Motors move from shifting caravans to planes

The Parvalux DC motor/gearbox units in the Mr Shifta caravan mover have been so successful that Shifta Products approached the company to help in the design of a similar device for aircraft.

Anyone who has tried to move a caravan around by themself will know how difficult it can be - particularly if the ground is soft or sloping.

As caravans have become longer and heavier, various powered devices have been developed to take the strain out of the task, and one of the most popular is the Mr Shifta caravan mover manufactured by Shifta Products.

The Shifta2 is the latest development of the caravan mover and uses a motor/gearbox unit manufactured by Parvalux.

Based in Bournemouth, Dorset, Parvalux specialises in small electric motors rated up to 650W and is one of a small number of companies that still manufactures in the UK.

The Shifta2 caravan mover is a self-contained, battery powered unit that attaches to the tow hitch of the caravan.

The Parvalux DC motor and integral gearbox drives the wheels of the mover, allowing the caravan to be manoeuvred with precision and ease.

With most modern caravans weighing in at well over 1500kg, the powerful Parvalux motor makes light work of moving even double axle caravans (weighing 2000kg) over uneven surfaces and up inclines as steep as 1:3.

Moving light aircraft around presents a similar problem, and an aircraft owner that had seen the caravan mover in action approached Shifta Products to see if the technology could be adapted to this demanding application.

Recognising the potential for the new product, Shifta Products contacted Parvalux for help with the development of a suitable motor/gearbox.

Moving planes from the hanger onto the apron requires considerable effort and great care to ensure the wing tips and tail are not damaged.

There are petrol driven mover devices that can be used to help and these are attached to the front wheel of the aircraft.

However, they can be difficult to start if they are only used occasionally or allowed to get damp.

Reversing is difficult and the operator needs to take great care with the mechanical clutch and gearbox to ensure smooth operation.

The first challenge for Shifta Products was to find a motor gearbox unit that would provide the necessary power to move an aircraft weighing 3000kg or more.

Several makes of motor/gearbox were evaluated but all failed either because they could not provide sufficient torque or because the gearbox did not have the mechanical strength required by the application.

The Parvalux motors used in the Shifta2 have proven to be both powerful and reliable and so the Parvalux application engineers were set the challenge of designing and manufacturing a motor and integrated gearbox that was up to the demands of the aircraft mover.

DC electric motors are ideal as they allow precise speed control and can be easily reversed using modern programmable electronic controllers.

The choice of gearbox was critical and Parvalux considered a number of options from its range, which includes single reduction worm gear, double reduction worm, in-line double reduction and multi-spur.

There is also a choice of gear materials with composites being used where noise is a consideration whist bronze or steel is required where high torques are involved.

The die-cast gearboxes all feature ball bearings and, being lubricated for life, are maintenance free.

As Barry Wilson of Shifta Products explains: "The application engineers at Parvalux were most helpful".

"We detailed our requirements and Parvalux quickly engineered and manufactured sample motors for our evaluation".

"Once installed, the power of the new motors was really impressive and they have transformed the performance of the aircraft mover".

The aircraft mover comprises a tough steel frame that houses the two 12V DC batteries and chargers, one positioned on each side of the unit.

The Parvalux motor/gearboxes are mounted adjacent to the drive wheels, which are attached directly to the output shaft of the gearbox.

Each motor and reduction gearbox gives an impressive output of up to 250Nm of torque - multiplied by two this is enough to move most light aircraft.

Control of the unit is by means of a joystick on the handle, which allows the acceleration and speed characteristics to be programmed to suit the performance of the motor.

This allows the unit to be driven forward or backwards at a controlled speed dependant on the deflection of the joystick.

The unit can turn on its own axis by reversing one of the motors in a differential effect.

There is also a small electric winch at the front of the unit to pull the front wheel of the aircraft onto the mover platform.

Special semi-traction batteries have sufficient capacity to allow the unit to be used all day and are recharged overnight.

A moulded cover protects the motors and batteries from dust and damp.

The unit was recently put through its paces at East Midland Airport and made light work of moving a Beech Baron 58P.

Built in 1980, this six-seater twin engined aircraft weights 2800kg has a range of over 1600km.

Owned by British Midland Airways it is used as personal transport for the company's executives.

Barry Wilson is delighted with the performance of the aircraft mover.

He said: "The unit is easy to use and its sensitive controls allow the aircraft to be moved slowly in confined areas or more quickly once it is out in the open".

"There is no noise or engine to start and the mover will be particularly attractive to owners that regularly need to move their aircraft single handed".

The success of the Mr Shifta mover has created opportunities in the industrial market and Shifta based machines have been supplied to many companies including, JCB Aston Martin, Walkers Crisps, Toyota, Sanyo, Phillips, Wade Pottery, Coates-Viyella, and Akzo Nobel.

These machines have a hard life, carrying heavy loads, often over three 8-hour shifts, seven days a week.

Many of them have been in regular use for several years now and during this time, Shifta products has not had a single motor failure on any of the Parvalux powered machines.

Barry Wilson concluded: "The Parvalux motors are a key component in the success of the Shifta movers and the engineers at Parvalux have been a great help to us".

"Based on their outstanding performance and reliability record, we will continue to use their excellent motors across our product range".

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