UH-1N FAM-106

FAM 106 Goal Review previously introduced maneuvers and procedures.

Requirement 1. Brief and discuss drive train system (engine, transmission, C-box, main rotor, 90/42 degree gear boxes, tail rotor), mast bumping, vortex ring state, and collective bounce. 2. Introduce simulated tail rotor malfunctions, high speed/low level approach, quick stop, low level autorotation, and APU start. 3. Review normal approach, steep approach, no hover landings, autorotations (including hovering/taxiing), SCAS  link building for small business off flight/landing, simulated single/dual engine failures, maximum power takeoff, and manual fuel operation.

Drive train system Primary purpose of link building the drive train system is to transmit power (Torque) from the engines to the main & T/R systems. Engine The engine is a T400-CP-400 turboshaft engine with an 1800 shp rating (900 each). Each engine has a three stage axial, single stage centrifugal compressor driven by a single stage turbine (Ng). The compression ratio is 7:1. Each engine has an annular combustion chamber with 14 fuel nozzles. After combustion the exhaust gases go through the two counter-rotating turbines and exits through the exhaust stacks.

The Ng gas producer turbine rotates at 38,100 rpm (clockwise) and drives the compressor and accessory gearbox. The Nf power turbine rotates at 33,000 rpm (counter clockwise) and drives the input section of the C-box. There is no direct mechanical linkage between the Ng and Nf turbines and the interaction between the two turbines is called ÃÂÃÂ¢ÃÂÃÂÃÂÃÂgas couplingÃÂÃÂ¢ÃÂÃÂÃÂÃÂ.

Each engine has an internal oil system with a capacity of 1.6 gal (0.75 gal usable with 0.5 gal expansion space). The oil sump and internal pump are located within the accessory gearbox. Site gauges are located on the side of the accessory gearboxes and checked on pre-flight. An oil cooler is located aft of the C-box.

Combining gear box The combining gearbox located on the aft portion of private blog network the engines has two identical reduction geartrains that transmit torque from each engine to a common output shaft. Each geartrain has three stages and a unidirectional drive clutch is incorporated with the third stage shaft allowing torque to be transmitted in one direction only. The C-box provides a 5:1 gear reduction from Nf to main driveshaft (33000:6600).

The main drive shaft (6600 RPM) is installed between the C-Box and the XMSN input drive quill. The driveshaft is hollow and hardened, allowing it to transmit tremendous torque loads while maintaining a light weight. K-Flex couplers allow for relative movement of the reduction gearbox and main XMSN and bending forces due to g loading.

The C-box has an oil system, separate from the engine oil systems, with a capacity of 1.25 gal. The oil level site gauge is located on the # 2 side and checked on pre-flight. The oil cooler is external and located aft of the C-box.

Transmission The XMSN is essentially a mechanical reduction gearbox that is supported by 5 pylon isolation mounts and 1 lift link. The transmission is coupled to the engine by a main driveshaft into the c-box and drives the main rotor mast (324 rpm), an internal XMSN oil pump (driven at 4498 rpm) and has accessory drives for two hydraulic pumps (#1 at 4302 rpm, #2 at 6600 rpm), the rotor brake disk (8322 rpm) Nr tach-generator (4302 rpm), and the tailrotor driveshaft (4302 rpm). The XMSN is limited Fresno Lawyer to 1290 shp. The freewheeling unit is located in the input quill and allows the main rotor and geartrain to turn freely when the engines are below rotor-turning speed. This unit provides a positive disconnect from the engines in case of power (engine) failure. The input quill is connected within the transmission case by spiral bevel gears to a two-stage planetary gear train. The planetary and bevel gears provide a 90ÃÂÃÂ¯ÃÂÃÂÃÂÃÂ° change of direction and a 20.37:1 gear reduction (6600 RPM to 324 RPM).

The 2.75 gallon oil supply is contained in the XMSN sump. Oil level is checked on preflight by site gauges on the # 2 side (the C/B for this light is near the co-pilot pedals). The oil is circulated under pressure from an internal pump (with an internal filter). Spray jet assemblies distribute oil to bearings and gears. Oil is routed to an external oil cooler at temps above 71 deg C. A pressure regulating relief valves keeps oil pressure at 50 +/- 5 psi. A chip detector is installed and acts as a drain plug. A red pop out indicator button on the external oil filter (checked on preflight/postflight) is the only indication of a clogged filter.

Main Rotor Rotates at 324 rpm, 48ÃÂÃÂ¢ÃÂÃÂÃÂÃÂ diameter. Two bladed, semirigid, flapping type employing preconing (2.5-3 deg) and underslinging. Rotor mast is splined on the upper and lower ends to provide for drive from the XMSN and mounting of the main rotor system.

90/42 degree gear boxes 42ÃÂÃÂ¯ÃÂÃÂÃÂÃÂ° gearbox is located at the base of the tail fin and changes the direction of the tailrotor driveshaft only. The 90ÃÂÃÂ¯ÃÂÃÂÃÂÃÂ° gearbox is located at the top of the vertical fin and provides 2.6:1 reduction from the tailrotor driveshaft to the tailrotor (4302 rpm to 1654 rpm). Both have magnetic chip detectors that illuminate caution lights when metal is detected in the gearbox and also act as drain plugs. Both gearboxes have vented filler caps, and sight gauges to view oil level (.375 pint capacity for 42 deg gearbox and 0.8 pint capacity for 90 deg gearbox).

Tail rotor T/R drive system consists of 6 drive shaft sections, 4 hanger bearings and 2 gearboxes. Couplings on the drive quill, gearboxes, and forward ends of the hanger bearings are flexible and compensate for the dynamic loads in flight. The T/R is two-bladed, rigid, flapping tractor type rotor blade employing preconing and underslinging that rotates at 1654 rpm. The T/R is 8ÃÂÃÂ¢ÃÂÃÂÃÂÃÂ 6ÃÂÃÂ¢ÃÂÃÂÃÂÃÂ in diameter and spins counter-clockwise.

Mast bumping Occurs when the rotor exceeds its critical flapping angle and the underside of the rotor hub contacts (bumps) the rotor mast. Normal flapping is 11 deg up and 11 deg down (22 total movement). Excessive flapping can also cause rotor blade contact with the tail boom or cockpit. Mast bumping generally occurs at, but is not restricted to the extremes of the operating envelope. The most influencial causes are (in order of importance): 1. Low-g maneuvers (below + 0.5)ÃÂÃÂ¢ÃÂÃÂÃÂÃÂ¦flight ops below +0.5 g is PROHIBITED 2. Abrupt roll reversals (larger flapping occurs during Left to Right reversals) 3. Rapid large control motion (especially from the cyclic) 4. Flight near longitudinal/lateral cg limits 5. High slope landings 6. Low rotor rpm (ie, main driveshaft failure, dual engine failure) Less significant causes are: maximum sideward & rearward flight, sideslip and blade stall conditions.

Should mast bumping occur, land as soon as possible while maintaining minimum power during descent and landing. 2. Maintain Nr with collective 3. Land as soon as possible
 * 1. Immediately apply aft cyclic, then center laterally (maintain G load on rotor)

Start/Shutdown Check collective full down and simultaneously move the cyclic in the direction from which the wind is coming. If possible, visually check the rotor for correct position.

Sideward/rearward flight with a high tail wind Apply directional control in a direction that will turn the nose more into the wind. Apply a slight amount of forward cyclic, ground clearance permitting. CAUTION: If main rotor rpm is below minimum power-on, do not add left pedal to initiate the turn or the mast bumping will be aggravated.

Sideward flight or hovering with a high crosswind Apply directional control in a direction that will turn the nose more into the wind. Reduce collective, ground clearance permitting. Simultaneously with pedal application, decrease the sideward flight speed by moving the cyclic toward center.

Slope landing At the onset of mast contact, abort the landing attempt by increasing the collective slightly while moving the cyclic away from the slope. Before an attempt is made, recheck the rotor rpm at maximum power-on rpm. If mast contact occurs while slowly lowering the collective after both skids are in ground contact, raise the collective enough to eliminate bumping. CAUTION: During slope landing, main rotor flapping will increase proportionally with the velocity of an upslope wind. For cross-slope landing, it is preferable to land with the Right gear upslope to minimize main rotor flapping.

Vortex ring state Vortex ring state is an uncommanded rate of descent caused by the helicopter settling into its own downwash. Zero net thrust is present throughout the rotor as airflow is upward near the center of the disk and downward in the outer portion. Vortex ring state is NOT restricted to high gross weight or high density altitude. It is most likely to occur at descent rates of greater than 800 fpm with airspeed less than 40 knots. Indications: rapid descent-rate increases, increase in overall vibration level, loss of control effectiveness. Recover by: 1. Reduce collective 2. Forward cyclic to gain airspeed WARNING: Increasing collective has no effect toward recovery and will aggravate the condition. During approaches at less than 40 knots, do NOT exceed an 800 fpm descent rate.

Collective bounce The collective control system requires a minimum of 8 pounds (measured at the center of the pilot No. 1 throttle) to prevent vertical oscillation. Before flight, ensure that at least 8 pounds of absolute collective friction is available. The aircraft should be running and the hydraulic boost system should be ON for the friction check. WARNING: When the absolute friction on the collective is less than 8 pounds, vertical oscillation can manifest itself in any flight regime, including ground operation, by rapid buildup of vertical bounce. The oscillation can be so severe that effective control of the aircraft will be lost. 1. Make a positive change of collective position (up or down) 2. Increase collective friction 3. Break arm (i.e. do not stiff arm)