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F4 Inertial Navigation

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  • Member since
    November, 2005
F4 Inertial Navigation
Posted by Anonymous on Saturday, October 22, 2005 4:42 PM
I have seen many things written about the INS on the F4, and I have noticed a lot of errors.
My knowledge comes from working INS on these airplanes from 1965 to 1976. The F4C, F4D, F4E and RF4C had basically the same system. The Litton designation was LN-12. The components were the computer(CP-733), platform(MX-7299), OSDU and control box(Off Stby Align Nav). OSDU is Output Signal Distribution Unit and it sat on top of the platform. It had a cooling fon for the platform.
The F4C had the ASN-48. The F4D had the ASN-63, the only difference from the C was the OSDU, which was bigger and heavier. It had additional parts to feed the WRCS(weapons release system on the D). The F4E had the ASN-63, same as the D. The RF had the ASN-56, different OSDU (I think) and an additional box, the Recon Adapter Unit. All 4 airplanes used the same computer (CP-733), same platform (MX-7299) same control box, and the same Dead Reckoning Nav Computer ASN-46A which gave present position and ground speed and a few other functions. It was a pain to work on; everything was in the rear cockpit. Very cramped. The rear seat bucket had to be removed to get the computer and/or platform out. Kept the egress guys busy.
The system was sensitive during the gyrocompass phase of fine align. NEVER saw wind cause the system to dump. Did see many systems dump when switching to NAV. But it was necessary for the aircraft to remain as still as possible during gyro compass. This was a north seeking system, and as such, used the rotation of the earth to align to north. Difficult to align in high latitudes. Kicking the chocks before the INS was in NAV could extend the alignment time, if the plane moved. It was a remarkable system for its time. It was accurate to 3MN per hour. I thing INS actually stood for I'm Not Sure.

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