Review of the Stribog from RTGModel

Introduction 

RTGModel (Milan Demčišák) released in 2016 his brand new flagship the STRIBOG. This is the successor of the Rotmilan Midi and the latest F3F glider of a family that started with the Extreme, then the Rotmilan followed by a smaller version with the Rotmilan Midi and it features some nice evolutions.  According to Wikipedia, "Stribog" is the god and spirit of the winds, sky and air. He is said to be the ancestor (grandfather) of the winds of the eight directions. The Stribog from RTGmodel has a 2.86 m wingspan which is ideally suited for F3F and slope soaring. 

What is new?

There are several interesting improvements or modifications that I wanted to highlight below: Wing section is a HN airfoil (Norbert Habe) but different from the Rotmilan Serie. It seems to have higher camber. I don't have unfortunately much detail as manufacturers are generally reluctant to communicate around this topic. The tail section is thinner. Particular flap shape with a smaller flap chord at the root: After exchanging with Milan I understand that the objective with the flap shape was to reduce the turbulence near the fuselage and, as a side effect improve the efficiency of the V-tail. Another advantage is that when down, the flap are not exceeding the bottom of the fuselage, limiting or avoiding damages if you forgot to retract them when touching the ground. Ailerons are running all the way out to the wingtip for better agility and maneuverability. The servos location is very different. Both flap and aileron servos are now very close to each other at the middle of the wing with a single servo cover. My guess for the flap servo location is that the objective was to control the flap at its largest chord.

Full photo album about the kit overview: here

RTGModel can provide a nice LDS option with counter bearing for a slop free control. It is noticeable that the fuselage is the one of the Rotmilan Midi, without modifications as you can see at the tail plane root. The fuselage uses the same convenient layout and features a canopy, a molded servo tray, a fuselage ballast tube, all pre-installed. The front of the fuselage till the end of the elevator servos is fiberglass and Kevlar, and then we can see the carbon fabric from this point. Molding quality is as usual with Milan Demčišák top notch, with perfect fit and alignment of all elements together, very thin join lines, nice paint, etc ... A very nice plane and kit, no doubt. 

Component weights are the following:

• Left Wing (with servo frames in place): 619gr 
• Right Wing (with servo frames in place): 614gr 
• Fuselage with canopy: 371 gr 
• Left Tail including the joiner: 41gr 
• Right Tail including the joiner: 41gr 
• Joiner: 84gr 
• Total: 1770gr 
• Ballast: 895 gr

Assembly

I usually starts the assembly by the wings. This time, as the frames were already installed, I just needed to screw the 2 MKS HBL6625 in place with the correct neutral position, the control rod being fix length. The external counter bearing makes the installation very tight and slop free. The servos is easily accessible and removable if needed. 

The fuselage being the same as the Rotmilan, layout is therefore the same. The most difficult operation is the wire routing which need some patience and care to be done properly. Here is how I proceeded: I succeeded to pass 2 x3 wires on each side of the ballast tube. I first prepare the cable on the servos side, with the JR/Futaba connector. Then, from the joiner hole, I used a flexible plastic rod that I passed along the ballast tube up to the nose; I tape 1x 3 wires to it, and pull. Then I repeat the operation 3 times, 2 servo cables on one side, 2 on the other side. Then I can complete the routing to the plug hole and solder the green plug on hit. To maintain the cables in place along the ballast tube, I used some hard foam.  A small piece of EPP works fine too. 

To secure the 6 pins connectors in place on the root, I prepared first a sort of plug print by using a first part made from 0.8mm plywood crossing the fuselage and a second layer, shorter to create a stop. Doing this, I can then glue firmly the plug which is maintained on every side. I also created a 3D printed template to position the plug well perpendicular to the root while gluing. Before gluing, I protect the wires with some hot gun standard glue, easy to remove, no altering the wire or shrink, and providing a larger surface for the gluing.

I used 2 x MKS HV6125E for the elevator. Once in place, comes the elevator snake installation. To terminate the elevator control snake on both ends, I first remove the Teflon sheath on few mm, and then used a MPjet threaded coupler drilled at 1.6mm, glued with rapid epoxy and pinched carefully in 2 points at 90°. I do the elevator end first, put the tail planes in place and at neutral position with some paper tape to immobilize them at the neutral position, I connect the elevator snake, with standard M2 metal clevises. On the servo end, I cut the snake at the right length, and do the same with the threaded coupler. The difference is that I use this time a plastic clevises on servo side.

Let's return to the wing. You can let the wing servos connectors free, or glue them in place. I prefer the second method even if it requires some attention to not glue everything in place. To do this, I protect the root of the wing and the fuselage with thin tape, put some polyvinyl alcohol release agent where needed on the fuselage plug, connect the wing plug on it and it on the wing side with the wing in place. This gives a perfect alignment. 

The battery is a 2S Li Ion 18650 format with 2900mAh of capacity (ref: NCR18650PF).  For the balance lead, I use some aluminium paper to wrap the nose, position the fuselage with aluminium vertically in the box with sand, remove the fuselage to let the aluminum in the sand. This creates a mold that I fill in with the correct weight of lead. Once cooled down, I grid/sand a bit and it is ready.

Full assembly log photo album : here

At the slope 

The maiden flight was in Ardèche on a nice cliff but in light conditions. Everything went well and I immediately felt that the Stribog was very different from its predecessors. When the Rotmilans were naturally fast  but were lacking a bit of grip in turns, especially in light conditions, the Stribog is clearly keeping the fast straight speed, but adds lots of grip in turn, and a very good agility. 

And the Stribog continue to perform when the wind and the lift is growing, and is not disturbed by strong wind.  By adding two tungsten slugs in the joiner, I could go to 1.400 kg of ballast, and the Stribog was still happy and continued to deliver.

Snap flaps are working great and the Stribog is happy whatever the turn style, bank and yank where it shows an excellent energy retention, reversal, energy management, if the settings is adapted to the chosen turn technique. The ballasting is easy in the fuselage, where you can carry up to 900g. Over 900gr you will need to find a solution to ballast in the joiner. Personally I reused some 10x10 slugs, but needed to 3D print spacer to secure the ballast horizontally. However, I know that RTGmodel can provide ad hoc joiner ballast slugs on demand as an option, which can be interesting.

Rapidly, I was confident enough to decide to engage the plane in the battle and use it during the summer in my preparation of the world championship, achieving my personal best, still in Ardéche on the same cliff, with a 26.21s. I also used it as my backup plane during the FAI/world cup contest of Col de Tende, doing the last 4 rounds with it, and winning this competition against some of the best F3F pilots. Then, in August, I used it in a league competition and won this competition.

Overall, the Stribog desmonstrated to be very competitive and at the level of other popular competition planes. I'm very pleased with the progress made on the performances in flight.

"Flying the Stribog" Photo album : here

In conclusion

In brief the Stribog is a real step forward compared to the Rotmilan and Rotmilan Midi. It keeps the best of the Rotmilan, the straight speed, and brings now the agility and grip in turns. On the market, the Stribog is a very affordable and a very competitive F3F plane, with a superb molding quality.

Nothing is better than few videos to illustrate what I wrote. I propose you the video of the maiden flight, one showing a 29 and a 30s flight during French team practice this summer, but the first one is a more edited video with some onboard and slow motion sequences.

Videos

Technical data:  

• wingspan 2867 mm
• Fuselage length 1463 mm   
• Airfoil HN Straak
• Elevator airfoil HN modif.    
• wing area: 55,2 dm2
• projected tailplane area: 5,7dm2
• Empty flying weight: 2320 gr
• Manufacturer website : RTGModel

Settings

CoG		106	mm
Elevator			7	mm UP	7	mm DOWN
Rudder			9	mm UP	9	mm DOWN
Ailerons		Flaps	15	mm UP	10	mm DOWN
		Ailerons	25	mm UP	15	mm DOWN
SnapFlap		Flaps	8	mm DOWN
		Ailerons	aligned
Thermal		Flaps	7	mm DOWN
		Ailerons	aligned
Speed		Flaps	1	mm UP
		Ailerons	aligned
Airbrake		Flaps	55	mm DOWN
		Ailerons	15	mm UP
		comp	5	mm DOWN