Rolls Royce Geared Turbofan / Viarable Pitch Blades

[Ozgrade3]

For eons I have said in class that you could never have a variable pitch N1 fan blade, Rolls comes out with this. A Fan system with variable pitch blades.

Rolls-Royce Reveals Next-Gen Engine Plan | Commercial Aviation content from Aviation Week (http://aviationweek.com/commercial-aviation/rolls-royce-reveals-next-gen-engine-plan-0)

Could anyone explain how this system could work, what sort of mechanism/governor system would be needed.

Curiosity is killing me.

[barit1]

Basically, the system would be related to a constant-speed prop i.e. N1 governor keeping the fan turning at constant speed. But the governor setting could be slaved to the throttle to simplify the cockpit.

Alternatively - Fan blade pitch (conversely "stagger angle") could be directly linked to the throttle, and then the fuel system demand slaved to fan speed to manipulate fuel flow. This would be analogous to "beta control" in a turboprop.

Or maybe R-R have a better idea... :E

[tdracer]

Modern FADEC turboprops use the FADEC to control the blade pitch. No first hand knowledge, but I'd expect Rolls to do something similar where the FADEC 'optimizes' the fan blade pitch for the specific operating conditions.


BTW, engine companies throw this sort of stuff around all the time to see 'what sticks'. Pratt started pitching the geared fan back in 1990 (for the initial 777) and it only started flying in the last few years and is still not in service. I also recall a Rolls pitch ~ 30 years ago for variable area turbine inlets. There are some dramatic potential improvements in operability and efficiency if the area of the turbine inlet can be optimized for the specific conditions - but of course putting variable geometry in the hottest part of the engine is non-trivial. Anyway, the concept is still out there but still hasn't seen the light of day.

[barit1]

Agreed that the implementation of the controls would be FADEC.

The actuation, however, would be the big issue. Variable-pitch props have often had control problems, needing pitchlocks, feathering, etc.

A beautiful replica aircraft and its builder/pilot was lost because of a broken prop counterweight. DEN03FA138 (http://www.ntsb.gov/aviationquery/brief.aspx?ev_id=20030815X01342)