Joacim Persson
10th Dec 2006, 16:11
Hello there, we are working on a simulator model of the Chinook for the freeware flight simulator FlightGear (http://www.flightgear.org/), aiming at the "D" model since that's the model for which there seem to be most accurate data available. (From, for instance, this excellent Chinook site (http://www.chinook-helicopter.com/), here (http://www.chinook-helicopter.com/Publications/Publications.html) in particular.)
We have however run into a bit of confusion here regarding the rotor design.
Gathering from a 1977 drawing from Boeing of the CH-47D model, the rotor heads are leaning forward with respect to the datum horizontal plane (floor or bottom of fuselage) of 9° for the forward rotor and 4° for the aft rotor. Then the CH-47 Theory of Operations (page 11-5) states the following about the LCT function:
19. Longitudinal Cyclic Trim Reduces flap-back to relieve bending stresses particularly on rear rotor shaft. In its automatic mode of operation, airspeed and altitude signals are processed by the AFCS units and used to position the two LCP actuators; the forward is controlled by the No. 1 AFCS unit, the aft by the No. 2 AFCS. When the aircraft clears the ground, the actuators retract from their ground position. At sea level, beyond 60 knots, the forward and aft actuators remain retracted, positioning the rotor disc planes relative to their masts by 1.2° and 3.25° respectively. From 60 knots to 150 knots, the actuators increase cyclic pitch linearly to 4° forward on both rotors. With increasing altitude, the LCT program is advanced. Provided that the AFCS units are receiving electrical power, LCT automatic operation continues. Driving signals are routed through the AUTO/MAN switch on the AFCS panel. Setting the switch to MAN disconnects signals from both AFCS units and permits manual operation of the LCT.
So my question is, what does "relative to their masts" mean exactly?
Is that relative to the 9° and 4° (Normal of the respective rotorhead drive shafts, i.e. the disc planes are, at hover up to 60kts, positioned at 9+1.25° and 4+3.25° with respect to the reference plane) or is that relative to the pylons (i.e. the normal to the reference plane)? (In the latter case, the forward rotor would always be tilted back relative to the rotor head, which seems odd.)
And, do the D model differ from earlier (or later) models regarding the rotor head design? (regarding rotor plane incidences)
We have however run into a bit of confusion here regarding the rotor design.
Gathering from a 1977 drawing from Boeing of the CH-47D model, the rotor heads are leaning forward with respect to the datum horizontal plane (floor or bottom of fuselage) of 9° for the forward rotor and 4° for the aft rotor. Then the CH-47 Theory of Operations (page 11-5) states the following about the LCT function:
19. Longitudinal Cyclic Trim Reduces flap-back to relieve bending stresses particularly on rear rotor shaft. In its automatic mode of operation, airspeed and altitude signals are processed by the AFCS units and used to position the two LCP actuators; the forward is controlled by the No. 1 AFCS unit, the aft by the No. 2 AFCS. When the aircraft clears the ground, the actuators retract from their ground position. At sea level, beyond 60 knots, the forward and aft actuators remain retracted, positioning the rotor disc planes relative to their masts by 1.2° and 3.25° respectively. From 60 knots to 150 knots, the actuators increase cyclic pitch linearly to 4° forward on both rotors. With increasing altitude, the LCT program is advanced. Provided that the AFCS units are receiving electrical power, LCT automatic operation continues. Driving signals are routed through the AUTO/MAN switch on the AFCS panel. Setting the switch to MAN disconnects signals from both AFCS units and permits manual operation of the LCT.
So my question is, what does "relative to their masts" mean exactly?
Is that relative to the 9° and 4° (Normal of the respective rotorhead drive shafts, i.e. the disc planes are, at hover up to 60kts, positioned at 9+1.25° and 4+3.25° with respect to the reference plane) or is that relative to the pylons (i.e. the normal to the reference plane)? (In the latter case, the forward rotor would always be tilted back relative to the rotor head, which seems odd.)
And, do the D model differ from earlier (or later) models regarding the rotor head design? (regarding rotor plane incidences)