Sponsor Message:
Aviation Technical / Operations Forum
My Starred Topics | Profile | New Topic | Forum Index | Help | Search 
757 Engine Fan Blade Speed  
User currently offlineIowaman From United States of America, joined May 2004, 4401 posts, RR: 6
Posted (5 years 8 months 3 weeks 3 days 11 hours ago) and read 5535 times:
AIRLINERS.NET CREW
FORUM MODERATOR

I recently had a friend fly on a 752 from DTW-SEA and he commented that the loud distinctive roaring sound heard on takeoff with the 752's was possibly the fan blades exceeding the speed of sound. Is this true, or just sheer power of the PW2040's? I doubt they are actually breaking the sound barrier.

[Edited 2008-12-27 15:10:06]


Next flights: WN DSM-LAS-PHX, US PHX-SJD. Return: US SJD-PHX, WN PHX-MDW-DSM
7 replies: All unread, jump to last
 
User currently offlineDanfearn77 From United Kingdom, joined Jul 2008, 1813 posts, RR: 8
Reply 1, posted (5 years 8 months 3 weeks 3 days 11 hours ago) and read 5508 times:

Good question. I would love to know. I seem to remember reading that the tip of the fan blade can indeed reach the speed of sound but i cannot remember where i read it or what aircraft it was regarding or even if it was true! So i look forward to knowing!


Eagles may soar high, but weasels dont get sucked into jet engines!
User currently offlineFlyASAGuy2005 From United States of America, joined Sep 2007, 7004 posts, RR: 11
Reply 2, posted (5 years 8 months 3 weeks 3 days 10 hours ago) and read 5413 times:

http://www.airliners.net/aviation-forums/tech_ops/read.main/237871

Yes 

I brought the exact thing up in Tech-Ops a while back as the subject always interested me. As a matter of fact, I first got this explanation from DL TOC and I would figure they know what they are talking about.

A tad off topic but i'd like to bring up something I said in the other thread:

Quote:
Side note that kind of has nothing to do with this, but has anyone ever stood on the ramp or atleast near a CRJ and hear those engines scream (I hope this is a better example than wang crossfingers )when they are spooled up for taxi or on take-off? It's the best sounding engine during that time IMO...



[Edited 2008-12-27 16:03:45]


What gets measured gets done.
User currently offlineTdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 79
Reply 3, posted (5 years 8 months 3 weeks 3 days 9 hours ago) and read 5346 times:



Quoting Iowaman (Thread starter):
Is this true, or just sheer power of the PW2040's? I doubt they are actually breaking the sound barrier.

It's sort of a tricky question, since different parts of the blade are going different speeds and the airflow speed varies quite a bit within the fan. But there are definitely pockets of locally supersonic flow.

Tom.


User currently offlineMarkC From United States of America, joined Apr 2006, 259 posts, RR: 0
Reply 4, posted (5 years 8 months 3 weeks 2 days 19 hours ago) and read 5217 times:

2000's max out at nearly 4,600 rpm I believe. Whats the fan diameter....84 inches I think? Thats 264 inches circumference or 22 feet. So the tips move at 101,000 ft/min or 19 miles/min or 1,150 mph.

Thats just simple math. To find out the local mach number at the pressure and tempurature which exists at the tips at full speed would need someone with a much better understanding of aero than me. But, 1,150 is right.


User currently offlineTdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 79
Reply 5, posted (5 years 8 months 3 weeks 2 days 15 hours ago) and read 5166 times:



Quoting MarkC (Reply 4):
To find out the local mach number at the pressure and tempurature which exists at the tips at full speed would need someone with a much better understanding of aero than me. But, 1,150 is right.

1150 mph is Mach 1.51 at standard sea level...even on the slow flow side of the blades, that's probably fully supersonic flow. It certainly would be on the fast side.

Tom.


User currently offlineTristarSteve From Sweden, joined Nov 2005, 4007 posts, RR: 34
Reply 6, posted (5 years 8 months 3 weeks 2 days 15 hours ago) and read 5163 times:



Quoting MarkC (Reply 4):
2000's max out at nearly 4,600 rpm I believe.

That sounds a bit fast to me. I would have said more like 3400 rpm.
Will look it up tomorrow.


User currently offlineMarkC From United States of America, joined Apr 2006, 259 posts, RR: 0
Reply 7, posted (5 years 8 months 3 weeks 2 days 6 hours ago) and read 5072 times:

Its OK, Steve, you really don't have to look it up.

If I really knew, I would have said max allowable is 4,575 rpm corresponding to 100.5% N1. But, for the purposes of this forum, lets just say 4.575 might be a lucky guess.


Top Of Page
Forum Index

Reply To This Topic 757 Engine Fan Blade Speed
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...
GE90 Fan Blade Donated To Cincinnati Art Museum posted Fri Dec 21 2007 12:32:06 by Jetlife2
Markings On Fan Blade Surface. posted Sat Nov 24 2007 01:44:58 by HAWK21M
TurboFan Engine: Fan Operating In Reverse? posted Thu Nov 15 2007 11:24:54 by Guessbb
EK Trent 'Fan Blade Failure' posted Tue Nov 28 2006 03:24:38 by BA777ER236
Trent Fan Blade Failure. posted Sun Oct 22 2006 05:33:39 by BOE773
757 Engine Thrust Comparison. posted Thu Oct 19 2006 05:09:36 by BOE773
AA 757 Engine Type Question.. posted Sat Oct 7 2006 05:16:04 by Airlinelover
Fan Blade Tip Curl posted Mon Mar 6 2006 07:59:06 by Troubleshooter
Fan Blade Tip Clearance posted Thu Dec 15 2005 15:19:27 by Thyengine
757 Engine Limits posted Mon Oct 24 2005 01:43:51 by Taguilo

Sponsor Message:
Printer friendly format