The prototype Berkut was designed and built by Dave H. Ronneberg as part of a business partnership between Ronneberg and Donald S. Murphy, called Experimental Aviation, that lasted from 1989 to 1992. In 1992 the partnership dissolved and Ronneberg, incorporating as Experimental Aviation, Inc., brought the aircraft to market as a kit, while Murphy wanted to shelve the project entirely. A subsequent series of lawsuits between the two resulted in bankruptcy for Ronneberg and Murphy as individuals and for Experimental Aviation as a corporation. The kit was resurrected in 1996 by Renaissance Composites, with Ronneberg working as a consultant. In January 2001, under pressure from Ronneberg, Renaissance sold the assets to Vicki Cruse, an American aerobatic pilot, who then formed Berkut Engineering and Design, Inc. That company withdrew the aircraft from the market in 2002. Ronneberg continued with the project, which is now directed at UAV markets. A deal was struck in 2003 to sell the project to Republic Aerospace, but the deal fell through. Cruse was no longer involved with day-to-day operations, but maintained ownership until her death on August 22, 2009, when the aircraft she was flying — a borrowed Zivko Edge 540 — crashed in Buckinghamshire, England, during a qualifying flight for the World Aerobatic Championships. Through the various incarnations, approximately 75 kits were sold and 20 airplanes completed.
Configuration
The Berkut is derived from the Rutan Long-EZ, with the primary differences being retractable main landing gear, dual canopies, and molded fuselage, strakes, and wing spar. Like the Long EZ, the Berkut carries two people in a tandem seating arrangement. The front seat occupant has access to all instrumentation and controls. The rear seat, normally holding the passenger, is equipped with a side stick and throttle, but no rudder pedals, brakes, or instruments. Aerodynamic optimizations to the original Long-EZ airframe were made to increase performance and interior space. The fuselage was stretched and the nose, canard, instrument panel and pilot moved forward one foot, to allow a heavier engine to be used in the rear. The main wingtrailing edge was straightened, removing a small bend in the trailing edge of the Long EZ wing. The lower winglet was removed and the aileron size increased in both chord and span, significantly increasing roll rate. Early Berkuts used wings and canard that were structurally similar to the Long-EZ and used solid blue 2 lb/cu. ft. density Dow STYROFOAM PI cores cut to shape with a hot-wire foam cutter, but with carbon fiber reinforced polymer skins instead of fiberglass. The fuselage and winglets remained fiberglass. Later versions used fully molded carbon fiber canards and wings with high density, 5 lb/cu. ft. 1/4" thick PVC or SAN foam cores, leaving only minor fairings and tip surfaces to be carved from foam. The Berkut has always used the Roncz 1145MS canard airfoil, which is more tolerant of insect and rain contamination than the GU 25-58 airfoil originally used on the Long-EZ. The Berkut used a retractable main landing gear system designed by Shirl Dickey for his E-Racer homebuilt. Originally, Berkut used gear parts produced by Dickey, but over time they were repeatedly re-engineered and strengthened. Later kits had gear components produced entirely in-house. Like the earlier Vari-Eze and Long EZ, the Berkut kneels with its nose gear retracted to prevent the aircraft from tipping over backwards when parked without a pilot in the front seat. Some early Berkuts utilized hydraulic nose-gear extension systems, but most have used an electro-mechanical jack-screw. With the electric system, the pilot and passenger can climb into the cockpit, then extend the nose gear, raising the airplane with occupants inside. While the Long-EZ, originally designed for the Lycoming O-235 108-118 hp engine, was closer in the design of the Berkut, the latter was designed from the outset for the larger Lycoming IO-360 180 hp engine. The aircraft was later adapted, with a different engine mount, cowls and battery location, to accept the 260 hp Lycoming IO-540, which most builders chose. With the O-540, some have reportedly reached speeds of 300 mph in level flight.
Selected accidents
Irrespective of cause, the Berkut has a poor overall safety record, with at least 6 of the 31 aircraft built having been involved in serious to catastrophic accidents or incidents. The manufacturer or somebody associated closely with the manufacturer has explained this as follows: "There were some accidents the first years caused by errors in the assembly, so it was decided to start selling it finished. There were also some accidents that were caused by pilot errors. But there has never been an accident caused by failures in the airplane or the design." Here are 5 "selected" accidents/incidents: ;N91DR ;N260DG ;N600SE ;N538AJ ;N827CM ;N5439N ;N3255U
