SkyTouch GPS settings
From the polar to the center of gravity to flight modes
Proper tuning and setup are crucial for high-performance flight. Whether you plan to soar in thermals, fly in a competition, or just relax at the field, precise tuning will result in significantly better flight characteristics and easier handling. This article guides you through the basic setup of the Center of Gravity (CG), control surface throws, and flight modes for the SkyTouch GPS competition model.
The wing airfoils have been designed with an emphasis on excellent performance for both cruising at speed and flying in thermal conditions. The polars of the airfoils themselves highlight the design's versatility, providing the pilot with confidence, efficiency, and the joy of flight in every situation.
Efficiency zone
This zone visually highlights the area where the wing achieves its best Lift-to-Drag ratio (L/D). It represents the region where the model is most aerodynamically efficient, traveling the furthest distance for every meter of altitude lost.
- The model achieves optimal gliding performance
The curves coincide with the points where theCL/CD ratio is at its maximum
- Thermal climbing is most efficient because the model's sink rate is minimal
When the model is in this zone, we say it is flying at 'best glide' or that it is in the performance 'sweet spot.' On the graph, this serves as a visual aid to help the pilot quickly understand which flight regime is the most efficient."
The speed for best glide is 10.6 m/s; at this speed, the model achieves its best glide ratio, covering the maximum distance per unit of altitude lost. For competition flights (where higher-speed transitions are required), we fly faster (14–16 m/s), even though glide performance is no longer optimal. However, in thermals or during economy cruising (typically in morning rounds), it pays to maintain a speed around 11 m/s. The values in the table show that at competition speeds (55–90 km/h), we operate within the Reynolds number range of Re = (1.9 – 3.3)×10⁵, which is ideal for our airfoils.
Time triangle (s) | Speed (m/s) | Speed (km/h) | Reynolds number |
|---|---|---|---|
60 | 28.17 | 101.4 | 340.000 |
90 | 18.78 | 67.6 | 290.000 |
120 | 14.08 | 50.7 | 172.000 |
150 | 11.27 | 40.6 | 138.000 |
180 | 9.39 | 33.8 | 115.000 |
The optimal and recommended Center of Gravity (CG) position for the SkyTouch GPS was determined through extensive flight testing and is located 103 mm back from the leading edge of the root airfoil.
At this setting, the model provides an ideal balance of stability, readability, and maximum glide performance, ensuring the full utilization of the aerodynamic design of both the wing and the tail surfaces.
A CG of 103 mm provides the pilot with precise control response and confidence during landings, even in demanding conditions.
Moving the CG back to 105–108 mm further enhances glide performance and thermal efficiency, though it requires more experienced piloting. Conversely, a setting closer to 100 mm ensures greater longitudinal stability and is suitable for maiden flights or a more relaxed flying style.
Creating a 'speed vs. flaps' table for a specific wing airfoil is a relatively complex task that requires simulating the entire model to determine the optimal flap angles for various flight modes.Flaps change the shape of the airfoil and thus its aerodynamic properties (CL, CD), which affects flight speed and efficiency.
Important notice: The table provided is a guideline based on general aerodynamic principles and typical flap usage. Positive angles are used to increase lift for slower flight and thermaling, while negative angles are used to reduce drag and increase penetration for higher speeds.
The values were determined using full-model software simulation* and verified by flight tests**.
* Flap Settings vs. Flight Speed – SkyTouch GPS
Flight Speed (approx. km/h) | Flight Phase | Flap settings | Description | Note to Re |
Very Slow Flight / Landing | Min. Speed Glide / Crow | +8° to +15° Brake +60° | Provides maximum lift and a significant increase in drag, allowing for a steeper descent and precise control of landing speed. | Re very low – increased airfoil drag, possible flow separation. |
Thermals / Slower glide (35–45) | Optimization for thermalling / Best glide ratio | +3° až +8° | Increases lift, lowers stall speed, and allows for better turning in tight thermals. Drag goes up a bit, but the glide ratio improves at lower speeds. | Low Reynolds numbers – Increased lift for the slowest and most efficient climb in thermals. |
Gliding / Standard (45–55) | Best glide (max L/D) | 0° až +3° | Slight camber for an improved lift-to-sink ratio. The wing "reads" the air better. The model maintains speed and efficiency. | Typical operational Re – airfoils designed for optimal performance in this range. |
Speed / Penetration (65–95) | Covering distance/ Flying into the wind | 0° až -2° | Reduces lift while lowering profile drag for higher speeds. | High Re – flaps help keep the flow laminar at high speeds. |
** SkyTouch GPS settings for various flight modes (deflection in mm at the airfoil trailing edge)
+ down, – up, = same "as", controlled flap = "lift" stick
Flight mode | THERMAL | CRUISE | SPEED | LANDING | START |
FLAPS | +3 | 0 | -2 | +2 (+60) | 0 (-3) |
AILERONS Inner | = flaps | 0 | = flaps | +2(-18) | 0 (+35) |
AILERONS Outer | = Ailerons | -1 | = Ailerons | -2 (-20) | -2 (-15) |
Controlled flap | +7 | +4 | 0 - Disabled | (crow) | (crow) |
ELEVATOR | +- 10 expo 30% | +- 10 expo 40% | +- 8 expo 40% | +-10 expo 30% | +-10 expo 40% |
RUDDER | +12 – 16 | +11-15 | +9-12 | +12-16 | +11-15 |
