MIL-S-5807A Sextant, Aircraft, Periscopic
Kollsman Instrument Corporation
MS part no. MS 28011-1
Up for auction a very rare Aircraft sextant that was patented in 1945 and used up into the 1980ís. What makes this one really rare is the the original storage containior with an Air Force letter stating it was decommissioned from service. The Timer works fine, all knobs work and move freely and there are extra bulbs in the case. The optics needs a good cleaning. You can see the crosshairs and some light coming in but that is about all. I donít want to take it apart to clean it since it has very delicate instruments inside. I donít know what kind of aircraft this came off of.
Here is some more information about this hard to find sextant.
This aircraft sextant was used for celestial navigation. I think it has been replaced by GPS and/or inertial navigation systems.
The patent is dated 1945 and the sticker on the sextant is June 1986. This instrument is a masterpiece of mechanical and optical engineering.
The bubble is there and can be controlled by the knob.
I think the idea is that the person sighting a star or the Sun, keeps it in the cross hair and at the same time keeps the bubble centered.
As the elevation control is moved up and/or down the clockwork mechanism is averaging the elevation over a period of time.
When the elevation dial is at 90 you are looking straight up and with it set for 0 you are looking at the horizon. The smallest division on the elevation counter is 1 arc minute ( 1/60 of a degree).
Note you can only see out the periscope after the clock lever is pressed, winding the clock AND pushing the button to start the averaging.
How you get the averaged answer is a mystery.
I have not wanted to break the seal, but if you did I expect that the clockwork inside would be very interesting.
There are two GE 327 lamps easily accessed behind metal covers.
The Filter Wheel (Fig 5) has 8 positions: 1= no filter, 2 = green, 3 = red, 4 = green+ND1, 5 = ND1+red, 6 = ND2+green, 7 = ND3+red, 8 = ND3+green. The Neutral Density filters starting at no. 4 are strong enough that you can look at the Sun. It's image is about the same size as the bubble.
To hold the sextant some type of support would be helpful, like a 2x4 with a hole to clear the 1.375" diameter periscope tube and a way to keep it from falling out (maybe use the pin on the side of the tube?). Unlike the sextants used on ships that are hand held, this one needs an external support.
US Patent 2516187 -Calculating Instrument application Feb. 24, 1945 covers some of the operation of this sextant. (see Fig 6 above)
The key feature is the "averager" that mechanically averages the elevation setting over time.
MIL-S-5897C(ASG) contains operational specifications such as:
3.3.1 Sextant. Hereinafter, the term "sextant" shall be construed to mean the sextant proper, Periscopic tube, connecting cable, and watch clip. The sextant shall be a bubble-type sextant built in the form of a periscopic telescope with the periscope projecting above the skin of the aircraft. Provision shall be made for 360 degree rotation of the instrument around the vertical axis and tilt of the sextant up to 14-1/2 degrees minimum from the vertical axis. The sextant shall conform essentially to Standard MS28011.
MS28011(AS) consists of three drawings:
sheet one (shown above) has the layout of the sextant
sheet two has information about the receptacle that mounts to the ceiling of the aircraft
sheet three shows the shipping case
A.F. Manual 51-40 Air Navigation has a little information on this sextant. Vol 1 has descriptive info and Vol 3 operational info
The ID palte reads:
Sextant, Aircraft, Periscopic
MS Part No. MS 28011-1
28 Volts A.C. or D.C.
Mfr's Part No. 1471B-01
Mfr's Serial No. 3870
Order No. NOas 52-535
Stock No. R88S0400-050-000
Kollsman Instrument Corporation
U.S. Property 35050-1
And the paper sticker says:
Aerospace Guidance and Metrology Center (AGMC)
Repair Date JUN 16 1986
Newark Air Force Station
Newark, Ohio 43057