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INS Alignment at Sea
How is the INS aligned at sea on a carrier that is moving at 30kts?
Actually it was quite a challenge. I was AEAN Flight Deck Troubleshooter assigned to VAW-116, launching the E-2C Hawkeye off the pointy end of the USS Constellation during the WestPac of 80-81 when we had to do a "handset align" of INS. We all stood around in a semi-circle (to keep dumb****s from walking thru the turning props) and when given the signal, I'd go into the island, call SINS and get our PP (present position). Then I'd go up into the cockpit where they already had a "rough align" and tell INS where we were. Of course we were just doing doughnuts out in the middle of the IO. This was called a "handset align" and was very common when SINS would not transmit via the cable and when an RF Align was not possible (like during EMCON). I've been in the cockpit of the Hawkeye (parked abreast the island) and seen the ground speed display 42 knots- we were HAULING! When they lit up all the boilers all four screws would really kick up a rooster tail. I had a ball on the two WestPac's I did aboard the Connie- that was a great ship with an even better crew :-) -- Larry AECS (AW/SW/MTS) Disabled Combat Veteran USN Retired 20 years of Navy in my rear view mirror and getting further away every day ;-) "Gary Watson" cf104@ihate spam.shaw.ca wrote in message news:yyWob.251407$pl3.192778@pd7tw3no... I am conversant with commercial INS and old military INS (LN3) and know that the best alignment occurs when the a/c is stationary. Now my question. How is the INS aligned at sea on a carrier that is moving at 30kts? Does the ground crew start an alignment below decks prior to bringing the a/c up for a launch? Also does the Captain have to realign heading on the catapult to ensure proper heading reference or is there a slaved compass system in naval military fighters? Gary Watson |
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On 11/1/03 4:35 PM, in article yyWob.251407$pl3.192778@pd7tw3no, "Gary
Watson" cf104@ihate spam.shaw.ca wrote: 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 Gary, Navy aircraft have two alignment modes. One for shore-based alignments and one for shipboard alignments. The shipboard alignments require Ship Inertial Navigation System (SINS) data via either a cable or from an RF data link. This gives a fairly high quality alignment--it even worked well on the A-6's IMU/INS. If for some reason (and it happens) you can't get SINS data, you can manually enter the ship's present position, speed, heading, and your deck spotting angle and set the INS up to perform an manual CV alignment. In the EGI/GPS equipped F/A-18 if THAT doesn't work, you can get a GPS in flight alignment (IFA) even on deck. --Woody |
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The shipboard alignments require Ship Inertial Navigation System (SINS)
data via either a cable or from an RF data link. This gives a fairly high quality alignment--it even worked well on the A-6's IMU/INS. In the days of the A-6A and its AN/ASN-31 inertial, shipboard alignments were sometimes colorful and problematic affairs. There were none of the goodies like RF links or GPS for us to play with. Mini-sea story #1: On CORAL MARU's 1973 cruise, we (VA-95) found that (1) most of the SINS cables were beat to hell and wouldn't work because (2) our predecessor A-6 squadron in CVW-15 - VMA(AW)-224 - didn't know what alignments were. It took us most of the cruise to weed out and survey the hopelessly irrepairable cables and gradually accumulate a set of reliable and maintainable ones. Mini-sea story #2: On 95's 1975 cruise (still with CVW-15 / CORAL MARU), an A-6 launched off Taiwan for a penetration flight to exercise ROC air defenses. The crew obtained an normal SINS alignment, launched (this time without the all-too-common inertial dump on the cat stroke) and commenced the penetration. The crew became quite concerned however when the CIP did not appear at all at the time and configuration briefed. Quickly - and correctly - determining that they were actually headed for the friendly shores of the Peoples Republic, they 180ed and bustered back to Mother. Cause of problem? SINS posit was 40 nm (yes, 40 nm!) in error. (There is a lot more to this second story than just the above.) Prurient trivia item #436: The control panel for the AN/ASN-31 is described in the NATOPS manual as the "Erection Controller Panel". Owl sends. -- Mike Kanze 436 Greenbrier Road Half Moon Bay, California 94019-2259 USA 650-726-7890 "When I read about the evils of drinking, I gave up reading." - Henny Youngman "Doug "Woody" and Erin Beal" wrote in message ... On 11/1/03 4:35 PM, in article yyWob.251407$pl3.192778@pd7tw3no, "Gary Watson" cf104@ihate spam.shaw.ca wrote: [rest snipped] |
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My 2 cents,,,basically the same as Larry's,,,on the Big 'E' IO in '84
and the Connie IO in '85 we had SINS cable inputs sometimes available for our US-3's, (Miss Piggy), . Otherwise we would Link with our ASW-25 (UHF) to get CAINS updated Lat/Longs for the LTN-72's.... our CODS only had gyros and AHRS (Attitude Heading Reference System), although we could hook up a RO-RO LTN-72, and an internal 500 gallon fuel tank for long haul repo flights. (Had a very uneasy feeling sitting in the cargo compartment with a frickin leaking JP-5 fuel cell, on numerous flights from PI to Singapore to Diego Garcia, etc.) I still believe the most cost effective system is a dual AHRS combined with GPS for the best representation of SA and Navigating. This type of setup would cost less than a quarter of the over redundant and way too expensive Ring Laser Gyro INS (over 150,000 per unit) and GPS sysytems that are predominant in the newer Hornets, Orions and Prowlers. On Sat, 1 Nov 2003 20:39:18 -0800, "Mike Kanze" wrote: The shipboard alignments require Ship Inertial Navigation System (SINS) data via either a cable or from an RF data link. This gives a fairly high quality alignment--it even worked well on the A-6's IMU/INS. In the days of the A-6A and its AN/ASN-31 inertial, shipboard alignments were sometimes colorful and problematic affairs. There were none of the goodies like RF links or GPS for us to play with. Mini-sea story #1: On CORAL MARU's 1973 cruise, we (VA-95) found that (1) most of the SINS cables were beat to hell and wouldn't work because (2) our predecessor A-6 squadron in CVW-15 - VMA(AW)-224 - didn't know what alignments were. It took us most of the cruise to weed out and survey the hopelessly irrepairable cables and gradually accumulate a set of reliable and maintainable ones. Mini-sea story #2: On 95's 1975 cruise (still with CVW-15 / CORAL MARU), an A-6 launched off Taiwan for a penetration flight to exercise ROC air defenses. The crew obtained an normal SINS alignment, launched (this time without the all-too-common inertial dump on the cat stroke) and commenced the penetration. The crew became quite concerned however when the CIP did not appear at all at the time and configuration briefed. Quickly - and correctly - determining that they were actually headed for the friendly shores of the Peoples Republic, they 180ed and bustered back to Mother. Cause of problem? SINS posit was 40 nm (yes, 40 nm!) in error. (There is a lot more to this second story than just the above.) Prurient trivia item #436: The control panel for the AN/ASN-31 is described in the NATOPS manual as the "Erection Controller Panel". Owl sends. |
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#7
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The dual AHRS/GPs updated types of systems work well in the slow movinn'
easy turning world of commercial air transport. I know the LTN 72, Carousel IV spinning iron systems from aircraft such as the G-II and L1011 etc and the RLGs are much much more reliable but this is not in the military environment. 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. BTW my interest is because I teach Nav systems to tech school students and we were discussing INS and the need for a stable airframe for alignment. I can now go back Monday and answer the question about aligning whilst the aircrafme is moving. Thanks guys Gary Watson "user" wrote in message ... Yeah good point for high performance aircraft, thanks for the input....How about for Commercial Air, and military slowmovers? On Sun, 02 Nov 2003 11:10:42 GMT, "Doug \"Woody\" and Erin Beal" wrote: On 11/2/03 12:56 AM, in article , "user" wrote: My 2 cents,,,basically the same as Larry's,,,on the Big 'E' IO in '84 and the Connie IO in '85 we had SINS cable inputs sometimes available for our US-3's, (Miss Piggy), . Otherwise we would Link with our ASW-25 (UHF) to get CAINS updated Lat/Longs for the LTN-72's.... our CODS only had gyros and AHRS (Attitude Heading Reference System), although we could hook up a RO-RO LTN-72, and an internal 500 gallon fuel tank for long haul repo flights. (Had a very uneasy feeling sitting in the cargo compartment with a frickin leaking JP-5 fuel cell, on numerous flights from PI to Singapore to Diego Garcia, etc.) I still believe the most cost effective system is a dual AHRS combined with GPS for the best representation of SA and Navigating. This type of setup would cost less than a quarter of the over redundant and way too expensive Ring Laser Gyro INS (over 150,000 per unit) and GPS sysytems that are predominant in the newer Hornets, Orions and Prowlers. Foodog, Dual AHRS/GPS wouldn't meet some of the specs required--especially in the z-axis velocities. --Woody |
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Whoa! A CVN at 42 knots? How many water skiers could she tow? What a wake to jump!
walt BJ |
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On 11/2/03 12:05 PM, in article CHbpb.260660$6C4.185337@pd7tw1no, "Gary
Watson" cf104@ihate spam.shaw.ca wrote: The dual AHRS/GPs updated types of systems work well in the slow movinn' easy turning world of commercial air transport. I know the LTN 72, Carousel IV spinning iron systems from aircraft such as the G-II and L1011 etc and the RLGs are much much more reliable but this is not in the military environment. 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. BTW my interest is because I teach Nav systems to tech school students and we were discussing INS and the need for a stable airframe for alignment. I can now go back Monday and answer the question about aligning whilst the aircrafme is moving. Thanks guys Gary Watson Gary and Foodog... With regard to slow movers... AHRS/GPS would be no problem for slow-movers in my opinion--whether UAV or domestic air carriers. I wouldn't want to take one overseas--and couldn't legally in the North Atlantic in RVSM airspace. With regard to USN INS's... Occasionally, the mechanical gyroed IMU/INS would dump on the cat when the alignment was weak or due to some mechanical or electronic glitch. 1/2 of the time you could IFA it and get it back. In my experience, the ASN-139 RLG INS doesn't care about the cat stroke. The mechanical INS's would also build insidious, non-obvious errors--occasionally until they'd dump entirely. Then you could IFA them if you had the time/airspace. The RLG fails fast and fails totally if it's broken. It's seldom that you'll get it back once it fails--unless you caused the failure yourself (due to incorrect initial coords during the alignment or bad SINS data). Accurate data (3-axis) is important for many things, but most importantly for transferring nav data to weapons--especially some of the newer more complex stuff. --Woody |
#10
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"WaltBJ" wrote in message
om... Whoa! A CVN at 42 knots? How many water skiers could she tow? What a wake to jump! When Sadat got assassinated, we were in port in Venice. At dusk we weighed anchor and made mega-neutrons enroute to the coast of Egypt. The Boat was going so fast that you couldn't even stand in the catwalks. I don't know what speed we were doing, but it's was as fast as I've ever experienced onboard any ship. __!_!__ Gizmo |
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