Length
42.45 ft (12.94 m) from main-rotor tip to the upper tip of the vertical stabilizer.
From nose to tail, the airframe is 35.86 ft (10.93 m)
Height
Top of the Starflex main-rotor hub is a half an inch shy of 11 ft tall (3.34 m)
Engine
Turbomeca Arriel 1D1
- Free-turbine engine (clutchless drive) with integral freewheel
- Modular design
- Cooling system and externally fitted oil tank
Arriell 1D1 weight
287 lbs/ 130 Kg
Main Rotor Hub (MRH)
- Starflex semi-rigid
- Bearingless hub (laminated glass-resin star) without a drag damper
- No grease nipples
- Modular, fail-safe design
Main Rotor Blades
- Spar made of fiberglass roving
- Glass fabric skin and foam core
- Fail- safe design
Main Rotor Mast
- Removable subassemblies
- Mast casing attached by 4 suspension bars which “support” the helicopter
- Includes the servo actuators
Main Gearbox
- Modular design
- Attached by flexible bidirectional suspension
- Two reduction gear stages (1 bevel gear drive, 1 epicylic gear train)
- Pressure lubrication with oil cooling system
- Includes rotor brake and hydraulic pump drive
Structural Subassemblies
A FEW WORDS ABOUT THESE NEW MATERIALS
They are synthetic resins divided into 2 main classes:
- Thermoplastics which soften when heated and harden when cooled, e.g. polyamides (Nylon, Rilsan), polycar- bonates, etc.
- Thermosetting resins which, under the combined ac- tion of heat and a hardener, hot-cure irreversibly to form a new product, e.g. epoxy resins, silicone, etc. Laminates and laminated honeycomb are reinforced plas- tics with very good mechanical strength properties. Laminated materials are produced from thermosetting resins and reinforcing materials (glass, carbon, graph- ite, boron or other fibers).
Tail Boom Strake
In sideways flight to the left, the main rotor downwash is deflected and accelerated over the RH side of the tail boom, which induces a negative pressure of approxi- mately 1 mbar/cm2 along the entire tail boom. This re- duces the effect of the tail rotor by roughly 5%. A strake added at 45° causes the main rotor downwash flow to separate and restores the pressure to the static value. The effect of the strake is thus to regain the 5% moment and to improve the tail rotor efficiency (including in hover).
The strake is secured longitudinally from the forward frame to the horizontal stabilizer. It is designed to gener- ate a pressure equal to the static pressure on the RH side of the tail boom.
Tail Rotor
- Hingeless, greaseless seesaw rotor with glass roving spar
- Pitch change by spar twisting
- Fail- safe design
Tail Rotor Gearbox (TGB)
Angle reduction gear with splash lubrication
Tail Guard
Protects the ventral fin
Vertical Fins
Dorsal (upper)
Ventral (lower)
- In cruise flight, the asymmetric NACA airfoil of the dorsal fin generates an aerodynamic force that opposes the main rotor’s counter torque and thus reinforces the tail rotor thrust.
- The ventral fin has a symmetric NACA airfoil to stabilize the helicopter about its yaw axis.
Horizontal Stabilizer
An asymmetric NACA airfoil, set at negative angle to the horizontal datum; creates nose-up moment with a relative wind
Landing Gear
Supports the helicopter
Protects the airframe on landing
Damps out vibration when the helicopter is on the ground with the rotor spinning
The landing gear assembly comprises:
- front and rear cross tubes
- two skids
- two hydraulic shock absorbers
Flexible Steel Strip behind Skid
A flexible steel strip bent downwards behind the skid in- creases the landing gear stiffness and changes its natu- ral frequency so that ground resonance can never occur.
Ground Resonance
When the helicopter is on the ground the vibrations have a support point via the landing gear
If the natural frequency of the landing gear coincides with the principal vibrational frequencies of the main rotor, the vibrations are augmented every blade revolution as they receive a new “reflected” impulse
The vibration amplitude then increases very rapidly
The vibration becomes divergent and the resulting oscillations can destroy and overturn the helicopter.
Main Rotor Drive System
Transmits engine power to the MR and TR drive shaft
Consists of:
- the engine/MGB coupling
- the main gearbox (MGB)
- the MGB suspension
Engine Controls
2 mechanical controls:
- The FFC operated by the pilot
- An automatic engine governor compensation control, coupled to the collective pitch control.
- Meters the fuel quantity to match the power demand (collective pitch function)
- At the same time, keeps the free turbine rpm constant
Engine Governing Control
Acts on the free turbine governor; the control reacts automatically to collective pitch variations and:
- it compensates for the STATIC DROOP of the centrifugal governor, by maintaining a CONSTANT rotor rpm (NR) irrespective of the fuel flow and hence irrespective of the power demand
- it has a very fast RESPONSE TIME to prevent surging during sudden accelerations and flameout during sud- den decelerations. This is why this control is also called an ANTICIPATOR since it acts prior to the normal reac- tion of the centrifugal governor.
Static Droop
Paraphrased: the small RPM difference due to the centrifugal governor’s reactions to power demand changes. Anticipator (attached to collective) acts prior to centrifugal governor’s normal reactrions.
The function of the free turbine governor is to maintain the Nf (and hence Nr) constant.
A simple Watt type governor, consisting of a directly acting, flyweight centrifugal governor operating in an “open loop”.
Open Loop: detects rpm variations and counteracts them but it does not check or correct the results of its action. Cannot operate “intelligently” because it is not informed of the effects of its action. In cybernetics, such a governing system is termed “open loop”, as opposed to “closed loop” systems where there is a feedback from the sensing element which compares the result with a reference value and modifies its magnitude.
Consequently, Nr is not strictly constant: compared to the selected governor speed, the rpm drops slightly when the power demand increases and rises slightly when the power demand decreases. This small rpm difference is called “static droop”.
Engine Power Parameters/Limitations
- NG - gas generator rpm: Power produced by the engine varies with NG, which directly depends on the amount of fuel ignited.
- T4 - gas temperature at the free turbine inlet depends mainly on the quantity of fuel ignited
- Torue (Cm): torque transmitted to the rotors by the free turbine; represents the power absorbed by the rotors. Power varies with the collective pitch.
Now the power absorbed by rotors = Cm x ω
As ω (rotor rpm) = constant, the power absorbed by the rotors is proportional to the engine torque.
NG and T4 limitations to protect the engine.
Torque (Cm) limitations to protect the MGB
Engine Torque Monitoring
measured at the intermediate pinion of the engine reduction gear
pinion has helical teeth and it is therefore subject to an axial thrust (PA) proportional to the engine torque and to an axial reaction RA equal to PA, i.e. the reaction itself is also proportional to the engine torque. The engine torque is then measured using the axial displacement of the pinion due to RA.
