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    Re: Hughes explanation of Chichester's navigation.
    From: Gary LaPook
    Date: 2014 Dec 3, 23:41 -0800
    I'm  a licensed glider pilot and I don't see how one could operate a sextant is the tiny cockpit of a glider. A Cessna has a much larger cockpit with lots of headroom so it not difficult using an octant. Most times I have been solo so the copilot seat was empty so I could place my stuff on it. Sometimes the copilot seat was stowed in the baggage compartment and a ferry tank put in its place so I could put my stuff on to of the tank. What really helped was the Polhemus which has a very compact plotting surface and is easily handled in a small cockpit. I started with the HO 249 on the seat next to me but later I programmed an SR-49 calculator to do the math. It would calculate the celestial data, determine the center of the "cocked hat," after advancing the earlier shots to the fix time. Then, based on the course and distance from the previous fix and an input for the heading and true airspeed, it calculated the winds and used these winds to compute the heading to use to the destination, the groundspeed and the ETA. 

    To take a sight with an averaging octant you preset it to the Hc, establish the heading, trim for constant speed, and at the planned starting time for the shot you look through the octant, line up the star in the bubble and push the start button. You then chase the bubble around with the star by moving the altitude knob, Since these are random accelerations the averager takes care of them. Airplanes and gliders are both stable in pitch so they can be trimmed to maintain a constant airspeed but they are both exhibit spiral instability so they will drop a wing and start turning. 
    Every 10 or 15 seconds you take the octant away from your eye, level the wings back on heading and then resume shooting the star. If the heading variations go both ways then the averager will deal with the deflection of the vertical caused by the changes in headings. You want to end up on the same heading at the end of the shot that you started with and this will most likely cancel out the variations by the action of the averager. If you are having real problems with the airplane staying on heading during the shot then turn the plane to put the object directly in front of you, two minutes off course will not cause a problem. Since the change in heading causes the bubble to slosh towards the wingtips, it results in a deflection of the vertical athwartship which causes errors in shots taken out by the wingtips but doesn't affect shots taken ahead or astern. We discussed these acceleration errors in the last couple of weeks and how to correct for them. So by moving the star to in front of you then the heading changes (wander) error goes away. There is an airpeed  change acceleration error that DOES affect shots on bodies ahead of you but the plane is stable in pitch and airpeed and, even if the airspeed does change, the magnitude of this error in much less than the turning error. . 


    From: Hanno Ix <NoReply_HannoIx@fer3.com>
    To: garylapook@pacbell.net
    Sent: Wednesday, December 3, 2014 9:16 AM
    Subject: [NavList] Re: Hughes explanation of Chichester's navigation.


    first, thank you for this copy. This will require a long study.

    May I ask a question a concerning the mechanics of CelNav
    while flying? I flew gliders for a long time so I may have some
    appreciation of the process.

    Both, operating the sextant or the Bygrave requires 2 hands, right?
    So how does one operate the yoke in the meantime to keep the plane
    in straight and level flight?

    Observing the plane's attitude and looking through the sextant at the
    same time seems difficult but you probably trained yourself to do that.
    I can also see you writing on a kneepad for the calculations.


    On Tue, Dec 2, 2014 at 3:01 AM, Gary LaPook <NoReply_LaPook@fer3.com> wrote:



    Attached File:

    (img/129498.chichester navigation.pdf: Open and save or View online)

    Attached File:

    (img/129498.chart to lord howe typed.pdf: Open and save or View online)

    Attached File:

    (img/129498.chart to norfolk.pdf: Open and save or View online)

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