The NRJ F3K is a new competition model from Anton Ovcharenko of OA Composites, with aerodynamic design by Christophe Bourdon. An NJR piloted by Pierre Meunier recently won the Nancy Cup in France.
The NRJ F3K project benefits from Anton and Christophe's vast experience of flying F3K events throughout Europe. Christophe started with careful observation about different model formulas and he has created a design that has realised the best overall DLG performance in currently available designs. Old DLG pilots have seen the impressive evolution in model weights, aspect ratios, speed range, launch height and of course manufacturing technologies. The NRJ (pronounced Energy) synthesises these improvements into a new state of the art model.
The NRJ flight style can be summarised as easy handling, excellent glide angle, good in slow speed situations, wide speed range, the ability to fly in wind without ballast due to keeping its energy so well. You can fly across large areas of sink and turbulences with improved stability, saving precious altitude. The combined structural optimisations (including one of the thinnest fuselages) and aerodynamic refinements result in a glider that uses the very minimum amount of energy, allowing longer flights more consistently from the launch and thermal energy available.
Aerodynamics Christophe Bourdon’s analysis is that in thermal flight, and for discus launched gliders in particular, we don't need so much camber on our airfoils. Camber consumes energy, wasting it in increased profile drag. As improving building technologies allow us to build lighter and lighter models it is logical to reduce the average airfoil camber and it is useful to morph the foils in other ways to tweak their shapes and lift-drag polars, especially at the wing tips with their critical lowest Reynolds number. Successfully achieving well attached flow at the tips has resulted in very forgiving handling qualities over the entire flight range, and especially very good slow flight and thermal climb capabilities.
The airfoil series has a thickness of 6.0% at the root down to 5.2% at the tips, with a good elliptic lift distribution, with no washout required. The airfoils were designed to keep the wing twisting moment (Cm) low and for it to change smoothly between speed and thermal flight conditions. This choice allows the glider’s speed to be changed easily without losing energy which is very useful in changeable flight conditions.
Easy To Fly With High Performance Because the well designed wing has smooth transitions from high speed to high lift working points the glider handles very progressively and is easier to tune to the pilot’s preferences. Also the flying techniques for obtaining full performance can be learned quickly and easily, even by average fliers.
The generous 7 degree dihedral allows small RC inputs to be used when maintaining thermal turns, minimising control drag. The special wing tip shape was chosen to help make the model more recognizable and thus easier to fly in crowded thermals as often found in competitions.
The NRJ may surprise some pilots because the wing working points were implemented in a unique way. However once the pilot adjusts to this flying becomes very natural and more relaxing than most high performance DLGs.
Kit Description The NRJ fuselage is very thin, to reduce weight and drag. However it conveniently incorporates a slip-on nosecone and a large opening for the RC. Instaling the radio gear is made even easier by the 3D printed servo mount. This is designed for KST X08 servos, though other servos can be fitted with a little extra work. The fuselage is carbon from the opening rearwards, but the very front is made from 2.4 Ghz friendly material so the receiver antennas can be safely installed internally. The rear of the fuselage has an underslung tail pylon ready molded in place. The fin and tailplane are extremely lightweight molded spread carbon jobs, and like the wing have an excellent surface finish.
The wings are beautifully molded with a thin airfoil, and large ailerons. Considering the light weigh it is very rigid and has a good finish. It is available in Light (CW40), Standard (CW40), and Strong (Textreme 60) layups. A ballast set is available for extending the performance envelope of the glider. The Light layup should only be flown with a max of 40 g of ballast, the Standard up to 60 g, and the Strong can take the full 98 g load.
The NRJ kit includes these accessories: 3D printed servo mount for 4 X08 servos, throwing blade, all control horns, and pushrods, wire for tail torque springs, pull cord wire and crimps, wing and tail screws. Like most high performance models no build instructions are included - most DLG modellers will already have the skills. See this RCGroups NRJ thread for build and flying info.
September 2019 Update: all models in stock use the latest V2 linkages and servo tray.
(C) 2019 Neil Stainton.
NRJ DLG Specifications
Wing span
1.5 m
59 in
Wing area
19.0 dm2
295 sq in
Length
96 cm
38.0 in
Flying weight from
198 g
7.0 oz
Wing loading
10.4 g/dm2
3.4 oz/sq ft
Aspect ratio
11.7
Wing airfoil
NRJ Series
Dihedral angle
7.0º
Centre of Gravity
64-66.5 mm from wing leading edge
Controls
Rudder, elevator, ailerons
NRJ DLG Ligh Layup Typical Weights
Fuselage
35 g
1.2 oz
Wing (light)
85 g
3.0 oz
Fin
4.5 g
0.2 oz
Tailplane
5.5 g
0.2 oz
Accessories
12 g
0.4 oz
Total structure
142 g
5.0 oz
Glue, mounts etc
2 g
0.1 oz
Receiver
5 g
0.2 oz
Tail servos
17 g
0.6 oz
Wing servos
17 g
0.6 oz
Battery
15 g
0.5 oz
Flying weight from
198 g
7.0 oz
Textreme wings are approx 10g heavier and tails 1g heavier.
Superb model from Anton. The finish on these planes is the best I’ve currently seen and I’ve tried a lot of other models, I have the strong layup and wing finish is like glass. And for a strong layup, my model still comes in at under 220g. Builds super fast, I had 80% of mine built with 2 hours of getting home from collecting.
The nose is a bit tight for space, but I can confirm that with a 350-380 sized 1s lipo that both the Spektrum ar410 (decased) and the Frsky G-RX6, RX4/6R fit nicely. With the Frsky rx’s you can get a 600mah gumstick shaped Turnigy Nanotech in there. Once released I will test the new Spektrum 6610T.
Overall a superb plane, coming from planes with 5.5 degrees of dihedral like Snipes, the handling takes a little getting used too, but I heard the same about the Flitz that Hyperflight also stock, but once you are comfortable with the plane it’s a serious weapon. The speed range of the NRJ is impressive too, pretty fast plane in Speed mode yet slows up nicely with 6mm camber and goes up in lift very well in this mode.
For me it took some time to bond with the plane but I would definitely buy another.