747400sp From United States of America, joined Aug 2003, 4033 posts, RR: 2 Posted (9 years 6 months 1 week 1 day 13 hours ago) and read 4498 times:
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.
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.
F14D4ever From United States of America, joined May 2005, 319 posts, RR: 4
Reply 2, posted (9 years 6 months 1 week 18 hours ago) and read 4448 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.
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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SCAT15F From United States of America, joined Feb 2007, 402 posts, RR: 0
Reply 6, posted (8 years 6 months 2 weeks 4 hours ago) and read 4126 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.
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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