Engine rotation

[Winkiepinkie]

Question for the engineers amongst you.

Right.

1) RR rotate clockwise, everyone else (GE, P&W) does the opposite, i.e. anticlockwise. Is there any reason why?


2) Finally, if I was able to take an engine and take all the blades out (compressor & turbine etc), rotate them (90 deg?) so the engine would have to turn in the opposite direction, would it make any difference (obviously ignoring the effects of where gearboxes and the likes are located and airflow disturbance etc.)

TIA, w.

[747FOCAL]

Same reason a toilet flushes in opposite directions in each hemisphere of the earth.

[A-FLOOR]

IIRC, in Roller engines the first and second stages run clockwise, and the third (which GE and PW don't have at all) runs counterclockwise. I have been told that this counter-rotation alone gives you 2% less specific fuel consumption on a Trent 700.

Wow.

[lomapaseo]

2) Finally, if I was able to take an engine and take all the blades out (compressor & turbine etc), rotate them (90 deg?) so the engine would have to turn in the opposite direction, would it make any difference (obviously ignoring the effects of where gearboxes and the likes are located and airflow disturbance etc.)

I believe you meant (180 deg.) which is possible. This has happened in a single stage and the engine will still run, but fatigue usually sets in ala EAL DC8 out of New York many moons ago (does anybody have the famous photos of it burning on climbout).

Actually if you do manage to install the blades backwards (180 deg out) the inciodence angle will still be somewhat effective although the pressure rise/drop will be less.

comments/corrections welcomed.

[Winkiepinkie]

I thought about this. If you rotate them 180, they are in the same position as before (albeit with opposite aerofoil shape of blades). But rotate through 90 and the engine rotation will have to be reversed to get the trust in the right direction.

[Panama Jack]

I suspect it has something to do with Rolls Royce being British, and British build reciprocal engines turned clockwise, while US build reciprocal engines turned counterclockwise. GE and P&W have their origins in the USA.

[Notso Fantastic]

The blades aren't at 45 degrees, so if you rotate 90 degrees, you will have one fined-out aerofoil with an engine that won't be able to compress. But you can't do the 90 degree rotation because the blades have firtree roots, so it's academic anyway.

[A-FLOOR]

Panama Jack

I thought Pratt & Whitney was originally Canadian?

[ramsrc]

I suspect it has something to do with Rolls Royce being British, and British build reciprocal engines turned clockwise, while US build reciprocal engines turned counterclockwise

I could be wrong here, but I seem to remember reading in the dim and distant that on the earlier Merlin powered Spitfires the engine turned clockwise, whereas the later Griffon engined versions turned anti-clockwise.

[Tim Zukas]

All Merlins turned the same way, didn't they? (Except for the Hornet and any other handed twins.) And yes, it was the exception among British recips.

[paulo]

not really answering the post, but was interested to see the 'Down Between Engines' A400 in FI recently. One of those funny things in aviation where you think "of course!".

Except you don't have 100m+ dev budget on hand to work your theory out. Back to the coalface.

[Panama Jack]

A-FLOOR,

Got me stumped there. I though P&W was originally US based (but it is now in Canada). Most modern Canadian things are made on the US convention anyhow.

[big bus driver]

Hi A-Floor,

In the T700, and all other RR engines the shafts rotate the same way to reduce relative speeds between the shafts and hence preserve bearing life. (i.e say IP shaft rotates at 7000rpm, HP at 10000rpm when shafts rotate same way, the intershaft bearings spin at 3000rpm, compared to 17000rpm if they were contra-rotating)

There was talk of the T900 for the A380 being RR's first contra-rotating engine as an improved bearing design had been produced. It has the advantage of reducing weight too as you can do away with a 2 stages of NGV's. Don't know if this design is going ahead for production or development only though.

Brgds,

[spannersatcx]

RR rotate clockwise, everyone else (GE, P&W) does the opposite, i.e. anticlockwise. Is there any reason why?

Technically speaking it's the other way round, i.e. P&W rotate clockwise as viewed ALF, as all engine identification is done.

[Old Smokey]

The Merlin rotated in exactly the same direction as all of the other British engines. An extra reduction gear caused the PROPELLOR to turn in the "American" direction.

[av8boy]

P&W was established in Hartford, Connecticut by Frederick Rentschler in July, 1925. The Pratt and Whitney Tool Company provided startup money, factory space, and the name for the new company.

To quote the P&W home page: "Pratt & Whitney's company headquarters is located in East Hartford, Connecticut. Home of our commercial and military engines and power systems businesses, Connecticut also represents the focal point for engineering, marketing, aftermarket services and customer support. Our business, regional and helicopter business, Pratt & Whitney Canada Corporation (P&WC), is based in Longueuil, Quebec."

Of course, P&W is a United Technologies Company.

Dave

[casual observer]

There was talk of the T900 for the A380 being RR's first contra-rotating engine as an improved bearing design had been produced

The Trent 900 will not have conter-rotating spools, but the Trent 1000 will, so will GE's B7E7 engine. GE's Unducted Prop Fan (UDF) had counter-rotating LP spools. The PW6000 will have counter-rotating HP-LP spools. In fact, because it has counter-rotating spools, the fan rotates in a direction opposite to all the other P&W commercial fans, that is, clockwise foward-looking-aft. See the picture in the following link:

http://www.pratt-whitney.com/prod_comm_pw6000.asp