War Paint

The "proper" Spitfire - Mk I, Summer 1940, Battle of Britain

        Colour references:

• Dark Earth (Humbrol HB2)
• Dark Green (Humbrol HB1)
• Sky (Humbrol HB5)
• Insignia Red (Humbrol HU153)
• Oxford Blue (Humbrol HU104)
• Insignia Yellow (Humbrol HU154) 
• Ensin White

266 Squadron Colours
I had not been able to determine with any accuracy the belly color applied to the 266 Squadrons Spitfires in August 1940  or if  Frank Cales Spitfire even had the single squadron prefix applied. The video link [0.41 sec] above supports the reply received from the RAF Museum that at that time most only carried the squadron marking.

The image above gives three [3] possibilities the sky green of the 2010 display aircraft to grey or sky blue. A chance viewing of a colour video called the Spitfire Documentary  [18.10 sec] showed that the under belly was most likely Sky Grey for a number of reason but put simply the weight saving from just applying Satin clear over grey etch primer has appeal.

The plan is to spray the underside grey etch primer then the top side in beige etch primer and finally the Earth and Green colour. 

One of the other issues is to obtain a soft edge and this will be tackled by applying string under the edge of the tape to hold it up and provide a round edge - reading has shown this works well in large scale models and if we regard the Tucano as a large stand off scale model, it should work.

At this time the use of decals for the roundels and tri color on the tail is an open issue.

This is not till next year but the decision has to be made. I will be spraying the aircraft myself for simple economic reasons and am currently digging through the RV blogs to see how they have tackled the task. 

It will be 2 - pack sprayed with a HVLP sprayer in a homemade plastic spray booth built in the hangar. I am looking at the idea of suspending the aircraft from my electric hoist on the roof with a custom spreader to lift it up for access to the underside. Spraying upside down on your back is akin to uphand welding - strictly for the experts.

Back to the wings, fuel line seats etc etc ........

Wing Installation - Part 4

This blog covers the installation of wing aileron and push rods.

Overview
The ailerons on the Tucano are operated by a series 7/8''  OD aluminium push-rods mounted on a series of rockers arms fixed to the rear spar with all holes and nut-plates factory installed.

Push-rods
The push-rods were all fabricated using the factory supplied tube, inserts and rod ends.
At installation of the rockers and aileron bell cranks had their location marked onto the face of the spar while in the neutral position, 60 mm was deduced from the center distance allowing the rod end and bush to be installed at the factory preferred starting length.

Note: The length of 30 mm is measured from the rod end center to the rear of the flange of the insert

The factory inserts were all little tight when trial fitted into the tube so it was decided to turn a whisker of metal off in the lathe using a  AN4 bolt as a mandrel to hold the insert for machining.

Turning inserts to create slip fit in tube

With the inserts prepared the tubes were cut to length, inserts riveted using four [4]  x 4 mm x 8 pop rivets. There is a recess machined in the rear of the insert  which are drilled into placing the center-line of the rivet center-line 2 mm from that point.

Note: Before assembly the inserts were primed as was the inside of the face of the tube

With the tubes fully primed a AN4 shear nut was installed in reverse onto the rod end and adjusted to place the rod end center 30 mm from the rear of the insets flange.

Note: To allow the nut to be used it was first installed in the correct direction, removed, rotated and reinstalled as described

Ailerons
The ailerons with this kit were supplied finished except for the front fairing. To install the fairing this had to be de-riveted and trimmed for installation. The rivets were removed and the edges trimmed using the factory supplied cutting guide and the Ofla knife. After trimming the edge was trimmed and sanded smooth with well watered 400 grit wet / dry paper.

Preparing aileron skins
Trimming aileron skin in place

The aluminium used is very thin, soft and will buckle or tear with little or no effort. The plans call for 3/32'' rivets but this kit had been tacked with 1/8'' rivets so it was decided to use these to allow the original rivets to be matched.

After trimming the fairing edge to overlap the skin was looking a little untidy and it was not all my fault so as per the elevator it was decided to install the edge under the structural skin.

To ensure a watertight seal it was decided this time to use a silicon bead under the main skin to ensure no water can enter in service. It was decided to use Selleys Solar Flex black silicon which is paintable, slow drying allowing time to clean up.

The structural edge had to be trimmed in position which was accomplished with the Ofla knife , protective strips and a file with a safety edge. With the edges ready the fairing was inserted and a handful of clecos installed. 

With the parts ready a tape edge was run along to collect the excess that will squeeze out. The temporary clecos were removed and a bead of silicon added using a handgun and then the edge was fully clecoed and finally the edge worked with the thumb to assist in squeezing out excess silicon. With the edge ready every second cleco was removed and riveted the remainder removed and riveted. Finally tape was removed and the edge cleaned up with thinners and lots of disposable hand towels.

The final task was to rivet the fairing and this is when problems occurred. All original holes were clecoed with 1/8'' clecos then the remainder fixed with 3/32'' clecos as required. At this point is was noted that the alignment was not good at a number of the holes.

"Let a sleeping dogs lie, it might 
not end up very pretty"

All the 1/8 holes were riveted and the plan was to enlarged all the holes with a #30 drill. Being a half a hole out is just a big problem and I managed to tear two of the holes as this material has no stiffness and the hole steered the drilling. 

Not happy but it is not fixable and as this is a fairing but it reflects on the person drilling the holes and the torn holes were riveted using a large head rivets as a cover up. To attempt to make this perfect would only create a bigger mess.

Assembly
With the components ready,  rockers, doubler plates were installed to the factory plans with the push rods. After all adjustments were completed the hinges were fitted onto the ailerons using AN3 bolts fitted into nut-plates.

The ailerons were installed remembering to insert washers between the face of the bearings and ailerons brackets, next the coupling, rod end bearings were assembled connecting the ailerons to the push-rods. The system was adjusted by eye into alignment, this will have to be finally trimmed later through the inspection hatches. 


A foul with the outboard hinge on the fairing had to be rectified and was modifyed to match the opening on the opposite side.

Aerilon issues

Note: The aileron mounting brackets were aligned with the flap installation and riveted to the main spar with pop rivets to fix their location with another small problem with the middle rocker rivet nut requiring modification [wrong rivet nut installed at factory]

Comment
The aileron fairing was a disappointment as the holes were poorly matched drilled and need extreme care during the whole installation process which was not recognised by the builder early enough.

Wing Installation - Part 3

This blog covers the installation of flap faring, inspection hatches, wiring and fuels systems into the starboard wing.

Overview
The starboard wing carry's the pitot mast, AOA, aileron trim plus the necessary wiring for navigation lights, auxiliary tank accessories and fuel return line.

Flap Shroud
The flap bay has a interior shroud to flare the opening with the flaps down and to support the trailing edge. The preformed shroud was initially fitted by laying it over the rear spar and the trailing edge, with the trailing edge clamped to the shroud with a aluminium angle to hold it straight using a pair of spring clamps. Next the top edge was marked off the upper skin to be cut about 3 - 4 mm from the edge with the excess at the spar marked for removal.  Once happy with the fit a number of of clecos were fitted to allow the alignment to be recovered when the lower skin is fitted.

Note: Lower skin was clecoed on for this task

The shroud was removed and trimmed, dressed, primed on the inside face and this task was repeated on the underside of the wing flap bat

The folded edge on the top skin at the flap bay is used to capture the upper edge of the shroud. This has to be opened up slightly and to do this a paint scraper was modified into folder with a 15 mm long lip at 45 degrees to the blade with the finished edge dress to allow easier insertion. This tool was fitted under the edge and used to lever it out to provide a gap of about 1 mm. 

Marking the trim allowance using trailing edge as reference after trimming the edge was marked with felt pen to aid final adjustments [image upper left hand corner]

To provide a guide on how deep the shroud was engaged into the lip a 10 mm wide line was applied using a big felt tip pen. The shroud was re-inserted and the fit checked - its a matter of looking correct and ensuring the edge has a minimum engagement of 5 -6 mm into the lip.

Installing second shroud

At installation the edge will be re-crimped with a pair of duck bill pliers and if possible a bead of silicon adhesive will be injected into the lip before installation but this is another day.

Access Hatches
Access needs to be provided for the end of the fuel tank, pitot mast / A.O.A. with all factory drilled access hatches had M3 rivet nuts installed.

The location for the fuel hatch was determined and a 100 mm OD hole installed using a nibbler and files to finish. Next the factory supplied covers were centered and all holes matched drilled using clecos for alignment during the process. 

At completion all holes were enlarged and M3 rivet nuts fitted. 

The next hatch was for the pitot / AOA which will provide access for both. This hatch was prepared as outlined above with the addition of a 0.020'' doubler which was match drilled with the cover. At installation the skin and doubler were riveted into location with four [4] countersunk 3.2 mm rivets and the eight [8] rivet nuts.

With the cover installed it was match drilled to match the pitot mask which was fitted with M4 screws and nylock nuts.

Pitot access hatch

The A.O.A. has to be installed withing 100 mm [4''] of the leading edge with the rib adjacent to the opening providing the mounting point. The mounting holes were prepared as specified and the A.O.A. generatortrial fitted. It is a little tight to insert the screws but it can be done with the wing upside down but in service would be a trial.

A.O.A. trial  installation

Wiring
The cores for a MAC trim tab, auxiliary fuel tank and strobes were fitted into a 10 mm loom tube and strung through the rear of the wing. The tube was secured using a series of 3 mm holes already punched in the spar but unused, these were all enlarged to 4 mm to allow a large head pop rivet to be used. Rubber U channel was secured to the sharp edges of the rib using contact cement to protect the loom tube from chafing.

Wiring loom located at rear of the spar

Note: Tube contains 2 x 18 gauge [pump] / 2 x 22 gauge [low fuel]/ 2 x 20 gauge [nav] / 5 core MAC trim cable

Fuel Return
Fuel return lines are installed in both wings and as a part of the weight reduction it was decided to install 3/'8'' aluminium tube with rubber hose for the final connect into the fuel filler neck when the tank is installed.

A.O.A. cable, pitot line and 3/8'' aluminium fuel return

The aluminium tube is supported in rubber grommets at each intermediate ribs and AN6 bulkhead fittings at each end rib.

Rubber U Channel were fitted to the rib and spar flange adjacent to the entry point past the rib that allow connection to the filler neck to prevent chafing.

Note: 5/16'' line is all that is required for the fuel return 

Comment
When written down it all sounds so simple but it took 30 hours + to achieve. All big jobs are generally the small ones and as they say the devil is in the detail.

Canopy - Restraint

This blog cover the installation of a canopy restraint

Overview
One of the issues created by the strut is its limited capacity to hold the canopy in a wind. This issue was raised by Franco from Flying Legend on the last visit.

Construction
A 3/32'' cable was selected for the task of restraining the canopy when opened using the existing canopy roller attachment and another point on the canopy spreader for attachment.

The existing pivot needed a machined swivel point from aluminium to allow the cable eye to swivel in normal operation. This required a slightly longer AN3 bolt to be installed with the swivel. 

Restraint attachment

Upper spreader before 
installation

The lower cable restraint was fitted to allow the attachment point to be determined with the o/a length set to hold the cable under tension by the strut when open. 

Once the mounting point was located it was drilled 3/16'' then the swivel was fitted and operation checked. The next issue was to spread the load on the spreader and to prevent the it from being crushed when the bolt was tightened.. 

A flanged shaft was machined 10 mm od allowing the bolt to be tightened allowing the cable to drop into the rear cockpit while not crushing the spreader. 

The cable would initially coil up but after being under tension for a while dropped neatly behind the roll bar.

Comment
Works as planned and in review it actually looks like it was designed not developed.

Another small job finished -- Woo - Hoo..!

Bits & Pieces - No 3

This blog covers small jobs undertaken while working on the wings

A Question of Weight
One of issues discussed on the recent visit was the end weight of the Tucano with Franco estimating 420 kg draining colour from the builder. Franco supplied copy of the the C.O.G calculator to run the numbers and to understand the weight distribution of the Tucano.

Going my way?

Without boring detail the Aircraft is VERY sensitive to weight measured on the nose wheel with only a few kilos extra required the addition of ballast at the tail. At this time a new engine mount was supplied that is 50 mm shorter and with the analysis fresh on the mind any reluctance to remove the original mount was removed.

While it would be very easy to have a forward c.o.g., short of giving a lift to Jabba the Hut I cannot see how you could have a rear c.o.g. issue.

Stiffener

Relocated fuel selector mount

Upgrades

With the mount removed a lingering problem of installing the lower engine mount stiffener upgrade was undertaken.

Also the position for the fuel selector was creating problems so it was modified and relocated to the port side. With all this work undertaken the new engine mount was refitted and all the components from the original one were transferred onto the new mount.

Aluminium Tube

It was decided to tackle the installation of the some of the fuel lines and this was a disaster as it was nearly impossible to create a flares. The Aeroflow aluminium tube that had worked previously would not grip the flaring tool - what changed is unknown so a new solution had to be looked at.

I was decided to use drawn 5052 from the local supplier, after picking up two [2] x 6 foot lengths and while driving through the Sydney traffic I remembered who I had looked at using coiled tube. 

New engine mount and what you get done with six [6] feet of 5052 tube

Estimating weight of finished aircraft
All components piled in and the finished estimated weight was 410 kg

At this point I would say before using a coil of aluminium tube is that you use the supplied flaring tool or you do some tests to verify the flares using your flaring tool.

Comment

We are now working on "Project 400" and I am reviewing the aircraft to remove all unwanted weight to reach a target of 400 kg.

Currently the starboard wing is being fitted out and this will be covered in the next blog as it has taken a few weekends to finish this exercise and that makes it hard to provide blogs regularly.