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BPR, Core Size, And The 737 Re-engine  
User currently offlinevoltage From United States of America, joined May 2007, 109 posts, RR: 0
Posted (4 years 5 months 2 weeks 5 days 3 hours ago) and read 4801 times:

So, with all this talk about the 737 recently, it seems that the BPR on a 737 Re-engine wouldn't be optimal because of the clearance issues. Which got me to thinking, BPR is after all a ratio, so why not keep the same fan size and reduce the size of the core? Is it just a matter of it being too expensive to pay out? I'm guessing that there is no way they could design it in time starting now, but why didn't the engine manufacturers have the 737 in mind when they started designing the LeapX and GTF? Would a smaller core just not provide enough power?

6 replies: All unread, jump to last
 
User currently offlinejetlife2 From United States of America, joined Jul 2006, 221 posts, RR: 25
Reply 1, posted (4 years 5 months 2 weeks 4 days 8 hours ago) and read 4702 times:

You are correct you can do both, increase the fan size and/or decrease the core size. If you want to decrease the core size at the same fan size, you still need to produce the same power to drive the LPT, right? So to produce the same power in a smaller core unit, you need to raise the operating pressure and temperature and shaft speed (do more work on less flow, or raise speed to pull more flow through less diameter). To raise the OPR and temperature you need two primary technologies: improved aero (higher pressure ratio without stalling) and improved materials (higher temperature without sacrificing durability since life=maintenance cost).

Hope that helps....


User currently offlinezeke From Hong Kong, joined Dec 2006, 9210 posts, RR: 76
Reply 2, posted (4 years 5 months 2 weeks 4 days 8 hours ago) and read 4701 times:

I read recently one of the main issues on a 737 re-engine project is the mass of the engines, just just the clearance.


We are addicted to our thoughts. We cannot change anything if we cannot change our thinking – Santosh Kalwar
User currently offlinevoltage From United States of America, joined May 2007, 109 posts, RR: 0
Reply 3, posted (4 years 5 months 2 weeks 4 days 6 hours ago) and read 4669 times:

Quoting jetlife2 (Reply 1):
You are correct you can do both, increase the fan size and/or decrease the core size. If you want to decrease the core size at the same fan size, you still need to produce the same power to drive the LPT, right? So to produce the same power in a smaller core unit, you need to raise the operating pressure and temperature and shaft speed (do more work on less flow, or raise speed to pull more flow through less diameter). To raise the OPR and temperature you need two primary technologies: improved aero (higher pressure ratio without stalling) and improved materials (higher temperature without sacrificing durability since life=maintenance cost).

Hope that helps....

thanks, very informative post!


User currently offlineXT6Wagon From United States of America, joined Feb 2007, 3424 posts, RR: 4
Reply 4, posted (4 years 5 months 2 weeks 4 days 2 hours ago) and read 4632 times:

Quoting voltage (Thread starter):
So, with all this talk about the 737 recently, it seems that the BPR on a 737 Re-engine wouldn't be optimal because of the clearance issues

Yes the core will be much smaller. To reach the full BPR desired they do want a modest increase in fan diamiter. However the race to the top in BPR for shorthaul planes isn't allways sensible. Sure its better at cruise, but you trade extra wieght for the larger fan making a engine with a lower BPR at the same technology level better for short haul.

I don't think the 737 will have any issues at all putting a new engine under the wing, and it won't suffer compared to a A320 re-engine. Why? Its 50% of the market and some engine maker is going to jump for the opportunity if offered. If they have to make a smaller fan version, they will. Why will the "less optimum" engine not matter for the 737? The 737 is already a good bit lighter than the A320, and will maintain a higher max altitude. So the differences might change a little in fuel burn between the two, its still going to leave the two in a tie here.


User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 5, posted (4 years 5 months 2 weeks 15 hours ago) and read 4401 times:

Quoting voltage (Thread starter):
So, with all this talk about the 737 recently, it seems that the BPR on a 737 Re-engine wouldn't be optimal because of the clearance issues.

There aren't any clearance issues...Boeing have already said they can fit the new engines under the 737. There are lot of obvious (and some not so obvious) ways to do that, but it's not like they're trying to strap a 777 engine under there.

Quoting voltage (Thread starter):
Which got me to thinking, BPR is after all a ratio, so why not keep the same fan size and reduce the size of the core?

That's absolutely part of what they'll do. Any increase in SFC necessarily means you need a smaller core anyway, so part of the bypass gain is "free."

Quoting voltage (Thread starter):
I'm guessing that there is no way they could design it in time starting now, but why didn't the engine manufacturers have the 737 in mind when they started designing the LeapX and GTF?

They did.

Tom.


User currently offlinejetlife2 From United States of America, joined Jul 2006, 221 posts, RR: 25
Reply 6, posted (4 years 5 months 1 week 6 days 9 hours ago) and read 4268 times:

Quoting tdscanuck (Reply 5):
Any increase in SFC necessarily means you need a smaller core anyway

Not quite....there's many ways to improve SFC without changing the core size. Witness many CFM, CF6, GE90 upgrade programs that improve SFC by changing flowpath parts. No change in the core size.


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