MerlinIIIB From Norway, joined Aug 2005, 120 posts, RR: 0 Posted (7 years 1 week 5 days 6 hours ago) and read 32767 times:
I am seeking facts regarding RPM of jet engines. Questions:
- What is the typical RPM of the fan (first stage) of a GE90 during take-off?
- What is the highest RPM (any stage) of an airline engine (old turbojet?)
Lightsaber From United States of America, joined Jan 2005, 10895 posts, RR: 100 Reply 3, posted (7 years 1 week 5 days 4 hours ago) and read 32767 times:
According to the sites I googled
GE-90-115
N1=2,550 (max) This is really high for that diameter! I believe the fan tips go supersonic at ~2,100 RPM during takeoff (but I'm going from memory). This implies a peak tip Mach #=1.2. That's much higher than what I'm used to seeing! (Peak M=1.1 to 1.15 is much more typical) Yes, a M=0.05 difference is huge!
High turbines turn anywhere from 8,000 to 15,000 RPM. The trend is back toward higher RPMs. For a long while, the trend was slower? Why? Best engine efficiency was obtained by putting one of the rows of compressor blades from the low turbine onto the high tubine. But this new row of larger diameter blades thus became the RPM limiting component on the high spool. Now with improved LPC efficiencies, we're seeing high spool RPMs creep back up. Obviously in a triple spool or GTF the trade study shifts to putting more onto the LPC due to the much higher RPM (~4,000) compared to the GE-90.
That said, the Trent 900 has high RPM's too (notice a trend in new engines?)
N1: 3,000 RPM with peak tip Mach#=1.5
N2: 7,500 RPM (Trent 800, I didn't find the 900's... close enough)
N3 (high spool): 12,500
As I've discussed before, the fan is powered by a turbine that is going so slow (too low Mach #) to be very efficient. So there has been a big push to optimize the fan shape for higher RPM. The curved blade fans actually gain most of their efficiency improvement by getting the LPT up to a decent mach #, not by fan efficiency. (Oh, there is some improvement... but what happens is that the fan efficiency at high mach #'s is way up shifting the trade study to a much higher RPM). I'll admit RR has a trick to get the tip mach to 1.5 that I don't know... Kudos to them. If someone proposed a fan with a M=1.5 tip speed, I would give them a whizquiz. But obviously RR figured out a neat aerodynamic trick. Good thing I don't engineer fans.
I'm a bit suprised by the 7,500 RPM "intermediate spool." This implies that some fancy work was done on the first two stages of the LPC (analogous to the curved fan blades).
High spool RPM (I call it N3) is low due to only a single turbine powering the HPC. I don't fully understand why RR doesn't do a two stage HPT... but obviously their trade studies say stick with one stage... Every trade study I've seen says go with a two stage HPT for a low cost 2% drop in fuel burn... Cest la vie. But drop the 2nd stage HPT for "high cycle" engines as the MX gets out of hand (break even at $40 to $50/bbl oil on short hops... wait... were at $70+/bbl)
SlamClick From United States of America, joined Nov 2003, 10062 posts, RR: 71 Reply 5, posted (7 years 1 week 5 days 4 hours ago) and read 32767 times:
F1 piston engine 18000 RPM. That means that each spark plug fires 150 times per second. If you could see into the combustion chamber I'd guess that the light would never go out.
Interesting comparison.
Happiness is not seeing another trite Ste. Maarten photo all week long.
What's incredible about that RPM is it involves reciprocating components. Each piston goes from 0 mph to god-only-knows mph, and back to 0mph in a fraction of a fraction of a second.
Dl757md From United States of America, joined May 2004, 1555 posts, RR: 18 Reply 7, posted (7 years 1 week 5 days ago) and read 32767 times:
Quoting Lightsaber (Reply 3): GE-90-115
N1=2,550 (max) This is really high for that diameter! I believe the fan tips go supersonic at ~2,100 RPM during takeoff (but I'm going from memory). This implies a peak tip Mach #=1.2. That's much higher than what I'm used to seeing! (Peak M=1.1 to 1.15 is much more typical) Yes, a M=0.05 difference is huge!
That sounds pretty low to me. I mean your numbers seem right if N1 Max is actually 2550 (I don't know). The CF6-80C2B7 on our 764 has a 96" dia. fan and a 100% N1 speed of 3280 RPM with a MAX N1 of 117.5%. So we get a 100% tip speed of 956.3 MPH or 1.26 Mach and MAX N1 speed of 1123.6 MPH or 1.48 Mach. The tips go supersonic at a measly 79.4% N1! which is when you start to hear the growl or buzzsaw sound that a turbofan makes at higher power settings.
Dougloid From , joined Dec 1969, posts, RR: Reply 8, posted (7 years 1 week 5 days ago) and read 32767 times:
The engine on your namesake turns at 43,750 rpm at 100 per cent Mistah IIIB.
I spent many happy times under, inside and on top of a number of Merlins and Metros that ranged from sweeeeet to raunchy. Pulled apart more than a few Garretts as well.
F14D4ever From United States of America, joined May 2005, 319 posts, RR: 4 Reply 10, posted (7 years 1 week 4 days 23 hours ago) and read 32767 times:
Quoting Dl757md (Reply 7): The CF6-80C2B7 on our 764 has a 96" dia. fan ...So we get a 100% tip speed of 956.3 MPH or 1.26 Mach and MAX N1 speed of 1123.6 MPH or 1.48 Mach.
Oops, you're quoting the fan diameter for the -80E1. The -80C2 variants have an 83 inch fan diameter. That knocks 100% Mach down to around 1.09.
MarkC From United States of America, joined Apr 2006, 259 posts, RR: 0 Reply 11, posted (7 years 1 week 4 days 23 hours ago) and read 32767 times:
2,550 does seem really high for that fan size.
Off memory, a 94" PW4000 is 3,900, a 100" is 2,800, and a 112" is 2,400. N2 is just over 10,000 in all.
PW2000's are a little smaller, I think they are 4,800 N1. Some of the old military stuff screamed. I think the TF30 was 10,000 N1, 14,000 N2. Lightsaber is right about the trend. Its what I heard also.
Dl757md From United States of America, joined May 2004, 1555 posts, RR: 18 Reply 12, posted (7 years 1 week 4 days 22 hours ago) and read 32767 times:
Quoting F14D4ever (Reply 10): Oops, you're quoting the fan diameter for the -80E1. The -80C2 variants have an 83 inch fan diameter. That knocks 100% Mach down to around 1.09.
Well in defending myself I've found we're both off. According to the 764 AMM it's actually 98" (which is what I used in my calculations so my tip speed numbers are correct, I just typed 96 rather than 98) and it's not the 7F but rather the 8F. You know 7...8....whatever it takes.
From the Boeing 767-400ER AMM:
CF6-80C2B8F ENGINE DATA
Nominal Thrust Class 63,500 lbs.
Installed Take off thrust (sea level, 92°F) 58,300 lbs.
Installed Climb Thrust (ECS on), 12,450 lbs. at 35,000 ft.
Maximum temperature (lat take off 86°F (30.0°C) rating
Exhaust gas temperature redline 1,760°F (960°C)
Installed Cruise thrust (ECS on), 11,550 lbs. at 35,000 ft.
MerlinIIIB From Norway, joined Aug 2005, 120 posts, RR: 0 Reply 13, posted (7 years 1 week 4 days 13 hours ago) and read 32767 times:
Quoting Dougloid (Reply 8): The engine on your namesake turns at 43,750 rpm at 100 per cent Mistah IIIB
You guessed it, that number from the Garrett has always impressed me. Thank you all for excellent feed-back on my initial question. Now I return my attention on the World Cup football events...
Lightsaber From United States of America, joined Jan 2005, 10895 posts, RR: 100 Reply 15, posted (7 years 1 week 4 days 1 hour ago) and read 32767 times:
Jet engines sure are awesome pieces of engineering. The forces they have to withstand are huge. Doesn't supersonic speed create sound issues? And thanks for such a nice post.
Quoting SlamClick (Reply 5): F1 piston engine 18000 RPM. That means that each spark plug fires 150 times per second. If you could see into the combustion chamber I'd guess that the light would never go out.
That's awesome too. It's incredible that in 1/150 seconds it has time to take the fuel, compress it and ignite it.
Dougloid From , joined Dec 1969, posts, RR: Reply 17, posted (7 years 1 week 3 days 8 hours ago) and read 32767 times:
Quoting Keta (Reply 16): Quoting SlamClick (Reply 5):
F1 piston engine 18000 RPM. That means that each spark plug fires 150 times per second. If you could see into the combustion chamber I'd guess that the light would never go out.
That's awesome too. It's incredible that in 1/150 seconds it has time to take the fuel, compress it and ignite it.
Kinda funny thing. The only thing I remember ever really wanting to be as a kid was a mechanic-a really good one.
Art From Lebanon, joined Feb 2005, 2979 posts, RR: 0 Reply 18, posted (7 years 1 week 3 days ago) and read 32767 times:
Quoting SlamClick (Reply 5): F1 piston engine 18000 RPM. That means that each spark plug fires 150 times per second.
Half as often in fact. It's a 4 stroke engine so the piston has to go from the top of its stroke to the bottom (half a revolution of the crankshaft) to pull in the fuel/air charge (induction stroke), then go to the top of the stroke (compression stroke), BANG then piston goes to bottom of stroke (power stroke), piston then goes to top of stroke (exhaust stroke).
As you can see, each spark plug only ignites the fuel/air mixture in its cylinder every 2 revolutions of the crankshaft. But, as you point out, that's still an awful lot of times a second!
The other point made that there is not much time to burn the mixture. The speed at which the fuel can be burnt in a controlled manner is a limiting factor.
Lightsaber From United States of America, joined Jan 2005, 10895 posts, RR: 100 Reply 19, posted (7 years 1 week 2 days 2 hours ago) and read 32767 times:
Yes and no... The supersonic blade tips due create shock waves. However, the fan is engineered in such a manner to ensure that these shock waves hit sound deadening material before going through the fan exit stators. Thus, thanks to increasing bypass ratios, we're actually seeing a drop in noise.
Also, the turbine exhaust remains the noisiest component of the engine. But as the bypass ratio increases, more work is removed from the core gases. Thus soon it will be other components creating the noise.
One disadvantage of the GTF is that under certain scenarios, the gear noise will be heard. Its like the Trent "buzz saw" noise, not a big deal, but will passangers except a new sound?
What I do know is as long as oil is above $50/bbl, you'll see a lot more effort put into fuel efficiency. This is good unless your a fan of "vintage jets." For the adoption of lean manufacturing policies (cheap purchase price) combined with the improved efficiency of new designs will force the retirement of old airframes at an earlier time in my opinion. Fuel cannot remain close to 30% of an airline's cost...
Bri2k1 From United States of America, joined Dec 2004, 988 posts, RR: 4 Reply 21, posted (7 years 1 week 1 day 1 hour ago) and read 32767 times:
Quoting Lightsaber (Reply 19): But as the bypass ratio increases, more work is removed from the core gases.
That, and there's a less turbulent transition from the hot and fast core exhaust to the stationary and cool ambient air. The bypass air cushions the mixing zone, acting a lot like organ pipe mixers on older lower-bypass-ratio huskit systems.
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Every trade study I've seen says go with a two stage HPT for a low cost 2% drop in fuel burn... Cest la vie. But drop the 2nd stage HPT for "high cycle" engines as the MX gets out of hand (break even at $40 to $50/bbl oil on short hops... wait... were at $70+/bbl) 
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From Lebanon, joined Feb 2005, 2979 posts, 
This is good unless your a fan of "vintage jets." For the adoption of lean manufacturing policies (cheap purchase price) combined with the improved efficiency of new designs will force the retirement of old airframes at an earlier time in my opinion. Fuel cannot remain close to 30% of an airline's cost... 
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