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A Little Atom, A Medium Mossie and a Big Cub


Chris Barlow
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After a lot of sanding last night I finally got to a point where I could try the components together and get a first look at what I was making. I have to say the Mossie has some of the sexiest curves I've ever sanded!

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And a couple of updates on the Atom. I wasn't happy with the wheels I was using so I cut the axle shaft down a little and fitted these which should reduce rolling resistance down the strip.

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I sprayed the inside of the cowl with flourescent yellow which when seen through the blue plastic looks gree and nearly matches the new wheels. The big hole underneath is for cooling!

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The ESC is also mounted externally for cooling and also because I didn't want all that RF energy and heat trapped under the canopy next to the RX!

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The rear boom is retained by a screw through a ply plates slotted into the fuselage floor behind the rudder servo.

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and a little decoration on the tail fins

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Finally, Bill sits in his office alongside the Mossie. Still got to think of a suitable name for the Mossie pilot but I'm sure that'll come to me when I start work on his cockpit.

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Posted by Martyn K on 03/01/2015 22:40:12:

Impressed - I hope your enthusiasm is triply infectious!

Watching

Martyn

Thanks Martyn.

I'm really looking forward to the Cub build but must stay focussed on completing the Atom and Mosquito first.

That's pretty much it and up to date for the last 6 days. Thank god for Christmas holidays!

Having a good tidy up in the shed tomorrow to get rid of all the balsa dust and get ready for work on Monday. Next week I should be adding the tail and electrics to the mossie and getting it ready for epoxy glassing.

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Yesterday in preparation for joining the wings and inserting into the fuselage I started on the wing control surfaces. First job was to draw some lines.

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A minor deviation from the plan is the flaps. These will be operated via torque rods through the wing and through the engine nacelles.

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Then with a bit of planning and jigging the two wing halves were joined with the ply wing brace and epoxy.

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The underside of the joint and brace is also covered with masking tape to prevent any epoxy from escaping and glueing the wing to the bench!

The assembled and now set wing is then inserted into the fuselage. Since the flap torque rods are now installed in the wing the plastic tabs are removed and the threaded ends pressed down into the balsa of the wing to allow them to pass through the wing slot in the fuselage. With the wing fitted in the fuselage it is checked to make sure it's central and square to the fuselage. This is done with a piece of fishing braid (non stretchy) from the point of the tail to each outer corner of the wing where the ailerons are cut out to make sure they are equal. Once accurately positioned the wing is tacked in place with 4 drops of cyano to the fuselage and then I covered the underside of the wing joint now inside the fuselage with GF cloth and epoxy extending to the fuselage sides and former and left to set for a day.

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Tonight I concentrated on hinging the control surfaces. The flaps were drilled out for the torque rods and slotted for pinned hinges. The pivot and hinge line for the flaps is as close to the bottom edge of the wing as possible. I chose pinned hinges because the mylar hinges would try to return to centre against the servo whilst the flaps are deployed. Pinned hinges will rest in whatever position they are moved to.

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When dry fitted the flaps were checked to make sure they finish flush with the upper and lower surfaces if the wing, have equal gap at the ends and are in line with each other.

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Then I started again on the other side. Ailerons were then hinged with fluffy mylar hinges and test fitted to make sure they clear the flaps.

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Easiest and quickest job of the evening was hinging up the tail surfaces and giving them a light sanding to round off the edges.

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Posted by Stephen Jones on 04/01/2015 00:15:25:

Hi Chris ,

I also was thinking of fitting the Esc on the outside of the Atom for the same reasons you have just stated thumbs up.

Steve

Hi Steve

I notice a lot of people have put it on the outside too. It might not even get warm inside the fuselage but the cooler it is the better!

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After all the control surfaces were hinged up I started installing servos and rods to drive them. Rudder & elevator are driven by 2 mini servos mounted through the wing inside the fuselage. The plan shows these mounted on HW rails but I thought the wing section inside the fuselage made a nice servo tray. The flaps are driven through a "y" push rod but I'm not happy with it and will be changing it later!

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I shall be gluing in some ply plates for the servos to screw into! The section of wing has been epoxy glassed and I don't think the 2 small cutouts are going to make any difference to it's strength.

Next up is some means of fitting the battery/servo hatch. The plan shows the hatch having a tongue at the rear, a screw at the front and a dowel across the opening halfway to maintain a bend in the hatch. This makes a kind of "suicide door" hatch arrangement and although it's unlikely, a lost/broken or forgotten screw means the hatch will pop open at the front into the slipstream. I wanted a tool less battery change so elected to install a tongue at the front of the hatch and magnets at the rear. A mylar hinge is set into the rear of the hatch just like on a control surface, and is bent 90 degrees to make a grip to open the hatch. Instead of a dowel to bend the hatch I bent it between 2 pieces of 1/4 balsa down to the bench whilst gluing 1/8 balsa to the inside of the hatch. This has laminated it and with a little sanding, has set the curve to match the fuselage.

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This hatch locates in the fuselage onto supports at the front for belly landings (impacts) and another pair of magnets at the rear. For once I didn't confuse myself and set a magnet the wrong way around!

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Fitted you can see the mylar pull tab which will bend back on landing.

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Not much for an evenings work! These fiddly bits seem to take up quite a bit of time. Either that or I'm just a bit too fussy?

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Before finishing tonight I made a start on glassing the airframe. I am using 24g/sqm cloth on the underside of the wings and everything from the wings back. The nose, belly and top of the wings will be done in 54g/sqm for a little extra strength.

24g cloth cut for the wings and 51g for the nose

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and 51g for the battery hatch

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The cloth for the nose has a few cuts to ease forming the shape.

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I used Aeropoxy to wet the areas ready for cloth and laid the pieces in place. The cloth was then stippled flat with the brush until the resin could be seen soaking through the cloth. Where it wasn't coming through a little more resin was applied and stippled through the cloth to the wood. Once all in place the excess resin was removed by blotting with blue tissue cloth until the cloth took on a matt textured look with no shiny areas from "pools" or resin. I made a close inspection looking for any voids or air pockets below the cloth and fixed them by stippling with a dry brush.

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The aeropoxy finishing resin is good in that it gives you a long working time to get the cloth down before it starts gelling. Unfortunately this also means it will have to be left untouched until tomorrow afternoon now!

Edited By Chris Barlow on 11/01/2015 03:37:17

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A couple of hours on the mossie this evening and now the epoxy is cured the edges can be trimmed. This is done by sanding the edges with some 180 grit wet & dry until it sands through the glass cloth.

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Hatch fit tested after covering.

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A light rub with 180 grit wet & dry highlights any high spots. The cloth will have a second thin coat of epoxy then another light sanding. This will fill some of the weave and add to the strength of the cloth.

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The top of the wings and forward fuselage are covered next. 51g/sqm cloth for the top of the wing and 24g/sqm for the upper fuselage and nose, the reverse of the underside.

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The nacelles and lower faces of the wing control surfaces have also been covered with 24g cloth.

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Should be ready for trimming tomorrow evening and will make a start on the rear fuselage and tail surfaces.

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  • 3 weeks later...

Unfortunately I've missed a bit of build time after having a cold for nearly 2 weeks! Started off by just feeling under the weather and tired but after 3 or 4 days turned into a full on cold, the kind only real men get!

So a bit of catching up to do now!

The engine nacelles were added to the wings with epoxy and the top fairings added. These were shaped to match the wing contour by placing a sheet of sandpaper on the wing matching it's curve and then sanding the fairing like a profile sander.

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These were then glued down withe epoxy on top of a 1/4 fillet to fill the gap.

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Next the control surfaces were all added. The torque rods and joiners were separated from the wing and tailplane with tape then lightly covered with epoxy. Epoxy was dribbled into the receiving slots and holes in the control surfaces which were then fitted into position and clamped to the wing and tailplane to keep them aligned.

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When set the tape was removed and the mylar hinges fixed with thin cyano.

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By adding flaps I have removed the option of controlling the ailerons with a torque rod as detailed on the plan so they will have to be operated directly from servos in the wing. Unfortunately the wing is too thin to build in servos although thin wing servos could be used if left projecting 3 or 4mm.

I could have mounted them in the engine nacelles but the outer flap would mean a crazy angle for the pushrods so the remaining option was external wing fuel tanks. These were blocked together from scraps of 3/8ths balsa from the wing off cuts. 2 templates were drawn for plan and elevation profiles, drawn onto the hollow blocks and cut/sanded to shape. A cutout was also formed to suit the servos with a Costa coffee stirrer cut and glued to the inside to screw into.

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The servo lead extension has to somehow get to these servos and my initial plan was to push them into a 2mm slot in the thicker part of the wing. I had some concerns about the wing splitting because of this slot so opted to rout out a shallow 6mm wide groove and set the lead in flat. This was tacked down with cyano then the entire groove filled with thinned slow setting epoxy which will bond the glass cloth back together and form a 3mm thick spar along the underside of the wing.

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The servo is positioned on the inside of the tank so that it will be hidden by the engine nacelles.

The radiators were formed but cutting 8 formers from 1/8 balsa and slotted onto the wing. These were covered with 1/16 balsa sheet top and bottom and will form a route for the power and servo leads to the esc's in the nacelles.

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The gap where the sheeting meets the top of the wing was bevelled with a little light weight filler which will reduce drag through the radiators and allow the air to escape under the wing.

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Access to the motors and ecs's is through a hatch in the top of the nacelles. I saved cutting these until the airframe was glassed and had a 2nd coat of finishing resin so I wouldn't have to cover the hatches seperately.

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With the radiators added it's looking more like a Mosquito!

The entire airframe was next sanded with 120G to flatted the 2nd coat of resin and provide a key for the filler primer. All dust was removed by blowing it off in the doorway with compressed air then the airframe was wiped down with a tack cloth.

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A coat of filler primer was applied by brush to get a thick coat od left to dry and harder for a couple of days.

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After allowing the primer to harden about 95% of it was sanded off, leaving the paint in any low spots, dimples or weave in the cloth missed by the 2nd coat of resin.

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A closer look shows how the primer is used to fill imperfections, even deep scratches left when sanding.

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Tonight it was time to add the flame suppressors to the engine nacelles and start to address the cooling issues for the motors/esc's. The suppressors were cut from 1/4 balsa and hollowed out with a round file. The hollowed out channels don't pass straight through and are chamfered to scoop air into the nacelles.

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The positions were then marked on the sides of the nacelles and holes formed with a Dremel, one at the front for cold air in and one at the back for warm air (hopefully not hot) out.

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The suppressors were then glued into position and the ducts opened up a little.

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Rear view. If the ecs's or motors ever burn out in flight it will look like a very realistic engine failure! surprise

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Edited By Chris Barlow on 30/01/2015 00:54:00

Edited By Chris Barlow on 30/01/2015 00:54:36

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  • 2 weeks later...

A couple of minor bits finished last night on the Atom before attempting a maiden this afternoon.

UC wires and mast painted in Humbrol silver.

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And a simple centering device for the castering tail wheel, just an elastic band looped around the uc leg and secured to the central fin with a bent wire pin.

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Then on with the maiden.........

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So onto the first maiden of my 2015 mass build models. I really like maidens. Some models you really don't know how they're going to behave and if they're home built with some care you really don't want them to fail either! My theory on the Atom was that having experience of helis and planes it should be somewhere inbetween both and I should be able to fly it to a reasonable standard. Hmmmm.

So after a simple message to Paul Marsh " Do you want to see a tangled crash this afternoon? " we went up to the field.

To say it was a bit foggy in Cheshire would be an understatement. We took up a couple of foam wings which disappeared into the mist at between 50-100ft, variable! Even LED lights weren't helping much up there!

Still, I wasn't expecting the Atom to go that high so after a few checks and rates adjustments Paul spun up the blades and I rolled off for takeoff. It lifted off too soon as I have seen in many videos and started a brief roll to the left which was countered with right aileron, rudder and a touch of down elev. That was enough to stop the stalled, clattering crash and a second after it was lifted up into the air, nose rising, and rising, and rising! Put in more and more down elevator and right aileron to counter the now slowing and stalling rotor disk! Levelish flight was resumed but the rotor had slowed to much and it was coming down from about 10ft. It hit nose down and the crack was so loud I suspected at least the mast had snapped, if not the tail boom as well.

Recovery revealed it was just the prop, everything else was fine so a new prop was fitted and trims adjusted ready for a second attempt. Again Paul spun up the blades and I gradually increased the throttle. This time it was easier to hold on the ground until the disk was up to speed then with no elevator input it lifted up on it's own. A little right aileron and up elev and it was away, slightly nose up. One circuit later and a few clicks more of down elev and proper flight was established. Left and right turns were very similar to flying a helicopter with a bit of rudder coordination required. A couple of fig 8 circuits and time for a landing.

When the Atom slows down from forward flight significantly more movement of the sticks is required to maintain control but it's not excessive or frantic, just small quick corrections very similar to transitioning to the hover with a heli. The Atom floated in at a slight glide angle just above walking pace with just enough throttle not to loose rudder control. At about 4ft off the ground I reduced throttle a bit more and flared back to arrest the forward motion, right aileron to balance the slowing disk and it floated down to a gentle vertical landing.

Second flight was even more fun than the first with several slow flybys' and another vertical spot landing. Even better, Paul videoed it with my Hudl which I'll put up as soon as it's uploaded.

Many thanks to Richard for a design even an autogyro novice can get to fly and for doing the development and crashing for us (I have seen the early videos!   and thanks to Paul for braving the cold and rediculous fog to help me. Finally good luck to those yet to maiden. The Atom flies like a dream, just don't let it lift early on the take off run and keep the rotors spinning!

Video soon. laugh

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