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Sunday, January 29, 2012

Dynam A-10 EDF RTF - Flight Review

I picked up this cool 42" Dynam 72 MHz Hog for less than $120, a few bucks cheaper than the PnP version.  Nothing my 2.4 GHz Rx spares drawer can't fix in 15 seconds or less.

Some of these photos look flat, but the finish is a moderate gloss.  It is depicted most accurately in the first shot:
Hmmm... no packing material.  The tail surfaces 
in the smaller boxes are also free floating.
The 72Mhz transmitter carries negative value.  Yay!
Dynam provided a high level of completion out of the box, the
model is sold as an RTF.  The paint could be a bit less mottled,
in places, but overall the finish looks very good for the price.
Paint chip from sliding around during shipping.
Minor crash damage in the box due to no packing material.
The business end looks good. 

At $119 for a 42.5" wingspan, twin 64mm (including a nice 72 MHz Tx and Rx), this jet seems well priced relative to competition.  Banana Hobby sells a 1 inch smaller twin 64mm A-10 for $165 including retracts and a right-size 2500 mAh 3S battery.  In more mainstream models, the old Parkzone Habu 15 size foam EDF jet with a single 69mm fan used to have a street price around $240 as a PnP. 

The electronics kit includes two 40A ESCs, pre-soldered to work as a unit from a single battery.  Both ESCs provide power to your choice of Rx via a custom reverse-Y connector, doubling your BEC Amps and presumably reliability.  The ailerons are each powered by individual servos and come attached to the receiver through a Y-connector by default.  The elevator push rod has to be attached to a pre-installed servo in the tail, same with the nosewheel steering to a pre-installed rudder servo.  There is no rudder control surface attached to the rudder servo, leaving room for improvement.

The fans were well balanced from the factory, so nothing special had to be done to get the jet in the air.  Thrust to weight ratio is high for an EDF jet, barely above 1:1 with the included 3S 2200 mAh 20C, but the smallish battery gets very hot supplying both of the fans at full stroke.  Flights with a 3000 mAh 40C resulted in a noticeably faster higher top end speed and a cool battery bay after landing.

I did my usual foam improvement mods to the jet before taxing out.  

The only non-standard mod I recommend is to open up some battery bay cooling airflow, especially when running the over-taxed included battery.  It might be smart to embed a carbon fiber main spar into the strong but very flexible wing.  The aft half of the fuselage seems like it could be a weak point, the foam fuse thins where the motors attach, so I used Gorilla Glue to glue the entire plane up even where only screws were specified.   No worries, this way.

Another possible mod is to mix differential thrust for rudder.  But that would require more prep time that I wanted to spend on a calm wind day.

One required tweak is to bend each landing gear outward about 10 degrees like a tripod, otherwise the plane is uncontrollable on the ground due to each flexing in different directions as speed builds.  

In the air:

Once the gear was pre-stressed, the jet had no problem jumping into the air after a shorter than usual EDF take off roll.  It's a little bit odd using the rudder stick for NWS only, I need to subtract a few points for that.  With the addition of larger wheels, the high engines would make this an ideal Forward Operating Base RC airplane, just like the real thing.

The jet climbed out strong and trimmed up quickly.  Once in trim, the A-10 makes for a simple hands-off flyer and a surprisingly capable glider.    CG tests were spot-on with the battery velco'd about an inch back from full forward position, leaving plenty of room for larger batteries positioned more aft.  Nice.

Even without a rudder, the jet was very controllable and quite maneuverable.  The small elevator surface made me wonder on the ground, but it became immediately apparent that the elevator is very effective in this jet.  It might be picking up a little thrust vectoring.  Aileron rolls were quick and positive at 125% throw.

The jet slows down nicely, and the straight wing stall characteristic are benign for a jet.  On the other end of the thrust curve, the plane is suprisingly fast for its somewhat stubby profile, once a larger 40C battery is under the cockpit.  It looks great in the air.

All in all, this A-10 would make a great first jet, while supplying plenty of fun for any skill level.  EDFs aren't as responsive as props, so although this airframe is docile and stable enough to serve as an great aileron trainer, the thrust curve is a little too flat to pull (push) beginners out of corners.  Additionally, the lack of an aerodynamic rudder can get a little tricky on take off, plus complicates and delays spin recovery.

Great price, great fun.  Time for grades:

Appearance: B-
Great presence.  Minor paint pitting. Two shipping dings.  Dainty gear.

Airframe:  B+
Maneuverable when pushed, otherwise trainer-like.  No aerodynamic rudder.

Power System: A-
Great push.  Good speed.  Fans aren't super responsive.   Stressed stock battery.

Build Quality/Durability:
Nice EPO foam with some flex, needs carbon.  Big battery bay and positive hatch. 

Value:  A
Low price makes up for a few finishing flaws and dainty landing gear.

Overall Grade:
Flight characteristics and value help overlook imperfect finish & weak battery.

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