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warhawk

Avro Lancaster canopy framing - internal or external?

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warhawk    80
Posted (edited)

Hello,

 

I've been musing myself with making a vac canopy for my model (since the Pavla Vac doesn't fit the Revell 1/72nd kit).
I have noticed that some frames are internal, to which the perspex is just screwed-on. Both wartime and restored example walk-arounds seem to confirm this:

 

Lanc-frames_01_zpsnhu1ahyq.jpg

 

But then, I found some more (both wartime and restored example) photos, which depict these (and all other) as external:

 

Lanc-frames_02_zpsl8nkov6o.jpg

 

Some drawings clearly show them as internal:

 

th_Lanc-frames_04_zpsrcejhuvj.jpg th_Lanc-frames_03_zpsj0kuyexg.jpg

 

While this one shows all frames of the same depth (i.e. external):

 

th_Lanc-frames_05_zpsofsx6be0.jpg

 

Soooo.... What's up with that?

I thought it might be an early-war / late-war machine difference, but my wartime external photo shows an early machine (as denoted by the small window on the fuselage), while "Just Jane" is restored to a late-war standard (wide props, bigger blisters and everything).

Or maybe it had something to do with the astro-dome size?

 

Any opinion is most welcome
Regards,
Aleksandar

Edited by warhawk

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sloegin57    541
Posted (edited)

This may help, from the Lancaster Course Notes RAF Wigsley May 1945 :-

 

IxXXjnX.jpg

 

Basically, moulded rear canopy over wooden formers held in place by external metal strips.

 

HTH

 

Dennis

 

Postscript :-

 

The Astrodome, referred to in the text as the "Astral" dome, was a separate item to the canopy and only differed in height on later aircraft - not diameter.  Asttodome is item 17 in the diagram and the loop aerial for the D.F. wireless is item 16 :-

 

ebfivuJ.jpg

 

Dennis

Edited by sloegin57
ASTRODOME INFO ADDED

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warhawk    80

Thanks for the info. Very interesting read.

Might there be an, let's say, early version with the spruce frames and metal strips on the outside,

and a late version with the internal metal framing and just bolt heads sticking out of the perspex?

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sloegin57    541
14 minutes ago, warhawk said:

Thanks for the info. Very interesting read.

Might there be an, let's say, early version with the spruce frames and metal strips on the outside,

and a late version with the internal metal framing and just bolt heads sticking out of the perspex?

 

No Warhawk.  The canopy as described was the same for the Manchester, right through the Lancaster production and, with only a slight increase in height, was also fitted to the Lincoln.   The only major change in that area was the increase in height of the astrodome to cater for a change in sextants late in the war.  

 

If, as you suggest, just bolt heads were on the outside, airframe vibration would have caused the moulded perspex to crack and eventually the whole perspex rear canopy would have been blown off.

 

Dennis 

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warhawk    80
1 hour ago, sloegin57 said:

If, as you suggest, just bolt heads were on the outside, airframe vibration would have caused the moulded perspex to crack and eventually the whole perspex rear canopy would have been blown off.

 

I would have to disagree with You.

 

You have proven that there was one type in use, the one with external frames.

But that does not exclude the other one, as my first two photos clearly show.

However, internal frames with rivet (or bolt?) heads outside could just also be a modern reconstruction thing... (?)

 

The reason You have noted, the vibration pulling the perspex off, doesn't seem valid, because of two reasons:

1) Not all frames of the rear section on the "internal frame photos" are internal, there are some external ones (namely the outermost and vertical ones), to provide some extra support.

2) There are two airworthy Lancs - PA474 and FM213 - with rear internal frames, flying around with no problems whatsoever.

 

lancaster-i-pa474-kc-a-617-sqn-bobmf-pre

 

lancaster-mk-x-kb726-vr-a-419-sqn-c-gvra

img source: JIM SIMPSON AIRCRAFT IMAGES

 

Regards,

Aleksandar

 

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Graham Boak    2,378

I don't know the reason for this change, but would suggest that modern perspex and bolts might well be considered stronger than wartime examples.  It would be interesting to find some confirmed wartime photos of these internal mountings.  If so, another explanation could be a difference in production standards at different sites.

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warhawk    80
Posted (edited)
27 minutes ago, Graham Boak said:

It would be interesting to find some confirmed wartime photos of these internal mountings.  If so, another explanation could be a difference in production standards at different sites.

 

Graham,

 

please take a look at the first photo I have enclosed:

That is a photo taken during Queen Elizabeth at 156Sqd RAF Warboys Feb 1944

 

Some more here:

http://s1087.photobucket.com/user/eurocoast/media/Lancaster Bomber/Queen_Elizabeth_at_RAF_Warboys_Feb_1944_IWM_TR_1554_zpsy9e0qzy0.jpg.html

 

Mildenhall.jpg

 

raf-bomber-crew-option2.jpg

 

e83e83742e8a14801738d88158431994.jpg

 

easy-two-crew.jpg

 

 

 

 

But the problem is that almost as many pictures depict external frames...

lanc-nose-art-7.jpg

 

lanc-nose-art-1.jpg

 

e54dad095f62f766f2d7b84ed7552e7e.jpg

 

http://media.gettyimages.com/photos/4th-september-1942-a-ground-crew-refuelling-and-reloading-a-lancaster-picture-id3421888

 

 

 

 

Edited by warhawk

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Andrew Jones    623
Posted (edited)

Since UK Lancaster production was dispersed around a least seven manufacturers and probably hundreds of component suppliers , it is entirely possible that slightly different production methods were used by some of them , hence the variations seen in the canopy construction. Incidently Lincoln's have the internal rear framing seen on some of the Lancasters here.

 

Andrew

Edited by Andrew Jones

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dogsbody    1,060
Jure Miljevic    274

Hello

Function of a metal strip, described in Lancaster Course Notes Dennis provided, is to fasten perspex onto wooden frame inside the canopy. Basically, the strip functions like a number of inter-connected washers with good part of the strip's length serving little or no purpose. Ordinary washers would work in exactly the same way and would eliminate need for a metal strip, hence no external frame. I see no reason why such method could not have been used during WWII. Cheers

Jure

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hovering    24

I suspect its as Jure described, for some (most likely later) airframes the individual washers were replaced with a metal strip, giving the impression of external framing.

I can't find any evidence of a change from wooden internal members to any type of metal framing for the rear canopy.

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warhawk    80
Posted (edited)

Thanks, Jure and Hovering, that makes sense from engineering point of view.

 

11 hours ago, hovering said:

I suspect its as Jure described, for some (most likely later) airframes the individual washers were replaced with a metal strip, giving the impression of external framing.

 

I agree with You, but it seems is that the change went the other way around - metal strip to washers.

The reason for my conclusion is that I found no period pics Manchester with washers and Lincolns with strips.

It also makes sense from a production economy viewpoint (washers are easier to manufacture and install than a specific strip with specific size and number of holes), and also aerodynamic standpoint - 

If You look at any other aircraft - Stirling, Halifax, etc - there is a clear tendency to reduce external framing in order to reduce drag.

 

Here's another proof of my theory - take a look at the mosquito prototype (W4050)

External metal strip is clearly visible.

 

DSC_0026.jpg

img source: Keypublishing forum

 

Now take a look at the rear canopy of a very-late-war later model:

Most longitudinal strips have been switched to washers

De_Havilland_Mosquito_IV_ExCC.jpg
img source: The de Havilland Flying Club

Edited by warhawk

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hovering    24
Posted (edited)

Interesting.. as mentioned above, maybe it comes down to who manufactured it?

This one from Aug 43 seems to be internal? (Although I'm beginning to question my judgement after looking through pics trying to work it out!)

https://www.awm.gov.au/collection/UK0387/

https://www.awm.gov.au/collection/UK0402/

 

Also interesting in that the perspex above the pilot/FE has an earlier repair.

 

G-George at the AWM has no external strap on those parts as she it today.

 

Presumably since it's not a join of perspex sheets there, the external strip isn't required for weather/strengthening reasons. It might help for repair/replacement if you don't have the long strip to content with.

The 1946 Lancaster course only mentions external metal stripping, but I guess it wouldn't be worth mentioning the slight variations for them.

 

Anyway.. you've added a new question when modelling a certain Lancaster.. Did it have internal or external canopy strapping? :)

The 1/32 guys can sand off any raised strip and put down a line of rivets :) *where applicable.

Seems the modern/colour photos show there isn't any attempt of camouflage on the outer face, and it remains black. 

 

 

 

Edited by hovering
spelling and figured that crack in the canopy would have given the FE more of a scare than the pilot :)

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warhawk    80
24 minutes ago, hovering said:

Anyway.. you've added a new question when modelling a certain Lancaster.. Did it have internal or external canopy strapping? :)

 

Yep, besides questioning types of bomb-sights, seats, props, canopy blisters, bomb-bay doors; presence of windows, H2S dome and heater fairing, various turrets and/or antennae; interior colors and what not,

clearly we needed another conundrum to spice this soup up! :think:

 

29 minutes ago, hovering said:

The 1/32 guys can sand off any raised strip and put down a line of rivets :) *where applicable.

 

1/32? I am asking this for a 72nd model (puts back his crazy-hat on)...

Cheers!

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Jure Miljevic    274

Hello

Warhawk, unfortunately your list is far from complete ...

So ... it has been established that Lancaster's canopies with or without external frames had been used. Is there a pattern or do we resign to fact, that this is another aircraft part for which a clear, high-resolution photo of a subject of our build is necessary to replicate it accurately? Cheers

Jure

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Brian    96

My information is that there was a combination of a stainless steel frame with a wooden frame in the rear section.  By the way, what other parts of the Lancaster used wood in their construction?  Navigators table doesn't count.  Sorry no prize other than gloating rights.  Cheers.

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hovering    24
Posted (edited)

7jI8ZzX.jpg

 

:)

 

But seems a bit of wood, turret rings, fin leading edge, and a quick read mentions main crew door and draught-proof doors down the back.

 

 

Edited by hovering

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