I'm not familiar with any 1- or 2-spool engines that have only the fan on N1. Which engines are so designed?

RB211-524 manual says:

C. The engine is a high by-pass ratio, three-shaft turbofan consisting,
basically, of a gas generator system and a mechanically independent L.P.
system.
D. The gas generator system comprises a seven-stage intermediate pressure
(I.P.) compressor, a six-stage high pressure (H.P.) compressor, an
annular combustion section and single-stage I.P. and H.P. turbines.
E. The L.P. system consists of a single-stage compressor (fan) driven by a
three-stage turbine.

The CF6-50 engine is a dual-rotor, axial-flow, gas turbine turbofan.
Basic design is based on a high compression, high bypass ratio concept.

B. An integrated, 4-stage, front fan and low pressure compressor is
driven by a 4-stage low pressure turbine which combines to form the N1
rotor.

The 14-stage high pressure compressor is driven by a 2-stage
high pressure turbine which combines to form the N2 rotor. Each rotor
is mechanically independent of the other.

@Intruder. I was thinking 3 spool. I can't think of any where the LP has anything except the fan.

Obviously a single spool engine would be unlikely to have just a fan stage (unless it was a centrifugal single stage, perhaps, and we hardly can call that a "fan"

The military TF34 is one, and the early CF34's too: Single-stage fan driven by a 4-stage LP turbine, and a 14-stage HP compressor and 2-stage HP turbine core. Said core is a scaled-up version of the T64 helo & turboprop engine.

Note the CF34-8 & -10 are altogether different in layout from these original engines.

I'm not aware of any single-spool engines with a fan, which would amount to in effect a "leaky" stage 1 of the compressor.

Single spool engines, with a fan... (aft fan in these cases) -
GE's CF-700 (aft fan version of the CJ-610/J-85) and
CJ-805-23 (on the CV 990) -
xxx
Strange, that in the case of CJ-805-23, GE kept the "CJ" designation.
xxx
Was the RR Conway R.Co 12 a single or twin spool...?
Had a fan, for its bypass but... cannot recall.
xxx
:)
Happy contrails

The RR Conway was 2-spool.

That makes sense -- evolving a free-turbine turboshaft or turboprop to a fan on the LP stage. Thanks.

the origin of the N in N1,N2, why not R1,R2 ?
 

Thanks guys. Just curious if anyone know the history of the word N?Mathematical terms & percentage!!

Maybe...
xxx
I remember my classes of math and physics, which were in French language, we used the value "n" as a designated or arbitrary amount. While in the Anglo-Saxon world, people will state "I owe you "x" number of dollars", a French language mathematician or physicist would say "I owe you "n" number of dollars"... maybe in an English language math of physics classroom lecture, the "n" is used as well as the French do, to designate a "number"...
xxx
With jet engines, the 100% "N" value is rather arbitrary. Some engine manufacturers might decide to call the maximum rated RPM as 100%, while others will decide the maximum RPM as 98.5% or 101.2%... then like the examples for N1, N2 and N3 (of the RB211) given in previous postings, but might not be the maximum or continuous RPM values...
xxx
We are all familiar with engine stations designations, such as "Pt-2" or "Tt-7" as pressure or temperature values for various "stations" from inlet to exhaust of engines, "N" is another conventional engineering value, expressing RPM...
xxx
This is my interpretation of what "N" means. On the J-85, the RPM indicator was simply called RPM, not "N1", as there was only one shaft. Since I made a major clean-up of my old manuals, for "paper recycling" some years ago, no idea as to where or what publication I can refer to.
xxx
:)
Happy contrails

On the CJ 805-3B (or the Mil. J79) CV 880 engine, max N1 was 103% rpm and 1% eng variation equaled 5% thrust variation.

That brings to mind what is the relationship of "redline" N value to the 100% value quoted by the manufacturer?

PS just a brain teaser :}

Another advantage for the 3-spool that I don't think I have seen here yet:

3 spools allows the engine to be smaller in cross-section because there is an extra spool developing some of the power. This reduces some of the overall drag and could also be a positive where, for example, an aircraft design requires more clearance from the ground when 'hanging an engine under the wing. On the BA 777s a RR Trent 800 has 2 feet less diameter on the engine casing than a GE 90.

Thanks guys

In my university, N was short for Number of rotations of the spools, N therefore.

Some of them may even be still alive. :O

Haha! rockytan, that's gotta be a record.... 15 years from response to acknowledgement..... You don't work for the CAA by any chance do you? :}