Yellow Dots in DH98 Mosquito Cockpit?

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MrSmoothie

Airman
66
64
Jan 21, 2019
In doing research for the cockpit on an R/C model of the DH98 (FB VI) Mosquito I'm doing, I noticed prominent yellow dots -- on both crew and pilot seat backs, as well as lower starboard instrument area. Can anybody explain their purpose?
 

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As memo serves there is no definitive answer to the question. One opinion says that the yellow disks were painted on the armour plates signifying that these were made of steel, an important consideration bearing in mind the proximity of such items to the aircraft magnetic compass. However, the second one states that these discs are the gas-sensitive indicators. The third thought is that these were a warning that the armour steel plates were much heavier than it might have appeared, so they shouldn't be tried to lift /remove without appropriate lifting equipment. Anyway I haven't seen them in pics with the Mosquito cockpits without the armour plates.
 
Many thanks for the interesting reply. I might have noted that these are for sure in the recently restored PZ474, which has to be among the most meticulously restored warbirds out there.

With respect to the gas-sensitive indicator theory, I'm reminded of the diamond shaped patches that appeared on Spitfires in the early days of the war.

There aren't as many good photos of original Mossie cockpits to reference.
 
The armour plate answer is most likely though the reason is likely more to do with the magnetic effect. Special lifting equipment is not required - I lifted one of these myself easily! This from the late Edgar Brooks:

The same thing appears on Lancaster seats (and one of the foremost authors of books, on the Lancaster, doesn't know, either.) Preparing for the inevitable reaction, I do have a (unprovable) theory; in November, 1940, there was a mod, on Spitfires (which only lasted for 9 days, before it was cancelled,) which read "To paint yellow markings on magnetic armour plates." Guessing, only, but maybe they found that the steel was too far away, to have any effect on the Spitfire's compass? On the Lancaster and Mosquito, though, it was always possible for the navigator, without realising, to get too close, with his hand-held compass, to said armour, and have its readings affected. It's been well known, for years, that yellow is the most prominent colour, in the dark, hence the yellow/black pull-handles. I can't see it being a gas warning; they were always on the outside of the aircraft, where the reaction would be that much quicker.

 
More on the yellow dot. Here is a poor rendering of the note carried on the drawing for the steel plate on bulkhead 2 of the Mosquito:

Capture2.JPG


It does not reveal much, except to confirm that the dot is placed on the FORWARD face of the bulkhead. This is also the case for the Navigator and Pilot seat armour plate. On the same drawing, the material spec is seen as:

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"Resista 116" and "I.T. 70D Demagnetized" get no Google hits on my side of the pond but perhaps someone knows what these specific materials were.

It has been suggested that the dots are to represent the side of the plate that has been face hardened for increased resistance but that would not explain why the dot is on the BACK of the Lancaster pilot seat and on the FRONT of the Mosquito seat. It would be interesting to see what, if any face hardening requirements are stated in the above specs.
 
I now think in the case of the British aircraft it indicates steel, or, far less likely, magnetic steel. That way it will be a warning to the Nav not to use his hand held compass near it.

I say far less likely magnetic steel because degaussing was a very common knowledge before WW2 so there should not have been any magnetic steel in any location where the hand held compass was used.

Given that the yellow dots appear in so many British aircraft there must be an AP that covers the subject. There were also Standard Notes for fitters, riggers, armourers etc so surely there was one for painting and doping (finishing?). The question is whether any copies remain. Hopefully someone with physical access to the PRO or Duxford or other archive can find one.

Of course there is the possibility that the AP or SN will reference another document like the American painting and marking TO 01-1A-9 does for such items on US aircraft.
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As far as those specs go I cannot help on them either. All the Brit metals of the period are BS, DTD or EN specs. I will see if I can find a D.T.D I.T. 70D though as some DTD specs did have a letter number combination
 
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re "Resista 116 I.T.70D"

Resista was a Hadfield brand name for a type of relatively high-hardness through-hardened homogeneous armour. It was a high-carbon high-manganese heat treatable alloy steel. I do not know what the 116 means.
The I.T. stands for Izod Test
The 70 indicates the level of resistance
The D indicates that the notch/penetrator used in the tests was of a higher sharpness (Shore D spec, I think)

In the WWII period the British used it on through-hard homogeneous plate between 3 and 30 mm. It measured break/shatter resistance under projectile impact. It was also used to estimate penetration resistance vs projectiles and likelihood of the plate shattering under blast effect indirectly through interpolation.
 
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As far as those specs go I cannot help on them either. All the Brit metals of the period are BS, DTD or EN specs. I will see if I can find a D.T.D I.T. 70D though as some DTD specs did have a letter number combination
My reference for DTD standards is here: BRITISH DTD

I did not find a DTD 70D and by 1944 it was cancelled according to the index. Not sure what the I.T. represents and if it's even part of the DTD standards.
 
I used TO 01-1A-9 US and Commonwealth Aircraft Materials 1944 and 1946 as my reference but both are silent on any DTD IT specs using ocr to search. I also have an Australian xref but that was also silent.

Fortunately Thomas P has solved that part of the question. Thank you
 
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I crossed posts with T ThomasP . Excellent info sir thanks. The idea that the dots indicated a face hardened plate would therefore be incorrect. I'm going with the thought that these warned against nearby compass use.
 
Yep so back to post 7 - Does Thomas or someone else have any RAF painting and doping publications or even know what they were called. it is amazing what you can find when you know the correct name of a publication - conditional of course on the web source spelling it exactly like the publisher did.
 
It has been suggested that the dots are to represent the side of the plate that has been face hardened for increased resistance but that would not explain why the dot is on the BACK of the Lancaster pilot seat and on the FRONT of the Mosquito seat.

Possibly because you can't see the back of the Mosquito seat and the back of the Lancaster seat is more visible to the rest of the crew, with the exception of the bomb aimer?
 
Hey MiTasol,

The info I have on things like dope and paint are a rather jumbled mix of D.T.D. and B.S. Spec. (British Standards Institute) specification numbers, as applicable to Aircraft Materials and Components, but not the specification detail descriptions themselves.

The B.S. Spec. are under the same umbrella as the B.E.S.A. specifications (British Engineering Standards Association). A couple examples current as of 1 June 1941 are:

B.S. Spec. 6F1 4oz Linen Fabric and Tape
B.S. Spec. 4F8 Mercerized Cotton Aeroplane Fabric (Grade 1)
B.S. Spen. 2D101 Properties of Aeroplane Doping Scheme

Among the B.S./B.E.S.A. stuff there are references to publications that cover the groups of materials. A couple examples are:

B.S. No. 83-1922 Standard of Reference for Dope and Protective Covering
B.S. No. 491-1933 Nomenclature of Timber for Aircraft Purposes. (Including Sources of Supply and Application to Aircraft)

Among the D.T.D. Specifications, current as of 1944, a couple examples are:

D.T.D.63A Cellulose Enamels and Primer (for Metals and Timber)
D.T.D.83A Aeroplane Doping Schemes
D.T.D.260A Pigmented Oil Varnish and Undercoating
D.T.D.407 4oz Linen Fabric and Tape
D.T.D.540 Linen Fabric and Tape
D.T.D.308 Matt Cellulose Finishes and Primer
D.T.D.314 Matt Pigmented Oil Varninshes and Primers

Is this the type of information you are looking for?
 
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Thanks Thomas
I have a small amount of the Aus equivalents to those you have but I was thinking of something more like APs or Standard Notes for fitters but for painters. Probably includes doping and fabric work as well though there is some of that in the fitters notes from memory but very very basic. Just looked at my RAAF Carpenter Riggers Course Notes and nothing there. Must get around to scanning it as makes searching so much faster. Despite the title it covers Wirraway, Battle and Hudson.
These are the US equivalent of what I was thinking of but all are very brief and it appears that Spec 98-24105 is more use. Never seen or heard of a copy though. THere are also these but again I have not seen copies
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The RAF had various training notes for most trades and they often cover things in quite a bit of detail. For example the Armourers notes provide 90% of what you need to set up a Browning .303.
 

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Possibly because you can't see the back of the Mosquito seat and the back of the Lancaster seat is more visible to the rest of the crew, with the exception of the bomb aimer?
That would make no sense. The argument, which I don't buy in to, goes that the dots were painted on the side of the plate that is face hardened. That side of the armour, were it one side only as postulated, would always face to the side most likely to be hit by projectiles, i.e. that rear. The Mosquito drawings clearly show the dots to be painted on the FRONT.

ThomasP has already stated that the armour plate spec is for a THROUGH-Hardened steel so there would be no need to distinguish one side from the other as both sides would offer equal resistance to impact.
 

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