This is a review of the T-Rex 450XL HDE kit. My thanks to Air Craft for the supply of this XL HDE kit, who stock a full range of T-Rex kits spares, electronics and upgrades as well as the Hyperion range of quality R/C components.
	I'm not going to cover an entire build of the T-Rex 450XL HDE as the existing build thread covers a build in detail and the 450XL is not massively different from the T-Rex 450X. The data here will cover the differences in the T-Rex 450XL compared to the 450X and at the end of the review I will compare the flight characteristics of the two helicopters. Without further ado lets get into the kit and look at the head assembly. This is where by far the majority of changes have occurred and the head setup is quite different to the 450X. The first difference is in the blade grips. The 450X blade grips are a two bearing setup where as the XL now has three bearings. Two insert as normal into the blade side of the blade grip. The new third bearing goes the hub side of the blade grip and is pictured below bottom left. This bearing locates onto the feathering spindle and provides a much nicer contact between blade grip and the feathering spindle than on the 450X. Also pictured below is the new head button that screws onto the top of the 450XL rotor hub, this we can consider a bit of 'bling'.
	Next up is the flybar hub. This is a plastic version of the recently released CNC flybar hub for the 450X. The flybar hub contains two bearings through which run the new small diameter flybar introduced with the aforementioned CNC flybar hub. This new flybar hub provides friction free rotation of the flybar and is a welcome addition to the XL as the previous flybar system left a lot to be desired. The new hub also has metal inserts for the mounting screws to locate into when it is bolted onto the rotor hub. Again this allows for a more free movement of the flybar.
	The new XL flybar mixer arms and seesaw cradle are the next two items to be changed on the XL. The original mixer arms had a single bearing and collar, the new mixer arms are double bearings with multiple washers to allow full freedom of movement. Also new is the cyclic seesaw, again this runs on bearings and has a double grub screw clamping onto the flybar. This item is direct replacement for the old Align flybar control levers which were plagued with stripping threads for the grub screw. No such problem with the new seesaw which clamps down nicely onto the flybar and provides a very good hold compared to anything the previous control levers were capable of providing. Below you can see the seesaw in place. Also improved are the mixer arms which again are now double bearing and are slop free and silky smooth once fitted. The last picture bottom right shows the new metal spacers that hold the dampers in place once the blade grips have been screwed onto the feathering spindle. All these items together vastly improve the T-Rex head over the original 450X.
	Also upgraded as part of the control system are the washout arms, again using double bearings and the washout hub has the brass bushing center introduced later on the 450X after the original all plastic washout hub. The hub also has moved away from the slotted design for the anti-rotation pins and now uses some holes into which the anti-rotation pins fit. Once fitted the washout arms are also smooth in movement and slop free. Pictured below are the washout arms :
	The swashplate is also changed on the 450XL, the whole design being different from the original 450X kit. Particularly the introduction of an anti-rotation pin on the swashplate. Movement of the ball is also much improved and the stiffness associated with the original 450X swashplate is better although not totally removed. The next updated item is the tail pitch slider and bell crank. This has long been one of my least favorite parts on the 450X and it is good to see some changes in this area, much of the tail wag issues often seen with the original T-Rex 450X can be attributed to the por design of the original 450X slider. The new design uses a double yoke connection from bell crank to the slider itself, this eliminates the twisting effect seen on the original 450X slider that was often responsible for the movement feeling sticky/jerky. Also improved is the bushing/bearing in the slider itself, again this had problems on the original 450X of the bushing cracking, so it is good to see this updated. Lastly the bell crank has been changed to a double bearing like all the other control levers on the XL, which provides a solid and slop free movement. The bell crank itself connects via a hole onto a pin on the slider, top and bottom, make the double yoke mentioned earlier. Together it makes for a much more solid and slop free movement without any of the twisting effect responsible for sticky movement and cracking of the bushing on the original 450X.
	Moving on to the tail blade grips, again we have changes. The grips are now built up with a bearing and collar in each grip, plus the grip itself uses a metal ball screwed directly onto the blade grip. Again these are improvements on the original 450X single bearing and plastic ball. Plus the blade grips are now more resilient as the original items used to suffer from the plastic ball breaking off in minor incidents.
	The last item to mention from a mechanical perspective is that Align have updated the jesus bolt (main rotor head fixing bolt) to be only a partially threaded design, this strengthens the bolt and reduces the chance of failure from metal fatigue. When looking at a T-Rex XL the main noticeable difference is the main canopy, which not only provides some more space for the lipo but also looks much more racey than the original canopy.
	Other items worth mentioning are that the T-Rex XL is a stretched T-Rex and so can accommodate the larger carbon blades from stock. It also comes supplied with the Align solid wood blades which are an improvement on the original partially hollow blades shipped with the original 450X. Align have included the carbon look paddles and the vertical stabiliser is now made of real carbon fiber. The stock tail blades are also now the carbon look versions. Which all adds up to the visual effect of the new XL. It now very much looks like the great little heli that it is. To complete the build overview here are some pictures of the completed item ready for flight testing.
	Flight Testing First hops proved to be a huge disappointment. It seems Align still doesn't know how to make a swashplate that stays together. Below you can see the results of 30 seconds of spool up .......
	Fortunately the heli hardly left the ground and no other damage was done as I noticed the swashplate come apart immediately it happened. Some strong epoxy has now been applied to the swashplate to secure it in place. So, minor repairs finished it was back to the field for another go at initial flight testing. Some initial time needed to be spent on getting throttle and pitch curves to an acceptable level as well as trimming out the machine and adjusting the gyro gain and tail pushrod length to get optimum tail hold. Once this was all sorted the XL was lifted into a hover and the controls given a good work over to see how she responds. It's fair to say I'm very impressed! Stability is excellent with controls being very responsive but progressive. I had not dialed in any expo or dual rates and it was relatively easy to hold the XL in a steady hover within a 1 foot square box. Tail response was also very good. There was a tiny bit of hunting but nothing I couldn't dial out by reducing the gain slightly. This was only present in heading hold mode, in rate mode the tail was very well behaved with no wag at all. I tried some very quick 90 degree movements of the tail to check the stopping power of the tail and that it was not wagging back and forth on the stop, this all checked out OK. The machine is an HDE, so I wasn't expecting this level of control, which is much more akin to a CCPM modified 450X V2. Side by side I would have difficulty telling the difference between one of my modified CCPM machines and this HDE XL machine. All those bearing upgrades and removal of slop from the control system is clearly paying dividends in the control response of this machine. In terms of flight testing the next steps are to try some flips and do some inverted work with the XL to see what other benefits the new head brings. I'll be doing this over the next couple of weeks and update the flight testing once it is complete. For the moment I don't see that it is going to be anything but an improvement on the 450X V2 in terms of responsiveness and precision. flight testing (advanced) For the advanced flight testing I fitted a set of 325 millimetre carbon blades.This allowed me to increase the head speed to allow for 3-D flight. Switching into idle up I proceeded to a safe height to try some basic flips. The first thing I noticed was a significant drop in head speed when trying to do forward flips. This was very much down to not running in governor mode as the speed control I had fitted did not have this option. After a quick trip home to swap to a governed speed control I then headed to the field again. This time flips were much more controlled although a little bit slow due to the Align blades being a little on the heavy side. Performing half rolls to inverted was very easy and the general flight characteristics of this model inverted are very stable considering it is a Micro helicopter. I then tried some inverted flips with a full pirouette through the vertical. The execution of these was very predictable and quite comfortable to perform. I also tried some funnels which were a little flat due to the motor not really having the power to hold the model through a true vertical funnel. I would need to run a high voltage setup in order to make funnels look a bit better.Overall I was more than satisfied with the performance of this model. It has certainly evolved from the previous T-Rex and has taken on some more predictable flight characteristics that you would normally expect to get in larger models. It will be interesting to see how far one can comfortably push the T-Rex on a 3S pack and setup with these new more stable and predictable flight characteristics.