The 'Whisper' is very light. Claimed weight is 1150 to 1250 grams and the review model came out at exactly 1200 grams (42.5 ounces), complete with 8 cell 1100 mAh battery pack. This is achieved by the use of quite delicate construction and the model needs careful handling.

At the root of it all is a very complex one-piece moulding which makes up the complete chassis, including all bearing housings and servo mounts. These mounts are fully adjustable and can accommodate full-size servos, although mini servos are obviously preferable. The chassis also includes a clamping socket for the tailboom, the motor mount and platforms for the gyro and receiver.

A miniature undercarriage, of the now familiar 'tuf-strut' type bolts to the bottom of the chassis. The kit includes a modified form of mounting which adds a damper between the U/C and the chassis. This is to avoid problems with ground resonance when flown from smooth surfaces. More on this anon.

Pitch input is via a modified form of the old 'Baron 50' system and utilises two swinging arms which translate a twisting motion of the pitch slider into an up and down motion. However, instead of one piece of wire moving in a slot in the mainshaft, two external wires take the movement up to the mixer unit. These wires pass through the top bearing and the swashplate. The really ingenious part of all this is that the swashplate moves on two gimbals, instead of a centre ball, leaving the centre of the swashplate clear and giving completely slop-free support. This is so obvious, that it took a genius to think of it! Watch out for many copies.

Apart from being made up of very skinny plastic mouldings, the rotor head design is very conventional. It utilises a 'flexiplate', rather like the original 'Cyclone', made of GRP material. A reinforcing plate supports it from below and prevents the rotor blades sagging. The mainshaft is a very thin walled tube, as is the flybar. This latter component is very easily bent and should be treated with respect.

Another thin tube is used for the tailboom which accommodates a very small toothed belt tail drive to the gem-like tail 'gearbox'. The drive is taken from the bottom of the first stage of the double reduction drive from the motor to the mainshaft. The fin is mounted on the side of the tailbox and there is no tailplane.

Between the main chassis and the U/C legs there are half formers which brace the whole unit. The front one of these also holds the canopy via four self tapping screws. Very similar in shape to the 'Baron Alpha' (known in the US as the 'Excalibur'), the canopy is very thin and light. Like the chassis, it sets very high standards of plastic moulding.

Almost like an afterthought, the drive battery is held by two reusable nylon tye wraps attached between the U/C legs. If the previously mentioned damper is not fitted, the canopy blends nicely into the battery and extra cooling is supplied via the nose intake.

Some thought has gone into the very comprehensive decal set. This not only includes two basic trim designs, but these are designed in such a way that they can be cut up into several pieces and used in numerous different ways. If your model looks like anyone elses, it is pure laziness on your part!

Also available, but not included in the kit are a new miniature gyro and a very compact MOSFET speed controller. The gyro has a single gain control and a neutral adjustment, plus a reversing switch, and weighs just 1.5 ounces. Included in the speed controller is a battery elimination circuit which supplies the power for the receiver, servos and gyro from the drive battery. A starter button is included so that you can check out the radio without any danger of the motor starting. There is no cut-out included to switch off the motor before the receiver voltage drops to a dangerous level. This is not a problem since, being a helicopter, the model stops flying well before the radio is affected. However, if you persist in running the motor beyond this point you can get a situation where the motor is still running slowly and you cannot switch it off.

As is now becoming standard practice, the kit box consists of a moulded foam tray housing the components, with many of the basic items pre-assembled. The main chassis unit has the mainshaft ready installed, together with the second reduction gear, pitch slider, swashplate and mixer unit. Rotor head and tailbox are fully assembled, but it does pay to check that threadlock has been used in vital areas.

Section 1 of the very comprehensive manual covers the assembly of all those items which are suppled pre-assembled and provides a useful maintenance check. Section 2 covers assembly from this point onwards. At the rear of the manual, there are some updating instructions which cover the fitting of the undercarriage damper unit and several other small improvements.

As stated earlier, the purpose of the damper is to avoid ground resonance problems when operating from a smooth surface. It adds around 1.2 ounces to the weight of the model and gives it a rather untidy appearance. If you intend to operate from smooth surfaces, particularly indoors, it should be fitted. However, for normal outdoor use, from grass, it can be omitted. If in doubt, fit it anyway! I fitted it originally and removed it later.

Having decided on that issue, the undercarriage and battery retaining tye wraps can be fitted and form a useful handhold for further work. With the half formers fitted between the chassis and U/C the whole unit becomes much more rigid and easier to work on. This and much of the rest of the assembly is carried out using self-tapping crosshead screws, usually of M2 size and frequently only 5mm long. Apart from my well publicised dislike of crosshead screws (purely personal - no criticism!), my rapidly aging fingers did have the odd problem handling these. My own reaction to this situation is to regard it as an enjoyable challenge, but those who have dexterity problems may need help.

The next stage is to add the flybar and paddles. The flybar is actually tapped to take the fixing screws, despite the fact that it is a very thin walled stainless steel tube. This is not immediately obvious and not referred to in the instructions. You can then make up the various linkages that complete the rotor head.

At this point, the manual moves on to fitting the tailboom and tailbox. I found it much easier to fit the servos and remaining linkages first since the model is much more manageable without the tailboom. The adjustable servo mounts work very well, but are very fiddly. You can go on to fit the receiver, gyro, speed controller and receiver too if you wish, since the boom is not essential to any of this. No recommendations are made in the instructions for the position of the switch and start button, which are part of the speed controller. I mounted the switch on to the cyclic servos with servo tape and the start button at the front of the chassis where it is accessible via the cooling intake. I always prefer to keep the actual canopy unencumbered by such things to make removal easier.

The motor position is adjustable to set the correct mesh to the first reduction gear. This gear includes the take-off point for the toothed belt tail drive and is normally added after installing the tailboom. However, if you do it my way you can install it temporarily to set the mesh and complete the radio installation without the boom. A reasonably tidy installation is possible with the use of miniature nylon tye wraps, although the collective servo lead will probably need extending. The lead from the recommended gyro to its electronic package is just long enough.

Fitting the boom is very straightforward apart from threading the drive belt through it and ensuring that it is not twisted (the belt, that is). Belt tension should be fairly light. After some years experience of toothed belt drives on various helicopters, I have come to the conclusion that the correct tension is the lowest that you can get away with.

The boom is braced to the rear undercarriage legs by two metal pushrods with adjustable clevices at each end. These seem to be mainly cosmetic at first glance, but try flexing the boom sideways with and without them and you will see that they stiffen things up quite considerably. The clevices supplied for this, and the head linkages, have quite a lot of moulding flash and need careful cleaning up. I still had difficulty getting them to work satisfactorily and resorted to using short lengths of silicon tube over them to act as 'keepers'. Kalt used to include some superb links of similar design, complete with keepers, in their kits for use on the tail rotor linkage. These are not in the same league.

Tail rotor control is via a piano wire pushrod in a plastic sleeve. This is attached to the boom by the usual vinyl tape and the manual insists that this must be dead straight. The problem here is that it passes around numerous protuberances along the way and the tape will deform its path considerably. I resorted to using plasticard packers, attached to the boom with cyano, at each tape point.

Very little trimming is needed on the body halves which are joined with cyano adhesive. The canopy needs some trimming to achieve a good fit and is secured by the usual Kalt system of small self-tapping screws. I have always found this system to work beautifully and am baffled that so many people seem to adopt other, less neat, methods of fixing. I did find it necessary to reinforce the hole points in this case since the body material is so thin. Interestingly, reinforcing pieces are supplied for the points where the body is attached to the chassis, but the manual makes no mention of them! Attachment is by means of 4 of the previously mentioned M2 x 5 self-tapping screws.

Finally, the main blades have to have reinforcing pieces fitted to the roots and are then covered with heatshrink material. The blades supplied were of composite wood construction, but the manual also refers to plastic blades. Slightly different root reinforcements are used and the kit contains both types. Care is needed when shrinking the covering to avoid crushing the soft balsa trailing edges of the blades. The completed wooden blades weigh 1.6 ounces (42.5 grams) each.

Recommended servo arm length for all four servos is 8mm. The review model used JR NES-307 servos, which are supplied with a miniature servo arm which is actually 7.5mm long. These were used throughout with no problems and proved just about ideal.

The recommended pitch range is 0 degrees at the low point, +9 degrees in the hover, and +12 degrees at the high end. If you are an experienced pilot and intend to perform aerobatics, these figures become -3 degrees, +8 degrees and +9 degrees respectively.

No recommendations are given for total control throw, but the servo arm length mentioned gave almost the maximum available movement of the swashplate. Full movement of the tailrotor bellcrank was also available, which gives a colossal range of tailrotor pitch (something like -15 degrees to +30 degrees at the blades).

Kalt's own speed controller has just one adjustment. This sets the bottom end of the range so that the motor can be set to stop at the lower end of the stick travel. Actually, I set things up so that the motor started at low stick and about half trim. I also set the throttle hold so that it prevented the motor from starting - belt and braces! If you start the motor by advancing the stick, the start will be quite sudden and the rotor blades will be thrown back with possibly damaging results. My method is to advance the trim slowly until the motor starts and then use the throttle stick.

A prototype model that I flew a little time ago had a speed controller which also stopped the blades very suddenly, which took some getting used to. The production version does not seem to have this problem and closing the throttle suddenly lets the blades coast gently to a stop. One thing you should be aware of, however, is that the full range of the speed controller is much less than the normal stick throw. This means that you will get full power at around half throttle, or less. This is no problem if you have a modern transmitter with adjustable throttle range, since you can reduce the stick range to suit the speed controller, but may give problems with older sets.

The miniature gyro available for the kit works very well provided that you do not turn the gain up too high. If you do, the neutral becomes very difficult to set consistently and the response to the transmitter becomes very excessive. This does not occur at less than about two thirds of the maximum gain, which is more than adequate for the 'Whisper'.

Charging the drive battery is a matter of individual taste - you don't have to use the recommended unit. As a kit review of a helicopter, the charger is not directly relevant to this article anyway, but I did find the Union Model unit which is available from J.Perkins (Distribution) Ltd, the Kalt importers, to be very efficient and easy to use. The fact that it is fully automatic, removes much of the 'hassle' from electric flight and it can be used with just about any drive battery having 4 - 8 cells. It includes a booster to give 15.5 volts from a standard car battery and is a good investment if you have other electric models.

At the time that I finished the model, the weather was being unco-operative and I really wanted to try it out. If you remove the main blades and are careful, you can run the model up in your hand by holding firmly on to the battery. Be especially careful with the tail rotor input if you do this - it is very powerful. In fact, I don't really recommend this practice at all, but if I didn't mention it, someone would try it anyway!

Don't be tempted to fly indoors unless you have lots of clear space available.

I did try flying indoors and found that ground resonance was a problem. I had set the model up with some negative pitch and the first reaction, when the model began to shake violently, was to turn it off. The result was a minor boom strike. I removed the negative, but soon learned that the only real solution to this situation is to open the throttle and power out of it.

The damper does help, but the biggest help is to have the main blades fairly tight in the blade holders so that they cannot move too easily. This is why opening the throttle is needed to get out of the condition, since it will pull the blades back into the correct position if they have moved. I have gone on somewhat about this to stress that you not fly indoors and/or on a smooth surface unless you are very experienced and have lots of room. trying to keep the model within a restricted area and cope with resonance is a recipe for disaster. Outdoors, it's a different story...

My first outdoor flight was in quite windy and turbulent conditions, but I couldn't wait any longer. The result was a total anticlimax. Simply opening the throttle produced a straight lift-off into an incredibly stable hover, with the throttle/collective stick well below the mid-point. Head speed was quite low and the blades adopted a noticeable coning angle, which accounts for the stability. I had started a stopwatch immediately before lift-off and 6 minutes and 40 seconds later the model sank gently to the ground.

Subsequent flights have revealed that there is a progressive change of tail rotor trim during the flight as the battery loses power. This is tied to the increased pitch which is needed to compensate for the power loss and it should be within the capabilities of the ATS system to trim it out.

I am not yet convinced that the hovering pitch figure of +9 degrees is at all necessary, as indicated by the low position of the throttle stick. However, the requirements to get photographs for this review before becoming too adventurous, together with a batch of bad weather, has so far prevented further experimentation. As ever, I will keep you informed.

It is a little fiddly to assemble, it needs some care in handling and you can't fly it in your front room. However, it is a practical model helicopter with a 'no-fuss' charging system.

My previous misgivings about the practically of electric helicopters have been shown to be completely unfounded. There has already been one drag racing event for electric helicopters at one of this years meetings and, given the performance potential, it would seem that the sky is the limit (did someone say "ouch"?).

Now, all I need is the optional autorotation unit and a steady westerly breeze and I'm off to Ivinghoe Beacon...