We now have the answer: - The "AEROBRAT", a very
attractive realistic looking model, easy to construct
& very easy to fly, is aerobatic and also very
forgiving, so let's get started.
The best way after studying the plan thoroughly,
mark out and cut all components out, I photocopy
all components off the plan, place the photocopy
face down on the timber and with a very hot iron,
iron the back of photocopy. This process transfers
the component shape onto the timber. To make the
assembly of all the sections easier, place all components
of the sections in plastic bags and label them accordingly.
tail feathers
I chose to build the tail feathers first. Lay the
plan out on a flat building board and cover with
grease proof paper or plastic film to protect the
plan. I purchased clear vinyl from one of the "cheapie
shops" for this purpose. Lay the components
out on the plan to trial fit. I use lead sinkers
to hold the components in position. When happy with
the fit start gluing the components together, I
use C.A. type glue for this purpose; it is very
light, very strong, and very quick drying. The lead
sinkers also hold everything flat till the glue
dries.
Repeat the same steps for elevators, fin, and rudder.
When these components are assembled, lightly sand
the faces to remove any prickles or high spots.
Next with slow setting C.A., glue the soft 1.5 mm
balsa skins onto these completed frames. When glue
has set, leading and trailing edges can now be sanded
to shape. Also bevel the leading edges of rudder
and elevator. The fin can now be glued into the
tailplane making sure it is square and true. All
the hinges can now be temporally fitted and checked
for true fit and sufficient travel.
wing
Next we will start on the mainplane,
once again lay the plan out on the building board
and protect with greaseproof paper or plastic film.
Place the lower main spar and again
hold down with pins or lead weights, also do the
same with the aileron spar. Fit and glue rib W1,
making sure it is angled for correct dihedral, now
fit, and align and glue ribs W2 through to W13 with
C.A. glue. Fit and glue the upper main spar. The
cross-grained sheerwebs can now be fitted and glued
between ribs across upper and lower spars.
The upper 1.5mm balsa wing sheeting
can now be fitted from main spar to leading edge.
When the glue has set the wing half
can be removed and the same steps taken to assemble
other half of the wing. Fit the undercarriage blocks
between W3 and W5 using epoxy glue on both wing
halves.
The slot for the dihedral brace can
now be cut into ribs W1 through to W4. The two wing
halves can now be glued together with the dihedral
brace DB1 using epoxy glue. Fit and glue dihedral
brace DB2 and 12.5mm support blocks and scrap balsa
infill on front edge. The lower front 1.5mm balsa
sheeting can now be fitted from lower main spar
to leading edge.
With a long piece of sandpaper glued
to a flat piece of wood, carefully sand the leading
edge till the sheeting is flat with the ribs. The
leading edge can now be fitted and glued.
Thee aileron controls should now be
fitted, I decided to fit servo's into the outer
wing panels instead of using bell cranks. Either
way it's up to you. I also fitted a very thin walled
plastic tube through ribs to take the servo leads.
Fit balsa blocks for the hold down
bolts between ribs W1 & W2. Sand the aileron
spar and hold down blocks to the contour of the
ribs. Now fit the 1.5mm balsa aileron capping. The
remainder of the upper and lower wing sheeting can
now be fitted together with rib capping.
Chamfer the aileron leading edge spar
to the profile shape of the aileron, then lay the
1.5mm balsa sheeting over the protected plan. Glue
on leading the edge, then ribs W5a through to W13a.
Fit 3mm ply between ribs W8a & W9a for the aileron
horn mounting. Sand a chamfer on the trailing edge
of lower sheet to line up with upper surface of
ribs, then fit upper 1.5mm balsa sheet. Repeat above
steps for other aileron. I leave the drilling and
fitting of the wing locating dowels until the wing
is being fitted to the fuselage.
The wing tips are laminated with 12mm
balsa and cut roughly to shape then glue them to
wing and sand to final shape.
Fuselage
Assemble the fuselage frames F3, F6,
F7, & F8 as per the plan. Lay the fuselage sides
on a flat building board with the tops together.
Fit and glue 6.5mm X 3mm spruce longerons, fit and
glue DB1 1.5mm ply doublers, fit and glue rear fuselage
doublers. Fit and glue 12.5mm balsa triangle longerons.
If you have a fuselage jig it makes
the assembly a lot easier. I will describe my method
using the jig.
The fuselage can be assembled in the
jig and aligned without glue to check the fit of
every part. When happy with the alignment and fit,
CA glue can be applied to all joints. It will wick
in and make a very strong joint. Epoxy was used
for 12.5mm balsa triangle to former F1. The 3.5mm
balsa tank floor and sides can now be glued into
position. Fit the 6.5mm square stringers on upper
deckings. Fit and glue fin/tailplane assembly, checking
for correct alignment.
Position the engine mounts and a tapered
block to give correct side & down thrust with
the centre of the propeller on the centre line of
the fuselage. Mark and drill holes through former
F1. Now fit and glue blind nuts on the inside of
the firewall. The upper 3mm balsa sheeting can now
be fitted and sanded. Remove the fuselage from the
jig and fit bottom 6.5mm square balsa stringers
and lower rear fuselage 3mm balsa sheeting.
Fit the wing to the fuselage leaving
0.4mm gap between the front of the wing & former
F3, also the top of wing to fuselage. I used scrap
pieces of 0.4mm ply for this purpose. I use rubber
bands to hold the wing in position. Check the incidence
of the main wing to centre line & also the tailplane
incidence. Adjust the wing seat till the correct
incidence and alignment is attained.
Drill a 6.5mm holes through former
F3 into the leading edge of the wing & insert
wing dowels but don't glue them at this stage. Now
drill 6.5mm holes through the rear wing mounting
plate [W M]. Fit and glue softwood tapered packing
blocks and blind nuts. The cockpit floor can now
be fitted & glued into place. Remove the wing
from the fuselage & permanently glue wing retaining
dowels into the front of the wing.
Cover top centre section of wing with
gladwrap or wax paper & refit wing, sandwiching
.4mm ply fillet between bottom. Apply CA glue along
the joint between wing fillet and fuselage. Glue
in contoured gussets between the base and fuselage
sides. Fit and glue trailing edge fillet.
Remove wing from fuselage, and then
lightly sand the upper edge of the fillet to contour
the curve. Fit and glue soft 1.5mm balsa sheet on
fillet from F4 back. I used super light balsa filler
to build up the front part of the fillet to match
the rear section. Refit the wing then fit and glue
the front bottom of fuselage. Fit scrap balsa infils
on bottom of wing to match bottom of fuselage.
The cowl is built up from 12.5mm
soft balsa sheet, carved & sanded to shape.
Completely sand complete model prior to covering.
I chose to dope & tissue the fuselage, tailplane;
fin, rudder & elevator then painted with pressure
pack enamel. The wings were covered in solarfilm.
Fit out the cockpit as desired,
a nice instrument panel here adds to the overall
appearance. Now fit canopy.
Motor
The motor chosen for the prototype
is an ASP61 2 stroke with a Pitts type muffler.
Install motor, fuel tank, radio gear, push rods
& horns, undercarriage, & tail-wheel at
this stage.
Controls were set with the following
throws. Elevator 12mm up & down, rudder set
at 40mm left & 40mm right. Ailerons were set
at 15mm up &15mm down. Travel was measured at
fuselage end of control surfaces.
Lets Fly
The "AEROBRAT" should
be now ready to eat up some sky, so off to the local
field to test this bird.
All systems were double checked,
the model fuelled up and the engine started. A range
check with engine running, all systems rechecked
then the model was taxied up and down the strip
to check ground handling, so far so good. Now to
test the handling in the air.
With the AEROBRAT lined up on the runway the throttle
was slowly opened the speed increased, Travelling
straight down the strip with no control input at
about 3/4 throttle it rose from terra firma slowly
climbing out, wings perfectly level, course straight,
I stood there amazed watching the AEROBRAT flying
by itself, completely hands off. Back to reality
I'd better turn this bird around before it gets
out of sight. Response to control is very smooth
but positive. After a few circuits for the camera
and to get the feel of it a few aerobatics were
tried, no problems, this bird flies on rails &
just keeps going where you point it. Now for some
height to check the stall characteristics. With
the throttle closed as the speed drops off up elevator
is slowly applied the tail drops slightly, at the
point of stall, the nose drops but the wings remain
level and very predictable.
After about 1/2 hour in the air & other pilots
checking it out, I lined up for a landing, low power
the angle of decent was excellent with good control.
The mains touched down followed shortly by the tailwheel.
A stunning performance I have never had a model
fly off the drawing board without trim adjustments
before, I always imagined other pilots were telling
a fisherman's story, but it does happen.
SUMMARY
This "AEROBRAT" is a
pussycat with bite, a good looker, and it looks
like a real aircraft. It would make a very good
second or third model for new or experienced fliers.
A very rewarding model.
