NavList:

     Yesterday I hand-flew a real C172S airplane whilst also operating a Bygrave slide rule fax, as if finding Hc for a pre-planned sextant shot. The procedure was partially repeated using a 10" rule, also hand-flying. I always carry a E6B/Dalton aviation circular slide rule.

     The calculated Hc could have been used to set up the box sextant in my bag. My aim was to compare the 3 slide rules. Practice, not theory.

     I used the Bygrave many times 6 years ago solo in an open Stearman biplane, with over 100 kts hurricane force prop slipstream. It worked then, and worked yesterday in the enclosed Cessna. A yoke is more useful than a single stick.

     The 10" can be held in either or both hands on a small yoke. Despite having practised successfully on the ground, I found the trig figures were too tiny to read and set easily, even when the values were known from the Bygrave worksheet. The area under the cursor was worst; it is easy to misplace settings. Hand-flying requires frequent scanning of attitude, height and speed and the eyes do not readily return to the right place on a 10". The a/b x c process to 3 sig figs was adequate. I don't doubt a dedicated navigator could solve the equations on his favourite rule. A metal rule could easily fall and jam control runs.

     The E6/Dalton was loaned to me by QE2. It has C and D circular scales effectively 13" long. In conjunction with the four A4 pages of trig tables on board, the bigger scale graduations and numeration made it practical. There is no cursor, but it worked.

     You cannot get a Bygrave. Slide rules are collectors' items. E6s are in every flying club, and trig tables easily printed.

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