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Saturday, July 23, 2011

Parkzone UM F4U Corsair Flight Review

Update: Jiggy Gets a Heart Transplant

Update:  Nano Corsair video link added.

A lot of people probably think I hate Horizon Hobby products. That's not true, I hate products that suck, and Horizon Hobby's value proposition generally sucks bad. As much as I wanted to like the little UM Corsair, it proved to be no exception to the "Horizon Hobby sucks" rule of thumb.  For the record, HH has plenty of representation on my highly recommended list, to the right.....
On the ground:
First the good news:  as you open the box, the little Corsair looks great, it has a few extra details over previous UM models from HH.  Also showing movement in the the right direction, Horizon has been listening to me (I say "me" with certainty, because this blog is the only source of much needed criticism on planet Earth-- all the other "glowing" internet reviews are bought and paid for by HH directly or indirectly; nothing more than thinly veiled advertising stunts) and this model is a bit more robust than their previous offerings.  It has a molded airfoil cross section wing unlike the usual, ultra-cheap stamped out or die cut flat-foil foam wing, as well as a molded tailplane.  For their willingness to take constructive criticism and improve, I give HH kudos.
Now the bad news: Unfortunately, HH still has a ways to go on build quality, the Corsair is still pretty flimsy overall. It still ships with exposed PCB, exterior mounted, very weak micro servos under the wings--the predicted durability of the wing servos alone is well below sea level.  An unfortunate artifact of Horizon trying to improve their lowly UM airframe durability is excessive weight, the UM Corsair weighs in at a portly 1.5 oz.

The antique brushed motor has an uphill battle to fight, and it is certainly not a winner. The little motor and gear box are overtaxed with the new 3-blade 110x80 prop. 4:50 minutes into my very first test run to determine typical flight time (50% throttle until LVC), the main reduction gear stripped to the point of chronic slipping. Subsequently, advancing the throttle above 40% produced nothing but pathetic screams, screeches, and wails. A new nylon reduction gear from an extra gearbox I had laying around in my misc micro parts drawer fixed the problem, for now.  PZ should not interface a hot brass motor pinion with a cheap nylon reduction gear when there is zero cooling airflow, due to the solid motor facade decal.

In order to keep heat under control on future runs, I sliced out a small inner circle from the engine sticker to expose the micro gearbox and motor to some cooling airflow, as shown behind the prop hub below:
Horizon continues to release seemingly untested, failure prone junk at premium price tags.  My UM Corsair was dead before it ever got airborne.  If the BBB doesn't lock Horizon Hobby's doors and fumigate the building, I'll keep hammering on their peculiar brand of gross negligence until they are shamed into competence.

Thrust from the 5 cent, brushed, 8.5mm can motor and the 3-blade prop is poor. Full throttle produced a whopping 0.7 oz of thrust, making the UM Corsair the most underpowered PZ UM yet with a 0.47 Thrust-to-Weight ratio.  Even the Hobby Zone Champ would clobber the UM F4U in a two circle rate fight, with its more respectable 0.77 T:W.

This UM F4U is way too pathetic to wear the venerable, 2800hp, 440 mph, twin-radial engine "Corsair" badge, so from this point on I'm going to call it Jiggy.  Switching out the prop to a 130x70 increased Jiggy's ultra micro horsepower substantially to 1.0 oz, resulting in a greatly improved T:W of 0.67.  That's about 42% more power with longer legs.  Still, it is nothing to brag about.  The only problem with the larger prop is the reason for a real Corsair's inverted gull wing configuration in the first place, on takeoff the prop tips begin to graze pavement as the tail rises under power.
A 130mm 2-blade results in 42% more installed thrust,
a welcome boost to anemic performance
I don't blame HH for wanting the scale look of a big honkin' 3-blade paddle. I do blame them for not understanding the very basics of aerodynamic propulsion.  A 3-blade absorbs more power per unit diameter, which is exactly why the original twin-radial Wasp used a 3, and later 4-blade propeller.  HH including their same, tired brushed motor to drive a decent size 3-blade was a plan doomed to fail upon conception. 

In order to make their wimp motor viable, HH reduced the diameter of their standard 13 cm prop offering to just 11 cm, apparently not understanding the consequences of installation error.  I'm sure their 11cm 3-blade test prop produced reasonable power compared to the old 13 cm 2-blade on the test stand, but Jiggy has a large, scale radial cowl.  The installation losses in such a configuration become unacceptably high as a percentage of total thrust as diameter decreases, because only a small portion of each paddle digs unblocked air.  The solution, of course, is to account for airframe installation losses in the design phase, but unfortunately, RC toy makers like Horizon are cluedo when it comes to deep-dive design, they just copy pictures.  I recommend that all HH toy designers read my blog article on this topic, before beginning another similarly doomed project. 
The decals look pretty nice, partly because I had to apply them.
The next glaring problem is value.  At $110 as a BNF, this 16" span mini pig costs way too much.  Even its  high-priced big brother (44") is a better value, and sports adequate performance.  Of course you can't fly a much larger plane in your front yard, but that's a small consolation prize for putting up with HH's rip-off price tag for mediocre performance with junk component quality.

The competition:
Unfortunately, Jiggy gets blown away by much higher performing, lower priced competition:
21.5" (cubed difference = 2.5 times larger model) 4ch, 10A brushless
motor with better scale detail and higher quality internal servos.  $69 PNP
or $84 as an RTF with a solid full size 4ch 2.4Ghz Tactic Radio

Hobby King 40" F4U Corsair PNP
This 40", 5ch 20A brushless Corsair is $69 PNP
32" Hobby King F4U Corsair PNP


31" 5ch, 10A brushless for $69 PNP
In the air:
Jiggy looks the best and flies the worst of the entire UM series.

My first test flight was cut short due to increasing winds, but was plenty long to confirm that Jiggy has Ultra Micro power.  My unrealized hope was that the high wing loading of the plane would make it a little more apt in light wind.  Bzzzzzzt.  No.  The plane was helpless in 5-8 mph winds, revealing both underpower and under-control.  Flying with the 130x70 nailed on is much more satisfying way to burn dinosaurs, but the plane is still light on thrust. This Corsair wannabe is begging for a brushless upgrade--but that's assuming the basic airframe is aerodynamically sound, which it's not.

Once trimmed up, the plane is fundamentally stable in roll but not pitch, making it too inconsistent to fly enjoyably across a range of airspeeds in sport mode. It wants to dart up/down, after it does it wants to roll over on its side for lack of power, or tear for the dirt due to an abundance of weight.  The plane is too underpowered to fly in any mode other than sport, which doesn't leave a lot of options. Could be tail heavy as shipped.

You'll need to move the aileron pushrods closer to the control surface to get more throw, the plane struggles to complete an aileron roll as set-up by PZ. Unfortunately, the plane has so little oomph that large deflections are lossy in the airspeed dept, so you still need to supplement with potential energy to pull off a decent roll.  Using high deflection ailerons also risks reverse direction rolls once slow, due to the up-going wing (down aileron) stalling shortly after airspeed poops in the gutter.   Loops are best accomplished from a downhill entry with the 3-blade installed, better with the wider 2-blade, but mild aerobatics are still thoroughly unsatisfying.

Rudder deflection is very effective, but the influence of the vertical stabilizer on straight line yaw stability is pretty low. I need full right rudder to takeoff but not to counter high throttle/low speed torque in the air, possibly a wheel friction differential or airstream blockage with the tail low.  In the air, rudder control definitely helps to get the plane lumbering in the right direction, but couples heavily with pitch-down.

Oddly, the plane has rare moments of solid high alpha, low speed flight--until the flight path needs to be corrected--then it falls off the rails from a lack of helpful control surface guidance, the inability to power out of any induced drag hole, and out-of-square wing root stalls, likely due to improper washout geometry in the inverted gull's airfoil.  A quick look down the wing, from tip to root, reveals that undercambered airfoil is at its highest AoA at the gull's wrists. This is certainly a contributor to Jiggy's bottom-feeder flight characteristics, since the most severely stalled wing-section tugs far too from the fuselage, inducing yaw which quickly couples to roll as the opposite wing gets kicked into the relative wind like a seesaw, resulting in forward sweep.  It's the same inherent instability and lousy tracking that one feels from leaving the flaps down during cruise.

The cheap Rx has discrete aileron servo plugs, but the internal electronics are a Y connection instead of 5 ch, eliminating the possibility of differential, spoiler, or flap movement.  That's unfortunate:  plenty of vices to iron out; limited options.


Z8RC Verdict:
This plane is woefully outclassed by relatively high amp, brushless competition selling for less money, and is a marginal performer in the air.  I can't imagine anyone, who is aware of the competition, buying Jiggy given it's price point, tiny scale, and handicapped performance.  Along those lines, after this HH UM sucked so bad, I decided to try the BlitzRCworks 21.5" 2 or 3-cell Nano Corsair for $69.  It rocked Jiggy's world:

In the end, gave the plane my lowest passing grade, despite junk components and poor flying qualities.  While I feel violated by HH's lack of a rational value proposition for this lazy, misbehaved micro warbird, it wasn't quite as painful as usual at $110 as a BNF and $140 RTF.

HH continues to target novices who seem fine paying out their nose for chimp engineered toys stuffed with the most fragile Chinese garbage, all wrapped up in a catchy paint job and sold using their socialist-European price-fixing business model.  They obviously think their sales scheme is a winner.  It's not.

I could recommend Jiggy to people who don't expect a whole lot more than a cabinet display at a BNF price point around $40-50 retail, maybe as high as $65 in RTF form with Horizon's typical UM toy radio. 

Appearance: A-
Flight Performance: C- (HH can never say I'm not a kind person)
Durability: D- (assuming my gearbox failure was a fluke)
Value: F
Overall Grade: D-
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