Gary's Atom Special build

[Richard Harris]

Gary,

Your Atom is progressing well, there are some well thought out ideas you are doing.

Rich

[Gary Manuel]

Thanks Rich,

Just minor tweaks to a very good basic design and picking the best from the early starters ideas.

Gary.

[Gary Manuel]

Made my own horns from 1.6mm fibre glass sheet as I explained on the rough sketch a few posts ago.

Aligned on centre rudder so that the pull-pull holes are just behing the hinge line to give the correct geometry. Then drew a line for the secondary hole positions. Horizontal line is 6mm above the top of the tailplane.

Vertical line drawn on outer fins. Again, the horizontal line is 6mm above the tailplane.

Slots cut for the horns using the previous pencil line positions. Horns trial fitted.

Trial fit using 2mm carbon rods and 2mm metal clevises.

Close up of centre rudder.

Looks OK so I'm going to epoxy the horns in after a light sanding to remove any surface coat they might have.

[john stones 1 - Moderator]

Nice work Gary t/wheel looks a good un, will be using commercial horns on mine I have some dainty ones

John

[Gary Manuel]

Dainty ones should be fine for a two rudder Atom.

I've only gone for high strength one because I see the centre rudder on mine as being a high stress area - especially with the steerable tail wheel.

[Gary Manuel]

The plan design has a tail skid at the rear, which lifts the rear end 30mm from the ground. My tail wheel results in the rear of mine sitting about 70mm from the ground. My rear end is therefore 40mm higher than the plan and will result in the rotor blades being at the wrong angle of attack.

To compensate for this, I need to raise my front end by 40mm.

The plan design is for a pair of lightweight 50mm front wheels. I will be using a re-claimed pair of 70mm wheels. This means that the front axles of mine will sit 10mm higher than the plan design. I still need to raise the undercarriage by a further 30mm to correct the angle of attack.

I have done this by extending the length of the undercarriage legs by 53mm, which gives approximately 30mm vertical lift.

This is my revised undercarriage wire template.

The next step involved the usual brute force and ignorance. Brute force is my Hammer and Ignorance is my vice (but not by only vice)

Holes drilled to take the undercarriage tabs.

A word of advice here. Take time to get the angle of the hole correct or the undercarriage will not sit right and need a bit more bashing. Don't ask me how I know

Trial fit.

Close up - maybe I should get myself some soft inserts for my vice

Home made custom saddle clamp. Made from 1.6mm fibre glass sheet, with an extra strip to fit the channel where the wires sit ....

.... like this. This is designed to put a bit of pressure on the wires to ensure that they are a tight fit. Note that I've also ground a slight groove in the ply plate where the wires sit. This should reduce the tendency for the undercarriage to work loose as it makes it's own groove during usage.

Outer edge beveled a bit to give a nice finish.

Trial fit to see the finished result. I'm not tightening the screws fully yet. I find that repeated screwing into wood loosens the grip and damages the screw head.

[john stones 1 - Moderator]

Nice job Gary, I like a man/woman who takes pride in their work.

John

[Gary Manuel]

8mm fibre glass epoxied to each side of the mast to fit the HK head.

I have extended the fibre glass down to the bottom of the thin / tapered part of the mast, as I see this as a potential weak spot. The fibre glass should add a bit of strength. Part laid to one side for later on.

These are the templates for my modified flex plates (see earlier on the thread) fixed to 0.8mm fibre glass sheet.

I have decided to make two because it allows the accuracy of one head to be checked against the other when rotated through 180 degrees, thus giving a very accurate way of checking for symmetry.

Roughly cut with a Dremel and diamond cutting disk.

One of the plates has been marked with straight lines which pass through one of the inner and one of the outer holes. The idea of this is to use as a guide for drilling with a pillar drill as described on another forum.

I tried it this way but wasn't happy with the accuracy.

I will describe an alternative way of drilling the plates, which I found to be more accurate and not requiring any special drilling equipment.

My recommended way of drilling the plated is simply to use a very small drill bit in a pin vice drill. These holes are 1.2mm and can be drilled very accurately by hand / eye.

All 7 holes then drilled out to 2mm. This size is critical for the three inner concentric holes as these are what located the flex plate to the top and bottom head plates. Note that the centre hole is NOT critical and just needs to be large enough to clear the centre bolt.

The outer holes are then drilled out to 3mm to fit the blade fixing screws. Centre hole drilled out to 5mm.

The holes are not rough edged. This is just the paper template.

If the holes are drilled accurately, you should be able to push the blade fixing screw through BOTH plates and be able to see straight through the three smaller holes, with the bottom plate in any of the three possible 120 degree rotations. Mine could be fitted without any problem

Both plates sanded together with the aim of trimming them to the centre of the outer line.

Paper template removed from both plates cleaned up a bit.

The one one the left is the one done on the pillar drill. Note the centre holes had to be elongated a bit because they did not quite line up with the head plates for some reason. These holes were elongated before I did the other one by hand / eye. The one on the right is spot on and is the one I'll be using although the other one is perfectly fine.

[Gary Manuel]

Hobbyking Head disassembled. These are the only parts needed for fixing the flex plate.

They are laid out in the order of assembly.

Here they are assembled. The nylon nut is tightened to give a firm but frictionless fit, then the lock nut is tightened onto the nylon nut.

Fibre glass packing at the top of the mast trimmed back to shape.

I found that the beam on mine was slightly out of true and not properly tightened, so I stripped it down ....

... and reassembled it with a bit of thread lock on the square block and threads.

This gimbal was a bit loose. It was also a little bit of a loose fit onto the top of the 6mm mast (untouched material thickness).

I ground a bit off the inner face of one of the blue plastic, which fixed both problems.

Nice and snug fit onto the mast now.

The other gimball was a bit of a tight fit, so I gently sanded a small amount of material from the inner face of the "C" shaped part, which made it much better.

Fully assembled and adjusted head, complete with flex plate.

[Gary Manuel]

Now for the bit I've been dreading ..... the blades.

I've bought a set of AJ blades, so the messy bit has been done.

I might have a go at making my next set, especially if I have a go at a 2 blade Atom.

Top and bottom blade reinforcers cut from 0.8mm fibre glass. The large ones are the bottom and the small ones are the top.

I intend folding the blades for storage, so I am making the cutouts in the root trailing edge. Cut out shape marked using the bottom reinforcers and a suitable diameter curve. I used a roll of masking tape.

Tip - take care to mark the ROOT of the blade trailing enge and not the tip (easy mistake to make I should think).

I was given this for Christmas and this is the first time I've used it.

It has a 1/4" wide sanding belt and two different feet, which can give pretty much any radius of curve you want. Ideal for concave curves in balsa!

Close up of the sanding tool business end.

It made a decent job of the blade cutouts.

Bottom blade reinforcers epoxied in place and left to set while I post this.

[john stones 1 - Moderator]

I think same as the blades you should make 3 flex plates, then balance against the heavier one

I may be able to help you out with the 2 unused ones

John

[Gary Manuel]

Posted by john stones 1 on 12/01/2015 20:06:11:

I think same as the blades you should make 3 flex plates, then balance against the heavier one

I may be able to help you out with the 2 unused ones

John

I'll see if I have enough fibre glass left to make another plate.

I suppose you'll be wanting the reinforcers as well

[john stones 1 - Moderator]

Take a wild guess

John

[Gary Manuel]

Following Rich's guide on balancing blades, I found it quite easy to find the cord-wise CG.

A line was then drawn 1mm behind the CoG position on each blade.

WARNING - don't assume that all three blades will balance at the same point!

These are a set of AJ blades and balance at different points.

At this point I weighed each blade as best as I could on the kitchen scales. At these low weights, they tend to vary or wander by a gram or two - presumably down to friction or build quality.

I found that the blades weighed 20g, 18g and 18g from top to bottom respectively in the photo below. It would appear that the spruce leading edge of the top blade is denser than the other two, even though they were bought as a set of three. I suppose that two blades can be made from the same length of stock balsa, but not all three, but I would have expected the wood for a set of blades to be selected with a bit more care.

Top reinforcer is positioned on the line drawn 1mm behind the CoG.

The blade is curved at this and is tapering towards the trailing edge. This results in the top reinforcer not sitting flat on the blade or parallel with the bottom reinforcer. This is probably not a big deal, but I decided to resolve it as it is very easy to do.

A few strokes with a fine file (wife's nail file actually), soon had a suitable flat surface where the top reinforcer goes.

This gives a better fit of the reinforcers before epoxying them into position.

The top roots of the blades now look like this.

[Gary Manuel]

Pencil line drawn on the bottom reinforcer, 10mm from the hole centre.

Shim made of a strip of 0.4mm fibre glass epoxied between the pencil line and the trailing edge.

Note that some strips are wider than others due to the different centre hole positions depending on cord-wise CoG.

Shim ground back to shape once epoxy set.

Trial fit of a blade to the flex plate - shown in the flying position .....

.... and then in the storage position.

Note that the shim is still engaged on the modified flex plate. I am happy that this modification is working as intended. There should be a constant (low) pressure between the blade shim and the flex plate throughout it's movement from storage to flying position with no tendency to "derail".

This is another area I considered doing something about, but decided not to at the moment. I may come back to it later and fill the void with a small wedge of dense wood.

As the blade sits on the flex plate, the only points of contact are at the leading edge and on the front edge of the shim. There is no contact around the blade fixing screw. This is likely to result in distortion of the blade profile as the tips are levered up and down during flight. Equally though, this gap allows the fixing nut and bolt to be "slightly" over-tightened, giving a nice tight fit, due to the spring of the bottom reinforcer. The modification above allows this not to cause a problem during folding for storage.

[Gary Manuel]

Blade balancing was done pretty much as described in Steve Jones' post here:

**LINK**

Thanks for that Steve

The only real difference is that I had one of these, that I bought as a propeller balancer, never expecting to use the rotor blade balancer attachment that comes with it. I highly recommend this - very good for about a tenner: Even uses 3mm thread, which is a perfect fit for these blades.

**LINK**

The heavy blade was marked with an "H" to avoid later mistakes.

The spanwise CoG was then found and marked......

.... the heavy blade in silver paint, the two lighter ones in pencil.

I then initially applied balsaloc to the two lighter blades, as close as possible to the tip to get them all to balance at the same spanwise position as the heavy blade (no photo of this bit).

Once they all had the same spanwise CoG, it was back onto the balancer. Balsa loc was then applied to the lighter blade, this time around the spanwise CoG position as shown in the photo, until the blades balanced.

The blades have drifted slightly out of balance again as the solvent from the Baslaloc has evaporated. I will repeat this process until they are balanced when the balsaloc is fully cured.

[Steve Jones 2]

Thanks Gary, glad it helped and yes my method seems to allow weight to be added to the lighter ones only

Steve

[Gary Manuel]

I found that once the servos were fitted, the control arms were a bit close to the canopy, so I decided to add another strip of balsa before cutting the exit slots.

Also fitted small magnets for holding the canopy in place.

Talking of the canopy, this needed to be made a bit smaller due to the added balsa strip behind it.

This shot also shows the magnets in the canopy.

And here's the completed canopy fitted to the fuselage (photos slightly out of chronological order due to the drying time of the canopy adhesive). Inside painted black and outside coated with HK yellow covering. Pilot cyano'd in place and screwed from underneath for good measure.

Rear edge of the fuselage shaped and small fillets added to the tail booms to continue the curve of the fuselage shape.

Controls fitted - these are 4mm Pete Tindal carbon fibre fittings I had left over from another recent project.

Note that the control slots are now well away from the canopy.

Close up of the bottom end of the controls.

and the top.

[Chris Barlow]

Your pilot looks like he's doing 100mph even inside the cockpit!

Looking very nice and again another slightly different Atom.

[Gary Manuel]

Fuselage covered - HK yellow. Contrasting trim will be added later.

Motor, ESC, undercarriage and radio gear added. Removable mast and uncovered tail loosely assembled as a trial fit.

I had a change of plan while fitting the radio gear.

The main receiver did fit in the fuselage with the battery, but it was very tight and meant pushing wiring out of the way just to get the battery in and out.

I decided to mount the main receiver here instead:

A piece of thin oxygen tubing glued to the mast provides a nice vertical aerial position.

The satellite receiver is still inside the fuselage, but now with horizontal orientation - secured to the fuselage flat bottom underneath the two servos.

.

[john stones 1 - Moderator]

All nice and tidy Gary, you had a trial at the c.g yet ?

And put those screws in the head servos will you, it's making me nervous

John

[Gary Manuel]

To be honest John, I haven't tried the CoG yet, and I can't even remember what it should be! I'll have a read up and find out before I declare it ready to fly. Feel free to remind me

I hate adding lead to any model, so I try to plan equipment placing to get the correct CoG "naturally". In this case though, the fuselage is so tight with the battery I'm using (I'm also too tight - to buy more), that the equipment has been places where it will fit. I dare say that moving the receiver back a bit will have helped. I've also added a bit more weight at the rear end due to tailwheel / three rudders and I'll be using 7 strand nylon coated steel wire for my pull - pull rudder.

Don't worry about the missing screws. They are in a plastic box with the mast / tail retaining screws and the blade fixing screws. If I don't finish up with an empty box, I'll know that I've missed something

Edited By Gary Manuel on 01/02/2015 23:24:10

[iqon]

Nice yellow -

[Gary Manuel]

Thanks Iqon.

Someone at our club has bet me that I won't be able to take it off and do a circuit.

It needs to be a nice bright colour, so that he can see me do it

[Bob Bertram]

We had better not fly ours together, seems like the future is Yellow!!!!