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Flight Test: Christen Eagle

PUBLISHED: 10:24 10 September 2013 | UPDATED: 10:24 10 September 2013

Compare propeller diameter to wingspan and you know you are in for some excitement

So you fancy owning a Pitts, Stearman or Tiger Moth, but can’t afford one − or maybe you suspect they’d be too hard to handle? Try a Christen Eagle, it’s cheaper and more practical, and its spectacular colour scheme turns heads wherever it goes. Simply dismounting from this ‘muscle biplane’ sets you apart from the crowd.

Veritable sports cars of the sky, 200hp Eagles out-perform similarly powered two-seat Pittses, but are easier to control. Going places, you can share your three-dimensional exploration with friends; two seats also let you have aerobatic coaching in your own aeroplane. Moreover, many Eagles have smoke systems, so you can lay down a smoke trail on arrival!

For pure flying excitement and adventure, you’ll find an Eagle hard to beat, the whole panoply of advanced aerobatics being well within the capability of most competent pilots. Nominally kit-built, Eagles cannot be used for paid instruction, but you can easily convert to type in one of the many Pitts S-2s. If you can land an S-2 with its bouncy bungees, you’ll find this one’s Cessna-like spring steel gear legs easy. Then you can progress to aerobatics − displaying or competing right up to Advanced level thanks to its symmetrical aerofoils, four ailerons and unlimited-time inverted fuel and oil systems.

Because it was amateur-built, I used to regard the Christen Eagle as a sub-standard Pitts, but that was quite wrong. The 200 horsepower, two-seat Eagle out-performs any 200hp two-seat Pitts. And its cleaner airframe is roomier, more comfortable, more affordable, better finished, and has superior visibility. As an aerobatic two-seat biplane, the Eagle’s ability is only surpassed by the six-cylinder Pitts S-2B with nearly fifty per cent more power (but lower g limits).

Part-owner David Brown let me fly this Eagle from both seats. The primary pilot occupies the comfortable and slightly reclined (for good positive g-tolerance) rear seat. The front seat is a little more upright, but both have sturdy five-point, ratchet-tightened Hooker 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, although perhaps it is a little close for the front-seater. Flying instruments are grouped around its periphery where the passenger’s head doesn’t obscure them.

Dominating the panel’s centre is an A5 sequence-card holder, presuming that competition or display aeros 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 two-up. Both occupants have primary controls, including brakes and proper quadrant throttles with tiny red PTT buttons embedded in their handles. Only the rear-seater has secondary controls, like the vernier propeller rpm control, mixture knob, elevator trim, starter, ignition, intercom, radio and even cabin heat!

The roomy cockpit has fibreglass and aluminium sheet side panels enclosing both structure and control cables − neater and safer than in many other biplanes of all eras. A long, distortion-free canopy is side-hinged on the right, firmly framed and damped by a slim hydraulic strut. It locks very securely both open and closed, and you can taxi with the canopy wide open at low powers, enabling you to look well ahead past the engine for excellent tail-down visibility. Alternatively, you can swing the canopy closed without pushing it forward, directing a great cooling blast to both occupants. 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 and it makes the Eagle much less draughty than a Pitts.

As you would expect, the Eagle’s controls have very 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 is bulged, so visibility is good, even with it shut. And the front-seater gets a good all-round view too (rather better even than from an Extra) provided he has enough firm cushions under his buttocks.

The engine is standard fuel-injected Lycoming, and the propeller is a constant-speed Hartzell − both common, well-understood components. With no parking brake, you simply press the pedals and crank the motor in lean. When it fires, go to rich, release the brakes and you’re off. That big four-banger makes its presence felt, rocking this light, compact airframe to its urgent beat. Compare propeller diameter to wingspan, and you know you’re in for some excitement!

Ground handling is often a good predictor of character, and this one’s surprisingly easy. Although operating via springs, its steerable tailwheel is positive, tightly turning this short-coupled aeroplane, and it can be unlocked with a kick for super-tight turns; tap a brake and you will pivot around one wheel. The brakes are good − as they should be to stop such a fast-landing aircraft − while the solid aluminium main legs are stiff but neither too rigid nor bouncy. The Eagle doesn’t waddle like some similar airframes.

To my surprise, considering the Eagle’s power-to-weight-and-size ratio, take-offs are easy from both grass and hard runways. Line up straight, add a bit of into-wind aileron, softly squeeze the right rudder, gently open the throttle, brace against its acceleration, ease the stick forward to set the cowling top on the horizon (and see directly ahead), tap-dance lightly on the pedals and you are off.

I had expected a fight to stay straight, but found it no harder to control than my Maule − probably easier. Okay, you can’t see much in the three-point attitude, but you can soon raise the tail, it comes up promptly, and there is no tendency to bounce or swerve, nor any propensity to dart for the trees. The whole process takes seconds and perhaps 200 metres − less when you know it better and can increase power more quickly.

Sitting so far back, you can sight along the whole fuselage to stay straight. Pin those cabane struts over the far threshold and hold them there. The Eagle’s big rudder gives such great control authority that any problems would be entirely self-induced. For my first attempt I am tensed like a bowstring, but it just is not necessary. I’m already enjoying this! Within seconds we are at 1,000 feet, throttling back and reducing rpm while bending into the circuit. Noticing I needed a steady right rudder input in the climb, I’ve discovered the Eagle’s Achilles heel. You do have to concentrate on its rudder, almost to the exclusion of the other controls. It is quite light and very effective, but this aeroplane has little yaw stability, so you are continually adjusting pedal pressures. Every change of power or speed requires a tiny correction − just like a Tiger Moth but more so − and this is absolutely the only similarity to that old war horse. This aeroplane is much more powerful, capable and draught-free (unless you want ventilation, in which case you can get a blast of air from the side vents).

There’s not much to check on downwind except fuel and propeller rpm; then it’s time to throttle back for the approach. Rarely flying biplanes nowadays, I have forgotten the delight of viewing our world through this web of wings and wires. Yes, there’s some reduction in forward visibility, but you sit well aft and can see all around; just not ahead without occasionally shifting the ironmongery.

I should prefer to make my first landing on grass, as I would in any fast, close-coupled, tailwheeler, but our airfield’s grass runway is too short for my initial attempt, so 
I make do with the long, wide bitumen runway at our local airport.

I find a circling, slightly sideslipped approach easiest. Turning left puts the ASI just where I want it, neatly in my peripheral vision without having to re-focus. In a steady bank I can hold the runway continuously positioned between our left wings, giving me instant information about our glide path, while a little sideslip keeps the fuselage out of my sight-line. Control forces are light; both bank and yaw are steady and instinctive. The Eagle flies its curved approach with minimal input from me−as though on helical rails.

Eighty knots works well on base leg, reducing to 75 over the threshold, and this little lovely is surprisingly speed-stable once it’s trimmed. I use a trickle of power (fifteen to eighteen inches) to modulate these highly-loaded wings’ comparatively steep descent. I can tell by the balanced-on-a-pin feel that anything below seventy knots will increase our sink, so I keep a vigilant eye on that ASI. Much faster and we’d have a long, blind float before touchdown. Slower and I might dig a hole if I didn’t judge my flare perfectly.

Crossing the threshold, a final glanceance confirms the airspeed’s trickling back through seventy knots as I concentrate on straightening and checking our descent before we thwack into the numbers. Again, I am surprised at the ease of this triple-axis manoeuvre, which can be quite tricky in some short-coupled aeroplanes. But it seems almost automatic as I gently raise the nose to arrest us at ten feet, holding our wings level while swinging it straight.

Squeezing some more rudder to align ourselves precisely with the runway, I carefully ease the throttle shut. The world is flashing past, and I can no longer see anything but Eagle ahead, nevertheless the runway’s edges are clearly equidistant and close below. They stay that way as I continue lifting our nose to the three-point attitude with my backside mere inches from the abrasive bitumen. All the controls are still very much alive, the aeroplane going precisely where I want it. Any deviation will be completely my own fault.

The speed quickly drops away, the aeroplane settling after a short float for a squeaking firm three-point touchdown on those stiff legs. We must be lined up dead straight, because even with hard tyres there is no ‘dart for the dirt’. But of course I have to meddle, treadling the pedals unnecessarily in my tension, and giving us both lateral whiplash before I calm down and let it do what it wants, which is merely to roll straight.

I can see nothing but airframe directly ahead, although, thanks to the low cockpit sills, all but the very centre of the runway is still clearly visible over the sides. Our rollout is longer than I expected thanks to a rather fast tickover, so I pull hard on the throttle lever to minimise residual thrust, and then brake gently, scrupulously applying identical pedal pressures. We gradually rumble to a halt. With these forward main legs, you would have to press those brakes pretty hard to lift the tail against such a powerful raised elevator.

Moving to the downwind side of the runway, I kick us around a 360 and backtrack for another go. We used perhaps 900 metres all told, so this is probably not a true short strip aeroplane, although I later used much less distance on grass − perhaps 500 metres. Oh, and did I mention we had a forty degree, ten knot crosswind for that first attempt? But with these powerful controls, I reckon even double that would be no problem.

It is all much simpler than I had anticipated. Getting the flare and drift push-off correct is the only challenge, and nothing like as hard as I’d expected. This potent Eagle is easier than many less daunting aeroplanes I’ve flown, and significantly easier than the Pitts S-2.

I fly a couple more circuits. Each is simpler than the last as I get used to it, although I am advised against wheelers; “They are difficult and unnecessary.” Even a go-around from the flare gives no problems, with instant acceleration and climb, no tendency to pitch up or roll, and surprisingly little yaw.

Leaving the circuit, I time our climb at 1,100fpm at 75kt − much less than kit-maker Aviat’s quoted 2,100fpm (at an unspecified weight and airspeed) − but this is a well-used example with an 1,800 hour engine. Others have been timed by experts at 1,250, 1,330 and 1,440 fpm, so they seem more likely. I don’t really believe Aviat’s claim, except perhaps at low weight.

For transits, 23.5 inches and 2,300 rpm represents 75 per cent power, giving us a comfortable 105-knot cruise IAS (110kt TAS), thanks to the Eagle’s comparatively clean airframe. Properly leaned, this should give two hours safe endurance, or a 200nm still air range from the ninety-litre tank. The interior is quite roomy, but a bit noisy without headsets; this is definitely an aeroplane for ANR.

Nevertheless, it’s surprisingly comfortable, especially seated on conformal foam cushions. The Eagle slices through turbulence so well you hardly notice any bumps. Your lower wings do obscure much of the forward horizon, but anything alongside can be seen clearly, and you need only half-roll to see everything below!

Once trimmed out, you can fly hands-off for long periods. A D-shaped locker behind your head carries 13.5 kilos of baggage − enough for a soft overnight bag for two, although you should be aware of this aircraft’s rear centre of gravity, deliberately designed for maximum manoeuvrability. If required, the battery can be moved forward from the rear fuselage to improve the aeroplane’s stabilities.

A BITEY LITTLE MONGREL?

We do 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 have no real problems. As you would expect of an advanced aerobatic mount, the Eagle is just positively stable in all axes, and all its controls remain light, even at high speeds (and those ailerons don’t have spades). The straight, power-off stall comes at 54 knots with a slight tendency for either wing to drop, depending on the slip ball’s position, while a power-off spin to either left or right is neatly entered, and quickly recovered in half a turn, regardless of the total number of rotations.

Now for the fun stuff − David flies his aerobatics at around 85% power, or 25 inches and 2,500 rpm, saving full power for competitions. A simple loop is easy, using a firm 4g pull from 135 knots, easing off to zero g over the top and then pulling hard again in the final quarter. This stuff is child’s play, although you do need to make precise corrective inputs with that sensitive rudder.

LIGHTNING-QUICK ROLLS

Half Cubans and half reverse Cubans are just as simple, and you don’t need anything like full aileron to make the upward and downward half rolls. About a quarter deflection nicely fills the 45-degree line.

With a quoted 184-degree-per-second rate, axial (‘slow’) rolls can be lightning-quick or super, super-slow, while the required rudder/elevator coordination is not at all difficult with such a powerful rudder and the Eagle’s excellent knife-edge performance. Barrel rolls can be big or tight. Ballistic aileron rolls are childishly simple − pitch up, stop, roll, stop − job done!

On the other hand, a stall turn requires some care and precise inputs, with a smooth rudder push (rather than a kick) at forty knots, but this is a boring manoeuvre without doing something else on the long up and down lines, as David demonstrates, his neat cartwheel topping thousand-foot vertical 360-degree rolls up and down. David also flies lovely, long, level, four- and eight-point rolls with dexterity and precision.

Positive flick rolls are straightforward too, and seem quicker than in a two-seat Pitts (probably thanks to the Eagle’s aft C of G) although further experimentation in this diminutive but potent aeroplane should produce more consistent results. My first flick is made at ninety knots, two up, with half fuel, and in a slight full-throttle climb at 5,000 feet. Yank, kick, push, whee, stop − the Eagle snaps around its flick roll far quicker than you can read it. This is such fun I do several more, both with and against the engine’s rotation, although, frustratingly, none of my subsequent efforts snaps quite as cleanly as that first one. Neverthless, my avalanche (a full positive flick roll at the top of a normal loop) goes delightfully well.

There is no time limit to the Eagle’s inverted flight, so I fly a few Derry turns and inverted turns, and then some outside loops, both upwards and downwards. Despite having ‘only’ 200hp and our being two-up, there is plenty of power to fly nice big, low-G outside loops. Negative flicks are well within the capability of this very competent machine, but I don’t try any because they’re beyond my personal abilities.

My own aeroplanes can only fly quarter- and half- upward or downward vertical rolls, so I grab the chance of making some full 360-degree ones. Solo, Aviat says the Eagle can fly two-and-a-half upward revolutions, but two-up we’ll be satisfied with just one rotation. So, fly south, accelerate in a dive to 160 knots, pull 4g, check with a forward prod, and whack the stick against your thigh. Stop when you’re heading south again − that’s if you get it right, of course.

If, like me, you are unfamiliar with both the aeroplane and full 360º vertical rolls, you might lose it part way around, one wing sagging as you slightly topple over on to your back. So you stop rolling, leave the power on, 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 yawing and then rotating rapidly as you wonder why the stick is being pulled forward in your hand.

Luckily David intervenes, closing the throttle and gently pulling back the stick to lower our nose and recover. “I didn’t think we’d cover inverted, power-on flat spins quite this early” he laughs, “Whatever happens in this aeroplane, if you lose it, just shut the throttle and it usually sorts itself out.”

Despite that blunder, more practice improves my vertical rolls, both upwards and downwards, although I never do quite find the exact fore-and-aft position to hold the control column while rolling to prevent pitch inputs and keep all those wings tracking steadily around the horizon.

IT’S ADDICTIVE

Thanks to this burly little biplane’s surprising capabilities, I so enjoyed myself that what had started out as an afternoon’s air test rather became an obsession, and I found myself flying with David again and again, at every opportunity that summer. Like so many before me, I had become a Christen Eagle addict.

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