Actual RB211 RPM

[SB4200]

I remember seeing some time ago a thread about what RPM engines such as the RB211 actually spin at. Unfortunately the 4 character minimum in the search function doesn't lend itself to finding a lot of topics in this TLA full industry and I can't find it.

So i'm interested in either finding that thread, or alternatively, could someone tell me what sort of RPM each spool is spinning at at 100%?

Thanks

[EGT Redline]

Which variant?

The figures for the -535 at 100 percent are:

N1 - 4500 RPM
N2 - 7000 RPM
N3 - 10611 RPM

Hope this helps.

[it will do the trip]

RB211-535E4 on 757

100% N1 = 4500 LP RPM
100% N2 = 7000 IP RPM
100% N3 = 10611 HP RPM

Thats confirmed then, must have posted at the same time

[SB4200]

Ah thanks a lot...

Any figures on the -524GT?

[Nepotisim]

RB211-524GT

All figures at 100%

N1 3900 RPM
N2 7000 RPM
N3 10611 RPM

Interesting to see that only the fan speed changes. Wouldn't have guessed that, considering the size difference of the engines.

Trent 900 figures anyone?

[barit1]

I'll wager that these are merely 100% gage calibration points. On a cold day N1% will certainly be lower than on ISA day. (Because of increasing air density).

At moderately higher OAT N1 will increase, but once above the flat-rate limit, N1 falls off again (for EGT protection).

[N1 Vibes]

barit1

the probe sensing the speed knows nothing of OAT or barometric press. The rpm vs % curve is directly related and unchanged at all temps.

Brgd's

N1 Vibes

[barit1]

You're right, the N1 gage knows nothing of OAT - but the ENGINE does.

To reach a given EPR, the engine doesn't have to turn as fast on a cold day (high density = high mass flow at a given N1). This is the whole concept behind using N1 for power management (eg a GE or CFM engine); You can't know what N1 to set until you know OAT (and also pressure altitude...)

[spannersatKL]

Barit sorry not sure if you are confused...the RB211 uses EPR for power calculation and not N1 unlike some other brands one sees!! So no N1 to set etc.....

[barit1]

spannersatKL - No, I understand fully the RR/PW EPR (IEPR) scheme.

I'm merely saying if you set EPR on a warm day and note the N1, then set the same EPR on a cold day and note the N1, you will come to the conclusion I stated: When the air is more dense, it takes less fan rpm to achieve a given EPR. :ooh:

The air doesn't care who makes the fan. :ooh::ooh:

[Sootikin]

It's even more confusing than some might think.

The percentage / shaft speeds relations quoted previously are purely reference numbers, and are not the actual operating limits. (I believe that these RPMs were the originally predicted operating speeds for the RB211-22B. Actual engine data showed that the operating limits would be different, but for convenience, the limits are quoted as percentages.)

So, for the RB211-524G/H/-T
Reference Speeds
100% HP = 10,611 rpm
100% IP = 7,000 rpm
100% LP= 3,900 rpm

MTO Operating Limits
HP Speed = 99.2%
IP Speed = 107.7%
LP Speed = 110.5% (i.e. 1.105 x 3900 = 4309.5 rpm)

(There are also Max Continuous and Max Overspeed / Overtemp limits, but lets not add to the confusion.)

The equivalent Trent 900 data you should find in the TCDS on the EASA site.

Hope This Helps.

[barit1]

Agreed, and for each different engine the numbers are different.

[N1 Vibes]

barit1,

what confused me was that you didn't mention EPR/N1 relationship in your first post:

I'll wager that these are merely 100% gage calibration points. On a cold day N1% will certainly be lower than on ISA day. (Because of increasing air density).

Of course you will have a different N1% on a cold day over a hot day, as you will be setting a different EPR, not because the indicated N1 % changes due to temp.

Hopefully you can see where there was confusion....

Sincerely,

N1 Vibes