Standard Beam Approach - Find the Aerial!

[trh01uk]

Originally Posted by jamesinnewcastl

The earliest AP (Dec 1938 - but Issued June 1940) I have lists the Type 3 aerial as the one used, it may well be inside the mast but I suspect I won't know unless I can dig deeper into some Stirling Information.

James,

I don't think the Type 3 would have been inside the mast, because if it was there would be little point in retracting it. We don't know for sure why it was retractable, but there was a general problem with drag on this early aircraft so we can surmise it was simply a fixed rod that could be pulled back into the airframe when it was not in use.

Your exercise here shows just how hard it is to get enough detail to be able to replicate exactly what was done - or even to understand what they did and why! I often get historians questionning why I am so interested in the detail of hardware etc - and I have to point out that there generalised "arm waving" approach leaves a host of awkward questions unanswered. Since they are not engineers (usually) they don't even understand the questions...


Richard

[GMB]

I agree.

I think this level of detail is really worth the trouble because it can sometimes give great insight into more significant issues.

E.g. I often wonder if the crappiness of the TR9 was possibly a significant factor in winning the Battle of Britain because to make up for its shortcomings we had to have a network of ground stations which had the side effect of tracking the fighters more accurately and thus improving the efficiency of our much smaller force.

It is a shame that museum exhibits are often stripped down late models that may have been used for other things after their main life, and these details are lost except in old documents and the minds of the few remaining engineers who actually worked on them.

[M0FYA Andy]

Was the TR9 particularly bad in the context of the time it was designed and built?
It is very easy to be critical with the benefit of hindsight, knowing how much better later developments were.
Andy

[GMB]

Yes, it was terrible - an obsolescent.

I have recently studied the detail of the early radios, and basically the white heat of radio development that occurred during WW1 just stopped when peace broke out. The TR9 is only about 2 stages of development from the very first R/T radios of WW1 - and it is basically the same circuit with a few extra valves for a bit more gain.

It was known that moving to VHF was the fix, hence no effort was put into upgrading it until the Fleet Air Arm wanted to for some reason (lead to TR1196). The snag was the shortage of production capacity for the new valve bases e.g. for EF50 etc. and that there was no mass production working for the new sets. It was so bad that the switch to VHF was reversed when it was clear that too many sets would be shot down and could not be replaced. The first proper use of VHF only lasted from 1st May 1940 to the 26th May, then reverted back.

[jamesinnewcastl]

Hi Andy

I've lost your email address! Can you send an IM with it in please?


Richard

I can't see why they would put anything other than a fixed wire in the mast - the Stirling did have quite a few 'specials', especially in its pilot controls. I need now to find out what the mast was made of - I am going to the RAF Museum soon and hope to be able to look at the 'repair' manual for the Stirling - hopefully some comments re the Mast


GMB

I was quite impressed by the modern 'plug-in' modules of the TR9 - no opinion about its performance or heritage, (sneaking suspicion of poor joints and microphony, but nevertheless...)


For all - a pic of the whip - looks like its suffered a little but its about as tall as the mast interestingly.


James

[GMB]

Oh yes, I forgot to mention....

Look at the mast and you see what looks like guy wires either side of it.
I think that may be the TR9 aerial done as an inverted V.

In the latest magazine from VMARS there is a reproduction of notes made by a radio operator and he has a little drawing showing a 2-engined plane with what looks like an inverted V on the mast that is annotated as the R/T aerial (as opposed to the W/T aerial as he calls the HF fixed one).

I have also seen this on a diagram of a Sterling so it is possible that the TR9 aerial was done like that.

[jamesinnewcastl]

Hi GMB

I would suspect that they are guy wires but I'm open minded and I don't kno about inverted Vs or of other aircraft radio systems. The feed for the TR9 goes up the bottom of the mast and so I guess could to any of the wires at the top of the mast.

Annoyingly I've never found a closeup picture or drawing of the mast, or of the bottom end of the guy wires, I assume that there would need to be an insulator there as opposed to a simple tensioner?

The guy wires are fastened to a point ahead of the mast which does suggest a mechanical function to stop the mast toppling. Perhaps I'll find out soon.

Andy

I have your address now thanks, apart from APs I have a load of MOD memorandums about the SBA system, most of them technical. For example it appears that there were two manufacturers one of whom achieved an acceptable sensitivity from the marker receiver while the other not. Turned out to be faulty valves - probably why the receivers have a note pointing out that the valves were specially chosen. Not sure if you are that interested but if anyone else is I'll send them on. A sample or two attached.

James

[Sparky67]

Originally Posted by GMB

In the latest magazine from VMARS there is a reproduction of notes made by a radio operator and he has a little drawing showing a 2-engined plane with what looks like an inverted V on the mast that is annotated as the R/T aerial (as opposed to the W/T aerial as he calls the HF fixed one).

Those notes are from a WW2 pilot's training course - I would imagine a radio op's training notes would cover the information in more detail?

There are cutaway drawings of a Stirling HERE and HERE which shows what could be antenna elements between the rear fuselage and the outer leading edges of the tailplane (I can't find an image with a legible key...!) and the above-fuselage long wire as what look likes two antennas with two feeds going inside. The first drawing is from The Aeroplane.

Martin

[jamesinnewcastl]

Hi Martin

The aerials from the rear of the fuselage to the leading edges of the tail plane are the IFF (friend or foe transponders for when the aircraft were scanned by British radar).

These were fitted to many military aircraft, even Spitfires.

The feed to the leading section of the long aerial is quite interesting, possibly it is artistic license, it isn't on the MKI - I'll keep an eye out for any such connection in the various photos I have.


Cheers
James

[jamesinnewcastl]

Hi All

Continuing in the great habit of eventually answering your own question......

Just made a 600 mile round trip to the RAF museum and found yet another version of the Stirling handbook, an even earlier one than the one I have and it appears that a much more artistic draughtsman had been employed - see attached.

Item 135 is described as 'Beam Approach Vertical Aerial'


James

[Radio Wrangler]

Something cantilevered out of the fuselage like that mast can experience vibration from turbulent airflow around it, especially with the attached wire antenna. If there wasn't a good support structure inside, this would lead to work-hardening and fatigue of the fuselage skin around its base. Guying the mast may have been found necessary to prevent failures.

David

[jamesinnewcastl]

Hi David

They did both - the aerial mast is aerodynamically shaped and there are two guy wires from the top at each side to just forward of the base.


James