# NavList:

## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

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Re: 3-Star Fix - "Canned Survival Problem"
From: Mike Burkes
Date: 2008 Jul 8, 16:46 -0700

```Hi GL that is pretty slick and I imagine the user would become
accustomed to that type if that was his only exposure. It seems it is
an advanced model i.e. I would assume the user has already visualized
the wind triangle ala E6b and/or rough sketch and does not wish to
fuss with pencil lines. Has anyone had experience with the Jepp Model
CB-1(charles bravo dash one)? As always great stuff and thanks much!
Mike Burkes

On Jun 14, 10:11�pm, "Gary J. LaPook"  wrote:
> Gary J. LaPook wrote:
>
> > Gary J. LaPook had written::
>
> > "The MB-2A is very similar to the MB-9 pictured here:
>
> >http://www.rekeninstrumenten.nl/pages%20and%20pictures/12071.jpg
>
> > except the true airspeed goes up to 1800 knots on the MB-9 while it
> > only goes up to 1000 knots on the MB-2A. Since I don't fly planes that
> > can exceed 1000 knots I prefer the MB-2A since its more limited speed
> > range allows an expanded scale for the range it covers.
>
> > It is very similar to the Felesenthal PT computer pictured here:
>
> >http://www.rekeninstrumenten.nl/pages%20and%20pictures/12141.jpg
>
> > in that each of these computers solve the wind triangle with trig, no
> > vector diagram is drawn."
>
>
> > In case you were wondering how you can solve the wind triangle with
> > trig on the MB-2A without a vector diagram �the answer is simple, the
> > law of sines. TAS/sin RWA = WS/sin WCA = GS/sin (RWA +/- WCA). To do
> > this on a digital calculator first figure the Relative Wind Angle (the
> > angle the wind is coming from compared the true course, WD - TC. Next
> > divide the True AirSpeed �by the sine of the RWA �and save that value
> > in a memory as you will use this constant twice. �Next divide the Wind
> > Speed by this constant, take the inverse sine and you have the Wind
> > Correction Angle. Finally add or subtract the WCA from the RWA,
> > subtract if the wind is a head wind and add if a tail wind, take the
> > sine of this angle and multiply by the constant to give you Ground Speed.
>
> > The MB-2A does this computation for you. First place the TC arrow on
> > the true course on the outermost RED scale and then read the RWA on
> > the next inner RED scale lined up with the WD. �This first image shows
> > this with the TC of 50, the WD of 100 giving a RWA of 50.
>
> > Next line up the TAS on the outermost BLACK "miles"scale with the RWA
> > on the "wind scale" which is a sine scale. The next image shows 120
> > knots lined up with 50 on the "wind scale."
>
> > The "constant" mentioned above is found uner the "1" index but you
> > make no use of this and you don't even have to notice, the computer
> > takes care of it for you.
>
> > Next look on the "miles" scale for the Wind Speed and take out the WCA
> > on the "wind scale." The next image shows a 20 knot WS on the "miles"
> > scale lined up with WCA of 7.3� on the "wind scale."
>
> > Subtracting this 7.3 WCA from the RWA of 50 we then set the cursor on
> > 42.7 on the "wind scale" and read out the GS on the Miles scale, 106
> > knots.
>
> > gl
>
> >>With the exception of the red numbers on the outside rings, your MB-2A
> >>computer looks remarkably similar to the Jeppesen CR series (CR-3,
> >>CR-6, etc.) - is it maybe a military version (or an earlier version)of
> >>the Jepp one?
>
> >> Gary LaPook responds:
>
> >> The MB-2A is very similar to the MB-9 pictured here:
>
> >>http://www.rekeninstrumenten.nl/pages%20and%20pictures/12071.jpg
>
> >> except the true airspeed goes up to 1800 knots on the MB-9 while it
> >> only goes up to 1000 knots on the MB-2A. Since I don't fly planes
> >> that can exceed 1000 knots I prefer the MB-2A since its more limited
> >> speed range allows an expanded scale for the range it covers.
>
> >> It is very similar to the Felesenthal PT computer pictured here:
>
> >>http://www.rekeninstrumenten.nl/pages%20and%20pictures/12141.jpg
>
> >> in that each of these computers solve the wind triangle with trig, no
> >> vector diagram is drawn.
>
> >> The Jeppesen CR-3 pictured here:
>
> >>http://sliderule.mraiow.com/wiki/Jeppesen_CR-3
>
> >> uses a diagram on the back to determine wind factors so its method is
> >> completely different than the previous computers. �All of these are
> >> similar in that they have the standard time-speed-distance scales and
> >> they allow for compressibility in computing true airspeed.
>
> >> The original E-6B pictured here:
>
> >>http://www.rekeninstrumenten.nl/pages%20and%20pictures/12081.jpg
>
> >> uses a wind vector diagram on the back and does not allow for
> >> compressibility in TAS computations.
>
> >> gl
>
>
>
> �IMGP4734-1.JPG
>
> �IMGP4735.JPG
>
> �IMGP4736.JPG
>
> �IMGP4737.JPG
>
> - Show quoted text -
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