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Monday, September 5, 2011

Parkzone UM F-27Q Stryker 180 Flight Review

UPDATE:  Video added of top speed, low speed and stalls

UPDATE:  Video added.

I don't usually buy airplanes that are not scale classics.  The F-27Q from Parkzone is the exactly the kind of RC proprietary plane I typically avoid.  If there had been any micro competition available on the store shelf, anything, I would have bought it instead.  Monopolies ...uhg.
The name is funny in more ways than one.  Why "180?"  Well, it comes with a brushless 180, but so do quite a few UM models without the 180 designation.  The appended number seems to  imply a different motor or in-between model scale may be offered in the future--mSR "120" style.  Or maybe it is the way they want to distinguish the micro from its big brother, since "UM" doesn't actually show up in the printed name, only on the corner logo of the box?  At any rate, a name that leaves a question mark over your head kind of sucks. 

The little Stryker is mostly cute, maybe that's what the Q stands for?  The color scheme is overdone and under-performing, a little awkward and ugly, like its big brother.  For some reason it reminds me of a pack of Sunday bicyclers in gaudy racing regalia--too many stripes, lightning bolts and bold colors.  But after all that supersonic speed implication, the motor looks like it is missing a nacelle.
The wing spans 17 inches and the airplane weighs almost 3 oz RTF.  Wing area isn't stated, it looks larger than most UMs, but the plane feels heavy.  That heavy feel is a good indicator that it'll need some speed.

On the Ground:

Ok, it's never good when the instructions require you to disassemble then reassemble a "BNF" airplane. This UM is not a BNF, as stated on the orange edged box.  The instructions call for a DX6i or better, but using the plane with a DX6i first requires taking the fuselage apart, removing the receiver form the mounting tape, carefully wiggling out two servo plugs so you can reverse them, then put the plane back together and re-tape the fuselage closed.  PITA--and what's worse, it didn't work. Now, my F-27 only mixes elevons properly when I reverse the aileron channel, not the elevator channel as stated in the manual.  So I probably didn't need to disassemble anything. Sheeeze.

The Stryker comes with a new 200 mAh 2S battery.  It's a pretty heavy battery setup, but the flying wing should be very efficient, so already I have to wonder what PZ was thinking?  The battery hatch is nice.  It is plastic instead of foam.

Another interesting thing is the inclusion of rudders.  The larger Stryker has vertical stabilizers without movable rudders.
Also in the "OMG they final learned" category are the servo covers on the bottom of the wing, protecting the delicate PCB servo gears from scrapage.

In the Air:

Launching a plane without landing gear is easy, you just give it a light toss.  Right?

Well ...maybe not if the prop spins right over your knuckles as you release it.  In an instruction manual crammed with dire Saftey Warnings and fire-prevention Cautions, wedged within a mountain of Notices and Disclaimers, Parkzone politely warns: never launch the plane with the motor running.

Clearly, a brilliant plan.  A pusher with no option but a hand launch--freaking dangerous design.  Parkzone graciously added a pinch hold, just in front of the million-RPM brushless propeller.

First dead stick toss sought grass.  Plop.  Second one.  Plop.  Trim adjustment based on two glide tests.  Third one: stall to 90 degrees of bank, pointing down, throttle up, pull up, ahh, wings rocking, whoops, up and over, upright, and, ooooooh woah, there she goes!  Simple as pie.

Or so I thought.  After landing I discovered that one of those plops cracked the nose almost all the way  through the foam, under the canopy.  The little pointy wing slat tips were rubbed off on one side by nicely manicured lawn grass.  The foam is weak. 

So if you don't mind breaking your first $160 foam frisbee the first time you dead stick it, which is Standard Operating Procedure for takeoff, the little bird is actually easier to launch after you manage to get it trimmed up.

Once plowing clean air, this little Styrofoam dentist drill goes pretty good.  The wedge design is interesting to fly.  Not exactly a drag machine, this UM flies quickly by default.  The nose is easy to control, and level flight can be dialed in with trim at a comfortable cruise pace.  The plane pulls pretty long and wide with an ability to change speed a lot faster than you can change trim, making throttle setting something you need to think about and prepare for, more than other planes.

In a straight line, dynamic stability is very good.  Static stability  is not.  The platform waggles at the slightest perturbation from a breeze.  After the plane waggles for a while you might get used to it, when it's tracking nicely you start to wonder why it's not waggling.
My kludgy Canon HD camera is arbitrarily 
limited to 10 min clips.  The horizon was straight, 
it is the camera that's tilted.
A slow speed, stabilized turn fits inside a baseball diamond; a top speed turn consumes the entire outfield.  Speeding up in a turn makes it hard to keep the nose from climbing, and vice versa.  The rudder is effective and can help guide the nose until the trim catches up to the airspeed, but I have to admit it is eerie feeding-in nose-down rudder on a 90 degree knife edge.  Slowing in a turn is a lot more dangerous, as the nose wants to fall strongly.  I have never seen an RC plane with such a wide range of required trim settings, it uses perhaps 75% of the available trim range, from full back to about half forward.

High rate, slow speed turns reveal some of the mini-Stryker's most endearing flight characteristics.  The flying wing is very resistant to stalling.  There is no discrete elevator to twist the wing on its lateral axis beyond critical Angle of Attack.  The wing itself must generate the force to go beyond critical, and once approaching critical AoA, any twisting moment needed to increase AoA is naturally reduced--result: great stall resistance!  The elevons tend to wash out and loose effectiveness before they can lift the nose into no man's land.  Burying the elevator stick more than halfway into your lap while reducing throttle results in very forgiving high alpha slow flight.  To wallow around just beneath the stall, the plane's elevons tend to stay more effective than the rudders.  Rudder airflow is partially asked by the wing at high angles of attack.

Bottom line on stall characteristics: as long as you increase back stick pressure smoothly (so the wing doesn't go ballastic to near-zero airspeed), the little Styker might wallow and waggle, but it will never quit flying.

The crank is a little reminiscent of flying an F-16.  As long as you maintain some speed in a turn, the nose continues to rate very strongly as vorticies roll off the steep strakes, up and over the the central area of the wing and lifting fuse.  The conventional main-wing sweep funnels span-wise flow to the tip vortex.  The result is a nose track that keeps on giving.  Important safety tip: don't get into a low speed dual with a cranked arrow unless you're sitting in one.  This thing is just plain fun to turn aggressively long after you think you can't.

Here is a video of the mini Stryker's top speed (impressive), bottom speed (pretty darn good), and full aft stick stalls (tame):
0:09 mins: Normal, Nerve-Racking Launch
1:17 mins: Full rate Aileron Rolls (note coupling)
4:45 mins: Bottom Speed, accelerating to:
5:45 mins: Top Speed 
6:00 mins: Loops
8:00 mins: Full Aft Stick Stall
Loops are bigger than one would expect for no elevator arm, and aileron rolls are not axial, they are surprisingly coupled--might need a control throw adjustment.  Pulling too hard on the nose occasionally couples to roll, especially when the plane is pointing away from gravity.  This plane isn't gonig to win any pattern competitions, but it is inherently stable in level flight.

Spin rate varies upon the spin mode, but all conventional modes have one thing in common, the ground comes up fast.  The Stryker has a conventional spin mode that resembles Barrel Rolls in the vertical.  Placing the sticks in various corners produces widely different spin traits, from spiraling down to winding up like a pinwheel.

If you enter a conventional spin with pro-spin aileron, then reverse direction and invert the elevator, the plane can be coaxed into a very rapid, pinwheel-like flat spin.  While a conventional spin leaves one wing flying (below critical angle of attack) around the other wing that is stalled (below critical angle of attack) causing auto-rotation, the aerodynamic driver of the pinwheel effect is less clear. The plane appears to rotate about  the front of the nose, with both wings subscribing the same flat arc around it.  The rate of fall is much slower than a convention spin mode.  My pinwheel spins aren't quiiiiite as tight as the Parkzone demo video, which appears to rotate around a point closer to the canopy.  I don't know why. 

Flight times are great with the included 200mAh battery, 15 minutes or more, but the plane is too heavy.  Again, a big swing and a miss on stock battery selection.  Maybe the designers were going for top speed and/or high speed stability, not realizing that weight slows the airplane and it is plenty stable flat out.  Slow speed handling quirks would benefit greatly form lightening the load.

The last thing worth covering is the small size for the huge speed envelope.  This little buzz saw can get hard to see in a hurry.  This is complicated by the flying wing design, which is inherently difficult to orient, and an ineffective color scheme in the air.
Overall, the UM Stryker is a design exercise in extremes.  It goes extremely fast, it spins extremely tight, it's slow speed nose tracking is extremely effective, and the foam nose is extremely weak.  What the daredevil does not do well is find middle ground.  Tooling around at a comfortable pace is not this plane's forte.  Still, it is relatively easy to fly, as long as you keep it in sight.

Appearance: B
It's ok.

Flight Performance: A-
Nice turning performance.  Some wing waggle.  Huge speed envelope.

Build Quality/Durability: C
Weak nose.  Finally included external servo covers.  Prop exposed on landing.

Value:  D+
Way too expensive for a UM boomerang.  Should be more like $79 BNF.

Overall Grade: B+
A- but too expensive.  Quirky, but fun.  Trim hard, trim often.  Find a BIG park.

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