puts the manifold pressure gauge over 30 inches, chances are excellent it was turbocharged.

Bill Beaton, supercharging pioneer.

But if exhaust-driven forced induction is aviation’s norm, crankshaft-driven supercharging has quietly made inroads on Experimentals lately. Why? Because turbocharging, efficient as it is, brings heat and plumbing headaches many judge not worth the trouble in low- to mid-altitude aircraft.

To performance-minded experimentalists, fabricating a relatively simple supercharger installation is easier and less maintenance intensive than working with turbochargers. Yes, they take a hit in fuel economy, but at lightly boosted manifold pressures it’s not much of a loss in the real world, especially when performance is key.

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While its characteristic stork-like gear legs give Bill’s plane the familiar Harmon Rocket stance, there’s nothing immediately suggestive of its nearly 300 mph straight-and-level potential to the casual observer. Closer inspection reveals filled and smoothed wings, along with a NACA engine air inlet. The propeller is a two-blade Hartzell blended airfoil with F8068DX blades.

In the last few years we’ve seen several promising home-brewed belt-driven superchargers. Thomas Shpakow’s gorgeous Acroduster Too features a blown 540, a useful device when flying from Thomas’ Denver, Colorado, home base. He notes great vertical performance from his Acroduster, and with several years’ experience with his Eaton TVS supercharger, Thomas reports great reliability. He even offers a basic blower kit, but cautions it’s only for knowledgeable enthusiasts and is not user friendly. Thomas’ installation can be seen at www.g3ignition.com.

Two custom applications we just got a good look at were Bill Beaton’s 540-inch Harmon Rocket and Dan West’s parallel-valve IO-390-motivated RV-6. Both Lycomings are boosted via Vortech centrifugal superchargers, giving us the chance to examine both 6- and 4-cylinder applications. In fact, Dan’s fitment uses some take-off parts from Bill’s earlier experiments, so this pair of supercharged Lycomings share some background.

Bill’s supercharger installation is 100% his creation, including the two-piece, 12.5-inch aluminum crankshaft drive pulley whittled from billet by a local machinist. There’s heavy tension on the green blower drive belt, so the thick, satin-black mounting brackets wrap 90 degrees around the polished aluminum supercharger.

We’ll also note Bill’s and Dan’s blower installations are custom fitments and have no connection with Thomas’ work or Forced Aeromotive Technologies, which has also offered Vortech-based Lycoming and Continental kits for some years. This month we’ll detail Bill’s airplane and follow up soon with Dan’s RV.

Also obviously hand-crafted, first-generation stuff is the inlet tubing. Here the supercharger is just out of frame to the right, the throttle body is gold anodized at bottom, and the blower bypass discharge is handled by the orange SCAT tubing. The block-off plate jutting up and forward denotes where the first, inadequately small blower bypass valve was located. The alternator pulley is also large diameter to maintain correct alternator rpm when driven by the oversized crankshaft pulley.

The Beaton Rocket

Bill’s 1998 Harmon Rocket II was built in Bakersfield, California, by Gary Banducci; in 2007 Bill imported it to his native Canada for sport flying. It was naturally aspirated with 10:1 pistons and then-current avionics. Bill logged about 850 hours in it, flying all over North America.

After enjoying the Rocket as is, Bill began improvements, and as is typical, he had some friends helping. Of those, Ralph Inkster has become the major rocketeer, with his thinking and handiwork throughout the machine. Bill and Ralph’s first upgrade was to fuel capacity. Gary had opted for “the short 42 gallon fuel tanks, and Ralph helped me build an auxiliary 14-gallon tank in the luggage compartment,” notes Bill. It’s a big plus when Bill, “gets up to 12,000 feet, makes 185 knots, and covers some ground.”

Crew chief Ralph Inkster removed the plenum cooling panel for the camera, revealing a visually conventional layout. Mainly this is because the EFI fuel lines run to the stock Lycoming ports, and the ignition coils are located outside the cooling baffles. To date initial ignition timing remains at 24 degrees BTDC; the SDS computer is tuned to retard spark 1 degree for every 3-inch rise in manifold pressure over ambient. Bill says now that he has the engine running coolly at race power, he can begin exploring different fuel and spark strategies, both at WOT and cruise power.

In fact, it was enough “to make you think it’s a fast airplane,” so in 2012 Bill raced the Rocket in the first Sport Air Racing League race in Coeur d’Alene, Idaho. “I complied by putting numbers on my airplane, and that was it.” After five or six races that year, Bill was the undefeated SARL Rocket champion and promptly retired (temporarily it turned out) from cross-country racing. But the original SARL numbers are still on the fuselage.

Bill credits his Rocket airframe’s speed to Gary. The wings are filled, with no visible rivets, and generally it was built straight and reasonably lightweight. Of course, there’s been weight creep since, so Bill’s currently chasing ounces where he can. At the 2016 Reno Air Races when we saw it, the plane weighed 1320 pounds. Bill claims he’s personally shed a few pounds, too.

Most of the visual action is viewed looking up at the bottom of Bill’s engine. We like the curved plate at the bottom of the firewall designed to smooth the in-cowling air discharge, for example. The black Sky Dynamics intake plenum contrasts nicely here; the small piping/AN fittings tucked under the plenum feed the three ADI discharge nozzles: they shoot into a spacer just aft of the gold throttle body and forward of the black intake manifold plenum. Bill repurposed an automotive throttle body to achieve a sufficiently large boost bypass valve; the SCAT tubing ducts the bypass air aft to better direct it out the cowling exit. The large, downward-facing, carbon-fiber duct at the upper right is the supercharger air inlet.

Bill also went through the engine completely when opting to supercharge it, as the existing 10:1 powerplant was optimized for natural aspiration. Working with Aero Sport Power in Kamloops, British Columbia, goal one was durability under boost, so a fresh set of lightened Ly-Con NFS 8:1 pistons went in, along with a blower-specific Ly-Con camshaft. Titanium connecting rods were considered but rejected due to a lack of long-term experience with same in the fleet. All the whirring bits were balanced, of course.

Durability was further enhanced by cryogenically treating the case, crankshaft, camshaft, cylinders, connecting rods, pistons, and piston rings. “Cyro,” as it’s popularly called, involves chilling the parts via liquid nitrogen to approximately -300 F; it’s been a popular trick in the aerospace and race car worlds for decades and is now proving itself in hot rod Experimental aircraft engines—fodder for another upcoming KITPLANES article.

Hand-ported Lycoming cylinders were prepared and reinforced with Sky Dynamics cylinder girdles. Besides Ly-Con’s funny cam, stock lifters with DLC coating were installed to work with the 1.4:1 high-lift rocker arms Bill already had. They, in turn, necessitated custom-length pushrods from Smith Brothers.

Like all Rockets, Bill’s sports wings shortened by one rib compared to its RV-4 starting point. The canopy may look low but is stock height.

Engine management fell to another Canadian outfit, Ross Farnham’s Simple Digital Systems (SDS). Their electronic fuel injection and ignition is perhaps more well known in the U.S. as the basis of the fuel and spark offerings from EFII. Bill’s fitment was the first SDS system to fit the electronic fuel injectors in the tappings normally housing Bendix fuel injectors, so his fuel is certainly shot closer to, and perhaps even through, the open intake valve and its seat than the more commonly seen intake runner mountings. Fully dedicated to digital engine management, Bill opted for a pair of SDS systems, complete with two electric fuel pumps, filters, and so on. The whole was broken in and verified naturally aspirated on the Aero Sport Power dyno before mounting on the Rocket airframe for the blower installation and tuning. Bill reports the complete 540 weighed a svelte 384 pounds without the propeller or supercharger, but with the crankshaft pulley.

Bill’s fuel plumbing employs a return-style layout as evidenced by the large inlet and return lines threaded into the black fuel rail. Because EFI meters the fuel at the injectors, the fuel rail is simply a common point to distribute fuel from. It has no pressure or metering functions.

Recidivist hot rodders will recognize the supercharger as the popular, durable Vortech V1 centrifugal. The blower is stone stock, uses engine oil for lubrication (requires one low-volume oil feed line from the front oil gallery and one oil drain line back to the sump), and turns 45,000 rpm with the 2.5-inch pulley fitted at Reno. That’s nicely within the time-proven Vortech’s rpm limits, thus keeping the blower near the sweet spot of its efficiency range—about 77% efficient.

If the supercharger is off-the-shelf, the installation is 100% custom by Bill and Ralph. Originally a 6-rib belt drive was used, but it proved inadequate on the 540 and was passed along to Dan West, along with the first-generation mounting brackets. The current bracketry is a muscular 8 pounds to avoid flexing and thus pulley mis-alignment—which will toss belts off their pulleys. Also custom is the 12.5-inch aluminum crankshaft drive pulley; it’s CNC whittled and hard anodized. The total installation of supercharger, pulleys, belt, brackets, etc. added 34 pounds to the empty weight.

SDS’s gold-anodized fuel injectors are Bosch units and are more tightly packaged than the more commonly seen fitments into the intake runners. One tactic not yet possible with Bill’s installation is to run closed-loop fuel and spark strategies (where the computer constantly fine-tunes the fuel/spark using input from rpm, manifold pressure, knock sensors, and exhaust oxygen content sensors); but it’s a goal for future development.

Greatly simplifying the installation, reducing many feet of bulky air ducting, and eliminating the cost of an air-to-air charge cooler (intercooler) is Bill’s reliance strictly on anti-detonation injection (ADI) for charge cooling. His system is from Devil’s Own, which offers bosses for AN fittings and gallon-per-hour rated nozzles, along with quality Teflon-lined hoses, robust pumps, and a progressive electronic controller. The system is activated by rising manifold pressure; there is no manual backup.

Flying Blown

As expected, developing the supercharger is an ongoing, multi-year journey. In 2014 Bill ran the Rocket at Reno normalized (29 inches Hg) with the first-generation setup, qualifying at 264 mph. In 2015 he returned with the supercharger and ADI system, running 274 mph, limited by belt slippage due to the narrow 6-rib drive belt, along with relatively minor heat issues. In 2016 the 10-rib belt drive debuted along with more ADI flow; they resulted in a 282 mph qualifying lap.

As you’d guess from the qualifying speed, there was also a boost increase for 2016. To please Canadian bureaucrats—who, like our own, seem happy to let you have a supercharger as long as you don’t use it (much)—boost was initially limited to 33-34 inches in 2015, making the Rocket little more than supernormalized.

By last September, Bill had moved up to 38-40 inches at 2700 rpm at Reno where the density altitude hovers around 8000 feet. That’s nearly 8 pounds of boost in the hot rodder’s argot, the useful limit given the current supercharger size, pulley ratios, engine rpm, and so on, says Bill. He’s sending the supercharger to Vortech for a different impeller (“trim” in blower-speak). The new impeller should yield more boost, or at least be more efficient, at race speeds.

Bureaucrats aside, there were multiple excellent reasons for Bill to sneak up on the boost, not the least is that 8000-foot density altitude at Reno in September. The thin air means a corresponding degradation in engine cooling, and with increased horsepower Bill’s 540 had more waste heat to shed. This led to fitting the ADI system. It emits water via three nozzles, and at first they spritzed a total of 7 gph of water/methanol mix. This wasn’t quite enough, so Bill upped flow to 11 gph. This worked well, but thinking it might have too much, Bill retreated to 9 gph. That proved not quite enough, so a quick nozzle change had the flow back at 11 gph. That yields CHTs just below 400 F at race power.

Unexpectedly, and likely the greatest time consumer in Bill’s engine program, has been re-fabricating the cowling and cooling plenum to accommodate the Sabre prop extension. But the extension yields needed blower and cowling streamlining real estate, so the effort pays off. The red anodized ignition triggers are just visible behind the starter ring gear.

Bill echoes what we’ve heard from other racers: Correct ADI flow is typically 20 to 25% of fuel flow, so one should initially jet the ADI system accordingly and fine tune from there empirically. We’ll also note the Devil’s Own system uses a progressive ADI controller keyed to manifold pressure. Bill’s system thus automatically begins flowing at 28 inches, then linearly ramps up the water pressure until maximum flow is reached at 38 inches.

As we’ve seen on other racers, ADI is an effective air chiller. Bill reported blower exit air as 210 F dry, falling to 100-110 F with the ADI flowing. Cylinder head temps also fall with the ADI, typically 30 to 50 F. In fact, Bill used spray bar water on the exterior of the cylinders in 2015, but higher ADI flows do the job by themselves, so he no longer sprays externally. Bill’s ADI mix is normally 50/50 water/methanol, although he’s run as high as 70% methanol.

If anything, at the current 40 gph of gasoline, Bill is nearing the flow limits of his Bosch fuel injectors, so he’ll have to upgrade those to safely support more power. The original 190-liters-per-hour (lph) Walbro fuel pumps have already been replaced by higher-output units (about 255 lph), so fuel volume is not a likely issue. Fuel pressure is set at approximately 50 psi in the fuel rails.

Of course, with electronic engine management, the fuel, ADI flows, and ignition timing can be adjusted—it’s the whole point of running an electronic system such as the SDS. Just as naturally, in the pre-Reno rush in 2016, Bill didn’t have the time to custom map his fuel/spark/ADI combination, nor was a suitable map available from others, so the majority of the tedious, time-intensive computer mapping still awaits. As the fuel/spark/ADI adjustments are interrelated, and nature doesn’t always provide the appropriate temperatures and density altitudes when you’re able to test, fine-tuning the SDS and ADI systems promises to take time.

Or, as Bill put it while sheltering from the burning desert sun in the shade of the Sport hangar at Reno, “We have cooler air at home.”

Ultimately, Bill envisions the 540 “could likely run 45 inches and it would hold. But what about VNE? This is 240 knots [276 mph] published on this airplane. I have done power-on descents at 310 mph doing flutter testing. It’s a robust airframe and a good build [but] there is a limit to the top end of the airframe. This one isn’t going to go any faster; it’s at its limit. I won’t do any more to it.”

Of course, like almost every other Sport racer at Reno, there’s the dichotomy of racing one week out of the year and owning a capable cross-country machine the other 51 weeks. “It’s a beauty to fly—the control harmony between pitch and ailerons…I’m also flying a Lancair 320 with a 540 in it, and it’s really pitch sensitive. The RV/Rocket are similar [to each other], with good harmony.

Racer but one week per annum, Bill’s Rocket is a plush cruiser the other 51 weeks a year. Shown in race trim on the Reno ramp, the back seat is consumed with removable ADI tanks. Specialized instruments for ADI, engine tuning, etc. are mainly clustered to the left of the primary Garmin display. The red rectangle with white dot on the right side panel is a panic button—most useful in pylon racing, we’re sure.

“What other airplane can you fly at 240 knots and land at 50 knots?

“This airplane I race one week a year. I can cruise at 11,000 or 12,000 feet; I typically don’t go higher. I’m cruising at 215 knots TAS, which is, ‘Wow! I can go somewhere.’ I do burn more fuel—around 16 or 17 gph. I lost efficiency with the lower compression [And driving the supercharger].”

By comparison, in naturally aspirated trim the Rocket cruised at 185 knots. That was at 11,000 feet, where typical manifold pressure is 18-19 inches. With the Vortech blower, Bill now sees 26 to 27 inches at the same altitude and the same 2300 engine rpm, so he’s lightly boosted while cruising; call it 4 pounds. Such low boost is key to the supercharger’s simpler, charge-cooler-less layout. Because inlet air temperature is so low, no charge cooling or ADI is needed. The ADI is only in play when racing at low altitude and high manifold pressures.

Also typical, Bill says he could save fuel during cruise by simply closing the throttle a little. “But for the speed bug, I could dial it back and get 12 gph, but once you get used to going fast…I flew 3 hours and 30 minutes, Calgary to Reno. That’s 22 hours driving, because Ralph did it!” Bill’s also running rich of peak so far, leaving lean-of-peak operation for later, after the fuel/air/spark tuning is more complete.

This Year

Expect to see Bill at Reno in 2017, but with only a small jump in speed, if any. Instead we hope to report on his engine-tuning success as he works toward his ultimate goal of single-power-lever engine management. In the meantime, his is a Harmon that really does rocket.

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