December 2010 Issue
Flight Review: The Enduring Eagle
For three decades, the Christen Eagle has been one of the most desirable kitbuilt aerobatic designs.
If you always hankered to own a Pitts, Stearman or Tiger Moth, but felt that you couldn’t truly afford one—or maybe you suspected they might be too hard to handle, try a Christen Eagle. It is inexpensive and practical, and its spectacular color scheme turns heads and draws attention wherever it goes. Although the Christen Eagle design is more than 30 years old, it is still competitive as a two-place aerobatic ship. Kits continue to be available from Aviat Aircraft, and pre-owned examples represent extremely good value.
With inverted fuel and oil systems, the Eagle can fly upside down as long as you can. Probably longer.
For pure flying excitement and adventure, you’ll find an Eagle hard to beat, while being well within the capability of most competent tailwheel pilots. Because it’s an Experimental/Amateur-Builts, you can’t give aerobatic instruction in an Eagle, but you can receive instruction in your own Eagle. Further, you can get transition training in one of the many Pitts S-2s around the country. If you can land an S-2, you’ll find the Eagle easy.
The Eagle was basically an improved, better styled and more competitive version of the Pitts, designed in 1976 by a wealthy semiconductor production equipment manufacturer, P-51 Mustang pilot and aerobatic competitor Frank Christensen, when he was thwarted in his attempt to buy out “Pappy” Pitts’s operation—much like the contemporaneous battle between Ferrari and Lamborghini.
After taking early retirement, Christensen rose through the competitive aerobatic ranks while making a modest income from manufacturing manual aircraft fuel pumps, aerobatic safety harnesses, Pitts-designed inverted oil systems (later bought out by Lycoming) and upmarket fuel testers. His operation was more a labor of love and enthusiasm than a big earner. Indeed, he is often quoted as saying, “There’s a lot of money to be made in general aviation. I know, ’cause I put it there!”
The two-seat tandem cockpit is of reasonable size yet still cozy for larger pilots.
Knowing that the old Pitts design could be greatly improved, and aware that Pitts wanted to sell his business, Christensen tried hard to buy it, but negotiations came to naught. Undaunted, Christensen designed his own Pitts-beater, which became this Eagle, with first flight and manufacture beginning in 1977. Unwilling to go through all of the FAA’s certification nausea, he set up kit production, and the rest is history.
In 1983, Christensen was able to acquire Pitts Aerobatics. His former company, Aviat, now owns production rights for all of the Pitts designs, this Eagle and the utilitarian Husky.
I used to regard the Eagle as a substandard Pitts, but I was wrong. The 200-horsepower Eagle outperforms any 200-hp two-place Pitts, and its cleaner airframe is roomier, more comfortable, more affordable, better finished and has superior visibility in addition to being easier to control. As an aerobatic two-place biplane, the Eagle’s ability is surpassed only by the six-cylinder Pitts S-2B with nearly 50% more power (but lower G limits).
The primary pilot occupies an Eagle’s comfortable and slightly reclined (for good positive G tolerance) rear seat. The front seat is a little more upright, but you both have sturdy five-point harnesses, with additional lap straps for extra security. There is only one instrument panel, right at the front, where everything is in focus and visible at a glance from the back. Flying instruments are grouped around its periphery where the passenger’s head won’t obscure them.
Wiggling the javelins is part of a good preflight because any movement here will help disclose loose or broken flying wires.
The panel’s center holds an A5 sequence-card holder, presuming that competition aerobatics would be flown solo. The only poorly placed indicator is the fuel sight tube on the tank’s rear face, ahead and up under the panel, where neither pilot can easily see it when two up. Both occupants have primary controls, including brakes and throttles, but only the rear-seater has secondary controls such as propeller rpm control, mixture, trim, intercom and radio.
Fiberglass and aluminum sheet side panels enclose both structure and control cables. A long, side-hinged canopy is firmly framed, and it locks securely both open and closed. You can taxi with the canopy wide open, enabling you to look well ahead past the engine for excellent tail-down visibility. Push it forward and lock it, and you can be certain it won’t open. This is the best-designed canopy I have ever encountered.
As you would expect, the Eagle’s controls have little static friction. Both occupants sit quite close to the ground, but that wide engine is well ahead of you, the cockpit sides are low, and the canopy sides are bulged, so visibility is comparatively good, even with it shut. The front-seater gets a good all-round view too (better than in an Extra) provided there are enough seat cushions.
The angle-valve Lycoming provides 200 horsepower, which is plenty for sub-1600-pound airplane. The large tank behind the No. 3 cylinder is the Christen inverted oil reservoir.
The engine is standard fuel-injected Lycoming with all its foibles, and the propeller is a constant-speed Hartzell—both common and well-understood components. Ground handling is often a good predictor of character, and this one’s surprisingly easy. The steerable tailwheel is positive, tightly turning this short-coupled airplane, and can be unlocked with a kick for super-tight turns; tap a brake and you pivot around one wheel. The brakes are good, as they should be to stop such a fast-landing aircraft, while the solid aluminum main legs are stiff but neither too rigid nor too bouncy.
To my surprise, considering the Eagle’s power-to-weight ratio, takeoffs are easy from grass or hard runways. Line up straight, add a bit of into-wind aileron, softly squeeze the right rudder, gently open the throttle, brace against the acceleration, ease up the tail to set the cowling top on the horizon (and see directly ahead), tap dance lightly on the pedals, and you’re off.
I had expected a fight to stay straight, but found it no harder than my Maule to control—possibly easier. All right, you can’t see much in the three-point attitude, but you can soon raise the tail, it comes up easily, and there is no tendency to bounce or swerve, nor any propensity to dart for the trees. The whole process takes seconds and perhaps 600 feet—less when you know it better and can increase the power more quickly.
Sitting so far back, you can use the fuselage’s whole length for instant indication of any veering tendency. Use the cabane struts as an aiming sight: Pin them on the far threshold and hold them there. The Eagle has such great control authority that any problems would be entirely self-induced. For my first attempt I tensed like a coiled spring, but it wasn’t necessary. I was really starting to enjoy this!
Within seconds we were at 1000 feet AGL, throttling back and reducing rpm while bending into the traffic pattern. I needed a steady right rudder input in the climb, and now I discovered the Eagle’s Achilles heel. You have to concentrate on its rudder, almost to the exclusion of the other axes. It is quite light and effective, but this short-coupled airplane has little yaw stability, so you are continually adjusting pedal pressures. Every change of power or speed will require a slight rudder correction.
There’s not much to check on downwind in such a straightforward machine except for fuel and prop rpm; then it’s time to throttle back and start the approach. Rarely flying biplanes these days, I had forgotten the pleasures of viewing the world through a web of wings and wires. The downside is inevitably some reduction in forward visibility, but you sit well aft and can see all around, just not ahead without occasionally shifting the ironmongery.
Handling on the runway, grass or pavement, is surprisingly good despite the Eagle’s short-coupled nature and quick-response controls.
Tackle Landings First
I would prefer to make my first landing on grass, as I would in any fast, close-coupled, semi-blind tailwheel design, but the only grass runway available was too short for an initial attempt, so I had to make do with the long, wide bitumen runway of a nearby airport. I found a circling, slightly sideslipped approach easiest. Turning left put the airspeed needle just where I wanted it, neatly in my peripheral vision without having to refocus. In a steady bank I could hold the runway continuously positioned between our left wings, giving me instant information about the glide path, while some slip kept the fuselage out of my line of sight. Control forces were light, both bank and yaw steady and instinctive. The Eagle flies its curved approach with minimal input from me—as though on spiral rails.
An Eagle watchpoint: The tabs that hold the central fuel tank can fracture, potentially allowing the tank to descend and block the front-seat rudder pedals.
With all that biplane drag, the power-off glide was too steep for comfort, so I used a trickle of power to modulate the comparatively steep descent of those highly loaded wings. I could tell by the balanced-on-a-pin feel that anything below 70 knots would cause more sink. Eighty knots worked well on base leg, reducing to 75 over the threshold. The
Eagle is surprisingly speed-stable once you get the trim set.
Crossing the threshold, a final glance confirmed the airspeed trickling back through 70 knots as I concentrated on straightening and flaring before we thwacked into the numbers. Again, I was surprised at the ease of this maneuver, which can be quite tricky in some other short-coupled airplanes.
Squeezing some rudder to align ourselves precisely with the runway, I carefully held the wings level, and then eased the throttle shut. The world is flashing past, and I can no longer see anything but Eagle ahead, yet the runway’s edges are clearly equidistant and close below. The speed quickly drops away, the airplane settling after a short float for a squeaking firm touchdown on those stiff legs. We must have been dead straight, because even with hard tires there was no “dart for the dirt.”
Do It Again, Sam
Moving to the downwind side of the runway, I kicked us around a 360 and backtracked for another go. We used perhaps 2800 feet all told, so this is probably not a short-airstrip airplane, though less distance could clearly be achieved with practice. Did I mention we had a 40°, 10-knot crosswind? With these powerful controls, I suspect even double that would be no problem.
I flew a couple more patterns. Each was significantly easier than the last, though I was advised against wheel landings, “They are difficult and unnecessary.” Even a go-around from the flare gave no problems, with instant acceleration and climb, no tendency to pitch up or roll and not too much yaw to counter.
Leaving the pattern, I timed our climb at 1100 feet per minute at 75 knots, much less than Aviat’s quoted 2100 fpm (at an unspecified airspeed), but this is a well-used example, with an 1800-hour engine. For cross-country work, you can select something like 23.5 inches and 2300 rpm (which represents 75% power), and you’ll get a cruise of 105 knots true. Properly leaned, this should give 2 hours’ endurance with the 25-gallon tank.
The interior is roomy, but a bit noisy without headsets; this is an airplane for active noise reduction. Nevertheless, it’s surprisingly comfortable, especially seated on my conformal foam cushions. The Eagle slices through turbulence so well you hardly notice any bumps.
How many Eagle kits were sold to those hanging on the airport fence and greeted with this view? Short answer: A whole bunch.
Wringing It Out
We did most of our subsequent flying at considerable altitude, in deference to my unfamiliarity and another shareholder’s comment, “Be careful, Bob, it can be a bitey little mongrel!” But we had no real problems. As you would expect of a potential advanced or unlimited aerobatic mount, the Eagle is barely (though still positively) stable in all three axes, with its particularly light and responsive rudder demanding careful attention at all times. The straight power-off stall came at 54 knots with a slight tendency for either wing to drop; a power-off spin was neatly entered and quickly recovered in half a turn to either left or right.
Now it was time for the fun stuff. Part owner David Brown does all of his aerobatic flying at around 85% power, saving full power only for competitions. A simple loop is easy, with a steady 4-G pull from 135 knots, easing off to zero G over the top. The fully inverted fuel and oil systems make all of this stuff child’s play. Half Cubans and half-reverse Cubans are no more difficult, and you do not need to use anything like full aileron to make the upward and downward half rolls. About a third of full stick deflection seemed to be all that was required.
No Jelly on the Roll
With a quoted 204°-per-second rate, level (slow) rolls can be lightning quick or super, super slow, while the required rudder/elevator coordination is not at all difficult with the Eagle’s excellent knife-edge performance. Barrel rolls can be big or tight, while ballistic aileron rolls are childishly simple.
On the other hand, a hammerhead turn requires some care and precise inputs, with a smooth rudder push (rather than a kick) at 40 knots. But this is a boring maneuver without doing something else on the long up and down lines, as Brown demonstrated, his neat cartwheel topping a 1000-foot vertical 360° roll. He also flew long, level, eight-point rolls with dexterity and precision.
Specifications are manufacturer’s estimates and are based on the configuration of the demonstrator aircraft. As they say, your mileage may vary.
Positive snap rolls were straightforward as well, and seemed quicker than in a Pitts (probably thanks to the Eagle’s more rearward CG), though further experimentation in this potent airplane should produce more standardized results. My first snap was at 90 knots, two up, with half fuel and in a slight full-throttle climb at 5000 feet. Yank, kick, push, whee, stop. The Eagle snapped around quicker than you can read this. It was such fun that I did several more.
Do you want to make a full vertical roll? Solo, the Eagle can make two-and-a-half upward revolutions, but two up we would have to be content with 360°. So we flew south, I accelerated to 160 knots, pulled 4 G, checked with a forward prod, and whacked the stick against my thigh. You stop when you’re heading south again—that is, if you get it right.
If, like me, you are unfamiliar with both the airplane and full 360° vertical rolls, you might lose it part way around, one wing sagging as you slightly topple over onto your back. Stop rolling, pull gently to humpty-bump out of trouble as you would in your accustomed mount, get halfway through it and watch the upside down world inexplicably begin rotating as you wonder why the stick is being pulled forward in your hand. Luckily, Brown guessed my puzzlement, closing the throttle and lowering the nose to recover. “I didn’t think we’d cover inverted, power-on, flat spins quite this early,” he said, laughing. “Whatever happens, if you lose it, just close the throttle and it will usually sort itself out.”
Despite the blunder, I did enjoy myself in this burly little biplane. Indeed, no sooner had we landed than I arranged for a second go. Like so many before me, I had become an Eagle addict.
For more information, call 307/885-3151 or visit www.aviataircraft.com.
Bob Grimstead is a longtime aero-journalist who has welcomed the opportunity to fly a wide variety of homebuilt and certified designs. He splits his time between Australia and the United Kingdom (chasing good weather, no doubt).
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