ZIVKO AERONAUTICS ZA-1 'EDGE' wing (for EDGE 360 and 540 series)
A lightweight yet sturdy wing redesign that has arguably made the EDGE series the best aerobatic aircraft ever!

"Wild Bill" Marcellus during his acrobatic routine in an EDGE
360 (N363WB) at Edwards AFB on September 9, 1999.

Several views of the magnificent Edge 540 prototype.

Type: replacement wing for unlimited aerobatics aircraft
          (based on the Stephens 'Acro' family of aircraft)



Powerplant: 1 x Lycoming O-360 (EDGE 360)
                    1 x Lycoming O-540 (EDGE 540, 540T)

Significant date: 1990 (wing flight tested)

Once described as "extraordinary craftsmen building extraordinary aircraft", Bill and Judy Zivko have set up their company, Zivko Aeronautics, Inc., on Guthrie Municipal northeast of Oklahoma City. By combining common sense with elbow grease and applying high tech where it does the most good, they have turned their small specialty house into the much sought-after manufacturers of the world class EDGE series of aircraft, and produce not only the newest, hottest aerobatic monoplane in the business, but have developed a composite capability that is increasingly being called on by aerospace corporations to do the prototype work they can't do themselves economically.

The Lazer was the grandaddy of all the modern aerobatic monoplanes. Based on the Stephens Acro design, Leo Loudenslager reworked the design until he had a whole new airplane, then he dominated the American aerobatics scene with it for about a decade. Walter Extra even based his design on it, and many modern aerobatic planes are derivatives of the Extra. In the late 1980s, the high-G world of unlimited aerobatics was proving too much for the Stephens/Lazer type monoplane wings. Even though the wood wings used railroad-tie spars, they were delaminating and actually breaking.

Even with all the mods worked into the wings by pilots such as Leo Loudenslager, the wing was still too marginal. It was a safety item they all worried about. Besides being a safety item, getting wood of high enough quality and long enough to make the 24 foot spar wasn't easy and was becoming increasingly expensive. Zivko looked at the wing and immediately saw an application for composites. He knew he could build a stronger, lighter wing and at the same time update the aerodynamics. The reason he had such confidence in himself was he had a cadre of friends, courtesy of his time with Scaled Composites and other similar projects, who were at the forefront of composites design and engineering.

Using input from pilots like Jones and Loudenslager, Zivko made up a list of factors that had to be primary design parameters. Those at the top included high roll rate, low stall speed and extrmely high strength. Bill knew pilots were pilots. They didn't want to worry about all that mechanical stuff. They wanted to pull and not worry about it. Since 10 G's wasn't unusual in an unlimited sequence, Bill decided his Lazer replacement wing would have a safety factor of two, giving the wing a 20 G ultimate. At that number he felt safe.

The final design, Zivco's EDGE™ ZA-1 wing, combined some of the industry's best. John Roncz designed a new airfoil that would have a low stall speed, would corner well and have predictable, well-behaved characteristics at both ends of the envelope. The preliminary wing layout was done by Paul Finn, while Dave Boldenow, a Boeing composite engineer, did the structures. When the prototype popped out of the oven, Zivko loaded it to 20 g's and found a deflection of only a little over four inches. The actual involvement of Scaled Composites in the EDGEdesign or construction is not clear, and apparently not documented. There is no mention of it in Zivco's press releases, and it only shows up once, mentioned by former Scaled engineer Dave Boldenow among a list of Scaled projects he had worked on. It is possible that Zivco started work on the EDGE project while still at Scaled, thus explaining the fact that it has been included.

The production wing weighs 224 pounds and is good for 20 Gs, versus the old wooden 12 G wing that usually weights around 250 pounds. The wing was first installed on Joe Olson's Lazer with many more following right on the heels of that one. Zivko Aeronautic's wing, the ZA-1 is earning a reputation for giving the Lazer a new lease on life. In fact, Livko even began custom building airframe components for customers who wanted their own airplane that incorporated the wing along with a bunch of other modifications engineered by Zivko. They call their four-cylinder airplane the EDGE 360.

Unfortunately, unlimited competition has very definitely become an area where last year's model just won't cut it. Laser's can't make the grade, if nothing else, because they don't have enough power. Bill and Judy looked at the track record being established by their wing and decided the next obvious move was to build their own high performance airplane around that wing. They wanted an airplane that could successfully bump heads with Sukhois and Extras. That mean't going to a six cylinder, IO-540 in place of the Lazer's O-360. There are lots of places in everyone's mechanical life where the only logical solution for a situation is a healthy dose of cubic inches. Or a bigger hammer.

By the time Zivko Aeronautics was getting ready to start into their own airplane project, they were already a production shop which had a client list including names like Tinker Air Force base, Leo Loudenslager and a most interesting client named Aurora Flight Sciences. Aurora's products were ultra-high altitude, unmanned aircraft which were aimed at doing all sorts of environmental surveying up where manned aircraft were nearly useless. These aircraft were designed to work between 80,000 and 100,000 feet while carrying payloads that sniffed the atmosphere for bad stuff or could loiter on top a hurricane for most of its life cycle. They measure their loiter times in days, not hours! The current production aircraft, the Perseus B has a loiter time that can be extended up to four complete days. They can do global-scale chemistry surveys over nearly half the earth's circumference in one flight.

Obviously these airplanes are special purpose and rely on light weight and long wings to do their thing. And that's where Zivko Aeronautics comes into the picture. The huge (59 foot) wings wouldn't be possible without composites and Zivko built not only the wings, but all composite components including the tail and fuselage as well. There are a lot of composite fabrication companies in the world that could build the components, so it says something that Zivko aced-out many much larger companies. With their moves into the big time world of composite engineering, a full-time engineer, Todd Morse (his great grandfather invented the code), was added to the staff along with complete CADCAM capabilities. All of this experience and capabilities were brought to bear on their unlimited bird, the EDGE 540 series.

The Zivko EDGE ZA-1 wing has had considerable success with aircraft in the aerobatics category, and has also been fitted to other types than the Stephens Lazer, such as the Rebel based Acrostar 330 and Freebird 300.


  • EDGE™ 360: a handful (Terry Pound's N37TP, Bill Marcellus' N363WB and Chris Huey's N360CH are known to have existed)
  • EDGE™ 540: about 40 altogether (22 currently registered in the US)


Crew/passengers: 1

Main sources:
- Zivko Aeronautics website

Bill Zivko: from Bede to Scaled

Some time in the late 1960's Bill decided working for a Wisconsin FBO wasn't taking him where he wanted to go. He didn't want to look down the road at his future and see an endless string of annual inspections with an occassional radio installation here and there. He wanted something with more excitement and color. He found it in Newton, Kansas with a guy named Jim Bede. At that time Bede was up to his neck in the famous BD-5 project and Zivko lent his talented hand in building up the mini-jets. The BD-5J. Since that day Zivko has never completely gotten away from the little jets. He worked with Bobby Bishop for years maintaining his airshow 5J and today still works with Leo Loudenslager on the Bud Lite Airforce's little kero-burner.

Bill wound up back in Wisconsin after the demise of the Bede project, but several years later received a phone call from another Bede alumnus, Burt Rutan, who asked Zivko to come work with him at Scaled Composites. They were just building up a head of steam to begin the Beech Starship project and Rutan needed people who knew how to get things done in a shop environment. Bill moved his family to the high desert of Mojave and he became shop manager for Scaled Composites. If he was looking for exciting projects, he was certainly in the right place.

Although Zivko's primary background had originally been in traditional aircraft materials, he was little by little moving deeper into the composites. By the time he left Scaled Composites in the mid 1980's he recognized the advantages of the materials and continued working with them in his own business. Bill and Judy spent a number of years in the Oklahoma City area before deciding to relocate their shop into a brand new hangar/shop/office complex on the Guthrie airport. At that stage of the game they were already going in two directions at once, one of which came about from their friendship with the late Tom Jones, a well known aerobatic competitor and airshow pilot. It was through Jones they were exposed to the ever changing arena of unlimited aerobatic competition.

Bill Zivko is an excellent study in how sport aviation technical fall-out is reaching past EAA-oriented markets to effect other parts of the economy, as well. Bill is often mistaken as being extremely quiet. Maybe even a little shy. But what people don't realize is that he isn't just being quiet. He is listening. He is soaking up what's around him and learning. If he has one characteristic, that's probably the dominate one. He always appears to be learning.

The old and the new: Zivko's EDGE 360 (front) and 540 (back).