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Thursday, October 25, 2018

Review: Judge F3B from Duffek model

Judge F3B from Duffek model

by Sylvain Coulomb

A new glider called Judge appears in May 2018. Look and design is close to most recent available toys (Pike 2, Pitbull 2). Little information available on design made by Jan Stonavsky and Duffek model:
  • Wingspan - 2980mm
  • Length - 1468mm
  • Wing area - 56,82 dm2
  • V-tail area (proj.) - 5,65 dm2
  • FAI area - 62,47 dm2
  • Weight - 1850 - 4685g
  • Wing loading - 30-75/dm2

After a first contact, I decided to make F3B version testing for next World Championship as an economic alternative to other very expensive gliders. I am helped by Julien Gourdet, our first French representative pilot for Jesenik 2019.
Data are available at http://www.duffek-model.cz/cz/index.php/kontakt-2
Duffek Model is close to Vaclav (Stinger, Sonic…) and they seems to share reasonable and fair commercial vision.
Filip Kalensky has done a great job to present F3F version, installation and setup at https://www.rcgroups.com/forums/showthread.php?3088222-Judge-f3f-f3b
Website says: This model is fabricated in diverse strength variants of the best composite materials. The model is an excellent competition machine for all types of weather conditions. Perfectly holds the selected flying line in a turbulent environment and, thanks to aerodynamic purity, has a high penetration rate in the wind. At high surface loads it retains good dexterity.
Our test is there to present F3B potential of the Judge and verify designer assertions, F3F information coming by Filip.
So I ordered the F3B Light version presented in this article. (And also a standard one not presented here). Both delivered with hook not supplied for F3F.

Parts weight :

  • Left wing : 600 g
  • Right wing : 602 g
  • Fuse : 206 g (with command)
  • conus :   34 g
  • Elevator L :   34 g
  • Elevator R:            32 g
  • Joiner : 125 g 
  • Accessories :   25 g
  • Supplied nose brass : 110 g

After installation, wiring and CG adjustment (102.8), empty flying weight is 2040g witch is very correct for F3B even if some models could be lighter. 
Model examination:
No particular remarks on manufacturing. Quality is equivalent to most high quality gliders (Baudis model, Samba…).
Some improvements have to be made and should be fixed shortly by Duffek models:
  • Servo caches are too small so I replaced them by transparent PVC  (I suppose an error easy to fix)
  • LDS system screw still delivered with MKS size and should be for KSTX10
  • Fuselage commands good for F3F replaced by me with lighter one to save back weight 
Actually the model is delivered without ballasts and wires, with wings and elevator bags. 
Prices are to be checked with manufacturer but are around 1500€ for the 3 versions.
I decided to mount available MKS servos but Judge is done for KSTX10. Both brands will fit in. LDS installation is easy but need attention before gluing servo supports.
Filip installation is on line so; I don’t develop except light changes.

I soldered LI-ION batteries with long wires to install them one by one with no change in existing holes to keep fuselage as is. No space problem to add servos, Zepsus, batteries, cables…
I hesitate to add ballast tube and forget it for this one. In distance, it could be interesting to quickly modify weight with no time to dismount wings.
So, in less than 8 hours, it was ready to fly … waiting for good weather!
Personal ballasts set:
I took an option with 4*40 g in the front 4*110g in the back in order to move CG backward if it fit after tests. Otherwise, I will reduce weight of back ones.  Front are 10*10, back are 20*12, Joiners are 8*8 … All this is adjustable depending of your habits and set up. For sure, it is possible to add more than 1800g ballast even if not so frequent for F3B.

Preliminary flight tests:
As a glider is long to set up, preliminary feeling will be confirmed in some flying sessions.
Two sessions were held on slope with poor conditions (no front wind) to verify CG and first command rates. Then we could test on field which is this version target.

Saturday October 20/ wind around 17km/h/sunny

Empty CG 102.9 2070g Distance light 103.2 /2500g Hook at 103 from leading edge.
First launch: not enough elevators (safety) ... so bad launch but Judge seems rigid and good zoom --> already average high compared to others
Second: nearly perfect, easy to drive and high altitude ... quite impressive because we have certainly better set up to test!
All day long: adjustments (differential flaps ...). Very good feeling and apparent stiffness
After adjustments: performance is there, quite easy to adjust everything to place the model where and how (attitude) you want. 
Butterfly is easy to manage with very good stability. Smooth landing with adjustable speed/distance to stop in target. 

Sunday October 21: Contest/wind around 13/15 km/h Conditions less good than Saturday on thermal standpoint.

We decided to have Julien flying the contest with Judge (and my TX) after problem on FS3 servo. He had launching difficulties all the day due to switches position on my TX ... so altitude and results could have been easily better with his own material.

Even though, he won all his durations, distances (3 To 5 laps more than others); and makes good speed (better and better time to adjust) including a 1000 in one round. 

Confirmation of Duffek model website:
  • Strongest parameter seems "facility" quite rare with an unknown new machine.
  • Second is clearly performance in distance and turning facility and precision (you really can choose your turn style depending on speed/conditions/ballast). Distance is really a pleasure and good cadence is easy to maintain. Julien liked it!  Setup to improve and maybe 102.8 better than 103.2 (little bit touchy - to be confirmed)
  • Speed to be confirmed but promising (Julien didn't ballast too much for first tests with a friend’s materiel)
Without the first 0 with FS3 servo trouble on duration, Julien would have been 2° at 5 point from the first. For a first test we couldn’t expect more!
Global balance is really positive.

Some points to check for potential improvement:
  •  Not really checked: Stiffness. Model seems quite stiff enough but has to be confirmed with more ballast. No bad feeling at this point because we made some "hard" zoom during set up and nothing bend ... To be confirmed in hard conditions.
  • Light F3B version is really much optimized and skin is really thin (60g carbon). This could be a concern close to the joiner because you need to be careful during wing mount to prevent fingers marks. High level pilots are used to and prefer to save weight. Normal pilots would probably prefer standard version for better model life. Weight increase is not really a problem with model duration capacities. Discussions are in progress with Duffek in order to add one more layer on the wings first 20 cm to definitively prevent the fingers marks risks.


Still confirmation to wait after more flight time but really a pleasant, easy (and performing) model compared to current models we have (FS3, Pike 2, Device) in the team. For sure, it will be long to confirm because high level performance is reached by best pilots after month of setup and flight hours but for normal good pilots like me, Judge is already a model better than my own flying skills limits.

Have fun and good flight, 



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