RAF Navigation procedures, 1940

Hah! We’ve all done it.

Yes requesting a QDM wouldn’t be at all unusual for a single seater where a Nav’s pride isn’t at issue.

I’ve done its modern day equivalent and calling D&D for a fix as ‘temporarily uncertain of position’ at least once for real.

Out for the rest of the day. I’ll return to this tonight.

Moggy

Sorry, yes, decimal point issues indeed. 1,800 ft. Cloud bases 1,800 to 1,500 ft! I amended the post to avoid confusion on the part of anyone reading that and not this – and to spare my blushes 🙂

Should have had a coffee first! Feel a bit silly now.

Another question – would it be usual for a lost fighter pilot to call for a QDM from a nearby station in the UK, or was this just a long-range nav thing? Who would they call? Feels like the sort of stuff I should know, but somehow it never came up – until now.

Thanks all, didn’t mean to sound curmudgeonly before.

To put my cards on the table, this was a local flight – staging between Exeter and St Eval. Cloud base was between 1,800 and 1,500 feet (from met reports of the day), from 5/10 to 10/10.

A direct route would have tracked right across Dartmoor, which goes up to 1,800 feet or so. Dangerous if they were using ground way points for navigation. The one survivor of the three said they descended to 300ft (must have been AGL) ‘near Bovey Tracey’. Cloud was occasionally down to 200ft AGL, so I imagine this was to get a view of the ground for navigation purposes. My contention is they were tracking so as go around the high ground, to the South. That’s the only way Bovey Tracey would make sense on a flight from Exeter to St Eval. (All this needs a map to visualise). However, the survivor said that he suddenly saw the ground rise up ahead of him.. and he climbed, and headed back to Exeter. No-one saw the others again.

Now, if one applies the 11.8 deg variation applicable at the time to the shortest ‘safe’ high-ground-skirting track from Exeter (as if an error had been made.. The survivor said they were lost at the point he left the flight around Bovey Tracey – probably because the visible ground features didn’t tally).. one has the remaining two flying at a height around cloud base right into the heart of Dartmoor, and not around it – and colliding with the high ground immediately East of Fox Tor Mire. Which is what our (second hand) eyewitness report says as well. They reported TWO aircraft flying over their farm near Dartmeet, and not being high enough to clear the ground to the South West (that they, the farmers, knew was there but which could have been invisible) That matches the hypothetical track very well.

No worries. It was at the end of a long evening.

Do remember all aviation compasses have a little card displayed beneath them giving error corrections found when the compass is swung on the ground. Wouldn’t this sweep-up declination also?

It’s annoying in that I know I had a copy of the AP, but initial searching of the chaotic shelves has failed to turn it up.

Moggy

Sorry Moggy, but I do mean magnetic declination and it IS in the horizontal plane. Just for clarirty. Please check your sources. Or just Google it.
http://www.google.co.uk/search?site=&source=hp&ei=27vBVeW3Fe6R7AaWo4rIAQ&q=declination&oq=&gs_l=mobile-gws-hp.1.0.41l3.0.0.0.2585.1.1.0.1.1.1.429.429.4-1.1.0….0…1c..64.mobile-gws-hp..0.1.64.3.9XzjJ16zbl4#q=magnetic+declination
I am familiar with a lot of the principal behind it too, being a graduate physical geographer and geomorphologist. My questions are further to that base knowledge. I do have the local variation for the area in December 1940. It was drawing this on a map that made me want to test a hypothesis. – but first I needed a few specifics. That AP sounds useful!

Try and search out a copy of Air Ministry AP1234: Air Navigation – it’s very thorough on the contemporary techniques.

Beermat,navigation can be very complex,and perhaps `Wiki` can help.You may wish to read up on `Great circle` and `Rhumb line` ,latitude convergency,variation/declination,deviation,..Also `map projections`,as one is trying to produce a curved surface as a flat projection. Please do not think this is `condescending` in any way,as it`s ATPL stuff,and was important for long distance flights.
However,if you are talking about a flight within the UK,then a lot of it will not be relevant as distances are fairly short.
You might also look up `magnetic variation over UK in 1940s` which may help.
Further info reqd. for a better answer.
Google Earth may be your friend,if you join two earth points at the same Latitude,ie Edinburgh-Moscow,and read the `track` then try Moscow-Edinburgh and read the track…That will give you a an idea about `convergency` and `grt.circle tracks`,and a constant heading change in flight`.If you now take the mid -point heading,in either direction,and it`s reciprocal,that would be a `rhumb line `track ie.constant heading,ignoring wind. GE always does `great circle tracks/shortest distance..`Rhumb lines you have to draw as a `path,or line`, giving a longer distance…….I need more red-wine…!!!

However, let’s think about single seater aircraft that obviously have no navigator. On the ground the pilot would plot his course on the chart then use a protractor to establish the track he wants to make. Then he’ll apply the forecast wind and correct for magnetic deviation on his computer as above. That will give him a magnetic heading to fly, using his magnetic compass as reference. And an elapsed time to each of his waypoints. He’d either scribble these on a knee board or the chart itself.

As long as he is visual with the ground he’d monitor landmarks such as towns, lakes etc. If they appear where and when expected then the forecast winds were accurate. If not he’d estimate and apply a correction for the next leg.

Moggy

Red herring.

Declination is in the vertical plane. An aircraft both climbs and descends so any declination angle will be constantly changing, there would therefore be no point in trying to fit a mechanism to compensate it for the declination in straight and level flight.

If you meant Magnetic Variation both it and forecast or calculated winds will be fed into the navigators computer, a circular slide rule with sliding centre section, a similar item is still in use by PPL students today.

[ATTACH=CONFIG]239669[/ATTACH]

Moggy

Maybe I should have been more specific and said ‘magnetic declination’ https://en.m.wikipedia.org/wiki/Magnetic_declination

Thanks Moggy

Not sure what ‘declination’ means in this context.

Would this earlier thread help at all?

Moggy

http://forum.keypublishing.com/showthread.php?121958-P11-Compass-information

Thanks Moggy. That has helped me clarify my thinking. In this case it is a flight of three single seater fighters transiting between airfields in very bad weather, routed so as to avoid high ground. Pointing out that ultimately it will be down to lines on a map orientated true North which would then need to be ‘translated’ to mag North compass bearings has crystised tbings a little. One more question.. and it’s a real novice one, I am afraid. Did the P-series compasses have a bezel that allowed correction for declination?

Well it would be appropriate to specify true or magnetic to avoid confusion.

However, if you think about it most navigation would be accomplished by drawing a line on a chart – say Scampton to Hamburg. The direction of that line would have to be degrees true, as nobody wishes to print a new chart each year as the magnetic variation… er…. varies. So chart North will always be true North. It is then up to the Nav to apply the magnetic variation for that position on the earth and that year.

He would then pass the heading to steer as a magnetic to the skipper, who only had a magnetic compass. Asking the pilot to do a mental calculation of a true heading to a magnetic would be inviting errors.

Does this make sense?

Moggy

Just an accumulation of references over the years, I guess.. one to hand is this, re QDM’s: http://www.bbc.co.uk/history/ww2peopleswar/stories/33/a2281033.shtml

..and the fact the order had to specify ‘true’ of course.

What’s the source of your belief that magnetic bearings were used?

Moggy