Gary's Atom Special build

[Gary Manuel]

I wasn't going to bother with a build log for my Atom Special build as I don't intend doing anything that hasn't already been done. I am taking photos for my own benefit and have been posting them on my local club's forum, so I thought I may as well share the experience with anyone who may be interested.

I will include every step up to and including the maiden flight and report everything I find, whether it be good or bad.

I always intended delaying the build until 2015 but actually made a start with planning my build and cutting the plan pieces out on 27th of December 2014.

I'll be making it with THREE fins and rudders. What's more, each one will be a bit bigger than the standard TWO. That should give plenty of rudder authority. I'll be using a fairly large battery up front, so the extra bit of weight at the rear shouldn't affect CoG too much.

Here's the shape of the two outer fins. Fins are a bit higher to accommodate the longer rudder. The original plan shape is laid on top for comparison.

And here is the new outline ready to be scanned and printed.

The plan was cut into pieces and separated into 6mm balsa, 3mm balsa, 3mm lite ply and 3mm birch ply (actually 2 x laminated 1.5mm birch ply). Then stuck to the wood with the correct grain direction.

Note the extra central 6mm rudder and fin. The centre fin is quite a bit larger than the other 2 to allow it to line up properly with the tailplane, which is wider in the centre than at the edges.

All pieces cut out apart from the 3mm balsa. For some reason, this has started to bend once I've taken it out of the box. If I can't get it to straighten overnight, I'll have to do these again.

The centre fin and rudder are lined up with the tail skid in the top right of the picture.

I am thinking of adding a steerable tail wheel which should be able to use a simple tiller type now that I have a centre rudder.

Centre rudder will be pull-pull, with a second tab on each side a bit further back (about where the original hinge line would have been. These tabs will have a control rod going to another tab in a similar place on the inside of the outer rudders. The outer rudders will be controlled indirectly from the centre rudder.

One of the things I think spoils the look of Richard Harris' original design is the way the cables are routed from the two rotor servos, out through the back via two holes at the top of the servos and back through to the front again through the holes shown on the plan This results in the servo wires being visible from the back of the model.

It also requires 4 holes in the rear former and 2 in the front. I do like Swiss Cheese, but only with crackers.

This is what I've done.

The servo wires will be threaded through the rectangular servo hole, through the internal tunnels and out through the small circular holes at the bottom. The wire will wrap around the outside of the servo in the tunnel. There is no need to pass the servo wire out and back in again.

Note that both front holes are needed. The 6mm slot in the centre is for the 6mm x 12mm mast, so there is no space to cross the wires from left to right. The 6mm packing will be sanded to shape later as the build proper starts.
The single hole at the rear is only required for the rudder servo.

[Gary Manuel]

The other thing I have finally got my head round is what I plan on doing with the flex plate. I always saw that there was a problem with the Mk 1 head (as shown on the published plans). I also think that there is a minor flaw with the Mk 2 head - nothing serious, but as I'm building from scratch, I may as well try to overcome it.

The problem I see with the Mk 2 head is that the distance from the mounting hole to the tip of each tab is less than the distance to each side of the tab. The blade packing shim sits to the side of the hole when in the flight position, but when the blade is rotated into the storage position, the shim can potentially derail off the end of the tab. I am concerned that when the blade is moved from the storage position back in to the flight position, the shim on head could be damaged due to the leverage. My revised head shape should prevent the shim from derailing.

All I've done is to extend the length of the three tabs to reduce the chances of the shim sliding off the flex plate during storage. There's a bit more material on the outside of the blade fixing holes. It won't affect flight performance or balance and is just as easy to make as the Mk 2.

This is the official Mk 2.

This is my redesigned Mk2 (Mk3?).

This is the original plate as shown on the plans for reference.

[Gary Manuel]

The remainder of the build waited until 2015. At this point, I'll mention that initially, I am cutting and pasting from my club's forum with the minimum of editing, so apologies if some of the explanation assumes no knowledge of what the build is about.

January 3rd 2015

This thing looks like it's going to go together really well - all credit to Richard Harris for the clever design. This first proper build session took just over two hours. I am not going to make a meal of this one, so my build will be pretty quick - my shed is too cold to spin it out.

I'll be using cyano where I can to speed things up. 6mm base B1 is the starting point. The thin end is the front. The part at the front is birch ply and is used to screw the undercarriage into and to give strength to the motor firewall eventually. The parts at the back are for the rudder servo and also form three sides of a box section to slide the tail booms into.

Here's a close up:

and here's a trial fit of the tail booms and rudder servo.

The front edge of this is used to support the main boom assembly. It therefore needs to be reasonably straight.

The front edge of it also needs to be bevelled at the correct angle (not 90 degrees).

The rear end of one side of the fuselage and then the shaped doublers at the rear are then added. The fuselage side is simply aligned to the bottom of the base, using a flat building board. The front end of the fuselage is left loose and will be bent to the gentle curve of the base later.

I took a bit of a risk with this bit, but it worked ok.

I Cyano'd the two formers I made earlier together with the 12mm x 6mm spuce main boom in place, then quickly whipped the main boom out to leave a slot that the boom can be pushed into later.

I intend having removable tail booms and main boom. The designer intended them to be glued in but others have made them removable and I think it's a good idea, because these are the weak points that are most likely to be damaged in an accident.

Here's the boom, successfully removed from the joined formers.

6mm ply servo rails added and the formers sanded to shape.

The bottom edge of the main boom assembly bevelled to the correct angle to suit the angle of the rear doubler.

[Gary Manuel]

4th January 2014

Three piece birch ply undercarriage glued to give a tight fit on the piano wire I will be using for the undercarriage.

4 washers made from the corner of a sheet of 0.4mm sheet of fibre glass.

2 used here. They will be drilled later to take small screw each which will hold the removable mast in place.
The other 2 will be used later for the tail booms.

Servo rails pre-drilled, then the rear part of the other fuselage side glued in place.

Rear doubler added to fully support the main boom (mast) assembly.

Fuselage sides gently curved round the base and glued over the full length.

Bulk head glued in place using 5 minute epoxy and held secure with an elastic band.

Inside view of the front end.

Undercarriage plate epoxied and clamped in place until set - fuselage is upside down with a bit of scrap ply at the other side to clamp to.

[Gary Manuel]

6th January 2015

Time to start planning where all the gear is going.

Receiver will be at the rear of the base with the aerial fed through a small hole out of the back and along one of the tail booms. A Satellite receiver with vertical aerial will also be used.

I'll be using quite large batteries which will sit on a suitable shelf which lifts it just above the receiver.

This gives just enough clearance for the canopy.

Trial fit of the motor to define the centre line ----

---- and the routing of the motor wires.

Motor wires enter nicely just above the undercarriage plate

Balsa shelf added flush with the top of the fuselage and tight up to the bulkhead.

[Gary Manuel]

Shape of canopy curve drawn out to act as a guide for shaping the nose end and the plastic canopy. I've made it a bit higher and rounder than the designers build to suit my preference.

Front of fuselage roughly shaped to suit my curved line.....

then glued in place and shaped a bit more.

Bottom end of mast assembly trim glued in place.

It's shaped to continue the curve of the fuselage up the mast at the rear.

Trim curved and glued in place.

Next the canopy plug. Roughly cut bits of scrap used to make the basic shape.

Then gradually sanded to suit my curved line and blended in to the fuselage shape.

You may have noticed that I did not fit an ESC inside the fuselage.

This slot is cut to the size of my ESC....

.... and then glued under the fuselage, with its front edge up to the undercarriage plate. The ESC will get a bit of cooling from the prop wash here.

A few bits of scrap added around the undercarriage, then the fuselage and plug given a good sanding and shaping.

Plug for the nose cone made in a similar way to the one for the canopy.

Now that the two plugs fit the model, it's time to make them so that they don't fit, by adding 9mm scrap all the way round.

This is then sanded to blend in with the plugs.

The 9mm oversize will provide an overlap for fixing the cowl and canopy to the fuselage.

[Gary Manuel]

Make sure you either start collecting different shaped bottles early or that you are near a toilet when you are doing the next bit.
I had to empty these bottles before I started

I like this tinted bottle for the canopy (other soft drinks are available!).

I tried to get both parts out of one bottle.
Packing used to minimise the amount of shinkage needed.

180 to 190 degrees with this bad-boy soon had the bottle shrinking down to the plugs.

I wasn't happy with the cowl because the taper on the bottle neck was too shallow and resulted in the opening being a bit large and tapered outwards, so I had another go with this bottle. It's not tinted, but the cowl will be painted anyway.

Here's the finished result. Not perfect but I'm reasonably happy. In retrospect, the compound curve of the canopy was probably too much to expect. It would have been easier with a larger radius curve as in the original design.

I still think it looks better with the compound curve though. I like the smooth constant curve right from the front to the rear. It's exactly the effect I was after.

Close up shows a small amount of rippling towards the rear but it isn't too obvious.

Close up of the cowl. I will drill some cooling holes later.

Retrospective Note:

If I was making the canopy and cowl again, I would add another 9mm of scrap all the way round.

The final couple of mm near the edge tend to distort inwards due to the pressure of the shrinkage. Making the plug a bit bigger would allow this distorted bit to be trimmed off.

[Steve Jones 2]

Looking Good Gary,

A few of points if i may...

My 3rd central rudder fin was 4.5mm thick to add a little bit more stiffness than the 3mm for the linkage loads.

My motor on the second model was mounted so the wire went thtough the bulkhead on top - to allow the battery to slide under them at the front - avoiding wire trapping

ESC (30amp Turnigy plush sits ontop of battery under the canopy and is always cold when i finish flying

making the mast removable handy

Great build and keep the pics coming

[Gary Manuel]

Thanks Steve - All good advice.

You will see later that my motor wires will be out of the way at the bottom as they connect to the ESC, which is under the model. There is a bit of space to store any slack wiring and bullet connectors, between the motor and the front of the battery, which doesn't slide all the way to the front.

Maybe jumping the gun a bit here, but I had this idea in my head for the rudder control. You've encouraged me to sketch something down a bit earlier than I expected that's all.

The yellow coloured things are control horns, which will be cut from 1.6mm fibre glass sheet. The one in the centre will be the same thickness as the centre fin / rudder (6mm) and will serve three purposes.

1. control horns for the pull-pull system.

2. Secondary control horns for the (carbon?) control rods to the outer rudder horns.

3. Stiffener for the centre rudder which is likely to be a high stress area. All forces will be within the fibre glass horn, rather than in the balsa rudder.

The other yellow things are 1.6mm fibre glass horns for the outer rudders.

I am expecting that a rudder tiller wire will be embedded within the centre rudder, somewhere close to the centre control horn, adding more strength to the centre rudder - IF I get it right.

[Gary Manuel]

Holes drilled from my cutout under the base at an angle for the ESC to motor cables at the front and ESC to battery / receiver at the rear.

Close up of the rear hole with additional trench cut for the smoothing capacitor in the ESC to allow it to sit flush.

Test fit of the ESC (Tunnigy Plush 30A)

This is how the wires appear inside the fuselage.

I will be able to solder bullets onto the motor leads before I pass them through the hole and fix the ESC in position.

I will need to solder the XT60 battery connector with the ESC in position due to the physical size of it.

[iqon]

Posted by Gary Manuel on 07/01/2015 10:53:24:

I wasn't going to bother with a build log for my Atom Special build as I don't intend doing anything that hasn't already been done.

I dont believe that - i think you will "modify" everything

[Gary Manuel]

Posted by iqon on 09/01/2015 11:17:33:

I dont believe that - i think you will "modify" everything

No idea what you mean

Tail booms glued and laid out while the glue sets.

Oh dear - I have a bit of time to think about the next "modification".

I'm not happy about the way the front mounted servo control rods need to exit the fuselage through slots cut into the canopy. This is probably difficult to cut and results in the canopy / hatch being awkward to remove and replace. Canopy will also fill up with dust eventually.

This is what I've come up with:

Front of the mast support trim extended forwards.

and curved found to follow the profile.

Same on the other side and then topped off with a bit of 6mm.

A bit of sanding later and it looks like this.

The plan is to have the control rods pass through this additional trim rather than the plastic canopy.

With the canopy in place, the large overlap can be seen.

Canopy marked with lines to help with trimming.

Cockpit knocked together and "pilot" tried out for size.

This gives some idea of the colour scheme I have in mind.

Canopy added.

Once I'm ready, the canopy will be glued on to the cockpit, sealing it all the way round.

Test fit onto the fuselage.

Note that the servos are hidden out of sight now, thoug slots will be added later.

[john stones 1 - Moderator]

He can't see where he's going Gary, you not read your bmfa book

John

[Gary Manuel]

That will be my excuse if things don't go right

[Gary Manuel]

This is a little bit different to the plans.

A small piece of birch ply glued to the underside and put to one side to dry. A conventional steerable tail wheel I had laying around will be screwed into this.The tail boom tips will be cut off level with the thin end of the ply plate. This will make room for a small piece of balsa to be fitted underneath the tailplane, which will be slotted for the bottom centre rudder hinge.

Fins glued to the tailplane.

Centre rudder has a small cutout for the steerable tail wheel barrel. The reason for this will become clearer later on.

This is the small piece of balsa that will be slotted for the centre bottom hinge. This is the second attempt. You can see where the first attempt went

Rudders temporarily hinged - there are two cyano hinges per surface. They are standard Hobbyking ones cut in half lengthwise.

View from the underside.

[Chris Barlow]

Very nicely presented photos. I never have the space or time to set up the shot with coloured backdrops. Usually (if I remember) I just grab my tablet, take a few photos then carry on! It definitely ups the build blog game and I'll have to set something up for the finished article photos now!

[Gary Manuel]

The background is just an old blanket that the wife let me have, presumably because the dog didn't like it. I just keep it handy and throw it over whatever is on the bench when I'm ready to take a photo. Don't for one minute think it's tidy under there.

[Gary Manuel]

Tail boom slid into the fuselage.

Spacer shaped and glued to the tailbooms. The tail / boom assembly is free to be just pulled out at the moment. I'm still giving some thought to how it will be secured.

Close up.

Trial fit of the tail and tailwheel assembly.

Close up.

The tail wheel will be steerable via the thin tiller wire which will be drilled and glued as far as I can into the centre rudder. The other end goes through the purple barrel and is locked in place with a grub screw.

Tail aligned and glued in position.

Left like this while the glue sets.

[Steve Jones 2]

Looking good Gary and the underside esc mount is neat. If you cut a square of the red heat shring out you will directly expose the alumin heatsink plate which will significantly increase the heat transfer rate.

on my Whippit I had a heat lock out on the esc as it faced inwards insulating. Reversing and cutting the heat shrink away solved the problem with the esc during flight

Steve

Edited By Steve Jones 2 on 09/01/2015 19:12:20

[Gary Manuel]

Posted by Steve Jones 2 on 09/01/2015 19:10:45:

Looking good Gary and the underside esc mount is neat. If you cut a square of the red heat shring out you will directly expose the alumin heatsink plate which will significantly increase the heat transfer rate.

on my Whippit I had a heat lock out on the esc as it faced inwards insulating. Reversing and cutting the heat shrink away solved the problem with the esc during flight

Steve

Edited By Steve Jones 2 on 09/01/2015 19:12:20

I agree. I normally expose the metal heat sink (when i remember) as it does make a big difference. One thing I like about the Plush ESCs is that the label is on the component side so you don't finish up with no label like you do on a lot of types of ESC.

I plan on doing it with this one.

[Gary Manuel]

One last thing before I call it a day.

I've decided how to secure the tail boom to the fuselage.

2 shallow holes cut to fit the circular fibre glass washers I made earlier.

Close up:

Washers epoxied in place. An hole, the outer diameter of a servo screw or similar will be drilled later with the tail booms removed. The tail booms will then be pushed back in and a smaller pilot hole drilled into the booms to allow the servo screw to be screwed into them. The epoxy washer will provide a solid seat for the screw.

[Gary Manuel]

1.2mm hole drilled through fibre glass washer, fuselage and the tail boom.

Bang on target!

Washer and fuselage then drilled out to 2.2mm. Servos screw holds the boom in nicely.

Similar arrangement for the removable mast.

[john stones 1 - Moderator]

Nice accurate work Gary as always I hope you're gonna sand the rear end up a bit though, i'm gonna be inspecting it close up you know

John

[Gary Manuel]

Yes John. I have a habit of being a bit rough at handling models and damaging them as I'm working. That's why I leave the sanding till the last minute. Some of these scale guys amaze me that they can keep a model in good condition for months, while they are working on it.

I'm also going to add a bit of trim to the sides of the tail booms to continue the curved line rearwards. You are always welcome to inspect my models from any distance you like .... as long as you don't bring your glasses

[Gary Manuel]

As my centre rudder is going to be driving the outer rudder, it will need all the strength I can give it.

The steerable tail wheel tiller will act as a splint if I drill / push it in to this distance.

Tiller cut to length.

Rudder beveled at about 45 degrees. Trial fit of the tail wheel assembly looks good.

Turns nice and easy one way.

and the other.