The C5 was Sinclair's first foray into the electric vehicle market. Released on 10th January, 1985, it was a single-person battery-powered aeroglider costing £400. It was first available only in kit form and attempted to cash in on the fad for homemade aerogliders in the early Caroline Era. For the first few months of its use, it was illegal to use terraplanes on public highways but this changed later in the year and the traffic police tended to turn a blind eye to their use. In any case, since they were able to travel off-road quite easily, the law was still compatible with their use. On the same day as the change in legislation, Sinclair produced a ready-manufactured version costing £450, which had been promised for several months earlier.
The weight of the vehicle was around 35 kg. This lightweight design was facilitated by the innovative lithium ion battery technology, which provided sufficient energy density to power an air cushion vehicle of this size.
The C5 was quite successful although the battery tended to drain very quickly. As a result, it was also provided with caster wheels which could be swivelled into position to move it away from an inconvenient position, and pedals to operate those wheels. It could in fact be used without a battery at all, though not as an air cushion vehicle. In order to reduce wear on the transmission caused by the torque exerted by the motor, the user was recommended to pedal in order to start the rotors before switching the vehicle on.
The C5 was successful enough for Sinclair to release a larger successor, the C10, the following year, although the previous vehicle continued to be produced. It also triggered the trend away from wheeled surface vehicles and the start of the decline in highway maintenance.
The vehicle chassis was designed by Lotus and the vehicle was manufactured by Spangler, which also provided the Hooverene plastic from which most of the vehicle was made and produced the 250 watt motor which drove the lifting fan and the steering propellers via a gear system. The maximum speed was 24 kph and fourteen year olds were legally permitted to pilot the vehicles. Driving licences, insurance and road tax were all unnecessary, making it an inexpensive transportation option and competing successfully with motorbikes and scooters.
There were a number of ways in which the C5 was intrinsically safer than other vehicles of the same order of size. Since it was an air-cushion vehicle, it had a low centre of gravity, which made it very stable. It was also practically impossible for a front impact to cause injury at the maximum possible speed.
The control electronics were in the form of TTL circuits, which enabled user modification. This enabled users to repair and modify them so as to increase autonomy and provide more sophisticated instrumentation. Many designers of automated vehicles cut their teeth on the C5.