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Sunday, September 23, 2012

ST Model DG-1000 EPO Brushless Glider RxR 79"–Build & Flight Review


Update 9/23/2012:  The sailplane is ironed out and a wonderful, relaxing glider.  It has become one of my favorite planes. 

It is a much more efficient glider than my balsa and fiberglass E-Flight Ascent; the DG-1000 has a fantastic glide ratio.  The EPO foam has proven to be extremely strong (not that I’ve ever tested it, with a nice smooth finish.

I cut a 0.5” x 12” thin aluminum landing skid and attached it using double sided indoor/outdoor mounting tape to the underside of the fuselage.  The plane will actually do touch and goes off pavement, as well as takeoff from a standing start.

Average flight time from a 1300 mAh 3S is 25-30 minutes without thermals to ride.  The DG-1000 easily climbs above 1000+ AGL in just a few minutes of motor run time, confirmed with an altimeter, so be sure to use a great full range Rx. 

Landings are best accomplished from about a .25 mile flat final.  Deploy some spoilerons to lose altitude, but not airspeed.  When a few inches above pavement (or grass), slowly retract spoilerons and carefully begin to extend flaperons to hold a few inches of altitude while slowing slow the DG to a lightly skimming straight skid to a stop in about 10 feet.  The wing tips stay level, and the plane usually stops on pavement with both tips still in the air.

My view is that this plane is well worth the hassle of adding metal gear servos, a workable ESC and a dedicated BEC.


Update 9/9/2012:  Once fitted with all new electronics (only the stock motor remains) and set-up with some trial and error, the DG-1000 is a fantastic sailplane. 

It’s a tough call to buy it for the airframe since the electronics change-out is not easy, especially the aileron servos which need to be soldered onto the existing leads.  For those who don’t mind the challenge, the retracted motor design makes for exceptionally clean soaring.

Circling with some Buzzards (motor retracted) - thermals took the sail plane up to visual limits, along with the birds.  Flight time was 55 minutes on a 1300 mAh 3S.

The following setup seems to be ideal:

- CG (motor in) on rearmost wing screws
- Switch X (on): 
     - Motor Extended (out)
     - Elevator Mix 15% Up (flat offset curve)
- Switch X (off):
     -
Motor Retracted (in) with 4 second servo travel slow down
     - Throttle Hold at 0%
     - Elevator Mix Normal
- ESC Brake – Off

INTRO                                                                                       

As Z8RC regulars know, I tend to like and thus review aviation classics.  I strayed a little from that philosophy my review of the Hobby King Deamon based on the potential of the airframe to produce an screamin’ 100mph+ sailplane.  Come to think of it, my E-Flight Ascent review wasn’t exactly a scale classic, either.

This review gets me back on the classic airplane track!

overview

I apologize in advance to those who’ve asked for a Parkzone Radian review.  I thought about it.  In the end, the ST Model(s?) sailplane offered a sport scale classic in a more interesting 6 channel package, with a retractable motor and dual ailerons allowing spoilerons.  The Radian seems less interesting with only 3 channels and a non-scale airframe, both of which are hard to swallow given my 3 ch non-scale Ascent. 

The ST DG-1000 RxR/PnP goes for around $120 street, the similarly sized 3 channel PZ Radian PnP is price-fixed by Horizon Hobby at $160 street.  The generally less well received 5 channel Radian Pro PnP sells for $185 street. 

The DG-1000 is more feature packed.  For one thing, you get a gorgeous scale body.  Another is ST Model’s retractable motor system (called RMS in most ads, but is called RPS on the box top), although it clearly impacts WCL (6.3) and it looks a little Rube Goldberg-ish from a reliability point of view. 

Then again, folding props are notorious finicky to set up, ESC-brakes vary in capability and consume power, they are hard to balance and often don’t fold cleanly.  Even when they are at the top of their game, folding props aren’t as streamlined and get beat up in landings.   Another plus for the RMS is that a windmill can be inserted into the airstream (ESC brake – off) to work as an effective speed brake.

I have no idea how the ST DG-1000 is going to work out, if not so great, maybe the Radian will get a chance to play after all. 

SPECS
-
Wingspan
: 79.1" (2010mm)
- Length: 38.2" (970mm)
- Flying Weight: 36.5oz (750g)
- Wing Area: 348.7 sq in (22.5 sq dm)
- Wing Loading: 10.9 oz/sq ft (33.3 g/sq dm)
- Wing Cube Loading: 9.6

  Gliders - 1 to 5
  Trainers - 5 to 8
  Aerobatic - 8 to 11 
<--ST Models DG-1000 = 9.6
  Scale - 11 to 15
  Racers - 15 and over

Fortunately, the manufacturer can’t do basic math.  Here are the true, measured numbers including the following upgrades:  25A ESC, Castle 10A BEC, 4 x Metal Gear servos, removal 1.3 oz of nose ballast…

- Wing Area: 434 square inches
- Flying Weight:  33.1 oz (including a 4.0 oz 1250 mAh 3S LiPo)
- Wing Loading: 10.9 oz/sq ft (the blind squirrel found a nut!)
- Wing Cube Loading: 6.3

  Gliders - 1 to 5
  Trainers - 5 to 8 <--ST Models DG-1000 = 6.3
  Aerobatic - 8 to 11
  Scale - 11 to 15
  Racers - 15 and over

FEATURES 
- RMS (Retractable Motor System)
- EPO foam construction

REQUIRES
- Receiver
- 1300 mAh 3S LiPo

PAID
- $120 (with Towerhobbies’ standard coupon)

UPGRADES
- NA

ON THE GROUND                                                                   

UNBOXING

boxinsideboxallrightspec
APPEARANCE / FIT N FINISH
 
 

The first thing I noticed about the appearance of the sail is the foam coloration.  There is no paint, just raw EPO.  The foam is white enough, but there were dirty marks in a lot of places, indicating the working environment in ST’s sweat shop probably doesn’t meet OSHA minimums, and giving the glider a 10% used look, right out of the box.  Paint is always an option, but it adds significant weight.

ST’s EPO foam is the traditional, incredibly strong type, not like Horizon’s soft and spongy, relatively weak “Z Foam.”  The surface finish is pretty hard and very smooth.  If painted, it would be hard to tell if the glider was foam or fiberglass from 5 feet away.

batterybaytail
The major pieces fit together beautifully.  The only trick is to make sure the ESC wires don’t get pinched between wing halves as you push the wings in, or they won’t quite squeeze all the way together.  The wings get a screw in the bottom which clamps the main carbon fiber spar, so there is no danger of the wings sliding out in flight.

The glider is a true RxR, all the servos are installed, as are all the pushrods and clevises.  The only link that has to be made is to thread the elevator’s control horn on the pushrod’s z-bend as you secure it with a single screw.  Assembling the big chunks is a breeze.  Total time to flight ready, minus receiver set-up, is about 10 minutes.  Fantastic.

BUILD QUALITY/SETUP

Receiver and battery installation, is where the fun stopped.

The receiver install was straight forward, including the automated retractable motor system.  The retractable pylon is operated by a full size servo, and is implemented just like a landing gear servo and is appropriately labeled “Channel 5.”

There is a custom sequencer board that intercepts the ESC and motor pylon servo, with an input and output for each, including tiny pots for making end point adjustments (EPA).  It worked, though I have no idea what’s going on inside the mind of the custom board.  I prefer less magic.  What if the custom board goes “Poof!”   Then what?

I plugged in the battery, and… no motor arming, but the flight control servos worked.  Unplugged and jiggled stuff, plugged back in, and, nothing.  The heavy accent Chinese instructions were no help. 

On a whim, I input put full down trim into the throttle.  “Dooo dweeet,” the motor armed after about 5 clicks of throttle-down trim.  The magic board’s EPA pot calibration is probably to blame. 

Once armed, the motor worked well and was tremendously strong near full throttle—which I decided to forgo until airborne, since the pylon looked a little stressed under all the static thrust.

After tucking the motor in, something smelled funny.  You know, that servo or ESC is burning smell.  I popped off the nicely executed, chunky, positive snapping battery hatch to see what was going on while I pulled the battery.  Battery out, more smoke.  Uh oh.  

Fortunately, the fire turned out to be the ESC that burned to a charcoal crisp (fortunate because I keep a stock of ESCs on hand).  But yikes.   That’s Made in China for you.

I have a rule here on Z8RC:  If a plane burns during a review, it get’s an F overall.  So that makes the overall grade easy.

What wasn’t so easy was replacing the ESC, since it was installed before the fuselage halves were factory glued together.  After snipping all the wires to it, the crispy critter finally ripped out, still smoking.

New ESC installed; on came the battery.  Nothing.  The green LED on the magic board was no longer lit.  Bypassing the custom board worked 100%.  I guess when the ESC went “Poof!” so did the custom mixing board.  Now what?

Disgusted, I walked away and did what I do best, thought for a while. 

A solution hit me: make the switch to retract the motor a throttle cut-off switch and put a servo speed delay in the retraction to allow the motor to spin down, catch the physical prop brake, and stow cleanly.

Ta da!  Works better than the original set up.   After some experimentation, a 4 second retraction and instant extension seemed to work best.

That’s when I noticed the rudder servo quit. The rudder and elevator servos were also installed before the plane halves were glued.  Rather than tear the plywood mounting bracket out of the plane to access the servo screws (both fuse servos are mounted to the plywood from the bottom, and sit nearly flush against the keel), I decided to take a different route.  I cut a servo access hatch in the bottom of the fuselage.  Both servos replaced with metal gear digitals after about 15 minutes.

Done.

That’s when the spring on the motor hatch door went “poing” and literally vanished from planet Earth.  Rubber bands installed, again, better overall function than the original config.

Finally, the glider was RTF.  It looks awesome.  The instructions were right about one thing: “if you take your time, you will wind up with a well built model.”

Crispy

Uhg. 

GROUND ISSUES
- ESC caught fire with the throttle in idle
- Dead RMS sequencer board (probably killed by the ESC short)
- Dead rudder servo (probably killed by the ESC short)
- Motor hatch doors are finicky; one of the springs flew off into a Wormhole.  It emerged in a Quasar some 12 billion light years away.  Unusable.

IN THE AIR                                                                              

BLUF

An excellent slope soaring airframe packaged with the worst electronics seen to date. 

Grass
GENERAL CONTROL

Once all of the servos were replaced with metal gears, the DG-1000 is a joy to fly.

The sailplane is designed for high efficiency wings-level flight, and consequently does not roll well.  Mixing 50% pro-rudder with aileron is very helpful for effective general control.

The various configurations of the sailplane take some getting used to, but are entirely predictable.  Generalizing on each basic config:

  • Motor retracted – great slope soaring character; light nose.  Excellent wind penetration.
  • Motor extended, low power – quiet, level+ flight; barely sips the battery.
  • Motor extended, high power – strong climbs or reasonably fast passes (the manual claims 60 mph+; looks about right)
  • Motor retracted, spoilers up – slightly nose high, high drag descents; easy landings
  • Motor extended, spoilers up – high alpha slow flight possible.

    BALANCE & AEROBATICS

    Loops can be large with impressive speed in the dives.  Barrel rolls are a little strained.  Axial aileron rolls are not in the model’s portfolio. 

    Balance is more interesting than normal, since the retractable pylon shifts motor weight substantially. 

    It makes sense to balance the plane for best glide performance with the motor retracted.  With the motor collapsed, the nose feels light and airy with the rearmost CG possible. 

    When the motor pops up, the CG becomes slightly nose heavy.  Applying a lot of power drives the nose down somewhat, given the high mount of the thrust line.  The sailplane has a strong tendency to climb as airspeed builds, so the motor-up/power-up flight character generally holds level as power is applied.  If you gun the throttle in the bottom half of the airspeed envelope, the motor will actually drive the DG-1000 downhill until enough speed accumulates and the bird transitions into an arcing, strong climb.

    Video shows a 1300 mAH 3S:



    cockpit
    POWER SYSTEM

    The retractable motor system was a pleasant surprise.  After some setup time to compensate for the dead, magic sequencing board, the RMS worked very well in the air. 

    That said, I initially experienced two glitches; both were easily and fully solved.

  • The motor occasional failed to pop up, caused by a tight fit between the motor housing and the walls of the engine bay.   Changing my Castle BEC voltage to 5.9V from the 4.8V default fixed the problem completely.  I strongly recommend a BEC given this power-hungry servo and the large control surfaces.**
  • The prop would occasionally stop sideways, causing the pylon to stop short of full retraction as a horizontal prop caught on the motor bay doors.  Removing the ESC brake allowed the prop to windmill until it caught the rubber brake, every time.

    ** Because the full sized pylon extension servo needs 6V to pop up reliably under load, causing a power high drain on the servo bus along with a motor spool up load and potentially large control surface loads on the servos, this DG-1000 should not be used in stock form with Spectrum/JR radio systems.  It will brownout the Rx and drop the link. 

    ADVANCED HANDLING CHARACTERISTICS

    NA

    APPROACH & LANDING

    Easy landings are aided by a nice decent rate with spoilerons extended. 

    Motor-up and wind milling is another high drag landing option,even with spoilerons up.  This landing config has the added benefit of easy go arounds or energy adjustments.  Still, I prefer spoilers up and motor closed, because it is easy to mildly cartwheel big gliders as they eventually lower a wingtip into the grass or pavement; having the motor up would seem to increase the likelihood of damage from side loads.


    IN-FLIGHT ISSUES

    1. Servos glitched without a dedicated 6V BEC

    2. Tail plane was cockeyed due to warped vertical stabilizer, possibly due to heat during shipping.  A carbon fiber poker, coated with gorilla glue, jammed up the DG’s tail inside the foam straightened it out.  That’ll teach it.

    3. One cheap aileron servo died on the first flight from gear slippage.  Replacing the aileron servos required snipping the servo leads and splicing-on a servo plug, since the existing plug is permanently embedded inside the wing.  Change all 4 servos to metal gear before flying.

    4. Motor pylon resonance was present at high throttle settings at low or no airspeed.  Reinforcement with  acarbon fiber truss solved the problem.  Additionally, the nose-down moment of the extended motor is best combated with low power settings at low speeds, including during hand launching (40-50% throttle works well; see video).

    OVERALL

    Once ironed-out, the DG-1000 is a blast to fly and sure to become one of my favorites, especially in high wind.  The RMS is a unique feature that adds a lot of utility and another level of required mastery, as the CG shifts and the high thrust line demands elevator anticipation and finesse.  

    The question is: how much ironing-out is required? 

    Answer: a lot!  All of the electronics have to be replaced before flying and a 6V capable BEC must be added.  Replacing the aileron servos is not plug and play since they have to be spliced-in. 

    The sailplane had no trouble handling todays 20 Gust 40 mph winds.  Nothing else I own could’ve flown today, with the exception of the HK Deamon but it is less stable.  Really quite amazing.

    GRADES                                                                           

    Appearance: A+
    Classic DG-1000 lines and proportions.  Well done. 

    Aerodynamics: A
    Quick.  Excellent slope soaring and wind penetration.  Best flown wings-level; poor roll agility.  WCL is a little on the high side.

    Power System: A
    Surprisingly strong motor.  RMS works very well but requires 6V servo bus voltage.  25 min flight times on a 1000 mAh 3S. 

    Build Quality/Durability: F
    Worst electronic component quality seen to date.  Super strong EPO airframe is almost worth the hassle.

    Value:  D
    Consider the low price an airframe kit (not a PNP) with a motor included.  The high level of completion goes unrealized.

    Overall Grade:  F
    Super-fun sailplane, when a servo isn’t slipping or the ESC on fire.

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