25-Jun-24 - 06:40 PM

Thermal Circle Text - Thermal Circle 53

Written by Hayden Daley - 09 September, 2022.
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Welcome to this edition of the Thermal Circle in this edition the new Pike Paradigm from Samba models!!! Please enjoy!

Our new project, which we are currently working on intensively, is PIKE Paradigm. This model is designed by Philip Kolb and Benjamin Rodax. The model is designed for the GPS Sport category, which is very well developed in Europe. Also it is great for slope alpine flying or flying for fun anywhere because it has an electric motor. The model will have a wingspan of 4726 mm, three-part wings. Diameter for spinner will be 38 mm. PIKE Paradigm will be the first model in this size category which will be made with full Rohacell core technology. Thanks to this technology, Pike Paradigm can be produced much stronger compared to sandwich technology at the same RTF weight. On the beginning it will be made with crosstail and later also as V tail version.

A short introduction how Pike PARADIGM came to life

(by Jaroslav Vostrel)


In May 2019, Philip Kolb first mentioned of the GPS SPORT to me and we created an idea of realizing a GPS-Triangle sportsclass model. We discussed it for some time and put up two possible scenarios. The first was to use the wings from the Pike Precision 2 and make a center panel, fuselage, elevator and rudder for them (but this proposal would be a compromise). The second concept was to design a completely new model. We decided on the second, more expensive, but in all other respects better option.

Philip Kolb and Benjamin Rodax who were to design this aircraft were therefore not limited by anything and could fully develop and use their design skills. By the end of 2020, the design of the model was completed. As we made real good progress using FRC-technology (Full Rohacell Core) with our latest designs, we aimed for this technology for this larger aircraft as well. This allowed us to make great use of the fact, that we were almost unrestricted by any means of airfoil thickness.
Wings built in FRC technology offers a way better weight/stiffness ratio than hollow moulded wings and can take torsional loads on thin wings much better. Nevertheless, the challenge for us was to produce such large composite-parts in electrically heated aluminum molds.
With the fairly large amount of carbon used it is not entirely easy due to build accurate parts due to the expansion of aluminum when heated and the contraction of a certain type of carbon.

Fortunately, we gained a lot of experience in this direction during the production of the Prestige 2 PK, which is also made utilizing FRC technology.
As a sides note, as far as I know, after many attempts and tests, we are now the only company which managed to produce an F3J-plane with full mechanical load capacity out of purebred F5J model., After this transformation, the F3J-version of Prestige 2PK withstand a competitive winch launches!

I am very happy that these planes were so successful in the 2022 F3J World Championship, that they took 1st (Martin Rajšner/CZE) and 3rd place (Jo Grini /NOR)!

 Back to the Pike Paradigm project;
I probably don't need to mention that all the aluminum molds were milled on precise CNC machines, which was quite an astounding effort for a 4,72m wingspan aircraft. In the end it was possible to produce that high aspect ratio wing with very thin airfoils at an amazing strength/weight-ratio, thanks to the above mentioned FRC technology.
For instance these wings feature a carbon-shell layup of 390g/m2 in the centerpanel and the sparcaps need to be made from UMS carbon to prevent excessive bending. As a relief to all the efforts, Philip Kolb managed to win the 1st World Master GPS sport class (World Championship) with Pike PARADIGM. Additionally Tobias Ebner finished second with Pike PARADIGM which reflects a phenomenal success for us.
Both planes were pre-serial versions and were already up to the competition.
Meanwhile we already addressed the “lessons learned” into an even more sophisticated layup, which we can now offer to you as our standard layups!


Besides that we are also working on a cost efficient drivetrain using a Dualsky outrunner motor at the moment as not everyone will use the Pike Paradigm primarily for competition. Especially for recreational flying you can also install larger batteries into the fuselage. While installing the batteries underneath the canopy hatch the weight of the batteries should not exceed 350 – 400g. If you want to use large batteries up to 6s 5000mAh, you can surely install them behind the canopy hatch by sliding them almost up to the leading edge of the wings. This is necessary to achieve a suitable CG.


Furthermore we are about to finalize the V-tail version for Pike Paradigm, which will of course also be perfectly suitable for GPS-Triangle sportsclass competition but puts high emphasis on alpine slope flying. Anywhere where landing sites might get rough, the V-tail will yield an advantage to prevent damage on landings. We recognize that there is a huge group of pilots longing to have such a “slopemachine” in their quiver.

Finally I would like to thank the designers Philip Kolb and Benjamin Rodax for creating this great model not only for the GPS SPORT category.

We wish you only the best experiences with Pike PARADIGM

Samba model team.

    Writeup from the designers Benjamin Rodax and Philip Kolb:

Since around 2015 the upcoming RC-soaring category of GPS-Triangle racing is creating new challenges to competitive soaring.
These new categories are not only very exciting and demanding, they also offer a new level of competition. In comparison to the classic RC-soaring duration tasks, one needs to maximize the climbing performance during thermaling to enhance the potential of covering as much ground as possible. Due to the utilization of real time GPS-navigation a whole new set of possibilities arise.
With the aid of this navigation technology it is now feasible to fill the gap between RC and full size soaring sports. It actually reflects a kind of paradigm shift in RC soaring competitions. With this as an initial perspective to develop a specific glider for the GPS-Triangle sportsclass, we once again teamed up with Benjamin Rodax and Philip Kolb to realize our new project called the “
Pike Paradigm!
In the following lines you can read about the essentials of the development process by the two designers:

To us, the GPS-Triangle classes reflect some really exciting fields of glider optimization. With navigational equipment on board of the planes new horizons for exceptional soaring experiences arise. Pilots are now able to get an instant feedback from their gliders about sink/climb, speed and the actual flight path. The on-board navigation unit and the telemetry furthermore are great assets for optimizing settings, i.e. flaps, trim, on an RC-aircraft.
The GPS-Triangle task itself reflects a fascinating assignment for competitors and call for extraordinary soaring machines.

To develop such a glider is a pure joy for a designer as the performance of a sportsclass glider will surely exceed those of smaller F3X-planes. Modern GPS-Triangle sportsclass gliders are true all-rounders offering almost the performance of a large scale glider but also the ability to climb in tight circles similar to an F3J ship.
The high speed end to the flight envelope of a GPS-Triangle sportsclass glider, when fully ballasted, can easily exceed the speeds of F3B planes!

In a GPS-Triangle sportsclass competition, the primary challenge is to glide around a virtual triangular course of about 1.7km length as often as possible within a task time of 30 minutes. The entry speed and entry altitude are limited to 120km/h and 400m respectively. Nowadays the best gliders are able to fly around the triangle 6 times in “dead air” and take about 12 minutes to fulfil this task. It is immediately clear to any soaring pilot, that with the extra 18 minutes to spare, the real fun begins as soon as thermals set in.

In the GPS-Triangle sportsclass the setup framework, which is fixed by the rules includes the following main parameters:

  • Maximum span: 5000mm
  • Maximum all up weight: 7000gr.
  • Maximum wing loading 75g/dm²

With these main boundary conditions, the freedom concerning the variety in design possibilities is certainly given, but as well dominated by one parameter: To meet the 7000gr. and 75g/dm² wing loading criteria at the same time, the wing area of a GPS-Triangle sportsclass model should be no bigger than 93.33 dm². So for the design of Pike paradigm we took in consideration that,

  • the wing area needs to be 93.33dm² (1)
  • the glider should have a wide optimal range of high L/D ratio rather than a “peaky” maximum. (2)
  • the glider should thermal exceptionally well to maximize climb performance in thermals, as this is the key-point to succeed in competitions. (3)
  • the glider should be able to fly fast for the speed task.* (4)

* In every competition there is a speed task flown, where the competitor needs to fly around the triangular course once in the fastest possible time. The average speeds thereby reach up to around 150km/h (short term speeds up to 210km/h). The plane and the pilot need to be up to reach these numbers in order to not to give away valuable points.

As the first factor (1) for the development is given by the rules (93.33dm²wng area), the number 2 factor needs to take some more investigation. It is important to understand at which speeds (and respective CL values) the sportsclass gliders are mostly flown. Studies of competition and practice flights show that 60% - 70% of the time the gliders fly below 60km/h (?16,5m/s). Only about 20%- 25% in the air are spent at speeds between 60km/h and 90km/h and only for a fraction of the flight time the planes fly faster than 100km/h. Of course this fraction is of importance, when it comes around to the speed task, where the 

score of the speed task can amount to up to 20% of the overall result.
Nevertheless the number 1 flight regime to consider optimizing is the low speed (thermaling at high lift coefficients) to intermediate speed (glide to cover distance) range.
With this in mind we set up a trial to find out the optimal wing planform. Thus 4 different “test-wings” were generated to especially compare the effects of aspect ratio.
With the wing area set to 93.33dm², enlarging the span results in enlarging the aspect ratio at the same time – but at the cost of reducing the chords of the wing. Modern building methods and materials surely allow these measures to be taken to a certain extent, whereas an eye needs to be kept on structural restrictions. When a wing gets more and more narrow at the same percentage of airfoil thickness, the effective thickness drops, resulting in either less structural strength or more structural weight (higher moments of inertia). Hence, we actually decided against a 6-servo-wing as the wingtips would get so thin that a 10mm servo would not fit inside the wingtips anymore – and we didn’t want to use 8mm servos on a 7kg-plane due to reasons of robustness and precision.

The clear advantage of high aspect ratio wings on the other hand is that they generate lower induced drag. At high lift coefficients, the predominant factor of drag is indeed the induced drag! So let’s take a look upon the optimization iterations we underwent.
One end was a wing with an aspect ratio of 21.
This was chosen as a representation of designs which are already being flown successfully in GPS-Triangle sportsclass competitions.
The other end of the spectrum was reflected by a wing with the maximum possible aspect ratio. When choosing the maximum allowed span of 5000mm and a wing area of 93.33dm², the aspect ratio results in 26.8 (we called it “27” in the upcoming sketches).
The two interpolated wings in between were generated with aspect ratios of 23 and 25.

Please note, that all 4 wings have the same wing area. The test wings were equipped with a proven set of airfoils which were not yet optimized separately for each and every wing. At this stage it was primarily important to understand and visualize the effects of aspect ratio. Each wing could later be optimized with individually designed sets of airfoils.

 To be able to compare the results, the wingloading was chosen to be identical for all wings, in this case the maximum allowed wingloading of 75g/dm² was chosen. The polars show quite obviously that larger aspect ratios result in better performance at lower speeds – below 18m/s flight speed. In return, the wing with the lowest aspect ratio shows better performance above 18m/s flight speed.

As explained before, the highest priority in the optimization was chosen for flight speeds below 60km/h, thus below the shown “cross-over-point” of 18m/s.
Additionally it needs to be mentioned that a glider which climbs better / faster in a thermal can make up for some worse L/D at higher speeds as it can start earlier to cover ground or from a higher altitude because it climbed faster. Of course this should be considered within reasonable boundaries!

The fact that the ultimate aspect ratio of 27 offered only little gain over the wing with the aspect ratio of 25 was very interesting. This made it clear that scaling the aspect ratio of a wing will not show linear gains in performance.
By taking a closer look into the “on-design-range” for flight speeds below 60km/h (Sketch 03) it is also visible that enlarging the aspect ratio on and on, will not only effect peak performance, but will narrow the range of optimum L/D.

After these first sets of calculations it became obvious that the optimum wing planform will feature an aspect ratio somewhere in the range between 23 and 25. With the superb building skills of Samba model using Rohacell-fullcore technology, it would have without any doubt been possible to build the “25 aspect ratio wing”, but we still wanted to put some emphasize towards faster speeds and decided to set the aspect ratio of Pike Paradigm to 23,9.
With this it should be a little bit easier to face the structural challenge of building a very thin high aspect ratio wing whilst still enabling us to build fairly lightweight wing tips, which really helps saving energy in rolling and yawing manoeuvres.

The next task was to design a set of transitional airfoils for the wings. These are developed in the same basic way as described in our design article of the Pike precision. If you are interested you can surely read about it here on the webpage too (Pike Precision F3F/F3B – Samba model (f3j.com)). Fundamentally each airfoil is optimized for the local Reynolds numbers at its local spanwise position to maximize the performance. All transitional airfoils thereby need to show the same zero lift angle (important for high speed flight) and very similar behaviour when changing the camber flap angle.

Beyond that, it was quite intriguing for us to find out what the demands on the airfoils are in each and every range of lift coefficients (respecting each and every range of possible flight speeds). To illustrate this we will look at sketch 04.


The most important flight speed ranges are marked inside the green bubbles which thereby show the areas of necessary optimization. As the aspect ratio for Pike Paradigm is set, the next questions were:

“What are the requirements on the airfoils for each designated “regime” of the flight, so to say each designated area of optimization?”
“What needs to be optimized on the airfoils to achieve the best possible solution for each designated “flight regime”?As a matter of course each area of optimization should be considered in the design of Pike Paradigm. However, while trying to optimize all points it gets quite obvious that the different areas of optimization are contradictory to each other to a certain extend. For example a reduction in drag in the cruise speed range can best be achieved by using very thin airfoils, while good thermaling performance and a late and smooth stall require sufficient airfoil thickness. Because of that quite a lot of iterations were computed to minimize the trade-offs in the end. The final wing now features a thickness distribution from 8.8% at the wing root to 7.0% at the tip.
To be competitive in the speed task, Benjamin took great care about elongating the laminar airflow especially on the lower side of the airfoil and was examining the development of laminar-turbulent transition at the lower corner of the laminar drag bucket.
The target here was to reach low lift coefficients of less than Cl=0.1 with fairly low quantities of negative flap deflection. To reach very low drag in high speed flight, it was necessary to keep the contour of the airfoil as smooth and steady as possible. The above mentioned fairly low amounts of reflex help avoiding distinctive kinks in the airfoils surfaces and thereby can keep the laminar airflow established in chordwise direction for a greater length, especially on the lower side of the airfoils.


Thus, the airfoils of the Pike Paradigm have a comparatively low camber of 1.7%.
As a consequence this means that only small amounts of reflex are necessary for the speed task and when flown in “zero flap position” Pike Paradigm is in a kind of “fast cruise configuration”, which can be used when crossing the starting line as close as possible to the maximum allowed speed of 120km/h.
Vice versa, normal cruise speeds (“normal flight phase”) needs to be flown with about +1 degree of positive flap deflection. To achieve high “L/D-ratios” and a slow speed for thermaling, extensive amounts of camber are necessary.


The ideal setup for each flight phase is shown in sketch 06:

For the wing a transition of 13 airfoils was developed. The airfoils in first degree were developed to meet the above mentioned performance criteria. In addition two aspects were particularly considered


1. Wing/fuselage intersection:
The wing close to the fuselage is not operating in a clean flow situation. The wing/fuselage intersection moreover makes it barely possible to establish laminar flow on the wing in the intersecting area.
To avoid excessive flow separation in this area, an airfoil was specifically designed for the turbulent flow anticipated there. A transition over three airfoils then blends the “turbulent” root airfoil into the “laminar” main airfoil.
This measure can reduce the interference drag generated by the wing/fuselage intersection to a larger extent than the airfoil drag is increased due to the reduced percentage of laminar flow on the airfoil at this particular area and thereby lead to an overall reduction of drag.

2. Preventing tip stall tendencies:
Great attention was paid to the stall behaviour of the Pike Paradigm. In GPS-Triangle sportsclass competitions it is usually beneficial to carry as much ballast as possible (so to say fly fully ballasted whenever possible), as a high wingloading yields better glide ratios at high speeds.
Due to this it is crucial that the plane is able to climb well even in narrow thermals when flown at the maximum allowed wingloading. The determining factor in this situation (high bank angle, high wingloading, low flying speed) is the amount of lift that can be generated by the wing and the amount of lift that particularly can be generated by outboard panel of the wing. Therefore we paid great attention that the tip airfoils of the Pike Paradigm can generate very high lift coefficients and show no abrupt stalls after reaching the maximum lift. This method might come at the cost of some additional drag at the high speed end, but will give the pilot security in tight thermal turns.

Saying this we should consider that a heat in a competition will last for 30 minutes. 30 very long minutes sometimes, when working a thermal to stay airborne and then carry on with the task or when working several thermals on the course during the flight. Taking quick decisions, focusing on tactics, watching the weather and adapting to changes in conditions as well as concentrating on the competition and the navigation system are very demanding and sometimes stressful to the pilots. Hence one should not only pay direct attention to the performance parameters of the aircraft, but also strongly consider its handling qualities to reduce the pilot’s workload of controlling the aircraft to a minimum.

Pike Paradigm was designed to be exceptionally easy to fly.
One key point for the design was to obtain a plane, which “tracks straight” along the triangular course. To realize this, directional flight stability of the aircraft is of great importance. To achieve good yaw stability the vertical tail volume of the aircraft is paramount. The vertical tail volume is mainly driven by the length of the tail arm and the surface of the fin. To enlarge particularly the fins surface seems to be more beneficial to the overall design in our view. Elongating the tailboom to very large extents, means increasing the most “draggy” part of the aircraft and increasing the drag by higher proportion than by increasing the surface of the fin.
Latter sees partly laminar flow, which results in less drag compared to the tailboom of the fuselage, which is operating in fully turbulent flow.

Another key point was to obtain a plane that is very easy to thermal. One crucial factor in this goal is increased rudder power which results in nice harmony of the controls around all three axis. Moreover the amount of the spiral stability plays one decisive role for thermal aircraft. The magnitude of spiral stability indicates how steep an aircraft can turn and recover from that steep bank angle itself (or not ?). To increase the spiral stability of an aircraft the vertical tailarm needs to be elongated or the dihedral needs to be increased (or both). According to these design parameters, an aircraft can be spirally instable, neutral or spirally stable. For a thermal glider, which is solely controlled by rudder and elevator it is predominantly important that it is spirally stable to prevent the need to use opposite rudder in thermal turns (as there is no opposite aileron available). For an aileron equipped thermal glider the need for a large amount of spiral stability is somewhat lower as the pilot can input the required amount of opposite aileron to coordinate the turn and prevent the glider from “tugging” in. Nevertheless having some spiral stability margin, even on an aileron glider, reflects some desirable amount of comfort while controlling the plane.
On the Pike Paradigm we chose to increase the dihedral to facilitate thermaling. Due to the reasons stated before, we didn’t want to elongate the tailboom to extreme values. Not only because of adding unwanted parasitic drag, but also due to the practical reason of transportation. The dihedral on the Pike Paradigm is similar to modern F5J planes. Because of the large span, the spiral stability value is slightly less than that of typical F5J planes but way higher than for F3B planes. It needs to be stressed that even with the relatively large dihedral, the Pike Paradigm tracks perfectly straight due to the large fin surface.
The most important flight mechanic values are:

  • Equivalent dihedral angle (EDA): 6.3 degrees
  • Vertical tail Volume (Vv): 0.028
  • Horizontal tail Volume (Vh): 0.456
  • Spiral Stability criterion (B): 2.69

These are the basic flight mechanical factors that determine “handling qualities”. Supplementary low moments of inertia will positively contribute the handling qualities of the plane. Here light tail feathers and wing tips are desirable. With the skills and technology of Samba model using “Rohacell full core technology” for all wings and tails, an ideal weight/strength ratio can be accomplished. It is almost incredible that no extra nose weight is necessary and heavy motor batteries even need to be pushed back considerably towards the wings leading edge in order to maintain a suitable CG.

Flying the Pike Paradigm is a pure joy and we are very happy that we undertook this endeavour together with Samba model. The model does everything that was asked for and delivers its pilot a machine of highest performance with an extremely wide operating range. From the “outskirts” of F5J to speed performance beyond that of F3B planes. After almost 4 month of flying, it became obvious, that the Pike Paradigm became the most flown aircraft in my quiver. In contests it absolutely holds up to the competition. The straight line and high speed performance is comparable to other competitive gliders, but we would say, that the Pike Paradigm has a little edge in thermaling!
Of course these versatile gliders are not only subject to the needs and wishes of GPS-Triangle pilots. Especially pilots who love to fly high performance gliders, no matter for what occasion, will be satisfied with the Pike Paradigm. For rough terrain like on high alpine slopes we are designing a V-Tail version right now, which with the help of Samba model should hopefully be available for the 2023 slope season.

Thats all from the Thermal Circle Happy safe and successful soaring!! Hayden Daley September 2022

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