Hi,
From HTTP://www.FAI.ORG
I am sharing the details for classification.
Perhaps this is known to all but I just add this for beginners.

F1 - Free Flight
F2 - Control Line
F3A - Radio Control Aerobatics
F3B - Radio Control Soaring
F3C - Radio Control Helicopters
F3D - RC Pylon Racing
F4 - Scale Models
F5 - Electric Flight
F6 - Airsports Promotion
F7 - Aerostats
S - Space Models
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F1
F1A

F1A/1.Flapped wing models, or other unlimited developments, are allowed at current weight and area specifications but have to be flown off a 40 metre line.

F1A/2.Bunting and Circle tow models are allowed at current weight and area specifications are allowed but have to be flown off a 50 metre line.

F1A/3. Models restricted to fixed, straight tow only hooks, simple Auto Rudder and DT only. Current area specifications but no minimum weight. Flown from a 60 metre line.
F1B

F1B/1. Unlimited technology allowed at current weight and area specifications but Rubber weight limited to 30 grams maximum.

F1B/2. Models restricted to fixed pitch/diameter propeller units, one tail movement (single VIT) and Auto Rudder; current area and weight specifications; Rubber weight 35 grams.

F1B/3. Models restricted to DT only (no functions at all). Current area specifications but no minimum weight. Rubber weight 40 grams.
F1C

F1C/1 Unlimited technology allowed at current weight, area and power specifications but Engine run limited to 4 seconds.

F1C/2 Models as per current area, weight and power specifications but restricted to direct drive engines and "fixed geometry"; Engine run 5 seconds.

F1C/3 Models restricted to DT and Auto Rudder only (no other trim changes permitted). A maximum area specification of 35sq. decimetres but no minimum weight. Engine restricted to direct drive, plain bearing, maximum size 2.5 cm3. Engine run 10 seconds.
F1E

F1E/1 Unlimited technology allowed at current specifications. (Note: current specifications produce acceptable performance but do not employ acceptable technology levels.)

F1E/2 Models restricted to "conventional" magnet units (electronic drives not permitted). Mechanically programmed rudder movements permitted but tail movements restricted to DT only. Time scores achieved are multiplied by 1.1 before "percentages" are applied to reach the final points score.
F1Q

F1Q/1 Unlimited technology allowed at reduced battery weight specification of 100 grams for Nickel types and 60 grams for Lithium types, 15 seconds maximum Motor run.

F1Q/2 Models restricted to "Brushed Motors" at present battery restrictions. 20 seconds Motor run.

In both F1Q categories Fly-off Motor runs would be reduced by 5 seconds in each round to a minimum of 5 seconds for Category 1, and 10 seconds for category 2.
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F2 - Control Line

The model aircraft compete for pure speed in the F2A category where the engine is restricted to 2.5cc maximum displacement. The use of tuned exhaust extraction systems allows high engine performance and speeds exceeding 300 kilometers per hour over a 9 lap course of 1 kilometer distance. Timing can be done with sophisticated electronic devices to assure accuracy.

In F2B aerobatics, all competitors perform the same sequence of maneuvers much as ice skating competitors formerly performed "school figures". A panel of 5 judges scores each of the flyer's maneuvers for precision adherence to the described form of the maneuver. Each competitor flies in 2 preliminary flights with the 15 highest scores entering a final. In the finals, each competitor flies three flights and the highest total sum of the scores of the best two finals flights wins the contest.

In F2C, the model aircraft race each other with three pilots flying their aircraft in the same circle simultaneously. Each model has a mechanic who starts the engine at the race starter's signal and catches and refuels the model when it runs out of fuel. In a 10 kilometer (100 laps of the circle) race, refueling is done twice on average because of the mandatory 7.0cc limit on fuel capacity. Speeds of 200 kilometers per hour are achieved and pilots must exercise great skill in overtaking competitors, and in takeoffs and landings, with this degree of model performance. Competition is close and many races are won by tenths of seconds which requires great pit stop skill on the part of the mechanics. Championship caliber mechanics catch the model, refuel it, restart the engine with 1 flick of the propeller, and release it in less than 4 seconds.

F2D is the combat category where again there are multiple pilots in the circle simultaneously. This time it is two, each with a mechanic on the ground. The aircraft are light in weight and very short from nose to tail so as to maneuver quickly in the air. Each has a 3 meter crepe paper streamer attached to the rear of the aircraft by a 1 meter string. Each pilot may attack the other's aircraft at the streamer only in an attempt to cut the streamer with his or her model's propeller or wing leading edge. Each cut scores 100 points. Each second the model is in the air scores a point and the match runs 4 minutes from the starter's signal to launch the aircraft. At the almost 200 kph speeds of the aircraft, mistakes of the pilots often lead to crash damage so two aircraft are allowed for each match. The mechanics (2 per pilot-contestant) are on the lookout for the crash and will quickly start the second aircraft, retrieve the streamer from the first and attach it to the reserve model before launching. The action is so fast that the new observer frequently cannot see the actual cuts of the streamers as they happen so quickly. Each competitor is allowed two losses before they are eliminated from the contest. The last survivor wins.
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F3A
The FAI/CIAM class of F3A involves complex aerial manoeuvres with a radio controlled model aircraft, where utmost precision and skill in controlling the model aircraft in any attitude and under all conditions is required. The model aircraft is 100% influenced by the wind and all manoeuvres in the aerobatic schedules are judged relative to a point on the ground. The competitor must therefore compensate constantly for possible wind drift. Typically, an F3A model aircraft will have a fuselage length of no more than 2 metres, a wing span of less than 2 metres, and the weight must not exceed 5kg's. The motive power is usually an internal combustion engine, with no power limitations, but the engine has to be adequately silenced. The on-board radio control equipment, receiving signals from the competitor's transmitter, actuates the control surfaces to enable aerobatic performance.

The F3A class is a team as well as an individual competition. FAI member countries may enter a team of maximum three competitors as a national team for world- and continental championships. Team results are the sum of the three competitors' scores.
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The "F3B subcommittee" was initiated long time ago, and was named respectively after the only Radio Control Glider class at the time, the "F3B". Today its name has changed to "RC-Soaring Subcommittee" as it is responsible for the development and monitoring of five more Radio Controlled Glider classes, a brief description of which is presented below.

F3B - Multi Task Thermal Soaring Gliders

This is the oldest of all R/C glider competition classes. Initially it was a simple "duration" event, but soon expanded to a multi task event, in which the pilot has to fly 3 different tasks, Duration, Distance and Speed in each round.

In the Duration task the goal is to fly the glider for exactly 10 minutes and land as close as possible to a designated spot. In the Distance task the pilot has 4 minutes working time in which his glider must cover as many times as possible the official course of 150 meters in either direction. Finally, in the Speed task the gliders must cover 4 legs of the aforementioned course as fast as possible.

For launching their gliders the competitors use specially made electric winches.

What it is more challenging in this class is the designing approach of the model, as all three tasks must be flown with the same model, which must be trimmed to achieve the minimum sinking speed in the first, the minimum gliding slope in the second, and the minimum drag in the third. In addition to these parameters, the model must be light, aerodynamically clean and exceptionally strong to withstand launching forces and speeds exceeding 200 Km/h.

World Championships in this class are organized bi-annually, in which more than 80 pilots are competing, in more than 9 flying rounds.

So far fifteen World Championships have been organized, 1st in 1977 at South Africa, 2nd in 1979 at Belgium, 3rd in 1981 at USA, 4th in 1983 at United Kingdom, 5th in 1985 at Australia, 6th in 1987 at Germany, 7th in 1989 at France, 8th in 1991 at The Netherlands, 9th in 1993 at Israel, 10th in 1995 at Romania, 11th in 1997 at Turkey, and 12th in 1999 at South Africa, 13th in 2001 at Czech Republic 14th in 2003 at Germany, 15th in 2005 at Finland. Next one is scheduled for this year at Switzerland.

F3F - Slope Soaring Gliders

As the name depicts, this event is flown in front of a slope, taking advantage of the updrafts created by the wind. In the single Speed task the pilot tries to fly its model over a 1000m course (composed of 10 X 100 meter legs) in the shortest possible time.

At least four rounds should be completed in order to determine the winner. This class has the provisional status, which means that World Championships cannot be organized in this class for the time being.

F3H - Soaring Cross Country Racing

F3H is a Cross Country racing for R/C gliders that is the single task is to fly a course from point A to point B or C etc. as fast as possible. The Contest Director before the start of the event decides the type of the course. This class is also provisional.
F3I - Aero-Tow Soaring Models

In this class of R/C Gliders, towing is performed by the use of a tug model provided by the organizer. The tug model tows the glider up to 200m where it is released. This class is a multi-task event (Distance and Speed) and is provisional as well.

F3J - Thermal Duration Gliders

This class is very popular as it is a single task event with simple rules. The competitors try to keep their models aloft for exactly 10 minutes and land as close as possible to a designated spot.

Launching the model is achieved by hand towing, where two persons with a 150m-monofilament line pull the model.

Pilots are divided in groups, after a matrix schedule, so that during the preliminary or qualifying rounds, they compete against as many as possible of the other pilots. Then the top pilots fly in a single group the Final or Fly-Off rounds, which determine the winner.

World Championships are also organized biannually, with more than 80 competitors participating in the senior's category and about 50 in the junior's category.

1st World Championship was organized in England in 1998, the 2nd in Greece in 2000, the 3rd in 2002 at Finland, the 4th in 2004 at Canada and the 5th in 2006 at Slovakia. The next one is scheduled for 2008 at Turkey.

F3K - Hand Launched R/C Gliders

Hand Launch R/C Gliders is a class with growing popularity. In this event the competitors fly comparatively smaller gliders, with a maximum wingspan of 1,5 m which are launched from the pilots themselves by hand. In last years the pilots use for launching a method similar to discuss toss.

For the contest the organiser chooses a set of tasks from an official list. The flying tasks different somehow from each other but in principal all call for a number of short duration flights in each round. The pilot usually makes fast relaunches and tries to use the thermal activity near the ground.

Similar rules denoted F6D are expected to be applied in the following World Air Games.

The CIAM FAI Plenary Meeting confirmed this year the promotion of the F3K class to the official status.
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F3C
For the FAI/CIAM F3C competition class pilots must perform complex hovering and aerobatic manoeuvres with a radio controlled model helicopter. Each manoeuvre must be executed with high precision and skill in any attitude and under all weather conditions. F3C model helicopters have a weight limit of 6.5 kg, a maximum rotor disc area of 250dm2 and are powered by internal combustion engines with a maximum displacement of 15ccm or electric motors with a maximum battery voltage of 51 Volts. The engines/motors must be adequately silenced to meet a specified noise limit. The on-board radio control equipment, receiving signals from the competitor's transmitter, actuates the engine throttle, main rotor lateral and longitudinal cyclic pitch, main rotor collective pitch and tail rotor pitch to guide the model helicopter through hovering and aerobatic manoeuvres.
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F3D
In pilon racing, the sound level and exhaust pipe details required within limit with muffler design.
For more information, check
http://www.fai.org/aeromodelling/system/files/F3D+Silencer+Implementation+Nov+09.pdf
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F4 - Scale Models

The FAI/CIAM Scale classes involves the art of illusion, that is to create and build a model of a full size aircraft and to fly this model in a manner that to the best of the modellers ability illustrates the way the full size aircraft flew. This require research into the history of the original, craftsmanship in both technical drawings and in building of the model and further precision in controlling the model while going through the manoeuvres typically for the full size aircraft

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F5
Current FAI competition classes
F5A Electric Aerobatics (for Airplanes up to 3 kg)
F5B Electric Motor Glider (FAI World Championships Class)
F5C Electric Helicopters
F5D Electric Pylon Racing Model Airplanes (FAI-World Championships Class)
F5E Solar Model Aircraft
F5F Electric 4 Cell Motor Glider
F5G Electric Big Glider.
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F6
Airsport Promotion
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F7
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S

Category: S-6: Streamer duration
Sub-class :S6A (Maximum weight 100 g)


Category: S-9: Gyrocopter duration
Sub-class :S9A (Maximum weight 60 g)
Sub-class :S9B (Maximum weight 90 g)
Sub-class :S9C (Maximum weight 150 g)
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Requested not to close this thread for further modification.
Requested to add more sub classification available to them.

Thanks

Now this is a informative thread for the one who are interested in discipline or to compete in any of the above class.

Definitely not for the people who just wants to fly around with no rules...

Free flight, Control line, F3A, F3C, Scale & Pylon racing are the class which we can compete here in India if we have decent flyers around the country. I am sure we have many RC people having good skills..  all we need is events that will promote & bring up the talented people 

Kalyan
Thax for posting here so that many more can see, but should you not have given credits to the FAI site from where it came?

+1 Captain... sources are to acknowledged as much as possible, and certainly in the case of verbatim copies.

There is one link to FAI website in the material posted, but that is not a direct attribution to the source.

Thanks for pointing.
Actually, I am totally confused in so much detailing and rearranging that I even forgot to mention. Really a mistake. Updated.