[Milsurplus] High & Mighty SCR-718

[D C *Mac* Macdonald]

I saw that scope and boy, did it ever take me back!

The same Radio Altimeter was being used in the T-29C
aircraft we had in Navigator Training at Harlingen AFB, TX
back in 1961.

The navigation method referred to by Breck was called
"Pressure Pattern" navigation.  Our instructor in that
phase of school laughingly said he used that method
three times to fly from the US to Europe and only
missed the continent once!

It is basically usable between latitudes 30 and 60
(either north or south).  It was of less accuracy
between 30 north and 30 south.  I have my doubts
about its utility in polar regions because it also relies
on ded reckoning locations plotted using magnetic
headings.

The amount of drift from magnetic course was
determined by how rapidly the difference between
absolute altitude and pressure alltitude was changing.
The drift direction was determined by the relationship
between the two altitudes.  I no longer remember
(over 40 years) whether radio altitude greater meant
which direction of drift.  I do remember that if the
two altitudes were identical there was zero drift and
your ded reckoning was probably pretty good.  Add
a single Line of Position (LOP) derived from a sextant
shot of sun or moon and you could get a decent FIX
during daylight hours.  You SHOULD be able to fix your
position within 5-10 miles, at least.

Mac, K2GKK/5
Nav Class 62-16, Harlingen AFB, TX
USAF - Retired


----Original Message Follows----

From: "b. smith" <smithab11 at comcast.net>
To: "milsurplus" <milsurplus at mailman.qth.net>
Subject: Re: [Milsurplus] High & Mighty SCR-718
Date: Sun, 31 Jul 2005 08:51:06 -0400

    Although the SCR-718 was utilized quite dramatically in the "High and 
The Mighty"  while the distressed aircraft was at lower altitudes  and  the 
aircraft approached SFO, the main purpose of the SCR-718 was for use by the 
navigator to determine the aircraft's Absolute Altitude during the enroute 
cruise portion of the flights.  The Absolute Altitude  of the SCR-718 was 
compared with the Pressure Altitude(Standard Barometric altimeter set to 
29.92 inches)  to determine the difference in feet (usually a value of 
several hundred feet). This  "sounding" was entered into a formula to 
determine the aircraft's drift angle.  If you knew the aircraft's True 
Heading and Drift  Angle you could find your way to your destination. 
Pressure Pattern navigation was a great aid and augmented celestial 
navigation, it  had no boundaries or restrictions  and even worked great in 
the  polar regions. The process was developed by Dr. John Bellamy.


73 breck k4che