To save weight at the rear, select light stiff timber for the
empennage. These were built over the plan as open frame structures
then sheeted both sides. Hint: make the fin
the full depth of the fuselage to give more secure mounting
and to more accurately ensure correct tailplane incidence.
After much deliberation I decided to build
the fuselage on the board from the bottom up. I cut out all
parts for the sides, bulkheads and doublers.
Hint: cut S2 3mm longer than shown to allow for front edge to
Glue 6.5mm sq longerons to S1, 2 &
3. Glue fuselage doubler and wing seat on S1; making sure you
have right and left sides. After cutting out the fuselage bottom
the positions for the bulkheads and doublers were marked on
sides and bottom.
Hint: use the fuselage side view to mark bulkhead
position on fuselage bottom or they will slightly out as the
bulkheads not at 90 deg to the bottom.
The fuselage bottom was tack glued to the building board. The
rear edges of F4 should be chamfered. Make sure F1, F3, F4 (I
glued F2 in place when the engine pod was installed but it could
be done now) are all in place before gluing any of them to the
fuselage sides and bottom. I did this for the trail fit but
left F3 out in the glue step and found it had to be cut in half
to get it in place past FS1 – not very clever.
Chamfer S2 at the front edge to butt against F4 then cut at
rear so S2 overlaps F5 by 1.5mm. Fit FS3 brace in position before
S2 is glued to S1 otherwise it is impossible to get FS3 in place
– as I found out! Now glue S3 in place. Elevator and rudder
push rods should be installed now (I used closed loop cables
on rudder and separate ny-rods for each elevator half). The
fin is best installed while the fuselage is pinned down to ensure
it is properly vertical. Fuselage top sheeting and WM is now
glued in place.
Hint: even though the fuselage has lots of room access is difficult
through the wing mount. If desired a hatch could be cut around
the rear top window or the front windscreen could be made removable.
Engine and mount combination should be chosen at this point
in case engine pod sides (T2) need to be lengthened or shortened.
Remember to make R & L sides as this sets right and
left thrust and also down thrust. Amounts shown on plan
prove to be sufficient during test flying.
Remember also to offset engine mount
to left of bulkhead centre line to ensure that engine crankshaft
exits the cowl in the centre. Assemble pod then glue in place
in fuselage. (The engine I used was a new in box YS-53 FS provided
by my friend Shane. The engine was run for one hour on a test
stand before being fitted to the aircraft.)
The canopy was made from a block temporarily
glued in place and shaped then removed and hollowed out and
refitted. Fuel proof everything forward of F3 before gluing
this on as it is easier to do at this point.
The cowl is made from soft
12mm sheet temporarily glued in place and shaped, then removed
and cowl mounting blocks fitted.
When building the cowl make sure there is plenty of area
for cooling air to exit. The left radiator area was blocked
off as air going in here does nothing to cool the engine
except it could create an air dam which will very quickly
cook your engine (I learnt this a long time ago from bitter
experience). The exit area should be about 2.5 times (or
more) the intake area.
Wing is conventional built-up spar and
rib construction, fully sheeted. It could be made using balsa covered
foam core if desired. A ply template was made to the airfoil section
and this was used to cut the ribs out by pinning the sheet to the
cutting board and cutting around with model knife. You could also
use the “Sandwich Method”.
The centre section was assembled over the plan including the dihedral
braces. Then removed and wing blocks and top/bottom sheeting added.
Hint: make sure holes are drilled for wing bolts
and the holes for flap/aileron leads are cut into ribs before adding
|The right and left wing panels were assembled over
the plan. The wing bottom skins were made sufficiently large enough
to go from leading edge to aileron trailing edge. The skin was
pinned to the building board and the wing panel was glued in place.
The flap/aileron LE and riblets were added at this point. A slot
should be cut in the first 3 ribs between the spars to allow for
the dihedral brace.
At this point strut mounting hardware should be added, I deviated
from the method shown on the plan although it would work just
as well except it made it a little more difficult to finish around.
A ply block was glued in place at the position shown, over the
bottom spar and a T nut (6-32) was fitted. The same method was
used for the mounting point in the fuselage with the strut being
screw on from below the fuselage. I also made the elevator support
struts removable for the same reason. Make up wing top sheeting,
it only needs to be wide enough to go from the false leading edge
to the rear spar. The flap/ailerons were cut from the rest of
the wing and the top sheeting added to these. The wing panels
are now glued to the centre section. The method I used was to
first tack glue a block at the tip of each panel to hold that
end the correct distance off the board, then the centre section
was pinned down flat and the panel epoxied to it. When dry the
other panel was added.
The temporary block is now removed and one wing panel
pinned down while supporting the other, (no wash out was used), and
glue top wing skin on; repeat for the other panel. Leading edge is
now added and shaped, the wing tips are also added and shaped. The
ailerons and flaps are now fitted to each panel and hinged, then separated
from each other.
The wing struts are made from two pieces of spruce epoxied together
with a strip of brass sheet sandwiched in-between at each end. When
dry these were sanded to a streamlined section then holes were drilled
through each end and toothpicks were glued through these to ensure
the strips do not pull out as the struts are functional.
The flap and aileron servo trays were now made and fitted in position.
Hint: standard size servo’s are a tight squeeze so smaller ones
could be used.
My preference was to tissue and dope then paint, but to
save time while various friends were searching the net for colour
schemes and markings I decided to use one of the paintable iron-on
films. This would allow me to use whatever colour scheme may come
to light. As it turned out we were unable to locate any information
re markings and colours so the aircraft was painted all over with
aluminium coloured high temperature engine enamel. The windows
were black sticky back film. A red star was added to each side
of the rudder and two thin red stripes were placed down each side
of the fuselage. The plan designation (SL-90) were added to the
wings - one set on top left wing panel and the other on the bottom
right. This completed the colour scheme and in flight looks good.
Elevator - 20mm up; 25mm down
With the aircraft finished and ready
to fly it was balanced and control throws were set up as follows :-
Aileron - 17mm up; 12 down
Rudder - 30mm each way
Flap - 22mm full down (the way these were hinged
limited the travel available, a bit more could be used if desired)
Weight – 3.7kg (8lbs 1oz)
|At the invitation of Brian Winch (Airborne Engineer)
flight-testing was carried out at his club field and he also took
the first flight pictures.
On arrival at the field we found it was open and flat and the
weather conditions hot, dry and calm. After assembling the aircraft
a series of ground shots were taken. It was now time for the first
flight. On taxiing out the first glitch appeared, full up elevator
would not stop the aircraft nosing over (I had added some lead
to the nose to ensure the CG was in a safe position). The undercarriage
was bent forward and the second attempt took place. We got to
the strip OK this time but on take-off enough up elevator was
not held in and the aircraft nosed over again (bugger!!!!). On
the next attempt full elevator was held in until a fair bit of
speed was gained then eased off and the plane ran along tail-up
(looked great) and gently lifted off and climbed out smoothly.
A couple of circuits were made while minor trim corrections were
made to enable straight and level flight (did not need much).
The aircraft was then brought in low, slow and close so that the
flight pics could be taken.
At height the stall was tested and with low throttle
and full elevator the plane just mushed straight ahead (did not drop
a wing, unless rudder was applied which lead to a gentle spiral dive).
The flaps were also tested; these proved to be effective with the
travel available. If applied with too much airspeed the plane zoomed
gently then settled into a slight nose-down attitude and slowed down.
If applied at normal approach speed the plane just assumed the slight
nose down attitude with no zoom. The landing was no problem and with
the flaps down it occurred at a very low airspeed on the main wheels
and rolled out perfectly. On the next flight the aircraft’s
aerobatic capabilities were tested –loops, rolls and inverted
flight were accomplished easily but it would not spin.
The lead was removed from the cowl and more flights
followed (still won’t spin with the rudder travel used). The
CG as shown on the plan combined with the suggested control throws
should result in a smooth flying aeroplane. The YS-53 provided sufficient
power while not being overpowered. Those present at the test flights
were impressed with its stability and performance.
All in all a very enjoyable aircraft to fly.