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    Re: Traditional navigation by slide rule
    From: Gary LaPook
    Date: 2016 Nov 12, 22:51 +0000
    There is a very significant difference between marine and air navigation. When that last drop of fuel goes through the engine, the plane is going to come down and it is much better to be sitting on the ramp at an airport at that time than to still be up in the air over mountains, deserts, cities or oceans. We know the rate that fuel is being burned and we know how much fuel in the tanks so we know how long the plane can stay up in the sky but we don't know how far we will go in that time until we compute our probable ground speed. That is why we have to do the "wind triangle" computation, to determine that probable ground speed and resulting range. Federal regulations require a minimum of 30 minutes of reserve fuel during daylight and 45 minutes if at night or in bad weather, and most pilots like to have at least an hour of fuel left when they land. , 

    "14 CFR §91.151   Fuel requirements for flight in VFR conditions.

    (a) No person may begin a flight in an airplane under VFR conditions unless (considering wind and forecast weather conditions) there is enough fuel to fly to the first point of intended landing and, assuming normal cruising speed—
    (1) During the day, to fly after that for at least 30 minutes; or
    (2) At night, to fly after that for at least 45 minutes.
    (b) No person may begin a flight in a rotorcraft under VFR conditions unless (considering wind and forecast weather conditions) there is enough fuel to fly to the first point of intended landing and, assuming normal cruising speed, to fly after that for at least 20 minutes."

    gl


    From: Bob Goethe <NoReply_Goethe@fer3.com>
    To: garylapook---.net
    Sent: Saturday, November 12, 2016 5:58 AM
    Subject: [NavList] Re: Traditional navigation by slide rule


    I think part of the issue is that things like the flight computers you illustrated are not common in the sailing world.  It is simply hard to carry out the computations you need quickly enough to make it worthwhile to even attempt them.  People all do current-vector diagrams to get their navigational certification from Sail Canada (previously called the Canadian Yachting Association) and then they never touch them again.
    If I can get on top of the fabrication of the 10" rule, I may create a simplified design and build a shirt pocket rule specifically optimized for solving the current triangle and doing speed/time/distance, for the helmsman to use without leaving the cockpit.
    Bob


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