The original motor supplied with the kit was a Mabuchi type, which gave an excellent performance for a very short time. I had neglected to run the motor in and this is probably the main reason for the short life. After 20 flights the performance was obviously dropping and so were the flight times. The motor was replaced after 38 flights, at which point the flight time was down to around two and a half minutes and the motor was getting very hot, although the battery remained cool.

With the kit I also received another motor 'to try'. The logo on the end bell said 'Air Supply', but no other details were available (no label). This motor was carefully run-in and, although not giving quite as good a performance as the original motor when new, stayed in the model for almost 200 flights with only a very slow, almost negligible, drop in performance. Towards the end of this period, the commutator was re-skimmed by a model car shop and new brushes fitted (Reedy type). This produced a noticable improvement.

In an attempt to improve the motor further, the can was sent off to be remagnetised. I haven't seen it since!

I now had a dilemma as I didn't have a motor and the importers could not supply either an original type or another example of the 'Air Supply' motor. I had heard reports that the MRI '19D' motor worked well, but this was also unobtainable at that time. The easiest way out seemed to be to look at the Kyosho range, and I eventually selected a 'Mega 20x2' (20 turns, double wound), as this seemed the nearest to a '19D' (19 turns, double wound) and it was fairly cheap.

At first, this looked like a mistake! There was barely enough power to lift the model out of ground effect. Advancing the timing (more on this later) didn't seem to help until I twigged that the instructions for doing this, which were enclosed with the motor, were actually wrong! In fact, they told you to rotate the end bell of the motor in the wrong direction. Turning it the right way made a huge difference and the motor was now as good as the 'Air Supply' motor. When I came to plot some graphs of the flight times for this article, I also realised that this particular motor showed only a small difference in flying times between indoor and outdoor flying.

This motor would probably still be in the model except that J Perkins sent me two more motors to try. These were labelled as (surprise!) Air Supply 'Trix Pro Series' triple wound motors. One motor has a blue label and is intended to be a 'duration' motor, while the other has a red label and is said to he a 'hot' motor.

Both motors were carefully run-in and the 'blue' motor fitted to the model. Initially this was also disappointing, but advancing the timing did the trick and, although the performance was not quite as good as the Kyosho motor, the flights were slightly longer. It would be a good idea to do some more flyimg on this motor since the times generally were very inconsistent. In particular, my original battery seemed to go through some kind of decline during this period, from which it has since recovered. The average flight times on this motor actually seem to be longer indoors than outdoors, which is curious.

I didn't bother to try the 'red' motor in standard trim, I advanced the timing right from the start. This gave by far the best performance since the early days of the original Mabuchi motor, but the flights were shorter. After 40 flights with this motor, the performance now seems to be dropping.

The original kit was supplied without any form of suppression on the motor and I did experience the occasional 'glitch'. Many motors are supplied with suppression capacitors already fitted, incuding the latest 'Air supply' types.

If none is present, the addition of a .05 - 0.1 microfarad capacitor between each brush and the motor can will normally prevent any interference problems. If you are having real problems here, it maybe necessary to fit RF chokes in the motor leads, but this will limit the motors performance. A better solution would be to try another receiver, or improve the installation. The receiver can be fitted immediately adjacent to the motor without problems.

The correct way to do this is to run the motor for several hours, unloaded, on a low voltage. If you have a large capacity glowplug supply, or power panel, this is ideal. Most manufacturers suggest around 8 to 10 hours running on this type of supply. The purpose of this is to run in the brushgear. Some authorities state that this process should be repeated every time the motor is dismantled.

My experience suggests that running-in is essential, but possibly not to the extent described above. If you have a friend, or aquaintance, who is heavily involved with R/C electric cars, ask him, he will usually have strong ideas on the subject.

Many of the motors currently available have a facility to alter the 'timing' of the brushgear by rotating the end bell which contains the brushes. Advancing the timing means that the motor will produce more power at the expence of drawing more current (which means shorter fiights). Assuming that the motor is giving adequate power, it can be taylored to give the required compromise between power and flying time. In helicopter use, it can be assttmed that most people just want the maximum power.

'Advancing' means that the brushes contact the commutator earlier in its rotation. This means that the brushes must be rotated against the direction that the motor is rotating. Assuming that you are looking at the brushgear and the motor rotates clockwise when viewed from that end, then the motor endplate should be rotated anticlockwise. Be warned that the amount of 'advance' that can be used is very limited.

A motor which is designed to have the timing altered will normally have some kind of scale to indicate the amount of change. This will normally allow for no more than 6 degrees each way. Try 4 - 5 degrees as a starting point.

For many reasons, an electric helicopter will fly for longer outdoors than indoors. Not only is there translational lift, which means that less power is needed, when you are flying around, but even in the calmest conditions, there is always some wind effect to produce translational lift when you are hovering. I use a different set-up for outdoor flying with a higher rotor speed. What seems to be very 'twitchy' indoors can he very tame outside.

Outdoor flight times will also vary much more due to the different types of flying that can he indulged in. Interestingly, however, a flight with lots of autorotations thrown in will not be any longer than a flight with no autorotations. This is due to the fact that much more power is used in climbing to altitude, before the descent. Another point to be considered here is that the better the motors performance, the greater the difference between indoor and outdoor flying times, due to higher current drain when the motor is heavily loaded.

From this, you could infer that if you want to assess the differing qualities, and flying times, of various motors, batteries, etc, you should fly indoors in a restricted space to even out the possible variables in flying style. This may be true, but the dangers are obvious, so be very careful if you try it.

I gather that the original 1100 mAH 'SCR' batteries, sold for the 'Whisper' are no longer available. As a result, other larger capacity batteries have been made available in a suitable pack. This means that three different sizes have been generally available for the 'Whisper': 1100, 1400 and 1700 mAh capacity - all in 8 cell packs.

Without the battery, the 'Whisper' weighs 29 ounces. This gives the following flying weights:

Battery	Battery Weight	Flying Weight
1100mAh	13.0 ounces	42.0 ounces
1400mAh	16.0 ounces	45.0 ounces
1700mAh	16.5 ounces	45.5 ounces

The 10% weight variation seems to make very little difference to the performance. The larger capacity batteries seem to have a little more 'zing' at the start of the flight, but this is largely an illusion caused by slightly higher revs and there is no increase in performance.

After averaging out the flight times acheived by the three different batteries indoors, the actual flying time seems to vary more or less pro rata with the capacity, on a given motor. However, the actual nature of the pack regarding the matching of cells, etc, has a considerable effect on the flight characteristics.

My original 1100 mAH pack has well matched cells and has always been charged and treated in the same manner. As a result it runs down (or 'dumps') very rapidly at the end of a flight (5 to 10 seconds), see Fig.1. I had amassed well over 100 flights on the original battery before I obtained another similar pack. This was acquired second hand, consistently flies for about 10% less time and has a much longer 'dump'. It was used as a shop demonstrator and certainly received rather variable treatment.

Fig.1 Comparison of indoor and outdoor flying times on 1100 mAh battery.

Soon after this, I was supplied with a 1400 mAh 'SCR' pack to try. Initially, I was rather disappointed with this, as the useful flight time was very little greater. The reason for this was that it had a very long rundown time (around 45 - 50 seconds). Expert opinion is that this is due to the cells being badly matched. It has improved somewhat with further use, although the duration, as you might expect, has reduced. In other words, the capacity has remained the same, but the characteristics have changed. So much for 'memory' effects! See Fig.2.

Fig.2 Comparison of indoor and outdoor flying times on 1400 mAh battery.

To complete the set, I now have a 1700 mAh 'SCRC' pack (originally supplied to Jon Tanner). This too seemed disappointing until I realised that this was the first time that I had flown the 'red' motor indoors and that all the batteries were producing poor flights. Going outdoors showed that this pack was producing the longest flights yet, but with disappointing power output. Hopefully, more use will produce an improvement.

All of my charging has been carried out using the original Union Model 'Pulse Charger' with 'Power Up' booster, which I believe is no longer available. At an early stage, I decided that some form of charge indication was necessary and I fitted an ammeter into the charging leads. The current normally jumps to around 9 amps at the start of the charge and drops to around 4 amps before cut-off. At the end of the charge, the battery is normally warm to the touch. Experience indicates that a battery which is not warm is not fully charged.

In normal circumstances, the 1100 pack takes about 16 minutes to fully charge it, while the 1400 takes 25 minutes and the 1700 pack takes 35 minutes. This tends to indicate that the charger is struggling a little with the larger packs.

The same speed controller has been in use throughout, this being the original Kalt unit, which is a low frequency type. There are two basic types of speed controller available - low frequency and high frequency. The low frequency type came first, mainly because they are easier and cheaper to produce. They are easy to identify, because at low throttle settings they buzz at about 50 cycles per second (AC mains frequency).

The high frequency types 'sing' or 'whistle'. They are supposed to be much easier on the motor if it is a normal ferrite magnet, type. I say 'supposed' because some people don't agree with this and because it is not borne out by my own experience. It is certainly possible that the high speed type gives the motor an easier time, but it would appear that careful running-in is much more important for good motor life.

If you talk to anyone in the electric model car world, they will tell you that the motor should be rebuilt after every race and certainly after a few runs or so, and replaced frequently. So anything over, say 10 flights, could be considered as a good motor life!

Despite the rapid demise (by electric flight standards) of the original motor, and despite comments published elsewhere, I don't feel that the low frequency Kalt speed controller has any detrimental effects on the motor.

The only replacement on the model in well over three hundred flights is the plastic pinion on the first reduction gear stage, which suddenly became badly worn after 260 flights.

An absolute essential is the carbon fibre flybar! The original stainless steel tube item can be bent by looking at it too hard! The carbon version can be treated anyway that you like, without damage. It is weIl worth fitting a second pitch control arm to the flybar, which eliminates a lot of slop in the system and makes it easier to balance the head.

Another worthwhile modification is some form of clamp, or brace, between the top of the motor and the frame, to stop the motor rocking from side to side. Apparently, some types of pen have a removable pocket clip which is a snug fit on the motor and this has been used to make a brace. I made my own from piano wire and tinplate.

Although the model autorotates very well, there have been a few 'arrivals' in nearly 400 autos. Despite this, the only damage has been a couple of boom strikes. These merely produced dents which, due to the thin boom material, can be pushed out with a suitable sized mandrel. I have never damaged an undercarriage strut, or the frame adjacent to the tailboom, both of which are supposed to 'weak' spots.

The technique used for autorotations is a little different to other models. In the descent the head speed is roughly twice that at the hovering speed. This means that the model drops at a high rate until the speed builds up. The actual landing is very gentle. Don't try to auto from the hover!

Taking the average flight times on the three motors which are currently available, we arrive at the results shown below.

Reference has already been made to the fact that the 'Blue' label motor seems to run for longer indoors than outdoors, but note the large difference in the times on the 'Red' motor

Motor	Kyosho 'Mega 20x2'	Air Supply 'Blue'	Air Supply 'Red'
1100 battery indoors	261	302	204
1100 battery outdoors	279	294	268
1400 battery indoors	332	370	276
1400 battery outdoors	349	361	340

All times in seconds.

Your opinion of the 'Whisper' will, inevitably, depend on your expectations of it and the use you intend to make of it. It is a low-tech approach to the problem of producing a successful (which it certainly is!) electric helicopter. It works by the simple expedient of cutting everything to the bone. In other words, it is designed to fly, not to crash.

Most of the modifications and upgrades which have appeared have involved compromises, which have disadvantages in some respect. Apart from the flybar modifications mentioned above, my own feeling is that the model in its original form, with an 1100 mAh battery, gives the best all-round performance. Although longer flying times are possible with larger capacity batteries, the extra weight means that there is very little increase in the useful flying time. Also note that variations in the motor certainly have much greater effect than variations in the battery used and this is a subject worthy of much further research.

I have heard comment, even from the importers staff, that Kalt should have put some development into the model. Where? Surely the only way to improve it would be to start with a blank sheet of paper and, if possible, a revolutionary new battery.

Look at the opposition and decide for yourself.