# NavList:

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

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Re: Fairchild A-10A in practice
From: David Pike
Date: 2017 Jul 6, 08:13 -0700

Bill Morris you wrote:  The median is preferred over the mean because it is a more robust estimate of central tendency in that it is less sensitive to skewed results and outliers. It also requires no calculation.

That’s an interesting concept Bill which our mathematicians will argue over for weeks.  However, as automatic ‘pecking’ is deemed preferable to manual ‘pecking’; you’d need an automatic pecker as in the A10-A.  You’d still need to find the 31st mark manually.  Do you know if in pre-digital times anyone ever patented an automatic median indicator?  My initial question was ‘How hard was it to find the 31st mark around the disc in the air in a dimly lit noisy navigator position'?  I’d also be interested to know, because my A10 and A10A are both jammed, how many degrees of sextant altitude correspond to 360 degrees of disc rotation?

You also wrote:  Additionally, the period of slow oscillation of many aircraft, called "phugoid oscillations" by Frederick Lanchester, is about 2 minutes, so 60 observations in 2 minutes tended to become the norm.

It’s interesting that the poor old phugoid, which takes place in the longitudinal plane only, has been rather made the scapegoat for acceleration errors, and it is responsible to some extent for errors in fore and aft (ETA) observations.  However, probably the greatest errors are due to the effect of track changes upon beam (Tracking) observations (see attached notes).  Now whilst these are corrected for, they don’t get the same mention in popular culture, probably because the reasons are harder to quantify.  Also, the period of Dutch Roll, which takes place in the lateral and directional planes, is usually less than the phugoid, so if you span the phugoid, you probably span two or three Dutch Rolls.  However, the motion is by no means connected with Dutch Roll only and during trials it was found that for beam observations too, a two minute observation was about right. DaveP

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