A BASIC GUIDE TO SUCCESSFUL
ELECTRIC FLIGHT

THE BASIC HARDWARE

The names given to the various sizes of motor used in electric flight mean very little. Don't worry about being confused, everybody is, not only beginners. As is often the case a name given by a manufacturer to it's own product has become a generic name for the type. Specifically the "SPEED" range of motors produced by Graupner. Robbe, Aeronaut and others market very similar motors under their own names. All of these motors will be referred to here under the generic "SPEED" name.

What has made the "SPEED" motors so popular is that they are supplied specifically for electric flight and more or less guarantee success if used in a well designed model of light structural weight. The most commonly used sizes of motor for low cost electric flight are the SPEED 400 and SPEED 600. Various high specification versions of both are available, intermediate sizes are also beginning to appear, the model examples listed later all use the basic type.

SPEED 400. (case length 37mm, dia. 27.5mm, shaft 2.3mm) Used as a direct drive motor (i.e. without a gearbox) the SPEED 400 will provide sufficient thrust for a streamlined sports or fighter type up to around 36" span. Likewise it will power a self launching glider of around 60" to 65" wingspan. The motor being driven by 7 x 700mAh cells in both cases. Propeller size near to 6 x 4.

SPEED 600. (case length 57mm, dia. 37mm, shaft 3.17mm) Used as a direct drive motor will power a clean aerobatic model or fighter type of around 48" span on a battery of 7 or 8 x 1200mAh to 2000mAh cells, driving an 8 x 4 or 8 x 6 propeller. Alternatively a self launching glider up to around 78" wingspan, on 7 cells using an 8 x 4 or 9 x 4 propeller.

The 400 size motor comes in two useful voltages 6v and 7.2v. The 600 comes in 7.2v, 8.4v and 9.6v. The voltages stated are again only intended as guidelines, electric flyers commonly "overdrive" motors by 1.2v (1 cell). That is to say use an 8.4v motor with an 8 cell battery pack (9.6v). Driving the motor harder to produce more thrust is acceptable even though it may shorten the life of the motor a little, simply because the motors are quite cheap to replace. In the 600 size the 7.2v and 8.4v are the most commonly used. For the thrust that the motor is capable of providing the weight of the 10 cell pack needed to drive the 9.6v version is prohibitive.

There is a lesson here that has been learned by people who have flown electric for many years. Models which were originally designed for the then available "buggy" or car motor (the 540 size), driven by seven or eight 1200mAh cells often struggled to fly with any authority. These models can now be flown successfully with the 400 size motor. Less thrust yes, but an awful lot less weight with seven 700mAh cells on board.

The SPEED500 should be mentioned here lest you think that it is forgotten, the fact is, it almost appears that it has been. Graupner recommends it for use in sports models with an all up weight of 1000-1250g (35-44oz), with a wing span not exceeding 1200mm (47in). I have come across few in use so cannot comment as to the accuracy of these recommendations. The motors come in an economy range, somewhat in the area of a 540 'buggy' type, and a high performance range, expensive units for competition use. I would not consider the SPEED500 therefore to be a 'generic' size as discussed here.

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