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Monday, July 18, 2011

E-Flite UMX Sbach 342 BNF Review


E-Flite's latest UMX is the Sbach 342 mono-wing aerobat. It looks damn fun.  Is it?
The Sbach is the first in the UMX series to include side force 
generators.  There are two sets included with the model, adding 
almost a penny of extra foam at no extra charge.
In typical E-Flight fashion, they've priced the UMXS342 like an unwatchable rerun of the Twilight Zone.  For $170 you get a 4ch micro-foamie, a 180mAh 2-cell chicklet battery, 2 pairs of die cut foam slip-on side force generators, and a 12V DC charger with no AC power cord so you cannot plug it in. Plugging in the battery charger will run you another $20.  The battery uses a proprietary 2S connector, so you'll need to buy another at about $20 street price.  Total cost to operate: around $210, before adding a transmitter.
But I'm willing to fly anything for the betterment of the Human race, so let's have a look.  Trust me, I'll let you know if the little guy is worth the money.  Unlike every other review you'll find on the sleazy RC sales forums, Horizon Hobby hasn't paid me to regurgitate a mandatory glowing review. 
The Scotch tape holding the plane together looks 
like it was applied by a 5 year old.
Black is one of the better colors to maintain a visual in the air.  
This is a nice contrasty color scheme.
The engine bay is reminiscent of the UMX Beast.  But E-flight
has included a 180mAH battery this time, instead of 120mAh,
making the $170 price tag a few percent less ridiculous.

It would be nice to fly the Sbach indoors, but like the Beast,
it will need a very large indoor venue
There's no doubt the Sbach 342 is a nice looking microbat.  My guess is, if you knew nothing about RC, you might peg the plane's price at $30 or $40, certainly not near the $170 that it'll carve out of your wallet. But I'm immune to E-flight's utter lack of self awareness at this point.

Unlike most of E-flight's UM(X) offerings, the Sbach has a molded airfoil cross section, more similar is the lack of structural reinforcement.  The control surfaces are exceptionally over-size, with the aileron consuming almost a third of the wing area, and the elevator and rudder consuming about 2/3rds of their respective stabilizer area.  The servos are the usual exposed PCB, linear travel, Rube Goldberg specials, with the plastic gears all set to scrape pavement resulting in instant death.  I might be teachable, and fashion some sort of protector before leaping above terra firma and landing in Horizon Hobby's overpriced parts isle.

Predicted usable lifespan: less than a month in the hands of a careful expert.
The plane's weight seems reasonable for its power system, which was lifted from the solidly aerobatic UMX Beast.  The Sbach weighs with a battery at 66 grams, or a touch over 2.3 oz, that's about 0.1 oz heavier than it's Beastie brother.  The additional weight is more than accounted for by it's 50% larger stock battery, which weighs 0.5 oz. Thrust to weight ratio should be the same at 1.3 to 1, at least for the first minute of flight or so.

Before we fly this whirling dervish, E-Flight's stratospheric pricing mandates a look at the broader market:

This gorgeous 39" span Hobby King Sbach 342 runs:

Quantity Product description Price Weight

Sbach 342 1000mm Balsa (ARF)
$85.99 2299

TURNIGY Basic 25A v3.1 Speed Controller $15.01 45

Turnigy 1300mAh 3S 25C Lipo Pack $19.98 350

HK-933MG Digital MG Servo 2.0k.. $33.44 140

Spin-40-4 - Spinner 40diam / 4mm shaft $3.42 29

Turnigy Park450 Brushless Outrunner 890k.. $13.05 119

Turnigy balancer & Charger 2S-3S $4.49 99

OrangeRx Spektrum DSM2 6Ch 2.4Ghz Rx $5.99 39
Total: $181.37 3120g

 Air Parcel (UNITED STATES) - $36.54
Your Total $208.38

Let's see that's 3120g vs. 66g.  In pre-built balsa and plywood, not foam.  In standard 3S, not proprietary 2S.  And in 6ch, not 4ch, with dual ailerons, not a Y-connection.  With a brushless 28mm, not a toy 8mm.  Has E-Flite gone bonkers?  Crooked scotch tape?  Really? 

This Extra 330 is $119 sold as an RTF, 
plus you get this great looking girl
Hey, is that an AC Adapter?
Flight review here, soon.  Here is a pretty lousy video of my Sbach's maiden voyage.  Unlike most of the maiden videos on the web, this actually is the maiden flight.  
Given how nose heavy E-Flite shipped their UMX Beast, I decided to use the Beast's 120mAH battery, it balance at the 25% chord mark.  The plane was perfectly balanced in the air with the lighter battery. 

The 120mAh battery flown in the video had been laying around a while and obviously wasn't fully charged.  Subsequent flights last about 8 mins with the 120mAh and as long as 12 mins with the included 180mAh.  The plane flies better on the smaller battery and unlike the draggy UMX Beast, the Sbach does not need the additional battery capacity.  It's another E-Flite miss on included standard equipment due to an unsophisticated understanding of basic aerodynamic trades.  It's not a big deal, the plane flies fine with the heavier nose and may be more suitable for the targeted amateur demographic, but the plane will be a stretch for beginners so if that was E-Flite's idea it makes little sense.

The UMX Sbach flew terrific right out of the box and is definitely suitable for intermediate fliers.  It takes a bit of rudder attention to keep the plane pointed where you want it to go, and it can hang on the motor, but the plane is very docile for an ultimate aerobat and can be slowed down a lot on about 45% power.  I started with 50% travel/50% expo for my initial low rates, but could have went with 60%/60% while retaining a bit of under-control.  100% throw is not outrageous, but rolls are quick.

What look like snap rolls (i.e. rudder induced auto-rotation) in the E-flight demo video (at 1:13) are actually quick and easy full rate aileron rolls.  Obviously, there is significant roll coupling due to the off-axis low wing.  But that only detracts from purists issuing grades, not from the fun of flying.

The 342 performed basic loop and rool aerobatics without issue, with the exception of roll coupling  from the asymmetrical wing placement (not on the thrust line or the longitudinal axis).  Full rate rolls are very fast, and loops can be very tight until the wings stall and roll out.  Inverted flight is good, with light down elevator required with the lighter battery, and moderate down input with the heavier battery.

Knife edge flight cannot be maintained in the base configuration, but is easily sustained with the SFGs on the wing tips.  The SFGs have a stabilizing effect in general, and make the plane a little lazier which some will find both more relaxing.

3D type maneuvers, including hovers are a challenge for such a tiny Reynolds Number, but the Sbach is as controllable on the prop as any micro I've flown.  Unfortunately, it stretches it's legs quite a bit and consumes a lot of airspace for a tiny plane, which will make ultra calm winds of indoor venues more difficult to enjoy.

The mini Pitts M12 Beast has the same big airspace footprint, is more toss-able, but not nearly as precise.   It is better on a knife edge, but not once the SFGs are attached.  The Beast is easier to slow down, and seems to have lower wing loading even if it is more nose heavy.

Slow speed flight is very possible with the Sbach, but will be more exploitable with considerable experience balancing high AoA with high power with required rudder--as torque becomes a dominant influence at lower airspeeds.  It's not a big wing floater, it hangs on the prop to go slow.

Thrust is copious.  No need for more, and that is saying a lot in my book.  At the same time, the nose is not too heavy and flight times are good at 8-12 minutes depending on a combination of battery size and throttle management.  The prop seems like a good choice, but I have a few GWS props in mind that might translate some of that long flight time into more performance.

Landing is about as easy as a micro gets due to the high alpha margin for error, fairly docile flight characteristics, and a well balanced glide especially with the 120mAh battery.

The UMX Sbach 342 is a great little airplane.  What a shame that it is so painful to purchase, especially when there is so much fabulous full size competition in it's price range.  Final grades are pretty easy:

Value: D+ (high price tag, lower priced competition, but great micro performance)
Build Quality/Durability: D (a bit more beefy than other unsatisfactory E-Flite micros)
Performance: A (more like an A- but with bonus points for great handling SFGs)
Overall: B+ (Recommended-  if you are stupid enough to break out $200)

Yes.  It is damn fun.
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