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

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]

"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

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.)
On 8 Nov 2003 18:34:14 -0800, (Kirk Stant)
wrote:

"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

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

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