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Re: [OM] Mammoth E-30 Product Review - Zone-10 Website

Subject: Re: [OM] Mammoth E-30 Product Review - Zone-10 Website
From: Chris Barker <ftog@xxxxxxxxxxxxxx>
Date: Tue, 10 Mar 2009 17:47:48 +0000
Sorry, Paul, I should have written "estimate".  I reckon the system  
starts off with an estimate of position (and true north), gained from  
the astrotracker (must have been a pioneer system!) to adjust the  
expected angular acceleration.  As the alignment progresses, this  
estimate is refined to improve accuracy.  They do use GPS now, but  
even that will be an estimate, however accurate, to get the system  
going.  Of course, it's possible that the GPS position is integral to  
the whole nav system so the alignment can be almost instant, but I  
have not heard of any instant alignments giving best system accuracy.

To illustrate, admittedly with experience from 20 years ago and before  
GPS integration, the wonderful system in the F16 (Block 32) allowed  
for a 15 minute align before good accuracy was achieved, even with the  
RLG platform.  But best system accuracy was achieved with an  
interrupted align: stop the align once it was complete, then taxi and  
stop at 90deg to the original heading and put it back into align.   
Then when you were ready to depart, put it into Nav again and it would  
be truly SH.

The Tornados I flew had GPS but it wasn't part of the alignment  
system; you used GPS to provide updates during a flight to counter the  
IN platform's wander, as an alternative to fixes off the ground.

The Hustler might have been a nightmare to maintain, but it was a  
gorgeous aircraft.  I remember making a model when I was about 12-14.

Chris

On 10 Mar 2009, at 17:02, Paul Laughlin wrote:

> The inertial guidance systems do not guess at all.  Even the system  
> in the
> B-58, which, incidentally was analog, used an astrotracker to  
> determine
> position on earth.  I am sure that, today, they use GPS.  There was  
> also
> input from a fluxgate compass so that the platform had a north  
> reference.
> The gyro-stabilized table is erected to be gravitationally level and
> pointing to North.  At this point there is zero static (gravitational)
> acceleration.  Now the gyroscopes maintain the platform at this  
> position.
> The aircraft rotates about it.  Any movement of the aircraft then  
> effects
> the accelerometers.  There are correction factors that are necessary  
> such as
> coriolis effect and others, which are taken into consideration, of  
> course.
> You can get aircraft pitch, roll and azimuth position by checking the
> aircraft attitude in reference to that stable platform.
> The B-58 system was pretty much a pioneer in Inertial Guidance for  
> aircraft.
> My primary responsibility was the in shop maintenance of the
> gyro-stabilization and astrotracker systems.  Troubleshooting and  
> repair.
> That was in the B-58 Test Force and later in the 43rd Bomb Wing.  As a
> completely useless piece of info, the B-58  was a maintenance man's
> nightmare.  Required something like 1000 hours of maintenance to get  
> 1 hour
> of flying time.  It did set several speed records, though.  Won the  
> Bleriot
> Trophy, and then while flying to the Paris Air Show to receive it,  
> set a
> speed record from New York to Paris.  Still stands, as far as I know.
> The Inertial Guidance systems are very much more sophisticated these  
> days,
> but the principles are pretty much the same.
> Paul in Portland OR

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