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SEABIRD Seeker-360
aircraft report (text
by manufacturer 2001)
The Seeker 360 is the helicopter alternative. It
is a two-seat observation and surveillance aircraft with excellent visibility. It has been
designed to provide good handling characteristics at low speeds and docile stall behavior
the aircraft has ample power to provide additional safety at low levels and has good
turbulence riding capabilities, which along with a lack of propeller slipstream gives high
crew comfort levels. The fuselage gives excellent crew protection and the sturdy nature of
the structure will ensure long aircraft lives in adverse operating conditions.
The Seeker 360 is a surprising aeroplane. It is even
more surprising to find that a completely new General Aviation Aircraft has, in fact, been
designed and certificated - not just in Australia - but anywhere (including the US), these
days. This level of certification makes the Seeker acceptable to worldwide
Regulatory Authorities, and enables it to carry out aerial work and charter operations
that lower category aircraft cannot legally undertake.
The Seeker is certificated to FAR 23 (the later U.S. standard which superseded CAR 3, the
standard to which most of the single engine Cessnas, Beechcraft and Pipers comply).
In fact, the Seeker currently meets FAR 23 Amendment 34, which puts it on a par with just
about any other contemporary light aircraft.
Because of its unusual configuration, the Seeker also has a full fatigue analysis, which
is a requirement of FAR 23 Amendment 38 - it has a good, long fatigue life and there are
no nasty surprises in this area.
Secondly, the Seeker has a surprisingly high build standard - pushrod controls for aileron
and elevator, and corrosion resistant grades of alloy in sheet metal areas: it has a
stout welded steel tube cabin "cage", and an oleo-leg on the tailwheel - not a
common feature on an aircraft in this size range.
TYPE:
Two-seat observation and surveillance aircraft.
WINGS:
Strut braced high-wing monoplane, with NACA 63£2 15 (modified) aerofoil section with
constant chord. Dihedral 2° from root. Incidence 4° at root, I° at tip. No sweepback.
All-metal skinned. Aluminum alloy structure, with top-hinged ailerons and mechanical
slotted flaps. Single bracing strut, with jury strut, each side.
FUSELAGE:
Pod and boom structure, of 4130 chrome molybdenum steel tube forward fuselage affording
maximum crew protection. FRP forward fuselage non-load-bearing skin. Aluminum alloy semi
monocoque tailboom. Removable doors and windows horizontally binged
TAIL UNIT:
Swept fin (with dorsal fin) and balanced rudder; non-swept fixed incidence tailplane with
one-piece horn balanced elevator. Construction similar to that of wings. Elevator trim.
LANDING GEAR:
Fixed, with Cleveland 8.00-6 mainwheels on cantilever spring steel legs Scott 8 inch
tailwheel with Oleo strut. Mainwheel tire pressure 1.38 bars (20lb/sq in); Cleveland disc
brakes. Alternative float gear to be developed.
POWER PLANT:
125kW (168hp) Lycoming O-360-B2C, driving a Bishton BB177 wooden 2-blade fixed pitch
propeller. Fuel in two integral wing tanks, combined usable capacity 180 liters (48 US
gallons, 40 Imp gallons). Runs on MoGas. Overwing flush fuel caps each tank.
ACCOMMODATION:
Side by side seats, adjustable fore and aft for pilot and observer/passenger in enclosed
and extensively glazed cabin including chin and overhead transparencies. Right hand seat
and controls are removable. Aircraft can be flown with both top opening doors removed.
Space for up to 45 kg (100 lb) baggage aft of seats. A third seat with maximum load
capacity of 90 kg is under development.
ELECTRICAL SYSTEM:
24V. 70A alternator.
EQUIPMENT:
Specialized Surveillance packages are available.
Variants:
SB7L-235 (first Prototyp)
SB7L-360 powered by a Lycoming O-360-B2C
Seeker Floatplane with Aerocet 2200 floats
Data:
Performance: speed 112kt at 75% with 40l/h,
"petrol" cruise 65kt with 22l/h
climb 944ft/min from SL
take off to 50' 513m (1683ft) at ISA SL
Weights: empty 595kg (1312lb), MTOW 897kg (1977lb)
increase to 925kg
Dimensions: span 11.07m (36ft 4in), length 7.00m
(23ft) , wing area 13.10mx2 ( 141sq ft)
the Seeker is definitely different from every angle. It is still
different when you strap it on - there isn't anything to aim it by. Taxiing makes
one aware of just how close to the nose you can see the ground - and since it is very easy
to taxi, you have ample time to reflect on such things. Run-up is normal for a
fixed-pitch propeller.
Line it up and open the throttle, and there is a slight difference - you don't lift the
tail on take-off, like most tailwheel aircraft; the best technique in the Seeker is
to leave it neutral and let it fly itself off. It definitely does the thing better if you
let it get on with the job and don't interfere other than to keep it straight.
Once airborne, the only differences are the visibility and the smoothness - you really
notice the lack of slipstream buffet around the canopy.
Climb, and it is more like an elevator than an aeroplane: a typical-weight sea level
take-off will show better than 1000 FPM. The Seeker is stable, trim it out, take
hands and feet off - it simply proceeds upwards, in the direction it was last pointed.
In general flying, there is just one really remarkable difference - there is not trim
change whatever with either power for flap. You can set it up in cruise, and with
hands off the stick, pull full flap on sharply - almost nothing happens. Similarly,
if you set it up with full flap in the glide, and abruptly apply full throttle, all that
happens is that the noise increases. Be a bit careful, though, the first time you
demonstrate this to another pilot - he'll probably make a grab for the stick when you haul
on the flap.
LONGITUDINAL STABILITY
The Seeker has quite solid stick force gradients at forward limit (around 2kts/lb) and
they are not much less at aft limit in the zero-flap cases: with full flap at aft
limit (the critical case for this aeroplane), the gradients ease to around 5 kts/lb, and
friction effects can start to be detected in calm air if one is careful.
Stick force per G at aft limit was too high to measure with the small spring balance which
I had, but appears to be of the order of 20 lb per G or better; it would take a very
determined pilot indeed to pull limit load!
The aircraft has quite a definite phugoid (always a healthy sign), and care is needed in
doing stick force tests not to excite it; the presence of a positive phugoid is
prima facie evidence of positive stick stability.
Short period oscillations are dead-beat in all cases.
The longitudinal trim system is a spring, in the form of a large rubber block in torsion;
there are fixed down-deflected tabs on the elevator, which work with the rubber
spring to give a significant "downspring" effect. The rubber block has the
advantage of a benign failure mode, unlike the usual form of spring-trim systems.
There are no moveable tabs to flutter.
DIRECTIONAL STABILITY
Aircraft of pod-and-boom layout are usually interesting in the directional stability area,
and the Seeker has been no exception in this regard, as the profusion of vertical surface
area at the back of the aeroplane says very clearly This reflects a peculiarity of
this conformation; at low power, high speed the "blockage" effect of the
propeller causes a partial separation on the rear of the lower cowl, which reduces the
dynamic pressure of the flow over the fin; this was sufficient to give marginal
directional stability when the aircraft was dived at speeds approaching Vne with idle
power. Hence the outboard fins, ventral fin etc; however when all this has
been done, there was still a rudder float problem at this high speed, low power condition;
this was eventually cured by the addition of a geared "weathervane" under
the cockpit. If the vane were to fall off, the pilot would only find an effect if he
dived the aircraft at speeds close to Vne with Zero power and applied rudder and then took
his feet off; the effect he would notice would be that the ball does not
re-centralise.
In other words, you would not notice the absence of the vane in any normal flight
condition.
In its present configuration, the directional stability is quite firm in all the normal
operating regime, and satisfactory in the extreme low-power high-speed case. The
large vertical keel surface contributes to the innocuous spin behaviour. Tendency to
weather cock on the ground in a crosswind is perceptible but manageable.
LATERAL STABILITY
The lateral stability is comfortably positive in all regimes, roll/yaw coupling is
sufficiently strong that one can fly the aeroplane with feet alone without the slightest
difficulty. Spiral stability appears to be about neutral; the aeroplane will
maintain a turn indefinitely if it is in lateral balance. There is no perceptible
tendency to Dutch roll directional "snaking" - in fact, the Seeker is a very
steady platform altogether
STALLING
With two up, the loading will be close to forward C.G. limit, and the Seeker will not
stall in this configuration; you can pull the stick onto the back stop, with your
feet on the floor, and rock the wings from side to side with the ailerons.
Flaps and/or power make no change to this (except that there is a sharpish buzz audible at
full flap with high power, no doubt due to the airflow
At aft limit, the behaviour is not much different, except you will need to use both rudder
and aileron together to rock the wings with the stick hard back, and there will be quite a
heavy buffet.
Turning stalls will show a very slight pitch and roll movement as the stall is approached
- almost imperceptible, some buffet will make itself felt, and if you persist to full back
stick (which takes a quite determined pull) it will eventually pitch down just a touch and
roll towards level flight.
In most cases the roll will stop automatically when level flight is reached, but
occasionally it will roll past the wings level position - but this can be caught with
aileron, even with the stick hard back. There are both visual and audible stall
warnings as well, of course.
SPINNING
The Seeker has been cleared of "inadvertent" spinning, in an extensive program
(because of its unique configuration) and has proven to be entirely "honest".
Its large vertical keel area aft, provides lots of yaw damping which ensures that the
spinning characteristics are entirely conservative.
LANDING
The Seeker is a "good" tail-wheel aeroplane - which means it is quite easy to
land safely - but not so easy to land with elegance. It has a heavy duty set of main
springs legs and 800 x 6.00 tyres on Cleveland wheels, so the odd bounce won't hurt
anything except the pilot's ego.
A pusher layout does have one peculiarity to bear in mind, however; a burst of power
in an undershoot situation gives no additional lift - so one cannot "pick it up by
the bootstrap" if one gets too low, too slow.
Pilots who try the "Super Cub" trick of approaching "on the back of the
drag curve" will be rewarded by some decidedly inelegant arrivals, the correct
technique is to maintain a steep, power off approach at 70 knots, all the way to the
initial flare - and then hold-off and 3-point in the usual manner.
This results in a quite steep, short landing profile - in effect, the short field
technique in the Seeker is the same as the normal technique, except that the power used to
extend the glide is held to the minimum, buy the use of a steep approach.
For crosswinds, one becomes aware of the strong directional stability due to all that
vertical surface area down the back; the weathercocking tendencies are quite strong,
giving a crosswind burst of 12 knots at 90°.
CONTROL HARMONISATION
The Seeker has desirable harmonisation, with aileron; rudder; elevator forces in the
proportions 1 : 2 : 4. Rate of roll is quite brisk, especially in view of the
wingspan, and adverse yaw is minimal. This attribute, with the strong longitudinal
stability, means that manoeuvring steeply at low levels is not as demanding of pilot
attention as in other aircraft of my experience; with the outstanding filed of view,
this is a most desirable characteristic for the aircraft's intended usage.
Overall, it is comfortable and easy to fly, gives a good ride in turbulence, and can chug
along at its patrol speed with minimal pilot attention to actually flying the aeroplane;
it is an easy aeroplane to fly with one's attention outside and will not lose speed
and try to "flick" the moment you look over your shoulder.
As the CAA test pilot commented: "A Gentleman's aeroplane".
The field of view - ha, the field of view - the Seeker spoils one for any other aeroplane.
If you have flown helicopters such as a Robinson R22, you will know what to expect.
Unless you have, there is no way to describe the effect of all that scenery.
Of course, that's what it's all about - observation. Helicopters (most of them) are
as good - if you can afford them - but they shake.
The Seeker gives a remarkably smooth ride; one is seated forward of the Centre of Gravity,
so the heave of the aeroplane in turbulence is offset (so far as the occupants are
concerned) by the accompanying pitch, with the result that the effects of turbulence are
greatly reduced, by comparison with an aeroplane of conventional layout.
(text by manufacturer
2001)
Seeker
information 2007
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