A Little Atom, A Medium Mossie and a Big Cub

[Chris Barlow]

Of the models chosen for this years mass build I voted for 2 of them and intended to build an Atom anyway so now I find myself in a position where I have 3 models to build & fly before RCM&E Greenacres!

The plans have been chosen and I have started to get some gear together. The plan is to build the Atom and Mosquito alongside each other since they're small enough for the bench, and finish with the Cub on it's own.

So first off, the Atom

Built from plan only and hopefully mostly from spares and the scrap balsa drawer! I suspect all I need to actually buy are the head, blades and head servos. I have already copied the plan and cut out templates.

Then the Mosquito. I chose the Tony Nijhuis 47" Mossie because it's going to be roughly the same scale as my Cambrian Models Hurricane Funfighter and hopefully it'll be easier to follow in the air with all the other Spitfires and ME 109's!

I ordered a complete pack to try to save a little time. I prefer to build from scratch but with a Cub also planned it might be a little tight for time!

Finally the Cub. It's a 79" David Boddington Super Cub which I hope to modify into a STOL version like you see in the full size STOL competitions. Hopefully I'll be adding flaps and tip slats with lots of thrust and bucket loads of lightness for good measure!

I have build a few models in the past but I'm far from an expert so I'd welcome any advice and criticisms offered!

But first I have a Tucano to finish and a shed to tidy up!

[Tony Bennett]

ambitious project sir.

but i expect you can do it.

[john stones 1 - Moderator]

Just spotted this one, you've a bit of work on there Chris but I reckon you're up to it

Looking forward to the Mossie because i'm tempted myself.

John

[Former Member]

[This posting has been removed]

[Chris Barlow]

One of the reasons I chose the DB Cub is because I like DB designs and use of traditional building techniques which will make alterations easier to implement. My Cub airframe will have to be a "good" one to minimise problems adding flaps and possibly slats during the build.

So over the Christmas period I made a start on the Atom and Mossie. I was beginning to get quite concerned about the timescale but after a good couple of days on the Atom first I hope to be started on the Cub before February!

First place to look for wood for the Atom was the scraps drawer!

Just a couple of pieces needed from the balsa stock and some 1/2 x 1/4 spruce ordered. I have had the head on order from HK for about a month now and was still waiting for it when I made a start!

First job was to cut all the parts. I had already copied the plan onto thick paper and cut out the templates so it was simply a case of drawing around the templates and cutting. The scroll saw is invaluable when it comes to ply parts. I always used to use a coping saw but the scroll saw is the best £40 I ever spent on modelling tools!

(Nearly) all the bits cut. Ready for some glue. I prefer aliphatic rather than cyano as it produces a more flexible joint, essential for some of my landings!

Mast mount

Fuselage sides

Undercariage block

And rudder servo mount

[cymaz]

I looked on the thread because of the title, got me interested.

"A Little Atom, A Medium Mossie and a big Big Cub walk into a pub". I hope you can see where I'm going with that!

Looking forward to watching the Cub build

[john stones 1 - Moderator]

It adds to the pleasure of a build when it comes out of a scrap box

Apart from the mods you're doing the Cub should be a fairly quick build Chris, like yourself I enjoy Boddos plans.

John

[Chris Barlow]

Motor bulkhead was glued up next then a start on the tail.

I decided to go with a third central rudder as some other have, partly for appearance and partly for more rudder authority. The central rudder was cut jigsaw fashion to interlock the top and bottom halves through the tail plane. The tail boom fillet was split and glued to either side of the bottom half first.

The top half was then glued to the tail plane

Then the side rudders

The ventral part which would have originally been the tail skid was then glued to the underside of the tail plane

Fluffy mylar hinges cut into the three rudders, supported with clamps to prevent splitting and aid glue contact

Hinged up

and tail booms added

Usually I'd cover the parts first then hinge up but my intention was to seal the airframe and airbrush it when complete.

[Chris Barlow]

I hope so John. I'm going to need a bit of time for the slats if I go that way, and a bit of flying time for the Atom. I do fly helis and planes but an autogyro is somewhere in between them!

Cymaz, there's a joke in there somewhere! I challenge you to find it!

[cymaz]

Ah, you got me there..

[Chris Barlow]

Just bringing the blog up to date whilst having a break from the shed!

The Atom fuselage was glued up and nose block added.

Landing legs bent to shape and flats ground in for the collet grub screws.

And plugged in.

[cymaz]

Burning the midnight oil Chris ?

[Chris Barlow]

Had a bit of a break from the Atom thanks to an extremely slow delivery service from Hong Kong so made a start on the Mossie.

Fist off a bit of a treat for myself! I usually wax the plans with a soft candle but along with a few bits of wood from Slec I also ordered a plan protection sheet.

There is a link to the RCM&E article for the 47" Mosquito on the Tony Nijhuis website so after a bit of a read and study of the plan I cut the fuselage sides out & made a start.

I've never used a TN plan before and found the "legend" of the balsa sheets showing the laser cut parts positions on the sheets very useful. Each part on the plan has a number in a circle and the parts shown in the legend have the corresponding number. This means that there are no numbers printed on the balsa to sand off before covering or painting.

The fuselage sides are in 2 pieces butt jointed together and splinted with the 1/2" triangular stock around the edges.

Yeah, and I'm not about to make that mistake!

For the Mossie I am using a combination of aliphatic in the centre of the joint with thin cyano on the edge as a "clamp" This works OK as long as the cyano isn't used where the aliphatic has squeezed out of the joint and speeds things up considerably whilst still making slightly flexible glue joints.

[Chris Barlow]

The formers were next & this is where I found the first discrepancy. The former 13 is 1/8" short of the top of the wing slot and former 14 below 13 is 1/8" over the slot. If glued in as they are it would not be possible to slide the wing into the fuselage later on.

The solution is simply to trim 1/8" off the chamfered end of F14. I know most kits require a little fettling during assembly but it would be nice if somebody actually assembled a kit from the production line just to see that it goes together properly! I am available for test building sample production kits if anybody requires my services!

All formers fitted to one side and triangular stock glued to the other...

...and the two halves brought together and squared up...

Cuts are made in the triangular stock at the nose end to allow the fuselage sides to bend when pulled together.

The battery tray was installed next, clamped in place with medium cyano and a blast of kicker to form a "fillet" where it meets the nose.

Cockpit floor added, glued with aliphatic and tacked with thin cyano. After a few problems with this method I have found that if I leave a gap in the aliphatic glue line in the corners of the part it leaves a clear spot for the cyano clamp.

Front and rear top decks were then added, which helped to form a bit of a curve in the fuselage.

With so much wet glue still drying I decided to stop and let it all dry for a bit!

[Chris Barlow]

Posted by cymaz on 03/01/2015 03:08:57:

Burning the midnight oil Chris ?

Yup! Finished in the shed. "The Worlds End" DVD on and trying to get the blog up to date.

It's the usual problem where I get started on something and the brain won't leave me alone until I've finished!

[Chris Barlow]

With the head now delivered I made a start on the blades and head modifications.

I ordered some blades from AJ Blades before Christmas and they've been sitting in the "safe place" in the shed since then. After 30 minutes trying to remember where the "safe place" was I found them! I had previously read the Atom thread and the articles regarding balancing the blades and was aware of the issue of a minimal seat for the 0.4mm shim on the GRP triangle.

The blades CG was found and the bolt hole drilled. I glued a 2mm ply reinforcing plate to the underside of the blades and cut the root relief. The ply plate was then sanded to a chamfer approximately 1.5mm at the leading edge to 2mm at the trailing edge which gives a shim of .5mm over the complete contact area at the blade roots. This isn't as hard as it sounds since the layers in the ply show through as you sand away!

A 2mm ply plate id added to the top of the blade to reinforce the balsa. The next photo hopefully shows the chamfer on the underside of the blade.

The head was completely stripped down, threadlocked and re-assembled with the new triangular GRP flap plate.

I wasn't very keen on the ball joints that come with the head as they seem to pop off too easily. Before test flying I will either add retaining washers or replace them!

Next up the Turnigy digital MG servos were installed. When assembling the shaft support former I hadn't made any cutouts in the balsa "filling" so I had to tunnel a route to get the servo wires out into the fuselage!

and to help with the probable repairs to the mast I didn't glue it in, choosing to retain it with one of those posh servo screws.

I added 2mm ply to the top and bottom of the spacer in the tail boom. I also added a second spacer at the tail plane end to stiffen up the booms and limit twisting in the tail...

this also provides a mount for the castoring tail wheel.

[Chris Barlow]

It's been a long tome since I've shrunk a pop bottle around a balsa plug (about 25 years!) and I don't remember ever getting a satisfactory result from it either, usually ending in a slightly wrinkled canopy or giving up and settling for the shape of the neck of the bottle instead. So I wasn't really looking forward to the next part!

The plug was made from scraps of balsa and lots of voids in the middle to save wood but also because I didn't want to start planing and jointing wood!

Unfortunately some of those voids started to re appear when sanding and require a bit of filler. The plug was inserted into a Tesco sparkling water pop bottle with the top and bottom cut off. The remaining space in the bottle was filled with scraps of 1/2" balsa. Using a craft heat gun I started heating the plastic at the front first letting it shrink back over the plug. To stop the plug from being pushed out of the bottle as the plastic shrunk I then heated the rear of the bottle, shrinking it around the back of the plug.

I don't know if the craft heat gun is more controlable of something but shrinking the remainder of the bottle around the plug was pretty straightforward with no ripples or blisters appearing. I don't know why I struggled with it so much all those years ago!

I cut a cockpit floor, front and rear from scrap 1/8" balsa and after wrapping the fuselage with cling film I glued the cockpit up in situ to get a good fit. A dash was added with 1/2" triangular stock and a seat back & support from 1/8" scrap. This was all painted with the last dregs of spctra gloss black.

Some time ago I bought two action figures off Ebay for 99p (+ postage!) One of these has taken up residence in my Axial Wraith rock crawler and the other thrown in the scraps drawer. It's very light and made of thin bendy plastic and a green "flight suit" overalls. Bill as he is now known was trimmed just above the navel and his arms persuaded into a hands on control column position with a little heat to his elbows. (no wonder he doesn't smile much!)

The newly formed canopy was trimmed to fit over Bills new home, masked & painted then screwed into position.

Needs a bit of a polish but fits rather nicely. The plan to airbrush my Atom was abandoned in favour of using up some black covering film bought for the Tucano from HobbyKing. I think I'll stick to Solarfilm in future!

I did use Solarfilm for the tail plane and the three rudders though. Due to the difficulties in covering after assembly I didn't want to make it harder by using poor film!

The rudder servo was fitted and control cables made from 50lb fishing braid added. Drag links between the centre rudder and outers is from 2mm wire and will be retained by swing keeps.

[Chris Barlow]

A final one for tonight before I try to get some sleep!

As well as planes I also fly a few helicopters so am used to balancing rotor blades. However I have never bothered to dynamicaly balance my blades before so this was new to me.

The span balance point was found for each blade using a scrap of 1/2" triangular stock and each one was marked. Two of the three blades were identical with the third balancing 4mm closer to the root. This blade was matched to the other two using balsaloc painted onto the tip end and by sanding the root cutout slightly further towards the tip end without reducing the depth of the cut out.

The blades were then balanced with each other, finding the heavier blade first then adding balsaloc to the span balance point until they were all the same. I liked the post in the Atom thread about colouring the blades to produce a bullseye effect when spinning so I covered the blades with three colours of solarfilm.

To see if this would produce the desire effect I spun the blades up by hand and photographed them with a slow shutter speed (and 2nd curtain flash)

Just the effect I was looking for! Unfortunately when re checking the balance of the blades one of them has gained a little weight so I had to apply a strip of tape to the other two blades. When I make a spare set of blades I'll pay more attention to the balancing whilst covering and make the adjustments under the film.

For some reason my portrait orientated photos have changed to landscape when uploading! I presume this is something to do with the gallery size format and will have to find out how to change it!

[Chris Barlow]

With the Mosquito fuselage glued up it was time to start the engine nacelles. First off all the parts were removed from their sheets and laid out on the bench.

1/4" doublers are glued to the sides which have been laid out handed first to eliminate the mistake of making 4 left handed sides!

And triangular stock added.

As this Mossie will be electric the main former is 1/8" balsa. There are ply formers in the pack for making an i.c version too.

Sheeting is added to the underside of the nacelles.

And balsa blocks made up from 2 pieces of 1/2" balsa added to the rear formers

[Chris Barlow]

I marked and cut the slot for the rudder post whilst the fuselage was still in box form as it's much easier to find the centre position. I also extended the cutout to include a fixed fillet below the rudder which is shown on the plan but not accounted for in the wood pack.

I also cut off the top section of the rudder post and glued it to the leading edge of the rudder to give a more scale appearance.

The rear of the cockpit is built up with balsa packers to give some meat for shaping later.

Back to the engine nacelles and 1/8" cross grain sheeting is added to the underside. There is a sheet for this in the wood pack but I used the remainder of the sheet from a laser cut sheet, and added the full sheet to my balsa stock!

[Chris Barlow]

The wings are a 3/8" solid sheet balsa affair with a ply brace joining the two halves.The centre section is simply cut to length then the trailing edge is cut. The sheet legend on the plan shows the centre sections taken from one sheet of balsa cut in half. This may be correct for the smaller span Mosquito but for the 47" version the centre section in longer than half a sheet. This shouldn't be a problem with the 47" wood pack except mine had an extra sheet of 1/2" instead of 3/8". This wasn't too much of a problem as I simply cut the leading edge from 2 offcuts and jointed them where the engine nacelles fit. If I need to I can add a ply brace over the joint which will be hidden but I doubt this will be neccesary.

The first trailing edge can then be flipped over and the second cut to match.

The leading edge and cross grain wing tips cut and all the joining faces sanded and trimmed to ensure a very good butt joint ready for glueing. The slot for the wing brace is cut out of the rear of the leading edge before glueing to the centre section.

I laid a sheet of clingfilm on the bench the glued up the first wing, rubbing the joints together to ensure 100% glue contact. The parts were pinned in position through the edges and the cling film doubled back over the wing.

The second wing was then glued up and assembled the same as the first and laid directly over the top. The two wings were then pinned together to prevent movement and weighted down to keep them perfectly flat whilst drying.

[Chris Barlow]

Double post!  The touch pad on my laptop is very sensitive!

Edited By Chris Barlow on 03/01/2015 18:46:12

[Chris Barlow]

Sheeting added to the top of the nacelles. After shaping a hatch will be cut in the top to allow access to the motors and secured with screws.

I couldn't get a 4"x4"x4" balsa block for the nose so I laminated 6 pieces of 1/2" together with aliphatic around the outsied edges and medium cyano as a clamp in the middle.

After the glue had dried the wings, fuselage and nacelles were roughly planed to shape with a sharp David plane.

This operation produced enough blonde curly balsa to make Shirley Temple jealous! A handy tip is to have a bin bag next to your feet otherwise you'll be ankle deep in shavings very quickly!

[Martyn K]

Impressed - I hope your enthusiasm is triply infectious!

Watching

Martyn

[Chris Barlow]

Next up is a lot of sanding. The profile of the fuselage and nacelles runs very deep into the 1/2" triangular balsa ad care has to be taken not to sand all the way through. First sanding was with 80 grit sandpaper to get the shape and curves right. Subsequent sanding will be with 180 then 240 grit to get a smooth finish.

You can see how far the sanding goes into the triangle at the front of the cockpit, creating an almost continuous 1/8" shell all round the corners.

The canopy was cut and positioned over the cockpit. Drawing around the rear of the canopy defines the limits of the required curve.

Last sanding operation yesterday was the wings. I started by sanding off the corners of the angle changes the started the aerofoil section by rocking the sanding block cross grain across the wing. Between small amounts of sanding, feeling the profile with my fingers and trying the wing in the slot in the fuselage eventually the correct profile is formed.