Flight test: Christen Eagle II
PUBLISHED: 10:44 18 May 2018 | UPDATED: 10:44 18 May 2018
Not to be reproduced without prior written permission of the author.
Forty years ago a revolutionary kit-build aerobatic biplane took to the Californian skies on rainbow-coloured wings — the Christen Eagle had landed. Words Lauren Richardson Photos by Lee Howard
Designed by Frank Christensen, the homebuilder’s kit for the Christen Eagle II (‘II’ for two seats−there were some single-seat Eagle I versions) was first introduced to the public at the EAA fly-in at Oshkosh in 1977, not long after the type’s first flight.
It changed the face of homebuilding as Christensen’s kit was far and away the most comprehensive, well-documented and revolutionary build system produced to date. It opened up the concept of building an aircraft to people who had never before even considered the possibility.
Christensen described the origins of the Eagle in this way:
‘We set out to produce a two-place aerobatic aircraft that could compete effectively with the Pitts S-2A as a result of better aerobatic performance, handling, appearance, comfort and convenience.
‘The second objective was to develop a kit system by which the aircraft could be built in limited time by anyone with reasonable mechanical aptitude using only hardware store tools. There would be a series of kits, 26 in all, to be purchased and built one-at-a-time in a specific order until the complete aircraft resulted. Absolutely everything would be supplied in the kits including parts, materials, tools and highly detailed and illustrated step-by-step instruction manuals.
‘Eagles were built by people from all walks of life; doctors, lawyers, airline pilots, military pilots, women, trade schools—and people who were not pilots, but who just liked to build things. The latter group surprised us somewhat. Some pilots bought the kits and had friends or employees do the building for them, most notably, Thomas J Watson, the retired Chairman of IBM and John Denver of country music fame.’
Made up of 25 small kits, plus a tie-down kit, the Eagle was designed to be within reach of anyone with enough enthusiasm to commit to start−no previous experience of aircraft building was required. Breaking the aircraft down into smaller kits for people to purchase whenever they were ready during their build hugely reduced the initial investment cost, while the exceptionally detailed build manuals and comprehensive inclusion of all materials and tools opened up the market to more people than ever before, transforming the homebuilding scene. Today’s popular kits such as the Van’s RV series will have taken inspiration from the pioneering approach of Frank Christensen’s Eagle.
At first glance you could be forgiven for mistaking this particular test Eagle for its cousin, the two-seat Pitts Special, especially as it isn’t painted with the traditional and instantly recognisable Eagle rainbow feathers. The Eagle name and paint scheme were actually created by design firm Steinhilber and Deutsch. I mention this because I love that their first name suggestion for this game-changing, pedigree aerobatic kit-plane was the Christen Ostrich, a bird well known for being flightless. (I suspect, however, this might become more apt should you happen to suffer an engine failure, such is the glide performance of the aircraft.)
On second glance the differences start to stand out. The Eagle seems to have more presence somehow−the larger spacing between the wings, the wide cockpit with large bubble canopy and the low-drag sprung steel undercarriage all set it apart from its cousin and, I would argue, provide some advantage.
The pre-flight walkround reveals a few things of note: firstly there are a lot of screws and fixings. This is a predominantly fabric-covered machine, with several sections of aluminium panelling around the cockpit, and a fiberglass-constructed cowling. Fairings around the wing root, gear legs and cabane struts are all screwed on. A traditional welded steel fuselage with wood and fabric wings make this a very simple yet strong flying machine, albeit with lots of small fittings to work loose periodically; a minimalist, monococque composite ‘wundastunta’ it is not.
Secondly, the bottom wing sits low − way low. Low enough to suffer damage on signs and lighting units on the sides of runways. Low enough that fitting spades to the underside of the bottom ailerons to lessen the roll ‘stiction’ just isn’t done. Low enough that any maintenance underneath them would be best carried out by a small child.
Despite the shocking lack of ground clearance (do not ground loop an Eagle−your chances of not catching a wingtip and doing serious damage are virtually non-existent), the bottom wings sit low for good reason: they make getting into and out of the cockpit remarkably easy. Their position also means that the pilot view in flight is better than any other biplane I’ve ever flown.
Helmet in hand, I approach the brightly coloured, bi-winged beauty, set down my aerobatic accoutrements and begin to check that all the usual major components like the wings and engine are in place and functional. I also make a very attentive check that the flying and landing wires are undamaged and taut because, of course, as with all conventional biplanes these are where the main strength of the aircraft’s structure really lies.
Once it’s apparent that all four wings are attached and braced correctly, and the engine is bolted to the nose as it should be etc, it’s time to climb in and find out the truth of what it means to fly like an Eagle.
Strapping into an aerobatic machine is something of a ritual for me. I like to be comfy, and able to see properly, as well as being capable of reaching full rudder throw−a balance that is sometimes hard to strike. I’m not the tallest person in the world, so some strategic cushion shuffling and squirming is required to optimise the visual height to rudder pedal reach ratio, but once there the cockpit proves to be extremely comfortable.
The large bubble canopy and low-set fuselage sides provide a stunning view of the outside world (at least in biplane terms), with the huge gap between the two sets of wings meaning it’s actually almost possible to see where you’re going when taxying. The 200hp-plus Lycoming IO-360 sitting high up front does however intrude on forward visibility, so the zig-zag taxi technique remains essential−this is still a purebred taildragger after all.
As the Eagle is a homebuilt kit type, flown on an LAA Permit to Fly, all of them are ever so slightly different. G-KLAW, the flight test Eagle not only wears a non-standard paint scheme, but also departs from the norm by sporting a Grand Rapids EIS4000 electronic engine management system, together with a tuned engine and electronic ignition alongside a standard impulse-coupled magneto. The electronic ignition does a wonderful job of assisting the start of the potentially finicky, high compression, injected Lycoming but does have one point of note when it comes to conducting power checks: there is no RPM drop as there is with the magneto.
There’s only one real drawback with the overall Eagle design, and that’s the instrument layout, or rather the instrument panel position: it’s all in the front cockpit and completely out of reach of the pilot who sits in the back. This is severely sub-optimal for anyone who is short-sighted. If you ever fly an Eagle solo, make sure to set the altimeter before you get in, and be prepared to do some mental arithmetic for QNH/QFE conversions if you’re going anywhere.
Having another person in the front is a mixed blessing. While they will be able to adjust the altimeter setting for you in flight, depending on how broad of stature they are they will also block your view of anything not situated on the very periphery of the panel. It’s good to pre-brief front seat occupants that you may ask them things like altitudes and airspeeds from time to time, or to shift themselves to the side a little. I believe this is why the builders of this particular Eagle chose to fit the EIS4000… it sits on the right hand side of the panel to be visible in most scenarios, and provides on a single LCD screen all the necessary information about the operation of the engine: RPM, manifold pressure, oil pressure, oil temperature, CHT, EGT, fuel flow etc.
The downside of this system is that it will only display limited pieces of information at once−and not necessarily those you might choose to have all on one display. Buttons for changing the display pages are on the panel next to the screen, but are also slaved onto remote buttons for the pilot in the rear seat, so it is absolutely useable, just a little different to having individual gauges constantly visible. It would take me some time to get used to having LCD numbers rather than needles to monitor, although the system does helpfully provide a warning light and audible beep for a wide variety of customisable parameters to make life a little easier.
Having successfully cushioned up, strapped in and locked the canopy shut, waking the sleeping Eagle is straightforward but noisy. My standard injected Lycoming starting technique of cranking the cold engine over after a prime using the electric boost pump, with the throttle slightly cracked and the mixture lean, yields a meaty roar as the cylinders fire and the propeller spins to life.
It’s exciting to feel the satisfying deep rumble emanating from the front of the machine, the low level vibration giving the unmistakably addictive feeling that the flight will be a real giggle. With the four cylinder growl settled to a gravelly purr, I run through some basic checks. There is very little to check on an aerobatic aeroplane, relatively speaking. Instrument checks are limited to setting the altimeter (which as I’m flying solo, strapped in out of reach of the instrument in question, I had set prior to committing to start), zeroing the G-meter (again, done prior to getting into the aeroplane) and monitoring the engine parameters on the EIS.
There is no artificial horizon or PFD (primary flight display), no direction indicator−nothing gyro-driven at all. No turn and slip, no radio navigation kit. This is a purposeful, minimalist aeroplane with one true specialism: fun.
Bright and roomy cockpit
For a biplane, the bright, open, roomy internals of the Eagle feel wonderfully refreshing−you really can see a stunning amount out of this aircraft, which is a genuinely nice surprise. The wings of course frame the forward view, but not to any great limitation. The big bubble canopy is gorgeous. As I nudge open the throttle and make my taxi calls I’m already smiling.
The taxi ride is straightforward−or, actually the opposite because straight forward is the one place I can’t see: the taildragger tack is essential to avoid the embarrassment of tangling with a runway marker. The ground handling characteristics reveal nothing unexpected, it’s much like any other modern American tailwheel machine−standard issue toe brakes provide differential braking that is effective but could be a touch more powerful. I’ve noticed with some of the other Eagles I’ve been lucky enough to fly that the brakes in the front require rather more pressure to operate fully than those in the back, and this one is no different.
The brake master cylinders sit on the pilot’s pedals (in the rear) with the front brake linkage being via some quite narrow diameter rods directly linking the two sets. They work, but it’s worth bearing in mind when front-seating that they may not be as effective as they are from the rear.
The Eagle has a sprung steel undercarriage that places the wheels a decent width apart and provides good stability on the ground. In fact, the ground handling is simple; more in common with the beautifully docile Extra, than the Pitts. Sat at the runway hold, gazing out across the vast expanse of Yeovilton’s concrete that for once I have all to myself, I carry out the very simple power checks, then, having double and triple checked that the canopy really is fully locked,
I take a deep breath and radio to the empty airfield that I am lining up. Opening the throttle smoothly rapidly kicks us into motion, the propeller screaming in my ears, the power dragging us forward and into the sky. The acceleration really is startling. Being the ‘adventurous’ aerobatic type, I decide to try a max rate climb after takeoff, pulling the nose higher and higher until reaching the target speed of 95mph. The angle of wing against horizon looks almost unsustainable. This Eagle can climb at around 2,000fpm with just me and a light aerobatic fuel load on board, making it a very capable performer.
Once at a sensible height I play around with the propeller, mixture and throttle to get an idea of what this aeroplane is like to live with as a VFR touring machine. Most aerobatic aeroplanes will of course go places, but aren’t particularly good at it, many being pretty slow and uneconomical in the cruise, and everyone knows that biplanes are drag monsters anyway.
With double the number of wings absolutely necessary to enable flight, plus the struts and bracing wires to accompany this scaffolded approach to aircraft construction, generally speaking these types of aircraft tend to operate at the more sedate end of the airspeed spectrum. Hence my surprise when, upon settling down with a suitable cruise propeller RPM and throttle setting (in this case just under 2,400rpm and around 23-24 inches of manifold pressure), a glance at the airspeed indicator tells me that I am motoring along at 130kt.
This airspeed also comes with a very respectable 34 lph fuel burn (once I have leaned the mixture, something helpfully indicated by the EIS). This Eagle will go even faster if I sacrifice the fuel burn but frankly I see no need.
Christensen designed the Eagle to be practical as well as capable, and the baggage compartment situated under the turtledeck/behind the pilot’s head is surprisingly roomy with, I would guess, space to fit enough kit for two people for a week or so. It’s not a big load carrier though and certainly not designed as a tourer, but nor is it as impractical as its looks may suggest.
With a lunatic grin...
Now I can no longer contain myself and the aerobatic testing has to begin. With a lunatic grin on my face, I set the propeller to 2,500rpm, the throttle to give a manifold pressure of around 25 inches, accelerate to around 160mph straight and level, and smoothly pull back on the stick, carving a simple, joyous loop through the sky.
You can of course go up to the redline of 2,700rpm and 27 inches to get the most out of the engine, but for ninety per cent of manoeuvres flown purely for fun it’s not really necessary. With a machine designed to hold its own in aerobatic competition, it would be unfair not to fly in the appropriate style, so I spend some time making the most of the inverted fuel and oil system by flying some fully rounded loops, floating the aeroplane over the top at less than 1g. It responds as if it were on rails.
With every variant of roll I get the same feeling−flawless aileron, slow, hesitation and barrel rolls come with minimal effort. Stall turns are a matter of merely thinking about making a clean turn, and so it comes out. The big metal propeller at the front of the Eagle makes flick rolling easy and great fun, with my favourite manoeuvre, the avalanche (a positive flick roll at the top of a loop) being an absolute joy to fly.
Negative g is just as unpleasant in the Eagle as in any other aeroplane, with the machine more than happy to push out as much as you have the audacity to ask for−outside loops and turns are easy, albeit not entirely pleasant due to their intrinsic nature.
The Eagle spins as a pedigree aerobatic machine should − simply, cleanly and with no vices. Recovery can be made in competition fashion: on a vertical downline at a precise exit heading with very little preemption; in a hurry for a standard emergency minimal-height-loss recovery; or with the ‘hands off, swap feet’ method of the confused ‘admission of defeat’ style exit when something spectacular has exceeded your understanding of aerodynamics, and you know the aeroplane is inwardly laughing at you.
Having eventually had my fill of loops, rolls, flicks and spins I eventually decide it is time to head home. I say eventually as this is the type of aeroplane that goads you into doing more and more aerobatic hooliganism, and it’s hard to resist. There does however come a point where, even for me, it’s time to stop. I’ve done enough rolling circles and outside loops to begin to feel less than perfectly able and thus it is that I know I am ready for a cup of tea. Landing is next up on the agenda.
On entering the circuit it is a relatively straightforward process to get set up and ready to fly the approach. There are only a few things to check and adjust in this very simple machine−there aren’t even any flaps to play with. Ensuring the mixture is set to rich and moving the propeller lever fully forward to the fine position are really the only things required beyond making standard radio calls.
Yeovilton’s circuit pattern is of the oval persuasion, and as such ideally suited to the likes of an Eagle, in which I would argue the approach is best flown entirely in a steep side-slip at around 90mph. Not only does the slip grant you actual visibility of your target (the runway), but it stabilises the aircraft beautifully with regard to airspeed. A steep approach angle also gives you a far greater chance of making the runway in the event of engine trouble on final, as the Eagle isn’t dissimilar to a brightly painted brick−or ostrich−in its glide characteristic once the lump up front goes quiet.
I fly the side-slip almost to the ground, straightening out into a gentle flare only just above the concrete, whilst simultaneously closing the throttle to balance the change in drag/thrust and continuing the gentle deceleration onto the ground. Like the Pitts, the Eagle responds well to this style of landing, but it’s much better mannered once the wheels are actually down.
A nice three-point landing sounds hideous as the wheels squeal on the concrete, but I hold the stick back and smoothly but firmly use the brakes to bring us to a halt. All that is left is to taxi back to the hangar, extricate myself from the surprisingly accommodating cockpit, and allow my facial muscles to recover from all the grinning!