Anyone knowledgeable about Aerial Masts?

Member for

9 years 3 months

Posts: 411

Hi All

A pretty esoteric question - I'm trying to track down the early SBA main aerial on the Stirling Bomber, it is either inside the tall aerial mast behind the canopy or was put on top of it. If it went on top I can only find one photo that supports that and even then it doesn't look long enough or near enough to an earth plane to be efficient, the photo I have is also unclear - the aerial could be a hair on the negative!

However if it is inside the mast then the mast would need to have a lot of insulated panels in it to allow the SBA signal to reach it and hence the question on mast construction.

There was also some sort of de-icing device on the front of the antenna but you can't really see this in any of the photos so again anyone know how these were made. I suspect it is some sort of inflatable tube but again does anyone know about these, have any drawings, etc.

Incidentally the SBA aerial was moved in late 1941 to a new retractable aerial on the mid fuselage, I'm not looking for info on that one.

Cheers
James

Original post
Profile picture for user Beermat

Member for

10 years 4 months

Posts: 3,441

Certainly the Spitfire aerial was also intended to be used as a receiver for blind approach.. though agreed it would be inefficient at the 40Mhz I seem to recall the system operated at? One would need around 6ft for an effective quarter-wavelength. Maybe the extra wire you saw was some kind of extension? One thing.. it is possible to use the outer skin of an aerial mast as the active part, as was the case with aerials used for VHF coms, eg TR1133, where the core was wood and the signal was passed to the metal cover.

Member for

9 years 3 months

Posts: 411

Hi Beermat

Firstly I'm rather embarrassed that someone has pointed out that the thin line on the photograph was actually the tip of the port inner prop!! That's a warning that if you want to see something you probably will, but I have to say that the alignment was quite amazing. But that's a good thing really as it clears away a false lead.

The frequency was adjustable 30 - 40 MHz roughly. I suppose that the whole mast could have been made of wood with a skin aerial - possibly the poor efficiency was what caused it to be changed to be a whip aerial on the mid fuselage. Certainly there was no attempt to remove and discard the old aerial in the Modification Notes.

Oh for a good close up photo of the Mast! I'm still interested in the de-icing method too - I assume that this might be an inflatable skin?

Cheers
James

Profile picture for user 12jaguar

Member for

12 years 10 months

Posts: 1,649

I doubt that there'd have been an inflatable skin James as it doesn't appear in the pneumatic schematic for the aircraft. I'd image that it'd more likely be the mustard coloured paste that would be applied as per the wing leading edges. in fact, why worry about de-icing it as the only critical items to be de-iced are the aerofoil leading edges and the props.

John

Member for

9 years 3 months

Posts: 411

Hi John

You are probably thinking of your Whee-Ha new-fangled MKIII Stirling, I'm looking at the original and probably crappy old MKI, see the attached clip from AP1660. Chapter 3 doesn't detail much more that to say where the control wheel is. I would have thought that a long thin object would have been subject to quite a torque if loaded with ice, but if the de-icing was taken away I guess not enough.

Now that you made me look again what does a de-icing 'shoe' look like?

I'm leaning towards the mast being made of wood and a wire SBA antenna being laid into a rebate, that seems to most closely fit the 'science' though I am not fully convinced myself.

Cheers
James

Attachments
Profile picture for user Beermat

Member for

10 years 4 months

Posts: 3,441

Looks like it's not unique, though I hadn't seen it anywhere else - http://www.flightglobal.com/FlightPDFArchive/1956/1956%20-%200909.PDF

As to what a shoe looks like, I can only assume it's what is more commonly called a de-icer 'boot', and that's easily Googled.

Might be worth looking for detail on the Mk.I Sunderland mast, as that looks very similar indeed.

Profile picture for user Beermat

Member for

10 years 4 months

Posts: 3,441

If anyone has the AP Volume III then the mast should be listed, possibly including the material spec.

Member for

9 years 3 months

Posts: 411

If anyone has the AP Volume III then the mast should be listed, possibly including the material spec.

Hi Beermat

I have a few APs for the Stirling I had a part of Vol 3 at one point I think but gave it away - great long list of numbers!

I'm off to the RAFM soon to their research rooms - some information might also be in the repair section of Vol 2, albeit indirectly.

I think that I have worked out the aerial arrangements for the MKI - see attached. There seems to be an unused section from the tail - then a section for the W/O then one for the Pilots TR9 then the SBA main antenna. Not shown are the SBA marker antenna (under the fuselage), the IFF and the trailing aerial.

James

Attachments
Profile picture for user 12jaguar

Member for

12 years 10 months

Posts: 1,649

If anyone has the AP Volume III then the mast should be listed, possibly including the material spec.

Would that we had a Vol 3:apologetic:

The RAFM have reams of pages from the Vol 3 which must amount to over 700 pages, but no diagrams and they don't appear to be in order. It's on the list of things to do to get them copied/scanned and try and get them into some semblance of order:highly_amused:

Profile picture for user Beermat

Member for

10 years 4 months

Posts: 3,441

James, that looks reasonable!

12Jag.. if you do get those Vol.3 pages scanned to pdf, let me know as there are various 'shortcuts' to turn that into a usable text file and/or spreadsheet, as we did for the WW (or rather a series of very dedicated volunteers did).

Profile picture for user 12jaguar

Member for

12 years 10 months

Posts: 1,649

Thanks Beermat, I might take you up on that suggestion. I've been collating Pt Nos from various sources and now have just under 3000, it's a slow and laborious task though

John