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Spitfire antenna base plate


TonyOD

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I'm building a Spitfire and I've noticed that the antenna masts were mounted on a kind of plate whose colour differed from the overall camo - well illustrated in this colour pic of a Seafire...

 

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Seems to be a sort of reddy-brown colour. Can anyone tell me what the material was? Was it on all Mk V's? Suggested choice of paint? (I use Humbrol enamels mainly)

 

Thanks

 

 

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Just a guess on my part based on knowledge of aircraft radio installations.

 

It'll probably be an insulating material, something like Paxolin maybe which is a resin impregnated with linen.  Paxolin ranges from a reddish brown to an almost dark brown, the exterior finish is glossy.

 

Hopefully somebody can confirm what the actual material is.

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28 minutes ago, modelmania said:

Can't say I've come across any pics of a Spitfire where this base plate was anything other than in the camo colour so this may have been a replacement item which has yet to have the paint applied?

 

It would make sense for it to be made from a non-conducting material to maintain electrical isolation for the radio, so some form of early plastic as in bake-lite would seem to be a possibility. Then painting over with the relevant camo wouldn't affect its isolation properties in any way.

 

Here you go then.

 

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sMz90MFfsqNPGBF0sZVDS82zzr2LiSDOe-isWzJ3

 

 

 

 

 

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44 minutes ago, modelmania said:

Can't say I've come across any pics of a Spitfire where this base plate was anything other than in the camo colour so this may have been a replacement item which has yet to have the paint applied?

 

It would make sense for it to be made from a non-conducting material to maintain electrical isolation for the radio, so some form of early plastic as in bake-lite would seem to be a possibility. Then painting over with the relevant camo wouldn't affect its isolation properties in any way.

Here it is on a brand new Mk.Ia in the Kotare instructions. They suggest Humbrol 70 or Tamiya XF79.spacer.png

Edited by wmcgill
Better image & added Tamiya paint suggestion.
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8 hours ago, TonyOD said:

I'm building a Spitfire and I've noticed that the antenna masts were mounted on a kind of plate whose colour differed from the overall camo - well illustrated in this colour pic of a Seafire...

 

spacer.png

 

Seems to be a sort of reddy-brown colour. Can anyone tell me what the material was? Was it on all Mk V's? Suggested choice of paint? (I use Humbrol enamels mainly)

 

Thanks

 

 

 

 

This resin mast says that it was bakelite.

 

https://www.scalemates.com/kits/grey-matter-figures-gmaa2406-spitfire-aerial-mast-with-bakelite-base--1281852

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4 hours ago, modelmania said:

This would suggest it was an insulating material to prevent electrical interference, both to the aerial wire/mast and the IFF wires/system as well.

 

I'm planning a visit to Duxford to sit in N3200 and notice that it has the aerial base plate painted in the camo colour so perhaps painted and unpainted could be observed?

Don't trust even the best restorations. If there's any discrepancy, period photos always trump modern. N3200's soft edge sprayed camouflage is also at odds with 1940 photos of similar Mk.I Spitfires.

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spacer.pngspacer.png

 

the insulation resistance of mast to earth to be not less than 5 MOhms so it was prescribe care taken to not paint insulators.

 

unfortunately the material of of insulator plate(547) is not noted, but it was probably bakelite or laminated plastic

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14 hours ago, Tbolt said:

 

But was it bakelite or somebody's interpretation of the material?  To the layman, bakelite and Paxolin look superficially similar but Paxolin is far more flexible and durable than bakelite (which doesn't age well under external environmental conditions and isn't flexible).  Paxolin is still in use in legacy systems to this day, it's extremely tough and durable, it withstands impacts and vibration well, anyone who's worked with it knows that it's an absolute sod of a material to work with hand tools but it can be machined.

 

13 hours ago, Peter Roberts said:

Similar coloured rings each side of the fuselage where the IFF wires entered, when installed.

8 hours ago, modelmania said:

This would suggest it was an insulating material to prevent electrical interference, both to the aerial wire/mast and the IFF wires/system as well.

 

I'm planning a visit to Duxford to sit in N3200 and notice that it has the aerial base plate painted in the camo colour so perhaps painted and unpainted could be observed?

 

This is common in aircraft antenna installations, there are some systems such as modern UHF/VHF/Tac VHF where the aerial requires a ground-plane,  the antenna base is bonded to the aircraft surface via conductive gaskets and /or sealant material but HF/low frequency VHF systems such as those fitted to wartime aircraft don't.  With these the aerial wire acts as a di-pole antenna, the Antenna Tuning Unit (ATU) electronically lengthens or shortens the antenna length depending upon the required frequency (the lower the frequency the longer the antenna due to λ = C/f (where λ = wavelength, C = speed of light and f = frequency).  I've worked with ATUs that do this electronically by induction, winding a length of wire onto an internal drum, others which do it using capacitive plates to provide tuning and more modern ones which do this through a whole load of electronic shenanigans.

 

The older systems used an insulated feeder which passed through the airframe which isolated the aerial from the airframe (if we got HF tuning problems we'd always check the feeder to make sure it hadn't deteriorated).

 

I'd be careful using N3200 as your reference, it may have the antenna wire fitted but I very much doubt it has an operational HF system fitted, there's no need, it's more likely to have a modern VHF set fitted which wouldn't use this antenna.  The antenna's just there as an historic representation.

 

1 hour ago, BS_w said:

the insulation resistance of mast to earth to be not less than 5 MOhms so it was prescribe care taken to not paint insulators.

 

unfortunately the material of of insulator plate(547) is not noted, but it was probably bakelite or laminated plastic

 

John, thanks for sharing that, it's interesting to see the rubber gasket beneath the insulator plate, that would allow the insulator to be secured to the airframe without damage to either, having said Paxolin is flexible, it is also quite unyielding, the rubber gasket would take up the subtle differences in the contours between the airframe and the underside of the insulator.

 

I've quoted Paxolin throughout this because that's a material I know which has been used on British aircraft from the 1940's through to the current time.  There was another material used for a long time which was similar to Paxolin but used paper impregnated into the resin rather than the linen of Paxolin, but for the life of me, I can't remember its name.  The paper or linen are there to provide the structural element to the resin.

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I have built lots of Spitfire kits in the past and two things that I always either forget or are too lazy to do are the aforementioned base plate and the upward firing signal location on the fuselage spine, I've just finished a Mk.IX and added neither, don't know why.

 

Cheers

 

Dennis

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34 minutes ago, Wez said:

 

But was it bakelite or somebody's interpretation of the material?  To the layman, bakelite and Paxolin look superficially similar but Paxolin is far more flexible and durable than bakelite (which doesn't age well under external environmental conditions and isn't flexible).  Paxolin is still in use in legacy systems to this day, it's extremely tough and durable, it withstands impacts and vibration well, anyone who's worked with it knows that it's an absolute sod of a material to work with hand tools but it can be machined.

 

 

I don't know, I've never used Bakelite SRBP, but Bakelite and Paxolin SRBP's are just basically the same thing made by different companies? Was one superior back then? From what Edgar said the SRBP seat in the Spit was made by the Aeroplastics, so did they also make the IP and mast base?

 

 

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3 minutes ago, Tbolt said:

 

I don't know, I've never used Bakelite SRBP, but Bakelite and Paxolin SRBP's are just basically the same thing made by different companies? Was one superior back then? From what Edgar said the SRBP seat in the Spit was made by the Aeroplastics, so did they also make the IP and mast base?

 

 

 

Quite possibly, Government procurement tends to favour certain manufacturers.

 

Bakelite and Paxolin aren't the same although they look similar as bakelite is just the resin whereas Paxolin is impregnated with layers of linen or apparently paper (I was always taught linen in trade training and having worked the stuff, it always looked like a cloth laminate).

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5 minutes ago, Wez said:

 

Quite possibly, Government procurement tends to favour certain manufacturers.

 

Bakelite and Paxolin aren't the same although they look similar as bakelite is just the resin whereas Paxolin is impregnated with layers of linen or apparently paper (I was always taught linen in trade training and having worked the stuff, it always looked like a cloth laminate).

 

Bakelite isn't just resin, they are a company which probably started with just a resin product but they make a number of products including SRBP just like Paxolin. I guess it's one of those company names that gets misused for one product. What they were producing when the Spit was being manufactured though I don't know.

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20 hours ago, modelmania said:

but I also don't recall seeing any Spitfires in the RFI which have the base plate painted as a separate colour to the camo

BRB, redoing all the base plates on my finished Spits. 

Kidding, of course - but it's one of those little details that escape notice fairly easily - especially with the Dark Earth scheme because that has nearly the same shade where the base plate is.
Once you know however, it's something to pay attention to.

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