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19AB67

DC-6 navigation without navaids

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Hi folks, 

 

waiting impatiently for the FSX DC-6 and after having read many of the 1950s DC-6 timetables (see my other thread http://www.avsim.com/topic/492268-dc-6-routings-timetables-lets-collect/ with most helpful links) now I wonder how navigation was done preGPS and preINS and preNAT. 

 

Maybe I should be more specific.

Of course I know about navigators using sextants etc. See also on Wiki article on 'Transatlantic flight'. This is on 'Where am I?' 

 

My question is more on the *aviate* in aviate-navigate-communicate. 

 

If I know where I want to fly to, how to set the heading appropriately? 

Without GPS or weather charts I know little about the actual wind situation outside and the drift resulting from it. In the aforementioned article we learn:

'To aid aircraft crossing the Atlantic, six nations grouped to divide the Atlantic into ten zones. Each zone had a letter and a vessels station in that zone, providing radio relay, radio navigation beacons, weather reports and rescues if an aircraft went down. The six nations of the group split the cost of these vessels.[47]'

 

However, before these radio navigation beacons, -- and within FSX -- there were/are no navaids. 

 

If I take the route from Shannon to Gander as an example, the great cycle is roughly: 

EINN N5320  N5330  N5240  N5050 CYQX 

 

The magnetic headings for 'no wind' are a starting point:

EINN 286° N5320  283° N5330  278° N5240  273° N5050 263° CYQX 

  1. Did the pilots simply fly this route until they picked up first navaids on the other side of the pond?
  2. What if the navigator calculates at e.g. 30W that you hit rather 52N or 54N? Correction to 282°/274°? Or rather extrapolation of the last section to the next, not knowing whether the wind is significantly different? 
  3. Did they make use of incoming aircraft, which just had been probes in the wind at a given, i.e. their crossing altitude? 
  4. A mixture of 1.-3.? 
  5. BTW: Did they already fear mid-air collisions and flew altitude separation?
  6. If we know the wind, e.g. taken from skyvector.com wind barbs, we can calculate with some trigonomy the heading to fly. 

Noooooo, I won't ask when the FSX DC-6 will be out.... but I start flying in my imagination!  B)  :BigGrin:

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Ups, the true waypoint across the Atlantic are of course ...

EINN 286° 5320N  283° 5330N  278° 5240N  273° 5050N 263° CYQX

... with the 'N' at the end. 

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Did the pilots simply fly this route until they picked up first navaids on the other side of the pond?

 

They attempted to fly whatever route they deemed suitable, yes. This could either be out over the waters, or an arc (with/without stops) over NE Canada, S Greenland, Iceland, Ireland and the UK.

 

 

 


What if the navigator calculates at e.g. 30W that you hit rather 52N or 54N? Correction to 282°/274°? Or rather extrapolation of the last section to the next, not knowing whether the wind is significantly different? 

 

Course corrections were normal, and usually involved calculating what pushed you out of position to help you make a better correction to continue.

 

 

 


Did they make use of incoming aircraft, which just had been probes in the wind at a given, i.e. their crossing altitude? 

 

You could, but their calculations of the actual wind are no better than yours, and weather constantly changes.

 

 

 


If we know the wind, e.g. taken from skyvector.com wind barbs, we can calculate with some trigonomy the heading to fly. 

 

Correct. Even without the wind barbs, you can still figure it out, and are encouraged to do so. This is best done prior to losing your ground references and navaids, as well: known positions, time to drift, etc. Navs all had slide rules (similar to, or exactly like, the E6B of today).

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Thanx Kyle, this gives the insight. 

 

 

 


They attempted to fly whatever route they deemed suitable

 

... but based on some early weather charts? 

 

 

 


but their calculations of the actual wind are no better than yours, and weather constantly changes

 

... right, but the incoming aircraft at EINN just had experienced the latest weather (the weather probe), while those heading from EINN to CYQX had to rely on whatever weather charts. 

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They had a navigator on board and an astrodome to shoot the sky. Celestial navigation was the primary means of getting across water. The NDB sites were unreliable in bad weather but that was it.  Good old fashion pilotage was and still is an art.

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Over land they also had the LFR Radio Range system for airways flying. There was also Decca navigator system which could be used over the ocean.

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Decca navigator system

 

Again, I assume this support knowing where you are. 

I'd like to learn more which methods where used to set the right course with the knowledge of your position, deviation from wanted position, but not knowing the winds outside. 

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Yes the Decca navigator could only identify current position. It's up to the flight crew to plot the course, estimate drift and compensate for it. That's why long range aircraft usually had a navigator in the crew.

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As has been mentioned, there would be a navigator on the crew who would be trained far more comprehensively in the art and science of navigation than any pilot, then or now. The various means of fixing position have been discussed -- celestial nav (including using the sun, during the day) could be used, as could the various radio-based systems described by Kevin.

 

Regarding applying a wind correction -- if you knew where you were, and you know your present position, you can plot the course you have flown on a chart. You can then use the time taken to get to from where you were to where you are now to determine your ground speed, and it is a simple matter of trigonometry to calculate the wind drift -- you have the actual ground track (if you knew your previous and current position) and you have the speed.

 

You could use either a computer (slide rule/E6B) to come up with a precise answer or you could use various rules of thumb such as the Maximum Drift (http://www.jenxs.co.uk/Navfiles/Maxdrft.html) method to approximate the required correction.

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... but based on some early weather charts? 

 

Not likely. If there was one, it was not usually trusted very well.

 

 

 


... right, but the incoming aircraft at EINN just had experienced the latest weather (the weather probe), while those heading from EINN to CYQX had to rely on whatever weather charts. 

 

Right, but unless you're on top of that aircraft, you're going to be later than it. If you're right behind it on approach, then sure, but the skies were not filled with aircraft back then like they were today.

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BTW: Did they already fear mid-air collisions and flew altitude separation?

 

Any knowledge on this? 

000° to 180° FL190, 210, 230, 250?

180° to 360° FL180, 200, 220, 240? 

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Any knowledge on this? 

 

What about it? What you've listed is the current separation standard.

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Any knowledge on this?

 

I would assume there was some sort of convention, if not necessarily mandatory, but I would have to do some research to find out for certain.

 

Mid-air collision was certainly a concern, though there was a lot of (perhaps justified to a certain extent) stall placed in the 'big sky' theory -- ie the sky is a big place and aeroplanes are relatively small. Arguably mid-air collision didn't really enter the forefront of consciousness until the Grand Canyon mid-air of 1956, which led to a number of changes in the ATC system to reduce the risk.

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What about it? What you've listed is the current separation standard.

 

Did they already adhere to something like this? Or a different agreement?

 

 


but I would have to do some research

 

That'd be great, Simon. 

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Over land they also had the LFR Radio Range system for airways flying. There was also Decca navigator system which could be used over the ocean.

 

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

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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'.

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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.

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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.

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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.

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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.

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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.

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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. 

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