RC Paraglider Profile Development at RC Para Aviation RC

The development of our RC Paraglider profiles

When we talk about the fascinating world of RC paragliders, we must not forget the impact that the profiles used have on the final performance and the flying experience achieved.
We place great importance on the development of "adapted" profile straks. Adapted in the sense that they are actually developed for the RC paraglider and not simply taken from a manned paraglider!

Here we can count on a very intensive collaboration with Philip Kolb. Philip is known for an almost unmanageable number of successful and winning designs in RC gliding and for about 3 years we have been working continuously on the optimization of paraglider profiles. Depending on the use of the RC model paragliders, this involves both the collapse resistance and the continuous performance optimization of our RC paragliders.

Each of our RC paragliders undergoes a comprehensive flow simulation during the development phase. This is done to ensure optimal flight results in all flight phases and conditions of our sports equipment. To give you an idea of ​​the approaches and the effort we put into them, we have described the development work regarding the flow simulation of RC paragliders below.

Preliminary thoughts that you have to make.....

When developing profiles for RC paragliders, two special features must be taken into account:

• Firstly, the "wing" is not a structurally stable construction
• Secondly, the wing cannot be operated at negative lift values, otherwise the RC paraglider will collapse

The structure of the RC Paraglider functions exclusively through the generated lift and collapses at negative lift values.
In our RC paragliding models, the internal pressure generated in the cell is crucial for the flight ability of the paraglider, but the shape of the profile is even more important for its performance.

Approaches that make our design so successful

In order to optimize both, it is important to be able to fly the entire range of positive lift coefficients without negative angles of attack.

The profile of an RC paraglider should therefore not have a strongly negative zero lift angle. This is especially important when we are in the accelerated state. That is, the flight state in which the angle of attack of the entire canopy is reduced in order to be able to fly forward as quickly as possible.

The difficulty in developing such profiles is that they are usually less able to provide maximum lift. The generation of the greatest possible lift reserves must therefore be achieved primarily through the design of the upper surface of the wing, i.e. the upper sail.
In addition, with the paraglider model we have the option of activating additional lift reserves through defined “braking”.

The laminar run length on the RC paraglider profile

As mentioned above, an RC paraglider is a structurally unstable structure, which also affects the aerodynamics of the upper sail.
Depending on the strength and quality of the fabric and the type of stitching, up to 25% laminar length can be achieved on the upper sail. This is the area of ​​the wing where the most lift must be generated if you want to save as much drag as possible.

The design of the upper sail is therefore of great importance. We try to accelerate the flow as much as possible and only as abruptly as necessary in order to generate as much lift as possible by maximising the negative pressure.

Acceleration with good gliding performance

An important side effect of these design measures is that this negative pressure also stabilizes the shape of the nose on the upper sail. This stabilization means that we can still fly a stable canopy at very small angles of attack, meaning that the "front collapse" only sets in very late! Our paragliders therefore accelerate better than average and retain their very good gliding performance even at high speeds.
Our approach was to develop an aerodynamically clean profile that would maintain sufficient tension in the upper sail even when accelerated to counteract the front flaps.

Our profile already provides the optimal contour for the rapid flight of the RC Paramotor.
In order to increase performance in slow flight, the profile can be advantageously adjusted for this flight condition by "lightly braking" - essentially bending downwards. In an RC paraglider, "braking" means that the trailing edge of the wing is deflected downwards, which can be imagined as a positive flap deflection.

To ensure that our RC paragliders arch the trailing edge like a flap, similar to an airplane, we have made certain design provisions in the interior of the canopy and the line geometry. This can be seen very clearly when looking closely at our RC paragliders in flight.
See also the following pictures of the Phasor 2.3 Rast

By applying targeted braking, the profile is changed in such a way that both the power (L/D) and the lift reserves are increased during slow flight.
The profiles on our paragliders are optimized and designed precisely for these aspects.

Reach your goal with optimal profile and wing geometry

We are not just studying a single profile, but the entire canopy, as the profile depth varies greatly in the spanwise direction. Consequently, different profiles must be used to achieve an optimal result. It was also necessary to analyze the optimal wing geometry and adapt it to the flight mechanics and aerodynamics.

Shark Nose

For manned paragliders

In manned paragliders, frontal collapse in accelerated conditions is mainly prevented by increasing the internal pressure of the canopy using a "shark nose" profile, with the cell opening facing the airflow in accelerated conditions. This aims to increase the internal pressure of the paraglider cell in order to structurally stabilize it via the air pressure.
The "front flap" is caused by a lack of pressure difference between the air inside and outside the canopy as well as by the high dynamic pressure that acts on the nose of the canopy during accelerated flight.

However, in the case of manned paragliders, this technology is not installed in everyday A or lower B class devices because it has too many disadvantages, such as increased profile drag in normal flight.

High-performance paragliders, which are primarily used for cross-country flying and in competitions, spend a large part of the flight in an accelerated state in order to cover distance. In very good weather conditions, up to 80% of the flight can be completed in an "accelerated state". Sharknose profiles are designed to prevent frontal collapses from occurring at high flight speeds, thus ultimately increasing the maximum speed of the paraglider.

However, this top speed comes at the cost of a higher drag coefficient, which the sharknose design unfortunately brings with it. Here, the desire for more top speed is therefore based on the need for greater safety. The result for manned paragliders is reflected in a shift in the maximum achievable speed from around 50 km/h to 63 km/h. However, the achievable glide ratios at these high speeds have not improved with the sharknose profiles - in fact, they have gotten worse.

At RC Paraglider

When developing our model paragliders, we examined sharknose profiles in detail. We looked at the usual Reynolds numbers at which our model paragliders operate. The Reynolds number is a dimensionless number and is used for comparability in fluid mechanics. It is described by the ratio of inertia to viscosity forces and thus characterizes the flow behavior. Our analysis showed that the use of sharknose profiles in RC model paragliders is significantly less advantageous than a correctly designed profile, especially on the leading edge and the upper sail. Due to its significantly smaller size, the additional drag of a "shark nose" has a proportionally higher effect on the performance of the RC paraglider and has a significantly more negative impact on it. For this reason, we consider it much more important to design the profile nose in such a way that it creates as little additional drag as possible and is designed in such a way that the stability of the paraglider canopy is ensured by the pressure distribution at the profile nose of the upper sail and not primarily by increasing the internal pressure via a sharknose design.

Since model paragliders fly 80% of the time without acceleration, a shark nose profile would tend to reduce gliding performance. Increasing the weight of the RC paraglider by just 12% would have the same effect, namely an increase in the internal pressure of the cell. Our goal is therefore to develop an aerodynamically efficient profile that generates suction forces and moments that prevent a front collapse even at high acceleration.

If a frontal collapse does occur when flying through very gusty air, i.e. turbulence, this is reduced by our innovative locking valve and stopped at the valve so that the RC paraglider canopy does not empty completely.

Conclusion:

To ensure the best flight experience with each RC paraglider model, we calculate the optimal profiles for each of our RC paraglider models using flow simulation. The result is a so-called profile pattern, which includes various profiles along the wingspan.

We also examine the effects of the wing geometry in these simulations in order to determine the optimal canopy geometry. This results in an aerodynamically clean RC paraglider wing that offers the greatest possible performance potential in different phases of flight. In this way, we try every day to develop the best material for the sport of RC paragliding.

Of course, we validate the simulations of the RC paraglider profiles and the geometric shapes of the wings through numerous flight tests and many prototypes in the field. We modify, recalculate and create further prototypes until we gradually achieve the optimal result. In the field, we also use scissors, glue, special tape for paraglider sails and more. The development and engineering of RC paragliders therefore only takes place partly on the computer. A large part of the time is devoted to flight tests and modifications on site. What is special is that we can see a clear correlation between simulation and reality. This confirms our calculations and strengthens our confidence in the next steps in the future development of RC paragliders. This process also corresponds to the industry standard in the development process of complex designs.