Sponsor Message:
Aviation Technical / Operations Forum
My Starred Topics | Profile | New Topic | Forum Index | Help | Search 
Turbofan RPM  
User currently offlineMonorail From United States of America, joined Sep 2004, 625 posts, RR: 4
Posted (10 years 1 day 23 hours ago) and read 23298 times:

Sorry if this has been discussed before but I couldn't find anything

How many RPM would a turbofan, like on a 737 cruising at 450 knots, be doing? How much does RPM at cruising speed vary from commercial jets, from a 717 to a 777?


Playoffs? Don't talk about playoffs!
36 replies: All unread, showing first 25:
 
User currently offlineAlessandro From , joined Dec 1969, posts, RR:
Reply 1, posted (10 years 1 day 16 hours ago) and read 23224 times:

Maybe you could contact these guys, http://www.geae.com/feedback.html
and ask. Can´t find anything on their homepage..


User currently offlineAir2gxs From , joined Dec 1969, posts, RR:
Reply 2, posted (10 years 1 day 14 hours ago) and read 23247 times:

CF680C2B6F max N1 rotor speed 3854 rpm, N2 speed 11055 rpm

PW4000 Max N1 rotor speed 4012 rpm, N2 speed 10,450 rpm

CFM 100% N1 rotor speed 5175 rpm, N2 speed @ 100% 14460

As you can see these are max numbers (except for the CFM). Cruise power rpm is dependant on power setting.


User currently offlineSlamClick From United States of America, joined Nov 2003, 10062 posts, RR: 68
Reply 3, posted (10 years 1 day 13 hours ago) and read 23184 times:

Also worthy of note, 100% is not necessarily the highest allowable RPM. It is a designation made somewhere along the development of the engine. It is not uncommon to see a power setting of 104% or so being called for. It is, however, a useful benchmark.




Happiness is not seeing another trite Ste. Maarten photo all week long.
User currently offlineAir2gxs From , joined Dec 1969, posts, RR:
Reply 4, posted (10 years 1 day 12 hours ago) and read 23164 times:

Slamclick is correct, the max allowable on a CF6 (as we operate it) is: 117.5%. That is why I made the distinction in my text.

User currently offlineTimz From United States of America, joined Sep 1999, 6835 posts, RR: 6
Reply 5, posted (10 years 1 day 5 hours ago) and read 23123 times:

So PW4000s fans (?) can turn at 4000 rpm-- so the tips are supersonic?

User currently offlineAir2gxs From , joined Dec 1969, posts, RR:
Reply 6, posted (10 years 16 hours ago) and read 23053 times:

As far as I know the tips never go supersonic. Sets up all kinds of nasty vibrations. Vibrations are very bad to jets. We do everything we can to minimize them.

User currently offlineYikes! From Canada, joined Oct 2001, 284 posts, RR: 1
Reply 7, posted (10 years 14 hours ago) and read 23043 times:

The fan is usually turned through a reduction gearbox. Don't know the ratio from type to type...

User currently offlineAir2gxs From , joined Dec 1969, posts, RR:
Reply 8, posted (10 years 14 hours ago) and read 23035 times:

The fan is not turned by a reduction gearbox. The fan is a directly connected to the N1 shaft, which is connected to the low pressure turbine. This is direct drive.

Propellers on turbo-props are driven by a reduction gearbox.


User currently offlineGaut From Belgium, joined Dec 2001, 344 posts, RR: 2
Reply 9, posted (10 years 7 hours ago) and read 22988 times:

The Fan tip never go supersonic; It's why bigger engines turn slower.




«Horum omnium fortissimi sunt Belgae.»
User currently offlineTimz From United States of America, joined Sep 1999, 6835 posts, RR: 6
Reply 10, posted (10 years 5 hours ago) and read 22966 times:

So does the PW4000 fan reach 4000 RPM or not?

Correct me if I'm wrong, but isn't the fan at least 94 inches across? If so, even 3000 RPM would make the tips supersonic.


User currently offlineYikes! From Canada, joined Oct 2001, 284 posts, RR: 1
Reply 11, posted (10 years 4 hours ago) and read 22948 times:

Can't argue, Air2gxs. Was thinking turboprop. My apology. Bottom line though, the lowest energised turbine wheel(s) turn(s) the fan and, through engine design, the fan turns at an optimum RPM. Hence the advantage during the takeoff run.

User currently offlinePrebennorholm From Denmark, joined Mar 2000, 6449 posts, RR: 54
Reply 12, posted (10 years 4 hours ago) and read 22940 times:

A 94 inches fan rotating at 4,000 rpm has a tip speed of almost exactly 500 m/s which is Mach 1.5 to 1.65 depending on altitude (Mach 1 speed varies according to air density).

To get the true airspeed at the tips we must add the forward speed component, so the airspeed at the fan tips at max N1 is closer to Mach 2 than Mach 1.

If the power setting is 50%, 100% or 117.5%, it doesn't change the rpm that much. Fan tips are always supersonic at anything but idle.



Always keep your number of landings equal to your number of take-offs, Preben Norholm
User currently offlineAir2gxs From , joined Dec 1969, posts, RR:
Reply 13, posted (10 years 1 hour ago) and read 22913 times:

I never did the math, I just assumed. A quick internet search shows that this is possible. I even saw a reference to the "buzz saw" noise being the tips going super-sonic. Now I can assure you, from experience, the "buzz saw" noise occurs nowhere near 50% N1 on a CF6, it seems to appear somewhere between 85% and 90% (haven't been on a run in a while).

I got a powerplant engineer buddy. I'll contact him and see what he says.


User currently offlineIndianguy From , joined Dec 1969, posts, RR:
Reply 14, posted (9 years 12 months 4 days 14 hours ago) and read 22835 times:

Whats the difference between N1 and N2?

User currently offlineAir2gxs From , joined Dec 1969, posts, RR:
Reply 15, posted (9 years 12 months 4 days 14 hours ago) and read 22831 times:

N1 is the low pressure compressor, including the fan. N2 is the high pressure compressor.

Unless you're talking Rolls Royce, they use a 3 spool engine:
N1 - Fan
N2 - Intermediate Pressure
N3 - High Pressure


User currently offlineBroke From United States of America, joined Apr 2002, 1322 posts, RR: 3
Reply 16, posted (9 years 12 months 4 days 13 hours ago) and read 22822 times:

The larger the diameter of the fan, the slower its maximum RPM. If you are watching an airliner taking off and you are to the front of the airplane, you will hear a sound similar to a large rotary blade saw cutting wood. That sound is the noise caused by the blade tip shock waves as they just exceed Mach 1.

Turbomeca, some years ago, did build a turbofan engine for the corporate aircraft market that used a reduction gearbox to drive the fan. I do not think it ever went into production. Most turbofan engines use a direct drive from the low speed (or low pressure turbine). This combined fan and low pressure turbine is usually (very little is absolute) called the N1 rotor.

The next rotor, which is the high pressure rotor on all but Rolls-Royce engines, is the N2. On RR turbofan engines, this is called the intermediate pressure rotor. They have added a third rotor, starting with the RB-211-22C engine, and that is the high pressure rotor or N3.

Free turbine engines, used on mostly helicopters but are on some airplanes, throw a whole other set of designations for the free turbine section.


User currently offlineTimT From United States of America, joined Jun 2001, 168 posts, RR: 0
Reply 17, posted (9 years 11 months 3 weeks 1 day 23 hours ago) and read 22613 times:

Another knot in the rope-- fan speed is also measured at the tip with magnetic sensor. I've still got the set of gauges for a P&W JT-9. The CF-6 also measured in that location.

User currently offlineDakotasport From Canada, joined Dec 2000, 228 posts, RR: 0
Reply 18, posted (9 years 11 months 3 weeks 1 day 22 hours ago) and read 22606 times:

Guys, i remeber in school that 2 spool engines (GE and Pratt as examples) DID have reduction gearing for N1 compressor (fan). Any insight??

User currently offlineAir2gxs From , joined Dec 1969, posts, RR:
Reply 19, posted (9 years 11 months 3 weeks 1 day 15 hours ago) and read 22585 times:

Dakotasport,

I know of no turbofan engines where N1 is driven through a reduction gearbox. The 2 GE's I've worked with (CFM56 & CF6) are direct drive and the PW's (JT3, JT8, JT9, PW2000 & PW4000) are also direct drive.

The low pressure turbine drives the low pressure compressor/fan.

Are there any smaller engines that use a reduction gearbox? I don't know, but it certainly seems a waste. Un-necessarily complex and there is an associated loss of power through the transmission.


User currently offlineMD11Engineer From Germany, joined Oct 2003, 14026 posts, RR: 62
Reply 20, posted (9 years 11 months 3 weeks 1 day 12 hours ago) and read 22568 times:

There was some talk about using a reduction planetary gearbox on one of the future really big fan designs, to keep the low pressure compressor speed close to an ideal value, while at the same time driving the fan at a much lower speed. I don´t know what happened to this design though. I think it was from P&W.

Jan


User currently offlineSanthosh From India, joined Sep 2001, 545 posts, RR: 1
Reply 21, posted (9 years 11 months 3 weeks 1 day 10 hours ago) and read 22554 times:

Are there Transducers attached to the engine to measure vibrations on N1 and N2?If so what are the normal Vibration readings during cruise for Airbus a/c .Does vibration measurement has some units?

George



Happy Landing
User currently offlineAir2gxs From , joined Dec 1969, posts, RR:
Reply 22, posted (9 years 11 months 3 weeks 1 day 9 hours ago) and read 22550 times:

Different engines have different vibration limits. These limits are also different between the high pressure shaft and the low pressure shaft. Some aircraft also have an overall vibration limit (broadband). The units are inches per second.

I don't believe I've ever seen an indicator that depicts in/sec, typically the manufacturer will assign a unit to a value and depict the indication as units. I know that the limit on a B767 (CF6) fan is 4 units, but I don't know what 4 units correspond to in in/sec.

I'm not sure I even understand what I just wrote.


User currently offlineAir2gxs From , joined Dec 1969, posts, RR:
Reply 23, posted (9 years 11 months 3 weeks 1 day 9 hours ago) and read 22547 times:

Here, I'll let Boeing explain it, from the B767 AMM:

With engine operating, the engine accelerometers generate signals proportional to engine motion in a radial direction. These signals are received by the AVM signal conditioner, where they are converted to signals suitable for the EICAS computer. Signals are then sent to the display unit from the computer where vibration displacement or velocity is read in units.


User currently offlineG4doc2004 From United States of America, joined Feb 2004, 123 posts, RR: 0
Reply 24, posted (9 years 11 months 3 weeks 1 day 5 hours ago) and read 22534 times:

I know for a fact that the Honeywell TFE-731 family of engines use planetary gear reduction for the N1 fan. The smaller engines spin faster. If I recall my TFE-731 schooling, the N2 rotor spins at around 20,000 RPM. The fan must be geared or it would be not only inefficient, but it would not survive the high rotational speed.


"Failure to prepare is preparing to fail"--Benjamin Franklin
25 Post contains images FinningleyMech : This is a pretty interesting flash animation, for the trent 800, shows details on each stages, fan, combustor, HP turbine etc, temperatures, rpm, and
26 WIDEBODYPHOTOG : PW4462 94in Fan (MD-11) 100% N1 rotor rpm is 3600rpm redline = 111.4% 4100rpm 100% N2 rotor rpm is 9900rpm redline = 105.5% 10450rpm Typical tip veloc
27 Bd5jdave : Hello folks. Since GEAP has a bad web site, and I am an GEAP engineer, maybe I can help. There's a lot of misunderstanding here, so I'll try to clear
28 Timz : So you're saying a PW4000 with a 94-inch fan never turns faster than 3000 rpm? Or are you saying the speed of sound is higher than normal-atmospheric
29 Bd5jdave : Slightly higher, yes. And yes, I doubt that it spins much more than 3000 rpm. But that's not my engine, so I can't be sure. It uses supercritical wing
30 Timz : More questions: You said almost all turbofan engines use free turbines. By that you mean a turbine that powers the fan and nothing else? On the CF6 fo
31 Bd5jdave : Yes, most turbofan engines have two shafts, one inside the other. Go here: http://www.geae.com/education/engines101 You'll learn what you want to know
32 WIDEBODYPHOTOG : Timz The fan on a CF6-80a or CF6-50 is 86.4in diameter. I'll assume that it's not a -80c or 80e. That fan, spinning at an angular speed of 3850rpm is
33 A/c train : Santhosh, Vibration indication works on the piezoelectric crystal method, were if you press down it, it builds up a charge goes back to original shap
34 WIDEBODYPHOTOG : OK, now for the more complicated stuff... Supersonic velocities at fan or compressor blade tips are really not a problem at all. As long as you have t
35 WIDEBODYPHOTOG : There are some notable examples of geared turbofan engines: Allied Signal TFE-731 (Bombardier learjet, Lockheed Jetstar) Allison ALF-502/507 (Avro RJ,
36 Post contains images Klaus : WIDEBODYPHOTOG: Supersonic velocities at fan or compressor blade tips are really not a problem at all. As long as you have the right aerodynamics ther
Top Of Page
Forum Index

Reply To This Topic Turbofan RPM
Username:
No username? Sign up now!
Password: 


Forgot Password? Be reminded.
Remember me on this computer (uses cookies)
  • Tech/Ops related posts only!
  • Not Tech/Ops related? Use the other forums
  • No adverts of any kind. This includes web pages.
  • No hostile language or criticizing of others.
  • Do not post copyright protected material.
  • Use relevant and describing topics.
  • Check if your post already been discussed.
  • Check your spelling!
  • DETAILED RULES
Add Images Add SmiliesPosting Help

Please check your spelling (press "Check Spelling" above)


Similar topics:More similar topics...
Turbofan Derivative Of The P&W JT-4? posted Fri Sep 8 2006 21:31:23 by A342
Tire RPM's For Takeoff-landings posted Tue Aug 15 2006 19:21:09 by 747LUVR
Does Bypass Flow On A Turbofan Decrease Noise? posted Tue Jul 25 2006 08:01:33 by Bio15
RPM Of Jet Engines During Take-off posted Fri Jun 9 2006 18:00:26 by MerlinIIIB
Turbofan C02 Emissions posted Wed Mar 15 2006 11:32:43 by Zarniwoop
Effect Of Temp/Density On HP/LP RPM posted Sun Jan 15 2006 22:10:18 by Tg 747-300
Cessna Cruise RPM Question posted Wed Dec 7 2005 18:17:21 by Tbar220
Starting Turbofan Engines And APU's posted Wed Sep 28 2005 14:27:19 by PMN
Spitfire/Warbird Prop Rpm posted Fri Sep 16 2005 15:18:08 by Redfox
Fastest-ever Engine RPM? posted Sat Jul 23 2005 01:37:31 by Timz
Geared Turbofan Obsoletes Airline Turboprop? posted Tue May 6 2008 10:14:22 by Cloudy
Question Re: Turbofan Climb Thrust Reduction posted Tue Mar 25 2008 14:49:42 by Boeing747_600
J-52 / JT8D / Swedish RM-8 Turbofan: Spool-up Time posted Sat Dec 29 2007 08:51:55 by Blackbird
Turbofan With Free-spinning Fan Section? posted Thu Dec 27 2007 14:49:58 by KELPkid
TurboFan Engine: Fan Operating In Reverse? posted Thu Nov 15 2007 11:24:54 by Guessbb

Sponsor Message:
Printer friendly format