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Litton INS - LTN-72RH

Old 23rd Apr 2020, 14:28
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Litton INS - LTN-72RH

Hi there - there is a long history of various inertial navigation systems from Litton from very early
mechanical ones until recent ones based on [email protected] gyros and GPS fusion. Recently I obtained a
LTN-72RH made by Litton Aeroproducts, Canada; part number 15200-05-02-36-71, serial 2836:




This unit obviously is of the latest generation using mechanical gyros on a gimbaled platform...



...together with a digital computer for navigation and user interaction. I have essentially three
questions on this unit and I am sure lot of experts and/or users should be in this forum:

(1) Does anyone know, where this LTN-72RH was used - I have been told, it was on DC10-300,
but not sure on this. Also would be interesting, what the additional letters "RH" mean - probably
some radio-nav addon included (Software revision is 72-71-06)?

(2) Of course: Any manual/schematics/pin-outs around helping me to better understand or even
fire up this unit? BTW: I have some experience in making equipment like this work again ;-) -
see my work on a
or an


(3) Which CDU does match the unit? From the WEB I know a very old type of CDU as used with
LTN-51 (Concorde and probably many others)...



Than there is a midle aged CDU which obviously already has alphanumeric displays:



And I came accross rather modern CDUs by Litton which more look like a FMS:



Any hints/discussion/comments are welcome...

Best wishes, Erik - erik - at - baigar.de



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Old 24th Apr 2020, 09:34
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I dont know if these people can help

https://www.vmars.org.uk/
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Old 24th Apr 2020, 11:03
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I associate the first CDU as being used with Litton INS, I have never seen the two later CDUs. I worked with multiple operators over the years until I retired in 2008. And would expect to find that equipment on DC10-10 and -30, Tristar and 747 2/300.
Concorde which you mention was as far as I am aware Carousel equipped.
Carousel was a quite common fit to Tristar too. Litton more usual on DC10 and 747 but as ever the fit was an operator option.
I do remember the INU being heavy !
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Old 24th Apr 2020, 11:40
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Hi, thanks for the answers! Will try my best with the guys at the VMARS, although they may be centered on radio stuff? Thanks also to Wodrick, yes, the unit is very heavy (25+kg), so for the tree units probably having been on the DC10 this makes the weight of an additional
passenger ;-)
I have seen in document 34-42 on the DC10, that there should have been three INUs and one CDU. But the first CDU in the series (which I actually have got) does not have the propsed switch to select which INU's values to show on the display. Also checking some signals on this CDU they do not match what is given in the sheet 34-43-1 I have got on the DC10, so there must be a different kind of CDU still...
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Old 24th Apr 2020, 13:11
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As the aircraft age then they get modified. "My" DC10s both 10-10 and 10-30 had triple installations with three CDUs one for each pilot and a third in the roof panel, usually over the Captain's head. I worked on DC10s from four different companies and all were different in some respect.
Have fun, sorry I can't help further, as I retired all my manuals and notes went to the recycling.
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Old 24th Apr 2020, 18:31
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Thanks for your comments, Wodrick! Sad, that your notes etc. went to the recycling, but can understand this after your retirement. Probably you remember whether you often encountered failures in these systems? I guess the navigation computer calculated a mean/most probable position from the input of the three drifting INS systems? Perhaps it is to long ago to remember how much miles they have been off position after e.g. crossing the atlantic?
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Old 24th Apr 2020, 22:23
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Originally Posted by baigar View Post
Probably you remember whether you often encountered failures in these systems? Not often, pretty reliable
I guess the navigation computer calculated a mean/most probable position from the input of the three drifting INS systems? You get ahead of the technology ! Each INS fed the on-side flight director/ Autopilot with a simple switch NAV/INS. either side could be selected to the alternate.
Perhaps it is to long ago to remember how much miles they have been off position after e.g. crossing the atlantic?
I might be confusing other systems, trans Atlantic up to eight miles or so. Could often be less. When they got to a consistent 20 miles or so time to change INU. In my company it was a Tech Log note INS Drift #1,#2,#3.
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Old 25th Apr 2020, 10:38
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Wow - cool; thanks for the information. So good to know and for the long flight time over the
Atlantic, 8 miles are not so bad. The military Ferranti systems from the 1970ties I restored
and have one working one mile per hour is claimed, although I guess they rarely really
where that good. You also have been pretty right, that there are lot of very different configurations
of panels if one looks at cockpit pictures on the WEB! In a PanAm manual available online I found
the following panels related to the INU kit (Claimed to be a DC10-30):

A mode selector panel:



Than a sensor display panel (with switch to select one out of three sensor units):


And what they call CDU, an unit doing navigation already with waypoints etc.:


So the search for the right panels will go on and I will check, whether the sensor pinout matches
what I have got...
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Old 25th Apr 2020, 18:26
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The pt. No. of your INU is: 452080-05.

The TSO for that unit is TSO-C5C which shows a LTN72 control panel as pt. No. 452090-02

That would suggest the first control panel depicted above, with the Dim selector in the middle, would be suitable. Litton were taken over by Northrop Grumman.

Inertial systems at the time had allowable drift of X number of miles.

Where X = 3+3T and T was the sector time.

For example, an 8-hour flight would mean the maximum allowable drift would be:

3 + (3 x 8) = 27 miles. The systems were quite reliable unless not used for some time, in which case they tended to fail at start up.

I have no idea what the RH represents, There are R and RL models as well.
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Old 26th Apr 2020, 10:25
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Hi QA1 - many thanks for your informative post! Given the part number for the LTN72 panel, I
indeed found a pictures on AeroBay - the panel indeed looks quite similar to the first, oldest
ones on my first posting. The panel I have got looks identical although it has got a different
part number.
There is a catalog of commercial items available from Northrop Grumman giving more part numbers
of various navigation kits - so also thanks for this hint! Will be a good starting point for more
research...
Thanks also for the formula on calculation of accuracy. Of course this linear+offset one is
some estimation - from a physical point of view (and what I saw in my restored systems) is,
that there usually is a strong oscillatory component in position (Schuler period) too ;-)
Thanks again for all the input!!
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