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Tuesday, October 12, 2010

Quick Take: Great Planes' $89 Fokker Dr.1 Triplane (ARF)

I like to collect classic airplanes, so the gorgeous little Great Planes Electrifly Fokker Dr.1 Tridecker was a natural choice.
Great Planes continues to release wonderful ARFs.  This kit is no exception.  For those used to foam airplanes forming the most popular RTF offerings, you are in for a treat.  The Great Planes ARF kits get you in the air in a reasonable amount of time and are in a much higher quality class than relatively junky RTF/ARF foam airplanes.  Thankfully the price is low enough to add quality servos and still come out ahead, at at least even with, foam RTF offerings from Parkzone and the like which are sold with junk electronics.  

This kit is balsa and ply, roughly 5 times stronger than foam, truer flying, and covered in Monokote with a high gloss finish that doesn't deteriorate with use.  

The plane has nice scale details, but for just $79 after Towerhobbies.com (no affiliation) usual discounts, nothing that will knock you over.  The Tridecker ships with is a thin plastic scale cowing the snaps in place using pre-installed rare earth magnets, a black radial engine bottom (I painted mine up a little), and two, pre-painted black balsa wood machine guns.  The wheels are sturdy and look great on the custom landing gear.  The "fouth wing" between the wheels is counted in Great Planes 300 square inch wing area, and 10-12 ounce wing loading calculations.  

My model finished up at 24.2 ounces including adding 2 ounces of lead in the nose for balance.  (since removed, no need)

I installed a Super Tigre .10 motor with a 10 x 6 hand-balanced Top Flight wooden prop. An 11 x 6 prop is shown, but is a bit power hungry for a 1300 mAh; flight times are only 6.5 minutes and thrust-to-weight is over-the-top.  Max thrust on a 1300 mAh 25C with a 10 x 6 is in the 29 ounce range, for about a 1.1 to 1 Thrust to Weight ratio at the Triplane's flying weight.  The $20 Super Tigre .10 is the perfect motor for this menacing presence in the sky, if not a bit too strong (is there such a thing?).  The motor is both too strong and too light for the plane, a thrilling combination.  Thrust is spectacular, as is top speed and agility.  Torque roll is an issue when slow, as the Triplane packs it's high aspect ratio 90" wingspan into just 30" on the top wing.

Construction is straight forward, but the plane is not, so it takes some thought to put this baby together.  The nose is so stubby you have to be absolutely obsessive about saving weight in the tail section.  Each ounce of heft here will mandate about 5 ounces of nose ballast.  That's a lot for a 24 ounce model.  Be careful.  Cram every component you install as far forward as possible, if not under the cowling.  I sliced out the plywood battery brace, to shove the battery about half an inch farther into the nose.

Balance is critical in a Tridecker, more so than most airplanes because there is so little nose moment arm. Make certain you balance the model using some sort of jig with a bubble level fixed to the horizontal stabilizer (but don't weigh down the tail).  I found the book CG of 2" back from the leading edge, a bit too nose heavy, so I removed about an ounce of the 2 ounces I originally installed for balance.  Yay--I really hate weighing down an airplane.

This kit has a reputation for a weak firewall, so I added medium balsa cross bracing behind mine, as well as 0.25" balsa studs butting up along the left and right sides.   The end result is strong enough for an even larger motor, and the ST .10 is so light you'll still probably need to add a little ballast up front.  

Visual control surface alignment is difficult, as the ailerons extend beyond the wings, and with 3.5 wings, one has to wonder how much twist and alignment error you can comprehend without simply giving it a try.  One wing shipped badly twisted--the one between the wheels.  A heat gun and some coercing untied about half the warp.  With that and a little aileron eyeballing, this WWI villain was ready to take to air.

Take off was easy.  The gear is solid, and I installed an ultra-light tail-wheel for control.  Once airborne, the initial setup was a handful.  The plane wanted to roll hard left, no doubt due to unanticipated non-offsetting errors from all the wings.   I pointed the nose toward a 3/4 Moon and ran the trim right. Ahhh, much better. 

Once trimmed up, this airplane flies great and looks even better.  What fun to see the abnormally tall three wing stack circling in sun-lit crimson.  As odd as the Tridecker is, it flies very well and is extremely agile in the air.  It has no apparent vices, but the excellent responsiveness and maneuverability need to be tamed with a healthy dose of expo. 

My first loop was only slightly ajar upon exit, due to a little cross control from my immature rudder and aileron trim settings.  After trimming out the glide, loops became axial.  Nose track around turns is tremendous, making the Dr.1 an ultimate single-circle fighter.  I was afraid speed would bleed quickly, given the nose rate, but the agile flying wing box never dropped a wing exiting from some uncanny turns.

One can feel the appeal of this age-old classic, you'll get a first hand appreciation for the men who loved piloting this vicious killer.  

The 3.5 wing arrangement is almost square when viewed nose or tail-on, which could also be described as a circle (circumscribing the square).  This makes for exceptional longitudinal in-stability.  This is a great attribute for a fighter, but it is not the most relaxing configuration for sport flying.  With a good computer radio (mine bound to a DX8) unwanted roll can be all but exterminated.  That is, until, you run out of airspeed.  Point the nose skyward, pull the power back to essentially hover, and away she goes, rotating absolutely uncontrollably, opposite prop torque.  The Dr.1 is a very interesting combination of supreme roll-ability inherent to the design, while at the same time suffering from a relatively ineffective, top-wing-only aileron design.  The rare combination adds up to some of the most outrageous torque roll's you'll see this side of Oshkosh.  Luv it!!

Landing? Who needs it.  Good thing cause this plane is a little bit of a handful.  My first landing was definitely hot, resulting is a well controlled, arcing bounce that quickly morphed into a miniature bouncing PIO.  Not too bad, no wing scrape and I rolled away.  The roll sensitivity is challenging, but also incredibly fun.    Nose authority remains high all the way through the round-out; greasing it on is definitely an option. 

Overall, this plane was a great buy, a very strong and equally unique flier.  It is certainly not a first or second plane due to the interesting scale handling and the ability to out-maneuver yourself.  But for classic scale lovers who want a better appreciation for the great designs of history: I give it a B (Recommended), plus bonus points for some really fun quirks.  


Well done, Great Planes, can we have a 40" version?



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