Flying an Eagle

Berkut takes canard airplanes to the next level.

by Vicki Cruse
Published in KitPlanes Magazine
October 1998

We’ve all seen them, those funny-looking airplanes with no tail and an engine in the back. They have a small wing up front, big swept main wing, tall vertical stabilizers and rudders at the wingtips, and parked on the ramp they look a lot like birds sipping at a watering hole--beak down, tail up.

They are often called names such as "flying pickle fork" and "Bullwinkle" (for the famous cartoon moose).  But despite their obvious oddities they have proven capable and effective flying machines. One of the best of these designs to appear on the scene is the high-performance tandem-two-seat Berkut, manufactured by Renaissance Composites in Santa Monica,California.

I had the opportunity to fly this aircraft--my first flight in a canard—and it was an experience worth reporting.

A History Lesson

 Canard-type aircraft have been flying sine the Wright Flyer, and in WW-II the Americans and Japanese both experimented with canard pushers and vertical stabilizers at the outboard ends of the wing. But the popular belief is that canard airplanes really came onto the scene due to the efforts of designer Burr Rutan.

Rutan's first design was the VariViggen, which went to the drawing board in 1961 and first flew in 1968. This aircraft was a small, tandem two-seat craft built of wood with a delta wing and retractable gear. Only a few were built, and the airplane was not very popular. Rutan started experimenting with a speed-wing version of the VariViggen, and what evolved was the VariEze, introduced in 1974 and awarded Outstanding New Design at Oshkosh that year.

The VariEze used a Continental 0-200, the same engine found in a Cessna 150, and plans were made available in 1975. The airplane had fixed maingear and a retractable nosegear. This was the beginning of the canard aircraft we recognize today, and additional designs would soon follow. After the VariEze came the Quickie in November 1977. A small, single-place aircraft built from plans, it did not have winglets like the Eze but was a tandem-wing aircraft with both wings the same size. A true biplane, 60% of the weight was on the forward wing. It was originally powered by a tiny 27-hp Onan engine.

Like the VariEze, this planform spawned its own line of descendants-- the side-by-side Q2, the Continental O-200-powered two place Q-200, the tricycle-gear Tri-Q, and the larger two-place Volkswagen-powered Dragonfly. Rutan even designed a racing version of the Quickie, the Amsoil racer, for the biplane class.

In June 1978, a variant of the VariEze, the Defiant, was introduced. It was originally designed for production, though plans were later dropped. Resembling a larger VariEze with an engine in the front and back, it seated four. A long-term building project, few Defiants were built.  Seeing a need for a more practical bird, Rutan went back to the drawing board and redesigned the Vari-Eze, and in June 1979 he was back, this time with the Long Eze. The Long Eze was 15% larger than the VariEze and it used a Lycoming O-235 or O-320. It too had fixed maingear and a retractable nosegear. The Long-EZ would become one of the most popular homebuilt airplanes ever designed, even though the Long-EZs were built from plans, although a few molded and metal parts were available, as well as materials kits from aircraft supply companies. Complete kits as we know them today were not offered.

The Long-EZ was the last homebuilt canard design from Burt Rutan, though he went on to design the globe-circling Voyager and other airplanes. But even after Rutan left the homebuilt scene, others picked up where he left off. A number of canard aircraft introduced, including the three- and four place Cozy, the four-seat Velocity, Shirl Dickey's speedy E-Racer, the German built Speed Canard, the new four-seat SQ2000, Steve Russel's four-place Aero Canard, and the Renaissance Berkut.

Bucking Convention

The original premise behind the canard airplane wasn't to have people stand in awe at the sight of a row of odd-looking, awkwardly parked aircraft. No, the main reason for these designs was to design an aircraft that did not stall as conventional aircraft do, and also to use the canard's aerodynamic strengths to increase performance. Because safety is always first in most pilots' minds, and since a canard airplane's main wing doesn't stall, the canard airplane won't spin, making all who fly in them breathe easier.

The canard airplane does this via aerodynamics and geometry. The canard wing is the horizontal stabilizer and elevator mounted up front. Its airfoil, and the angle of incidence at which the canard is mounted, determine the critical angle of attack, or stall speed of the canard wing.  This is all set so the canard stalls before the main wing does. For example, when the nose of the aircraft is pitched up and reaches the canard's critical angle of attack, it will stall while the main wing is still flying. At the stall, the canard's elevator no longer produces pitch input, so pulling back on the stick does nothing. The nose then drops slightly, which reattaches flow to the elevator.

Keeping the stick back starts a safe, stable, rocking-horse motion where the nose of the aircraft bobs up and down slightly, but the main wing never stalls. But there can be problems. Some pilots cite the canard' s potential to enter a deep stall as a major fault of these aircraft and a reason to never fly in one. A deep stall is a non-recoverable stall of the main wing. How can this occur in a canard aircraft if the canard stalls first and there is no elevator authority to continue to the nose-up attitude? The answer is to load the aircraft aft of its critical c.g. 

Early Long-EZs using an 0-320 or O-360 have to watch the flight envelope carefully, and weight often must be added in the nose. This is why EZs and other related tandem canard aircraft are flown solo from the front seat. But deep stalls are not just limited to canard airplanes. Conventional aircraft are subject to similar unrecoverable modes when loaded with a too-far-aft c.g.

A Different Bird

In the late 1970s and early '80s a man named Dave Ronneberg got the homebuilding bug. Working for Tom Abede at Compton Airport near Los Angeles, he helped build a Starduster II, several Pittses, a Mong Sport, and he helped restore a Stearman. On his own he built a Lancair. A fan of composite construction, he built seven Long-EZs. During the building process he noted what he would like to change and incorporate into one special airplane.

Each Long-EZ required what was effectively a new pattern, requiring that each airplane be shaped, filled and surfaced to  perfection. Ronneberg figured if molds were used, duplicate components could be created allowing for a time savings of several hundred hours. Being a fairly tall guy (6 feet, 2 inches) he also wished for more headroom and a longer, wider fuselage. As the saying goes, be careful what you wish for you just might get it. In 1986, Ronneberg started fulfilling his wishes. Sam Kridell, head of space shuttle design for North American Rockwell, used a Cray supercomputer to produce a set of full-size templates of the fuselage and bulkheads that Dave had designed over the previous five years.

Using these templates, a full-size model of the fuselage was built. It was also around this time that Dave was involved with Rutan and the Voyager project. The fuselage model was shelved but not forgotten. !

The Berkut Is Born

While working for Rutan, Dave continued to dream about his airplane and noted additional changes he would like to see in a canard aircraft. He also toyed with the idea of producing kits instead of an airplane built from plans. Over the next few years the dream became a reality. In 1989 construction began on the prototype bird, now called the Berkut.

If you're wondering, a Berkut is a small but vicious predatory Eagle bred by the Kirghizia tribesmen of south-central Russia to hunt wolves from horseback.

The prototype airplane incorporated new features into the canard body. The model of the fuselage built in 1986 was 12 inches longer, 3.5 inches wider, and provided 4 inches more headroom than the Long-EZ. These features were retained in the prototype Berkut. This airplane would emerge with fully retractable gear, designed by Shirl Dickey, designer of the E-Racer.

Ronneberg acquired the rights to use Dickey's gear in the prototype and future Berkut kits.   Dickey continues to manufacture the carbon fiber gear for the Berkut. The prototype Berkut used a Lycoming IO-360 engine by Demars rated at 205 hp. LightSpeed Engineering's Klaus Savier designed the electronic ignition, which retains a traditional magneto backup.   The Berkut differs from the EZ in a number of other ways.

The canopy of the Long-EZ is a single-piece unit, whereas the Berkut canopy is two pieces--a canopy for each person similar to those used on modern two-seat-tandem fighter jets. The  Berkut ailerons are 6 inches longer than on an EZ and have a slightly larger chord. The lower winglets and rudder horns have been eliminated by incorporating them into the wing on the Berkut. The strakes (the triangle portions between the fuselage and wing) have a convex upper surface instead of the flat surface found on the EZ.

The Berkut also makes use of carbon fiber and Kevlar in the design. Carbon fiber is found in the canopy frame, wing skin, and in the mainwing sparcaps and the canard sparcaps. Carbon fiber is stiffer and stronger than fiberglass, and in its Berkut application it prevents unwanted flexing, particularly in the wing, making for a much more rigid wing with no weight penalties. Kevlar is used in the belly, under the glass outer skin, to protect the underlying skin in the event of a gear-up landing.  The prototype Berkut was completed in the summer of 1991, and flown to Oshkosh. The reception was outstanding, but Ronneberg was not ready to sell kits just yet. He used the next year to acquire the financing, tooling, and materials necessary for producing a kit, as well as writing a construction manual. At Oshkosh 1992, orders were taken for kits, and deliveries began in January of 1993.

Despite the success at Oshkosh, the return home found a financial partner who wanted out of the airplane building business. According to Richard Riley, vice president of Renaissance, a buyout was agreed upon prior to Oshkosh 1992, but in late '92 the financier changed his mind with regard to the terms of the buyout. A lawsuit resulted, and then, in mid-1995, Rick Fessenden, the company test pilot and airshow pilot, crashed in Santa Paula, California, in the prototype Berkut. Months later, a judgment in the lawsuit was made providing for the financier to receive a lump sum payment that represented the return of his investment.

Ronneberg could not make the entire payment and began planning for bankruptcy.  Vendors with outstanding accounts were paid and all outstanding kit segments were finished and delivered.  Experimental Aviation filed for Chapter 7 bankruptcy and under the protection of the bankruptcy court, the final judgment for the lawsuit filed by the financier was never made. With the company in Chapter 7, Ronneberg and Riley continued to provide customer support and constructed composite parts for use outside the aircraft industry.

They could not, however, sell kits.

In April 1997, the assets of Experimental Aviation, namely the molds, were awarded to Ronneberg and company.  Renaissance Composites was formed, and the sale and delivery of kits resumed.  

The Test Ship

The Berkut I was scheduled to fly is based in Santa Monica and is owned by Mishka Kasyan. It is equipped with a 260-hp IO-540. The idea for using a IO- 540 in a Berkut had been in the back of Ronneberg's mind since 1991, but nothing became of it until a builder, wanting to use the Berkut for airshows, decided to install an IO-540. Ronneberg provided the cowlings and other necessary parts. Unfortunately, this airplane's mechanical fuel pump seized and the airplane crashed on a highway just off the Santa Paula airport. Fortunately, no one was killed. The IO-540 is now an option for the Berkut and promises to be more popular than the 0-360.

The IO-540 turns a Klaus Savier fixed-pitch propeller 67 inches in diameter, with a whopping 105-inch pitch (the IO-360 prop has a 91-inch pitch).  The pitch of a propeller is the theoretical revolution if there were no slip. Therefore, the higher the pitch the bigger the bite of air taken by a prop. This translates into speed. Fixed-pitch propellers can be of three types: climb, cruise and standard, which is a happy medium between the other two. So the higher the pitch, the faster the cruise speed--but you'll need a longer takeoff distance.

For comparison, the pitch on a typical Cessna 152 prop is 58 inches with a diameter of 69 inches. The prop on the Berkut was designed for cruising fast, and its small diameter in relation to pitch means it turns very fast and grabs a lot of air. On the ground the Berkut's prop limits the engine to 2000 rpm, but rpm builds rapidly as the speed comes up. Full throttle produces 2900 rpm.

This airplane is equipped with a Vision Microsystems Engine Monitoring System, navcom, GPS, autopilot, transponder, and the standard instruments. The panel is small compared with panels in side-by-side seat airplanes, so the Vision Microsystems functions and display are ideal. All of the instruments and switches are easily reachable and none are blocked from view. The fuel selector is low and between your knees, but easily reachable.    

Flying It

Dave Ronneberg ran me through the systems of the airplane, a thorough preflight, and then went over the emergency procedures before we went flying.  The nosegear uses a unique jackscrew that allows the nose to raise and lower  while parked, with a pilot in the cockpit.  This unique feature is an attention-getter on the ramp. The maingear uses an electro-hydraulic system, protected by an airspeed sensing cut-out switch. In the air all three gear work together, activated by a single up/down gear switch, but on the ground the switch only controls the nosegear. Once seated in the airplane, the nosegear is lowered, and the bowing Berkut now takes on the flying stance.

Once at your destination, make sure the nosewheel is straight by looking through a small window between your knees, retract the nosegear and get out of the airplane. OK, OK so how does it fly?

I was fortunate enough to get three flights in the Berkut, and I have my size to thank for it. The factory Berkut is not set up for people 5-foot-2 to fly, therefore my first visit was to take a look at the manufacturing facilities, ask a lot of questions, and be measured for a set of rudder pedals Ronneberg would make for me.  My introductory flight was from the back seat, which includes a throttle and stick but no rudder pedals or instruments.  Getting into the back cockpit requires a bit of a hop, butt first onto the strake then swinging your legs into the cockpit. Yet it's roomy, comfortable, and legroom is plentiful. A four-point harness is installed in this aircraft. One of the biggest complaints about the EZ family is baggage space; the Berkut also has this problem.

Baggage may be placed in the strakes, which are quite cavernous but only 8 inches tall at the opening. With two people on board, baggage can be placed at the feet of the backseat passenger since there are no rudder pedals to contend with.  This flight showed the power of the Berkut and allowed me to get used to the stubby control stick on the right arm rest. The backseat passenger in this particular airplane does not have a trim control, so changes must be conveyed to the person in the front. Builders, however, may opt for trim on the back control stick. Trust me, trim is necessary on this airplane. Your wrist gets tired fast if you don't trim the airplane. We attempted a few landings to get me used to the speeds involved and the orientation of the airplane in the pattern. From the backseat I couldn't see the instruments, nor could I see out the front very well.

Next we flew the airplane to get used to what it feels like; essentially the feeling is fast, very fast. We went through the stall series and since this was my first time in a canard aircraft, it was interesting to feel what a canard stall is really like. The best comparison I can make is much like a rocking chair. At the stall the nose visibly drops about 2 feet, and if you keep the stick back it comes backup again and then drops until you release the back pressure and fly away. One cycle of nose up and down takes about 2-3 seconds. Power-off stalls will result in an altitude loss of less than 50 feet through two cycles or bobs of the canard. Add in a little power--1200 rpm--and no altitude is lost. You can slowly turn the airplane in the Stall configuration, but the controls are more mushy than in normal flight, as they are with most airplanes.

With the first flight under my belt we flew back to Santa Monica and I awaited word to come back and try out my new rudder pedals.  

Front Seat Anxiety

I must admit, I almost dreaded the day I got the call to come back to Santa Monica and try out the pedals. I went back knowing that I was going to have to fly the Berkut from the front seat and that Dave, sitting in the back, would not have rudder controls, brakes, avionics or instruments. I was intimidated by this airplane from the start: It's fast, really fast. I haven't flown 1000 different airplanes nor do I have 13,000 hours, so if I could fly this airplane then most pilots ought to be able to as well, which was part of why Dave was giving me that seat...to prove a point. 

I currently fly a Christen Eagle, and more than half of my 400 hours is in that airplane. Dave told me that I would have no trouble flying the Berkut. He also said there was no way he wanted to fly my airplane in exchange. It turns out the two airplanes have some things in common. The pattern speeds are identical, both have no flaps and are slowed on touch down by bringing the nose up.  Still, I had a lot of anxiety going into the first flight from the front seat. The rudder pedals built for me were 14 inches in front of the existing pedals and connected to them with a steel tube. The pedals in the Berkut are slightly different from the norm; they are independent of one another. Pressing on the right rudder does not move the left pedal at all, and the rudders only swing outward of the winglets. For brakes, keep pressing the pedals and the brakes take effect just as the rudder hits full deflection. Although it sounds a bit strange, it takes only a few tries at braking to get used to it. In addition to modifying the pedals for me, about 35 pounds was added to the nose to compensate for the c.g. shift with me in the front. The Renaissance crew went to a lot of effort to make this airplane flyable for me.

Flying It from the Front

After putting a few cushions in my seat and strapping in, the next task was starting the airplane. Crack the throttle,  mixture full forward, turn on the magneto, flip on the battery, and push the start button. If it cranks six times before starting, stop, turn on the boost pump for about two seconds, open the throttle a bit more, and hit the start button. Once it fires, turn on the electronic ignition, throttle back and you are ready to raise the nose. Flip on the master switch and lower the nosegear. The nose rises to full extension and stops.  The airplane taxis with ease and getting used to the brakes is a piece of cake.

Steering is by means of a full-castering nosewheel and differential braking on the mains. The runup is done on the fly because the prop has so much pitch that if you run it up while standing still, it will suck up rocks (or even sand) and blast the surface of the prop, especially the leading edge. That's also the reason you start the beast with the nose down. Since there is no constant-speed prop, a simple mag check is all that's needed. A check of the engine instruments and everything is ready to go. Pull up to the hold-short line, lower the canopies, latch them and you' re set.  

The Eagle Takes Flight

Dave told me I'd need a little right rudder on takeoff but advised that I use it sparingly. We were cleared for takeoff. On the centerline I pushed the throttle about half way to avoid sucking rocks into the prop. At about 40 knots, full throttle is applied and I applied a bit of right rudder. Rotation occurs at 70-75 knots, and the climb is steep. Rudder inputs were unnecessary from here on out. In about one and one-half minutes the airplane had quickly climbed to 4000 feet, and the throttle was brought back to 2700 rpm. I lowered the nose and started trimming the airplane using the switch on the stick. We were at 200 knots quickly and ready for smooth flying, tremendous visibility flight.

Once trimmed, the airplane is easy to fly. It doesn't take long to get used to the side stick on the right. In addition to the trim button, the stick also includes the push-to-talk and a switch to raise and lower the belly brake. Dave suggests holding the stick from the base and resting your arm on the arm rest. This takes away the tendency to overcontrol the airplane. Rolling the airplane from side to side is easy. The sensitivity of the control is not overly light and it's not hard, but just right. Pitch, on the other hand, is less sensitive than roll. When attempting a tight turn you can feel the stick forces increasing the more you pull.

In a 360° turn, the tendency is to begin to let off the pull because your arm gets tired. This stability characteristic is brought over from the Long-EZ and allows for a lower workload. This is especially nice during cross-country flights--a fortth of the Berkut.   Rolling the airplane is easy and fun, but not like my Eagle. You must bring the nose up about 20° before commencing the roll; using full deflection brings about a nice roll most people would be comfortable with. Add rudder to the roll and the roll  gets faster, but not as quick as my Eagle. The Berkut is primarily a long-range, high-speed cruising machine, so it doesn't have the symmetrical airfoils that allow aerobatic airplanes like the Eagle to fly inverted so well. But if a builder equips it with an inverted fuel and oil system, it will withstand -10 G.

Bringing It Home

After having fun terrorizing the skies of Southern California it was time to head home. This was perhaps my biggest fear of all: landing. Prior to our flight, Dave had briefed me on the speeds and power settings for the pattern. On downwind, throw out the gear, fly at 100 knots and bring the throttle back to 1400 rpm. The gear was designed to be lowered at any airspeed, and it creates a lot of drag, helping to slow the airplane.  The base leg should see 90 knots, and landing is at 80 knots, with the throttle coming back on the base-to-final turn. My first attempt found us quite high on final, which wasn't a problem. I deployed the landing brake and cut the power; the airplane began a comfortable sink. The Berkut is also very comfortable in a slip, Ronneberg says.  Maintaining an 80-knot final wasn't a problem, but Dave warned me that lowering the nose would cause the speed to come up fast. I came over the threshold slightly crabbed, which was easily fixed with a little right rudder. The landing technique was fairly straightforward: fly the airplane about 1 foot off the runway and let the maingear touch. Hold the nose off until the canard settles and touches. Apply the brakes and go eat your $100 hamburger.

What I envisioned as a scary flight in an airplane I didn't think I could fly turned out better than I expected. The airplane is a lot easier to fly than it looks, and it's fun. Making a long cross-country in a short time wouldn't take much getting used to. The handling, both on the ground and in the air is easy once you get the feel for it. If you've only flown Cessnas or Pipers, it would take a little getting accustomed to the increased speeds of the Berkut, particularly in the pattern, but it' s nothing a little practice wouldn't fix.

The Kit

A lot of foresight has gone into the Berkut kit and the materials that accompany it. The builder gets a detailed instruction manual and construction videos (totaling approximately 40 hours), both of which detail each of the three sections of the kit. Upon receiving the 10% kit deposit, the manual and videotapes for the "A" kit are shipped. The manual includes sections on working with composites, how to set up your workshop, and a comprehensive list of tools you'll need. Once kit A is paid for, the materials and hardware are shipped. The A kit consists of the wings, winglets, canard and elevators. Kit B consists of the fuselage, main spar, front gear, bulkheads, and cowls. Kit C includes the maingear, strakes, engine mount and canopy frames. Most of the kit consists of premolded parts, a total of 70 including the various bulkheads. The latest kits will include a molded canard, wing panels and winglets.   These pieces were previously constructed using oversize precut foam cores sanded to their proper size with the aid of templates. While this new construction technique doesn't reduce building time, it changes the type of building. Most of the filling and sanding has been eliminated in favor of fitting and assembly.

Markings are incorporated into the pieces to ensure proper alignment. All of the structures in the Berkut are built with room-temperature epoxy resins, which eliminate the need for oven curing. Build time is estimated between 1500 and 2000 hours.  To date 56 kits have been sold. Five have flown with another four set to fly this year.

Technical support is unique to say the least and is spelled out in the contract.  Renaissance is available for support from  9AM  to 5PM Pacific Standard Time Monday through Friday, except during Oshkosh and Sun 'n Fun. The truth is there is usually someone available later than that and on weekends. Here's the kicker, quoted from the first page of the manual: "Please remove [this page] from your plans and keep it safe somewhere else. Below are Dave's and Richard's home phone numbers. If it's really a crisis, you have tried everything else you can think of and you're afraid that you're about to destroy a major part of your project, call us at home if you need to."

So, do Dave and Richard get tech support calls at home? Yes, but rarely, and it's usually when they are in the shower.

Summing Up

While I don't plan on replacing my Eagle with a Berkut, I truly enjoyed my experience flying the Berkut. Having never flown anything this fast before, I especially enjoyed the speed. If you are looking for an up-to-date canard design that incorporates a number of features EZs and Ezes don't have, look no farther; as a bonus this one is built from an exceptionally well-designed kit.  While the Berkut takes its lineage from the EZ family and joins its cousins in the characteristic stance on the flight line, the airplane is in a league of its own and will never be found bowing to the competition.