B J Craft Anthem build - 2 m FAI F3A class aircraft and Debowski TMCR contra

[Peter Jenkins]

The B J Craft Anthem is a 2-metre class aerobatic aircraft designed to the FAI F3A specification by a South Korean B J Park.  Park has been the S Korean F3A champion many times and represents his country in the FAI international competitions.  I have had 2 other designs of his, the Agenda and the Element which is my current F3A competition machine.  In both, I used a contra drive system produced by an Austrian, Ralph Schweizer, called the RS CRS which uses an in-runner motor driving through an epicyclic gearbox to turn 2 output shafts in opposite directions.  The reduction provided by this gearbox arrangement is a 13.5:1 ratio allowing the in-runner to produce a maximum prop RPM of around 4,500 turning a front prop of 22 x18 and rear of 22 x 20 inches.

The CRS requires the gearbox to be greased every 50 flights via a greasing point mounted on the front of the gearbox.  This does require the props to be removed.  At 150 flights, the gearbox must be removed, cleaned, checked for wear and any worn washers or gears replaced, and then regreased and refitted.  This means the whole motor/gearbox assembly must be removed from the aircraft and loses the fine tuning of the thrust line necessitating a couple of flights afterwards to re-establish these settings.

 

Adam Dębowski is a Polish F3A pilot who has designed and manufactured two very useful items.  The first was an ESC that maintains a set motor speed called the D3.  The FAI has cleared the use of the feature for international competition.  The D3 then will hold whatever prop speed your throttle stick has commanded for straight and level flight and during any climbing or diving even if you don’t move the throttle setting.  The effect of this is to enhance the ability to fly at a constant speed.  The other item is a twin motor contra rotating motor (TMCR).  As the name implies, there are 2 motors mounted on the same axis driving in opposite directions each with its own D3 ESC.  The great advantage of the TMCR is that the motors are both outrunners and so do not need gearing down in order to turn the propellers at around 4,000 RPM max.  Being outrunners, there is no maintenance required which was a big attraction to me.  The other big attraction is that outrunners while obviously needing cooling are not as critical in this area as the in-runner is.

 

[Peter Jenkins]

The Anthem is built to meet the FAI F3A specification, that is, wing span and fuselage length must not exceed 2 m and the weight must not exceed 5,000 g.  No flight assistance is allowed, other than as I’ve already mentioned, an ESC that provides proportional braking (the D3 fits this rule), the use of rates, expo, switches to achieve certain set control positions (e.g. snap roll).  That means no gyros and nothing that will perform a pre-ordained series of control inputs or any timing device.

 

The Anthem follows the practice first seen by the current World Champion, Christophe Paysant-Le Roux (CPLR for short) in his design of a couple of years ago which is a swept wing.  That is not just the leading and trailing edges but the mean chord line is swept backwards. 

 

Why a swept wing?  Well, the theory is that the aircraft becomes more stable in yaw.  That is why some swept wing jet fighters have the wing arranged with anhedral to reduce the stabilising effect of their more highly swept wings.  The reason wing sweep causes this effect is that as the aircraft is yawed, the forward going wing presents more of its span to the airflow travelling chordwise and thus increases lift and drag.  The rearward going wing experiences a slight loss in lift and drag as a result of an increase in spanwise and reduction in chordwise airflow. 

What the designer also claims is that there is now no need to have any difference in the side thrust set up for single or twin contra prop designs.  It will be interesting to see how powerful is this effect in flight!

 

The Anthem is only the second 2 m F3A airframe that I have bought new since 2012!  The others have all been second hand and have had the advantage that, apart from fitting a different motor to the original, the rest of the airframe is flight tested.  This time, I took the decision to buy the aircraft in September 2022 and placed an order with Bondaero who are the UK agents for B J Craft.  Due to the Corona Virus lockdowns in China this order didn’t appear until mid-February 2023!  Chris Bond, the owner of Bondaero, handed over a large quite heavy box with the Anthem inside it.

The photos show the box as it was handed over to me and with the lid removed.  The aircraft is made in China (isn’t everything these days!) and had been shipped by airmail from Hong Kong.  Thankfully, there was only a slight scuff mark on the plywood.

 

As you can see, the whole lot was extremely well packaged with the fuselage supported by an attachment that ran through the wing tube and was bolted to the sides of the box.  This serves to prevent the box being squeezed and the contents damaged.

So, the first job was to unpack everything, check for damage and to ensure that everything was there.  I was delighted to find no damage whatsoever and everything appeared to be there.

 

That having been said, there were 2 sheets of ply wood with laser cut parts some of which were marked with their function but others unmarked.  So, after trying to figure out what these bits were for, I had to admit defeat and call Chris Bond to get him to tell me what the ply parts were for. 

Ultimately, I decided to go with a different battery tray, wing incidence adjusters, tail wheel and main wheel axles.  More on them later.

The issue with B J Craft is that they don’t provide any instructions on the sequence of putting the model together other than the blurb describing the aircraft that gives a CG range.  A call to someone else who had built and Anthem elicited that the setup should be:  level the fuselage so that the Tail plane is at 0 deg, Wing at 0.7 deg and motor at -1 deg.

 

So, the next task was to set out all the processes that I needed to go through to assemble the aircraft and install all the equipment into it ready for the maiden.  This required the 3 major elements to be dealt with:  the fuselage and canalyser; the 2 tailplanes and the 2 wings.  I decided to start with the fuselage.

[Peter Jenkins]

The first job was to fit the motor into the fuselage.  As I mentioned earlier, the motor consists of 2 outrunners driving through concentric shafts.

There are 2 ESCs that are fed by the same 10S LiPo pack and drive each motor.  The motor is mounted using the provided nose mount using rubber bobbins that you can see behind the rear prop driver.  The front prop driver is slid onto the front shaft once the rear prop is installed.  There is a rear mount which you can just see between the 2 motors and this is bolted to a ply former that I made and glued into to the fuselage.  The thickness of the ply former has to be gauged by providing a 2 mm gap between the spinner backplate and the fuselage nose ring.  This required a degree of fettling so that everything lined up once it was bolted into place.

 

The next task was to reinforce the undercarriage mounting plate with carbon fibre cloth since with the long undercarriage legs that a 23 inch prop set require.  Once that was done and dry, I was able to crack on with making and fitting the rear motor mounts and gluing them into place.  I find the easiest way to do this is to bolt the motor into place with the side supports bolted to the rear mount, or in this case the mid mount before gluing the ply mounts in place.  I use Hysol for this as it is has thixotropic properties (doesn’t run) and left it overnight.

 

The next task was to set up the Tx memory and bind the Rx to it.  I have a JR XG11 Tx and decided to use the Xbus capability to reduce the cable run to the rear mounted rudder and twin elevator servos to a single cable.  I had a 4 way convertor, of which I only needed 3 leads, to which to connect up my non-Xbus servos.  Adam Debowski recommended that I use separate channels for the 2 ESCs.  This sounded like a good idea since the XG11 supports a dual channel for twin motors.  However, I just couldn’t work out how to get the 2 channels linked to my 2 throttle curves!  There’s a guy on RC Universe who is an absolute glutton for punishment on how to do this stuff with the JR XG11 Tx.  A quick call for help and just over a day later back came the suggestion of how to do this. 

 

While I was waiting for this advice, I soldered both ESCs battery input cables into two 4 mm bullet connectors thus wiring them in parallel.  I also soldered 3 mm sockets onto the two sets of 3 phase output wires on the ESC.  The motors already had the 3 mm plugs soldered to them.

A good deal of button pressing later, I had the 2 motor channels connected to the throttle curves as well as the motor hold working on both motors.  I then set up the Rx, an Rx battery and switch, and plugged in the 2 servo leads from the 2 ESCs into the appropriate twin throttle channels.  Now the moment of truth!  Connect everything up and see if the motors work and then work out if they are going in the right direction!  Thankfully, the ESCs armed and gave off the required tones to indicate a successful arming.  Of course, it was too much to hope that the motors were going in the correct directions!  The rear motor must turn clockwise while the front motor must turn counter clockwise.  So, swapped over a couple of the 3 phases wires and all was well.  I then put the correct colour coding onto the six 3 phase wires so that I wouldn’t have this problem again.

[GrumpyGnome]

Very very nice. But a tad pricey for me ......

 

I'll follow with interest.

[Peter Jenkins]

3 hours ago, GrumpyGnome said:

Very very nice. But a tad pricey for me ......

 

I'll follow with interest.

There are smaller (50-70 size) airframes that fly almost as well for considerably less dosh GG.  You wouldn't start driving in F1 in an F1 car but a much much cheaper go-kart 😀

 

Just thought folks might be interested to see how these 2 m aerobatic models come together.  There are, to my knowledge, 3 pilots who build and compete with their own design and built models very successfully.  You also don't need a contra drive to be competitive.  The world champ flies an IC engine with a single prop.  I just wanted to try out this configuration.

Edited March 23, 2023 by Peter Jenkins

[GrumpyGnome]

Oh, I'm definitely interested, don't get me wrong.... 🙂

[Colin Carpenter]

As a lover of F3A models I’m watching! Colin

[Peter Jenkins]

Welcome aboard fellas.  Just in case you folks who are reading this think I'm a fast builder, I started the assembly at the end of Feb but I'm just catching up on the words!

 

The next task was to cut the fuselage for the cooling holes so out came the motor to protect it from all the dust!  BJ Craft had provided ply templates for the intake and exhaust holes.  First task was to mark the holes onto the fuselage using a marker pen and then to use my Dremel to cut out the waste material.  I always find this the most nerve-wracking part.

I started with the holes on the underside of the fuselage since this was flat.  The photos show the initial marking and subsequent outcome.  Dealing with the front intake was a bit more difficult both in transferring the pattern and in cutting out the hole!

 

 

 

 

The last photo above, shows the reinforcement of the rather weak structure between the 2 front air intake holes with some carbon tows.  On my Agenda, which had a similar intake, the middle divider broke and so I decided to pre-empt this problem at the build stage.

 

The next task was to fit the tail wheel that I had bought.  It is widely used in these airframes and was relatively easy to fit.  You just drill a hole, in the right place(!), and then screw the tail wheel into the fuselage.  The big advantage is that if the tail wheel ever suffers damage, it is simply a matter of unscrewing the broken unit and screwing in the new one – always assuming that the manufacturer keeps on making them!

 

[Peter Jenkins]

Having cleaned up the debris from the hole cutting exercise, my next task was to run wires down to the tail of the aircraft for the 3 servos that would be mounted there – 2 elevator and 1 rudder.  As the aircraft had come with a cut out for the rudder servo under the tail plane, I decided to go with that option particularly as the recommended rudder servo was a mini servo but with the same power as the full size rudder servo I had planned to use.  The mini servo has a quoted torque of 10 Kg cm so was certainly up to the task and weighed half as much as the full size servo of the same power.

 

In my current aircraft, the B J Craft Element, I have run a standard servo cable and just a signal cable to the 2 elevator servos in the tail. This reduces the weight of the leads in the long rear fuselage.   I made up a harness at the tail to provide 2 sets of servo plugs with the power cables feeding both servos.  While pondering how to deal with 3 servos, a friend suggested I use the JR Xbus system. As it happens, I’d bought 2 Xbus converter leads second hand about a year ago.  These have a single servo input with 4 outputs converted to provide 4 output plugs for standard PWM servos.  The single connection plugs into the Rx’s Xbus port while I can use 3 of the 4 outputs to drive the elevator and rudder servos.  Perfect.  So, I made up an extension lead to stretch from the Rx to the converter and with a bit of fiddling around got the 3 leads I needed positioned to allow the 3 servos to be plugged into them.

 

Thank goodness for You Tube as I found a guide on how to set up the Xbus system as my Tx manual didn’t mention it!  However, it took several goes before I was able to sort out the process of getting the servos allocated to the Elevators and Rudder and moving in the correct directions!

[Nigel R]

Watching with interest.

 

Is the fuselage a single skin glass? Or something more exotic?

 

On 22/03/2023 at 13:31, Peter Jenkins said:

some swept wing jet fighters have the wing arranged with anhedral

 

Can also be done to combat Dutch roll, as well as the more obvious general reduction in stability, for reasons of agility. Everything since the 1970 generation of jet fighters are fly-by-wire, and the stability needs to be very low to allow the flight computer to maximise the agility of the airframe (I expect I'm not saying much you don't already know PJ). Even larger military transport aircraft use anhedral now, although their goal is typical more a neutral stability, rather than the fighter 'slightly negative' stability.

[Nigel R]

9 hours ago, Peter Jenkins said:

Xbus system

 

I'm sure you've done the math, as it were. How does the XBus converter setup compare (weight, complexity, time to get it working) to the low tech solution of making a 5 wire harness with 3 standard servo plus each end?

[Peter Jenkins]

Hi Nigel

 

The fuselage is of single skin glass fibre construction with some form of wood integrated into the front from the wing tube forwards but stopping before the motor area - see the photos above showing the mounted motor and u/c reinforcement.  I believe the fuselage is painted in the mould.  The wings and tailplane are traditional wood construction with film covering.  I meant, and forgot, to put in the component weights since weight is a big issue in F3A.  The weights (in grams) for the bare components are as follows:

 

Port Wing   .....................316
Stbd Wing .................... .315
Port TP and elevator ......88
Stbd TP and elevator .....88
Canalyser ..................... 102
Fuselage ............... .....1044
Rudder ........................... 60
Canopy .......................... 82
Wing joiner .....................65
TP joiner rods ............... 10

 

I've not included the undercarriage, spats, wheels and other hardware as I was going to use other stuff.  I was very impressed with the wings being within 1 g of each other and the TPs being the same. weight. Well done B J Craft.

 

As regards the Xbus weight trade off, the weights are as follows:

• Xbus converter  = 13.2 g
• Single extn lead = 11.3 g
• Total with plugs = 24.6 g
• 3 extn leads w/o plugs = 36 g
• Minimum weight saved = 11.4 g

Since the 11.4 g saved would have been at 50 cm aft of the CG that was a significant moment to remove from the tail.  The complexity is a function of not knowing how to set up Xbus so let's call that a learning curve.  I probably spent around 4 hours trying to understand and set up the Xbus system.  Once I got used to that then I would say that setting up the elevators so they were exactly equal in their displacement across the whole range of movement was comparable with setting up the elevators in my Element using the standard PWM servo setup.  However, the Xbus system allowed many more corrections such that I could achieve the same movement over the entire range from full up to full down compared with the standard system that has a finite number of changeable points.  So, on that basis Xbus, or if you were using Futaba and Sbus, has the advantage.  A single servo wire with 2 additional signal wires would have taken a lot longer to fabricate than the single wire I had to make for the Xbus converter.

 

As regards Dutch roll and swept wings, there is a combination of inertia and aerodynamic forces that need to be factored into the effect.  Most airliners suffer from Dutch roll but use a yaw damper to sort it out and I would expect that today's 4th and 5th gen fighters have this controlled by the flight control software so the pilot will be completely unaware of it.  I have been using a key chain camera mounted on the rear canalyser bolt on my Element, unswept wing, and there is absolutely no sign of Dutch roll with that airframe.  I will put the camera onto the Anthem when it's ready to fly and will be interested to observe whether Dutch roll is present and will report back.

Edited March 24, 2023 by Peter Jenkins

[Peter Jenkins]

While on the topic of making up servo lead extensions, I'm not sure how many forumites do that but for those who don't here's a short "how to".

 

Many years ago, I took up making my own servo lead extensions.  The advantage is that you can make the lead to exactly the length you want.  Additionally, you can reduce the standard servo lead to the length you want which is what I did for the twin elevator servos on the Anthem.  However, like everything in life, you must have the right tools!  This photo shows what’s needed. 

Firstly, you need a wire stripper and the orange coloured set of pliers is just that.  You need to strip about 3 mm of covering off the wires and this tool allows you to see how much you will strip and do all 3 servo wires simultaneously.

Next you need a pair of needle nosed pliers.  You need these to close the “wings” on the wire crimps that hold the wire and the insulation.

Finally, you need a pair of good quality crimping pliers.  You must buy the sort that is suitable for crimping servo wire and aim for an automatic action i.e. one that you can press home fully and that will then crimp to a set pressure and then release itself and spring open when you release the pressure on the handle.

You must also buy the plastic plugs and crimps but those are readily available.  You can get Futaba style plugs with the little flat that provides correct orientation or JR style plugs that don’t have these little flats.  If you cut off the flats on Futaba style plugs you can use them on JR sockets and, of course, you can use JR plugs on Futaba sockets but the onus is on you to get the orientation correct.

So, having got all these bits, this is what you do next.

First, strip the wire using the stripper pliers.  The photo shows that I’m making the plug with the male connector.

   

 

Next, separate the 3 wires.  I find making a small cut with a sharp modelling knife to start the separation process is very helpful if your nails aren’t particularly strong!  Then twist the ends of the wires together to stop them spreading out.

 

Then, work out which way up you need to have the 3 wires to attach the crimps.  The signal wire, white here, must always be on the left with the crimp positioned as shown in the picture.  This will keep the wires in the correct configuration and the bar across the crimp at mid section will be locked into the socket when inserted.  The next task is to squeeze the 2 “wings” on the left of the crimp in the photo.  This is the slightly fiddly bit!  You need to hold the wire and crimp with one hand and use the needle nosed pliers (small non needle nose pliers are OK) to squeeze the “wings” together as in the next photo.

 

If you don’t do this, the next part of the operation becomes decidedly iffy as the crimp falls off as you touch it with the crimping pliers!  I learned that the hard way early on!

 

Finally, apply the crimping pliers making sure that you don’t cover the bar across the crimp as that will destroy it!  Close the pliers completely till you hear the click signifying that the correct amount of pressure has been applied and the crimping force has been released.  Then allow the handles to open and remove the perfectly formed crimp!  Well, it might take a few dummy runs to get it right but learning how to do this is a great help when you want to avoid a large amount of wire cluttering up a small space.

   

 

 

 

 

 

 

Good luck!

 

 

 

 

Edited March 24, 2023 by Peter Jenkins
Sorting the pictures to fit!

[Ron Gray]

I used to do it that way too Peter, fixing the flex holders (wings) onto the insulation first but now I don't bother, I just squeeze the 2 wings together slightly just enough for it to be held in the crimp tool. I then insert the wire through the crimp sufficiently far that I can see the bare wires through into the front crimp then close the handles. Doing it this way cuts out the fiddly bit of using the pliers which I always found to be a right pain!

[Graham Bowers]

That is *Exactly* how I do it @Peter Jenkins I have some to make for the Mythos 50e I've just taken delivery of - the chain of events leading to it's acquisition that began with a correspondence with your good self ;-)

[Peter Jenkins]

1 hour ago, Ron Gray said:

I used to do it that way too Peter, fixing the flex holders (wings) onto the insulation first but now I don't bother, I just squeeze the 2 wings together slightly just enough for it to be held in the crimp tool. I then insert the wire through the crimp sufficiently far that I can see the bare wires through into the front crimp then close the handles. Doing it this way cuts out the fiddly bit of using the pliers which I always found to be a right pain!

Well folks, there's another way of skinning the cat.  Use which ever suits you.

[Peter Jenkins]

The next task was to tackle the tail planes but before I did that, I wanted to check that the alignment of the wing and tail plane was correct.  The wing is mounted by sliding it onto a carbon tube that sits inside a tube in the fuselage.  There are front and rear anti rotation pins in the wing to stop it twisting from its set position and the wing is retained in place by 4 mm screws to hold it to the fuselage.  The latter are very lightly stressed since the main structure loads are taken by the carbon tube and twisting is taking by the anti-rotation pins, also small carbon tubes at the front and rear of the wing.  You can see this in the photo.  The oval hole is for the aileron leads to connect up.

 

This was also an opportunity to check the fixed relationship between the tail plane and wing incidence.  I use a Robart analogue incidence gauge for this.  The required incidences are:

·        Tailplane set as datum at 0 deg

·        Wing set at 0.7 deg

·        Motor downthrust -1 deg

I “booked” the kitchen for doing this task as there is much more room there than in my shed!

 

As it happened, the fixed location of the wing indicated that B J Craft had managed to get their jigs spot on as the wing incidence came out at 0.7 deg!  While I was de-rigging the aircraft, I took the opportunity of checking the wing sweep and the kitchen floor tile pattern provided the ideal way to do so!  It’s about 18-19 deg sweep back.

 

It seemed a good time to put the tail plane together.  The TP comes with the elevator dry hinged to the fixed part.  The first job was to locate the elevator servo hole and then carefully cut the covering back but leaving sufficient around the edge to stick that down into the servo recess to stop the edge peeling off!

  

 

As you can see, the servo is a very snug fit and the provided servo tray was designed for a thinner servo.  So having measured how deep I wanted the servo to go, I then eased the ply servo plate into position, sanded to give a tight fit, then secured it with cyano and cut off the ply joining the to ends of the tray.  That allowed the servo to be positioned, holes to be drilled and the servo bolted into place.

 

The 2 TP halves are retained to the fuselage by 2 carbon rods that pass through tubes in the fuselage.  Each TP half is retained in place by having a long screw inserted from the underside of the TP through each carbon rod.  I decided that, based on my previous experience, it was only necessary to secure one of the carbon rods in this way.  Again, the B J Craft jigging was spot on and when I tried the dry fit there was a tight but exact fit.  So, next task was to face each elevator root rib with some thin felt to provide a filling for any possible gap between the fuselage and the TPs.  After that, the next delicate task was working out where to drill the holes for the TP retention while hitting the middle of the carbon tubes.

 

 

 

As you can see from the photo, I drew 2 lines to show the position of the carbon tube marking its depth of engagement as well.  Careful application of the drill provided the connecting hole in the carbon tube and, phew, both screws worked as required!

The next task to connect the servos was quite a fiddle as the extension lead on the 4 wire output from the Xbus converter only just allowed them to be held with a pair of forceps!  I also took the opportunity to reduce the length of the servo leads to the minimum necessary to allow them to be manipulated and plugged into the Xbus lead.  I did the same with the rudder servo to reduce the amount of weight at the extreme back end of the aircraft.  Once connected electrically, I fixed the servo arm as close to being parallel to the elevator hinge line.  Turning over the JR servo arm provides some mechanical help in this but I need a couple of clicks of sub trim to get the arm properly positioned.  The rudder servo has a Futaba type spline so can use Futaba servo arms.

 

I have never before used a Z bend to connect to the servo on an F3A aircraft but one of the UK team pilots does this and says it works fine for him provided the Z is held tightly in the servo arm.  The other end of the rod is threaded for a 2 mm ball end adjuster.  As BJ Craft provide all the pushrods with Z bends it was a case of winding in the ball end to get the connection to the horn right on the hinge line.  B J Craft supplies a jig, ply former, for centring the elevators onto the TP which proved very helpful in getting both elevators level.

 

Talking of the horn, these are supplied in the kit and are fibre glass.  They provide a template for cutting the slot for the horn which I then used 5 min epoxy to glue in place.  Once the horns were glued in place, I re-checked the hinging and then used thin cyano to glue the hinges into each elevator half and then into the tail plane.  It’s a good idea to have some cyano remover handy to clean off any cyano that runs!

 

After connecting up the pushrods, I was then able to check that the elevators moved together over the whole range of movement.  My JR Tx has a servo match function to allow you to do that by applying slight corrections to the slaved servo to make sure they both move exactly the same amount.  Using Xbus disables this function as the elevators cannot be “seen” by this part of the computer program!  A careful look at what was available from the Xbus screen on the Tx showed a possible way forward.  After a good deal of fiddling around, I found, more by trial and error, that the Xbus allowed each servo to be matched throughout the range.  In order to measure the elevator movement, I taped two brand new pencils with sharp tips to each elevator so that the 2 pencil points were aligned – not having the rudder installed helped with this.  It was then a simple matter of keeping those points aligned throughout the full range of movement and tweaking the control whenever there was a divergence.  Wow – another reason for using Xbus!

[Peter Jenkins]

Now seemed a good time to install the main undercarriage.  It’s a lot easier moving the fuselage around without a pair of long u/c legs sticking out! 

 

The u/c legs come pre-drilled with two fixing holes and an axle hole.  The fuselage mounted u/c box, that I had reinforced with carbon fibre has two elongated slots for sideways adjustment for the two 3 mm u/c fixing bolts.  There is no adjustment for fore and aft adjustment.  The u/c leg has a straight edge at the front and this is used by B J Craft to key the u/c position fore and aft.

 

 

 

The u/c slot in the fuselage needed a small amount of relieving to allow the leg to enter flush against the front of the box.  Once positioned so that the down angle of the leg was level with the fuselage it turned out that the bolt holes in the retaining ply plate and the u/c leg were aligned!  I was amazed and very pleased!

 

 

Incidentally, it is the top row of holes in the photo above that are used.  The two outboard holes have additional ply plates to increase their strength.

 

The next job was to fit the 3 mm spike nuts to the underside of the attachment hole of the leg.  I used the 3 mm bolts to draw the nuts into the leg and then gave the nuts a dab of cyano to stop them dropping off when the legs are removed!

 

I also checked that the wheel flats on the legs were aligned fore and aft with the legs bolted in place and I’m pleased to say that they were!  Full marks to B J Craft for this bit of precision engineering!

 

Not so good were the axles that were provided!  A quick call to Chris at Bondaero had a pair of his axles that also provide for the outside of the wheel spat to be clamped to the axle.  If you take the RCM&E magazine, take a look at April 2023 edition and Keith Jackson’s article on page 68.  (Incidentally, if you look at the photo on page 70 you will see that I started out in aerobatic competition with a Wot 4!). 

 

There is a top hat section on the inboard end of the axle that requires a 6 mm hole in both the spat and the u/c leg.  The axle has a flat plate with a 10 mm flat on the end of the axle which after adding the wheel and washers butts up against the top hat section.  The axle is hollow and threaded for a 3 mm bolt.  Once the bolt has been tightened up, using a 10 mm spanner on the outer flat section of the axle to enable the bolt to be tightened, the last part is to use the 1 mm bolt and snazzy red anodised washer to clamp the outside of the spat to the axle.

 

 

 

[Peter Jenkins]

Next up were the wings.  Relatively little to do here but first things first, get the servos in.  Again, I’m using powerful mini servos for the ailerons as they have as much torque as my full size servo I would normally use for the ailerons.

 

As for the TP, the first job was to open up the aileron aperture in the wing and seal the covering edges down into the hole.  The laser cut servo tray as, as per the TP, a tight fit in the servo aperture.  The key thing to note here is that the servo is aligned fore and aft while the swept wing means that the servo arm must be aligned with the aileron hinge line – see photo.

 

 

 

Once that was sorted out, I could install the control rods.  As noted before, B J Craft provide threaded rods with Z bends but the distance between the mini servo arm and the control horn hole was too small to get the provided rods to fit even with the 2 mm ball link screwed right in.  I tried to make a new Z bend but the wire provided is so brittle that it cracked when I used my Z bend pliers on it!  So, I have had to order some 2 mm threaded rod and will make up the link when they arrive.

 

Of course, the aileron servo lead had to be extended so that it emerged at the wing root with just sufficient length to make plugging it into the aileron lead in the fuselage.  The next task was to use a glue gun to deposit some hot glue inside the wing and press the aileron lead into it so that it was fixed in place and would not fall into the wing during transport!

 

The next job was to fix the 4 mm spike nut to the inside of the wing to accept the wing bolt.  B J Craft give the option of placing the bolt either in front of or behind the wing tube.  I opted to have it in front of the tube.  The provided ply discs were a bit too thin for my liking as the spikes went right through them.  So, cut a piece of 4 mm ply, drilled a 5 mm hole in it and installed the spike nut.  Gluing this onto the inside of the root rib required a dab of Vaseline on my finger to anchor the spike nut before inserting it into the wing and positioning it lined up with the pre-drilled access hole.  I used Uhu glue for this as it gave time to position the nut and then tighten up the wing bolt to hold the ply with the nut in position till the glue set.

 

The final critical job on the wing was to cut and fit the front carbon wing tubes but I decided to leave those until I had installed the fuselage mounted incidence adjusters.

[Peter Jenkins]

Time to fit the incidence adjusters.  These are a simple device consisting of a captive 3 mm bolt with a plastic moulding that will take the front anti rotation carbon tube that I mentioned earlier and that I had not glued into the wing till I reached this stage.

 

I marked the fuselage for the required slot to allow the adjuster to work.  Chris (Bondaero) had supplied some 3D printed carbon plates that reinforced the fuselage sides.  These were ideal as drilling jigs to drill through the fuselage.  The holes needed countersinking to allow the retaining bolts to sit flush with the fuselage sides.

 

 

 

 

Once the incidence adjusters were fitted, I used them to dry fit the front anti-rotation pins into the wings, made sure the fit was good and then glued the carbon tubes in place as shown in the photo.

 

 

The next task was to fit the rear anti-rotation carbon tube and its retaining brackets.  The brackets are slotted to allow the wing incidence to be changed and have a locking mechanism built into them that is engaged and released by a hex headed bolt.  The photo shows both sides of this device.  The wood part is glued to the fuselage while the paxoline plate can slide up and down to accommodate incidence adjustment.  It is a bit fiddly to loosen and tighten the bolt but it is perfectly possible to do that at the field.  This is very useful when you want to make small adjustments to wing incidence between flights.  It is also a useful feature to take out any aileron trim that is needed to trim for S&L flight.  You just have to increase the wing incidence on the side that has a touch of down aileron so that you end up with zero aileron trim on the servo.

 

 

The next step was to mount these adjusters.  In order to align with the wing, I used a slow curing glue, Uhu, to glue each rear anti-rotation bracket in place so that the slot in the fuselage aligned, then put the wing in place and inserted the anti-rotation tube so that everything fitted before the glue set.  Same procedure for the other bracket.  After leaving the glue to set, both wings slid off smoothly – phew!

 

With the wings off, it was time to seal the aileron hinge gaps.  To do this, I cut some red film covering to a 5 mm width and then folded it along its length so that it would drop into the V formed by the aileron and fuselage.  In order to keep the V gap to a maximum, I used masking tape to hold the aileron in the fully deflected position.

 

 

 

 

I used a steel rule placed into the V to hold the film in place and used my sealing iron to fix the covering to the fuselage and aileron.  The before and after photos are below.

 

 

 

I did the same for the elevator hinge gaps.  However, the rudder has multiple colours and so I will use transparent tape to seal the rudder hinge gap.

Edited March 26, 2023 by Peter Jenkins

[Peter Jenkins]

Time to fit the control rods.  Sadly, the rods supplied for the aileron and rudder were a little too long.  I suspect this might have been a function of using mini as opposed to full size servos.  So, I ordered some 2 mm threaded rods, with solder extenders and 2 mm ball links.  Sadly, when they arrived the rods were 1.5 mm diameter.  However, the solder extenders which had threaded ends were just able to slide over the 2 mm unthreaded rods that I had.  So, I ended up with ball joints at both ends for the ailerons and rudder!

 

 

After that, it was just a matter of getting their length right so that the ailerons were flush with the wing and the rudder central when the rod was installed.  It’s important to note that you should zero any sub trim you may have on the servo and then fit the servo arm so that it is parallel with the hinge line of the control surface.  Futaba provide a 4 arm horn that can be rotated to each present each arm in a slightly different position at neutral.  I find it rate to need any sub trim to get the servo arm in the right position.  JR servos have a similar adjustment trick but as they only come with 2 arms you have less opportunity not to use sub trim for the final adjustment but it is usually less than 5 clicks of sub trim.  This is very important as using large amounts of sub trim to achieve the neutral position can cause unequal movement of the servo arm and is to be avoided particualarly for aerobatic aircraft.

 

Time now to assemble the aircraft and check and set the required incidences.  You may remember that this was to set the TP at zero degs, the wing at +0.7 degs and the canalyser at +0.7 degs.

 

Once again, I “borrowed” the kitchen to do this job! 

 

I used various books and magazines to pack up the aircraft stand to achieve the TP at the datum 0 deg.

 

 

In order to achieve an accurate reading, you must have the radio system on so that the elevator and aileron servos can hold neutral with the weight of the Robart incidence adjuster resting on them.  I fine tune thickness of the packing by only using part of a magazine as you can see in the photos.

 

I use a selection of books and magazines to achieve this datum setting as you can see from the photo.  The disadvantage is that this arrangement is not rock solid so I have to double and triple check the datum as well as the wing incidence for every reading.

 

 

So, this was the result:

 

   

 

The canalyser proved to be almost +3 deg so I packed up the rear until it also showed 0.7 deg - yes, it looks more like 7.5 deg but I'll see how that goes.  Another pilot who is flying his Anthem advised setting the canalyser to this incidence as it worked better like that.  The packing was 5 mm thick so I will have to make a suitable balsa packing piece with will fill the gap between the canalyser and the fuselage in case that leads to some odd aerodynamic forces or noise.

 

I also set up 3 rates for all three flight controls.  These are all operated by the Flight Mode switch which gives the lowest deflections for aerobatics, a smidge more for landing and full elevator and rudder for spinning.  I will also be setting up the throttle curves and other logical switches in the next instalment.

Edited March 26, 2023 by Peter Jenkins

[Outrunner]

Peter, the solder on your pushrods doesn't look like it has joined very well. Might be just be the photo but I wouldn't trust those joints.

 

Good luck with the project.

[Peter Jenkins]

Hi Outrunner

 

You are right.  I re-did them using my 80 watt soldering iron as the 125 watt one seems to be sick!  Thanks for pointing out the dodgy soldering as shown in the picture.

[Outrunner]

 

3 hours ago, Peter Jenkins said:

Hi Outrunner

 

You are right.  I re-did them using my 80 watt soldering iron as the 125 watt one seems to be sick!  Thanks for pointing out the dodgy soldering as shown in the picture.

That's good news Peter👍

[Peter Jenkins]

On the home straight now!  First thing to do was to assemble the aircraft and do some final geometry checks.

 

The first job was to bolt the motor back into place.  The 2 ESCs are shown connected in the photo.

 

 

What I also wanted to do was to identify the centre line of the motor so that I could arrange to fit the drive battery tray so that the mid-point of the flight pack was aligned with the motor centre.  I wanted to reduce as much as possible any off-centre weight when rolling.  Remember that the flight pack, 2 x 5S 5000 mah LiPos weight 1.2 Kg!  Offering up the battery tray with the flight batteries nailed to it was a great help in identifying the correct mounting height.

 

With the motor back in, I then bolted the u/c back on.  I also took the opportunity to remove the wheel spats and but some rubber solution on the face of the spat that abuts the u/c leg.  This gives a good grip of the spat but allows some compliance if the spat hits something hard!

The tailplanes and canalyser were next to be bolted into position followed by the wings.  I had already marked the wings with the 3 CG positions of forward, middle and aft.  The measurements from the LE were 280 mm forward, 300 mm centre and 320 mm aft.  I taped a piece of strong parcel string at the mid-point CG at the wing root so that I could feel the mid-point when I lifted the aircraft with my fingers.

 

I had previously measured that the rear of the canalyser needed to be raised by 5 mm to get the canalyser to an incidence of 0.7 deg or the same as the wing’s incidence.  I then checked the canalyser to see if it was square to the wing.  I measured from each edge of the canalyser to the wing immediately below it using a steel rule.  This showed that the canalyser was tilted by a small amount to port.  A bit of trial and error showed that this required 2 thicknesses of 1 mm ply to be placed just behind the front starboard bolt to level the canalyser.  The tail plane appeared to be horizontal.

After those checks, I placed the Rx, the Optipower Ultra guard (a battery backup), the switch and the Rx battery at the mid-point of the CG.  Then placed the battery tray with 2 LiPos held in place with Velcro straps at a best guess location. 

 

Next, I bolted on the 2 props and spinners, taped the canopy with its 2 canopy latches in the correct place and then checked the CG by standing at the front of the aircraft and lifting it by finger tip on the two bits of carpet thread I had taped to the wings.

 

 

 

 

 

If you look carefully, you will see a piece of masking tape with the forward and rear limits of the CG and the piece of carpet thread at the mid-point.

The result was that the aircraft was only just nose heavy.  In the description of the Anthem on Bondarero’s site, B J Park states that he used the CG position at 300 mm aft of the LE as his CG but went on to say use the most aft position you fell happy with.  The battery tray mounting system allows the packs to be slid forward and aft by a maximum of 20 mm each way.  The mounting system also allows for more than one position for the tray to be set – I’ll show a picture of this later on.

 

The next photo shows the positioning of all the loose equipment in the fuselage.

 

 

The next task will be to mount and secure the 2 ESCs, the battery tray and the Rx and it’s associated bits of kit.

 

I have one more item to fit and that is the Flight Coach hardware.  This is a very clever piece of software that has been developed by a group of F3A pilots spread between Britain and New Zealand.  It uses a GPS module with a small processor that captures the aircraft’s flight path and attitude so that you can play back your flight on your PC to see how and where you flew.  I’ve had this system for some time but never got round to fitting it to my current aircraft.  More on this after a few flights with it.