Fury Extreme Wren Turbine
Conversion by Darren Clark

Having seen the quality and performance of turbine powered helicopters available it was only a matter of time before the club was to have its first. I decided that the way to go was a two stage turbine unit rather than a belt driven set of mechanics. I wanted to build the turbine myself too so as to keep the cost to a minimum and to get some idea of how the engine actually worked.
 

Having read through the instruction manual I set about putting the engine together. Three hours later the engine was built as it is fairly straightforward following the instructions carefully. I had also ordered a pre-balanced turbine which cut down the assembly time by around two hours. The only slight snag in assembly came from the fact that the instructions were written around the turbo jet engine and this missed fitting the extra pressure take off feed for the power turbine assembly used in turboprop and helicopter applications. I believe Wren have included this now in their newer instruction manuals.
 

Once the engine was completed I constructed a suitable test bench for running the engine and setting up the FADEC ECU. Model turbine engines will run on either Jet-A1 or Kerosene (Paraffin) with a 40:1 turbine oil or marine TCW-3 two stoke oil mixture so a suitable fuel was sourced from my local B&Q Warehouse in the form of 'Parasene' which is a low odour paraffin and my local marine specialist supplied me with some TCW-3 oil.
Initial test starts on the bench lead to some interesting 'flamethrower' and smoke effects which, after lots and lots of head scratching by a number of people, it was discovered that I had incorrectly connected the fuel and front bearing feeds the wrong way around leading to the engine being over fuelled considerably. This was soon rectified that night and the following day the engine started immediately with no fuss, spooled up and settled down to its flight idle at 40,000rpm. The throttle was then slowly opened and the engine raced away to its initial maximum rpm setting of 100,000rpm. Closing the throttle quickly caused the engine to 'flame-out' so the ECU delay was adjusted to slow the engine at a rate that kept it running happily right back to idle. A few more runs were made with no further problems on the bench so it was time to fit it into a helicopter.
 

Initially I had thought about getting either a Century Predator or a Robbe Cuatro, both of which had already been converted to take turbine power by others, but I finally settled on converting my X-Cell Fury Extreme to take the Wren power plant. Once the engine and gearbox were joined together as a complete unit the modifications could begin. Firstly the helicopter was stripped of it's OS91 C-Spec, fan housing and fuel tank. The aluminium cooling fan was inverted and re-attached to the Baileys gearbox ready to line back up into the Fury's clutch. With gritted teeth the Fury's side frames were cut and replaced with home made carbon frames spaced out with suitable turned aluminium spacers so as to hold the much larger 1200cc Dubro fuel tank which was now at the rear of the helicopter as near to being under the main mast as possible. A gearbox mount was made from aluminium to hold the gearbox in place below the clutch and the engine was hung from the front frame using stainless steel straps. Finally all the plumbing and wiring for the FADEC ECU was added to the helicopter along with the tiny gas cylinder and solenoid valve for remote starting the engine. To give me slightly more fuel capacity and to remove all air bubbles from the system two small Dubro header tanks were added on either side of the main tank and plumbed in accordingly.
 

Initial flight tests showed that I had a restrictor missing from the engine which was causing over fuelling and clouds of white smoke to appear from the exhausts. It was also emptying the 1200cc fuel tank and header tanks in around 6 minutes which did seem rather excessive! A quick phone call soon rectified the problem allowing me to get the helicopter flying properly with a smoke free engine and a flight time of around 12 minutes.
 

Once the canopy was trimmed and fitted correctly it was just a case of finishing it in a suitable paint scheme. Having seen the Jason Krause design done by Arizona Heli Canopies I had a go of painting the same scheme myself on the JR Vigor CS canopy with reasonable success including the carbon effect graphics on either side. The only other modifications made after the first initial flights were to fit two 7.2V 2600 mAh Polycell 2C1P Li-Po battery packs for the ECU and also for the radio supply running through a Duralite 5.1V voltage regulator. An uprated Wren turbine FOD screen and starter motor mount was also fitted to the front of the engine.

A video clip of it flying can be viewed by clicking HERE

Recent Modifications

Having flown the model for over a year I decided to extend the model to allow me to run up to 810 mm main blades. I wanted to continue to use the original Fury carbon fibre tail boom rather than trying to get a one off longer boom so I needed to move the plastic clamp back 10 cm. I made a pair of side frame extensions from 2 mm carbon sheet and positioned the original plastic tail clamp 10 cm further back using some 2 mm spacer plates. The horizontal fin and boom supports were then adjusted further forward on the boom to compensate. That was the relatively easy bit. I now needed to extend the tail tube drive. This was done by removing the pinned nylon connector and replacing this with an aluminium extension moving the nylon connector 10 cm rearward. I also fitted an extra bearing just in front of the connector and made an aluminium bearing block to hold this between the side frame extensions where the boom clamp originally sat. To stiffen up the entire conversion I made up two aluminium plates to sandwich between the original side frames and the new extensions. Finally I extended the tail servo pushrod by 10 cm using some aluminium rod. I changed blades to the new style Carbon Twill NHP 800mm blades as you can see in the pictures below. I also opened up the blade grips to take 5mm blade bolts for added security of these longer blades. Initial test flights showed that the extra drag created by the longer blades had reduced the rotor rpm by around 300 to 400 rpm. To keep the same throttle curves I needed to increase the turbine rpm from 120,000 rpm to 125,000 rpm on the ECU. This now gives me an idle-up head speed of around 1900 rpm which is nice and smooth with plenty of power for aerobatics and 'gentle' 3D flying - it's still a heavy machine after all! In flight the increased performance was extremely noticeable with much quicker climb out rates than before on the shorter blades. The model feels even more stable and precise when doing flips and rolls too. Having done an auto with the model on the 710 mm blades I can only assume that the auto performance will have increased dramatically too but I will leave that for now until I have to do one for real if the engine flames out again....

There are more pictures of the finished helicopter on the websites Gallery page.

Wren Turbine powered Fury Extreme Specifications

Miniature Aircraft X-Cell Fury Extreme with 8.18:1 gear ratio.
Wren MW54 mk2 turbine with FADEC ECU, full autostart system, exhaust and second stage power turbine - 125,000rpm maximum.
Baileys turbine gearbox.
Dubro 1200cc main tank with two Dubro header tanks.
Parasene (kerosene) fuel with 40:1 TCW-3 marine oil.
Futaba R149 DP receiver with QuickUK receiver case.
Three digital Futaba 9252 cyclic/collective servos.
Futaba GY601 gyro with digital 9251 tail servo.
7.2V 2600 mAh Polycell 2C1P Li-Po battery packs for ECU power supply.
7.2V 2600 mAh Polycell 2C1P Li-Po battery pack with heavy duty switch and Duralite 5.1V voltage regulator for radio.
NHP Carbon Twill 800mm carbon main blades.
V-Blade 105mm carbon tail blades.