NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
MA-1 bubble sextant
From: Gary LaPook
Date: 2007 Feb 19, 18:59 -0800
From: Gary LaPook
Date: 2007 Feb 19, 18:59 -0800
I have 6 Kollsman periscopic sextants, 1 MA-2 (just like the periscopic but without the periscope), 1 A-7 and 1 A-10 all of which use a bubble for reference. I just purchased on E-Bay an MA-1 which is very similar to the MA-2 but uses a pendulous mirror instead of a bubble. Does anybody have any information about this type of sextant or the similar periscopic ones with a pendulous mirror? Since the bubble ones are much more common is the reason for this that the bubble ones work better or are they less expensive to manufacture? Any source for a manual for the MA-1? I removed the modern type of electronic averager from one of my periscopic sextants and installed it on the MA-1 and it works very well except the averager eats batteries ( 3 nine volt batteries in series) since it uses 150 ma. just for the averager. The illumination on the MA-2 and the other Kollsman sextants for night observations only draw 75 ma. I thought of using this averager on the MA-2 but decided against it because you can use the MA-2 during the day without any electricity since the averager is mechanical. The MA-1 always needs power to light up the reference line (65 ma) so it made sense to put the electronic averager on it. I am taking a series of sights with both of them to compare their accuracy. I especially like the reference line in the MA-1 and use it for lower limb sights of the sun. With the bubble sextants you have to center the sun in the bubble which may make it less exact. I plan to go flying next weekend and will take several sights with the MA-1 and the MA-2 to see how they compare. I have taken many shots with the MA-2 and many many shots with the A-10 in flight and have been happy with the results. I will let you know how these shots work out. A link to a site with description of these sextants is: http://home.earthlink.net/%7Es543t-24dst/airnav/index.html#PERISCOPIC The following was copied from this web site. MA-2 Sextant The MA-2 is a hand held bubble sextant for use in aircraft where space will not permit installing an automatic or periscopic sextant. The main body of the sextant, including the controls, averager, and bubble control, are identical to the periscopic sextant. The MA-2, here illustrated, is also provided with a hook for use in astrodomes of older aircraft. The sextant has a field of vision of 12�� and is capable of measuring altitudes from -10� to +92�. The averager provides an average altitude accurate to two minutes of arc over any period of time from 30 seconds to 2 minutes. MA-2 exterior COMPONENTS The MA-2 sextant has four main systems: the horizon, the optical, the altitude recording and averaging, and the electrical system. All systems, other than the optical system, are identical to the periscopic sextant. For information on these systems refer to the section on the periscopic sextant. MA-2 optical path Optical System. Light entering the objective window passes through the index prism, objective lens system, and filters, as shown in accompanying diagram. It is then directed to the eye by a pentaroof fixed prism and forms a real image at the focal plane of the field lens. On the field lens is a reticle, consisting of a vertical and horizontal line, which indicates the center of the field. The focal plane of the eyepiece lens system coincides with that of the field lens and reticle. The eyepiece may be adjusted for focus by rotating the knob directly behind the rubber eyepIece. Daylight for the illumination of the bubble enters through the diffuser at the top of the bubble chamber. The image of the bubble passes downward through an objective lens and through the pellicle to a retro-reflector. I t is then reflected to the pellicle which in turn reflects it to the focal plane of the main optical system. If the diffuser prevents the entrance of sufficient daylight for the illumination of the bubble, artificial illumination is provided by a 28-volt lamp controlled by a rheostat. Checking the Sextant. Preflight, inflight, and postflight procedures are identical to those given for the periscopic sextant. MA-1 Sextant The MA-l sextant, as illustrated, is very similar to the MA-2. The major difference is the artificial horizon system. Where the MA-2 uses the conventional bubble artificial horizon, the MA-l utilizes a pendulous mirror to reflect the image of a horizontal line that is used as an artificial horizon. MA-1 exterior As shown in the optics diagram of the MA-l, illumination for the horizon system is supplied by a lamp located at the top of the sextant body. The intensity of the light is controlled by a rheostat on the front of the sextant. Light is projected downward through a condenser lens and a reticle pattern. This pattern is projected through the pellicle and continues to the pendulous mirror chamber. The mirror pattern is reflected back to the pellicle which in turn reflects it to the plane of the main optical system. MA-1 optical path Preflight, in-flight, and postflight checking procedures are identical to those given for the periscopic sextant, except for the bubble adjustment. Gary LaPook --~--~---------~--~----~------------~-------~--~----~ To post to this group, send email to NavList@fer3.com To , send email to NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---