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Tuesday, August 30, 2011

Blade CX3 Flight Review

Update:  Downgraded to D+, see:  CX3 on 3S

Update:  I decided to try an aluminum swash to see if it improved the precision of the heli. While I had it apart, I manually balanced both sets of blades which were out of whack as shipped. To my pleasant surprise, the combination provided a big improvement in precision and handling.  I think part of that difference isn't the actual function of the swash plate, but fatigued plastic ball joints giving a little bit under the substantial force of normal flight.  Unfortunately, before I could enjoy the $20 upgrade, one of the shoulder pins on the lower head (which is plastic; the upper hub and shoulder pins are aluminum) sheared during a stabilized hover, making the heli vibrate moderately and perpetually drift right.  Looks like a another $15-$25 for an aluminum lower head.  And the CX3 is down again for maintenance.  

The good news is I'm convinced the copter can be made to handle much better than stock.+$40

I was never interested in the CX, CX2 or CX3 at $180, but recently I found a CX3 BNF version selling for $119 in my LHS (also on the web).  That did the trick, so I snagged one.  I'm happy I did.  Although this CX3 has about the same capability, and is overall less stable and more twitchy than my mCXs, I think the larger scale makes it more fun.
 I've never been in love with the MD 520N Police body that ships standand on the CX3, but after living with it a few days I like it better.  I tried to remove the "Police" sticker from the tail boom, but with a small corner peeled away, the sticker began to disintegrate, so I left it in place.
There are several compatible bodies available for the CX2 and CX3 available, they run $20 to $40 and include a Blackhawk and a classic Jet Ranger.
Looks aside, the CX3 advertises a few improvements over the CX2, namely a heading lock gyro, an AR6100e Rx, and an aluminum head. I don't have a CX2, so I can't compare to one of those.  But I do have several mCXs, and they are roughly 25% more stable in a hover than the CX3, and they seem about 40% more maneuverable due to the lighter mass.

The mCX also has better heading stability than the CX3 and is easier to trim out.  If the CX3 gyro has better heading control than the CX2, then I would not purchase a CX2 as the CX3 nose has a tendency to wander quite a bit, especially with power changes.  I suspect my upper and lower blades may not be well matched out of the box, causing the heading to drift a little with power changes, but I have yet to replace them so I'm not 100% sure.

The CX3 is also unique in that it has no tail boom integral to the helicopter frame, the boom is part of the body design.
All that said, even if you've never flown a decent RC helicopter, you are in for a treat.  The CX series is easy to fly in a reasonably large room inside your house.  The counter rotating coaxial design eliminates the need for a tail rotor to counter single rotor torque, and the long shaft results in a pendulum effect that inherently stabilizes the helicopter, somewhat similar to a high wing airplane's gravity-power tendency to return to level flight.

The fairly large size of the CX3 (13.6" rotor diameter) makes it a lot more impressive and less toyish than the mCX or mSR series, making it more fun.   At 8 oz flying weight, it is roughly 8x larger, but still not large enough to seriously injure some one.  The 8x larger size has the unpleasant affect of making your room feel smaller by about 1/2 in each linear dimension (= 1/8th scale) compared to more cooperative micros.  The CX3 is definitely more of a handful in any confined space.

Maneuvering the CX3 is straight forward and reasonably predictable.  The CX3 is too sensitive in yaw, and about right in pitch and roll.  A programmable radio with rates and exponential tailored for each axis makes a huge difference in how the helicopter handles and trims.  You'll want a DX6i or better.  Interestingly, the heli uses a proper receiver instead of incorporating an integral Rx in the motherboard, raising the possibility of using a better brand of Rx/Tx.  I might convert it later.

Durability seems good, but Quality Control is iffy.  My CX3 had a high frequency tail wobble right out of the box.  Horizon's site has posted a fix on their website to reduce the gyro gain, but I wasn't convinced it was a gain issue since it seemed inconsistent while holding the heli running in my hand.  Shaking the heli a little produced the gyrations, it seemed more like a loose gyro platform than a gain issue.  Taping the gyro firmly to the plastic shelf fixed the problem entirely, though the shelf where the gyro sits is weak and very pliable.

Another strange issue is the usual stance of the body.  The rotor shaft is canted backwards when the heli sits normally on its skids.  Why?  I don't know.  But it makes it harder to takeoff without drifting backwards, especially from a soft surface like a rug or cushion where the amount of forward control authority can't overcome the rearward vector.

This is a good first helicopter.  It is easy to fly, can take a hard crash or two, looks great in the air, has good flying time, and the price is marginal but acceptable.   If you are starting from scratch, or buying for someone less than mechanically inclined, the smart thing to do is forgo the larger scale CX3 and spend less on a smaller, lighter, less expensive, and better flying mCX.  But if you value a little more fun over frugality, go for a CX2 or CX3.

Appearance: B-
Good size and presence.  Selection of police body seems adolescent.

Flight Performance: B-
Stable design is not very maneuverable, nor designed to be.  mCX is better.

Build Quality/Durability: C
Gyro platform was loose out of the box.  Cheap swashplate.  Crash survivable.

Value:  C-
Nothing special at $119 BNF, but better than it used to be. Needs aluminum upgrades.

Overall Grade: B-
Cool factor is high for the money.  Not the best flyer its price range.
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