Originally Posted by R le Page
think its the propeller condition lever that alter the pitch of the propeller which makes it sound like the RPM is changing.Its very noticable on air craft like the Dash8 and ATR,especially the older models,I think on newer models[Q400 and ATR-500 its computer controlled and the change in pitch sound is less prominent.]
Big difference here. The Trislander is
PISTON ENGINED and the Dash8 and ATRs are
TURBINE
On the Trislander the throttles controls Manifold Pressure - in other words the raw power in the engine, and the prop levers control the RPM. The engine can take (and provide) more of the raw power when the props are spinning faster. However, in different phases of flight you need different power settings. So, after takeoff the pilot will reduce the manifold pressure with the throttles and then reduce the RPM. Less power = less fuel = less noise (which is quite something with the Trislander).
On, say the ATR, the condition levers control the fuel flow to the engine for starting and shutdown (via a small lever at the base of the main lever) and RPM, and the throttles control the torque - again, the raw power.
As for the Trislander and the many myriad adjustments made by the pilot? Well, simply to keep the props in synch and try and reduce the noise in the cabin. Each aircraft (and I'm talking the Aurigny fleet of Tris that I flew for two years) had different positions for the prop levers for a certain RPM. The levers would be staggered differently for each 'plane. We would learn the sort of positions required - and then the engineers would re-rig during the normal checks and we'd have to re-learn the required prop synchs!!
Depolox4 - you are correct in that the prop levers alter the RPM and give a different bite of air. As I said the throttle controls raw power as an accelerator does in a car. They are NOT physically interconnected on the Trislander, although the pilots have standard settings such as 25" Manifold Pressure and 2500 RPM for the climb.
Hope this helps. I like talking about the Tri having flown it for so many years
