With a fully charged battery, a properly set up 'Whisper' is capable of quite startling performance, once you realise that its characteristics are different from a glow powered model. Applying a lot of pitch will cause the rotors to slow down quite dramatically. With an IC engined model, this could be disastrous, but with an electric powered model the motor draws more current and produces more torque and the result is a startling climb rate.

This performance is achieved by keeping the weight down to the absolute minimum and the result is quite a fragile model. There have been several articles in US magazines which lay great emphasis on this relative fragility - as if it were something to criticise - and go on to say that better materials could be used. It must surely be obvious that a more robust machine made from heavier materials would be a marginal flyer. It never ceases to amaze me that the average modeller thinks that models should be designed to crash, rather than fly.

My own opinion is that the design is a marvel of 'just enough' engineering and could not be improved. The one item that should be treated with extra care is the flybar, which is a very thin-walled stainless steel tube. Having said that, I must stress that I am very careful about just who I allow to handle the model.

It is very easy to treat any electric model with contempt and assume that it cannot do you much harm. In fact, they are more dangerous in many ways than glow powered models. You actually have to work to start a glow motor. Make one mistake with an electric model and it will start itself! Stall a glow motor and it will stop. Do the same with an electric motor and it will draw more current and hit you harder. Apply enough resistance to stop it and it will restart again when the resistance is removed. Hold it in a stalled state for more than a few seconds and it will set fire to something!

Have you got the message? Adopt a starting sequence that reduces the possibility of mistakes and ensure that you can stop it when required. With an electric motor, minimum speed means maximum torque. What this means is that if you start your model by simply opening the throttle, the probable result is that the rotor blades will be left way behind the rotor head and the model will destroy itself!

The set up that I use is as follows:
1) The throttle hold is set up to stop the motor.
2) Low throttle stick and low trim stops the motor.
2) Idle up is set up so that low throttle stick and low trim does not stop the motor.

Starting procedure:
1) Turn on transmitter and set the throttle stick and trim to low, throttle hold 'on' and idle up 'off'.
2) Turn on the receiver and check that the controls work.
3) Press 'arming' button on speed controller and stand clear.
4) Throttle hold to 'off'.
5) Advance throttle trim slowly until motor starts.
6) Open throttle to just below lift off point and turn idle up 'on'.

You can now fly the model without any danger of inadvertently stopping the motor in the air by lowering the throttle stick or trim. If necessary, the motor can be stopped by the throttle hold switch.

I imagine that the models designer must have presented himself with quite a dilemma when he came to the rotor blades. Part of the models performance can certainly be attributed to the fact that the rotor blades are very light - and we all know that heavy blades fly better, don't we?

Originally, I had lots of problems with the blade tracking. Having got the model to fly reasonably well in still air, even the lightest wind would send the blades way out of track and produce lots of shaking. A discussion with Jim Davey produced the consensus that the blade CG was too far back. I made various attempts to correct this without success, until I realised that the real problem was that the chordwise CG's of the two blades were markedly different - not an easy thing to check.

Because the blades are so light (about 1.3 ounces in unfinished state), the quality of the balsa wood used in the trailing edges is very critical. Two apparently identical blades (same weight and spanwise CG location) were found to have chordwise CG's at 32% and 39%. No amount of added weight to the leading edge of the blades could correct this situation. After much experimentation, I now have a set of blades which run quite well, but one of them actually has lead tape added to the trailing edge!

It would seem that the only practical way to produce very light blades with a well forward CG is to add a piece of piano wire to the leading edge. If this is wrapped around the blade root, it is about the safest way of adding weight. A quick check reveals that 16 swg wire (1.5 mm) will add about 8.5 grams to each blade (a 20% increase) which seems about right. I intend to try this and will keep you informed.

Unmatched blades will contribute considerably to ground resonance problems - particularly in still air. I believe that part of the problem lies in the fact that the lower fin is very close to, or in contact with, the ground. The kit includes an undercarriage damper which, apart from cushioning the vibration, also raises the fin above the ground. I very soon discarded this damper since it did not really seem to help very much and it added 1.2 ounces to the weight.

Ground resonance is caused by one of the blades moving so that the rotor disc is out of balance. This starts a shaking which is made worse by the fin hammering on the ground. In this situation, you should not reduce power - it will make things worse. The correct action is to increase power to pull the blades back into line. It helps a lot to have the blade fixing bolts fairly tight. Loose blades make things much worse.

You can get into a situation here where you want to stop the motor and find that every attempt gets you into the resonance, whereupon you have to add power to stop it and you eventually become afraid to stop the motor - with the battery rapidly running down. The solution is to set up the throttle hold switch so that it stops the motor. When the resonance starts, add power and hit the hold switch. Keep the pitch on until the motor stops. This will add drag to stop the rotors as soon as possible and also ensure that you don't get a boom strike.

The alternative is to keep the throttle open and wait until the battery runs itself completely flat. You will lose control of the radio well before this point so it is not recommended.

Incidentally, trying to stop a wildly shaking helicopter by closing the throttle is guaranteed to produce a boom strike.

Many people have told me that the use of a speed controller with a normal ferrite magnet motor will result in a short motor life. Let's say straight away that my own direct experiences with the 'Whisper' do not confirm this - at least, I don't think so!

Before flying the model, I charged the battery a couple of times and discharged it by running the model without the main blades fitted. This could just about qualify as 'running in' the battery, but not as running in the motor. In retrospect, this is a very important omission.

The first flight was outdoors in very blustery conditions and was timed at 6 minutes 40 seconds, all in the hover. The next few flights were all in similar conditions and all lasted between 6.5 and 7 minutes, though they were not timed with a stopwatch as was the first flight.

A reasonable day eventually arrived and I was at last able to indulge in some circuit flying. Throwing the model around and indulging in some rapid vertical climbs to considerable height resulted in flight times of around 5 minutes 50 seconds.

The onset of a long spell of poor weather led me to find a site where I could fly the model indoors. This gave a very good means of checking the motor performance as all flights consisted of a still air hover (the worst case) and were directly comparable. Some 20 flights were made in these conditions with a slow but steady reduction in flying time becoming apparent. Initially, this was around 6 minutes, but after a total of 28 flights, the average flying time was down to 4 minutes 20 seconds.

Venturing outdoors again gave flights of around 5 minutes, but with a very obvious lack of power compared with earlier flights. A check of the battery capacity showed this to be 1240 milliamphours - well above the rated 1100.

Around this time, an article appeared in an American magazine regarding the short life of normal ferrite magnet motors (not 'cobalt') when used with speed controllers. The point made was that the actual switching rate of the controller was very important. An average controller will switch at the frame rate of the radio equipment (around 50 cycles/second) - this being a cheap and convenient way of doing the job. For best results, it was claimed that a high switching rate was needed (Typically 3000 cycles/second). This being what is known as a 'high rate' speed controller.

After a total of 38 flights, an examination of the motor revealed that the brushes were now very worn. The indoor duration was down to around 3.5 minutes and all flights ended with a very hot motor and a virtually cold battery! This made it fairly obvious that the problem lay in the motor and made that magazine article look very convincing.

At the time that the 'Whisper' kit was supplied for review, I received another motor to try. This appeared to be a cheaper type with less robust brushes and with no facility to adjust the timing. This was 'run-in' by running on 2 volts (actually a glowplug supply) for about 5 hours. It was then given a short run on 4.8 volts and fitted to the model.

Back to my indoor test site and a first flight of 5.5 minutes. The curious point here is that it has never approached that duration since! Flight number two was 4 minutes 35 seconds and it has remained almost exactly the same ever since. A few minutes before typing this paragraph, I flew the model again (the 86th flight) and obtained 4 minutes 30 seconds. Far more important is the fact that it is just as lively as it ever was and there is no apparent decline in performance.

What have we learned from all this? Well, there is certainly some evidence that 'high rate' speed controllers are preferable with ferrite motors (as opposed to 'cobalt' motors, which appear to be alright with 'low rate' controllers), and certain of my clubmates are very convinced of this, based on their own experiences. However, from my own point of view, it would appear that this is far less important than careful running in of the motor.

It would also appear that, in the current state of development, 'tuned' ferrite motors have very little to offer. This was always the case in my fixed wing flying with electric models, when the 'standard' Mabuchi 540 motor seemed as good as anything.

If there is someone out there who is able to give an informed comment on the issue of 'high rate' versus 'low rate' speed controllers, I'm sure we would all like to hear from you.

You will by now have gathered that the Kalt speed controller recommended for the 'Whisper' is a 'low rate' device. How can you tell, you may ask? If you run the motor at very low speed by slowly advancing the trim as recommended above, the motor will 'tick' and move in a series of jerks. The ticking speed will be around 50 times per second. This may sound fast but it is roughly the same speed as 'mains hum' which we are all familiar with. A 'high rate' controller will give a much smoother take up and will make the motor 'sing' or 'whistle'.

The above controller has only one adjustment which sets the slow end to suit your transmitter. It has a very narrow input range, which means that you will get maximum power around the mid point on the stick. The model can be flown quite satisfactorily like this but it is better if a programmable transmitter is used and the throttle range reduced to expand the speed range over the whole stick travel.

The miniature gyro which is available for this model is made by Aisonics and is now produced in a Mark 2 version. This has a smaller electronics package than the Mark 1 and no reversing switch. Some very early Mark 1 versions were sensitive to both voltage and temperature variations and could not be run at high gain.

The Mark 2 version works very well and has more than enough gain for this and any other model. I always find it rather fiddly to set the gain correctly when this has to be adjusted on the model itself but, in this case, I set it at about 80% initially and have not touched it since.

There is still a noticeable change in the tail trim during the flight but this is directly related to the amount of pitch being used and can be trimmed out with the ATS system. As the battery runs down and the motor slows slightly, more pitch is required to maintain a hover. As the ATS system works by mixing the pitch channel into the rudder channel it can be used in the normal manner. More pitch means more torque, which means more tail rotor pitch.

When set up correctly, the tail is very stable yet powerful enough to perform pirouettes in blustery conditions.

The instructions recommend no less than 9 degrees of pitch in the hover, which sounds a little extreme. In fact the model flies very nicely at this setting, but the throttle stick is well below the mid point, RPM is quite low and there is a pronounced coning angle. This set up works well indoors.

For general flying, I found it better to use rather less pitch to bring the throttle stick back to the middle and run rather faster at about 1250 RPM. This makes the model very twitchy indoors, however.

There does not seem to be any limit to the maximum pitch which can be used. The manual recommends 12 degrees and this gives a very good climb rate. Most experienced helicopter flyers automatically feel that this is wrong and reduce the pitch to give a higher speed. This makes the model behave much more like the familiar glow powered model, but it does not give the same performance.

The biggest problem here is just how much time you can safely allow for flying around the sky and throwing the model about. When the battery runs out it happens quite quickly and there is little time to get the model down. If the battery and motor are both healthy, you can realistically allow about 3 minutes.

Here again the experienced flyer may find that the different response takes some getting used to. Certainly there is no point in 'feathering' the pitch to keep the RPM up - remember, the slower it goes the more torque you have. My own fear is that of overloading the rotor at low RPM and damaging the head flexiplate by bending it too far, but this has not happened - yet.

Loops are quite straightforward, just pull the stick back and keep the pitch on. Rolls are a little odd since it wants to rotate around the battery and any attempt to combat this will produce a pronounced 'barrel' roll. You need high RPM for this too to avoid the roll rate disappearing as it attempts to heave the battery up and over.

I don't have an autorotation clutch fitted and the prospect of stopping that battery at the bottom of an auto is a little intimidating. The prospect of some auto slope soaring is an intriguing one though!

This has happened to me once when I got carried away. The answer is to dive towards the ground and attempt to flare out as low as possible - rather like an autorotation with light blades. I got away with it - just!

If the model is in the hover and at less than about three feet altitude, you can just let it sink gently to the ground. Try to arrive at the ground with full throttle applied to avoid any chance of a boom strike (the boom is quite fragile too).

During the above I have referred several times to flying the model indoors. This is not to be attempted lightly. There are all sorts of funny effects when flying in a limited space and a mistake could be quite nasty. I did consider not mentioning the subject at all since it can encourage others to try it. However, not mentioning indoor flying would probably be even worse. Likewise, mentioning it then advising you not to do it would be unrealistic. It's rather like the widespread practice of stopping the rotor head by placing your hand on top of it. No sensible person would actually recommend this practice, but everyone does it. It's your choice.

I like it. The case rests.