WW2 war-birds hold a fascination with most people
that love the look of a great aircraft. During this era planes
developed from slow flying bi-planes to sleek 400 mile per hour
single wing fighters. There is nothing like a war to accelerate the
development of aircraft and none more so than the period of the
second world war. The Mustang stands as one of the pinnacle fighters
of this era, being loved by all who have flown in them or had
anything to do with this wonderful piece of history. When the
Airborne team told me they had drawn up a new plan for the Mustang,
I jumped at the opportunity to build it and do an evaluation and
flight test on this ‘Cadillac of the skies’.
This plan is about 1:6th scale, with a wing span
of 1.6m, (65inches), and a fuselage length of 1.4m. A good .60
2-stroke, or if you hate the scream of a two’eee, .80 to .90
4-stroke like the Magnum .91 I will be using, will do just fine. A
war bird should sound as close to the real thing as possible, so a 4
stroke is just the ticket in my opinion.
Just how much balsa will you need to build this plane?
In all the construction articles I’ve read, no one has said just how
much material is needed to complete the project. So I’ll set a new
standard for others to follow.
(All sheets are 1.2m x 100mm) 12 sheets x 1.6mm for
wing and tail surface covering; 5 sheets x 2.5mm for wing ribs; 4 sheets x
3.2mm for fuselage sides and formers; 1 sheet x 9.5mm for the fuselage
bottom engine cowl and elevators; 1 sheet x 12mm for the radiator and
500mm x 200mm of 1.5mm for fuselage doublers and wing
servo covers; 200mm x 400mm of 3mm for wing brace, retract mount doubler
ribs and fuselage formers; 300mm x 100mm of 6.5mm for engine mount former
and retract mounting plates.
It is a good idea to kit up all your parts before the
building frenzy takes place. If you have access to a photocopier use it to
copy the parts from the plan and then use a clothes iron, (hopefully not
the one your better half uses for the clothes), to transfer the image of
the part onto the balsa or ply. I used a band saw to cut out the ply parts
and the wing ribs in their corresponding left and right pairs. The rest
was cut out using a hobby knife and a razor saw, take your time to make a
good job of this, making sure that all cut outs are a snug fit for the
stringers and spars that go into them. Finish off all edges with a sanding
bar to level off any ups and downs, checking the fit of the part over the
plan to make sure it is a perfect fit. You are now ready; let the building
Use a nice flat building surface to make the plane on,
I got hold of some cork faced display board, which is great for pinning
parts onto as the glue sets.
The two 1.5mm ply doublers and spruce longerons
need to be epoxied onto the 3.2mm balsa side pieces, making sure
there is a left and right side and not two left or two right sides!
Formers F1 and F2 are epoxied together with the tank side crutches,
which fit into slots cut into each former. Make sure they are
squared up before the glue sets. Mark the position of the formers on
the inside of each sidepiece to make it easier to line them up over
the plan. Once the parts have cured the sides and the rest of the
formers can be fitted in place over the plan or set up in a building
jig to keep everything lined up nice and square.
Because the fuselage sides need to be curved from just behind the
wing, use some ammonia and water mixed 50/50 to wet out the balsa to
allow it to follow the required curves of the rear formers. This
part didn’t fit into the jig properly so I just lined up the
centreline of the formers using pins placed in the top of each and
then eyeing up through the pins to make sure they were all perfectly
in line. I used rubber bands to hold the sides in contact with the
formers until the glue and balsa dried. After the glue had dried,
the front and rear top sections were cut to size and again wet out
with ammonia and water to allow them to follow the tight curves of
the formers. I used Saturn Hobbies Gator Bond to glue these pieces
in position, as it allows you working time to position the parts in
the correct spot. The cockpit bottom was then cut out and fitted
into position. At this stage I decided to fit a retractable tail
wheel, I used the medium sized Robart mechanical retract. A 3mm ply
former was fitted from underneath to mount the unit securely into
position. The bottom was then sheeted with 9.5mm balsa. The fuselage
was then sanded to the required shape, getting rid of the ups and
downs and other rough bits.
Almost finished fuselage with
sheeting in progress
This is where I didn’t follow the plan. Instead of
making up a balsa cowl, (I hate carving and sanding block balsa), I used
polystyrene foam to shape the cowl, using a bastard file to do the initial
shaping, followed by 80 grit sandpaper then 220 grade paper to finish it
off. Once smooth it was coated with PVA glue to stop the epoxy resin from
sticking to it and soaking into the foam. It was then covered with two
layers of 4oz fibreglass cloth, wet out with laminating epoxy resin. Once
cured the surface was then coated with micro-balloons and epoxy resin
mixed up to a thick paste, this fills up the weave of the cloth and any
surface imperfections. It was then put aside for a week before sanding it
off to a smooth surface ready for painting. The cowl ends up very strong
but also very light and will probably outlast the rest of the model.
I was very tempted to make up templates and go ahead
and make up a foam wing, as this is my preferred method of building good
straight wings. But as it didn’t have them drawn on the plan, a built up
wing it had to be as it is my job to make sure the plan is correct in
every detail and that all the parts fit together correctly.
All built up wing showing the flap and aileron
|The ribs from R1 to R10 were
first drilled with a 12mm drill in line with the wing mounted
aileron servos to allow the wiring to pass through the wing. A sheet
of paper can be rolled up and made into a tube so the wiring doesn’t
get snagged when going through the ribs. This can be fitted just
before the wing halves are joined together.
The wing is built in two halves over the plan by first pinning
the spruce spars in position. The ribs from R2 outward were fitted
to the spar, using a small square to make sure they were at 90
degrees to the building surface. (The centre rib R1 is fitted at a
slight angle when the two halves are joined together to achieve the
correct dihedral angle.) As the wing tapers towards each end in cord
width and thickness, the rear of the ribs were packed to the correct
height using a strip of balsa along the trailing edge. The plan
shows two degrees washout built into the wing, and having had a few
less than pleasant experiences with high and low speed stalls with a
Spitfire and a Kittyhawk, two degrees of washout was a good idea.
The 9.5mm aileron rear spar was fitted to the rear of
the ribs, checking that the washout was still set in the wing section.
Next the 3mm false leading edge was glued into position, the 1.5mm shear
webbing was then fitted to the rear edge of the main spare, by this stage
the wing is starting to stiffen up nicely. The 3mm ply doublers for the
retracts were epoxied into position before removing the wing half from the
plan. With the wing upside down the rear 6.5mm drag spar was fitted as
well as the 6.5mm ply retract mounting plate. With the two halves finished
to this stage it was time to join them together using the ply dihedral
brace. One half was weighted down on the board with the other end being
set at 110mm above the building surface, giving 55mm dihedral under each
tip. Slow set epoxy was used to give a strong bond and allow ample time to
set it up without unwanted twists and other nasties.
Wheel wells were custom made by making moulds then
vacuum forming the sheet over the moulds.
|After the glue had cured the
wing was checked with an incidence meter just to make sure there was
still two degrees of washout in each tip. The ribs were then sanded
with a 300mm sanding T bar to take any high spots off them before
sheeting. The 1.5mm balsa sheeting was first glued together to the
required width before sanding it flat and smooth. PVA was used to
fit the sheeting in position with a few pins and rubber bands used
to hold the sheeting tight against the ribs as the glue dried. A few
mm overlap on the false leading edge was left so that it can be
sanded off before gluing on the leading edge to get a snug fit up to
the pre-shaped leading edge. The servo mounts were then fitted in
position for the ailerons, mechanical retracts and flaps. A 100mm
fibre-glass bandage was then epoxied around the centre joint, just
to be on the safe side.
A bell crank was fitted to
one of the retract rods to allow it to move at right angles to the
rod so that it activated the retractable tail wheel from the one
servo. A quick release ball coupling allowed it to be connected up
as the wing is put in position. The wing tips were made of block
balsa sanded to shape and hollowed out to save some weight, before
gluing them on the ends of the wing. The wing was fitted up to the
fuselage and the underwing radiator section was made up and fitted
into position using foam and fibreglass for the job instead of the
suggested balsa on the plan, purely a personal touch as the build-up
version is easily made if you don’t like the fibreglass idea. The
wing then just needed a final sanding before covering.
Finished retracts and air scoop.
Fixed under carriage is optional.
The ailerons and flaps were then built up separately
from the wing over the plan using ribs and sheeting with ply doublers
fitted in the control horn mounting areas. Both wing control surfaces are
hinged near the top edge, so each bottom edge was chamfered to allow the
control to move up and down the required amount.
These went together very easily, just like a very
small wing really. The horizontal stabiliser was built up by first
joining the tips, and leading and trailing edges together over the
plan. I then packed it up so that the high point of the centre rib
just touched the plan, then glued the rest of the ribs in position,
working from the centre out to the tips. Once the glue has dried,
remove it from the plan and sheet it with 1.5mm balsa. The vertical
stabiliser and the rudder and elevators were built up in the same
manner. Everything was then sanded smooth and the leading edges
rounded off nicely, ready for fitting up to the fuselage.
The elevator control rod is fully enclosed in the
fuselage so I had to manufacture a U piece which fitted into each
elevator half with an arm in the middle to connect up to the control
rod. This was made up using piano wire bent up with the arm bound
with copper wire and then sweat soldered in position.
This was then fitted to the 8mm dowel control rod
using a metal clevis and fitted into the fuselage from the rear. The
horizontal and vertical stabilisers were then epoxied into position,
making sure they were all square to the centre line of the fuselage.
The control surfaces were then hinged using Dubro medium sized
hinges, cutting the slots but not yet gluing them, this will be done
just before it is painted.
Fin and Rudder are built up then sheeted
Elevators are solid balsa, the single
torque rod is about to be fixed in place.
Rear of the fuselage with the elevator
torque rod about to be fitted to the elevator.
|It was time to put everything in position and see where
the C of G was going to be. With the 91 MAGNUM four stroke up front I
suspected a nose heavy plane and with the servo tray in the plan position
this was very much so. Being a plumber in a past life I don’t like lead
and won’t put it in a lovely aeroplane so things needed to be shifted
around so that ballast was unnecessary. This was achieved by reducing the
size of the full width wing mounting plate to allow the servos to be
mounted as far back as possible but still allow easy access to them. The
battery and receiver were also mounted under the servo tray, with this
small change the balance point worked out spot on.
I have always wanted to try panel lines and rivets and
all that stuff that makes them look like the real thing so this is how I
did it. The whole ‘plane was sanded down with a final 320-grit paper
before all the panel lines were marked in position with a soft pencil then
each panel piece was cut out of a $2.00 roll of brown paper, leaving 5mm
extra for overlap. Starting from the back and the bottom work towards the
top and the front, glue each piece on using 50/50 PVA and water. The paper
has a dull and shiny side so remember to put it on shiny side out as it
gives a much better finish. Once it’s dried, coat the paper with the
50/50 mix on the outside, let it dry and then lightly sand with 600 wet
and dry. Do this again and it’s ready for the rivets and removable
covers to be put on.
Servos were mounted as far back as possible
because of the larger engine up front, still plenty of room
The Mustang had flush rivets, so drops of PVA wouldn’t
do for rivets. After a bit of thought I came up with the idea of using the
end of a hypodermic needle ground flat. This was then pushed into the
surface without braking through the paper and rotated to form a round
dimple, the effect looked very authentic. The quick release fasteners were
copied by using a piece of 1/8th brass tube used in the same way. The
covers were cut out of light card and glued in position with PVA. A final
light coat of PVA and water, another light sand and she’s ready for the
Fully sheeted P-51 with custom cowl.
I love the look of a silver Mustang but everyone paints
them silver, so camouflage it had to be. Seeing Col and Judy Pay’s
Mustang at Avalon air show this year and taking heaps of photos of it made
it an easy choice as the colour scheme of the 3 Squadrons Mk IV Mustangs
that served in the Italian campaign could be copied from them.
I had some sample pots of satin acrylic mixed up at the
local hardware store at $6.00 per 250ml pot. The colours were chosen from
the Dulux colour chart and matched the green and dark grey spot on. Some
white toner was then just added to half a pot of the grey to lighten it up
for the underside of the ‘plane. I used an airbrush to apply the paint
only using 50ml of each colour. The acrylic dries very quickly and was
easily fuel-proofed by giving it 2 coats of satin Estapol to keep the matt
war-bird finish. Once it was dry, the decals that a sign writer friend
made up for me on his computer were fitted in position. A final coat of
estapol over these to seal the edges and to take the gloss off them
completed the job.
After refitting all the gear and the motor to the nylon
engine mount and checking and rechecking everything that has to work
properly, all was in readiness for a safe and happy first flight. The
flight pack was charged up overnight ready for a Sunday flight at my local
club near Hamilton in the Western District of Victoria.
Let’s Light the Wick
Having heard glowing reports on the latest CNC operated
factories in China that are producing the Magnum range of engines, I
contacted Chris White, the man behind Hobby Wholesale Traders, the
importer of Magnum engines. After some discussion Chris recommended the
XL91FS for the Mustang and also suggested I use one of the Magnum
aluminium spinners for it as well.
Magnum 91FS motor provided plenty of grunt for
|A few days later a package arrived at my local hobby
shop with the motor and spinner inside. The motor was bolted to the test
bench and fuelled up with the recommended mix stated in the instructions.
The main mixture needle valve was set at the recommended 2 to 2 1/2 turns,
with the low speed one left as it came out of the box. The choke flap was
closed against the venturi and the prop rotated 4 or 5 times. Releasing
the choke, the glow-driver was attached and the 14 x 6 prop flicked
backwards onto compression. The motor burst straight into life and sang
like a bird! The running-in instructions were followed by running the
motor at full throttle and controlling its speed by richening up the
mixture then leaning it out for progressively longer intervals of time.
This was done for 3 tank fulls, about 1/2 an hour total running time. This
initial running showed that the engine was a very easy to start and a
The power plant was then put away while the Mustang was
completed. This would be the real test for the Magnum, being fitted
inverted in a very tight fitting cowl with minimal air flow. The motor was
fitted to a nylon mount with a thrust plate fitted to give 2 degrees side
and 1 degree of down thrust. To provide air flow the vent under the
spinner was opened up and the cowl was cut out to allow the rocker cover
to protrude through. Air could exit through the front four scale exhaust
pipes on each side as well as the vented panels on each side and
perforations drilled behind the glow plug access hole. A quick calculation
had the correct 1 to 4 ratio of air going in and air coming out.
|The motor was fitted up the night before the big day. I
had just finished reading the latest Airborne and got an idea from Winchy’s
‘Engin-Ear’ article on oil recycling in Airborne issue number 182. As
the motor is fitted upside down I would just run the breather pipe above
the carburettor venturi and the oil will drip into it and end up out the
exhaust pipe. Finishing the job at about 10pm, I filled the tank and
primed it by holding my finger over the end of the exhaust pipe and
turning the prop over 2 or 3 times, fitted the glow driver and, as I did
on the test bench, flick it back onto compression. It again fired up
instantly and settled down to a fast idle. A few rev ups and I stopped it
so as not to upset the neighbours. A restless nights sleep was had,
thinking about things that I might have forgotten to do before the test
flight the next day. All was in readiness for the big test for both plane
Make dummy exhaust from scrap balsa and brass
Off into the Wide Blue Yonder
The local group of modellers gave the Mustang a
critical look over and gave it the big seal of approval. The strip was
mown specially for the occasion before the obligatory walk to the other
side of the strip, transmitter in hand, for a range check on the JR 388s
and Hitec supreme 7 channel receiver combination. Everything worked fine
and I couldn’t find any more excuses to delay proceedings. The motor was
again easily fired up with a quick flick and set slightly rich for the
first flight. A video camera was taken to the side of the strip to record
the event, which put extra pressure on me to make it a perfect take off.
Rates were set to low before taxiing to the edge of the strip, a quick
check to make sure all controls moved in the right direction. The throttle
was slowly increased as full elevator was held in as it built up speed
then centred as the tail wheel left the ground. Another 20 meters and a
small amount of up stick and the Mustang was airborne, flying away from
the strip without any trim changes needed at all. (Good straight building
or just plain luck!)
The plane was pulled skyward in a surprisingly short
distance for the size and weight of the airframe. It was then flown around
at various throttle settings for about ten minutes and brought back to
idle to do a stall test and a test for flap authority and both times,
throttled back instantly to cruise away. My other 4 strokes hate being
upside down and refuse to idle for more than a few seconds before cutting
out. The Magnum fitted with an OS FS plug will happily sit there idling
for a couple of minutes and still throttle up without any hesitation. The
motor pulled the Mustang around the sky with great authority and even
though it was still very tight and still set on the rich side pulled the
plane vertically for a few hundred meters before stalling out. When it is
fully loosened up it will go out of sight! Overall I must say that I am
very impressed with this motor, it starts almost by merely looking at it
and runs very smoothly indeed. For the bargain price of just under $400
from your favourite hobby ship, you will get a good reliable motor that I
am sure will give years of happy flying.
The plan is very close to scale and lends itself to
going all the way and doing a full detailing job. This is a fairly
straightforward plan to build, and you could go down a different track and
not fit the flaps or the retracts if you don’t want to. The wings could
also just be covered with a film as well. All these mods would reduce the
weight greatly and make for a very light wing loading. This would speed up
the building time considerably and still give you a very nice looking and
easy to fly war-bird. The flying characteristics are very forgiving, as it
shows no sign of tip stalling on both take-off or landing. I’m looking
forward to many missions with this great ‘plane.