MerlinIIIB
Topic Author
Posts: 97
Joined: Sat Aug 20, 2005 7:32 pm

RPM Of Jet Engines During Take-off

Sat Jun 10, 2006 1:00 am

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.
 
Woodreau
Posts: 1185
Joined: Mon Sep 24, 2001 6:44 am

RE: RPM Of Jet Engines During Take-off

Sat Jun 10, 2006 1:07 am

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.
 
EMBQA
Posts: 7797
Joined: Sat Oct 25, 2003 3:52 am

RE: RPM Of Jet Engines During Take-off

Sat Jun 10, 2006 1:50 am

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 avatar
lightsaber
Crew
Posts: 11830
Joined: Wed Jan 19, 2005 10:55 pm

RE: RPM Of Jet Engines During Take-off

Sat Jun 10, 2006 2:35 am

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
"They did not know it was impossible, so they did it!" - Mark Twain
 
777wt
Posts: 828
Joined: Wed Jan 19, 2005 7:45 am

RE: RPM Of Jet Engines During Take-off

Sat Jun 10, 2006 2:40 am

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
 
SlamClick
Posts: 9576
Joined: Sun Nov 23, 2003 7:09 am

RE: RPM Of Jet Engines During Take-off

Sat Jun 10, 2006 2:59 am

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.
 
2H4
Posts: 7960
Joined: Tue Oct 19, 2004 11:11 pm

RE: RPM Of Jet Engines During Take-off

Sat Jun 10, 2006 3:10 am




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
 
dl757md
Posts: 1482
Joined: Mon May 24, 2004 9:32 am

RE: RPM Of Jet Engines During Take-off

Sat Jun 10, 2006 6:28 am

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!
 
Dougloid
Posts: 7248
Joined: Tue Jul 05, 2005 2:44 am

RE: RPM Of Jet Engines During Take-off

Sat Jun 10, 2006 6:45 am

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.
If you believe in coincidence, you haven't looked close enough-Joe Leaphorn
 
ArmitageShanks
Posts: 3755
Joined: Tue Dec 30, 2003 5:30 am

RE: RPM Of Jet Engines During Take-off

Sat Jun 10, 2006 7:19 am

130,000 rpm is not uncommon for those model jet engines.
 
F14D4ever
Posts: 306
Joined: Sat May 07, 2005 3:20 am

RE: RPM Of Jet Engines During Take-off

Sat Jun 10, 2006 7:19 am

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."
 
MarkC
Posts: 238
Joined: Tue Apr 25, 2006 8:10 am

RE: RPM Of Jet Engines During Take-off

Sat Jun 10, 2006 7:55 am

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
Posts: 1482
Joined: Mon May 24, 2004 9:32 am

RE: RPM Of Jet Engines During Take-off

Sat Jun 10, 2006 8:44 am

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!
 
MerlinIIIB
Topic Author
Posts: 97
Joined: Sat Aug 20, 2005 7:32 pm

RE: RPM Of Jet Engines During Take-off

Sat Jun 10, 2006 5:55 pm

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 
 
dl757md
Posts: 1482
Joined: Mon May 24, 2004 9:32 am

RE: RPM Of Jet Engines During Take-off

Sun Jun 11, 2006 5:14 am

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 avatar
lightsaber
Crew
Posts: 11830
Joined: Wed Jan 19, 2005 10:55 pm

RE: RPM Of Jet Engines During Take-off

Sun Jun 11, 2006 5:55 am

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
"They did not know it was impossible, so they did it!" - Mark Twain
 
keta
Posts: 405
Joined: Thu Mar 24, 2005 7:14 am

RE: RPM Of Jet Engines During Take-off

Sun Jun 11, 2006 6:11 pm

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
 
Dougloid
Posts: 7248
Joined: Tue Jul 05, 2005 2:44 am

RE: RPM Of Jet Engines During Take-off

Sun Jun 11, 2006 10:24 pm

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.
If you believe in coincidence, you haven't looked close enough-Joe Leaphorn
 
art
Posts: 2679
Joined: Tue Feb 08, 2005 11:46 am

RE: RPM Of Jet Engines During Take-off

Mon Jun 12, 2006 6:21 am

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 avatar
lightsaber
Crew
Posts: 11830
Joined: Wed Jan 19, 2005 10:55 pm

RE: RPM Of Jet Engines During Take-off

Tue Jun 13, 2006 4:29 am

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
"They did not know it was impossible, so they did it!" - Mark Twain
 
F14D4ever
Posts: 306
Joined: Sat May 07, 2005 3:20 am

RE: RPM Of Jet Engines During Take-off

Wed Jun 14, 2006 4:48 am

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."
 
bri2k1
Posts: 952
Joined: Sun Dec 19, 2004 4:13 am

RE: RPM Of Jet Engines During Take-off

Wed Jun 14, 2006 5:30 am

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.
Position and hold

Who is online

Users browsing this forum: FAST Enterprise [Crawler], Florianopolis, Web500sjc and 14 guests