Powered with two Rolls Royce Merlin engines the
Mosquito's performance far exceeded expectations.
Having a top speed of over 600kph it was faster
than some single engined fighters of its time.
It first flew in 1941 and a total of 7,781 were
built including some which were built at Bankstown
in Australia.
Many victorious combat missions were attributed
to the Mosquito squadrons making it one of the most
famous warbirds of all time. Airborne now has released
it 1:7.5 scale model of the Mosquito bomber.
At a sizeable 2.2 metre wingspan it only requires
two .46 two stroke engines to give it all the necessary
power for sensational scale realism. Being of conventional
balsa/ply construction it will appeal to the dedicated,
experienced scale builder who thrives on praise
and attention at large scale or warbird rally's.
This model is a stand out winner!
The prototype I have built for Airborne is modelled
on the Mosquito based at No. 1 RAAF Squadron, Laubaun,
North Borneo in mid 1945. I have only built one
other twin engined model, which was Airborne's de
Havilland Comet, and found it a very rewarding plane
to fly so I welcomed the opportunity to build one
of my all time favourites, the DH98 Mosquito.
building the model
Study the plans carefully and prepare yourself
mentally for a major project.
Great care and accuracy must be taken particularly
with thrust lines, washout and wing incidences.
Any warps or bows in the structure will affect its
crucial flight performance.
Make a kit of all the ply and balsa components and
group them into their respective areas.
The Wing
The wing incorporates split flaps and ailerons
with their respective servos as well as the engine
nacelles and retracts. It is quite a heavy load
for a sharply tapered wing, therefore careful wood
selection is very important. Use strong spruce for
the main spar and a good quality ply for the wing
brace. Build one side at a time. When one side is
finished, build the other around the wing brace
with correct dihedral as marked on the the plan.
I covered the plan with cling wrap and then pinned
down the spruce spars, aileron and flap spars over
the plan.
I then laid all the ribs, W1 - W13 and dihedral
brace DB into position (note 2O washout) and placed
the top spar over them before gluing them together
with cyano. Add shear webbing between W6 - W13.
Glue the false leading edge onto the ribs. Note
that the leading edge protrudes into the centre
wing section between W1 - W14.
Shape the balsa wedge blocks for the rear centre
wing section, do not drill the wing bolt holes just
yet. Also add the wedges for ailerons and flaps.
Prepare the 1.5mm balsa skin by gluing the sheets
together on the bench using cyano with tape behind
the join. I find this a good quick method to use.
Sand the sheets flat before gluing them to the top
surface of the wing panels. When set lift the wing
off the board. Add the square balsa pieces for the
servo bays used for the ailerons and flaps.
Now sheet the wing entirely, bottom side first,
then double check the 2O washout before locking
in the wing structure with the top skin.
Add the leading edge and wing tip blocks then sand
to shape. Carefully cut away the ailerons and flaps.
I used small Dubro hinges with metal pins to hinge
all the control surfaces. Take care with the flap
hinges as they are very close to the bottom skin.
Angle them into the spar for better security.
The Engine Nacelles
Mark out the nacelle position on the wings. Glue
all the formers to the bottom of the wing with the
retract mounting blocks epoxied into place. Build
up the plywood engine mounting boxes, which also
become fuel tank bays rear of the firewall.
Note: Left engine thrust line is 0O, while the
right engine has a 2 1/2O right thrust.
The remainder of the engine nacelle and engine cowl
is planked with 3mm balsa. the hatch covers and
top rear nacelles are shaped from balsa block. Carve
and shape the exhaust shrouds from balsa. I made
all the doors for the wheel bays but did not use
them on the initial flights due to the complexity
of the closing mechanism (not shown on plan). They
would however give the model a really good scale
finishing touch.
After sanding and shaping the nacelles I mounted
the engine, throttle servos and the retracts themselves.
The engines I used were two OS .46FX two strokes
with standard mufflers.
The retracts were Custom Retract units from Peter
Gow (see advertisement in this issue) as drawn on
the plan. I utilised 180mm Dubro fuel tanks on my
model with three fuel lines to the tanks.
Fuel proof the insides of nacelles, the firewalls
and fuel tank bays.
The fuselage is constructed in two half shells then
glued together. With the engines mounted in the
wing, the fuselage is relatively simple to construct.
Frame up the left fuselage side over the plan.
With the doubler glued onto F5, add the longerons
and wing and tailplane saddles to the formers. Plank
the frames. Build up the belly pan (F5a - F10) as
part of the fuselage then cut away after completion
of smoothing and shaping of the planks.
The tailcone is made up of balsa block, hollowed
out for the retractable tail wheel unit.
Trace the plan (fuselage side view) or brush cooking
oil onto the plan to make it semi transparent to
give you a mirror image. Repeat the construction
procedure for the right side of the fuselage.
Before gluing the two shells together install the
control rods to the rudder, elevator and tail wheel
retract unit.
Glue the two fuselage halves together checking for
true alignment.
Decide on whether you will use the clear pre-formed
plastic nose cone which is available from Airborne
or make a solid balsa front end, depending on which
Mosquito variant you wish to build.
Epoxy the wing mounting plate into the fuselage.
Position the wing accurately on to the fuselage
and drill and tap for the nylon wing bolts and blind
nuts.
The belly pan under the wing is detachable and held
on with spring latches. This allows for access to
wing mounting bolts and radio gear which must be
kept as far forward as possible to aid in balancing
the model.
Tail Surfaces
The tail plane and fin are of built up construction
of balsa then covered with 1.5mm sheet. This is
a simple and lightweight method but take care to
keep the tailplane straight. The tailplane can now
be fitted to the fuselage, carefully checking the
incidence with the plan. The elevators and rudder
have a central sheet with ribs added to the outer
sides. Sand to shape and hinge onto the tailplane
and fin respectively.
Covering & Finishing
After the entire airframe was finished I covered
it with 21g fibreglass cloth (personal choice only)
with the exception of the rudder and elevators which
were covered with Sig Coverall.
I then hinged and pinned all the flying surfaces.
I applied the fibreglass cloth with dope and then,
to fill the weave, I thinned the dope and sprayed
8 to 10 coats before priming the airframe. I then
pained the underside of the airframe with the light
blue. I then proceeded to mask and paint the remainder
of the airframe with the green base coat. I then
sprayed the tan camouflage markings before applying
the roundels and lettering. All the roundels and
lettering are cut in vinyl. The airframe was then
sprayed with a two pack clear with a matting agent
for the scale effect.
Radio gear used was all JR 577 servos with the
exception of 371’s on the throttle and a 591
on the elevator. I used one servo for each aileron,
flap and rudder and separate throttle servos. I
used Dubro servo savers to adjust the throttle servos
to make synchronising the transition from idle to
full throttle easier. I put the aileron and flap
servos as close as possible to the surface and only
needed short pushrods. the rudder and elevator servos
were as far forward as possible and I used carbon
tube as their pushrods. I used a Dubro adjustable
valve for the retracts and a medium tank.
The propellers I used were APC 11x7’s. The
engines had the baffle removed from the muffler
for better performance. This was a good combination
even with the 100mm spinners. The engines run at
12,000rpm and sound fantastic as they produce the
harmonies of a twin.
The all up weight of the model is 6.3kg with the
balance point at 25% of the wing root chord.
Flying
The day arrived for the test flight,
somewhat windy but warm and fine. I did a test run
of the engines and tuned them to run at similar
revs at full throttle. I then cycled the retracts
a few times to check how many operations I would
get from a full tank. After refilling the retracts
tank I then taxied the Mosquito and went to full
throttle to see the tendencies it had.
