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size of .303 machine gun ports in spitfire wing?


Johnson

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Hi Folks,

 

I'm building the old Airfix 1/24 Spitfire 1a.

 

The 8 holes in the front of the wings are pretty much a disaster. Different sizes, don't line up top to bottom etc. I've decided that the only solution is to fill them with CA/talc mix and re-drill the holes. But what size? :shrug:

 

I can take a guess, based on photos in the excellent Spitfire walkaround here on BM.

 

d%2046.jpg

 

But if anyone knows for sure, that would be fantastic.

 

TIA

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Going by Tamiya's recent 1/48 release, I can fit snugly a 1.2mm brass tube into the gun openings.

 

So for 1/24:

 

1.2mm x 48 = 57.6

57.6 divide by 24 = 2.4mm

Hopefully someone comes along to officially verify  the measurement.

 

I'd suggest obtaining if possible  2.6mm tubing (inner diameter 2.4mm) and insert these into the holes and then sand flush.  This is what I did with Arma's Hurricane 72nd scale:

 

spacer.png

 

regards,

Jack

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38 minutes ago, JohnT said:

A long time ago I “cheated” and did the red patches over the gun ports to get around that wee issue

 

Thanks John. That was what I was going to do and indeed is still my fallback plan. But I'd like to have the option of having the ports open, post flight as it were.

 

21 minutes ago, JackG said:

So for 1/24:

 

1.2mm x 48 = 57.6

57.6 divide by 24 = 2.4mm

 

That's great Jack, many thanks. Looking at the existing, rather variable Airfix holes, and comparing them to the pic above,  I was erring towards 2.5mm. I'll try drilling them to start and see how that looks. I do have some brass tube around... somewhere! The advantage of a brass tube is that it would be similar to the actual blast tube in the wing.

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Hi Charlie,

 

Monforton quotes 2.5" for the outboard 0.303 gun tubes for the Mk IX in his book. I think it unlikely they were changed from the Mk. I for the outboard Browning positions on the Universal Wing (C-Wing).  I also get 2.5" if you scale the general assembly wing drawings for the Mk. I.  There is always a danger in doing this, a crude measure and as all draughtmen say "Do Not Scale", but in this case there is close correlation with Monforton. I have the GA's and not the part drawings that would give the definitive answer.

 

I used this dimension on a previous build and was happy with the result. In my case a little bigger than @JackG at a 1/48 1.3 mm or a 2.6 mm in 1/24. Anyway you can start small and work your way up till you get what you like. If I was doing this in 1/24, I would be inserting some very thin tube as Jack did.  Here's a drawing for the leading edge on Gun 2, by the time you get to the most outboard Gun 4 the form of the hole becomes quite elongated. All nicely flushed to the leading edge. It does seem it was a thin walled tube, maybe something like 20 SWG (0.91 mm) 

 

Spitfire Mk.! Gun Tunnel


As an aside, the gun tubes (called by Supermarine - "Gun Tunnels") were stainless steel to specification D.T.D. (Directorate of Technical Development) 207. I have not found a drawing specifying the diameter and length of tube used. Someone might have it buried in their Spitfire parts list documentation. 

 

To @BS_w I am very interested in the title of the drawing where you posted the snippet. Sadly, I cannot read the numbers, but what is in this construction that would need reference to something being "top secret" as noted in the text above the wing? Edit: answered my own question "top sheet".

 

 

Ray

 

Edited by Ray_W
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3 minutes ago, JackG said:

2.5 inches

 

Hi Jack,

Agree. However, if it is a "tube", typically measured on the OD as opposed to a "pipe" measured on the ID, then it might be 2.5" minus the wall thickness to get to the bore diameter. Although, my guess is it is a very thin wall tube and 2.5" is close to the mark. DTD 207 would probably answer this. 

Ray

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Certainly close enough, as modelers we are also limited by the available market of brass tubes, without going custom made.

 

Doing a check on the Hurricane I did, and assuming they too had the 2.5 inches gun openings:

 

2.5 inches = 63.5mm

 

63.5 divided by 72scale = 0.881mm

 

This works out good, as I went with 0.9mm for inner diameter of the holes as linked in the photo above. 

 

regards,

Jack

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50 minutes ago, Ray_W said:

 I am very interested in the title of the drawing where you posted the snippet. Sadly, I cannot read the numbers, but what is in this construction that would need reference to something being "top secret" as noted in the text above the wing?


drawing 30008 "nose covering bottom sheet", page 48


unfortunately it's not easy to read.
When you wrote 2.5", is this diameter or radius?

 

 

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Just now, BS_w said:

When you wrote 2.5", is this diameter or radius?

 

Thanks for coming back so quickly. 2.5" is the diameter.

 

Ray

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@BS_w. Thanks for posting. It would appear that we all agree at about 2.5"

 

Thanks Ray, I'd not heard of the Monforton book, looks useful, I'm always on the lookout for a new Spitfire book. But looking on Abe Books I see only one for sale in the USA at £204, plus shipping of course. I may have to miss that one. But the figure you give certainly seems about right.

 

I did some rough calculations from photographs based on the spinner diameter and the size of the hole on this photo and it gave me around 2.4", and these are obviously very rough measurements!

 

y4mJBn2UtrvMcfT0CqCkN8PY144vYb4uwgHbLF1w

 

So I will go with 2.5" (or 2.6mm @ 1/24). Now just got to judge the height/position of the hole relative to the centre of the leading edge!

 

y4mgvlOmEYxuXRyvLJCfliaLWOcdmRqzisA7rMuY

 

Thanks everyone yet again!

 

 

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5 minutes ago, Johnson said:

Now just got to judge the height/position of the hole relative to the centre of the leading edge!

 

I have something on that. Let me dig it out.

 

Ray

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Hi Charlie,

 

Note position of gun ports near constant above the datum line through the wing:

 

Spitfire Ia gun positions

 

 

Couple that with the image in the earlier post from @BS_w and I think you' should be able to do the rest.

 

32 minutes ago, Johnson said:

But looking on Abe Books I see only one for sale in the USA at £204,

 

I bought the electronic version, much cheaper and still useful.

 

Ray

Edited by Ray_W
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Would the datum line run along the same point at which the top wing meets bottom wing surfaces?  In the close up photos, it appears the holes dip a bit below  the leading edge - unless the painted surfaces meet slightly above the datum line?

 

It could be the diagram is illustrating the gun muzzle position, and then the added diameter of the blast tube (not illustrated) dips it below the datum?

Only diagram I have to offer is of the browning muzzle measurement:

 

5PAWBY5.jpg

 

regards,

Jack

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14 hours ago, JackG said:

Would the datum line run along the same point at which the top wing meets bottom wing surfaces?  

 

Short answer is no. Although for modelling purposes, even in 1/24, it is probably OK to assume so. If you look at the full blue print of the bottom leading edge sheet, a snippet gratefully provided by @BS_w, you will see the wing datum line and the sheet top front edge line do not coincide starting wider apart and then tapering together out towards the wing tip. Don't get too excited though, this variation is probably at its maximum in the order of 1"(25.4 mm) and I suspect by the time it gets to the inboard gun position we're talking at most 0.75"(19.1 mm). See below. I labelled the wing datum line

 

Spitfire Ia gun positions 2

 

The gun port positions do not follow either the wing datum line or the sheet join line (the lovely bespoke Spitfire). Here are gun port positions 1,2 and 3. Position 1 being the most inboard. The wing datum line being the faint line below the broken line. Positions 2 and 3 are approximately the same, as you would expect being close together, while position 1 sits higher from the wing datum line and, yet, is set more into the sheet.

 

Spitfire Ia gun positions 3

 

 

Sadly, I do not have a legible copy to just read off the dimensions and had to rely on scaling.

 

When scaling the drawing from the gun port centre line to the wing datum line, position 1 is in a similar position to the most outboard gun port 4.  Position 2 and 3 share an approximate, be it closer, distance to the wing datum line.  Monforton quotes for the Mk.IX a gun centre line to wing datum line for outboard No.4 gun of 1.20"(30.48 mm) and next inboard gun No.3 at 1.00"(25.40 mm). This gives a clue as to what dimensions to use in lieu of better information. That is, using a scaled 1.2" above the wing datum line for guns 1 and 4 and 1.0" for guns 2 and 3.

 

The greater difficulty for the modeller is estimating the wing datum line or alternatively making a slight adjustment to the position using the front sheet join line and the latter only if the kit manufacturer has it in the right position. I suspect, within the vagaries of plastic modelling, some judgment will be needed. The most important thing will be does it just look right. Most of the dimension variations are small even in 1/24. I suspect no one is going to say "Your model is wrecked, the inboard gun port is a scale 1/4" (1/24 0.26 mm) too low!" 

 

Ray

 

 

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The Spitfire wing has 2 degrees washout near the tip (avoiding the need for slats near the stall) which is (one reason) why the wing datum line doesn't match the actual leading edge all the way out to the tip.  The 1970s Airfix 1/72 kit represented this but I don't think it is as well represented on any of the other kits produced since.  As for larger scales: I don't know but have my doubts.

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I think for modelling purposes, it's better just to follow the existing layout of the gun openings - unless they are blatantly wrong after knowing what to look for , ie. the datum line.   Filling in the holes completely and then drilling them out, doing all this by eye, you do run the risk of not having the openings running a straight line to one another.

 

Can understand the need to fill in the surrounding inside the wing, so that once drilled out there is some depth to the holes.  I'd suggest once the putty is in place but still malleable, tamp it inwards with the opposite end of the required drill bit size.   Once dry, then you have a good starting point to bore out the hole.

 

regards,

Jack

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5 hours ago, JackG said:

I think for modelling purposes, it's better just to follow the existing layout of the gun openings - unless they are blatantly wrong after knowing what to look for , ie. the datum line.   Filling in the holes completely and then drilling them out, doing all this by eye, you do run the risk of not having the openings running a straight line to one another.

 

I wish I'd taken this picture prior to filling the holes, they're a bit hard to see. I took a series of photos at slightly different angles to the plane of the wing (if you follow :crosseyed:) and this was the best one 'head on', as it were (all slightly out of focus, the camera wanted to focus on everything but the wing!).

 

Anyway, eyeballing it against the various diagrams, most notably Ray's from above, the gun ports are slightly low, it's just the way Airfix constructed the wing with the join more or less along the datum line. Jack's point about re-drilling the holes and getting them in the right position is well made, but I'm minded to try raising them slightly. 

 

y4m7Sl5cMbRoPIkPK-yy2al7rbImE1g1sf-jzumF

 

If it works, great. If not, I guess they are going to be covered ports!

Spitfire Ia gun positions

 

 

 

 

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It may be obvious, but I would suggest starting with a "punch" (a pointy thing) to locate desired centers, then drill a pilot hole with the smallest bit you've got, and work your way to the final hole in another step or two.  That way you can hopefully fix a wander before you have to fill and start over.

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On 2/14/2021 at 8:04 PM, Ray_W said:

Hi Charlie,

 

Note position of gun ports near constant above the datum line through the wing:

 

Spitfire Ia gun positions

 

 

 

 

Ray

 

to be exact, the height above datum line is
gun 1: 1"
gun 2: 0.9"
gun 3: 1"
gun 4: 1.2"

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19 minutes ago, BS_w said:

to be exact, the height above datum line is
gun 1: 1"
gun 2: 0.9"
gun 3: 1"
gun 4: 1.2"

Excellent for future reference, now I have to file this somewhere and not lose it. 

 

Ray

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14 minutes ago, Ray_W said:

Excellent for future reference, now I have to file this somewhere and not lose it

 

you can add this detail (drawing 30062/sheet 1 "arranegment of gun installation")

 

spacer.png

Edited by BS_w
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