Roban Bell 407

Roban Bell 407

When talking about helicopters, the machine that often comes to mind is the Bell JetRanger and as the LongRanger is a stretched version of it, it too is a very familiar machine. The Bell 407 is the latest incarnation of this machine retaining the single engine but with a 4 blade rotor head while retaining the 2 blade tail rotor – all of which makes it an ideal subject to model. The design can be traced back to 1960 as a United States Navy ‘Request For Proposals’ for a Light Observation Helicopter, and the prototype Bell 206 first flew in 1962. This early design was known as the ‘Ugly Duckling’ and was stretched to provide more passenger and cargo space to become the Bell 206A JetRanger. The ‘stretched’ 7 seat Bell 206L LongRanger was first delivered in 1975, which was further developed to finally become the Bell 206L-4 LongRanger IV.

Development of Bell’s replacement for the 206 series started in 1993, and 2 years later, the Bell 407 prototype took to the air with its 4 blade rotor head – interestingly the 407 demonstrator was a modified 206L-3 LongRanger. Delivery of the Bell 407 began with some 140 being produced in 1997, and the 1,000th rolled off the production line in 2010. The Bell 407 is used across multiple roles, from corporate and HEMS, to gas and oil platform servicing, law enforcement and military roles are performed by the latest Bell 407GT. No wonder it is so recognisable.

From a modelling perspective, the simple design makes an ideal RC model subject. It has a big doghouse where the mechanics can be located and the tail boom is high with a straight run to the tail rotor. The fuselage itself is spacious providing endless opportunities for scale detail. The skid undercarriage is also simple to model, so all in all the Bell 407 is ideal for any scale modeller and particularly for someone looking for their first scale model.

The Roban Bell 407
I’m sure many readers will be familiar with Roban’s approach to presenting their models… A large plain cardboard box contains a fully painted fuselage, and further boxes contain ready assembled mechanics, in this case a 4 blade main rotor head and tail rotor gearbox with rotor blades, plus the tail boom and tail drive shaft. Then there is the included scale detail such as the ready to fit cockpit with lighting system, control sticks and pedals, 7 seats, navigation lights, aerials and wire cutters, and a large set of water slide decals to match your chosen colour scheme. This means you will need: motor and ESC, cyclic and tail servos, receiver and 3-axis gyro, Rx battery/BEC and flight battery packs. The specs of the model are:

Fuselage Assembly
The kit did not include a manual, so the first job was to download it from the Roban website (www.robanmodel.com/cms/index.php/home/instruction-manuals). This is a 55 page pdf file, which I didn’t print but worked from the computer screen – pages 8 to 34 cover the actual build, but you will need to refer to the parts listing to help identify what’s what.

The front fuselage section is a lovely moulding and has the complex woodwork installed including the cockpit floor, which is painted. The 4 main opening doors are already fitted and glazed, and the cargo door is also functional. Removing the top cowls gives excellent access and the mechanics will simply drop in place – the rear cowl is screwed in place while the front is held with magnets and locating pins. This means that unlike the Apache I did before, the mechanics are accessible – another example of why I think the Bell 407 is such a practicable scale model…

First job is screwing the pre-painted undercarriage to the fuselage; the u/c is the ‘tall’ set with the cross tubes fitting into recesses in fuselage floor – 4 screws hold it in place and mock clamps cover these to simulate the full size. This gives you a stable model to work on. The tail section is a tight slide fit onto the front section and is held in place with 6 screws into plywood reinforcing plates. Alignment was correct so I was happy to drill the fixing holes at this time.

A foam damper is slid into the tail end of the tail section so the boom will pass through it preventing any movement between the two. The vertical tail fin is screwed to the boom – the supplied anti-collision beacon has to be installed first. This is a bit of a fiddle as the LED has to pass through the hollow fin and you may want to open up the access hole – be careful with it as I managed to damage the LED! A white tail LED is also fitted and extension leads are provided that run through the tail section to the control board that takes its power from the Rx.

Next are the horizontal stabilisers that are moulded with the leading edge slats and very nice they are too! The small end fins are screwed on and navigation lights are added with the wires running through into the tail section. It is worth noting that the outer ends of the stabilisers are cut at an angle so the fins angle outwards at the front – the square cut end is glued into the recesses in the tail section. Be sure to make a good job of gluing them in place and that they are horizontal as their weight does tend to make them drop a little. The manual also shows the Nav. light wires glued inside the tail, this is a good idea otherwise the tail boom could snag them…

Mechanics
As mentioned the mechanics are supplied assembled ready to accept motor, servos, rotor head and the tail boom. These mechanics use a 2-stage reduction with a toothed belt drive from the motor to a lay shaft behind the main shaft that drives the main gear through a second reduction gear set. The lay shaft also drives a set of speed up gears for a second shaft running down to a gear box that then drives the tail drive shaft. This lower gearbox is a tail drive gearbox cleverly rotated so the ‘output’ shaft is used as the input, which means the shaft is properly supported both sides of the bevel gear. The side frames are carbon sheet with metal bearing blocks and motor mount with further carbon spacer plates bracing the assembly. This layout means that the main drive components are very compact and will therefore fit into the ‘doghouse’ with the tail drive dropping down behind.

These SM2 ‘compact mechanics’ are used throughout Roban’s super scale range of 12+ models with the only difference being the position of the tail drive and boom clamps. As a comparison I have included a photo of the AH-1 Cobra mechanics where the vertical section of the side frame is much longer taking the tail drive lower to suit the low slung tail on the Cobra.

The 4-blade rotor head is supplied fully assembled; all you need do is check the length of the pitch control rods. Having said that I did check that the screws were all tight and the blade grips rotate smoothly without axial play – they passed my tests. The all metal swashplate is also supplied ready to fit – the manual says to fit these to the mechanics at this point, but I decided to do this later.

Attention turns to the tail boom, which is supplied cut to length and so just needs the tail tube drive installing – use oil on the bearing supports to help them slide in. The boom support clamps can be removed from the frames and fitted to the boom – a screw into the boom locates the rear one, while the front support is recessed to accept the boom, all of which makes it easy to fit. The servo support, control rod supports and boom stay support are slid in place and the boom assembly reinstalled into the mechanics.

Electrics
Powerful metal geared servos are recommended and I chose Spektrum H6040, which match the spec, 3 for the eCCPM and another for tail control. The servos drop into place and I chose to use JR heavy duty arms with the ball on the inner hole. The reason for using the inner hole (11 mm radius), is that the servo control rods run to bellcranks that double the output making the controls very aggressive. I believe this is to help keep the control assembly as compact as possible but it’s a good idea to compensate by using short servo arms.

I decided to use a Spektrum AR7200BX receiver that includes a BeastX 3-axis gyro, and it is mounted on a tray at the rear of the mechanics. I mentioned that removing the rear cowl on the Bell 407 provides full access, so it’s easy to access the gyro should any fine tuning be needed – with the Cobra and Apache the gyro is completely buried inside the fuselage… The next job was to run through the BeastX set up so I could adjust the pushrods etc. I was pleased to discover that when setting the Cyclic Pitch Geometry on the BeastX, 6º cyclic gave a blue LED showing the geometry was correct.

It is also a good idea to fit the tail rotor gearbox so that you can set up the tail control and check the gyro response. You will find that the tail rotor rotates with the leading edge running down through the main rotor downwash. The boom stays need to be fitted with the boom clamp under the boom; I made a couple of spacers so the carbon stays would pass the boom.

Motor and ESC etc.
All Roban 700 size super scale models are designed for 12S LiPo power and in this case with the 4 blade rotor head specify a 450 Kv motor, which with the standard gear ratio of 13.83:1 will give a governed rotor rpm of about 1300. I chose a KONTRONIK PYRO 700-45L (you ideally need the long shaft version) and a KONTRONIK JIVE Pro 120+ HV ESC, which includes their excellent governor as well as their very reliable 5 – 8 V BEC that’s rated 8 A continuous and 20A peaks – plenty for this and any model! Another benefit of using the JIVE Pro for this scale model is that the optional KONTRONIK ProgUNIT allows you to vary the spool up time (8 – 60 sec), and it also has an internal log that can be accessed by optional modules that are plugged into the sensor port (see http://www.kontronik.com/).

The motor slides into place and the primary drive belt pulley is added – I suggest using a good quality ball ended hex driver for tightening the securing M4 screws. The belt is tensioned by a pair of screws that pull the motor mount forward before tightening the motor securing screws that also lock the mount in place. It is worth checking the belt tension after a few flights.

I always like to use a EMCOTEC SPS (Safety Power Switch) that operates as an electronic switch between the LiPo packs and ESC, operated by a remote switch – I use the magnetic ‘remove before flight’ plug version. The advantage of the SPS is that you can connect the packs in complete safety and the system is only live when you pull the plug, it also includes an anti-flash circuit that prevents the spark when connecting some ESCs – the JIVE has its own circuit for this…

Assembly
Having finished the mechanics with the 3-axis set up, it’s time to install them into the fuselage, but first 2 spacers need to be glued to the rear mounting point, which tilts the main shaft forward as per the full size. With the tail rotor gearbox removed, the boom slides into the body and with a little fiddling the mechanics drop into place. The fuselage tail section is slid over the boom, making sure it passes through the foam positioner and you then attach the tail gearbox, but you may need to move the tail section about to make space and access the fixing screws. With the mechanics and tail section secured, it looks like a real helicopter.

This leaves the job of fitting the ESC and in my case SPS, which I positioned on either side of the mechanics so the battery connections were at the front, talking of which… The full size has a structural vertical box section running floor to ceiling through which the control rods run, and this is nicknamed the ‘broom cupboard’. Roban have cleverly enlarged this so one of the 6S LiPo packs can slide into it and the second lays across the top on a support plate. A photo shows the convenient layout and you’ll see how I mounted the SPS switch (see later…).

Scale Bits
We start with the consul with its illuminated dials, all you do is glue it place, add an extension lead to the LED control panel and it’s done. Next you glue in place the joy sticks and pedals, followed by the cup holder (!) and seats, which looked a bit plain so I painted the seat belts. The front screen is cut to shape and a couple of screws hold it place; a hole needs drilling through the top coinciding with the wire cutter that’s fitted later – I made this a slot so I can slide the screen out without disturbing the cutter.

Next shown was the mock U/C clamps that I’d already fitted, followed by the step rails that use 90º plastic mouldings with plastic brackets that make a good job of securing them – I used a general purpose adhesive for all these scale fittings. Antenna are added to the top and sides and then the 2 wire cutters. A pitot tube is included and I took the trouble to paint the nozzle black. The last detail to add is the steps just behind the passenger doors.
This leaves the decals, which I find the easiest job to mess up! The good thing is that Roban have improved the quality of these water slides – they are now pre-cut with a transparent clear film on top. So cut out each one oversize, soak it in water until it’s ready to slide, position it and gently slide the backing out, leaving it in place. Now use a soft cloth to squeeze out excess water and air bubbles – then leave it alone to dry completely! You can peel off the top layer from each decal, but be aware the decal itself is very thin and so could be easily damaged (no need to explain how I found out…).

The main 700 mm semi-symmetrical rotor blades are supplied ready painted – I checked the weights using a very accurate set of scales; 143.8 g, 143.5 g, 143.8 g and 144 g which is good enough! The finished model with rotor blades but no LiPo came out at 6.7 Kg. I intend to fly it using 2 OptiPOWER 6S 4300 mAh packs which will bring the flying weight to a very reasonable 7,275 Kg.

Flying
I had to wait ages for the weather to cooperate – the UK winter seems to have been very windy and wet and when it wasn’t, it was too cold! Eventually a suitable day arrived and I met Denis Stretton for the first test flights. I didn’t fit the top cowls for this as I wanted access to the tuning ‘pots’ on the AR7200BX. Freshly charged OptiPOWER 6S 4300 packs were fitted but when I removed the magnetic plug from the EMCOTEC SPS, nothing happened! It had worked on the workbench, so what had gone wrong? The short-term solution was to bypass the SPS and Denis kindly made up a wiring harness to achieve this. Back home, I discovered that when I fitted the SPS magnetic switch, I had mounted it too close to one of the canopy magnets, which meant the switch was permanently off! I tuned the switch round and all is now fine!

The rotors spooled up smoothly, the tracking looked pretty good and up she came into the hover. The head gyro gain felt a bit low, so this was increased using the ‘pot’ and this time it felt more locked in, however when moving it around the tail power was found to be lacking and changing the gain didn’t seem to help. I decided to increase the rotor rpm which helped to some extent, and also improved the rotor head control, so I returned the gyro ‘pot’ to the stock position. The conclusion with these first test flights was that the mechanics were running smoothly and well, the AR7200BX was a good choice but longer tail blades were needed to increase the tail power.

For the next flights I replaced the supplied 105 mm tail blades with a pair of NHP 110 mm blades which improved matters somewhat so I decided to try a pair of NHP 120 mm blades and these made the tail control much more solid with the tail easily holding side on to the side stiff breeze. At this point we checked the main rotor speed – it was quite low at 1180 rpm, so I increased this to 1240 rpm and now the whole model felt properly locked in with a good feel to the rotor head and a powerful tail. The final ‘setting up’ was to find the blade that was slightly out of track!

This was a couple of weeks before the UK’s first main fly-in at Charmouth and so this would be its first public viewing… It was a matter of dodging the rain, but when the sun came out it was lovely and as I wanted more photos I asked Kevin Lever to fly the model for me while I snapped away. Kevin is well acquainted with Roban models and felt very ‘at home’ with the set–up pronouncing the tail response was excellent! He also didn’t want to hand the controls over and by the time he did it was raining again!

Summing Up
Roban Models have a real winner with this model and it should be attractive to anyone wanting a practicable scale model that isn’t complicated. The SM2 mechanics were introduced quite a while ago and have stood up well to the test of time. The quality of the fuselage is stunning and the bright Denver AirLife colour scheme makes it stand out that much more – as is usual with Roban, there are other colour schemes to choose from as well. I do think tail power in its standard form is lacking, which I fixed using longer tail blades, but a higher speed tail would also provide more power; knowing Roban I am sure they will take notice. One comment on flying the 407 is that the forward rake of the main shaft means is takes a little getting used to as with a level fuselage, it’s in fast forward flight and the tail sits low in the hover. As I say it’s just a matter of getting used to the orientation.

So there we are, a great scale model that stands out from the crowd. It is easy and straight forward to assemble and will fly really well with one of the simplest 3-axis gyros. I am really impressed…. However, I now see that Roban have released more models in the range adding 800 versions of the Bell 212 and Bell 412…. What next!