I've been doing a lot of thinking about the seemingly endless debate about preferred fingerings for Bb and F#. Some of the confusion and mystery might be cleared up by looking more closely at the actual mechanism of the flute and some of (one anyway) of the principles used when Boehm created his amazing compromise between playability and intonation on the flute. I'll attempt to put into words what I tell my students about these fingerings. Doing this without the luxury of demonstration with a real flute is quite a challenge so please bear with me - I'll do my best to put it into words that hopefully will have some meaning. :-))|
One crucial point about how the flute works is that the flute is intended to be an OPEN STANDING tube. That means that all tone holes BELOW any given note should be open standing in order to produce the best possible sound. Since all the higher notes are actually harmonics of the fundamentals we need be concerned with only the bottom octave to understand what is going on. The Eb/D# key is pressed (opened) most of the time in order to conform to the open standing tube concept. The open or closed G# concept also comes into play in this regard but attempting to explain that without the luxury of demonstration will likely confuse the issue way too much so I'll leave that bit out.
With the Boehm system mechanism that has become standard in the flute world there is NO direct access to the Bb key or to the F# key. I will speak in terms of key names in this message rather than tone hole names since I believe that most people tend to relate better to using key names. For those interested in understanding more about the difference between key names and tone hole names I would recommend a visit to Those Whatchamacallits On Your Flute where you will find a graphic created by Alton McCanless, Robert Bigio, and myself that shows the difference.
The Bb key is located between the C and A key. If we had just one more finger on the left hand then all the problems would vanish. We could simply use that extra finger to press the Bb key. Since additional fingers are not very likely there are three linkages that provide different ways to manipulate that key - thumb Bb, Bb shake, and right hand first finger. When using the thumb to get a Bb then all of the tone holes below Bb are open standing - things are as they should be according to the open standing tube principal. When using the Bb shake key then all of the tone holes below the Bb are also open - once again a good thing. When using the fist finger of the right hand on the F key there are two holes (the F key and F# key) below the Bb that are closed. According to the open standing tube theory, the 1+1 Bb fingering should be considered slightly inferior to the other two fingerings because there are tone holes closed below the Bb key. Fortunately there are three open tone holes between the F key and the Bb key so the 1+1 fingering is not all that bad. Quite a nice compromise actually.
That's basically the science as I see it but then comes the music. In practice I try always to use the best and most suitable fingering for the moment. In fast Bb Major arpeggios the 1+1 fingering works great. For quick G minor arpeggios I nearly always use the thumb Bb. For fast passages in flat keys that don't contain any B naturals, or F#3's or B3's (the thumb Bb can't be pressed for those notes) I use thumb Bb mostly. I have developed the ability to roll my thumb on and off the thumb Bb quite quickly but not so quickly that I can use it for say fast chromatic passages. I tend to prefer to use the Bb (A# if you like) shake when playing in keys with lots of sharps. I use that shake key a lot when playing in B minor. I use the middle finger F# for E to F# trills in the bottom two octaves. In the third octave I often use the middle finger for F# (especially if it is a loud F#3). In my last lesson with Peter Lloyd I was playing the Poulenc Sonata for him. I took note of the fact that each time he demonstrated one of those fast high passages in the third movement he chose to use middle finger for the F#'s.
I thought I might get through this rather long message without a Geoffrey Gilbert quote but that will not be the case. Mr. Gilbert said with respect to a fingering question, "The most important thing about your question is to make up your mind and have a system." I agree with his assessment that it is important to know which fingering to choose, why you are choosing it and then practice accordingly.
I wonder if it occurred to Boehm as it has to me that the best solution to this Bb and F# fingering problem would be for us humans to somehow grow an additional finger on each hand in order to eliminate the problem entirely. :-))) If you made it this far then thanks for doing all that reading. I do believe that the act of trying to write this fingering stuff will help me the next time I try to explain it all to a student.