Sorry Kevin,

But I have to correct you on the Decca Navigator System.

Decca was only covering on land and =Coastal waters= up to 400 nm in day and 200 to 250 nm at night, and only in certain area of the world, thus could not be used on an entire ocean crossing.

A very nice description of the Decca Navigator System can be found here:   http://www.wow.com/wiki/Decca_Navigator_System

 

True, but it could still be used to help establish wind and therefore wind correction prior to the signal dropping for the 'pitch' until you pick up a signal on the other side for the 'catch'.

Sorry Kevin,

But I have to correct you on the Decca Navigator System.

Decca was only covering on land and =Coastal waters= up to 400 nm in day and 200 to 250 nm at night, and only in certain area of the world, thus could not be used on an entire ocean crossing.

A very nice description of the Decca Navigator System can be found here: http://www.wow.com/wiki/Decca_Navigator_System

Yes you're right, but in my defence there was a higher power development, Dectra, which had transatlantic capability. It wasn't widely adopted and INS finally killed it off.

In addition to Decca, 1950s-era navigators also made use of Loran-A, a pulsed radio navigation system. Unlike the later Loran C which was very popular in GA aircraft in the late 1980s, (and had a user interface similar to early GPS units), Loran-A required the navigator to tune in various Loran ground stations enroute, display the received signals on an oscilloscope, which gave him a set of numbers, which were then transferred to paper charts to plot lines of position.

 

Each Loran ground system had a range of about 500 miles by day, and 1500 miles by night. There were Loran systems on the US east coast, in the Canadian Maritime Provinces, southern Greenland, Iceland, Scotland and Ireland.

 

In the late 1950s, another system known as pulsed Doppler became available, which operated somewhat like a radar altimeter. A Doppler Nav system transmitted 4 narrow radio beams, two facing forward, and two facing aft. By measuring the Doppler shift of the reflected signals, it was possible to calculate aircraft heading, ground speed, and wind drift. Doppler was only useable over the ocean, but in the hands of a skilled navigator, it was almost as accurate as the later INS systems that became available in the late 1960s - early 1970s.

 

In any case, the navigator was busy during an entire oceanic crossing using a broad range of techniques to establish position, course, speed etc. The pilots flew specific headings given to them by the navigator, who also kept a continuing running estimate of time enroute and fuel consumption.

 

Now, of course, all these functions are done automatically by the FMS in conjunction with inertial Nav and GPS.

 

Getting back to your original question, there is really no way to simulate these various systems and techniques (celestial Nav, Decca, Loran, Doppler) in X-Plane. Of course, the PMDG DC-6 has been equipped with a modern basic GPS unit, which would be perfectly useable for an oceanic crossing - but if you want to emulate how it was done "back in the day", the only option is to use NDBs, combined with Dead Reckoning and charts.

 

 

A Doppler Nav system transmitted 4 narrow radio beams, two facing forward, and two facing aft. By measuring the Doppler shift of the reflected signals, it was possible to calculate aircraft heading, ground speed, and wind drift. Doppler was only useable over the ocean, but in the hands of a skilled navigator, it was almost as accurate as the later INS systems that became available in the late 1960s - early 1970s.

 

The USAF/Lockheed C-141 Starlifter had such a Doppler system as well as an INS.  The INS has come a long ways thanks to the laser ring gyro; but the early days with mechanical gyros and the inertial platform were not as accurate after a few hours as a good celestial set of shootings. If I recall, the doppler was used over land as well as water for drift.  Another interesting thing about the air data computer on the C-141 was that its primary memory was a rotating drum.

Another device found on aircraft that operated over water or otherwise in remote areas was a sight instrument that allowed you to watch detail on the surface you were over-flying, and align markers with where they entered/left the field of view. This provided a very accurate measurement of drift angle.

 

Rob Smith.

Another device found on aircraft that operated over water or otherwise in remote areas was a sight instrument that allowed you to watch detail on the surface you were over-flying, and align markers with where they entered/left the field of view. This provided a very accurate measurement of drift angle.

Rob Smith.

Drift sight - yep. Kinda a carry over from the mil side.

Interesting discussion about a largely lost art.

 

As Jim Barrett mentioned the Loran system was very important for both civil and military transport aircraft on the north atlantic routes in the 1950s and 60s. Most current aircrew will not be familiar with this or the various other paper chart systems which we once had to rely on, ( anyone remember Gee? ).

 

One small correction to his description of pulsed Doppler is that the Doppler itself only provided groundspeed and drift information. The drift was then applied to the compass heading, after correcting for magnetic variation and local deviation, to give the true track.

 

The Doppler worked fairly well over land, but less well over the sea where it tended to unlock at regular intervals. This also occurred over large desert areas, which like the sea, resulted in a weaker reflected signal. This caused us some problems because those were precisely the areas where other navigation aids were least available. In the 1960s Decca produced a newer version of the Doppler system which was much more consistent over difficult terrain.

 

The other related piece of equipment not mentioned is the Ground Position Indicator, (GPI), which worked in conjunction with the Doppler system. This was a wonderful analogue computer, comprising a large box full of gears and cams, which could be set to the lat and long of the start point. It then used the doppler and heading information to compute a current position throughout the flight, displayed as rotating digits in small windows.  When the Doppler unlocked, the GPI could still be fed with the best estimate of groundspeed and drift. It would then be updated at the next available fix, and this would also be done every 30 minutes or so when good fixes were available.

 

The previously mentioned drift sight was a surprising accurate device. As well as providing drift for pure navigation purposes, a variation of this was used for air photography with vertical cameras at medium to high altitude. The sight was used to align the aircraft with the target line by offsetting for drift. The switch on point for the cameras was defined by markers on the sight lining up with a particular point on the ground. The technique took a while to master, but was very effective.