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Saturday, October 22, 2011

Yak vs. Yak Standings

Yak vs Yak is complete for the current field.  I will add more Yaks over time.  This competition was a lot of fun and very eye opening into (1) how good the basic Yak airframe is, and (2) how much difference there is among models.

If there is a lesson learned, it is that foamies are not in the same league as Balsa and Ply models.  The dominant winner was the Great Planes Yak-55M.   This won't surprise people familiar with my blog, as the 55M is the Z8RC all time fav RC airplane.  The value this plane delivers is off-the-charts.  For just $170 for the basic airframe, it leaves plenty of room for extremely precise digital metal gear servos and your favorite electrics.

Another LL was that if you are going to buy a good Yak, you get what you pay for.  If you are going to buy a cheap foam Yak, there is not a lot of difference between carbon reinforced foam models, so one might be better off skimping.

Carbon rods and slats are cheap and easy to add to the models that don't have enough support, like the Carbon Z's un-reinforced, somewhat fragile fuselage.  The Art-Tech Yak-54 ships with no carbon, I sliced and pressed-in a $6, full-wingspan carbon fiber slat as tested.  The inexpensive Hobbyking Monster Yak-54 ships with by far the most carbon and plywood, in both the wings and fuselage, but it needed a new engine to compete favorably with this group.
Click to Enlarge
All of these planes are phenomenal aerobats; even the lowest rated can fly the pants off most planes.  And all of these Yaks are quite forgiving, with no apparent trade off for the docile handing, especially at low speeds, while maintaining roll, pitch and yaw rates that are something special (some, more special than others).

After this showdown, I can highly recommend both the 1st place airplane, the Great Planes Yak-55M, on pure aerobatic prowess.  I also recommend the last place airplane, the Art-Tech Yak-54, for min investment and max fun--after significant hop-ups, its price tag still led the field.  The Great Planes 41" Yak-54 is another standout for it's compact size while maintaining exceptional capability and precision.

Thursday, October 6, 2011

Flyzone Micro Super Cub RTF (14") Flight Review

Updated the videos and expanded my comparison to the Hobbyzone Champ.

Can the new Hobbico Flyzone Micro Super Cub RTF knock off the venerable Hobbyzone Champ as the Z8RC top beginner RC airplane? The answer follows...
Hobbico packs the wings on the diagonal, making
their box size much smaller and more convenient 
and shippable than Horizon micros.
On the Ground:
My first impression of the Flyzone Super Cub is that it looks a little stretched in the longitudinal axis (or maybe the fuselage is squeezed a bit too thin along the lateral axis) and it seems to have ;dihedral.  The long snout could be promising, it might indicate a fairly light motor and prop in proportion to the airframe.

The SCub ships with two V-shaped struts equipped with three sticky pads to attach the ends to the wing and fuse.  There is a corresponding divot under the cabin, and the underside of the wings have recessed squares to accept the sticky tape from the struts. I left my struts off because they were a bit too long and too flexible, bowing them out and increasing main wing dihedral even more; I thought the uneven bend might adversely affect flight characteristics. The wing is plenty strong, so why add weight and induce asymmetric parasite drag?
The plane comes with stick-on wing struts (see 
unboxing photo, above).  I decided to save the 
drag and the wieght.
The landing gear is narrow, which might make ground operations a little difficult, but the wheels are large for a micro of this size and weight, which allows the mini Cub to handle some ground imperfections. Sadly, the tail wheel is fixed and does not turn with rudder movement.  On the ground engine torque is more than sufficient to turn left with rudder deflection, but there is not enough control to turn right, imputing full right rudder is only enough to go straight.
The tailwheel is stationary.
Nice paint scheme details for a micro, and the 
empennage looks great and is made of stronger 
and stiffer than Horizon micros even with no 
carbon reinforcement
The included battery is a 130 mAh 1S with Flyzone branding, but there is just enough room for a 150 mAh 1S stick.  The battery bay is designed so the connectors and excess wire can be slid inside the fuselage--kind of nifty--but the battery position is located well in front of the CG so changing battery capacity is going to affect flight characteristics substantially.
The battery compartment is just big enough to fit a 150 mAh 1S.

The propeller is very large with a beefy airfoil chord.  The motor and reduction gearing are well up to the task of spinning it, flight tests indicated that this tiny Cub has almost a 1:1 Thrust-to-Weight ratio.  Although hard to see clearly in the picture above, the motor shaft has no right thrust bias to redirect its plentiful power, leading to a lot of torque compensation by altering rudder position across the power band.

The included radio is smaller than it probably 
looks.  The Cub's wingspan is only 14".


In the Air:
If the design goal of this Super Cub was about light wing loading causing a wonderful flying experience, Hobbico did a sensational job!   The plane floats like crispy fall tree leaf, but with a 1:1 T:W power system to rocket skyward.

Speaking of engine power, the little Cub is demands full right rudder to roll straight on take off due to significant torque. This right stick input can be mostly released as soon as the airplane becomes airborne.  Again, the main reason is a stationary tail wheel. It's a bit tricky to roll straight, but at the same time the cub is forgiving enough to teach beginners the art of countering high throttle torque, without looming consequences.  As long as there isn't an obstacle between straight ahead and about 30 degrees left, take off is still pretty easy to accomplish even if not pretty.

Tossing the plane into the air is easier than a ground roll, because setting any throttle above 40% results in a strong, slightly left-spiraling climb as soon as the peppy yellow bird flies from your fingers.

With only 1 oz total weight, the power system is not stressed at all. Flight times are excellent at 10-12 minutes of battery life with mixed aerobatics (= full power loops and steep turns). The wing loading is so miniscule, that the plane can maintain level flight at 20-30% throttle, which if maintained, would extend the battery flight time to perhaps double or more the figure quoted above.
The Super Cub's paint scheme looks very nice, 
and there are some nice scale details like a 
gradient sticker windscreen and windows, reasonably 
tactful racing stripes, traditional Cub logos on the 
vertical stabilizer, and molded wing ribs for looks 
and strength.  The wing airfoil is flat with under-camber.
  Overall, the plane is very strong for its feather weight.
Once the plane is climbing away, you'll need half to almost full right rudder between 50% and 100% throttle respectively to track straight.  About 1/16th inch of right rudder deflection, as trimmed on the ground, is sufficient to track the airplane straight ahead at comfortable cruise power, around 40%.

The plane is very stable in level flight due to the pronounced dihedral, but rolling out of turns on a precise heading can be tricky due to some mild pendulum oscillations as the plane hunts for a wings level equilibrium.   Even with its very positive dynamic and static stability, keeping the plane tracking straight is a bit of balancing act due to the large draggy prop and plentiful thrust.  Any change in power setting produces a corresponding change is the Cub's desire to roll.  Adding just 10% more power above stabilized, straight and level flight will produce a positive climb rate and a mild left corkscrew skyward.  Reducing power 10% has the exact opposite effect, as the trim required for straight-ahead flight dictates a right corkscrew with a throttle reduction.  Since the mini SCub comes with a dedicated radio, there is no way that I know of to use a computer mixing radio to help straighten things out.

Slow flight is absolute impressive in absolute terms--the plane is so small and stable that adding about 75% back stick under gentle power slows the airplane near walking speed.  That said, stall characteristics of the undercambered airfoil are unrefined.  Pull back more than about 75% on the elevator and the plane will slip off to one side as one wing drops, tugging the nose down with it.  Recovery altitude varies with stall severity, but its never a whole lot due to the super light airframe's desire to start flying as soon as possible.

The only exception to the stall sequence discussed above is when the plane is already established in a steep turn.  If smoothly entered, the Super Cub will stabilize in a steep turn in either direction, with full left or right rudder (which is mapped to the aileron stick) plus full up elevator.  Jamming the stick in either rear corner of the radio gimbal, with anywhere from half to full throttle produces an easily sustained min-radius turn.  The plane turns tighter to the left due to additive motor torque.  The tightest (left) turn circle is about 8 feet in diameter.  The plane can reverse course in even less lateral space than 8 feet if you add a little vertical spaghetti; perhaps 3 feet, wall to wall.

1:32 - Slow flight to stalling speed                  
1:42 - Full stall, wing drop                             
1:50 - Stick planted in bottom left corner        
3:40 - Thrust demonstration                            
4:30 - Climbing at 5% throttle (throttle shown)
5:30 - Min-radius turns                                   
5:38 - Stick planted in back right                     
corner (torque pulls plane out left)
5:55 - Sweet landing                                       
Speaking of turning, the SCub is light on rudder throw as shipped, even beginners will want to move the push-rod to the inner most hole on the rudder control horn.  Still, there is not quite enough rudder throw for my liking.  The elevator is just the opposite--a tad touchy--so while you are adjusting the rudder horn, move the elevator push-rod to the outter most hole on the control horn.  Much better.  But there still is not enough rudder authority, or too much dihedral, to accomplish anything resembling a barrel roll.  Inverted flight is unsustainable.

Spins are as benign as they come, but if you keep full power or down elevator in, the plane can bee-line for the ground.

Lastly, the included radio is worth comment.  I prefer the form factor of the SCub radio to the cheap Horizon Hobby equivalent.  The trim buttons function well compared to the sub-standard Flyzone Albatross radio.  That said, my radio developed noticeable binding between the dome shaped gimball covers and the stick frame, and while it didn't ever result in diminished control, it was quite distracting.

Tooling around on a windless morning (don't fly this little yellow feather in any wind) with this miniature kite with a tiny rocket motor could not be more fun.  Though not as refined as the Hobbyzone Champ, the Flyzone Micro Super Cub is an endearing trainer.  In a way, it is a better trainer than the Champ because it brings many of the same vices as it's big brothers, but without the wing loading to create sustained momentum in a bad direction, or the mass to do any damage during a crash.  Without any experience or assistance, one could learn to fly the SCub as long as you stay over grass and spend 30 minutes in ground school, first.

Flyzone Super Cub advantages over the Hobbyzone Champ:
  1. Smaller flying area requirement
  2. Slower minimum speed
  3. Rough runway ops
  4. More benign spins and hands-off landings
  5. Thrust-to-Weight Ratio
  6. Feather light wing loading
Hobbyzone Champ advantages over the Flyzone Super Cub:
  1. More refined slow flight and stall behavior
  2. Proper thrust vector; less need to compensate for torque
  3. The right mix of stability and agility from less dihedral
  4. Top speed
  5. Better ground handling and controlability during Touch and Goes
  6. Flightpath precision
Due to its slower flying speed, the Flyzone Super Cub is a easier to handle than a Champ in smaller spaces, or to stay ahead of, even in a larger space.  As long as you stay away from the Cub's absolute  air speed limits (no full throttle or full stalls) this Super Cub is quite possibly the easiest first trainer to keep aloft.

That said, the SCub strongly displays and even exaggerates the traditional vices of a stereotypical single engine airplane--it has an affinity for torque roll to the left under mild to moderate power, correspondingly, it spirals right in idle, and it slides into a sharp bank with a nose drop as a wingtip stalls.  Flyzone's floaty micro trainer has outstanding power for its weight, with an almost magical ability to callously yank the airy foamie out of square corners.

I see conflicting attributes and redemptions with Flyzone's excellent little Super Cub as a practical RC trainer.  One one hand, with superb power and a centered thrust line, is it an excellent little torque trainer because throttle and airspeed and rudder are a constant balancing act.  Learning the skills to cope with torque as a function of engine power an airflow over the rudder will serve students very well as they progress to larger, more powerful single engine RC models. 

On the other hand, the combination of very strong power and feather light wing loading defies real world concerns when it comes to managing flight path momentum.  This paper-weight Cub is unrealistic in its ability to instantly power out of tricky situations, and probably not the best trainer as a means to an end beyond guiding a feather.

Overall, the refined flight characteristics, larger scale and aircraft feel, and the slow speed precision of the Champ are well worth the extra $10.  The Champ is a more realistic and satisfying first-step into the realm of RC flight and is just as easy to fly, given double the airspace.

Appearance: A-
A little cartoony.  Very nice paint scheme.  Vibrant visibility.

Airframe: B-
Strong.  Unrefined slow speed wing.  Unsteerable tailwheel.

Power System: A
Gobs of power.  Little loud.  Great battery efficiency.

Build Quality/Durability: B+
Strong tail.  Light mass has a hard time sustaining damage.

Value:  A
$79 RTF - one of the best trainer deals.  Not bindable.

Overall Grade:  A-
Very easy to fly! Hard to balance motor torque.  A few rough edges.

Monday, October 3, 2011

Parkzone UM Mosquito Mk VI BNF Flight Review

Update: After several more trips tot he field, I am upping the Mosquito's overall grade to A.

Update: Added a discussion of slow flight characteristics and some video footage.

Geoffrey de Havilland's idea of mating two Rolls Royce
Merlins (of P-51B-D fame) to a balsa and ply wooden 
airframe covered in doped fabric was just crazy 
enough to work.  The resulting Mosquito was a fast 
fighter-bomber and a logical choice for Horizon's 
first UM twin engine.  Still, one has to wonder why the 
more famous and graceful P-38 didn't make the cut?
Parkzone's UM Mosquito Mk VI BNF is an interesting Ultra Micro for two reasons: (1) it is the first twin engine UM, (2) the Mosquito was not exactly one of WWII's most glamorous fighters.   The wooden "Mossie" was reasonably fast and a good performer, but the design never fully caught the public's imagination. I have a feeling de Havilland's Mosquito carries a little more mystique in the British culture where its UK heritage tugs on heart strings, thus its slightly frumpy looks are more easily forgiven.

The UM Mosquito is also distinguished by the model's mass, which is a larger than other 1S UMs at 2.6 oz, though it has  the same wingspan as a 1.3 oz Hobbyzone Champ.  Of course, twin 1S motors drawing power in parallel sounds a lot like 2S power flow.

The box is also much bigger than others in the Ultra Micro series, and the plane isn't exactly a tight fit. 

I first noticed Horizon's new trend toward oversize boxes with the recent remake of the full sized Stryker, which has the same dimensions as the original, but more than twice the box size.  Do we need yet another HH marketing scam?  Really?  Hurting customers by pumping shipping costs and disappointing kids with mostly empty boxes at Christmas time?  Sheeze. 
Unboxing.
Specs:
Wingspan: 20.5 in (520mm)
Overall Length: 15.2 in (387mm)
Flying Weight: 2.60 oz (74g)
Motor Size: 8.5mm coreless brushed
Radio: 4 channel transmitter minimum
Servos: AS2000L linear long throw servo x2
CG (center of gravity): 38mm from leading edge of wing at fuselage
Prop Size: 110 x 80mm 3-blade
Recommended Battery: 250mAh 20C Li-Po
Minimum Age Recommendation: 14 years
Experience Level: Intermediate
Recommended Environment: Indoor/Outdoor
The Mosquito box is large enough to fit a full size transmitter.
Horizon apparently felt they could capture the brutish personality of the twin-Merlin Mosquito by including twin 5 cent brushed 8.5mm can motors running on 1S.  The resulting 10 cent design is light on performance, but has enough power to sustain comfortable flight.  The twin 3-blade props are geared at a low pitch to keep the nickel motors from experiencing a 6 cent meltdown.
 
Switching to two 2-blade props would result in more speed and power, but the unlike the hopelessly wimpy 3-blade UM Corsair (aka Jiggy) the UM Mosquito's landing gear are not easily lengthened to accommodate increased prop diameter, nor does it have inverted gull wings specifically suited to purpose.  At least the Mossie has enough power to comfortably fly, unlike their heavy, woefully underpowered 3-blade UM corsair.

To develop decent thrust, the cheap tin cans swing a pretty flat pitch 3-blade.  This gears the engine lower which is both good and bad.  You get adequate power at low speed, but lose the ability to go very fast.  Horizon's junk motors sentence this big brute to perpetual servitude stuck in second gear (to draw a car metaphor).
Mosquito battery (left) vs Blade mCPX battery (right).  
Note the connectors aren't the same.  Either Horizon 
Hobby's left hand doesn't know what the right 
hand is doing, or they routinely engage in intentional 
incompatibility scams to rip off their most loyal 
customers.  Take your pick, either way the company 
is consistently hard to do business with.
The included E-Flite battery (so much for the fabricated appearance of competition among Horizon subsidiaries) is a customer hassle.  The battery's connector is incompatible with some 1S batteries, like the 200mAh 1S 25C sold with the Blade mCPX, but it is a match with the E-Flight Tandem Rescue helicopter.  Using a 1S parallel connector with two smaller 1-cells is probably the best idea for UM battery compatibility.

The landing gear design, or as the Mossie's UK fan base would say, its undercarriage, is one of the best things about this micro airplane.  The double strut is a lot more study that other UMs, and the larger wheels can handle a few bumps in the runway, or even the thin gravel of a High School track around a football flying field.
Photo shows the real Mosquito had a busty, brawny look that the micro fails to fully capture. The Mossie's scale-ish double-strut landing gear design is very sturdy and serves the UM version well. 
The canopy details and four-machine gun nose 
(which form a battery hatch handle) are nice little 
scale details.  Four cannon in the belly are 
indicated by molded foam.
The foam airframe of the UM Mosquito is big enough to house and protect Horizon's usual Rube Goldberg servos, making it a aerodynamically clean and very durable build for a micro.  The paint job is scale and very effective blending into the landscape; which means it is not so effective if you are trying to see your plane.  The scheme is most visible on a cloudy day.
The gray/green camo scheme is extremely effective 
blending into the kind of villiage-scapes 
the Mossie once attacked or protected.
The plastic nose doubles as a battery hatch which is clever, but the included battery flies nose heavy.  There is some room to push the battery back, but it becomes difficult to fish out of the nose compartment.  The tip of the nose position of the battery hatch makes it difficult to increase capacity/weight without shifting the CG even farther forward.
The battery hatch in the nose is plenty deep to 
use 1S batteries from other Horizon products, like 
the Blade mCPX, but the connectors are different.
Using the 25C Blade mCPX battery with a cord adapter is a decent solution for more power and better CG balance, plus the longer cord allows you to fish the battery out.   Unfortunately, the 200 mAh battery capacity is lacking, the plane is initially more energetic, but become even more lethargic in short order.

In the Air:

The Mosquito's twin motors seemed well matched during a few quick ground runs.  But on takeoff, the plane required some right rudder, which is odd, because the counter-rotating props should be devoid of torque issues.  It could be a difference in wheel friction, or slightly mismatched motor thrust.  More testing required (after several more flights I think that was an anomaly of early wheel friction differential).

In the air the plane wanted to mildly turn left, which I attributed to aileron trim since the motors should cancel.  Once trimmed out, the little Mosquito flew surprisingly well.  I was impressed by the plane's airborne stability given the forward sweep of the mean chord line, the mid-wing mount, small rudder (for a twin) and under-cambered molded airfoil cross section.   The flight silhouette displays ample dihedral, no doubt aiding the roll stability.  Yaw is the least stable axis.  The seemingly conservative rudder dimensions explain that, and could present a real challenge to salvage the aircraft if only one motor quits.

It is refreshing to fly an airplane with a throttle that isn't tied to the rudder.  Full blast or idle, the Mossie's flight path is stable and true.   Loops are easy to keep on axis as a result, and the twin delivers enough power to get over the top gracefully.  Aileron rolls are a different story, where the non-axial location of engine mass present a moment arm challenge to the large ailerons.  Rolls are sloppy at low speed, dropping the heavy nose by completion.  With enough forward momentum, the plane can roll adequately, but still requires a little down elevator when inverted with a minor rudder swap to keep the nose level, or a nose high entry.

The mass of the plane leads to diving turns without significant elevator application to hold the nose up.  Pulling power out (or losing it) also drops the nose toward China without a trim or manual elevator adjustment.  I think at least part of the plane's excellent observed stability is due to the nose heavy condition.  I would love to play with a more aft CG, as the plane could use another dose of general agility, but the forward battery hatch could limit experimentation.

Novice fliers will probably like the factory setup more than advanced flyers, as the nose tracks well at all speeds and the plane has good roll stability to match.  There is plenty of wing to land on, and the elevator stays effective at all speeds, so lifting the heavy front-end of the CG seesaw is very achievable as long as you catch the slow speed, or high bank angle, nose droop with enough back stick.

Landings are probably the easiest of all the UMs, due to a lack of unidirectional torque and cancelling P-factor.  The plane is very well behaved throughout the flare and touchdown.  The left/right props spin in the correct direction to minimize P-factor with engine speed variance.

Stall characteristics are shown in the middle video at times 2:20 (full stall--froze stick at critical Angle of Attack) and 4:05 (fully developed stall--full back stick with 100% servo travel).  The full stall characteristics of this big wing twin are very forgiving.  The elevator and tail oscillates up/down ever-so-gently while the plane continues to plow straight ahead with minimum altitude loss.  There is no yawing tendency common to single engine airplanes without enough airflow over rudder to counter torque and P-factor.  Burying the stick at the back stop, with limited power applied, starts the same way, then develops into a mild but slowly intensifying wing rock.  Ultimately, severe wing rock ensues, but it remains predictable and mostly level until the stick is buried.  At the full development limit, the bank angles generated by near 90 degree bank angles from wing oscillations are sufficient to dump lift and lose altitude rapidly, but you have to wantonly stuff the stick for a long time to get to that point.  That could conceivable apply to an exceptionally prolonged panic scenario, but I say if you suck that bad you deserve to die.

All in all, I give the Mosquito exceptionally high marks for maintaining a usable level platform until egregious and prolonged pilot error rule the day.  This is one forgiving old chap, with zero tendency to auto-rotate.   An better CG balance might improve full stall behavior even more, due to less elevator travel required to lift the heavy end of the seesaw.

Spin behavior is benign.  You have to apply pro-spin rudder to make the plane rotate, releasing the controls immediately pops the plane out..  There is no tendency to spin, even when fully stalled, the plane will stabilize in light to severe wing rock,. but it resists falling off to one side.  Even in high alpha slow flight, there is very little tendency to drop a wing.  Several spins are shown in the bottom video, above (some setups are partially out the top of the video frame).  Overall, the Mosquito displays excellent spin and tip stall resistance.

Another delightful surprise was that, aerodynamically, the Mosquito handled the choppy wind better than other plane in my UM fleet, but it does have some trouble swimming upstream due to a lack of high gear thrust.
The Mossie looks at home performing any type of industrial raid.
All things considered, the plane flies like a warbird.  Stable and nose heavy, but without the needy rudder of a big torquey single engine beast.   The Mossie is a fun and unique UM that executes its twin engine design surprisingly well.

Parkzone specs say this plane is suited to intermediate fliers.  I disagree.  The plane's inherent lack of torque, excellent longitudinal axis stability, robust airframe, and forgiving slow flight characteristics make the Mosquito a fine choice for beginners as well.  The only minor vice is the need for elevator to counter moderate nose droop during steep turns and 90 degree-plus aerobatics.  Flown conservatively, the Mossie is the best behaved micro class airplane next to a refined high wing trainer like the Champ.

Appearance: B-
Nice scale details, but falls short of capturing the Mosquito's brawn.

Airframe: B+
Clean.  No servo exposure.  Very stable.  Could be more agile.

Power System: B+
Two antique can motors are better than one.  Well executed twin.

Build Quality/Durability: B+
Very sturdy UM airframe and landing gear.  Cheap motors and servos. 

Value:  B-
$120 seems like a decent price for a twin.  All HH UM prices are silly.

Overall Grade:  A
Whole is greater than the sum of parts.  Fun and unique.  Flies great!
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