25-Jun-24 - 06:16 PM

Thermal Circle Text - Thermal Circle 12

Written by Hayden Daley - 12 September, 2007.

In this edition of the soaring circle we will take a look at the International competitive classes for competive soaring F3j,F3f and f3b.Also wing servos in competition and other sailplanes and the better choices that are available to glider pilots from the leading radio equipment manafacturers and a useful scale aero tow release..

Competitive Soaring

All over the world there are thousands of aero modellers who compete in sailplane competitions using the rules of the international soaring classes f3j,f3f and f3b. These international class rules are governed by the F.A.I, or the Federation Aeronautique Internationale and all modifications or amendments to these rules must be approved by the F.A.I. There are sub commitees which suggest new rules or amendments to the F.A.I which are then voted into or out of the rules.

It is events under these rules which are hotly contested as it provides the opporunity for a fair and even contest and the possibility of becoming a world champion in the class the sailplane pilots have deceided to compete. The FAI holds world championships in these clases and contest events are flown in different countries to decide the world champion in that class.


F3b is the name under which the multi task soaring rules are named. This soaring class has three disciplines thermal, distance, and speed. The thermal element of the event requires a ten minute flight to be completed as well as a spot landing which is indexed into the score. The distance task involves flying laps of a 150 Metre course you must fly as many laps as possible in four minutes. The distance task is a tactical event and requires choices in ballast, as being under weight can cost many laps on a good distance course with lift. The speed task is to fly four laps of a 150 Meter course with four minutes in which to complete the task and you can also launch again in this four minutes if you feel you can acheieve a faster time.

The f3b rules have strict laws governing launching equipment used in these events. The winch must meet a strict load test, it is locked up so the drum cant move and the electrical current draw is tested, too much curent draw and winch is illegal and must be resistored until legal. The rules also specify the maximum size of the 12 volt battery to be used as a power source, if the battery is to large it is illegal and wont be allowed to be used in competition. The winch line length used in this event is 400 metres or 200 metres to the turn around.

The rules also state that the maximum weight of an f3b sailplane is 5kg, a maximum surface area of 150 dm squared and the minimum radius of the nose is 7.5 mm. The radius law is a safety law and stops people making noses of sailplanes to sharp and therefore more dangerous. A competitor may only enter three models for each competition and is able to interchange parts to complete another working model if all three are damaged..

The models used in these events are almost exclusively moulded competition gliders. There are still people who make there own competition sailplanes but generally most people are happy to buy the models with which they compete. There are also modellers who compete with there own vacuum bag wings, moulded fuselage models. The models can be built for around three hundred dollars per model in materials and done properly are competitive in this event albeit a little heavier. They involve cutting foam wing cores and laminating or skinning the cores with fibreglass and carbon fibre and making a fuselage from moulds.

The molded models come from very accurate computer milled moulds. They are cut to exacting tolerances to try and achieve the best shapes and profiles that produce an accurate finished model. You will find that pretty much all moulded model will come with an exceptional finish, be exceptionally strong and the added bonus of being very light in weight.

There are many league and other events held world wide if you wish to compete in the class f3b. Regular competitions are held all around Australia by soaring and other clubs and are well attended and well run by the contest directors.


F3j is the international soaring class for thermal flying. The event involves flying for ten minutes during the heats as well as a spot landing which is indexed to the score. The required heats are then flown and the top ten or so pilots will make the fly off, this fly off involves a 15 minute flight and spot landing, the person with highest score at the end of the fly off heats is declared the winner.

The event is flown with a 150 metre hand tow as the launching equipment and is the most labor intensive of the competive classes, you need at least three helpers for each pilot to fly a heat. People required are a timer and two people for the hand tow. The line length of a f3j hand tow is limited to 150 metres.

This makes for a difficult but fair event, the law was introduced to provide a fair launching method for all competitors and makes completing the 10 minute heat flights and 15 minute fly off times hard and a massive challenge to fly consistantly.

There are plenty of competitive f3j sailplanes available to be purchased from many different manafacturers around the world. These f3j models are genreally built lighter as they do not have to have the strength required for punishing winch launches. You will find the average weight for an f3j model is around 1900 grams compared to an f3b competition sailplane which is around 2200-2400 grams complete. The logic here is a light wing loading for more “hang” time to achieve the ten and fifteen flights and then to add ballast as the wind increases. This is why you can buy lightweight versions of a lot of competition designs, but always keep in mind when buying light weight versions is that some of the strength has gone, and that they are not really suitable for the really windy days, and may break or flutter during these conditions.

F3j is contested all over Australia and is a very challenging class in which to compete. The rules allow for a very even and fair competition with similar launching equipment for all competitors. Australian David Hobby is the current world champion in this class and is the first Australian to achieve the difficult goal of becoming the f3j world champion. It will be interesting to see if he can defend this title at the next world championships..


F3f is the international class for slope soaring racing. This event requires a 1000 metre distance to be flown on a 100 metre course, so ten laps will be required to complete the flight and the flight time covering the distance is submitted as the score. The fastest pilot will score 1000 points and the slower pilots will receive an indexed score againt the winners time. A minimum of four rounds must be flown. This is an exciting event and unfortunately not really supported as a competition class in Australia but is very popular in Europe where the bigger contests will get 100 or more entries.

In this class there are limits on the suraface area of the model, the weight of the model and the wing loading or amount of ballast to be added. The maximum surface area is 150 dm squared or 2330 square inches. The maximum flying mass is 5 kg and the maximum wing loading is 24.5 oz per square foot. There is also a wind requirement, the minimum wind speed required is 6 mph whilst the maximum flyable wind speed is 55 mph. If these requirements are not met then the contest is delayed or abandoned.

The models used in these events vary from f3b sailplanes, specifically designed models, to scale sailplanes and anything in between. A lot of fast and succesful designs and moulded models fit into the restrictions of this class and for this reason I believe f3f is the least expensive of the international classes in which you can compete.

Finally on molded models I here many people talk of the massive expense of molded models and the difficulty in affording the hobby. Personally, I believe that the ability to purchase the same equipment that the best pilots are using has levelled the playing field in competive soaring, and explains the cost of these models.

Wing Servos for Competition Soaring

Deceiding which wing servos to use in your new sailplane can be a difficult choice with many servos available that fit into the catergory of glider wing servo. Personally, many different wing servos have gone into my competition and other sailplanes with some being more successful than others.

Some of the better servos for glider wings are, the Airtronics 94141 is a powerful metal geared wing servo and unfortunately not available here but are easy to purchase online from the bigger U.S online hobby stores. They have lugs that can be trimmed for side and normal mounting and with the current dollar they are also excellent value. The J.R DS368 metal geared digital servo is an excellent wing servo with good power and torque and good holding power, these servos were used on the large surfaces of the Caracho f3b sailplane and did not fail in heavy conditions. The German made Volz servos have been very reliable over the years with many Victorians using these servos exclusively in there competive models. The wing-maxx digital and others are supurb with powerful outputs and metal gears making them a durable competition servo. Multiplex has been an innovative leader in the glider wing servo market with many different choices. All of the Multiplex servos and other equipment are of good quality and are a now being offered to hobby shops in Australia. Check your local hobby shop for the specifications of this and other Multiplex equipment.

Aerotow Releases

If you require a good, scale like aerotow release you could do worse than use the Graupner nose release in your new scale sailplane. This release is excellent value with Model Flight listing the item at $19.00 and the item has the part number GRP 1065. I have used this release in my scale gliders and have never had a hang up or failure. It is suitable for scale models ranging from 3 metres upwards so this includes all the s2g kits right up to large one-third scale sailplanes. This item looks very realistic and comes thoroughly recommended, with proven reliability and well engineered.

Custom Wiring

Model sailplanes require diferent wiring for servos than most other types of models. The servos are generally far out in wings and long leads from receivers are required to reach the servo. This causes problems when trying to purchase servo leads of the correct length for the model. This results in the need for custom wiring, the ability to make your own leads with suitable plugs to the right length required, Before I give you the serial numbers and names of this equipment I must say that this equipment is expnesive and better bought by a syndicate of 4-5 people, the crimping tool alone is $420.00. . The swiss company Molex make this gear and it can be purchased from electronics suppliers. In time with enough leads made the costs will be recovered. The crimping tool serial number is EDP 11-01-0209 ENG CR 60930b. The male crimp serial number is 16 – 02 - 0108 M 70021-0204. The female crimp serial number is 16-02-0096 M70058 0204. The block connector three wire serial number is 00 50 57 93 03. This equipment will allow custom wiring looms to be made.

That’s it from the soaring circle, Hayden Daley.

Click on any banner ad to transfer to the website

Text-based competition soaring information website established 2007