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INS Alignment at Sea
I am conversant with commercial INS and old military INS (LN3) and know that
the best alignment occurs when the a/c is stationary. Now my question. How is the INS aligned at sea on a carrier that is moving at 30kts? Does the ground crew start an alignment below decks prior to bringing the a/c up for a launch? Also does the Captain have to realign heading on the catapult to ensure proper heading reference or is there a slaved compass system in naval military fighters? Gary Watson |
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Thanks Mike, a good descriptio0n. I worked on Cf104s back in the 60s with
the LN3. Often we had terminal errors of 20+ miles after a 11/2 hr flight - if the platform remained erect. I have worked witht eh latest Litton and Honeywell commercial RLG based platforms and indeed they provide a very nce package in a Falcon 900Ex of Global Express Gary W "Mike Kanze" wrote in message news Gary, I was intersted to hear that the alignments would go "south" during the catapult stage. Did air alignments work out ok as I realize you were getting lat/long info from another aircraft but can't imagine having the time to carry out the process. In the early 1970s A-6A, inflight alignments of the AN/ASN-31 inertial navigation system were both common and more often than not "reasonably" accurate - at least for providing a stable reference of aircraft heading, attitude, and horizontal and vertical velocities. The A-6A/B/C NATOPS referred to these as "rough alignments". ("Reasonably accurate" = accurate enough to complete the mission successfully.) An inflight alignment of the ASN-31 required true heading (which one got from the magnetic wet compass and then adjusted for local magnetic variation), aircraft velocity and the latitude of the inflight alignment starting point. B/Ns made it a point to write down the ship's current LAT/LONG during shipboard (SINS) alignments, since the cat shot was the most likely flight phase for an inertial dump and the inflight alignment could be started almost immediately after launch. Entering the LONG in addition to the other three parameters above usually produced a fix for the inertial accurate to +/- 3 to 5 miles, depending upon the distance traveled by the ship between SINS alignment and inertial dump. (There was also a fair amount of dead reckoning thrown in here as well, using inputs like ship's estimated course and speed changes since SINS alignment.) In the A-6A, the real keeper of position was the AN/ASQ-61 ballistics / nav computer and not the ASN-31. It obtained its initial reference from the ASN-31's aligned position, and took as inputs throughout the flight the velocities generated by the ASN-31. The ASQ-61 also took inputs from the aircraft's pitot-static system, radars, and the knobology activities of the crew. During the mission the crew would update the ASQ-61's position with fixes off the search radar, or visually if crossing a known position like the CIP. These updates minimized computed position errors. At least that was how it was SUPPOSED to work. g As Woody and others point out things are much different today, especially the need for accurate posit inputs into the smart weapons we didn't have back in the early 1970s. -- Mike Kanze 436 Greenbrier Road Half Moon Bay, California 94019-2259 USA 650-726-7890 "When was the last time in world history in which 'suicide' and 'martyrdom' were the code of enlightened action admired by any society?" - Roy Fassel (WALL STREET JOURNAL, 10/27/03) "Gary Watson" cf104@ihate spam.shaw.ca wrote in message news:CHbpb.260660$6C4.185337@pd7tw1no... [rest snipped] |
#3
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"J. McEachen" wrote in message ...
Boy do I feel old. In the true bomber days of the A-3 we actually carried a chronometer and a bubble sextant, shot the stars and got a three-point fix. Ditto the sun and LAN local apparent noon. Plus a "potty" of sorts and a working p-tube. Box lunches were in order, 3 or 4 hour cycles were the norm (I even flew once with Charlie James refueling from A-4 tankers for eight hours.) We'd estimate surface winds by checking the sea, and we even did pressure pattern navigation out to Bermuda. What's all this about gyros and other gizmos? (OK, Whidbey started getting ASB-7 c. 1961 while we on the east coast stuck with the modified Norden ASB-1a bombing system.) Joel McEachen VAH-5 (Mushmouths) Pressure! Navigation by altimeter! When they taught us that at Nav School (Mather AFB, CA, T-43s, 1977) I thought it was a joke! But damned if it didn't work. But I was determined to get into the back seat of an F-4 so all I cared about was looking out the window, with an occasional TACAN cut - and that worked for me (It helped that I had been flying for 9 years heh heh). Then, a few years later, I was in the PI flying (surprise) F-4s when we got the magic ARN-101 system - fancy INS/LORAN gizmo, lots of buttons, lots of ways to screw up and get lost... On one deployment to the Kun in the winter the winds were so strong that we couldn't get the INS platforms to align as the jets were rocking; tried everything including putting down the hook and having crewchiefs (preferable big, well-fed ones) hang on the wingtips - anything to damp the motion. Only solution was to park the jets in revets that blocked the wind - which wasn't all of them! Soon after, a software upgrade "fixed" the problem. Kirk Old F-4 IWSO |
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user wrote in message . ..
Hi Kirk, I read your story and couldn't help but ask,,,what is a crewchief??? You mean a plane captain right? (Oh never mind, I just read a little closer and saw the Mather AFB thing, sorry,,,must be an Air Farce thing.) Correct, in the Air Force the crewchief owns the jet, the pilot just borrows it for a while and tries not to break it, and the WSO tells the pilot where to go...a banana tied to the end of a stick works pretty good; you wave it in the direction that something interesting is going on...Then when you get to the target area the front seat stick actuator rows the boat while the guy in back shoots the ducks. Especially true when PGMs came into widespread use (AGM-65/130s, GBU-10/12/15, and now WCMD/JDAM/JSOW etc). Another post in this thread mentioned tankers leading fighters through the murk in bad weather due to better nav systems. For awhile after the F-4E got the ARN-101, we had a much better nav system (integrated INS/LORAN) than the common KC-135 tankers, so were often asked for a position update on long overwater hops. Always happy to oblige (not that we were in any position to refuse!). It's funny, now 20 years later - I own and fly a racing sailplane (LS6-b) that has more communication and navigation gear installed than any F-4 ever had: 2 independent comms (OK, one is a cell phone but it works!, other is a VHF) and 2 independent GPS's, with moving maps, aviation and terrain data bases, glide computers, and probably more computing power than the old Rhino. But looking out the window is still the best way to aviate and navigate! Kirk |
#6
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Kirk,
a banana tied to the end of a stick works pretty good Ditto for the A-6 community, except we didn't need the stick. Pointy sticks were a hazard, and unnecessary in a side-by-side cockpit. The bananas popped out from underneath the pilot's annunciator panel. We were forced to abandon this motivational tool because the peels became both a slip hazard to the pilot (the A-6 cockpit was large enough to accommodate a handball court) and potential FOD to the engines. BG But looking out the window is still the best way to aviate and navigate! True, but only if there's something to look AT. Once you get above or inside of the giant aspirin tablet, you need other stuff. -- Mike Kanze "Owl", B/N A-6A, A-6B (PAT ARM), KA-6D 436 Greenbrier Road Half Moon Bay, California 94019-2259 USA 650-726-7890 "Kirk Stant" wrote in message om... user wrote in message . .. Hi Kirk, I read your story and couldn't help but ask,,,what is a crewchief??? You mean a plane captain right? (Oh never mind, I just read a little closer and saw the Mather AFB thing, sorry,,,must be an Air Farce thing.) Correct, in the Air Force the crewchief owns the jet, the pilot just borrows it for a while and tries not to break it, and the WSO tells the pilot where to go...a banana tied to the end of a stick works pretty good; you wave it in the direction that something interesting is going on...Then when you get to the target area the front seat stick actuator rows the boat while the guy in back shoots the ducks. Especially true when PGMs came into widespread use (AGM-65/130s, GBU-10/12/15, and now WCMD/JDAM/JSOW etc). Another post in this thread mentioned tankers leading fighters through the murk in bad weather due to better nav systems. For awhile after the F-4E got the ARN-101, we had a much better nav system (integrated INS/LORAN) than the common KC-135 tankers, so were often asked for a position update on long overwater hops. Always happy to oblige (not that we were in any position to refuse!). It's funny, now 20 years later - I own and fly a racing sailplane (LS6-b) that has more communication and navigation gear installed than any F-4 ever had: 2 independent comms (OK, one is a cell phone but it works!, other is a VHF) and 2 independent GPS's, with moving maps, aviation and terrain data bases, glide computers, and probably more computing power than the old Rhino. But looking out the window is still the best way to aviate and navigate! Kirk |
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