Right, I'm aware that there's counter rotating spools in the same engine, I thought we were talking about having left and right engines rotate in opposite directions.

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Agree with their being no need for 'counter rotating engines' on jets but they do have a critical engine it's just that it's not always the same.

It's the outboard engine on the upwind wing.
That still doesn't make it a 'critical engine'. Just makes it aerodynamically critical; nothing to do with the engine though.
tmpffisch is offline Report Post Reply


It certainly is, anyway the effect of a critical engine is most certainly aerodynamic no matter what the type or installation.

Oh dear oh dear, the engines don't turn different ways on different wings, the engines have counter rotating shafts as in the LP turns one way and the HP turns the other. This is the first counter rotating Hi Bypass ratio turbine engines I have come across on modern aircraft. :rolleyes:

Technically speaking it is contra rotating rather than counter rotating, which is what I thought the originator was alluding too, perhaps not, so I'll leave it to the more technically adept people who know more! :ugh:

Aaaaah! Halcyon days brought back in earnest!

The sweet sound of 4 x Rolls-Royce Griffons at full chat prior to 15+ hours wheels-off to wheels-on.

Not quite a counter-rotating jet, but a magnificent sound now only heard on the DVDs and videos. :{

Just put GE's on one side and RR's on the other.
Problem solved.

"Critical Engine" is a term used in certification. Given that the VMCG/A data is for zero crosswind (these days) there is no critical engine on a jet.

There is however an engine who's failure will require more control that the other in a cross wind. This is due to the fin not the engine.

The affect is still the same FEH, that's the point I was trying to make.


Best wishes.

P1127 and Kestrel/Harrier had contra-rotating spools to counter gyroscopic effects. The test pilots insisted on this after bending the Bell X-14 during training flights. I recollect Bedford/Merewether? Ah, yes, Merewether X-14 with Vipers. Subsequently J-85s. Okay, Mr Farley?

Actually the OP wants to know about non-coutner-rotating engines.....

Henry

As you say the Pegasus low pressure and high pressure spools have always rotated in opposite directios to minimize any gyroscopic moments in the hover. Given the simple non autostabilised reaction control system used on the P1127 to control attitude in the hover if gyroscopic couples had existed the thing would have been impossible (rudder would have made it pitch and pitch would have made it yaw for example). Bedford, Merewether and Robin Balmer (the controls and aero man) are all dead so I don't know how much the US experience counted. My feel is that it only confirmed what they already realised and so insisted on with Bristol before the first Pegasus was designed.

The engine men were naturally reluctant to have contra rotating spools because this hugely increased the inter spool bearing speeds to numbers outside their ken.

The A350 engine you refer to is the R-R Trent XWB: Trent XWB - Rolls-Royce

How about "CACA" on the Airbus A400M.
The change in prop rotation is made in the gearbox.