SIROKO– Giving the Jedï a Successor After 31 Years

Introduction

More than three decades (!)  after the creation of the famous Jedï in 1992 — a glider co-designed with my friend and club mate Olivier Bordes, and using a RG14 airfoil — the time had finally come to imagine its successor. Designing a new aerobatic glider was not about nostalgia, but about applying 30 years of accumulated experience, modern aerodynamics, and today’s moulding standards to create a truly versatile slope machine.

 

The Jedï 3 in action

I am therefore very happy to share the story of a collaboration with Miroslav Laurenčík (CZ) on this aerobatic glider project called "Siroko".

Design Philosophy: One Glider, All Conditions

The ambition behind the Siroko was clear from the beginning: to offer a polyvalent aerobatic soarer, capable of flying easily in very light conditions, yet fully comfortable in strong winds thanks to significant ballast capacity. The idea was simple in theory but demanding in practice: If you had to go to a slope with only one glider, this would be it.

This led to a design positioned halfway between:

• very light, low-inertia VTPR-style gliders, optimized for precision and energy conservation at low wing loading, and
• heavier, highly loaded machines such as Stingray or large Swifts around 3 m, designed almost exclusively for fast, ballistic aerobatics.

The Siroko aims to bridge that gap.

Aerodynamics and Airfoil Choices

The overall shapes — fuselage, wings, and fin — are the result of multiple influences and inspirations, with a constant desire to achieve a modern, clean, and efficient look.

The wing features a near-elliptical lift distribution planform, combined with Thierry Platon’s TP66 / TP66S airfoils.

The objective was not necessarily to outperform the well-known SB96V/SB96VS in pure light-lift performance, but rather to:

• improve speed and acceleration,
• enhance energy retention, especially in vertical figures,
• reduce drag losses during rolls.

About the TP66 / TP66S

The TP66 airfoil proves to be just as efficient as the SB96V in light conditions, with equivalent polars at low Reynolds numbers and high Cz. However, it clearly stands out thanks to a much better Cx.min, regardless of Reynolds number.

This translates directly into:

• better acceleration,
• higher maximum speed,
• superior energy conservation.

Another key point is the lower aileron drag, meaning less energy loss on the roll axis. As a result, the glider remains efficient even when rolling aggressively during aerobatics.

The TP66S, used at the wing tips, further improves manoeuvrability and snap roll capability. Polar comparisons with the SB96VS again show a noticeable drag reduction while maintaining excellent performance at high Cz.

This TP66 / TP66S combination perfectly meets the requirements of both:

• VTPR aerobatics (energy conservation on lightly loaded gliders), and
• wide, ballistic aerobatics (high speed and strong vertical restitution when ballasted).

The tailplane uses the well-known TP29 airfoil in its 9% thickness version, renowned for its efficiency and its absence of a dead zone around neutral — an essential quality for precise aerobatic control.

General Characteristics

• Wingspan: 2.75 m
• Wing area: 50 dm²
• Construction: fully moulded
• Manufacturing: proudly made in Europe
• Ballast capacity: up to 1.2 kg, centered on the CG

From CAD to Prototype

Miroslav first worked extensively on the CAD drawings, and about a year after sending him the initial 2D drawings, the project took a decisive step forward.

When I finally received the first Siroko prototype, the impression was immediate. The moulding quality was simply outstanding.

The paint, fit and finish, adjustments, and level of detail are all at a very high level. Everything feels precise, clean, and thoughtfully executed.

Notable features include:

• elevator articulated on ball bearings,
• reinforced tray and rib structure,
• wiring already installed in the fuselage,
• wing bags included,
• ballast compatible with the Quantum F3F series,
• spacers and elastic spacer,
• Velcro included for an optional electric version.

Personally, I love the fuselage lines too much to add a spinner, so this prototype remains a pure slope glider.

Component Weights:

• Right wing: 592 g
• Left wing: 594 g
• Tails + joiners: 71 g
• Fuselage (canopy, tray, rib): 525 g
• Wing joiner: 110 g
• Ballast set: 1200 g

The next step was naturally assembly, mainly installing the wing servos, as everything else was already well advanced.

Assembly

Nothing special to report about the Siroko assembly. Miroslav had already done the wiring in both the wings and fuselage, so all I had to do was install the servo frames in the wings. I went with MKS HV6160 servos for the flaps and MKS HBL 6625 Mini servos for the ailerons. In the fuselage, I opted for a large elevator servo (probably oversized in this case), an MKS HV 747, and an HV6125e for the rudder. The receiver battery is a 2S 3000mAh Li-Ion with a Practical-RC magnetic switch. The receiver is a REX10, which I later replaced with a Slim REX7 ASSIST. A quick check on the scales: 2.6 kg for a 102mm center of gravity.

I can't tell you how excited I was heading to the local slope for the maiden flight...

Maiden Flight: Promising Beginnings

The maiden flight took place in far-from-ideal conditions. We had barely a one-hour window before a thunderstorm, with initially very light wind, then a slight increase and some usable thermals. The initial CG was too far forward, but once moved back, the glider immediately started to “breathe”. Despite minimal tuning, the Siroko already showed a very healthy flight envelope:

• efficient thermalling,
• good speed,
• convincing aerobatic potential,
• excellent stability and energy retention.

A very encouraging first flight — the glider was clearly well born !

Flight Testing: A True All-Rounder

A second session took place in excellent conditions, with around 7 m/s wind. I flew most of the afternoon empty at 2.6 kg, then added 300 g of ballast toward the end. The verdict was clear:

I am more than happy with the Siroko. It is a joy to fly — easy, stable, and incredibly efficient in the vertical. Vertical eights are effortless, rolls can be slow or fast, perfectly axial, even in four-point rolls. Most importantly, aileron deflection does not slow the glider down, allowing it to retain speed throughout aerobatic sequences.

I even managed some very enjoyable dynamic soaring with it. In short: a true all-in-one slope glider.

I also experimented briefly with a gyro receiver. The damping mode showed some potential, but heading mode made the glider feel too heavy on the sticks. More tuning is required there.

Long-Term Impressions

After almost 2 years since I received the prototype, which is still in perfect condition, I never get tired of the aesthetics of the Siroko — nor of its undeniable flight qualities.

The design goal of maximum versatility has clearly been achieved. In light winds, the glider remains pleasant and efficient, allowing you to chase thermals, gain altitude, and perform clean aerobatics. When the wind picks up, adding ballast (up to 1.2 kg at the CG) transforms it into a fast, energetic machine perfectly at home in strong conditions.

The Siroko occupies a unique position between lightweight precision gliders and heavily loaded ballistic machines. It allows academic aerobatics at moderate speeds, with perfect trajectory control and outstanding energy retention in vertical figures — even when unloaded.

The TP66 airfoil works wonders in roll: effective ailerons with limited deflection reduce drag and preserve energy throughout manoeuvres.

Add to that the exceptional build quality delivered by Miroslav, and you get a glider that is well-behaved in all circumstances. With its 2.75 m wingspan, it remains compact and easy to transport — even in a backpack for mountain outings. Every slope session with the Siroko brings genuine satisfaction.

More Information

A series of videos dedicated to the Siroko is available my YouTube channel:

https://www.youtube.com/playlist?list=PL3CGmV_dY01g5ESFVoE6Ffx2sQ0mcU2ay

For information about layups, kit content, pricing, and availability, you can contact Miroslav Laurenčík directly: https://l-model.eu/