Low F-string, 5 string viola

Q: I am building a solid body electric 5 string viola for a friend. he wants to go with a low F string setup F-C-G-D-A on a small body 15 inch style. will this be a problem for the F string if I go 14 inch nut to bridge length? or do I need a longer scale to avoid a floppy F string?
thanks for your advice
Rod

A: There is a formula for choosing strings which relates length, tension, and mass. You can raise the pitch of a string by shortening it, increasing the tension or decreasing the mass. You avoid a floppy string by adjusting the factor that is variable. Your scale length is 14", your tension should be about 10 lbs. Your only variable is the mass of the string. The last time I put a low F string on a viola I had it custom made by D'Addario (it might have been an 1/8 size cello G or something). Now there are Sensicore Octave strings available from Super-Sensitive. An Octave G string (one octave below a violin G) would be pretty close to the F you need. I have that string in stock, for $19.00. These are nylon core so they would balance best with D'addario Zyex, Thomastic Dominant, etc. or, obviously, with Sensicore.

Steve Mason