Grumman F6F-3K Hellcat Drone
converted 1/144 Revell kit (cat.nr. 04931)

Introduction

Kit

This Revell Grumman F6F-3 Hellcat is one of a series of old 1/144 scale model kits, some of which got re-released in 2013 as 'Micro Wings' series.
The F6F-3 kit has fine, mostly raised, surface details and is generally accurate.
The kit got surpassed by a series of Platz F6F kits (some of which were also released by Eduard).
Bringing the Revell kit up to a level of detail closer to the Platz kits is not that hard, it is the poor fit of parts such as fuselage halves, canopy, cowling and wings where the Revell kit is showing its age.

Original

After WW2 the US Navy converted a number of surplus aircraft into remotely controlled drones for general use.
The Grumman F6F Hellcat was phased out of service in favor of the F4U Corsair and as there was plenty of life left in these sturdy aircraft, a number of F6F became drones.
Initially F6F-3s were converted, later on also some F6F-5s. F6F airframes converted into drones were given a 'D' or 'K' subtype.
Early in 1946 a fleet of F6F-3K drones was stationed at Naval Air Station Atlantic City, New Jersey. These drones were later used for taking aerial photographs, air samples and other measurements during Operation Crossroads, the 1946 atomic bomb tests at Atol Bikini.
The drones were painted in bright colors: overall red with the entire tail section painted in one of a range of bright colors, indicating its radio control frequency.
A number consisting of 1 or 2-digits was painted on the tail in either black or white (depending on the background color), this number was repeated in white on the cowling sides and forward wheel doors.

Usually a number of features can be checked to tell the Hellcat sub-types apart:

However looking at pictures of the drones it is clear that F6F-5 parts were retrofitted to some of the F6F-3 drones, so the only way to tell an F6F-3K from an F6F-5K is by looking for the fuselage windows behind the canopy.

Preparation

The first thing to do is to carefully trim any flash (along the edges of the fuselage halves, the wing halves and the cowling, along the propeller blades, in the prop shaft hole of the cowling, at the tip of antenna mast and at the rear of the canopy).
Also plug the hole for the stand using either the tip of the stand or a tapered piece of stretched sprue.
There are shrink marks in the side of the cowling, in the sides of the forward fuselage, in the lower wing roots, in the lower wing halves, in the pylon of the aux tank and in the main landing gear.

Note that the grade of polystyrene used for these kits is rather soft, so any thin parts and fine edges will be fragile and prone to breaking or chipping.

The 'Micro Wings' release comes with 4-view painting instructions based on accurate scale drawings. The scale of the main drawings works out to 1/179 so these are too small to be used for checking and correcting shapes.
However the separate drawing of the propeller is at 1/144 so this can be helpful for correcting the shape of the blades.

Construction

All planned modifications to the model in 'bullet points' (circle = yet to do):

• correct alignment of fuselage halves to make wing stub leading edges line up
  
• determine exact location of canopy and fill either forward edge below windshield or cut spine and move that plus canopy forward
  
• add basic cockpit interior
  
• plug hole for display stand
  
• add 0.5mm strip between stbd fin tip and rudder
  
• add wedges to inboard wing leading edges
  
• add mounting stubs for main landing gear
  
• scribe lower outlines of flaps, outer edges of lower ailerons, trim tab on port aileron, trim tab on rudder, starboard edge of rudder balance, canopy rails
  
• fill sink mark on main wheel hubs and improve details on landing gear
  
• widen main wheels by inserting 0.5mm plasticard
  
• add about 4mm length to front of aux tank (sprue)
  
• check size and shape of aux tank; make straps and struts for tank
  
• add port side of tail wheel mount (missing from kit)
  
• add tail wheel extension (steel wire, like Spitfire)
  
• add pitot tube to starboard lower wing tip
  
• 
  

fuselage

The gap between the tip of the fin on the starboard side and the rudder is too big, adding a strip of about 0.5mm tall to the starboard part of the fin fixes this.
The starboard vertical edge of the rudder balance needs to be scribed and the gap forward of this edge filled. The rudder trim tab should be scribed.
Only half of the tailwheel leg is present on the starboard side, the port fuselage just has a gap so a thin piece of plastic needs to be added to the port side of the leg.
The hole for the display stand should be plugged.
The edges of the cockpit and the canopy need some careful trimming to make the canopy fit properly, the gap in front of the base of the windshield should be filled or plugged.
The canopy rails need to be scribed.
The cowling has the flaps molded in a slightly opened position, this means that below the nose the shutters for the oil cooler and intercoolers should also be open.

The oil cooler shutter can be formed out of the kits raised rectangular section but a slight bulge needs to be added in front of it.
The intercooler shutters have to be made from scratch.

The fuselage comes with parts of the wing roots molded on. I decided to line up the fuselage halves so that the wing roots (and cockpit recess) are perfectly aligned. To achieve this, the entire starboard fuselage needs to be shifted forward by a few tenths of a mm.
To do this, the forward edges of the holes for the alignment pins need to be enlarged slightly.
It also means that the edge of the nose needs to be trimmed to make the cowling fit properly and that the gap between the tail fin and the rudder hinge line needs to be reduced.

The F6F-3K was fitted with a non-retractable tail wheel on an extended strut, the extension was presumably added to make a remote controlled take off easier.
For extending the tail wheel strut I picked a stainless steel magazine staple of 0.5mm diameter.
I did not measure the exact length of the extension, but just looked at the pictures and noticed that the extension was about as tall as the original tail wheel mount, doubling its total height.
The tail wheel needs to be cut off at its swivel point, first thing I did was wrap a piece of masking tape around the tiny wheel to make sure it would not get lost. Then I cut the wheel off using a JLC saw and carefully drilled a 0.5mm hole in either side.
Then I measured the depth of the holes and based on that cut a length of wire out of a straight part of the staple.
After test-fitting I glued the wire to the tail wheel using a drop of CA glue.
I will glue the tail wheel back on its mount after painting the model.

I also drilled a row of 3 small holes through the drag strut of the tail wheel as those are quite noticable on the real aircraft.

I added a tail wheel door from a piece of scrap plastic, sanded into a curved cross-section. Size: 2.5mm long, 1.75mm wide at the fuselage, 1.5mm wide at the lower end.

cockpit

The kits cockpit is empty, but since I planned to keep the canopy closed, I decided to only add details that are clearly visible through the canopy.
So I added a simple rear bulkhead with headrest and seat and added an instrument panel with coaming to the hole below the windshield.
I turned the large kit number '24' tab into a flat bulkhead of 8.0mm tall and 6.0mm wide with the top 3.5mm tapering to a blunt inverted V-shape.
I mounted the bulkhead a bit too low in the fuselage to allow the canopy to fit over it.
A piece of the thick outer sprue frame was split in halves with one half turned into an instrument panel, the panel was scraped down to form a coaming that extends 0.5mm beyond the panel.
Finally another piece of thick sprue was turned into a basic seat, not very accurate but it only serves to suggest something is there below the murky canopy.

The front of the recess for the cockpit is tapered, however the windshield is flat, so this leaves a gap.
To fill the gap I first applied a strip of masking tape over the cockpit, marking the inside edge of the windshield.
The I carefully applied some Tamiya White Putty to the gap and sanded it into shape once cured.

canopy

The canopy is a single piece and is not very clear.
The canopy shape is wrong: the windshield tapers too much in top view, the center pane of the windshield is curved (should be flat), the angle of the front of the windshield is too shallow (is about 44°, should be 48°, which makes the canopy hatch too short in length) and the top of the canopy is flat (should be curved in side view).
The plastic of the part is not thick enough to correct the shape properly, the windshield center pane can be sanded more flat, but correcting the angle takes more work (cut windshield off of hatch, adjust base and rear frame of windshield, add new frame to hatch for length).
I only sanded the top more curved and the windshield more flat without correcting the angle of the windshield.
The image shows the canopy after sanding and polishing.

There are raised frames visible, most of these are accurate, but the horizontal frames on the sides are missing, the center frame on the sides should not continue upwards from the (missing) horizontal frames and the horizontal frame on the windshield should be a continous line.
Also note that the corners of the horizontal frames should be filled with 45° triangles and the corners of the frames on the windshield should be curved.

wings

The wings have basic detailling with a fine texture on the aileron surfaces representing the fabric covering.
The insides of the wings, particularly of the lower wing tips, need to be trimmed for a flush fit. Ejector pin marks and even the raised part numbers need to be removed before the wing halves fit correctly.
The mounting tabs need some trimming in both lateral and vertical directions to make the wings align properly with the wing stubs.
I scribed the missing contours of the flaps and outboard aileron edges on the lower wing halves, and scribed the outline of the trim tab on the port aileron.
I added a fixed trim tab from a 1.8mm by 0.5mm strip of polystyrene foil to the starboard aileron.
There are '['-shaped mounting brackets for the main landing gear inside the upper wing halves. However the landing gear legs come with pegs that do not fit the brackets. Trying to fit the landing gear legs to those brackets would result in most of the forward facing gear doors disappearing into the wheel wells.

I cut the mounting brackets for the landing gear off of the insides of the upper wing halves, cut pieces of sprue of 2.0mm tall and fitted those as mounting points for the landing gear legs.
I later trimmed the mounts down to 1.0mm, drilled a 0.8mm hole for mounting the leg and removed any excess parts of the sprue.

At the roots the wings turned out to be almost 0.4mm too thin compared to the wing stubs on the fuselage.
The plastic for the wing stubs is too thin to sand down by 0.4mm, so I used my JLC saw to cut a wedge out of sprue and cut open each wing root leading edge. Then I inserted the wedges into the wing leading edges (next time I will fit the wedges before joining the wing halves).
The wedges measure 8mm wide by 3.7mm and taper from 0.5mm thick on the inboard sides to 0.0mm outboard.

On the real aircraft the lights in the wing tips stand out clearly against the bright paint, so I cut a gap in the wing tips of 0.5mm wide and 1.0mm long.
For the lenses I sanded bits of clear sprue into a rectangular shape, made a tiny diagonal JLC-saw cut across each inside corner and applied some red paint to one and green paint to the other cut.
Then I fitted each lens to a wing tip using a 'generous' amount of CA glue. Once the glue had cured I sanded the clear lenses flush with the wing tips.

With the wing tip light finished, the final part to add is the pitot tube.
There are two types of pitot tubes used: early F6F-3 had a short pitot (1.5mm at 1/144) mounted underneath the wing, late F6F-3 and all F6F-5 had a longer pitot (3.5mm at 1/144) monted further forward with the tip of the tube ahead of the wing leading edge (by 1.5mm at 1/144).
On the pictures the F6F-3K drones can be seen with either type, Nr.11 was fitted with the early style pitot.
There is a mounting slot in the correct location for an early type in the kits starboard lower wing, however no pitot is included in the kit.

For my first attempt at making a pitot I took some 0.3mm diameter metal wire (same as for the tank straps), made a curved 90° bend in one end and filed the tip into a sharp point.
Then I took a piece of 0.25mm plasticard, sanded a square corner into the same radius as the wire and used a JLC-saw to cut a groove in the rear and lower edges to mount the wire in.
The forward edge was sanded into a taper, then the wire was glued into the groove using CA glue.
This proved a bit too ambitious as the plasticard part broke off and vanished before I could glue the pitot to the wing tip.

The second pitot was again made out of 0.3mm metal wire, with a 90° bend and a sharp pointy tip but this time I squeezed the mount flat between a pair of pliers, similar to what I do with copper wire for making antennae.
After adjusting the size of the slot in the wing I glued the new pitot into the slot with a drop of CA glue.

main landing gear

The main landing gear legs are single pieces with the wheel and doors molded on, despite this the parts are fairly accurate and the leg is at a correct inwards angle. The tire is 1.0mm wide, this should be 1.5mm.

First I carefully applied some putty to the shrink marks in the wheel hubs, using the tip of a knife to recreate the spoke details of the hubs.
To enhance the looks I cleaned up the details, sanded the edges of the wheel doors thinner and scratched an undercut between the tires and the doors.
After 'opening up' the lower edge of the doors I fitted a tiny semi-circular piece of sprue to each wheel to represent the end of the legs.

To widen the wheels I cut the front of the wheels off using a JLC saw (top part of picture), added a piece of 0.5mm plasticard and glued the front parts back on.
The lower part of the picture shows a comparison between the original wheel on the left and the widened wheel on the right.

Finally I used some stretched sprue to add brake lines to the landing gear legs.
On regular Hellcats these lines are black rubber and stand out against the usually white or grey landing gear, but on the drones the lines were painted red, as was the rest of the landing gear.

cowling

The hole for the propeller shaft is partially covered by flash, making it off-center and too narrow, the hole can be opened up with a 1.2mm drill bit inserted from the inside.
The cowling itself has some vague details representing exhaust covers and partially opened upper and lower cowl flaps. The cowl flaps have soft edges and a hollow cross section.
The exhaust covers are the wrong size and shape.
During F6F-3 production the lower cowl flaps were deleted and these are not present on the aircraft I wanted to depict.
So I sanded off the lower cowl flaps and build up the upper cowl flaps using slices of sprue. Once the glue had cured I sanded the cowl flaps into shape.
The covers for the upper exhaust clusters were sanded off and replaced with D-shaped sections of sprue (2x2mm, 0.5mm thick), the new cowl flaps and exhaust covers can be seen in the picture.

After letting the glue cure for a couple of days, gaps were scribed in the rear of the cowl flaps and of the exhaust covers using the tip of an X-Acto nr.11 blade.

To be able to fit the propeller after assembling and painting the model, I picked a piece of soft vinyl power cord insulation with an inside diameter of about 1.0mm and cut a small ring off.
To position the vinyl ring behind the hole for the propeller shaft, I fitted a piece of Evergreen tubing and glued a plug out of sprue to its rear.

I added a snug fitting piece of Evergreen tubing to the firewall of the fuselage, this not only should help with aligning the cowling but also will serve as a grip during painting.

propeller

The kits propeller looks fairly close to the actual item, just the flash and sprue gates need to be cleaned up and the undersize hub needs to be beefed up somehow.
Any trimming has to be done with utmost care as the propeller is very delicate and the plastic is quite soft, so it is easy to break off a prop blade.
The picture shows the propeller after cleaning up the blades. I added a piece of hub from behind. This piece was cut from the locking ring (part nr.13) after enlarging its hole to 1.5mm with the top 1mm enlarged to 1.9mm to fit around the old hub. Before cutting the piece off, recesses for the blades were cut using a rats tail file.
A spare version of this piece of hub can be seen in the picture just below the propeller.

aux tank

The auxilary tank supplied in the kit is about 4mm too short and its front has an incorrect shape. Its plastic is very thin, so the front needs to be replaced by either a piece of sprue or part of a donor tank.
The main sprue in the kit is circular in cross section and has a large enough diameter to fit the tank, so I cut a 6mm section of sprue and sanded that into a replacement front section.

The slot in the fuselage belly for the pylon should be moved forwards by 1.5mm. The forward part of the pylon on the tank should be enlarged to a total length of 4mm and sanded into a tapered cross section.
The tank should be mounted with its centerline at a 3° nose-down angle compared to the fuselage centerline.

I made straps and struts for the aux tank out of steel wire, for the struts I used 0.5mm and 0.3mm for the straps.
I drilled holes in the fuselage for mounting the straps, based on the Detail&Scale scale drawings. However when the holes were drilled and I test-fitted the tank and straps, the result did not look like actual pictures: the distances between the pylon and the straps were off.
So I plugged the holes for the straps with stretched sprue, waited for the glue to cure and drilled new ones, now based on measurements I took from pictures.
The new locations for the straps do look right to me as the picture of the loosely assembled tank and straps shows.

Painting

The aircraft will be painted as one of the drones that were stationed at Naval Air Station Atlantic City, New Jersey in March of 1946.
I decided to do yellow-tailed nr.11.
It is not clear to me if these drones were painted in Fluorescent Red-Orange (ANA.633) or in Bright Red ANA.619 (note that in ANA Bulletin 157a dated March 24 1944, ANA.619 was renamed from 'Insignia Red' to 'Bright Red').
On most pictures the drones have a warm orangy tint whereas ANA.619 is a cool saturated color. I do not know the exact composition of ANA.619 but its FS.11136 equivalent is made up of red, white, violet and blueish black pigments and not containing any yellow or orange pigments.
Aside from that if you look at preserved aircraft of the era that had prolonged exposure to the elements you will see that Insignia Red tends to fade initially to a brighter shade of red (due to the violet pigments fading first) then to a cool pink shade, without ever turning into a warmer orangy shade.
I picked Fluorescent Red-Orange (ANA.633) for the overall color.

The only model paints I know of that come close to ANA.633/FS.28913 are XtraColor X161 and Humbrol Fluorescent Fire Orange (205), unfortunately I found both these paints to have some undesirable properties.
However Revell 25 Leuchtorange does have fluorescent properties and behaves like a normal enamel paint so it can be mixed with other Revell enamel colors.
Apart from Revell enamel, both Pactra Acrylic and Vallejo offer a range of acrylic fluorescent base colors that can be mixed to the right red-orange shade.
Fluorescent paints are translucent so an even base coat is required, a coat of flat white is recommended but since I mix the color anyway I plan to use the same matt yellow as for the tail and adjust the mixed color accordingly.

Only the insignia will be used from the kit decals, the numbers will be taken from my the spares box.

Apart from a few black details the entire cockpit interior should be painted Interior Green ANA.611, including the seat.

Engine colors: Engine Gray ANA.513/FS.16081 crankcase, gearbox and magneto; satin black pushrod covers. Cylinders casings were bare aluminum, often with tan heat-stained fins.

There is heavy exhaust fume staining on the fuselage sides and wing roots visible on all pictures of these drones, apparently the basic remote controls did not allow for the engines to run at optimal settings.

References

• 'Grumman F6F Hellcat', Corwyn Meyer & Steve Ginter, Naval Fighters Nr.92, ISBN 0-9846114-5-2
  
• 'F6F Hellcat in Detail & Scale', Bert Kinzey, Detail & Scale Series vol.26, ISBN 0-8306-8036-5
  
• Tailhook Topics blog - F6F Drones
  
• WarDrawings - Grumman F6F-3K Hellcat Drone
  
• Image of F6F drones at World War II Database
  
• Image of F6F drones at Wikimedia.org
  
• Grumman F6F Pilot's Handbook (PDF) at Airplanes & Helicopters Flight Manuals