747400sp
Topic Author
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GE F-101 Medium Or Low By-pass

Sat Apr 01, 2006 4:21 am

Hello Everybody

I know this may sound like a stupid question, but I just got to ask it. The F-101 has a pretty large fan, much larger than it's core mates the F-110 and F-404. It fan is very closes to the smallest CFM 56 high by-pass turbo fan which is also built off the same core. I know being a super sonic after burning turbo fan it could not be high by-pass, but could it be medium by-pass or is it low by-pass like I thought. Another reason I ask this question, is the fact that article or reading about the F-101 never call it a low by-pass engine or talk about it's by-pass at all. So is a medium by-pass or low by-pass turbo fan.
 
B2707SST
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RE: GE F-101 Medium Or Low By-pass

Sat Apr 01, 2006 2:42 pm

Global Security gives a BPR of 2:1; it is usually a very reliable source.

http://www.globalsecurity.org/wmd/systems/b-1a.htm

I would call this the high end of low-BPR or the low end of medium-BPR, but the boundaries are pretty arbitrary. That BPR is appropriate for the B-1's mission profile, high subsonic cruise with low supersonic dash, but can generally support higher supersonic speeds; the canceled B-1A could achieve Mach 2+ at altitude due to its variable-geometry intakes, which were deleted due to cost and changing mission requirements.

--B2707SST
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F14D4ever
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RE: GE F-101 Medium Or Low By-pass

Sat Apr 01, 2006 11:55 pm

Quoting 747400sp (Thread starter):
The F-101 has a pretty large fan, much larger than it's core mates the F-110 and F-404.

"core mates"? The F-404 does not share a core with the -101/-110 family. F-404 is derived from the YJ-101, while the -101 et seq. are children of the GE9, the GEAE offering for the Advanced Manned Strategic Aircraft (B-1) program.

Quoting 747400sp (Thread starter):
[F-101's] fan is very close to the smallest CFM 56 high by-pass turbo fan...

What do you consider very close? The F-101 is a <350 pounds/second machine, while the smallest CFM does around 640.

The F-404 has a bypass ration less than one and considered low-bypass (in fact some call it a leaky turbojet). The CFM is high-bypass; that leaves the F-101 somewhere in the middle. If you really need to attach a label, call it medium-bypass.
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Blackbird
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RE: GE F-101 Medium Or Low By-pass

Sat Mar 24, 2007 3:24 am

The F-101's core is the same as the CFM-56?

Andrea Kent
 
Pyrex
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RE: GE F-101 Medium Or Low By-pass

Sat Mar 24, 2007 7:26 am

Quoting Blackbird (Reply 3):
The F-101's core is the same as the CFM-56?

It is essentially the same core but you know jet engines, no-one really starts from a clean sheet of paper - you start building one on top of the other, put in a new fan here, a redesigned combustor there... when you're finished, and depending on the versions, you have engines with the same core with almost no parts in common...
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Blackbird
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RE: GE F-101 Medium Or Low By-pass

Sun Mar 25, 2007 5:05 am

So you're saying it has the same core geometry as the F-101 BUT it doesn't have a single part in common with the F-101 :-p

Andrea Kent
 
SCAT15F
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RE: GE F-101 Medium Or Low By-pass

Mon Mar 26, 2007 2:06 pm

Quoting B2707SST (Reply 1):
Global Security gives a BPR of 2:1; it is usually a very reliable source

The giant "Great Book of Modern Combat Aircraft" book from the mid-80's has a HUGE super-comprehensive section on the B-1A/B-1B and especially F-101. The F-101 according to this source has a bypass ratio of 2.2 to 1, with a 55" maximum diameter.
 
prebennorholm
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RE: GE F-101 Medium Or Low By-pass

Tue Mar 27, 2007 4:57 am

Quoting Blackbird (Reply 3):
The F-101's core is the same as the CFM-56?

The CFM56-2 (used on DC-8-7x and various C-135/B707 related military a/c) is in most respects based on the core of the F101 and the fan and LP turbine of the cancelled SNECMA M56 engine.

The CFM56-3 and CFM56-5A (737 Classic and early A320) are rather similar to the CFM56-2, but with accessory redundancies optimized for twin operation. The -3 has a faster rotating reduced fan diameter to fit under the wing of the low sitting 737.

The CFM56-5B and CFM56-7B (A320 except the earliest, and 737NG) are a different engine family which has lost practically all commonality with the F101. Again the -7B has a reduced fan, but slightly larger than the -3 fan.

The CFM56-5C technically belongs to the same family as the -5B/-7B, but the -5C is a roughly 50% heavier and more powerful thing which definitely has nothing more than probably an oil tank cap in common with the F101.
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