Micoheli CNC T-Rex 450 QNC rotorhead

Written by Ashley Davis Sunday, 11 December 2005 00:00

Rotorhead

The following is a product review of the MicroHeli Precision QNC RotorHead. My thanks to MicroHeli for supplying the part for review.

First let's take a quick look at what you get in the box.....

The box contains a pre-assembled rotor hub and blade grips, complete with antirotation pin, extra dampers and blade grip washers. As with any pre-assembled part, caution should be taken and the whole unit should be disassembled and rebuilt with loctite on the appropriate screws.

Also in the box is an exploded diagram of the whole assembly which was very useful in understanding exactly what this new head has to offer.

The unit is anodized blue, which is new for MicroHeli which traditionally have polished aluminium finish. I prefer this blue look to the usual polished aluminium look. Build quality is excellent and the whole thing looks like a step up in quality from the standard Align head. It also has a more compact look and feel to it than the Align offering. However, this is just on looks and quality of machining the question of technical capability also needs asking. I will come onto this later.

The head is configurable for soft (beginner) or hard (3D) dampening. The head comes pre-assembled with soft dampening installed, this is just one rubber damper and an aluminium spacer. For 3D damping you remove the aluminium spacer and add the second damper giving two o-ring dampers per blade grip. I didn't test both and for my flying style selected the double dampers for the flight testing on this upgrade. This configurable head damping is common in larger helis where harder or softer dampers can be installed for different flying styles. Soft dampers suit more scale like and smooth flying characteristics, hard dampers are needed for 3D to stop mid-air boom strikes and to give the collective crisp response for moves like tic-tocs.

The blade grips themselves are secured to the feathering spindle by use of a bolt and washer, exactly the same as the Align stock and upgrade blade grips. Loctite MUST be used on these bolts when assembling. The pre-built head did not have any loctite on these bolts so do not install this directly to your T-rex without first disassembling and applying loctite.The antirotation pin for the washout hub bolts around the bottom of the rotor hub and is secured in place with a very small grub screw. This does make the overall length of the rotor hub and how far it sits down on the main shaft once installed, again more on this later.

The most important aspect of this rotor head and grips is that it is thrust raced, unlike the Align blade grips. Thrust races are specially designed to bear longitudinal forces and rotor speed beyond 3000RPM should be feasible with this head and grips. The Align head starts to suffer from bearing freeze once you push up beyond 3000RPM and it is possible to have the bearings lock up. The use of thrust races is a very welcome addition as it allows for a much smoother running blade grip when utilizing 3D rotor speeds in the upper 2800 to 3000RPM. The positioning of the thrust race can be seen below in the blow up picture of the instructions. Bearing quality is also good.

Build / Setup

Overall the build quality is excellent, if I was looking to compare I would say it is as good if not better than the Align hub and grips. Installation was a relatively straight forward affair but caution should be taken as it is not just a simple case of swapping one rotor head for another.

I fitted the MicroHeli flybar mixers and cradle to the rotor hub to finish the main rotor head off ready for fitting to the main shaft. I quickly discovered that the MicroHeli rotor hub sits further down on the main shaft than the standard or upgrade Align rotor hub. The effect of this was that the washout hub would bind on the bottom of the rotor hub at full collective pitch. The arms from servos to swashplate needed to be shortened to sit the swashplate and mixers lower down the main shaft. The control rods from swashplate to flybar mixers could then be lengthened to account for this. Having done this a pitch range of -10 to +10 is easily achieved. Make sure that you have horizontal mixers arms and 0 degrees of pitch at mid stick, my initial attempts required significant adjustment. It took some time to get this right but the effort is worth it for nice predictable flight characteristics. I inserted BlueBird 320mm carbon blades for the flight testing and use of the supplied blade spacers was required to get a nice snug fit.

Although I didn't install or use the single dampers and aluminium bushes you can see the aluminium bushes in the picture above left. The top plastic bushes press against the dampers and hold them in place in the rotor head, the aluminium bushes sit at the center of the main hub. The o-ring damper itself sits between the aluminium bush and the plastic bush.

Double damping is achieved by just removing the aluminium bush and replacing with an o-ring.

Note: following one of the blade grip control arms coming loose on my own machine (causing tracking issues) please make sure you use a good strong loctite (such as loctite 243) on the two small bolts holding the control arm onto the blade grip.

Flight characteristics

I didn't test the single damping option because although it is an option the majority of pilots buying this head upgrade are looking for 3D performance.

Initial hovering had me thinking the machine felt quite soft and I was concerned that 3D may not be particularly good. Having completed a pack of hovering, trimming, setting up tracking etc etc my conclusion was that the head was certainly accurate and control was almost identical to what I have come to expect from the Align metal head and grips.

Next two flights were all out 3D, flips, piro-flips and tic-tocs, I also threw in some loops, rolls and inverted push overs as well as some inverted hovering, just to get a feel for the machine inverted on this new head and grips.

The machine I used was a 4S powered 450TH as I wanted to put some real power through this head and see how it coped.

Tracking was slightly out but it was not varying with collective so a small adjustment will be required but in the interests of time (as light was failing) I chose to leave it and get on with the flying. I would only be concerned about this if the tracking was varying wildly through collective changes, which it wasn't, so it's a simple case of just getting it adjusted correctly on the next flight. Additionally it was only a very small deviation in tracking (about 1 cm) and no vibration was being induced , so I could asses flight performance without any worry of this affecting performance. Tracking was corrected on the following flight without issues.

I did some fast circuits and stall turns to get a feel for the machine and it felt locked in and solid. I setup for a loop and checked inverted power at the top to make sure she would hold OK through flips or inverted hover. The machine responded with some but in my view not enough inverted climbout so I landed and electronically added some extra throw on the collective at the low end. Back in the air I did the same again and this time she punched up nicely at the top of the loop. Turning back on the downwind leg I tried a slow roll with an extended inverted stage, again it felt locked in and responsive with no wandering off track. I then pulled a few fast rolls, some more loops and some stall turns but using the collective to hold steady the vertical position in the wind. Again all nice and positive and confidence was starting to build to try some more adventurous stuff.

At this point in the flight I would be hard pressed to distinguish between the Align head and grips and the new MicroHeli QNC rotor head but that was about to change.

Coming down and flying lower I went for a basic stationary forward flip. She whipped over quite quickly but at the switch from positive to negative pitch I noticed a harder edge than I am used to in the response. Normally on the Align head the swap from positive to negative pitch feels a bit soft and there is some blade slap, the MicroHeli QNC rotor head was different and it took several more flips to start to get a feel for what was different. The MicroHeli head definitely has a harder and crisper edge to it on collective changes, the pitch comes in harder and holds better than the Align head. This also translated into a more positive tic-toc later in the flight where quick pitch changes need to have that hard edge for the tic-toc to look and feel right. I also noticed that on flips it was easier to catch the T-Rex and not lose height than on the Align head. As a last flight check I pulled a couple of piro-flips and although they were a bit messy due to the tail being a bit quick (I must reduce the piro rate slightly on the gyro end points) I was rewarded with a reasonable collective response through the flip.

The second flight just served as a check and balance on my initial thoughts and throughout the crisper collective response could be felt in the collective based 3D moves. I also did some inverted hovering just to see if inverted would feel any different to normal hovering but the response was consistent whatever way up I decided to hover. I left the field quite pleased overall as I had initially thought that I might struggle to differentiate between this head and the one from Align. The designs are very similar in terms of damping, with the only major difference being around the ball bearings used.

Overall conclusion

MicroHeli always try to build some level of innovation or performance based ingredient into their products. In this case the most obvious being the thrust races in the blade grips. These I'm sure allow the blade grips to function smoothly when under the extreme load characteristics of 3D flight. On the whole the QNC rotor head only shows it's true colours as you start to push the T-Rex quite hard, leading up to this point it behaves very similarly to the Align head and grips. Therefore in terms of who would benefit from this upgrade I would have to point directly at the hard core 3D fliers rather than those at the beginner or sport flying stage. Having said that, this is a product that can grow with your abilities as it behaves exactly like the Align head for sport flying.

The last MicroHeli review I performed was for their Carbon Frame and I had mixed feelings throughout the review on whether the frame was to my liking, particularly around design but as usual for MicroHeli products the flight performance was good. This item from MicroHeli is entirely different, the design is right, it improves upon the Align product (stock and upgrade) and the performance is top notch. It also looks great on the machine and I'm very pleased that MicroHeli now offer anodized parts which in my opinion look better than the usual polished silver. MicroHeli have always targeted performance seeking pilots and in this instance they appear to have got their sums right.

I recommend this product for confident 3D pilots who can push the T-Rex to gain the performance benefits offered. Beginner or intermediate pilots may not benefit from this upgrade over and above the Align upgrade head and grips but it is a product that can grow with the abilities of the pilot and offer more as the pilot demands more.

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