Engine control system

1. A power turbine speed control system for a helicopter comprising:

a) means for generating a power turbine speed signal based upon a demanded speed;

b) means for filtering the power turbine speed signal by effectuating a rapid attenuation of main and tail rotor torsional frequencies in the power turbine speed signal without compromising phase at low frequencies;

c) a governor for providing isochronous power turbine speed and rotor speed control based upon the filtered power turbine speed signal; and

d) damping means for actively damping main and tail rotor torsional frequencies.

2. A power turbine speed control system as recited in claim 1 , wherein the damping ineans includes means for estimating a plurality of engine states based upon a single measured engine state.

3. A power turbine speed control system as recited in claim 2 , wherein the single measured engine state is power turbine shaft torque.

4. A power turbine speed control system as recited in claim 1 , wherein the damping means includes a linear quadratic regulator that provides combustive damping.

5. A power turbine speed control system as recited in claim 1 , further comprising means for selectively activating the damping means.

6. A turbine speed control system as recited in claim 1 , wherein the damping means is tuned to provide attenuation of resonant frequencies so as not to influence low frequency response of the system.

7. A power turbine speed control system as recited in claim 6 , wherein the damping means includes a high pass filter.