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Tim Sullivan's Subaru-Powered Super Zodiac CH 601 HDS

Part 1 | Part 2

Story and photos by Pat Panzera, EAA 555743


When Timothy P. Sullivan of Newhall, California, undertook the task of building an experimental aircraft, he didn’t have a pilot certificate. He in essence was dared by his father to build a plane at the same time he was building his Murphy Rebel. By the time Tim actually accepted the dare, his father was two months into his project, with a completed empennage. 

Tim is a regular “Joe,” a licensed plumbing contractor, working hard to support his family, but he’s a very crafty and frugal individual with some pretty good resources.

Tim built the plane per the plans, with just a few minor modifications or improvements. Somehow he was under the impression that when he ordered his kit, it would be delivered both precut and predrilled. But that’s not the way it came, and he’s now proud to point out that he drilled each and every hole by hand. But even as skilled as Tim might be, he wasn’t confident enough to tackle the construction of his center wing spar, so he ordered it completely prefabricated from the factory.

The landing light in the plans specifies two lamps in the leading edge of the wing, both on the pilot’s side, one used for landing and the other for taxi. Tim deviated from both the installation and wiring specifications by locating one on each wing and wiring them together so that one switch powers both lamps at the same time.

Although the plans didn’t call for it, Tim designed and installed his own electric aileron trim tab in the trailing edge of the right aileron. His reasoning was sound yet unwarranted. He mistakenly doubted his ability to build and rig the plane true. “I didn’t know if I was going to be building a straight plane, one that would fly straight and level, but it actually it does. It flies completely hands-free,” Tim said. Since installing the trim tab, Zenith Aircraft Company (ZAC) has come out with a similar modification to its plans, but according to Tim, it had the foresight to place it on the left aileron, well in the line-of-sight of the pilot. With Tim’s installation, he doesn’t have the luxury of viewing it in flight. Since the trim is electric and subject to “runaway” conditions, Tim installed a switch to cut the power to it. For an added layer of safety, the test pilot elected to leave it off for the initial flight, but it wasn’t needed anyhow.


The center console as built from the ZAC plans seemed to be a bit too “flimsy” by Tim’s standard. Ingress and egress is dependant on the ability to place a huge amount of one’s body weight on the console. Early on in the build process Tim had a chance to spend some flight time with another HDS builder and soon found out that the console/armrest wasn’t up to his expectation. He found that the top piece would cave in when weight was applied, and the entire unit could not handle the required side loads imposed when entering or exiting. By upping the material to 0.025 and adding doublers, Tim now describes his console as being “bombproof.”

The upholstery as it is now was inspired by the (late) Boyd Coddington’s TV show, American Hot Rod. Tim was viewing an episode where the project car was wheeled to the upholstery shop for a custom job, and the upholsterer used an electric carving knife and started carving the foam to shape. Fully inspired, Tim headed out to the garage, carving knife in hand, and half a day later emerged with the foam shaped as you see it in the photo. Some pieces were adhered to others using spray glue. “I just built foam pieces that looked halfway decent, took them to an upholstery shop, and I said make them look like an airplane interior,” Tim said. The same method was used to create custom panels to complete the professional look. But this was not the first go at it; Tim’s previous attempt at upholstery netted an appearance that he likens to motorboat upholstery.

Although a bit difficult to make out in this photo, the plans called for a pair of “T” handles to protrude from either panel end (one on the pilot’s side, the other on the passenger’s) to be used for dual throttle. The pilot’s side handle would have been located approximately where Tim has his choke located now. The location of the vernier throttle control is now much more comfortable and logical. Larger view

Under the cowl we noticed remnants of an abandoned attempt at dual throttles, specifically a cross bar mounted on the firewall that was used to interconnect two push-pull cables mounted in the instrument panel at both outboard ends. This gave throttle control to the pilot’s left hand and the passenger’s right hand. The cross connect on the firewall was fitted with a pair of bell cranks that controlled their respective carburetor. Although the plan looked good on paper, the actual mechanics of it didn’t pan out. The ergonomics of the cockpit lever plus the sensitivity of the system (due in part to the lack of rigidity and poor geometry) led to rpm change while simply rolling down the taxiway, plus over- or undershooting while trying to change rpm. The solution was to forgo dual throttles and have a custom vernier cable manufactured that split off to the two individual carbs. “I wanted to go with a vernier type throttle control in the first place, but I just didn’t know how to do it.” Once Tim bit the bullet and sought the advice of experts in the field and paid for a split cable, he was very happy with the results. Throttle control is now very fluid and accurate. He even improved the ergonomics to where he can rest his left wrist on his knee and the control is right there where it belongs.

The rudder pedals and brake system were modified slightly to give more leverage to the brake cylinders. The standard brake pedal and subsequent brake cylinder attach point is about half as tall as what Tim constructed, pictured above.

The standard ZAC design calls for cables to actuate the ailerons. Tim didn’t much care for that design, so he eliminated the aileron cabling system all together and installed pushrods. “With my system, if I were to lose one pushrod, the other two pushrods will still work both ailerons. With the old system, if I were to lose one cable, I’d lose everything. Not that it’s likely to ever lose a cable, but at the time I thought I’d prefer the redundancy of the pushrod system.”

Sharp eyes would have already noticed that in three of the preceding photos, the canopy was hinged the wrong way. That’s no illusion. If built to plans, the HDS canopy can be opened from either side.

The plans Tim worked from specified a simple yet elegant way to hinge the canopy, which can be opened either to the left or to the right. Once he found out about the more popular forward-hinging canopy option, he was too far into the project and didn’t want to backtrack. But Tim has no regrets; he really likes the way the canopy functions as it is.

The Garmin 300XL was a gift from Tim’s boss who was in the process of refitting his L-39 Albatros, and the transponder came out of his boss’s Cessna 421 refit.

Tim told us that he built the panel probably five times before he was happy with it. He fabricated it out of wood at first, which became the pattern on which his router bit would ride when cutting the aluminum used for the actual piece. With the wood templates still available, remaking the panels from a different material at a later date should be a snap.

Part of Tim’s day-to-day activities have him installing or otherwise refitting ATMs at local banks. This process nets him scrap aluminum. All the aluminum instrument panel parts came from these otherwise scrap pieces. If the aluminum was too thick, such as some of the 0.125 he used, Tim would route out the back to thin it down, in the hopes of saving some weight.

The panel’s professional appearance and the traditional six-pack layout was no accident. Tim was not a pilot when he built the plane and didn’t get much in the way of guidance when designing his panel. “I copied it from magazines,” he told us. “I’m not a pilot, and I wasn’t around airplanes when I was working on the panel, so I just copied it from what I saw in the aircraft magazines.” In my estimation, Tim got lucky, as I’ve seen some pretty bad designs (in magazines) over the years, and he could have very easily copied something that was less than desirable. As it was, Tim missed installing a VOR. “I didn’t even know what a VOR was, never even heard of one when I was building the thing. I didn’t have airplane on the brain yet. Actually, if I would have known about it, I would have incorporated it in somewhere.”

Tim purposely divided his instrument panel into flight, navigation and communication, engine and fuel, then ignition, with each section being panelized so that he can pull them out and gain access individually. An access hatch was cut into the forward deck for additional access to the maze of hoses and white wires that makes up a typical IFR (instrument flight rules) panel. This is one modification that he’s particularly glad he did, as he’s already needed to get back there 20-some odd times by his estimation.

An access panel in the forward deck facilitates the access to the back side of the instrument panel. Larger view

For driving the gyros, Tim paid a visit to Wentworth Aircraft, Inc. St. Paul, Minnesota, (the world’s largest single-engine Cessna and Piper aircraft junkyard) and picked up a $300 electric-driven emergency backup vacuum pump out of a Bonanza and mounted it behind the seat. He already had a venturi in place, so he’s going to tie them both together and use it as a backup as intended. This was a bit of an impulsive extravagance, especially since it’s highly unlikely to be needed any time soon, but he’s happy with his decision.

During the airplane’s first flight the airspeed indicator and the vertical speed indicator were nowhere near indicating accurately. The flight had to be conducted using the GPS since the steam gauges were not reliable. Most of you reading this will know instinctively that this would be a pitot/static failure, and you’d be right. “I had a leak in every single fitting that could leak, and I’m a certified plumber,” Tim said. “While building I opened the Spruce catalog, and I ordered all this expensive stuff and I plumbed up. When I pulled it all out after the first flight, all these old-timers were like, ‘Get that stuff out of there. Go to Home Depot and get some barbed fittings and hose and stick it on there,’ so that’s what I did. It works now.”

While calibrating the airspeed, Tim was amazed at just how little pressure the pitot system actually sees. “When I opened up the box my airspeed indicator came in, I noticed a warning to not blow into this instrument; I was so tempted…but a couple of inches of water and a piece of hose [home-made manometer], just making the water go back and forth from the hose on the pitot tube moves that thing a hundred miles an hour.”

Tim, opening a wing locker to show us the auxiliary fuel tank he’s plumbed in place. Larger view

“Wing lockers” are an option many 601 builders choose to install. There’s not a lot to them, they don’t add any real weight, complexity, time, or money to the build, so there’s really no reason not to include them. The plus side is the additional storage, on the center of gravity, adds utility to the plane. Although Tim elected to install them, he’s filled them almost completely with removable fuel tanks. The standard HDS comes with a 16-gallon header tank, and optional leading edge wing tanks are available.” I didn’t know about the optional leading edge fuel tanks until it was too late,” Tim said. “It would have been a lot cleaner, and it certainly would be nice to have full access to the wing locker as intended.”

Wing tank
Larger view

Although the plans call for typical barbed fittings and hose clamps for the fuel system, Tim went the extra mile and used nothing but AN hardware, braided stainless hoses, or flared rigid lines. This complicated the connection of the fuel line to the Bing carbs. It seems that the inlet threads for the carb fuel fitting are metric, and Tim couldn’t find a 10 mm to AN-4 fitting at his usual supplier, so he improvised and bought (and sacrificed) 10 mm banjo fittings, cut the threads off, and welded AN-4 fittings to them.

The fuel handling system was copied from a Lancair 360 Tim saw at Whiteman Airport. Now he is able to transfer fuel from tank to tank or run the engine from whichever tank he pleases, but under normal conditions the header tank is the “main,” and he transfers from the wing tanks to the header, which then gravity feeds to the dual Bings under the cowl.

Another modification to the system includes external fuel vents on all three tanks, each approximately 1/4 inch in diameter, rather than simply venting inside the wing.

The gascolator is designed for fuel-injection pressurization, for high-pressure systems. Tim tried a standard unit but blew the seals with just 5 psi. Since he has the capability of pumping from both wing tanks at the same time, with independent electric fuel pumps, he felt it necessary to jump up to a gascolator that is capable of handling high pressure. Looking at the firewall from either side, one can see the remnants of the old gascolator.

One thing that most people find interesting about the HDS is the way the main gear legs protrude through the top skin of the wing. The strut is suspended via a bungee cord and is capped with a little plate that keeps the leg from dropping out of its mount while in flight. On the ground, the cap will sit above the skin, giving an illusion of a fuel filler cap or other access cover, but once the weight is off the gear, the plate sits flush.

Gear Cap
Larger view

Gear Cap
Larger view

When Tim first built the plane, there was enough elasticity in the system to keep the cap flush even when the plane was on the ground. But as time has gone by, the gap has been opening. Not related to the gap, but certainly worth mentioning, on the first flight of this little plane the landing was a little rough. A fall from an honest 5 feet prompted the tower to call twice to ask if they (plane and or pilot) were okay. The steel landing gear struts were primed before being installed, and any relative movement between the mounting block and the strut itself would leave telltale marks. When the plane was inspected after the landing, the marks showed very little travel, indicating to Tim that the gear did its job.

“I wish I would have had the gear struts chrome plated,” Tim said. “Either that or powder coated. I didn’t do anything to all three of them, and they look pretty bad with just zinc chromate.” Tim’s initial thought was to go with powder coating like he’s done on the engine mount, valve covers, and oil pan, but his experience with two local powder coaters left him with a distaste for the industry in general. “I dropped off stuff [at the second of three different shops] to be powder coated, and when I went back three weeks later, it was in the same exact place I left [it]; it never moved. I said, you know what, give it back. I then took it to another place, and they still took a couple months.”

Although this photo is intended to illustrate the beautifully installed wheelpants, it also helps illustrate the location of the venturi and the radiator belly scoop—more on that and the Subaru engine it cools in Part II. Larger view

The wheelpants are stock Zenith parts, but with an additional 30 hours of body work on them.

Throughout the interview with Tim, he continually referenced his experience with Baja Bugs and other off-road VW conversions he’s worked on in the past. In fact, because of his familiarity with VW engines, he was initially interested in installing one in his HDS, but he realized that the 100-hp, water-cooled Stratus Subaru was a much better choice for him.

Drawing from his automobile experience but lacking in aviation knowledge, Tim went after wiring the plane like it was an automobile. “I wired this thing like I wired a Volkswagen Baja Bug, mostly because I just didn’t know anything about airplanes. But then after I brought it here [EAA chapter hangar] and a few of the local geniuses took a look, I was in better shape. One advisor, who was an electrical engineer, drew sketches of how to rewire certain things, so learning from that I rewired a bunch of things. I’m not an electrician, so I really can’t explain exactly what I did, but everything works.”

“There’s just a ton of wire. I was amazed, I kept ordering wire from Spruce, and it’d be gone. Order more, it’d be gone. I’d have to order more. I mean just for the wings alone running wires out to the lights, to the strobe, and to my fuel sender unit.”

Every piece of wiring was done by Tim; the Ray Allen stick grip itself is a maze of wires with the elevator and aileron trim micro switches, in addition to the push-to-talk. There are a similar set of Ray Allen grips on the CONTACT! Magazine CH 601 yoke, and by the time the bundle exits the bottom of the stick, it’s almost 1/2 inch in diameter.


Rather than the traditional rotating beacon mounted on the top of the vertical stabilizer, Tim installed a custom flashing beacon that is actually just a big-rig brake signal lamp mounted on the top of the rudder and hooked to a traditional automobile signal flasher unit.

Tim told us that if he were to lose the alternator or the battery, he could turn the master bus off and switch to the secondary electronic ignition and secondary 20-amp battery. “That way everything is off except for the ignition, which is just running on the secondary battery, so we have at least an hour.” Since Tim doesn’t have an “essential bus” to fall back on, once the system is shut down, communication and lighting are gone. “Right now,” Tim said, “I don’t have any form of over voltage protection on anything, but I’m considering changing that.”

Part of Tim’s electrical design calls for a multiple battery isolator mounted under the cowl. Larger view

While building his plane, Tim read of a Pietenpol that crashed in a cornfield due to an engine failure, directly related to a lost ground to the engine. “I raced down to the hangar the next day and added another ground strap from the firewall to the engine case.” Tim said, “With everything on the motor being rubber-mounted, I thought I’d better add more than just one ground after reading that.”

Tim’s rather robust ground terminal. Larger view

The second of two batteries located behind the seats. Larger view

As the title implies, the next issue of Experimenter will contain Part II, where we’ll take an in-depth look at the Stratus Subaru engine Tim installed.


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