Matchbox Airfix Lancaster bulged doors

[woody37]

It's my understanding (possibly incorrectly) that all deep bomb bay doors had the pinch at the rear whether a ventral turret was fitted or not. I'm sure the CMR B.ii conversion came with the two types of deep bay doors and both had the pinched rear ends.

[Guest]

I can't currently get at mine to check, unfortunately.

[brewerjerry]

6 hours ago, Miggers said:

That looks like a brand spanker out on the grass at Woodford. No mods to that one at squadron level,so a good

accurate photo.

 

 

Hi

    A canadian built mk X, so maybe slightly different ? 

    cheers

      jerry

[brewerjerry]

Hi

   Interesting thread, but if a shape is correct or not should surely be based on drawings/ manuals ?

  not on the shape of aftermarket parts, which may or maynot be correct.

  cheers

     jerry

   

 

[RJP]

Jerry makes a valid point.  I don't see how it moves the ball comparing one part to another which is itself unproven.

 

Assuming one hasn't got a set of original Lancaster bomb doors handy - I certainly haven't room in my basement model workshop for a set - one needs to make a judgment about how to assess.  It's a mug's game to blithely assume.

[RJP]

I have in my downloads that same shot of KB783 referenced above.  The caption notes it as having Mod 925, a 50 calibre weapon mounted ventrally. It was also an early (the first?) example of the Martin m/u installation. I suppose that's why it was at Boscombe Down?  Not sure how any of that bears on the bomb doors.

[Finn]

From here:

http://www.baesystems.com/cs/Satellite?c=BAEHeritage_C&childpagename=Canada%2FBAELayout&cid=1434575554649&pagename=CanadaWrapper

 

Three types of bulged bomb bay were used on the B.II, the prototype having a narrow bulge running from just aft of the cockpit to the end of the bomb bay, while early production examples had a full width bulge that ran the same length and on late production examples the bomb bay doors were prominently bulged throughout their length.

 

Jari

[Finn]

Although the caption in the lower photo says it's a Halifax bomber, it's actually a Lancaster bay that shows the back end of the bulge on the fuselage:

 

 

Jari

[old thumper]

8 hours ago, brewerjerry said:

Hi

   Interesting thread, but if a shape is correct or not should surely be based on drawings/ manuals ?

  not on the shape of aftermarket parts, which may or maynot be correct.

  cheers

     jerry

   

 

 

Yes but who has the drawings.

My idea was to use freightdogs and Airfixs latest bomb doors as a research tool, I know manufacturers don't always get things correct but in this day and age there isn't very much that they can get away with without someone starting a hue and cry.

From my understanding the BII bulged bomb doors were not unique to that model of Lancaster. The answer I got from reading through other Britmodeller topics while researching my own tallboy Lancaster build last year was that standard cookie bulged doors were used for the tallboy. 

The freightdog tallboy and airfix Lancaster BII doors look one and the same to me.

 

[brewerjerry]

Hi

    I only query it as :- 

the cookie was 30" in dia

the tallboy 38" in dia

  plus whatever 'hangar' was used for each bomb 

   So personaly i would have expected different sized doors

    cheers

      jerry 

   

[Graham Boak]

Just to remove one variable, the Tallboy and the 12000lb cookie were effectively the same weight, so the same heavy duty carrier would do for both.  

 

I suggest that the Avro Heritage group has the drawings, plus additional records, and are still contactable. http://avroheritagemuseum.co.uk/  It is shut to the public today.  However, according to what it says in the link, the Archives are only open to members and pre-arranged visits on Tuesdays and Thursdays.

Edited March 7, 2017 by Graham Boak

[old thumper]

3 hours ago, brewerjerry said:

Hi

    I only query it as :- 

the cookie was 30" in dia

the tallboy 38" in dia

  plus whatever 'hangar' was used for each bomb 

   So personaly i would have expected different sized doors

    cheers

      jerry 

   

 

I am hoping for one of those people who know everything that there is to know about the Lancaster to step in and give the nod either way. Where are they when you need them.

I am just repeating what I have read in other threads etc and have no first hand knowledge.

[brewerjerry]

Hi

    Likewise I have not much knowledge of the lanc

   but I have a few in the pending pile, so any knowledge gained by me before the build is great  

 

 The experts usually turn up after i complete a build  

   cheers

     jerry

[stevehnz]

Fwiw, I have long been under the impression the Mk II & Tallboy doors were different, something along the lines that the Mk II ones began with a double curve & ended in a cutout for a ventral turret, the Tallboy ones had a shorter steeper front curve & tapered into the belly at the rear. On phone at the no but will try to dig up some refs later if I remember.

Steve

[Miggers]

17 hours ago, brewerjerry said:

 

Hi

    A canadian built mk X, so maybe slightly different ? 

    cheers

      jerry

i reckon you could be right there Jerry,KB range serial and a .50 cal.m/u turret could give the game away.

[Wm Blecky]

28 minutes ago, Miggers said:

i reckon you could be right there Jerry,KB range serial and a .50 cal.m/u turret could give the game away.

Of the differences, as I have been informed, the engines were Packard Merlins, meaning that the nuts and bolts were imperial standards versus metric standard of the Lancasters built in Britain.  Not exactly anything that is visible.  That being said, if you look at some post war pictures of the Canadian Mk.Xs, there is a fuselage strengthening plate around the turret of the .50 cals that Miggers makes mention of:

 

From what I recall, the reasoning behind the strengthening plate was that the mid upper turret position had been moved forward (I do not recall by exactly how much).  I might still have some better pictures of the plate and will post if I find them.

[KevinK]

16 minutes ago, Wm Blecky said:

Of the differences, as I have been informed, the engines were Packard Merlins, meaning that the nuts and bolts were imperial standards versus metric standard of the Lancasters built in Britain.

 

Nothing built in metric in the UK in WWII: what I think you're thinking of is the difference between American SAE threads on the ancilliaries on the Packard engines and Whitworth threads (BSF/BSW) on UK-built hardware. The UK started adopting SAE post-WWII and didn't generally go to metric until the late '60's, although there were always exceptions.

 

It's interesting that the Packard Merlin itself did use Whitworth threads to conform to RR practice, but several of the US-sourced external units didn't.

Edited March 7, 2017 by KevinK
Corrected misstated facts

[Finn]

To further clarify, the 4000lb Cookie had a dia of 30" while the 8000lb, 12,000lb Cookies and Tall Boy had a dia of 38", of course the Tall Boy had the tail fins to worry about. Here are a few more pics of bulged bomb bay doors, the back ends give them away:

 

 

 

 

Jari

[brewerjerry]

Hi

   Interesting, So the bigger cookies had a different diameter  

I had previously always thought they were just 4000's bolted together

   Thanks for the info

     cheers

       jerry

[NZKIWI]

From memory the cross section of the fuselage on these two kits is different around the lower fuselage .

 

[stevehnz]

Further to my previous post, finding photos of Tallboy Lancs that show the bomb bay shape well on line is not easy, photos in my copy of "Dambusters in Focus" show that the bulge starts from the front of the bomb bay & extends its full length before chopping off fairly abruptly. The tail end appears similar to the enlarged cookie doors as used by some Mk IIs & of couse Mk Is/IIs. The difference in the cookie doors on the Mk IIs, certainly as modelled by Airfix, is the the bulge does not begin till about 2 metres back from the front of the bomb bay doors & of course had the fairing at the rear back to the ventral turret, as seen here & here.

One photo I found on the net shows a Tallboy being loaded & a smooth curve from the front of the bomb bay.

Steve.

[old thumper]

1 hour ago, stevehnz said:

Further to my previous post, finding photos of Tallboy Lancs that show the bomb bay shape well on line is not easy, photos in my copy of "Dambusters in Focus" show that the bulge starts from the front of the bomb bay & extends its full length before chopping off fairly abruptly. The tail end appears similar to the enlarged cookie doors as used by some Mk IIs & of couse Mk Is/IIs. The difference in the cookie doors on the Mk IIs, certainly as modelled by Airfix, is the the bulge does not begin till about 2 metres back from the front of the bomb bay doors & of course had the fairing at the rear back to the ventral turret, as seen here & here.

One photo I found on the net shows a Tallboy being loaded & a smooth curve from the front of the bomb bay.

Steve.

 

Tallboy Lancaster pictures are unbelievably scarce and difficult to get hold off, and that is exactly why I find this topic so interesting.

You are right the bulge does start some way back on the BII, but this only confuses me further. As for the tallboy being loaded picture it is difficult for me to get the bulge into perspective. To be honest I can't see a bulge at all, although thankfully I can still see the tallboy.

I would assume that Frieghtdog did thorough research when  creating their after market Tallboy conversion set and hope they have got it right, but still doubt looms. I am especially confused by the pinched rear end of the Freightdog doors as the pinch looks like can only be there to merge onto a ventral turret as with the BII. Maybe the pinch is to accommodate the Tallboys fin, and that the tallboy for some reason needed to be loaded as far to the rear of the bomb bay as possible? 

[Graham Boak]

The reason for loading the Tallboy where it is, is a matter of getting its c.g. as close to the aircraft's aerodynamic centre as possible, to avoid trim effects especially on release.  The effect on the external shape at the rear of the bay just had to be accepted.  However it pretty well filled the bomb bay anyway.  Possibly it simply was as good a shape as Avros could get and the resulting base drag just had to be accepted.  Just carrying the beast internally was a pretty fine achievement.  It's perhaps surprising that an external fairing wasn't scabbed onto the rear fuselage, but if this was being kept free for their open ventral gun position this is understandable.

Edited March 8, 2017 by Graham Boak

[old thumper]

38 minutes ago, Graham Boak said:

 Just carrying the beast internally was a pretty fine achievement. 

 

It absolutely was.

[stevehnz]

The Freightdog shape agrees with the Hasegawa shape & afaics the Matcbox shape. I did wonder if the rear shape was the way it was as a result of these doors being modfied from Cookie doors for want of a better term. ie as fiitted to some Mk IIs, the Mk IIs had a fairing from the rear of that rectangular section to the ventral turret. re The aircraft loading the Tallboy, look at the seam that begins about the front centre of the door & how it appears to taper away upwards towards the door hinge line, that effect is caused by the bulge of these doors, quite a long gentle taper. On regular doors, that seam would appear more or less paprallel to the hinge line.

Steve.