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What is an E20? 

Why E20 

Free Flight Duration is an exciting and challenging branch of aeromodelling but is it probably true to say that the numbers of people engaging in the sport have steadily diminished over recent years. There are lots of reasons for this, and here is not the right place to go into it. E20, however, might represent a ray of light by providing an accessible way into Free Flight Duration competition. Models are small, relatively cheap and easy to build, can be flown on small fields with reduced motor runs and yet are capable of high-performance flights and long duration. Models can range from simple all-sheet balsa construction to carbon fibre composite materials with geodetic wings. The limits placed on the motor run, power, weight and size, mean that pretty basic models can compete on a fairly basic playing field with their more sophisticated counterparts. The skill comes down to the trimming and the picking of the air – the essence of Free Flight duration competition.


The Rules

E20 is an evolving class. In its most basic form, an E20 is an Electric powered model that has a 20 inch projected (not flat) wingspan. The motor run is short anything from 8-20 secs. The idea is that the model will climb quickly and then transition into a glide at the end of the motor run, which will then form the majority of the flight.


The NFFS (National Free Flight Society) in the USA have adopted these rules for the Class:

Model Eligibility Projected wingspan not to exceed 20” (monoplane only)

No auto-surfaces except dethermalizers

Model Weight Model must weigh at least 1 ounce

Motor Eligibility Models must use an 8.5 mm x 20 mm coreless electric motor No gear drives are allowed.

Propeller: The propeller is not to exceed 2.7 inches in diameter.

Battery The battery required is a single cell Lipo battery. There is no limit on Mah capacity. (Voltage limit has also been dropped for 2022)

In the UK, The Peterborough Model Flying Club have championed E20 and have tailored rules specifically for a smaller flying site, two sets of rules were developed. The first, Ferry 500 was flown on a fixed power system to provide a level playing field for small field competition. (see  As motors and batteries for Ferry 500 became increasingly hard to obtain and in order to encourage experimentation in the class, Peterborough developed an Open E20 class which is currently flown in Club competitions and at Flying Aces and SAM 35 events in the UK. These rules are:

  1. Models must have a maximum 20" projected wingspan (not flat span) maximum 20" overall length including the propeller. (This rule on length of model has now been omitted, March 2022)

  2. Any airframe design is permitted within the above limits.

  3. Any motor, propeller and timer are permitted.

  4. The flight battery must be sized so as to be capable of three motor runs.

  5. The motor run will be less than 8 seconds.

  6. Models must have a dethermalizer fitted.

  7. No minimum or maximum model weight.

  8. The competition comprises of three flights to a max decided on the day (up to 60 seconds.) A flight of less than 10 seconds will be considered an attempt.

The Ferry 500 and Open E20 events, with the 8-second motor run, are perfect for small field flying and suit smaller flying sites perfectly.  There are, however, some drawbacks. The motors and batteries designated for the Ferry 500 Class are no longer readily available, and equivalents are hard to come to by. Furthermore, whilst the FET timers are excellent, they can be off-putting to those of us who only have a rudimentary electrical and soldering ability.

 E20, as a class, has enjoyed far more popularity in the USA than in Europe. In the US E20 has been flown for several years under provisional rules developed by the NFFS (National Free Flight Society) which is a specialist group within the AMA (American Model Airplane Association), which would be roughly the equivalent of the BMFA in the UK. These rules have now become codified into the E20 class and echo that which is already being flown in other parts of Europe. This means that what an E20 looks like in terms of model specification and power train is now clearer.  Whilst it’s true that we, in the UK, have not adopted any formal or universal E20 rules as of yet, it would be logical to take into consideration what is now an up and coming Free Flight Class in America.

Another development of note concerns the availability of E20 timers, motors, and batteries. Recently, Melih Karakelle of BMK Free Flight Products has produced and made available ingenious lightweight E20 timers. These timers, incorporate the motor run time with a simple coil element that heats up and burn through a rubber band for a d/t.


He fits them all with micro JST plugs, so no soldering is required, it really is plug and go! Importantly, these motors, timers, and batteries are configured for the now accepted US (and what is becoming European) standard E20 rules.

What is significant about the US rules is that 8.5 mm x 20 mm motors are available everywhere, they are standard for micro drones, inexpensive and powerful. Shop around and you can buy four just under a tenner! Another major difference is the weight of the model and the motor run. With the E20s flown to Peterborough Ferry 500 Class, the model was restricted, as the specified motor and battery combination means that you were flying a model around 55/60 grams. Now a tiny motor, battery, and timer which combined weigh less than 13g, meaning an airframe of around 30g is easily achievable. This combined with a 20-sec motor run makes a 1:30 max a real target and offers a fun, accessible, and relatively cheap introduction to Free flight Electric Duration.

Does this mean Peterborough style E20s are no more? 

No, Peterborough Open E20 rules already allow for any motor/any battery model so provided that it's 20 inches projected span, you could use this setup and fly to an 8 Sec run at a small flying site No change would be needed and models could compete alongside Ferry 500 class for the 40/60 second Max. As previously noted there are events run by The Peterborough Model Flying Club and SAM 35 to these rules. 

But there is more! Several of us in the UK have been experimenting with BMK timers. Peter Gibbons, Chris Edge, Mark Benns and I are keen to promote E20 duration, adopting largely, the NFFS rules as we feel it’s a great class for Free Flight Duration and offers an excellent entrance into the competitive free flight scene. 

To this end, events are already planned for the British Nationals as well as monthly meetings at BMFA Buckminster.  Of course, this year we also have the World E20 Postal competition, the brain child of Peter Gibbons,  which is a celebration of this exciting class and coincides with the BMFA celebrations for a hundred years of Model flying in the UK! 


BMK band burner on an E20 Timer in action, light, reliable and easy to use!

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