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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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