View Full Version : RB 211 r.p.m.
Noah Zark.
5th May 2004, 22:05
I'm not connected with the industry at all (only by enthusiasm, if that counts).
I've just been to New York from Manchester and return, courtesy B.A. (excellent service, I might add, even for us in Steerage), and whilst we were gently wafting our way back across the Atlantic, listening to the 211's thrumming away outside, the thought occurred - Whilst at cruise, given "Average" everything, weather, weight, altittude, W.H.Y?, what r.p.m. are the engines turning at?
N1 RPM is in the order of 4,000
N2 7,000
N3 11,000
All figures +/- 10% and typical cruise figures
Noah Zark.
6th May 2004, 20:59
jtr,
Thanks for the reply, but not being in the profession, I don't know what the "N" numbers represent.
I'd be obliged if you could explain.
Thanks. N.Z.
woderick
6th May 2004, 21:52
Rolls, uniquely in the modern era, use three spool engines.
N1 refers to the Low Pressure shaft (that’s the one you can see at the front and back of the engine)
N2 is the intermediate pressure shaft, and strangely N3 is the High pressure shaft.
They are commonly abbreviated to LP, IP, & HP.
Pratt & GE use two shaft engines i.e. N1 & N2.
I know this is over simplistic but it is outside my area of expertise what with me being a simple Avionic sort of chap, I have no idea why Rolls plough their own, particular, furrow.
Noah Zark.
6th May 2004, 22:21
Well, thanks for the info, guys. I am perhaps fortunate in that I never cease to be amazed at the engineering miracle that is Aviation.
Just based very broadly on the figures given, the N3 shaft in each of the 211's that carried me turned over 4 million in one crossing of the Atlantic.
They performed the same coming back over here, then to my knowledge, performed the same again a few days later bringing me home again!
And as far as I know, they did it a few more times whilst I was there, and are probably still doing it now!
What a lump of kit.!
Someone has too much time on their hands!
Not really all that impressive, only takes about 4 revolutions to move 1 metre, consider how much suck, squeeze, bang, blow is going on in your car to do the same at cruise speed.
Takes about 2 revolutions/mt on my car.
Sitting by for technical corrections
Flight Detent
7th May 2004, 10:26
Hi jtr,
that suck, squeeze, bang and blow is going on in ALL combustion engines, automotive as well as aviation (and all others!).
Just thought I'd mention it!!!
No probs,
Cheers:)
Yeh, ahhh thanks for the heads up FD:ok:
The trauma of the SSBB in a recip engine all occuring in the same place was my (unstated) point.
But while you are here, can you tell me why a Roller will give an EPR <1.0 when in idle descent?
gas path
7th May 2004, 11:46
In descent at idle ram pressure will be greater than exhaust pressure so the indicated EPR will be less than 1 (typically 0.9).
At idle on the deck, EPR will read about 1.02.
lasernigel
7th May 2004, 13:55
woderick Working with those in the know apparently:- the design makes them lighter as there are less compressor stages and also because of this they are inherently shorter.
A couple of points.....
Firstly, EPR in a high speed descent (in my experience) will only get down to 0.97.... Not 0.9, that's REALLY low!!!
And secondly, I believe that the economics of the three spool engine (in addition to the above) come from the fact that more compressor stages are working at optimum RPM with the addition of the intermediate pressure turbine...
BN2A
:cool:
TopBunk
8th May 2004, 09:29
In the IAE V2500 the N1 gets down to about 0.87 in the descent - and derating for take off in a 319 often sees about 75% N1 - some derate!
N1 at 0.87???
Who needs speedbrakes!!!
:p
Yeh, I'm with coldstream on this one. Had checker tell me it was because the outlet pressure sensors are only hotstream (have a look up the back of a trent 772 sometime) I didn't buy it.
TopBunk
9th May 2004, 06:31
Whoops. I meant EPR of course!