More on the Link Trainer and BABS etc..

[John Hill]

We are pushing on with our replica and functioning Link Trainer but nothing really physical to see as yet.

Researching the library has turned up a briefing chart c.1953 showing a number of Range stations including Christchurch, Paraparaumu (near Wellington), New Plymouth, Mechanics Bay (water, Auckland) and Whenuapai. In the South Pacific I found Nadi and Aitutaki. These facilities are pretty much forgotten but they must have been quite significant in their time.

As an aside, I received an old Roland pen plotter which was DOA but minor surgery got it going again. I will take another feed from the Link Flight Simulator of lat/long and convert that to Roland DXY format so we will be able to produce hard copy flight records as per the old days. Actually, we do have an original Link 'crab' unit but that is 80 years old and enjoys protected relic status. That custom software is coming along nicely.

We have engaged a team of likely lads from one of the clubs for gentlemen where they have a comprehensive wood shop and they will be helping us build the 'Blue Box' etc. But no actual progress so far as unfortunately I am currently confined to quarters with the 'Hundred day cough', fortunately I only get it every three months or so.


Now about these RDG (Radio Range), they were a bit thin on the ground over the Pacific but enough to provide I would say, contiguous guidance from our little aerodrome to St John's, Newfoundland. Maybe this link will work for you https://www.google.com/maps/d/u/0/viewe ... 258277&z=8

If the link works you will see dozens of stations around the world and all the ones I looked at are termed TACAN and of course the RDGs I am interested in were not TACAN and predated TACAN by about 20 years so I don't have a clue as to how widespread RDGs were across Asia and Europe.

When the Blue Box is fully operational we may allow punters to try their hand at a RDG to Christchurch, letdown and approach on a frosty August evening with coal smoke clag down to letter box height.

I know there were various systems in Europe around the time of WWII including BABS. Now BABS had a lot of similarities with RDG but were much more local and more of an approach aid that en-route, I understand BABS was installed near the threshold and produced a number of beams in a narrow fan with individual morse code idents.

Fortunate am I to have Air Publication 1751 for night time reading..

[Pontius Navigator]

Vague memories of the RDG as a predecessor to VOR. I seem to remember feathered fan markers from Airways RP shown on the en route maps of the time for left or right of the centre line.

[Boac]

A fascinating map, John, thanks. It opens up a whole new world of aerial navigation to me! Looking at the UK it seems a lot of stations were basic 'area nav' type and transmitted on a 045/135 cross (why not 360/90??) whereas elsewhere, Lisbon, for example, appears to be a runway (03) aid.

[John Hill]

The four legs of the RDG could be arranged somewhat off the 90 degree angles and this was done to gain advantages where possible. It seems they rarely arranged them so that a beam led directly to a runway and the RDG transmitter site was usually(?) a few miles from the nearest runway. The beams at the RDG nearest here (which was Christchurch NZ) had one beam that passed right over our NDB 60 or so miles away.

The RDG itself did not provide any distance fix except where fan marker beacons might have been added, but usually not as far as I can see.

I guess the basic procedure was to follow a beam while keeping an eye on the clock and aiming to be at a minimum altitude when crossing the 'cone of silence' at which time in many cases there would be a slight turn to where the runway should be, descend to minimum safe (decision level) and either land or climb to pickup one of the beams.

The cone of silence of course is the point where the four beams originate and the signal level is zero.

[Boac]

It seems they rarely arranged them so that a beam led directly to a runway

More common than you suggest, John, possibly outside NZ?

[John Hill]

https://media.discordapp.net/attachment ... av0202.jpg

You can see in this illustration how the RDGs were arranged to produce an interconnected mesh.

So in the late 20' to early 50's you could have flown IFR all around North America and much of the Pacific guided only by the tones in the 'phones and no clunky radio compass or ADF.

The beams were wider of course the further from the RDG site but they narrowed down to be just a few tens of yards when nearing the intersection. Interpreting the beam signal sounds simple enough although writers of the time did complain of the tedium of following the beams for hours especially in bad weather (static etc).

There was a steady tone to be heard when on the centre of the beam with Morse letters 'A' on one side and 'N' on the other. Experienced pilots tried to fly in the 'twilight zone' where the main tone was still loud and the letter code could be heard at a somewhat lower volume.

I do not know how things were arranged in UK and Europe where I believe there were a number of systems in use and few if any RDS.

[Boac]

Not sure what an 'RDS' is, John? (Apart from Radio Data, of course)

[John Hill]

It seems they rarely arranged them so that a beam led directly to a runway

More common than you suggest, John, possibly outside NZ?

I am somewhat unconvinced but I must stress that I am talking about RDG (radio range) and not any of the other systems that may have been in use including of course BABS. BABS, Standard Beam Approach and Lorenz et al had transmitters right on the field whereas the five 'local' RDGs I have found (Christchurch, Aitutaki, Nadi, Whenuapai and Mechanics Bay the beams are not aligned with the runway (but rather close at Nadi), at Whenuapi the beam transmitter looks about 4nm from the runways.


Look at this one for Joliet...


You can see the runways are a few miles from the RDG site and that it is necessary when descending on 068leg to turn to 126. This sort of arrangement seems to have been quite common with RDG approach.

[Boac]

Essentially the RDG 'approach' is a cloud break manoeuvre, but where possible and desirable it makes sense to align the radial with the runway to avoid having to throw a turn at 1300' to point to the airfield! Can you access the chart for Lisbon out of interest?

Still asking about RDS?

[John Hill]

Oops RDS, should be RDG.

A chart for Lisbon for the era, I can take a look around.

[Boac]

We actually need knowledge of the 'route' structure around Joliet, John, and why the radials were set as they were. I would suggest that once the beacon was in position and transmitting, someone set about designing a 'procedure' for the airfield. Whether the beacon had been positioned roughly aligned to R13 or not we will probably never know unless you can find some wrinkled old installer in Illinois.

[John Hill]

Without finding ancient Portugese plates I can say that the coordinates I have for the 'TACAN', I suppose it might be a TACAN but this listing shows frequency 245 and four radials so it looks like a RDG.

Code, Frequency & Radials
PL 245 34/124/214/304
Type
TACAN
Name
Lisbon
Latitude
38.8105
Longitude
-9.103525
Range
Long

Jepperson says

General Info
Lisbon, PRT
N 38° 46.4' W 09° 08.0' Mag Var: 4.9°W


...so you can see whatever it is it was some, distance from the airfield reference point.

The runways are 03/21 and 17/35 so how does that line up with the above radials? (Applying correction for magnetic is outside my pay scale.)

[Boac]

1) Ignore the word 'TACAN'. Not sure why it has arisen in the map you linked, but TACAN beacon does not have 'fixed' radials. (Mind you, an RDG is in fact a 'Tactical Air Navigation' facility )

2) The beacon position you have given is just off the northeast end of R03 at Lisbon, making it ideal for cobbling together a runway approach on either 03 or 21.

3) 030 is, of course, an ideal inbound course for the route for traffic from the Canaries etc

My feeling, having looked at all this, is that we should not get over-obsessed with the 'runway/airfield' approach bit. I think essentially the RDGs were for route nav BUT where they were or could be 'conveniently placed' could be adapted for the former.

[John Hill]

Thanks for working that out.

Yes, I agree that the RDG was principally a route aid and that is certainly how the old books presented them.

On the subject of old books, 'Air Navigation and Meteorology' by Captain Richard Duncan, published Goodheart-Willcox Company, 1941, is a thoroughly good read and IMHO well worth the modest effort required to study it.

''Through the Overcast' by Assen Jordanoff published by Funk Wagnalls, 1938. This is a bit of an easier read than AN&M and is readily available. I often see it referred to as a 'must read' for anyone seeking the US airline industry at the time.

Who has not read Ernest K. Gann? His 'Flying Circuit' has a chapter or two on foul weather flying and is pleasant enough reading in the 'pipe and slippers' vein (I say that owning neither a pipe nor slippers.)

Back to the route vs. approach issue. The BABS system is easily confused with the RDG in that the BABS was also a 'dots' and 'dashes' deal but BABS was definitely an approach aid.

BTW, BABS could be used with earphones and/or a panel instrument and I am almost certain that the instrument in our genuine Link is a BABS type device.
As far as I can determine we only had one BABS equipped airfield in NZ (Ohakea RNZAF).

John