The kit - Assembly - Installation - Flying - Specification
It has been said before that the problem with kit reviews is that the better the model is, the less there is to write about. This could easily have been a problem in this instance, were it not for the fact that the model concerned could be said to break new ground and has other features well worth considering in depth. The term 'could be said' is used since it would actually be more accurate, perhaps, to say that it has found a new way of digging ground which others had previously found to be unproductive.
The way in which this particular review came about is already familiar to regular readers. Suffice it to say that the model had received some bad press from certain writers in the USA and I had been unwise enough to repeat them. John Gorham of Gorham Model Products felt that the only way to resolve the issue was to send me one to play with - for which I am becoming increasingly grateful.
When it comes to the packaging of helicopter kits, there is very much a standard way of doing things these days. Sub-assemblies are packed in numbered bags which correspond to numbered sections in the instructions. In the case of the 'Legend' there is an indefinable impression of neatness and attention to detail which makes an immediate impact. Having assembled the kit you then become aware that everything was included and nothing was wrongly supplied.
The manual describes every assembly in detail, with very clear diagrams of each stage and precise instructions as to which bolt should be used with which type of nut and whether there is, or is not, a washer fitted. You may not always agree with the length of bolt, or provision of washer, but do it their way and you will find the quantities supplied to be exactly right. It is virtually impossible to get anything right first time when it comes to producing instructions, but these are about the best yet. The few small glitches which crept into early copies should be corrected by now.
'Manual' is, in fact, a misnomer since there are actually five manuals:
1) Basic assembly.
2) Controls set-up.
3) Main rotor blades.
4) How to fly.
5) Main rotor head.
The last named is merely an exploded diagram, since the head itself comes fully assembled.
This sectional approach to the instructions has been chosen to cater to the fact that the 'Legend' is available in several forms. Two types of rotor head are available - with more to come - and there is a choice of belt or shaft drive to the tail rotor. There are also several other models in the GMP range and some of the manuals are also applicable to some of these. In the review kit, the standard belt drive and Delta 3 head were supplied.
There is very little plastic used in the construction. The main material used is aluminium (or should that be aluminum?) and this is nearly all anodised a very attractive purple/violet colour. A few minor fittings are supplied in black which matches the very few plastic parts.
I am acutely aware that my reputation as a writer requires that I should be fairly critical where this is necessary and - having searched desperately for something to criticise - the swashplate driver has come to my rescue. This, like several items used in the kit, is of Hirobo origin. It is one of the few plastic items and, although it is undoubtedly quite able to do the job it is designed for, it is simply not of the same quality as the rest of the model. It is clamped around the main shaft by a bolt and there is a very specific warning against overtightening this. The actual drive to the swashplate is via a small diameter shaft which is merely held in place by friction.
One of the few wooden parts of the model is the servo tray, which is supplied fully assembled. It will accommodate all of the current standard sized servos and the instructions are very precise as to the layout of the servos and linkages. A preshaped ply floor is supplied on which to mount the receiver and battery pack and this also serves as a runner which the cabin/canopy slides onto. Actual retention of the canopy is by means of a 'Cam-loc' which passes through a grommet in the top and engages with a plate attached to the main mechanics. It is advisable to fit the grommet in position by 'eyeballing' the size of the hole into which it fits. The suggested hole size is a little on the large side. For extra security, it is a.good idea to make an ident in the retaining plate to prevent the 'Cam-loc' from rotating due to vibration.
An interesting feature is the use of an octagonal tailboom, also of Hirobo origin. This is immensely strong and cannot rotate in the fittings. It also accommodates the toothed belt tail drive very neatly. The tail 'gearbox' is very simple and consists mainly of two side plates with flanged ball bearings to take the tail rotor shaft. These bearings are used in several locations throughout the kit and have to be epoxied into position. In fact the design is such that the bearings are all retained mechanically and the epoxy merely eliminates any movement and does not take any real load.
Main rotor blades are of the usual hardwood/balsa composite construction, but with a much larger hardwood section than usual. This is grooved to accept the lead weights supplied. Instructions are very explicit as to the finished weight of the blades with a very small range being permissible. I found that using all of the weight supplied produced a set of blades which were bang on the upper limit. Full marks. Heatshrink covering is supplied for the final finish. This is only the second time that I have used this material and I am rapidly becoming converted to it. I did anticipate some visibility problems with the material supplied, since it was black. However, this has caused no problem at all in use. The tail blades are plastic mouldings, white in colour. To avoid a clash with the rest of the machine, I painted these black! All tips are painted orange to avoid nasty accidents
As already mentioned, the rotor head is supplied fully assembled. For reasons which will become obvious, it was my intention to write a complete kit review without any reference to the Delta 3 head and then, right at the end, add as an afterthought, "Oh, by the way, it does not have a flybar". This approach is not really practical, unfortunately, although it would certainly have been appropriate. There have been numerous attempts in the past to produce a practical model rotor head which more accurately resembled that fitted to most full size machines. In the meantime, the term 'flybarless' has almost come to imply that the model was lacking in some way. This is far from true with the 'Legend' - but we are getting ahead of ourselves, back to the...
This was very straightforward - one could almost say boringly so. In fact, I did not have a suitable engine available when the kit arrived but could not resist the temptation to press on. Two evenings later I had a complete helicopter - sans paint and engine. Having acquired an engine - old type OS 61 FSR-H - a certain amount of dismantling was necessary, but the machine was complete in one more evening.
As this was the first model that I had built involving a cone start shaft which was part of the clutch, and having read many lengthy articles describing setting up such a system, I was agreeably surprised to find just how simple it was. Having fitted the fan to the motor, using the special spanner provided, I checked the run-out with a dial gauge and found that it was spot on. "It can't be that easy", said he, bolting the clutch to the fan. What's this, thirty thou' run-out? Help! So, unbolt the clutch; turn it through 180o and retry. Half a thou' run-out!
Along with certain other sources, I did investigate fitting a Super Tigre 61 Hely to the model and found that, although it was an attractive idea, it would be necessary to modify both the heatsink and the motor mounting lugs to accommodate it. The heatsink is too wide and requires the removal of the outer two fins, while the mounting holes are far too narrow to fit the predrilled mount (possibly the optional 50 sized mount might be a better bet). It is also necessary to open up the first 1/4" or so of the fan hole to suit the unthreaded portion of the crankshaft. Strangely enough, the ST 90 hely fits both the fan and the shroud and only needs the mounting holes to be doctored. The OS drops straight in - although the later, long stroke, motor may give problems.
The main mechanical assembly is very straightforward and gives no problems whatsoever. However, I do have some doubts about the tension of the tail drive belt. The instructions advise that the belt should be neither tight nor loose. Previous experience with toothed belts suggests that they are best left on the loose side and that tension is taken up by centrifugal force where the belt leaves the pulleys. On the 'Legend' set-up, it is possible to make the belt slip around the pulleys even when the tension is fairly high. We are talking about static conditions here, of course - which is not a fair test. With the tension set as suggested, any sudden opening of the throttle produces a sound which suggests that the belt is slipping. Having agonised about the situation at some length, it must be said that the tail drive has given no problems whatever, so perhaps I am just being paranoid!
Joining the canopy halves is another subject on which much has been written elsewhere and which proved to be extremely simple. I used the method suggested in Ray Hostetler's book and trimmed the flanges of the two halves to slightly different widths (1/4" and 3/16") and then clamped them together. After running cyano around the inside of the joint, the clamps were removed and cyano added to the outside via the protruding surface of the larger flange. Too much cyano will make the plastic blush, but this is easily hidden by painting a strip down the centre of the clear windscreen area. Reinforce the top and bottom rear edges with scrap plastic.
The canopy is positioned by moulded plastic runners which are glued inside each half. These slide along the outer edges of the ply floor previously mentioned. There is a natural position for these which is dictated by the mouldings. However, in this position the runners are not quite parallel and it is advisable to check this before gluing the second one into position.
The tail surfaces are an interesting composite material consisting of 1/8" balsa sandwiched between two thin layers of glass/epoxy laminate. Very stiff and strong, but it is necessary to accept very sharp edges or add material if you wish to round the edges off. This material would make superb ribs and formers for large models.
Painting presents no problem and there do not appear to be any compatibility or adhesion problems with the type of plastic used for the cabin. The review model was painted with 'Dupli-colour' spray-on car cellulose and finished with two brushed coats of 'Aerokote'.
Here again, this is very straightforward. All of the required linkages are shown full size and the length given in millimetres. The pre-assembled servo mount is arranged so that there is only one way that the servos can be mounted without modifications.
The only area which is a little vague relates to the way in which the tail linkage negotiates the various linkages and bolt heads on the left hand side plate. If the linkage is allowed to follow its natural path it arrives at the servo about 1/8" to 3/16" too high. This is confirmed by the fact that the exploded diagram of the linkages shows a kink in the pushrod wire at this point. An alternative here is to pack up the rudder servo by a suitable amount. However, clearance to the aileron linkage is very restricted, so proceed with caution.
Suggested control movements are given in terms of cyclic pitch movement at the blades and this is facilitated by supplying a simple pitch gauge which is attached to one blade holder by means of a rubber band. This is used in conjunction with your transmitter aerial or other suitable height indication. Zero pitch is easily found by means of a small spirit level or by sighting against any convenient horizontal surface. This is very convenient to use and the suggested cyclic movement worked out just right.
It did prove to be necessary to expand the collective range somewhat to suit the writers autorotation preferences and to limit the RPM at full throttle. At around 9o positive pitch, the RPM still borders on the acceptable limit in a (very fast) vertical climb! The actual physical limits on the total pitch range available are at least 20o which should be more than ample for any requirement.
A gyro platform is incorporated which neatly accommodates GMP's own gyro. This is based on the KO stick preferential type, which is well known in the UK under a number of different labels. My previous experience of the type had left me feeling that I did not like 'pilot authority' gyros. Either my flying style is changing or this one is different. It works well and will be discussed in the 'Hovering About' column in the near future.
The tank supplied is of around 9 ounces capacity, which is much smaller than the space available for it. If you would prefer something bigger, a Kalt 'Cyclone' or 'Baron 50' tank fits very well and still leaves room for lots of packing.
The model was completed by a 'Cyclone' silencer, five JR '4001' servos, a PCM 9 receiver and a 1200MAh battery pack and came out at 9lb 2 ozs, ready to fly.
I usually enjoy the first lift off of any new model, of any type, but must admit to a certain amount of trepidation in this case. What followed was almost anticlimatic. The blades were in track, the trims were almost spot on, the response was just about right and there were no odd characteristics. Much more pitch was required since the head speed was very high and the throttle stick was well above the mid point.
After sorting that out, I found that the model flew quite nicely at only moderate head speed. As soon as the throttle was advanced for a climb, or forward flight, the head speed and the response increased, which is an effect which I find I like.
Once into forward flight, I found that the model handles much more like a fixed wing aerobatic model than any other helicopter that I have flown. In fact the characteristics are rather like a very high powered fixed wing model with a lifting wing section. By this I mean that increasing forward speed requires increasing forward cyclic to maintain level flight. Other writers Have commented that the model requires forward cyclic to continue forward flight. This implies that if you let go of the stick it will stop, which just ain't so - it will climb. Comments made in the US about other quirks are also totally unfounded.
One thing which John Gorham himself warned me about was a tendency for the model to drop its nose sharply if the collective was rapidly reduced in forward flight. The effect is certainly there, but it is no worse than some other models and certainly no problem. This effect has already been discussed in 'Hovering About' and will now be dealt with again in the near future. It did prevent me from doing a decent roll for a while, but that is just a matter of practice.
One thing which the model revels in is looping. At any speed, from any height and as many as you like (no, we are still talking about helicopters). In fact, it loops like a control-line model - and that is a real compliment.
Well now, you are asking, what about autorotations? With no flybar drag, weighted blades and a thrust race between the auto unit and the lower mainshaft bearing, these are quite exceptional. The clutch also works well in this situation and it is nice to land with the tail blades stationary.
I must confess that I am becoming totally addicted to the thing and everything else seems tame and underpowered by comparison. There are those who are saying that it is overpowered with a 61, and a 50 might be better - they must be closer to the wheelchair than I thought!
My apologies to regular readers who have reached the conclusion that this is being written by someone else using my name - normal service will be resumed as soon as possible.
|Model||GMP 'Legend' helicopter|
|Engine/main rotor ratio||8.6:1|
|Main rotor/tail ratio||1:4.75|
|Power||50 - 61cu in|