Pilot Notes


When considering a biplane, the first questions you invariably ask yourself concern transportation and convenience, i.e. will it go in the car in one piece, and is it easy to put together at the field? In this case the answers here are yes, and yes, for this 54” (1370mm) span, 1/4-scale Eagle slips gingerly into the back of my hatchback saloon fully assembled. That said, wing transportation frames are included with the kit meaning that assembly at the field won’t take long.
Pretty, isn’t it? Offered as both single- and twin-seater, the Christen Eagle was designed to offer build and performance improvements over Curtis Pitts’ classic bipe. They’re both lovely aeroplanes, however the colour scheme Frank Christensen chose for his home-build, twin-seat aerobatic bipe, back in the late ‘70s, must go down as one of the most iconic, indeed 30 years down the line, it’s still incredibly eye-catching.

Constructed from laser-cut balsa and ply, the airframe is nicely covered and sports that stunning multi-colour Eagle trim scheme on both upper and lower surfaces. The spats and (large) cowl are fibreglass items, the latter being supplied nicely painted and decorated. All the usual hardware you’d expect is supplied, including wheels, tank, spinner, a pre-fitted pilot figure and a fine set of instructions, for which Hangar 9 have few peers.
A large, removable canopy hatch provides access to the interior, and a battery tray is supplied upon which to sit the 8s Li-Po that’s suggested if an electric motor (E-flite Power 90) is to be used (see 2014 update). It’s an aeroplane for which a two-stroke isn’t even suggested, Hangar 9 clearly being of the opinion that a 1.20 four-stroke is the perfect match. And indeed it is; my O.S. has been easily accommodated within the huge cowl after a genuinely modest amount of trimming.


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Construction is entirely traditional in the ARTF sense, so the Eagle comes together quickly, save a few little challenges that crop up along the way. The pilot figure was the first of these. He’s a factory fit and although made from a solid moulding is prone to coming loose, spot-glued, as he is, to the film-covered canopy interior. I made him into a more permanent fixture by cutting a hole in the base and securing him using screws fitted from the underside.
The u/c and spats are very strong, and spat alignment is cleverly taken care of by moulded spat channels into which the u/c foot rests. Unfortunately, the landing gear fairings don’t follow suit, these being thin, brittle plastic pieces that need trimming with plenty of care to avoid cracks. Fibreglass items would have been far better.
The elevator and rudder pushrod wires are too soft. As the model uses just a single pushrod for each you’d expect something reasonably beefy, yet those supplied are horribly malleable and ripe for replacement. At the other end of the pushrod you’ll find servo cut-outs that are too small for Spektrum servos, and the same goes for the wing servo mount arms. All, then, require trimming. Wheel clearance isn’t too bad, but there’s scope to improve matters by filling the cavernous spats with wheels that are larger than the 3” (75mm) diameter examples supplied.
There are lots of good things going on around the model, of course, in particular the general fit of parts and quality of the various assemblies. Amongst other things, I like the way the control surfaces have been pre-drilled to accept the horns – a horrible job at the best of times.
Top and bottom ailerons are connected by strong, clevis-tipped threaded rods, driven by lower wing servos. The cabanes and struts slot into place effortlessly, but it’s important not to get carried away by fitting the fuel tank first as it’ll impede the cabane fitting process. Both top and bottom wings are two-piece affairs which, when combined with the wing supports, make for easy assembly – just slot the wings home, connect the servos and secure everything with three small bolts.

Those fitting an outrunner will find a motor standoff in the kit, and although a two-stroke installation isn’t described, there’s every chance the cowl will accommodate most silencers; a Pitts-type muffler would look particularly good. While we’re on the subject, the only issue you’ll face if fitting a four-stroke concerns placement of the muffler. Here, an extension will be required if cowl-cutting is to be kept to a minimum and the muffler outlet positioned on the underside. It’s worth opening up both forward-facing air intakes and cutting a sensible size exit hole to promote the flow of cooling air past the engine. Some airflow deflectors are provided, but the intake holes are large enough so I’ve not used these.
Aerobatically this model is designed to produce traditional patterns, so strong analogue servos will suit, although sport digitals are Hangar 9’s suggestion. Five are required in total, my choice being a Spektrum A6000 for the throttle and 6kg torque A6010s elsewhere, power coming from a two-cell 1200mAh LiFe battery distributed and regulated through a PowerBox Digiswitch.


Biplanes always seem heavy when you pick them up. It’s an illusion, of course the wing loading calculation serving to reassure. My model balances a little nose-heavy when measured at the suggested C of G starting point (5.25” / 133mm back from the top wing l.e.) but it’s proved to be fine and at no time have I felt the urge to deviate from it.
Incidentally, you’ll find that even the suggested low-rate control throws offer a pretty lively response, so it’s best to start with these, noting that 30% exponential softens the ailerons, whilst 20% takes care of the elevator.

This is a very pleasant aeroplane that offers no surprises. The brevity of the take-off run surprised me; even on a calm day, the Eagle is airborne after a surprisingly short roll. Be careful, though, since whilst there’s no noticeable pull to the left, the tail is up very quickly and although she’s easy to balance on the main wheels with elevator, hold in too much and she’ll lift sooner than expected. Reassurance will come from the fact that the slow speed handling is very good, indeed the stall is predictable and benign, evidenced by a mushy nod or slow wing drop.
I’ve been very happy with the Eagle’s performance on the 1.20. Sure, it’s perfectly possible to fit a smaller engine (a .91 – 1.00 four-stroke would fly the model), however the 1.20 pulls this impressive machine around with the vertical punch and authority it deserves. This being the case, I really don’t think it’s necessary to fit anything bigger, the model simply doesn’t need it.
The Eagle is predictable and, whilst it tracks well, one or two biplane traits lurk just beneath the surface. For example, a little more elevator than you’d expect is required to pull it through turns. Even so, knife-edge needs no more than a hint of rudder, the fat, aerodynamic fuselage shape undoubtedly helping. Unsurprisingly, the model wants to screw out of knife-edge but can be held manually without too much trouble. It’s pretty sprightly where spins and flicks are concerned, spin entry and exit being easy, with very little rudder required to start things off.
Landing is uneventful enough. Biplanes are draggy things so the ground can rush up if you’re not careful on the throttle management side. That said, whilst it never feels unsafe, it does appreciate a nice, gentle arrival for it needs little excuse to get in the air again. Drop it down and it’ll bounce right back, so it’s important to bleed off plenty of speed during the approach. On the endurance side, the supplied 14oz (425cc) tank provides a comfortable 15 minutes of flying.


What I really like about this model is the way it can carve big lines, big loops and… well… big everything! Did I mention the whistle? It’s probably all that struttery, but something certainly makes a nice ‘swish’ noise as the Eagle tracks past. Mix this with the howl of a four-stroke at full chat and you’ve got the sort of aeroplane that people will stop to watch. Even so, it’s a friendly, well mannered-machine that good intermediate and experienced pilots will be at home with.
Shown some old photos by a clubmate recently I was reminded how heavy some early ARTF machines could be, and how badly some of them flew. How things have changed! This Eagle has clearly been designed with weight reduction to the fore, which is evident in the way it flies. Things have come a long way on the ARTF front in the last ten years, and whilst there are a few niggles here, if you fancy an impressive yet unintimidating bipe, they really don’t get a lot better than this.

Well, that was all two years ago. The Eagle flew i.c. for its first season but was swept along as I converted my fleet to electric power in 2013. It now sports a Turnigy G110 spinning an 18 x 12 prop with power from 8 cells – usually 2 x 4000-4500mAh packs Velcro'd securely to the sliding tray that's found under the hatch. I can't understate the importance of Velcro strips and straps by the way, if either pack came loose in flight then the results would be catastrophic so it's a vital aspect. With just four servos, albeit metal gear digitals, a 5-cell NiMH pack provides the juice distributed using a Powerbox Digiswitch. Flight duration is a comfortable 7 minutes.  

The airframe has thanked me for the conversion. The vibration from that big old four-stroke meant every nut and bolt needed checking on a regular basis and the covering edges were starting to show the effect from meeting fuel on a regular basis.


In the air the model seems just a little smoother, just as fast though and still imposing. It's a machine that eats sky so pilots must stay ahead of it. In that respect it's fine if you're a good intermediate or experienced flyer.  


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