1518
SA.360 DAUPHIN
which decides whether torque or engine temperature is
dominant and feeds this information to the indicator
needle. As long as the pilot does not pull more than 100
per cent indicated, he will exceed neither torque nor
temperature limit. Moreover, the temperature is calculated in the form of thermal load based on compressor
delivery pressure (P2), fuel mass flow and turbine inlet
temperature (T3). This gives an accurate indication of
the actual thermal load on the individual engine, whatever its condition.
While the pilot needs only to respect his power gauge,
he will probably want to know from time to time which
limit is dominant. Beneath the power dial, therefore, there
is an instrument-sized circular panel on which one of
two small white lamps illuminates to identify the
dominant limit. To read the non-dominant value, the pilot
presses a button beneath the extinguished lamp and the
gauge instantly swings to indicate that percentage. If in
flight he reaches limiting power, a red light in the power
gauge warns him: it shines steadily if the thermal limit
has been reached, and flashes for the torque limit. The
pilot can see out of the corner of his eye which it is.
In the centre of the dial is a vernier adjuster which the
pilot uses to set the specific gravity of the fuel he is
carrying on any particular day. If he then presses a third
button on the dial, the power-gauge needle will swing to
indicate—against the figures on the percentage scale—
the number of kilogrammes of fuel he will burn in 20min
if the current power level is held. This gives him a handy
means of calculating his endurance by mental arithmetic.
Fuel contents are gauged in kilos by a capacitance
system which gives an accurate indication of fuel energy
remaining. Finally, the Dauphin fuel tank contains a small
20 lit sump which can be drained by the engine to the
very last drop. When fuel contents fall to the level of
this sump, a red light illuminates to tell the pilot that he
has exactly 20 usable litres left, enough for a few minutes
of flight.
M a k i n g it easy
Dauphin carries a maximum of 660 lit of fuel and uses
1 lit/km (80kg/100km) in the cruise. Aerospatiale has
evolved an astuce to reckon payload range by using the
symbolic number 15. Five passengers can travel for
10X 100km (5+10=15); six passengers can fly 9X 100km
(6 + 9 = 15). A pilot alone could notionally fly 1,500km; in
practice, the gross weight would aliow that much fuel to
be carried, but extra tanks would have to be fitted to
hold that quantity. To put it another way: if the boss says
"How many people can you take from Marseilles to
Paris?", the 600km flying distance allows for nine passengers (15—6 = 9). Actually, that flight would leave a
mighty thin fuel reserve, but the initial answer can be
given in seconds.
The Dauphin, like other helicopters, has two independent powered-control systems. The two groups of servos
are mounted respectively at the rotor pylon and beneath
the forward cabin floor. Aerospatiale has dreamed up a
safety device, a spring link on the valve of each poweredcontrol servo containing two successive microswitches. The
link senses the difference, or the lag, between the pilot's
manual control input and the response of the poweredcontrol servo. If one servo is having trouble overcoming
rotor loads, the difference reaches a certain level; the
first switch is then closed to light a warning sign right in
the front of the pilot and sound a warning warbler. At
this point the control effort being demanded at the rotor
is approaching the structural limit of controls and airframe and the pilot must ease off.
Should a powered-control servo or its valve actually
jam, the link will be further compressed, the second
switch will close and a horn and light will tell the pilot
to isolate one control system. He cannot be expected in
the heat of that nasty moment, with the cyclic or collective lever possibly jammed, to make a detailed assessment
FLIGHT International, 5 lune 1976
of which system to isolate. But the sensing switch automatically identifies the faulty system and the pilot has
only to move a sliding switch on top of the collective lever
for the appropriate hydraulic system to be depressurised.
A caption on the central warning panel will then tell him
which system he has cut.
This can be tried out on the ground before take-off to
give confidence and to check individual hydraulic systems.
Finally, very high control loads on the cyclic servos tend
to feed back on to the collective servo and slightly reduce
collective pitch, thereby automatically lowering the load
factor and making for a gentler manoeuvre. Apparently,
the jack-stalls experienced with Gazelle do not occur in
the Dauphin.
The pilot can fly the Dauphin right to its limits by
referring to his instruments, but the machine is also
designed to be flown to the edge of its limits "head-up,"
without looking at the gauges. The collective lever therefore has two flexible stops (butees souples) which warn
the pilot by touch that he is approaching his upper and
lower collective-pitch limits. The upper flexible stop is
adjusted for individual flight conditions by setting a
knurled wheel, located at the base of the collective lever,
to the prevailing outside air temperature. The lever will
then reach this stop at 90 to 95 per cent of normal engine
power, warning the pilot that he should refer to the gauges
before pulling yet more
power. The lever reaches its final
mechanical stop at 15J2° collective pitch.
At the lower end of the collective lever's travel, the
flexible stop is felt as collective pitch drops to 5°, a
minimum which prevents rotor overspeeding during autorotation at high gross weights or high load factors. The
lever can be pressed through
this stop to reach its minimum flight setting of 3 1 2 °, which can be used for autorotation at low weights.
H e a d - u p warnings
There are two further "head-up" warnings. Normal
rotor r.p.m. is 350. If this climbs to 385, a rapid "beepbeep-beep" sounds, and if it falls to 325 a slow, deep
booming is heard. A margin of nearly 30 rotor r.p.m. either
side of datum is generous, and during autorotation
revolutions can be built up very easily to allow a quite
prolonged flare before touchdown, as I was later shown.
Following Aerospatiale tradition, the Dauphin cycliccontrol system carries only a friction-damper, and not an
adjustable centring or feel spring. Both friction-damper
and centring spring can produce acceptable control forces
and a kind of trim, but comfort ultimately depends on the
stability of the machine as a whole, and the Dauphin is
stable enough to cruise hands-off at a great variety of
speeds with about 100 grammes of friction applied to the
stick. Some friction is vital because the stick, if left free,
would topple over to full control deflection and take the
helicopter with it. That would be over-exciting.
The Fenestron tail rotor is now a well known feature
and Aerospatiale has learned to tune it for performance.
In the cruise the Fenestron is completely unloaded, with
its blades at zero pitch and the rudder pedals central.
Virtually all the engine power goes into the main rotor,
but the smallest pitch change entrains air through the
duct and produces a powerful directional response. All
torque compensation in cruise comes from the aeroplanelike fin and the small additional fins on the tips of the
tailplane, which are slightly toed-in to make them more
effective. The fins are powerful enough to permit autorotation without tail-rotor drive down to around 30kt, and
a run-on landing could be made at this speed.
The tailplane incorporates a characteristic, highly
cambered inverted aerofoil with a stall strip running along
the upper surface. It is tuned to be effective at airspeeds
above 60kt. Below that speed it stalls without fuss in
order to avoid excess pitch-axis stability during autorotation.
For my flight with Coffignot, Dauphin 1001 was carrying
120kg, 2651b of test equipment plus two VHFs, two ADFs
and a transponder and its empty weight was 1,818kg,
4,0001b. Coffignot, M Lemuhot, assistant to helicopter