Electric flight

Internal-combustion-powered models have reached a high level of predictability regarding their performance, by consideration of well-established interactive elements such as wing span, wing loading, engine capacity, and general layout: Electric-powered flight on the other hand is relatively new and the technology is developing at a breathtaking pace, particularly regarding motors and batteries. So what constitutes state of the art this week becomes normal practice next week, only to be superseded the week after -- or so it seems.

So, advice to newcomers to electric flight is difficult, but based on equipment available  we would suggest the following -

1. Seek out a club member whose specific interest is Electric Flight, not just anyone who happens to be flying fixed-wing. His advice at this stage could prove invaluable, and he will be able to give an opinion on what set-up is most suitable for you and for the specific flying site, and will cover the following topics:

2. Battery could be Nickel Cadmium (NiCad), Nickel Metal Hydride (NiMH), or Lithium Polymer (LiPo), though the first two types are the most common at the moment. (A variant of LiPo is Lithum-Ion (LiIon) which should be treated as a LiPo so far as charging and discharging is concerned.) The battery should be capable of being fast charged so that it can be recharged at the flying field between flights, and to endure and provide fast discharge rates during flight without damage. NiCad and MiMH batteries are reasonably priced and are now proven technology, though they are quite heavy; LiPo on the other hand are many times lighter (an obvious advantage in a flying model), are rather more expensive and are more hazardous than NiCad and NiMH batteries if not treated with respect and understanding. LiPo and LiIon batteries also require a dedicated charger and under no circumstances should they be charged using anything else -- you have been warned.

3. Speed controller can range from a simple on-off switch to a completely variable electronic speed controller, which also provides power to the radio receiver by way of a Battery Eliminator Circuit (BEC). The prices of variable speed controllers for brushed motors are reasonable enough these days, so on-off switches are rarely seen, but brushless motors require specialised electronic speed controllers. These are much more expensive, but the brushless motors won't run without them. Note that speed controllers designed for brushless motors cannot be used with brushed motors, and vice versa. The speed controller (with or without BEC) goes between the battery and the motor and is controlled by a signal from the radio receiver to govern the speed of the motor. If it has a BEC, then you don’t need a separate power supply for your radio receiver.

4. The motor. If you can afford it a modern brushless motor powered by a LiPo battery can produce equivalent power to an average internal combustion engine, and could therefore be substituted for the i.c. engine in a trainer aircraft. But this is still an expensive way to go -- probably more expensive than the equivalent i.c. engine and a considerable supply of fuel! Also, they require a dedicated variable speed controller. Brushed motors, also sometimes referred to as ‘can’ or ‘buggy’ motors are relatively cheap and have been around for several years. Certain of these, e.g. ‘Speed 400’ or ‘Speed 600’ can produce a very satisfying performance for the beginner when installed in a suitable model, and there are many models designed with them in mind.

5. Battery charger. There are many chargers available at reasonable prices that enable NiCad and NiMH batteries to be re-charged in the field at a fast rate (about 45 minutes per charge) taking power from a car battery. It is vital to repeat this warning -- do not attempt to use this type of charger to charge LiPo or LiIon batteries.

6. The aircraft. If you use a brushless motor with LiPo batteries, the world is your oyster so far as choice of aircraft is concerned. At the other end of the scale are models, often made entirely of foam, sold by toyshops, with motors and radio thrown in. If you want something you can call your own, to fly around partially under your control but mainly relying on its own inherent stability, then one of these might suit, and hopefully induce you to learn to fly a real radio controlled aircraft which requires you to pilot it. The middle of the road approach, most common at the present, is to start with an aircraft designed for Speed 400 or 600 motor(s) using 7- or 8-cell batteries. If you buy a ‘full house’ model (with aileron, elevator, rudder, and motor controls) you will eventually be rewarded for a slightly more complex learning period by being able to manoeuvre in and out of smaller fields in more-adverse weather conditions than with a ‘three-channel’ model (either motor, rudder and elevator or motor, ailerons and elevator), thus gaining more opportunities to fly. If you do go for ‘three channel’, it is better to go for motor, ailerons and elevator rather than motor, rudder and elevator.

7. The transmitter. One disadvantage of some of the cheaper ‘two-channel’ packages is that they sometimes come with various permutations of two or occasionally three "channel" controls consisting of knobs, switches and sticks which are unique to one particular model. If you are going to progress beyond your basic trainer you must have a transmitter with two sticks, which are each capable of moving left-right and forward-backwards. The transmitter should be configured as "mode 2" (the left stick’s forward-backward movement, for motor control, will be on a ratchet so that it will stay in any position you put it, whereas its left-right movement, for rudder control, and both the movements of the right stick, for aileron and elevator control will be spring-loaded self-centering) because that’s what most of the club flyers who are going to assist you will be used to. The transmitter should normally be on a channel in the 35Mhz band, though 27Mhz or 459Mhz bands are acceptable but are shared by other types of models and are thus less secure.

Despite all the advances, and the ability of brushless motors with LiPo batteries to perform as well as i.c. engines, at the time of writing the i.c. engine still wins in the power-per-£ stakes. But, if you’re looking for clean and quiet flying, with the ability to just plug-in and fly, then electric flight is for you. And if electric aircraft are a bit more demanding at the moment because of the heavy motors and batteries they have to lug around, then things are going to improve rapidly with the advent of cheaper high-powered brushless motors and less expensive high-capacity LiPo (or whatever new development) batteries with their specialised chargers. So, go to a club field and talk to experienced electric model flyers before parting with your hard earned cash. Then remember that if you take care, stay alert, and follow the rules and instructions, a thoroughly safe, fascinating and rewarding hobby can be yours to enjoy.

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The article above is now slightly out of date as brushless motors now seem to be the norm. They have transformed models that were previously powered by 'speed 400s' etc. which struggled to fly due to the low power to weight ratio.

A motor giving the same power as a speed 400 now costs about £25 with the matching speed controller. when combined with a LiPo battery, which is a similar sort of price, the performance is sparkling as the model is far lighter using this setup, giving a much higher power to weight ratio.

Below is a typical example of this type of motor

Generally, a motor using a 2 cell pack will turn a larger propeller than the same motor with a 3 cell lipo battery pack, but at much lower RPM. Therefore, a 2 cell pack is preferred for slower indoor flight & a 3 cell lipo for outdoors to obtain more power.