Welcome to the NavList Message Boards.

NavList:

A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

Compose Your Message

Message:αβγ
Message:abc
Add Images & Files
    or...
       
    Reply
    Re: Lockdown Escape (Madness?)
    From: Gary LaPook
    Date: 2020 Apr 30, 14:43 -0700

    Something to keep your brain cells active, learn the Bygrave method. You can access all the information on this here:     https://sites.google.com/site/fredienoonan/other-flight-navigation-information/modern-bygrave-slide-rule

    Or you can just try it out on a simple three memory calcualtor. . Here is the step by step process: 


    CHECKING YOUR COMPUTATIONS

    An easy way to check the computation on a Bygrave is to do the same computation on a calculator since this allows you to check the intermediate steps.

    Just use the standard Bygrave formulas in the three step process following along on the form I have posted.

    First calculate co-latitude and save it in a memory in the calculator. If you are using a value for hour angle that is not a whole number of degrees you might want to make the conversion to decimal degrees and save it in a memory since it will we used twice. If you are using whole degrees then this step is not necessary.

    Then you calculate "W" using the formula:

    tan W = tan D / cos H

    and sum it to the memory where you have saved co-latitude which is then X and then make any adjustment necessary to convert X to Y. (If you are just making trials you can avoid this step by your choice of the trial values.) There is no reason to store W itself since it is not used again. You can then convert W to degree and minute format to compare with the Bygrave derived value.


    Then you compute azimuth angle using the formula:

    tan Az = (cos W / cos Y ) x tan H.

    If you want you can also convert Az to degree and minute format to compare with the Bygrave.

    The last step is to calculate altitude with the formula:

    tan Hc = cos Az x tan Y.

    Then convert to degree and minute format to compare with the Bygrave result.



    (When entering values in the format of degrees minutes seconds, change decimal minutes to seconds, 6 seconds per tenth of a minute, in your head  before punching in the assumed latitude, declination  and hour angle if necessary.)


    Using whole degrees for declination, assumed latitude and hour angle, using a TI-30 with only 3 memory locations the key strokes are:

    ---------------------------------------------------------------------

                 (co-latitude = 90 - Assimed latitude)

    90
    -
    Assumed Lat
    =
    STO 1  (co-latitude stored in memory 1)

    ---------------------------------------
                   
                   
    (tan W = tan D / cos H)


    Declination  
    tan
    /
    H
    cos
    =   
    inv
    tan    (computed W)
    SUM 1  (X now stored in memory 1)(change X to Y if necessary)

    --------------------------------------


           
    (tan Az = (cos W / cos Y ) x tan H)

    cos    (of W from prior step)  
    /
    RCL 1  (recalls Y from memory 1)
    cos
    x
    H
    tan
    =
    inv
    tan (computed Azimuth angle)



    ------------------------------------

           
    (tan Hc = cos Az x tan Y)


    cos    (of Az from prior step)  
    x
    RCL 1  (recalls Y from memory 1)
    tan
    =
    inv
    tan  (computed altitude, Hc)


    2nd
    D.D - DMS (changes Hc in decimal degrees to degrees, minutes and seconds)




    DONE

       
    Reply
    Browse Files

    Drop Files

    NavList

    What is NavList?

    Join NavList

    Name:
    (please, no nicknames or handles)
    Email:
    Do you want to receive all group messages by email?
    Yes No

    You can also join by posting. Your first on-topic post automatically makes you a member.

    Posting Code

    Enter the email address associated with your NavList messages. Your posting code will be emailed to you immediately.
    Email:

    Email Settings

    Posting Code:

    Custom Index

    Subject:
    Author:
    Start date: (yyyymm dd)
    End date: (yyyymm dd)

    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site