- Reaction score
- 21,945
- Points
- 1,360
George, the Griffon's mast is about as big as you could reasonably design without making it relatively stronger than several other components. Scoobs is right that for the rotor system of the 412, the mast (along with the glass-fibre blades) principally limits how much power you can apply to the main head...if you added more, however, you would have to beef up other components along the way.
Not sure if everyone caught the nuance of a single power-pac that is actually made by twinning two separate engines into a unified power pack. There are actually two PT6 turbines add their power together in a combining gear box (CBOX) which is then output from the power pack into the main transmission. The main transmission only sees a single input shaft and doesn't really care where the power is coming from, just that there is enough to balance off the aerodynamic loads of the blades to keep the drive system from slowing down (i.e. rotor from "drooping") The PT6 Twin Pac turbine system can in most conditions still provide much more power than the Bell 412's dynamic system is capable of reasonably absorbing...what this means is that by down-rating the engines, they will actually operate much more reliably and with fewer problems -- kind of like using only 50-60% max power of the engines in normal operation. OEI (one engine inoperative) will max out a single engine (which on its own could provide up to ~71% of the main transmission requirements)...and in some extreme cases (we're talking like 60*C) may actually put the combined power sections near the upper combustion/exhaust component temperature limit.
Frankly, I think the weakest link (in terms of how close a component's actual strength compared is to its minimum design load limit requirement) is the tail structure...specifically the fin, and some of the tail rotor components. I scared the crap out of myself once by playing "door kicker" once in the back of the chopper and took a look back at the tail rotor when the guys up front were pulling into the flare to insert the guys.... Note to self: don't look at how much the skin wrinkles on the inboard side of the tail fin...eeeks!
Scoobs, arriving in weeks few...stuff to clean up in current life. No, I missed crossing paths with you while you were up in the "Den". See you at the next Gathering!
Cheers,
Duey
Not sure if everyone caught the nuance of a single power-pac that is actually made by twinning two separate engines into a unified power pack. There are actually two PT6 turbines add their power together in a combining gear box (CBOX) which is then output from the power pack into the main transmission. The main transmission only sees a single input shaft and doesn't really care where the power is coming from, just that there is enough to balance off the aerodynamic loads of the blades to keep the drive system from slowing down (i.e. rotor from "drooping") The PT6 Twin Pac turbine system can in most conditions still provide much more power than the Bell 412's dynamic system is capable of reasonably absorbing...what this means is that by down-rating the engines, they will actually operate much more reliably and with fewer problems -- kind of like using only 50-60% max power of the engines in normal operation. OEI (one engine inoperative) will max out a single engine (which on its own could provide up to ~71% of the main transmission requirements)...and in some extreme cases (we're talking like 60*C) may actually put the combined power sections near the upper combustion/exhaust component temperature limit.
Frankly, I think the weakest link (in terms of how close a component's actual strength compared is to its minimum design load limit requirement) is the tail structure...specifically the fin, and some of the tail rotor components. I scared the crap out of myself once by playing "door kicker" once in the back of the chopper and took a look back at the tail rotor when the guys up front were pulling into the flare to insert the guys.... Note to self: don't look at how much the skin wrinkles on the inboard side of the tail fin...eeeks!
Scoobs, arriving in weeks few...stuff to clean up in current life. No, I missed crossing paths with you while you were up in the "Den". See you at the next Gathering!
Cheers,
Duey