# NavList:

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

Message:αβγ
Message:abc
 Add Images & Files Posting Code: Name: Email:
Re: Use of Marine Sextants in Aircraft
From: David Pike
Date: 2018 May 9, 01:29 -0700

Fred you wrote: My trig is very rusty and i’m having a hard time solving your problem, yet it is occupying my mind.  In the interest of helping me get back to an important project, would you please provide a solution.

For the distance off I was simply using the 1 in 60 rule (or 1 in 57 for the purist).  One foot on the circumference of a 57 ft radius circle subtends one degree of arc at the centre.  As far as I remember a nautical mile is still 6080 ft, and I guessed a typical warship would be about 300ft long (poor guess, Bismarck was 820ft long!).  Therefore, using more realistic values, at ten miles range Bismarck would subtend a horizontal sextant angle of 820 in 10x6080 or 0.82 in 60.8 which is near enough 0.82 in 57 or 0.82 degrees or 49 minutes of arc (or the classroom answer without a tight flying helmet on in a cold noisy aeroplane: angle subtended = 820/10x6080 radians x 57 x 60 = 46 minutes of arc).  It’s just like distance-off from lighthouses during yacht pilotage.

For the R34 Airship I feel on less secure ground.  I only came across it because I was once asked to read another speaker’s talk for him and had to seriously modify it before I was even moderately happy with it.  The quote I had, and I don’t know from where it originates, was Using the sextant they

measured the angle subtended by the length of the shadow; knowing the length of

the ship was 640ft they calculated their height to be 2,100ft – the aneroid

barometer indicated 1,200ft an apparent error of some 900ft, fortunately on this

occasion on the safe side. When they eventually obtained an accurate pressure

setting from a ship some 50-60 miles away they found that the actual error was

Browse Files

Drop Files

### 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)