Sunday, December 17, 2017

The Mont-blanc


Whatever the model photographed, the Mont Blanc (highest summit in europe with 4807m) as background is always inspiring ! All the following pictures were taken from the col du glandon (Altitude 1924m).







Sunday, December 10, 2017

Mistral Soaring - Rognac


Yesterday we had a good friendly winter contest in Rognac, between Aix en Provence and Marseille. I left Grenoble aroudn 7am under the snow, but quickly retrieved dry and safe roads driving south.

Temperatures were around 5 degrees on the slope and the wind was blowing between 15 and 18 m/s.
we managed 15 rounds at 7 pilots (3 timed flights in sequence for each pilot before to land). Best time in 32.23s for Aubry Gabanon and JL Foucher.

I flew the Stribog and managed some good times (33.39s for the fastest), but unfortunately I cut at almost every round on the right turn that was a trap visually, because of the shape of the cliff. I used between 1kg and 1.2kg of ballast.

Thanks to Aubry and Joël for the organisation !

Photo album here:  https://photos.app.goo.gl/NSFrMiAhGFMnfHdn1


Thursday, December 7, 2017

Gravity, a design exercice



After 26 years since the design with my clubmate Olivier Bordes of the Jedi ( in 1992 !!!), a 2.6m aerobatic saiplane, I took again the pencil to create a new aerobatic plane. So let me share with you the result of this design exercice. The plane name is "Gravity".


Few words about the approach I choose: I'm not a big fan of symetrical sections, too radical from my point of view. If they are the best for pure aerobatic in good lift, the rest of the time, they are more delicate, not really pleasant for thermalling, having often a low tail attitude at low speed. Flying in the alps, I don't have big lift very often and have to fly in small to medium condition too. Also, even if I like to watch heavy load glider video such as the Stingray and all the declination within the same 2.9 to 3 meters family, I find them also far too radical to fly in all conditions.





The objective with the Gravity is too obtain a polyvalent aerobatic glider, capable of thermalling, as good in low speed aerobatic (VTPR) as in academic aerobatic, capable of more ballistic flights with some ballast, the kind of plane you take alone whatever the conditions are, especially when you have to walk to reach the slope, as we usually do in the french Alps.




The 3 views plan has been drawn using Inscape, a very good vector drawing freeware.The 3D rendering has been done by Matthieu B. who obsiously masters the 3D cad software as he  did it just in few hours. Many thanks Matthieu for your great help !

I'm pretty happy with the result and how good the plane looks. I hope you will like it too ! Now it is just a drawing for now. I would love to see this plane coming alive, one way or another. If a manufacturer is reading this and is interrested to manufacture and sell it, please contact me in private.

An inverted V-tail design plane



A Curious F3F plane seen in 2004 at the viking race in Rügen. This plane belongs to Fritz Kristoffersen from Norway. Fritz was inspired by the swallows when he designed this curious plane.
Because of its shape, landing must be done inverted. I remember Fritz has a mixer he could activate to reverse the ailerons. I don't think I could even fly this plane. I'm already confused only looking at it...


Tuesday, December 5, 2017

Winter Aerial Pictures


A selection of aerial pictures taken the past years around Grenoble during winter, using a digital camera or the GoPro attached on a foamy glider such as the EasyGlider or the Easystar.
This is an exercice that is not more possible with the antidrone law that is coming, despite there is no FPV, no downlink, just a camera attached on the side or the top of the plane, triggered remotely.

Sunday, December 3, 2017

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



Sunday, November 26, 2017

Wing covering with adhesive films

Wing covering with adhesive films

 By Pierre Rondel

(Pictures: Gerard Prat, Thierry Martinet and Pierre Rondel)

INTRODUCTION

About 20 years ago, Thierry Martinet, a friend of mine who is graphist/designer decided to investigate with Gerard Prat, an experimented modeller, the possible use, for foam/veneer wing covering, of a material he was using everyday for his job: colored vinyl (adhesive film). This material is usually used for vehicle lettering, light-box advertising, decoration of flexible-face material or windowpanes, and those for both indoor and outdoor use.

The main advantages of the vinyl are the following: Brilliant shades and a large color selection, excellent life-spans and stability (between 5 to 7 years which is much more than the average life expectancy of our gliders).In addition they have good plotting and application characteristics. The thickness is between 0.07 and 0.09 mm and includes the glue.

The main drawback is its weight, which is around 90 gr/m2 where classical covering films are from 50 gr/m2 to 70 gr/m2 (Solarfilm, Ultracote, etc…). So we can tell that the extra weight is about 20 to 40 gr/m2. But now consider the absolute extra weight for a 3 meters glider for example:

The covering area for such glider will be: 60 dm2 x 2 (under and upper side) = 1.2 m2 The extra weight will be around: 30 gr/m2 x 1.2 m2 = 36 grams And finally, these 36 grams corresponds only to 1.5 % of the final weight of the glider (2.4 kg).

In conclusion, I would say that the excess load is minor compared to all the advantages of this covering material. But, I agree that at the beginning, it’s not really obvious to imagine that this material can cover entirely a wing, especially the wing tips. So, my objective with this article is to share with you the expertise of Thierry and Gérard (and they encouraged me doing so!). I just hope that septic people will be convinced at the end of this paper!

WHAT REFERENCE TO USE?

There is lot of different brands and references of adhesive films, but they are not all well adapted to our application. The main vinyl brands we use are JAC and ORACAL. The best ratio price/quality for our use if the Oracal plotterfolie serie 651. Lot of different colors are available in this range. You can also have a look on the JAC Serilux product range.



The standard packaging is a roll of 25 m x 0.5 m if you order directly to the manufacturer. I recognize that it can be a little bit expensive if you just want to cover a rudder or a tailplane ! For 5 years now, french kit manufacturers sell this vinyl retail at a reasonable price (~ 2.4 £ for 1m x 0.5m).

In the operating mode, we can distinguish 3 main steps, which are:
  1. Preparation (maybe the most important step!)
  2. Covering
  3. Finishing

PREPARATION

Like classical covering materials (i.e Solarfilm, Oracover....), the surface quality obtained will depend of your skills, of the wood type and the vinyl quality.

A very good surface quality will be difficult to obtain with balsa (which is too soft), but will be obtained easily with wood veneer. The best result is obtained with the Aningre (Latin name: Aningeria ) which has the particularity to have a very strong surface and thin grain (its color is dark brown). Between these two extremes, the Obechi give also really good result, with a little preparation.

Do not bypass this stage because the final result is directly linked to the care taken during the preparation.

For the preparation of the wing surface, we usually use abrasive paper (commonly use with water but that we use dry, of course). It is very resistant and can be vacuum-cleaned some times before being thrown.

But before sanding, it can be necessary to apply some filler cement, either to eliminate a large defect, or to make the wood fibers almost invisible. The ideal filler cement exists: Its aspect is comparable to the toothpaste. In all cases, the objective will consist in depositing what it is just necessary to fill in spaces between wood fibers. You will thus avoid a tiresome sandpapering. Unfortunately, I won’t give you any references because they are certainly different in each country.

Small detail, which helps for the finishing: We intercalate between the hold and the abrasive paper, a piece of foam, very flexible, of approximately 10 mm thick. Thus we obtain perfect curves (even visible to the eye under oblique light) and an impeccable surface quality by using a grain from 320 to 350 for balsa, 250 for samba and 220 with Aningre. A sanding with thinner sandpaper does not bring anything better to the finish after the covering.

If you have installed elastic flaps (using nylon ribbon), cut out and articulate the control surfaces (ailerons, flaps), installation of the A.F, etc.

During its handling, the vinyl attracts any kind of dust (static electricity). The only solution is to transform yourself into a beautiful cleaning lady: Pass the vacuum cleaner everywhere in the room where you plan to operate. I personally use an ironing board as worktable because the cotton sheet, which covers the table, is less sensible to the dust.


Outdoor or in another room, clean conscientiously your wings (and wing blanks) with an air compressor or a vacuum cleaner and finally with a clean rag by “whipping” the wings (and not by “rubbing”) in order to avoid new static electricity. Never use a wet rag to fix the dust, because the wood fibers will react immediately by inflating, and you will certainly have to redo the previous sanding operation.




For the very final cleaning of the surface of the wings, simply use your hands: This is, for the moment, the best tool that we found, and moreover which is equipped with very efficient sensors! Actually, you will feel under your hand the least dust or roughness, which, if you insist, will disappear. The hand’s skin acts like a thin sandpaper (grain: 400 or 600). Of course, all these advises are also applicable with any type of covering materials, not only adhesive films.

THE TOOLS

A minimum set of tool is necessary to complete the covering:
  • A (preferably) non synthetic rag which does not become fluffy
  • A cutter equipped with a brand new blade
  • An iron for solarfilm.
  • A hairdryer.
  • A soldering iron

COVERING

Thanks to Thierry Martinet and Gérard Prat who made an exceptional job by doing all these pictures, I propose to you to see how to operate, step by step, as if you were there!

Prior to the beginning of the operations, cut your 4 vinyl panels with the correct planform of your wings plus a few extra centimeters of margin (width and length). The longer your wing is (or if it is you very first covering using vinyl) the larger the margin will be. For example, 6 cm on each side (leading edge + trailing edge = 12 cm) for a half wing of 2 m is a good value. Begin with the covering of the under-surface. You can use the wing core blanks to avoid your wing to slip on your worktable, but this is not mandatory. Vacuum-clean also the two faces of the vinyl panels before spreading it over the under-surface of the wing.


STEP 1

Center and align the vinyl panel and maintain the whole in place on the wing by using magazines (your entire QFI collection for example !) or phone directories.







STEP 2

Begin the covering by the wing root. For that, separate the vinyl from its protection sheet on 30 cm. Then, stretch the vinyl panel and apply it progressively starting from the root cord. This is the most delicate step to start the covering, because it is necessary to well align the panel and have no surprise when arriving at the wing tip … if you see what I mean! If needed, don't hesitate to ask some help for this particular stage.

STEP 3

To stick the vinyl on the wing, rub it with the rag by starting each time from the middle of the cord towards the leading edge and from the middle of the cord towards the trailing edge. To avoid any fold that would be tragic for the result, progress gradually towards the wing tip and stick the vinyl on the LE and TE only upstream of the point where you have sticked the vinyl at the middle of the cord. If you progress too rapidly on the LE and TE, you are certain to have wonderful folds… Progress that way by steps of 30 cm by separating the vinyl from its protection sheet and by making it slip on the wing. The adhesive used on the film behaves like all other adhesives and reaches its maximum adherence only after a certain period of time. If something wrong occurs during the covering, peel off immediately the vinyl and eventually heat it a little bit with the hairdryer. However, even if you limit the damage on the wood, you certainly will have to throw the panel of vinyl out and do it again with a new one.





STEP 4

Wing tip covering: The funniest stage is the covering of the wing tip: The vinyl is now completely removed from its protection sheet, and widely exceeds the wing tip. Immobilize the wing on the worktable with something heavy: Then with a hairdryer in one hand, warm carefully the film while pulling it with the other hand. You will see that the vinyl becomes soft and can easily follow the wing tip shape.





STEP 5

Cut the extra vinyl and With a cutter cut the excess vinyl around your wing. Once done, apply the iron or soldering iron to perfect the sticking at the periphery of the adhesive film. To fold back and stick the vinyl against the root, first cut the vinyl with a small margin (3 to 4 mm), then vigorously rub the vinyl on the edge (with the rag or directly with the finger) to heat it and it will take the angle almost alone. Eventually, you can sandpaper the join line to reduce it at the maximum before to start the covering of the upper side.

STEP 6

Upper side covering : The under side of the wing being covered, repeat the previous operation (Steps 1 to 5) with the upper side. This time cut the vinyl with a small margin before to wrap the leading edge and obtain a join around 5mm large. On the trailing edge, you can cut the vinyl very short or let a margin and wrap the trailing edge. Personally, I prefer to cut very short and avoid a double layer of vinyl at the junction. Then, I use the iron to perfect the fixing of the vinyl on all edges.



     

FINISHING

Clear the servos holes, air brake slots. Depending of the building technique used, you will have to cover the control surfaces separately, and install them with hinge tape. If control surfaces are articulated with nylon ribbon during the construction (this is often the case today), free them by cutting the vinyl underside and at each extremity. Then apply the nail of your soldering iron along the control surface slit while taking care to operate the control surface in order to widen the slit. Repeat the operation 2 or 3 times.




DECORATION

You have finally finished to cover your wings? Congratulations! You can now think about how to decorate them. CorelDraw, interfaced with a cutting machine, is the perfect configuration. This software allows to vectorize any drawing and then to pilot the cutting machine. The only limit is the range of color you have and your imagination. I joined one or two pictures to show you some decoration examples.

If you don't have access to a cutting machine, you can also by wall stickers (Ebay, or amazon) and find some nice ones, in different colors and combination and create your own color scheme. This is what I did on my Excel 4004 recently, and I'm satisfied of the result. Just make sure the stickers are coming with a transfert tape which is not aways the case.

It is also possible to plot (with special inks) on the vinyl (before the covering of course!) and obtain incredible results like the one shown on this picture. Unfortunately, this printing technology is not accessible to us yet and the cost price is still prohibitive.



MAINTENANCE / CLEANING

You can use Acetone, white spirit, and other distillate without any problem. If you have to repair some damages on your wing, a small vinyl patch will be fine and remains discreet. In case of removing entirely the covering, use an hairdryer to warm up the film and then peel it off with precaution. However, a new sandpapering will be necessary before covering again.


CONCLUSION

I think that you now know everything about the topic. The vinyl is certainly not perfect, but with a little experience, you will manage a covering in record time to obtain a very good finishing for your wings. The surface quality obtained will surpass easily conventional covering materials and the preparation and operating mode is accessible to everyone and does not necessitate special tools. Also The durability of this covering material is just great and will last for years


Tuesday, November 21, 2017

RC Soaring Digest December issue


December issue of RC soaring Digest is available with plenty of interresting articles. Just follow the link below !

The Mont-blanc

Whatever the model photographed, the Mont Blanc (highest summit in europe with 4807m) as background is always inspiring ! All the follow...