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RPM Of Jet Engines During Take-off  
User currently offlineMerlinIIIB From Norway, joined Aug 2005, 121 posts, RR: 0
Posted (8 years 4 months 2 weeks 7 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?)

Answers or links are most welcome.

21 replies: All unread, jump to last
 
User currently offlineWoodreau From United States of America, joined Sep 2001, 1049 posts, RR: 7
Reply 1, posted (8 years 4 months 2 weeks 7 hours ago) and read 32767 times:

I'm just throwing out a number, I have no idea on how it compares to other jet engines.

40,560rpms 104% N1 PT-6-67B engine



Bonus animus sit, ab experientia. Quod salvatum fuerit de malis usu venit judicium.
User currently offlineEMBQA From United States of America, joined Oct 2003, 9364 posts, RR: 11
Reply 2, posted (8 years 4 months 2 weeks 6 hours ago) and read 32767 times:

Quoting MerlinIIIB (Thread starter):
Answers or links are most welcome.

Did you try the GE Aircraft Engine web site...?? It's loaded with really cool demo's and information.



"It's not the size of the dog in the fight, but the size of the fight in the dog"
User currently offlineLightsaber From United States of America, joined Jan 2005, 13248 posts, RR: 100
Reply 3, posted (8 years 4 months 2 weeks 6 hours ago) and read 32767 times:
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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!

N2=10,850 RPM (which is actually slow for a high turbine)
http://www.turbokart.com/about_ge90.htm

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  wideeyed   wideeyed   wideeyed 
N2: 7,500 RPM (Trent 800, I didn't find the 900's... close enough)  wideeyed 
N3 (high spool): 12,500  yawn 

RPM Of Jet Engines During Take-off (by MerlinIIIB Jun 9 2006 in Tech Ops)
http://www.rolls-royce.com/civil_aerospace/technology/threeshaft.jsp

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.  Smile

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...  Wink 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)  scratchchin 

I'd like to say more, but work calls...

Hope this helps,
Lightsaber



Societies that achieve a critical mass of ideas achieve self sustaining growth; others stagnate.
User currently offline777WT From United States of America, joined Jan 2005, 877 posts, RR: 1
Reply 4, posted (8 years 4 months 2 weeks 6 hours ago) and read 32767 times:

Quoting MerlinIIIB (Thread starter):
- What is the typical RPM of the fan (first stage) of a GE90 during take-off?

Fan speed = 2,552 RPM.

Core speed = 10,850 RPM


User currently offlineSlamClick From United States of America, joined Nov 2003, 10062 posts, RR: 68
Reply 5, posted (8 years 4 months 2 weeks 5 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.
User currently offline2H4 From United States of America, joined Oct 2004, 8955 posts, RR: 60
Reply 6, posted (8 years 4 months 2 weeks 5 hours ago) and read 32767 times:
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Quoting SlamClick (Reply 5):
F1 piston engine 18000 RPM.

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.

Incredible.




2H4





Intentionally Left Blank
User currently offlineDl757md From United States of America, joined May 2004, 1562 posts, RR: 17
Reply 7, posted (8 years 4 months 2 weeks 2 hours 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.

DL757Md



757 Most beautiful airliner in the sky!
User currently offlineDougloid From , joined Dec 1969, posts, RR:
Reply 8, posted (8 years 4 months 2 weeks 2 hours 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.


User currently offlineArmitageShanks From UK - England, joined Dec 2003, 3630 posts, RR: 15
Reply 9, posted (8 years 4 months 2 weeks 1 hour ago) and read 32767 times:

130,000 rpm is not uncommon for those model jet engines.

User currently offlineF14D4ever From United States of America, joined May 2005, 319 posts, RR: 4
Reply 10, posted (8 years 4 months 2 weeks 1 hour 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.



"He is risen, as He said."
User currently offlineMarkC From United States of America, joined Apr 2006, 259 posts, RR: 0
Reply 11, posted (8 years 4 months 2 weeks 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.


User currently offlineDl757md From United States of America, joined May 2004, 1562 posts, RR: 17
Reply 12, posted (8 years 4 months 2 weeks 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.

Bypass ratio 5.3 to 1

Compressor pressure ratio 27.4 to 1

Maximum N1 rpm 3,854 rpm (117.5%)

Maximum N2 rpm 11,055 rpm (112.5%)

Weight (bare engine) 9,327 lbs.

Nominal Engine Length 170 inches

Nominal Fan Diameter 98 inches


I'll measure one tonight at work just to be sure.

DL757Md



757 Most beautiful airliner in the sky!
User currently offlineMerlinIIIB From Norway, joined Aug 2005, 121 posts, RR: 0
Reply 13, posted (8 years 4 months 1 week 6 days 14 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... smile 


User currently offlineDl757md From United States of America, joined May 2004, 1562 posts, RR: 17
Reply 14, posted (8 years 4 months 1 week 6 days 3 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.



Quoting Dl757md (Reply 12):
Well in defending myself I've found we're both off. According to the 764 AMM it's actually 98"



Quoting Dl757md (Reply 12):
I'll measure one tonight at work just to be sure.

It is indeed a 98" diameter fan on the 80C28F. I measured it last night on the number 1 engine of N840MH.

DL757Md



757 Most beautiful airliner in the sky!
User currently offlineLightsaber From United States of America, joined Jan 2005, 13248 posts, RR: 100
Reply 15, posted (8 years 4 months 1 week 6 days 2 hours ago) and read 32767 times:
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Oops,

I miss-remembered the N1 rotor RPM on Pratt's and the mach number. Good thing that's not what I engineer.  Wink
http://www.aviacao-civil.ifi.cta.br/Espec/EM-2004T03i.pdf

~3,155 RPM on the pw4098

Although, the Trent 900's tip mach number is impressive.  Smile

I'll go back to engineering sub-sonic flows.  Wink

Lightsaber



Societies that achieve a critical mass of ideas achieve self sustaining growth; others stagnate.
User currently offlineKeta From Germany, joined Mar 2005, 448 posts, RR: 0
Reply 16, posted (8 years 4 months 1 week 5 days 14 hours ago) and read 32767 times:

Quoting Lightsaber (Reply 3):

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.



Where there's a will, there's a way
User currently offlineDougloid From , joined Dec 1969, posts, RR:
Reply 17, posted (8 years 4 months 1 week 5 days 10 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.


User currently offlineArt From United Kingdom, joined Feb 2005, 3382 posts, RR: 1
Reply 18, posted (8 years 4 months 1 week 5 days 2 hours 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.

[Edited 2006-06-11 23:36:44]

User currently offlineLightsaber From United States of America, joined Jan 2005, 13248 posts, RR: 100
Reply 19, posted (8 years 4 months 1 week 4 days 4 hours ago) and read 32767 times:
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Quoting Keta (Reply 16):
Doesn't supersonic speed create sound issues?

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?  scratchchin 

What I do know is as long as oil is above $50/bbl, you'll see a lot more effort put into fuel efficiency.  hyper  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...

Lightsaber



Societies that achieve a critical mass of ideas achieve self sustaining growth; others stagnate.
User currently offlineF14D4ever From United States of America, joined May 2005, 319 posts, RR: 4
Reply 20, posted (8 years 4 months 1 week 3 days 4 hours ago) and read 32767 times:

Quoting F14D4ever (Reply 10):
The -80C2 variants have an 83 inch fan diameter.

I was mistaken. Internal GE Aircraft Engines reference book says -80C2 fan diameter is 93 inches and -80E1 fan is 96.2 inches.

Quoting Dl757md (Reply 14):
It is indeed a 98" diameter fan on the 80C28F. I measured it last night on the number 1 engine of N840MH.

Interesting. How and where did you measure? Blade tip to blade tip?



"He is risen, as He said."
User currently offlineBri2k1 From United States of America, joined Dec 2004, 988 posts, RR: 4
Reply 21, posted (8 years 4 months 1 week 3 days 3 hours 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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