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GE F-101 Medium Or Low By-pass  
User currently offline747400sp From United States of America, joined Aug 2003, 3862 posts, RR: 2
Posted (8 years 12 months 3 days 15 hours ago) and read 3993 times:

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.

7 replies: All unread, jump to last
User currently offlineB2707SST From United States of America, joined Apr 2003, 1375 posts, RR: 59
Reply 1, posted (8 years 12 months 3 days 4 hours ago) and read 3964 times:

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


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.


Keynes is dead and we are living in his long run.
User currently offlineF14D4ever From United States of America, joined May 2005, 319 posts, RR: 4
Reply 2, posted (8 years 12 months 2 days 19 hours ago) and read 3943 times:

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.

"He is risen, as He said."
User currently offlineBlackbird From , joined Dec 1969, posts, RR:
Reply 3, posted (8 years 6 days 16 hours ago) and read 3711 times:

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

Andrea Kent

User currently offlinePyrex From Portugal, joined Aug 2005, 4191 posts, RR: 30
Reply 4, posted (8 years 6 days 12 hours ago) and read 3699 times:

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...

Read this very carefully, I shall write this only once!
User currently offlineBlackbird From , joined Dec 1969, posts, RR:
Reply 5, posted (8 years 5 days 14 hours ago) and read 3655 times:

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

User currently offlineSCAT15F From United States of America, joined Feb 2007, 402 posts, RR: 0
Reply 6, posted (8 years 4 days 5 hours ago) and read 3621 times:

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.

User currently offlinePrebennorholm From Denmark, joined Mar 2000, 6661 posts, RR: 54
Reply 7, posted (8 years 3 days 14 hours ago) and read 3588 times:

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.

Always keep your number of landings equal to your number of take-offs, Preben Norholm
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