Microheli T-Rex 450 tail gear case & pitch slider
Written by Ashley Davis Tuesday, 05 July 2005 00:00
Tail CaseThe following is a review of the MicroHeli tail kit case and tail pitch slider (SE)
initially let's take a look at the tail gear case....
The tail gear case is very nicely made and has the usual bling factor one has come to expect from MicroHeli. As usual one has to ask the question as to why you would want to fit this to your helicopter? There are several elements attractive within the MicroHeli design, first and foremost it is an open case design as is the norm with this type of upgrade. Open case designs provide ease of maintenance as well as allowing easy identification of wear to gears, bearings and belts. Open case designs also do not provide any where for dirt to settle and collect, which again reduces wear and tear on components. The case itself uses a single two millimetre Alan bolt in order to clamp the tail case onto the end of the tail boom. Initially I was a little concerned at only having one clamp but in practice this works extremely well. However, I do have to bear in mind that this is a single point of failure should for any reason this screw come undone. Therefore I would recommend copious amounts of blue loctite on this particular screw to make sure that this unfortunate event does not happen. Having clamped the tail gear case onto the tail boom the case does grip the boom in a vice like manner and there is no way this tail case will rotate on the boom as I have seen on several occasions with the stock plastic tail gear case. The MicroHeli case comes with a set of bearings for the tail shaft as well as two bearings which act as the tail belt tensioner. The tail case itself is made up of several CNC parts and there are a number of Alan bolts holding the entire assembly together. The bearings themselves appear to be of a reasonable quality, although I'm not sure they offer a level of quality above and beyond that which come with the standard kit. The tail case also has the all-important mounting point for a tail pitch slider. This mounting point is the most significant reason for buying an upgrade tail case as it provides a good solid platform for an upgraded tail pitch slider bell crank. One thing that caught my eye with regard to this case was that their appear to be double bolts securing most other parts of this tail gear case but only a single bolt for the clamp.
I particularly like the double bearing approach for the belt tension and the system works extremely well and provides a nice wide platform for the belt to run against. The main tail rotor shaft bearings are of an open case design so one can see the ball bearings running within the race. The unit also comes preassembled and whilst MicroHeli quality control has been very good of late I would always recommend that one takes the case apart and loctite the various screws to make sure that everything stays secure in flight.
In the following photographs you can see the installation of the MicroHeli extended tail rotor shaft. I will be reviewing this separately shortly.
So, onto the second part of this review, the tail pitch slider....
The tail pitch slider is designed around a cup and ball type approach with the normal ball link screwing onto the control horn at the opposite end to the plastic cup. The servo control rod attaches to this ball as per the stock slider. The ball was a very nice fit in the cup and moved very freely, this looks like being a very smooth bell crank design. The bell crank itself is fitted with a single bearing and is secured onto the tail case using an Alan bolt and washers. The tail pitch slider itself is almost identical to the tail pitch slider I reviewed several months ago from MicroHeli except that instead of having a pin that locates into the stock bell crank the SE unit has a ball which locates into the bell crank cup. This provides a much more solid and free running movement from the tail pitch slider and should provide more accurate and precise control response. Also their previous design with the peg going into a hole in the bell crank was susceptible to wear and eventually the peg would become sloppy and loose in the hole. This design should alleviate that problem. Also as the bell crank itself is now a CNC part there should be no flex whatsoever making again a more precise movement.
See below for pictures of the pitch slider being fitted to the tail case...
Once the tail case and CNC pitch slider are built and installed the advantages of the system are immediately evident. The tail pitch slider movement is silky smooth and utterly without slop. This is where the advantages of all CNC parts for the tail case and tail slider come into play. The only remaining area in the tail system where a minute amount slop can get back into the control system is where the ball links attach onto the pitch slider itself. This last piece of slop can be mostly eliminated by tightening down the ball links as far as possible but without causing any binding or interference with their ability to rotate.
So having completed the build onto flight testing.
The MicroHeli case is working in conjunction with a CSM 420 gyro and and HS 50 servo, these two components together have worked very well for me and I wasn't expecting to get any wag from the tail system. I wasn't disappointed, on first lift off apart from having to adjust the control rods as distances had changed slightly the tail system was rock solid. I was able to get quite high gain settings before wag started to introduce itself into the system.
Overall, this is another pair of upgrades that I think work very well on the T-Rex. As mentioned previously the whole point of fitting a tail gear case is it provides a solid mounting platform for tail pitch slider system. Whilst one might gain some advantage in terms of bearings and open case design The tail gear case itself isn't a performance enhancing part. The tail pitch slider and bell crank is a different matter altogether. These parts make up the performance element of this combination and based on my own testing they work extremely well in providing a slop free tail control system. The stock T-Rex tail pitch slider does not have a great bearing within it, in contrast the MicroHeli tail pitch slider uses a double bearing design and is a significant improvement on the stock part.
This upgrade does not offer any weight advantages over the stock tail gearbox or slider, however, it does introduce a significant bling factor as well as enhancing the performance of the tail system as a whole. I therefore do not have any reservations in recommending this as an upgrade which will enhance the performance of your tail system.
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