The
elegant fuselage shows several clever refinements. The front section hosts
the compact Mid-West rotary engine, which is installed from the top
between the carbon fibre engine carriers. The upper cowling, with its
shark-like cooling gills, is held by two spring steel wires, which are
pushed in from the front side and locked by snapping them behind a safety
plate. Beneath the engine, the air intake and exhaust section is covered
with a removable cover. In between engine and cockpit is a ballistic
recovery system, mandatory for micro lights in Germany. In an emergency,
it fires upwards through a lid held on only by clear adhesive tape. The
cockpit itself forms a modern safety cell, the basic idea of which has
been borrowed from Formula 1 racing car designers. Into the outer
honeycomb structure of the fuselage, an Aramid fibre cell is fitted. The
carbon fibre seat-pan with its stiff backrest to protect the pilot's spine
can be removed to enable the control systems to be reached. Behind it, in
the rear fuselage tube, a baggage compartment can be fitted, its loading
capacity limited by the centre of gravity, depending on the pilot's weight
(he sits behind the C of G). The pilot is strapped to the safety cell by a
modern four-point-harness, and the cell is directly fixed to the BRS. This
is a very safe cockpit, professionally manufactured.
The electrically retractable main undercarriage
is hinged at the fuselage and rotates backwards around a diagonal axis.
While the 'legs' remain outside at the wing root bottom, the wheels with
their hydraulic disc brakes disappear almost completely into wells which
are half in the wing and half in the fuselage. Doors screwed to the legs
cover the wheels when retracted. The small covered tail wheel is
double-sprung a spring acting telescopically in the fuselage takes the
vertical loads, and a rubber block just above the wheel allows it to swing
backwards when small obstacles on the ground are hit.
The control system is simple and
well-thought-out. Elevator and ailerons are operated by pushrods, the
rudder by cables and the flaps via a torsional drive by an electric motor
in the fuselage. The spring elevator trim is also electrically actuated.
Like a glider, the Silence can be rigged and derigged for hangaring or
transport in only ten minutes. Rigging is simple, and, if the fuel tanks
are empty, may be carried out by only one person. Once the wings are slid
into their slots in the fuselage, one eccentric bolt for each wing
underneath the seat pan serves to pull the wings in by swinging the bolt's
lever behind the securing spring metal sheet hook. The torsional drive of
the flaps connects automatically during assembly, while the aileron
pushrods have to be connected to the lower end of the stick by bolts with
securing Fokker safety pins. The fuel hoses, the wires of the fuel
indicators of both wings and the pitot pressure hose from the right wing
are connected by reaching through the undercarriage openings below the
fuselage. Finally, the tail plane halves are slid onto the aluminium tube
spar ends at the fuselage and secured by a spring steel wire pushed in
from behind, the elevator connecting automatically via a hexagon head
torsional link. If the rudder has also been taken off, it is inserted from
above and secured by two Fokker pins. A look underneath the cowling to
check whether there is enough cooling liquid and oil in the reservoirs
(the Mid West Harrier uses about 2.5% of the fuel consumed as 'lost
greasing oil'), before refuelling the tanks, and the Silence is ready to
fly.
The cockpit is easily entered from the front side
by stepping onto the tire and then the narrow fuselage section of the wing
root. After pushing forward the canopy locking lever at the outside
fuselage surface, the canopy can be swung open towards the right side. The
pilot then slides easily into the well-upholstered,
ergonomically-designed, but non-adjustable seat: there is enough space
here even for tall pilots. A head-rest had not yet been installed on the
one I saw, but this can easily be done. The rudder pedals can be adjusted
separately by turning two knobs in the instrument panel: the designers are
considering connecting these two knobs together to avoid asymmetric
settings. The cockpit's large instrument panel is well equipped. The BRS
handle at the front frame is within easy reach and can be secured with a
lock. At the left cockpit wall, there is one small fuel cock. In spite of
the fact that there are two tanks, one fuel cock is enough because the
tanks are inter-connected.
The engine
takes the fuel from the left tank, which has no ventilation and is
refilled from the ventilated right tank. This system is very simple, but
comes with the disadvantage of asymmetric wing loading during flight.
However, as the tanks are close to the fuselage, this is not expected to
greatly affect the flying characteristics. Nevertheless, the manufacturer
plans to install separate fuel cocks in later aircraft to preclude the
possibility of asymmetric wing loading. The throttle is placed in the spot
where you would find the pilot's left hand in a relaxed position. The two
buttons for trim operation and also the transmitter button are placed on
top of a fighter-like control stick. The trim setting is indicated by an
electronic instrument. A knob in the instrument panel serves to set the
flaps to 0, 10, 20 or 30°, and a covered switch besides it operates the
undercarriage. In case of a failure of the electrical system, there is a
red emergency extension handle between the pilot's legs. If this handle is
pulled, the undercarriage is disconnected from its spindle drive and then
pulled out, assisted by gravity, until it is in the 'down and locked'
position. The status of the undercarriage (up, in transit and down) is
indicated by LEDs, other LEDs warn if the engine is operated outside its
normal parameters, although there are also conventional instruments
fitted.
When I test-flew the
Silence V2 at Bielefeld-Windelsbleiche airfield on September 5, 2002, it
was not yet in final serial condition in fact, it had only made its maiden
flight the day before. The wheel covers for the undercarriage legs were
not yet fixed in place and the propeller was still a shortened, fixed
two-blade Helix unit. The planned three-blade electrically adjustable
Silence propeller, already used on the first prototype where it rotates
right-hand, was not yet available in the left-hand rotating version needed
for the Mid-West. Finally, the engine power was not yet fully available,
and resonance problems still required some adjustment to the air supply
system.
On closing the canopy, it can be locked by
pushing backwards the small knob on the left cockpit wall. The main switch
and starter function are united in an ignition key lock similar to that on
a car. After switching the key to 'ON', the two ignition switches and the
two fuel pump switches beside the key are switched on. With the Mid-West
engine nothing runs without fuel pressure, so the second pump is a
mandatory safety feature for take-off and landing. With the throttle set
to a little above idle, the engine starts immediately on turning the key
to the 'start' position. It runs a bit rough below 4,000rpm and only
becomes smooth above 4,000rpm typical behaviour of one-disc rotary engines.
To protect the ears from the relatively high frequency engine noise, a
good headset is recommended. The time needed to warm up is short, and
after checking the ignition and fuel pumps, the Silence is ready for
take-off. During taxiing I found the separate toe brakes effective and
easy-to-operate, and the tail wheel, spring-connected to the rudder, easy
to steer. By using differential braking, quite tight turns are possible.
My eyes were just at the height of the narrow front cowling tip, so I did
not need to taxi in a zigzag to get a decent view.
This Silence weighs
exactly 441lb empty. With me in the cockpit and 11 Imp gal of fuel
(standard 92 oct car fuel), it weighs 683lb: even with full tanks I would
still be below the maximum permitted 750lb. The centre of gravity is in
the forward range. For take-off, I turn the flaps knob to 10° and set the
trim to neutral. After pushing the throttle forwards until I reach 1cm
behind the front stop (because of the resonance problem mentioned earlier,
the engine starts coughing with more throttle), I accelerate quickly with
the stick held slightly forward.
As soon as the tail wheel lifts off, I
need a small amount of left rudder to compensate for the propeller torque.
At 43kts it lifts off, and I let it accelerate to 60kts before starting to
climb. At a safe height I retract the undercarriage, set the flaps to 0°
and switch the second fuel pump off. In this clean configuration, I find
the best climb rate at 65kts, and although the engine performance is not
fully available it climbs at about 790ft/min. With the engine problem
solved, I expect the aircraft to climb in excess of 1,000ft/min. The
heavier prototype with the 65hp engine which I flew in the spring climbed
at nearly 1,180ft/min. Trimmed to the best climb speed of 65kts, only a
small amount of left rudder is needed to keep it flying straight. On
reaching 2,500ft, the engine's three minutes of permitted full power
operation have passed and the cooling liquid temperature comes close to
its maximum. I reduce the power to the maximum continuous setting of
7,100rpm and continue climbing at 70kts, with the result that the
temperatures remain in the green arc.
During
cruise flight, this rpm limit is already reached at 86kt with the current
Helix propeller. The prototype, equipped with the Silence-developed
three-blade variable pitch propeller, reaches more than 108kts with no
problems. In this aircraft, and probably also the Mid West-powered ones
equipped with the new propeller, the 17.6 Imp gal of fuel makes possible
620-mile flights at a cruise speed of around 100kts.
I am particularly impressed with the handling of
this little aircraft. The control forces remain very low, though positive,
for just about the whole speed range. The Vne of the 'Experimental'
version is calculated as 162kts, though it is only 140kts for the micro
light version due to the limited operating speed of the BRS. The
sensitivity of the Silence gives the impression of flying a
fully-aerobatic aircraft, and trimmed to cruise speed it flies beautifully
stable in the 'hands off' position. However, if the right fuel tank is
empty and the left one full, a small amount of aileron deflection is
needed to keep the wings level.
These excellent general handling
characteristics are further supported by the excellent view through the
big canopy and the good fresh air supply through the nozzles in the front
cockpit frame. Cabin heating is also installed, though in the current warm
weather I feel disinclined to test its efficiency. The only thing I miss
is a small 'direct-vision' panel in the canopy I once experienced outside
cabin icing when descending with a cold glider through an inversion layer
into warm, humid air, and opening this window then saved me from being
'blind' and lost... How does such an elliptic, fully-symmetric wing behave
when it is stalled?
I was quite astonished at the gentleness of the
stall. With the engine running at idle and the flaps at 0°, the Silence's
controls start feeling soft at 43kts: at 40kts the stall starts buffeting
and speed increases to 43kts again in the staggering stall, where it can
be held by using the rudder. With the elevator further back, staggering
increases and I start feeling as if I am sitting on a wild horse, though I
can still prevent it from departing into spin with the rudder. I think
this effect is caused by the turbulence separating behind the wing root
(which was probably stronger than usual due to the uncovered retracted
wheels underneath the wing) hitting the tail. With its forward C of G
position, the Silence starts dropping the nose, but immediately the
airflow comes back to the tail plane, the game starts again.
Setting the flaps results in the same
behaviour,
with the minimum indicated speed decreasing by about 2kts per 10° of flaps
set. With full throttle, the indicated speeds are again 1kt lower. The ASI
of this aircraft had not yet been calibrated and seems to over-indicate
slightly with the prototype, a calibrated airspeed of 35kts at 750lb AUW
has been demonstrated during the certification. When I flew this prototype
with an aft C of G and the wheel covers fitted, the staggering was less
pronounced. It did try to drop a wing, although the incipient spin could
be stopped immediately by relaxing the stick and applying opposite rudder.
The Silence shows excellent control harmony. With the engine running at
idle and trimmed to 70kts, it raises the nose and starts climbing at 65kts
once the throttle is opened fully. Setting the flaps (below 65kts) to
different positions does not really influence the trimmed speed. Its roll
rate is impressive: when full rudder and aileron are applied, even at the
slow speed of 59kts it rolls from 45° to 45° bank within 1.5 seconds
without side slipping. This roll rate is practically aerobatic, and care
has to be taken not to stall the lower wing when applying full aileron and
not enough rudder against the rolling direction. But even in such a
situation the Silence is straightforward a kick into the rudder against
the rotation direction stops the initial snap roll immediately.
The
manoeuvring speed, up to which full control deflections are permitted, is
97kts, and the maximum allowed speed to fly through stronger gusts is 119
kts, clearly above cruising speed. Compared to other fast micro lights, in
which you should cut your flying speed considerably when flying on a day
with strong thermals, this gives a good margin of safety. Of course, these
flying characteristics may tempt some to try a few aerobatics. However,
the rules of the micro light category set clear limits aerobatic are
generally prohibited in these aircraft. Anyone with ambitions in the
direction of aerobatics could always buy the strengthened kit Silence
Aircraft offers. If the builder completes it at home and certifies it as
an aerobatic aircraft in the 'Experimental' category, there are no limits
to gambolling around the sky (and probably outclassing the Tipsy Nippers
and RF-4s you can hardly ever find in the second-hand market...).
The electric flap drive acts rapidly. Within
three seconds the flaps reach their maximum of 30°: the undercarriage
needs 7.5 seconds for retraction and 9 seconds for extension. The maximum
speed in landing configuration with the flaps set to 30° is limited to
65kts. Under calm weather conditions, I find an approach speed of 56kts
comfortable and perfectly safe. Before landing, I switch the second fuel
pump on again. The flaps are effective, and with the engine running at
idle it is easy to control the glide path. Side slipping is very easy and
effective, permitting very steep approaches and further improving the
pilot's (already good) view of the runway it also feels as if it's the
right way to land an aircraft resembling a Spitfire!
Provided you stopped side slipping after holding
the Silence off until the nose was at the correct attitude, and that you
centralized the rudder before the wheels touched the ground in a proper
three-point attitude, the Silence will land gently. If you do not follow
the advice given above, it will 'dance'
a little on the runway, due to the un-damped, but
sufficiently sprung undercarriage. Even a strong or gusty crosswind causes
no problems, though some tail dragger experience is useful to produce a
good landing on a concrete runway (and to keep the aircraft there
afterwards!) For new Silence pilots, I would recommend making your first
few landings on a more forgiving grass strip. The rudder has to be used
carefully during the ground run the separate toe-operated hydraulic disc
brakes are easy to use and quite powerful. As the main undercarriage is
well in front of the C of G, the risk of nosing over is relatively low.
As a single seater of the upper micro light
class, the Silence is not for everyone, and it does require the pilot to
have a certain level of tail dragger experience. Flying it is enormous fun
as it offers a high level of performance combined with excellent safety
features. The Mid West 'Harrier' single disc rotary engine suits its slim
appearance, though it consumes a relatively large amount of fuel and is
not the smoothest of engines, particularly at low rpm. With this in mind,
Silence Aircraft is considering equipping the aircraft with the 75hp
Walther Minor IIIB air-cooled in-line four cylinder engine. Used as a
micro light, the Silence's operational range is fairly limited by the
definition of this aircraft category however strengthened versions
certified in the 'Experimental' category, built at home from a
pre-fabricated kit, may be used for aerobatics and show the full range of
this design's abilities. The great interest that these first 'little
Spitfires' attracted whenever they appeared demonstrates clearly that a
large market is out there waiting for the Silence!
On reaching 2,500ft, the engine's three minutes
of permitted full power operation up to 7,750rpm have passed, and the
cooling liquid temperature comes close to its maximum. Reducing the power
setting to the permanently permitted 7,100rpm and continuing climbing at
70kts results in the temperatures staying in the green arc. Right Straight
from the box the kit is well-produced and has the benefit of considerable
prefabrication.
specifications
powerplant
propeller
length
height
wing span
wing area
seats
empty weight
useful load
gross weight
fuel capacity
range |
80 HP
JABIRU 2200
2.blade
GT propeller
x
x
x
x
1
500
lb.
x
880
lb
21 US
gal
800 nm |
performance
takeoff distance,
ground roll
rate of climb
max speed
cruise speed
landing distance, ground roll
service ceiling |
x
1500 ft/min
x
127
kts
x
x |
limiting and recommended speeds
design manoeuvring speed (Va)
never exceed speed (Vne)
stall, power off (Vsl)
landing approach speed |
135
kts
196
kts
41
kts
x |
All specifications are based on manufacturer's
calculations
|